Conical third-harmonic generation in a hexagonally poled LiTaO3 crystal

We experimentally observed conical third harmonic generation (THG) in a two-dimensional periodically poled LiTaO3 nonlinear photonic crystal. The conical THG was attributed to cascaded quasi-phase matching (QPM) processes assisted by scattering fundamental waves in the nonlinear photonic crystal. The characteristics of the generated conical beam, such as the emit angle and beam size, varied with the fundamental wavelength because it changed the scattering-assisted QPM configuration. Our experimental results demonstrated that scattering light can be effectively involved in a cascade nonlinear optical process through QPM, which provides a possible way to produce short-wavelength conical beams to meet the demands of practical applications.