[1] DESY, Ctr Free Electron Laser Sci, Notkestr 85, D-22607 Hamburg, Germany
[2] Hamburg Ctr Ultrafast Imaging, Luruper Chaussee 149, D-22761 Hamburg, Germany
[3] Polish Acad Sci, Inst Nucl Phys, Radzikowskiego 152, PL-31342 Krakow, Poland
[4] Univ Hamburg, Dept Phys, Jungiusstr 9, D-20355 Hamburg, Germany