Study on a high refractive index sensitivity four-band tunable absorber based on AlCuFe quasicrystals at terahertz frequencies

Abstract

Optical devices operating in the terahertz band have enormous potential applications, and research in this band is attracting increasing attention from researchers. In this paper, an absorber based on AlCuFe quasicrystals is proposed in the terahertz band, accompanied by four perfect narrow peak absorptions. The bottom layer of the model is gold, mainly serving a reflective function, above the gold is silicon dioxide, with a Dirac semimetal AlCuFe quasicrystal microstructure with hollow spaces around its edges and central region on the top layer. The finite element method is used for simulation calculation, followed by data post-processing and analysis of the device performance. Analysis revealed that this absorber achieved perfect absorption, with absorption rates exceeding 94% at frequencies of 4.99 THz, 6.138 THz, 7.846 THz, and 9.05 THz, with three of these frequencies reaching absorption rates above 97%. The physical mechanism was analyzed in detail using cavity resonance (CR), impedance matching and equivalent circuit theories. The effects of geometrical parameters, electromagnetic wave incidence angle, and the external environment's refractive index on the absorber were thoroughly investigated. The absorber's maximum value of the refractive index sensitivity S was calculated to be 2800 GHz RIU⁻¹, indicating high detection accuracy. In the field of detection, the quality factor Q value of an absorber is used to measure its energy loss and high selectivity, while the figure of merit (FOM) value plays a role in evaluating its sensing performance. We calculated the Q value and FOM value, with maximum values of 117.1 and 20.42, respectively, demonstrating that the terahertz perfect absorber proposed in this paper possesses exceptional detection performance.