Reducing energy spread in the interaction of intense laser pulses with relativistic electrom beams

Summary form only given. The interaction of high-intensity laser beams with relativistic electron beams has a number of important applications including X-ray generation by Thomson backscatter, and laser-pumped free-electron lasers. However, there are a number of issues to be resolved in order to realize these applications. These include transverse gradients in the high- intensity drive laser, space charge effects, and beam emittance. These effects can increase the effective electron energy spread and degrade the resonant interaction. For example, in a laser-pumped free-electron laser, the energy spread must be less than the lasing efficiency, which is typically 0.01% for X-ray generation. In this presentation, we discuss using higher order (Laguerre-Gaussian) laser modes to reduce the energy spread due to both transverse gradients and space charge. We use a modal distribution for the drive laser that, for a cold electron beam, cancels the induced energy spread to high order. Using a relativistic 3D particle code, we model the interaction of a high-intensity laser pulse with an electron beam having space charge effects and finite emittance and investigate the inclusion of higher order modes as a means to reduce the effective energy spread.