Attosecond X-ray pulses have reached a new intensity record at the European XFEL. Researchers focused hard-X-ray flashes lasting an estimated 300 attoseconds onto a spot just 180 by 330 nanometres, concentrating the light into an area roughly 100,000 times smaller than the cross-section of a typical human hair, according to a release from the facility. The team published the experiment, carried out in April 2026, in the journal Optica.
What makes these attosecond X-ray pulses a record
“This is a world record in intensity and fluence for a hard-X-ray attosecond pulse,” said Ichiro Inoue of the University of Tokyo, first author of the publication. The release explains that hard X-rays are light waves with a particularly short wavelength, that fluence measures how much energy light delivers to a given area, and that intensity also accounts for how quickly that energy arrives. An attosecond is a billionth of a billionth of a second.
How the team focused the pulses
The pulses passed through two extremely precise mirrors, an advanced Kirkpatrick-Baez (AKB) optical system. One mirror focused the beam vertically and the other horizontally, so each flash reflected four times in total. The result was the 180 by 330 nanometre focal spot.
DESY scientist Jiawei Yan, one of the corresponding authors, noted that the team had shown terawatt-scale hard X-ray attosecond pulses at the European XFEL a few years ago. “But generating powerful pulses is only the first step,” he said. “For experiments, what really matters is what we can deliver to the sample.”
How they checked the intensity
The researchers say they independently verified a peak intensity of more than 1020 watts per square centimetre by shining the pulses on a copper foil. The X-rays knocked electrons out of deep inner shells of the copper atoms, leaving holes. When other electrons filled those holes they emitted X-ray light, and at very high intensities that light can stimulate other excited atoms to emit more light in the same direction, a process called amplified spontaneous emission.
Anders Madsen, group leader at the MID instrument where the study was conducted, called it “almost magical” to see the light cone condense into the forward direction once the threshold was crossed. The signal rose rapidly with pulse energy and then levelled off, which the team says is expected only at extremely high intensities and supports the intensity estimate.
The other side: what comes next, and what is not shown
The release says the method could enable detailed studies of how electrons behave in atoms and molecules and, in the long term, might even allow control of electrons during chemical reactions. That is a long-term possibility, not something demonstrated in this experiment. The pulse length is also described as an estimate.
The mirror system used was brought in from Japan. European XFEL expects delivery of its own AKB system in early 2027, funded through a collaboration with the University of Hamburg and support from Germany’s Federal Ministry of Research, Technology and Space. Only after it is installed and commissioned will researchers using the MID instrument have regular access to such pulses. The announcement raises no security concerns.
You may also like our stories on the first working nuclear clock and the X-ray movie of penicillin being made.
My view on attosecond X-ray pulses
As a writer, I feel what stands out is the shift from “how strong can we make the pulse” to “how much of it can we actually put on the sample”. That is the practical question for experimenters. I would stay cautious about the talk of controlling chemical reactions, since that is a distant goal, but a verified record is a solid step on the way.
FAQ: attosecond X-rays at the European XFEL
What is an attosecond?
An attosecond is a billionth of a billionth of a second. The pulses in this experiment lasted an estimated 300 attoseconds.
How small was the focal spot?
The X-rays were focused to 180 by 330 nanometres, an area about 100,000 times smaller than the cross-section of a typical human hair, according to the release.
When can other scientists use this?
European XFEL expects delivery of its own advanced Kirkpatrick-Baez mirror system in early 2027. Once installed and commissioned, it is intended to give researchers access to such pulses at the MID instrument.