Optical Properties and Defects of Congruent Crystals of Doubly Doped Lithium Niobate

The effect of complex defects, associated with the presence of protons, on the optical characteristics of LiNbO3:Y(0.24):Mg:(0.63 wt.%) and LiNbO3:Gd(0.25):Mg(0.75 wt.%) crystals was investigated by IR absorption spectroscopy in the region of the stretching vibrations of the OH groups, by photoinduced and Raman light scattering, and by laser conoscopy. It was shown that the LiNbO3:Y(0.24):Mg:(0.63 wt.%) crystal has a larger photorefraction effect than the LiNbO3:Gd(0.25):Mg(0.75 wt.%) crystal and a congruent crystal. It was found that the speckle structure in the indicatrix of photoinduced light scattering for the LiNbO3:Y(0.24):Mg:(0.63 wt.%) crystal appeared anomalously quickly (<1 s).