1. Experimentelle Physik II, Universität Dortmund, D-44221 Dortmund, Germany.
2. A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, Russia.
3. Naval Research Laboratory, Washington, DC 20375, USA.
4. School of Computational Sciences, George Mason University, Fairfax, VA 22030, USA.
5. Institute of Physics, St. Petersburg State University, 198504, St. Petersburg, Russia.