[1] Z. Xu and X. Li, Chin. Opt. Lett. 5, 1 (2007).

[2] E. Persson, K. Schiessl, A. Scrinzi, and J. Burgdorfer, Phys. Rev. A 74, 013818 (2006).

[3] G. Ding, X. Zhao, Y. Wang, W. Zhao, and G. Chen, Chin. Opt. Lett. 4, 222 (2006).

[4] H. Leblond, S. V. Sazonov, I. V. Mel'nikov, D. Mihalache, and F. Sanchez, Phys. Rev. A 74, 063815 (2006).

[5] L. Wang, K. Xia, H. Sun, Y. Niu, and S. Gong, Chin. Opt. Lett. 5, 126 (2007).

[6] Luís E. E. de Araujo, Phys. Rev. A 73, 053821 (2006).

[7] S. Hughes, Phys. Rev. Lett. 81, 3363 (1998).

[8] J. Xiao, Z. Wang, and Z. Xu, Phys. Rev. A 65, 031402 (2002).

[9] R. W. Ziolkowski, J. M. Arnold, and D. M. Gogny, Phys. Rev. A 52, 3082 (1995).

[10] Y. Loiko and C. Serrat, Phys. Rev. A 73, 063809 (2006).

[11] X. Song, S. Gong, R. Li, and X. Zhan, Phys. Rev. A 74, 015802 (2006).

[12] W. F. Yang, X. H. Song, S. Q. Gong, Y. Cheng, and X. Z. Zhan, Phys. Rev. Lett. 99, 133602 (2007).

[13] G. L. Lamb, Jr., Rev. Mod. Phys. 43, 99 (1971).

[14] R. Netz and T. Feurer, Phys. Rev. A 64, 043808 (2001).

[15] C. M. Bowden and J. P. Dowling, Phys. Rev. A 47, 1247 (1993).

[16] N. Wang and H. Rabitz, Phys. Rev. A 51, 5029 (1995).

[17] M. E. Crenshaw, K. U. Sullivan, and C. M. Bowden, Opt. Express 1, 152 (1997).

[18] O. G. Calderón, M. A. Antón, and F. Carreno, Eur. Phys. J. D 25, 77 (2003).

[19] R. S. Bennink, Y. Liu, D. D. Earl, and W. P. Grice, Phys. Rev. A 74, 023802 (2006).

[20] K. Xia, S. Gong, C. Liu, X. Song, and Y. Niu, Opt. Express 13, 5913 (2005).

[21] A. V. Tarasishin, S. A. Magnitskii, V. A. Shuvaev, and A. M. Zheltikov, Opt. Express 8, 452 (2001).

[22] R. J. P. Engelen, Y. Sugimot, Y. Watanabe, J. P. Korterik, N. Ikeda, N. F. van Hulst, K. Asakawa, and L. Kuipers, Opt. Express 14, 1658 (2006).

[23] S. L. McCall and E. L. Hahn, Phys. Rev. Lett. 18, 908 (1967).