1. Department of Applied Physics and Chemistry and Insititute of Laser Science, University of Electro-communications, Chofugaoka 1-5-1, Chofu, Tokyo, 182-8585 Japan, JST, ICORP, Ultrashort Pulse Laser Project, 4-1-8 Honcho, Kawaguchi, Saitama, Japan, Institute of Laser Engineering, Osaka University, Yamadakami 2-6, Suita 565-0871, Ibaraki 567-0047, Japan, and Department of Electrophysics, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 300,Taiwan
2. Department of Applied Physics and Chemistry and Institute of Laser Science, University of Electro-communications, Chofugaoka 1-5-1, Chofu, Tokyo, 182-8585 Japan, and JST, ICORP, Ultrashort Pulse Laser Project, 4-1-8 Honcho, Kawaguchi, Saitama, Japan
3. Department of Applied Chemistry, Hiroshima University, Higashi-Hiroshima 739-8527, Japan