1. The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg, Germany
2. Center for Free-Electron Laser Science CFEL, Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
3. School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia
4. Department of Physics, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany