May 15 2014
A free-electron laser is a kind of laser that employs a beam of high-speed, relativistic electrons moving freely with an optical field, via a magnetic structure. Transverse electron oscillations are produced in the free-electrons laser by means of an undulator.
Free-electron lasers are of two types, which are high-gain laser and low-gain laser.
A high-gain laser produces spontaneous emissions from the start, and interacts with electron beams.
A low-gain laser, on the other hand, produces spontaneous emissions trapped in an optical cavity.
These lasers have high tunability, which ranges from the wavelength of microwaves to infrared, visible light, X-ray, or ultraviolet.
Basic Principle
A typical free-electron laser consists of a wiggler, or magnetic undulator, a particle accelerator, and an electron injector. A beam of free electrons, from the electron injector, is forced into the particle accelerator. The electrons are accelerated at near the speed of light by the accelerator.
The undulator is a series of magnets, having alternating north and south magnetic poles, through which the electrons pass. With the undulator, the electrons move back and forth, emitting light of a particular wavelength at each bend.
The wavelength of the emitted light depends on the spacing of the magnets within the undulator. Therefore, the laser can be tuned by varying the spacing of the magnets.
Applications
The key areas of use for free-electron lasers include the following:
- Medical applications
- Defense applications
- X-ray studies
References