Uncertainty of Cesium-Beam Time Standards Due to Beam Asymmetry

As a consequence of the spatial phase distribution in the resonators of cesium-beam time and frequency standards, the generated frequency depends on the specific path of the atomic beam. A change of the position of the atomic beam source may result in a beam displacement normal to the beam direction. For a deflection system consisting of a combination of quadrupole and hexapole magnets for two-dimensional beam deflection, the displacement of the center of mass of the beam resulting from a misalignment of the beam source is computed. To this end, the distribution of the beam intensity on the collector is first determined. It is shown that for the cesium-beam time and frequency standard CSI of the Physikalisch-Technische Bundesanstalt (PIB), the uncertainty of the position of the center of mass of the beam entails a contribution to the uncertainty of the standard of less than 1 X 10-15. The amount of the displacement of the center of mass of the beam can be determined from the decrease of the beam flux on the collector caused by an adjustment of the beam source.     

Newly Designed Dipole-Beam Optics System for Cesium-Beam Frequency Standards

A new dipole-beam optics system has been put forward. It has all the basic advantages of the hexapole-beam optics system and can be made into a flop-in system. These advantages have been proven. We have used these beam optics in a beam tube with a cavity length of 3.7 m and observed Ramsey line width of 22-23 Hz.     

复现90温标定义固定点时杂质引起的偏差估算

本通过介绍一种计算杂质在复现各定义固定点温度时引起的偏差的方法,从实验及理论分析计算的角度讨论了在高纯金属凝固（或熔化）过程中,样品中的杂质对相变温度的影响。     

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.     

Characterization of Frequency Stability: Uncertainty Due to the Autocorrelation of the Frequency Fluctuations

We considered the general sampling form for the estimate of the Allan variance which is the proposed measure of frequency stability in the time domain, and we defined a variable proportional to the difference between the average fractional frequency fluctuations over the time interval ? to derive the autocorrelation coefficient of the process to which the variable belongs. Calculations of the variance of the estimated Allan variance proved that it may be convergent to its true value with infinite sample number for considered spectral densities of frequency noise. We also applied the results to estimations of frequency measurements to know the influence of the autocorrelation of the process considered. In order to obtain some direct estimates of the confidence of the estimate, distributions of the estimate were plotted by means of computer simulations, and were compared with the chi-square distribution. Those results suggested that for white-and flicker-phase noises (and white-frequency noise) we have to take into account the autocorrelation of the process, while for flicker-or random-walk-frequency noise we may regard the process as a nearly independent (and Gaussian) one.     

基于谱线漂移校正模型的实验室光谱定标修正

针对色散型高光谱成像仪实验室光谱定标方法进行了研究,在实验室光谱采集过程中仪器内部产热导致波段中心波长的漂移,由于高光谱带宽较窄,波段内中心波长的偏移会对光学遥感器的辐射定标精度产生影响。鉴于此,提出了谱线漂移校正模型来校正光谱定标结果。在文章最后分析了模型的精度并分别根据校正前后的光谱定标结果反算出积分球出射口处的辐亮度,与真实积分球数据对比,结果证明应用谱线漂移校正模型可以很好地校正谱线温漂的现象。     

残余应力对RF MEMS开关谐振频率偏移的影响

由沉积工艺产生的残余应力对RF MEMS开关的动态特性有重要影响。利用变量分离法推导出桥模式RF MEMS开关的频率方程组。给出二分法求解频率方程的流程图,并进行实例计算。计算结果表明,残余应力引起的频率偏移随着t/L的减小而增加;残余应力与频率偏移之间呈现出明显的非线性特性。     

Uncertainty Propagation for NIST Visible Spectral Standards

Uncertainties in the NIST spectral standards for detectors and sources in the visible wavelength range are propagated from the high accuracy cryogenic radiometer measurements, taking correlations into account at every stage. Partial correlations between spectral values at different wavelengths, important for subsequent radiometric calculations, are estimated. Uncertainty propagation through fitting and through transfer spectral measurements is described in detail. Detector uncertainties are propagated through the spectral comparator facility for external calibrations and for internal photometric quantities. Uncertainties in spectral irradiance are derived for the detector-based temperature determination, then propagated through working standards to calibrated artifacts. Spectral irradiance calibrations are generally provided at a limited number of wavelengths. Interpolation, rather than fitting, is recommended for the interpolation of NIST-provided spectral irradiance values.     

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.     

Primary Atomic Frequency Standards at NIST

The development of atomic frequency standards at NIST is discussed and three of the key frequency-standard technologies of the current era are described. For each of these technologies, the most recent NIST implementation of the particular type of standard is described in greater detail. The best relative standard uncertainty achieved to date for a NIST frequency standard is 1.5×10⁻¹⁵. The uncertainties of the most recent NIST standards are displayed relative to the uncertainties of atomic frequency standards of several other countries.     

The Problem of Estimating the Uncertainty of the Fixed Point Temperature Due to the Presence of Impurities

The main problems in estimating the uncertainty due to the presence of impurities in the material: the absence in the documents of a unique definition of the quantity being measured – the fixed point temperature, the lack of agreed methods of realizing the fixed points and the insufficient justification of the equations used for the estimate, are analyzed. The results of a measurement of the melting point of gallium are presented, which differ in the conditions in which they were realized – with one and two liquid-solid interfaces and different solidification conditions, are presented. The reasons for the considerable difference between the values of the temperatures obtained in these experiments are discussed.     

