Researchers at the European XFEL have set a new record for the intensity and fluence of hard X-ray attosecond pulses, achieving flashes that last approximately 300 attoseconds while being focused into an exceptionally small area. The experiment, which was conducted in April 2026, concentrated X-ray energy into a focal spot measuring just 180 by 330 nanometers—roughly 100,000 times smaller than the cross-section of a human hair—resulting in peak intensities exceeding 10²⁰ watts per square centimeter.
To achieve this concentration, the team employed a specialized optical system called an advanced Kirkpatrick-Baez arrangement, which consists of two precisely engineered mirrors that focus the X-ray beam in perpendicular directions. The system allowed the researchers to direct each pulse through four reflections, with one mirror handling vertical focusing and the other horizontal focusing. According to Ichiro Inoue from the University of Tokyo, the lead author, this represents a world record in intensity and fluence for hard X-ray attosecond pulses.
To validate their findings, the researchers directed the focused X-rays at a thin copper sheet and observed the emission of X-ray light through a phenomenon called amplified spontaneous emission. Under normal fluorescence conditions, emitted light travels in multiple directions regardless of the incoming beam’s direction. However, when the X-ray intensity reached the threshold achieved in this experiment, the emitted light began to condense into the forward direction, producing an amplified beam. This behavior, along with saturation patterns observed at higher energies, provided independent confirmation of the record-breaking intensity.
The breakthrough carries significant implications for studying electron behavior at unprecedented timescales and intensity levels. Electrons move on extraordinarily brief timescales while playing central roles in atomic bonding, molecular interactions, and chemical reactions. The combination of ultrashort X-ray flashes with extreme intensity could allow researchers to observe electron movements before the incoming radiation substantially alters the material being examined. The European XFEL is preparing to receive its own advanced Kirkpatrick-Baez system, with delivery expected in early 2027, which will enable scientists worldwide to access these capabilities for further research into fundamental electron processes.
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