Terahertz Hybrid Detection of Chiral Enantiomers With Intrinsic Low Absorption Enabled by Metasurface

The recognition of chiral enantiomers has great significance in biomedical fields such as drug detection, as they exhibit distinctive absorption characteristics in the terahertz (THz) region. However, there are certain biomolecules without prominent spectral features within specific frequency bands, making direct identification through THz time-domain spectroscopy challenging. Therefore, metasurface is employed to stimulate local field enhancement and increase the interaction between analyte and waves. Current studies on meta-sensors typically focus on detecting various types of biomolecules or different concentrations of the same biomolecules. To realize the identification of enantiomers, size-multiplexed broadband sensing technology with various scaling factors of unit cells is employed to achieve a broadband-enhanced sensor for analyzing spectral distinctions of enantiomers. It amplifies subtle absorption differences in the longitudinal direction, enabling the identification of chiral enantiomers even within weak absorption bands. In addition, we converted it from an achiral metasurface to an extrinsic chiral metasurface by incident angle manipulation with a maximum modulation rate of 52.5%, to excite extrinsic chiroptical responses. Here, besides the transmission rate of linearly polarized waves, circular dichroism (CD) spectra of circularly polarized waves are further extracted as sensing indicators additional with refractive index sensitivity of 39.4 GHz/RIU and $\Delta $ Amp of 29.0%, for enriching the evaluation standards. It also provides opportunities for dynamic modulation of the circularly polarized wave. This work is based on a traditional refractive index sensing mechanism, employing size-multiplexed broadband fingerprinting sensing technology and sensitive extrinsic chiral excitation, to realize multitechnical hybrid detection for enantiomers with intrinsic low absorption.