Improvements in Atomic Cesium Beam Frequency Standards at the National Bureau of Standards

The National Bureau of Standards Frequency Standard, NBS-III, a cesium beam with a 3.66-meter interaction region, has been in operation since 1963. The last published (1966) accuracy capability for NBS-III was 1.1 ? 10-12(l?). Recently, several new solid-state broad-band frequency-multiplier chains have been constructed. Reduction of the random phase noise by more than 20 dB compared to the previous state of the art has been obtained consistently. In addition, a solid-state servo system has been installed to control the frequency of the 5-MHz slave oscillator. Comparisons were made between NBS-III and one of the commercial cesium standards in the NBS clock ensemble. The relative fractional frequency stability ?(N = 2, T = 7 days, ? = 1 day) = 1 ? 10-13 was observed for nine weekly comparisons. The very-long-term frequency stability for this recently improved NBS-III system has not been evaluated fully. Due to the improvements both in electronic systems and evaluative techniques, however, an accuracy of 5 ? 10-13(1?) for a single evaluative experiment is reported. Substantial effort is being expended toward improvement of the accuracy and figure of merit (presently 10) of the NBS cesium standard. The modified system, to be called NBS-5, is expected to be in operation in the latter half of 1970 and to exhibit a figure of merit in excess of 500.     

Recent Progress of Single-Ion Optical Frequency Standards

Recent progress of single-ion optical frequency standards is reported. Based on clock transitions in single ions trapped and laser-cooled in ion traps, measurements with fractional uncertainties down to the 10^?18 level have been achieved. Overview of the measurements reported so far is described. New attempts to overcome the limitations of the measurements are also reviewed.     

Recalibration of the NBS Glass Standards of Spectral Transmittance

In 1934, Gibson, Walker, and Brown developed sets of four colored glass filters to serve as working standards of spectral transmittance for checking the reliability of spectrophotometers. Several sets of these glasses were measured carefully and reserved and designated as future reference standards. Duplicate standards evaluated by comparison with the reference standards are available by purchase to the public. The current set of reference standards was established in the years 1945 to 1947, and one of these reference standards (selenium-red) was recalibrated in 1952. This paper reports a recalibration, made in 1961 and 1962, of all four glasses (selenium-red, carbon-yellow, copper-green, cobalt-blue) on three spectrophotometers (Cary 14, Beckman DU, König-Martens). Except for the cobalt-blue standard, the values of spectral transmittance found differ from those previously assigned by amounts differing at some wavelengths by as much as or slightly more than the uncertainties estimated for the present values, though not by amounts exceeding the combined uncertainties of the present and previous determinations. The indicated changes for these three standards are fairly regular, however, and support the view that the selenium-red and carbon-yellow standards are changing chiefly by formation of a reflectance-reducing film on the surfaces. The indicated rate of upward drift is slow, and suggests that it takes about 10 years for the drift to exceed the assigned uncertainity.     

Recent Progress in Cs Beam Frequency Standards at the NRLM

Some causes and cures of frequency uncertainty in the cesium beam frequency standard, NRLM-II, are described. Accuracy reevaluation indicates about 2.2 × 10-13, and the standard frequency is about 8 × 10-14 below that of the International Atomic Time (TAI) scale. The frequency stability is estimated as better than 8 × 10-12 ?-1/2 for short-term and 4 × 10-14 for 1-2 day averages.     

小型光抽运铯束频标在不同抽运-检测机制下的光频移

本文对光抽运铯束频标中４种不同的光抽运、光检测机制下的光频移及其对频标频率准确度的影响作了计算。同时还计算了铯炉温度、微波功率及激光功率等因素的变化对光频移引起的频率移动的影响。     

An Intercomparison of Hydrogen and Cesium Frequency Standards

Intercomparisons of average frequency and of frequency stability were made among one Hewlett-Packard 5060A cesium beam, two Varian Associates H-10 atomic hydrogen masers, and the National Bureau of Standards NBS III cesium beam designated as the United States Frequency Standard. Each of the standards displayed a white noise frequency fluctuation behavior with a transition into an approximate flicker of frequency fluctuation behavior for longer time intervals. The rms fractional frequency fluctuation between adjacent samples, ?(?, N = 2), was 6 × 10-11?-1/2 down to a flicker level of about 3×10-13 for the hp 5060A cesium beam (102 ? ? ? 104s), 1 × 10-11?-1/2 down to a flicker level of less than 1×10-13 for NBS III cesium beam (102 ? ? ? 104s), and 5×10-13?-1/2 down to a flicker level of about 1×10-14 for the H-10 hydrogen masers (1 ? ? ? 104s). The accuracy capabilities of NBS III and H-10 #4 are now 1.1×10-12 and 0.47×10-12, respectively (1? estimate). A discrepancy of only 1.1 parts in 1012 was observed between the average frequencies of the hp 5060A cesium beam and the NBS III cesium beam, with the former being higher in frequency. In terms of the frequency of the Cs133 hyperfine transition (F=4, mF = 0)?(F=3, mF = 0), defined as 9 192 631 770.0000 Hertz, the measured frequency of the H1 hyperfine transition (F=1, mF = 0) ?-F = 0, mF = 0) was vH=1 420 405 751.7864±0.0017 Hertz.