THE EFFECTS OF SLIPPAGE AND DIFFRACTION IN LONG-WAVELENGTH OPERATION OF A FREE-ELECTRON LASER

The Free-Electron Laser user facility FELIX produces picosecond optica l pulses in the wavelength range of 5-110 mu m. The proposed installat ion of a new undulator with a larger magnetic period would allow exten sion towards considerably longer wavelengths. This would result in the production of extremely short, far-infrared pulses, with a duration o f a single optical period or even less. In order to investigate the pu lse propagation for free-electron lasers operating in the long wavelen gth limit, a three-dimensional simulation code was developed. Using th e FELIX parameters, with the addition of a long-period undulator, the effects of slippage, diffraction losses, changes in the filling factor , as well as the effects of the optical cavity geometry were studied f or wavelengths up to 300 mu m, with electron pulses in the ps regime. It is shown that slippage effects are less restrictive for long wavele ngth operation than the increasing losses due to optical beam beam act ion.