Low Background Infrared (LBIR) Facility

The Low-Background Infrared (LBIR) Facility is designed to calibrate user-supplied blackbody sources and to characterize low-background IR detectors and attenuators.It is also equipped with an IR Collimator to calibrate transfer standard radiometer. The LBIR facility employs an ACR (absolute cryogenic radiometer) as its primary detector. A low-temperature blackbody has been commissioned for use in the LBIR Facility. Capable of functioning in a 20 K environment, the source has an operating range from 100 K to 450 K. With a built-in aperture and filter wheels, it is being used for detector calibration and optical materials characterization. The instrument, housed in a vacuum chamber, also serves as a source for evaluating the ACR performance in the LBIR facility. The LBIR Facility is available to service the user community to characterize infrared radiometric sources, transfer standard radiometers, detectors and optical components in a low background environment. The facility has calibration capability and serves as the foundation for research and development for technology applications in space and other areas where highly sensitive infrared sensors are used.

The LBIR facility has two low-background test chambers. The first one is the broadband calibration chamber (BCC) and It has an internal cylindrical testing volume of approximately 48 cm diameter by 150 cm in length. The testing volume is completely enclosed by cryoshrouds capable of reaching 25 K. The second one is the spectral calibration chamber (SCC) that has an internal cylindrical testing volume of approximately 50 cm diameter by 125 cm in length. The testing volume of the SCC is surrounded by cryoshrouds capable of reaching 17 K. The SCC, originally intended for spectral work, was fitted with a dedicated infrared source, monochromator, detector paddle stage and the absolute cryogenic radiometer (ACRII).

LBIR Facility

The absolute cryogenic radiometers (ACRs) at the LBIR facility are the primary standards for measuring optical power. These instruments are trap detectors where the power incident on a receiver cone is measured by electrical power substitution. Due to the trapping nature of the ACR design, it is very sensitive to all wavelengths of radiation from soft x-rays to microwaves. The original ACR has been in use since 1989 has a noise floor of approximately 50 pW and a time constant of about 20 s.

A newer lower noise absolute cryogenic radiometer (ACRII) has since been designed and implemented. It has a noise floor of 10 pW and a time constant of 10 s. So ACRII is twice as fast as the first ACR. The ACRII was used to measure the lower power associated with the narrow bandwidth light output from the monochromator in the SCC. Spectral calibration of detectors was achieved with this equipment by making direct intercomparisons between the signal measured from a detector and the power measured by the ACRii for the same beam at a particular wavelength.

The LBIR facility is continuing to strive for improvement in power measurement capability.

The 10 cm collimator has been built to provide a collimated beam for the characterization and calibration of the transfer standard radiometers.

The source side of the 10 cm Collimator contains the blackbody source and some relay optics to focus radiation onto the defining aperture of the primary mirror. Between the blackbody source and the defining aperture there are two filter wheels and a collimated portion that could be used for future optical features such as a monochromator, a Fourier transform spectrometer, or additional filter wheels.

The side profile view shows the opposite side of the optics plate and the location and orientation of of the primary collimating mirror and pointing mirror.