1. Physics Department, University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
2. Physik-Department E20, Technische Universität München, James-Franck-Straße 1, 85748 Garching, Germany
3. Walther-Meißner-Institute, Walther-Meißner-Straße 8, 85748 Garching, Germany
4. Physics Department and Center for Free-Electron Laser Science, University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
5. DESY Photon Science, Notkestraße 85, 22607 Hamburg, Germany