1. Charles University in Prague, Faculty of Mathematics and Physics, V Holešovičkách 2, 18000 Prague 8, Czech Republic
2. Faculty of Biomedical Engineering, Czech Technical University in Prague, Sítná sq. 3105, 27201 Kladno, Czech Republic
3. Institute of Physics, ASCR, Cukrovarnická 10, 16253 Prague 6, Czech Republic