Extremely high-<i>Q</i> Mie voids for ultrasensitive terahertz metasensor

Light–matter interaction at terahertz frequencies is limited by wavelength mismatch between incident radiation and atomic size of analytes. Dielectric metasurfaces such as quasi-bound states in the continuum and Huygens metasurfaces offer strong subwavelength field confinement, low-loss, and high-quality (Q) resonances, but practical use is limited as fields remain trapped within high-index materials, restricting interaction with external systems. This work proposes a novel class of all-dielectric terahertz metasurfaces employing Mie voids within high-refractive-index silicon resonators to realize ultrahigh-Q resonances with minimal intrinsic losses. By carefully engineering air-filled voids, resonant electromagnetic fields are confined predominantly within the low-index regions, thereby, enhancing light–matter interaction field strength by a factor of 87. Three metasurface geometries were investigated: a solid silicon cuboid (device 1), a cuboid with a central cylindrical void (device 2), and a void-enhanced cuboid with an additional rectangular void (device 3). Numerical simulations yield maximum Q-factors of 384, 5980, and 14 280, for devices 1, 2, and 3, respectively. Using a 6 μm-thick analyte layer with a refractive index ranging from 1.0 to 2.0, device 3 exhibits a high sensitivity of 12.15 GHz/RIU along with an exceptional sensing Figure of Merit (FoM) of 586 RIU−1 and remarkably low Detection Limit (DL) of 0.000 087 RIU. The proposed platform enables high-performance sensing, lasing, and spectral filtering, paving the way for advanced terahertz photonic systems.