1. Institute of Laser Engineering, Osaka University 2-6 Yamada-oka, Suita, Osaka 5650871 Japan
2. Dept. of Advanced Energy Engineering Science, Kyushu University, Kasugakohen, Kasuga 8168580 Japan
3. National Institute for Fusion Science, 322-6 Oroshicho, Toki 509-5292, Japan