Nonlinear Terahertz Resonances from Ballistic Electron Funnelling

TL;DR

This paper proposes a novel mechanism for efficient second-harmonic generation in THz resonators using ballistic electron funneling, enabling low-field, tunable THz upconversion in graphene.

Contribution

It introduces a new geometrical rectification mechanism for second-harmonic generation that does not rely on potential barriers, significantly reducing the required field intensity.

Findings

Funneling reduces the field intensity needed for second-harmonic generation by 3-4 orders of magnitude.

Particle-in-cell simulations highlight the importance of femtosecond electron-surface scattering.

Design guidelines for resonant funneling-induced second-harmonic generation are provided.

Abstract

We introduce a new mechanism for second-harmonic generation through geometrically rectifying-funneling-ballistic electrons in THz optical resonators. Our resonant rectifiers inherently act as second-order harmonic generators, rectifying currents without the presence of a potential barrier. Particle-in-cell simulations reveal that femtosecond electron-surface scattering plays a critical role in this process. We differentiate electron funneling from nonlocal plasmonic drag and bulk Dirac anharmonicity, showing that funneling can reduce the required field intensity for second-harmonic generation by 3-4 orders of magnitude. We provide design guidelines for generating funneling-induced second-harmonic generation, including resonance mode matching and materials selection. This approach offers a practical pathway for low-field, geometrically tunable THz upconversion and rectification, operating from sub-10 THz to multiple tens of THz in graphene.