1. Department of Physics and Materials Science Centre Philipps University Marburg Hans-Meerwein-Str. 6 35032 Marburg Germany
2. Institute of Experimental Physics I Justus Liebig University Heinrich-Buff-Ring 16 35392 Gießen Germany
3. Department of Chemistry and Materials Science Centre Philipps University Marburg Hans-Meerwein-Str. 4 35032 Marburg Germany
4. Karlsruhe Institute of Technology Light Technology Institute Engesserstraße 13 76131 Karlsruhe Germany