Radiation Reaction Effects in Ultrahigh Irradiance Laser Pulse Interactions with Multiple Electrons

When ultrahigh irradiance laser pulses interact with high energy electrons, the emission of radiation from these electrons can significantly affect the motion of the electrons themselves (radiation reaction). Since the spatial grid resolution necessary to self-consistently simulate high intensity laser interactions with electrons via particle-in-cell methods is prohibitive, in this paper we describe a particle-particle code to simulate such interactions. We directly solve the interaction between the electrons numerically allowing an accurate description of the dynamics. We examine the collective effects of the simplest case of two electrons with equal energies of 1 GeV, but with initial spatial offsets along the laser propagation direction undergoing strong radiation reaction effects. We find that for a 30 fs laser pulse of intensity 2x1022 W/cm2 that both electrons lose 96% of their kinetic energy in less than 10 microns and that the electron in front receives a large kick from the radiation emitted by the electron in back. This makes possible a high power gamma ray source.