1. Department Chemistry—Biology, University of Siegen, Adolf-Reichwein-Strasse 2, 57076 Siegen, Germany
2. Department Physics, University of Siegen, Walter-Flex-Str. 3, 57072 Siegen, Germany
3. National Institute of Optics (INO), National Research Council (CNR), Via Nello Carrara 1, 50019 Sesto Fiorentino, Italy
4. Department of Applied Science of Technology (DISAT), Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy