Degrees of coherence of partially polarized light: invariance and information properties

Abstract

We address the problem of defining degrees of coherence for partially polarized Gaussian light. Some previously published approaches provide efficient solutions to this problem, but we will show on simple examples that they do not clearly separate partial polarization and partial coherence effects. We thus introduce intrinsic degrees of coherence, which characterize partial coherence independently of the choice of coordinate systems and of the partial polarization state of each field. The larger of these degrees has a clear physical meaning since it corresponds to the largest scalar degree of coherence that can be obtained after propagating the light waves through polarization modulators and perfect polarizers. Another interesting physical interpretation is obtained by relating the intrinsic degrees of coherence to the Shannon entropy, which is a classic measure of the "disorder" of a physical phenomenon.