Ultra-Broadband, Polarization-Independent, and Wide-Angle Near-Perfect Absorber in Mid-Infrared With One-Dimensional Metasurface for Radiative Cooling

Radiative cooling, a technique that operates without energy consumption, requires achieving ultra-broadband high absorption/emission within atmospheric window band (8- $13~\mu $ m), posing a challenge for the design of cooling structure. In this work, we propose and investigate an ultra-broadband near-perfect metasurface absorber comprising a titanium (Ti) metal layer, a magnesium fluoride (MgF2) dielectric layer, and a one-dimensional MgF2 grating overlaid with Ti grating. The absorber structure is optimized using an improved genetic algorithm. In the normal incidence range of 8- $13~\mu $ m wavelength, the optimized structure achieves 96.1% average absorption for transverse electric polarization and 92.2% for transverse magnetic polarization. Moreover, the average absorption for unpolarized light reaches 94.1%. Then, we also examine how each layer in the proposed absorber impacts the absorption characteristics. In addition, the relationship between absorption and the angle of incidence is studied, and the proposed structure exhibits strong angular insensitivity. The proposed structure’s electromagnetic field distribution is analyzed to probe its underlying physical mechanism. Additionally, the optimized structure exhibits excellent nighttime radiative cooling performance, with 121.8 W/m2 net cooling power at 300 K ambient temperature. The proposed structure exhibits excellent potential for application in the field of thermal management related to radiative cooling.