锶光晶格钟一级冷却的实现
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摘要
光钟是目前公认的最具有发展潜力的原子钟,理论上预期光钟的频率不确定度可达10-18,有望成为国际新一代时间频率基准。基于囚禁中性原子的光晶格钟具有更多的原子数目,有利于提高原子谱线的信噪比,且由于使用“魔术”波长来构成光晶格,能使得原子钟跃迁的基态和激发态的Stark频移相同,最终使原子钟跃迁频率保持精确不变。
在光钟的研制中,对于冷原子样品的制备很关键,由于稳频激光最终要锁定至原子跃迁谱线上,因此它的谱线质量要非常好,也即要求我们冷却的原子样品温度尽量低且数目足够多,最终对钟整体性能起到很大提高作用。
本文介绍了以碱土金属锶作为光钟冷原子样品的实验研究,对于锶原子的冷却分为两级,一级冷却利用偶极跃迁(5s2)1S0—(5s5p)1P1 ,对应辐射波长461nm,二级冷却使用(5s2)1S0—(5s5p) 3P1能级跃迁,对应辐射波长689nm。目前已完成锶冷原子样品的一级冷却实验,即Blue MOT,正在进行二级冷却的实验准备工作。具体地,文章先主要介绍了用于一级冷却的实验装置,包括锶原子束源的产生装置、实验用多台激光器、塞曼减速磁场线圈及反向赫姆霍兹磁场线圈等,然后在此实验装置的基础上实现了对锶原子的冷却和俘获,利用荧光收集法对冷原子数目进行测量,然后分别采用飞行时间法和原子云膨胀法对冷原子温度进行测量,最后简要介绍了用于二级冷却实验的689nm半导体激光光源的稳频、线宽压窄以及相关时序控制系统的重要性。
Optical clock is the most promising atomic clock and its uncertainty will reach to 10?1 8 theoretically, which could be the time and frequency standard of the next generation. Optical clock based on the trapping neutral atoms has a large number of atoms which is useful to improve the Signal-to Noise of the atomic spectroscopy. Besides, the lattice composed by“magic wave”can make the ground state and the excited state of atomic clock transition have the same Stark frequency shift. And then the frequency of atomic clock transition can be unchanged ultimately.
It is very important to obtain the cold atomic samples in the optical clock. The stabilized laser will be locked to the atomic spectroscopy ultimately, so this spectroscopy is required to be good. That is to say, the number of those cooled atoms can be as more as possible and the temperature can be as low as possible. Finally it has played a significant role in raising the performance of the clock.
In this paper, the experiment research of alkaline-earth metals Strontium(Sr) as the cold atomic sample in optical clock is reported. It has two stages to cool Sr atoms. The dipolar energy-level transition (5s2)1S0—(5s5p)1P1 whose corresponding wave-length is 461nm is used for the first-stage cooling. The transition (5s2)1S0—(5s5p)3P1 whose corresponding wave-length is 689nm is used for the second-stage cooling. We have finished the first-stage cooling of Sr atomic samples, Blue MOT in our laboratory at present. And we prepare the second-stage cooling of Strontium. Concretely, the experiment setup for the first-stage cooling of Sr is represented firstly in this paper, including the equipment of producing thermal atomic beam、lasers、Zeeman slower、Anti-Helmholtz coils for the optical-magnetic trap(MOT) et al. Based on those equipments, the first-stage cooling of Sr is realized. And then its number is measured experimentally using the method of collected fluorescence. The temperature of the cold atoms is measured using the ways of time of flight and expansion measurement. Finally, stabilizing the frequency and narrowing the line-width of 689nm laser used for the second-stage cooling is introduced. And the importance of the time controlling system about red MOT is presented briefly.
