FASCAL 2: a new NIST facility for the calibration of the spectral irradiance of sources

The facility for automated spectroradiometric calibrations (FASCAL) is the primary facility for calibration of spectral irradiance and spectral radiance at NIST and has been in continuous use since the early 1970s. Due to the increasing demands for spectroradiometric calibration, especially for supporting the monitoring of global environmental changes, a new facility, FASCAL 2, dedicated to calibrating spectral irradiance has been 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 nm to 8 nm when measuring a 1000 W FEL lamp at a distance of 50 cm with a receiving aperture of 1 cm(2). The facility will also be capable of calibrating deuterium lamps from 200 nm to 400 rim. The facility has six independent source stations, with four of the stations dedicated to measurements with spectral irradiance lamps and two stations reserved for the realization of spectral irradiance scales and checking the accuracy of automated wavelength. After verifying that the calibrations of spectral irradiance performed in FASCAL and FASCAL 2 agree within their combined uncertainties, FASCAL 2 will become the primary NIST facility for calibration of spectral irradiance.