HZDR and Synchrotron SOLEIL operate laser-plasma FEL near Paris; first stable, reproducible high-gain operation

HZDR and Synchrotron SOLEIL operate laser-plasma FEL near Paris; first stable, reproducible high-gain operation

Speedy electrons for brilliant laser light

Press release of September 14, 2026

Speedy electrons for brilliant laser light

Research team paves the way for compact, inexpensive free-electron lasers

Extremely short and intensive light flashes are in great demand to investigate atoms, molecules and new materials. Free-electron lasers (FELs) produce these flashes. But around the world, the beam time available at large-scale user facilities is in short supply and waiting times are long. Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the Synchrotron SOLEIL near Paris have taken a crucial step along this path: for the first time, they managed to operate a laser-plasma FEL in a stable and reproducible manner in the so-called high-gain regime – an operating state with particularly high amplification of the radiation generated. The research group presents its findings in the journal Physical Review Letters (DOI: 10.1103

In the undulator, the electron beam from a compact laser-plasma accelerator interacts with a laser pulse. This interaction enhances the generated FEL radiation and enables higher pulse energies.

“Stability – that is, light flashes that constantly maintain high quality over hours or even days – is extremely important for all experiments involving an FEL,” says Dr. Arie Irman of HZDR’s Institute of Radiation Physics . Conventional large-scale facilities have long since achieved this stability, but not the laser-plasma FEL. Now, after years of research, Irman’s team has managed to solve this problem. They generated ultraviolet light flashes on a wavelength of 272 nanometers and high pulse energy. The FEL power exhibited the exponential growth characteristic of the high-gain regime. “This is significant progress in comparison with the results we published in 2023,” Irman adds.

Surfing on the plasma wave

In principle, a laser-plasma FEL works like a conventional free-electron laser: for the intensive light flashes, the researchers initially need high-energy electrons that fly at almost the speed of light. They then enter an array of magnets, known as an undulator, that force the electrons into a wiggling trajectory which, in turn, forces the electrons to form tiny parcels that emit intensive, coherent light flashes.

So far, large-scale accelerators have been required to drive the electrons to the necessary energy, accelerators that are anything up to approximately two kilometers long. “In a laser-plasma FEL, this distance can be reduced by a factor of about a thousand,” says Dr. Marie Labat of Synchrotron SOLEIL. “The electrons effectively surf on a wave of plasma.” After just a few millimeters, they reach energies for which a conventional accelerator needs many meters.

The key to success lay in precisely controlling the interaction between the laser and the plasma. To do so, the team used HZDR’s high-performance laser DRACO . Its infrared pulses generated the required plasma in a millimeter-thin beam of gas. “We managed to precisely tune the laser to match to the plasma,” says HZDR physicist, Dr. Susanne Schöbel. This was anything but easy because the interaction between the laser and the plasma is determined by non-linear processes that are difficult to control. “Thanks to the well-controlled electron beam we were able to generate intensive ultraviolet light flashes in a stable and reproducible manner using our undulator.” A characteristic feature of this was the exponential growth in radiation output power which the team observed for the first time.

However, this success is not the end of the development story. The researchers want to optimize the interaction between the laser and the plasma as well as the undulator route yet further to increase the quality of the light flashes. “Light flashes on this ultraviolet wavelength are just the beginning,” says Irman. Their next goal is extreme ultraviolet light (EUV). Radiation like this could be utilized for more efficient quality control of nanostructured computer chips, for instance. While it will certainly take a few years before compact laser-plasma FELs complement large-scale facilities, there is already a lot of interest.

M. Labat, S. Schöbel, A. Ghaith, F. M. Herrmann, M. LaBerge, E. Roussel, U. Schramm, P. Ufer, M.- E. Couprie, A. Irman, Laser-Plasma Based Seeded Free Electron Laser in the High-Gain Regime, in Physical Review Letters (2026) (DOI: 10.1103

Dr. Arie Irman | Dr. Susanne Schöbel Institute of Radiation Physics at HZDR Phone: +49 351 260-3043 | -2611 Email: a.irman@hzdr.de | s.schoebel@hzdr.de

Dr. Marie Labat Synchrotron SOLEIL, France Phone: +33 01 69 35-98 63 | Email: marie.labat@synchrotron-soleil.fr

Simon Schmitt | Head Communications and Media Relations at HZDR Phone: +49 351 260-3400 | Email: s.schmitt@hzdr.de