RP Photonics

Encyclopedia … combined with a great Buyer's Guide!

VLib
Virtual
Library

Free Electron Lasers

Acronym: FEL

Definition: laser devices where light amplification occurs by interaction with fast electrons in an undulator

German: Freie-Elektronen-Laser

Category: lasers

How to cite the article; suggest additional literature

A free electron laser is a relatively exotic type of laser where the optical amplification is achieved in an undulator, fed with high energy (relativistic) electrons from an electron accelerator. Such devices have been demonstrated with emission wavelengths reaching from the terahertz region via the far- and near-infrared, the visible and ultraviolet range to the X-ray region, even though no single device can span this whole wavelength range.

free electron lasers
Figure 1: Setup of an undulator, as used in a free electron laser. The periodically varying magnetic field forces the electron beam (blue) on a slightly oscillatory path, which leads to emission of radiation.

In the undulator, a periodic arrangement of magnets (permanent magnets or electromagnets) generates a periodically varying Lorentz force, which forces the electrons to radiate with a frequency which depends on the electron energy, the undulator period, and (weakly) on the magnetic field strength. Both spontaneous and stimulated emission occur, allowing for optical amplification in a certain wavelength range.

The greatest attractions of free electron lasers are:

Compared with other synchrotron radiation sources (pure undulators and wigglers), FELs can generate an output with a much higher spectral brightness and coherence. This is very useful for a number of applications, including fields such as atomic and molecular physics, ultrafast X-ray science, advanced material studies, ultrafast chemical dynamics, biology and medicine.

The big drawback of FELs is that their setups are very large and expensive, so that they can be used only at relatively few large facilities in the world. The most ambitious free electron laser project is currently pursued in Hamburg (XFEL, within the TESLA project) with the goal of obtaining hard X-ray output with unprecedented performance features: wavelengths down to 0.085 nm and pulse durations below 100 fs. So far, wavelengths down to 6.5 nm have been achieved in the smaller FLASH facility. The LCLS at SLAC has already achieved lasing with 0.15 nm wavelength.

Bibliography

[1]D. A. G. Deacon et al., “First operation of a free-electron laser”, Phys. Rev. Lett. 38 (16), 892 (1977)
[2]C. A. Brau, “Free-electron lasers”, Science 239 (4844), 1115 (1988)
[3]K.-J. Kim and A. Sessler, “Free-electron lasers: present status and future prospects”, Science 250, 88 (1990)
[4]G. R. Neil and L. Merminga, “Technical approaches for high-average-power free-electron lasers”, Rev. Mod. Phys. 74, 685 (2002)
[5]W. Ackermann et al., “Operation of a free-electron laser from the extreme ultraviolet to the water window”, Nature Photon. 1, 336 (2007)
[6]P. Emma et al., “First lasing and operation of an ångstrom-wavelength free-electron laser”, Nature Photon. 4, 641 (2010)
[7]J. N. Galayda et al., “X-ray free-electron lasers – present and future capabilities”, J. Opt. Soc. Am. B 27 (11), B106 (2010)
[8]The World Wide Web Library on Free Electron Lasers, http://sbfel3.ucsb.edu/www/vl_fel.html
[9]The LCLS (Linac Coherent Light Source) at SLAC (Stanford), http://lcls.slac.stanford.edu/
[10]The European X-ray laser project XFEL, http://xfel.desy.de/

(Suggest additional literature!)

See also: ultraviolet light, ultraviolet lasers, X-ray lasers
and other articles in the category lasers

How do you rate this article?

Click here to send us your feedback!

Your general impression: don't know poor satisfactory good excellent
Technical quality: don't know poor satisfactory good excellent
Usefulness: don't know poor satisfactory good excellent
Readability: don't know poor satisfactory good excellent
Comments:

Found any errors? Suggestions for improvements? Do you know a better web page on this topic?

Spam protection: (enter the value of 5 + 8 in this field!)

If you want a response, you may leave your e-mail address in the comments field, or directly send an e-mail.

If you enter any personal data, this implies that you agree with storing it; we will use it only for the purpose of improving our website and possibly giving you a response; see also our declaration of data privacy.

If you like our website, you may also want to get our newsletters!

If you like this article, share it with your friends and colleagues, e.g. via social media:

arrow