透射型光折变体全息光栅对超短脉冲激光光束衍射的特性

在Kogelnik耦合波理论的基础上，考虑光栅记录介质的色散效应的影响，研究了光折变体全息光栅对不同偏振状态的超短脉冲激光光束衍射的性质，讨论了高斯型入射脉冲激光光束的谱宽与光栅的有效衍射谱宽之比不同时，衍射和透射光束的光谱宽度、时间宽度、波形和衍射效率的变化。结果表明，光栅的有效衍射谱宽受光栅参量及入射条件的影响，对衍射性质的影响很大，且在考虑光栅记录介质的色散效应时减小。当入射脉冲的偏振方向垂直于入射面时，光栅的有效衍射谱宽大于偏振方向平行于入射面的情形，衍射效率在入射脉冲宽度较大时小于偏振方向平行于

Anomalous behaviour of photorefractive grating erasure owing to existence of both negative and positive carriers

In LiNbO3:Fe, anomalous behaviour of grating erasure is observed with different wavelenghts, i.e. rapid grating erasure in the short wavelength range, which deviates from the results predicted by the electron transport band model. The deviation is related to the coexistance of electrons and holes in photorefraction, and charge-transfer process including electrons and hole has been proposed. The electron and hole contributions to photo-excitation coefficient S of the Fe centre on the wavelength.