Design and Characterization of a Nonlinear Graphene Metasurface for Enhanced Third Harmonic Generation in the Terahertz Spectrum

We introduce a novel strategy employing ultrathin nonlinear metasurfaces that incorporate graphene ribbon to tackle inherent efficiency challenges in nonlinear processes. Our primary goal is to elevate third harmonic generation, specifically targeting the far-infrared and terahertz frequency ranges. Through the stimulation of localized plasmons along the graphene surface and the incorporation of a metallic substrate, we achieve precise confinement and substantial signal amplification. This arrangement results in a narrowed resonant response bandwidth, causing zero transmission and the establishment of standing waves. The distinctive design significantly enhances the efficiency of third harmonic generation. These compact metasurfaces present a promising solution for nonlinear sources in the far-infrared and terahertz spectrum, with potential applications spanning frequency generation, wave mixing, nonlinear THz spectroscopy, and noninvasive THz imaging.