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| Occupational Safety & Health Administration | ||||||
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Directives
STD 01-05-001 - PUB 8-1.7 - Guidelines for Laser Safety and Hazard Assessment |
Directives - Table of Contents |
| • Record Type: | Instruction |
| • Directive Number: | STD 01-05-001 |
| • Old Directive Number: | PUB 8-1.7 |
| • Title: | Guidelines for Laser Safety and Hazard Assessment |
| • Information Date: | 08/05/1991 |
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OSHA Instruction PUB 8-1.7 August 5, 1991 Directorate of Technical Support Subject: Guidelines for Laser Safety and Hazard Assessment A. PURPOSE. This instruction provides guidelines to Federal OSHA and Plan States compliance officers, 7(c)(1) consultants, and employee for the assessment of laser safety. B. SCOPE. This instruction applies OSHA-wide. C. ACTION. Regional Administrators and Area Directors shall provide copies of the attached Guides for Laser Safety and Hazard Assessment to the appropriate State and Federal personnel and shall ensure that copies are available for distribution to the public upon request. D. FEDERAL PROGRAM CHANGE.
E. STATE CONSULTATION PROJECTS.
F. BACKGROUND. With the increase development, manufacturing, and use of devices and systems based on stimulated emissions of radiation (Lasers) in industrial applications, the compliance officer is now, more than ever, in need of a comprehensive laser reference. Because some primary users often misunderstood the different orders of magnitude of intensity levels found in the operational environment and the probability of potential accidental exposure, it was necessary for this reference laser document to be comprehensive, easily read and understood. Gerard F. Scannell Assistant Secretary Distribution: National, Regional and Area Offices State Plan Designees 7(c)(1) Consultation Project Managers NIOSH Regional Program Directors All Compliance Officers
Occupational Safety and Health Administration United States Department of Labor Washington, DC 20210
I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . I-1
II. LASER TYPES AND OPERATION. . . . . . . . . . . . . . . .II-1
III. LASER HAZARDS. . . . . . . . . . . . . . . . . . . . . III-1
IV. LASER STANDARDS: . . . . . . . . . . . . . . . . . . . .IV-1
V. LASER CLASSIFICAITONS: . . . . . . . . . . . . . . . . . V-1
VI. LASER HAZARD EVALUATION: . . . . . . . . . . . . . . . .VI-1
VII. CONTROL MEASURES:. . . . . . . . . . . . . . . . . . . VII-1
VIII. PERSONAL PROTECTIVE EQUIPMENT:. . . . . . . . . .VIII-1
IX. LASER TRAINING:. . . . . . . . . . . . . . . . . . . . .IX-1
Appendix A. Glossary of Laser Terms: . . . . . . . . . . . A-1 Appendix B. Subject Index: . . . . . . . . . . . . . . . . B-1 Appendix C. References:. . . . . . . . . . . . . . . . . . C-1
I. INTRODUCTION _____________________________________________________________________ A. PURPOSE OF GUIDELINE: This guideline is designed to provide a general overview to lasers, laser uses, laser hazards and hazards analysis that are required to provide appropriate background for understanding the applicable industry standards and regulatory requirements. B. USE OF GUIDE: The guide is divided into eleven topical sections. Sections I to III provide background information on laser and laser beams, laser bioeffects and ancillary hazards. Pertinent definitions are in the glossary in Appendix A. Sections IV to VI cover the aspects of laser standards, classifications and overall hazard analysis. Sections VII and VIII review laser controls and protective equipment. Section IX covers training requirement. A comprehensive reference listing is provided in Section X. In general, each section is designed to cover one major aspect of the laser story and can be reviewed separately from the balance of the review. There is, of course, some need to have understanding of the earlier sections to fully apply information in the later sections, especially Section VII on laser hazard evaluation. C. WHO USES LASERS? Estimates of the number of workers involved on a routine basis with laser devises are difficult to perform. One method to estimate the number of workers is through the number of subscribers to the various laser related trade magazines. Estimates indicate that the number of non-overlapping subscribers to the three major laser/electro-optics magazines is approximately sixty thousand. This number is based upon a comparative evaluation of the total number of subscribers for each magazine using sample statistical information for the number of non-overlapping subscribers. It should be stressed that these are controlled circulation magazines and are received by only 10-30% of the individuals at each facility involved with laser and electro-optics activities. Hence, one can estimate, using a multiplier ranging from three to ten, that the "total" laser worker universe in the early 1980's ranges from 180,000 to 600,000 people. Using estimates of the projected growth over the next decade of 20% to 25% per year, one can project a total laser-worker universe total in the early 1990's ranging from 520,000 to perhaps as high as 6,000,000 people. A NIOSH report estimated that by 1980 about 9 million workers would have been potentially exposed to lasers and different arcs. These results were based upon U.S. Census Bureau estimates and other Government reports. This data was divided into the following major census bureau occupational categories as shown in Table I-1. (Table I-1. Comparison of Occupational Category And Number of Workers, see printed copy) If it is assumed that only 60% of the workers are potentially exposed to arcs alone, this would mean that 3.6 million workers are potentially exposed to lasers alone. This estimate is of the same basic magnitude as the estimate obtained previously (0.5 to 6 million) based upon magazine subscription data. Comparison of these two estimates permits the general conclusion that one can, with some certainty, conservatively project in excess of one million workers involved with the applications of lasers by the mid-to-late 1990's. Inspection of Table I-1 also indicates that the greatest percentage of those involved with lasers fall in the categories of craftsman, operator and service. These represent approximately 89% of the total number. This would indicate that the potential for accidental exposures to laser radiation will shift from the developmental engineer and scientist group (where a high percentage of the previous incidents have occurred) to the general occupational work force. One might wonder how many more incidents will occur with this shift to personnel who are much less aware of laser damages? D. LASER APPLICATIONS: The following will review some of the more important laser applications and types of lasers used. Emphasis will be placed upon those lasers with the largest number of applications and, hence, involve the largest number of workers. The major categories of laser uses are summarized in Table I-2. While the listing is extensive, it is certainly not exhaustive. The listing indicates numerous occupational and industry areas are involved in the laser use. The heading of "Research" was not included, although it is certainly a major area for each of the categories listed as-well-as in the area of laser research itself. All of this indicates that potential for exposure to laser light has expanded beyond the scientific laboratory and workplace into the entertainment arena, museum, public building lighting, and even the home. E. PROJECTIONS FOR THE 1990'S: The current scope of laser applications is certainly extraordinary. Virtually every industry group is represented. The question to be asked is, perhaps, "WHAT NEW AREAS OF LASER APPLICATIONS WILL BE EXPLORED IN THE NEXT DECADE?" First, there will be the normal extension of the current applications across industry lines. Also, the use of higher power systems to serve multiple work stations on a beam time sharing basis will become more common. Most laser devices will be dedicated systems, designed for a specific application. New applications will most probably center on the use of tunable wavelength and ultraviolet laser devices (perhaps a second generation of excimer lasers). This lends itself to photochemistry and/or photobiological work where the need for a specific wavelength(s) is paramount for the application. Medical applications will be expanded with the use of various adjuvants with the treatments. For example: dye injections will be administered to the patient which are selectively absorbed in tumors to enhance the selective absorption of laser energy in the tissues and provide a more specific therapy. The uses of lasers with fiber optics will include, in addition to communications - which could become the singularly largest application area of all laser uses - more uses in the industrial laser area. For example, the natural extension of laser materials processing would be the incorporation of laser fiber optics to conduct the beam to remote places as in the field of robotics.
All other new applications will bring certain unknowns from a laser hazard and overall occupational health point of view. For example, development of the Free Electron Laser (FEL), although now located at only a few isolated research centers, has combined electron accelerator, high magnetic field and tunable laser technology together in a single installation. In addition, research is underway for lasers to emit in the X-ray spectrum. All of these developments implies that the hazards associated with laser facilities will most probably be more complex in the future. In addition, it is most probable that the use of the laser with new procedures and processes will produce new and, perhaps, unknown substances that can present new hazards. It will be necessary, therefore that each of these new applications areas be approached with some caution and that the laser interaction be studied and, where hazards are identified, methods of control be established. II. LASER TYPES AND OPERATION ______________________________________________________________________ A. BASIC LASER OPERATION: The term "LASER" is an acronym. It stands for "Light Amplification by Stimulated Emission of Radiation." Thus the laser is a device which produces and amplifies light. The mechanism by which this is accomplished, stimulated emission, was first postulated by Albert Einstein in 1917. The light which the laser produces is unique, for it is characterized by properties which are very desirable, but almost impossible to obtain by any means other than the laser. To gain a better understanding of the laser and what it can do, a review is included of some of the phenomena involved. B. ENERGY LEVELS: Light can be produced by atomic processes, and it is these processes which are responsible for the generation of laser light. Let's look first at atomic energy levels and then see how changes in these energy levels can lead to the production of laser light. A number of simplifications will be made regarding the concept of the atom. It can be assumed, for the purposes of this discussion, that an atom consists of a small dense nucleus and one or more electrons in motion about the nucleus. The relationship between the electrons and the nucleus is described in terms of energy levels. Quantum mechanics predicts that these energy levels are discrete. C. RADIATIVE TRANSITIONS: The electrons normally occupy the lowest available energy levels. When this is the case, the atom is said to be in its ground state. However, electrons can occupy higher energy levels, leaving some of the lower energy states vacant or sparsely populated. One way that electrons and atoms can change from one energy state to another is by the absorption or emission of light energy, via a process called a radiative transition. D. ABSORPTION: An electron can absorb energy from a variety of external sources. From the point of view of laser action, two methods of supplying energy to the electrons are of prime importance. The first of these is the transfer of all the energy of a photon directly to an orbital electron. The increase in the energy of the electron causes it to "jump" to a higher energy level; the atom is then said to be in an "excited" state. It is important to note that an electron can accept only the precise amount of energy that is needed to move it from one allowable energy level to another. Only photons of the exact energy acceptable to the electron can be absorbed. Photons of slightly more (or slightly less) energy will not be absorbed. Another means often used to excite electrons is an electrical discharge. In this technique, the energy is supplied by collisions with electrons which have been accelerated by an electric field. The result of either type of excitation is that through the absorption of energy, an electron has been placed in a higher energy level than it originally resided. As a result, the atom of which it is a part is said to be excited. E. SPONTANEOUS EMISSION: The nature of all matter is such that atomic and molecular structures tend to exist in the lowest energy state possible. Thus, an excited electron in a higher energy level will soon attempt to DE-EXCITE itself by any of several means. Some of the energy may be converted to heat. Another means of de-excitation is the spontaneous emission of a photon. The photon released by an atom as it is de-excited will have a total energy exactly equal to the difference in energy between the excited and lower energy levels. This release of a photon is called spontaneous emission. One example of spontaneous emission is the common neon sign. Atoms of neon are excited by an electrical discharge through the tube. They de-excite themselves by spontaneously emitting photons of visible light. ----------------------------------------------------------------- NOTE: The exciting force is not of a unique energy, so that the electrons may be excited to any one of several allowable levels. ----------------------------------------------------------------- Now let's look at the third, and probably the least familar, type of radiative transition. F. STIMULATED EMISSION: In 1917, Einstein postulated that a photon released from an excited atom could, upon interacting with a second, similarly excited atom, trigger the second atom into de-exciting itself with the release of another photon. The photon released by the second atom would be identical in frequency, energy, direction, and phase with the triggering photon, and the triggering photon would continue on its way, unchanged. Where there was one photon now there are two. These two photons could then proceed to trigger more through the process of stimulated emission. If an appropriate medium contains a great many excited atoms and de-excitation occurs only by spontaneous emission, the light output will be random and approximately equal in all directions. The process of stimulated emission, however, can cause an amplification of the number of photons traveling in a particular direction - a photon cascade if you will. A preferential direction is established by placing mirrors at the ends of an optical cavity. Thus the number of photons traveling along the axis of the two mirrors increases greatly and Light Amplification by the Stimulated Emission of Radiation may occur. If enough amplification occurs, LASER beam is created. G. POPULATION INVERSION: Practically speaking, the process of stimulated emission will not produce a very efficient or even noticeable amplification of light unless a condition called "population inversion" occurs. If only a few atoms of several million are in an excited state, the chances of stimulated emission occurring are small. The greater the percentage of atoms in an excited state, the greater the probability of stimulated emission. In the normal state of matter the population of electrons will be such that most of the electrons reside in the ground or lowest levels, leaving the upper levels somewhat depopulated. When electrons are excited and fill these upper levels to the extent that there are more atoms excited than not excited, the population is said to be inverted. H. LASER COMPONENTS: A generalized laser consists of a lasing medium, a "pumping" system and an optical cavity. The laser material must have a metastable state in which the atoms or molecules can be trapped after receiving energy from the pumping system. Each of these laser components are discussed below:
I. SPECIFIC LASER TYPES:
(Table II-3. Laser Types for Current Applications, see printed copy)
J. LASER BEAM PARAMETERS: The following seven properties are common to the beams emitted from all laser types and are the factors which, when combined together, distinguish laser outputs from other sources of electromagnetic radiation:
Each of these laser beam properties are briefly reviewed in the following sections. K. SINGLE FREQUENCY OPERATION (MONOCHROMATICITY): The frequency of any electro-magnetic wave is related to the number of cycles the electric or magnetic field undergo each second. A completely coherent, monochromatic wave oscillates exactly at a constant frequency. Most laser systems display a narrow multifrequency characteristic. This frequency spread is, however, very narrow when compared to the average laser frequency. In most lasers, the frequency degeneracy is solely dependent upon the quantum transition characteristics of the active media, and the geometry of the laser resonator cavity (Fabry-Perot). In this sense, the laser media may be considered as a high number of isolated light generators placed between two mirrors. The electromagnetic field developed between the mirrors may be regarded as a superposition of plane waves at each of the slightly different frequencies which the laser media generates and allows to oscillate. These different frequencies are termed the "modes" of the laser resonator. The off-axis modes result from plane waves propagating at an angle with respect to the axis of the resonator. These different modes are produced by diffraction effects in the Fabry-Perot cavity. The lowest order axial mode is designated as the TEM(oo) mode. This mode has the lowest diffraction losses and often will be the predominant mode of oscillation. For each transverse mode, there will be many longitudinal modes which can oscillate; hence the output of a multimode laser will actually contain a superposition of plane waves oscillating at many discrete frequencies. However, as previously mentioned, this frequency spread will be very small. In each laser, there will be specific "allowed" frequencies of the resonator cavity (Fabry-Perot modes). For most cases, the average wavelength at which the laser oscillates is sufficient to describe it's operation. If more precision is needed, then the frequency spread or bandwidth is given. Depending on the type of laser, bandwidths range typically from 10(-4) to 10(-9) times the average frequency of the laser; although bandwidths as low as 0.1 Hz. have been reported for stabilized gas lasers. The wave nature of light most often allows adequate description of the output of the laser, and for most cases it will be sufficient to use geometrical optics to describe the output as a beam with well defined edges and some beam divergence. The beam is emitted from the laser with a beam diameter (alpha) and a beam divergence (PHI), as though it came from a small point source far behind the laser output aperture. L. POINT SOURCE EMISSION: The emission from most lasers can be considered as emanating from a "virtual point source" located within or behind the laser device. A "virtual point source" is one which really doesn't exist, but the properties of the emitted beam are such that there appears to be a source at this position. The distance of the point source behind the front mirror of the laser can be related to the size of the beam at the mirror (X) and the laser beam divergence (phi) by the equation:
Thus, the virtual point source is located two meters behind the exit mirror. M. GAUSSIAN DISTRIBUTION OF THE BEAM: The intensity profile across a TEM(oo) laser beam will be in the form of a bell-shaped (Gaussian) distribution. The decrease in intensity at the edge of the beam is the result of diffraction effects produced at the edges. The spatial intensity distribution of this mode may be expressed by equation:
where R is the radius and W is a constant which defines the mean radius and is commonly referred to as the "spot size." At this point the intensity has fallen to e(-2) of the peak intensity at the center of distribution. In fact, the edges of the laser beam are not well defined. If one were to measure the energy or power per unit area point by point across the center of the output aperture, a Gaussian beam distribution is defined. The peak intensity is in the center of the beam and approaches zero as one moves from the center. This shape is maintained as the beam propagates through space subject to broadening and distortion by atmospheric effects. Important points on the distribution curve are the e(-1) and e(-2) intensity points since they are used as standard quantities to define the laser beam divergence parameter. (The e is the natural number associated with the natural logarithm and is equal to: e= 2.7183). The e(-1) point is where the intensity is reduced by the factor
or approximately 63% of the energy (or power) is contained within the aperture of diameter (a) centered in the beam. -------------------------------------------------------------------- Note: In most all laser safety and compliance standards, the output aperture, a, and the beam divergence, (PHI), are defined relative to the e(-1) points. The total laser energy (Q(t)) or beam power (PHI) is defined as that which is collected from the entire beam (total values). -------------------------------------------------------------------- Many manufactures specifications use the e(-2) i points to define beam divergence. In this case, e(-2) i = 0.1353, or the total power (energy) is: 100% - 0.13 3 x 100% = 86.47% or approximately 86% of the total energy /power is within the e(-2) aperture. In some cases, they specify relative to the 90% point. Note that the beam divergence is larger at the e(-2) or 90% point. Hazard calculations are sensitive to the beam divergence and conversions from e(-2) points to e(-2) power points are often performed on beam sizes. The beam diameters at the two points are related:
Departure from the Gaussian distribution arise when independent oscillation occurs within the resonator at higher order modes. For example, some gas lasers may be designed to have sufficient gain to support simultaneous oscillation in many different transverse modes. Mode selection may often be accomplished by slight adjustment of the mirror alignments. With this technique, one can observe the different complex intensity distributions of each mode. The lowest order TEM(oo) mode with the nearly Gaussian intensity distribution has the lowest cavity losses and hence will generally be the dominant mode of oscillation. Optically pumped solid-state lasers such as the normal mode Nd:YAG laser usually display a randomly varying mode output. Thermal gradients in the optical media (i.e., the crystal) caused by nonuniform absorption of the pump light give rise to lens effects in the crystal which change during the pumping cycle. The result is a sporadic switching of transverse modes during the laser pulse. The time average is generally a bell-shaped distribution which is dependent upon the optical purity of the laser crystal, the pumping scheme, and the level at which the system is operated above lasing threshold. Some pumping schemes produce pronounced "hot spots" in the intensity distributions. For long range transmission, atmospheric effects can also produce intensity variations by a factor of ten over localized regions of the beam. Such non-uniformities distribution make it difficult to specify the cross sectional area of the beam. As a result, an average value of beam radius must be chosen. Typically, this is often (1) the half-power point; (2) the e(-1) power point; or (3) the e(-2) power point. A more precise laboratory practice is to measure the diameter at the stated power point on a densitometer recording obtained from a photographic negative of the output beam distribution. In the case of optically pumped solid-state lasers, the size of the beam cross section is generally a function of the pumping level of the laser. In general, the higher the pumping level, the wider the beam size. Only when pulsed lasers are operated near threshold, or in special cavity conditions, will the zero order mode (lowest beam spread) predominate. N. BEAM DIVERGENCE Beam divergence is a very important laser parameter and is often expressed in units of milliradians. The symmetry of the laser beam allows the geometry to be reduced to the two dimensions of a plane. The angle (phi), in radians can be related to degrees by noting that for a full circle, phi is 360 degrees. For some smaller angle, the arc length(s) intercepted along the circumference of the circle can be used to define the angle as:
The minimum beam divergence, called the diffraction limited beam divergence, is related by the equation:
This concept is expanded to three dimensions by introducing the concept of solid angle. The solid angle (OMEGA) is expressed in units of steradians (sr) and is determined by using the area cut out of a surface of a sphere divided by the square of the distance to that surface; that is:
For a sphere, the solid angle may be opened up to include the entire sphere surface area (A = 4 pi R(2)), therefore:
The output of a typical laser will be confined to less than 10(-6) sr. O. INTENSITY OF LASER EMISSION: In many applications, the most important laser beam charactertic is the enormous intensity of the beam. Intensity is related to the beam power the cross sectional area and the manner in which the beam spreads from one point in space to the next. Power, by definition, is the time-rate at which work is done; specifically, it is the rate at which energy is used or produced. Energy relates the ability to do work. As with other forms of energy (eg, chemical, mechanical, electrical), electromagnetic energy (light energy) is a conserved quantity. The relationship between energy, power, and time is defined by the integral equation:
The intensity of the laser is usually expressed by the IRRADIANCE (power/area) of the beam. This is determined by dividing the average value of beam power by the average value of the beam cross section. Irradiance units are expressed in Watts per square centimeter. In pulsed laser operation, instantaneous (peak) Irradiances in excess of 100,000 W/cm(2) are quite easily generated in an unfocused high energy pulsed solid state laser pulse. If this output were contained within a typical beam divergence of 20 milliradians and focused by only moderate power optics, the Irradiance at the focal plane would be increased at least one-hundred fold. A CW laser is rated in Watts and a pulsed laser is normally rated according to the total energy (Joules) per pulse. Pulsed outputs are also expressed as a RADIANT EXPOSURE in units of Joules per square centimeter. In order to determine the peak power of pulsed laser, it is necessary to know the pulse shape and duration. The peak power may be closely approximated by assuming a triangular pulse shape and dividing the energy per pulse by the pulse duration at half power. That is: (Equations, see printed copy) For example, a 100 mJ/pulse laser with a pulse of 20 ns will have a peak power in excess of:
If the beam is focused to a 1 ?m spot, the Irradiance at the focal plane will be:
This average power is an important factor for high PRF lasers when determining the laser classification and maximum permissible exposure levels. The radiometric units of RADIANCE and INTEGRATED RADIANCE are used to describe the diffuse reflection of a continuous wave or pulsed laser beam. Radiance is expressed, by definition, as the Irradiance per unit solid angle (Watts per square centimeter per steradian). Integrated Radiance is expressed as the Radiant Exposure per unit solid angle (Joules per square centimeter per steradian). The unit of solid angle is defined such that all space about a point source (i.e., the source of light) will encompass 4 pi sr. P. FOCUSED LASER BEAMS: The beam from an ideal laser, i.e., a laser which emits a coherent wave, can be considered as a diffraction-limited beam. In this case, divergence of the beam is limited to the effects of diffraction at the beam edges. The emission from such a laser will display a far-field diffraction pattern at a distance (Equation, see printed copy) where a is the diameter of the emergent laser radiation. The TEM(oo) beam from a typical helium neon laser will display a 0.5-1.0 milliradian beam spread at a distance of 1.0-2.0 meters from the laser. Due to the high degree of coherence of a laser beam, it is theoretically possible to focus the beam to the diffraction limit of the wavelength of light. Typically, however, the laser will have a finite beam spread and can be expressed by the simple equations of geometrical optics. The spot diameter (d) is given by the simple equation:
where: d = spot diameter at focus f = focal length of lens phi = laser beam divergence (radians) As an example, one can calculate the spot size of a beam focused on the human retina. For this case, consider a "typical" HeNe laser where: phi = 1.0 milliradian and assume that the effective focal length (f) of the human eye is 1.7 cm. Thus: d = f phi