在光钟的研制中,对于冷原子样品的制备很关键,由于稳频激光最终要锁定至原子跃迁谱线上,因此它的谱线质量要非常好,也即要求我们冷却的原子样品温度尽量低且数目足够多,最终对钟整体性能起到很大提高作用。
本文介绍了以碱土金属锶作为光钟冷原子样品的实验研究,对于锶原子的冷却分为两级,一级冷却利用偶极跃迁(5s2)1S0—(5s5p)1P1 ,对应辐射波长461nm,二级冷却使用(5s2)1S0—(5s5p) 3P1能级跃迁,对应辐射波长689nm。目前已完成锶冷原子样品的一级冷却实验,即Blue MOT,正在进行二级冷却的实验准备工作。具体地,文章先主要介绍了用于一级冷却的实验装置,包括锶原子束源的产生装置、实验用多台激光器、塞曼减速磁场线圈及反向赫姆霍兹磁场线圈等,然后在此实验装置的基础上实现了对锶原子的冷却和俘获,利用荧光收集法对冷原子数目进行测量,然后分别采用飞行时间法和原子云膨胀法对冷原子温度进行测量,最后简要介绍了用于二级冷却实验的689nm半导体激光光源的稳频、线宽压窄以及相关时序控制系统的重要性。
Optical clock is the most promising atomic clock and its uncertainty will reach to 10?1 8 theoretically, which could be the time and frequency standard of the next generation. Optical clock based on the trapping neutral atoms has a large number of atoms which is useful to improve the Signal-to Noise of the atomic spectroscopy. Besides, the lattice composed by“magic wave”can make the ground state and the excited state of atomic clock transition have the same Stark frequency shift. And then the frequency of atomic clock transition can be unchanged ultimately.
It is very important to obtain the cold atomic samples in the optical clock. The stabilized laser will be locked to the atomic spectroscopy ultimately, so this spectroscopy is required to be good. That is to say, the number of those cooled atoms can be as more as possible and the temperature can be as low as possible. Finally it has played a significant role in raising the performance of the clock.
In this paper, the experiment research of alkaline-earth metals Strontium(Sr) as the cold atomic sample in optical clock is reported. It has two stages to cool Sr atoms. The dipolar energy-level transition (5s2)1S0—(5s5p)1P1 whose corresponding wave-length is 461nm is used for the first-stage cooling. The transition (5s2)1S0—(5s5p)3P1 whose corresponding wave-length is 689nm is used for the second-stage cooling. We have finished the first-stage cooling of Sr atomic samples, Blue MOT in our laboratory at present. And we prepare the second-stage cooling of Strontium. Concretely, the experiment setup for the first-stage cooling of Sr is represented firstly in this paper, including the equipment of producing thermal atomic beam、lasers、Zeeman slower、Anti-Helmholtz coils for the optical-magnetic trap(MOT) et al. Based on those equipments, the first-stage cooling of Sr is realized. And then its number is measured experimentally using the method of collected fluorescence. The temperature of the cold atoms is measured using the ways of time of flight and expansion measurement. Finally, stabilizing the frequency and narrowing the line-width of 689nm laser used for the second-stage cooling is introduced. And the importance of the time controlling system about red MOT is presented briefly.
引文
[1] Norman F. Ramsey. A molecular beam resonance method with separated oscillating fields [J]. Phys.Rev.Lett, 1950,78: 695
[2]王义遒.斜光检测激光抽运铯原子束频率标准[J].物理, Vol23(2) :77
[3]翟造成,杨佩红.原子钟的发明与我国原子钟发展简述[C]. 2009年全国时间频率学术会议, 2009:1
[4]王义遒.原子的激光冷却与陷俘[M].北京:北京大学出版社,2007. 336 ~350
[5] Forman P. Proc. IEEE., 1985, 73: 1181
[6] S.Chu, L.Hollberg, J.E Bjorkholm, et al. Three-dimensional viscous confinement and cooling of atoms by resonance radiation pressure [J]. Phys.Rev.Lett, 1985,55:48
[7] Mark A. Kasevich, Erling Riis, and Steven Chu et al. Rf spectroscopy in an atomic fountain [J]. Phys.Rev.Lett, 1989, 63:612
[8] A.Clairon et al. Quantum projection noise in an atomic fountain: a high stability Cs frequency standard [C]. Proceedings of the 5th symposium on frequency standard and metrology, J.C.Berguist Ed (World scientific, London, 1965):49
[9] Arnaud Lecallier, Yann Le Coq, Giovanni Rovera, et al. Accuracy Evaluation of an Optical Lattice Clock with Bosonic Atoms [J]. Optics Letters, 2007.1:1-18.
