Abstract

In the VUV and soft x-ray region photoelectron yield data are frequently used to estimate absolute photon fluxes. Calibrated photoemissive diodes are not available for the photon energy range above 250 eV. In the visible uncertainties as low as 0.1% have been achieved with semiconductor photodiodes, for which the responsivity can be calculated from a few basic parameters of the diode, using the so-called self-calibration technique. Since stable photodiodes for the soft x-ray range are now available, a similar technique can be used also in this spectral range. The thicknesses of surface dead-layers and depletion layer as well as the diffusion length are determined by fitting the measured angular dependence of the photocurrent according to a model using absorption coefficients from the literature. For the absolute responsivity the mean energy for electron-hole pair creation is determined with the known photon flux of the electron storage ring BESSY. Total uncertainties of 4% for the spectral responsivity in the photon energy region 90 eV–4 keV are achieved. The result of our calibration is compared to conventional calibration techniques as well as to measurements with an electrically calibrated cryogenic bolometer.

© 1991 Optical Society of America