Predicted effect of mode cooperation and white-light lasing in warm-beam free-electron lasers.

The saturation process of free-electron-laser oscillators (FEL's) in the warm-beam regime is examined, considering radiation-extraction efficiency and spectral width. The spectral width and conversion efficiency can be estimated in both highand low-gain regimes when the laser-oscillator mode population is sparse enough. Under certain conditions, which can be achieved in a relativistic FEL with a Fabry-Perot resonator, a superinhomogeneous-broadening saturation process is predicted in which a hill-heaping effect will accompany the hole burning in the gain curve. In an oscillator, the resonator modes will interact and tend to spread both the emission spectrum and the electronbeam distribution uniformly and over a wide region.