Strongly Enhanced and Directionally Tunable Second-Harmonic Radiation by a Plasmonic Particle-in-Cavity Nanoantenna

TL;DR

This paper demonstrates a plasmonic particle-in-cavity nanoantenna that significantly enhances second-harmonic generation and allows for directional tuning of the emitted radiation, advancing nonlinear nanophotonics.

Contribution

It introduces a novel particle-in-cavity nanoantenna design that achieves high SH enhancement and tunable emission direction through hybridization and symmetry breaking mechanisms.

Findings

Giant SH enhancement from hybridized gap plasmon resonance.

Unidirectional SH emission achieved by symmetry breaking.

Wide-angle beam steering via particle position tuning.

Abstract

Second-harmonic (SH) generation is tremendously important for nonlinear sensing, microscopy and communication system. One of the great challenges of current designs is to enhance the SH signal and simultaneously tune its radiation direction with a high directivity. In contrast to the linear plasmonic scattering dominated by a bulk dipolar mode, a complex surface-induced multipolar source at the doubled frequency sets a fundamental limit to control the SH radiation from metallic nanostructures. In this work, we harness plasmonic hybridization mechanism together with a special selection rule governing the SH radiation to achieve the high-intensity and tunable-direction emission by a metallic particle-in-cavity nanoantenna (PIC-NA). The nanoantenna is modelled with a first-principle, self-consistent boundary element method, which considers the depletion of pump waves. The giant SH enhancement arises from a hybridized gap plasmon resonance between the small particle and the large cavity that functions as a concentrator and reflector. Centrosymmetry breaking of the PIC-NA not only modifies the gap plasmon mode boosting the SH signal, but also redirects the SH wave with a unidirectional emission. The PIC-NA has a significantly larger SH conversion efficiency compared to existing literature. The main beam of the radiation pattern can be steered over a wide angle by tuning the particle's position.