To give some idea of how small this focused spot is, consider that 17 micrometers is approximately the size of two or three human blood cells stacked end-to-end. Using the equation for the area of a circle (Equation, see printed copy), one can now calculate the focused beam area:
The Irradiance (power per unit area) of a 1 mW He-Ne laser beam focused by the lens of the eye into the retina (assuming no reflection of transmission losses) will be:
As the spot diameter approaches the wavelength of light, the spot becomes diffraction-limited. For example, the beam from a highly coherent single transverse mode (TEM(oo)) gas laser will produce a Gaussian intensity pattern when focused. This distribution may be described mathematically by an equation where it is considered that the beam energy will be contained in a diameter defined at the e(-2) power point:
Therefore, the smallest possible spot size of a focused laser beam will approach the dimensions the wavelength of light which is being focused. Combining the equations above can yield an expression for the spot area:
Thus, the Irradiance (power per unit area) of a focused laser beam will vary inversely with the square of the focal length of the lens and with the square of the beam divergence angle. Hence, these two factors have dramatic effects on the power distribution at the focal plane of the lens. Consequently, either a reduction in the focal length of the lens used to focus the beam or a reduction in the beam spread by a factor of ten will produce a one-hundred fold increase in the irradiance at the focal plane of the lens. Simultaneous reduction of both by a factor of ten would increase the Irradiance at the focal plane by a factor of 10(4). In practice, however, it is usually the beam divergence value that limits the focal spot diameter. This is especially true with pulsed laser systems. To achieve high power outputs, the laser crystal is usually pumped well over threshold; consequently, the beam will contain a conglomerate of high order "off-axis" modes which subsequently increase the beam size. Typical beam divergence values for gas lasers (helium-neon, argon, etc.) will be about one milliradian, (1 milliradian = 3.44 minutes of arc). Solid-state ruby and neodymium lasers generally have a higher beam spread (1- 30 milliradians), due primarily to the high beam divergence associated with the random multimode operation of such devices. Q. SCANNING LASERS: Some laser applications employ electro-mechanical or electro-optical scanner units to allow a raster-scan capability to the beam. In this way, the beam can be scanned over a large area (such as in a laser print maker) or over a small area (such as a laser UPC label reader) in a repeated geometry. The relationships for a scanning laser geometry appropriate for laser hazard analysis are as follows:
For example, the ocular exposure for a Helium Neon laser (beam size 1mm) scanner with 20 degrees scan angle located at a distance of 30 cm from the eye (r = 30 cm) which scans at a rate of 50 Hz will be: (assume d(p) = 7mm):
R. COHERENCE: The coherency of a laser beam relates to the constancy of the spatial and temporal variations in the radiation wavefronts. A high degree of coherence implies a constant phase different between two points on a series of equal-amplitude wavefronts (spatial coherence), and in a correlation in time between the same points on different wavefronts (temporal coherence). The two coherence terms are a part of the overall four-dimensional coherence function which completely describes the degree of coherency of the beam. If the laser beam is considered as a plane wave traveling in one direction, it will be spatially coherent due to the perpendicularity of the wavefronts in the direction of propagation. Also, due to the monochromatic nature of the laser light, the beam will be temporally coherent; that is, it will display a fixed-phase relation between a part of the beam emitted at one time and portion emitted at another. Should the wavelength (or frequency) change, then the temporal coherency would degrade. In 1802, Thomas Young performed his classic double-slit experiment to demonstrate the wave nature of light. Sunlight though one pinhole was allowed to illuminate two closely spaced pinholes. Each pinhole acted as a "new source" for light and the waves from each of the two pinholes interfered with one another so-as-to produce corresponding light and dark regions (or fringes - as they are called) at the observation screen. If light was not a wave, it would travel in a straight line from one pinhole to another to fall at two points on the screen. As a wave, however, it is diffracted and bent about the edges of the pinholes such that each pinhole illuminates the entire screen. In part, if it were not for the diffraction effects produced as a light wave passes through a finite aperture, the plane wave output of laser could theoretically be focused by a lens (such as the human eye) to a real point with minimal spot diameter. Thus, the image Irradiance , (Equation, see printed copy) would have an infinite value. That would indeed be hazardous! Due to the wave nature of light and the corresponding diffraction effects produced by finite apertures, the image a point source of light (provided by any real optical system) is not actually a point. Such a distribution has a bright central area surrounded by light and dark rings. The diameter of the first dark ring of this distribution, which is called the Airy Disk (D(AD)) is given by the equation:
When an optical system's resolution is only limited by the diffraction effects, it is said to be diffraction limited. Even in this condition, a point is "spread out" as it is imaged. The more defects and aberrations introduced by the optical system, the more the spreading. Each lens images a point with some spreading and the manner which it behaves is defined as the point spread function. Since an optical system spreads a point source image, there is a corresponding limit to its resolution or ability to separate two points close together. This is especially important when looking at stars through a telescope. There are at least two criteria used to define the resolution of two points close together. A simple one, and the one most commonly used, is the Rayleigh criterion. This states that when the peak of one Airy disk is over the first dark ring of the other, the points are resolved. This is normally defined in terms of the apparent angle between the two points and is given by the equation:
Lasers are often referred to as coherent sources, but in fact, they really only partially coherent. Only absolutely monochromatic or single frequency waves are truly coherent; however, lasers are so close, relative to anything else, that a loose definition may seem justified. The degree to which two waves are coherent determines how well they interfere when brought together at some point in space. A thorough treatment of the subject of partial coherence is far beyond the scope of this guideline; however, there are a few properties worth discussing. One frequently encounters the terms spatial and temporal coherence. Temporal coherence effects are those which arise from the finiteness of the spectral band. An increase in fringe visibility with a decrease in source size is a measure of the spatial coherence. An important measure of coherence is the coherence length, dL, which can be conceptually related to the duration of an uninterrupted wavetrain. Even in the beam from an "ideal" laser, there will be random fluctuations in the phase difference of the electromagnetic fields at two separate points on a wavefront. The distance between points on the wavefront for which the average of this phase different is equal to (Equation, see printed copy) adians is generally defined as the lateral coherence distance. Recombination of the light samples from points separated by a distance equal to, or less than, this amount can produce interference fringes. The distance is a classical measure of the spatial coherence of a light beam as observed in the famous "double slit" experiment of Young. The temporal coherence is a measure of the length of time that the beam is truly monochromatic. Since lasers have a finite spectrum width (d(v)), the "coherence time" is defined as:
This may be considered as the time during which the amplitude of the electromagnetic field will remain constant at a given point in space while the phase varies linearly with time. During this time, the beam will travel a length dL = c dT defined as the coherence length (where c = 3 x 10(8) m/sec., the velocity of light). Thus the coherence time is the time required for light to travel the coherence length in the direction of travel of the beam. By virtue of this argument, it is seen that the frequency bandwidth is actually a measure of temporal coherence. Thus a frequency stabilized HeNe gas laser (d(v) = 3-5 hertz) will have a coherence time of several hundred milliseconds and a corresponding coherence length of 10(5) km. In contrast to the high spectral purity of gas lasers, the coherence lengths of pulsed ruby lasers are in the order of 15 meters with corresponding coherence times in the order of only 100 nanoseconds. S. POLARIZATION OF THE LASER OUTPUT: The polarization of most lasers is directly related to the nature of the resonator. For example, many high power gas lasers are built with Brewster's angle windows on both ends of the gas discharge tube. Such windows present virtually no losses to a beam which has a linear polarization component lying in the plane of incident. Hence the output will be linearly polarized in this plane. In some solid-state crystal lasers, for example, the ruby laser, the output will be linearly polarized. This is a result of the birefringent nature of the crystal in which the slower "ordinary" polarized photons will have a longer time to interact with the excited chromium ions, thereby favoring a polarized output in this plane. This is generally only true for ruby crystals operating near lasing threshold unless Brewster's angles are fabricated on the ends of the crystal. This latter practice is often necessary for very high power Q-switched laser systems. In diode lasers, linear polarized light is also observed. This may be attributed to the linear symmetry of the junction region. T. ELECTRICAL FIELD STRENGTH: The electromagnetic theory of light depicts a light wave as having instantaneous electric and magnetic fields which oscillate at the same frequency. The electrical (E) and magnetic (H) fields are fixed at right angles and are mutually perpendicular to the direction of propagation of the wave. Of particular importance in the description of laser beam interactions is the magnitude of the electric field associated with the beam. From classical considerations (using Maxwell's equations) the electric field (E) in volts per centimeter associated with a light beam in a vacuum (or air) of average power (PHI) in Watts, spread over a cross-sectional area (A) in cm(2) is given by:
Prior to lasers, the electric fields associated with commonly occurring light sources were most nominal. For example, the electric field of sunlight occurring at the earth's surface is about (Equation, see printed copy). This constitutes an average field spread over all the wavelengths present in the "white light" of the sun. In contrast, the instantaneous electric field associated with an unfocused "Q- Switched" Nd:YAG laser burst operating at a level of 100 megawatts and confined to 3 mm beam diameter will approach (Equation, see printed copy). Should this beam be focused to 100 micrometer spot, the field at the focal plane would exceed
Such strong fields are also found elsewhere in nature, as they are at the magnitude of the electrostatic cohesive forces which bind atomic structures. Such binding forces range from (Equation, see printed copy). Consequently, when a laser beam with a field of comparable magnitude enters a transparent structure, an instantaneous massive redistribution of the electric system of the material can occur due to the interaction of the fields. At the present, the interaction of these enormous electromagnetic fields is not fully understood, to be sure. The production of free electrons, ionized atoms, and X-rays have been detected in the reaction association with the interaction of high power laser beams. U. COMPARISON WITH OTHER SOURCES: Light from conventional thermal sources is emitted over a wide spectral band. The polarizations of the photons are distributed over all possible states of polarization and leave the source in all possible directions (Lambertian source). In contrast, a laser source has a very narrow spectral linewidth even in comparison to special, narrow band thermal sources; the photons may have, essentially, the same polarization and they are highly directional as they leave the laser cavity. Conventional optical sources can most certainly constitute a hazard to the human eye and/or skin, particularly close up and when focused. For example, one's first introduction to optical physics might well have been using a magnifying glass to focus the sun's rays on dry leaves to start a fire. However, even a relatively small laser is capable of producing power/energy distributions much greater that conventional sources. In addition, the hazard can exist at very long ranges due to the highly directional nature of the laser output. A conventional thermal source will emit light into a sphere or hemisphere. The power/energy per unit area (intensity) may be large at the source; however, the intensity at the observer falls off rapidly as the observer moves away from the source. The intensity at the observer can be dramatically increased by using optics to reduce the divergence, making a searchlight; however, the effect is limited by the size of the source. The output of the laser has a very small divergence, typically less that 1 milliradian (1 mrad = 0.0573 degrees), and the intensity decreases very slowly as the distance to the observer increases. It would take a very powerful thermal source to put as much power into as tight a beam as offered by even the smaller lasers. If one were to insert a very narrow bandpass filter into the searchlight (in order to approximate the spectral purity of monochromatic nature of the laser output), the laser would be brighter than any thermal source by an enormous factor, where brightness is defined as the power output per steradian of solid angle. To illustrate the relative brightness of the laser over its narrow band, one notes that the sun emits, at its surface, approximately 10(4) W/cm(2)/sr/?m and lasers can produce greater than 10(10)W/cm(2)/sr/?m in single pulse. Therefore, it is not difficult for a laser to be a million times brighter that the sun. Indeed, a laser can not only burn dry leaves, but some are used to weld metal. The most significant factor is not total power, but rather the power per unit area, where the laser may be focused to an extremely small spot (approximately a wavelength in diameter). For example, a one milliwatt laser focused to a one micrometer spot will produce a focused irradiance greater than 1x10(5) W/cm(2). III. LASER HAZARDS ______________________________________________________________________ A. GENERAL OVERVIEW: Laser radiation of sufficient intensity and exposure time can cause irreversible damage to the skin and eye of man. The most common cause of laser induced tissue damage are thermal in nature. The process is one where the tissue proteins are denatured due to the temperature rise following absorption of laser energy. The thermal damage process is generally associated with lasers operating at exposure times greater than 10 microseconds and in the wavelength region from the near ultraviolet to the far infrared (0.315 - 103 ?m). Other damage mechanisms have also been demonstrated for other specific wavelength ranges and/or exposure times as shown in Table III-1. For example, photochemical reactions are the principal cause of tissue damage following exposures to either actinic ultraviolet radiation (200 - 315 nm) for any exposure time or "short- wave" visible radiation (400 - 550 nm) when exposures are greater than 10 seconds. Tissue damage may also be caused by thermally induced acoustic-shock waves following exposures to very short-time laser exposures (submicrosecond). The principle tissue damage mechanism for repetitively pulsed or scanned laser exposures is still in question. Current evidence would indicate that the major mechanism is a thermal process wherein the effects of the individual pulses are additive. There appears to be a different damage process for repetitively pulsed laser exposures when the individual pulses are shorter than 10 microseconds than when the pulses are longer. Both acute and chronic exposures to all forms of optical radiation can produce skin damage of varying degrees. Numerous types of lasers have been explored rather extensively for the treatment of skin disorders. Certainly, skin injury is of lesser importance than eye damage; however, with the expanding use of higher-power laser systems, the unprotected skin of personnel using lasers may be exposed more frequently to hazardous levels. (Table III-1. Summary of Basic Biological Effects of Light, see printed copy) For the common laser sources in the 0.3 to 1.0 ?m range, almost 99% of the radiation penetrating the skin will be absorbed in at least the outer 4 mm of tissue. The absorption of light in tissues obeys an exponential relationship:
Values for the absorption coefficient are shown in Table III-2. In most all cases, the absorption will occur in tissue thicknesses less than 4mm. For wavelengths greater than 400 nm, the reaction of the skin to absorbed optical radiation is essentially that of a thermal coagulation necrosis. This type of injury can be produced by any optical radiation source of similar parameters and is, therefore, not a reaction specific to laser radiation. It is similar in causality and clinical appearance to the tissues reaction of the deep electrical burn. For pulsed laser irradiation, including exposures of the picosecond domain, there may be other secondary reactions in the tissue. Studies have shown that the volume of vaporized tissues produced by high-level irradiation with laser pulses in the millisecond domain can backscatter a significant portion of the incident energy. This effectively reduces the amount of absorbed radiation in the tissues. The principal thermal effects of laser exposure depend upon the following factors:
B. ULTRAVIOLET EFFECTS ON THE SKIN: The ultraviolet spectrum is divided into three specific regions which are related to the different biological responses of these regions. In the skin, UV-A (315 - 400 nm) can cause erythema and hyperpigmentation. In addition to thermal injury caused by ultraviolet energy, there is the possibility of radiation carcinogenesis from UV-B (280 - 315 nm) either directly on DNA or from effects on potential carcinogenic intra-cellular viruses. (Table III-2. Absortion Coefficients of Human Skin, see printed copy) (Table III-3. 50% Minimal Reactive Dose Levels for Skin Laser Damage, see printed copy) There is limited data available describing the reaction of skin exposed to ultraviolet radiation in the range from 200 nm to 280 nm from highly monochromatic laser sources. Chronic exposure to narrow-band, non-laser ultraviolet wavelengths in this range can result in carcinogenic effects on the skin as well as producing a severe erythematous response. On the basis of these studies with non-coherent ultraviolet radiation, exposure in the UV-B range is most injurious to skin. Exposure in the shorter UV-C (200 - 280 nm) and the longer UV-A ranges seems less harmful to human skin. The shorter wavelengths are absorbed in the outer dead layers of the epidermis (stratum corneum) and the longer wavelengths have an initial pigment-darkening effect followed by erythema if there is exposure to excessive levels. It should be kept in mind that phototoxic and photosensitizing chemicals in the skin may potentiate the effects of laser operating in the visible and ultraviolet regions. Studies on the stimulating effect of very low level exposures of the ruby laser on hair growth, phagocytosis index and wound healing are of interest in any consideration of chronic effects. Recent studies with Excimer ultraviolet lasers have, however, demonstrated a specific, nearly non-thermal, tissue reaction that causes a molecular bond breaking at wavelengths below 340 ?m. This may offer a unique tool in the future for some surgical applications. Biological effects of laser radiation have not been observed on internal organs of man except for very severe conditions where the outer tissues were either surgically removed or massive laser exposures were delivered to the tissue surface to cause surface ablation. In this condition sufficient energy may be transmitted to the underlying organs and produce tissue damage. The results of studies on the exposure levels required to produce minimal reactions in the human skin for six common laser types emitting in the visible and IR are summarized in Table III-3. The data presents the minimal reactive dose (measured at the 50% probability level) for the different wavelengths and lasers. The variations, or spread, in the data were found to be directly related to the degree of absorption in the tissues. The thermal reaction of absorbed radiant energy in tissues is strongly dependent upon both duration and area of the exposure. The early work of Henriques and Moritz investigated the time-temperature response for tissue exposures of thermal insults of to 70 deg. C. Their data indicates that skin can withstand brief temperature rises for very short exposure times. The response appears to be logarithmic as the exposure times become shorter. For example, a 21 deg. C rise above body temperature (37 deg. C) to 58 deg. C will produce cell destruction for exposures longer than 10 seconds. Tissues, however, can withstand temperatures up to 70 deg. C if the duration of the exposure is maintained less than 1 sec. The basic mechanisms of thermally induced tissue destruction result from denaturation of cell protein, interference with basic cell metabolism and secondary effects such as interference with vascular blood supply. Healing of laser induced skin lesions is similar to any localized thermal wound and should be medically treated in a similar fashion. Laser induced lesions on the retina tissues of the eye will usually cause irreversible vision function loss and is difficult to medically treat. C. OCULAR EFFECTS OF LASER RADIATION: The principal hazard associated with laser radiation is exposure to the eye. This is particularly important in the visible and near-infrared spectral regions (400 - 1400 nm). There are, however, other serious potential hazards in other spectral regions as outlined in the following sections. The eye may be conceptually considered as a slightly flattened globe which is transparent to the light passing through an aperture pupil) and which has an efficient light absorber on the inside (retinal surface), opposite the aperture. The transparent region of the eye includes several structures which operate to control the exposure to the retina. The cornea, the transparent window, is the primary refracting structure of the eye. Because of the differences in refractive indices of air and the cornea, more than 80 percent of the refraction of light takes place as the light enters the eye. Between the cornea and the lens is one of the two chambers of the eye. The aqueous chamber contains the aqueous fluid. The lens is the dynamic refractive medium in the eye, and is responsible for the range of focus of the eye. The retina is the light absorbing structure of the eye containing the neural receptors which initiate the vision process. A blind spot in the retinal surface is located at the point where the optic nerve enters into the eye. The fovea is the portion of the retina which is most sensitive to detail and which discriminates color. This structure fills an angle of approximately two degrees in the central portion of the retina. The fovea is located in a small dip in the center of the area called the macula lutea. The macula fills an area of about 1 mm diameter. The various structures of the eye transmit, reflect, and absorb optical energy. The effects of laser exposure on the retina are influenced by the transmission losses of the ocular media. The transmittance of the ocular media are such that retinal effects can be anticipated only for laser wavelengths between 400 nm and 1400 nm. Outside that range, structures other than the retina are affected. The retinal effects of visible optical radiation are also influenced to some degree by the size of the retinal image and the time duration of the laser exposure. Early in the history of lasers, it was recognized that lasers and great potential for causing retinal injury. The reason was that a laser could produce retinal intensities orders of magnitude greater than conventional light sources, and, in fact brighter than the sun. The optical system of the eye, like any optical system, will have a limitation (called the diffraction limit) on the smallest size of image it may resolve and focus. To determine the effect of a source imaged on the retina it is necessary to know the retinal image size. A large amount of the research on retinal burns indicates that the size of the source is an important variable. For a first approximation, one can show that a laser with a 1 milliradian beam spread can produce a retinal spot of approximate size of 17 ?m if sharply focussed. If an unaccommodated eye (an eye focused at infinity) views a collimated source such as a distant star in the night sky or a laser, a "point" image should be produced on the retina. In practice, however, a true point image of that light source is not produced. The optical system of the eye, or any optical instrument, has certain limitations caused by diffraction which will cause the light rays passing through an aperture to bend. The aperture of an optical system is the edge which produces the diffraction. The aperture in the eye is the iris. If a laser beam is larger than the pupil, diffraction of the beam occurs at the edge of the iris. If the beam is smaller than the pupil, spherical aberrations and forward scattering cause the "point" image to spread. The actual distribution of light from a point source will be spread out somewhat rather than be focused to a diffraction limited spot. In general, the larger the pupil, the smaller the point spread and the greater the magnification factor (concentration) of light at the retina as compared with the irradiance at the cornea. Estimations of the magnification factor, based on diffraction effects only, range from 10(5) to 10(7) for pupil diameters between 2 and 7 mm. In any event, the optical gain for a 7 mm diameter pupil is at least 1 x 10(5) and may be greater, depending on the magnitude of the experimental error in determining the data used in the estimates. The location of the exposure in the eye determines the degree of incapacitation from a retinal injury. The fovea (the central two degrees of the visual field) is the region of the retina which is most sensitive to visual detail. The remainder of the retina, the parafovea to the peripheral retina, is increasingly less sensitive to light. However, the parafovea and peripheral retina are not as sensitive and do not contribute significantly to fine detail in the vision process. Therefore, and injury to the fovea will severely reduce visual functions of visual detail and resolution. An injury to the parafovea or peripheral retina is less incapacitating and may be undetectable from a functional point- of-view. D. EXTENDED SOURCE VIEWING: When viewing an extended source, such as the reflection of a laser from a highly reflective diffuse surface, the geometry of the situation results in a retinal image which is of constant brightness (constant retinal irradiance) until the observer moves away so far that the eye can no longer resolve the spot of the laser light. At this point a critical image size is reached. When this occurs, the brightness will stay constant or decrease in value. Retinal spot size effects are related to the differential effects of conduction of heat away from the image which are a function of both exposure time and image size. For long exposures, the large and small image size damage thresholds are different because of thermal conduction. By thermal conduction in this context is meant the cooling of laser heated tissue by contact with surrounding tissue and by circulation of the blood. E. EYE EFFECTS AT DIFFERENT WAVELENGTHS:
F. BIOLOGICAL DAMAGE MECHANISMS: Until the late 1970's, it was assumed that all permanent retinal injury from intense visible light sources was thermal in nature when exposures durations exceeded more than 10 microseconds. It had been recognized that there would be a temporary loss of visual function (flashblindness) from sudden exposure to bright light, but it was not known that photochemical retinal injury mechanisms existed in addition to thermal injury. The laser safety thresholds and exposure limits for exposure durations from 10 microseconds up to 10 seconds seem to follow a constant power function which is dependent upon exposure duration which implies only a thermal damage process. In this time domain, the retinal tissue is raised in temperature to a point where protein (or enzyme) damage takes place.
