FASCAL 2: A New NIST Facility for the Calibration of the Spectral Irradiance of Sources
Howard W. Yoon, J E. Proctor, Charles E. Gibson
The Facility for Automated Spectroradiometric Calibrations (FASCAL) is the primary facility for spectral irradiance and spectral radiance calibrations at NIST and has been in continous use since the early 1970's. Due to the increasing demands for spectroradiometric calibrations, especially for supporting the monitoring of global environmental changes, a new facility, FASCAL 2, dedicated to spectral irradiance calibrations was built. This facility will enable faster responses to calibration requests and, ultimately, result in lower uncertainties in the disseminated spectral irradiances. The FASCAL 2 facility is designed with the objective of achieving a signal-to-noise ratio exceeding 1000-1 from 250 nm to 2500 nm in a bandwidth of 4 um to 8 nm when measuring a 1000 W FEL lamp at a distance of 50 cm with a receiving aperture of 1 cm2. The facility will be also capable of calibrating deuterium lamps from 200 nm to 400 nm. The facility has six independent source stations, with four of the stations dedicated to spectral irradiance lamp measurements, and two stations reserved for spectral irradiance scale realizations and automated wavelength accuracy checks. After verifying that the spectral irradiance calibrations performed to FASCAL and FASCAL 2 agree within their combined uncertainties, FASCAL 2 will become the primary NIST facility for spectral irradiance calibrations.