铷原子频率标准DH1001说明书

Saturated Absorption SpectroscopyandFrequency Modulation Spectroscopyof Rubidium Atoms铷原子的饱和吸收光谱和频率调变光谱Dan LeeGrade 98, School of Physics, Department of Technical Physics摘要在这个实验中，我们测量了85Rb和87Rb原子的饱和吸收光谱和频率调变光谱．在饱和吸收光谱中，87Rb原子的|F=1〉→|F＇=0,1,2〉和|F=2〉→|F＇=1,2,3〉,85Rb原子的|F=2〉→ |F＇=1,2,3〉和|F=3〉→|F＇=2,3,4〉以及它们的交错信号都被完全的捕捉住.这里,F表示的是5S1/2基态的超精细能级，而F＇则表示的是5P3/2激发态的超精细能级. 87Rb 原子的｜F=2〉→|F＇=1,2,3〉的谱线则被用于调频技术．AbstractWe have measured Dtransitions of 85Rb and 87Rb atoms with saturated2absorption spectroscopy and frequency modulation spectroscopy. These saturated absorption spectra, |F=1〉→ |F’=0,1,2〉and |F=2〉→ |F’=1,2,3〉of 87Rb atoms, |F=2〉→ |F’=1,2,3〉and |F=3〉→ |F’=2,3,4〉of 85Rb atoms, and their crossover lines are completely resolved, where F indicates the hyperfine level of the 5S1/2 ground state and F’ indicates that of the 5P3/2 excited state. The derivatives of the |F=2〉→|F’=1,2,3〉 spectra of 87Rb atoms are obtained with the technique of frequency modulation.As we know, the Rubidium atom is one kind of boson. It obeys the Bose-Einstein statistics. In 1995, Rubidium atom was successfully used to realize the Bose-Einstein condensation.In the nature, there are two types of isotopes of Rubidium: 87Rb and 85Rb. If we consider the hyperfine structure of the isotopes of 87Rb and 85Rb, we can get the figures for their energy levels. The hyperfine structure is resulted from the spin of the nucleus, which is called Zeeman effect that can lead to the separation of the energy levels in magnetic field.Fig. 1 below shows us the hyperfine structure of the 87Rb.Fig. 1. The hyperfine structure of the energy levels of87RbFig. 2 below shows us the hyperfine structure of theRb.Fig. 2. The hyperfine structure of the energy levels of 85RbThe two figures are similar to each other. The small differencebetween them is that the separation of energy levels of 85Rb is less thanthose of 87Rb. Another difference between the two isotopes is that the spin of the nucleus of 87Rb is 3/2 and that of 85Rb is 5/2.I did such a following experiment to study the main energy level and the spectrum at first. The experimental setup is shown schematically in Fig. 3.Fig. 3. Experimental setup for the absorption spectrum of the RubidiumThe diode laser is driven by the current from the laser diode driver and is controlled by the temperature controller.We choose the diode laser as the laser resource here because it has too many advantages: the inexpensive price, the small line width that is less than 100 kHz , the high output power which can reach more than 10 mW, the large tunable range of wavelength which is more than 20 nm , the high stability and the high sensitivity. All above, the most important merit is that it can provide the laser whose frequency is just what we need in such experiments.In this experiment, we also use a function generator to output a triangular wave with appropriate frequency and amplitude. We input this wave into the laser diode driver and then make the laser current changein a proper range. The amplitude of the triangular wave decides the range. So the wavelength (or frequency) of the laser changes with the triangular wave. The Rubidium atom will absorb some photons from the laser when their frequency is proper. The spectrum is shown in Fig. 4, where the amplitude of the triangular wave is 200 mV and its frequency is 80 MHz.Fig. 4. The absorption spectrum of the RubidiumOne thing that we must emphasize is why we do not choose the square wave or serrated wave but triangular wave. The current from the laser diode driver that drive the laser cannot be changed too drastically. Otherwise the diode laser would be damaged. From the Fig. 4, we can see the four apparent spectra lines. From right to left, we mark them as a, b, c, d.In fact, each line of a, b, c, d contains fine spectra. The a-line contains the spectra lines from 87Rb |5S 1/2,F=2> to |5P 3/2,F’=1,2,3>. Theb-line contains the spectra lines from 85Rb |5S 1/2,F=3> to |5P 3/2,F’=2,3,4>. The c-line contains the spectra lines from 85Rb |5S 1/2,F=2> to |5P 3/2,F’=1,2,3>. The d -line contains the spectra lines from 87Rb |5S 1/2,F=1> to |5P 3/2,F’=0,1,2>.But because of the Doppler broadening effect, we cannot distinguish the fine spectra lines. The reason is interesting. We know that only theatoms can absorb a certain kind of photons whose energy (or frequency) exactly matches the separation of the energy level of the static atom. In fact, all the