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

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 WSe 2 monolayer strongly coupled to a single gold nanorod. The pumpfrequency 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.

Tunable Nonlinearity and Efficient Harmonic Generation from a Strongly Coupled Light-Matter System

“…The emergence of polaritonic peaks in χ (2) ijk accounts for the two distinct peaks in Fig. (3 b,c) and highlights that the generated second-harmonic signals has its origins in the strongly coupled light-matter system as observed in experiments [19,23,25,30]. Alternatively, the modification of χ (2) ijk can be inferred from the sum-over-states (SOS) model of nonlinear optics [52] where for the coupled system, the SOS includes the energies and transition state amplitudes of the polaritons.…”

“…For example, strong light-matter interaction within optical cavities have been explored to identify 2p excitons for terahertz lasing devices [19], polariton assisted down-conversion [20,21], frequency conversion for a strongly coupled system [22], efficient second-harmonic generation (SHG) [23,24], and third-harmonic generation (THG) [25,26] from polaritonic states. Also, using nanoplasmonic devices there has been work aimed at efficient SHG [27][28][29][30][31]. These examples show the different aspects of nonlinear optics that can be engineered, optimized, or controlled under conditions of strong lightmatter interaction.…”

Nonlinear Strong Coupling by Second‐Harmonic Generation Enhancement in Plasmonic Nanopatch Antennas

“…In an earlier theoretical work, [30] Drobnyh and Sukharev demonstrated a Rabi splitting up to 68 meV at the SH frequency by incorporating emitters that have an absorption band at the fundamental frequency of nanohole arrays. A recent work by Li et al [37] has experimentally demonstrated a large Rabi splitting at the SH frequency of a strongly coupled plasmonic nanorod and WSe 2 monolayer. We believe that for an optical platform that has a narrower resonance bandwidth (or higher quality factor) than the currently employed NPAs, a wider energy splitting and more pronounced nonlinear polaritonic states can be achieved.…”

Unlocking Coherent Control of Ultrafast Plasmonic Interaction

“…In these nanostructures, the manipulation of the geometrical parameters have enabled the observation of extraordinary linear and nonlinear optical properties. [15][16][17][18][19][20][21][22][23] Also, the highly-dense radiation initiates complex local dynamics on several time scales (see Figure 1a). [24,25] First, it excites a collective coherent electronic redistribution (localized plasmons).…”