Free-electron laser
Laser using electron beam in vacuum as gain medium / From Wikipedia, the free encyclopedia
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A free-electron laser (FEL) is a fourth generation light source producing extremely brilliant and short pulses of radiation. An FEL functions much as a laser but employs relativistic electrons as a gain medium instead of using stimulated emission from atomic or molecular excitations.[1][2] In an FEL, a bunch of electrons passes through a magnetic structure called an undulator or wiggler to generate radiation, which re-interacts with the electrons to make them emit coherently, exponentially increasing its intensity.
As electron kinetic energy and undulator parameters can be adapted as desired, free-electron lasers are tunable and can be built for a wider frequency range than any other type of laser,[3] currently ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible spectrum, ultraviolet, and X-ray.[4]
The first free-electron laser was developed by John Madey in 1971 at Stanford University[5] using technology developed by Hans Motz and his coworkers, who built an undulator at Stanford in 1953,[6][7] using the wiggler magnetic configuration. Madey used a 43 MeV electron beam[8] and 5 m long wiggler to amplify a signal.