G. EXPOSURE LIMITS
C(B) = 1.0 in the range 0.400-0.550 ?m
(blue light)
LAMBDA = Laser wavelength (?m).
(Table III-4. Summary: Maximum Permissible Exposure Limits, see printed copy)
H. MAXIMUM PERMISSIBLE EXPOSURE LIMITS: A summary of Maximum Permissible Exposure (MPE) limits for direct ocular exposures for some of the more common lasers is given in Table III-3. For further information on MPE values, refer to the Z-136.1 "Safe Use of Lasers" Standard of the American National Standards Institute. A summary of Maximum Permissible Exposure (MPE) limits for direct ocular exposures for some of the more common lasers is given below in Table 17-4. For further information on MPE values, refer to the ANSI Z-136.1 "Safe Use of Lasers" Standard. The information in Table III-4 provides the MPE value for different lasers operating for different overall exposure times. The times chosen were:
The "safety" exposure limits (MPE's) in Table III-4 are expressed in irradiance terms (W/cm(2)) that would be measured at the cornea. Note that they vary by wavelength and exposure time. I. ASSOCIATED (NON-BEAM) LASER HAZARDS: In some laser operations, particularly in the research laboratory, other aspects may require consideration.
IV. LASER STANDARDS: _______________________________________________________________________ A. OVERVIEW OF STANDARDS: In the United States the are four major activities concerned with regulations regarding safety of laser systems. These organizations are the American National Standards Institute (ANSI), the Center for Devices and Radiological Health (CDRH), the Occupational Safety and Health Administration (OSHA), and the various state governments. ANSI is an organization for which expert volunteers participate on committees to set industry consensus standards in various fields. ANSI has provided the basis for numerous existing federal standards as-well-as the more recent Suggested State Regulations for Lasers (SSRL). The ANSI-Z-136.1 (1986) standard provides requirements and recommendations for the safe use of lasers with which the personnel who operate, maintain and service lasers must be familiar. The CDRH is a regulatory bureau within the Federal Food and Drug Administration of the Department of Human Services. It has been chartered by Congress to standardize the manufacture of laser products. The laser products manufactured after August 2, 1976 which have been entered into interstate commerce must comply with these regulations. In addition, CDRH also has the responsibility for enforcing compliance with the Medical Devices Legislation. All medical laser manufacturers must obtain either pre-market approval (PMA) or clearance (510K) of their laser surgical devices through the CDRH. It should also be noted that FDA sanctions the exploratory use of lasers for specific procedures through a process known as an Investigational Device Exemption (IDE). Approval of an IDE permits the limited use of a laser expressly for the purpose of conducting an investigation of the laser's "safety and effectiveness." Once an IDE has been done and the CDRH clears the device, the manufacturer may then actively market the laser for that specific medical/surgical procedure. (Table IV-1. Summary of Current State Laser Regulations, see printed copy) (Table IV-2. Tabulation of FDA/CDRH Requirements for Laser Products, see printed copy) (Table IV-2. Tabulation of FDA/CDRH Requirements for Laser Products (Continued), see printed copy) Laser regulations within the various states vary considerably from state to state and are generally concerned with the registration of lasers and the licensing of operators and institutions. This is summarized in Table IV-1. At present, physicians and medical lasers generally are exempt from most state requirements. The complexity of state laser regulations may change in the future pending adoption by states of the "Suggested State Regulation for Lasers" which is currently being promulgated by the Conference of Radiation Control Program Directors. The regulatory administration of the U.S. Department of Labor with the responsibility of assuring a safe work place is vested in the Occupational Safety and Health Administration (OSHA). At this time, OSHA does not have an all encompassing and comprehensive laser standard. There is an OSHA standard which covers the use of lasers in the construction field only (29 CFR 1910). However, there have been OSHA citations issued relative to lasers using the authority vested under the "general duty clause" of Public Law 91-596; the Occupational Safety and Health Act of 1970. In these cases, the OSHA inspectors have asked the employers to revise their reportedly unsafe work-place using the recommendations and requirements of such industry consensus standards as the ANSI Z-136.1 Standard. B. BACKGROUND OF LASER STANDARDS: The initial development of laser safety standards began during the mid-1960's as new biological data was made available. Revisions occurred and the various standards reached their present state during the period of 1973-1986. In 1972 two primary group in the United States were developing laser standards. One was a consensus group of industry, university and governmental experts on lasers, laser biological effects and safety, who developed standard Z-136.1 (1973) under the auspices of the American National Standards Institute (ANSI) in New York City. This committee created the concept of classifying lasers according to a scheme of graded risk of exposure and risk of injury evolved. Due to the large variety of lasers, difficulties of laser measurements, and the complexities of laser hazard evaluation, the committee felt that the scheme of not more than five classes of graded risk would help laser users to determine hazards. If hazards were known, then proper safety controls could be applied according to the classification. The different control measures were also graded according to this classification scheme. Hence, a user with a high risk laser (Class IV) would follow more stringent control measures than would apply to a low risk laser (Class II). During this same period the Bureau of Radiological Health within the Food and Drug Administration developed regulations limited to performance requirements that apply to manufacturers. In 1982, the Bureau of Radiological Health was merged with the Bureau of Medical Devices and renamed the National Center of Devices and Radiological Health (NCDRH). The name was shortened soon thereafter to simply the Center of Devices and Radiological Health (CDRH). In addition to lasers, the CDRH also has regulatory responsibility for the Medical Devices Legislation. The basic law under which gave the CDRH regulatory authority over lasers was the Radiation Control for Health and Safety Act of 1968 (PL-90-602). The act empowered the CDRH to set standards of performance for electronic products that emitted radiation. This is the same public law that applies to X-rays, ultrasonic devices, microwave ovens, etc.. Most of the CDRH's regulations pertains to very specific applications of a particular type of source of electromagnetic radiation. For instance, they do not have a standard for all microwave devices, but they do have a standard for microwave cooking ovens. Similarly, they have specific standards for X-ray emission from your color TV sets, X-ray emission from diagnostic X-ray units, etc. In the case of lasers, however because of the precedent of the ANSI approach (which included all possible laser applications), the CDRH chose to try to adapt the basic concept of ANSI and formulate a set of performance and labeling requirements based on a classification scheme according to the level of laser radiation accessible during operation. This was obviously a bold approach to undertake for a large class of products which were relatively new or unknown at the time that the standard was written. It is, therefore, not surprising that there have been some difficulties both in basic concepts and in interpretation of the standard since many have evolved since the standard was initially written. The standard has been amended twice since its initial issuance. To summarize then, the CDRH Laser Product Performance regulates the manufacturer and the commercial laser products, not the user. The standard does not contain specific design specifications, but is a conceptual, performance standard which the designer of laser product must consider. The intent is to insure laser product safety from the manufacturer's standpoint only, as the CDRH does not "regulate the user" of electronic products. In addition, the CDRH laser standard applies to all laser products that are sold or otherwise transferred to users. The ANSI-Z-136 standard is "For the Safe Use of Lasers" and is available for voluntary adoption by users of equipment. Although the Z-136.1 Standard in not "a law" it has had direct impact on all laser standards worldwide. C. STANDARDS VERSUS REALITY: When the potential hazard from any real product is considered, there is always a distinction between the real hazard and that which may be implied by the regulations and standards. The writers of standards and regulations are always forced to make general statements which will inevitably have exceptions. Complete accuracy is often sacrificed for simplicity. For example, notwithstanding the complexity of the CDRH regulations, the classification limits still do not, in all cases, fit the reality of current biological knowledge. For example, corrections for repetitively pulsed lasers have not been incorporated into the CDRH standard although this has been a part of the ANSI and other international standards for more than a decade. This may be related to the elaborate requirements for the review and comment revision process for CDRH regulation which is slow and cumbersome or to the lack of sufficient biological data to support the issue. In contrast, the revision process for an ANSI Standard is considerably less cumbersome, which is reflected in the fact that a massive revision was adopted and published in 1976, only two years after the original publication. A second massive revision was completed in 1980 by the ANSI committee to correct previous difficulties, particularly in organization as well as compatibility with the CDRH standard. A third complete revision was finished in 1986 and led to the publication of the fourth edition (ANSI Z-136.1-1986) in the early part of 1986. Work is now underway for major revisions and a new edition for 1991-1992 period. The CDRH laser standard has undergone only two minor revisions since it was first released. Some changes were proposed in November, 1980 and finally approved in August, 1985 to become effective, in most part, by September 1986. At present, the manufacturer of a laser product is faced with two concerns:
To some extent, in certain cases, there is a third consideration. The necessity to avoid unwarranted fear and concern by the user about the safety of the product. D. U.S. FEDERAL LASER PRODUCT PERFORMANCE STANDARD (FLPPS): A requirement of compliance with U.S. regulations is required by organizations/personnel involved in the design, fabrication and manufacture of laser products. This is applicable to lasers or laser systems to be sold by a company within or imported inside the U.S. It can also apply in some cases when a laser or laser system is transferred within a company for internal use within the U.S. The compliance procedure requires implementation of the procedures and requirements as set forth in the U.S. Federal Laser Product Performance Standard: Title 21 of the Code of Federal Regulations; Part 1000; [parts: 1040.10 and 1040.11]. This also pertains to commercial laser products that are placed into commerce by a company either directly, after modification, and/or after being incorporated into a laser product. The FLPPS regulates the manufacturer and the performance of the product by specifying performance features:
The laser manufacturer establishes the required specifications, and is responsible for compliance with federal CDRH laser product requirements. The laser product will encompass one of the following categories:
Under the requirements of the FLPPS, the manufacturer is required to classify the laser as either a Class I, Class II, Class IIA, Class IIIA, Class IIIB or Class IV laser product certify by means of a label on the product, and submit an initial report demonstrating compliance with all requirements (performance features) of the standard. These requirements are detailed in Table IV-2. E. REPORTING GUIDELINES (FLPPS): The COMPLIANCE GUIDE FOR LASER PRODUCTS, which is available from CDRH, summarizes the requirements of the U.S. Federal Laser Product Performance Standard which a Manufacturer should use to ensure that the laser product complies with the CDRH regulations (performance requirements, labeling, reporting, classification, etc.) The Compliance Guide is available from The Center for Devices and Radiological Health (CDRH), Food and Drug Administration (FDA). This guide should also be consulted prior to the completion of Initial, Model Change, or Annual Reports by personnel responsible for these reports (product engineers, designers, developers, etc.) An Initial or Model Change Report shall be prepared, for each laser product or product family, by the responsible personnel for the location which is manufacturing the product and submitted to the FDA prior to introducing the laser product into commerce. An Annual Report for all manufactured laser products is also required by the FDA. All locations which manufacture lasers that are introduced directly into commerce must report to FDA/CDRH all lasers manufactured from July 1 of any year to June 30 of the next. V. LASER CLASSIFICATIONS ____________________________________________________________________ A. INTRODUCTION: The basis for the classifications in this document are:
The intent of laser hazard classification is to provide warning to users by identifying the potential hazards associated with the corresponding levels of accessible laser radiation through the use of labels and instruction. It also serves as a basis for defining appropriate control measures and medical surveillance. Lasers and laser systems received from manufacturers shall be classified and appropriately labeled by the manufacturer. However, the classification may change whenever the laser or laser system is modified to accomplish a given task. Also, the Laser Safety Officer (LSO) shall effect the classification designation in cases where the laser or laser system classification is not provided or where the class level may change because of alterations to the laser or laser system. It should be mentioned that the U.S. Federal Government does not "approve" laser systems. The manufacturer of the laser system first classifies the laser and then certifies that it meets all performance requirements of the Federal Laser Product Performance Standard (FLPPS). Therefore, all lasers and laser systems that are manufactured by a company, or purchased by a company and relabeled and placed into commerce, or incorporated into a system and placed into commerce, shall be classified in accordance with the FLPPS. The classification shall be confirmed by the LSO at the laser installation. B. LASER HAZARD CLASSES: Virtually all of the U.S. and international standards divide all lasers into four major hazard categories called the laser hazard classifications. The basis of the classification scheme is the ability of the primary or reflected primary beam to cause biological damage to the eye or skin during intended use. The criteria is established (TABLE V-1. Laser Classifications: Summary of Hazards, see printed copy) relative to the Maximum Permissible Exposure (MPE) levels that are accessible during operation of the laser. Lasers and laser systems are assigned one of four broad Classes (I to IV) and Optical Fiber Communications Systems (OFCS) are assigned one of four service groups (SG1, SG2, SG3a, SG3b) depending on the potential for causing biological damage. The laser hazard classes are summarized in Table V-1 and are given as:
Since lasers are not classified on beam access during service, most all Class I industrial lasers will consist of a higher class (high power) laser enclosed in a properly interlocked and labeled protective enclosure. In some cases, the enclosure may be a room (walk-in protective housing) which requires a means to prevent operation when operators are inside the room.
NOTE: Class IIA is a special designation that is based upon a 1000 second exposure and applies only to lasers that are "not intended for viewing" such as a supermarket laser scanner. The upper power limit of Class IIA is 4.0 ?W. These are products whose emission does not exceed the Class I limit for an emission duration of 1000 seconds.
NOTE: There are different labeling requirements for Class IIIA lasers with a beam irradiance that does not exceed 2.5 mW/cm(2) (Caution logotype) and those where the beam irradiance does exceed 2.5 mW/cm(2) (Danger logotype).
EMBEDDED LASER: A Class II, Class III, or Class IV laser or laser system contained in a protective housing and operated in a lower classification (Class I, Class II or Class III). Specific control measures may be required to maintain the lower classification. C. OPTICAL FIBER COMMUNICATION SYSTEMS (OFCS): Optical Fiber Communication Systems (OFCS) and the associated optical test sets use semiconductor lasers or LED transmitters that emit energy at wavelengths typically greater than 700 nm into the lightguide fiber optic cables. All OFCS are designed to operate with the beam totally enclosed within the fiber optic and associated equipment and, therefore, are always considered as Class I in normal operation. The only risk for exposure would occur during installation and service when lightguide cables are disconnected or during an infrequent accidental cable break. Optical Fiber Communication Systems (OFCS) are assigned into one of four service group designations: SG1, SG2, SG3a, SG3b, depending on the potential for an accessible beam to cause biological damage. The service group designations relate to the potential for ocular hazards to occur only during accessible beam conditions. This would normally occur only during periods of service to a OFCS. Such designations apply only during periods of service in one of the following four service groups (SG):
NOTE: OFCS where the total power is at or above 0.5W do not meet the criteria for optical fiber service group designation. In this case, the OFCS are treated as a standard laser system. D. LASER CLASSIFICATION MEASUREMENTS: The measurement and test parameters for purposes of laser classification are outlined in detail in 21 CFR Part 1040. For convenience, they are summarized below: Tests on lasers and laser systems, for purposes of classification, shall be made during operation, maintenance or service as appropriate:
At points in space to which human access is possible in the configuration which is necessary to determine compliance with each requirement, e.g., if operation may require removal of portions of the protective housing e.g., disconnection of an optical connector for OFCS, and defeat of safety interlocks, measurements shall be made at accessible points with the measuring instrument detector positioned and so oriented with respect to the laser or laser system as to result in the maximum detection of radiation by the instrument. Accessible emission levels of laser and collateral radiation shall be based upon the following measurements (or their equivalent) as appropriate: For laser products intended to be used in a locale where the emitted laser radiation is unlikely to be viewed with optical instruments, the radiant power (W) or radiant energy (J) detectable through a circular aperture stop having a diameter of 7 millimeters and within a circular solid angle of acceptance of 10(-3) steradians with collimating optics of 5 diopters or less (i.e., a maximum distance of 20 cm). A 50 millimeter diameter aperture stop with the same collimating optics and acceptance angle shall be used for all other laser products. For scanned laser radiation, the direction of the solid angle of acceptance shall change as needed to maximize detectable radiation, with an angular speed of up to 5 radians/second. A 50 millimeter diameter aperture stop with the same collimating optics and acceptance angle stated above shall be used for all other laser products. The irradiance (W/cm(2)) or radiant exposure (J/cm(2)) equivalent to the radiant power (W) or radiant energy (J) detectable through a circular aperture stop having a diameter of 7 millimeters and, for irradiance, within a circular solid angle of acceptance of 10(-3) steradian with collimating optics of 5 diopters or less, divided by the area of the aperture stop (cm(2)). The radiance (W/cm(2) sr) equivalent to the radiant power (W) or radiant energy (J) detectable through a circular aperture stop having a diameter of 7 millimeters and within a circular solid angle of acceptance of 10(-5) steradians with collimating optics of 5 diopters or less, divided by that solid angle (sr) and by the area of the aperture stop (cm(2)). For diode lasers coupled to an optical fiber, the radiant power (W) or radiant energy (J) detectable through a circular aperture stop having a diameter of 7 mm can be calculated from the output power measured at the connector (closed system) and the numerical aperture (for a multimode fiber) or the mode-field diameter (for a single mode fiber). This procedure, described in ANSI Z- 136.2, provides a conservative estimate, i.e., yields values slightly in excess of the corresponding measured values. VI. LASER HAZARD EVALUATION ______________________________________________________________________ A. LASER ENVIRONMENTAL FACTORS: Three aspects of the application of a laser or laser system influence the total hazard evaluation:
All three aspects must be considered in order to establish control measures commensurate with the potential hazard. The environment in which the laser is used may vary with each application. It is extremely important, however, that the environment in which the laser is used be considered in order to determine whether or not the control measures in are adequate, or if some are unnecessary. For example, the controls for a laser robotic system used on a production floor would be expected to be considerably different from those used in a research laboratory. As a minimum, the following shall be considered:
B. LASER SAFETY OFFICER (LSO): The conditions under which the laser is used, the level of safety training of individuals using the laser and other environmental and personnel factors are important considerations in determining the full extent of safety requirements. Since such situations require informed judgments by responsible persons, major responsibility for such judgments has been assigned to a person with the requisite authority and responsibility, namely the Laser Safety Officer (LSO). The LSO shall have the authority and responsibility to monitor and enforce the control of laser hazards, and to effect the knowledgeable evaluation and control of laser hazards. This shall be done at each location or administrative area where Class III or Class IV lasers or laser systems are used or manufactured. Designation of an LSO is generally not required for operation of a Class II or Class IIIA laser or laser system. Designation of an LSO is generally not required if maintenance and service are limited to Class I and Class II laser systems which do not contain embedded lasers of a Class higher than Class II. If service is performed on a laser product having an embedded Class IIIA, Class IIIB, or Class IV laser, there shall be a designated LSO. Depending on the number and classification of lasers and laser systems, within a location or administrative area, the position of LSO may not be a fulltime assignment. C. STANDARD OPERATING PROCEDURE: One of the most important, but often least used, control measure is the requirement to develop a written Standard Operating Procedure (SOP). The key to an effective SOP is the participation, during its preparation, of all individuals (including the LSO) that will operate, maintain, monitor, and/or service the equipment. A good starting point for an SOP would be the instructions for safe operation suggested by the manufacturer; however these may not always be appropriate for a specific application due to special use conditions. An SOP is considered as an administrative/procedural control and is required for all Class IV lasers and laser systems. An SOP is recommended for Class IIIB lasers, especially those CW lasers operating above 200 mW in an open configuration. D. LASER PERSONNEL: The personnel who may be in the vicinity of a laser and its emitted beam(s) and the operator can influence the total hazard evaluation. Hence, they can influence the decision to adopt additional control measures not specifically required for the class of laser being employed. The type of personnel influences the total hazard evaluation. It must be kept in mind that for certain lasers or laser systems (for example, some Class IIIA lasers used for alignment tasks), the principal hazard control rests with the operator; that it is his or her responsibility not to aim the laser at personnel or flat mirrorlike surfaces. If individuals unable to read or understand warning labels are exposed to potentially hazardous laser radiation, the evaluation of the hazard is affected and control measures may require appropriate modification. The following are considerations regarding operating personnel and those who may be exposed:
E. THE NOMINAL HAZARD ZONE: The Nominal Hazard Zone (NHZ) associated with Class IIIB and Class IV lasers shall also be determined. The NHZ describes the space within which the level of direct, reflected, or scattered radiation during normal operation exceeds the appropriate MPE's and is determined from the following characteristics of the laser:
----------------------------------------------------------------- NOTE: Examples of NHZ calculations are given in the appendix of ANSI Z136.1 (1986). In addition, computer software is also available to assist in the computations for NHZ, protective eyewear optical densities and other aspects of laser hazard analysis. ------------------------------------------------------------------ It is often necessary in some applications where open beams are required (vis: industrial processing, laser robotics) to define the area where the possibility exists for potentially hazardous exposure. This is done by determining the Nominal Hazard Zone (NHZ) which is, by definition, described by the space within which the level of direct, reflected or scattered radiation exceeds the level of the applicable MPE. Consequently, persons outside the NHZ boundary would be exposed below the MPE level and are considered to be in a "safe" location. The NHZ boundary may be defined by direct (intrabeam) beams, diffusely scattered laser beams as-well-as beams transmitted from fiber optics and/or through lens trains... etc. In other words, the NHZ perimeter is the envelope of MPE exposure levels from any specific laser installation geometry. The purpose of an NHZ evaluation is to define that region where control measures are required. Thus, as the scope of laser uses has expanded, the classic method of controlling lasers by enclosing them in an interlocked room has become limiting and, in many instances, can be an expensive over-reaction to the real hazards present.
