Chiral Plasmons Enable Coherent Vortex Smith–Purcell Radiation
Zi‐Wen Zhang, Juan‐Feng Zhu, Chao‐Hai Du, Fei Gao, Feng‐Yuan Han, Pu‐Kun Liu
Abstract
Abstract Recent advances in vortex Smith–Purcell radiation (V‐SPR) have spurred many breakthroughs in the generation of vortex beams for their potential applications in chiral detection, particle acceleration, communication, and imaging. However, advanced multi‐mode applications of the V‐SPR suffer from the incoherent spectrum and poor purity in producing high‐order topological charges. Here, by exploiting the rotational symmetry and Brillouin‐folding phenomenon, it is proved that the coherent V‐SPR with independently steerable high‐order topological charge is directly emitted from chiral spoof surface plasmons. Moreover, both topological charges and operation frequencies can be readily tuned, thus enabling flexible adaptability over a broad bandwidth. A proof‐of‐concept prototype is designed and fabricated in the microwave regime, in which the method is demonstrated from the perspective of symmetry and tunability. The proposed methodology can be exploited as a platform to investigate the interaction between chiral plasmons and swift electrons, promising a feasible scheme for generating coherent and tunable vortex beams from the microwave to the terahertz band.