Quantum images in non degenerate optical parametric oscillators

Quantum images, that is inhomogeneous field distributions purely generated by quantum fluctuations, persist when passing from the degenerate to the no n-degenerate case of optical parametric oscillators (OPO). Below the thresh old for parametric oscillation where the near-held distributions are homoge neous both in intensity and phase, appropriate spatial correlation function s anticipate the transverse spatial pattern that appears above threshold. I n particular, the angular dependence of the far field spatial correlation f unction is able to reveal the travelling-wave nature of the phase pattern a bove threshold typical of nondegenerate OPOs. Cross-correlation functions b etween signal and idler intensities show clear evidence of the non-classica l nature of the output light.