1. Institute of Micro- and Nanostructure Research and Center for Nanoanalysis and Electron Microscopy (CENEM), Department of Materials Science, Universität Erlangen-Nürnberg, Cauerstraße 6, D-91058 Erlangen, Germany
2. Chair of Laser Physics, Department of Physics, Universität Erlangen-Nürnberg, Staudtstraße 1, D-91058 Erlangen, Germany