Microwave Nonlinearities in Anisotropic Dielectrics and Their Relation to Optical and Electro-Optical Nonlinearities

Earlier measurements of the three-frequency microwave nonlinear susceptibility coefficient have been extended to include all of the nonzero tensor components of dᵢⱼₖᵐ(-ω₃,ω₂,ω₁) of LiNbO₃ and LiTaO₃. These results are interpreted, using the formalism developed by Lax and Nelson, to describe nonlinearities associated with electronic and ionic modes of anisotropic crystalline materials. The linear dispersion parameters for each material are first approximated by a single-electronic and a single-ionic normal mode. Nonlinear elements are then added to this normal-mode model. A macroscopic-bond-charge model is developed. With some simplifying asumptions and knowledge of the optical nonlinear coefficient dᵢⱼₖᵒ and the electro-optic coefficient dᵢⱼₖᵉᵒ, a good fit with the measured values of dᵢⱼₖᵐ can be obtained. The same parameters used to fit dᵢⱼₖᵐ are used to calculate the pyroelectric coefficients for LiNbO₃ and LiTaO₃. In both cases, the correct signs and magnitudes within a factor of 2 of experimental values are obtained.