Abstract

The area of application of Second Harmonic Generation (SHG) technique is broadening now. Besides the search for new nonlinear crystals there are examples of SHG researches of equilibria of ferroelectric solid solutions and investigations of kinetics of noncetrosymmetric phases formation in the course of chemical reactions in mixtures and gels or during crystallization in glasses. In order to solve these problems on the basis of SHG data it became necessary to suggest a more unified approach to SHG measurements for the variety of non-centrosymmetric and ferroelectric substances. To provide standard conditions for SHG measurements, the materials prepared either by growth of crystals, sintering of ceramics, or by "wet" chemical synthesis should in all cases be reduced to thin powders. When powders with size partides (L) smaller than the maximum coherent length are used the intensity of second harmonic (I_2ω) appears to be a good quantitative measure of nonlinear polarizability. In most oxides this is guaranteed if L < 3 mcm. Under this condition coherent length can be eliminated from the equation for the SH-intensity. The effect of the sample thickness on I_2ω is eliminated by measuring the radiation from sample in the backward direction.

© 1994 IEEE