1. Institute of Solid State Physics, Technical University of Berlin, Hardenbergstraße 36, D-10623 Berlin, Germany
2. Laboratory for Optical Spectroscopy of Nanostructures, Department of Experimental Physics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
3. JCMwave GmbH, Bolivarallee 22, D-14050 Berlin, Germany
4. Zuse Institute Berlin, Takustraße 7, D-14195 Berlin, Germany