Anomalous index modulations in electrooptic KTa(1-x)Nb(x)O(3) single crystals in relation to electrostrictive effect

KTa(1-x)Nb(x)O(3) is known for its huge Kerr effect, which is a second order electrooptic (EO) effect. By utilizing the large refractive index change Δn of this EO effect, a fast optical beam deflector has been realized. However, anomalous spatial distributions of Δn were observed with this beam deflector. This anomaly is ascribed to distortions caused by the electrostrictive effect that occurs when voltage is applied. We assumed a spheric distortion and used a variational method to deduce an analytic solution for the strains that accompany this distortion. The analytic solution coincides with numerical results obtained with the finite element method. In addition, the solution agrees well with the experimentally obtained Δn distribution.