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Among several kinds of traditional atomic clocks, rubidium atomic clock shows more extensive applications for its small size, low power and simple structure. In last 20 years, driven by the demands of satellite navigation and relevant fields, the Rb atomic clock has been greatly improved on its frequency stability. Now the long-term stability of satellite-borne Rb atomic clock is better than \(5 \times 10^{ - 15}\) at one day. However, when Rb clock runs under atmospheric condition, its long-term stability performance deteriorate seriously. There is a 10 to 100 times deterioration at \(10^{4}\) s and one day, which makes Rb clock impossible to reach \(10^{ - 15}\) level. For solving these problems, to develop a high-stability, low-drift and compact-structure type of high performance Rb clock which could fit the atmospheric environment, we conducted a sufficient research on high-performance Rb clock’s environment adaptation. Finally, we developed a prototype whose stability reached \(6.5 \times 10^{ - 13} /\sqrt \tau\), \(7.0 \times 10^{ - 15}\) at \(10^{4}\) s and \(5.0 \times 10^{ - 15}\) at one day.

This paper proposes a miniature optically pumped cesium-beam atomic frequency standard with a volume of 38.4 l and a weight of 28 kg and examines the main factors that affect its signal-to-noise ratio (SNR). Methods to improve the SNR are proposed, which improve the short-term frequency instability: installing a collimator at the exit of the cesium oven, using the beam fluorescence spectrum with the fiber-coupled output to stabilize the laser frequency, and using the 4–5 cycling transition of the cesium D2 line for the atomic detection. We also examine several frequency shifts that affect the long-term frequency instability and detail methods to reduce these shifts. At present, the frequency instability achieved by the Peking University miniature optically pumped cesium-beam frequency standard has reached 3.12×10−12/τ.

Rubidium atomic frequency standard (RAFS) is the most widely used frequency standard in space. The light used to pump the atoms and detect the resonance signal is emitted by rubidium spectrum lamp, so the light intensity of rubidium spectrum lamp directly determines the performance of RAFS. This paper discussed on-board RAFS’ output frequency fluctuations caused by rubidium spectrum lamp. The reason of frequency fluctuations from rubidium lamps was described. To obtain stable lamp light intensity, analysis and optimization of the lamp was developed. Relevant experiments were carried out to verify the optimization. The study content of this paper is beneficial to improve the performance of a single temperature controlled space RAFS physics package.

We report our progress on a high-precision microwave frequency standard that is based on trapped $^{\mathbf{171}} \mathbf{Yb} ^{\mathbf{+}}$ ions. In the presence of a buffer gas, a short-term stability of 8e13 at 1s and $1e-12/\sqrt{\tau}$ for times less than 100 s is demonstrated. Laser-cooling is demonstrated to produce a crystal whose unique decay pattern prohibits closed-loop clock operation.

In the Rb atomic frequency standard (RAFS), the 2ndharmonic signal, S2, is routinely taken as a “Status-of-Health” indicator for the atomic signal. In part, this role for S 2 derives from the Quasi-Static Approximation (QSA), where harmonic signals are taken as proportional to derivatives of the static lineshape. However, clock operating conditions violate the assumptions of the QSA, and so justification of the relationship between S 2 and $\text{dS}_{1}/\mathrm{d}\Delta\vert_{\Delta=0}$ (i.e., the correction signal's slope on resonance) is questionable. To better understand S 2 and its potential as a status-of-health indicator, we are continuing a series of experiments begun in our laboratory. Here, we discuss the role of temperature gradients on S 2 , and the extent to which temperature gradients might or might not influence S 2 's ability to monitor clock health.

The rubidium (Rb) atomic frequency standard (RAFS) is quite literally the workhorse of atomic timekeeping in space. Consequently, there is considerable interest in improving its frequency stability and reliability. Chief among the RAFS' components, the rf-discharge lamp is arguably the most problematic. The rf-discharge lamp not only determines the signal-to-noise ratio of the device, but fluctuations in its intensity and/or spectrum map onto the clock's output frequency via the light-shift effect. Understanding the rf-discharge lamp's operation and behavior would therefore seem important for understanding the limitations of a RAFS' frequency stability and reliability. It is surprising then to find that at present no well-articulated theory of the lamp's operation exists. To remedy that situation, we have begun a research project to develop a model of rf-discharge lamp operation, with the eventual goal of uncovering pathways for rf-discharge lamp, and thereby RAFS, improvement. In the present work, our purpose is to employ a semi-quantitative theory of the rf-discharge lamp to better understand the relation of electron number density and Rb light emission to lamp temperature.

