Determination of the optical sign of a crystal by a conoscopic method

Abstract

To determine the optical sign of an investigated crystal plate, a conoscopic pattern of the latter is changed in an optical system without a polarizing microscope. To change the conoscopic pattern, an auxiliary plane-parallel crystal plate of arbitrary thickness and known optical sign is used. Such a plate, which is either capable of rotation about its vertical axis or fixed at a small angle to the investigated plate, is introduced into the optical system. Upon rotation of the auxiliary crystal plate, isochromatic rings on the conoscopic pattern are offset. Based on the direction of the offset from the centre of the pattern, a conclusion is drawn about the optical sign of the investigated crystal plate. When the auxiliary crystal plate is fixed at a small angle to the investigated plate, either two or three conoscopic patterns are observed on the screen. The optical sign of the investigated crystal plate is determined by the number of conoscopic patterns on the screen. If there are three patterns, then the optical signs of the auxiliary and the investigated plates are the same. If there are two patterns, then the optical signs of the auxiliary and the investigated plates are opposite.

Complex study of the structural and optical homogeneity of lithium niobate crystals

“…This tech nique was described in detail in [11,12]. In patterns obtained by laser conoscopy, in contrast to the cono scopic patterns observed in a polarization microscope, the large image size makes it possible to perform a detailed analysis of distortions in crystals both in the center of the field of view and at the periphery.…”

“…Raman spectros copy is the only method for the simultaneous study of the optical damage and the fine variations in the crys tal structure caused by this effect. The conoscopic pat terns obtained by passing a narrow monochromatic laser beam through a single crystal make it possible to perform a detailed analysis of fine structural features (both in the center field of view and at the periphery), including the ones caused by optical damage [11,12].…”

A birefringent polarization modulator: Application to phase measurement in conoscopic interference patterns

“…As a result, the fringe pattern moves according to the phase shift between components, allowing the identification of a number of properties. 18 However, we go further in order to obtain a phase map of the sample under study. This procedure not only allows us to clean the interferogram from unwanted illumination effects (removing almost everything but phase information) but also to characterize a crystal sample by means of the phase shift introduced.…”

“…(4)) and modifies the fringe pattern. 14,18 We follow the procedure indicated in Ref. 28 in order to recover the phase map of the DUT.…”

Visualization of Optical Uniformity Alloyed Single Crystals of Lithium Niobate

“…The conoscopic method received a qualitatively different level with the advent of lasers, computers with powerful software, in connection with the modern achievements of nonlinear optics and optics of photorefractive crystals, and also due to the need for high-quality optical materials for holography, laser media and radiation conversion. The observation method in converging (or diverging) polarized radiation (the conoscopic method) allows us to study the optical properties of anisotropic crystals, which manifest themselves differently depending on their orientation with respect to the direction of observation and the polarization of the radiation [1][2][3][4]. The radiation is passed through a polarizer and a crystal plate.…”