High-accuracy, infrared, spectral responsivity scale

This paper describes the establishment of a high-accuracy, infrared, spectral responsivity scale in the 8 mum to 12 mum atmospheric window through the 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 this spectral region has been achieved mainly through the use of improved transfer standard detectors and the direct calibration of these detectors against the cryogenic radiometer. This paper describes these new transfer standards, the intensity-stabilized CO2 laser facility, its use with the NPL cryogenic radiometer and the improved methodology.