P-REPRESENTATION OF THE CROSS-SPECTRAL DENSITY

Pursuing the similarities between the cross-spectral density in classi cal coherence theory and the density operator of the radiation field i n quantum optics, we present an alternative to the coherent mode repre sentation for the cross-spectral density, which is termed the P-repres entation. In this new representation, any cross-spectral density acqui res a diagonal expression in terms of the universal set of coherent-st ate functions. We demonstrate the P-representation explicitly for the Gaussian Schell model source.