Nonlinear response of Q-boosting metasurfaces beyond the time-bandwidth limit

Abstract Resonant nanostructures, such as photonic metasurfaces, have created an unprecedented case for enhanced light–matter interactions through local field engineering. However, the presence of resonances fundamentally limits bandwidth interactions. Here, we report on amending nonlinear optical response a semiconducting metasurface Q-boosting, where Q-factor rapidly increases with time. The coupled-mode theory reveals overcoming limit by coupling broadband signal to bandwidth-matched resonance and Q-boosting at timescale faster than resonator lifetime. A control–excitation experiment simulation using tailored silicon-germanium predicts third-harmonic enhancement factors 8 (peak) 4.5 (integrated) against best-case static metasurface. An analysis free-carrier losses based experimental data shows robustness nonradiative offers viable pathway increasing beyond limit, implications in quantum optics, sensing, telecommunication technologies.