Physics

Nonlinear system

Bound state

Second-harmonic generation

Asymmetry

Nanoscopic scale

Laser

Nonlinear optics

Optics

Photonics

Nanophotonics

Quantum mechanics

High harmonic generation

Coupled mode theory

Refractive index

Optoelectronics

Radiative transfer

ACS Photonics

Nonlinear nanostructured surfaces provide a paradigm shift in nonlinear optics with new ways to control and manipulate frequency conversion processes at the nanoscale, also offering novel opportunities for applications in photonics, chemistry, material science, and biosensing. Here, we develop a general approach to employ sharp resonances in metasurfaces originated from the physics of bound states in the continuum for both engineering and enhancing the nonlinear response. We study experimentally the third-harmonic generation from metasurfaces composed of symmetry-broken silicon meta-atoms and reveal that the harmonic generation intensity depends critically on the asymmetry parameter. We employ the concept of the critical coupling of light to the metasurface resonances to uncover the effect of radiative and nonradiative losses on the nonlinear conversion efficiency.

Nonlinear Metasurfaces Governed by Bound States in the Continuum