[1] [1] Y. F. Chen, Optics Letters 29, 1915 (2004).

[2] [2] S. Z. Fan, X. Y. Zhang, Q. P. Wang, J. Z. Liu, L. Li, Z. H. Cong, X. H. Chen and X. L. Zhang, Optics Communications 284, 1642 (2011).

[3] [3] A. J. Lee, H. M. Pask, P. Dekker and J. A. Piper, Optics Express 16, 21958 (2008).

[4] [4] Z. C. Wang, C. L. Du, S. C. Ruan and L. Zhang, Optics & Laser Technology 42, 716 (2010).

[5] [5] S. Ding, M. Wang, S. Wang and W. Zhang, Optics Express 11, 13052 (2013).

[6] [6] Z. G. Wu, Z. H. Cong, X. H. Chen, X. Y. Zhang, P. Q. Wang, W. X. Lan and Y. G. Zhang, Optics & Laser Technology 54, 137 (2013).

[7] [7] M. Q. Wang, S. H. Ding, W. Y. Yu and W H Zhang, Laser Physics Letters 10, 045403 (2013).

[8] [8] J. Y. Peng, Y. Zheng, Y. X. Shi and J. P. Shen, Optics & Laser Technology 7, 2175 (2012).

[9] [9] Y. F. Chen, Optics Letters 29, 2632 (2004).

[10] [10] W. Tian, C. Wang, G. Wang, S. Liu and J. Liu, Laser Physics Letters 4, 196 (2007).

[11] [11] Y. G. Zhao, Z. W. Wang, H. H. Yu and X. G. Xu, IEEE Photonics Journal 4, 2285 (2012).

[12] [12] M. Maier, W. Kaiser and J. A. Giordmaine, Physical review letters 26, 1275 (1966).

[13] [13] Y. F. Chen, M. L. Ku, L. Y. Tsai and Y. C. Chen, Optics Letters 19, 2279 (2004).

[14] [14] T. T. Basiev, S. V. Vassiliev, V. A. Konjushkin, V. V. Osiko, A. I. Zagumennyi, Y. D. Zavartsev and I. A. Shcherbakov, Laser Physics Letters 5, 237 (2004).

[15] [15] Y. T. Chang, H. L. Chang, K. W. Su and Y. F. Chen, Optics Express 14, 11892 (2009).

[16] [16] J. A. Morris and C. R. Pollock, Optics Letters 8, 440 (1990).