Ce∶BaTiO3中光折变光栅衍射效率上升现象及分析

在对Ce∶BaTiO3晶体进行双光束干涉光折变光栅暗衰减特性的实验研究中,发现了暗条件下光折变光栅归一化衍射效率长时间上升的异常现象：在e光偏振、大入射角度产生光折变光栅的实验中,衍射效率在长逾8 h的时间内持续上升.而在e光干涉、小入射角度和o光干涉时均未出现衍射效率长时间上升的现象.分析认为：由于自泵浦位相共轭光的产生和晶体中的两个深能级参与了光折变过程,形成了衰减速度不同、光栅方向垂直的两个光栅,导致了暗衰减时衍射效率的长时间上升.

Behaviors and Analysis of Diffraction-Efficiency Ascending of Photorefractive Grating in Ce: BaTiO3

Anomalous long-time ascending of the diffraction efficiency is observed in dark-decay experiments of photorefractive gratings formed by interference of two writing beams in Ce∶BaTiO3. In the experiments with e-polarized and larger-angle writing beams, the diffraction efficiency kept rising over 8 hours. The diffraction efficiency, however, did not exhibit rising behaviors in the experiments of both e-polarized with smaller angle and o-polarized. It is deduced that the forming of two mutually perpendicular gratings with different decay rates and the long-time diffraction-efficiency ascending are caused by the self-pumped phase-conjugate beam and two deep traps involved in the photorefractive grating.