1. Institute of Physics of the Czech Academy of Sciences, Na Slovance 1999/2, 182 21 Prague 8, Czech Republic
2. Institute of Optoelectronics, Military University of Technology, Kaliskiego 2 Str., 00-908 Warsaw, Poland
3. Lebedev Physical Institute of the Russian Academy of Sciences, Leninskij Prospekt, 53, 119991 Moscow, Russia