Dramatic enhancement of second and third harmonic generation in gold nanogratings in the visible and UV ranges

TL;DR

This paper demonstrates a significant enhancement in second and third harmonic generation in gold nanogratings due to plasmonic resonances, with experimental and simulation results showing over three and four orders of magnitude improvements respectively.

Contribution

It provides the first detailed experimental and numerical analysis of nonlinear harmonic generation enhancement in gold nanogratings across visible and UV ranges.

Findings

Harmonic generation efficiencies are dramatically increased in gold nanogratings.

The enhancement correlates with plasmonic resonances dependent on incident angle.

Model predictions align closely with experimental results.

Abstract

Notwithstanding its long history, the study of nonlinear optics from metal surfaces is still an active field of research. For instance, in view of the presence of absorption questions remain concerning the possibility of significantly enhancing harmonic conversion efficiencies in the visible and UV ranges. While to many it may seem that metals do not easily lend themselves to that purpose, they are nevertheless crucial materials in the development of nanophotonics, and more generally, to electromagnetism at the nanoscale. Here, we report our experimental observations and numerical simulations of second and third harmonic generation from a gold nanograting, which exhibits a plasmonic resonance whose spectral position depends on incident angle. All things being equal, the enhancement of nonlinear optical processes from the UV to the near IR range manifests itself in dramatic manner: second harmonic generation conversion efficiencies increase more than three orders of magnitude compared to a flat gold mirror, while third harmonic generation conversion efficiency increases by nearly four orders of magnitude, both in excellent agreement with predictions. The clear inferences one may draw from our results are that our model describes the dynamics with unprecedented accuracy, and that much remains to be revealed in the development of nonlinear optics of metals at the nanoscale.