| Summary: | This paper proposes an ultra-broadband absorber numerically demonstrated with the finite-difference-time-domain method (FDTD). The absorber is composed of a bottom layer of refractory metal tungsten (W), an intermediate dielectric layer of aluminum trioxide (Al2O3), and a top layer of refractory metal titanium (Ti) nanodisks, which are arranged periodically and symmetrically in an elliptical array. The optimization results show that the average absorptivity of the designed absorber is 94% within the wavelength range of 500 ~ 1800 nm with an absorption bandwidth at 1300 nm, which can reach 100% at 1200 nm. It was further found that the perfect absorption and broadband absorption performance is revealed by the coupling of surface plasmon resonance (SPR) and local surface plasmon resonance (LSPR) by analyzing the distribution of electromagnetic fields. The designed absorber with polarization insensitivity and wide angle characteristics is simple and easy to manufacture, which can be applied in many fields including solar absorbers, photodetectors and optical imaging.
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