Titanium resonators based ultra-broadband perfect light absorber

We propose a new approach for achieving ultra-broadband perfect absorber by using titanium (Ti) resonators. Near-unity absorption with a high average absorptivity of 91.4% is achieved through the whole spectral range from 0.4 μm to 2 μm for the double-period lattice of Ti resonators array on the top of a silica layer coated on the opaque Ti substrate. In contrast to the common metal-insulator-metal (MIM) absorbers only with tens of nanometers absorption bandwidth, the Ti based ultra-broadband perfect absorber (T-UPA) can show a perfect absorption window (i.e., the absorptivity exceeding 90%) with the spectral bandwidth over 1007 nm from visible to near-infrared region (i.e., from 0.485 μm to 1.492 μm). The cooperative effects of the propagating surface plasmons and the corresponding localized plasmonic resonances of Ti resonators contribute to the broadband absorption response. Moreover, the ultra-broadband perfect absorption is polarization-independent and angle-insensitive, which hold the proposed T-UPA with strong practicality and high tolerance in the complex electromagnetic environment (i.e. sun radiation). Furthermore, the absorption window for this T-UPA can be greatly broadened via using a thin anti-reflection coating film, which shows a perfect absorption with the bandwidth of 1555 nm in the visible and near-infrared range. The numerically demonstrated thin-film absorber configuration facilitates the scalability to optoelectronics applications such as thermal photovoltaics and hot-electron devices.