Conditioned photon statistics of an optical parametric oscillator

The output of a degenerate optical parametric oscillator (DOPO), for weak driving fields, is highly bunched. The photons tend to come out in pairs. Nonclassical behaviour is evident in the output of the DOPO, but usually involves interferometric investigations, as in the spectrum of squeezing, or a Mandel-Hong-Ou interferometer. We discuss a conditioned measurement of the second-order intensity correlation function g(2)(tau) that yields antibunching. By only measuring the second-order intensity correlation function g(2)(tau) after a photon has been detected, large bunching is turned into almost perfect antibunching.