STRUCTURAL STATE AND THE SECOND ORDER NONLINEAR OPTICAL CHARACTERISTICS OF LITHIUM NIOBATE CRYSTALS DOPED WITH RARE EARTH ELEMENTS

Theoretical calculations of the nonlinear optical susceptibility tensor components dij according to structural studies were carried out for lithium niobate crystals doped by low concentrations of rare earth elements (Lu, Sm, Tb, Er, Tm, Dy). The dopant concentrations ranged from 0.2 to 0.8 mol%. It was shown that the efficiency of conversion to the second harmonic depended on the type of dopant. The most noticeable increase of the nonlinear optical coefficient d33 was observed in a dysprosium-doped crystal.