Eq. 1:
Eq. 2:
Eq. 3:
Eq. 4a:
Eq. 4b:
Eq. 5:
Eq. 6:
Eq. 7:
Eq. 8:
Eq. 9:
7. FIBER-OPTIC ON LASER NOMINAL HAZARD ZONE:
Eq. 10:
F. INTRABEAM OPTICAL DENSITY DETERMINATION: Based upon these typical exposure conditions, the optical density required for suitable filtration can be determined. Optical density is a logarithmic function defined by the equation: Eq. 11:
Based upon the worst case exposure conditions outlined above, one can determine the optical density recommended to provide adequate eye protection for this laser. For example, the minimum optical density at the 1.06 ?m Nd:YAG laser wavelength for a 10 second direct intrabeam exposure to the 100 watt maximum laser output can be determined as follows: Where: PHI = 100 Watts MPE = 5.06 mW/cm(2) (10 second criteria) d = 7 mm (worst case pupil size) Computing the worst case exposure H(o):
Substituting into Equation 11, we have:
An extremely conservative approach would be to choose an 8 hour (occupational) exposure. In this case, the optical density at 1.06 ?m is increased to OD = 5.2 for a 100 watt intrabeam exposure because the 8-hour (30,000 seconds) MPE is reduced to 1.6 x10(-3) W/cm(2). The OD values for a number of common laser types are given in Table VI-1. G. SURGICAL FIBER OD HAZARD ANALYSIS: A hazard analysis of a typical Nd:YAG surgical laser with a fiber optic hand-piece attachment could be based upon the following parameters:
Using these parameters, a mathematical hazard analysis can be done to estimate the general region around the surgical site where hazardous exposures may be possible. Although, the following analysis is based upon one specific unit, it is representative of Nd:YAG surgical lasers. This analysis is based upon the maximum permissible exposure (MPE) criteria of the ANSI Z-136.1 standard. The "worst case" MPE value for a direct intrabeam Nd:YAG laser exposure of 10 seconds is 50.6 millijoules/cm(2). The MPE for a 10 second diffuse reflection of this laser is 10(8) Joules/cm(2) sr. contained within an apparent visual angle (alpha min) which is not smaller than 24 milliradians. The 10 second MPE value for skin exposure is 10.5 Joules/cm(2). To estimate a diffuse reflection from the site, one can estimate, using the inverse square law, an approximate scattering distance of 40 cm from the beam (on the tissues) to the eye. Using the ANSI Z-136.1 point source criteria (because the focused beam acts as a point source), the irradiance at the eye will be 19.9 mW/cm(2). This produces a radiant exposure of nearly 200 mJ/cm(2) during a ten second exposure. The optical density required for safe viewing of the diffuse reflection off tissues is substantially reduced from the 100 watt intrabeam case. Using a 40 cm "viewing distance", and assuming a "point source condition, the required optical density at 1.06 ?m would be OD = 0.6 for a 10 second exposure and OD = 1.1 for an 8 hour (occupational) exposure. (Table VI-1, Optical Densities for Protective Eyewear for Various Laser Types, see printed copy) The "worst case" conditions suggest than an optical density ranging from 0.6 to 5.2 depending upon viewing time and conditions.
VII. CONTROL MEASURES: ----------------------------------------------------------------- A. CONTROL MEASURES - OVERVIEW: Control measures shall be devised to reduce the possibility of exposure of the eye and skin to hazardous laser radiation and to other hazards associated with the operation of lasers and laser systems. This applies during normal operation and maintenance by users, as well as by Manufacturers during the manufacture, testing, alignment, servicing, etc. of lasers and laser systems. There are four basic categories of controls useful in laser environments. These are engineering controls, personal protective equipment, administrative and procedural controls, and special controls. The controls to be reviewed here are based upon the recommendations of the ANSI Z-136.1 standard. The controls specified by the ANSI Z-136.1 standard have been rather universally adopted by industry, medicine and government as the "user requirements" of lasers. In general, the controls are rather easily implemented by the LSO of the facility. A summary of controls is given in Table VII-1. For all users of lasers and laser systems, it is recommended that the minimum radiation level be used for the required application. If levels higher than the MPE are required, it is recommended that such higher powered lasers be "embedded" in a Class I laser system configuration whenever feasible. (Table VII-1. Summary: Laser Protection Control Measures Recommended by ANSI Z-136.1 (1986), see printed copy) Designs for lasers, laser systems, and the associated work areas shall be predicated upon the classification of the laser or lasers used. Generally, all purchased systems will be classified by the manufacturer in accordance with the Federal Standard. However, it is the responsibility of the LSO to confirm the classification and recommend or approve all control measures prior to laser equipment or facility use. Important in all controls is the distinction between the functions OF OPERATION, MAINTENANCE AND SERVICE. First, laser systems are classified on the basis of level of the laser radiation accessible during operation. Maintenance is defined as those tasks specified in the user instructions for assuring the performance of the product and may include such tasks as routine cleaning or replenishment of expendables. Service functions are usually performed with far less frequency than maintenance functions (vis: replacing the laser resonator mirrors, repair of faulty components) and often will require access to the laser beam by those performing the service functions. Service functions should be clearly delineated as such in the product's manuals. B. LASER SAFETY OFFICER: The LSO has the authority to monitor and enforce the control of laser hazards and effect the knowledgeable evaluation and control of laser hazards. The LSO administers the overall laser safety program where the duties include, but are not limited to items such as confirming the classification of lasers, effecting (or doing) the NHZ evaluation, assuring that the proper control measures are in place and approving substitute controls, approving SOP's, recommend and/or approve eyewear and other protective equipment, special appropriate signs and labels, approve overall facility controls, effect proper laser safety training as needed, effect medical surveillance and designate the laser/incidental personnel categories. The LSO should receive detailed training including an understanding of lasers, laser bioeffects, exposure limits, classifications, NHZ computations, control measures (including area controls, eyewear, barriers ...etc.) and medical surveillance. In many industrial situations, the LSO will be a parttime activity, depending on number of lasers and general laser activity. The individual is often in the corporate industrial hygiene department or may be a laser engineer with safety responsibility. Some corporations implement an internal laser policy and effect safety practices based upon the ANSI Z-136.1 standard as-well-as their own corporate safety requirements. C. BEAM PATH CONTROLS: There are some uses of Class IIIB and IV Class IV lasers where the entire beam path may be totally enclosed, other uses where the beam path is confined by design to significantly limit access and yet other uses where the beam path is totally open. In each case, the controls required will vary as follows:
(Table VII-2. NHZ distance values for various Lasers, see printed copy) D. LASER CONTROLLED AREA: When the entire beam path from a Class IIIB or Class IV laser is not sufficiently enclosed and/or baffled such that access to radiation above the MPE is possible, a "laser controlled area" is required. During periods of service, a controlled area may be established on a temporary basis. The controlled area will encompass the NHZ. Those controls required for both Class IIIB and Class IV installations are as follows:
E. CLASS IV LASER CONTROLS - GENERAL REQUIREMENTS: Those items recommended for Class IIIB but required for Class IV lasers are as follows:
F. ENTRYWAY CONTROL MEASURES (CLASS IV): In addition, there are specific controls required at the entryway to a Class IV laser controlled area. These can be summarized as follows:
(Table VII-3. Administrative and Procedural Control Measures for the Four Laser Classes: ANSI Z-136.1(1986), see printed copy) G. ADMINISTRATIVE AND PROCEDURAL CONTROLS: Administrative and Procedural Control Measures are summarized in Table VII-3 and detailed below:
(Table VII-4. Engineering Control Measures for the Four Laser Classes: ANSI Z-136/1 (1986), see printed copy)
H. ENGINEERING CONTROLS: The most universal controls are so-called engineering controls (see Table VII- 4). Usually, these are items built into the laser equipment that provide for safety. In most instances, these will be included on the equipment provided by the laser manufacturer as so-called "performance requirements" mandated by the FLPPS. Specifics on some of the more important engineering controls recommended in the ANSI Z-136.1 standard are detailed as follows:
I. SAFETY PROCEDURES - GENERAL BASIC PRECAUTIONS: The LSO shall be notified of the purchase of any laser, regardless of the class. Such notification should include the classification, media, output power or pulse energy, wavelength, repetition rate (if applicable), special attachments (frequency doublers...etc.), beam size at the laser aperture, beam divergence and users. No attempt shall be made to place any shiny or glossy object into the laser beam other than that for which the equipment is specifically designed. Eye protection devices which are designed for protection against radiation from a specific laser system shall be used when engineering controls are inadequate to eliminate the possibility of potentially hazardous eye exposure (i.e., whenever levels of accessible emission exceed the appropriate MPE levels.) This generally applies only to Class IIIB and Class IV lasers. All laser protective eyewear shall be clearly labeled with optical density values and wavelengths for which protection is afforded. Skin protection can best be achieved through engineering controls. If the potential exists for damaging skin exposure, particularly for ultraviolet lasers (200-400 nm), then skin covers and or "sun screen" creams are recommended.
-------------------------------------------------------------------- DIRECT EXPOSURE on the eye by a beam of laser light should always be avoided with any laser, no matter how low the power. --------------------------------------------------------------------
J. ENGINEERING CONTROL MEASURES: Engineering control measures (items incorporated into the laser or laser system by the Manufacturer or designed into the installation by the user) shall be given primary consideration in instituting a control measure program for limiting access to laser radiation. These are summarized in Table VII-4. If engineering controls are impractical or inadequate, administrative and procedural controls and personnel protective equipment approved by the LSO shall be used. If, during periods of service to a laser or laser system, the level of accessible emission exceeds the applicable MPE, temporary control measures may be instituted, as deemed appropriate by the LSO.
K. OPTICAL FIBER (LIGHTWAVE) COMMUNICATION SYSTEMS (OFCS): Under normal operation such systems are completely enclosed (Class I) with the optical fiber and optical connectors forming the enclosure. Under installation or service conditions, or when an accidental break in the cable occurs, the system can no longer be considered enclosed. If engineering controls limit the accessible emission to levels below the applicable MPE (irradiance), no controls are necessary. If the accessible emission is above the MPE, the following requirements shall apply:
VIII. PERSONAL PROTECTIVE EQUIPMENT: ----------------------------------------------------------------- A. PROTECTIVE EQUIPMENT - OVERVIEW: Protective equipment for laser safety generally means eye protection in the form of goggles or spectacles, this includes special prescription eyewear using high optical density filter materials or reflective coatings (or a combination of both) to reduce the potential ocular exposure below MPE limits. Some applications, such as use of high power excimer lasers operating in the ultraviolet, may also dictate the use of a skin cover if chronic (repeated) exposures are anticipated at exposure levels at or near the MPE limits for skin. In general, it is recommended that other controls be employed rather than reliance specifically on the use of protective eyewear. This argument is predicated on the fact that so many accidents have occurred when eyewear was available but not worn. There are many reasons cited for this, but the most common is that laser protective eyewear is often dark, uncomfortable to wear and limits vision.
B. LASER PROTECTIVE EYEWEAR: A wide variety of commercially available optical absorbing filter materials (glass and plastics) and various coated reflecting "filters" (dielectric and holographic) are available for laser eye protection. Some are available with spectacle lenses ground to prescription specifications. Protection for multiple laser wavelengths is becoming more common in the research environment as more applications involve several laser types. In this case, dual filters are often the design of choice; frequently mounted in a "flip-up" style goggle or spectacle frame. The spectral absorption of the filter at the laser wavelength determines the percentage of the beam absorbed by the protective filter. If properly designed, the filter will reduce the "worst case" exposure of the beam to the MPE level. In general, the stronger the filter's absorption ability, the higher the laser power for which the filter provides protection. This is specified by the filter "optical density" (OD) as is detailed below. Filters are designed to make use of selective spectral absorption by colored glass or plastic, or selective reflection from dielectric coatings on glass, or both. Each method has its advantages. Historically, the most common eye protection has been the use of special colored glass absorbing filters. These are generally the most effective in resisting damage from general use as-well-as from exposure to intense laser sources. Unfortunately, not all absorbing glass filters used for laser protection can be easily annealed (thermally hardened) and, consequently, do not provide adequate impact resistance. In some goggle designs, however, impact resistant plastic filters (polycarbonate) can be used together with non-hardened glass filters in a goggle design where the plastic is placed in front and behind of the non-hardened laser filter glass. In some tests, glass filter plates have cracked and shattered following intense Q-switched pulsed laser exposures. In some instances, the shattering occurred after one-quarter to one-half hour had elapsed following the exposure. Also, at least one glass filter type has been shown to photobleach when exposed to the short pulses of a Q-switched laser. The advantage of using reflective coatings is that they can be designed to selectively reflect a given wavelength while transmitting as much of the remaining visible spectrum as possible. However, some angular dependence the of spectral attenuation factor may be present. The advantages of using absorbing plastic filters materials are greater impact resistance, lighter weight, and convenience of molding the eyeprotection into comfortable shapes. The disadvantages are that they are more readily scratched and the filters often "age" poorly in that the organic dyes used as absorbers are more readily affected by heat and/or ultraviolet radiation which cause the filter to significantly darken. In addition, as will be discussed, the plastic materials generally display a lower threshold for laser beam penetration. It should be stressed that there are few known materials that can withstand laser exposures which exceed 10(5) W/cm(2) since the electric fields associated with the beam will exceed the bonding forces of matter. Most materials will begin to degrade at levels far below these field strength levels due to thermal or shock effects. Typical CO(2) laser eyewear products are often made from polycarbonate plastics. These materials are light in weight, relatively inexpensive, and have a high optical density at the 10.6 ?m CO(2) wavelength. It should be noted that such plastic protective eyewear has a penetration threshold level (PTL) of about 5 W/cm(2). It has been shown that for an "arms length" distance of 50 centimeters, the maximum allowed laser beam power limit for a raw beam exposure condition on such plastic eyeprotectors should be less than 20 watts. If beam expansion is present (such as occurs beyond the focus of a simple lens), the power limit is increased to about 200 watts; well above the levels generally experienced without optical enhancement. The upper power limitation for use with plastic eyewear when exposed by a diffuse reflection at 50 cm is well above the power available in commercially available CO(2) lasers. Therefore plastic eyewear should be acceptable for most laser use situations. It should be strongly noted, however, that the use of plastic eyewear becomes questionable when exposure conditions are closer than "arms length" from the laser and/or under conditions of a direct "raw beam" exposure above a 20 watt level. Such exposures are not likely in most laser facilities; especially for support staff standing at a some distance from the laser. A 20 watt "raw beam" exposure would be far more likely to occur during servicing to the laser equipment or to the operator of a open (Class IV) laser while working at close distances where the irradiance could easily exceed the 5 W/cm(2) limit. While direct raw beam exposure onto eyewear is certainly not recommended under any normal condition, it does occur. At least one intrabeam eye accident with thermal puncture of plastic laser eyewear has been reported with a Nd:Yag laser in a research laboratory. Those using CO(2) laser devices should be reminded that materials which do not appear specular (mirror-like) to the eye may be specular at the 10.6 ?m far infrared wavelength, e.g., brushed metal surfaces and enamel-metal surfaces. The beam should not be directed near any such surface, particularly if flat. Where possible, optical elements which have convex surfaces to diverge the beam should be used in or near the beam path. C. SELECTING LASER EYEWEAR: For all personnel using Class IIIB and Class IV lasers, whether in the production facility, research lab, out-patient clinic or surgical environment must be informed to make the correct and optimum choice of laser protective eyewear. This means, in general, the need for a more complete understanding of such topics as:
It should be stressed that laser hazards can also include hazards associated with electrical power supplies, flammable or toxic chemicals and materials, fuel hazards, respiratory hazards from laser induced fumes and vapors, and noise hazards. These factors should also be considered in selection of protective equipment; especially eyewear. These conditions may result in hazards from laser related operation (flash tubes, chemicals, fumes, etc.). Consult ANSI Z-87.1: The American National Standard Practice for Occupational and Educational Eye and Face Protection, as-well-as ANSI Z136.1. It should be noted also that a separate edition of the ANSI standard that pertains only to medical lasers is also available. This edition is ANSI Z136.3 (1988), and is entitled: "Safe Use of Lasers in Health Care Facilities". This standard addresses the MPE requirements, NHZ specifications, training needs and equipment features, eye and skin protection needs, beam measurement requirements, fume and toxic gas control, equipment and facility audits as-well-as all other appropriate area controls and procedural needs for medical laser usage. D. SELECTION CRITERIA: The basic requirements for protective eyewear as proposed in the ANSI Z-136.1 standard can be summarized as follows:
The laser parameters of wavelength and exposure time are the most important in determining the maximum permissible exposure (MPE) levels for a specific laser. The ANSI Z-136.1 standard provides charts and tables that allow determination of such levels. E. LASER OUTPUT FACTORS: As the laser industry has grown and matured, more lasers have become available with even more complex outputs. Now such exotic terms as: super-pulsed, Q-switched, mode-locked, femtoseconds, Excimers...etc. are used to describe the laser performance. In addition, more safety equipment suppliers provide different types of eye protection; and we hear arguments about alignment versus full protection, plastic versus glass, "laser safe" frames versus untested frames ...etc. The eye protection selection process has become more complex as the industry has grown. The different modes of operation of a laser are distinguished by the rate at which energy is emitted. These include such factors as CW, normal pulse mode, repetitively pulsed, Q-switched and mode-locked. (See Glossary, Appendix A) These lasers are by no means representative of the vast number of different lasers which are manufactured. It is evident that even these most common laser types produce a wide range of output levels and specific beam characteristics which are dependent in a complex way upon the particular laser media and the manner in which it is operated. This makes a general broad comparison of all laser devices a difficult, if not impossible task, especially for safety eye protection specifications. For pulsed lasers, the peak power characteristics are all important, and typically, the output specifications are expressed in terms of the pulse energy (Joules) for a given pulse length (seconds). When the output beam is repetitively pulsed, the output beam specifications are usually expressed in terms of average power (Watts), pulse repetition rate (Hertz or pulses-per-second), and single pulse duration (seconds). In addition, the peak power (Watts) of the individual pulse is also often specified. Depending upon design, the beams will, in general, be delivered in a single pulse, in a series of repetitive pulses, or as a continuous wave (CW) level of radiant power. The major parameters needed when selecting laser protective eyewear are listed below: WAVELENGTH(S): The wavelength(s) of laser radiation limits the type of eye protection chosen to only that type which reduce the power level at a particular wavelength(s) from reaching the eye at hazardous levels. It is emphasized that many lasers emit more than one wavelength and that each wavelength must be considered. Considering the wavelength corresponding to the greatest output intensity is not always adequate. For example, a frequency doubled Nd:YAG operating at 0.532 ?m may emit about 2 watts at the green wavelength while the Nd:YAG laser itself (operating at 1.064 ?m in the near infrared) emits 50 watts. But some safety filters which strongly absorb the 0.532 m wavelength may absorb essentially nothing at the 1.064 ?m wavelength. This is big problem for dye lasers which have a variable or tunable wavelength ability. In such cases, the eyewear can only be specified over a narrow band of wavelengths where the therapy is to be done. OPTICAL DENSITY: Optical density is a parameter for specifying the attenuation afforded by a given thickness of any transmitting medium. Since laser beam intensities may be a factor of a thousand or a million above safe exposure levels, percent transmission notation can be unwieldy and is not used. As a result, laser protective eyewear filters are specified in terms of the logarithmic units of Optical Density (usually referred to as "OD"). The optical density (OD) of a specific filter at a given laser wavelength is related by the equation:
where H(o) is the anticipated "worst case" exposure (usually directly out of the laser) and is expressed in the units of W/cm(2) or J/cm(2) depending upon whether the laser in question is CW, repetitively pulsed or single pulse. The MPE is expressed in the identical units as the MPE limit. It should be noted that since the MPE values are distributed over the pupil diameter (limiting aperture), the calculation for H(o) for beams smaller than the limiting aperture requires that the limiting aperture be used instead of the smaller beam size. That is, the calculation is made as though the beam were spread over the limiting aperture. (See example below.) Because of the logarithmic factor, a filter attenuating a beam by a factor of 1,000 (or 10(3)) has an optical density of 3, and attenuating a beam by 1,000,000 or (10(6)) has an optical density of 6. The required optical density is determined by the maximum laser beam intensity to which the individual could be exposed. The optical density of two highly absorbing filters when stacked together is essentially the linear sum of two individual optical densities. LASER BEAM INTENSITY: The maximum laser beam power (Watts) or pulse energy (Joules). In some cases, the beam size is needed where pulsed lasers are expressed in radiant exposure units of Joules/cm(2) and CW lasers in terms of beam irradiance in Watts/cm(2). VISIBLE TRANSMITTANCE OF EYEWEAR: Since the object of laser protective eyewear is to filter out the laser wavelengths while transmitting as much of the visible light as possible, the visible (or luminous) transmittance should as high as possible. A low visible transmittance (usually measured in percent) creates problems of eye fatigue and may require an increase in ambient lighting. However, adequate optical density at the laser wavelengths should not be sacrificed for improved visible transmittance. There can be, in some instances, significant differences between the luminous transmission of different filter types for a given laser. In one instance, a specific (green) plastic filter for Nd:YAG lasers has less than 35% visible transmittance while several corresponding glass filters (with only a slight tint) can yield luminous transmissions above 85%. In both cases, adequate OD's are provided for filtration of the Nd:YAG beam. It is simply more difficult to see through the darker green plastic filters and the clearer glass filter is better suited. Low visible transmittance has been repeatedly linked with the common practice of "cheating" (i.e., removing the laser eyewear in order to see the area where the beam will hit). This has obvious impact on laser accidents. LASER FILTER DAMAGE LEVEL: (Maximum Irradiance). At some specific beam intensity, the filter material which absorbs the laser radiation can be damaged. Plastic materials have damage thresholds much lower than glass filters and glass (by itself) is lower than a dielectric coated glass. The damage threshold is especially important for those who work closely to the beam interaction site where there is a much higher probability to receive a direct exposure. Typical damage thresholds for CW lasers fall between 400 and 1000 watts/cm(2) for dielectric coated glass, 100 to 300 watts/cm(2) for uncoated glass and 1 to 10 watts/cm(2) for plastics. The German eye protection standard (DIN 58 215), for example, requires that both the filter and frame be designed to withstand an exposure of 10 seconds (CW or PRF 10 hz) or 100 pulses (prf hz) without a loss of rated optical density. A similar test exposure criteria is not specifically required by the ANSI Z-136.1 standard, although the standard does indicate that the radiant exposure or irradiance and the corresponding time factors at which damage occurs (penetration), including transient bleaching, is a important factor in determining the appropriate eyewear to be used. However, unless the eyewear is designed to meet the German DIN standard requirements, damage threshold limits may be difficult to identify and evaluate. A 1979 FDA study EVALUATION OF COMMERCIALLY AVAILABLE LASER PROTECTIVE EYEWEAR (HEW Publication (FDA) 79-8086) reported limited testing of laser protective eyewear available at that time. For example, tests were reported for Q- switched rubylaser exposures (0.694 ?m) on various manufacturer's protective eyewear. The plasticlaser protective eyewear displayed damage thresholds (surface pitting) ranging from 3.8 to 18 J/cm(2) while glass filters required a radiant exposure ranging from 93 to 1620 J/cm(2). Detailed damage threshold data for protective eyewear of more recent vintage is not readily available. F. OPTICAL DENSITY DETERMINATION: Two major factors are required to establish the OD; namely the laser output level and the MPE value for that laser wavelength and at the specified exposure time. For CW lasers, exposure times can be selected as short as the "blink reflex" time (0.25 second) for some visible lasers; to 10 seconds for some infrared lasers; 600 seconds for viewing diffuse reflections (when they do not act as extended sources). The maximum "worst case" would be an 8 hour (30,000 seconds) exposure that is considered as a maximum daily "occupational" exposure. For pulsed lasers, the individual pulse time is needed and the pulse repetition rate. the MPE value is determined using the ANSI standards. For "worst case" conditions, the beam is considered to be confined to a size of a dark adapted pupil (7 mm). As an example of a single pulse laser, consider the case of an 80 milliJoule single-pulse (50 nanosecond), Q-switched Nd:YAG laser emitted in a 2 mm beam diameter. This would be a Class IV laser and reference to the ANSI Z-136.1 (1986) standard yields an MPE value for a single pulse of: MPE = 5.0 J/cm(2). The OD is calculated by first determining the value of H(o). From the parameters above, one calculates first the worst case exposure spread over the 7 mm limiting aperture (not the 2 mm beam diameter). The laser beam "area" may be calculated using the equation for a circle as follows:
Thus a filter with OD = 4.6 would provide adequate protection for one pulse from this laser. A wide variety of commercially-available optical filter glass (and plastics) are available for laser eye protection. Some are available in eye-spectacles ground to prescription specifications. One filter-type may be applicable to more than one wavelength. Some filters have a high optical density below a certain "cut-off" wavelength, usually limiting overall visibility. Consequently, protection devices must be selected based upon the specific operational characteristics of the laser being used. One cannot always be assured that the protective device which may be applicable for one laser will apply to another laser of the same media. For example, the eyewear OD requirement for a repetitively pulsed, Q-switched Nd:YAG (Table VIII-1. OD Requirements for ND:YAG Lasers of Different Output Specifications, see printed copy) ophthalmic laser WILL NOT BE THE SAME as selected for a 100 watt CW surgical system or, for that matter, for a 15 watt CW Nd:YAG featuring a diffusing probe on a fiber optic delivery. Each unit contains a Nd:YAG laser but each should receive a separate evaluation for optimum laser eye protection because of the system performance differences. See Table VIII-1. It should be clear that there would be significant difficulty in providing a "one fix - cures all" approach for eyewear selection. The advantages introduced by a broad spectrum of available laser sources is, of itself, a disadvantage when attempting to provide a uniform "all purpose" laser safety code. G. EYE PROTECTION FOR SUPPORT STAFF AND SPECTATORS: Is eye protection needed for the ancillary staff? The answer is YES! In most cases, there can be the possibility of hazardous diffuse reflections and even a diffuse reflection off the wall can exceed the safe exposure limit. If a power less than 500 milliwatts is considered to be a "safe level" to view as a diffuse reflection long-term, and the laser emits 1000 milliwatts, then the potential exposure is well above the safe level, and the beam on the wall could be potentially hazardous to view. The common sense solution is to simply require the use of eye protection. H. FLASHBACK FILTERS FOR VIEWING SYSTEMS: Reflections of argon and neodymium laser radiation back through a microscope or endoscope (flash-back) must be attenuated with protective filters built into the optical systems viewer. For example, studies have shown that the reflections back through the laser catheter were of the order of 2 mW for a specular reflection flashback returning through an endoscope PER WATT OF POWER incident at the distal end of the fiber-optic delivery system used with a Nd:YAG laser; and less than 1mW per watt for the argon laser systems. Thus, filtration would be required to protect the user's eye from injury during viewing. Computations can show that filters having an optical density of 5.4 would be required at the argon laser wavelengths (assuming a 10 W maximum power) to provide protection as well as comfortable viewing during extended exposures. An optical density of at least 2.1 would be required at the Nd:YAG wavelength assuming 100 watts maximum power. I. SELECTION PROCESS: Selection of laser eyewear first requires an analytical review of a specific laser's output parameters and selection of the proper maximum permissible exposure limit from the ANSI standard. From this information, the required filter optical density can then be specified using the equation for OD given earlier. Some will find the logarithmic optical density computation to be beyond their scope of expertise. Those individuals may need to seek assistance from those more experienced in such mathematics or, perhaps, utilize existing computer software programs that are designed to easily provide the answers needed.
