Distribution function of the intensity of optical waves in random systems

Statistics of coherent radiation propagating in a random medium is analyzed in the framework of diagram technique. The distribution function for radiation intensity is calculated and it is shown, that only for small values of the argument the distribution function is a simple exponential, as predicted by Rayleigh statistics. For larger values of intensity the distribution function differs drastically from the simple exponential, and the asymptotical behavior is a stretched exponential. The results obtained are confirmed by numerical simulations.