Pulse Propagation and Laser Lethargy in the Free-Electron Laser
We discuss coherent pulse propagation in the free-electron laser (FEL). The effect of laser lethargy is seen to play an important role in the pulsed FEL, as it does in conventional swept-gain amplifiers based on an atomic medium. Numerical calculations of FEL pulse propagation are presented giving good agreement with the Stanford experiment.
In this paper we discuss the physics of a pulsed free-electron laser of the Stanford type.1,2 We point out that the physics is similar to that of conventional types of swept-gain lasers. In particular, the phenomenon of laser lethargy, which was first discovered3–5 in calculations involving conventional swept-gain amplifiers, plays a crucial role in FEL pulse propagation.6–9 A major goal of this paper is to describe this role.
We begin by summarizing, without much mathematics, the basic physics of the pulsed FEL, and then compare the pulsed FEL with conventional swept-gain lasers. Next we describe the role of laser lethargy both in the conventional lasers and in the FEL. Finally, we present numerical calculations of pulse propagation in the regime of the Stanford experiment, and show that good agreement with the experimental data is obtained in such matters as the power-tuning curves and the electron energy distribution.
KeywordsPulse Propagation Optical Pulse Laser Field Electron Pulse Electron Bunch
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