LiNbO3:Fe晶体中光感应自衍射观察

用He-Ne激光束沿LiNbO₃:Fe晶体的x轴或y轴方向聚焦照射较薄样品时,在晶体后面的屏上观察到十分规则的衍射图样。这与前人在该晶体中观察到的由晶体中光折变形成的位相噪音栅引起的光感应光散射现象迥然不同。我们观察到的这种自衍射图样,可用聚焦激光束入射时在晶体中形成的复杂类透镜效应和自衍射理论来解释。它可以清楚地表明聚焦激光束入射时晶体中光折变过程的特点、还可由衍射条纹的数目直接推算晶体中光折变△n的最大值。文中还实验研究与讨论了光感应自衍射的形成条件及其与光感应光散射的竞争关系。 关键词：

OBSERVATION OF LASER-INDUCED SELF-DIFFRACTION FROM LiNbO3:Fe CRYSTAL

We have observed very regular diffraction patterns on the screen behind the crystal when focusing He-Ne laser beam illuminates the thin sample along X or Y axis of the LiNbO₃:Fe crystal. This is utterly diffent from photoinduotd light scattering phenomenon which arises from phase-noise-gratings produced by optical-induced refractive index change in the crystal, it had been observed long ago. This self-diffraction pattern can be explained by selfdiffrac-tion theory and complicated lens-like effect formed in the crystal when focusing laser beam illuminates it. These diffraction patterns can show the feature of optical-induced refractive index change in the crystal clearly, and the maximum of optical-induced refractive index change △n can be calculated directly from the number of diffraction ring. Furthermore, we have also studied and discussed the conditions of formation of laser-induced self-diffraction and its competition behavior with photo-induced light scattering.