THE COMBINED ELLIPSOMETRIC METHOD OF COMPLETE OPTICAL CHARACTERIZATION OF CRYSTALS. II. DETERMINATION OF THE OPTICAL CONSTANTS OF CRYSTAL

Viktor Belyukh, Bohdan Pavlyk

Abstract


This part of the article describes the second stage of the combined ellipsometric method of complete optical characterization of crystals. The testing of the second stage was carried out on crystals of lithium niobate (LiNbO3) and cadmium tungstate (CdWO4). The obtained results of measurements of an optically uniaxial LiNbO3 crystal fully confirmed the correctness of the proposed method and its applicability for optical characterization of crystals. In particular, the values of the principal refractive indices {no = 2.280(±0.003), ne = 2.202(±0.002)} and birefringence {Δn = – 0.0775(±0.0015)} of the LiNbO3 crystal are in good agreement with the values of these quantities, obtained by other researchers by other methods. Studies of the optically biaxial CdWO4 crystal were important for analyzing the accuracy of determining the optical constants. For generality of this analysis, measurements were performed in different measurement configurations at several angles of incidence of the laser beam. In particular, according to the results of measurements in two configurations (angle of incidence 45°), the following values of the principal refractive indices of the CdWO4 crystal (doped from the melt 0.375 wt.% PbO) were obtained: ng = 2.249±0.002, nm = 2.185±0.002, np = 2.130±0.008. Based on these values of ng, nm, and np, the angle between the optical axes and the optical sign of the crystal were determined. It has been shown experimentally that the CdWO4 crystal is a pronounced biaxial crystal with an angle between the optical axes close to 90°. Possible ways to improve the accuracy of determining the optical constants of crystals are also analyzed.

Key words: ellipsometry, optical indicatrix, principal refractive indexes, uniaxial and biaxial crystals.


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References


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DOI: http://dx.doi.org/10.30970/eli.16.11

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