A review of free-electron lasers

Abstract

Free-electron laser (FEL) theory and experiments are reviewed. The physical mechanism responsible for the generation of coherent radiation in the FEL is described and the fundamental role of the ponderomotive wave in bunching and trapping the beam is emphasized. The relationship of the FEL interaction to the beam–plasma interaction is pointed out. Various FEL operating regimes are discussed. These include the high-gain Compton and Raman regimes, both with and without an axial guiding magnetic field. The linear and nonlinear regimes are examined in detail, with particular emphasis on techniques for achieving efficiency enhancement. The quality of the electron beam used to drive FEL’s is a critical factor in determining their gain and efficiency. The subject of electron beam quality, for different accelerators, is discussed. Key proof-of-principle experiments for FELs in an axial guiding magnetic field, as well as those driven by induction linacs, rf linacs, electrostatic accelerators, and storage rings, are reviewed. Finally, the requirements on wigglers and resonators are discussed.

Single-mode operation of a Bragg free-electron maser oscillator

“…Free-Electron Lasers (FELs) or Masers (FEMs), as they should be termed for the microwave region of the spectrum, are tunable sources of intense coherent electromagnetic radiation [1,2]. Some of their most remarkable properties include tunability [3], wide bandwidth [4], high gain [5], and the large phase shift that the resonant beam-wave interaction induces on the amplified electromagnetic wave [6].…”

Methods for Conditioning Electron Beams in Free Electron Lasers

“…These sources include traveling wave tubes and free electron lasers (FELs) [1][2][3][4][5][6][7]. The degree to which an electron beam can be bunched is a strong function of the beam quality.…”

“…The degree to which an electron beam can be bunched is a strong function of the beam quality. The two independent contributions to the electron beam quality are the intrinsic energy spread and emittance, both of which lead to a spread in the axial electron velocity and limit the operating wavelength, gain and efficiency of the device [7][8][9][10]. A method for conditioning, i.e., reducing the axial beam velocity spread, was recently proposed in which the beam was propagated through a periodic array of focusing, drift, defocusing, drift channels and microwave cavities excited in the non-axially symmetric TM 21 Q mode [11].…”

A universal characterization of nonlinear self-oscillation and chaos in various particle-wave-wall interactions

“…The significance of the slippage in determining the nonlinear amplitude has also been recognized for a homogeneous beam-plasma instability 15 and for an FEL system. 16 For a homogeneous beam-plasma instability, 15 Eq. ͑2͒ can be expressed as…”