Two spectral responsivity scales have been established at the National Physical Laboratory, UK. High quantum efficiency silicon photodiodes have been used to establish a continuous spectral responsivity scale for the spectral region 400 nm to 920 nm. The scale can be disseminated by the NPL with an uncertainty of f 0 , l YO. Pyroelectric detectors fitted with a reflecting hemispherical cavity have been used to establish a spectral responsivity scale for the spectral region 1 pm to 20 pm. This scale has an uncertainty of less than f l,6 YO.

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This paper describes the establishment of a high-accuracy, infrared, spectral responsivity scale in the 8 µm to 12 µm 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 CO 2 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 CO 2 laser facility, its use with the NPL cryogenic radiometer and the improved methodology.

This paper describes the measurement of the uniformity, linearity, noise and spectral responsivity of different types of photodetectors to evaluate their suitability as transfer standards for the infrared spectral region.

The paper describes the establishment of an infrared spectral responsivity scale at NPL with an uncertainty of 1.6% and the development of facilities to characterise the optical properties of infrared detector, arrays and cameras. The paper will illustrate the use of the calibration facilities with examples of uniformity, linearity and spectral responsivity measurements on a range of detectors.