Mid-infrared tunable absorber based on an Ag/SiO/VO/Ag/VO multilayer structure and its molecular sensing capability.

We present a design of middle-infrared modulation absorbers based on vanadium dioxide (VO). By using the electron beam evaporation technique, the Ag/SiO/VO/Ag/VO multilayer structure can achieve double band strong absorption in the mid-infrared, and dynamically adjust the absorption performance through VO. The simulation results demonstrate a remarkable absorption rate of 91.8% and 98.9% at 9.09 µm and 10.25 µm, respectively. The high absorption is elucidated by analyzing the field strength distribution in each layer. Meanwhile, based on the phase change characteristics of VO, the absorber has exceptional thermal regulation, with a remarkable 78% heat regulation range in the mid-infrared band. The size altering of the absorbing layer is effective in enhancing and optimizing the structure's absorption performance. The structure is used to characterize probe molecules of CV and R6 G by mid-infrared spectroscopy, which illustrates an impressive limit of detection (LOD) of 10 M for both substances. These results provide valuable insights for designing future high-performance tunable optical devices.