SPATIAL QUANTUM SIGNATURES IN PARAMETRIC DOWN-CONVERSION

We calculate the normal and time ordered spatial intensity correlation function of the signal field in a degenerate parametric oscillator below threshold, with spherical mirrors. In the far field, it exhibits a two peak structure, and the correlation is maximal between points opposite each other with respect to the axis of the system. This feature provides direct spatial evidence of the twin photon emission, and identifies states of the radiated field with local nonclassical squeezing properties.