Single-beam noise characteristics of quantum correlated twin beams
  We investigated the intensity noise spectra of the single beam of a pump-enhanced continuous-wave (cw) optical parametric oscillator (OPO), which was used to generate quantum correlated twin beams, as a function of the pump power. With a triply (pump-, signal-, and idler-) resonant cavity, the oscillation threshold of our OPO was about 8.5+/-1.3 mW and the measured slope conversion efficiency was 0.72+/-0.02. A twin beams with power of 240 mW were generated at pump power of 350 mW. The relaxation oscillation frequencies, which depend on the pump power, were observed when the pump power of OPO was from 12.5 mW to 28 mW. The experimental results confirm the predicted increase in OPO relaxation frequency with pump power. Squeezing of the single beam intensity was for the first time inferred experimentally by exploiting nature of quantum noise dependent on loss. 
Yun Zhangx, Katsuyuki Kasai, and Kazuhiro Hayasaka