Switching atomic fountain clock microwave interrogation signal and high-resolution phase measurements

This paper focuses on the development of tools aiming to solve several problems related to the microwave interrogation signal in atomic fountains. We first consider the problem related to cycle synchronous phase transients caused by the sequential operation of the atomic fountain. To search for such systematic phase variations deeply buried in the microwave synthesizer phase noise, we have developed a novel triggered-phase transient analyzer capable of processing the microwave signal to extract the phase in a synchronous manner even in the presence of frequency modulation. With this device we check in vivo the LNE-SYRTE fountain's interrogation signals with a resolution approaching 1 microradian. In addition, using this device, we investigate an innovative approach to solve a second problem, namely, the shift caused by microwave leakage in the fountain. Our approach consists of switching off the fountain microwave interrogation signal when atoms are outside the microwave cavity. To do that, we have developed a switch that is almost free of phase transients and is thus able to eliminate the frequency shift caused by microwave leakage without inducing significant phase transients on the interrogation signal.     

Design and metrological features of microwave synthesizers for atomic fountain frequency standard

In this paper we describe the improved redesign of the microwave frequency synthesizers for Laboratoire National d'Essais-Systèmes de Référence Temps-Espace (LNE-SYRTE) atomic fountains. The synthesizers use a cryogenic oscillator to generate both Cs and Rb hyperfine frequencies based on a new distribution frequency of 1 GHz. The main metrological features (phase noise, long-term phase stability, and spectral purity) of the synthesizers have been measured in situ connected to an atomic fountain and are compatible with an accuracy goal of 10(-16) for the atomic fountains. The simultaneous test of two different synthesizers on the FO2 atomic fountain at the 10(-16) level also is reported.     

First performance results of PTB's atomic caesium fountain and a study of contributions to its frequency instability

At the Physikalisch-Technische Bundesanstalt (PTB), an atomic caesium fountain was constructed. Ramsey fringes with a full width at half maximum (FWHM) of 0.86 Hz were obtained by launching the atoms to a height of 83 cm above the cooling region (40 cm above the microwave cavity center). A first measurement of the homogeneity of the magnetic flux density yields 0.33 nT (rms), only 0.16% of the mean value of 0.205 muT used in normal operation. The inherent elementary noise contributions of the fountain and of a thermal beam atomic clock are compared in some detail.     

Power dependence of distributed cavity phase-induced frequency biases in atomic fountain frequency standards

We discuss the implications of using high-power microwave tests in a fountain frequency standard to measure the frequency bias resulting from distributed cavity-phase shifts. We develop a theory which shows that the frequency bias from distributed cavity phase depends on the amplitude of the microwave field within the cavity. The dependence leads to the conclusion that the frequency bias associated with the distributed cavity phase is typically both misestimated and counted twice within the error budget of fountain frequency standards.     

Frequency equilibration in the vapor-cell atomic clock

Over the past several years, anecdotal evidence has grown indicating that Rb vapor-cell frequency standards exhibit a long "frequency equilibration" period following activation (i.e., time constant /spl sim/10/sup 2/ days). Though this long equilibration period can have important implications for diverse timekeeping systems, the mechanism driving the behavior is not well understood and has been the subject of debate. In this paper, we investigate this phenomenon for a number of Rb vapor-cell clocks with the purpose of 1) establishing the validity of frequency equilibration as a generic vapor-cell atomic clock phenomenon and 2) obtaining characteristics of the equilibration process that can be used to constrain hypothesized frequency-equilibration mechanisms. Consistent with anecdotal evidence, results on three separate manufacturers' clocks indicate that frequency equilibration is a generic vapor-cell clock phenomenon, observable in both laboratory-based and space-based systems. However, the experimental data also casts doubt on the two mechanisms most often offered to explain frequency equilibration: helium permeation through the resonance cell's glass envelope, and the intensity-dependent light-shift effect. To help guide further research, we propose two alternate mechanisms for frequency equilibration: alkali surface diffusion on the resonance-cell and lamp walls, and the spectrum-dependent light-shift effect.     

