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IEEE Photonics Journal Short-Wavelength Free-Electron Lasers
Short-Wavelength Free-Electron Lasers
Keith A. Nugent 1 and William A. Barletta 2;3
(Invited Paper)
1 Australian Research Council Centre of Excellence for Coherent X-ray Science,
School of Physics, The University of Melbourne, Melbourne, Vic. 3010, Australia
2 Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
3 Sincrotrone Trieste, 34149 Trieste, Italy
DOI: 10.1109/JPHOT.2010.2044654
1943-0655/$26.00 Ó2010 IEEE
Manuscript received February 10, 2010. Current version published April 23, 2010. Corresponding
author: K. A. Nugent (e-mail: keithan@unimelb.edu.au).
Abstract: This paper presents a short review of the development of and the motivation for
short-wavelength free-electron lasers. The first observation of coherent X-ray production
was reported from the Linac Coherent Light Source in April 2009.
Index Terms: X-rays, Lasers, free-electron lasers, synchrotrons.
X-ray science has been developing with remarkable rapidity in recent years. There have been
exceptional increases in the coherent output of the available sources, and a great deal of work has
been published on the development of coherent X-ray methods [1].
The source of many of the gains in the brightness of X-ray sources has been the improvement in
the electron beam quality and the use of structured magnetic arrays (known generically as insertion
devices) to improve the X-ray output from the beam.
Several proposals [2]–[4] have suggesting that the underlying developments in beam physics,
accelerator technology, and insertion-device technology could lead to stimulated emission of
radiation and subsequent high-gain amplification from an electron beam. The electron beam acts as a
gain medium for free-to-free energy transitions and was first demonstrated in a low-gain system by
Madey in 1973 [5], [6]. Such a free-electron laser (FEL) combines a linear accelerator and with a long
insertion device. In an FEL, electrons pass through a magnetic structure of alternating dipoles
producing X-rays which then interact with the electrons in such a manner as to further enhance the
radiation outputVa process known as self-amplified spontaneous emission (SASE). The high-gain
SASE process was first demonstrated in 1986 [7] and extended to visible wavelengths in the last ten
years or so [8], and it has led to the development of a number of FEL facilities.
Over the last five years or so, vacuum ultraviolet free to soft X-ray FELs have been operating in
Hamburg, Germany (the FLASH facility) [9], and in Japan [10], with further facilities being constructed
or proposed elsewhere [11]. The long term goal for X-ray science is the establishment and operation
of X-ray FEL systems that can produce highly coherent beams with wavelengths in the range of 0.1 to
40 nm. The first FEL hard X-ray beam at 0.1 nm was produced at the SLAC National Accelerator
Laboratory in April 2009 [12].
A high-profile, but by no means the only, motivation for the development of hard X-ray FEL
facilities is that the extraordinary brightness of FEL sources will such that it might be possible to
image single biomolecules without the need for crystals [13]. Conventional macromolecular
crystallography, as performed at synchrotron facilities, requires the formation of a crystal of the
biomolecule of interest, the acquisition of X-ray diffraction data, and the inversion of that data to
Vol. 2, No. 2, April 2010 Page 221
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