[10] Masao Takamoto, Feng-Lei Hong, Ryoichi Higashi, et al. An optical lattice clock [J]. Nature, 2005, 435: 321
[11]王义遒.原子钟及其进展[J].物理教学,2003,25(4): 2
[12] S.A.Diddams, Jones D, Ye J, et al. Direct link between microwave and optical frequencies with a 300 thz femtosecond laser comb [J]. Phys.Rev.Lett, 2000, 84:5102
[13]马龙生.光钟[J].物理,2008,37(10) : 716
[14]王育竹.激光冷却以及在科学技术中的应用[J].物理学进展,2005,25(4):347
[15] Xavier Baillard, Mathilde Fouch′e*, Rodolphe Le Targat et al. Accuracy Evaluation of an Optical Lattice Clock with Bosonic Atoms [J]. Optical Letters, 2007, 32(13):1812
[16]费立刚,朱均,张书练.光学频率标准与光钟的实现[J].光学与光电技术,2006,4(66):55
[17] Oskay W H, Itano W M, Berguist J C. Measurement of the 199Hg+ 5d9+6s22D5/2 electric quadrupole moment and a constraint on the quadrupoleshift [J]. Phys.Rev.Lett, 2005,94:1
[18]Neuhauser W, Hohenstatt M, Toschek P E. Localized visible Ba+ mono-ion oscillator [J]. Phys.Rev.Lett, 1980,22 :1137
[19] A.D.Ludlow , T.Zelevinsky, G.K.Campbell et al . Sr Lattice Clock at 1×10-16 Fractional Uncertainty by Remote Optical Evaluation with a Ca Clock [J]. Science, 2008, 319(5871): 1805
[20] Drever R W et al Laser phase and frequency stablization using an optical resonator [J]. Appl Phys B,1983,31:97
[21] Everson X M et al. Appl Phys Lett,1973,22:192
[22]高克林.离子光频标的研究进展和空间应用展望[J].物理, 2008,37(10):720
[23]翟造成,杨佩红.新型原子钟及其在我国的发展[C].激光与光电子学进展, 2009,3:21
[24] Katori H. // Gill P.ed. Proc. 6th symp. freq. standards & metrology. Singapore: World
[25] Martin M. Boyd. High Precision Spectroscopy of Strontium in an Optical Lattice: Toward a New Standard for Frequency and Time [D]. B.S., University of Washington, 2002, 23
[26] Takamoto M, Katori H. Spectroscopy of the (5s2)1S0—(5s5p) 3P0 clock transition of Sr 87 in an optical lattice [J]. Phys.Rev.Lett,2003,91:22300
[1] F.Sorrentino, G.Ferrari, N.Poli, R.Drullinger and G.M.Tino. Laser Cooling and Trapping of Atomic Strontium for Ultra-cold Atoms Physics, High-Precision Spectroscopy and Quantum Sensors [J]. Modern Physics Letters B, 2006, 20(21): 1287
[2]周炳昆,高以智,陈家骅等.激光原理[M].国防工业出版社, 1995
[3] Rabb E L , Prentiss M , Cable A et al . Trapping of neutral sodium atoms with radiation pressure [J]. Phys. Rev .Lett . , 1987, 59 (23) :2631
[4] T. Hansch, A. Schawlow, Cooling of gases by laser radiation [J]. Opt.Commun., 1975, 13(1): 68
[6] Letokhov V S, Minogin V G, Pavlik B D, Opt. Commun., 1976, 19: 72.
