Intercomparison between the NIST LBIR Absolute Cryogenic Radiometer and an Optical Trap Detector

The goal of the Low Background Infrared (LBIR) calibration facility at the NIST is to provide the infrared user community with a measurement base for both broadband and spectral radiometric calibrations in a low background environment. The standard detector used in this facility is the Absolute Cryogenic Radiometer (ACR). The ACR is an electrical substitution radiometer which is capable of measuring between 20 nW and 100 μW of radiant power. By using an optical trap detector, an intercomparison with the ACR is made as part of a programme to monitor the long-term stability of the ACR. A comparison is also made between the optical trap detector and an in-house trap detector that was calibrated using the High Accuracy Cryogenic Radiometer (HACR).