atoms move in all directions. Due to Doppler effect, the atom can be excited by those photons whose frequency is slightly away from the exact ones; meanwhile the separation among the energy levels of the hyperfine structure of Rubidium is tiny, too. All of above lead to the result that we are not able to distinguish the fine spectra.If we want to distinguish these fine spectra, we can use the method to get the saturated absorption spectrum. The experimental setup is also displayed as a brief outline in Fig. 5.Fig. 5. Experimental setup for the saturated absorption spectrumWhen the laser comes to the BK7, most of it will penetrate the BK7, which is called saturation beam, and only a small part of it will be reflected, which is called probe beam.The saturation beam and the probe beam nearly overlap each other in the opposite directions. As the chopper rotates, it will chop the saturation beam at a certain frequency. If it always covers the saturation beam, we will get the same spectra as the Fig. 4 shows. But that thesaturation beam works or not at a certain frequency will provide a reference signal (one kind of TTL signal) and the lock-in amplifier will deal with the TTL signal and the signal from the probe beam that has passed the Rubidium vapor cell.The detailed spectrum will be shown as following:Fig. 6. The spectrum of a-line in the saturated absorption spectrum experimentThe parameters of this experiment are listed below:Lock-in amplifier: Time Constant: 10 msSensitivity: 1 mVTriangular wave: Amplitude: 25 mVFrequency: 100 MHzFig. 6 shows us 6 spectrum lines obviously. From right to left,we mark them as a1, a2, a3, a4, a5 and a6. The a1-line, a3-line, a6-line representthe spectrum lines from 87Rb |5S1/2,F=2> to |5P3/2,F’=1>, from 87Rb |5S1/2,F=2>to |5P3/2,F’=2> and from 87Rb |5S1/2,F=2> to |5P3/2,F’=3>, respectively. Thethree other lines stand for crossover lines, which appear due to the Doppler effect. So there is a crossover line between each two lines of a1, a3 and a6.The parameters of this experiment are listed below:Lock-in amplifier: Time Constant: 10 msSensitivity: 1 mVTriangular wave: Amplitude: 20 mVFrequency: 80 MHzFig. 7 also shows us 6 spectrum lines obviously. We mark them as b1, b2, b3, b4, b5 and b6 in the same way. The b1-line, b3-line, b6-linerepresent the spectrum lines from 85Rb |5S1/2,F=3> to |5P3/2,F’=2>, from 85Rb|5S1/2,F=3> to |5P3/2,F’=3> and from 85Rb |5S1/2,F=3> to |5P3/2,F’=4>,respectively. The three other lines stand for crossover lines.Fig.8. The spectrum of d-line in the saturated absorption spectrum experimentThe parameters of this experiment are listed below:Lock-in amplifier: Time Constant: 10 msSensitivity: 1 mVTriangular wave: Amplitude: 20 mVFrequency: 50 MHzFig.8 shows us 5 spectrum lines but not obviously. D1, d2, d3, d4 and d5 are marked in the same way. The d1-line, d2-line, d5-line representthe spectrum lines from 87Rb |5S1/2,F=1> to |5P3/2,F’=0>, from 87Rb |5S1/2,F=1>to |5P3/2,F’=1> and from 87Rb |5S1/2,F=0> to |5P3/2,F’=2>, respectively. Thetwo other lines stand for crossover lines. In my opinion, another crossover line exists but we are just not able to measure it.It is the most difficult to get the saturated absorption spectrum for c-line. Fig.9 shows the experimental result and its appearance is far below that for a-line or b-line.The parameters of this experiment are listed below:Lock-in amplifier: Time Constant: 10 msSensitivity: 1 mVTriangular wave: Amplitude: 20 mVFrequency: 20 MHzSuch a figure is frustrating. I have tried to find the reason leading to such a bad result. There is no problem with the experimental setup because we can get good spectrum lines for a-line etc. Maybe the reason is that the instruments are not stable as the time goes on. But we can get as the same wonderful figure for a-line as before. Strictly speaking, I do not get success in the saturated absorption spectrum experiment for c-line. But I have to do the further experiment and I am told that only spectrum lines we need to apply to the further experiment are those for a-lines. So I give up making it clear before the fifth week.To make the figure more clearly, we design the experiment below. The experimental setup is given briefly in Fig.10. The left function generator produces sin-wave with high frequency and small amplitude as a referencesignal. The right function generator outputs a triangular wave with relatively low frequency and high amplitude. The former