Absolute scale of second-order nonlinear-optical coefficients

The absolute scale of the second-order nonlinear-optical coefficients of several important nonlinear-optical materials has been obtained with improved accuracy. Second-harmonic generation, parametric fluorescence, and difference-frequency generation measurements have been made at several wavelengths in the near-infrared region. The second-harmonic generation measurement was performed at the fundamental wavelengths of 1.548, 1.533, 1.313, 1.064, and 0.852 µm. The materials measured included congruent LiNbO3,1%MgO:LiNbO3,5%MgO:LiNbO3,LiTaO3,KNbO3,KTiOPO4,KH2PO4, quartz, GaAs, GaP, α-ZnS, CdS, ZnSe, and CdTe. We made the parametric fluorescence measurement to determine the nonlinear-optical coefficients of congruent LiNbO3 and 5%MgO:LiNbO3 at pump wavelengths of 0.532 and 0.488 µm. We made the difference-frequency generation measurement for congruent LiNbO3 at a pump wavelength of 0.532 µm. The second-harmonic generation, parametric fluorescence, and difference-frequency generation measurements yielded consistent data on the nonlinear-optical coefficients of the materials. We found that many of the currently accepted standard values are overestimated because of neglect of the multiple-reflection effect in (nearly) plane-parallel-plate samples. The dispersion of the nonlinear-optical coefficients showed that Miller’s Δ is barely constant over the wavelength range measured and thus that Miller’s rule is not so good as other methods for wavelength scaling of the nonlinear-optical coefficients.