1. P. Han, J. B. Huang, and C. Chen, Acta Phys. Sin., 38, 272–276 (2009).
2. W. J. Wang, J. Y. Zhou, and W. N. Xiao, Acta Phys. Sin., 34, 1086–1089 (2005).
3. M. P. Jiang, X. F. Jiang, and X. M. Shen, Chin. J. Quantum Electron., 22, 612–616 (2005).
4. L. Zhang, L. Liang, and L. L. Zhang, Acta Phys. Sin., 37, 1815–1818 (2008).
5. R. Zhang and J. C. Cao, Acta Phys. Sin., 59, 3924–3930 (2010).