Xcalib: a focal spot calibrator for intense X-ray free-electron laser pulses based on the charge state distributions of light atoms

Koudai Toyota, Zoltan Jurek, Sang Kil Son, Hironobu Fukuzawa, Kiyoshi Ueda, Nora Berrah, Benedikt Rudek, Daniel Rolles, Artem Rudenko, Robin Santra

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


The xcalib toolkit has been developed to calibrate the beam profile of an X-ray free-electron laser (XFEL) at the focal spot based on the experimental charge state distributions (CSDs) of light atoms. Characterization of the fluence distribution at the focal spot is essential to perform the volume integrations of physical quantities for a quantitative comparison between theoretical and experimental results, especially for fluence-dependent quantities. The use of the CSDs of light atoms is advantageous because CSDs directly reflect experimental conditions at the focal spot, and the properties of light atoms have been well established in both theory and experiment. Theoretical CSDs are obtained using xatom, a toolkit to calculate atomic electronic structure and to simulate ionization dynamics of atoms exposed to intense XFEL pulses, which involves highly excited multiple core-hole states. Employing a simple function with a few parameters, the spatial profile of an XFEL beam is determined by minimizing the difference between theoretical and experimental results. The optimization procedure employing the reinforcement learning technique can automatize and organize calibration procedures which, before, had been performed manually. xcalib has high flexibility, simultaneously combining different optimization methods, sets of charge states, and a wide range of parameter space. Hence, in combination with xatom, xcalib serves as a comprehensive tool to calibrate the fluence profile of a tightly focused XFEL beam in the interaction region.

Original languageEnglish
Pages (from-to)1017-1030
Number of pages14
JournalJournal of Synchrotron Radiation
Publication statusPublished - 2019 Jul 1


  • Ab initio calculation
  • Beam profile
  • Calibration
  • Characterization
  • Charge state distribution
  • First-principles calculation
  • Spatial fluence distribution
  • X-ray free-electron laser
  • XFEL

ASJC Scopus subject areas

  • Radiation
  • Nuclear and High Energy Physics
  • Instrumentation


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