V-Shaped Metasurface-Induced Tightly Confined SSPP for Terahertz Sensing Enhancement

Terahertz (THz) metasurfaces have garnered significant interest in biochemical sensing due to their ability to confine field energy in deep subwavelength areas, dramatically enhancing the light-matter interaction. However, the substrate effect prevalent in conventional metasurfaces prevent the enhanced field penetrating into the substrate from interacting with matter, thereby severely limiting the sensitivity. Here, a 1-D V-shaped THz metasurface using a high refractive index HR-Si prism as an external coupler is reported. Tightly confined spoof surface plasmon polariton (SSPP) modes are excited on its all-metallic surface for strong light-matter interactions. The electric field is highly confined within the V-shaped resonant cavity, without any negative effects from the substrate. Owing to this, the metasurface exhibits outstanding performance in the sensing process with a sensitivity of 0.45 THz/RIU, a quality (Q) factor of 140.1, and a figure of merit (FoM) of 54.9 RIU
$^{-{1}}$
. Crucially, the dynamic modulation of plasmon modes allows for a close match with molecular vibrations, enhancing the characteristic absorption of L-histidine by 33.34-fold. This integrated sensor with metasurfaces and prisms shows great potential for the THz detection of trace molecules.