Dual-Band Chiral Nonlinear Metasurface Supported by Quasibound States in the Continuum

This paper presents an all-dielectric chiral metasurface composed of an array of two-layer distorted square structures with nanoholes. This metasurface can simultaneously generate dual-band opposite chiral responses, which can be attributed to the bound states in the continuum (BICs) and the distorted chiral structure. By combining the BICs with chirality, a dual-band chiral nonlinear metasurface and a chiral-sensing method are proposed. The simulated results show that the third harmonic generation (THG) conversion efficiency can reach the order of 10(-4) for two peaks with a peak-pump intensity of approximately 5.3 GW cm(-2) in the near-infrared region. Moreover, the third-harmonic circular dichroism for each peak can reach up to 0.99 and -0.94, respectively. Furthermore, it is theoretically demonstrated that this metasurface can be used for chiral sensing with high sensitivities. These results provide new insights for linear and nonlinear spin-dependent applications.