Argonne National Laboratory

Research Highlight | Materials Science

Splitting ultrafast X-ray pulses to measure dynamic systems
In a study published in Nature Communications, researchers showed how reliable speckle contrast values can be extracted even from very low intensity free electron laser speckle patterns by applying maximum likelihood fitting.
Schematics of the hard X-ray delay line instrument. An incoming ultrashort X-ray pulse is split with a thin silicon single crystal splitter (SP1). The pulses are directed along different pathways via reflective Bragg optics (R1–R6). The relative path length difference between the lower branch (LB) and the upper branch (UB) introduces a time delay Δ t (here 1.3 ns) between the split pulses.

Scientific Achievement

Using split X-ray pulses at the LCLS, nanoscale nanosecond equilibrium structural dynamics were measured in a colloidal liquid, marking the first demonstration of split-and-delay ultrafast hard X-ray photon correlation spectroscopy. 

Significance and Impact

This work enables the study of atomic-length-scale dynamics of materials over time scales of femtoseconds to nanoseconds at X-ray laser light sources, filling a critical gap in measuring equilibrium dynamics in complex systems.

Research Details

  • A split-and-delay instrument was used to temporally separate individual LCLS pulses by 1.3 nanoseconds, and two-pulse speckle patterns were measured from a suspension of gold nanoparticles in hexane at different scattering vectors.
  • Contrast was extracted from very weak speckle patterns using maximum likelihood fitting, enabling dynamics to be observed.

Work was performed at Argonne and SLAC National Laboratories.

DOI: 10.1038/s41467-018-04178-9

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