J. SUMMARY: Reviewing numerous laser accident conditions has shown that having laser eyewear is not the major problem. The major problem is having the laser personnel wear available eyewear. How does one reinforce the wearing safety eyewear? In any Class IV laser environment the use of eye protection should be a procedural requirement. If laser protective eyewear has been deemed as mandatory for a given procedure, then: ---------------------------------------------------------------- LASER EYEWEAR MUST BE ON BEFORE THE LASER CAN BE TURNED ON! --------------------------------------------------------------- The person who has specific laser safety responsibility of turning on the laser and making sure all the safety features are operational during the process must also be responsible for proper laser eye protection. One positive aspect that comes from a frequent evaluation of a laser safety program is keeping the level of hazard awareness so high that the personnel wear protective eyewear automatically. The eyewear selection process first requires basic laser parameter understanding and some fundamental mathematical skills. The decision process is then reduced to an interrelated combination of task analysis, economics and vendor choice. IX. LASER TRAINING --------------------------------------------------------------------- RECOMMENDED LASER TRAINING REQUIREMENTS: The LSO shall insure that all employees assigned to service, maintain, install, adjust, and operate laser equipment be appropriately qualified and trained. The training program should be designed appropriate to the Class of laser radiation accessible during the required task(s) of the personnel. Laser area supervisors shall maintain the names of all persons trained and date of training and inform the LSO of training completions and requirements. A. CLASS I TRAINING: Class I training can be limited, in general, to information contained in the operation/maintenance manuals of the laser Manufacturer. No additional operator training is necessary provided the Class I status is maintained. B. CLASS II, CLASS IIA AND CLASS IIIA TRAINING: Class II, Class IIA and Class IIIA training can include information contained in the operation/maintenance manuals of the laser Manufacturer and, where appropriate, additional basic safety guide literature of a general topic nature. Short, concise audio-visual programs can also enhance understanding of hazards in some use scenarios especially where Class II, Class IIA or Class IIIA laser systems are subject to frequent operator changes. C. CLASS IIIB AND CLASS IV TRAINING: Class IIIB and Class IV training is recommended for those working with Class IIIB and Class IV lasers, including operators, maintenance personnel, service persons as-well-as those on the technical support staff, technicians, ..etc. The training should provide a complete understanding of the requirements of a safe laser environment and include discussion of the hazards, safety devices required, procedures related to operating the equipment, warning sign requirements and description of medical surveillance practices. Emphasis should be placed on practical, safe laser techniques and procedures as well as safety devices that provide an overall safe environment. D. LASER SAFETY OFFICER TRAINING: Laser Safety Officer training is required for the facility LSO. This can be a comprehensive multi-day course which covers the all key aspects of laser safety and a indepth review of the appropriate standards, OSHA requirements, and needs for state and local compliance, as appropriate. A topical outline of such a training program is given in Table IX-1. E. UPDATE TRAINING REQUIREMENTS: Update training requirements have been shown to be appropriate, especially for research and service personnel where beam alignment is a frequent work requirement. For example, one published account by an individual who lost the sight of one eye when protective eyewear was not used, concluded: "But more important than the actual event is the idea that this incident could have been avoided. Don't let it happen to you or a co-worker. Take time to assess safety conditions, and do it again in 6 months or a year; additional hazards arise in an ever-changing research environment. Safety deserves your thoughtful considerations, now, before your accident." F. TAILORED TRAINING SESSIONS: There often will be a need to tailor the laser safety training session for each of the different groups that use lasers in the facility. Often the type of laser(s) and locations will impact the content of the training program. For example, the hazards and controls recommended for the far-infrared CO(2) lasers are usually different than those for a near-infrared Nd:YAG laser or a visible Argon Ion laser or an ultraviolet Excimer laser. Where possible, the specific course content should be designed for the lasers and personnel in the environment.
----------------------------------------------------------------------- ABSORB To transform radiant energy into a different form, with a resultant rise in temperature. ABSORPTION Transformation of radiant energy to a different form of energy by the interaction of matter, depending on temperature and wavelength. ABSORPTION COEFFICIENT Factor describing light's ability to be absorbed per unit of path length. ACCESSIBLE EMISSION LEVEL The magnitude of accessible laser (or collateral) radiation of a specific wavelength or emission duration at a particular point as measured by appropriate methods and devices. Also means radiation to which human access is possible in accordance with the definitions of the laser's hazard classification. ACCESSIBLE EMISSION The maximum accessible emission level. LIMIT (AEL) permitted within a particularly class. In ANSI Z- 136.1, AEL is determined as the product of Accessible Emission Maximum Permissible Exposure limit (MPE) and the area of the limiting aperture (7mm for visible and near infrared lasers). ACTIVE MEDIUM Collection of atoms or molecules capable of undergoing stimulated emission at a given wavelength. AFOCAL Literally, "without a focal length"; an optical system with its object and image point at infinity. AIMING BEAM A laser (or other light source) used as a guide light. Used coaxially with infrared or other invisible light may also be a reduced level of the actual laser used for surgery or for other applications. AMPLIFICATION The growth of the radiation field in the laser resonator cavity. As the light wave bounces back and forth between the cavity mirrors, it is amplified by stimulated emission on each pass through the active medium. AMPLITUDE The maximum value of the electro-magnetic wave, measured from the mean to the extreme; simply stated: the height of the wave. ANGLE OF INCIDENCE See Incident Ray ANGSTROM UNIT A unit of measure of wavelength dual to 10(-10) meter, 0.1 nanometer, or 10(-4) micrometer, no longer widely used nor recognized in the SI system of units. ANODE An electrical element in laser excitation which attracts electrons from a cathode. APERTURE An opening through which radiation can pass. APPARENT VISUAL ANGLE The angular subtense of the source as calculated from the source size and distance from the eye. It is not the beam divergence of the source. AR COATINGS Antireflection coatings used on optical components to suppress unwanted reflections. ARGON A gas used as a laser medium. It emits blue/green light primarily at 448 and 515 nm. ARTICULATED ARM CO(2) laser beam delivery device consisting of a series of hollow tubes and mirrors interconnected in such a manner as to maintain alignment of the laser beam along the path of the arm. ATTENUATION The decrease in energy (or power) as a beam passes through an absorbing or scattering medium. AUTOCOLLIMATOR A single instrument combining the functions of a telescope and a collimator to detect small angular displacements of a mirror by means of its own collimated light. AVERAGE POWER The total energy imparted during exposure divided by the exposure duration. AVERSION RESPONSE Movement of the eyelid or the head to avoid an exposure to a noxious stimulant, bright light. It can occur within 0.25 seconds, and it includes the blink reflex time. AXIAL-FLOW LASER A laser in which an axial flow of gas is maintained through the tube to replace those gas molecules depleted by the electrical discharge used to excite the gas molecules to the lasing. See gas discharge laser. AXICON LENS A conical lens which, when followed by a conventional lens, can focus laser light to a ring shape. AXIS, OPTICAL AXIS The optical centerline for a lens system; the line passing through the centers of curvature of the optical surfaces of a lens. BEAM A collection of rays that may be parallel, convergent, or divergent. BEAM BENDER A hardware assembly containing an optical device, such as a mirror, capable of changing the direction of a laser beam; used to repoint the beam, and in "folded," compact laser systems. BEAM DIAMETER The distance between diametrically opposed points in the cross section of a circular beam where the intensity is reduced by a factor of e(-1) (0.368) of the level (for safety standards). The value is normally chosen at e(-2) (0.135) of the peak level for manufacturing specifications. BEAM DIVERGENCE Angle of beam spread measured in radians more milliradians (1 milliradian = 3.4 minutes-of-arc or approximately 1 mil). For small angles where the cord is approximately equal to the arc, the beam divergence can be closely approximated by the ratio of the cord length (beam diameter) divided by the distance (range) from the laser aperture. BEAM EXPANDER An optical device that increases beam diameter while decreasing beam divergence (spread). In its simplest form consists of two lenses, the first to diverge the beam and the second to re-collimate it. Also called an upcollimator. BEAM SPLITTER An optical device using controlled reflection to produce two beams from a single incident beam. BLINK REFLEX See aversion response. BREWSTER WINDOWS The transmissive end (or both ends) of the laser tube, made of transparent optical material and set at Brewster's angle in gas lasers to achieve zero reflective loss for one axis of plane polarized light. They are non-standard on industrial lasers, but a must if polarization is desired. BRIGHTNESS The visual sensation of the luminous intensity of a light source. The brightness of a laser beam is most closely associated with the radio-metric concept of radiance. C.I.E. Abbreviation for Commission International de l'Eclairage, the French translation for: International Commission on Illumination. CALORIMETER An instrument which measures the energy, usually as heat generated by absorption of the laser beam. CARBON DIOXIDE Molecule used as a laser medium. Emits far energy at 10,600 nm (10.6 ?m). CATHODE A negatively charged electrical element providing electrons for an electrical discharge. CLOSED INSTALLATION Any location where lasers are used which will be closed to unprotected personnel during laser operation. CO(2) LASER A widely used laser in which the primary lasing medium is carbon dioxide gas. The output wavelength is 10.6 ?m (10600 nm) in the far infrared spectrum. It can be operated in either CW or pulsed. COAXIAL GAS A shield of inert gas flowing over the target material to prevent plasma oxidation and absorption, blow away debris, and control heat reaction. The gas jet has the same axis as the beam,so the two can be aimed together. COHERENCE A term describing light as waves which are in phase in both time and space. Monochromaticity and low divergence are two properties of coherent light. COLLIMATED LIGHT Light rays that are parallel. Collimated light is emitted by many lasers. Diverging light may be collimated by a lens or other device. COLLIMATION Ability of the laser beam to not spread significantly (low divergence) with distance. COMBINER MIRROR The mirror in a laser which combines two or more wavelengths into a coaxial beam. CONTINUOUS MODE The duration of laser exposure is controlled by the user (by foot or hand switch). CONTINUOUS WAVE (CW) Constant, steady-state delivery of laser power. CONTROLLED AREA An locale where the activity of those within are subject to control and supervision for the purpose of laser radiation hazard protection. CONVERGENCE The bending of light rays toward each other, as by a positive (convex) lens. CORRECTED LENS A compound lens that is made measurably free of aberrations through the careful selection of its dimensions and materials. CRYSTAL A solid with a regular array of atoms. Sapphire (Ruby Laser) and YAG (Nd:YAG laser) are two crystalline materials used as laser sources. CURRENT REGULATION Laser system regulation in which discharge current is kept constant. CURRENT SATURATION The maximum flow of electric current in a conductor; in a laser, the point at which further electrical input will not increase laser output. CW Abbreviation for continuous wave; the continuous-emission mode of a laser as opposed to pulsed operation. DEPTH OF FIELD The working range of the beam in or near the focal plane of a lens; a function of wavelength, diameter of the unfocused beam, and focal length of the lens. DEPTH OF FOCUS The distance over which the focused laser spot has a constant diameter and thus constant irradiance. DICHROIC FILTER Filter that allows selective transmission of colors desired wavelengths. DIFFRACTION Deviation of part of a beam, determined by the wave nature of radiation and occurring when the radiation passes the edge of an opaque obstacle. DIFFUSE REFLECTION Takes place when different parts of a beam incident on a surface are reflected over a wide range of angles in accordance with Lambert's Law. The intensity will fall-off as the inverse of the square of the distance away from the surface and also obey a Cosine Law of reflection. DIFFUSER An optical device or material that homogenizes the output of light causing a very smooth, scattered, even distribution over the area affected. The intensity will obey Lambert's law (see Diffuse Reflection). DIVERGENCE The increase in the diameter of the laser beam with distance from the exit aperture. The value gives the full angle at the point where the laser radiant exposure or irradiance is e(-1) or e(-2) of the maximum value, depending upon which criteria is used. DOSIMETRY Measurement of the power, energy, irradiance or radiant exposure of light delivered are two crystalline materials used as laser to tissue. DRIFT All undesirable variations in output either amplitude or frequency). ANGULAR DRIFT Any unintended change in direction of the beam before, during, and after warmup; measured in mrad. DUTY CYCLE Ratio of total "on" duration to total exposure duration for a repetitively pulsed laser. ELECTRIC VECTOR The electric field associated with a light wave which has both direction and amplitude. ELECTROMAGNETIC RADIATION The propagation of varying electric and magnetic fields through space at the velocity of light. ELECTROMAGNETIC SPECTRUM The range of frequencies and wavelengths emitted by atomic systems. The total spectrum includes radiowaves as well as short cosmic rays. Wavelengths cover a range from 1 hz to perhaps as high as 1020 hz. ELECTROMAGNETIC WAVE A disturbance which propagates outward from an electric charge that oscillates or is accelerated. Includes radio waves; X-rays; gamma rays; and infrared, ultraviolet, and visible light. ELECTRON Negatively charged particle of an atom. EMBEDDED LASER A laser with an assigned class number higher than the inherent capability of the laser system in which it is incorporated, where the systems lower classification is appropriate to the engineering features limiting accessible emission. EMERGENT BEAM DIAMETER Diameter of the laser beam at the exit aperture of the system in centimeters (cm) defined at e(-1) or e(-2) irradiance points. EMISSION Act of giving off radiant energy by an atom or molecule. EMISSIVITY The ratio of the radiant energy emitted by a any source to that emitted by a blackbody at the same temperature. EMITTANCE The rate at which emission occurs. ENCLOSED LASER DEVICE Any laser or laser system located within an enclosure which does not permit hazardous optical radiation emission from the enclosure. The laser inside is termed an "embedded laser." ENERGY The product of power (watts) and duration (seconds). One watt second = one Joule. ENERGY (Q) The capacity for doing work. Energy is commonly used to express the output from pulsed lasers and it is generally measured in Joules (J). The product of power (watts) and duration (seconds). One watt second = one Joule. ENERGY SOURCE High voltage electricity, radiowaves, flashes of light, or another laser used to excite the laser medium. ENHANCED PULSING Electronic modulation of a laser beam to produce high peak power at the initial stage of the pulse. This allows rapid vaporization of the material without heating the surrounding area. Such pulses are many times the peak power of the CW mode (also called "Superpulse"). ETALON A Fabry-Perot interferometer with a fixed air gap separation. Such a device also serves as a basic laser resonant cavity. EXCIMER "EXCITED DIMER." A gas mixture used as the active medium in a family of lasers emitting ultraviolet light. EXCITATION Energizing a material into a state of population inversion. EXCITED STATE Atom with an electron in a higher energy level than it normally occupies. EXEMPTED LASER PRODUCT In the U.S., a laser device exempted by the U.S. Food and Drug Administration from all or some of the requirements of 21 CFR 1040. EXTENDED SOURCE An extended source of radiation can be resolved into a geometrical image in contrast with a point source of radiation, which cannot be resolved into a geometrical image. A light source whose diameter subtends a relatively large angle from an observer. F-NUMBER The focal length of lens divided by its usable diameter. In the case of a laser the usable diameter is the diameter of the laser beam or a smaller aperture which restricts a laser beam. FABRY-PEROT INTERFEROMETER Two plane, parallel partially reflective optically flat mirrors placed with a small air gap separation (1-20 mm) so as to produce interference between the light waves (interference fringes) transmitted with multiple reflections through the plate. FAILSAFE INTERLOCK An interlock where the failure of a single mechanical or electrical component of the interlock will cause the system to go into, or remain in, a safe mode. FEMTOSECONDS 10(-15) seconds. FIBEROPTICS A system of flexible quartz or glass fibers with internal reflective surfaces that pass light through thousands of glancing (total internal) reflections. FLASHLAMP A tube typically filled with Krypton or Xenon. Produces a high intensity white light in short duration pulses. FLUORESCENCE The emission of light of a particular wavelength resulting from absorption of energy typically from light of shorter wavelengths. FLUX The radiant, or luminous, power of a light beam; the time rate of the flow of radiant energy across a given surface. FOCAL LENGTH Distance between the center of a lens and the point on the optical axis to which parallel rays of light are converged by the laser. FOCAL POINT That distance from the focusing lens where the laser beam has the smallest diameter. FOCUS As a noun, the point where rays of light meet which have been reflected by a mirror or refracted by a lens, giving rise to an image of the source. As a verb, to adjust focal length for the clearest image and smallest spot size. FOLDED RESONATOR Construction in which the interior optical path is bent by mirrors; permit compact packaging of a long laser cavity. FREQUENCY The number of light waves passing a fixed point in a given unit of time, or the number of complete vibrations in that period. GAIN Another term for amplification. GAS DISCHARGE LASER A laser containing a gaseous lasing medium in a glass tube in which a constant flow of gas replenishes the molecules depleted by the electricity or chemicals used for excitation. GAS LASER A type of laser in which the laser action takes place in a gas medium. GATED PULSE A discontinuous burst of laser light, made by timing (gating) a continuous wave output - usually in fractions of a second. GAUSSIAN CURVE NORMAL Statistical curve showing a peak with even distribution on either side. May either be a sharp peak with steep sides, or a blunt peak with shallower sides. Used to show power distribution in a beam. The concept is important in controlling the geometry of the laser impact. GROUND STATE Lowest energy level of an atom. HALF-POWER POINT The value on either the leading or trailing edge of a laser pulse at which the power is one-half of its maximum value. HEAT SINK A substance or device used to dissipate or absorb unwanted heat energy. HELIUM-NEON (HeNe) LASER A laser in which the active medium is a mixture of helium and neon. Its wavelength is usually in the visible range. Used widely for alignment, recording, printing, and