1. Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka 565-0871, Japan
2. Research Center for Development of Far-Infrared Region, University of Fukui, Bunkyo 3-9-1, Fukui, Fukui 910-8507, Japan
3. O. Ya. Usikov Institute for Radiophysics and Electronics IRE NASU, 12, ac. Proskura str., Kharkiv 61085, Ukraine
4. Fukuda Crystal Laboratory Co., Ltd., 6-6-3 Minami-Yoshinari, Aoba, Sendai 989-3204, Japan