In a monumental leap forward for quantum physics and ultrafast optics, an international team of researchers has established a new world record by producing extraordinarily intense X-ray flashes that endure for a staggering 300 attoseconds. To put this into perspective, an attosecond is a billionth of a billionth of a second—an almost unimaginably brief window of time that now allows humanity to peer into the subatomic realm with unprecedented precision.
Utilizing the European XFEL, a state-of-the-art and exceptionally powerful X-ray research facility, the scientific team concentrated these ultrashort flashes into an extraordinarily confined area. The resulting focal spot measures roughly 100,000 times smaller than the cross-section of a typical human hair. By squeezing an immense amount of X-ray energy into such a microscopic space, the researchers have engineered a high-fluence, high-intensity beam capable of opening entirely new frontiers in the study of electron behavior inside atoms and molecules. This historic breakthrough, achieved during experiments in April 2026, has now been formally documented and published in the peer-reviewed scientific journal Optica.
Record-Breaking X-Ray Flashes Last Just 300 Attoseconds
"This is a world record in intensity and fluence for a hard-X-ray attosecond pulse," highlights Ichiro Inoue from the University of Tokyo, who serves as the first author of the published study.
Hard X-rays are a specialized form of high-frequency electromagnetic radiation characterized by extremely short wavelengths. When physicists evaluate the raw power and capability of these beams, they rely on two critical metrics: fluence and intensity. Fluence quantifies the total amount of energy delivered to a precise area, while intensity incorporates a temporal dimension, measuring how rapidly that specific volume of energy is deployed into the target.
In this groundbreaking experiment, each individual X-ray pulse was measured at an estimated duration of just 300 attoseconds. Capturing events on this ultrafast scale provides researchers with a vital observational tool, granting them the ability to investigate physical and chemical phenomena that unfold far too rapidly for conventional scientific instruments to record.
To achieve this extreme concentration of photons, the research team deployed a sophisticated optical configuration known as an advanced Kirkpatrick-Baez, or AKB, system. This cutting-edge apparatus is constructed from two exceptionally precise mirrors designed to shape and focus the beam along different directional axes. Over the course of each pulse, the X-ray beam underwent four total reflections, with one specialized mirror governing vertical convergence and the second handling horizontal focus.
The culmination of this meticulous optical engineering was an astonishingly small focal footprint measuring a mere 180 by 330 nanometers, where a nanometer represents a billionth of a meter. By funneling the dense energy packets into this sub-micron domain, the team successfully vaulted past previous limitations to achieve record-shattering peak intensity.
"A few years ago, we demonstrated terawatt-scale hard X-ray attosecond pulses at the European XFEL," notes DESY scientist Jiawei Yan, one of the corresponding authors of the research. "But generating powerful pulses is only the first step. For experiments, what really matters is what we can deliver to the sample. With this advance, we can now use attosecond X-rays to explore highly nonlinear interactions between X-rays and matter."
These complex nonlinear interactions occur when exceptionally intense illumination forces matter to respond in abnormal ways that would never manifest under weaker, standard irradiation. Delving into these extreme physical regimes promises to uncover previously hidden dynamics regarding how atoms and their constituent electrons react under severe environmental stresses.
An Extraordinary Reaction Inside Copper Atoms
To empirically validate the unprecedented intensity of their newly generated X-ray pulses, the research team directed the focused beam at a thin, high-purity sheet of copper. This diagnostic test yielded independent, concrete evidence that the concentrated flashes successfully surpassed peak intensities of 10²⁰ watts per square centimeter.
When the ultra-dense X-rays slammed into the copper target, they possessed enough energy to violently knock electrons directly out of the atoms’ innermost electron shells. This disruptive impact left behind unstable vacancies known in physics as ‘holes’. Almost instantaneously, electrons residing in higher energy levels within the copper atoms cascaded downward to fill these vacant inner positions, shedding their excess energy by emitting secondary bursts of X-ray light.
Under normal, everyday experimental circumstances, this secondary fluorescence radiates outward in a diffuse scatter across all possible directions. However, when the incoming primary X-ray beam crosses a critical threshold of extreme intensity, a dramatic physical transformation occurs. The newly emitted light gains the capacity to stimulate neighboring excited copper atoms, compelling them to release additional X-rays that march in coherent lockstep with the original beam, thereby creating an amplified and directional output.
Physicists refer to this captivating phenomenon as amplified spontaneous emission, or ASE.
"It is almost magical to see this happening," remarks Anders Madsen, group leader at the MID instrument station where the experimental campaign was carried out. "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."
In addition to witnessing directional amplification, the team documented another textbook signature of extreme-intensity physics. As they steadily dialed up the energy of the incoming X-ray pulses, the resulting amplified signal initially spiked dramatically. Yet, as the pulse energy was pushed even higher, the rate of signal growth began to taper off before eventually plateauing entirely—a classic physical phenomenon known as saturation.
This characteristic curve is theoretically predicted to occur only under conditions of extraordinary X-ray illumination. Its clear observation during the copper target test provided robust, independent confirmation of the record-breaking intensity figures calculated from the primary pulse energy, temporal duration, and the dimensions of the microscopic focal spot.
A New Way to Explore the Hidden World of Electrons
Beyond the prestige of securing a new world record, this technological triumph significantly broadens humanity’s window into nature’s most transient processes.
Electrons serve as the foundational architects of chemistry, dictating the precise mechanisms by which atoms forge chemical bonds, how complex molecules interact with one another, and how chemical transformations unfold from start to finish. Because the physical movements of electrons occur on unimaginably rapid timescales, capturing them in action has historically remained one of the most stubborn hurdles in experimental science.
By fusing ultrashort attosecond timescales with extraordinarily high pulse intensity, researchers are now equipped to capture high-resolution snapshots of electronic motion before the ionizing radiation has sufficient time to structurally alter or destroy the material under observation. This capability paves the way for a much clearer, undistorted picture of electron behavior within atomic and molecular structures. In the long term, this foundational understanding could lay the groundwork for pioneering techniques designed to actively influence and direct electron pathways during chemical reactions.
The advanced Kirkpatrick-Baez mirror system that made this milestone achievement possible was transported directly from research partners in Japan. Capitalizing on this momentum, the European XFEL facility is already making active preparations to house its own permanent AKB system, with official delivery slated for early 2027.
This upcoming equipment acquisition is being funded through a close institutional collaboration with the University of Hamburg, alongside vital financial backing provided by the Federal Ministry of Research, Technology and Space (BMFTR).
Once the dedicated system is fully installed, calibrated, and commissioned at the MID instrument, an international community of visiting scientists will gain direct access to these revolutionary, hyper-short, and hyper-intense X-ray pulses. This imminent expansion of analytical infrastructure will empower researchers to investigate fundamental electronic behavior at a level of granular detail previously deemed unattainable, drawing science ever closer to fully comprehending—and potentially mastering—the microscopic forces that govern the universe’s most basic chemical reactions.
