RELATIVE SIGNS OF NONLINEAR OPTICAL COEFFICIENTS OF POLAR CRYSTALS

Abstract
A determination of the relative signs of the nonlinear optical coefficients that give rise to second harmonic generation has been made for each of the following crystals: LiNbO3, LiTaO3, BaTiO3, ZnO, and LiGaO2. It is found that d33 and d31 have the same signs in LiNbO3, LiTaO3, BaTiO3, and LiGaO2. In ZnO, LiGaO2, and LiTaO3, the ratios d33/d31, d33/d32, and d31/d22, respectively, are negative.