TEMPERATURE-DEPENDENCE AND DISPERSION OF ELECTROOPTIC AND ELASTO-OPTIC EFFECT IN PEROVSKITE CRYSTALS

We relate the linear electro-optic coefficients to the quadratic polar ization-optic and the elasto-optic tensors by analyzing the dielectric phenomena driven by the spontaneous and induced polarization as well as the mechanical effects given by the deformation of the crystals. We determine the temperature dependence and the wavelength dispersion of the electro-optic tenser in all the ferroelectric phases from a small er set of data: the quadratic polarization-optic tenser of the cubic p hase, the dielectric permittivity, and the spontaneous polarization, U nder the assumption that the elasto-optic tenser at constant polarizat ion is constant, the elasto-optic coefficients at constant electric fi eld in the ferroelectric phases are derived. Numerical evaluations of these coefficients for two perovskite crystals KNbO3 and BaTiO3 are pr esented. Modifications of the electro-optic properties in doped crysta ls, mainly due to a change of the dielectric permittivity, are discuss ed as well. (C) 1995 American Institute of Physics.