Simulations of high-power free electron lasers with strongly focused electron and optical beams

A high-power free electron laser (FEL) is being designed in collaboration with Jefferson Laboratory, University of Maryland and Advanced Energy Systems, using short Rayleigh-length resonators to increase the spot size at the mirrors and hence avoid mirror damage. A short Rayleigh length implies a very small optical mode waist in the center of the cavity. It may be desirable to strongly focus the electron beam as well, to improve overlap with the intense optical fields in the interaction region. Three-dimensional simulations are used to study the effects of varying the electron beam radius and angular spread to enhance FEL gain and efficiency. The effects of off-axis shifting and tilting of the electron beam are also studied.