Improved near-infrared spectral responsivity scale

A cryogenic radiometer-based system was constructed at the National Institu te of Standards and Technology for absolute radiometric measurements to imp rove detector spectral power responsivity scales in the wavelength range fr om 900 nm to 1800 nm. In addition to the liquid-helium-cooled cryogenic rad iometer, the system consists of a 100 W quartz-tungsten-halogen lamp light source and a 1 m single-grating monochromator for wavelength selection. The system was characterized and the uncertainty in spectral power responsivit y measurements evaluated. A variety of photodetectors, including indium gal lium arsenide photodiodes (InGaAs), germanium (Ge) photodiodes, and pyroele ctric detectors, were subsequently calibrated. Over most of the spectral ra nge, the spectral power responsivity of the photodetectors can be measured with a combined relative standard uncertainty of 0.4 % or less. This is mor e than a factor of two smaller than our previous capabilities, and represen ts a significant improvement in the near infrared (NIR) spectral power resp onsivity scale maintained at NIST. We discuss the characterization of the m onochromator-based system and present results of photodetector spectral pow er responsivity calibrations.