1. SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
2. Institut für Physik, Universität Rostock, 18051 Rostock, Germany.
3. Los Alamos National Laboratory, Bikini Atoll Road, Los Alamos, NM 87545, USA.
4. Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada.
5. Department of Electrical and Computer Engineering, University of Alberta, Edmonton, AB T6G 2V4, Canada.
6. Faculty of Physics and Centre for Nanointegration Duisburg-Essen, University of Duisburg-Essen, Lotharstrasse 1, D-47048 Duisburg, Germany.