Electromagnetic waves carrying orbital angular momentum (OAM), namely, vortex beams, have a plethora of applications ranging from rotating microparticles to high‐capacity data transmissions, and it is a continuing trend in manipulating OAM with higher degrees of freedom. Here, an approach to control terahertz (THz) near‐field plasmonic vortex based on geometric and dynamic phase is proposed and experimentally demonstrated. By locally tailoring the orientation angle (geometric phase) and radial position (dynamic phase) of aperture arrays embedded in an ultrathin gold film, the excited surface waves can be flexibly engineered to form both spin‐independent and spin‐dependent THz plasmonic vortex field distributions, resulting in multi‐degree of freedom for controlling OAM of THz surface plasmon polaritons (SPPs). Arbitrary OAM values of THz plasmonic vortex and coherent superposition between two OAM states are investigated based on near‐field scanning terahertz microscopy (NSTM) system. The proposed approach provides unprecedented freedom to modulate THz near‐field plasmonic vortex, which will have potential applications in THz communications and quantum information processing.

中文翻译：

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基于几何和动态相位的太赫兹等离子体激元涡旋处理

携带轨道角动量（OAM）的电磁波，即涡旋光束，具有广泛的应用范围，从旋转微粒到高容量数据传输，这是操纵具有更高自由度的OAM的持续趋势。在此，提出了一种基于几何和动态相位的太赫兹（THz）近场等离子体激元涡旋控制方法，并进行了实验验证。通过局部定制嵌入超薄金膜中的孔阵列的取向角（几何相位）和径向位置（动态相位），可以灵活地设计激发的表面波，以形成自旋无关和自旋依赖性的THz等离子体激元涡旋场分布，从而产生了用于控制THz表面等离振子极化子（SPPs）的OAM的多个自由度。基于近场扫描太赫兹显微镜（NSTM）系统，研究了太赫兹等离子体激元涡旋的任意OAM值和两个OAM状态之间的相干叠加。所提出的方法为调制太赫兹近场等离子体激元涡旋提供了前所未有的自由度，它将在太赫兹通信和量子信息处理中具有潜在的应用。