Analysis of beam wandering and influence of partial coherence on fourth-order moment of the light field in turbulent atmosphere

Abstract

The method of photon distribution function (PDF) is used to study the fluctuations of light beams propagating through a turbulent atmosphere. Our analysis concerns the regime of saturated fluctuations. The focus is on the phenomena of beam wandering and the effect of partial coherence on photon density fluctuations. The size of the quasiclassical part of wandering is shown to decrease with the propagation distance, while the quantum part increases. We explain this qualitative difference by beam fragmentation that is accompanied by a loss of correlation between individual parts. The effect of the phase diffuser on the fourth moment of the irradiance is taken into account. An explicit expression obtained for the fourth moment indicates the possibility of a significant reduction of noise in the communication channel. The diffuser changes the shot noise from delta-correlated (in the spatial domain) to smoothly distributed. The theory developed here can be used to estimate the influence of the phase diffuser on light fluctuations.