Speedy electrons for brilliant laser light: Research paves the way for compact, inexpensive free-electron lasers

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Extremely short, intense light flashes are in high demand to investigate atoms, molecules and new materials. Free-electron lasers (FELs) produce these flashes.

But around the world, 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 stably and reproducibly in the so-called high-gain regime—an operating state with particularly high amplification of the radiation generated. The work is published in the journal Physical Review Letters.

"Stability—that is, light flashes that consistently 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 achieved this stability, but laser-plasma FELs have not.

Now, after years of research, Irman's team has managed to solve this problem. They generated ultraviolet light flashes at a wavelength of 272 nanometers with 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. In principle, a laser-plasma FEL works like a conventional free-electron laser: For intense light flashes, researchers initially need high-energy electrons that travel 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 them to form tiny parcels that emit intense, coherent light flashes.

So far, large-scale accelerators have been required to drive electrons to the necessary energy—accelerators that can be up to approximately 2 kilometers (1.2 miles) 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.