NATIONAL-INSTITUTE-OF-STANDARDS-AND-TECHNOLOGY HIGH-ACCURACY CRYOGENIC RADIOMETER

A high-accuracy cryogenic radiometer has been developed at the Nationa l Institute of Standards and Technology to serve as a primary standard for optical power measurements. This instrument is an electrical-subs titution radiometer that can be operated at cryogenic temperatures to achieve a relative standard uncertainty of 0.021% at an optical power level of 0.8 mW. The construction and operation of the high-accuracy c ryogenic radiometer and the uncertainties in optical power measurement s are detailed.