1. Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871
2. RIKEN XFEL Project Head Offi ce, 1-1-1 Koto, Sayo, Hyogo 679-5148
3. Institute for Laser Science, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585
4. Japan Synchrotron Radiation Research Institute, 1-1-1 Koto, Sayo, Hyogo 679-5198