Observatoire de Neuchâtel (ON) has recently started breadboarding activities for an Optically-pumped Space Cesium-beam Atomic Resonator in the frame of an ESA-ARTES 5 project. The goal is to demonstrate a frequency stability approaching σy = 1x10-12 τ-1/2 with the simplest optical scheme (a single optical frequency for both the atomic pumping and detection processes). This development constitutes a fundamental step in the general effort to reduce the mass of the on-board clocks, while keeping or even improving its performances. It will take advantage of previous activities at ON in the late ’80 and of the latest progresses in the field of tunable and narrow-band laser diodes.

Optical pumping on the cesium (Cs) D1 transition at 894 nm, as compared to the Cs D2 line at 852 nm, can present advantages for e.g. Cs thermal beam atomic clocks or other atom-based sensors and instrumentation, due to its simpler hyperfine structure, larger atomic level splitting, and absence of cycling transitions. Here we report on the realisation and spectral characterisation of custom-made narrow-band DFB laser diodes emitting at 894 nm.

The Quantime project aims at developing a miniature atomic clock suited for the telecom market, requiring a wide operating temperature range (from -40 to +85°C), and a low production cost. The CPT (Coherent Population Trapping) technique for atomic interrogation is used for miniaturization and low power consumption. In the first phase of the project, the clock architecture was chosen, and the main sub-systems were developed. A clock breadboarding demonstrator was assembled and the measured Allan deviation of 1E-11 at 400 s confirms the operation of all the sub-systems.

Thales Electron Devices is leading a French-Swiss industries and research institutes consortium aiming at developing an Optically-pumped Space Cesium Clock for Galileo. The technical objective of this development is to demonstrate a frequency stability of 1x10(-12) tau(-1/2) compatible with an operational lifetime of twelve years. The present clock demonstrator combines the simplest and best technologies available, among those the single optical wavelength scheme and the dark fringe Ramsey cavity. Presently a clock operational signal-to-noise ratio of 21'300 Hz(1/2) has been recorded for a Cs oven heated at 100 degrees C. The clock frequency stability has been measured to be 2.3x10(-12) tau(-1/2). The current limitations and future improvements arc discussed.

Thales Electron Devices has been pursuing since 2003 frequency standards activities. In the framework of these activities, Thales established a consortium for the development of a space Cs atomic clock for Galileo. This consortium is composed by two of the best scientific laboratories in the European Time-Frequency community: the Observatoire de Neuchatel (ON) and the SYRTE Observatoire de Paris, and by two space industrials: Oerlikon Space AG (OSAG) and Thales Electron Devices. The name of the project is OSCC for Optically pumped Space Cs Clock. The first phase (phase A) of this development started in June 2006 under an ESA contract.The purpose of this phase A is a feasibility study of Cs clock technology for Galileo with the manufacturing and the test of a new compact optically pumped Cs clock breadboard. This technology is well known in laboratories but it has never been industrialized, even for ground applications. This study starts with a strong background at SYRTE and ON, but also with new industrial developments realized at Thales during the last years. Frequency stability in order of 1 to 3x10(-12).tau(-1/2) has been already demonstrated in lab with different configurations.This document will first synthesize the last results obtained by each Partner, followed by the results of the existing hardware analysis performed in the first step of the project. This analysis allowed Partners to share their know-how and to identify the limits of each existing breadboards with respect to the objectives of the project. As a result of this analysis, it was possible to define the atomic resonator best configuration for each subsystem. At least, this document presents a few design drivers of the new OSCC devices.

Observatoire de Neuchatel has developed a compact optically-pumped cesium beam frequency standard in the frame of an ESA-ARTES 5 project. The simplest optical scheme, which is based on a single optical frequency for both preparation and detection processes of atoms, has been chosen to fulfill reliability constraints of space applications. With the last evolution of our laboratory demonstrator, we have measured a frequency stability of sigmay=1.14 times10-12 tau-1/2, which is compliant with the Galileo requirement and our frequency stability goal of sigmay=1.14 times10-12 tau-1/2. Present performance limitations are discussed and further improvements are proposed to possibly increase the frequency stability.

Atomic Clock Ensemble in Space (ACES) is a mission in fundamental physics that will operate a new generation of atomic clocks in the microgravity environment of the International Space Station. Fractional frequency instability and inaccuracy at the 10(-16) level will be achieved. The on-board time base, distributed on Earth via a microwave link; will be used for space-to-ground as well as ground-to-ground comparisons of atomic frequency standards. Based on these comparisons, ACES will perform fundamental physics tests and develop applications in time and frequency metrology, universal time scales, global positioning and navigation, geodesy, and gravimetry. After a. general overview of the mission concept and its scientific objectives, the present status of ACES instruments and sub-systems will be discussed.

In the frame of the scientific mission Atomic Clock Ensemble in Space (ACES), Observatoire de Neuchâtel (ON), Switzerland, is developing the Space Hydrogen Maser (SHM) in collaboration with Contraves Space AG (CSAG), Switzerland. The Physics Package of the Engineering Model is assembled and performs as specified: for nominal operational parameters, the long-term frequency stability is 1×10-15 @ 10'000s, thanks to the Automatic Cavity Tuning (ACT). The ACT concept based on a pulsed interrogation scheme of the cavity has been developed and demonstrated with a laboratory demonstrator at ON. The space compatible electronics package is being assembled by CSAG and preliminary functional tests are satisfactory.

