Attosecond X-ray pulses partially reverse electronic bleaching, Nature Communications study finds

An international team led by the University of Hamburg and SLAC National Accelerator Laboratory reports that ultrafast X-ray pulses can partially reverse damage they cause while still producing bright images, phys.org reported. The work appears in Nature Communications (DOI: 10.1038/s41467-026-75969-8). Intense X-rays normally strip electrons and bleach samples before usable images form, a limit for free-electron laser imaging of molecules and nanoparticles. Researchers illuminated neon nanoparticles with pulses lasting only a few hundred attoseconds - roughly 100 to 1,000 times shorter than earlier FEL imaging flashes - tuned near the neon K-edge. First author Anatoli Ulmer said attosecond-scale pulses outrun the usual damage cascade and that stimulated emission pushes some electrons back toward their original state, actively reducing electronic bleaching. Comparing 300-attosecond pulses with pulses 50 times longer at similar brightness showed longer pulses produced hotter free-electron clouds and more bleaching, the report said.