[1] Y. Wang and Z. Jiang, Chin. Opt. Lett. 4, 141 (2006).
[2] J. Liao, H. Meng, H. Wang, B. Guan, Y. Zhou, Q. Zhang, and W. He, Chinese J. Lasers (in Chinese) 34, 135 (2007).
[3] F. Zhang, C. Wang, Z. Tong, T. Ning, and S. Jian, Chinese J. Lasers (in Chinese) 34, 470 (2007).
[4] L. Shang, Z. Song, and Q. Mao, Chinese J. Lasers (in Chinese) 34, 755 (2007).
[5] C. Wang, F. Zhang, Z. Tong, T. Ning, and S. Jian, Chinese J. Lasers (in Chinese) 35, 61 (2008).
[6] S. Liu, Y. Li, Y. Gao, L. Ding, H. Wang, S. Chen, and K. Lü, Acta Opt. Sin. (in Chinese) 27, 1663 (2007).
[7] J. Chen, Z. Sui, F. Chen, Z. Liu, M. Li, J. Wang, and Y. Luo, Chinese J. Lasers (in Chinese) 33, 298 (2006).
[8] Y. Jeong, J. K. Sahu, D. N. Payne, and J. Nilsson, Opt. Express 12, 6088 (2004).
[9] V. Gapontsev, D. Gapontsev, N. Platonov, O. Shkurikhin, V. Fomin, A. Mashkin, M. Abramov, and S. Ferin, in Proceedings of 2005 Conference on Lasers and Electro-Optics Europe 508 (2005).
[10] S. Norman, M. Zervas, A. Appleyard, P. Skull, D. Walker, P. Turner, and I. Crowe, Proc. SPIE 6102, 61021P (2006).