Effect of optical activity on electro-optic measurements in crystals of the potassium dihydrogen phosphate family

Abstract

Crystals of the potassium dihydrogen phosphate family in their paraelectric phase belong to point group \overline 4 2m, which allows for natural optical activity and electric field-induced optical activity related to the linear and nonlinear electrogyration effects. This work presents a theoretical analysis of the influence of these effects on measurements of the linear, quadratic and fourth-order electro-optic coefficients. Both the polarimetric technique and a method based on Michelson interferometry are considered. A number of configurations of the light path and the electric field directions were analyzed, and it was found that the influence, when it appears, is usually negligibly small. Thus, no previously reported experimental data need a new interpretation. However, in future measurements of some effective coefficients of the quadratic electro-optic effect using the dynamic polarimetric technique, the contribution of the quadratic electrogyration may no longer be negligible after improving the resolution from 10−21to 10−22 m2 V−2. This work also shows that the quadratic electrogyration described by the β31coefficient may be decoupled from the linear and quadratic electro-optic effects in measurements performed by the polarimetric method.