1. ISAS- Institute for Analytical Sciences, Bunsen-Kirchhoff-Strasse 11, D-44139 Dortmund, Germany
2. Technische Universität Dortmund, Otto-Hahn-Strasse 6, D-44227 Dortmund, Germany
3. IPHT- Institute for Photonic Technology, Albert-Einstein-Strasse 9, 07745 Jena, Germany