铯冷原子喷泉Ramsey跃迁实验

中国计量科学研究院利用冷原子喷泉实现了9.19GHz微波与铯原子作用的Ramsey跃迁。文中介绍了NIM4#喷泉钟相关的微波 光学系统在时序控制下完成原子选态 激励 探测 信号处理的原理和装置,给出了Ramsey实验曲线:喷泉高度74cm时,Ramsey中心条纹FWHM约为0.95Hz,信噪比S N约40。实验结果的Ramsey中心条纹宽度、Rabi台宽度与相应的理论计算符合很好。     

利用电子回旋共振放电提高氢原子制备效率方法研究

基态氢原子的制备是氢原子钟工作的基础,提高氢原子的生成率极为重要.针对电离泡内氢等离子体中的原子成分不易直接被探测的情况,本文将软件仿真模拟与实验光谱诊断相结合,研究泡内原子成分.采用COMSOL软件建立射频感应耦合等离子体(ICP)和微波电子回旋共振(ECR)两种放电模型,模拟了一定输入功率、不同气压下氢等离子体中原...     

原子系统的光发射量子理论

根据电磁辐射场的量子化理论,结合SU(1,1)Lie代数理论和SO(3)Lie代数理论,得到原子系统光发射的量子论。作为例子,结出了氢原子发射时原子的跃迁寿命。     

拉曼光频移对原子干涉测量中原子数的影响

冷原子干涉测量技术在重力加速度测量等领域已经超越传统测量方法,成为量子精密测量的重要发展方向。在干涉测量过程中,由于原子受到重力场影响,速度不断变化,因此激光相对原子具有多普勒频移效应。本文通过对原子跃迁概率及速度选择的理论分析,计算了在拉曼激光脉冲持续时间内,由于多普勒频移造成的原子跃迁概率改变。进而,具体计算了π/2-π-π/2干涉方案中,频移造成的有效原子数损失,及其对干涉条纹对比度产生的影响。     

环境温度对氢原子钟性能的影响

本文探讨了被动型氢原子钟在宽温度环境下的频率特性,为小型、易搬运、高可靠、环境适应性强、高性能氢原子钟的研制提供了参考.将被动性氢原子钟置于温箱,测量其在不同温度下的开机特性、频率稳定度、频率准确度等参量.本文在10℃~35℃的宽温度范围内进行测试分析,研究了环境温度对氢原子钟开机特性、频率准确度及频率稳定度的影响.对于被动型氢原子钟在恶劣环境下的研制和应用提供可靠的依据和参考,也可为研究其它类型原子钟受温度的影响提供借鉴.     

被动型小氢钟的试验研究

介绍了上海天文台被动型小氢钟的设计和研制 ,给出了初步的测试结果。这种小氢钟应用了电极负载腔。在伺服环路上采用被动的工作方式和腔的自动调谐 ,用方波调制的方法得到误差信号。和传统的主动型氢钟相比 ,它的整体体积减小 ,重量降低。经过初步测试 ,这种被动型小氢钟的频率稳定度为σ(2 ,τ) =1 0× 10 - 1 1 τ- 1 2 (1s<τ <5× 10 4 s)。     

能级和能级跃迁

在国际单位制的七个基本单位中,有两个单位的定义中引用了“能级跃迁”这一术语,它们是:米定义—米等于氪-86原子的2P_(10)和5d。能级之间跃迁所对应的辐射在真空中的1650 763.73个波长的长度;秒的定义—秒等于铯-133原子基态的两个超精细能级之间跃迁所对应的辐射的9 192 631 770个周期的持继时间。那么,什么叫做能级、超精细能级和能级跃迁呢?我们以氢原子为例,简单予以说明。氢原子具有最简单的原子结构(如图1),     

核磁共振豫时间与磁共振成像

<正> 1.核磁共振驰豫时间(T_1,T_2)当氢原子核被置于固定的强磁场中时,会分成顺磁场和逆磁场两种方向排列,而形成两种能级状态。这时若用无线电波来照射这些氢原子核,各氢原子核会因周围环境的差异而吸收不同频率的无线电波的能量从低能级向高能级跃迁,这种现象称核磁共振(NMR)。使氢原子核发生核磁共振的条件是:ω=26753H_0式中 H_0表示氢原子核周围磁场的强度,ω表示使该氢原子核产生共振跃迁的无线电波的频率,比例常数26753,是氢原子核的旋磁     

被动型氢原子钟吸气剂泵的应用研究

描述了上海天文台在2008年为提高被动型氢原子钟真空系统的可靠性所研制的由非蒸散型吸气剂泵和小离子泵组成的复合泵的实验过程,吸气剂泵在室温下吸收2.1MPa.l的H2气后仍可达到3.2×10-5Pa的真空度,2l/s的离子泵电流工作在0.30μA,证明了复合泵可以维持氢钟13年以上的正常工作。经过再激活固定了激活工艺,吸气剂最终吸氢6.0 MPa.l仍没有饱和,证明了吸气剂的强大吸氢能力。至今复合泵已成功应用在4台被动型氢钟上。     

探知铷原子420nm精细能级结构的一种方法

本文通过研究针对V型能级结构的原子中弱振子强度跃迁谱线,提供一种速度转移激光光谱测量其精细能级结构的方法。利用高激发态不同原子能级跃迁产生谱线通过不同速度原子,转移到原子中低激发态跃迁线频率对应探测激光扫频记录的谱数据上。测量的速度转移谱具有亚多普勒的特征,而且是无交叉峰,又可以同时测量两个不同频率能级的光谱,这是传统饱和吸收谱做不到的。     

Investigation of the Limiting Short-Term Instability of the Output Signal of a Passive Hydrogen Frequency Standard

The limiting short-term frequency instability of the output signal of a passive hydrogen frequency and time standard is calculated. A technique for experimental measurement of the figure of merit of a quantum discriminator is set forth. The frequency instability of the standard is estimated on the basis of the obtained data. The effect of spectral line splitting of a maser with increasing excitation signal discovered in the course of the study represents an obstacle against achieving any decrease in the instability of the standard.     

