OPTICAL PROPERTIES OF DOUBLE DOPED LiNbO₃:Gd:Mg CRYSTALS

By direct alloying of congruent melt with magnesium and gadolinium oxides, compositionally uniform nonlinear optical single double doped crystals with different content of dopants have been grown: LiNbO3:Gd3+(0,003):Mg2+(0,65 wt. %), LiNbO3:Gd3+(0,23):Mg2+(0,75 wt. %) and LiNbO3:Gd3+(0,25):Mg2+(0,75 wt. %). The results obtained by laser conoscopy and photoinduced light scattering indicate a high structural perfection of the grown crystals. The results give grounds to assert that LiNbO3:Gd:Mg crystals are close to a stoichiometric crystal in some of their properties. A low value of the coercive field (approximate to 2,3 kV/cm) is one of such properties of stoichiometric and magnesium-doped LiNbO3 crystals, which are important for creating materials for laser radiation conversion on periodically polarized submicron-sized domains with flat boundaries. In this case, the grown LiNbO3:Gd:Mg crystals have a much higher optical uniformity than a stoichiometric crystal. Crystals of LiNbO3:Gd3+(0,003):Mg2+ (0,65 wt. %) and LiNbO3:Gd3+(0,23):Mg2+ (0,75 wt. %) have the highest optical uniformity and the absence of the photorefraction effect. Increase of gadolinium concentration to 0,25 wt. % leads to increased distortion of the conoscopic pattern and to the appearance of a significant photorefractive response of the LiNbO3:Gd3+(0,25):Mg2+(0,75 wt. %) crystal.