Coherent radiation from relativistic lepton beams in intense laser fields

The generation of coherent radiation from relativistic particle beams interacting with intense laser fields is crucial for advanced light source development, impacting precision measurement, fundamental physics, and ultrafast science. This study derives the analytical conditions for coherent radiation emission, including frequency combs, from a lepton beam colliding with a laser pulse modeled as a plane wave. We highlight the benefits of using few-cycle laser pulses to ease monoenergeticity requirements for coherent emission. Additionally, for quasineutral electron-positron beams, the symmetry between electrons and positrons stabilizes the system, allowing dense microbunches to form rapidly over just ten micrometers. This enables the emission of broadband coherent extreme ultraviolet (XUV) light, corresponding to a train of attosecond pulses with an 8-as duration and 92-as intervals. Finally, we explore the role of interparticle fields in inducing microbunching and ensuring energy-momentum conservation during coherent emission.