Broadband Terahertz Near-Perfect Absorbers.

Broadband Terahertz (THz) absorbers are highly desired in detection, modulation, receiving and imaging devices. We report a design and successful implementation of a novel broadband THz metasurface with a near-perfect absorption. Different from the traditional metal/dielectric/metal three-layer structures, the as-designed THz absorber has one more metal layer and a dielectric spacer atop, both 200 nm thick. Although the total thickness increased by ~7%, the near-perfect THz absorption band significantly broadened 4 times, achieving a broadband absorption of 270 GHz. Broadband, polarization-insensitive, and near-perfect THz absorptions are also observed over wide incident angles in these meta-absorbers, in which the electric field and power loss are mainly concentrated in the additional thin dielectric layer. Such a broadband THz absorption is achieved through electromagnetic coupling between the top and middle metal layers and the resultant overlapping of the resonance frequencies. This strategy can be adapted to other spectrum shaping devices.