Laser-plasma-based particle accelerators could provide easier access to X-rays in the so-called water window, according to model simulations by a European research team. Heinrich Heine University Düsseldorf (HHU) reported the findings. Radiation with wavelengths of about 2.3 and 4.4 nanometres is particularly suited to studying biological samples in their natural, aqueous environment, but has so far been technically difficult to obtain in sufficient quality and intensity. The study was published in „Nature Communications“ (DOI: 10.1038/s41467-026-78880-4).
Biological systems consist largely of water, while biological molecules contain elements such as carbon and nitrogen. To image such molecules at high resolution, radiation is useful that is transparent to water but strongly absorbed by other atoms – exactly the case for soft X-rays in the water window. Bernhard Hidding, head of the Strong-Field Laser-Plasma Physics group at HHU and corresponding author of the study, said the research community had so far depended on kilometre-long free-electron laser facilities to obtain sufficiently brilliant radiation for biological investigations. Together with the ELI Beamlines Facility in Dolní B?ežany and the University of Strathclyde, he said, the team is taking a different path, aiming to use a compact electron accelerator based on laser-plasma technology co-developed in Düsseldorf.
In a laser-plasma accelerator, a high-intensity laser pulse creates a plasma wave in a gas, whose very high field strength accelerates electrons to nearly the speed of light within just a few centimetres. Lily Berman, a doctoral student in Hidding’s group at the University of Strathclyde and first author of the study, said the simulations show that the novel, high-brilliance electron pulses could produce X-ray flashes in magnetic undulators after only a few metres, converting a maximum of electron energy into X-ray energy; the method should also be very robust and flexibly tunable. Fahim Habib of ELI said whether such a radiation source works as a free-electron laser depends crucially on the quality of the electron beams. The study shows that a novel hybrid laser-plasma accelerator would provide the necessary conditions; the approach will be tested experimentally in the near future.
According to Hidding, such a facility can be built very compactly and at lower cost than conventional particle accelerators, making it suitable for universities, research institutions or commercial purposes. Water-window X-ray imaging and spectroscopy could thus be brought from a few large national laboratories into the broader research landscape. The study was carried out within a strategic partnership between HHU and ELI Beamlines and supported by the German Research Foundation, the Federal Ministry of Research, and European research funding programmes such as EuPRAXIA.
