Multiple high-quality quasi-bound states in the continuum based on terahertz all-metallic gradient slit arrays

Here, we experimentally investigate multiple high-quality quasi-bound states in the continuum (BICs) in all-metal metasurfaces operating at terahertz frequencies. The metasurface integrates several slits with varying lengths, forming gradient slit arrays that enable the generation of multiple quasi-BICs induced by structural symmetry breaking. By tuning the geometric parameters of the slits, the performance of quasi-BICs can be precisely controlled. Experimental findings reveal that two resonances with quality exceeding 40 are induced in three-slit arrays. Results demonstrate that integrating multiple resonators of varying sizes enables the achievement of numerous resonant modes. Benefiting from their fully metallic architecture, such metasurfaces are highly suitable for wave manipulation in terahertz applications.