What is Free-electron laser?
[[File:FELIX.jpg|thumb|Free-electron laser FELIX at FOM ([[w:en:Nieuwegein|Nieuwegein]])]] A '''free-electron laser''', or FEL, is a [[laser]] that produces a very bright beam of light. It is basically a super flashlight. It shares the same [[optics|optical]] properties as conventional lasers such as emitting a beam consisting of [[coherence (physics)|coherent]] [[electromagnetic radiation|electromagnetic]] [[radiation]] which can reach high [[power (physics)|power]]. The FEL used operating principles to form the beam that are very different operating principles of a conventional laser. Unlike [[gas laser|gas]], [[liquid]], or [[solid-state laser|solid-state]] lasers such as [[diode laser]]s, in which electrons are excited while bound to atoms, FELs use a [[relativistic electron beam]] as the [[active laser medium|lasing medium]] which moves freely through a magnetic structure, hence the term ''free electron.''<ref>{{cite web| title=Duke University Free-Electron Laser Laboratory| url=http://www.fel.duke.edu/| access-date=2007-12-21| archive-date=2007-12-20| archive-url=https://web.archive.org/web/20071220125609/http://www.fel.duke.edu/| url-status=dead}}</ref> The free-electron laser has the widest [[frequency]] range of any laser type, and can be widely tunable,<ref>[[F. J. Duarte]] (Ed.), ''Tunable Lasers Handbook'' (Academic, New York, 1995) Chapter 9.</ref> currently ranging in [[wavelength]] from [[microwave]]s, through [[terahertz radiation]] and [[infrared]], to the [[visible spectrum]], to [[ultraviolet]], to [[X-ray]]s.<ref>{{cite web |title=SLAC National Accelerator Laboratory| url=http://home.slac.stanford.edu/pressreleases/2009/20090421.htm}}</ref> Free—electron lasers were invented by [[John Madey]] in 1976 at [[Stanford University]]. The work builds on research done by [[Hans Motz]] and his coworkers who made the first [[undulator]] at [[Stanford University|Stanford]] in 1953 using the [[wiggler (synchrotron)|wiggler]] magnetic configuration which is at the heart of a free-electron laser. Madey u