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In this paper, we theoretically design and numerically verify a broadband plasmonic absorber that works continuously in ultraviolet to near-infrared region. Different from the traditional metal-insulator-metal (MIM) three-layer structure, our perfect absorber is based on insulator-metal-insulator-metal (IMIM) four-layer structure. This perfect absorber has 280 nm ultra-thin thickness, and the combination of refractory metal titanium nitride and high-melting-point insulator silica gives our absorber strong thermal stability. The novel titanium nitride ring-square array layer combines the absorption of different wavelength bands so that the absorber can achieve a continuous absorption of more than 90% from wavelength 200 to 1200 nm. Finite-difference time-domain (FDTD) calculated average absorption rate reaches 94.85%, which 99.40% maximum absorption at wavelength 270 nm and 90.30% minimum absorption at 390 nm. In addition, polarization independence under normal incidence and large incident angle insensitivity under oblique incidence, making our perfect absorber more advantageous in applications such as solar energy collection, photothermal conversion, and invisibility cloak.
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