1. Leibniz Universität Hannover - Quantum Optics Institute; Welfengarten 1 Hannover 30167 Germany
2. QUEST Centre for Quantum Engineering and Space-Time Research; Hannover Germany
3. Laser Zentrum Hannover; Germany
4. University of Konstanz - Department of Physics and Center for Applied Photonics; Konstanz Germany
5. Universität Bielefeld - AG Dünne Schichten Physik der Nanostrukturen; Bielefeld Germany