1. Institute for Technical and Macromolecular Chemistry; University of Hamburg; Bundesstr. 45 D-20146 Hamburg Germany
2. Department of Physics; University of Osnabrück; Barbarastr. 7 D-49076 Osnabrück Germany
3. Center for Free-Electron Laser Science; Attosecond Research and Science Group; University of Hamburg; Luruper Chaussee 149 22761 Hamburg Germany