European XFEL Focuses Hard X-Ray Pulses to 180 Nanometres
An optical mirror system concentrates 300-attosecond pulses to achieve record intensities exceeding 10²⁰ watts per square centimetre.
Physicists at the European XFEL research facility have squeezed hard X-ray flashes lasting just 300 attoseconds into a spot measuring 180 by 330 nanometres. The optical innovation, reported in the journal Optica, delivers power densities exceeding 10²⁰ watts per square centimetre to track electron dynamics during chemical reactions.
Four reflections compress attosecond light
Generating ultra-short pulses of high-energy light is only half the battle in modern X-ray science. In an experiment conducted in April 2026 at the European XFEL, researchers directed hard X-ray flashes lasting an estimated 300 attoseconds into a specialized optical system to concentrate their energy, as reported by ScienceDaily.
The team relied on an advanced Kirkpatrick-Baez optical arrangement, known as an AKB system. This configuration uses two precise mirrors that redirect and focus the beam along horizontal and vertical axes across four total reflections. By folding the beam into an area roughly 100,000 times smaller than the cross-section of a human hair, the apparatus produced a focal spot of 180 × 330 nanometres. The resulting energy concentration achieved a new benchmark in fluence and intensity for attosecond hard X-rays.
“This is a world record in intensity and fluence for a hard-X-ray attosecond pulse.”
— Ichiro Inoue, first author from the University of Tokyo
“It is almost magical to see this happening. 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.”
— Anders Madsen, group leader at the European XFEL MID instrument
Stimulated emission confirms extreme power in copper
To verify the beam density, the scientists targeted a thin sheet of copper at the Materials Imaging and Dynamics instrument, known as the MID instrument. The incoming beam ejected electrons directly from the innermost shells of the copper atoms, leaving vacant core positions.
When outer electrons fell into these holes, they released secondary X-ray radiation. Under ordinary illumination, this fluorescent light scatters in all directions. At peak beam intensities beyond 10²⁰ watts per square centimetre, the process shifted into amplified spontaneous emission, creating a directed forward beam. As pulse energies climbed higher, this emission signal eventually hit saturation, providing independent confirmation of the calculated focus.
Capturing electron motion before radiation damage occurs
Observing how electrons shift between atoms requires speeds faster than chemical bonds can break. Ultrashort flashes allow researchers to probe matter before incoming radiation alters molecular structure. Such precision mirror assemblies represent the kind of physical invention that underpins advances in high-energy physics laboratories.
While industrial patents rarely cover one-off beamline optics built for synchrotron facilities, the intellectual property behind extreme precision surface manufacturing continues to spread across semiconductor lithography and metrology. The team from the University of Tokyo and the DESY research centre now aims to use the focused beam to study nonlinear light-matter interactions that were previously inaccessible.
Read also on The Patent: ITER Powers 330 Tonne Superconducting Magnet to 34 Kiloamperes · Oldest dinosaur blood cells and heme found in 115-million-year-old fossil
