Partial coherence and polarization in electromagnetic interference

While the theories of the optical coherence of scalar fields and the polarization of beam fields are well established, a general theory for the coherence and polarization of true electromagnetic fields appearsmore subtle. With random vector fields coherence may reside among any or all of the electric-field components, leading to a modulation of the optical intensity or the polarization state, or both, on two-beam interference. We discuss the recent formulations of both the polarization and the coherence, and we show that the electromagnetic degree of coherence is characterized by the modulation of all the four Stokes parameters (representing intensity and polarization state) in a two-pinhole Young's setup. This also leads to a new experimental interpretation for the degree polarization of a random electromagnetic beam. Certain important results pertaining to electromagnetic coherence, which are fully analogous to their scalar counterparts, are emphasized.