基于铷原子振荡器的DDS精密时钟源设计

该文介绍了一种基于FE-5680A铷原子振荡器和DDS(直接数字频率合成)芯片AD9851的频率可调精密时钟源设计方案.阐述了高速铁路大系统测试环境下精密时钟信号对于各传感器网络之间同步的重要性,以及对后期数据处理、数据融合所起到的积极作用;详细说明了该时钟源的基本工作原理,并给出了时钟源系统的软硬件实现方法.实验调试结果表明各项指标均达到预期要求.     

Pressure sensitivity of the vapor-cell atomic clock

Although atomic clocks have very low levels of frequency instability, they are nonetheless sensitive (albeit slightly) to various environmental parameters, including temperature, power supply voltage, and dc magnetic fields. In the terrestrial environment, however, atmospheric pressure (i.e., the air's molecular density) is not generally included in this list, because the air's density variations near the surface of the Earth will typically have a negligible effect on the clock's performance. The situation is different, however, for clocks onboard satellites like Galileo, where manufacturing and testing are done at atmospheric pressure, while operation is in vacuum. The pressure sensitivity of atomic clocks, in particular vapor-cell atomic clocks, can therefore be of significance. Here, we discuss some of the ways in which changes in atmospheric pressure affect vapor-cell atomic clocks, and we demonstrate that, for one device, the pressure-sensitivity traces back to a pressure-induced change in the temperature of the clock's filter and resonance cells.     

微波等离子化学气相沉积金刚石膜新型微波谐振腔设计

提出新型微波谐振腔用于化学气相沉积金刚石薄膜,腔体有效体积可以调节,采用环形介质窗口,置于沉积基台的下方,允许产生较大并且温度较高的等离子体。同轴内导体与沉积台相连接,微波从谐振腔底端传输经同轴导体耦合进入腔体。采用有限元的方法优化谐振腔的尺寸,使其能耦合进更大的微波能量,优化后,最大电场区域位于沉积台上方,并且均匀分布,在腔体内其它区域和介质窗口附近电场强度则很小,满足设计要求。采用时域有限差分法模拟了谐振腔在一定微波输入功率下产生等离子体的特性,并对设计的谐振腔进行试验研究,实验观察到的等离子体位置与模拟结果一致。     

Construction and evaluation of the first Brazilian atomic clock

For the past two years we have been implementing a program for the establishment of scientific time and frequency metrology in Brazil. The main objective of this program is to construct an atomic fountain and use it as a primary standard. As a first step toward this goal, we have constructed a (133)Cs beam optically pumped conventional clock. In this paper we describe the system and the results of its evaluation. The possible limitations of our short-term stability are discussed.     

Spatial variations of field polarization and phase in microwavecavities: application to the cesium fountain cavity

Wall losses in microwave cavities will generate a phase difference between the components of the field, and give rise to spatial phase variations which are related to the geometry of complicated shaped metal boundaries. Such effects are important to the design of the cavities used in the field of atomic frequency standards. Past attempts at calculating spatial phase variations in microwave cavities have been either limited to 1-D models or based upon an idealized model of the cavity, which simplifies its boundary shapes and neglects the effect of the source. In this paper, a numerical implementation of an electromagnetic field approach is used to overcome these limitations. The finite element method (FEM) is used to solve the driven form of the electromagnetic wave equation. The results show good agreement with transmission line predictions for a structure having simply shaped metal walls. The spatial phase distribution is then calculated for a 2-D approximation of the fountain cavity operating in the cylindrical TE₀₁₁ mode, which has been recommended for use in a Cs fountain frequency standard. A physical interpretation of the gradient of the phase in the cavity is presented, which shows it to be proportional to power flow     

Detection of atomic clock frequency jumps with the Kalman filter

Frequency jumps are common anomalies in atomic clocks aboard navigation system satellites. These anomalous behaviors must be detected quickly and accurately to minimize the impact on user positioning. We develop a detector for frequency jumps based on the Kalman filter. Numerical simulations show that the detector is fast, with high probability of detection and low probability of false alarms. It also has a low computational cost because it takes advantage of the recursive nature of the Kalman filter. Therefore, it can be used in applications in which little computational power is available, such as aboard navigation system satellites.     

