Detector Based Radiometry

Radiometric calibration of radiation detectors at PTB using synchrotron radiation is based on the utilisation of cryogenic radiometers as primary detector standards. Different beamlines provides continuously tunable monochromomatised synchrotron radiation for detector based radiometry in the wavelengths regions of the vacuum-ultraviolet (VUV), extreme ultraviolet (EUV), and x-rays. For the different regions, different types of photodiodes has proven to be suited best for defining a scale of spectral responsivity, e. g. Schottky-type PtSi-nSi diodes in the VUV range, or nSi-pSi diodes in the EUV and x-ray range. The selection of the photodiodes particularly depends on their characteristics concerning stability, homogeneity and linearity. Calibration of the detectors is realized by comparison of the detector signal with the incident radiant power of the dispersed synchrotron radiation determined by the cryogenic radiometer. The largest uncertainty contributions to this process come from the detector itself and from the stray- and false light effects in the monochromatized synchrotron radiation beam. PTB maintains and disseminates a scale of spectral responsivity with synchrotron radiation between 3 eV and 60 keV (see figure). Based on this, PTB offers a certified calibration service to customers, for the radiometric calibration of suitable photodetectors, e. g. semiconductor photodiodes, photocathodes, or CCD devices.