1. Institute of Applied Physics, Abbe Center of Photonics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743 Jena, Germany
2. Institute of Theoretical Solid State Physics, Karlsruher Institut für Technologie, Wolfgang-Gaede-Str. 1, 76128 Karlsruhe, Germany
3. Institute of Condensed Matter Theory and Solid State Optics, Abbe Center of Photonics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743 Jena, Germany
4. Institute of Nanotechnology, Karlsruher Institut für Technologie, P.O. Box 3640, 76021 Karlsruhe, Germany
5. Fraunhofer-Institut für Angewandte Optik und Feinmechanik IOF, Albert-Einstein-Straße 7, 07745 Jena, Germany