Thermal characterization of a cryogenic radiometer and comparison with a laser calorimeter

We have developed a finite-element-analysis thermal model to study the temperature distribution in a laser-optimized cryogenic radiometer (LOCR). Our modelling showed that the worst-case inequivalence between electrical and optical power is 0.0004%. We used the thermal model, empirical testing, and research performed at other laboratories, to conduct a detailed uncertainty analysis for laser power calibrations based on the LOCR. Using photodiode trap detectors at laser wavelengths of 633.0 nm and 1550.4 nm as intermediate standards, we showed that the cryogenic radiometer and the NIST C4 laser calorimeter agree within 0.1%.