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Free-Electron Lasers

  1. Claudio Pellegrini,
  2. Sven Reiche

Published Online: 15 OCT 2009

DOI: 10.1002/3527600434.eap697

Encyclopedia of Applied Physics

Encyclopedia of Applied Physics

How to Cite

Pellegrini, C. and Reiche, S. 2009. Free-Electron Lasers. Encyclopedia of Applied Physics. 533–560.

Author Information

  1. University of California, College of Letters and Sciences, Physics and Astronomy Department, Los Angeles, CA, USA

Publication History

  1. Published Online: 15 OCT 2009


Free-electron lasers (FELs) are radiation sources, based on the coherent emission of synchrotron radiation of relativistic electrons within an undulator or wiggler. The resonant radiation wavelength depends on the electron beam energy and can be tuned over the entire spectrum from micrometer to X-ray radiation. The emission level of FELs is several orders of magnitude larger than the emission level of spontaneous synchrotron radiation, because the interaction between the electron beam and the radiation field modulates the beam current with the periodicity of the resonant radiation wavelength. The high brightness and the spectral range of this kind of radiation source facilitate the study of physical and chemical process on a femtosecond scale with angstrom resolution.


  • free-electron laser;
  • undulator;
  • microbunching;
  • FEL oscillator;
  • FEL amplifier;
  • FEL parameter;
  • gain length