Environmental factors and hydrogen maser frequency stability

It is necessary to have a complete understanding of the environmental sensitivities of cavity-tuned hydrogen masers to obtain optimum frequency stability and to avoid common-mode frequency fluctuations. Measurements of environmental sensitivities (temperature, relative humidity, atmospheric pressure, line voltage and magnetic field) made at the National Institute of Standards and Technology have demonstrated that the frequency stability of a cavity-tuned, active hydrogen maser is not significantly degraded if the maser is operated in a moderately controlled environment. Under these conditions, common-mode frequency fluctuations caused by the observed environmental factors also are negligible.     

Studies of dielectrically loaded cavities for small size hydrogenmasers

A dielectrically loaded cavity made of a hollow alumina cylinder, which is used to reduce hydrogen maser size, is considered. The results of a theoretical study of the effect of the cavity geometry on the frequency stability capability of the maser are reported. The active mode as well as the passive mode of operation are considered and the achievable performances are compared. It is shown that the frequency stability capabilities do not differ very much for both modes of operation with, however, a slight advantage to the active mode     

Measurement of the Effect of Thermal Noise on the Amplitude of Oscillation of a Maser Oscillator

Experimental verification of the effect of thermal noise on the oscillation amplitude of a maser is described. Two different masers are considered, the H maser with an homogeneous atomic line and the Rb maser with an inhomogeneous line. The effect is characterized by the spectral density of the relative amplitude fluctuations and this parameter is measured with a conventional superheterodyne AM receiver for various maser saturation factors. Experimental results show good agreement with theoretical predicted values. At high saturation factors, a peak appears with a maximum at a frequency close to the Rabi frequency. Observed values at high Fourier frequencies allow a measurement of the atomic power by the knowledge of the absolute temperature of the cavity and the prediction of the oscillator short-term frequency stability. Furthermore, the effect on amplitude and on frequency noise of an external feedback loop used to increase the cavity quality factor is discussed.     

Theory of Ultra-high-resolution Optical Raman Ramsey Spectroscopy

A non-perturbative theoretical analysis of Ramsey interference lineshapes in three-level lambda systems excited by laser fields has been developed for the general case of several interaction regions. In conventional Ramsey excitation, two laser fields excite the lambda system each in two separate spatial interaction regions. Here we examine how increasing the number of interaction regions or altering the interaction times change and improve the lineshape characteristics such as fringe visibility. For short interaction times the fringe pattern is strongly dependent on the number of interaction regions, with the n = 2 sinusoidal fringes replaced by sharper fringes of greater visibility. With larger interaction times, the fringe pattern is virtually unchanged on increasing the number of interaction regions. The optimum fringe pattern is obtained with short interaction times and a larger (n a 9) number of regions.     

一种基于星载氢钟误差信号提取的实现方法

针对中国新一代卫星导航系统的高精度定位要求,星载氢原子钟以极其优异的长期稳定性、漂移率以及温度特性,作为频率基准大规模应用于该系统.双频方案的被动型星载氢原子钟由物理部分及电路部分两大部分组成,微波激励信号对物理部分微波腔激励后产生了腔频误差信号及高稳晶振误差信号.对于如何提取并处理这两种误差信号,提出了一种对调幅信号...     

Majorana Effect on Atomic Frequency Standards

The Majorana effect on the hydrogen maser and the cesium (Cs) beam frequency standard is studied. In the hydrogen maser, the Majorana transition is used to the state selection successfully to eliminate the atoms in the [F = 1, mF = 1] state. As the result, a good performance of the hydrogen maser operation is obtained. In the Cs beam frequency standard, the remarkable phenomena due to this transition are described, such as the change of beam detection current, the change of the pattern in the low-frequency Zeeman transition, and the change of the velocity distributions.     

Cavity Pulling in Passive Frequency Standards

Assuming a Lorentzian shape for the atomic line, we calculate the cavity-pulling factors of passive frequency standards, taking into account the modification of the applied electromagnetic field by the atomic radiation. The calculation is therefore valid for all values of the gain of the atomic medium and gives, in particular, the cavity-pulling factor when the oscillation threshold is approached. The effect of saturation of the line by the field is included. Two expressions of the cavity-pulling factor are derived. One applies when the electromagnetic field level in the cavity is measured, and the other when the population of the atomic levels is analyzed. Consequences of these results are discussed. An experimental verification of the theoretical results is given, when the resonance of the field level in a hydrogen maser cavity is monitored in conditions where the oscillation threshold is approached.     

Exchange Collisions, Wall Interactions, and Resettability of the Hydrogen Maser

Experiments were performed in order to verify the resettability of the hydrogen maser. The method consisted of measuring the output frequency of one maser against the hydrogen pressure. It was found that at a given tuning of the cavity no shift larger than 2.1 parts in 1013 was observed for a change of 4 to 1 in pressure. This experiment also showed that the pressure shift due to exchange collisions, predicted by Bender, could not be observed for the field-independent transition in the hydrogen maser. Two masers, having the same storage bulb design and the same wall coating, were tuned by this technique and were found to have a frequency difference of 7.6 parts in 1013. Experiments on the wall coating of the hydrogen maser storage bulb were made. Relaxation and decorrelation times of various materials were measured. The hyperfine splitting of the ground state of hydrogen measured against cesium is also given.