Excess-noise-enhanced parametric down conversion - art. no. 033811

We calculate the influence of excess noise on parametric down conversion in an unstable optical parametric oscillator (OPO), using a quantum quasimode description. We find a strongly enhanced pair photon generation rate below threshold as compared to a conventional stable cavity setup of comparable gain and loss. In addition, the oscillation threshold is lowered due to the influence of the excess noise and the squeezing properties of the emitted light are significantly changed. In general, the maximal quantum-noise supp ression in one quadrature component is reduced, which poses strong limitati ons for the practical usefulness of a geometrically unstable OPO source. Th e analytical results from our quasimode description are in good agreement w ith numerical simulations using a positive-P representation of the field in mode space and in position space.