Smith–Purcell radiation (SPR) is the electromagnetic wave generated by free electrons passing above a diffraction grating, and it has played an important role in free-electron light sources and particle accelerators. Orbital angular momentum (OAM) is a new degree of freedom that can significantly promote the capacity of information carried by an electro-magnetic beam. In this paper, we propose an integrable method for generating vortex Smith–Purcell radiation (VSPR), namely, SPR carrying OAM, by having free-electron bunches pass on planar holographic gratings. VSPRs generated by different electron energies, with different topological charges of the OAM, radiation angles, and frequencies are demonstrated numerically. It is also found that, for high-order radiation, the topological charge of the OAM wave will be multiplied by the radiation order. This work introduces a new way to generate SPR with OAM and provides a method to achieve an integratable and tunable free-electron OAM wave source at different frequency regions.

中文翻译：

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使用全息光栅产生 Vortex Smith-Purcell 辐射

史密斯-珀塞尔辐射 (SPR) 是自由电子在衍射光栅上方通过时产生的电磁波，它在自由电子光源和粒子加速器中发挥了重要作用。轨道角动量 (OAM) 是一种新的自由度，可以显着提高电磁束携带的信息容量。在本文中，我们提出了一种产生涡旋史密斯-珀塞尔辐射 (VSPR) 的可积方法，即携带 OAM 的 SPR，通过让自由电子束通过平面全息光栅。由不同电子能量产生的 VSPR，具有不同的 OAM 拓扑电荷、辐射角和频率，以数值方式证明。还发现，对于高阶辐射，OAM波的拓扑电荷将乘以辐射阶数。