Cascaded Nanorod Arrays for Ultrabroadband, Omnidirectional and Polarization-Insensitive Absorption

Ultrabroadband and ultrathin absorber based on an encapsulated T-shaped metasurface

Ultrabroadband absorbers are vital for applications such as solar energy harvesting and integrated optoelectronic devices. Herein, we design, fabricate and characterize a novel ultrabroadband and ultrathin absorber based on the encapsulated T-shaped metasurface (ETM). The ETM consists of a 20 nm Cr film and a Cr substrate sandwiched by the T-shaped polymethyl methacrylate (PMMA) arrays. The Cr film provides a robust absorptive surface with improved impedance matching, and ultrabroadband absorption can be achieved via the excitation of the localized surface plasmon (LSP) of this ultrathin film. The average absorption of simulated and experimental results of the ETM in the visible range of 400-800 nm for the TM (TE) polarization are 96.4% (96.3%) and 90.6% (89.4%), respectively. Three-dimensional (3D) power dissipation density distributions of the proposed structure have been investigated, which indicates that the synergistic absorption effect of different parts of the T-shaped ultrathin Cr film contributes to the major absorption enhancement. The absorption of the ETM is very robust to the changes of geometrical parameters and the symmetry of the structure, and it can be maintained almost the same even if T-shaped profiles are changed to L-shaped profiles. Moreover, the absorption performance of the ETM exhibits polarization-insensitive and wide-angle features, which has advantages for many potential applications.

Ultrabroadband Absorption Enhancement via Hybridization of Localized and Propagating Surface Plasmons

Broadband metamaterial absorbers (MAs) are critical for applications of photonic and optoelectronic devices. Despite long-standing efforts on broadband MAs, it has been challenging to achieve ultrabroadband absorption with high absorptivity and omnidirectional characteristics within a comparatively simple and low-cost architecture. Here we design, fabricate, and characterize a novel compact Cr-based MA to achieve ultrabroadband absorption in the visible to near-infrared wavelength region. The Cr-based MA consists of Cr nanorods and Cr substrate sandwiched by three pairs of SiO₂/Cr stacks. Both simulated and experimental results show that an average absorption over 93.7% can be achieved in the range of 400–1000 nm. Specifically, the ultrabroadband features result from the co-excitations of localized surface plasmon (LSP) and propagating surface plasmon (PSP) and their synergistic absorption effects, where absorption in the shorter and longer wavelengths are mainly contributed bythe LSP and PSP modes, respectively. The Cr-based MA is very robust to variations of the geometrical parameters, and angle-and polarization-insensitive absorption can be operated well over a large range of anglesunder both transverse magnetic(TM)- and transverse electric (TE)-polarized light illumination.