Use of an ADP four-crystal electrooptic modulator in ellipsometry

Abstract

Some theoretical considerations and experimental techniques in application of an ADP 45° X-cut four-crystal electrooptic modulator (EOM) to fast retardation modulation ellipsometry are described, emphasis being placed on the thermal stabilization. First to solve the thermal instability problem and to analyze systematic errors resulting from use of the EOM, the Jones matrix for the EOM is theoretically constructed which includes the effect of axial misalignment of the ADP crystals, multiple reflection at crystal-matching-dielectric liquid interfaces, temperature differences among the four crystals, and modulator cell windows. As a result, temperature-dependent factors in EOM characteristics are made clear. Second, a practical matrix form of the Jones matrix is determined from experiments on the bias-voltage dependence of the transmitted light intensity. Last, a thermal stabilization technique introduced by the matrix representation is demonstrated in the application of the EOM to ellipsometry, which enables us to obtain ellipsometric parameters of a sample, (Ψ,Δ), independent of the thermal drift and imperfections that accompany the EOM.