and the later are input into the adder at the scale of 1/10:1. How do they modulate the laser diode driver? We know that the frequency of the laser will oscillate as the current from the driver oscillates and the current is controlled by the input-signal. t f f f t I I I m L L m ωωcos cos 00+=⇒+= Because m f is far less than L f 0, the signal S (m f )that the photo detector receives can be in the form of Tailor expansion as the following:......!2)())((cos ))(()()cos ()(222_+++−−−−−→−+=t Cos f f S df d t f f S df df S t f f S f S m oL L m oL LoL ExpansionTaylor m oL L ωωω Generally speaking, Hz f oL 14108.3⨯≈Hz f m 610≈Hz 4102⨯≈πω1<<oL m f fFig.10. Experimental setup of the differential saturated absorption spectrum of RubidiumSo we can ignore the third item and later ones. The)(oL Lf S df din the second item is just the differential signal that we need. After the lock-in amplifier deal with the S(f L ) signal and the reference signal, we can get the differential signal.Fig. 10 does not show us where the neutral-density filters are. In my opinion, their quantities and their locations are not important because they are just used to adjust the power of the saturation beam and the probe beam in order to get an ideal result revealed in Fig. 11.To summarize, we have demonstrated three kinds of experiments to get the spectrum of Rubidium. All above these help us study the energy level and the structure of the Rubidium better. A5, the most distinguished spectrum line in all, is what we just need to use to lock in the frequency in the experiment of low-temperature-atom spectrum, which is another interesting experiment.AcknowledgementsIn the past four weeks, I spent an ordered and instructive time on such a special subject. It is the first time for me to come to the department of physics, NTHU. Such an experience will be remembered forever.I am grateful to Hui-Chun Chin and Tsung-Dao Lee Chinese Undergraduate Research Endowment (CURE), the Peking University, Beijing and the National Tsing Hua University, Hsinchu, which provide me such an opportunity to have a so precious experience.I am grateful to my instructor, Prof. Yu, an erudite and vigorous man. He is always not only enthusiastic to me but also strict with me. Under his wise guidance, I have such a chance to shoot a glance at the research field of the laser cooling.I also appreciate my elder school-sister Hsin-Ying Chiu and my elder school-brothers: Ying-Cheng Chen, Yean-An Liao, Hsih-Kuang Tung, Yun-Fan Chen, Guan-Qi Pan, Hong-Wen Zhuo, Jun-Jie Liao. They are warm-hearted to help me. They give me many good suggestions on study. I hope they would not mind that my bothering them during the last month.De-Hong Chen is another lab-mate that I must thank to. He provides me with much facility. It is he who makes my life here more convenient.I always hold the view that I can finish my report without a hitch due to the help of all others.Thanks all.References[1] Li-fu Mao, “Development and Study of Dark Magneto-Optical Trap”, the master’s thesis of Tsing Hua University, Hsinchu, Taiwan ,1998.[2] 施宙聪，陈皙墩，《稳频半导体雷射》，科技新知14卷5期, 第30页.[3] M. J. Snadden, R. B. M. Clarke, and E. Riis, “Injection-locking technique for heterodyne optical phase locking of a diode laser”, Opt. Lett. 22, 892 (1997).The Introduction to My Advisor:Ite Albert. Yu(余饴德)Name: Ite Albert, YuResearch Interests: Optics, Atomic & Molecular Physics, Laser (Exp.) E-mail addressAddress: 101 Section 2 Kuang Fu Road, Hsinchu, TaiwanDepartment of Physics, National Tsing Hua University, Hsinchu, Taiwan Telephone: (03)5742539 Fax: (03)5723052Education:1987-1993 Ph.D..1980-1984 B.S. in Physics, National Tsing Hua University,Hsinchu, Taiwan.Employment:1995-present, Associate Professor of Physics, Tsing Hua University, Hsinchu, Taiwan1993-1995, Postdoctral Researcher of Harvard-Smithsonian Center for Astrophysics,Research Interests:Experimental Atomic and Molecular PhysicsLaser Trapping and CoolingBose-Einstein CondensationNonlinear SpectroscopyQuantum OpticsSelected Publications:Selected Papers:Y. C. Chen, C. W. Lin, and I. A. Yu, "Role of degenerate Zeeman levels in electromagnetically induced transparency", Phys. Rev. A 61, 053805 (2000).Y. C. Chen, Y. W. Chen, J. J. Su, C. Y. Huang, and I. A. Yu, "Pump-probe spectroscopy of cold 87Rb atoms for various laser-polarization configurations", Phys. Rev. A 63, 043808 (2001).Other Publications:雷射冷却与低温原子的非线形光谱物理双月刊廿二卷五期 2000年10月 443页443-451 (2000).。

