Electrostatic accelerator free electron lasers

The amplification of short wavelength coherent electromagnetic radiation by relativistic electrons moving through a spatially periodic transverse magnetic field was first demonstrated at Stanford University. These experiments were carried out using the bunched electron beam emerging from a radio frequency linear accelerator. Although the electron beam quality was ideally suited to study the most important operating characteristics of the free electron laser, the small amount of available average electron beam current coupled with only a small laser extraction efficiency contributed to limit both the amount of average laser power produced (P=0.5 watts) and the overall operating efficiency of the device (e<0.1%). Since the Stanford experiments a considerable amount of work has been done to study various schemes directed toward the development of efficient high power free electron lasers. In some of the schemes high single pass laser extraction efficiency is pursued using for example variable parameter wigglers, constant period wigglers consisting of only a few magnet periods and constant period gain-expanded wigglers. In other schemes the electron beam is recirculated several times through the laser interaction region increase total overall efficiency while retaining the characteristically small single pass efficiency of a constant period wiggler.