1. Department
of Theoretical Physics, Faculty of Physics, Vilnius University, Sauletekio Avenue 9, Building 3, LT-10222 Vilnius, Lithuania
2. Institute
of Physics and Biophysics, Faculty of Science, University of South Bohemia, Branišovská 1760, 37005 České Budějovice, Czech Republic
3. Photonics Institute, TU Wien, Gusshausstrasse
27, 1040 Vienna, Austria