High-harmonic generation enhancement with graphene heterostructures

TL;DR

This paper demonstrates significant enhancement of high-harmonic generation in graphene heterostructures using metallic nanoribbons and insulating spacers, enabling efficient nonlinear optical processes at modest pump powers.

Contribution

It introduces a method to amplify high-harmonic signals in graphene via heterostructures with metallic nanoribbons and insulating layers, achieving record enhancement factors.

Findings

Enhancement factors of 1600 for third-harmonic and 4100 for fifth-harmonic generation.

Observation of third- and fifth-harmonic generation at modest pump powers.

Dependence of nonlinear signals on ribbon width, spacer thickness, and polarization.

Abstract

We investigate high-harmonic generation in graphene heterostructures consisting of metallic nanoribbons separated from a graphene sheet by either a few-nanometer layer of aluminum oxide or an atomic monolayer of hexagonal boron nitride. The nanoribbons amplify the near-field at the graphene layer relative to the externally applied pumping, thus allowing us to observe third- and fifth-harmonic generation in the carbon monolayer at modest pump powers in the mid-infrared. We study the dependence of the nonlinear signals on the ribbon width and spacer thickness, as well as pump power and polarization, and demonstrate enhancement factors relative to bare graphene reaching 1600 and 4100 for third- and fifth-harmonic generation, respectively. Our work supports the use of graphene heterostructures to selectively enhance specific nonlinear processes of interest, an essential capability for the design of nanoscale nonlinear devices.