[1] [1] M. Takamoto,F. Hong,R. Higashi et al.. An optical lattice clock [J]. Nature,2005,435:320-324

[2] [2] I. Coutillot,A. Quessada,R. P. Kovacich et al.. Design of a cold atom source for a neutral strontium optical frequency standard [C]. IEEE,2002. 220-221

[3] [3] C. Schwedes,E. Peik,J. Von Zanthier et al.. Narrow-bandwidth diode-laser-based blue and ultraviolet light source [J]. Appl. Phys. B,2003,76(2):143-147

[4] [4] A. D. Saenz. 461nm laser for studies in ultracold neutral strontium [D]. Houston:Rice University,2005. 54

[5] [5] R. Le Targat,J. J. Zondy,P. Lemonde. 75%-efficiency blue generation from an intracavity PPKTP frequency doubler [J]. Opt. Commun.,2005,247(4-6):471-481

[6] [6] Zang Erjun,Cao Jianping. Stable second harmonic generation using a monolithic ring laser and an external ring cavity [J]. Acta Optica Sinica,2003,23(3):335-340

[7] [7] Wang Xubao,Wu Qiang,Chen Jimin et al.. Study of beam quality and focus of frequency doubling in a KTP crystal on Nd∶YAG laser by the resonant external ring cavity [J]. Chinese J. Lasers,2004,31(10):1169-1172

[8] [8] Dong Jingxing,Lou Qihong,Cheng Xusan et al.. 480 nm blue laser by direct frequency doubling of laser diode [J]. Acta Optica Sinica,2006,26 (4):567-570

[9] [9] G. D. Boyd,D. A. Kleinman. Parametric interaction of focused Gaussian light beams [J]. Appl. Phys.,1968,39(8):3597-3639

[10] [10] Y. Kaneda,S. Kubota. Theoretical treatment,simulation,and experiments of doubly resonant sum-frequency mixing in an external resonator [J]. Appl. Opt.,1997,36(30):7766-7775

[11] [11] Y. Asakawa,H. Kumagai,K. Midorikawa et al.. 50% frequency doubling efficiency of 1.2-W cw Ti∶sapphire laser at 746 nm [J]. Opt. Commun.,2003,217(1):311-315

[12] [12] T. W. Hansch,B. Couillaud. Laser frequency stabilization by polarization specroscopy of a reflecting reference cavity[J]. Opt. Commun.,1980,35(3):441-444

[13] [13] H. R. Telle,D. Meschede,T. W. Hansch. Realization of a new concept for visible frequency division:phase locking of harmonic and sum frequencies [J]. Opt. Lett.,1990,15(10):532-534

[14] [14] A. Hemmerich,D. H. McIntyre,C. Zimmermann et al.. Second-harmonic generation and optical stabilization of a diode laser in an external ring resonator [J]. Opt. Lett.,1990,15(7):372-374

[15] [15] R. W. P. Drever,J. L. Hall,F. V. Kowalski et al.. Laser phase and frequency stabilization using an optical resonator [J]. Appl. Phys. B,1983,31(2):97-105