Intercomparison between two independent primary radiometric standards in the visible and near infrared: a cryogenic radiometer and the electron storage ring BESSY

Abstract

An intercomparison has been performed in the visible and near infrared between two radiometric standards: the electron storage ring BESSY and a cryogenic absolute radiometer. The spectral irradiance of the continuum source BESSY can currently be predicted with a relative systematic uncertainty of 3 × 10−3, whereas the radiant power of monochromatic laser radiation can be measured by the cryogenic radiometer with a relative systematic uncertainty of 10−4. In this intercomparison the responsivity S of a specially designed transfer radiometer was measured using synchrotron radiation (SSR) and the cryogenic radiometer (SRAD). The mean of the ratios SRAD/SSR for different measurement conditions was 1.0013 with a standard error of the mean of 0.0006 for a wavelength of 676 nm and 0.9990 with a standard error of 0.0007 for a wavelength of 799 nm. The systematic uncertainty of the ratio is 3.8 × 10−3 caused by the uncertainty of SRAD of 1.5 × 10−3 and by the uncertainty of SSR of 3.5 × 10−3. Both radiometric standards agree well within the combined systematic uncertainties of the two methods. The result confirms the 3 × 10−3 uncertainty of BESSY. This source standard has therefore a smaller uncertainty than present source standards based on high temperature blackbody radiators. The work also demonstrates how detector- and source-based radiometric standards can be intercompared or transferred between laboratories with a relative uncertainty of <3 × 10−3.