Plasmon-Amplified Third Harmonic Generation in Metal/Dielectric Resonators

Enhancing ultrafast nonlinear processes at a nanometer scale has the potential of creating novel nano-sources of energetic photons or particles useful for many applications, especially for embedded diagnostics. In this work, we investigate the plasmonic amplification of the third harmonic generation (THG) from a metal-dielectric-metal (MDM) nano-resonator in the near-terawatt intensity regime. In our geometry, the Fabry-Pérot plasmonic resonator reaches a high local enhancement of the laser electric field over a large volume of a SiO₂ dielectric film. The THG signal is amplified by more than one order of magnitude, with a higher efficiency compared to previous plasmonic geometries. The polarization dependence with respect to the fundamental laser allows an ON/OFF switch of the THG enhancement in the nanostructures which is a strong signature of the plasmonic origin of the THG amplification. Furthermore, the dispersion scan shows that the third harmonic spectrum is strongly redshifted with respect to the peak of its linear extinction spectrum. Using the nonlinear anharmonic model, we confirm that the third harmonic behavior dominantly arises from the silica layer.