# Anomalous Non-linear Optical Response Of Graphene Near Phonon Resonances

## TL;DR

This study investigates the third-order non-linear optical response of graphene, h-BN, and their heterostructure, revealing an anomalous decrease in anti-Stokes emission in graphene near phonon resonances, linked to q coupling effects.

## Contribution

It is the first to demonstrate the anomalous non-linear optical response of graphene near phonon resonances using coherent anti-Stokes Raman Spectroscopy.

## Key findings

- Enhanced anti-Stokes emission in h-BN at phonon resonance
- Anomalous decrease in graphene's anti-Stokes emission near phonon energy
- Graphene/h-BN heterostructure response dominated by graphene's anomaly

## Abstract

In this work we probe the third-order non-linear optical property of graphene, hexagonal boron nitride and their heterostructure by the use of coherent anti-Stokes Raman Spectroscopy. When the energy difference of the two input fields match the phonon energy, the anti-Stokes emission intensity is enhanced in h-BN, as usually expected while for graphene a anomalous decrease is observed. This behaviour can be understood in terms of q coupling between the electronic continuum and a discrete phonon state. We have also measured a graphene/h-BN heterostructure and demonstrate that the anomalous effect in graphene dominates the heterostructure optical response.