High-Harmonic Generation Enhancement with Graphene Heterostructures

摘要

High-harmonic generation (HHG) in graphene heterostructures, consistingof metallic nanoribbons separated from a graphene sheet by either a fewnanometerlayer of aluminum oxide or an atomic monolayer of hexagonalboron nitride, is investigated. The nanoribbons amplify the near-field at thegraphene layer relative to the externally applied pumping, thus allowing theobservation of third- and fifth-harmonic generation in the carbon monolayerat modest pump powers in the mid-infrared. The dependence of the nonlinearsignals on the ribbon width and spacer thickness, as well as pump powerand polarization are studied, and enhancement factors (EF) relative to baregraphene reaching 1600 and 4100 for third- and fifth-harmonic generation,respectively, are demonstrated. The work supports the use of graphene heterostructuresto selectively enhance specific nonlinear processes of interest,an essential capability for the design of nanoscale nonlinear devices.