High-Q terahertz metasurface absorber empowered by quasi-bound states in the continuum

High-performance terahertz (THz) absorbers are essential components for a variety of applications, including THz detection, secure communications, radar stealth, sensing, and imaging. Bound states in the continuum (BICs), which utilize their flexible control over radiation loss and local field enhancement effects, have emerged as a fundamental mechanism for designing optimal metasurface absorbers. This study innovatively constructs band-folding-induced BICs (BF-BICs) within metasurfaces. We analyze their eigenmodes based on band theory and elucidate the correlation between their topological properties and radiation behavior. Furthermore, employing temporal coupled-mode theory, we systematically clarify key performance metrics of these absorbers: absorption efficiency exceeding 99%, wide-angle stability of ±60 ∘ , and multi-band cooperative response. The findings not only enhance theoretical research on BICs but also present promising applications in THz devices and metasurface optoelectronics.