Terahertz vortex radiation source based on Cherenkov wakefields

Vortex electromagnetic fields feature a helical wavefront and carry orbital angular momentum (OAM), offering radiation solutions for communications and imaging. In this paper, we propose a terahertz narrow-band vortex electromagnetic radiation source scheme based on a hollow dielectric cylinder loaded with a metallic helical structure. When a sub-picosecond electron bunch propagates along the axis of the structure, it excites Cherenkov wakefields within the dielectric cylinder, realizing the conversion of electron kinetic energy into electromagnetic modes. Subsequently, the metallic helical structure applies azimuthal modulation to the wakefields, enabling them to radiate as a vortex radiation field carrying azimuthal information. This structure combines both narrow-band radiation and vortex modulation capabilities: the partially dielectric-filled structure achieves frequency-selective characteristics, resolving the broadband dispersion problem associated with traditional Cherenkov radiation. Furthermore, the open metallic helical structure facilitates the efficient conversion of bound-state wakefields into free-space vortex fields, and the vortex mode order can be flexibly tuned by adjusting the helix handedness and multi-helical configurations. By maintaining the high power and high coherence of Cherenkov wakefields while introducing the OAM dimension, this scheme expands the functional boundaries of terahertz radiation sources, providing a novel narrow-band vortex radiation source for applications including terahertz communications, high-resolution imaging, and quantum information processing.