Imaging conoscope for investigation of optical inhomogeneity in large boules of uniaxial crystals

Abstract

The name “conoscope” in Greek suggests that this tool should be used for observing interference patterns of birefringent crystals in the convergent beam of light. As such, the conoscope has been frequently used in laboratories for quick and usually qualitative estimation of optical inhomogeneity of crystals. In this paper we have described details of the computer-controlled imaging conoscope used for quantitative investigation of optical inhomogeneity in uniaxial crystals. To the best of our knowledge, this is the first conoscope used in an automated arrangement. Its working is based on equations derived for a plane–parallel uniaxial crystal plate cut out obliquely to the optical axis, which is next applied for two specific plate orientations practically investigated, i.e. for plates cut out perpendicularly and parallelly to this axis. It was found that these equations are more accurate than those published by other investigators. A practical investigation of a LiNbO3 crystal pulled by the Czochralski method from a congruent melt has been presented. Two birefringence inhomogeneity maps acquired for the above-mentioned two specific orientations in this crystal were used for eliminating its inhomogeneous areas from further use in optics. A theoretical error analysis carried out also in this work has shown that the optical inhomogeneity could be detected with a relative error usually not exceeding a small fraction of a percent.

Structure Deformation in GdCOB Single Crystals Grown by the Czochralski Method

“…Optical conoscopic images were obtained using the convergent beam of light, for example, refs and from the He−Ne laser. Birefringence dispersion parameters were calculated from the spectropolarimetric measurements.…”

Visualizing the conoscopic isochromatic interference fringes in anisotropic crystals by spinning polarizer and analyzer

“…The isochromatic fringes, also called the isochromates, occur when the optical path length difference between the two eigenwaves equals an integer plus half-number of wavelengths, so that constructive interference occurs. In most of the above-mentioned applications, there is a common demand of accurately measuring the isochromates [4][5][6][7][8][9][10][11][12]. However, the isochromates are intrinsically and unevenly masked by the isogyres, which are broad extinction bands whose shape assumes a complicated third-order equation [13].…”

“…For example, the human cornea has been found to be a negative biaxial material [3]. The conoscopic interference patterns have been used to accurately measure the orientation [4][5][6], the refractive indices, and the thickness [7], as well as the optical inhomogeneity [8] of crystals. The conoscopic interference patterns are sensitive to external influences, such as strains and electric fields, which allows the evaluation of the photoelastic parameter [9] and the electro-optic coefficient [10] of crystals.…”

A Study of Optical Uniformity of Lithium Niobate and Paratellurite Crystals by the Method of Conoscopy

“…In more recent papers based on some additional approximations the authors arrive at a conclusion that isochromates are described by curves of second order [2,3,7,9,1214]. The available experimental or calculated isochro- In the present work we study the optical uniformity of large-size lithium niobate and paratellurite crystals by the method of laser conoscopy.…”

“…Analysis of the available publications on this matter shows that even the simplest case of uniaxial crystals rests on a number of approximations resulting in uncertainties regarding to the shape of isochromates [2,3,9,1214]. Born and Wolf in their monograph [15] relied on a minimum of simplications and arrived at a conclusion that the isochromates of uniaxial crystals correspond to curves of fourth order.…”