Mode-matching in multiresonant plasmonic nanoantennas for enhanced second harmonic generation

TL;DR

This paper introduces a novel asymmetric plasmonic nanoantenna design that achieves highly efficient second harmonic generation by optimizing mode overlap at both excitation and SHG wavelengths, advancing nanoscale nonlinear optics.

Contribution

The study presents a new nanoantenna design lacking axial symmetry that enhances SHG efficiency through mode matching, a significant improvement over symmetric structures.

Findings

Unprecedented SHG conversion efficiency achieved

Effective mode overlap at excitation and SHG wavelengths demonstrated

Design principles for optimizing nanoscale nonlinear light sources established

Abstract

Boosting nonlinear frequency conversion in extremely confined volumes remains a key challenge in nano-optics, nanomedicine, photocatalysis, and background-free biosensing. To this aim, field enhancements in plasmonic nanostructures are often exploited to effectively compensate for the lack of phase-matching at the nanoscale. Second harmonic generation (SHG) is, however, strongly quenched by the high degree of symmetry in plasmonic materials at the atomic scale and in nanoantenna designs. Here, we devise a plasmonic nanoantenna lacking axial symmetry, which exhibits spatial and frequency mode overlap at both the excitation and the SHG wavelengths. The effective combination of these features in a single device allows obtaining unprecedented SHG conversion efficiency. Our results shed new light on the optimization of SHG at the nanoscale, paving the way to new classes of nanoscale coherent light sources and molecular sensing devices based on nonlinear plasmonic platforms.