A Growth Spurt for X-ray Lasers

January 17, 2013

Four years after SLAC’s Linac Coherent Light Source opened, blazing new trails in studying ultrafast processes at the scale of atoms and molecules, the field of X-ray laser science is exploding. More than a dozen X-ray free-electron lasers, or XFELs, are now under construction or planned across the globe.

Free-electron lasers, which were developed by Stanford University researchers in the 1970s, use bunches of electrons accelerated to nearly light speed to generate laser beams. They have the advantage of being highly tunable, so they can produce laser light in a wide range of wavelengths. And when tuned to produce X-rays, they are the brightest sources of X-ray light on the planet.

XFELs have opened a new frontier in scientific exploration, allowing scientists to capture details of chemical reactions and other processes that transpire in millionths of billionths of a second. These studies have already achieved important milestones in determining protein structures, identifying the fundamental chemical processes at work in photosynthesis and unraveling mysteries in "superhot" plasmas.

The first XFEL, FLASH at Germany’s DESY laboratory, opened to the international scientific community in 2005 and produces “soft,” or low-photon-energy, X-ray light. LCLS became the first higher-energy, or “hard” X-ray, FEL when it opened for experiments in 2009. Then, Japan’s SACLA hard-X-ray FEL opened in 2012.

Hard X-rays can penetrate samples more deeply and better resolve their structural details at a molecular scale.

The world has taken note of groundbreaking research using XFELs: Fifteen more XFELs are planned, proposed or being built worldwide, and five of those are in the United States.

To maintain its position among the front-runners in XFEL science, SLAC is already planning an expansion of LCLS – known as LCLS-II – that will bring more capacity and broader capabilities. Construction is expected to begin this year with operations launching as soon as 2017.

“It is wonderful for us at SLAC to help create the new field of X-ray laser science and to watch its growth all over the world,” said LCLS Director Jo Stöhr.

Here's a list of XFEL projects that are completed, planned, proposed or under construction worldwide:

XFELs in Operation and Under Construction

Linac Coherent Light Source (LCLS and LCLS-II)

Location: SLAC National Accelerator Laboratory, Menlo Park, Calif.

Status: Opened for experiments October 2009. LCLS-II construction scheduled to start in 2013.

Current experimental stations: 6

Planned experimental stations: 10 by 2018, 12 by 2025

Current X-ray lasers: 1

Planned X-ray lasers: 3 by 2018, 4 by 2025

About: LCLS is one of only two hard X-ray lasers in operation. SLAC’s 2-mile-long linear accelerator, built almost 50 years ago, produces an electron beam that is converted to intense X-ray pulses. LCLS-II will allow multiple simultaneous experiments for the first time. At full build-out, expected in 2025, the facility will operate two soft X-ray lasers and two hard X-ray lasers.

SACLA (SPring-8 Angstrom Compact Free Electron Laser)

Location: RIKEN Harima Institute, Hyogo, Japan

Status: Opened for experiments in 2012.

Current experimental stations: 5

Planned experimental stations: 10 by 2018

Current X-ray lasers: 1

Planned X-ray lasers: 5 by 2018

About: Japan's SACLA, the only hard X-ray FEL in operation besides LCLS, is more compact than LCLS or the European XFEL project that is now under construction. SACLA was built on the site of the SPring-8 synchrotron, and experiments can focus both XFEL and synchrotron radiation beams on the same samples.


Location: German Electron Synchrotron (DESY), Hamburg, Germany

Status: Opened for experiments in 2005.

Current experimental stations: 5

Planned experimental stations: 6 by 2014, 8 by 2016, possibly 11 by 2020

Current X-ray lasers: 1

Planned X-ray lasers: 2 by 2014, possibly 3 by 2020

About: FLASH was the world's first "soft," or lower-photon energy, XFEL. An extension called FLASH II is under construction; it will add one more X-ray laser with the potential for adding another, FLASH III, both at soft X-ray wavelengths.

European XFEL

Location: Hamburg and Schenefeld, Germany

Status: Under construction. Commissioning expected to begin in 2015.

Planned experimental stations: 6 by 2015, 8 by 2016, up to 15 by 2020

Planned X-ray lasers: 3 by 2016, up to 5 by 2020

About: Tunneling was completed this year. European XFEL will be unique in its ability to deliver up to 27,000 X-ray pulses per second. It is also designed to achieve a higher electron beam energy, peak brilliance and shorter-wavelength hard X-ray pulses than other XFELs.


Location: Pohang Accelerator Laboratory, Pohang, South Korea

Status: Construction began in 2011. First phase scheduled for completion in 2014.

Planned experimental stations: 3 by 2014, 5 by 2018

Planned X-ray lasers: 2 by 2014, with a maximum of 5

About: The Pohang XFEL project will initially feature one hard X-ray laser and one soft X-ray laser, with plans to add two more hard X-ray lasers and one soft X-ray laser.


Location: Paul Scherrer Institute, Canton of Aargau, Switzerland

Status: Construction to begin in 2013. Completion of hard X-ray laser in 2017 and soft X-ray laser in 2019.

Planned experimental stations: 6 by 2018

Planned X-ray lasers: 1 hard X-ray laser by 2017, 1 soft X-ray laser by 2019

About: Both hard and soft X-ray lasers at the SwissFEL are designed to operate simultaneously, achieving pulse durations as short as five femtoseconds, or quadrillionths of a second.

FERMI@Elettra FEL-2

Location: Elettra laboratory in Trieste, Italy.

Status: In commissioning.

Current X-ray lasers: 1 (in commissioning)

Current experimental stations: 3 (for use by both FEL-1 and FEL-2).

Planned experimental stations: Up to 6, with the fourth station already under construction.

About: The FERMI@Elettra FEL-1 laser, which began operating in 2010, delivers pulses in ultraviolet wavelengths; FEL-2 will produce soft X-ray wavelengths. FEL-2 features an external laser that “seeds,” or refines the properties of the electron beam, and the radiation this generates is used in the second part of the system to re-seed the electron bunch and reach X-ray wavelengths. The technique creates a sharper energy peak and a more uniform shape for the beam.

Planned or Proposed XFELs

  • ALPHA-X, University of Strathclyde, Glasgow, Scotland
  • JLAMP, Thomas Jefferson National Accelerator Facility, Newport News, Va.
  • MaRIE, Los Alamos National Laboratory, Los Alamos, N.M.
  • New Light Source (NLS), United Kingdom
  • Next Generation Light Source (NGLS), Lawrence Berkeley National Laboratory, Berkeley, Calif.
  • SINAP XFEL, Shanghai Institute of Applied Physics, Shanghai, China
  • SPARX, University of Rome Tor Vergata, Rome, Italy
  • WiFEL, University of Wisconsin, Madison, Wis.
  • ZFEL, University of Groningen, Netherlands

Sources: When possible, the information above has been verified with the operators or agencies responsible for the XFEL or proposed/planned XFEL. Some information here was provided by the authors of the "Free Electron Lasers in 2011" report and other online XFEL reports and resources.