Theory of photoinduced changes in refractive index and spontaneous polarization

Abstract

Changes in the refractive index n and spontaneous polarization Ps associated with lattice reordering in the vicinity of ionized or excited shallow and deep impurity centres are considered. Distortions corresponding to both the nonpolar and ferroelectric phonon soft branches are taken into account in continuum approximation. The changes of n and Ps due to excited deep and shallow impurity centres are shown to differ, as a rule, only in sign. The temperature dependence of the refractive index change is ascertained to be different for ferro- and non-ferroelectrics.