The sinusoidal oscillatory diffraction induced by strong refractive index change in reduced Fe:LiNbO_3 crystals

摘要

In this paper two-beam interference experiments are performed to investigate the diffraction characteristics of volume gratings in Fe:LiNbO_3 crystals (0.15 wt% Fe_2O_3), the results show that the dependence of the diffraction characteristics on the oxidization-reduction state and the oscillatory diffraction can be found in the reduced crystals. The theoretical analysis shows that the strongest space charge field can be formed in the reduced crystals, which induce the strong refractive index change, and because of the sin~2 relation between refractive index change and diffraction efficiency, the oscillatory diffraction can be found in the reduced crystals. In application for high diffraction efficiency the oxidized treatment should be performed for Fe:LiNbO_3 crystals so that the depth integral of saturated refractive index change is equal to π/2.