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At the ATHOS beamline of SwissFEL, PSI researchers demonstrated a technique known as mode-locking, which allows fully coherent, ultrashort X-ray pulses to be produced. In the photo, several undulator modules are visible (blue); between each pair are magnetic chicanes used to delay the electrons. Photo Credit: © Paul Scherrer Institute PSI/Markus Fischer |
Scientists at the Paul Scherrer Institute PSI have, for the first time, demonstrated a technique that synchronises ultrashort X-ray pulses at the X-ray free-electron laser SwissFEL. This achievement opens new possibilities for observing ultrafast atomic and molecular processes with attosecond precision.
Scrutinising fast atomic and molecular processes in action requires bright and short X-ray pulses – a task in which free-electron lasers such as SwissFEL excel. However, within these X-ray pulses the light is internally disordered: its temporal structure is randomly distributed and varies from shot to shot. This limits the accuracy of certain experiments.
To tame this inherent randomness, a team of PSI researchers has succeeded in implementing a technique known as mode-locking to generate trains of pulses that are coherent in time. “We can now obtain fully ordered pulses in time and frequency in a very controlled manner,” says accelerator physicist Eduard Prat, who led the study, published in Physical Review Letters. Selected by the journal as Editor’s Suggestion, the study, funded by the EU/ERC project “HERO”, represents a significant step towards the generation of tailored attosecond X-ray pulses and a range of new experiments that are only possible with precisely timed, synchronized light pulses.