Compact laser accelerator generates bright water window X-rays in computer models
Simulations show that plasma wakefields can replace kilometer-scale particle accelerators for biological imaging.
Physicists have demonstrated that a tabletop laser-plasma accelerator can produce bright, coherent soft X-ray pulses suited for observing living cells. The technological innovation, detailed in Nature Communications by researchers from Germany, Scotland and Czechia, creates pulses in the water window wavelength range using an apparatus measuring only a few meters.
Shrinking the accelerator to lab scale
Traditional free-electron lasers require conventional electron accelerators that stretch across several kilometers to generate high-intensity beams. According to a study published in Nature Communications, a research team from Heinrich Heine University Düsseldorf, the University of Strathclyde and the ELI Beamlines facility has found an alternative method through a remarkable scientific innovation. By replacing kilometer-long tunnels with laser-driven plasma waves, the team managed to reach relativistic electron energies across just a few centimeters.
“Whether a radiation source like that can work as a free-electron laser depends primarily on the quality of the electron beams.”
— Dr. Fahim Habib, principal investigator at the ELI research facility
Peering through the biological water window
The simulation targets soft X-rays with wavelengths between 2.3 and 4.4 nanometers, a region known in physics as the water window. At these specific wavelengths, water remains transparent while elements such as nitrogen and carbon absorb radiation strongly. This allows researchers to image biological specimens inside natural liquid solutions without damaging or artificially staining them. Lead author Lily Berman, a doctoral researcher in Hidding's working group at the University of Strathclyde, noted that novel electron pulses inside magnetic undulators can yield intense X-ray flashes across a distance of only a few meters.
Plasma wakefields and magnetic undulators
The setup relies on the ARCTURUS laser at Düsseldorf, where green pump pulses feed titanium-sapphire crystals to emit high-intensity near-infrared light into gas. This light triggers a plasma photocathode wakefield that rapidly gathers and accelerates electrons. The accelerated particle bunches then enter a magnetic undulator: an array of alternating dipole magnets that forces the particles into a sinusoidal path. As the electrons oscillate, they emit radiation that bunches subsequent particles into synchronized packets, triggering an avalanche effect identical to a free-electron laser. The research marks a potential step forward for technology transfer, moving X-ray spectroscopy out of national synchrotron sites and into university laboratories.
Moving toward an experimental prototype
While the numerical simulations confirm that the hybrid laser-plasma system is robust and flexible, practical realization remains the next milestone. Dr. Fahim Habib, principal investigator at ELI Beamlines in Dolní Břežany, explained that beam quality determines whether the assembly functions as an authentic free-electron laser. The multinational team plans to validate their invention by constructing a physical laboratory prototype for experimental testing in the near future.
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