Superior terahertz sensing metasurface based on ultrahigh-Q toroidal dipole governed by quasi-BIC

Abstract Sharp quasi-bound states in the continuum (quasi-BIC) in all-dielectric metasurfaces with high quality-factor ( Q -factor) resonance provide an important platform for terahertz (THz) sensing technology because of its ability to enhance the strong light-matter interaction between THz waves and analytes. In this paper, we propose an ultrasensitive sensing substrate based on an all-dielectric metasurface consisting of an array of stacked high-index structures. By introducing a geometry asymmetry along the horizontal direction in the unit cell, a toroidal-dipole–dominated quasi-BIC transitioned from a distorted symmetry-protected BIC is excited with a Q -factor as high as , which could maintain at a high level as the structure geometry varies. After characterizing the surface sensing performance, an ultrahigh surface sensitivity is achieved to be 263GHz per refractive index unit, while the resultant figure of merit reaches , which outperforms the existing designs. The proposed metasurface is promising for superior label-free sensing performance at THz regime.