Second Harmonic Generation from a Single Plasmonic Nanorod Strongly Coupled to a WSe₂ Monolayer

TLDR

Monolayer transition metal dichalcogenides coupled to metal plasmonic nanocavities have emerged as new platforms for strong light–matter interactions, expected to exhibit nonlinear‑optical properties enabling entangled photon sources, compact wave‑mixing devices, and other photonic elements. The study experimentally investigates the nonlinear properties of a WSe₂ monolayer strongly coupled to a single gold nanorod by observing second harmonic generation. Numerical simulations based on a nonperturbative nonlinear hydrodynamic model of conduction electrons confirm the coupled‑oscillator interpretation and reproduce the experimental second‑harmonic data. The pump‑frequency dependence of the second‑harmonic signal displays a pronounced splitting that can be explained by a coupled‑oscillator model with second‑order nonlinearities, laying the groundwork for understanding the nonlinear properties of strongly coupled nanoscale systems.

Abstract

Monolayer transition metal dichalcogenides, coupled to metal plasmonic nanocavities, have recently emerged as new platforms for strong light–matter interactions. These systems are expected to have nonlinear-optical properties that will enable them to be used as entangled photon sources, compact wave-mixing devices, and other elements for classical and quantum photonic technologies. Here, we report the first experimental investigation of the nonlinear properties of these strongly coupled systems, by observing second harmonic generation from a WSe2 monolayer strongly coupled to a single gold nanorod. The pump-frequency dependence of the second-harmonic signal displays a pronounced splitting that can be explained by a coupled-oscillator model with second-order nonlinearities. Rigorous numerical simulations utilizing a nonperturbative nonlinear hydrodynamic model of conduction electrons support this interpretation and reproduce experimental results. Our study thus lays the groundwork for understanding the nonlinear properties of strongly coupled nanoscale systems.