European XFEL Sets Record With 300-Attosecond Hard X-Ray Flashes
Researchers at European XFEL focused 300-attosecond X-ray pulses to a record intensity. How they proved it with copper, and what it means for studying electrons.
Physicists have focused hard X-ray flashes lasting about 300 attoseconds into a spot 180 × 330 nanometers across, setting a world record for the intensity of such pulses. The work was done at the European XFEL, a large X-ray laser facility in Germany, and is published in the journal Optica (DOI: 10.1364/OPTICA.613284).
An attosecond is a billionth of a billionth of a second. Flashes that short, and that concentrated, could let scientists watch electrons move inside atoms and molecules, which is where chemical reactions are decided.
How small and how fast
According to European XFEL, the focal spot is roughly 100,000 times smaller than the cross-section of a typical human hair. The pulses are hard X-rays, light with very short wavelengths. The researchers describe their strength with two measures: fluence, the energy delivered to an area, and intensity, which also counts how fast that energy arrives.
“This is a world record in intensity and fluence for a hard-X-ray attosecond pulse,” said first author Ichiro Inoue of the University of Tokyo. The experiment ran in April 2026.
Two mirrors, four reflections
To squeeze the beam, the team used an advanced Kirkpatrick-Baez (AKB) system: two very precise mirrors, one focusing the X-rays vertically and the other horizontally. Each pulse bounced four times before reaching its target. That mirror system was shipped from Japan for the experiment.
DESY scientist Jiawei Yan, a corresponding author, said the team had shown terawatt-scale attosecond pulses at the facility a few years earlier. The new step is getting that power onto a sample, which opens the way to studying nonlinear effects, where matter under very intense X-rays behaves differently than it does under weak light.
Proof from a sheet of copper
The intensity figure comes from the pulse energy, duration and spot size, so the team checked it with a separate experiment. They fired the pulses at thin copper foil and measured peak intensities above 10²⁰ watts per square centimeter.
The X-rays knocked electrons out of the innermost shells of copper atoms. Other electrons dropped into those gaps and gave off X-ray light. Normally that light spreads in all directions. Above a certain intensity, the emitted light triggers neighboring excited atoms to emit in the same direction, building an amplified forward beam. Physicists call this amplified spontaneous emission, or ASE.
Anders Madsen, who leads the MID instrument where the study ran, said the glow can be seen shifting into “the forward direction” once the threshold is crossed. The team also saw saturation: as pulse energy rose, the amplified signal first grew sharply, then slowed and leveled off. That pattern appears only under extremely intense X-rays, so it served as a second check on the record.
What it means for chemistry
Electrons decide how atoms bond and how molecules react, but they move too fast for most instruments to follow. Very short, very intense pulses could record what electrons are doing before the X-rays themselves disturb the material much. In the longer term, the researchers hope this could lead to ways of steering electron motion during reactions. For now, the result is a demonstration of the light source, not a study of any reaction.
What happens next
European XFEL is preparing to receive its own AKB system, with delivery expected in early 2027. The equipment is funded through a collaboration with the University of Hamburg, with support from Germany’s Federal Ministry of Research, Technology and Space (BMFTR). Once it is installed and commissioned, visiting scientists using the MID instrument are expected to get access to the same kind of flashes.
Source: ScienceDaily
