Theoretical tools for atom laser beam propagation

We present a theoretical model for the propagation of non self-interacting atom laser beams. We start from a general propagation integral equation, and we use the same approximations as in photon optics to derive tools to calculate the atom laser beam propagation. We discuss the approximations that allow to reduce the general equation whether to a Fresnel-Kirchhoff integral calculated by using the stationary phase method, or to the eikonal. Within the paraxial approximation, we also introduce the ABCD matrices formalism and the beam quality factor. As an example, we apply these tools to analyse the recent experiment by Riou et al. [Phys. Rev. Lett. 96, 070404 (2006)]

Measurement of excited-state transitions in cold calcium atoms by direct femtosecond frequency-comb spectroscopy

We apply direct frequency-comb spectroscopy, in combination with precision cw spectroscopy, to measure the ${\rm 4s4p} ^3P_1 \to {\rm 4s5s} ^3S_1$ transition frequency in cold calcium atoms. A 657 nm ultrastable cw laser was used to excite atoms on the narrow ($\gamma \sim 400$ Hz) ${\rm 4s^2} ^1S_0 \to {\rm 4s4p} ^3P_1$ clock transition, and the direct output of the frequency comb was used to excite those atoms from the ${\rm 4s4p} ^3P_1$ state to the ${\rm 4s5s} ^3S_1$ state. The resonance of this second stage was detected by observing a decrease in population of the ground state as a result of atoms being optically pumped to the metastable ${\rm 4s4p} ^3P_{0,2}$ states. The ${\rm 4s4p} ^3P_1 \to {\rm 4s5s} ^3S_1$ transition frequency is measured to be $\nu = 489 544 285 713(56)$ kHz; which is an improvement by almost four orders of magnitude over the previously measured value. In addition, we demonstrate spectroscopy on magnetically trapped atoms in the ${\rm 4s4p} ^3P_2$ state.Comment: 4 pages 5 figure

Conditions d'émergence et de viabilité des organisations de producteurs et des coopératives au Costa Rica

Cette communication propose une analyse des stratégies des organisations de producteurs (OP) au Costa Rica et des politiques destinées à les renforcer. L'analyse de l'évolution des organisations de producteurs au cours des trois phases qui ont marqué l'histoire agraire du Costa Rica, montre que (i) l'émergence et le renforcement des OP sont dépendants de la nature des politiques publiques et des possibilités d'accès aux marchés, (ii) les conditions économiques et institutionnelles actuelles sont plus défavorables aujourd'hui aux exploitations familiales et limitent fortement le développement des OP, (iii) pour une grande majorité d'OP le renforcement du capital humain et social est prépondérant par rapport à l'accroissement de la dotation en ressources économiques pour expliquer les évolutions. (Résumé d'auteur

Atomic fountains and optical clocks at SYRTE: status and perspectives

In this article, we report on the work done with the LNE-SYRTE atomic clock ensemble during the last 10 years. We cover progress made in atomic fountains and in their application to timekeeping. We also cover the development of optical lattice clocks based on strontium and on mercury. We report on tests of fundamental physical laws made with these highly accurate atomic clocks. We also report on work relevant to a future possible redefinition of the SI second

Tapered-amplified AR-coated laser diodes for Potassium and Rubidium atomic-physics experiments

We present a system of room-temperature extended-cavity grating-diode lasers (ECDL) for production of light in the range 760-790nm. The extension of the tuning range towards the blue is permitted by the weak feedback in the cavity: the diodes are anti-reflection coated, and the grating has just 10% reflectance. The light is then amplified using semiconductor tapered amplifiers to give more than 400mW of power. The outputs are shown to be suitable for atomic physics experiments with potassium (767nm), rubidium (780nm) or both, of particular relevance to doubly-degenerate boson-fermion mixtures

