1. Laboratory for Optical Spectroscopy of Nanostructures, Department of Experimental Physics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, Wybrzee Wyspiańskiego 27, 50-370 Wrocław, Poland
2. Technische Physik, University of Würzburg and Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Am Hubland, D−97074 Würzburg, Germany
3. SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, United Kingdom