Sally S. Bruce

The NIST High Accuracy Scale for Absolute Spectral Response from 406 nm to 920 nm

We describe how the National Institute of Standards and Technology obtains a scale of absolute spectral response from 406 nm to 920 nm. This scale of absolute spectral response is based solely on detector measurements traceable to the NIST High Accuracy Cryogenic Radiometer (HACR). Silicon photodiode light-trapping detectors are used to transfer optical power measurements from the HACR to a monochromator-based facility where routine measurements are performed. The transfer also involves modeling the quantum efficiency (QE) of the silicon photodiode light-trapping detectors. We describe our planned quality system for these measurements that follows ANSI/NCSL Z540-1-1994. A summary of current NIST capabilities based on these measurements is also given.

Spatial uniformity of responsivity for silicon, gallium nitride, germanium, and indium gallium arsenide photodiodes

For almost a decade, the National Institute of Standards and Technology (NIST) has supplied to its customers calibrated photodiode standards and special tests of photodetectors for absolute spectral responsivity from 200 nm to 1800 nm. During this time spatial responsivity measurements have been made on several dozen Hamamatsu silicon S1337-1010BQ photodiodes. We have found that the spatial responsivity changes with wavelength, sometimes significantly as the wavelength approaches the bandgap. The most significant changes appear to be caused by defects in the photodiode material and are not apparent over most of the wavelength region where the photodiode operates. The change in spatial uniformity with wavelength can significantly contribute to measurement uncertainties. These measurements have been repeated and the spatial responsivities have remained constant over several years. Measurements have also been made on other types of Si, GaN, Ge, and InGaAs photodiodes. The measurement equipment, method, and results are presented.

Vacuum Processing Technique for Development of Primary Standard Blackbodies.

Blackbody sources with nearly unity emittance that are in equilibrium with a pure freezing metal such as gold, silver, or copper are used as primary standard sources in the International Temperature Scale of 1990 (ITS-90). Recently, a facility using radio-frequency induction heating for melting and filling the blackbody crucible with the freeze metal under vacuum conditions was developed at the National Institute of Standards and Technology (NIST). The blackbody development under a vacuum environment eliminated the possibility of contamination of the freeze metal during the process. The induction heating, compared to a resistively heated convection oven, provided faster heating of crucible and resulted in shorter turn-around time of about 7 h to manufacture a blackbody. This paper describes the new facility and its application to the development of fixed-point blackbodies.