Specimen Coherent Scattering and Compensator Defects in Ellipsometry*

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Abstract
An imperfect optical component between the polarizer and analyzer is replaced by its ideal counterpart and an imperfection-containing plate. Such a procedure allows use of a previous analysis of imperfections in cell windows to deal with other component imperfections, excluding depolarization. For the conventional ellipsometric arrangement with the compensator set before reflection at ±π/4 azimuth to give near π/2 retardation, two-zone averaging yields a correct value of the ratio of the diagonal reflection coefficients in the presence of small spurious off-diagonal reflectances, i.e., the effects of p ↔ s coherent scattering due to specimen roughness, optical activity, etc., cancel in a two-zone average. A procedure is developed for correcting the effects of optical activity and birefringence in compensators, which do not cancel upon averaging over two conjugate zones. The one significant off-diagonal element in the analyzer Jones matrix does not appear in two-zone averages, to first order.