Focused Laser Irradiance Fluctuations in a Turbulent Medium

A standard diagrammatic technique is used to obtain an integral representation for the fourth moment of the field of irradiance in a random weakly inhomogeneous medium. For the case of an incident focused coherent wave, it is shown that the spectral and correlation properties of the random field of intensity depend in an essential manner upon the magnitude of the phase structure function, computed on the transmitter aperture size. The region of large values of this parameter is of particular concern, where an analytical expression for the correlation function of intensity fluctuations is derived, and saturation of the magnitude of the normalized variance of intensity fluctuations is investigated.