1. Graduate School of Engineering, Osaka University, Suita, Osaka 565 0871, Japan
2. Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299, USA
3. General Atomics, San Diego, California 92121-1122, USA
4. Department of Mechanical and Aerospace Engineering, University of California at San Diego, La Jolla, California 92093, USA
5. Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109, USA