1. Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 18221 Prague 8, Czech Republic
2. Joint Laboratory of Optics, Palacky University Olomouc, Av. 17. listopadu 50A, 77207 Olomouc, Czech Republic
3. Institut für Physik, Universität Greifswald, Felix-Hausdorff-Str. 6, 17489 Greifswald, Germany
4. Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Brehova 7, 11519 Prague 1, Czech Republic