Moments of the Sum of Photocounts in Gaussian Light

The statistics of the sum of photocounts in partially coherent Gaussian light is investigated. Both the case of detection at $L$ discrete points and the case of an extended surface of detection are considered. The combinatorial-analysis approach is applied to derive the moments and cumulants of the distribution. They all can be expressed in terms of the second-order correlation function. The results are generally valid independent of the ratio of the observation time to the coherence time of light. A comparison between the theoretical moments and the moments computed from experimental distributions as a function of the detector surface is carried out with the help of a pseudothermal source.