[1] V. Shah, S. Knappe, L. Hollberg, and J. Kitching, Opt. Lett. 32, 1244 (2007).

[2] L. Yi, X. Qi, W. Chen, D. Zhou, T. Zhou, X. Zhou, and X. Chen, Chin. Opt. Lett. 7, 36 (2009).

[3] Ch. Andreeva, Y. Dancheva, M. Taslakov, A. Markovski, P. Zubov, and S. Cartaleva, Spectroscopy Lett. 34, 395(2001).

[4] H. Yan, G. Yang, J. Wang, and M. Zhan, Chin. Opt. Lett. 6, 307 (2008).

[5] M. D. Levenson and S. Kano, Introduction to Nonlinear Laser Spectroscopy (Academic Press, Boston, 1988).

[6] M. Tetu, N. Cyr, B. Villeneuve, S. Theriault, M. Breton, and P. Tremblay, IEEE Trans. Instrum. Meas. 40, 191(1991).

[7] J. Ye, S. Swartz, P. Jungner, and J. L. Hall, Opt. Lett. 21, 1280 (1996).

[8] M. H. Anderson, J. R. Ensher, M. R. Matthews, C. E. Wieman, and E. A. Cornell, Science 269, 198 (1995).

[9] Y. Lin, W. Chen, T. Li, P. Lin, P. Wang, and N. Liu, Chinese J. Lasers (in Chinese) 36, 1075 (2009).

[10] Y. Wang, Principle of Quantum Frequency Standards (in Chinese) (Science Press, Beijing, 1986).

[11] F. Riehle, Frequency Standards:Basics and Applications (Wliey, Weinheim, 2005).