Researchers at SLAC’s Linac Coherent Light Source generated and measured X-ray pulses lasting between 100 and 400 attoseconds at photon energies near 9 kiloelectronvolts. Published on 20 October 2026, the achievement sets a record for the shortest high-energy pulses ever recorded at an X-ray free-electron laser.
Making an attosecond pulse at high photon energies is exceptionally difficult, but measuring flashes this short pushed experimental diagnostics further. Lead author Ichiro Inoue proposed an indirect measurement technique using amplified spontaneous emission at the Linac Coherent Light Source. The method splits an X-ray beam into two paths: one heads directly to a detector to record the energy spectrum, while the remaining light focuses onto a 150-nanometer spot on copper foil to produce forward fluorescence.
Combining readings from both detectors allowed the team to calculate the fleeting duration of the beam. Agostino Marinelli, a study author and professor at SLAC, noted that the diagnostic finally proved the pulses lasted only a few hundred attoseconds after years of development.
Hard X-Rays Penetrate Dense Matter with Atomic Precision
The record-breaking pulses extend attosecond science into photon-energy ranges around 9 kiloelectronvolts, marking an order-of-magnitude leap beyond soft X-ray experiments operating below 5 kiloelectronvolts. Lower-energy soft X-rays examine outer-shell chemical bonds, whereas hard X-rays penetrate deep into dense matter with atomic precision.
Plasma physics is very messy. Normally, we excite our sample, then the system relaxes and recombines before we can extract a measurement. We’re often forced to rely on modeling and make assumptions about what exactly is happening.
Sam Vinko, professor of physics at the University of Oxford
Vinko studied plasmas at the Linac Coherent Light Source this spring, utilizing X-rays energetic enough to penetrate and fast enough to freeze core-excited states in extreme systems like inertial fusion energy experiments before motion could blur the data. Researchers also emphasized that the extreme speed of the flashes outruns radiation damage. Because the pulse finishes before structural decay occurs, scientists capture electronic states in pristine condition.
Controlling Light-Matter Interactions at LCLS
The milestone opens the user facility to a broader community. Ichiro Inoue, a professor at the University of Tokyo, described the breakthrough as an important milestone for researchers who want to use attosecond hard X-rays at LCLS
. Tais Gorkhover, head of the advanced ultrafast X-ray imaging group at the University of Hamburg, intends to apply the pulses to sharpen nanoscale absorption and scattering images.
Gorkhover previously used attosecond soft X-rays for diffraction imaging. She noted that hard X-ray pulses offer extremely high temporal resolution to disentangle nuclear and electronic dynamics while opening pathways to actively control light-matter interactions and potentially reverse damage mechanisms.
Future Applications in Quantum Dynamics
The research received support from the Department of Energy Office of Science, with the Linac Coherent Light Source operating as a DOE Office of Science User Facility. The findings were documented in Nature Photonics on 20 October 2026 under the citation DOI: 10.1038/s41566-026-02026-7. By providing a camera shutter faster than atomic decay, the diagnostic technique gives physicists a tool to observe quantum matter without relying on modeling assumptions.