Broadband Ag/SiO2/Fe/TiO2 ultrathin planar absorber with a wide acceptance angle from visible to near-infrared regions

Abstract

We present theoretical and experimental evidences of a broadband ultrathin optical absorber, constructed using Ag(85 nm)/SiO2(70 nm)/Fe(13 nm)/TiO2(60 nm) planar films, with a wide acceptance angle and effective admittance similar to that of air. Calculations show that this system displays near-complete visible to near-infrared absorption owing to admittance matching. The electromagnetic distribution within the layered film reveals that the high absorption rate is primarily attributed to the deep subwavelength Fe film. Maximum absorption of 99.3% is achieved even with a 13-nm-thick Fe absorptive film, and an average absorption rate of 94.8% is observed in the 400–1100 nm wavelength range. Notably, even at 60° oblique incidence, the fabricated absorber sustains an absorption rate of 85.4% (for unpolarized light). Such absorbers can be applied to efficient thermal generation and various other applications owing to their minimal heat capacity, expansive area, and fabrication simplicity.