铷原子频率标准检定规程一、概述铷频标是一种被动型原子频标，是利用铷同位素Rb87原子基态超精细结构中（O－O）能级间跃迁微波谱线的中心频率6834.68…MHz，去锁定控制晶体振荡器频率，从而输出准确稳定的标准频率。

它属于频率准确度需要定期校准的二级标准频率源，广泛应用于工程、科研及计量等领域。

二、技术要求1输出频率：1MHz,5MHz,10(或0.1)MHz；2频率漂移率2.1日漂移率Dd：1×10-11~6×10-133.2月漂移率Dm：1×10-10~1×10-114时域频率稳定度δy(t)如表1取样时间tδy(t)1s5×10-11~5×10-1210s2×10-12~2×10-12100s5×10-12~5×10-131d1×10-11~1×10-12表15频域频率稳定度ψ(f)如表2傅里叶频率ψ(f)/(dBc·Hz)100-70~-90101-100~-120102-110~-125103-125~-140表26频率复现性R：(5~2)×10-117开机特性V：开机t a小时后，优于5×10-11；t a及进入稳定的工作时间t w按产品说明书规定8谐波及非谐波分量8.1谐波分量：-(20~40)dBc;8.2非谐波分量：-(50~70)dBc;9频率准确度A：2×10-10~5×10-11注：检定时以被检铷频标产品说明书为准。

三、检定条件10环境条件10.1环境温度：可在(18~15)℃范围内任选一点，在检定过程中铷频标周围的环境温度的变化不超过±1℃；10.2相对湿度：小于80%；10.3电源电压：220（1±5%）V；50（1±5%）Hz；10.4负载：在检定过程中，负载应固定不变。

作者： 李帅 王延辉
作者机构： 北京大学信息科学技术学院量子电子学研究所,北京100871
出版物刊名： 科技资讯
页码： 6-7页
年卷期： 2010年 第23期
主题词： 铷原子频标 温度系数 C8051F020 温度传感器
摘要：气泡式非自激型铷原子频标的输出频率受外界温度影响较大,因此需要设计专门的外部控温系统以减小温度对量子频标的影响。

传统铷原子频标的控温系统采用的是模拟电路方式,在外界温度范围变化较大的情况下,温度稳定性并不理想,温度系数指标较差。

本文利用单片机C8051F020,采用模拟和数字电路相结合的方式对小型铷原子频标的控温系统进行设计与改进,优化铷原子频标的温度系数指标。

通过实验验证,改进后的铷原子频标的温度系数可以有超过一个量级的提高,该方法具有较强的实际应用价值。

铷原子频率标准装置不确定度的评定作者：王文庆来源：《科技信息·下旬刊》2017年第01期摘要：时间、频率是科学范畴中的重要物理量，在各个应用领域中都是一项关键的技术指标。

铷原子频率标准装置通常作为参考频标对下一级频标（如晶振）进行量值传递，为确保产品质量，给科研生产及测试提供准确的时频类测试仪器，就必须保证该仪器的性能符合指标要求。

本文主要介绍铷原子标准装置的工作原理和测量方法，数学模型，系统地分析了铷原子标准装置测量不确定度来源。

关键词：铷原子频率；短期频率稳定度；频率准确度；标准装置；合成标准不确定度；扩展不确定度1.工作原理、测量方法和测量依据铷原子频率标准装置由铷原子频率标准及频稳测试仪组成。

铷原子频标由高性能铷原子振荡器送出一个10MHz的基准信号，经过隔离放大，由分频器分别产生1MHz和10MHz两种信号，最后由调谐放大器输出高稳定性、高负载能力、谐波抑制性能高的频率标准信号。

频稳测试仪的参考信号由外部输入，被测信号经过输入通道放大、倍频到10MHz送时间计数器完成数据采集、处理。

铷钟提供长稳标准信号，频稳测试仪给出稳定度及准确度测试结果。

该标准装置为直接测频法。

由于被测频标和参考频标的输出信号的幅度已经足够大，从而消除了信号幅度对频率测量值的影响。

因此通过对频率的测量来评定此装置的测量不确定度。

测量依据JJG180-2002电子测量仪器内石英晶体振荡器检定规程。

2.数学模型3.标准不确定度分量的评定3.1短期频率稳定度测量不确定度的评定短期频率稳定度不确定度的来源有三个方面：测量重复性引入的不确定度分量，采用A类标准不确定度评定；铷原子频标的短期频率稳定度引入的不确定度分量，采用B类标准不确定度评定；频稳测试仪频率稳定度引入的标准不确定度分量，采用B类方法进行评定。