[7] Wolfgang Ketterle, Alex Martin, Michael A. Joffe, and David E. Pritchard et al., Slowing and cooling atoms in isotropic laser light [J]. Phys. Rev.Lett., 1992, 69: 2483
[8] Barelaan H, Padua S, Yang D H, et al. Slowing of 85Rb atoms with isotropic light [J]. Phys. Rev. A, 1994, 49: 2780
[9] M. Zhu, C. W. Oates, J. S Hall. Continuous high-flux monovelocity atomic beam based on a broadband laser-cooling technique [J]. Phys. Rev. Lett., 1991, 67:46
[10] W. D. Phillips, H. Metcalf. Laser deceleration of an atomic beam [J]. Phys. Rev. Lett., 1982, 48: 596
[11] Ovchinnikov Y B. A Zeeman slower based on magnetic dipoles [J]. Opt.Comm. 2007, 276: 261
[12] Monroe C, Swann W, Robinson H , Wieman C. Very cold trapped atoms in a vapor cell [J] Phys . Rev. Lett . 1990 65:1571
[13] Stean A M, Chowdhury M, Foot .C J. Radiation force in the magneto-optical trap [J] . Opt . Soc. Am. B 1992 9: 2142
[14] Lindquist K, Stephens M, Wieman C. Experimental and theoretical study of the vapor-cell Zeeman optical trap [J] Phys . Rev. A, 1992, 46: 4082
[15]张礼.近代物理学进展[M].北京:清华大学出版社,第一版,1997.
[16] Metcalf Berfeman, Erez. Magnetostatic trapping fileds for neutral atoms [J]. Phys . Rev.A , 1987,35: 1535
[17]闫树斌.用于腔量子电动力学实验的铯原子双磁光阱及其冷原子输运研究,山西大学博士论文,2006.
[1] T. Day, F. Luecke, and M. Brownell. Continuously tunable diode lasers[J]. Lasers and Optronics.1993,6:15
[2] Helen K. Holt Theory of Laser Saturation Spectroscopy [J] Phys.Rev.Lett 29:1138~1140
[3]王启明.半导体激光器的进展(1)(2). [M].物理.1996,25~140.
[4]陈扬懿,杨晓华.激光光谱测量技术.[M].华东师范大学出版社,2006年第一版:140~143.
[5]吴慧,赵亚楠,常宏,张首刚.偏振光激发的Sr原子电偶极辐射[J].量子光学学报,15(3):248
[6]赵凯华,陈熙谋.电磁学上册[M]高等教育出版社1985年第二版
[7]王心亮.用于87Sr冷原子光晶格钟原子冷却装置的塞曼减速器研究[D].西安:西北大学,2008:23~32
[8]杨福家.原子物理学[M].北京:高等教育出版社,1999. 390~395
[1]王军民.铯原子汽室磁光阱装置的建立及激光冷却与俘获铯原子的实验研究[D].太原:山西大学光电研究所,,1999:95
[2]田晓,王心亮,常宏等利用塞曼减速法实现锶同位素的磁光阱俘获[J],光学学报2010,30(3):898
[3] Chu S, Hollberg L, Bjorkholm J E, et al. Three-dimensional viscous confinement and cooling of atoms by resonance radiation pressure [J] Phys. Rev. Lett. 1985,55: 48
[4] Lett P D, Watts R N, Westbrook C I, et al Observation of Atoms Laser Cooled below the Doppler Limit [J] Phys. Rev. Lett . 1988, 61:169
[5]陈帅. 87Rb原子玻色-爱因斯坦凝聚实验研究北京:北京大学物理学院2004:90
[6] Tomasz M Brzozowski, Maria Maczynska, Michal Zawada, et al. Time-of-flight measurement of the temperature of cold atoms for short trap-probe beam distances [J] J.Opt.B, 2002,4:62
[7] Xinye Xu, Thomas H.Loftus, Matthew J.Smith et al. Dynamics in a two-level atom magnetic-optical trap[J]. Phys. Rev.A. 2002,66: 011401
[1] Day T, Gustafson E K, BER R L, et al. Sub-hertz relative frequency stabilization of two-diode laser-pumpde Nd:YAG lasers locked to a fabry-perot interferometer [J]. IEEE J Quantum Elect, 1992,28(4):1106
[2] Hyodo M, Carty T, Sakai K. Near shot-noise-level relative frequency stabilization of a laser-diode-pumped Nd:YVO4 microchip laser [J]. Appl Opt,1996,35(24):4749
[3] Musha M, Kanaya T, Nakagawa K, et al. The short-and long-term frequency stabilization of an injection-locked Nd:YAG laser in reference to a Fabry-Perot cavity and an iodine saturated absorption line [J]. Opt Commun,2000, 183(1/9):165
[2]王义遒.斜光检测激光抽运铯原子束频率标准[J].物理, Vol23(2) :77
