1. Department of Electronic Materials
Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 0200,
Australia
2. National Laboratory
for Infrared Physics,
Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083, China
3. Department of Physics, Dong-A University, Hadan-2-dong, Sahagu, Busan 604-714,
Korea