HOLOGRAPHIC GRATINGS BY SPATIAL MODULATION OF THE CURIE-WEISS TEMPERATURE IN PHOTOREFRACTIVE K1-XLIXTA1-YNBYO3-CU,V

We present experimental evidence indicating the formation of metastabl e dipolar gratings in potassium lithium tantalate niobate at the parae lectric phase. These dipolar gratings result from the formation of loc al metastable changes in the Curie-Weiss temperature, which, in the pr esence of an external electric field, induce changes in the low-freque ncy polarization. The polarization changes create spatially correlated birefringence gratings due to the electro-optic effect. The dipolar g ratings are formed in a slow spontaneous process, to compensate for re gular photorefractive gratings immediately after the creation of the l atter.