Detection and analysis of depolarization artifacts in rotating-compensator polarimeters

Absolute constraints, namely, the Schwarz inequality and a complementary expression derived by us, are used to obtain corresponding absolute constraints on the Fourier coefficients of the intensity transmitted through rotating-compensator polarimeters and ellipsometers. These expressions allow the investigation of artifacts that result in mixed or apparently mixed polarization states over the cross section of the beam, the averaging time of the detector, or the frequency passband of the dispersing element. Examples include multiple internal reflections or inhomogeneous strain within an element, scattered light, and other types of system and component defects that cannot be accessed by means of polarization-state data alone. We apply these results to our polarizer-sample-compensator-analyzer (PSCA) ellipsometer to illustrate capabilities. A simple analytic model is shown to give a quantitative description of depolarization in systems for which the resolution is finite and the retardation varies with wavelength.