All‐Dielectric Terahertz Metasurface with Giant Extrinsic Chirality for Dual‐Mode Sensing

Metasurface‐based sensors, with their planar compact structure and excellent sensing performance, have become one of the emerging technologies in metasurface and nanophotonics in recent years. In particular, chiral metasurfaces show unique advantages for chiral molecule detection and enantiomer identification. Herein, a scheme of dual‐mode sensing based on all‐dielectric terahertz metasurface via chiral and achiral spectroscopy is proposed. The proposed achiral meta ‐atoms show great extrinsic chirality. The transmitted linearly polarized spectrum and the circular dichroism (CD) can be used as the sensing indicator under normal and oblique incidence of the terahertz waves, respectively. Among them, the working mode based on linear polarization spectrum only needs to measure the transmission spectrum once, which means wide applicability. The other mode using CD can eliminate the achiral terahertz absorption of the analyte through multiple measurements and has a higher signal‐to‐noise ratio. The results show that the maximum refractive index–frequency change rates of the two operating modes are −128.5 GHz/RIU and −124.7 GHz/RIU, respectively. In addition, there are two resonant peaks available in both working states, for both high‐precision and wide‐range refractive index detection. This new scheme is expected to be applied in industrial fields such as terahertz biochemical detection.