Observation of Ultrafast Self-Action Effects in Quasi-BIC Resonant Metasurfaces
Ivan Sinev, Kirill Koshelev, Zhuojun Liu, Anton Rudenko, Konstantin Ladutenko, А. А. Щербаков, Zarina Sadrieva, М. А. Баранов, Tatiana Itina, Jin Liu, Andrey Bogdanov, Yuri S. Kivshar
Abstract
High-index dielectric metasurfaces can support sharp optical resonances enabled by the physics of bound states in the continuum (BICs) often manifested in experiments as quasi-BIC resonances. They provide a way to enhance light-matter interaction at the subwavelength scale bringing novel opportunities for nonlinear nanophotonics. Strong narrow-band field enhancement in quasi-BIC metasurfaces leads to an extreme sensitivity to a change of the refractive index that may limit nonlinear functionalities for the pump intensities beyond the perturbative regime. Here we study ultrafast self-action effects observed in quasi-BIC silicon metasurfaces and demonstrate how they alter the power dependence of the third-harmonic generation efficiency. We study experimentally a transition from the subcubic to supercubic regimes for the generated third-harmonic power driven by a blue-shift of the quasi-BIC in the multiphoton absorption regime. Our results suggest a way to implement ultrafast nonlinear dynamics in high-index resonant dielectric metasurfaces for nonlinear meta-optics beyond the perturbative regime.