Interferometric measurement of refractive indices of LiNbO3

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Abstract
An interferometric method for the determination of refractive indices is described which uses the shift in the optical path length when a parallel plate sample is rotated in one arm of a Michelson-type interferometer. High precision is achieved by including appropriate numerical fit procedures in the evaluation of the experimental results. We could prove that an accuracy of about 2.10−4 can be reached with the method. Sample nonidealities (slight wedge or lens shape) have only moderate effects on the determination of the refractive index. Measurements on LiNbO3 show that not only the extraordinary index of refraction varies with the Li/Nb ratio — which is in good agreement to earlier results —, but also the ordinary one.