Quantum plasmon enhanced nonlinear wave mixing in graphene nanoflakes

TL;DR

This paper demonstrates that graphene nanoflakes support quantum plasmons that significantly enhance nonlinear optical wave mixing, enabling advanced nanoscale optical devices and sensors.

Contribution

The study introduces a quantum-mechanical approach showing molecular-scale GNFs support quantum plasmons that boost nonlinear wave mixing, including second- and third-order processes.

Findings

Quantum plasmons in GNFs enhance nonlinear wave mixing.

Embedding cavities enables second-order processes by breaking symmetry.

Significant enhancement occurs when frequencies match plasmon resonances.

Abstract

A distant-neighbor quantum-mechanical method is used to study the nonlinear optical wave mixing in graphene nanoflakes (GNFs), including sum- and difference-frequency generation, as well as four-wave mixing. Our analysis shows that molecular-scale GNFs support quantum plasmons in the visible spectrum region, and significant enhancement of nonlinear optical wave mixing is achieved. Specifically, the second- and third-order wave-mixing polarizabilities of GNFs are dramatically enhanced, provided that one (or more) of the input or output frequencies coincide with a quantum plasmon resonance. Moreover, by embedding a cavity into hexagonal GNFs, we show that one can break the structural inversion symmetry and enable otherwise forbidden second-order wave mixing, which is found to be enhanced by the quantum plasmon resonance too. This study reveals that the molecular-sized graphene could be used in the quantum regime for nanoscale nonlinear optical devices and ultrasensitive molecular sensors.