1. Department
of Physics, National Tsing-Hua University, Hsinchu 30013, Taiwan
2. Department
of Physics, The University of Texas at Austin, Austin, Texas 78712, United States
3. Department
of Materials Science and Engineering, National Tsing-Hua University, Hsinchu 30013, Taiwan
4. Department
of Electrophysics, National Chiao-Tung University, Hsinchu 30010, Taiwan
5. Center
for Nanooptics (CeNO) and Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, United States
6. Fakultät
für Physik, Ludwig-Maximilians-Universität, Geschwister-Scholl-Platz 1, D-80539 München, Germany
7. Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany