Mid-infrared to terahertz ultra-broadband absorber based on all-dielectric metamaterial

A mid-infrared to terahertz ultra-broadband all-dielectric absorber is proposed and numerically verified, which consists of a single medium of tantalum pentoxide (Ta₂O₅) with pyramid arrays on a film substrate. Absorption is higher than 0.9 between 0.72 and 100 THz with a bandwidth of 99.28 THz and a relative bandwidth of 197%. It is higher than 0.9999 between 2 and 100 THz. The ultra-broadband absorption in 0.72~100 THz results from the particular permittivity of Ta₂O₅ and the optimized structure. The inner mechanism is studied by the spectra and impedance match of different parts of the structure and the distributions of electromagnetic fields and loss at different frequencies. Furthermore, the ultra-broadband perfect absorber is insensitive to polarization angle, incident angle, structure parameters as well as structure shape. These characteristics make the proposed absorber more practical in mid-infrared to terahertz ultra-broadband stealth, imaging and thermal emission.