A method is described which allows the determination of the ellipticity of light (i.e., the degree of polarization as well as the phase difference of the mutually perpendicular electric field components) by intensity measurements behind two reflection polarizers. The method yields simultaneously the complex reflection coefficient of the first polarizer and its optical constants if it consists of only one mirror. The method is especially suited for the extreme ultraviolet where neither transmission polarizers nor simple phase shifters are available.
M. Schledermann and M. Skibowski, "Determination of the Ellipticity of Light and of Optical Constants by Use of Two Reflection Polarizers," Appl. Opt. 10, 321-326 (1971)