STUDIES OF PHOTOREFRACTIVE DIFFRACTION DYNAMIC IN PARAELECTRIC KTA1-XNBXO3 CRYSTALS

The dynamics of photorefractive diffraction in paraelectric KTa1-xNbxO 3 crystals during writing, reading, and erasing have been studied syst ematically. Experimental observations related not only to the diffract ion from the first-order photorefractive grating but also to that from the second-order photorefractive grating, and where a writing beam wi th spots smaller than, as well as larger than, the entrance surface of the crystal was used. All the complicated behaviors observed have bee n explained qualitatively. An electron-hole transport model and a none quilibrium screening model have been applied, and the existence of an internal dc electric field induced during writing simultaneously by an optical field and an externally applied field has been suggested and demonstrated. The significant influence of this induced field is indic ated.