Monochromator-based cryogenic radiometry between 1 mm and 20 mm

The spectral responsivity of Ge photodiodes and thin-film thermopiles has been measured between 1 mm and 20 mm. These detectors are used as transfer standards for the spectral responsivity measurements made at the Nederlands Meetinstituut-Van Swinden Laboratorium (NMi-VSL) monochromator-based cryogenic radiometer facility. For measurements beyond 2.5 mm we used an Ar maxi-arc as infrared source in combination with a single-grating monochromator. Below 2.5 mm 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 cryogenic radiometer with negligible residual astigmatism. In this paper we discuss the design of the facility, the characteristics of the transfer standards used and the estimated uncertainty budget of the infrared measurements.