Quad-band plasmonic perfect absorber using all-metal nanostructure metasurface for refractive index sensing

A quad-band plasmonic perfect absorber (PPA) based on all-metal nanostructure metasurface in infrared regime has been proposed and investigated numerically, which could be applicable for refractive index (RI) sensing. The proposed PPA is made of all-metal nanostructure with an assembly array of vertical split-ring and multiple cylinders. The proposed PPA can achieve the absorbance of 99.34 %, 99.87 %, 99.85 %, and 99.85 % at 86.05 THz, 239.35 THz, 297.45 THz, and 344.35 THz, respectively. In addition, the quality-factor (Q-factor) of the PPA is about 9.6, 23.9, 40.7, and 74.1, respectively. The quad-band perfect absorptions are mainly originated from the hybrid modes between the surface plasmonic resonances (SPRs) and guided modes (GMs). Due to its higher Q-factor, it is believed that the proposed PPA could be served as a RI sensor. As a proof, a designed PPA based sensor has been demonstrated a high sensitivity of about 4367, 2162, 1059, and 908 nm/refractive index unit (RIU), respectively. Relying on its excellent performance, the proposed quad-band PPA could be found potential applications in the sensing, detecting and infrared spectroscopy.