We present a compact optical frequency standard based on two-photon spectroscopy at 778 nm in a rubidium vapor cell. We demonstrate fractional instability of 3e-13/, √τ/s for timescales up to 10,000 s. Additionally, we describe a secondary system operation in which the short-term stability is improved (though at the expense of the long-term stability) using increased laser power, resulting in 1 s instability < 1e-13. The system has been designed as an advanced atomic frequency standard for GNSS applications, and is currently being investigated for demonstration on AFRL's Navigation Technology Satellite 3 (NTS-3), an upcoming space flight experiment to middle earth orbit scheduled for launch in 2022.

Atomic clocks onboard satellites are of importance for Global Navigation Satellite Systems (GNSS). Frequency jumps are common in rubidium atomic frequency standard (RAFS). Real-time detection and correction of these jumps are of vital importance due to the direct impact on the GNSS positioning, navigation and timing (PNT) performance. The latest BDS C13 satellite is an IGSO satellite in replacement of the old MEO. This paper preliminarily analyzes the characteristics of BDS C13 onboard satellite clocks using the methods of block averaging (BLKAVG), sequential averaging (SEQAVG), cumulative sum (CUMSUM). Results show that C13 satellite clock underwent several frequency jumps and a clock switch during the investigated period.

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.

In the rubidium atomic frequency standard (RAFS), an rf-discharge lamp produces the device's atomic signal. As a consequence of the light-shift effect, variations in the lamplight's intensity result in variations in the RAFS' output frequency. While the basic physics of the light-shift is reasonably well understood, its operational implications for GNSS performance are only beginning to be fully appreciated. Here, we summarize results examining decade-long histories of on-orbit GPS RAFS lamplight variations. In addition to a deterministic variation that is well modeled by the sum of an exponential and linear trend, the stochastic variations appear to be of three types: lamplight jumps, repeating lamplight ramps, and non-stationary lamplight noise. Employing an estimated GPS RAFS light-shift coefficient, these variations can be used to infer lamplight-induced RAFS frequency variations.

There are many different atomic frequency standard technologies but only few meet the demanding performance, reliability, size, mass, and power constraints required for space operation. The Jet Propulsion Laboratory is developing a linear ion-trap-based mercury ion clock, referred to as DSAC (Deep-Space Atomic Clock) under NASA’s Technology Demonstration Mission program. This clock is expected to provide a new capability with broad application to space-based navigation and science. A one-year flight demonstration is planned as a hosted payload following an early 2017 launch. This first-generation mercury ion clock for space demonstration has a volume, mass, and power of 17 L, 16 kg, and 47 W, respectively, with further reductions planned for follow-on applications. Clock performance with a signal-to-noise ratio (SNR)*Q limited stability of $1.5{\rm E}-13/\tau^{1/2}$ has been observed and a fractional frequency stability of 2E–15 at one day measured (no drift removed). Such a space-based stability enables autonomous timekeeping of $\Delta t with a technology capable of even higher stability, if desired. To date, the demonstration clock has been successfully subjected to mechanical vibration testing at the $14\,{\rm g}_{\rm rms}$ level, thermal-vacuum operation over a range of $42^\circ{\rm C}$ , and electromagnetic susceptibility tests.

Precision navigation and timing is an important focus in the Air Force Research Laboratory's experimental efforts. The development and testing of an optical frequency standard is suitable for an array of both terrestrial and space based applications. An optical atomic clock based upon a two-photon transition at 778 nm in rubidium, is an ideal candidate to meet the requirements of Global Satellite Navigation System (GNSS), while being a viable option for other applications. Here we demonstrate that a simple architecture, using off-the-shelf components and an external cavity diode laser system that is confined to less than 3 ft2 of breadboard, exhibits a frequency instability of 7 x 10-13/??, for times less than 100 seconds.

This paper investigates the absorptive spectral lines of four-level atomic system driven by a coupling, probe and microwave fields. Due to the perturbation of the microwave field, the original electromagnetically induced transparency is changed to electromagnetically induced absorption and the absorptive spectral line can be very narrow. This ultranarrow spectral line has potential applications to the microwave atomic frequency standard and the measurement of very weak magnetic field.

To commemorate the fiftieth anniversary of the development of the first atomic frequency standard, we present some notes about the work of Louis Essen at the National Physical Laboratory. In addition, we publish below some personal recollections of Essen on his work, which have previously been available only on the Internet (http://www.btinternet.com/~time.lord/TheAtomicClock.htm).

