Nonlinear THz‐Nano Metasurfaces

Abstract Extreme terahertz (THz) science and technologies, the next disruptive frontier in nonlinear optics, provide multifaceted capabilities for exploring strong light‐matter interactions in a variety of physical systems. However, current techniques involve the need for an extremely high‐field free space THz source that is difficult to generate and has limited investigations to a rather weak and linear regime of light‐matter interactions. Therefore, new approaches are being sought for the tight confinement of THz waves that can induce nonlinear effects. Here, a nonlinear “tera‐nano” metasurface is demonstrated exhibiting extremely large THz nonlinearity and sensitive self‐modulation of resonances at moderate incident THz field strengths. A record deep‐subwavelength (≈λ/33 000) confinement of strongly enhanced ( ≈ 3200) THz field in a nano‐gap (15 nm) exhibits remarkable THz field‐tailored nonlinearity. Further, ultrafast injection of photocarriers reveals a competition between nonlinear THz field‐induced intervalley scattering and optically driven interband excitations. The results on “tera‐nano” metasurfaces enable a novel platform to realize enhanced nonlinear nano/micro composites for field‐sensitive extreme THz nonlinear applications without the need for intense THz light sources.