Evolution of Long Pulses in a Tapered Wiggler Free-Electron Laser

摘要

The evolution of a long pulse (pulse length much greater than the slippage distance) in a tapered wiggler free-electron laser is studied by numerical solution of the 1-D theoretical model for a realistic set of magnet, electron beam, and optical resonator parameter values. Single-pass gain curves are calculated for low and high light intensity. We find that an initial, low-amplitude, incoherent pulse grows into a coherent pulse whose growth rate agrees with the calculated small signal gain. The transient evolution of coherent pulses is calculated for several different cavity length detunings, and a quasi steady-state desychronism curve is given. The frequency changing behavior of the optical pulse is shown to occur through sideband generation associated with synchrotron oscillations. Pulse evolution with an ideal intracavity high-pass optical filter is calculated. (ERA citation 08:054510)