As part of a programme to implement scientific time and frequency metrology in Brazil, the caesium-beam frequency standard of the Instituto de Fisica de Sao Carlos has been improved in order to obtain greater accuracy. Our most recent evaluation shows an Allan standard deviation of σy(τ) = (1.8 ± 0.2) × 10-11τ-0.5, corresponding to an improvement of two orders of magnitude over our previous evaluation. Estimates of the main shifts of the frequency standard, such as second-order Doppler shift, end-to-end cavity phase shift, and Rabi frequency value, have been performed employing two different methods that allow the results to be extracted from the Ramsey pattern.

This paper summarizes the experience and results throughout the development process of the Spaceborne Rubidium Atomic Frequency Standard (SRAFS) in Beidou navigation satellite system, analyzes the characteristics of SRAFS, as well as the effect of different states between the in orbit operation status and the ground test status. It presents the ground test program and the main requirements in the development process of SRAFS and puts forward issues need to pay attention, so that the technology level and product quality of the China SRAFS are improved and standardized.

The influence of a stabilized laser's fluctuations in an optically pumped atomic frequency standard is considered. It is important to use a laser with narrow linewidth and select the modulation frequency where the laser's free-running frequency fluctuation at twice the modulation frequency is the lowest. Employing these considerations, the stabilized laser for our optically pumped cesium beam frequency standard is designed. © 2001 Scripta Technica, Electr Eng Jpn, 136(2): 31–37, 2001

The SI unit of mass, the kilogram, is defined by a single artifact, the International Prototype Kilogram. This artifact, the primary mass standard, suffers from long-term instabilities that are neither well understood nor easily monitored. A secondary mass standard consisting of a 1-kg quartz resonator in ultrahigh vacuum is proposed. The frequency stability of such a resonator is likely to be far higher than the mass stability of the primary mass standard. Moreover, the resonator would provide a link to the SI time-interval unit. When compared with a laboratory-grade atomic frequency standard or GPS time, the frequency of the resonator could be monitored, on a continuous basis, with 10(-15) precision in only a few days of averaging. It could also be coordinated, worldwide, with other resonator mass standards without the need to transport the standards.

We have proved experimentally that the frequency shift formula of AC Zeeman effect presented by us is correct. In a 87Rb atomic frequency standard we add a new microwave field which causes the frequency shift of 0-0 transition frequency of 87Rb atomic ground state. This frequency shift as a function of frequency and power of the added microwave field is measured. The experimental results agree with theory.

Recent progress are reported on a compact cesium cell atomic frequency standard based on pulsed Coherent Population Trapping interaction in the Dicke regime. Main short term and long term limiting parameters have been identified. Last improvements have permitted to reach a stability of 7×10−13 at 1sec and 2×10−14 at 2000 s. The noise characterization process is presented in this article.

We demonstrate a high-performance laser-pumped rubidium-cell atomic frequency standard exhibiting a short-term stability of < 3×10−13 τ−1/2. The key components of this standard are a Rb vapor cell of 25mm diameter and a newly developed compact microwave resonator cavity. The overall volume of the clock's physics package - including the frequency-stabilized laser head and physics package - is < 3 liters, which shows the potential of this compact clock for future portable applications.

We have been developing a compact frequency standard based on cold cesium atoms. The operation of this experiment is different from conventional cold atoms fountains, since all the steps are sequentially performed inside the microwave cavity.

Frequency stability of an atomic frequency standard depends mainly on the Signal to Noise Ratio (SNR) of atomic discrimination signal. For a Rubidium Atomic Frequency Standard (RAFS), the SNR is closely related to the characteristics of the cavity-cell assembly in physics package. The RAFS in our laboratory is designed based on the slotted tube cavity, and a typical stability of 1.5 × 10−12 τ−1/2 (1–1000 s) has been achieved. The current cavity used in our design is of a disadvantage of field inhomogeneity. To improve further the stability of the RAFS, a modification of the cavity has been carried out. With this modification, the field homogeneity has been greatly improved, and the cavity size was increased also, enabling to hold a larger absorption cell. According to a theoretical evaluation, the SNR of physics package was enhanced by nearly two times, meeting the need to design a RAFS with a stability better than 1.0 × 10−12 τ−1/2.

In this article we present our development of a high performance laser-pumped Rubidium gas-cell atomic frequency standard based on the continuous microwave-optical double resonance interrogation. A larger resonance cell is employed and no laser noise cancellation is required to reach a short-term frequency stability below 4×10−13/√τ for 40 < τ

In this paper, the study advances of a high performance rubidium atomic frequency standard (RAFS) will be reported. The RAFS is a traditional passive rubidium frequency standard. Some important performance test results have been obtained. The RAFS has realized short-term stability of

Rb lamp is a very critical component of the Rb atomic clock’s Physics Package. The Rb lamp’s performance is very sensitive to temperature and its stability. In this paper we discuss the behaviors of Rb Lamp with temperature. The Rb lamp exciter power and temperature of Rb bulb are very important parameters in controlling the performance of the Rb Lamp. It is observed that at temperatures beyond 110° C, the lamp mode changes from the ring to red mode resulting in abnormal broadening of emission lines and self reversal. The results of our studies on spectral analysis of Rb lamp under various operating conditions are reported in the paper.

