Background Insensitive Polarization-Independent Ultra-Broadband Metamaterial Perfect Absorber in Mid-Infrared Regions

Abstract

The mid-infrared absorber is an important device for effective capture of high by atmospheric infrared transparent window, and has been a research hotspot in military, medical, biological and other fields. In this paper, a kind of ultra-thin mid-infrared ultra-broadband absorber with background insensitive is realized by stacking four metal/dielectric films (Si/Ag/Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) on silver substrate and periodically arranged cross-anchor metal pattern in a method of finite-difference time domain. The results show that the absorption rate is more than 90% and the relative absorption bandwidth is 95.5% in the wavelength ranging from 9.1 μm to 24.1 μm. The average absorptivity is 92% in the range of background refractive index ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> = 1∼1.8), A proof of the device's insensibility to background refractive index. At a large incidence angle (θ ≤ 50°), the lowest absorption rate is up to 80%. The thickness of the optimized device is only 1.7 μm. The research results have important application value in infrared remote sensing, pollution monitoring, disease diagnosis and other fields.