Enhanced third harmonic generation using plasmonic metamaterials

The work investigates the enhancement potential for nonlinear effects of periodically arranged metallic nanostructures consisting of a pair of gold nanowires separated by a thin dielectric spacer of magnesium fluoride (MgF₂) . Emphasis is put on chi⁽³⁾ nonlinearities for which it is assumed that the intrinsic nonlinearity of MgF₂ prevails against those in the metallic nanostructures. To access theoretically the nonlinear properties, rigorous diffraction theory is employed, taking into account the entire tensor of MgF₂ and the dispersion for gold as tabulated in literature. For the rigorous analysis, an adapted Fourier modal method is adapted. The method is extended towards nonlinear interaction processes in the undepleted pump approximation. It assumes a negligible feedback of the generated TH signal to the pump field. A plasmonic resonance is hence successfully employed to enhance nonlinear wave interaction which leads to a strongly enhanced third harmonic generation.