Wide frequency tunable Terahertz vortex radiation with adjustable topological charge numbers

Terahertz (THz) vortex, which carries an orbital angular momentum, is increasingly significant for many scientific frontiers. However, the generation of THz vortex with both tunable frequency and tunable topological charge number is still a challenge for most existing methods. Recently, a narrowband THz vortex generation by vortex laser-beam interaction has been proposed to obtain THz vortex radiation (Zhang et al., IEEE Photonics Journal 14.1 (2022): 1–8). In this paper, a method to produce THz vortex with both tunable frequency at wide range and tunable topological charge number is introduced by combining the mentioned vortex laser-beam interaction and linear energy chirp compression technique, and detailed analyses are also presented. The 3D numerical simulation results show that the method can generate THz vortex with pulse energy of several $\mu J$ and tunable frequency by undulator radiation, while the transverse mode purity deteriorates with increase of topological charge number due to the diffraction effects. The coherent transition radiation (CTR) can produce THz vortex radiation with different topological charge numbers and relatively lower pulse energy, while preserving the transverse mode purity.