Transverse properties of radiation eigenmodes in a sheet-beam free-electron laser

Radiation guiding properties in a sheet-beam free-electron laser are investigated. The relative roles of refractive guiding and gain guiding have been identified by scanning the wiggler strength from the Raman to Compton limits. A gradual transition of the eigenmode confinement property has been observed with a power law W∼ηs, where W is the eigenmode width and η is a diffraction parameter. The power s decreases from ∼0.71 in the Raman limit to 0.6 in the Compton limit. (author)