Free Electron Laser Simulation Tool Based on Fdtd/pic in the Lorentz Boosted Frame∗

Free Electron Lasers (FELs) are the only radiation sources generating electromagnetic from THz to hard X-rays. Therefore, it is crucial to develop rigorous simulation tools. Our work is motivated by the desire to develop compact X-ray sources based on radiation generated with optical undulators. The currently existing softwares are usually written to tackle special cases allowing for particular approximations, such as 1D FEL theory, steady state, slow wave and forward wave approximation, wiggler-averaged electron motion and slice approximation. Many of the above approximations are hardly valid when sub-femtosecond bunches interact with intense optical lasers. The presented software aims at the analysis of an FEL interaction without using any of the above approximations. The developed tool apparently suffers from a long computation time but offers a more accurate picture of the radiation process. In order to overcome the problem of multiple scales, we exploit the Lorentz boosted coordinate system and implement a Finite Difference Time Domain (FDTD) method combined with a Particle in Cell (PIC) simulation in this frame.