1. Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan
2. Graduate Institute of Electro-optical Engineering, Tatung University, Taipei 104, Taiwan
3. Advanced Ultrafast Laser Research Center and Department of Engineering Science, Faculty of Informatics and Engineering, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan