Ultra-broadband and angle-insensitive perfect absorber in the mid-infrared atmospheric window

An ultra-broadband and angle-insensitive absorber is proposed and demonstrated in the mid-infrared (MIR) atmospheric window. The structure is coated with periodically arranged metal grating on top of a metal-insulator-metal (MIM) plate. The average absorption is up to 96.6% in the range of 8–14 µm. Due to the structural characteristics, the absorption properties are polarization-dependent, and the perfect absorption can be realized for a TM-polarized wave when the incident angle is smaller than 50°, bandwidth of 90% absorption reaches approximately 6 µm. The absorption characteristics can be feasibly manipulated via tuning the geometrical parameters. The electrical field intensity distributions are studied to disclose the broadband absorption mechanism. The proposed broadband absorber has many potential applications, including polarization detectors, heat radiators, infrared sensors and so on.