Compression Effect of Ultrashort Pulse in Far Infrared Waveguide Free Electron Laser

Compression mechanism of ultrashort pulse in far infrared waveguide free electron laser driven by radio frequency linear accelerator was investigated. With a pertinent waveguide gap b, when the original phase velocity of the electron bunch ensures the positive gain and the refractivity of the optical pulse monotone increasing along the dative slip distance, the longitudinal length of optical pulse will be continuously shortened so that the pulse power increases quickly until saturation occurs. To offset the "lethargy" effect, an optimal cavity detuning ΔL_c has been accurately determined.