# Enhancing second harmonic generation using dipolar-parity modes in non-planar plasmonic nanocavities

## TL;DR

This paper demonstrates that nonplanar metal-insulator-metal nanocavities with nonlinear spacers can significantly enhance second harmonic generation, overcoming parity constraints of modes in plasmonic systems.

## Contribution

It introduces a novel nonplanar MIM nanocavity design with a nonlinear spacer that boosts SHG despite same parity modes, a challenge in plasmonic nonlinear sources.

## Key findings

- Nonplanar design enhances SHG efficiency.
- Bulk nonlinearity of spacer contributes to enhancement.
- Experimental and numerical results confirm the effectiveness.

## Abstract

There is an active demand to develop efficient nanoscale nonlinear sources for applications in photonic circuitry, quantum optics and biosensing. To this end, plasmonic systems have been utilized to boost the nonlinear signal generation, however high efficiencies of frequency conversion for realistic applications remain a challenge. Metal-insulator-metal (MIM) nanocavities are good candidates for strongly concentrating the fields at the nanoscale to enhance the optical nonlinearities, however they typically suffer from the requirement to have a quadrupolar resonance at the emission wavelength. Here, we introduce nonplanar MIM nanocavities with a nonlinear spacer that can strongly enhance the second harmonic generation (SHG) despite of having fundamental and emission modes of the same parity. Our experimental and numerical results indicate that the enhancement is due to the non-planar design of the cavities and the bulk nonlinearity of the spacer layer.

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Source: https://tomesphere.com/paper/1905.03816