1. Department
of Physical Optics, Belarusian State University, Nezavisimosti ave., 4, 220030 Minsk, Belarus
2. Taras Shevchenko National University of Kyiv, Volodymyrska str., 64\13, 01601, Kyiv, Ukraine
3. Department
of Physics, AlbaNova University Center, Stockholm University, S-106
91 Stockholm, Sweden
4. Faculty
of Physics, Vilnius University, Sauletekio al. 9-3, LT-10222 Vilnius, Lithuania