1. Department of Physics, University of California–San Diego, La Jolla, CA 92093-0319, USA.
2. Stanford PULSE Institute, SLAC National Accelerator Laboratory Menlo Park, CA 94025, USA.
3. Center for Free-Electron Laser Science (CFEL), Deutsches Elektronensynchrotron (DESY), Notkestrasse 85, 22607 Hamburg, Germany.
4. Department of NanoEngineering, University of California–San Diego, La Jolla, CA 92093-0448, USA.
5. Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA.