1. Institute of Applied Physics University of Münster Corrensstraße 2 48149 Münster Germany
2. Leibniz Institute of Photonic Technology Albert‐Einstein‐Str. 9 07745 Jena Germany
3. Otto Schott Institute of Material Research Friedrich Schiller University of Jena Fraunhoferstr. 6 07743 Jena Germany
4. MESA+ Institute for Nanotechnology University of Twente Enschede 7500 AE The Netherlands