[3]翟造成,杨佩红.原子钟的发明与我国原子钟发展简述[C]. 2009年全国时间频率学术会议, 2009:1
[4]王义遒.原子的激光冷却与陷俘[M].北京:北京大学出版社,2007. 336 ~350
[5] Forman P. Proc. IEEE., 1985, 73: 1181
[6] S.Chu, L.Hollberg, J.E Bjorkholm, et al. Three-dimensional viscous confinement and cooling of atoms by resonance radiation pressure [J]. Phys.Rev.Lett, 1985,55:48
[7] Mark A. Kasevich, Erling Riis, and Steven Chu et al. Rf spectroscopy in an atomic fountain [J]. Phys.Rev.Lett, 1989, 63:612
[8] A.Clairon et al. Quantum projection noise in an atomic fountain: a high stability Cs frequency standard [C]. Proceedings of the 5th symposium on frequency standard and metrology, J.C.Berguist Ed (World scientific, London, 1965):49
[9] Arnaud Lecallier, Yann Le Coq, Giovanni Rovera, et al. Accuracy Evaluation of an Optical Lattice Clock with Bosonic Atoms [J]. Optics Letters, 2007.1:1-18.
[10] Masao Takamoto, Feng-Lei Hong, Ryoichi Higashi, et al. An optical lattice clock [J]. Nature, 2005, 435: 321
[11]王义遒.原子钟及其进展[J].物理教学,2003,25(4): 2
[12] S.A.Diddams, Jones D, Ye J, et al. Direct link between microwave and optical frequencies with a 300 thz femtosecond laser comb [J]. Phys.Rev.Lett, 2000, 84:5102
[13]马龙生.光钟[J].物理,2008,37(10) : 716
[14]王育竹.激光冷却以及在科学技术中的应用[J].物理学进展,2005,25(4):347
[15] Xavier Baillard, Mathilde Fouch′e*, Rodolphe Le Targat et al. Accuracy Evaluation of an Optical Lattice Clock with Bosonic Atoms [J]. Optical Letters, 2007, 32(13):1812
[16]费立刚,朱均,张书练.光学频率标准与光钟的实现[J].光学与光电技术,2006,4(66):55
[17] Oskay W H, Itano W M, Berguist J C. Measurement of the 199Hg+ 5d9+6s22D5/2 electric quadrupole moment and a constraint on the quadrupoleshift [J]. Phys.Rev.Lett, 2005,94:1
[18]Neuhauser W, Hohenstatt M, Toschek P E. Localized visible Ba+ mono-ion oscillator [J]. Phys.Rev.Lett, 1980,22 :1137
[19] A.D.Ludlow , T.Zelevinsky, G.K.Campbell et al . Sr Lattice Clock at 1×10-16 Fractional Uncertainty by Remote Optical Evaluation with a Ca Clock [J]. Science, 2008, 319(5871): 1805
[20] Drever R W et al Laser phase and frequency stablization using an optical resonator [J]. Appl Phys B,1983,31:97
[21] Everson X M et al. Appl Phys Lett,1973,22:192
[22]高克林.离子光频标的研究进展和空间应用展望[J].物理, 2008,37(10):720
[23]翟造成,杨佩红.新型原子钟及其在我国的发展[C].激光与光电子学进展, 2009,3:21
[24] Katori H. // Gill P.ed. Proc. 6th symp. freq. standards & metrology. Singapore: World
[25] Martin M. Boyd. High Precision Spectroscopy of Strontium in an Optical Lattice: Toward a New Standard for Frequency and Time [D]. B.S., University of Washington, 2002, 23
[26] Takamoto M, Katori H. Spectroscopy of the (5s2)1S0—(5s5p) 3P0 clock transition of Sr 87 in an optical lattice [J]. Phys.Rev.Lett,2003,91:22300
[1] F.Sorrentino, G.Ferrari, N.Poli, R.Drullinger and G.M.Tino. Laser Cooling and Trapping of Atomic Strontium for Ultra-cold Atoms Physics, High-Precision Spectroscopy and Quantum Sensors [J]. Modern Physics Letters B, 2006, 20(21): 1287
[2]周炳昆,高以智,陈家骅等.激光原理[M].国防工业出版社, 1995
[3] Rabb E L , Prentiss M , Cable A et al . Trapping of neutral sodium atoms with radiation pressure [J]. Phys. Rev .Lett . , 1987, 59 (23) :2631
[4] T. Hansch, A. Schawlow, Cooling of gases by laser radiation [J]. Opt.Commun., 1975, 13(1): 68
[6] Letokhov V S, Minogin V G, Pavlik B D, Opt. Commun., 1976, 19: 72.
