Radiation absorbers have increasingly been attracting attention as crucial components for controllablethermal emission, energy harvesting, modulators, etc. However, it is still challenging to realize thinabsorbers which can operate over a wide spectrum range. Here, we propose and experimentallydemonstrate thin, broadband, polarization-insensitive and omnidirectional absorbers working in thenear-infrared range. We choose titanium (Ti) instead of the commonly used gold (Au) to constructnano-disk arrays on the top of a silicon dioxide (SiO2) coated Au substrate, with the quality (Q) factorof the localized surface plasmon (LSP) resonance being decreased due to the intrinsic high loss of Ti.The combination of this low-Q LSP resonance and the propagating surface plasmon (PSP) excitationresonance, which occur at different wavelengths, is the fundamental origin of the broadbandabsorption. The measured (at normal light incidence) absorption is over 90% in the wavelengthrange from 900 nm to 1825 nm, with high absorption persisting up to the incident angle of ~40°. Thedemonstrated thin-film absorber configuration is relatively easy to fabricate and can be realized withother properly selected materials.
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