Effects of coherence and polarization changes on the heterodyne detection of stochastic beams propagating in free space

We evaluate the heterodyne efficiency of a heterodyne (coherent) detection system for partially polarized, partially coherent, quasi-monochromatic beams. The beam-coherence-polarization (BCP) matrix is used for the description of the statistical ensemble of this class of stochastic beams. We investigate the dependence of the efficiency of the detection process on the beams parameters as the beams propagate in free space. We discuss how the optimization of the detection system can be performed for received beams with different coherence and polarization properties by adjusting the corresponding properties of the local oscillator beam. The dependence of the mixing efficiency on the size of the receiving aperture is emphasized. We derive an analytical expression for the heterodyne efficiency in the case when both the received beam and the local oscillator beam belong to a broad class of so-called electromagnetic Gaussian Schell-model beams. Our analysis is illustrated by numerical examples.