ИСТИНА

The process of parametric downconversion (PDC) represents the decay of photons of monochromatic radiation (pump) with a frequency ωp on pairs of correlated photons at lower frequencies, ωs +ωi =ωp. When studying twin beams produced under a frequency degenerate PDC, the covariance, the noise reduction factor (NRF) and other related characteristics are usually considered as non-classical parameters, which are determined based on measurements of the current readings of optical detectors of the signal and idler PDC channels. We propose to consider properties of biphotons with extremely diff erent frequencies, when the signal photon frequency ωs is very close to the pump frequency, while the idler frequency ωi hits the terahertz range. Under the high parametric gain conditions, it would be more convenient for recording and utilizing the quantum properties of optical-terahertz fields. We consider a theoretical approach that can be applied to detectors operating in the analog recording mode.The method is based on the fact that the signal and idler beams generated by PDC have the same fluctuations in the number of photons for any parametric gain coeffi cient. Applicability of the detector calibration method based on the measurement of NRF, previously developed for photon-counting detectors only, is studied. The fluctuations in the single-photon pulse amplitudes of non-countable detectors are taken into account.