CRYOGENIC BLACKBODY CALIBRATIONS AT THE NATIONAL-INSTITUTE-OF-STANDARDS-AND-TECHNOLOGY LOW-BACKGROUND INFRARED CALIBRATION FACILITY

The Low Background Infrared Calibration Facility (LBIR) at the Nationa l Institute of Standards and Technology has been in operation for cali bration measurements of the radiant power emitted from infrared radiat ion (IR) sources, such as cryogenic blackbodies, for more than 2 years . The IR sources are sent to NIST by customers from industry, governme nt, and university laboratories. An absolute cryogenic radiometer is u sed as the standard detector to measure the total radiant power at its aperture. The low background is provided by a closed cycle helium ref rigeration system that maintains the inner parts of the calibration ch amber at 20 K. The radiance temperature of the blackbody is deduced fr om the measured power and compared with the blackbody temperature sens or data. The calibration procedures and data analysis are illustrated using the measurements of a typical blackbody.