measuring. HERTZ (Hz) Unit of frequency in the International System of Units (SI), abbreviated Hz; replaces cps for cycles per second. HOLOGRAM A photographic film or plate containing interference patterns created by the coherence of laser light. A three dimensional image may be reconstructed from a hologram. Here are transmission, reflection or integral holograms. IMAGE The optical reproduction of an object, produced by a lens or mirror. A typical positive lens converges rays to form a "real" image which can be photographed. A negative lens spreads rays to form a "virtual" image which can't be projected. INCIDENT LIGHT A ray of light that falls on the surface of a lens or any other object. The "angle of incidence" is the angle made by the ray with a perpendicular to the surface. INFRARED RADIATION (IR) Invisible Electromagnetic radiation with wavelengths which lie within the range of 0.70 to 1000 ?m. These wavelengths are often broken up into regions: IR-A (0.7-1.4 ?m), IR-B (1.4-3.0 ?m) and IR-C (3.0-1000 ?m). INTEGRATED RADIANCE Product of the exposure duration times the radiance. Also known as pulsed radiance. INTENSITY The magnitude of radiant energy. INTRABEAM VIEWING The viewing condition whereby the eye is exposed to all or part of a direct laser beam or a specular reflection. ION LASER A type of laser employing a very high discharge current, passing down a small bore to ionize a noble gas such as argon or krypton. IONIZING RADIATION Radiation commonly associated with X-Ray or other high energy electro-magnetic radiation which will cause DNA damage with no direct, immediate thermal effect. Contrasts with non-ionizing radiation of lasers. IRRADIANCE (E) Radiant flux (radiant power) per unit area incident upon a given surface. Units: Watts per square centimeter. (Sometimes referred to as power density, although not exactly correct). IRRADIATION Exposure to radiant energy, such as heat, X-rays, or light. JOULE (J) A unit of energy (1 watt-second) used to describe the rate of energy delivery. It is equal to one watt-second or 0.239 calorie. JOULE/cm(2) A unit of radiant exposure used in measuring the amount of energy incident upon a unit area. KTP Potassium Titanyl Phosphate. A crystal used to change the wavelength of a Nd:YAG laser from 1060 nm (infrared) to nm (green). LAMBERTIAN SURFACE An ideal diffuse surface whose emitted or reflected radiance (brightness) is dependent on the viewing angle. LASER An acronym for light amplification by stimulated emission of radiation. A laser is a cavity, with mirrors at the ends, filled with material such as crystal, glass, liquid, gas or dye. A device which produces an intense beam of light with the unique properties of coherency, collimation and monochromaticity. LASER ACCESSORIES The hardware and options available for lasers, such as secondary gases, Brewster windows, Q-switches and electronic shutters. LASER CONTROLLED AREA See CONTROLLED AREA. LASER DEVICE Either a laser or a laser system. LASER MEDIUM (Active Medium) material used to emit the laser light and for which the laser is named. LASER OSCILLATION The buildup of the coherent wave between laser cavity end mirrors producing standing waves. LASER PRODUCT A legal term in the U.S. See 21 CFR 1040.10, a laser or laser system or any other product that incorporates or is intended to incorporate a laser or a laser system. LASER ROD A solid-state, rod-shaped lasing medium in which ion excitation is caused by a source of intense light, such as a flashlamp. Various materials are used for the rod, the earliest of which was synthetic ruby crystal. LASER SAFETY OFFICER (LSO) One who has authority to monitor and enforce measure to the control of laser hazards and effect the knowledgeable evaluation and control of laser hazards. LASER SYSTEM An assembly of electrical, mechanical and optical components which includes a laser. Under the Federal Standard, a laser in combination with its power supply (energy source). LEADING EDGE SPIKE The initial pulse in a series of pulsed laser emissions, often useful in starting a reaction at the target surface. The trailing edge of the laser power is used to maintain the reaction after the initial burst of energy. LENS A curved piece of optically transparent material which depending on its shape is used to either converge or diverge light. LIGHT The range of electromagnetic radiation frequencies detected by the eye, or the wavelength range from about 400 to 760 nanometers. The term is sometimes used loosely to include radiation beyond visible limits. LIGHT REGULATION A form of power regulation in which output power is monitored and maintained at a constant level by controlling discharge current. LIMITING ANGULAR SUBTENSE The apparent visual angle which divides intrabeam viewing from extended-source viewing. LIMITING APERTURE The maximum circular area over which radiance and radiant exposure can be averaged when determining safety hazards. LIMITING EXPOSURE DURATION An exposure duration which is specifically limited by the design or intended use(s). LONGITUDINAL OR AXIAL MODE Determines the wavelength bandwidth produced by a given laser system controlled by the distance between the two mirrors of the laser cavity. Individual longitudinal mode standing waves within a laser cavity. LOSSY MEDIUM A medium which absorbs or scatters radiation passing through it. MAINTENANCE Performance of those adjustments or procedures specified in user information provided by the manufacturer with the laser or laser system, which are to be performed by the user to ensure the intended performance of the product. It does not include operation or service as defined in this glossary. MAXIMUM PERMISSIBLE EXPOSURE (MPE) The level of laser radiation to which person may be exposed without hazardous effect or adverse biological changes in the eye or skin. MENISCUS LENS A lens which has one side convex, the other concave. METASTABLE STATE The state of an atom, just below a higher excited state, which an electron occupies momentarily before destabilizing and emitting light. The upper of the two lasing levels. MICROMETER A unit of length in the International System of Units (SI) equal to one-millionth of a meter. Often referred to as a "micron". MICRON An abbreviated expression for micrometer which is the unit of length equal to 1 millionth of a meter. See MICROMETER. MICROPROCESSOR A digital chip (computer) that operates, controls and monitors some lasers. MODE A term used to describe how the power of a laser beam is geometrically distributed across the cross-section of the beam. Also used to describe the operating mode of a laser such as continuous or pulsed laser. MODE LOCKED A method of producing laser pulses in which short pulses (approximately 10-12 second) are produced and emitted in bursts or a continuous train. MODULATION The ability to superimpose an external signal on the output beam of the laser as a control. MONOCHROMATIC LIGHT Theoretically, light consisting of just one wavelength. No light is absolutely single frequency since it will have some bandwidth. Lasers provide the narrowest of bandwidths that can be achieved. MULTIMODE Laser emission at several closely-spaced frequencies. NANOMETER (nm) A unit of length in the International System of Units (SI) equal to one-billionth of a meter. Abbreviated nm - a measure of length. One nm equals 10(-9) meter, and is the usual measure of light wavelengths. Visible light ranges from about 400 nm in the purple to about 760 nm in the deep red. NANOSECOND One billionth (10(-9)) of a second. Longer than a picosecond or femto-second, but shorter than a micro-second. Associated with Q-switched lasers. Nd:GLASS LASER A solid-state laser of neodymium: glass offering high power in short pulses. A Nd doped glass rod used as a laser medium to produce 1064 nm light. Nd:YAG LASER Neodymium:Yttrium Aluminum Garnet. A synthetic crystal used as a laser medium to produce 1064 nm light. NEAR FIELD IMAGING A solid-state laser imaging technique offering control of spot size and hole geometry, adjustable working distance, uniform energy distribution, and a wide range of spot sizes. NEMA Abbreviation for National Electrical Manufactures' Association, a group which defines and recommends safety standards for electrical equipment. NEODYMIUM (Nd) The rare earth element that is the active element in Nd:YAG laser and Nd:Glass lasers. NOISE Unwanted minor currents or voltages in an electrical system. NOMINAL HAZARD ZONE (NHZ) The nominal hazard zone describes the space within which the level of the direct, reflected or scattered radiation during normal operation exceeds the applicable MPE. Exposure levels beyond the boundary of the NHZ are below the appropriate MPE level. NOMINAL OCULAR HAZARD DISTANCE (NOHD) The axial beam distance from the laser where the exposure or irradiance falls below the applicable exposure limit. OBJECT The subject matter or figure imaged by, or seen through, an optical system. OPACITY The condition of being non-transparent. OPEN INSTALLATION Any location where lasers are used which will be open to operating personnel during laser operation and may or may not specifically restrict entry to observers. OPERATION The performance of the laser or laser system over the full range of its intended functions (normal operation). It does not include maintenance or services as defined in this glossary. OPTIC DISC The portion of the optic nerve within the eye which is formed by the meeting of all the retinal nerve fibers at the level of the retina. OPTICAL CAVITY (Resonator) Space between the laser mirrors where lasing action occurs. OPTICAL DENSITY A logarithmic expression for the attenuation produced by an attenuating medium, such as an eye protection filter. OPTICAL FIBER A filament of quartz or other optical material capable of transmitting light along its length by multiple internal reflection and emitting it at the end. OPTICAL PUMPING The excitation of the lasing medium by the application of light rather than electrical discharge. OPTICAL RADIATION Ultraviolet, visible and infrared radiation (0.35-1.4 ?m) that falls in the region of transmittance of the human eye. OPTICAL RESONATOR See Resonator. OPTICALLY PUMPED LASERS A type of laser that derives energy from another light source such as a xenon or krypton flashlamp or other laser source. OUTPUT COUPLER Partially reflective mirror in laser cavity which allows emission of laser light. OUTPUT POWER The energy per second measured in watts emitted from the laser in the form of coherent light. PHASE Waves are in phase with each other when all the troughs and peaks coincide and are "locked" together. The result is a reinforced wave in increased amplitude (brightness). PHOTOCOAGULATION Use of the laser beam to heat tissue below vaporization temperatures with the principal objective being to stop bleeding and coagulate tissue. PHOTOMETER An instrument which measures luminous intensity. PHOTON In quantum theory, the elemental unit of light, having both wave and particle behavior. It has motion, but no mass or charge. The photon energy (E) is proportional to the EM wave frequency (v) by the relationship: E=hv; where h is Planck's constant (6.63 x l0(-34) Joule-sec). PHOTOSENSITIZERS Chemical substances or medications which increase the sensitivity of the skin or eye to irradiation by optical radiation, usually to UV. PICOSECOND A period of time equal to 10-12 seconds. PIGMENT EPITHELIUM A layer of cells at the back of the retina containing pigment granules. PLASMA SHIELD The ability of plasma to shop transmission of laser light. POCKEL'S CELL An electro-optical crystal used as a Q-switch. POINT SOURCE Ideally, a source with infinitesimal dimensions. Practically, a source of radiation whose dimensions are small compared with the viewing distance. POINTING ERRORS Beam movement and divergence, due to instability within the laser or other optical distortion. POLARIZATION Restriction of the vibrations of the electromagnetic field to a single plane, rather that the innumerable planes rotating about the vector axis. Various forms of polarization include random, linear, vertical, horizontal, elliptical and circular. POPULATION INVERSION A state in which a substance has been energized, or excited, so that more atoms or molecules are in a higher excited state than in a lower resting state. This is necessary prerequisite for laser action. POWER The rate of energy delivery expressed in watts (joules per second). Thus: 1 Watt = 1 Joule x 1 Sec. POWER METER An accessory used to measure laser beam power. PRF Pulse Repetition Frequency. The number of pulses produced per second by a laser. PROTECTIVE HOUSING A protective housing is a device designed to prevent access to radiant power or energy. PULSE A discontinuous burst of laser, light or energy, as opposed to a continuous beam. A true pulse achieves higher peak powers than that attainable in a CW output. PULSE DURATION The "on" time of a pulsed laser, it may be measured in terms of milliseconds, microsecond, or nanosecond as defined by half-peak-power points on the leading and trailing edges of the pulse. PULSE MODE Operation of a laser when the beam is intermittently on in fractions of a second. PULSED LASER Laser which delivers energy in the form of a single or train of pulses. PUMP To excite the lasing medium. See Optical Pumping or Pumping. PUMPED MEDIUM Energized laser medium. PUMPING Addition of energy (thermal, electrical, or optical) into the atomic population of the laser medium, necessary to produce a state of population inversion. Q-SWITCH A device that has the effect of a shutter to control the laser resonator's ability to oscillate. Control allows one to spoil the resonator's "Q-factor", keeping it low to prevent lasing action. When a high level of energy is stored, the laser can emit a very high-peak-power pulse. Q-SWITCHED LASER A laser which stores energy in the laser media to produce extremely short, extremely high intensity bursts of energy. RADIAN A unit of angular measure equal to the angle subtended at the center of a circle by a chord whose length is equal to the radius of the circle. RADIANCE Brightness; the radiant power per unit solid angle and per unit area of a radiating surface. RADIANT ENERGY (Q) Energy in the form of electromagnetic waves usually expressed in units of Joules (watt-seconds). RADIANT EXPOSURE (H) The total energy per unit area incident upon a given surface. It is used to express exposure to pulsed laser radiation in units of J/cm(2). RADIANT FLUX RADIANT POWER - The time rate of flow of radiant energy. Units-watts. (One [1] watt = 1 Joule-per-second). The rate of emission of transmission of radiant energy. RADIANT INTENSITY The radiant power expressed per unit solid angle about the direction of the light. RADIANT POWER See Radiant flux. RADIATION In the context of optics, electromagnetic energy is released; the process of releasing electromagnetic energy. RADIOMETRY A branch of science which deals with the measurement of radiation. RAYLEIGH SCATTERING Scattering of radiation in the course of its passage through a medium containing particles, the sizes of which are small compared with the wavelength of the radiation. REFLECTANCE OR REFLECTIVITY The ratio of the reflected radiant power to the incident radiant power. REFLECTION The return of radiant energy (incident light) by a surface, with no change in wavelength. REFRACTION The change of direction of propagation of any wave, such as an electromagnetic wave, when it passes from one medium to another in which the wave velocity is different. The bending of incident rays as they pass from one medium to another (eg.: air to glass). REPETITIVELY PULSED LASER A laser with multiple pulses of radiant energy occurring in sequence with a PRF greater than or equal to 1 Hz. RESONATOR The mirrors (or reflectors) making up the laser cavity including the laser rod or tube. The mirrors reflect light back and forth to build up amplification. ROTATING LENS A beam delivery lens designed to move in a circle and thus rotate the laser beam around a circle. RUBY The first laser type; a crystal of sapphire (aluminum oxide) containing trace amounts of chromium oxide. SCANNING LASER A laser having a time-varying direction, origin or pattern of propagation with respect to a stationary frame of reference. SCINTILLATION This term is used to describe the rapid changes in irradiance levels in a cross section of a laser beam produced by atmospheric turbulence. SECURED ENCLOSURE An enclosure. to which casual access is impeded by an appropriate means (e.g., door secured by lock, magnetically or electrically operated, latch, or by screws). SEMICONDUCTOR LASER A type of laser which produces its output from semiconductor materials such as GaAs. SERVICE Performance of adjustments, repair or procedures on a non routine basis, required to return the equipment to its intended state. SOLID ANGLE The ratio of the area on the surface of a sphere to the square of the radius of that sphere. It is expressed in steradians (sr). SOURCE The term source means either laser or laser-illuminated reflecting surface, i.e., source of light. SPECTRAL RESPONSE The response of a device or material to monochromatic light as a function of wavelength. SPECULAR REFLECTION A mirror-like reflection. SPONTANEOUS EMISSION Decay of an excited atom to a ground or resting state by the random emission of one photon. The decay is determined by the lifetime of the excited state. SPOT SIZE The mathematical measurement of the diameter of the laser beam. STABILITY The ability of a laser system to resist changes in its operating characteristics. Temperature, electrical, dimensional and power stability are included. STERADIAN (sr) The unit of measure for a solid angle. STIMULATED EMISSION When an atom, ion or molecule capable of lasing is excited to a higher energy level by an electric charge or other means, it will spontaneously emit a photon as it decays to the normal ground state. If that photon passes near another atom of the same frequency, the second atom will be stimulated to emit a photon. SUPERPULSE Electronic pulsing of the laser driving circuit to produce a pulsed output (250-1000 times per second), with peak powers per pulse higher than the maximum attainable in the continuous wave mode. Average powers of superpulse are always lower than the maximum in continuous wave. Process often used on CO(2) surgical lasers. TEM Abbreviation for: Transverse Electro-Magnetic modes. Used to designate the cross-sectional shape of the beam. TEM(oo) The lowest order mode possible with a bell-shaped (Gaussian) distribution of light across the laser beam. THERMAL RELAXATION TIME The time to dissipate the heat absorbed during a laser pulse. THRESHOLD The input level at which lasing begins during excitation of the laser medium. TRANSMISSION Passage of electromagnetic radiation through a medium. TRANSMITTANCE The ratio of transmitted radiant energy to incident radiant energy, or the fraction of light that passes through a medium. TRANSVERSE ELECTROMAGNETIC MODE The radial distribution of intensity across a beam as it exits the optical cavity. See TEM. TUNABLE LASER A laser system that can be "tuned" to emit laser light over a continuous range of wavelengths or frequencies. TUNABLE DYE LASER A laser whose active medium is a liquid dye, pumped by another laser or flashlamps, to produce various colors of light. The color of light may be tuned by adjusting optical tuning elements and-or changing the dye used. ULTRAVIOLET (UV) RADIATION Electromagnetic radiation with wavelengths between soft X-rays and visible violet light, often broken down into UV-A (315-400 nm), UV-B (280-315 nm), and UV-C (100-280 nm). VAPORIZATION Conversion of a solid or liquid into a vapor. VIGNETTING The loss of light through an optical element when the entire bundle of light rays does not pass through; an image or picture that shades off gradually into the background. VISIBLE RADIATION (LIGHT) Electromagnetic radiation which can be detected by the human eye. It is commonly used to describe wavelengths which lie in the range between 400 nm and 700-780 nm. WATT A unit of power (equivalent to one Joule per second) used to express laser power. WATT/cm(2) A unit of irradiance used in measuring the amount of power per area of absorbing surface, or per area of CW laser beam. WAVE An sinusoidal undulation or vibration; a form of movement by which all radiant electromagnetic energy travels. WAVELENGTH The length of the light wave, usually measured from crest to crest, which determines its color. Common units of measurement are the micrometer (micron), the nanometer, and (earlier) the Angstrom unit. WINDOW A piece of glass with plane parallel sides which admits light into or through an optical system and excludes dirt and moisture. YAG Yttrium Aluminum Garnet; a widely used solid-state crystal which is composed of yttrium and aluminum oxides which is doped with a small amount of the rare-earth neodymium.
