High-accuracy, infrared, spectral responsivity scale

This paper describes the establishment of a high-accuracy, infrared, spectr al responsivity scale in the 8 mu m to 12 mu m atmospheric window through t he calibration of specially designed HgCdTe/sphere detectors. The scale has been established using intensity-stabilized laser radiation from a grating -tuned CO2 laser directly with the primary standard cryogenic radiometer of the UK National Physical Laboratory (NPL). The factor-of-10 improvement in the uncertainty over the NPL's previous spectral responsivity scale in thi s spectral region has been achieved mainly through the use of improved tran sfer standard detectors and the direct calibration of these detectors again st the cryogenic radiometer. This paper describes these new transfer standa rds, the intensity-stabilized CO2 laser facility, its use with the NPL cryo genic radiometer and the improved methodology.