其它如环境、温度、湿度和振动等可忽略。

3.1.1来源于被测源测量重复性引入的标准不确定度分量，可通过连续测量得到测量列，采用A类方法进行评定。

WR-1011铷原子频率标准技术说明书目 录1、概述2、技术指标3、结构特征4、连接端口及通信协议5、/A抗振加固型说明1、概述1.1 主要特性☆ 宽温度范围☆ 短期稳定度好☆ 低漂移率☆ 低功耗☆ 快速启动☆ 小体积☆ 长使用寿命☆ 标准接口输出☆ RS232通讯接口☆ 抗振动（/A选项）1.2 主要应用☆ 同步光网络☆ 移动通信、有线数字通信☆ 供电网运行监测系统、广播电视系统☆ 舰载、车载、机载及其他振动环境（/A选项）2、技术指标指标项技术要求/T、/D选项电气特征输出频率10MHz（5MHz、20 MHz可选）输出路数1路（**2路可选）频率稳定度3×10-11/1s（**1.5×10-11/1s）1×10-11/10s（**5×10-12/10s）3×10-12/100s（**1.5×10-12/100s）相位噪声（10MHz）-70dBc/Hz at 1Hz（**-80dBc/Hz at 1Hz）-80dBc/Hz at 10Hz（**-100dBc/Hz at 10Hz）-115dBc/Hz at 100Hz（**-130dBc/Hz at 100Hz）-135dBc/Hz at 1KHz（**-140dBc/Hz at 1KHz）-140dBc/Hz at10KHz（**-145dBc/Hz at 10KHz）频率漂移率（无秒脉冲同步）±1.2×10-11/天（通电1天后）±5×10-11/月（通电1月后）±5×10-10/年（通电1年后）频率数字调节范围细调1.27×10-9（±10%）粗调1.27×10-7（±10%）频率数字调节精度细调1×10-11（±10%）粗调1×10-9（±10%）精细调节6.8×10-13（±10%）频率模拟调节范围＞±1×10-9（依客户要求有此功能）/频率同步精度/ ＜5×10-12（秒脉冲同步12小时后）1PPS同步精度/ ±50ns（秒脉冲同步8小时后）1PPS波形/ 正极性脉冲，宽度：10ms±20ns 1PPS上升沿宽度/ ≤10ns1PPS输出方式/ 3.3V TTL输入PPS电平/ 3.3V TTL输入PPS占空比/ ≤0.6时间保持能力（无秒脉冲同步时）/ ＜1 us/天（通电1天后）频率复现性±5×10-11锁定/预热特性＜10分钟锁定（常温）15分钟＜5×10-10（常温）出厂准确度±1×10-10输出波形正弦波输出幅度＞+5dBm|50Ω谐波抑制＞40dBc杂波抑制（f0±100k）＞100dBc锁定指示信号 3.3V TTL——Lo：未锁Hi：锁定（电平提升方法见4.3）供电电源单直流+24V（±5%） 可选单直流+12V（11～17V）启动功率≤36W稳态功率≤12W（常温）环境特性地磁场敏感度±2×10-11(X、Y、Z三个方向)储存温度[1]-40～+80℃（**-55～+85℃[2]可选）工作温度[1]-25～+60℃（**-45～+70℃[2]可选）频率温度特性＜5×10-10|工作温度范围力学环境符合GJB367A-2001有关条款物理特征主体尺寸77×75.5×36.5mm3（±0.5）重量＜350g体积0.212L（±5%）对外接口DB9(9针)＋SMA可选**DB9(9针)＋2×SMA可靠性MTB F：100,000小时注：[1]环境温度，空气对流；[2]特殊订制；**项目为优选或特制型，将产生额外费用。

