We show a model based on the polarization matrix formalism and the theory of statistical distributions on Poincaré Sphere, which describes a controlled depolarization method for a partially polarized beam passing through a rotating retarder.

Based on the fact that the degree of polarization of a light source is given in terms of the absolute value of its complex degree of coherence, we design a depolarization experiment using a variable retarder in which we measured the degree of polarization as a function of the retarder’s birefringence. We show that if the incident light is previously linearly polarized we can perform a direct measurement of the light source’s coherence using a Stokes meter.