1. A. F. Ioffe Physico-Technical Institute of RAS, 194021 St.-Petersburg, Russia
2. Spin Optics Laboratory, St.-Petersburg State University, 198504 St.-Petersburg, Russia
3. Physikalisches Institut, Universität Würzburg, 97074 Würzburg, Germany
4. Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland