The interaction between relativistic electron beams and intense laser fields has been extensively studied for generating high-energy radiation. However, achieving coherent radiation from such interactions has proven to be exceptionally challenging due to the inherent phase mismatches and stochastic nature of the electron-laser dynamics. In this study, we demonstrate that coherent attosecond radiation can be produced when the interaction occurs at a grazing angle, where the electron beam intersects the laser field at a very small angle. The electrons oscillate in the laser field and are modulated with a superluminal phase, coherent ultrashort pulse trains are produced in the far field at the Cherenkov angle. This is verified by theoretical modeling and numerical simulations, including three-dimensional particle-in-cell (PIC) simulations and far-field time-domain radiation simulations. Based on our proposed scheme, high-repetition, compact, and high-energy attosecond pulse sources are feasible.
 

attosecond pulse,relativistic electron beam,femtosecond laser