Femtosecond electronic structure response to high intensity XFEL pulses probed by iron X-ray emission spectroscopy

Roberto Alonso-Mori; Dimosthenis Sokaras; Marco Cammarata; Yuantao Ding; Yiping Feng; David Fritz; Kelly J Gaffney; Jerome Hastings; Chi-Chang Kao; Henrik T Lemke; Timothy Maxwell; Aymeric Robert; Andreas Schropp; Frank Seiboth; Marcin Sikorski; Sanghoon Song; Tsu-Chien Weng; Wenkai Zhang; Siegfried Glenzer; Uwe Bergmann; Diling Zhu

doi:10.1038/s41598-020-74003-1

Femtosecond electronic structure response to high intensity XFEL pulses probed by iron X-ray emission spectroscopy

Sci Rep. 2020 Oct 8;10(1):16837. doi: 10.1038/s41598-020-74003-1.

Authors

Roberto Alonso-Mori¹, Dimosthenis Sokaras², Marco Cammarata³, Yuantao Ding⁴, Yiping Feng⁴, David Fritz⁴, Kelly J Gaffney⁴, Jerome Hastings⁴, Chi-Chang Kao⁴, Henrik T Lemke⁵, Timothy Maxwell⁴, Aymeric Robert⁴, Andreas Schropp⁶, Frank Seiboth⁶, Marcin Sikorski⁷, Sanghoon Song⁴, Tsu-Chien Weng⁸, Wenkai Zhang⁹, Siegfried Glenzer⁴, Uwe Bergmann⁴, Diling Zhu¹⁰

Affiliations

¹ SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA. [email protected].
² SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA. [email protected].
³ Univ Rennes, CNRS, IPR (Institut de Physique de Rennes), UMR 6251, 35000, Rennes, France.
⁴ SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
⁵ SwissFEL, Paul Scherrer Institute, 5232, Villigen, Switzerland.
⁶ Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, 22607, Hamburg, Germany.
⁷ European XFEL, Holzkoppel 4, 22869, Schenefeld, Germany.
⁸ School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, China.
⁹ Department of Physics and Applied Optics Beijing Area Major Laboratory, Center for Advanced Quantum Studies, Beijing Normal University, Beijing, 100875, China.
¹⁰ SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA. [email protected].

Abstract

We report the time-resolved femtosecond evolution of the K-shell X-ray emission spectra of iron during high intensity illumination of X-rays in a micron-sized focused hard X-ray free electron laser (XFEL) beam. Detailed pulse length dependent measurements revealed that rapid spectral energy shift and broadening started within the first 10 fs of the X-ray illumination at intensity levels between 10¹⁷ and 10¹⁸ W cm^-2. We attribute these spectral changes to the rapid evolution of high-density photoelectron mediated secondary collisional ionization processes upon the absorption of the incident XFEL radiation. These fast electronic processes, occurring at timescales well within the typical XFEL pulse durations (i.e., tens of fs), set the boundary conditions of the pulse intensity and sample parameters where the widely-accepted 'probe-before-destroy' measurement strategy can be adopted for electronic-structure related XFEL experiments.