[1] L. Chong, J. Ge, and J. Chen, Opt. Laser Technol, 39, 169 (2007).

[2] J. Chen, X. Wu, J. Ge, A. Hermerschmidt, and H. J. Eichler, Appl. Phys. Lett. 85, 525 (2004).

[3] X. Gao, Y. Zheng, H. Kan, and K. Shinoda, Opt. Lett. 29, 361 (2004).

[4] Z. Su, Q. Lou, J. Dong, J. Zhou, and R. Wei, Opt. Express 15, 11776-11780 (2007).

[5] W. A. Clarkson and D. C. Hanna, Opt. Lett. 21, 375 (1996).

[6] Z. Su, Q. Lou, J. Dong, J. Zhou, and R. Wei, Chin. Phys. Lett. 24, 2587 (2007).

[7] B. Liu, Y. Liu, and Y. Braiman, Opt. Express 16, 20935 (2008).

[8] P. Zhao, Q. Li, W. Guo, B. Liu, and T. Zuo, Chin. Opt. Lett. 5, 284 (2007).

[9] Q. Li, P. Zhao, and W. Guo, Appl. Phys. Lett. 89, 231120 (2006).

[10] B. Liu, Y. Liu, and Y. Braiman, Opt. Express 18, 7361 (2010).

[11] J. M. Verdell and R. Freyieee, IEEE J. Quantum Electron. 26, 270 (1990).

[12] M. Chi, N. S. Bogh, B. Thestrup, and P. M. Petersen, Appl. Phys. Lett. 85, 1107 (2004).

[13] M. Chi, B. Thestrup, and P. M. Petersen, Proc. SPIE 5336, 33 (2004).

[14] J. R. Leger, Appl. Phys. Lett. 55, 334 (1989).