Less is more - enhancement of second-harmonic generation from metasurfaces by reduced nanoparticle density

TL;DR

Reducing nanoparticle density in metasurfaces significantly enhances second-harmonic generation due to lattice-mediated interactions, surface-lattice resonances, and local field amplification, as confirmed by experiments and simulations.

Contribution

This study demonstrates that lowering nanoparticle density in metasurfaces can substantially boost SHG, highlighting the role of lattice interactions and resonances in nonlinear optical enhancement.

Findings

Halving nanoparticle density yields over five-fold SHG increase.

Lattice interactions induce spectral narrowing of plasmon resonances.

Experimental results align with numerical simulations including lattice effects.

Abstract

We investigate optical second-harmonic generation (SHG) from metasurfaces where noncentrosymmetric V-shaped gold nanoparticles are ordered into regular array configurations. In contrast to expectations, a substantial enhancement of the SHG signal is observed when the number density of the particles in the array is reduced. More specifically, by halving the number density, we obtain over five-fold enhancement in SHG intensity. This striking result is attributed to favorable interparticle interactions mediated by the lattice, where surface-lattice resonances lead to spectral narrowing of the plasmon resonances. Importantly, however, the results cannot be explained by the improved quality of the plasmon resonance alone. Instead, the lattice interactions also lead to further enhancement of the local fields at the particles. The experimental observations agree very well with results obtained from numerical simulations including lattice interactions.