Experimental Determination of the Landé g-Factors for 5s~2 ~1S and 5s5p ~3P States of the ~(87)Sr Atom

We present an experimental determination on the Lande g-factors for the 5 s~2 ~1 S_0 and 5 s5 p ~3 P_0 states in ultra-cold atomic systems, which is important for evaluating the Zeeman shift of the clock transition in the ~(87)Sr optical lattice clock. The Zeeman shift of the 5 s5 p ~3 P_0-5 s~2 ~1 S_0 forbidden transition is measured with the π-polarized andσ~±-polarized interrogations at different magnetic field strengths. Moreover, in the g-factor measurement with the σ~±-transition spectra, it is unnecessary to calibrate the external magnetic field. By this means, the ground state 5 s~2 ~1 S_0 g-factor for the ~(87)Sr atom is-1.306(52) ×10~(-4), which is the first experimental determination to the best of our knowledge, and the result matches very well with the theoretical estimation. The differential g-factorδg between the 5 s5 p~3 P_0 state and the 5 s~2 ~1 S_0 state of the ~(87)Sr atoms is measured in the experiment as well,which are-7.67(36) ×10~(-5) with π-transition spectra and-7.72(43) X 10-5 with σ~±-transition spectra, in good agreement with the previous report [Phys. Rev. A 76(2007) 022510]. This work can also be used for determining the differential g-factor of the clock states for the optical clocks based on other atoms.     

Speckle analysis in laser scanning display system

The theory of speckle formation in laser scanning display system is established based on the averaging effect of eye response as laser beam scanning through an eye resolution spot. It is analyzed that speckle reduction can be obtained by averaging states of speckle during scanning. The theoretical results show that a smaller correlation length of screen surface and the narrowing of laser beam in scanning direction can reduce speckle contrast for this system.     

基准原子钟的发展及国家授时中心光学原子钟的研制进展

本文简要介绍了基准原子钟的发展历程;目前,光学原子钟的频率不确定度已达到了10-18量级,是现在人们公认的最可能新的时间基准.国家授时中心担负着国家综合原子时的建立和保持,是国际原子时TAI建立的主要参加单位.文中介绍了国家授时中心锶光学原子钟研制工作的最新进展.     

利用飞行时间法测定锶原子5s5p3P1亚稳态能级寿命

本文结合TOF法和吸收光谱测量技术,利用连续光场测定了锶原子亚稳态能级的寿命。实验中,利用689nm激光连续泵浦基态锶原子至5s5p3P1亚稳态能级,然后在距泵浦区域不同距离处观测处于5s5p3P1态的原子对688nm探测光的吸收强度,得到锶原子5s5p3P1态的能级寿命,我们利用TOF法实验得到的能级寿命为21.9±0.8μs。本文给出的方法具备实验装置简单的优点,同时可获得较高的测量精度。     

锶玻色子的“魔术”波长光晶格装载实验研究

光晶格中性原子光钟的不确定度已达到10^-18量级. 本文介绍了碱土金属锶原子玻色子⁸⁸Sr在“魔术”波长处的一维光晶格装载, 实现冷锶原子的囚禁并使锶原子的钟跃迁能级(5s²) ¹S₀-(5s5p) ³P₀在此波长处的交流斯塔克光频移一致. 实验中半导体激光器产生“魔术”光波长(813 nm), 通过实验搭建光学驻波场并获得晶格激光聚焦光束, 束腰半径为38 μm. 经过一级冷却和二级冷却后温度约为2 μK的冷锶原子被此“魔术”波长光晶格囚禁. 通过实验测量得到锶原子玻色子⁸⁸Sr光晶格寿命为270 ms, 数目约为1.2×10⁵, 温度在3.5 μK左右, 此外研究了晶格光功率对晶格囚禁原子数目及温度的影响作用. 原子的光晶格装载为后续的钟跃迁提供了长的探测时间, 为进一步的光钟闭环提供了实验基础.     