We report on the design, construction, and preliminary measurements on the resonator of a continuous Cs fountain frequency standard. The construction of the resonator is described, preliminary measurements of the available atomic flux, and of the beam temperature are presented, along with the first Ramsey fringes (width /spl sime/1 Hz) obtained in this new type of fountain. We discuss theoretical aspects of the interrogation scheme with a special view on how aliasing or intermodulation effects are suppressed in a continuous fountain.

We report on the primary frequency standard now under construction at the Observatoire de Neuchatel (ON). The design is based on a continuous fountain of laser-cooled cesium atoms, which combines two advantages: the negligible contribution of collisions to the inaccuracy and the absence of stability degradation caused by aliasing effects encountered in pulsed operation. The design is reviewed with special emphasis on the specific features of a continuous fountain, namely the source, the microwave cavity (TE(021) mode), and the microwave modulation scheme. The possible sources of frequency biases and their expected contributions to the error budget are discussed. Based on present data, an accuracy in the low 10(-15) range and a short-term stability of 7.10(-14) are attainable simultaneously under the same operating conditions.

A laboratory frequency standard based on a continuous fountain of cold cesium atoms is under development. The resonator is assembled and the continuous fountain is now in operation. Measurements of atomic flux and temperature are under way. An analysis of noise in Ramsey resonators shows that, in continuous operation, the atomic noise rather than aliasing effects will remain the limit to the relative frequency instability down to the low 10/sup -14/ range with presently available quartz local oscillators.

To achieve a primary frequency standard based on a continuous fountain of laser cooled cesium atoms, we report on the production of a bright, slow and cold continuous atomic beam. Atoms are cooled from a thermal vapor in a 45° laser geometry and launched directly from the optical molasses by the moving molasses technique. The effects of the source fluorescence on the continuous beam (average velocity, temperature and flux) have been observed, and ways to optimize simultaneously the atomic capture and the continuous beam are presented. Flux measurements rise to 2×108 at/s from a 2D magneto-optical trap at 7 m/s. The initial velocity is easily tunable from 1 to 10 m/s. If the longitudinal temperature is about 70 μK, additional transverse cooling even reduces the transverse temperature in one dimension below 30 μK. By extrapolating the obtained atomic flux to the continuous fountain under construction, we expect a short-term stability of 7×10-14τ-1/2. Other applications of continuous beams of cold atoms are suggested

A primary frequency standard based on a continuous fountain of laser cooled cesium atoms is investigated. Results on a feasibility experiment demonstrate the ability of the moving molasses technique to extract a sufficiently intense cold continuous atomic beam. A general overview of such a device and its main parts is described. Stability and accuracy issues are discussed.

We report the first part of an extensive study of friction at a multicontact interface between nominally flat bodies, rough on the micrometer scale, made of polymer glasses. Temperature is controlled between 20 $\ifmmode^\circ\else\textdegree\fi{}$C and the glass transitions of poly(methyl metacrylate) and polystyrene. In this article, we focus on static friction force. The static friction threshold to macroscopic slip increases with the contact time. Increasing temperature is found to accelerate markedly the aging process. This effect is correlated with the strong increase of the sensitivity of plastic creep to the strain rate on approaching the glass transition. A constitutive law for creep is established, taking into account the triaxial nature of the deformations at microcontacts between asperities. This is included into a simple model which provides a satisfactory account for the aging process in terms of creep growth of the overall contact area. A strong effect of the shear force sustained by the interface during the aging process is evidenced and discussed. The possible role of healing due to chain diffusion across the interface is considered as a concomitant strengthening process in the glass transition region.

By the moving molasses technique we have extracted laser-cooled cesium atoms in a continuous way directly from an optical molasses. The mean launching velocity is precisely tunable from 1 to 12 m/s. The atomic beam has a flux of 1.3 x 10(8) atom/s at 7 m/s and a longitudinal temperature of 70 mu K; which represents the highest flux and lowest velocity spread obtained so far in a continuous beam of cold atoms. These features makes it well suited for atomic fountains. The atomic flux can be slightly increased in a two-dimensional magneto-optical trap operation (+40%). A simple model accounts for the observed dependence of the flux with the magnetic-field gradient. [S1050-2947(99)51212-2].

Starting from a 2D magneto-optical trap where cesium atoms are permanently subjected to 3D sub-Doppler cooling and 2D magneto-optical trapping, we have produced a beam of cold atoms continuously extracted along the trap axis. The simplest extraction mechanism, presently used, is the drift velocity induced by a constant magnetic field. We have used this continuous beam of atoms to produce Ramsey fringes in a microwave cavity as a first demonstration of an atomic resonator operating continuously with laser cooled atoms. The shape of the resonance pattern allows an estimate of the axial temperature, typically 200 μK. The average velocity can be adjusted from 0.7 to 3 m/s; the trap-to-atomic-beam conversion efficiency is close to one.