1. Institute of Physical Chemistry
and Abbe Center of Photonics, Friedrich Schiller University, Helmholtzweg 4, D-07743 Jena, Germany
2. Institute of Photonic Technology, Albert-Einstein-Strasse 9, 07745 Jena, Germany
3. Quality and Safety Department, Nestlé Research Center, Vers-Chez-Les-Blanc,
1000 Lausanne 26, Switzerland