Kilohertz-resolution spectroscopy of cold atoms with an optical frequency comb

We have performed sub-Doppler spectroscopy on the narrow intercombination line of cold calcium atoms using the amplified output of a femtosecond laser frequency comb. Injection locking of a 657-nm diode laser with a femtosecond comb allows for two regimes of amplification, one in which many lines of the comb are amplified, and one where a single line is predominantly amplified. The output of the laser in both regimes was used to perform kilohertz-level spectroscopy. This experiment demonstrates the potential for high-resolution absolute-frequency spectroscopy over the entire spectrum of the frequency comb output using a single high-finesse optical reference cavity.Comment: 4 pages, 4 Figure

An Ultra-Stable Referenced Interrogation System in the Deep Ultraviolet for a Mercury Optical Lattice Clock

We have developed an ultra-stable source in the deep ultraviolet, suitable to fulfill the interrogation requirements of a future fully-operational lattice clock based on neutral mercury. At the core of the system is a Fabry-P\'erot cavity which is highly impervious to temperature and vibrational perturbations. The mirror substrate is made of fused silica in order to exploit the comparatively low thermal noise limits associated with this material. By stabilizing the frequency of a 1062.6 nm Yb-doped fiber laser to the cavity, and including an additional link to LNE-SYRTE's fountain primary frequency standards via an optical frequency comb, we produce a signal which is both stable at the 1E-15 level in fractional terms and referenced to primary frequency standards. The signal is subsequently amplified and frequency-doubled twice to produce several milliwatts of interrogation signal at 265.6 nm in the deep ultraviolet.Comment: 7 pages, 6 figure

Transfert de la notion de développement durable dans les politiques publiques centroaméricaines : lecture croisée des évolutions de référentiels et des trajectoires de politiques rurales au Costa Rica et au Nicaragua

Depuis le Sommet de la Terre en 1992, le développement durable (DD) s'est imposé comme le paradigme pour une orientation renouvelée des politiques publiques, notamment celles affectant les espaces ruraux. Adopté par de nombreuses institutions nationales et internationales, ce référentiel justifie un nombre croissant de politiques nationales. Vingt ans plus tard, en Amérique Centrale, des difficultés subsistent pour atteindre les trois dimensions du DD et la mise en oeuvre des politiques rurales intégrant effectivement le DD demeure un enjeu crucial. Notre communication vise à analyser comment certains pays centroaméricains ont intégré le référentiel du DD dans leurs politiques rurales et pourquoi ce concept s'est intégré de manière différenciée selon les pays. Nous répondons à ces questions sur la base d'une analyse comparée des trajectoires de politiques publiques de deux pays aux conditions contrastés : le Costa Rica, pays à revenus intermédiaires reconnu pour son modèle social et ses politiques environnementales, et le Nicaragua, pays à faible revenu, marqué par de fortes inégalités et en proie à la dégradation de ses ressources naturelles. Nous montrons que le concept de DD a été effectivement incorporé dans les cadres de politiques publiques rurales au Costa Rica et Nicaragua. Cette incorporation s'est opérée de manière différenciée dans les deux pays. Quatre facteurs permettent d'expliquer cette situation : le poids relatif des différents secteurs au sein du système politico-administratif, la relation entre les acteurs publics et la coopération internationale, le degré d'avancement du processus de décentralisation, et les capacités des acteurs à défendre leurs intérêts. Dès lors, le nouveau cadre de politique de développement territorial centroaméricain pourrait constituer une voie d'avenir pour surmonter les difficultés actuelles, et favoriser le développement territorial rural de manière durable. (Résumé d'auteur

Ultrastable lasers based on vibration insensitive cavities

We present two ultra-stable lasers based on two vibration insensitive cavity designs, one with vertical optical axis geometry, the other horizontal. Ultra-stable cavities are constructed with fused silica mirror substrates, shown to decrease the thermal noise limit, in order to improve the frequency stability over previous designs. Vibration sensitivity components measured are equal to or better than 1.5e-11 per m.s^-2 for each spatial direction, which shows significant improvement over previous studies. We have tested the very low dependence on the position of the cavity support points, in order to establish that our designs eliminate the need for fine tuning to achieve extremely low vibration sensitivity. Relative frequency measurements show that at least one of the stabilized lasers has a stability better than 5.6e-16 at 1 second, which is the best result obtained for this length of cavity.Comment: 8 pages 12 figure