Gate- and Optically Controlled Nonlinear Optical Response in Graphene via Non-Perturbative Ultrafast Carrier Dynamics

TL;DR

This study demonstrates ultrafast, reversible spectral control of nonlinear optical signals in graphene through gate and optical excitation, revealing a non-perturbative, carrier-driven mechanism for tunable photonic applications.

Contribution

It introduces a non-perturbative, ultrafast spectral modulation technique in graphene using a suspended platform with electrostatic gating and high damage thresholds.

Findings

Spectral shifts up to 8 THz in THG and SFG signals.

Reversible control of spectral shifts via Fermi level and excitation conditions.

A hot-carrier dynamics model explains the spectral evolution.

Abstract

While the Dirac band structure of graphene has established it as a leading platform for ultrafast optoelectronics, its non-perturbative nonlinear response under intense excitation remains poorly understood. Here, we report ultrafast spectral modulation of nonlinear optical signals in graphene. By utilizing a robust suspended-graphene platform that allows for both wide-range electrostatic gating and high optical damage thresholds, we observe dramatic frequency shifts (up to 8 THz) in third-harmonic generation (THG) and sum-frequency generation (SFG) driven by pump-induced nonequilibrium carrier dynamics. The magnitude and even the direction of this spectral shift can be reversibly controlled by the Fermi level and excitation conditions. A quasiequilibrium theoretical framework based on hot-carrier dynamics quantitatively reproduces the measured spectral evolution, elucidating the critical interplay between carrier heating and the Fermi level. These findings establish a universal mechanism for carrier-mediated spectral control, providing a practical route toward high-speed, gatetunable nonlinear photonic architectures.