Affiliation: | 1. Electrotechnical Laboratory , Umezono, Tsukuba-shi, Ibaraki , 305 , Japan;2. Phone: +81-298-61-5394 Fax: +81-298-61-5394 E-mail: oyanagi@etl.go.jp;3. Joint Research Center for Atom Technology—National Institute for Advanced Interdisciplinary Research , 1-1-4 Higashi, Tsukuba-shi, Ibaraki , 305 , Japan;4. Joint Research Center for Atom Technology—National Institute for Advanced Interdisciplinary Research , 1-1-4 Higashi, Tsukuba-shi, Ibaraki , 305 , Japan;5. A. F. Ioffe Physico-Technical Institute , St. Petersberg , Russia |