Null ellipsometry is analyzed for components with depolarizations for unpolarized incident light. Serious imperfections include sample depolarization D <0.2, misalignment (δC <2°) and off-quarter-wave retardance (δT <5°) of the compensator. The four-zone null positions are derived analytically to the second order of serious imperfections and are also simulated based on Mueller matrices with depolarization, Errors of all four-zone nulls increase with increasing D. Depolarizations of all components except the analyzer cause errors to the nulls. The errors associated with D always couple with the second order of δC and δT and are enhanced by csc~(2) 2ψ. These divergent errors limit the applicable region of null ellipsometry where the errors in ψ and A are within 0.1°, and the simulation agrees well with the analytic solutions.
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