Near-Unity\nAll-Optical Modulation of Third-Harmonic\nGeneration with a Fano-Resonant Dielectric Metasurface

We demonstrate all-optical modulation with a near-unity\ncontrast\nof nonlinear light generation in a dielectric metasurface. We study\nthird-harmonic generation from silicon Fano-resonant metasurfaces\nexcited by femtosecond pulses at 1480 nm wavelength. We modulate the\nmetasurface resonance by free carrier excitation induced by absorption\nof an 800 nm pump pulse, leading to up to 93% suppression of third-harmonic\ngeneration. Modulation and recovery occur on (sub)picosecond time\nscales. According to the Drude model, the pump-induced refractive\nindex change blue-shifts the metasurface resonance away from the generation\npulse, causing a strong modulation of third-harmonic conversion efficiency.\nThe principle holds great promise for spatiotemporal programmability\nof nonlinear light generation.