Propagation of the Fourth-Order Coherence Function in a Random Medium*

Abstract

In this paper we consider propagation of the fourth-order coherence function in a homogeneous isotropic random medium. The treatment is restricted to light with small angular spread about a principal propagation direction. In addition, the index-of-refraction fluctuations in the random medium are assumed to be small. Using the method of small perturbations, a solution is obtained for the coherence function if the wave is quasimonochromatic and initially plane. The correlation of irradiance fluctuations, a contracted form of the fourth-order coherence function, may then be calculated and in this case is shown to yield the same result as that given by Tatarski. The solution for the fourth-order coherence function may be used to check the measurement procedure recently proposed by Beran, DeVelis, and Parrent.