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An effort to develop a trapped-ion-based fieldable frequency standard with a stability of 4*10/sup -13// square root tau for averaging times tau >

A study of velocity distributions of hydrogen atoms effusing out of radio frequency (RF) discharge is presented. The velocity distributions of hydrogen atoms effusing out of an RF discharge dissociator having a geometry and operating parameters resembling those of a maser dissociator were determined. Realistic calculations of the velocity-dependent transmission of hexapole-magnet state selectors were performed. Designs yielding good matches between atomic velocity distribution and magnet transmission were investigated and the consequences of possible mismatches were explored. An analysis of the focusing properties of hexapole magnet state selectors shows that the efficiency of hydrogen use by the maser can be increased significantly by optimizing the state selector design for the actual atomic hydrogen velocity distribution. Some test results are presented. >

The high C-field Cs beam frequency standard is presently a working machine which is undergoing first accuracy evaluations. The projected 10/sup -14/ accuracy goal is as yet unattained mainly because of inadequate C-field uniformity and stability. An analysis of the projected possible C-field improvements and the consequent uncertainty is here reported.

This paper reports on the design and evaluation of a high-stability current control developed for energizing the C-field magnet of the high-field cesium standard experiment, currently in progress at the Politecnico di Torino. This source must supply about 0.8 kW dc power with a current stability in the 10^-7 range up to more than one hour.

Cesium atomic frequency standard is under development at the Politecnico di Torino. The whole resonator is conceived to reduce a number of systematic effects which are difficult to evaluate at the 10/sup -14/ accuracy level in traditional schemes. Some new solutions such as C-field value, cylindrical microwave cavity design and state selection method have been introduced in order to meet this goal. The overall design guidelines and the first results are reported and discussed.

Research on the magnetron cavity used in the rubidium atomic frequency standards is developed, through which the main characteristic parameters of the magnetron cavity are studied, mainly including the resonant frequency, quality factor and oscillation mode. The resonant frequency and quality factor of the magnetron cavity were calculated, and the test results of the resonant frequency agreed well with the calculation theory. The test results also show that the resonant frequency of the magnetron cavity can be attenuated to 6.835 GHz, which is the resonant frequency of the rubidium atoms, and the Q-factor can be attenuated to 500–1000. The oscillation mode is a typical TE011 mode and is the correct mode needed for the rubidium atomic frequency standard. Therefore these derivative magnetron cavities meet the requirements of the rubidium atomic frequency standards well.

Electric dipole polarizabilities of atoms are very important in many different physical applications, such as the precision atomic frequency standard. Calculations of these properties are very important and challenging. We propose a calculation strategy to calculate the frequency dependent dipole polarizabilities with high precision variationally by using a set of high quality orbital bases where the electron correlations can be taken into account adequately. The static polarizabilities of the ground state of Na are calculated accurately by such a method and can be compared with precision experiment measurement directly. The calculation result is in excellent agreement with the available experimental measurements within about 0.1%, which demonstrates the validity of our strategy. Our calculation strategy has a wide usage, not only in polarizibilies, but also in other fields such as theoretical treatment of electron-atom scattering processes. Using the same orbital bases, we carry out precision calculation of Na− affinities. Our calculated affinity is in excellent agreement with precision laser spectroscopy measurements within 0.1%.

Using a set of high quality orbital basis, we carried out precision calculations of the static polarizabilities of Na at ground state and the affinities of ground Na−, where the accurate experimental measurements are available. By taken into account the electron correlations adequately, our calculation results are in consistent with precision experimental results within about 0.1%. Using this high quality basis, we would be able to calculate the frequency-dependent polarizabilities with high accuracy, which is very important for ac Stark coefficients calculations used in atomic frequency standard.

According to our measurement, the coefficient of microwave power shift in the 87Rb frequency standard is always positive. The previous explanation about microwave power shift can not explain this phenomenon. The theory presented in the present paper, starting from the view of AC Zeeman effect caused by microwave field, can explain it.

