1. Department of Physics and NTIS–European Centre of Excellence, University of West Bohemia, Univerzitní 8, 301 00 Plzeň, Czech Republic
2. New Technologies–Research Centre, University of West Bohemia, Univerzitní 8, 301 00 Plzeň, Czech Republic
3. Département de Physique, Université de Cergy-Pontoise, 5 mail Gay-Lussac, 95031 Cergy-Pontoise, France
4. Center of Materials and Nanotechnologies, University of Pardubice, Studentská 95, 532 10 Pardubice, Czech Republic