Photoelastic Properties of Trigonal Crystals

All possible experimental geometries of the piezo-optic effect in crystals of trigonal symmetry are studied in detail through the interferometric technique, and the corresponding expressions for the calculation of piezo-optic coefficients (POCs) πim and some sums of πim based on experimental data obtained from the samples of direct and X/45°-cuts are given. The reliability of the values of POCs is proven by the convergence of πim obtained from different experimental geometries as well as by the convergence of some sums of POCs. Because both the signs and the absolute values of POCs π14 and π41 are defined by the choice of the right crystal-physics coordinate system, we here use the system whereby the condition S14 > 0 is fulfilled (S14 is an elastic compliance coefficient). The absolute value and the sign of S14 are determined by piezo-optic interferometric method from two experimental geometries. The errors of POCs are calculated as mean square values of the errors of the half-wave stresses and the elastic term. All components of the matrix of elasto-optic coefficients pin are calculated based on POCs and elastic stiffness coefficients. The technique is tested on LiTaO3 crystal. The obtained results are compared with the corresponding data for trigonal LiNbO3 and Ca3TaGa3Si2O14 crystals

Calcium Tungstate is a Perspective Acousto-Optic Material. Photoelastic Properties

Abstract -Acousto-optic modulators are main component of communication fibre-optic systems. From the other side the studies of the absolute piezo-optic effect (POE) are one of the important steps to estimate the acousto-optic efficiency of optical materials. In this article the investigation results of POE in calcium tungstate crystals (CaWO 4 ) has been represented. It is also proved that this crystal is essentially better acousto-optic material in comparison with lithium niobate (LiNbO 3 ) widely used in acousto-optic devices. Keywords -acousto-optic efficiency, elastic constants, piezo-and elastooptic coefficients, interferometric method The absolute piezo-optic coefficients (POCs) have been studied using the interferometric method taking into account the real lack of parallelism of sample faces. eliminates the influence of inconsiderable sample wedgeshaping on the error, indices m, k, i denote the directions of one axis pressure, light propagation and is polarization accordingly, is the wave length. Experimental values fort the main geometries of the experiment (i, m = 1, 2, 3) has been given in the table 1. The sign "+" or "-" at values of control stresses denote the increasing or decreasing of the natural optical light beam path induced by the change of the light path through the one axis. Besides that is necessary to take into account, that to the mechanical compression stresses assigned the "minus" sign. The estimated values of the main coefficients im are given in the tabl. 2. + ) and is ± 10% (is verified by multiple measurements), and the error of the second summand is caused of the elastic coefficient S km (± 5%). We see in the tabl. 2, that POE value of the calcium tungstate is greater as POE of lithium niobate: the corresponding POC of CaWO 4 crystals are more then ~ 2-7 times higher, and the sum of absolute values of im is 3 times higher. Nevertheless for estimating the acousto-optic efficiency of calcium tungstate it is necessary to determine the elastooptic coefficients (EOCs) p in , using the determined im and known tensor relation p in = im mn , where mn denote the elastic stiffness constants

Single-pulse femtosecond laser fabrication of concave microlens- and micromirror arrays in chalcohalide glass

International audienceThe diffraction-limited piano-concave microlens- and micromirror arrays were produced in chalcohalide glass of 65GeS(2)-25Ga(2)S(3)-10CsCl composition transparent from similar to 0.5 to 11 mu m. Only a single 200 fs laser pulse with 800 nm central wavelength is required to form microlens, which after metal coating becomes a concave micromirror. This process can serve as a basis for flexible technology to fabricate regular microlens and micromirror arrays for optotelecom applications, its performance being limited only by repetition rate of the laser pulses (typically 1000 microlenses per second)