激光抽运铷原子频标实验研究宁小玲;康松柏;赵峰;钟达;梅刚华【摘要】Polarization spectroscopy of saturated absorption was used to lock laser frequency and set up an experimental system of laser-pumped rubidium atomic frequency standard. A preliminary frequency stability measurement was carried out, the results of which showed that a short-term frequency stability of 1.2× 10-11τ-1/2 was achieved. By analyzing the results, we proposed some approaches to improve the performance of the frequency standard.%采用饱和吸收偏振稳频半导体激光器,建立了激光抽运铷频标实验系统.实现了该系统的闭环锁定.进行了频率稳定度的初步测试,短期稳定度为1.2×10-11τ-1/2.对测试结果进行了分析,并提出了相应的改进措施.【期刊名称】《波谱学杂志》【年(卷),期】2011(028)001【总页数】6页(P109-114)【关键词】铷原子频标;外腔半导体激光器;激光稳频;频率稳定度【作者】宁小玲;康松柏;赵峰;钟达;梅刚华【作者单位】中国科学院原子频标重点实验室(武汉物理与数学研究所),湖北武汉430071;中国科学院研究生院,北京100049;中国科学院原子频标重点实验室(武汉物理与数学研究所),湖北武汉430071;中国科学院研究生院,北京100049;中国科学院原子频标重点实验室(武汉物理与数学研究所),湖北武汉430071;中国科学院原子频标重点实验室(武汉物理与数学研究所),湖北武汉430071;中国科学院原子频标重点实验室(武汉物理与数学研究所),湖北武汉430071【正文语种】中文【中图分类】O455.1引言铷原子频标以其体积小、功耗低、可靠性高[1]等特点而被广泛应用于定位导航、时间同步、同步通讯等领域. 传统铷原子频标采用无极放电灯作为抽运光源，光功率谱密度低，抽运效率受到限制，使得物理系统原子利用率只有千分之几. 因此，传统铷原子频标的短期稳定度被限制在1×10-12 τ-1/2左右[2]. 激光具有光谱纯、线宽窄、功率谱密度大的特点，利用半导体激光器替代传统铷频标中的无极放电灯作为抽运光源，可以有效提高物理系统原子利用率，从而使铷频标的稳定度指标得到改进. 目前实验上已经实现的激光抽运铷频标， 87Rb原子抽运效率达到41.3%[3]，短期稳定度达到3×10-13 τ-1/2 [4].本文在传统铷频标基础上，用一台稳频外腔式半导体激光器(ECDL)替代光谱灯作为抽运光，搭建了一套激光抽运铷频标实验系统，进行了实验测试及分析.1 实验原理与装置实验装置如图1所示. 实验采用的激光器为Optoquantum 公司生产的Hawkeye780型外腔半导体激光器，激光波长约为780 nm，线宽<500 kHz. 激光束由偏振分光镜PBS1分为2束，光束A进入激光稳频系统，用于激光稳频，光束B进入铷钟腔泡系统，对原子进行抽运. 激光稳频采用饱和吸收偏振稳频方案[5]. A光束经厚玻片Slide分为一束弱的探测光与一束强的抽运光. 探测光经过λ/2片后，变为偏振面与PBS2的Z主轴成45°夹角的线偏振光，再穿过充有天然铷的饱和吸收泡，经PBS2分束后，由光电池D1与D2探测. 抽运光通过λ/4片后变为圆偏振光，经45°M与90°M的反射，沿探测光反方向进入饱和吸收泡. 由于圆偏振抽运光σ+(或σ-)仅能诱导Δm=1(或Δm=-1)的原子跃迁，导致原子基态的子能级布局不均匀，等效于相对角动量取向各向异性，类似于法拉第效应，使线偏振探测光通过吸收泡时发生双折射，偏振面发生微小转动[6]， D1与D2探测到的两路信号将有微小差异. 两信号经过差分后送入激光稳频电路，通过处理得到直流纠偏电压，并反馈到激光器压电陶瓷PZT上，将激光频率锁定在87Rb 原子饱和吸收峰的中心频率上.图1 实验装置图Fig.1 The set-up diagram of experiment铷钟的工作过程为，稳频激光输出的B光束经过凸透镜L1与L2扩展为Φ8 mm 的平行光束，射入充有87Rb蒸汽原子及缓冲气体的吸收泡，将87Rb原子从基态的F=1抽运到F=2上，形成粒子数反转. 压控晶体振荡器VCXO输出10 MHz 信号，该信号经倍频、综合和调制后，输出约6 834.68 MHz的受调微波信号，激励铷原子基态的(0， 0)跃迁，光电池D3将探测到交流鉴频信号. 该信号经相敏检波及放大后，转变为一定极性的直流纠偏电压，反馈到VCXO压控端，将其频率锁定在原子谱线中心频率上.2 实验结果激光稳频采用规格为Φ20 mm×100 mm的饱和吸收泡. 无抽运光时，旋转λ/2片使PBS2分束的2路光光强相等. 图2是87Rb原子D2线b线的饱和吸收谱. 激光频率稳定在F=1→F′=CO 0-1的饱和吸收峰上，吸收峰的半高宽约为25 MHz，激光稳定后的波长为780.232 nm.图2 87Rb原子D2线b线的饱和吸收谱Fig.2 87Rb saturated absorption spectrum of line b in D2该铷频标直接采用本实验室现有的电路模块. 物理系统由稳频激光器和腔泡系统构成. 该腔泡系统采用本实验室研制的开槽管式微波腔[7]，腔的有载Q值约为400. 吸收泡外径为14 mm，内部充有同位素87Rb，工作温度为68 ℃. 腔内馈入的微波功率约为-25 dBm. C场电流为3 mA，在腔内约产生0.03 mT的平均磁场，背景光强约为50 μW/cm2. 通过调试与参数优化，实现了铷频标的闭环锁定. 初步测量了频标的稳定度指标，如图3所示. 100 s以下的短期稳定度为1.2×10-11 τ-1/2.图3 激光抽运铷频标稳定度Fig.3 Frequency stability of laser-pumped 87Rb frequency standard3 结果分析与讨论铷频标的频率稳定度(Allan方差)与其噪声功率谱密度Sy(f)的关系为[2， 8]：(1)(1)式中fm为微波的调制频率. 设铷频标的噪声为散弹噪声，推出铷频标的短期稳定度为[2， 8]：(2)(2)式中为散弹噪声， q为电子电量， Ibg为背景光电流，νRb为铷钟的跃迁频率(6.834 GHz)， D为鉴频斜率. 实验测得散弹噪声约为3 鉴频斜率D为0.85nA/Hz. 将上述两值带入(2)式，可得到铷频标短期稳定度的理论值为3.5×10-13 τ-1/2.频率稳定度的实测值为1.2×10-11 τ-1/2，远不如理论预测值，这说明系统存在其他更主要的噪声，破坏了稳定度指标. 通过实验分析，我们认为这种噪声主要是激光的幅度噪声.激光的幅度噪声通过光频移来影响频率的稳定度. 根据电磁场的Stark效应理论，在激光光场中，铷钟跃迁频率的频移量ΔνRb为[4]：(3)(3)式中νL为激光频率，ν0为87Rb原子从基态F=1能级到激发态52P3/2能级的跃迁频率，即铷钟的抽运跃迁频率，1/Γ为原子激发态的寿命，ΩR是激光的Rabi频率，激光光强I与|ΩR|2成正比. 