1. a Department of Physics , Aichi University of Education , Igaya-cho, Kariya , Aichi , 448 , Japan
2. b Department of Physics , Faculty of Science, Osaka City University , Sugimoto, Sumiyoshi-ku, Osaka 558, Japan
3. c Osaka Prefectural Technical College , Saiwai-cho, Neyagawa, Osaka 572, Japan
4. d Advanced Glass R and D Center, Asahi Glass Co. Ltd , 1150, Hazawa-cho, Kanagawa-ku, Yokohama 221, Japan