Huygens metasurface supporting quasi-bound states in the continuum for terahertz gas sensing

TL;DR

This paper presents a novel all-dielectric metasurface with quasi-BIC resonances for highly sensitive, compact terahertz gas sensing, capable of detecting low concentrations of gases like HCN and SO2.

Contribution

It introduces a design that supports quasi-BIC resonances with electric and magnetic dipoles, achieving high sensitivity and miniaturization for THz gas sensors.

Findings

Outperforms standard THz sensors in sensitivity and size.

Effectively detects low concentrations of HCN and SO2.

Achieves detection with 100- to 1000-fold shorter path length.

Abstract

We investigate a terahertz (THz) gas sensing platform based on all-dielectric metasurfaces that support quasi-bound states in the continuum (quasi-BIC) with both electric and magnetic dipole resonances. The structure is designed to achieve the first Kerker condition, minimizing backscattering and maximizing light-matter interaction, which significantly enhances the sensitivity of the sensor. By optimizing structural parameters, this metasurface selectively resonates at characteristic absorption frequencies of target gases, facilitating detection even at low concentrations. We validate the approach using two gases with strong but distinct THz absorption profiles: hydrogen cyanide (HCN) and sulfur dioxide (SO2). Furthermore, the free-standing design maximizes gas interaction on both sides of the metasurface, eliminating substrate-induced losses and enabling a reduced physical footprint. Our findings indicate that this metasurface outperforms standard THz sensing approaches in terms of compactness and sensitivity per path length unit, obtaining the same detection threshold as sensing in free space with a path length between 2 and 3 orders of magnitude shorter, underscoring its potential for industrial applications where the available space for sensing can be limited.