High-Q, high-sensitivity THz guided-mode resonances in metallic thin-film metagratings

Detecting trace amounts of molecules–-from explosives to biomarkers–-requires sensitive sensors. The characteristic vibrational and rotational modes of many such molecules lie in the THz range and act as molecular fingerprints, enabling label-free spectroscopic detection. However, the limited interaction between freely propagating THz waves and dilute analytes limits sensitivity. Metasurfaces can enhance both sensitivity and selectivity via sharp resonances that respond to changes in the local refractive index. Realizing high-performance THz structures remains challenging due to material losses and designs relying on stringent geometries. Here, we introduce a metagrating platform that employs a guided-mode resonance in a polyimide thin-film substrate to achieve a figure of merit (FOM) of 276RIU&\#x2212;1, a sensitivity of S$=$403GHzRIU&\#x2212;1, and an experimental quality factor of Q$=$466. These results demonstrate a cost-effective and manufacturing-tolerant platform that is well suited for demanding trace detection.