Atom interferometry based on light pulses : application to the high precision measurement of the ratio h/m and the determination of the fine structure constant

In this paper we present a short overview of atom interferometry based on light pulses. We discuss different implementations and their applications for high precision measurements. We will focus on the determination of the ratio h/m of the Planck constant to an atomic mass. The measurement of this quantity is performed by combining Bloch oscillations of atoms in a moving optical lattice with a Ramsey-Bord\'e interferometer

Precise determination of h/m_Rb using Bloch oscillations and atomic interferometry: a mean to deduce the fine structure constant

We use Bloch oscillations to transfer coherently many photon momenta to atoms. Then we can measure accurately the ratio h/m_Rb and deduce the fine structure constant alpha. The velocity variation due to the Bloch oscillations is measured thanks to Raman transitions. In a first experiment, two Raman $\pi$ pulses are used to select and measure a very narrow velocity class. This method yields to a value of the fine structure constant alpha^{-1}= 137.035 998 84 (91) with a relative uncertainty of about 6.6 ppb. More recently we use an atomic interferometer consisting in two pairs of pi/2 pulses. We present here the first results obtained with this method

1S-3S cw spectroscopy of hydrogen/deuterium atom

We study the 1S-3S two-photon transition of hydrogen in a thermal atomic beam, using a homemade cw laser source at 205 nm. The experimental method is described, leading in 2017 to the measurement of the 1S-3S transition frequency in hydrogen atom with a relative uncertainty of $9 \times 10^{-13}$. This result contributes to the "proton puzzle" resolution but is in disagreement with the ones of some others experiments. We have recently improved our setup with the aim of carrying out the same measurement in deuterium. With the improved detection system, we have observed a broadened fluorescence signal, superimposed on the narrow signal studied so far, and due to the stray accumulation of atoms in the vacuum chamber. The possible resulting systematic effect is discussed

SiNx:Tb3+--Yb3+, an efficient down-conversion layer compatible with a silicon solar cell process

SiN x : Tb 3+-Yb 3+, an efficient down-conversion layer compatible with silicon solar cell process Abstract Tb 3+-Yb 3+ co-doped SiN x down-conversion layers compatible with silicon Photovoltaic Technology were prepared by reactive magnetron co-sputtering. Efficient sensitization of Tb 3+ ions through a SiN x host matrix and cooperative energy transfer between Tb 3+ and Yb 3+ ions were evidenced as driving mechanisms of the down-conversion process. In this paper, the film composition and microstructure are investigated alongside their optical properties, with the aim of maximizing the rare earth ions incorporation and emission efficiency. An optimized layer achieving the highest Yb 3+ emission intensity was obtained by reactive magnetron co-sputtering in a nitride rich atmosphere for 1.2 W/cm${}^2$ and 0.15 W/cm${}^2$ power density applied on the Tb and Yb targets, respectively. It was determined that depositing at 200 {\textdegree}C and annealing at 850 {\textdegree}C leads to comparable Yb 3+ emission intensity than depositing at 500 {\textdegree}C and annealing at 600 {\textdegree}C, which is promising for applications toward silicon solar cells.Comment: Solar Energy Materials and Solar Cells, Elsevier, 201

Bloch oscillations of ultracold atoms: a tool for a metrological determination of h/mRbh/m_{Rb}

We use Bloch oscillations in a horizontal moving standing wave to transfer a large number of photon recoils to atoms with a high efficiency (99.5% per cycle). By measuring the photon recoil of $^{87}Rb$, using velocity selective Raman transitions to select a subrecoil velocity class and to measure the final accelerated velocity class, we have determined $h/m_{Rb}$ with a relative precision of 0.4 ppm. To exploit the high momentum transfer efficiency of our method, we are developing a vertical standing wave set-up. This will allow us to measure $h/m_{Rb}$ better than $10^{-8}$ and hence the fine structure constant $\alpha$ with an uncertainty close to the most accurate value coming from the ($g-2$) determination

Combination of Bloch oscillations with a Ramsey-Bord\'e interferometer : new determination of the fine structure constant

We report a new experimental scheme which combines atom interferometry with Bloch oscillations to provide a new measurement of the ratio $h/m_{\mathrm{Rb}}$. By using Bloch oscillations, we impart to the atoms up to 1600 recoil momenta and thus we improve the accuracy on the recoil velocity measurement. The deduced value of $h/m_{\mathrm{Rb}}$ leads to a new determination of the fine structure constant $\alpha^{-1}=137.035 999 45 (62)$ with a relative uncertainty of $4.6\times 10^{-9}$. The comparison of this result with the value deduced from the measurement of the electron anomaly provides the most stringent test of QED

Détermination de l'état de mouillage aux échelles micro/nano par caractérisation acoustique haute fréquence.

