Hybrid KTP-plasmonic nanostructures for enhanced nonlinear optics at the nanoscale.

The search for miniaturized components for nonlinear optical processes needs a way to overcome the efficiency loss due to the effective size reduction of the active medium. We investigate here a combination of a nanosized nonlinear dielectric crystal and metallic nanoantennas that benefits from both the intrinsic nonlinear conversion efficiency of the nonlinear medium and the local-field enhancement of plasmonic resonances in metallic nanostructures. Careful comparison between experiments and numerical simulations reveals that the observed 10 to 1000 fold enhancement in Second Harmonic Generation intensity between isolated elements and their hybrid structure can be attributed unequivocally to the field enhancement effect of plasmonic resonances on the nonlinear crystal for gold - crystal structures, while the enhancement observed in aluminum-based hybrid structures is attributed to linear dielectric effect on the plasmonic antennas.