1. EMPA, Swiss Federal Laboratories for Materials Science and Technology, Feuerwerkerstr. 39, CH-3602 Thun, Switzerland
2. Institute of Photonic Technology, Albert-Einstein-Strasse 9, D-07745 Jena, Germany
3. Max Planck Institute for the Science of Light, Günther Scharowsky-Strasse 1, 91058 Erlangen, Germany