1. PULSE Institute, SLAC Accelerator National Laboratory, Stanford University, Stanford, California 94025, United States
2. Science Institute and Faculty of Physical Sciences, VR-III, University of Iceland, 107 Reykjavík, Iceland
3. Department of Physics, Technical University of Denmark, 2800 Lyngby, Denmark
4. LCLS, SLAC National Laboratory, Menlo Park, California 94025, United States
5. Department of Chemistry, Technical University of Denmark, 2800 Lyngby, Denmark