1. Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, Prague 2, CZ-12116, Czech Republic, and Laboratory of Physics and Helsinki Institute of Physics, Helsinki University of Technology, P. O. Box 1100, FIN-02015 HUT, Finland
2. Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, Prague 2, CZ-12116, Czech Republic
3. Department of Ophthalmology, University of Helsinki, and Helsinki Biophysics & Biomembrane Group, Institute of Biomedicine, University of Helsinki, Finland
4. Laboratory of Physics and Helsinki Institute of Physics, Helsinki University of Technology, P. O. Box 1100, FIN-02015 HUT, Finland