Enhanced THz Nonlinearity in a Multi-Layer Graphene Device on a Metasurface

We demonstrate enhanced third harmonic generation (THG) at terahertz (THz) frequencies in stacked graphene layers integrated with a wire-grid metasurface. This architecture extends the nonlinear interaction length and enhances the local field. In comparison to the THG observed with a single graphene layer, we observe a 33-fold increase with a stack of 6 graphene layers, and an additional 2-fold enhancement when using a metasurface substrate. We use a table-top configuration and custom spectral filters to sensitively monitor the spectral components arising from nonlinear frequency mixing. Our results highlight the potential of metasurface-integrated graphene-based devices to explore new applications in THz nonlinear photonics.