Ultrathin, broadband, omnidirectional, and polarization‐independent infrared absorber using all‐dielectric refractory materials

Abstract Broadband long‐wavelength infrared (LWIR) optical absorbers have important applications in thermal emission and imaging, infrared camouflaging, and waste heat and biothermal energy utilization. However, the practical application of broadband LWIR optical absorbers requires low‐cost and facile fabrication of large‐area structures with limited thickness. This paper reports the design and fabrication of an ultrathin, broadband, omnidirectional, and polarization‐independent LWIR optical absorber composed of anodized aluminum oxide and highly doped Si using the gradient refractive index strategy. The average absorption of the broadband optical absorber is higher than 95% in the 8–15 μm wavelength range, and it has wide incident angle and polarization tolerances. More than 95% of the optical energy in the wavelength range from 8 to 13 μm was absorbed within a depth of 8 μm, making this absorber the thinnest broadband LWIR dielectric absorber so far. The absorption remained above 90% after annealing at 800 °C in air. The infrared camouflage of the proposed absorber was successfully demonstrated with a human body background. With the advantages of facile fabrication, low‐cost materials, restricted absorption thickness, and excellent thermal stability, the developed broadband LWIR optical absorber is very promising for the practical applications mentioned above.