Abstract
Multiple beam interference (MBI) in anisotropic crystals introduces a systematic error in the measurement of the optical linear birefringence Δ n. The error δϕ in determining the phase difference is calculated by treating the sample as a birefringent Fabry-Perot interferometer. For a given reflection coefficient r, the phase error is less than δϕ max = 2 r 2(rad). In a Δ n( T) study, the temperature dependence of both the refractive indices and the sample thickness contribute to the MBI effect and lead to a characteristic beat pattern in δϕ. As an example, the MBI error is calculated for Δ n( T) of Sb 5O 7I near the structural phase transition. Quantitative agreement with the experiment is obtained. For a Landau-type analysis of Δ n( T) the influence of the systematic birefringence error on the model parameters is analysed in detail. Roughening of the crystal surfaces reduces the MBI effect. This is demonstrated by a model calculation and by the experiment.
Published Version
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