Measurement of mode patterns in a high-power microwave cavity

A wet thermal paper method for measuring of mode patterns and heat distributions in a high-power microwave multimode cavity is developed. The exposure time of the paper is evaluated. It is shown that this method allows measuring and recording mode patterns in the loaded and unloaded cavity, and the heat distribution inside the cavity with a load movement. The mode patterns and heat distributions along horizontal and vertical planes of the cavity are presented. Possible applications of the method in medicine and biology are discussed, and a calibration protocol of a microwave oven for microwave radiation exposure on cell cultures in the cavity is given.     

Simple theory of microwave induced transparency in atomic and molecular systems

Abstract

In recent years the idea of electromagnetically induced transparency in atomic systems using a microwave coupling field has been discussed. We present theoretical work on how this may be achieved in both Doppler systems, and by extension in non-Doppler broadened systems. By considering the specific example of atomic rubidium we demonstrate the feasibility and practical difficulties of such an experiment. By considering systems with appropriate rotational-vibration structure we conclude that microwave induced transparency in gas vapours is more readily achievable in molecular systems.     

微波密封消解--原子荧光光谱法测定尿中汞

本文采用微波密封消解尿样,以原子荧光光谱法测定尿汞。与目前广泛采用的尿汞测定方法相比,具有操作简单、灵敏度高、线性范围宽等优点。是理想的测定尿汞的方法,尤其适用于大批量样品的检验。     

Fabrication and RF properties of the microwave cavity made of YBaCuO and BiPbSrCaCuO superconductors

After the discovery of new metal oxide superconductors with higher transition temperatures raised the possibility of a new class of superconducting microwave devices operating at temperatures well above liquid He, a feasibility study of the superconductor devices at r.f., microwave, and millimeter-wave frequencies, i.e., cavity resonator, transmission lines, waveguide, mirror, and antenna, was started at JAERI (Japan Atomic Energy Research Institute), Tokai in April 1987. In order to examine the feasibility of such devices and to investigate the nature of the superconductivity in these new superconductors, we have studied the microwave response of the oxide superconductors. In addition, we have also studied the fabrication and microwave properties of these devices using the new superconductors. We report here the status of the feasibility study, especially about the BSCCO and YBCO superconductor cavities, and the r.f. characterization apparatus using several cavity resonators. The cavities have potential applications for particle accelerators, resonant filters, ultrastable clocks, and so on.     

制图竞赛管理系统的设计与实现

为了高效、有序地组织"高教杯"制图竞赛,采用VB6.0开发语言、Access数据库、Excel表格工具及Crystal Reports报表工具设计开发了制图竞赛管理系统。该系统结合WindowsAPI编程和Excel VBA开发实现了包含图片信息的批量录入功能,使用CrystalReports报表工具实现包含图片信息的批量输出和打印。该系统的设计和实现为其它同类需求软件的开发提供了借鉴。     

轮胎压力监测系统的设计与实现

针对高速公路上爆胎事故频繁发生的现象,设计了基于LabVIEW虚拟仪器的轮胎压力监测系统,对系统的数据采集、保存、读取以及测量数据的融合和行车速度安全分析等设计进行了详细的说明。实验结果表明,该系统能够达到对轮胎温度和压力的准确测量,当胎压过高或过低及温度过高时自动报警,并能够对行车速度进行正确的安全分析,以提醒驾驶员用最适当的车速行使,研究表明,该系统对防止汽车爆胎的发生有着实际应用价值。     

Effects of cavity damping on the entanglement for a three-level atomic system

Based on the master equation for the density matrix, the dynamics of the entanglement of the three-level atom interacting with single-mode field in a finite-Q cavity are studied. It was found that the cavity damping leads to growing entropy and a strong degradation of the entanglement, therefore the coherence loss and entanglement is very sensitive to any change in the cavity damping parameter.