1. Lawrence Livermore National Laboratory, Livermore, California 94550, USA
2. Division E4, Max Planck Institute for Plasma Physics, 17491 Greifswald and 85748 Garching, Germany
3. The Gérard Mourou Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109, USA
4. Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623, USA