SOME PROBLEMS IN REALIZING AN INFRARED SPECTRAL-IRRADIANCE SCALE FROM1500-NM TO 2400-NM AT THE NRC

The spectral-irradiance scale in the infrared at the National Research Council of Canada is being realized using electrical-substitution abs olute radiometers in conjunction with interference filters to calibrat e FEL tungsten-halogen lamps as primary source standards. This paper d iscusses some preliminary measurements associated with the second phas e of this work, the realization of a scale in the range 1500 nm to 240 0 nm. Some characteristics of the spectroradiometer that will be used to measure the transmittance of the interference filters under conditi ons as close as possible to the final configuration are presented. Var ious problems encountered in configuring the liquid-nitrogen-cooled In Sb detector used are discussed. The larger effect of atmospheric water absorption bands in this wavelength range presents a greater challeng e in determining the choice of passband wavelengths for the filters. M easurements to determine the extent of these absorption bands are pres ented.