[1] L. J. Guo, X. Cheng, and C. Y. Chao, J. Mod. Opt. 49, 663 (2002).
[2] S. Baudach, J. Bonse, J. Kruger, and W. Kautek, Appl. Surf. Sci. 154, 555 (2000).
[3] X. C. Ni and C.-Y. Wang, Laser & Optronics Progress (in Chinese) 39 (12), 4 (2002).
[4] M. Will, S. Nolte, and A. Tuennermann, CLEO Technical Digest 127, (2002).
[5] X. C. Ni, C.-Y. Wang, Z. Wang, M. L. Hu, Y. F. Li, and L. Chai, Chin. Opt. Lett. 1, 429 (2003).
[6] J. Sun, R. Zhang, Q. Wang, L. Chai, D. Pang, J. Dai, Z. Zhang, K. Torzuka, T. Nakagawa, and T. Sugaya, Appl. Opt. 40, 3539 (2001).
