The effect of stoichiometry on nonlinear optical properties of

From the chemical bond viewpoint, second-order nonlinear optical (NLO) tensor coefficients of have been investigated. The single-bond contributions to the second-order NLO susceptibility and the linear susceptibility were determined. The tensor values thus calculated are in good agreement with experimental data. Based on theoretical results of with Li/Nb = 1, we also have calculated linear and nonlinear optical properties of nonstoichiometric samples with Li/Nb < 1. In the calculation, we find that the Li - O bond is an important type of chemical bond in these samples, which have large NLO contributions to the total nonlinearities. The refractive indices and second-order NLO tensor coefficients have been determined as a function of the stoichiometry.