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Ultrafast dynamics of atoms and molecules with x-ray free-electron lasers
Sang-Kil SonAttosecond Physics at the Nanoscale
(Center for Theoretical Physics of Complex Systems, Institute for Basic Science, Daejeon, Korea, October 29-November 2, 2018) [invited talk]
X-ray free-electron lasers (XFELs) have brought an impact on various scientific fields, including AMO physics, material science, astrophysics, and molecular biology. Understanding how matter interacts with intense x-ray pulses is essential for most XFEL applications. X-ray beams generated from XFELs feature ultrashort and ultraintense pulses. A typical pulse duration of XFEL pulses is about femtoseconds, moving forward an attosecond regime, and the x-ray beam is tightly focused to a sub-micron size. Recent advances of XFELs make it possible to deliver extremely high peak intensities exceeding 100 exa watts per square centimeter. With these unprecedentedly high-intensity x-ray pulses, we are able to explore new intriguing, counterintuitive phenomena of ultrafast dynamics of atoms and molecules. For examples, ionization is suppressed when a pulse duration becomes shorter, in other words, intensity becomes higher (frustrated absorption), ionization is enhanced due to resonances when an energy bandwidth is broad (resonance-enabled x-ray multiple ionization), and ionization is dramatically enhanced due to intramolecular charge transfer (charge-rearrangement-enhanced x-ray ionization of molecules). In this talk, I will discuss these new phenomena, introduce dedicated theoretical tools for studying the XFEL-matter interaction, XATOM and XMOLECULE, and present our recent theoretical and experimental results of Xe atoms and iodomethane molecules. I will also discuss how to apply these new findings for potential XFEL applications such as femtosecond x-ray nanocrystallography.
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