[1] K. Bi, X. Xu, L. Xi, S. Zeng, and Q. Luo, Chin. Opt. Lett. 6, 893 (2008).

[2] A. Hengerer, A. Wunder, D. J. Wagenaar, A. H. Vija, M. Shah, and J. Grimm, Proc. IEEE 93, 819 (2005).

[3] G. Wang, Y. Li, and M. Jiang, Med. Phys. 31, 2289 (2004).

[4] W. Cong, G. Wang, D. Kumar, Y. Liu, M. Jiang, L. V. Wang, E. A. Hoffman, G. McLennan, P. B. McCray, J. Zabner, and A. Cong, Opt. Express 13, 6756 (2005).

[5] Y. Lv, J. Tian, W. Cong, G. Wang, J. Luo, W. Yang, and H. Li, Opt. Express 14, 8211 (2006).

[6] L. V. Wang and H. Wu, Biomedical Optics: Principles and Imaging (Wiley, New Jersey, 2007) pp.83-118.

[7] Q. Zhang, L. Yin, Y. Tan, Z. Yuan, and H. Jiang, Opt. Express 16, 1481 (2008).

[8] H. Niu, P. Guo, X. Song, and T. Jiang, Chin. Opt. Lett. 6, 886 (2008).

[9] M. Wang and M. Shao, The Basic Principle and Numerical Methods of Finite Element Method (in Chinese) (Tsinghua University Press, Beijing, 1997) pp.12-20.

[10] J. Lu and Z. Guan, The Numerical Solution of Partial Differential Equations (2nd edn.) (in Chinese) (Tsinghua University Press, Beijing, 2004) pp.187-210.

[11] Z. Zhu, Q. Zhou, and J. Yin, Theoretical Mechanics (in Chinese) (Peking University Press, Beijing, 1997) pp.18-23.