Scientists created a record-breaking attosecond X-ray flash that could help reveal how electrons move inside atoms and molecules.
A camera flash can freeze a sprinter’s motion in a photograph because its light lasts only an instant.
Inside an atom, electrons rearrange themselves in attosecondsand there are more attoseconds in one second than there have been seconds since the Big Bang.
X-ray flashes that short are hard to make, and physicists have now made one about ten times more intense than any attosecond X-ray laser pulse reported before it.
Researchers at the European XFELan X-ray laser in Schenefeld, Germany, focused the flash into a spot a few hundred times narrower than a human hair.
They then checked the record by watching copper atoms do something only extreme light makes them do.
“This is a world record in intensity and fluence for a hard-X-ray attosecond pulse,” said Ichiro Inoue of the University of Tokyothe first author of the paper. The team ran the experiment in April 2026.
Why intensity matters
Hard X-rays are the most energetic kind of X-ray, with wavelengths about the size of an atom. Physicists judge a flash by two numbers once it reaches a sample.
One is how much energy lands on each bit of area, which is called fluence. The other is how fast that energy arrives, which is intensity.
A high fluence matters for samples smaller than the beam. A high intensity makes matter respond in ways that weak light can’t trigger.
“A few years ago, we demonstrated terawatt-scale hard X-ray attosecond pulses at the European XFEL,” said Jiawei Yan of the German research center DESYone of the corresponding authors.
“But generating powerful pulses is only the first step.”
“For experiments, what really matters is what we can deliver to the sample,” Yan added.
“With this advance, we can now use attosecond X-rays to explore highly nonlinear interactions between X-rays and matter.”
Two mirrors squeezed the beam
The machine starts with a tightly packed bunch of electrons lasting just a few femtoseconds.
A long line of magnets with alternating poles makes the bunch give off an X-ray flash.
Measured just past those magnets, each flash carried 140 microjoules on average, more than ten times the energy of earlier hard X-ray attosecond pulses.
A pair of mirrors brought in from Japan focused the beam nearly 1 kilometer (0.6 miles) beyond the magnets.
Each flash bounced four times, one mirror focusing it vertically and the other horizontally, inside a vacuum chamber.
Scanning fine gold wires across the beam showed a focal spot about 7 by 13 millionths of an inch (180 by 330 nanometers). A human hair is a few hundred times wider.
Sorting the flashes
A curved diamond crystal recorded the spread of energies in every flash without disturbing it.
Ordinary X-ray laser pulses, which last femtoseconds, typically show several tens of spikes in that spread.
Of 74,000 flashes here, 13.7% showed a single spike, consistent with the light coming from one ultrashort slice of the electron bunch.
At the focus, the single-spike flashes carried an average of 45 microjoules, with some reaching 100 microjoules.
Their energy spread of 6 electronvolts implies a duration of about 300 attoseconds, if each pulse is as short as its spectrum allows.
That is a flash so brief that light itself travels less than the width of the spot before it ends.
From those numbers, the fluence came to 67,000 joules per square centimeter and the peak intensity to 210 billion billion watts per square centimeter.
Both are roughly ten times the previous best for attosecond X-ray laser pulses.
They also rival the best focused femtosecond pulses, with one very recent exception that reached roughly 50 times higher.
Copper confirmed the record
The team wanted an independent check on that intensity. They put a copper foil less than one thousandth of an inch (20 micrometers) thick at the focus, with a detector about 2 feet (600 millimeters) behind it.
A 10,000-electronvolt X-ray photon can knock an electron out of the innermost shell of a copper atom.
When another electron drops into that hole, the atom gives off an X-ray of its own.
At high enough intensity, those X-rays stimulate neighboring excited atoms to emit in the same direction. Physicists call it amplified spontaneous emission, or ASE.
“It is almost magical to see this happening,” said Anders Madsen, group leader at the European XFEL’s MID instrument, where the study was conducted.
“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.”
The copper glow climbed steeply as pulse energy rose to about 20 microjoules, slowed after that, and leveled off above 50 microjoules.
One possible reason for the leveling is that the pulse strips electrons out of the atoms faster than the atoms can glow.
The estimated intensity was close to the level at which this electron stripping should occur, supporting that explanation.
What these flashes could reveal
The 300-attosecond figure is an inference from the energy spread, not a direct measurement of the pulse in time.
Only about one flash in seven came out as a single spike, and the leveling of the copper glow has one possible explanation rather than a proven one.
The team wrote that pulses this intense could drive higher-order interactions between X-rays and matter and capture a structure before the X-rays damage it.
Split into two timed flashes, they might also control how electrons move in atoms and molecules. This paper reports just the flash and the copper test.
Flashes this short and intense are meant to show what electrons do before the X-rays change the sample.
European XFEL expects its own focusing mirrors in early 2027, funded with the University of Hamburg and Germany’s research ministry.
The new mirrors would make these flashes available to researchers worldwide, opening more opportunities to study electrons in motion.
The full study was published in the journal OPTICAL.
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Source: www.earth.com