This paper describes the new twin laser-cooled Cs fountain primary frequency standards NIST-F2 and ITCsF2, and presents some of their design features. Most significant is a cryogenic microwave interrogation region which dramatically reduces the blackbody radiation shift. We also present a preliminary accuracy evaluation of IT-CsF2.

We propose a scheme of obtaining Ramsey fringes based on pulsed coherent optical information storage. Unlike the usual frequency references where the Ramsey fringes are obtained by detecting the population of a certain state, we get the Ramsey fringes by detecting the atomic coherence. The central line of the Ramsey fringes can be used as a frequency reference in an absorption-cell-based atomic frequency standard. This scheme is free of light shifts as the interrogating process is separated from the optical pumping process, and the cavity pulling effect is negligible due to the low $Q$ requirement. Encoding the Ramsey interference into the retrieval light pulse has the merit of high signal-to-noise ratio. This scheme is promising for building small, compact, and stable atomic clocks.

Many perturbations that affect atomic frequency standards vary during the period of measurement. To include this time variation, we introduce 3 time-dependent weight functions built from the solution of the unperturbed equations of motion of a 2-level system. The integral of the time-dependent part of a perturbation with a weight function gives the associated first-order change in transition probability. Biases are then found easily. The same weight function may be used for different perturbations, thus unifying the derivation of their associated biases. We give several examples of the use of weight functions.

This paper describes the new twin laser-cooled Cs fountain primary frequency standards NIST-F2 and IT-CsF2, and presents their most innovative design features. Most significant is a cryogenic microwave interrogation region which dramatically reduces the blackbody radiation shift. We present as well a preliminary accuracy evaluation of IT-CsF2.

A new prototype atomic fountain clock working in the micro-gravity environment is proposed. The successive Ramsey interactions of cold atoms and oscillatory field are realized by means of computer-controlled periodic motion of oscillatory field while the cold atoms stay still relatively in the prototype. Preliminary analyses in comparison with the atomic fountain clock working on the ground show that higher stability is obtainable in the prototype.

Reported is the original implementation of a microcell (1 mm 3 ) in which a stable cesium vapour is generated after the cell is sealed. This new type of microcell is suitable for chip scale atomic clocks (CSACs) and can be realised at the industrial scale in an economic way

This paper devoted to some aspects of OCXO application in an output stage of atomic frequency standard. The specific requirements that the OCXO must meet are excellent short term frequency stability and good total operational stability during very long life time. Also, we consider the low power consumption of the OCXO as a very important feature particularly for autonomous and Space applications. The main target of this project was a significant improvement of short term stability of basic OCXO designed with Internally Heated Quartz Resonator (IHQR).

The Kenschaft model is a relatively simple, yet accurate, means to simulate the response of the physics package of a rubidium gas cell passive atomic frequency standard to a modulated microwave interrogating signal. It is based on an analysis of the response of a two-level atomic system to modulated RF, and can be represented in the form of a block diagram. This model allows the relevant physical parameters to be identified and adjusted, and yields responses that show remarkable agreement with actual hardware.

We discuss a design for a space based atomic frequency standard (AFS) based on Hg/sup +/ ions confined in a linear ion trap. This newly developed AFS should be well suited for space borne applications because it can supply the ultra-high stability of a H-maser but its total mass is comparable to that of a NAVSTAR/GPS Cs clock, i.e., about 11 kg. This paper compares the proposed Hg/sup +/ AFS to the present day GPS Cs standards to arrive at the 11 kg mass estimate. The proposed space borne Hg/sup +/ standard is based upon the recently developed extended linear ion trap architecture which has reduced the size of existing trapped Hg/sup +/ standards to a physics package which is comparable in size to a Cesium beam tube. The demonstrated frequency stability to below 10/sup -15/ of existing Hg/sup +/ standards should be maintained or even improved upon in this new architecture. This clock would deliver far more frequency stability per kilogram than any current day space qualified standard. >

The specific application of several analytical total quality control tools is discussed. One example deals with the restructuring of the method of handling cesium beam tube (CBT) work orders. The result is a reduction of manufacturing cycle time as well as a reduction of the total word-in-progress inventory. A corresponding improvement of the CBT performance is observed. The influence of total process control on existing and potential suppliers of CBT parts is discussed. >