Angular‐Dispersive Narrowband Absorption Induced by Quasi‐BIC in SiO₂‐Au Metamaterial

Quasibound states in the continuum (BIC) have earned extensive attentions due to the capability to realize extremely high quality‐factor (Q‐factor) resonance. Here, a metamaterial composed of silicon dioxide (SiO₂) with low refractive index (≈1.45) on gold (Au) reflection mirror is proposed to realize narrowband perfect absorption with the assistance of quasi‐BIC and surface lattice resonance. The proposed SiO₂‐Au absorber based on SiO₂ metamaterial is composed of two tilted SiO₂ cubes into a unit cell and periodically arranged on Au reflection mirror. By optimizing the geometry parameters, the proposed absorber presents both accidental quasi‐BIC and symmetry‐protected quasi‐BIC modes with near‐perfect absorptivity and high Q‐factor of 2330 and 1438, respectively. The Q‐factor can be further improved to 10⁴ by increasing the thickness of SiO₂ cubes to micrometer level. Meanwhile, the wavelength of absorption peak shows linear sensitivity of 16.67 and 17.88 nm per degree to incident angles as the absorptivity is higher than 92% and 75% in the spectra range of 215.0–141.0 nm, respectively. These results open the avenue for the metamaterial absorber in emitter, imaging, and biosensing applications.