Windows in ellipsometry measurements

The effect of windows or lenses placed between the polarization-state generator and the polarization-state detector in a general ellipsometry measurement is examined. It is found that three parameters are required for describing the effects of the window retardation on the ellipsometry measurements. Two of these window parameters can be measured at the same time as the sample parameters if the sample is isotropic, but the third window parameter cannot be determined independently and must be measured separately. If the sample is anisotropic, then none of the windows parameters can be measured independently at the same time as the sample parameters. An example is given in which the strain-induced retardation in fused-silica focusing lenses is measured with a two-modulator generalized ellipsometer and the results are used to correct the sample data.