Free‐Standing Single‐Layer Metasurface for Efficient and Broadband Tailoring of Terahertz Wavefront

During the past decade, metasurfaces have provided a versatile platform for controlling the amplitude, phase, and polarization of electromagnetic waves, thus showing great potential for developing compact photonic devices. However, compact and broadband terahertz (THz) components are still scarce for high-speed communication and spectroscopy analysis. Here, a free-standing metasurface is designed to realize broadband and efficient wavefront manipulation in the THz regime. The proposed metasurface consists of a single patterned metallic layer on an ultra-thin flexible substrate. The full-span phase control of circularly cross-polarized waves can be achieved based on the Pancharatnam-Berry phase mechanism only by spatially varying the element orientation. Besides, it can operate in a broadband range of 0.35-1.21 THz (relative bandwidth of 111%), with the efficiency approaching the theoretical limit of the ultra-thin single-layer metasurface. It is demonstrated that the free-standing metasurface can be used for numerous applications, including but not limited to THz beam steering, focusing, and vortex generation. The broadband performances allow the pulsed spectral imaging system to record the evolution process of broadband vortex beam in real-time. The proposed metasurface may trigger many exciting opportunities in THz wireless communication, medicine, and spectroscopy applications.