The course of development of measuring time from early days to the present has been described. Different time scales like the astronomical universal time UT1 UTa and Ephemeris have been explained. The use of atomic frequency standard and the associated atomic time scale have been discussed particularly with regard to their relationship with astronomical time-scale.

There are two concerns regarding the civil use of the Global Positioning System (GPS). The first is “integrity,” which is the possibility that GPS transmits an erroneous navigation signal to the user. A malfunction of the atomic frequency standard in the satellite is regarded as a possible integrity problem. The second concern is the areas of degraded performance. Although four satellites may be visable, because of poor satellite geometry the accuracy of navigation can be severely degraded for a short period of time. This paper discusses an approach to the solution of each of these two issues. It is shown that a communications type geostationary satellite is a common element to the solution of both concerns. Also common to both is a network of integrity monitoring and control stations. The paper discusses a system to cover the North American continent and also how it might be expanded to become worldwide.

RF traps are widely used nowadays in high resolution hyperfine spectroscopy. The spectrum of the microwave hyperfine transition at 40.5 GHz of the fundamental level2S1/2 of199Hg+ is phase modulated at the secular frequency of the stored ions and it consists of a narrow central line and lateral bands broadened by the ion trajectory and velocity distribution. The central line itself is shifted by the second-order Doppler effect which is the most important systematic error of stored ions frequency standards. In this paper the relativistic Doppler effect in the case of199Hg+ stored ions is deduced applying a mathematical formalism and using physical parameters that we have measured experimentally.

Atomic beam frequency standards may be placed into two categories: field standards and laboratory standards. While this distinction is somewhat artificial, because the two types of standards are interdependent, each category does have different requirements of accuracy, size, and cost. Despite this separation, generally the developments which produce the best laboratory standards eventually give rise to improved field standards. Existing field standards are limited in long term fractional frequency stability to σy (τ) ∼ 3 x 10-13, for τ ∼ 6 months. A laboratory standard such as NBS-6, the U.S. primary cesium standard, is limited in inaccuracy to Δy ∼ 8 x 10-14. Proposed new cesium field standards are expected to yield long term stabilities of σy(τ) ∼ 1 x 10-14 (τ = 6 months). Stored ion standards, prime candidates for new laboratory frequency standards, are expected to have better than Δy = 1 x 10-15 inaccuracy. As other approaches to atomic beam frequency standards are considered, they should attempt to compete favorably with these emerging technologies.

Recent advances towards the realization of an absolute frequency standard in the submillimeter region are reported. The3p 1 -3 P_{0} \Delta m_{j} = 0 fine structure transition in the metastable triplet of24Mg has been observed in an atomic beam with both Rabi and Ramsey interrogation techniques. Experimental results and theoretical predictions are compared and discussed in view of an Mg frequency standard.

The results of various studies concerning the lifetime and reliability of the rubidium discharge lamp used in the rubidium atomic frequency standards are reported. The primary life-limiting process in these lamps involves diffusion of the rubidium atoms into the glass envelope of the lamp, making them unavailable to the discharge. The rate at which rubidium atoms diffuse into the glass is dependent on lamp conditions, including lamp size, type of glass, lamp temperature, and rf drive power. The calorimetric technique to measure the elemental rubidium content in a lamp and its use for quality control in the lamp manufacturing process are discussed. Keywords include: Alkali discharge lamps, Atomic frequency standard, Rubidium atomic clocks, Rubidium lamps.

Countless are nowadays the applications of Time/Frequency methods and systems to science and technology: the daily production of more than 300 000 quartz units, with precisions ranging from 10E-5 to 10E-10, barely satisfies the needs of factories making wristwatches, cars, PCs, dishwashers, etc..