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Alpha min.. . . . . . . . . . . . . . . . . . . . . . . . . .VI-6 Absorber. . . . . . . . . . . . . . . . . . . . . . . . . . .II-3 Absorbtion Coefficient. . . . . . . . . . . . . . . . . . . III-2 Absorption. . . . . . . . . . . . . . . . . . .II-1, III-1, III-3 Access. . . . . . . . . . . . . . . . . . . . . . . . . . . VII-8 Access Panels . . . . . . . . . . . . . . . . . . . . . . . VII-9 Accessible Emission Levels. . . . . . . . . . . . . . . . . . V-3 Acoustic Shock Waves. . . . . . . . . . . . . . . . . . . . III-1 Acute Exposure. . . . . . . . . . . . . . . . . . . . . . . III-1 Administrative Control. . . . . . . . . . . . . . . . . . . VII-6 Administrative Controls . . . . . . . . . . . . . . .VII-1, VII-5 Airy Disk . . . . . . . . . . . . . . . . . . . . . . . . . II-15 Alarm System. . . . . . . . . . . . . . . . . . . . . . . .VII-12 Alignment . . . . . . . . . . . . . . . . . . . . . . . . .VII-11 Alignment Eyewear . . . . . . . . . . . . . . . . . . . . .VIII-7 Alignment Procedures. . . . . . . . . . . . . . . . . . . . VII-6 Amplification . . . . . . . . . . . . . . . . . . . . .II-2, II-3 Angular Dependence. . . . . . . . . . . . . . . . . . . . .VIII-2 Annual Report . . . . . . . . . . . . . . . . . . . . . . . .IV-6 ANSI. . . . . . . . . . . . . . . . . . . . . . . . . .IV-1, IV-4 ANSI Z-136. . . . . . . . . . . . . . . . . . . . . . . . . .IV-4 ANSI Z-136.2. . . . . . . . . . . . . . . . . . . . . . . . . V-4 Aqueous Fluid of the Eye. . . . . . . . . . . . . . . . . . III-4 Aqueous Media . . . . . . . . . . . . . . . . . . . . . . . III-6 Arc Lamps . . . . . . . . . . . . . . . . . . . . . . . . .III-12 Area Control. . . . . . . . . . . . . . . . . . . . .VII-5, VII-8 Argon . . . . . . . . . . . . . . . . . . II-4, II-5, II-9, III-8 Arms Length . . . . . . . . . . . . . . . . . . . . . . . .VIII-2 Associated Laser Hazards Arc Lamps. . . . . . . . . . . . . . . . . . . . . . .III-12 Collateral Radiation . . . . . . . . . . . . . . . . .III-12 Electrical . . . . . . . . . . . . . . . . . . . . . .III-12 Flammability of Enclosures . . . . . . . . . . . . . .III-12 Fumes. . . . . . . . . . . . . . . . . . . . . . . . .III-11 Industrial Hygiene . . . . . . . . . . . . . . . . . .III-11 RF . . . . . . . . . . . . . . . . . . . . . . . . . .III-12 Ultraviolet Radiation. . . . . . . . . . . . . . . . .III-12 Vapors . . . . . . . . . . . . . . . . . . . . . . . .III-12 Ventilation. . . . . . . . . . . . . . . . . . . . . .III-11 X-Ray Emission . . . . . . . . . . . . . . . . . . . .III-12 Authorization . . . . . . . . . . . . . . . . . . . . . . .VII-11 Axial Gas Flow. . . . . . . . . . . . . . . . . . . . . . . .II-6
Bandpass Filter . . . . . . . . . . . . . . . . . . . . . . II-17 Beam Divergence . . . . . . . . . . . . . . . . . . . . . . II-11 Beam Stop . . . . . . . . . . . . . . . . . . . . . . . . . VII-8 Beam Trap . . . . . . . . . . . . . . . . . . . . . . . . .VII-11 Biological Damage . . . . . . . . . . . . . . . . . . .III-7, V-1 Biological Safety Factor. . . . . . . . . . . . . . . . . . III-7 Birefringent. . . . . . . . . . . . . . . . . . . . . . . . II-16 Bleaching . . . . . . . . . . . . . . . . . . . . . . . . .VIII-5 Blind Spot. . . . . . . . . . . . . . . . . . . . . . . . . III-6 Blink Reflex. . . . . . . . . . . . . . . . . . . . . . . .VIII-6 Blocking Barriers . . . . . . . . . . . . . .VII-5, VII-8, VIII-1 Blue Light. . . . . . . . . . . . . . . . . . . . . . . . . III-8 Bonding Forces. . . . . . . . . . . . . . . . . . . . . . .VIII-2 Brewster's Angle. . . . . . . . . . . . . . . . . . . . . . II-16 BTL . . . . . . . . . . . . . . . . . . . . . . . . VII-8, VIII-1
Carbon Dioxide. . . . . . . . . . . . . . . . . . . . . . . .II-4 Carbon Dioxide Laser. . . . . . . . . . . . . . . . . . . . .II-6 Carcinogenic Effect . . . . . . . . . . . . . . . . . . . . III-3 CAUTION Sign. . . . . . . . . . . . . . . . . . . . . . . . VII-4 Cavities. . . . . . . . . . . . . . . . . . . . . . . . . . .II-7 Cavity. . . . . . . . . . . . . . . . . . . . . . . . . . . .II-4 CDRH. . . . . . . . . . . . . . . . . . . . . . . . . .IV-1, IV-4 Certification . . . . . . . . . . . . . . . . . . . . . IV-5, V-1 Chemical Pumping. . . . . . . . . . . . . . . . . . . . . . .II-2 Chromium. . . . . . . . . . . . . . . . . . . . . . . . . . .II-7 Chronic . . . . . . . . . . . . . . . . . . . . . . . . . . III-8 Chronic Exposure. . . . . . . . . . . . . . . . . . . . . . III-1 Class I . . . . . . . . . . . . . . . . . . .V-2, VII-2, VII-8, . . . . . . . . . . . . . . . . . . . . . . .VII-10, VII-13 Class II . . . . . . . . . . . . . . . . . . V-2, VII-4, VII-10 Class IIA . . . . . . . . . . . . . . . . . . . . . . . . . . V-2 Class III . . . . . . . . . . . . . . . . . . . . . . . . . .VI-1 Class IIIA. . . . . . . . . . . . . . . . . . . V-2, VI-1, VII-4, . . . . . . . . . . . . . . . . . . . . . . . VII-9, VII-10 Class IIIB. . . . . . . . . . . . . . . . . . . .V-2, VI-1, VI-4, . . . . . . . . . . . . . . . . . . . .VII-2, VII-3, VII-4, . . . . . . . . . . . . . . . . . . . VII-5, VII-9, VII-10, . . . . . . . . . . . . . . . . . . . . . . VII-11, VII-13 Class IV. . . . . . . . . . . . . . . . . . . . . V-2, VI-1, VI-4 . . . . . . . . . . . . . . . . . . . .VII-2, VII-3, VII-4, . . . . . . . . . . . . . . . . . . . .VII-5, VII-8, VII-9, . . . . . . . . . . . . . . . . . . VII-10, VII-11, VII-12, . . . . . . . . . . . . . . . . . . . . . . .VII-13, VIII-2 Classification. . . . . . . . . . . . . . . . . .IV-5, V-1, VII-2 Clothing. . . . . . . . . . . . . . . . . . . . . . . . . .VIII-1 CO(2) . . . . . . . . . . . . . . . . . . . . . . . . . . . .II-4 Coagulation Necrosis. . . . . . . . . . . . . . . . . . . . III-2 Coherence . . . . . . . . . . . . . . . . . . . . . . II-9, II-15 Coherence Time. . . . . . . . . . . . . . . . . . . . . . . II-16 Collateral Radiation. . . . . . . . . . . . . . . . . III-12, V-3 Collision Pumping . . . . . . . . . . . . . . . . . . . . . .II-2 Communications. . . . . . . . . . . . . . . . . . . . . . . .II-8 Compact Disc Players. . . . . . . . . . . . . . . . . . . . .II-8 Compliance Procedure. . . . . . . . . . . . . . . . . . . . .IV-5 Compliance Guide for Laser Product. . . . . . . . . . . . . . . . . . . . . .IV-6 Computer Code . . . . . . . . . . . . . . . . . . . . . . . VII-8 Conjunctiva . . . . . . . . . . . . . . . . . . . . . . . . III-5 Connect-Disconnect Switch . . . . . . . . . . . . . . . . .VII-12 Continuous Wave . . . . . . . . . . . . . . . . . . . . . . .II-4 Control Administrative . . . . . . . . . . . . . . . . . . . . VII-6 Area . . . . . . . . . . . . . . . . . . . . . . . . . VII-8 Blocking Barrier, Curtain, Screen. . . . . . . . . . . VII-5 Computer Code. . . . . . . . . . . . . . . . . . . . . VII-8 Defeatable Entryway. . . . . . . . . . . . . . . . . . VII-5 Engineering. . . . . . . . . . . . . . . . . . . . . . VII-8 Entryway . . . . . . . . . . . . . . . . . . . . . . .VII-10 Key. . . . . . . . . . . . . . . . . . . . . . . . . . VII-8 Master Switch. . . . . . . . . . . . . . . . . . . . . VII-8 Non-defeatable Entryway. . . . . . . . . . . . . . . . VII-5 Procedural . . . . . . . . . . . . . . VII-6, VII-10, VII-11 Procedural Entryway. . . . . . . . . . . . . . . . . . VII-5 Control Measures. . . . . . . . . . . . . . . . . . .VII-1, VII-2 Control, Entryway . . . . . . . . . . . . . . . . . . . . . VII-5 Control-Disconnect Switch . . . . . . . . . . . . . . . . .VII-10 Controlled Areas. . . . . . . . . . . . . . . . . . . . . .VII-11 Controls Administrative . . . . . . . . . . . . . . . . . . . . VII-1 Engineering. . . . . . . . . . . . . . . . . . VII-1, VII-11 PPE. . . . . . . . . . . . . . . . . . . . . . . . . . VII-1 Procedural . . . . . . . . . . . . . . . . . . . . . . VII-1 Cornea. . . . . . . . . . . . . . . . . . . . . . . . . . . III-6 Correction Factor, ANSI . . . . . . . . . . . . . . . . . . III-9 Cosine Law. . . . . . . . . . . . . . . . . . . . . . . . . .VI-3 Cosine Scattering . . . . . . . . . . . . . . . . . . . . . .VI-3 Countdown Procedure . . . . . . . . . . . . . . . . . . . .VII-11 Crystals. . . . . . . . . . . . . . . . . . . . . . . . . . .II-7 Curtains. . . . . . . . . . . . . . . . . . .VII-5, VII-8, VIII-1 CW. . . . . . . . . . . . . . . . . . . . . . . . . .II-4, VII-12
DANGER Sign . . . . . . . . . . . . . . . . . . . . . . . . VII-4 De-excitation . . . . . . . . . . . . . . . . . . . . . . . .II-1 Defeatable Entryway Control . . . . . . . . . . . . . . . . VII-5 Diffraction Effects . . . . . . . . . . . . . . . . . . . . II-10 Diffraction Limit . . . . . . . . . . . . . . . . . . . . . III-4 Diffraction Limited . . . . . . . . . . . . . . . . . . . . II-15 Diffraction Limited Beam. . . . . . . . . . . . . . . . . . II-13 Diffraction Limited Spot. . . . . . . . . . . . . . . . . . III-5 Diffuse Reflection NHZ. . . . . . . . . . . . . . . . . . . .VI-5 Diffuse Reflections . . . . . . . . . . . . . III-6, III-8, VI-3, . . . . . . . . . . . . . . . . . . . . . . . VII-5, VIII-7 Extended Source. . . . . . . . . . . . . . . . . . . . .VI-5 Diffusely Reflected Laser . . . . . . . . . . . . . . . . . .VI-4 Dimer, Excited . . . . . . . . . . . . . . . . . . . . . . .II-7 Diode Lasers . . . . . . . . . . . . . . . . . . . . . . . .II-8 Direct Exposure . . . . . . . . . . . . . . . . . . . . . .VII-10 Divergence . . . . . . . . . . . . . . . . . . . . . . . . .II-9 DNA . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-3 Doorways . . . . . . . . . . . . . . . . . . . . . . . . . VII-5 Dye . . . . . . . . . . . . . . . . . . . . . . . . . . . . .II-3 Dye Lasers . . . . . . . . . . . . . . . . . . . . . .II-4, II-9
ED(50). . . . . . . . . . . . . . . . . . . . . . . . . . . III-7 Einstein, Albert. . . . . . . . . . . . . . . . . . . .II-1, II-2 Electric Field . . . . . . . . . . . . . . . . . . . II-9, II-16 Electrical Hazards. . . . . . . . . . . . . . . . . . . . .III-12 Electromagnetic Field . . . . . . . . . . . . . . . . . . . .II-9 Electromagnetic Field Strength . . . . . . . . . . . . . . .II-9 Emission. . . . . . . . . . . . . . . . . . . . . . . . . . .II-2 Enclosed Beam Path. . . . . . . . . . . . . . . . . . . . . VII-2 Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . VII-8 Endoscope . . . . . . . . . . . . . . . . . . . . . . . . .VIII-7 Energy . . . . . . . . . . . . . . . . . . . . . . . . . . II-12 Energy Levels . . . . . . . . . . . . . . . . . . . . . . . .II-1 Engineering Control Measures . . . . . . . . . . . . . . .VII-11 Engineering Controls . . . . . . . . . . . . . . . .VII-1, VII-8 Entryway Control. . . . . . . . . . . . . . . . . . VII-5, VII-10 Entryways . . . . . . . . . . . . . . . . . . . . . . . . . VII-5 Epidermis . . . . . . . . . . . . . . . . . . . . . .III-3, III-5 Erythema . . . . . . . . . . . . . . . . . . . . . . . . . III-2 Etalon . . . . . . . . . . . . . . . . . . . . . . . . . . .II-5 Excimer Lasers . . . . . . . . . . . . . . . . . . . II-7, III-3 Excitation . . . . . . . . . . . . . . . . . . . . . . . . .II-1 Excited Dimer . . . . . . . . . . . . . . . . . . . . . . . .II-7 Excited State . . . . . . . . . . . . . . . . . . . . . . . .II-1 Exfoliation . . . . . . . . . . . . . . . . . . . . . . . . III-5 Extended Source . . . . . . . . . . . . . . . . . . . . . . III-5 Extended Source Diffuse Reflections . . . . . . . . . . . . .VI-5 Extended Source Viewing . . . . . . . . . . . . . . . . . . III-6 Eye Accidents . . . . . . . . . . . . . . . . . . . . . . . VII-6 Eye Injury . . . . . . . . . . . . . . . . . . . . . . . . III-1 Eye Loupe . . . . . . . . . . . . . . . . . . . . . . . . .VII-13 Eye Movements . . . . . . . . . . . . . . . . . . . . . . . III-8 Micronysogmic . . . . . . . . . . . . . . . . . . . . III-9 Saccadic . . . . . . . . . . . . . . . . . . . . . . . III-9 Eye Protection . . . . . . . . . . . . . . . . . . . . . . VII-9 Eyewear . . . . . . . . . . . . . . . . . . .VII-2, VII-5, VII-6, . . . . . . . . . . . . . . . . . . .VII-11, VII-12, VIII-1 Alignment . . . . . . . . . . . . . . . . . . . . . .VIII-7 Glass . . . . . . . . . . . . . . . . . . . . . . . .VIII-8 Laser Resistant . . . . . . . . . . . . . . . . . . .VIII-8 Plastic . . . . . . . . . . . . . . . . . . . . . . .VIII-8 Selecting . . . . . . . . . . . . . . . . . . . . . .VIII-3 Selection Criteria . . . . . . . . . . . . . . . . . .VIII-3 Thermal Shock. . . . . . . . . . . . . . . . . . . . .VIII-2 Transmittance. . . . . . . . . . . . . . . . . . . . .VIII-5
f alpha . . . . . . . . . . . . . . . . . . . . . . . . . . .VI-5 Fabry-Perot Cavity . . . . . . . . . . . . . . . . . . . . .II-9 Failsafe. . . . . . . . . . . . . . . . . . . . . . . . . . VII-9 Far-field Diffraction Pattern . . . . . . . . . . . . . . . II-13 Far-Infrared Wavelengths A, B, and C . . . . . . . . . . . . . . . . . . . . . III-6 FEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-3 Femto . . . . . . . . . . . . . . . . . . . . . . . . . . . .II-5 Fiber-Optic on Laser NHZ . . . . . . . . . . . . . . . . . .VI-7 Filter Damage . . . . . . . . . . . . . . . . . . . . . . .VIII-5 Filtered Eyewear . . . . . . . . . . . . . . . . . . . . .VIII-1 Flammability of Laser Beam Enclosures . . . . . . . . . . .III-12 Flashback . . . . . . . . . . . . . . . . . . . . . . . . .VIII-7 Flashblindness . . . . . . . . . . . . . . . . . . . . . . III-7 Flashing Light . . . . . . . . . . . . . . . . . . . . . . VII-9 FLPPS . . . . . . . . . . . . . . . . . . . . . . . . . IV-5, V-1 Focal Plane . . . . . . . . . . . . . . . . . . . . . . . . .VI-6 Focused Laser Beams . . . . . . . . . . . . . . . . . . . . II-13 Fovea . . . . . . . . . . . . . . . . . . . . . . . .III-4, III-5 Frequency Bandwidth . . . . . . . . . . . . . . . . . . . . II-16 Full Protection . . . . . . . . . . . . . . . . . . . . . .VIII-7 Fumes . . . . . . . . . . . . . . . . . . . . . . . . . . .III-11
Gallium Arsenide . . . . . . . . . . . . . . . . . . .II-4, II-9 Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . .II-3 Gas Discharge Tube . . . . . . . . . . . . . . . . . . . . .II-6 Gas Lasers . . . . . . . . . . . . . . . . . . . . . . . . .II-4 Gaussian . . . . . . . . . . . . . . . . . . . . . . . . . .II-9 Gaussian Beam Distribution . . . . . . . . . . . . . . . . II-10 Gaussian Intensity . . . . . . . . . . . . . . . . . . . . II-14 Glass Eyewear . . . . . . . . . . . . . . . . . . . . . . .VIII-8 Goggles . . . . . . . . . . . . . . . . . . . . . . . . . .VIII-1 Ground State . . . . . . . . . . . . . . . . . . . . . . . .II-5
H2(O) . . . . . . . . . . . . . . . . . . . . . . . . . . . .II-6 Ham, William T. Jr. . . . . . . . . . . . . . . . . . . . . III-8 Hazard Class Class I . . . . . . . . . . . . . . . . . . . . . . . . V-2 Class II . . . . . . . . . . . . . . . . . . . . . . . . V-2 Class IIA . . . . . . . . . . . . . . . . . . . . . . . V-2 Class IIIA . . . . . . . . . . . . . . . . . . . . . . . V-2 Class IIIB . . . . . . . . . . . . . . . . . . . . . . . V-2 Class IV . . . . . . . . . . . . . . . . . . . . . . . . V-2 Hazard Classes . . . . . . . . . . . . . . . . . . . . . . . V-1 Hazard Evaluation . . . . . . . . . . . . . . . . . . . . . .VI-1 HeNe . . . . . . . . . . . . . . . . . . . . . . . . .II-4, II-5 Holograms . . . . . . . . . . . . . . . . . . . . . . . . . .II-5 Hot Spots . . . . . . . . . . . . . . . . . . . . . . . . . II-11 Human Access . . . . . . . . . . . . . . . . . . . . . . . VII-3 Hyperpigmentation . . . . . . . . . . . . . . . . . . . . . III-2
IDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . .IV-1 Image Size . . . . . . . . . . . . . . . . . . . . . . . . III-5 Initial Report . . . . . . . . . . . . . . . . . . . . . . .IV-6 Injury Threshold Levels . . . . . . . . . . . . . . . . . . III-7 Integrated Radiance . . . . . . . . . . . . . . . . . . . . II-13 Intensity . . . . . . . . . . . . . . . . . . . . . . II-9, II-12 Intensity Distribution . . . . . . . . . . . . . . . . . . II-10 Interference Fringes . . . . . . . . . . . . . . . . . . . II-16 Interlocks . . . . . . . . . . . . . . . . . . . . . . . . VII-8 Intrabeam Nominal Hazard Zone . . . . . . . . . . . . . . . .VI-2 Intrabeam Viewing . . . . . . . . . . . . . . . . . . . . . III-6 Inverse Square Law . . . . . . . . . . . . . . . . . . . . .VI-4 Ion Lasers . . . . . . . . . . . . . . . . . . . . . . . . .II-5 Iris . . . . . . . . . . . . . . . . . . . . . . . . . . . III-5 Irradiance . . . . . . . . . . . . . . . . . . . . . . . . II-12 Irradiance (W/cm(2)). . . . . . . . . . . . . . . . . . . . . V-4
Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII-8 Krypton . . . . . . . . . . . . . . . . . . . . . . . .II-4, II-5
Labels . . . . . . . . . . . . . . . . . . . . . . . . . . VII-2 Lambert's Cosine Law . . . . . . . . . . . . . . . . . . . .VI-3 Lambertian Source . . . . . . . . . . . . . . . . . . . . . II-17 Lambertian Surface . . . . . . . . . . . . . . . . . . . . .VI-3 Laser . . . . . . . . . . . . . . . . . . . . . . . . . . . .II-1 CO(2) . . . . . . . . . . . . . . . . . . . . VII-3, VIII-2 Q-switched . . . . . . . . . . . . . . . . . . . . . .VIII-6 Laser Controlled Area . . . . . . . . . . . . . . . VII-4, VII-10 Laser Media . . . . . . . . . . . . . . . . . . . . . . . . .II-3 Laser Personnel . . . . . . . . . . . . . . . . . . . . . . .VI-1 Laser Resistant Eyewear . . . . . . . . . . . . . . . . . .VIII-8 Laser Safety Officer . . . . . . . . . . . . . . . . . V-1, VI-1 Laser Safety Officer Training . . . . . . . . . . . . . . . .IX-2 Lasers Argon . . . . . . . . . . . II-4, II-5, II-9, III-8, VIII-7 Carbon Dioxide . . . . . . . . . . . . . . . . . . . . .II-4 CW . . . . . . . . . . . . . . . . . . . . . . . . . .VII-12 Dye . . . . . . . . . . . . . . . . . . . . . . .II-4, II-9 Gallium Arsenide . . . . . . . . . . . . . . . . .II-4, II-9 Gas . . . . . . . . . . . . . . . . . . . . . . . . . .II-4 H(2)O . . . . . . . . . . . . . . . . . . . . . . . . .II-6 HeNe . . . . . . . . . . . . . . . . . . . . . . .II-4, II-5 Ion . . . . . . . . . . . . . . . . . . . . . . . . . .II-5 Krypton . . . . . . . . . . . . . . . . . . . . .II-4, II-5 ND: YAG . . . . . . . . . . . . . . . . . . . . . . .VIII-7 Nd:YAG . . . . . . . . . . . . . . . . . . . . . . . . .II-4 Nitrogen . . . . . . . . . . . . . . . . . . . . . . . .II-9 Pulsed . . . . . . . . . . . . . . . . . . . .VII-12, VIII-2 Q-switched . . . . . . . . . . . . . . . . . . . . . .VIII-2 Rhodamine 6G . . . . . . . . . . . . . . . . . . . . . .II-9 Ruby . . . . . . . . . . . . . . . . . . . . . . . . . .II-7 Scanning . . . . . . . . . . . . . . . . . . . . . . . II-14 Semiconductor. . . . . . . . . . . . . . . . . . . . . .II-4 Semiconductor Diode . . . . . . . . . . . . . . . . . .II-8 Solid State . . . . . . . . . . . . . . . . . . . . . .II-4 Tunable Dye . . . . . . . . . . . . . . . . . . . . . .II-8 Xenon . . . . . . . . . . . . . . . . . . . . . .II-5, II-6 Lasing Medium . . . . . . . . . . . . . . . . . . . . . . . .II-2 Lens . . . . . . . . . . . . . . . . . . . . . . . . . . . II-13 Lens of the Eye . . . . . . . . . . . . . . . . . . . . . . III-6 Lens on the Laser NHZ . . . . . . . . . . . . . . . . . . . .VI-6 Limited Open Beam Path . . . . . . . . . . . . . . . . . . VII-3 Limiting Aperture . . . . . . . . . . . . . . . . . . . . .VIII-5 Long Term Exposure . . . . . . . . . . . . . . . . . . . . III-8 LSO . . . . . . . . . . . . . . . . . . . . . . V-1, VI-1, VII-2, . . . . . . . . . . . . . . . . . . . .VII-3, VII-4, VII-6, . . . . . . . . . . . . . . . . . . .VII-9, VII-11, VII-13, . . . . . . . . . . . . . . . . . . . . . . . .VIII-1, IX-1 Luminous Transmission . . . . . . . . . . . . . . . . . . .VIII-8
Macula . . . . . . . . . . . . . . . . . . . . . . .III-4, III-6 Magnetic Field . . . . . . . . . . . . . . . . . . . II-9, II-16 Magnification Factor . . . . . . . . . . . . . . . . . . . III-5 Maintenance . . . . . . . . . . . . . . . V-3, VII-2 VII-6, VII-9 Master Switch Control . . . . . . . . . . . . . . . . . . . VII-8 Maximum Permissible Exposure . . . . . . . . . . . III-9, III-11 Maxwell's Equations . . . . . . . . . . . . . . . . . . . . II-17 Medical Surveillance . . . . . . . . . . . . . . . . . . . VII-2 Metastable State . . . . . . . . . . . . . . . . . . . . . .II-2 Microlithography . . . . . . . . . . . . . . . . . . . . . .II-7 Micronystagmic Eye Movements . . . . . . . . . . . . . . . III-9 Microscopes . . . . . . . . . . . . . . . . . . . .VII-13, VIII-7 Microsurgery . . . . . . . . . . . . . . . . . . . . . . . .II-7 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . .II-9 Mode Locked . . . . . . . . . . . . . . . . . . . . . . . . .II-5 Model Change Report . . . . . . . . . . . . . . . . . . . . .IV-6 MPE . . . . . . . . . . . . . . . . . . . . . III-9, III-11, V-2, . . . . . . . . . . . . . . . . . . . . VII-1, VII-3, VII-5 . . . . . . . . . . . . . . . . . . . . . . . VII-6, VIII-3 Multimode Fiber Optic . . . . . . . . . . . . . . . . . . . .VI-7
