1. Max-Planck-Institut für Quantenoptik (MPQ), Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany.
2. Department of Physics and Astronomy, King Saud University, Riyadh 11451, Kingdom of Saudi Arabia.
3. Center for Free-Electron Laser Science, Deutsches Elektronen Synchrotron, Notkestrasse 85, 22607 Hamburg, Germany.
4. Department of Physics, University of Hamburg, Jungiusstrasse 9, 20355 Hamburg, Germany.
5. Department für Physik, Ludwig-Maximilians-Universität (LMU), Am Coulombwall 1, D-85748 Garching, Germany.