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介绍了喷泉频标的原理与发展.喷泉频标是一项近20年来发展起来的原子钟技术,它以激光冷却技术为基础,利用该技术实现了冷原子介质的俘获与上抛.冷原子介质在上抛下落过程中首先完成原子态制备,然后两次通过微波谐振腔实现Ramsey作用,在两次作用之间原子经历自由演化,最后原子经过探测区,通过双能级荧光探测法探测原子跃迁概率得到鉴频的Ramsey干涉条纹,并实现频率锁定,其中心条纹的线宽在1Hz左右.频率稳定度和频率不确定度是喷泉频标的两个重要指标.影响喷泉钟频率稳定度的因素主要有量子投影噪声和电子学噪声,目前喷泉钟的短期稳定度为(10~(-13)—10~(-14))τ~(-1/2),长期稳定度在(10~(-16)—10~(-17))量级.喷泉频标的频率不确定度主要受二阶塞曼频移、黑体辐射频移、冷原子碰撞频移以及与微波相关的频移等的影响.目前喷泉钟的不确定度在小的10~(-16)量级.作为基准频标,喷泉钟的工作介质主要是~(133)Cs,~(87)Rb.国际各大计量机构都研制了喷泉频标,它在各地协调世界时的建立、国际原子时的校准等方面发挥着越来越重要的作用.此外,喷泉频标还用于研究高精度时频基准和时间比对链路、验证基本物理理论等. 相似文献
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中国计量科学研究院实现74cm高的冷原子喷泉 总被引:1,自引:0,他引:1
用磁光阱和光学粘胶方法制备超冷原子样品 ,把原子冷却到绝对零度附近 (~ 10 - 6 K) ,随后赋予其一定的向上运动速度 (例如几米 /秒 ) ,让原子只在重力场作用下作弹道运动飞行 ,便形成冷原子喷泉———原子上升到一最高点然后散落下来 .这种原子喷泉首先在改进原子钟性能上获得重要应用 :在原子弹道飞行的路径上设置微波谐振腔 ,应用冷原子与微波辐射场相互作用产生的谐振信号 ,将使原子钟的准确度至少提高一个数量级 .1995年以来 ,法国、美国和德国相继研制成功铯原子喷泉钟 ,现在达到的频率不确定度约为 2× 10 - 15,相当于走时两千万年… 相似文献
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文章介绍了半个多世纪以来北京大学在原子钟与相关物理学研究方面的简况,其中包括光抽运碱金属汽室型、原子束型、激光抽运频率标准以及冷原子物理的研究.文章阐明了原子钟的基本工作原理、主要性能及其与各种物理因素的关系,叙述了提高汽室频标光抽运效率与降低各种频移和减少谱线增宽因素影响的方法.此外,还介绍了原子束频标中的Majorana跃迁研究、光抽运铯钟中解决长期工作与长期频率稳定度难题以及冷原子钟的一些设想等研究成果. 相似文献
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低噪声微波在冷原子光钟、光子雷达、大科学装置远程同步等领域具有重要的应用价值.本文介绍了一种基于光学-微波相位探测技术的低噪声微波产生方案,利用光纤环路光学-微波鉴相器,将超稳激光的频率稳定度相干传递至介质振荡器.实验采用梳齿相位参考至超稳激光的窄线宽掺铒光纤飞秒光学频率梳,结合光纤环路光学-微波鉴相器和精密锁相装置,将7 GHz介质振荡器同步至光频梳重复频率的高次谐波,同步后的光脉冲序列与微波信号的剩余相位噪声为–100 d Bc/Hz@1 Hz,定时抖动为8.6 fs [1 Hz—1.5 MHz];通过搭建两套低噪声微波产生系统,测得7 GHz微波的剩余相位噪声为–90 d Bc/Hz@1 Hz,对应的频率稳定度为4.8×10–15@1 s.该研究结果对基于光学相干分频的低噪声微波产生提供了一种新思路. 相似文献
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喷泉钟量子化轴磁场的空间均匀性和时间稳定性是制约原子钟输出频率稳定度和不确定度的重要因素.从外磁场屏蔽、磁场线圈设计、线圈电流源稳定性等方面考虑,构建并优化设计了一套可搬运铷喷泉原子钟量子化轴磁场系统.为了消除环境磁场对量子化轴磁场的影响,使用5层坡莫合金磁屏蔽进行外磁场的屏蔽;利用4组对称的补偿线圈,通过计算给予合适的电流,获得喷泉钟内部30 cm原子自由飞行尺度内磁场波动小于1 nT;通过改善C场供电电流方式,从而优化量子化轴磁场的时间稳定性,磁场随时间的波动小于0.1 nT.优化后喷泉钟长期频率稳定度达2.9×10-16,磁场空间分布不均匀性带来的二阶塞曼频移不确定度为3.4×10-19,由磁场随时间波动带来的二阶塞曼频移的不确定度为5.1×10-17. 相似文献
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用于激光冷却与原子布居数探测的激光光源是冷原子钟的重要组成部分,选用工业技术成熟的1560 nm光纤激光器和光纤放大器分别作为种子源和光放大器,经非线性倍频晶体对放大后的激光进行倍频,得到较大功率的780 nm的激光,通过饱和吸收稳频得到冷却激光,一部分冷却激光利用电光调制器和声光调制器移频6.8 GHz得到重泵浦激光,对上述激光进行适当的功率分配后提供给冷原子钟。对该套激光装置关键器件进行了特性测试,将稳频后的倍频激光与锁定在超稳激光上的光学频率梳进行拍频,得到的激光的线宽在74 kHz左右,其短期稳定度比外腔半导体激光器提高半个多数量级。将这样的激光光源应用于冷原子钟,可以减小探测激光频率噪声对喷泉钟稳定度的限制。 相似文献
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Pereira Dos Santos F Marion H Bize S Sortais Y Clairon A Salomon C 《Physical review letters》2002,89(23):233004
We present a new method based on a transfer of population by adiabatic passage that allows one to prepare cold atomic samples with a well-defined ratio of atomic density and atom number. This method is used to perform a measurement of the cold collision frequency shift in a laser cooled cesium clock at the percent level, which makes the evaluation of the cesium fountain accuracy at the 10(-16) level realistic. With improvements, the adiabatic passage would allow measurements of density-dependent phase shifts at the 10(-3) level in high precision experiments. 相似文献
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Tian-chu Li Ping-wei Lin Ming-shou Li Ping Wang Wei-liang Chen Nian-feng Liu Yi-ge Lin 《Frontiers of Physics in China》2009,4(2):155-159
The second laser cooling cesium fountain clock NIM5 at the National Institute of Metrology (NIM) China adopts the (1,1,1)
direct optical molasses ( OM) configuration. NIM5 has been running with a stability of 3×10−15/d and an operation ratio of 99% since 2007. Preliminary evaluations of NIM5 in 2008 showed a typical combined uncertainty
of 3×10−15. The NIM5 clock is operating in parallel with NIM’s first fountain clock NIM4. NIM4 and NIM5 are used to steer the frequency
of the calculated NIM atomic time TA-c(NIM) and the first set of results are promising. We are now at the stage of comparing
the frequency of NIM5 with UTC to support the independent frequency shift evaluations of NIM5 and contribute to the international
atomic time in the near future.
相似文献
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Design and test of the microwave cavity in an optically-pumped Rubidium beam frequency standard 下载免费PDF全文
