Present State of the PTB Primary Standard for Radiant Power Based on Cryogenic Radiometry

The PTB primary standards for radiant power in Braunschweig are the German national standard for detector calibrations within the spectral range of 200 nm to 2,5 μm. This paper presents the progress in development and optimization of a high accuracy measurement facility using a cryogenic radiometer as the primary standard. The following features are highlighted: method of dynamic power substitution; temperature dependence of the absorptance of the cavity; error reduction by distance-error-free calibration transfer; and concept of window-correction-free transfer.