DIPOLAR HOLOGRAPHIC GRATINGS INDUCED BY THE PHOTOREFRACTIVE PROCESS IN POTASSIUM LITHIUM TANTALATE NIOBATE AT THE PARAELECTRIC PHASE

We present experimental evidence indicating the formation of dipolar h olographic gratings in potassium lithium tantalate niobate at the para electric phase slightly above the phase transition, These gratings are formed in the dark, following the writing of space-charge-based photo refractive gratings, under an external electric field. The dipolar gra tings create a spatial modulation of the low-frequency dielectric cons tant, and the latter induces a spatially correlated modulation of the polarization, which is transformed into birefringence gratings through the quadratic electro-optic effect. (C) 1997 Optical Society of Ameri ca.