摘要
BaTiO<sub>3</sub> was the first oxide ferroelectric material to be discovered. Recently, in the study of the nonlinear optics its photorefractive effects have been of great interest among photorefractive materials because its very large electro-optical tensor component (r<sub>42</sub>=r<sub>51</sub>=1640 pm/V) leads to correspondingly large values of four-wave-mixing reflectivity and beam-
