1. Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
2. Department of Physics, AlbaNova University Center, Stockholm University, 10691 Stockholm, Sweden
3. Center for Free-Electron Laser Science, Department of Physics, University of Hamburg, 22761 Hamburg, Germany
4. Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
5. Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany