Spectroradiometric Detector Measurements: Part III--Infrared Detectors
Alan L. Migdall, George P. Eppeldauer
The National Institute of Standards and Technology (NIST) supplies calibrations of IR photodetector's spectral radiant power response from 1.8 υm to 20 υm. The spectral responsivity of a detector under test is determined by comparison to an absolute detector standard. That absolute detector standard is a cryogenic composite Si bolometer. The spectral radiant power response of the bolometer is based on detector measurements traceable to the NIST High Accuracy Cryogenic Radiometer (HACR) and on material transmittance and reflectance measurements. Silicon and Germanium phodetectors and pyroelectric detectors are used to transfer radiant power responsivity from the HACR to the bolometer over a range of wavelengths. Reflectance and transmittance measurements of the bolometer absorber and window are used to determine the continuous relative spectral responsivity of the bolometer. This relative responsivity determination combined with the absolute responsivity measurements allows a continuous absolute spectral responsivity of the bolometer to be realized. The comparison between the detector under test and the bolometer is performed using a monochromator-based facility. The detector scale relative expanded uncertainty (k = 2) is typically 1.6 % throughout the spectral range. The uncertainty of a responsivity calibration of a specific detector will generally be the uncertainties associated with that detector summed in quadrature with the 1.6 % of the detector scale uncertainty. A description is given of the procedures, equipment, and techniques used to perform these calibrations. Detailed estimates and procedures for determining uncertainties of the reported values are also presented.