Vortex beams carrying orbital angular momentum (OAM) open a new perspective in various terahertz research. Multichannel and divergence controllable terahertz vortex beam generation holds the key to promoting the development of OAM related terahertz research. Here, we introduced and experimentally demonstrated quasi-perfect vortex beam (Q-PVB) with a controllable divergence angle independent of the topological charge and multichannel Q-PVBs generation with all-dielectric multifunctional metasurfaces. By superimposing specific phase functions together into the metasurfaces, multiple vortex beams and four-channel Q-PVBs with different topological charges are generated as well as focused at separated positions. High resolution characterization of terahertz electric field shows the good quality and broadband properties of Q-PVBs. Interestingly, compared with conventional perfect vortex beam; Q-PVB displays a smaller divergence angle and thinner ring width. The metasurfaces proposed here provide a promising avenue to realize multichannel vortex beams generation in compact terahertz systems; benefiting OAM related researches such as mode division multiplexing, vortex beam related plasmonic enhancement and spinning objective detection.

中文翻译：

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多功能超表面实现多通道太赫兹准完美涡旋光束生成

携带轨道角动量 (OAM) 的涡旋光束为各种太赫兹研究开辟了新的视角。多通道发散可控太赫兹涡旋光束的产生是推动OAM相关太赫兹研究发展的关键。在这里，我们介绍并通过实验证明了具有可控发散角的准完美涡旋光束 (Q-PVB)，其发散角独立于拓扑电荷和具有全电介质多功能超表面的多通道 Q-PVB 生成。通过将特定相位函数叠加到超表面中，产生多个涡旋光束和具有不同拓扑电荷的四通道 Q-PVB，并聚焦在不同的位置。太赫兹电场的高分辨率表征显示了 Q-PVB 的良好品质和宽带特性。有趣的是，与传统的完美涡旋光束相比；Q-PVB 显示出较小的发散角和较薄的环宽。这里提出的超表面为在紧凑型太赫兹系统中实现多通道涡旋光束生成提供了一条有希望的途径；有利于 OAM 相关研究，例如模分复用、涡旋光束相关等离子体增强和旋转物镜检测。