Investigation of electric internal field in congruent LiNbO3 by electro-optic effect

We investigate the effect of the defect-induced internal field on the electro-optic behavior of z-cutcongruent lithium niobate crystals. We measure, by a spatially resolved interferometric technique,the phase retardation due to an external applied voltage occurring in two regions with oppositeferroelectric polarization. When measurements are performed just after electrical poling, the twoopposite domains show a different electro-optic behavior. We interpret this as due to an elasticcomponent of the internal field. In fact, the asymmetric behavior disappears when the sample isthermally annealed, i.e., when the internal field vanishes.