Hierarchical Conical Metasurfaces as Ultra-Broadband Perfect Absorbers from Visible to Far-Infrared Regime

Wideband perfect absorbers are widely demanded for various applications, including efficient photodetection, radiation cooling. However, achieving perfect absorption across an extensive range of wavelengths on engraved structured substrate remains a challenge due to the complex light responses. It presents a hierarchical conical metasurface that demonstrates distinct perfect absorption from visible to far-infrared range (0.4-16 mu m), which is composed of surface-engraved high aspect ratio nanogratings on microcones. The perfect absorption in the typical reststrahlen band of 4H-SiC primarily relies on a light-trapping-enhanced surface phonon polaritons (SPhPs) mechanism, where the microcones effectively confine and enhance the SPhPs excited by the nanogratings through light trapping. Outside the reststrahlen band, the dominant mechanism for light antireflection is the light trapping of microcones assisted by nanogratings, which act as an equivalent antireflection layer. The hierarchical cones exhibit exceptional broadband performance, achieving an average absorptance of 98% over the spectrum of 0.4-16 mu m with wide-angle feasibility, and are fabricated using one-step ultrafast-laser ablation with ring-shaped vector beams. Notably, the hierarchical cones can be applied to various materials, showing significant potential for use in photodetectors. Wideband perfect absorbers are essential for photodetection and radiation cooling. In this paper, a novel hierarchical conical metasurface is introduced that achieves perfect absorption from visible to far-infrared wavelengths (0.4-16 mu m). Through the integration of surface-engraved nanogratings on microcones, the underlying mechanism, including surface phonon polaritons and light trapping, is examined. This technology holds significant promise for photodetection applications.image