[7] Wolfgang Ketterle, Alex Martin, Michael A. Joffe, and David E. Pritchard et al., Slowing and cooling atoms in isotropic laser light [J]. Phys. Rev.Lett., 1992, 69: 2483
[8] Barelaan H, Padua S, Yang D H, et al. Slowing of 85Rb atoms with isotropic light [J]. Phys. Rev. A, 1994, 49: 2780
[9] M. Zhu, C. W. Oates, J. S Hall. Continuous high-flux monovelocity atomic beam based on a broadband laser-cooling technique [J]. Phys. Rev. Lett., 1991, 67:46
[10] W. D. Phillips, H. Metcalf. Laser deceleration of an atomic beam [J]. Phys. Rev. Lett., 1982, 48: 596
[11] Ovchinnikov Y B. A Zeeman slower based on magnetic dipoles [J]. Opt.Comm. 2007, 276: 261
[12] Monroe C, Swann W, Robinson H , Wieman C. Very cold trapped atoms in a vapor cell [J] Phys . Rev. Lett . 1990 65:1571
[13] Stean A M, Chowdhury M, Foot .C J. Radiation force in the magneto-optical trap [J] . Opt . Soc. Am. B 1992 9: 2142
[14] Lindquist K, Stephens M, Wieman C. Experimental and theoretical study of the vapor-cell Zeeman optical trap [J] Phys . Rev. A, 1992, 46: 4082
[15]张礼.近代物理学进展[M].北京:清华大学出版社,第一版,1997.
[16] Metcalf Berfeman, Erez. Magnetostatic trapping fileds for neutral atoms [J]. Phys . Rev.A , 1987,35: 1535
[17]闫树斌.用于腔量子电动力学实验的铯原子双磁光阱及其冷原子输运研究,山西大学博士论文,2006.
[1] T. Day, F. Luecke, and M. Brownell. Continuously tunable diode lasers[J]. Lasers and Optronics.1993,6:15
[2] Helen K. Holt Theory of Laser Saturation Spectroscopy [J] Phys.Rev.Lett 29:1138~1140
[3]王启明.半导体激光器的进展(1)(2). [M].物理.1996,25~140.
[4]陈扬懿,杨晓华.激光光谱测量技术.[M].华东师范大学出版社,2006年第一版:140~143.
[5]吴慧,赵亚楠,常宏,张首刚.偏振光激发的Sr原子电偶极辐射[J].量子光学学报,15(3):248
[6]赵凯华,陈熙谋.电磁学上册[M]高等教育出版社1985年第二版
[7]王心亮.用于87Sr冷原子光晶格钟原子冷却装置的塞曼减速器研究[D].西安:西北大学,2008:23~32
[8]杨福家.原子物理学[M].北京:高等教育出版社,1999. 390~395
[1]王军民.铯原子汽室磁光阱装置的建立及激光冷却与俘获铯原子的实验研究[D].太原:山西大学光电研究所,,1999:95
[2]田晓,王心亮,常宏等利用塞曼减速法实现锶同位素的磁光阱俘获[J],光学学报2010,30(3):898
[3] Chu S, Hollberg L, Bjorkholm J E, et al. Three-dimensional viscous confinement and cooling of atoms by resonance radiation pressure [J] Phys. Rev. Lett. 1985,55: 48
[4] Lett P D, Watts R N, Westbrook C I, et al Observation of Atoms Laser Cooled below the Doppler Limit [J] Phys. Rev. Lett . 1988, 61:169
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