Elementary responses of analog photodetectors and absolute calibration of their efficiency

A modified Klyshko method for standardless calibration of analog photodetector efficiencies is suggested and experimentally implemented. The method is based on the measurement of the number of incident photons using correlation properties of biphotons generated under spontaneous parametric downconversion, and on the determination of the mean number of discrete elementary responses of a photodetector by deconvoluting the statistical distribution of the output photocurrents. As an example, the generalized efficiency of an analog photomultiplier is measured as the ratio of the average number of elementary current responses to the average number of incident photons. The statistical properties of the elementary responses of an analog photodetector depend not only on the detector itself, but also on the parameters of the subsequent electronic circuit. Nevertheless, it has been shown that the generalized efficiency determined by this way allows one to calibrate the photon fluxes by the analog photodetector without involvement of any reference sources or detectors.