Division 844 > Division 844 Facilities > Spectrophotometry > Spectrophotometry Facilities

Facilities We maintain the national reference instruments for measurements of both bi-directional and directional-hemispherical spectral reflectance, regular spectral transmittance, and visual diffuse transmission density. In addition, we have commercial spectrophotometers to complement the measurement capabilities of the reference instruments. Reference Instruments Reflectance Transmittance Commercial Instrument Reference Instruments The conditions of measurement and measured quantities for the two reference instruments are given in Table 1. Additional details for each instrument are given below. Reflectance The Spectral Tri-function Automated Reference Reflectometer (STARR) is the national reference instrument for spectral reflectance measurements of spectrally neutral, non-fluorescent samples at room temperature. The illuminator has two sources, a Xe arc lamp and a quartz-tungsten-halogen incandescent lamp, order-sorting filters, a shutter, a single-grating monochromator, a parabolic mirror, a chopper, and a polarizer. An in-plane goniometer is used for bi-directional measurements, meaning the sample normal, illumination axis, and receiver axis are all in a horizontal plane. The receiver is attached to the goniometer and has a precision aperture, a lens, and a photodiode detector, either Si, Ge, or InGaAs. An integrating sphere is used for directional-hemispherical measurements, and can accommodate Si, Ge, InSb, and InGaAs photodiode detectors. Photo of Spectral Tri-function Automated Reference Reflectometer (STARR).

Transmittance The Reference Transmittance Spectrophotometer (RTS) is the national reference instrument for regular spectral transmittance measurements of non-fluorescent samples at room temperature. The illuminator has two sources, a D2 arc lamp and a quartz-tungsten-halogen incandescent lamp, a spherical mirror, a chopper, a prism-grating monochromator, a parabolic mirror, a polarizer, and an iris. A sample carriage moves the sample in and out of the influx beam. The receiver has a block for the efflux beam, a spherical mirror, and integrating sphere, and a detector, either a PMT or a Si, InSb, or InGaAs photodiode. Photo of the Reference Transmittance Spectrophotometer (RTS). Table 1. Measurement conditions for spectrophotometry reference instruments. Reflectance - STARR, transmittance - RTS   STARR RTS   Bi-directional Directional-hemispherical Condition Specular Diffuse   Geometrical     Illumination Angle 0° to ± 80° 0° to ± 80° 6° (specular included) 0° (specular excluded) 0° Viewing Angle 0° to ± 80° 0° to ± 80° Hemisphere 0° Sampling Aperture 17 mm 17 mm 25 mm 4 mm to 20 mm Spectral     Wavelength 250 nm to 2500 nm 250 nm to 1100 nm 250 nm to 2500 nm 250 nm to 2500 nm Bandwidth 15 nm 15 nm 15 nm 1.5 nm, 3 nm Polarization 0° to 90° 0° to 90° Slight 0° to 90° Sample Size 50 mm to 300 mm 50 mm to 300 mm 50 mm to 300 mm 10 mm to 50 mm, cuvette Measurand     Quantity Reflectance BRDF fr, Reflectance Factor R Reflectance Factor R Transmittance Technique Absolute Absolute Relative to PTFE Absolute Range 0.001 to 1 0.001 to 1 0.001 to 1 0.001 to 1 Uncertainty (k=2) 0.1 % to 0.2 % 0.15 % to 0.6 % 0.15 % to 0.6 % 0.1 % to 0.3 %

Commercial Instrument A Varian Cary5E commercial spectrophotometer is used to complement the reference instruments. It perform this function by measuring samples relative to standards calibrated on the reference instruments. The instrument measures non-fluorescent samples at room temperature. The conditions of measurement and measured quantities for this instrument are given in Table 2. The illuminator has two sources, a D2 arc lamp and a quartz-tungsten-halogen incandescent lamp, order-sorting filters, a double-grating monochromator, and a chopper. The sample compartment has two beams, one for the reference and one for the sample. Integrating sphere accessories are added for diffuse reflectance and transmittance measurements. The receiver has collection optics and PMT and PbS detectors. Photo of a Varian Cary5E spectrophotometer. Table 2. Measurement conditions for the Varian Cary5E spectrophotometer   Transmittance Reflectance Condition Regular Diffuse     Geometrical   Illumination Angle 0° 0° 3.3° (specular included) 0° (specular excluded) Viewing Angle 0° Hemisphere Hemisphere Hemisphere Sampling Aperture 13 mm by 5 mm 22 mm by 10 mm 15 mm by 4 mm 15 mm by 4 mm Spectral   Wavelength 200 nm to 2500 nm Bandwidth 0.05 nm to 20 nm Polarization Slight Sample Size 10 mm to 50 mm, cuvette 25 mm to 50 mm 25 mm to 100 mm 25 mm to 100 mm Measurand   Quantity Transmittance Transmittance Reflectance Factor Reflectance Factor Technique Absolute Absolute Relative to PTFE Relative to PTFE Range 0.001 to 1 0.001 to 1 0.001 to 1 0.001 to 1 Uncertainty 0.2 % - 0.5 % 0.2 % - 0.5 % 0.2 % - 1 % 0.2 % - 1 % Top

Division 844 > Division 844 Facilities > Spectrophotometry > Spectrophotometry Facilities

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For technical information or questions, contact:

David Allen Phone: (301) 975-3680 FAX: (301) 840-5700 Email: david.allen@nist.gov

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