1. Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
2. SIMES, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
3. Pohang Accelerator Laboratory, Pohang 37673, Republic of Korea
4. Faculty of Physics and Astronomy, Ruhr-University Bochum, 44780 Bochum, Germany
5. Department of Organic Chemistry, Universidad Autónoma de Madrid, 28049 Madrid, Spain
6. Physics Department, University of Wisconsin Madison, Madison, Wisconsin 53706, United States
7. LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States