3-5 μm Mid-Infrared Broadband Perfect Absorber Based on Ti Ring Embedded Structure

In this work, a 3-5 μm mid-infrared broadband perfect absorber is proposed. The proposed absorber is only composed of an aluminium oxide (Al₂O₃) dielectric layer on the top, a silicon (Si) dielectric layer with an embedded titanium (Ti) ring in the middle and a high loss metal substrate. It exhibits an extremely perfect absorption performance in the entire range of 3-5 μm mid-infrared band, with the highest and average absorption rates of 99.91% and 98.57%, respectively. The excellent absorption at 3-5 μm is attributed to the intrinsic absorption of the two dielectrics and the excitation of the surface plasmon resonance (SPR). Moreover, the average absorption rate can be still maintained above 91.33% when the incident angle of TE/TM or unpolarized wave reaches 60°, and there is almost unchanged in the absorption rate when the polarization angle of the incident wave gradually changes from 0° to 90°, which shows the insensitivity of the absorber to the incident and polarization angle. The absorber with simple structure and high stability has potential application prospects in infrared stealth and detection.