Third harmonic generation from graphene lying on different substrates: Optical-phonon resonances and interference effects

TL;DR

This paper explores how substrate properties influence third harmonic generation in graphene, revealing significant enhancements due to phonon resonances and interference effects, which can optimize nonlinear optical responses.

Contribution

It demonstrates that substrate choice and structure can dramatically enhance graphene's third harmonic generation through phonon resonances and interference effects.

Findings

Third harmonic intensity can be increased by orders of magnitude.

Polar dielectric substrates can make the response frequency independent.

Interference effects in metalized substrates enhance harmonic generation.

Abstract

Graphene is a nonlinear material which can be used as a saturable absorber, frequency mixer and frequency multiplier. We investigate the third harmonic generation from graphene lying on different substrates, consisting of a dielectric (dispersionless or polar), metalized or non-metalized on the back side. We show that the third harmonic intensity emitted from graphene lying on a substrate, can be increased by orders of magnitude as compared to the isolated graphene, due the LO-phonon resonances in a polar dielectric or due to the interference effects in the substrates metalized on the back side. In some frequency intervals, the presence of the polar dielectric substrate compensates the strongly decreasing with $\omega$ frequency dependence of the third-order conductivity of graphene making the response almost frequency independent.