We are developing a compact rubidium atomic beam frequency standard with optical pumping and detection.The cavity for microwave interrogation is an important part of the clock.The cavity in our design is a Ramsey-type,E-bend one,which is the same as the conventional method in most cesium beam clocks.Requirements for the design are proposed based on the frequency shift associated with the cavity.The basic structure of the cavity is given by theoretical analysis and detailed dimensions are determined by means of electromagnetic field simulation with the help of commercial software.The cavity is manufactured and fabricated successfully.The preliminary test result of the cavity is given,which is in good agreement with the simulation.The resonant frequency is 6.835 GHz,equal to the clock transition frequency of87Rb,and the loaded quality factor is 500.These values are adjustable with posts outside the cavity.Estimations on the Ramsey line width and several frequency shifts are made. 相似文献
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The magnetic field in the microwave interaction zone of the fountain atomic clock was measured by stimulated Raman transitions.By measuring the two-photon transition frequency between the Zeeman levels of the two ground states,we achieved a magnetic field measurement accuracy of the order of 0.28 nT.This method is immune to the Doppler shift and the AC Stark shift.The second order Zeeman shift of the fountain clock is 170.7×10-15,with the uncertainty of 7.2×10-16. 相似文献
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Improvement of the short-term stability of atomic fountain clock with state preparation by two-laser optical pumping 下载免费PDF全文
《中国物理 B》2021,30(5):50602-050602
To improve the signal to noise ratio(SNR) and the short-term stability of cesium atomic fountain clocks, the work of two-laser optical pumping is presented theoretically and experimentally. The short-term stability of the NIM6 fountain clock has been improved by preparing more cold atoms in the |F = 4, mF= 0〉 clock state with a shortened cycle time.Two π-polarized laser beams overlapped in the horizontal plane have been applied after launching, one is resonant with|F = 4〉→ |F = 4〉 transition and the other is resonant with |F = 3〉→ |F = 4〉 transition. With optical pumping, the population accumulated in the |mF= 0〉 clock state is improved from 11% to 63%, and the detection signal is increased by a factor of 4.2, the SNR of the clock transition probability and the short-term stability are also improved accordingly. 相似文献
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《中国物理 B》2021,30(7):70601-070601
Caesium atomic fountain clock is a primary frequency standard, which realizes the duration of second. Its performance is mostly dominated by the frequency accuracy, and the C-field induced second-order Zeeman frequency shift is the major effect, which limits the accuracy improvement. By applying a high-precision current supply and high-performance magnetic shieldings, the C-field stability has been improved significantly. In order to achieve a uniform C-field, this paper proposes a doubly wound C-field solenoid, which compensates the radial magnetic field along the atomic flight region generated by the lead-out single wire and improves the accuracy evaluation of second-order Zeeman frequency shift. Based on the stable and uniform C-field, we launch the selected atoms to different heights and record the magnetically sensitive Ramsey transition|F = 3, mF=-1 → |F = 4, mF=-1 central frequency, obtaining this frequency shift as 131.03×10~(-15) and constructing the C-field profile(σ = 0.15 n T). Meanwhile, during normal operation, we lock NTSC-F2 to the central frequency of the magnetically sensitive Ramsey transition |F = 3, mF=-1 → |F = 4, mF=-1 fringe for ten consecutive days and record this frequency fluctuation in time domain. The first evaluation of second-order Zeeman frequency shift uncertainty is 0.10×10~(-15). The total deviation of the frequency fluctuation on the clock transition induced by the C-field instability is less than 2.6×10~(-17). Compared with NTSC-F1, NTSC-F2, there appears a significant improvement. 相似文献