Modulations in Stokes parameters due to electromagnetic longitudinal spatio-temporal coherence

We establish a generalized interference law characterizing longitudinal electromagnetic spatio-temporal coherence to determine the intensity and polarization modulations of light fields in the longitudinal direction. It is observed that under specific conditions, other interference laws can be deduced from the generalized interference law. Furthermore, the impact of different polarization and amplitude attributes of the source plane on the intensity and polarization modulations in the field has been quantified using two examples. In the case of orthogonal polarization features at the source points, we investigate the dependence of the degree of polarization (DOP) at the observation plane on the longitudinal shift and the angular spectra of the source for the time difference less than the coherence time. The weightage of the constituent orthogonal components plays a decisive role in governing DOP modulations. We obtain a constant DOP at the field point for identical polarization properties at the source points, independent of the coherence time. We have experimentally determined the DOP for both the polarizations, validating our theoretical findings.