Recent work in which reflection polarizers were used to make ellipsometric measurements in the far uv employed the tacit assumption that the incident light was in a coherent state of polarization. However, since the most general state of light is that of partial polarization, i.e., a mixture of polarized and unpolarized components, a significant modification to the experimental techniques used hitherto is shown to be necessary.
R. H. W. Graves, "Ellipsometry Using Imperfect Polarizers," Appl. Opt. 10, 2679-2684 (1971)