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.