Validations of Detector-based Radiometric Calibrations using Fixed-point Blackbodies

The developments of laser-based radiometric calibration facilities enable possibilities of achieving lower measurement uncertainties than those obtained with traditional sources such as lamps or lamp-based integrating sphere sources. These facilities are being developed at institutions other than major national measurement institutes due to the availability of easily tunable lasers which can span a wide range of wavelengths. Due to the extremely low claimed uncertainties of the calibrations from such facilities, it is not easy to test such claims using lamps or lamp-based sources. One way to test such claims is to utilize metal fixed-point blackbodies which are used to disseminate the International Temperature Scale of 1990 (ITS-90).

We describe the validation of the NIST Spectral irradiance and Radiance Calibrations with Uniform Sources (SIRCUS) using radiometers calibrated for spectral radiance responsivity which then are used to measure ITS-90 fixed points as well as higher temperature metal-carbon eutectic cells. We describe the SI-traceable calibration procedures and how these calibrations enable direct measurements of thermodynamic temperatures.