Environmental-adaptable near perfect chirality with ultra-high Q-factor based on BIC metasurface

Abstract Metasurfaces based on bound states in the continuum (BICs) present a promising opportunity for chiral responses with high quality factors ( Q -factors). Although some significant progress has been made in BIC-based chiral metasurfaces, most studies are primarily focused on intrinsic chirality and unpredictable extrinsic chirality, whose chiral behaviors are sensitive to the refractive index of the environment. In this work, we propose a strategy to design metasurface with near perfect chirality and ultrahigh Q -factor simultaneously in various environments, where the incident angle corresponding to the extrinsic chirality can be accurately predicted by the position of C -point. The chirality is attained by successively introducing the geometric perturbation to break the in-plane C 2 symmetry, and employing oblique incidence to break the out-of-plane mirror symmetry of the whole system. To verify the validity of the design approach, specific metasurface in terahertz band is constructed. As the surrounding refractive index changes in a wide range, the chirality can be optimized by the incident angle to achieve circular dichroism close to 1. Consequently, metasurface with near perfect chirality and high Q -factor can be obtained based on this design strategy, whose chiral response exhibits excellent environmental adaptability. This work provides a feasible pathway toward chiral pharmaceutical analysis and chiral molecule detection in various scenarios.