Tungsten based anisotropic metamaterial as an ultra-broadband absorber

• Published in: Optical materials express Vol. 7; no. 2; pp. 606 - 617
• Main Authors: Lin, Yinyue, Cui, Yanxia, Ding, Fei, Fung, Kin Hung, Ji, Ting, Li, Dongdong, Hao, Yuying
• Format: Journal Article
• Language: English
• Published: 01.02.2017
• Subjects: Absorption; Absorption spectra; Anisotropy; Arrays; Dipping; Nanostructure; Tungsten; Wavelengths
• ISSN: 2159-3930; 2159-3930
• DOI: 10.1364/OME.7.000606

We show theoretically that an array of tungsten/germanium anisotropic nano-cones placed on top of a reflective substrate can absorb light at the wavelength range from 0.3 [mu] m to 9 [mu] m with an average absorption efficiency approaching 98%. It is found that the excitation of multiple orders of slow-light resonant modes is responsible for the efficient absorption at wavelengths longer than 2 [mu] m, and the anti-reflection effect of tapered lossy material gives rise to the near perfect absorption at shorter wavelengths. The absorption spectrum suffers a small dip at around 4.2 [mu] m where the first order and second order slow-light modes get overlapped, but we can get rid of this dip if the absorption band edge at a long wavelength range is reduced down to 5 [mu] m. The parametrical study reflects that the absorption bandwidth is mainly determined by the filling ratio of tungsten as well as the bottom diameter of the nano-cones and the interaction between neighboring nano-cones is quite weak. Our proposal has some potential applications in the areas of solar energy harvesting and thermal emitters.