Optical homogeneity and second harmonic generation in Li-rich Mg-doped LiNbO3 crystals

A series of Mg-doped LiNbO3 crystals were grown using Czochralski method with fixed 5 mol% Mg doping and a variety of Li/Nb ratio (Li/Nb = 0.946–1.08). From the UV–vis absorption spectra, it is found that the absorption edges of the off-congruent crystals successively shift to the violet band in comparison with that of congruent pure LiNbO3. The birefringence gradient of these crystals was measured to investigate the optical homogeneity. In second harmonic generation (SHG) experiment, the SHG conversion efficiency was enhanced by the Mg doping and the increase of Li/Nb ratio. The dependences of the UV–vis absorption edges, the homogeneity and SHG properties on the Li concentration were explored. The results indicate that the crystal of Li/Nb = 1.02 is the most proper media for SHG application among the five crystals in the paper.