Nonlocal Contributions to Degenerate Four-Wave Mixing in Noncentrosymmetric Materials

Cascaded second-order and piezoelectric contributions to degenerate four-wave mixing in noncentrosymmetric materials are analyzed in detail. The effective third-order susceptibility measured in degenerate four-wave mixing becomes strongly dependent on experimental parameters that do not normally influence the third-order response in centrosymmetric materials. This introduces important new requirements for reliable reporting of experimental results. A new technique that allows us to experimentally relate the third-order susceptibility to the high-frequency electro-optic and dielectric properties is introduced and demonstrated in ${\mathrm{BaTiO}}_3$ and ${\mathrm{KNbO}}_3$.