Microwave cavities, or microwave resonators, are used in a variety of applications, including filters, oscillators, frequency meters, and tuned amplifiers. The ever-increasing demand for compact and/or portable telecommunication systems drives the need for further miniaturization of such structures for improved integration. In this thesis, new miniature microwave cavity solutions are proposed, which are useful in at least two scopes of application. In the first scope, the new devices are used as microwave front-ends of a short-range radar system for on-line blade tip monitoring in gas turbines (i.e. land-based large-frame turbines, aero-derivatives and aero-engines). In general, microwave sensors are advantageous for blade tip sensing: contrary to other existing techniques, they can survive to high temperatures for extended period of operation, unaffected by contaminants, like gases and dirt. Nonetheless, the microwave front-end of such systems is of difficult implementation, due to the strict thermal-mechanical constraints of the specific field of application (i.e. a large temperature change, the presence of vibrations, dirt and combustion by-products) and the tight requirements on the size of candidate probe designs. Antenna-based solutions are currently used as tip monitoring probes, with the disadvantage of being complex structures with radiation characteristics that are not entirely well suited for short range sensing. As a valid alternative, we propose two cavity-based probe solutions, namely a miniature waveguide resonator probe and a coaxial resonator probe, which represent an elegant compromise between robustness, miniaturization and simplicity of operation. Tests in laboratory and on real turbine engines demonstrated the suitability of such devices for the aimed application and several improved characteristics with respect to other comparable techniques, like antenna-based and eddy-current sensors. In the second scope, the new proposed solutions are used as microwave resonators in miniature rubidium atomic clocks. Attempts to miniaturize such kind of systems are usually limited by the dimensional constraints of standard microwave cavity resonators (MWR) , which account for a large part of the volume of the physics package. We propose a new miniature MWR based on a loop-gap resonator structure, also referred to as the μ-LGR. This cavity design meets the desired field configuration for the atomic clock operation and achieves an interesting size-reduction. A laboratory experiment of an atomic clock integrating the μ-LGR achieved unmatched results of stability compared to other microcell clocks. Finally, we propose a miniature planar MWR for the integration of 2D microfabricated cells.

In this study, we investigate a concept that can be used to improve the magnetic field homogeneity in a microwave cavity applied in a novel, high-performance atomic frequency standard. We show that by modifying the boundary conditions in the case of a loop-gap geometry, a good improvement of the field homogeneity can be obtained. Such a design demonstrates high potential to improve the frequency stability; it is compact and hence suitable for a future generation of compact, high-precision frequency standards based on vapor cells and a pulsed optical pumping (POP) regime (POP atomic clocks).

Device of pulse optical pumping and pulse sampling optical detection is presentedto reduce the light shift in Rb87 atomic frequency standard. The 0-0 transitionlineshape and light shift is calculated. It is qualitatively, inagreement with the experimen-tal results. With this device, one may expect to improve the long term frequency sta-bility of the passive Rb87 atomic frequeney standard.

SEVERAL atomic frequency standards of different types are now in use for comparisons with astronomically determined time. As the adopted frequencies of these atomic standards have been derived from the smoothed universal time U.T. 2, which is itself variable in time1, they disagree by several parts in 109. In order to obtain a uniform base for the atomic times determined by the different standards, their frequencies have to be compared directly. This has been done between caesium resonators at the National Physical Laboratory in Teddington and the Naval Observatory in Washington using the GBR 19.6 kc./s. transmissions. Later the same comparison was repeated between similar caesium resonators at the National Physical Laboratory2.

An experimental miniaturised rubidium frequency source which has been built in a volume of a little more than 100 in3 provides a stability of better than 1 part in 108 over one year and a warm-up time of 5 min. This long-term stability lies between that of a good crystal frequency standard and a high-grade rubidium atomic frequency standard.

The use of two extremely stable radio-frequency oscillators, one stationary and the other mobile, is described for measuring relative phase difference between widely separated elements of large aerial arrays. Results of measurements made at 80MHz on the 96-aerial Culgoora radioheliograph, using an atomic frequency standard for the mobile unit, demonstrate that the method is suitable for phase-calibration purposes.