Three-dimensional simulation of finite pulse effects in SASE via Lienard-Wiechert fields

The common method of modeling 3D free-electron laser physics is based on the numerical treatment of paraxial wave equation coupled to the relativistic single-particle equations of motion. The following analysis of self-amplified spontaneous emission (SASE) employs an alternative approach using Lienard-Wiechert solution of the four vector wave equation for point charges in conjunction with Lorentz force equations to determine electronʹs motion and the evolution of the resulting 3D radiation fields. Besides its inherent simplicity, the approach allows to include important aspects of SASE-FELs, such as start-up from initial spontaneous emission, slippage of the optical pulse, interelectron Coulomb fields, multifrequency effects and transverse mode behavior of the optical wave. Simulation results illustrating electron phase dynamics as well as temporal, spectral and spatial characteristics of the radiation fields generated by a short pulse are presented and compared with available theory.