Speaker：Koudai Toyota, Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, Hamburg, Germany
Invited by：Prof. Xiong Wei
Time：15:00-17:00, June 4, 2018
Venue: A101
Biography:
Dr. Koudai Toyota completed his PhD degree in 2010 under the supervision of Prof. Shinichi Watanabe at University of Electro-Communications in Japan. His expertise is theoretical atomic, molecular, and optical physics. After the postdoc studies at Vienna University of Technology in Austria and Max-Placnk-Institute for the Physics of Complex Systems (MPI-PKS) in Germany, Dr. Koudai Toyota started a postdoc position at Deutsches Elektronen-Synchrotron (DESY) since the April of 2015 under the supervision of Prof. Robin Santra. His current research interest is to study atoms or molecules interacting with X-ray free-electron laser (XFEL) pulses at ultrahigh intensity. At DESY, he has been developing theory and computer codes to explore new ionization dynamics of atoms triggered by such an unprecedented light. I am a main developer of the xatom toolkit in the group. The xatom toolkit is a set of computer codes to calculate atomic structure and ionization dynamics of atoms in XFEL pulses based on rate equation approach. Dr. Koudai Toyota has also been developing the xcalib toolkit to calibrate a beam profile of an XFEL pulse at a focal spot employing machine learning technique.
Abstract：
This talk reports on two of the recent progresses. In the first part, it shows the new ionization dynamics of Xe atoms at ultrahigh hard X-ray intensity found in a recent experimental work at LCLS. The experimental Xe charge state distribution (CSD) showed a peculiar oscillatory structure at 5.5keV. The structure becomes less outstanding at 6.5keV, and finally invisible at 8.3keV. Therefore, it strongly depends on photon energy. Our theoretical calculations clarified that the structure originates from resonant excitations between core orbitals. The significant relativistic energy corrections for Xe L-shell play a crucial role for the emergence of such resonant excitation channels. In the second part, It will show the xcalib toolkit. xcalib calibrates the spatial intensity profile of a XFEL pulse at a focal spot using CSD of light atoms. This is required to calculate a focal averaging of theoretical result to compare it with experimental data. The calibration is essential to analyze and understand physics imprinted in experimental results. xcalib automates the calibration procedures which our group manually conducted in previous studies. Thus xcalib offers an efficient tool to handle massive amount of experimental results.
