Anisotropic self-diffraction in Mg-doped LiNbO3

The characteristics of anisotropic self-diffraction were studied for undoped LiNbO3 crystals and LiNbO3:Mg at doping levels of a few mole percent. From the absolute magnitude and the time dependence of the signal, it was possible to determine the induced refractive-index change and the conductivity of the charges involved in the photorefractive effect for each sample. For these excitation conditions, only charge migration perpendicular to the c axis contributes to laser-induced grating, and thus the conductivity is associated with charge diffusion. The results show that the total refractive-index change causing the self-diffraction is only slightly smaller for the Mg-doped samples than for undoped LiNbO3 while the conductivity is 1 order of magnitude greater for the Mg-doped samples.