[1] Kominis K et al 2003 Nature 422 596

[2] Robbes D 2006 Sensors and Actuators A 129 86

[3] Budker D et al 1998 Phys. Rev. Lett. 81 5788

[4] Budker D et al 2000 Phys. Rev. A 62 043403

[5] Budker D et al 2002 Phys. Rev. A 65 055403

[6] Arimondo E 1996 Prog. Opt. 35 257

[7] Scully M O and Fleischhauer M 1992 Phys. Rev. Lett. 69
1360

[8] Fleischhauer M and Scully M O 1994 Phys. Rev. A 49 1973

[9]Hwang Lee, Fleischhauer M and Scully M O 1998 Phys. Rev. A
58 2587

[10] Schwindt P D D et al 2004 Appl. Phys. Lett. 85 6409

[11] Knappe S et al 2006 J. Opt. A: Pure Appl. Opt. 8 S318

[12] Xia H et al 2006 Appl. Phys. Lett. 89 211104

[13] Farthing W H and Folz W C 1967 Rev. Sci. Instrum. 38
1023

[14] Vanier J 2005 Appl. Phys. B 81 421

[15] Du R C et al 2008 Spectroscopy and Spectral Analysis
(accepted) (in Chinese)

[16] Bevilacqua G et al 2005 Phys. Rev. Lett. 95 123601

[17] Merimaa M et al 2003 J. Opt. Soc. Am. B 20 273

[18] DENG J L et al 2006 Chin. Phys. Lett. 23 1745

[19] Knappe S et al 2004 Appl. Phys. Lett. 85 1460

[20] Lutwak R et al 2005 The MAC-A Miniature Atomic Clock, 37th
annual Precise Time and Time Interval $($PTTI$)$ Meeting (Vancouver, BC,
Canada) p 752

[21] Vanier J and Audoin C 1989 The Quantum Physics of Atomic
Frequency Standards (Bristol: IOP Publishing) p 37

[22] Levi F et al 2000 Eur. Phys. J. D 12 53