由(3)式可知，频移量与激光的光强和频率有关.定义铷钟的跃迁频率随激光光强变化的频移系数α为:(4)由(3)、 (4)式可知，频移系数α与激光频率νL及能级寿命1/Γ有关. 激光频率νL 偏离ν0的失谐量越小，α越小，则激光的幅度噪声通过光频移对铷钟稳定性的影响越小. 在激光幅度噪声的影响下，铷频标输出10 MHz标准频率信号的稳定度可表示为[9]：(5)图4 87Rb原子能级跃迁图 Fig.4 The scheme of 87Rb atomic transtion (5)式中RIN为激光光强在调制频率fm处的相对强度噪声，根据已有文献[7]的测量结果， ECDL激光器在136 Hz处的RIN约在1×10-12 Hz-1量级. 在铷钟锁定时，实验测得光强相对变化量ΔI/I为1%时，铷钟的跃迁频率相对变化量ΔνRb/νRb约为6.5×10-8，带入(5)式算得铷钟的频率稳定度为4.6×10-12τ-1/2. 频移系数α偏大是造成上述稳定度值较大的主要原因. 引起频移系数α偏大的原因有多种. 首先，激光的锁定频率νL偏离ν0的失谐量较大，使频移系数α较大. 图4给出了激光锁定频率νL与铷钟抽运跃迁频率ν0对应的87Rb原子能级跃迁，由图可知，二者之间的失谐量约为266.1 MHz. 考虑到吸收泡内缓冲气体会造成ν0一定程度上的压力频移，该失谐量会发生改变，但变化量相对较小. 其次，由于激光光谱线性与谱灯光谱线性存在很大的差异，而吸收泡内的缓冲气体种类、配比及气压是针对减小谱灯抽运引起的光频移设计的，直接将其应用于激光抽运铷频标中，会使频移量对光强的变化较敏感[4].综上所述，对于本实验的铷频标系统，激光幅度噪声是影响其短期稳定度的主要原因，其短期稳定度被限制在4.6×10-12τ-1/2. 该结果与实验结果仍然存在差异，这是由于实验光路较长，系统抗震性较差，外界震动容易通过光路及稳频电路破坏激光幅度及频率的稳定性，造成实际激光幅度噪声与频率噪声比上文引用的典型值要大，从而影响铷钟的稳定性. 优化光路，加强系统机械结构的稳定性，能将该激光抽运铷频标的稳定度提高到10-12τ-1/2量级. 除此之外，激光的频率噪声也会通过光频移影响铷钟频率的稳定度.由(5)式可知，减小频移系数α，能有效提高铷钟的短期稳定度. 因此，采取以下几种措施可降低光频移的影响. (1)运用声光调制器AOM调节激光频率，减小激光频率与ν0之间的失谐量，从而减小光强的频移系数α. (2)适当调整吸收泡内缓冲气体气压，利用压力频移来减小激光频率与ν0之间的失谐量，以减小频移系数α [4]. (3)改用DAVLL激光稳频方案，理论上能将激光频率锁定在原子多普勒吸收峰上的任何一点，可自由调整激光锁定频率，从而减小光强的频移系数α. (4)针对激光抽运优化吸收泡内缓冲气体种类及配比，以减小频移系数α. 除此之外，改进激光稳频方案、减短光路、防止空气流动，均能减小外界震动引起的激光幅度及频率噪声，从而减小二者通过光频移对铷钟频率稳定度的影响.4 结论采用了饱和吸收偏振稳频法，将激光频率稳定在87Rb原子D2线b线的F=1→F′=CO 0-1饱和吸收峰上. 基于传统的铷频标系统，利用稳频激光器代替传统谱灯作为抽运光，搭建了激光抽运铷频标实验系统，实现了闭环锁定. 初步测量该系统的短期稳定度为1.2×10-11 τ-1/2，与理论预计值3.5×10-13 τ-1/2尚存在较大差异. 对此分析了引起短稳指标变差的原因，并提出了相应的改进措施. 相信通过进一步的参数优化，能将激光抽运铷频标的短期稳定度指标不断提高，以至最终接近理论预期值.参考文献:【相关文献】[1] Wang Yi-qiu(王义遒), Wang Qing-ji(王庆吉), Fu Ji-shi(傅济时)， et al. The Theory of Frequency Standards (量子频标原理)[M] . Beijing(北京): Science Press(科学出版社), 1986. 366-395.[2] Mileti G, Deng J Q, Walls F L, et al. Recent progress in laser-pumped rubidium gas cell frequency standards[C]. International frequency control symposium, IEEE, 1996.[3] Besedina A, Gevirkyan A, Zholnerov V. The efficiency investigation of 87Rb atomic beam laser pumping for designing a quantum discriminator for high-performance space-borne atomic beam frequency standard[C]. France: Proc of the 19th EFTF, Besancon, 2005. 324-330.[4] Deng J Q, Mileti G, Jennings D A. Improving the short term stability of laser pumped Rb clock by reducing the effects of the interrogation oscillator[C]. International frequency control symposium, IEEE, 1997. 438-445.[5] Xu Ke-zun(徐克尊). The Advanced of atomic and molecule Physics(高等原子分子物理学)[M]. Beijing(北京): Science Press(科学出版社), 2006. 275.[6] Pearman C P, Adams C S, Cox S G, et al. Polarization spectroscopy of a closed atomic transition: applications to laser frequency locking[J]. J Phys B: At Mol Opt Phys, 2002, 35: 5 141-5 151.[7] Mei G H, Zhong D, An S F, et al. 2001 Miniaturized microwave caviey for atomic frequency patend No.6 225 870 B1[C]. 2001.[8] Mileti G, Thomann P. Study of the S/N performance of passive atomic clocks using a laser pumped vapor[C]. Proc 9th European Frequency and Time Fortum, 1995. 271-276.[9] Vanier J, Mandache C. The passive optically pumped Rb frequency standard: the laser approach[J]. Appl Phys B, 2007, 87: 565-593.。

