A broadband omnidirectional absorber incorporating plasmonic metasurfaces
An omnidirectional broadband absorber incorporating 170 nm thick metasurfaces was proposed, where silicon dioxide cylinder arrays with a low aspect ratio were covered by 80 nm thick titanium nitride metal. The developed absorber achieves a peak absorption of 0.97 (0.96, experiment), with an average absorption of up to 0.93 (0.91, experiment), in the wavelength range of 250 nm to 800 nm. Its absorptions show an angular tolerance of up to 60° for the simultaneous excitation of the surface plasmon resonance and the cavity resonance. Moreover, with rear illumination, an average absorption of ∼0.8 in the wavelength range of 250 nm to 400 nm is obtained due to the light trapping of titanium nitride metal. Remarkably, a large-scale (1 cm × 3 cm) absorber was fabricated by continuously variable spatial frequency photolithography. This device outperforms previously reported absorbers in terms of being lower cost and shows great potential in applications for photothermal and ultraviolet protection.