FIRST RESULTS WITH THE NEW PTB CRYOGENIC RADIOMETER FOR THE VACUUM-ULTRAVIOLET SPECTRAL RANGE

In the radiometry laboratory of the Physikalisch-Technische Bundesanst alt (PTB) at the Berlin electron storage ring BESSY, a new cryogenic e lectrical-substitution radiometer with a cavity absorber is now in ope ration as the primary detector standard for the vacuum-ultraviolet spe ctral range. The instrument is optimized for use with narrowband synch rotron radiation, as dispersed by a monochromator. It is capable of me asuring spectral radiant powers of a few microwatts with a resolution of 1,5 nW and a relative uncertainty of 0,2%. The cryogenic radiometer has been employed at a new detector-calibration facility for the norm al-incidence spectral range. Calibrations of Hamamatsu S1337 and G1127 photodiodes have been performed in the 170 nm to 500 nm spectral rang e with a relative uncertainty of the spectral responsivity less than 1 %. At four laser wavelengths, agreement was found with a calibration a gainst the laser-operated cryogenic radiometer of the PTB at Berlin.