如何检定铷原子频率标准？铷原子频率标准也称之为铷频标是一种被动型原子频标。

铷频标内晶振的振荡频率通过频率合成技术产生一个微波激励信号，铷同位素87Rb的原子在激励信号的感应下发生跃进，原子跃进对微波信号起鉴频作用而产生的误差信号，通过锁频环路伺服晶振的频率，使激励信号频率锁定到原子跃进频率，实现晶振输出频率的高度稳定和准确。

1、铷频标概述GNSS控制的铷频标是利用全球导航卫星系统信号不断调整铷频标的输出频率，使其具有更高的频率准确度。

铷原子频率标准广泛应用于无线电导航与定位、数字通讯工程和时间频率测量等领域。

如何检定铷原子频率标准的各项性能指标是否符合实际需求，一般可送检计量单位，依据JJG292-2009铷原子频率标准检定规程进行各项检定。

具体的检定项目有：外观及工作正常性、输出信号、谐波与非谐波、开机特性、频率稳定度、相位噪声、日频率漂移率、频率复现性、频率调整范围和频率准确度。

2.检定器具检定铷原子频率标准的过程当中需要准备的计量器具有：频率稳定度参考频标、频率漂移率和频率准确度参考频标、相位噪声参考频标、示波器、频谱分析仪、频标比对器、频差倍增器、比相仪、分频器、通用计数器和相位噪声测量系统。

其中通用计数器可参考使用SYN5636型高精度通用计数器。

该款计数器性能可靠，测量范围宽，灵敏度高，动态范围大。

有外频标功能，满足测量范围10Hz~100MHz。

频标比对器推荐使用SYN5609型对输入的频率标准信号的短期稳定度、频率准确度进行测量。

通过某种数据处理和计算，可计算出频率日波动、开机特性和频率漂移率等参数。

频差倍增器外接计数器，用于测量两频率信号的频率差，输入频率1MHz，5MHz和10MHz，频差倍增器引入的测量不确定度应优于被检铷频标稳定度的3倍。

3、检定方法铷频标检定的具体方法和连接示意图JJG292-2009检规中有详细的阐述，在此只提出部分项进行说明。

厂家直销：刘女士189****7619QQ：2563113967输出信号项检定主要是用示波器检测铷频标的频率信号和秒脉冲信号，其中示波器的阻抗为50Ω。