HIGH-ACCURACY DETECTOR CALIBRATION IN THE 3-1500 EV SPECTRAL RANGE ATTHE PTB RADIOMETRY LABORATORY

State-of-the-art detector calibration in the UV/VUV and soft Xray spec tral ranges at the Physikalisch-Technische Bundesanstalt (PTB) is base d on the primary detector standard SYRES, a cryogenic electrical subst itution radiometer capable of measuring radiant power of a few mu W. A t the PTB radiometry laboratory at the synchrotron radiation facility BESSY, two dedicated beamlines are operated, providing monochromatic r adiation of high spectral purity, high radiant power and tunable photo n energy in the 3-1500eV range. The spectral responsivity of detectors , e.g. photodiodes, can be measured with a relative uncertainty of abo ut 1% by direct comparison with SYRES, as will be demonstrated for PtS i/Si and GaAsP/Au Schottky and silicon n-on-p photodiodes. The calibra tion of photon-counting detectors traceable to SYRES can by accomplish ed by exploiting the unique capability to scale the spectral photon fl ux over several orders of magnitude by changing the stored electron cu rrent. Calibrations of CCDs and photomultipliers are presented as exam ples.