Researchers at The University of Osaka have hit a vital milestone toward creating tabletop x-ray lasers, with the goal of building ultracompact high-energy electron accelerators.

Osaka, Japan – Using high-intensity lasers, researchers have taken an important step towards miniaturization of particle accelerators by demonstrating free-electron laser amplification at extreme ultraviolet wavelengths (27–50 nm), with an acceleration length of only a few millimeters. By generating high-quality, monoenergetic electron beams (i.e. beams where all the electrons have nearly the same energy), they have achieved a key milestone toward compact accelerator technologies.

The research team led by The University of Osaka’s Institute of Scientific and Industrial Research (SANKEN) in collaboration with Kansai Institute for Photon Science (KPSI), National Institutes for Quantum Science and Technology (QST), RIKEN SPring-8 Center (RSC), High Energy Accelerator Research Organization (KEK), used a technique called laser wakefield acceleration to create plasma waves that generate extremely strong accelerating electric fields, thanks to waves within the plasma that travel at almost the speed of light. These potent electric fields are more than 1000 times as strong as conventional accelerators.

“Our work has made several substantial improvements over previous techniques, allowing us to achieve free-electron laser amplification at extreme ultraviolet wavelengths,” says lead author Zhan Jin. “We have used laser pulse shaping to improve focusing accuracy. When combined with our specially developed supersonic gas nozzles, we can create more stable wavefronts, enabling precise control of the plasma source.”

Using free-electron laser amplification in this way is essential for reducing the distance required to accelerate electrons. Conventional systems can require hundreds of meters, but the powerful fields generated by laser wakefield acceleration can potentially reduce this to just millimeters. These results show that laser wakefield acceleration is approaching the performance required of practical, high-quality electron accelerators. Demonstrating this at extreme ultraviolet wavelengths is an important milestone, but the research team intends to push this even further.

“Laser wakefield acceleration has long been considered impractical, because of the difficulty in stabilizing the plasma it relies on,” explains senior author Tomonao Hosokai. “We have greatly enhanced the stability and quality of our electron beams, which will allow us to dramatically miniaturize future accelerators, opening the possibility to create compact x-ray free-electron lasers.” This work shows that laser wakefield acceleration can perform on par with practical high-quality high-energy electron accelerators.

Demonstrating free-electron laser operation in the extreme ultraviolet range is a crucial first step toward extending the technology to shorter wavelengths, ultimately enabling compact x-ray free-electron lasers. These exceptionally powerful light sources generate coherent x-rays 10 billion times brighter than the sun and produce ultrashort femtosecond pulses. Their use is currently restricted to large facilities, but miniaturization of these lasers would allow their use in conventional laboratories. Currently, laser wakefield acceleration is one of the most promising ways to accomplish this. The work accomplished by the research team to stabilize the plasma these accelerators rely on is an essential step toward this goal.

Desktop-sized instruments are essential in day-to-day research, and developing compact accelerators and x-ray free-electron lasers will enable advances across fields such as life sciences, materials science, semiconductor development, and quantum science. Constructing desktop-sized accelerators would allow small labs to perform research that currently requires large-scale accelerator facilities.

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The article, "Optimized laser wakefield acceleration: Generating stable, high-energy, monoenergetic electron beams and demonstrating extreme-ultraviolet free-electron lasers" was published in Physical Review Research at DOI: https://doi.org/10.1103/qvg7-ng8n

About The University of Osaka
The University of Osaka was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan's leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world. Now, The University of Osaka is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.
Website: https://resou.osaka-u.ac.jp/en