Free electron laser

A free-electron laser (FEL) is a kind of laser whose lasing medium consists of very-high-speed electrons moving freely through a magnetic structure, hence the term free electron. The free-electron laser is tunable and has the widest frequency range of any laser type, currently ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible spectrum, ultraviolet, and X-ray.

The free-electron laser was invented by John Madey in 1971 at Stanford University. The free-electron laser utilizes technology developed by Hans Motz and his coworkers, who built an undulator at Stanford in 1953, using the wiggler magnetic configuration which is one component of a free electron laser. Madey used a 43 MeV electron beam and 5 m long wiggler to amplify a signal.

To create a FEL, a beam of electrons is accelerated to almost the speed of light. The beam passes through a periodic arrangement of magnets with alternating poles across the beam path, which creates a side to side magnetic field. The direction of the beam is called the longitudinal direction, while the direction across the beam path is called transverse. This array of magnets is called an undulator or a wiggler, because due to the Lorentz force of the field it forces the electrons in the beam to wiggle transversely, traveling along a sinusoidal path about the axis of the undulator.

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