Statistics of twin-beam states by photon-number resolving detectors up to pump depletion

We use hybrid photodetectors endowed with partial photon-number resolution to characterize the photon-number distribution of twin-beam states produced at different intensity regimes up to pump depletion. To match the detectors’ dynamics, the light of signal and idler is strongly attenuated by neutral-density filters. Since the filters do not modify the nature of any classical-light statistics, we find that signal and idler are described by a multimode thermal distribution at any pump power. The number of modes decreases at increasing pump power until pump depletion, when the number starts increasing again. The effect is qualitatively interpreted as a selective mode amplification induced by the high-gain parametric process.