Photometric Comparison between Two Calculable Vacuum-Ultraviolet Standard Radiation Sources: Synchrotron Radiation and Plasma-Blackbody Radiation

Two important principles exist for the calibration of the vuv spectral radiance of secondary-standard lamps by means of calculable standard radiation sources: (1) use of blackbody radiation emitted by a plasma of known temperature and (2) use of electron-synchrotron radiation. Because both methods are rather difficult, a comparison of the two calibration procedures seems necessary. This study demonstrates that in the long-wavelength vuv at λ = 165 nm, significant errors do not occur in the spectral-radiance calibration with either synchrotron radiation and plasma-blackbody radiation. The maximum deviations of the calibration of secondary-standard lamps applying these two calibration methods are within ±20%. Under optimum experimental conditions, the agreement of the two calibrations is within 8%. Furthermore, this study shows that it is possible to do photometry in the vuv by use of secondary-standard gas discharge lamps in a way comparable to the routine technique with tungsten-strip lamps in the visible.