High-efficiency operation of free-electron-laser amplifiers

A high-efficiency regime was studied for free-electron-laser (FEL) amplifier configurations that employ a helically symmetric wiggler and a uniform-axial-guide magnetic field. Efficiencies on the order of 50% are found to be possible in the presence of axial fields sufficiently strong that the Larmor period is shorter than the wiggler period. This operating regime is accessible for electron-beam energies greater than approximately 400 keV.<
>