Precision frequency measurement of ~1S_0–~3P_1 intercombination lines of Sr isotopes

We report on frequency measurement of the intercombination(5s2)1S0–(5s5p)3P1transition of the four natural isotopes of strontium,including88Sr(82.58%),87Sr(7.0%),86Sr(9.86%),and84Sr(0.56%).A narrow-linewidth laser that is locked to an ultra-low expansion(ULE)optical cavity with a finesse of 12000 is evaluated at a linewidth of 200 Hz with a fractional frequency drift of 2.8×10-13at an integration time of 1 s.The fluorescence collector and detector are specially designed,based on a thermal atomic beam.Using a double-pass acousto-optic modulator(AOM)combined with a fiber and laser power stabilization configuration to detune the laser frequency enables high signal-to-noise ratios and precision saturated spectra to be obtained for the six transition lines,which allows us to determine the transition frequency precisely.The optical frequency is measured using an optical frequency synthesizer referenced to an H maser.Both the statistical values and the final values,including the corrections and uncertainties,are derived for a comparison with the values given in other works.     

锶原子二级Doppler冷却及温度的测量

为了减小锶原子跃迁谱线的多普勒增宽及频移,需要对锶原子进行激光冷却以降低它的速度,而一级冷却只能将原子温度降低至mK量级,这样的原子其速度过大而无法有效地装载至光晶格中,因此必须进行二级冷却.锶原子存在单重态与三重态(5s2)1S0-(5s5p)3P1间互组跃迁,利用与其跃迁波长在689 nm的窄线宽激光对锶原子进一步冷却,可将锶原子团温度降低至μK量级.利用时序有效、准确地控制磁场和光场与原子相互作用时间,通过飞行时间法对锶冷原子温度进行了测算.实验中应用计算机精确控制磁光阱区域中冷原子团下落时间,EMCCD记录冷原子团初始时刻和下落20 ms后的状态.经过分析计算二级冷却温度为4.39 μK,不确定度仅为0.19 μK,二级冷原子团数目约为1.2×10 7.低温二级冷却锶原子温度及原子数目的获得为锶光钟跃迁信号的信噪比估计提供实验参考,也是实现高精度时间频率标准的前提.     

Theoretical calculation of the quadratic Zeeman shift coefficient of the 3P0o clock state for strontium optical lattice clock

In the weak-magnetic-field approximation, we derived an expression of quadratic Zeeman shift coefficient of $^3P^{\rm o}_0$ clock state for $^{88}$Sr and $^{87}$Sr atoms. By using this formula and the multi-configuration Dirac-Hartree-Fock theory, the quadratic Zeeman shift coefficients were calculated. The calculated values $C_2$ = $-23.38(5)$ MHz/T$^2$ for $^{88}$Sr and the $^3P^{\rm o}_0$, $F = 9/2$, $M_F = \pm9/2$ clock states for $^{87}$Sr agree well with the other available theoretical and experimental values, especially the most accurate measurement recently. In addition, the calculated values of the $^3P^{\rm o}_0$, $F = 9/2$, $M_F = \pm9/2$ clock states were also determined in our $^{87}$Sr optical lattice clock. The consistency with measurements verifies the validation of our calculation model. Our theory is also useful to evaluate the second-order Zeeman shift of the clock transition, for example, the new proposed $^1S_0$, $F = 9/2$, $M_F = \pm5/2$-${}^3P^{\rm o}_0$, $F = 9/2$, $M_F = \pm3/2$ transitions.     

锶原子光钟中repumping光频率锁定系统的研制

锶原子光钟里两束repumping光的频率对应锶原子三重态系跃迁(5s5p)3P0-(5s6s)3S1和(5s5p)3P2-(5s6s)3S1,由于其跃迁基态处于亚稳态,所以较难利用原子的跃迁线作为参考对这两台激光器进行锁频.本文介绍一种基于腔传递的数字伺服系统实现这两台半导体激光器任意频率的同时锁定.通过一台F-P腔将He-Ne激光器的频率高稳定性同时传递到两台受控激光器上.LabVIEW程序自动搜索激光透射峰信号从而得到误差信号,由比例积分算法得出控制电压,并反馈回激光器.可视化界面易于操作和观察,可直接完成对激光器的锁定,并自动记录实验结果.该方法使用方便,锁定后激光器频率波动为±4 MHz左右.该系统易扩展,可实现多台激光器的同时锁定.将锁定后的repumping光加入蓝MOT后,磁光阱内俘获的原子荧光强度增大了12倍,寿命提高了13倍,对于锶原子光钟一级冷却的研制有重要的应用价值.