Scientists at the European XFEL have shattered records by producing 300-attosecond X-ray pulses concentrated into a focal spot measuring 180 × 330 nanometers, a breakthrough that could unlock the secrets of electron behavior in chemical reactions. This achievement, published in Optica, marks a critical leap in our ability to observe and potentially manipulate the ultrafast dynamics of matter at the atomic level.
The Attosecond Frontier: Squeezing Unimaginable Power into a Microscopic Point
At the heart of this development is a feat of temporal and spatial compression. The team generated X-ray flashes lasting 300 attoseconds—a billionth of a billionth of a second. The true innovation lies in focusing this immense energy into an area measuring 180 × 330 nanometers.
This was accomplished using an advanced Kirkpatrick-Baez (AKB) mirror system, a piece of optical engineering of extraordinary precision. The AKB system employs two mirrors to focus the beam in two perpendicular planes. Each pulse undergoes four reflections total—one mirror for vertical focusing, the other for horizontal. The result is a beam of unprecedented intensity. “A few years ago, we demonstrated terawatt-scale hard X-ray attosecond pulses at the European XFEL,” says DESY scientist Jiawei Yan. “But generating powerful pulses is only the first step. For experiments, what really matters is what we can deliver to the sample.”
This isn’t theoretical. The team directed these focused pulses at a thin sheet of copper and observed a phenomenon known as amplified spontaneous emission (ASE). This effect, where emitted light is stimulated to travel in the same direction as the incoming beam, only occurs when the X-ray intensity surpasses a critical threshold. The observation of ASE, along with a subsequent saturation effect in the signal, provided concrete proof that the peak intensity exceeded 10²⁰ watts per square centimeter—a world record in intensity and fluence for a hard-X-ray attosecond pulse.
What This Means for Electron Dynamics
Electrons are the workhorses of chemistry. Their movements dictate how atoms bond, how molecules form, and how reactions unfold. These processes happen on attosecond timescales, making them notoriously difficult to observe with any clarity without perturbing the system itself. The new method offers a way to capture information about electron behavior before the incoming radiation has a chance to significantly alter the material being studied.
This could provide a clearer, more direct picture of the fundamental choreography of electrons. In the longer term, the implications are profound. By understanding electron motion at its most fundamental level, scientists may eventually develop methods to control it.
The EU’s Next Hardware: AKB Mirrors and the 2027 Upgrade Path
The AKB mirror system used in this record-setting experiment was transported from Japan. However, the European XFEL is not resting on its laurels. The facility is actively preparing to receive and install its own permanent AKB system, with delivery slated for early 2027. This new equipment is a significant investment, funded through a collaboration with the University of Hamburg and supported by the Federal Ministry of Research, Technology and Space (BMFTR).
Once installed and commissioned, this upgraded capability will be available to the international scientific community using the MID instrument.
Yan said that with this advance, researchers can now use attosecond X-rays to explore highly nonlinear interactions between X-rays and matter—effects that occur when extremely intense X-rays cause matter to respond in ways that would not normally happen under weaker illumination, potentially revealing new details about how atoms and electrons behave under extreme conditions.
