Changes in the intensity fluctuations of a class of random electromagnetic beams on propagation

We discuss fourth-order correlation properties of wide-sense statistically stationary, quasi-monochromatic, electromagnetic beams, assuming that the fluctuations in the electric field at any point are governed by Gaussian statistics. In particular, we derive expressions for the covariance function and for the contrast (scintillation index) of the fluctuating intensity of an electromagnetic Gaussian Schell-model beam, propagating in free space. For such beams we also derive expressions relating to fluctuations in the power and discuss the effects of transmitter and receiver aperture averaging. We show that the fluctuations of the intensity and of the power of the beam can be controlled by suitable choice of the states of coherence and of polarization of the source.