Visible Quintuple Narrowband Metasurface Absorber Based on Gallium Arsenide Square Cavity for Multispectral Sensing Application

In this study, we introduce a novel five-band metasurface absorber (MSA) design for optical multispectral refractive index (RI) sensing. This design is built upon a square cavity nanostructure array of gallium arsenide (GaAs) that is seamlessly integrated with a continuous gold (Au) film, enabling high sensitivity in visible region. Simulation results show that the designed MSA achieves a high absorbance of 97.7%, 99.8%, 96.9%, 92.3%, and 99.3% at 349.2, 451.2, 508.4, 597.6, and 656.1 THz, respectively, which are in agreement with the values obtained by coupling mode theory (CMT) calculation. The high Q-factors of about 68.47, 46.04, 33.01, 66.4, and 62.47 are also obtained, approaching the CMT values of 60.84, 40.23, 34.93, 68.25, and 53.71. The observed five-band stronger absorption of the designed MSA is mainly attributed to the hybridized coupling effects of surface plasmon polariton (SPP) mode, waveguide modes, and cavity modes excitations. The multiband absorption properties of the designed MSA can be adjusted easily by changing the geometric parameters of the unit cell. The MSA-based RI sensor has a higher Q-factor and narrow bandwidth, yielding a sensitivity of about 16, 32, 68.8, 49.6, and 112 THz/RI unit (RIU). The proposed visible MSA has great potential in applications such as detecting, sensing, and enhanced spectroscopy.