Absolute calibration of photodetectors based on spontaneous parametric down-conversion biphoton field

A new method of absolute calibration of photodetector sensitivity based on spontaneous parametric down-conversion (SPDC) biphoton field is described. The process of SPDC is studied theoretically. The single photon detection probability and two-photon coincidence probability are derived and the calibration principle for photodetectors is explained. An experimental system has been set up. The sensitivity of a photon-counting photomultiplier tube was measured, and the results were compared with those obtained using conventional method.