Spectral measurement of coherence Stokes parameters of random broadband light beams
All light sources, natural or man-made, are more or less partially polarized and partially coherent. The extreme cases of fully coherent, fully polarized beams and completely incoherent, unpolarized sources are good approximations, e.g., for single-mode lasers and thermal radiators, respectively. However, several light sources that fall in between these two extremes exist, as exemplified by multimode lasers and LEDs. While the scalar-field treatment is sufficient for uniformly fully polarized field, partial polarization adds a new dimension and the complete coherence characterization necessitates the use of electromagnetic coherence theory and development of methods to measure the related important parameters. The information pertaining to the coherence of vectorial, partially polarized optical beams is conveniently expressed in terms of the two-point (coherence) Stokes parameters introduced relatively recently.