Monochromator-based cryogenic radiometry between 1 mu m and 20 mu m

The spectral responsivity of Ge photodiodes and thin-film thermopiles has b een measured between 1 mum and 20 I-Lm These detectors are used as transfer standards for the spectral responsivity measurements made at the Nederland s Meetinstituut-Van Swinden Laboratorium (NMi-VSL) monochromator-based cryo genic radiometer facility. For measurements beyond 2.5 mum we used an Ar ma xi-are as infrared source in combination with a single-grating monochromato r. Below 2.5 mum a quartz-tungsten-halogen lamp is used as light source in conjunction with a double-grating monochromator. An optical system based on three mirrors is used to match the f-numbers of the monochromator and cryo genic radiometer with negligible residual astigmatism. In this paper we dis cuss thr design of the: facility, the characteristics of the transfer stand ards used and the estimated uncertainty budget of the infrared measurements .