Coherence modulation in the interference of random electromagnetic beams

We analyze the modulation of the spatial coherence of a random, stationary electromagnetic light beam in Young's two-pinhole interference. We derive a spectral interference law that governs the behavior of the four coherence (two-point) Stokes parameters and elucidates the contributions of spatial coherence and polarization of the incident field on the coherence properties of the superposition wave. We also show that these parameters as well as the degree of electromagnetic coherence generally exhibit spatial modulations that arise either from the nonvanishing coherence or the polarization properties of the fields in the openings. The formalism is demonstrated through a set of examples.