second- and third-order optical nonlinearities in ABO3 compounds measured in fast four-wave mixing experiments

Abstract In a crystal without inversion symmetry there is a direct and an indirect contribution to the third-order nonlinear optical processes. In polar KNbO3 crystals degenerate four-wave mixing is measured in several geometries in order to evaluate the direct contribution and the contribution of the second-order effects to the observed third-order hyperpolarizabilities. Contributing second-order processes are mostly related to optical rectification and to linear electro-optic effect. Cubic KTaO3 is investigated as a reference material in which only pure third-order processes are allowed.