European XFEL team reports record intensity for attosecond hard X-ray pulses
European XFEL researchers report record intensity and fluence for hard-X-ray attosecond pulses, above 10^20 watts per square centimeter. The beam was focused to 180 by 330 nanometers, about 100,000 times smaller than a hair's cross section.
The Scientist · Science desk
Key figures: the pulses lasted an estimated 300 attoseconds, and the focal spot measured 180 by 330 nanometers.
| Figure | Value | Note | Claim |
|---|---|---|---|
| Pulse duration, estimated | 300 attoseconds | 6 | |
| Focal spot, short side | 180 nanometers | 5 | |
| Focal spot, long side | 330 nanometers | 5 |
What happened
- The pulses lasted an estimated 300 attoseconds, a duration the researchers give as an estimate rather than a direct measurement.
- Two precision mirrors in an advanced Kirkpatrick-Baez system focused each pulse, one vertically and one horizontally, so every flash reflected four times.
- To check the intensity, the team watched amplified spontaneous emission from copper foil rise with pulse energy and then saturate.
- The results were published in Optica from an experiment carried out in April 2026, with Ichiro Inoue of the University of Tokyo as first author.
Why it matters
- What's now possible capability The aim is pulses short and intense enough to record information about electrons before the X-rays have substantially changed the sample.
- What it limits constraint The mirror system used was brought in from Japan, so visiting MID users cannot count on this focus until the facility's own system, expected in early 2027, is installed and commissioned.
- What it sets up precedent Controlling electrons during chemical reactions is described only as a long-term possibility; the near-term use is detailed observation of electrons in atoms and molecules.
The intensity in this experiment was estimated from the pulse energy, the pulse duration and the size of the focal spot [13], and the duration is itself an estimate of 300 attoseconds [6]. Fluence measures how much energy the light delivers to a given area, while intensity also takes into account how quickly that energy arrives [15].
So the team looked for a physical signal that appears only at extreme intensity. They aimed the pulses at a copper foil [3]. The X-rays knocked tightly bound inner-shell electrons out of the copper atoms, and when other electrons dropped into the vacancies they left, the atoms gave off X-ray light [10]. At very high intensities, that emitted light can trigger further excited copper atoms to release X-rays travelling the same way, a process called amplified spontaneous emission, or ASE [11].
Anders Madsen, group leader at the MID instrument where the study was conducted, described what the detector sees [9]. "Normal fluorescence goes in all directions, regardless of the direction of the incoming beam," he said. "But when the ASE threshold is crossed, you see the light cone starting to condense into the forward direction." [12]
The ASE signal rose quickly with pulse energy and then levelled off at higher energies. According to the researchers, that saturation is expected only at extremely high intensities, and it independently confirmed the intensity estimated from the other three quantities [13].
The report states the peak intensity as more than 10^20 watts per square centimeter, a lower bound [3]. Phys.org's account does not give the previous record, the pulse energy or the number of shots, so neither the size of the improvement nor how tight that confirmation is can be judged from it. The "world record" label is Inoue's [2].
Jiawei Yan, a DESY scientist and one of the corresponding authors, said the group demonstrated terawatt-scale hard X-ray attosecond pulses at the European XFEL a few years ago [14]. "For experiments, what really matters is what we can deliver to the sample," he said [18]. "With this advance, we can now use attosecond X-rays to explore highly nonlinear interactions between X-rays and matter." [19]
In the account, the sample the pulses were delivered to is the copper foil used for the intensity check [3].
What to watch
- Delivery and commissioning of European XFEL's own advanced Kirkpatrick-Baez system, which Phys.org says the facility expects in early 2027.
- Measurements of pulse duration, energy and shot count that would narrow the 'more than 10^20' watts per square centimeter figure.
- A first experiment that points these focused attosecond pulses at molecules or a reaction.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence68
- Adoption
- Not scored
- Hype gap+15
- Incentives
- Not scored
- Confidence55
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
Researchers used the European XFEL to create X-ray flashes that were extremely short and reached record intensity for this type of pulse.
- [2]
"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.
- [3]
The researchers independently verified a peak intensity of more than 10^20 watts per square centimeter by shining the pulses onto a copper foil.
- [4]
The researchers focused the X-rays to an area roughly 100,000 times smaller than the cross section of a typical human hair.
- [5]
The focal spot was 180 x 330 nanometers.
- [6]
The pulses used in the experiment lasted an estimated 300 attoseconds.
- [7]
The pulses passed through a set of two precision mirrors, an advanced Kirkpatrick-Baez (AKB) optical system; one mirror focused the pulse vertically and the other horizontally, so each flash reflected four times in total.
- [8]
The team published the results of the experiment, carried out in April 2026, in the journal Optica.
- [9]
Anders Madsen is group leader at the MID instrument, where the study was conducted.
- [10]
The X-rays removed electrons from deep inner shells of the copper atoms, leaving 'holes'; when other electrons filled these holes, they emitted X-ray light.
- [11]
At very high intensities, the emitted light can stimulate other excited copper atoms to emit more X-ray light in the same direction, amplifying the signal; this process is called amplified spontaneous emission (ASE).
- [12]
"Normal fluorescence goes in all directions, regardless of the direction of the incoming beam. But when the ASE threshold is crossed, you see the light cone starting to condense into the forward direction," said Anders Madsen.
- [13]
The ASE signal initially increased rapidly as pulse energy rose, then saturated at higher energies; this behavior is expected only at extremely high X-ray intensities and provided independent confirmation of the intensity estimated from pulse energy, duration and focal-spot size.
- [14]
Yan said that a few years ago the group demonstrated terawatt-scale hard X-ray attosecond pulses at the European XFEL.
- [15]
Fluence measures how much energy light delivers to a certain area; intensity also takes into account how quickly that energy arrives.
- [16]
The AKB mirror system used in the experiment was brought in from Japan; European XFEL expects delivery of its own AKB system in early 2027.
- [17]
Once installed and commissioned, European XFEL's own AKB system is intended to give researchers using the MID instrument access to X-ray flashes short and intense enough to capture information about electrons before the X-rays can cause substantial changes in a sample.
- [18]
"For experiments, what really matters is what we can deliver to the sample," said DESY scientist Jiawei Yan, one of the corresponding authors.
- [19]
"With this advance, we can now use attosecond X-rays to explore highly nonlinear interactions between X-rays and matter," said Jiawei Yan.
- [20]
The method could enable detailed studies of how electrons behave in atoms and molecules and, in the long term, could even allow researchers to control electrons during chemical reactions.
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