Broadband Terahertz Near-Perfect Absorbers

TLDR

Broadband terahertz (THz) absorbers are highly desired for detection, modulation, receiving, and imaging devices. The study reports the design and successful implementation of a novel broadband THz metasurface with near‑perfect absorption. The metasurface adds an extra metal layer and a 200‑nm dielectric spacer above the conventional three‑layer stack, achieving broadband absorption through electromagnetic coupling between the top and middle metal layers that overlaps resonance frequencies. The 7 % thicker design broadens the near‑perfect absorption band fourfold to 270 GHz, remains polarization‑insensitive and effective over wide angles with energy concentrated in the thin dielectric layer, and the approach is transferable to other spectrum‑shaping devices.

Abstract

Broadband terahertz (THz) absorbers are highly desired in detection, modulation, receiving, and imaging devices. We report the 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 on top, both of which are 200 nm thick. Although the total thickness increased by ∼7%, the near-perfect THz absorption band significantly broadened by 4×, achieving a broadband absorption of 270 GHz. Broadband, polarization-insensitive, and near-perfect THz absorptions were also observed over wide incident angles in these meta-absorbers, where the electric field and power loss were mainly concentrated in the additional thin dielectric layer. Such a broadband THz absorption was 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.