An exact expression for calculating the complex reflectance ratio of a surface, from data obtained with a rotating-analyzer ellipsometer system using optically active quartz Rochon prisms, shows that optical activity affects relative values of measured quantities by an amount of the order of 1%. For component settings near the normal modes of the system, these effects can be much greater. By contrast to null ellipsometry, there is no surface for which these effects vanish in calibration. Therefore, corrections of the order of 1% (0.5º) are necessary in the calibration of the azimuth scales of these ellipsometer systems, even in the most-favorable cases.
D. E. Aspnes, "Effects of component optical activity in data reduction and calibration of rotating-analyzer ellipsometers," J. Opt. Soc. Am. 64, 812-819 (1974)