Realization of the spectral irradiance scale in the air-ultraviolet using thermal radiators

In a new facility, the use of thermal radiators such as FEL lamps and very- high-temperature black bodies as standards of spectral irradiance has been extended for the first time down to 200 nm, thus covering the whole air-ult raviolet range. This improvement is based on a significant increase of the throughput and signal-to-noise ratio of a spectroradiometer and on a large reduction in the effects from stray light within this new calibration facil ity. The reliability of this facility is demonstrated in a comparison betwe en calibrations of spectral irradiance using a black body with different ra diometric temperatures, and in a comparison of the calibration of an FEL la mp and a deuterium lamp with the existing scale. The uncertainties achieved are as low as or better than those of the standard facility in this spectr al range.