NCDRH . . . . . . . . . . . . . . . . . . . . . . . . . . . .IV-4 Nd: YAG . . . . . . . . . . . . . . . . . . . . .II-4, II-6, VI-8 . . . . . . . . . . . . . . . . . . . VII-3, VIII-5, VIII-6 Necrosis . . . . . . . . . . . . . . . . . . . . . . . . . III-2 Neodymium: YAG . . . . . . . . . . . . . . . . . . . . . . .II-4 Neural Receptors . . . . . . . . . . . . . . . . . . . . . III-4 NHZ . . . . . . . . . . . . . . . . . . . . . VI-2, VII-2, VII-3, . . . . . . . . . . . . . . . . . . . . . . . VII-8, VII-10 Diffuse Reflection . . . . . . . . . . . . . . . . . . .VI-5 Fiber-Optic on Laser . . . . . . . . . . . . . . . . . .VI-7 Intrabeam . . . . . . . . . . . . . . . . . . . . . . .VI-2 Lens on the Laser . . . . . . . . . . . . . . . . . . .VI-6 NIOSH . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-1 Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . .II-9 Nominal Hazard Zone (NHZ) . . . . . . . . . . . . . . . . . .VI-2 Non-Beam Hazards Ultraviolet Radiation . . . . . . . . . . . . . . . .III-12 Non-defeatabIe Entry Control . . . . . . . . . . . . . . . VII-5 Normal Mode . . . . . . . . . . . . . . . . . . . . . .II-4, II-7 NOTICE Sign . . . . . . . . . . . . . . . . . . . . VII-4, VII-10 Nystagmus . . . . . . . . . . . . . . . . . . . . . . . . . III-9
Ocular Effects . . . . . . . . . . . . . . . . . . . . . . III-4 Ocular Media . . . . . . . . . . . . . . . . . . . . . . . III-6 OD . . . . . . . . . . . . . . . . . VI-8, VII-6, VIII-3, VIII-6 Surgical Laser . . . . . . . . . . . . . . . . . . . . .VI-8 OFCS . . . . . . . . . . . . . . . . . . . . . . . . V-2, VII-13 OFCS Service Group SG1 . . . . . . . . . . . . . . . . . . . . . . . . . . V-3 SG2 . . . . . . . . . . . . . . . . . . . . . . . . . . V-3 SG3A . . . . . . . . . . . . . . . . . . . . . . . . . . V-3 SG3B . . . . . . . . . . . . . . . . . . . . . . . . . . V-3 OFCS Service Groups . . . . . . . . . . . . . . . . . . . . . V-3 Operation . . . . . . . . . . . . . . . .V-3, VII-2, VII-6, VII-9 Optic Nerve . . . . . . . . . . . . . . . . . . . . . . . . III-4 Optical Cavity . . . . . . . . . . . . . . . . . . . . . . .II-2 Optical Density . . . . . . . . . . . . . . . . . . . . . . .VI-8 Optical Fiber . . . . . . . . . . . . . . . . . . . . . . .VII-13 Optical Fiber Communication Systems . . . . . . . . . . . . . V-2 Optical Gain . . . . . . . . . . . . . . . . . . . . . . . III-5 Optical Pumping . . . . . . . . . . . . . . . . . . . . . . .II-2 Optical Viewing Microscopes, Telescopes, Viewing Ports. . . . . . . . . . . . . . . . . . . . . VII-8 OSHA . . . . . . . . . . . . . . . . . . . . . . . . . . . .IV-1 Output Aperture . . . . . . . . . . . . . . . . . . . . . . II-10 Output Factors . . . . . . . . . . . . . . . . . . . . . .VIII-4 Intensity . . . . . . . . . . . . . . . . . . . . . .VIII-5 Optical Density . . . . . . . . . . . . . . . . . . .VIII-4 Wavelength . . . . . . . . . . . . . . . . . . . . . .VIII-4
Panic Button . . . . . . . . . . . .VII-5, VII-9, VII-10, VII-12 Parafovea . . . . . . . . . . . . . . . . . . . . . . . . . III-5 Performance Features . . . . . . . . . . . . . . . . . . . .IV-5 Personal Protection Equipment . . . . . . . . . . . . . . . VII-1 Personal Protective Equipment . . . . . . . . . . . VII-6, VIII-1 Photobleach . . . . . . . . . . . . . . . . . . . . . . . .VIII-2 Photobleaching . . . . . . . . . . . . . . . . . . . . . .VIII-5 Photochemical . . . . . . . . . . . . . . . . . . . .III-7, III-8 Photochemical Lesion . . . . . . . . . . . . . . . . . . . III-8 Photochemical Reactions . . . . . . . . . . . . . . . . . . III-1 Photokeratitis . . . . . . . . . . . . . . . . . . . . . . III-5 Photons . . . . . . . . . . . . . . . . . . . . . . . . . . .II-1 Photophobia . . . . . . . . . . . . . . . . . . . . . . . . III-5 Photosensitizing . . . . . . . . . . . . . . . . . . . . . III-3 Phototoxic . . . . . . . . . . . . . . . . . . . . . . . . III-3 Pico . . . . . . . . . . . . . . . . . . . . . . . . . . . .II-5 Pigment Epithelium Layer . . . . . . . . . . . . . . . . . III-6 Plastic Eyewear . . . . . . . . . . . . . . . . . . . . . .VIII-8 PMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . .IV-1 Point Image . . . . . . . . . . . . . . . . . . . . . . . . III-4 Point Source . . . . . . . . . . . . . . . . . . . . . . . II-10 Point Source Diffuse Reflector . . . . . . . . . . . . . . .VI-5 Polarization . . . . . . . . . . . . . . . . . . . . . . . II-16 Polarized . . . . . . . . . . . . . . . . . . . . . . . . . .II-9 Population Inversion . . . . . . . . . . . . . . . . . . . .II-2 Power . . . . . . . . . . . . . . . . . . . . . . . . . . . II-12 PPE . . . . . . . . . . . . . . . . . . . . .VII-1, VII-2, VII-5, . . . . . . . . . . . . . . . . . . .VII-6, VII-11, VII-12, . . . . . . . . . . . . . . . . . . . . . . . . . . .VIII-1 Prescription Eyewear . . . . . . . . . . . . . . . . . . .VIII-1 Printers, Computer . . . . . . . . . . . . . . . . . . . . II- 8 Procedural Control . . . . . . . . . . . . . . . . .VII-3, VII-5 Procedural Controls . . . . . . . . . . . . . . . . VII-1, VII-5, . . . . . . . . . . . . . . . . . . . . . . .VII-10, VII-11 Procedural Entryway Control . . . . . . . . . . . . . . . . VII-5 Protective Clothing . . . . . . . . . . . . . . . . . . . .VIII-1 Protective Housing . . . . . . . . . . . . . . . . . . . . VII-8 Protective Housing Interlock . . . . . . . . . . . . . . . VII-9 Protein Denaturation . . . . . . . . . . . . . . . . . . . III-4 PTL . . . . . . . . . . . . . . . . . . . . . . . . . . . .VIII-2 Pumping System. . . . . . . . . . . . . . . . . . . . . . . .II-2 Pumping Systems Chemical . . . . . . . . . . . . . . . . . . . . . . . .II-2 Collision . . . . . . . . . . . . . . . . . . . . . . .II-2 Optical . . . . . . . . . . . . . . . . . . . . . . . .II-2 Pupil . . . . . . . . . . . . . . . . . . . . . . . . . . . III-4
Q-switched . . . . . . . . . . . . . . . . . . . . . .II-4, II-7
R sub max . . . . . . . . . . . . . . . . . . . . . . . . . .VI-6 Radial Symettry . . . . . . . . . . . . . . . . . . . . . . .VI-4 Radiance . . . . . . . . . . . . . . . . . . . . . . . . . II-13 Radiant Exposure . . . . . . . . . . . . . . . . . . II-12, VI-4 Radiant Exposure (J/cm(2)). . . . . . . . . . . . . . . . . . V-4 Radiative Transitions . . . . . . . . . . . . . . . . . . . .II-1 Radio Frequency Discharge . . . . . . . . . . . . . . . . . .II-5 Raman Shifter . . . . . . . . . . . . . . . . . . . . . . . .II-8 Rangefinders . . . . . . . . . . . . . . . . . . . . . . . .II-9 Rapid Egress . . . . . . . . . . . . . . . . . . . . . . .VII-10 Rayleigh Criterion . . . . . . . . . . . . . . . . . . . . II-15 Reflected Irradiance . . . . . . . . . . . . . . . . . . . .VI-4 Reflective Coating Eyewear . . . . . . . . . . . . . . . .VIII-1 Remote Interlock . . . . . . . . . . . . . . . . . . . . . VII-9 Remote Positions . . . . . . . . . . . . . . . . . . . . .VII-12 Remote Sensing Systems . . . . . . . . . . . . . . . . . . .II-9 Repetitively Pulsed . . . . . . . . . . . . . . . . . II-4, III-1 Exposure . . . . . . . . . . . . . . . . . . . . . . . III-9 Report Initial, Model Change, Annual . . . . . . . . . . . . .IV-6 Resonator Mirrors . . . . . . . . . . . . . . . . . . . . . .II-5 Retail Scanners . . . . . . . . . . . . . . . . . . . . . . .II-8 Retina . . . . . . . . . . . . . . . . . . . II-13, III-4, III-6 Retinal Image . . . . . . . . . . . . . . . . . . . . . . . .VI-5 Retinal Image Spot . . . . . . . . . . . . . . . . . . . . III-6 Retinal Injury . . . . . . . . . . . . . . . . . . . . . . III-4 Retinal Spot Size . . . . . . . . . . . . . . . . . . . . . III-5 Thermal Conduction . . . . . . . . . . . . . . . . . . III-5 Revision Process, ANSI . . . . . . . . . . . . . . . . . . .IV-5 RF . . . . . . . . . . . . . . . . . . . . . . . . .II-5, III-12 RF Discharge . . . . . . . . . . . . . . . . . . . . . . . .II-5 Rhodamine 6G . . . . . . . . . . . . . . . . . . . . .II-4, II-9 Ruby . . . . . . . . . . . . . . . . . . . . . . . . . . . .II-7
Saccadic Eye Movements . . . . . . . . . . . . . . . . . . III-9 Safety Factor, Biological . . . . . . . . . . . . . . . . . III-7 Sapphire . . . . . . . . . . . . . . . . . . . . . . . . . .II-7 Scanning Lasers . . . . . . . . . . . . . . . .II-4, II-14, III-1 Scattering Coefficient . . . . . . . . . . . . . . . . . . III-2 Screens . . . . . . . . . . . . . . . . . . . . . . VII-5, VIII-1 Selecting Eyewear . . . . . . . . . . . . . . . . .VIII-3, VIII-7 Comfort and Fit . . . . . . . . . . . . . . . . . . .VIII-3 MPE . . . . . . . . . . . . . . . . . . . . . . . . .VIII-3 OD . . . . . . . . . . . . . . . . . . . . . . . . . .VIII-3 OD Label . . . . . . . . . . . . . . . . . . . . . . .VIII-3 Visible Light Transmission . . . . . . . . . . . . . .VIII-3 Selective Spectral Coating Eyewear . . . . . . . . . . . .VIII-2 Semiconductor . . . . . . . . . . . . . . . . . . . . . . . .II-3 Semiconductor Diode Lasers . . . . . . . . . . . . . . . . .II-8 Semiconductor Lasers . . . . . . . . . . . . . . . . . . . .II-4 Service . . . . . . . . . . . . . . . . . . . .V-3, VII-2, VII-4, . . . . . . . . . . . . . . . . . . . .VII-6, VII-9, VII-13 Service Group 1 . . . . . . . . . . . . . . . . . . . . . . . V-3 Service Group 2 . . . . . . . . . . . . . . . . . . . . . . V-3 Service Group 3A . . . . . . . . . . . . . . . . . . . . . . V-3 Service Group 3B . . . . . . . . . . . . . . . . . . . . . . V-3 Service Groups . . . . . . . . . . . . . . . . . . . . . . . V-3 Sign Warning . . . . . . . . . . . . . . . . . . . . . . .VII-12 Signs . . . . . . . . . . . . . . . . . . . . . . . .VII-2, VII-4 Single Frequency Bandwidth . . . . . . . . . . . . . . . . .II-9 Single Mode Operation . . . . . . . . . . . . . . . . . . . .II-5 Single Pulsed . . . . . . . . . . . . . . . . . . . . . . . .II-4 Skin . . . . . . . . . . . . . . . . . . . . . . . . . . . VII-6 Skin Injury . . . . . . . . . . . . . . . . . . . . . . . . III-1 Skin Protection . . . . . . . . . . . . . . . . . . . . . . VII-9 Snellen Chart . . . . . . . . . . . . . . . . . . . . . . . III-6 Solid State . . . . . . . . . . . . . . . . . . . . . . . . .II-3 Solid State Lasers . . . . . . . . . . . . . . . . . . . . .II-6 SOP . . . . . . . . . . . . . . . . . . . . . VI-1, VII-2, VII-3, . . . . . . . . . . . . . . . . . . . . . . . .VII-6, VII-9 Spatial Coherence . . . . . . . . . . . . . . . . . . II-9, II-15 Coherence . . . . . . . . . . . . . . . . . . . . . . II-16 Speckle Pattern . . . . . . . . . . . . . . . . . . . . . . III-8 Spectators . . . . . . . . . . . . . . . . VII-6, VII-11, VIII-7 Spectral Band . . . . . . . . . . . . . . . . . . . . . . . II-17 Specular Reflection . . . . . . . . . . . . . . . . . . . . III-6 Splicing Operation . . . . . . . . . . . . . . . . . . . .VII-13 Spontaneous Emission . . . . . . . . . . . . . . . . . . . .II-1 Spot Diameter . . . . . . . . . . . . . . . . . . . .II-13, II-14 Spot Size . . . . . . . . . . . . . . . . . . . . . . . . . II-10 SSRL . . . . . . . . . . . . . . . . . . . . . . . . . . . .IV-1 Standard Operating Procedure (SOP). . . . . . . . . . . . . .VI-1 Stimulated Emission . . . . . . . . . . . . . . . . . . . . .II-2 Stratum corneum . . . . . . . . . . . . . . . . . . . . . . III-5 Subtense Angle (alpha). . . . . . . . . . . . . . . . . . . .VI-5 Sun Screens . . . . . . . . . . . . . . . . . . . . . . . . VII-9 Support Staff . . . . . . . . . . . . . . . . . . . . . . .VIII-7 Surgical Laser . . . . . . . . . . . . . . . . . . . . . . .VI-8
Telescopes . . . . . . . . . . . . . . . . . . . . . . . .VII-13 TEM(oo) . . . . . . . . . . . . . . . . . . . . . . .II-10, II-11 TEM(oo) Mode. . . . . . . . . . . . . . . . . . . . . . . . .II-9 Temporal Coherence . . . . . . . . . . . . . . . . .II-15, II-16 Temporary Laser Controlled Areas . . . . . . . . . . . . .VII-13 Thermal Conduction . . . . . . . . . . . . . . . . . . . . III-5 Thermal Damage Process . . . . . . . . . . . . . . . . . . III-7 Thermal Gradients . . . . . . . . . . . . . . . . . . . . . II-11 Thermal Source . . . . . . . . . . . . . . . . . . . . . . II-17 Threshold Levels . . . . . . . . . . . . . . . . . . . . . III-7 Time Modes . . . . . . . . . . . . . . . . . . . . . . . . .II-4 Mode Locked . . . . . . . . . . . . . . . . . . . . . .II-5 Normal Mode . . . . . . . . . . . . . . . . . . . . . .II-4 Q-switched . . . . . . . . . . . . . . . . . . . . . . .II-4 Repetitively Pulsed . . . . . . . . . . . . . . . . . .II-4 Scanning . . . . . . . . . . . . . . . . . . . . . . . .II-4 Single Pulsed . . . . . . . . . . . . . . . . . . . . .II-4 Tissue Damage . . . . . . . . . . . . . . . . . . . . . . . III-1 Training . . . . . . . . . . . . . . . . . . .VII-2, VII-5, IX-1 Class II, Class IIA, and Class IIIA . . . . . . . . . .IX-1 Class IIIB and Class IV. . . . . . . . . . . . . . . . IX-1 LSO . . . . . . . . . . . . . . . . . . . . . . . . . .IX-2 Update Requirements . . . . . . . . . . . . . . . . . .IX-2 Training Update Requirements . . . . . . . . . . . . . . . .IX-2 Transient Bleaching . . . . . . . . . . . . . . . . . . . .VIII-5 Traverse Gas Flow . . . . . . . . . . . . . . . . . . . . . .II-6 Tunable Dye Lasers . . . . . . . . . . . . . . . . . . . . .II-8
Ultraviolet A . . . . . . . . . . . . . . . . . . . . . . . III-5 Ultraviolet B . . . . . . . . . . . . . . . . . . . . . . . III-5 Ultraviolet C . . . . . . . . . . . . . . . . . . . . . . . III-5 Ultraviolet Radiation . . . . . . . . . . . . . . . . . . . III-3 Unenclosed Beam Path . . . . . . . . . . . . . . . . . . . VII-3 UVA . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-5 UVB . . . . . . . . . . . . . . . . . . . . . . . . . . . III-5 UVC . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-5
Vapors . . . . . . . . . . . . . . . . . . . . . . . . . .III-12 Ventilation . . . . . . . . . . . . . . . . . . . . . . . .III-11 Verbal Countdown . . . . . . . . . . . . . . . . . VII-9, VII-11 Viewing Ports . . . . . . . . . . . . . . . . . . . . . . .VIII-1 Viruses . . . . . . . . . . . . . . . . . . . . . . . . . . III-3 Visible light . . . . . . . . . . . . . . . . . . . . . . . .II-1 Vision Function . . . . . . . . . . . . . . . . . . . . . . III-6 Visitors . . . . . . . . . . . . . . . . . . . . .VII-11, VIII-7
Warning Light . . . . . . . . . . . . . . . . . . .VII-10, VII-12 Warning Sign . . . . . . . . . . . . . . . . . . . . . . .VII-12 Warning Signs . . . . . . . . . . . . . . . . . . . . . . . VII-4 Warning System . . . . . . . . . . . . . . . . . . . . . . VII-9 Wave Nature of Light . . . . . . . . . . . . . . . . . . . II-15 Wavelength Selector . . . . . . . . . . . . . . . . . . . . .II-5 Windows . . . . . . . . . . . . . . . . . . . . . . VII-5, VIII-1
X-Ray . . . . . . . . . . . . . . . . . . . . . I-3, III-12, IV-4 Xenon . . . . . . . . . . . . . . . . . . . . . . . . .II-5, II-6
Young, Thomas . . . . . . . . . . . . . . . . . . . .II-15, II-16 Yttrium Aluminum Garnet . . . . . . . . . . . . . . . . . . .II-4
Z-136 . . . . . . . . . . . . . . . . . . . . . . . . . . .IV-4 Z-136.2 . . . . . . . . . . . . . . . . . . . . . . . . . . V-4
------------------------------------------------------------------ 1. American National Standards Institute, 1986. AMERICAN NATIONAL STANDARD FOR THE SAFE USE OF LASERS: ANSI Z-136.1 (1986), Laser Institute of America: Orlando, FL. 2. Food and Drug Administration: PERFORMANCE STANDARD FOR LASER PRODUCTS, Center for Devices and Radiological Health, Food and Drug Administration (DHHS), Code of Federal Regulations (CFR), 50 (161): pp. 33682-33702, Tuesday, August 20, 1985. 3. American National Standards Institute, 1988. AMERICAN NATIONAL STANDARD FOR THE SAFE USE OF OPTICAL FIBER COMMUNICATION SYSTEMS UTILIZING LASER DIODE AND LED SOURCES: ANSI Z-136.2 (1988). Laser Institute of America: Orlando, Florida. 4. American National Standards Institute, 1988. AMERICAN NATIONAL STANDARD FOR THE SAFE USE LASERS IN THE HEALTH CARE ENVIRONMENT: ANSI Z-136.3 (1988). Laser Institute of America: Orlando, Florida. 5. Rockwell, R. J. 1986. LASER CONCEPTS, TISSUE INTERACTIONS, AND SAFETY PRACTICES. In: Complications of Laser Surgery of the Head and Neck, (M.P. Fried, J. H. Kelly and M. Strome, Editors). Year Book Medical Publisher, Inc.: Chicago, IL. 6. Rockwell, R.J. 1988. SAFETY PROCEDURES FOR Nd:YAG LASER SURGERY. In: Advances in Nd:YAG Laser Surgery. (S.N. Joffe and Y. Oguro, Editors). Springer Verlag: New York 7. Tolonen, S. L. 1987. LASER SAFETY IN THE OPERATING ROOM. In: Laser Applications in Neurosurgery. (R. Sawaya and J.M. Tew, Editors) State of The Art Reviews, Vol.2., No. 2. Haney & Belfus, Inc.: Philadelphia. 8. Rockwell, R.J., editor. 1987. LASER SAFETY IN SURGERY AND MEDICINE, (Second Edition) Rockwell Associates, Inc.: Cincinnati. 9. R. James Rockwell, Jr. 1986. FUNDAMENTALS OF INDUSTRIAL LASER SAFETY. In: Industrial Laser Annual Handbook, edited by (M. Levitt and D. Belforte, Editors) pp. 131-148, Penn Well Books: Tulsa. 10. Laser Institute of America, Safety Information on Electrical Hazards, LASER NEWS, Laser Institute of America, 6(5): 8-14, 1984. 11. Rockstron, T. J., and Mazumber, J., 1987. SPECTROSCOPIC STUDIES OF PLASMA DURING CW LASER MATERIALS INTERACTION. J.APPL. PHYS. 61 (3):917-923. 12. Herziger, G., 1986. THE INFLUENCE OF LASER-INDUCED PLASMA ON LASER MATERIALS PROCESSING. In: Industrial Laser Annual Handbook. (M. Levitt and D. Belforte, Editors) Tulsa, Okla., Penn Well Books: Tulsa. pp. 108-115. 13. Doyle, Daryl and Kokasa, John, 1986. Laser Processing of Kevlar: Hazardous Chemical Bi-products, PROCEEDINGS OF ICALEO, Laser Institute of America: Orlando. 14. Doyle, D. J., and KoKosa, J. M. 1985. HAZARDOUS BY-PRODUCTS OF PLASTICS PROCESSING WITH CARBON DIOXIDE LASERS. In: Laser Welding, Machining and Materials Processing. (C. Albright, Editor.) Proceedings of ICALEO, IFS LTD.: Bedford, U.K., pp. 201-203. 15. Rockwell, R. James, Jr. and Moss, C.E. 1983. Optical Radiation Hazards of Laser Welding Processes Part I: Nd:YAG Laser, THE JOURNAL OF THE AMERICAN INDUSTRIAL HYGIENE ASSOCIATION. 44(8):572-579. 16. Rockwell, R. James, Jr. and Moss, C.E. 1989. Optical Radiation Hazards of Laser Welding Processes Part II: Carbon Dioxide Laser. THE JOURNAL OF THE AMERICAN INDUSTRIAL HYGIENE ASSOCIATION. 50(8)419-427. 17. Rockwell, R. James, Jr., Editor. 1989. LASER SAFETY TRAINING MANUAL. (6th Edition) Rockwell Associates, Inc.: Cincinnati. 18. R. James Rockwell, Jr. 1986. Analyzing Laser Hazards. LASERS AND APPLICATIONS, 5(5)97-103. 19. Sliney, David H. and Wolbarsht, Myron L. 1980 SAFETY WITH LASERS AND OTHER OPTICAL SOURCES. Plenum: New York. 20. Rockwell Laser Industries. LAZAN: LASER HAZARD ANALYSIS COMPUTER PROGRAM. Rockwell Laser Industries: Cincinnati. 21. Rockwell, R. James, Jr. 1984. Ensuring Safety in Laser Robotics. LASERS AND APPLICATIONS, 3(11): 65-69. 22. National Institutes of Occupational Safety and Health, 1984. REQUEST FOR ASSISTANCE IN PREVENTING INJURY OF WORKERS BY ROBOTS. [DHHS(NIOSH) Publication No. 85-103], NIOSH: Cincinnati. 23. R. James Rockwell, Jr. 1986. Controlling Laser Hazards. LASERS AND APPLICATIONS, 5(9):93-99. 24. Laser Institute of America. 1989. GUIDE FOR THE SELECTION OF LASER EYE PROTECTION (2nd Edition), The Laser Institute of America: Toledo. 25. R. James Rockwell, Jr. 1989. Selecting Laser Eyewear, MEDICAL LASER BUYER'S GUIDE, Penn Well Books: Tulsa. pp: 84-92 26. Envall, K.R. and Murray, R., 1979. EVALUATION OF COMMERCIALLY AVAILABLE LASER PROTECTIVE EYEWEAR, DHEW Publication (FDA) 79- 8086. 27. R. James Rockwell, Jr. 1989. Laser Accidents: Are They All Reported and What Can Be Learned From Them? JOURNAL OF LASER APPLICATIONS, 53-57,. 28. Hardy, J.D., et al. 1956. Spectral Transmittance and Reflectance of Excised Human Skin. J. APPL. PHYSIOL. 9: 257-264. 29. Ham, W.T. Jr., Mueller, H.A., and Sliney, D.H. 1976. Retinal Sensitivity to Damage from Short Wavelength Light. NATURE. 260(5547):153-155. |
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