1. Institute of Solid State Physics; University of Bremen; 28359 Bremen Germany
2. Institute of Experimental Physics I; Justus Liebig University Giessen; 35392 Giessen Germany
3. Philipps-Universität Marburg; Renthof 7 35037 Marburg Germany
4. Department of Nanophotonics and Metamaterials; ITMO University; St. Petersburg 197101 Russia
5. Institute for Veterinary Physiology and Biochemistry; Justus Liebig University Giessen; 35392 Giessen Germany
6. Universität Hamburg; Center for Hybrid Nanostructures; Luruper Chaussee 149 22607 Hamburg Germany