[1] Slovak Acad Sci, Inst Expt Phys, Watsonova 47, Kosice 04001, Slovakia
[2] Polish Acad Sci, Inst Mol Phys, 16 Smoluchowskiego Str, PL-60179 Poznan, Poland
[3] Wigner Res Ctr Phys, Inst Solid State Phys & Opt, Konkoly Thege Miklos Ut 29-33, H-1121 Budapest, Hungary