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A new frontier in understanding electron dynamics: Imaging with attosecond short X-ray flashes

Attosecond science, honored with the 2023 Nobel Prize in Â鶹ÒùÔºics, is transforming our understanding of how electrons move in atoms, molecules, and solids. An attosecond—equivalent to a billionth of a billionth of a second—enables "slow-motion" visualization of natural processes occurring at extraordinary speeds.

However, until now, most attosecond experiments have been limited to spectroscopic measurements due to the constraints of attosecond light pulse sources.

Using the powerful X-ray Free Electron Laser (FEL) at SLAC National Laboratory in California, the Hamburg team studied how ultrashort pulses interact with nanoparticles. They uncovered a previously unexplored phenomenon: transient ion resonances that enhance image brightness.

These fleeting resonances, which occur when FEL pulses are shorter than those used in most experiments, significantly amplify X-ray scattering efficiency. This discovery not only improves the quality and detail of diffraction images but also marks a crucial step toward atomic-scale imaging. The findings are in Nature Communications.

"We were initially puzzled by the unexpectedly strong X-ray diffraction signals during our experiments at the Linac Coherent Light Source (LCLS)," says Tais Gorkhover, one of the study's lead authors from the University of Hamburg and a researcher in the Cluster of Excellence CUI: Advanced Imaging of Matter. "After rigorous quality checks and independent verification from simulations, we confirmed the effect."

Typically, when intense X-ray pulses strike matter, electrons—the primary contributors to X-ray diffraction—are stripped away through ionization, leaving ions that scatter X-rays less effectively. The current study, however, reveals that under extremely short and specifically tuned FEL pulses, these ions can increase their diffraction efficiency by orders of magnitude.

"This discovery offers a novel approach to enhancing both the brightness and resolution of X-ray diffraction imaging," explains Stephan Kuschel, the study's first author. "This technique opens the door to visualizing ultrafast processes, such as chemical reactions and catalytic transformations, in their natural environments with remarkable temporal resolution."

The findings emphasize the importance of pushing technological boundaries in X-ray imaging to unveil the invisible dynamics of matter. With further advancements, this breakthrough promises impacts in fields such as chemistry, materials science, and nanotechnology.

"This is a step closer to the ultimate goal of capturing individual atoms in motion," the researchers note. "By fine-tuning X-ray pulse conditions, we will be able to observe details that were previously beyond reach."