Les ondes acoustiques ultrasonores dans la gamme du GHz sont exploitées dans les pour réaliser l'imagerie de propriétés élastiques à l'échelle microscopique. Il est, dans ce cas, possible d'obtenir une résolution de l'ordre du micromètre dans l'eau (comparable à la résolution optique) grâce à la microscopie acoustique au GHz. Cette solution a permis de réaliser des études en transmission et en réflexion pour des fréquences allant jusqu'à plusieurs GHz. Les ondes peuvent être focalisées vers la structure à analyser par l'intermédiaire d'un milieu couplant comme l'eau, pour assurer la transmission acoustique. Les applications concernent la caractérisation de défauts à l'échelle micrométrique dans des matériaux qui ne sont pas transparents optiquement. Nous avons développé une méthode de caractérisation acoustique haute fréquence intégrée afin de pouvoir caractériser des interfaces liquide / solide [1]. Le matériau étudié est le silicium, milieu opaque, qui présente une structuration aux échelles micrométriques ou nanométriques. Afin d'atteindre nos objectifs de caractérisation par ondes acoustiques aux échelles micrométriques et nanométriques, nous avons dû travailler au développement et à l'intégration de transducteurs ultrasonores hautes fréquences sur substrat silicium, notamment à partir des technologies couches minces. La particularité de la méthode est que le transducteur acoustique haute fréquence est réalisé directement en face arrière du substrat dont l'interface supérieure avec un liquide est à caractériser. L'avantage principal est de pouvoir s'affranchir de l'utilisation d'un couplant dont l'utilisation est très délicate voire rédhibitoire dans la gamme de fréquence visée. D'autre part, l'augmentation de la fréquence des transducteurs acoustiques est directement liée à la diminution des longueurs d'onde et donc à la possibilité d'analyser des interfaces micro ou nanostructurées. L'étude de la stabilité de l'interface triple liquide / air / solide sur des structures superhydrophobes réalisées à l'échelle micrométrique puis nanométrique s'est déroulée sur dispositifs issues de l'industrie de la microélectronique (imageurs réalisés par ST Microelectronics). En effet cette industrie est particulièrement intéressée par l'efficacité du nettoyage par voie humide au cours des procédés de fabrication des composants. Dans le cadre du développement de cette méthode de caractérisation, nous avons pu montrer qu'il était possible de caractériser des interfaces dont la taille des structures solides (répétées en motifs périodiques) sont plus de 100 fois plus petites que la longueur d'onde la plus faible dans le matériau de propagation. Nous avons également modélisé le comportement des ondes acoustiques afin de pouvoir interpréter les signaux acoustiques mesurés. Enfin les informations obtenues par la méthode acoustique ont été confrontées à la méthode goniométrique, méthode classique de caractérisation du mouillage mais donnant essentiellement une information macroscopique. [1] Li S.; Lamant S. ; Carlier J. ; Toubal M. ; Campistron P. ; Xu X.; Vereecke G. ; Senez V. ; Thomy V. ; Nongaillard B., 2014; High Frequency Acoustic for nanostructure Wetting Characterization, Langmuir, 30, 25, 7601-7608

σ-Phase Formation in Super Austenitic Stainless Steel During Directional Solidification and Subsequent Phase Transformations

The solidification path and the σ-phase precipitation mechanism in the S31254 (UNS designation) steel are investigated thanks to Quenching during Directional Solidification (QDS) experiments accompanied by scanning electron microscopy observations and electron backscattered diffraction (EBSD) analysis. Considering experimental conditions, the γ-austenite is found to be the primary solidifying phase (1430 °C), followed by δ-ferrite (1400 °C, ≈ 87 pct solid fraction). The σ-phase appears in the solid-state through the eutectoid decomposition of the δ-ferrite: δ → σ + γ2 (1210 °C), whereas the σ-phase is predicted to form from the austenite at 1096 °C in equilibrium conditions. The resulting temperatures of solidification path and phase transformation are compared with Gulliver–Scheil model and equilibrium calculations predicted using Thermo-Calc© software. It is shown that the thermodynamics calculations agree with experimental results of solidification path. The EBSD analysis show that the δ-ferrite has δNW2 ORs with the σ-phase

Solidification path and phase transformation in super-austenitic stainless steel UNS S31254

The solidification path and the σ-phase precipitation mechanism of UNS S31254 alloy were studied on the basis of directional solidified experiments accompanied by scanning electron microscopy observations and energy dispersive X-ray a nalysis. The resulting temperatures of solidification paths and phase transformation were compared with Gulliver-Scheil and equilibrium calculations predicted using ThermoCalc© software. It was confirmed that the experimental solidification path was in agreement with the thermodynamic calculations. The complementarity of the results have made it possible to propose a solidification path and a σ-phase precipitation mechanism for the UNS31254 steel