Optimization of two dimensional chiral photonic crystal nanostructures

A chiral photonic crystal (CPC) in 2D is a structure that presents the variation of the dielectric permittivity and the chirality parameter along two directions of space. The objective of this paper is to simulate and study geometric effects on the characteristics of 2D chiral photonic crystal based on dielectric material using Comsol Multiphysics 5.0 environment. The properties of Chiral Photonic Crystal are discussed based on transmission coefficient (S21) and reflection coefficient (S11)

I.C.E.: An Ultra-Cold Atom Source for Long-Baseline Interferometric Inertial Sensors in Reduced Gravity

The accuracy and precision of current atom-interferometric inertialsensors rival state-of-the-art conventional devices using artifact-based test masses . Atomic sensors are well suited for fundamental measurements of gravito-inertial fields. The sensitivity required to test gravitational theories can be achieved by extending the baseline of the interferometer. The I.C.E. (Interf\'erom\'etrie Coh\'erente pour l'Espace) interferometer aims to achieve long interrogation times in compact apparatus via reduced gravity. We have tested a cold-atom source during airplane parabolic flights. We show that this environment is compatible with free-fall interferometric measurements using up to 4 second interrogation time. We present the next-generation apparatus using degenerate gases for low release-velocity atomic sources in space-borne experiments

Microscopie de photodétachement (rôle du gradient de champ électrique et effet du champ magnétique)

Cette thèse a pour objectif d identifier et de caractériser les phénomènes qui pourraient perturber les mesures d affinités électroniques effectuées à l aide du microscope de photodétachement. Le premier effet étudié est celui d un gradient de champ électrique. Il a été démontré que ce gradient est à l origine d une dispersion importante des points de mesure. Une méthode statistique de traitement de données accompagnée d une méthode d acquisition a été mise en place dans le but de quantifier ce gradient. L affinité électronique du soufre est du coup déterminée à 2,4 10-7 près ce qui est la meilleure précision au monde. Dans le même but, une expérience de microscopie de photodétachement à deux couleurs a été réalisée. La superposition d images obtenue peut être utilisée comme vernier spectral pour déterminer l affinité électronique sans avoir à connaître le champ électrique appliqué. Le deuxième effet étudié est celui d un champ magnétique résiduel sur la phase d interférence. Un calcul perturbatif qui se base sur l approximation semi-classique montre que dans nos conditions expérimentales, la phase d interférence reste inchangée. Des bobines entourant la zone d interaction ont été placées afin de créer un champ magnétique dans toutes les directions de l espace. Aucun effet sur la phase d interférence n a pu être observé ce qui est en accord avec les calculs réalisés.Enfin, une étude préliminaire de la microscopie de photodétachement en onde p est décrite. A l aide d une nouvelle source dite à spallation , des images classiques sont obtenues et ont permis une mesure de l affinité électronique de l or.This thesis aims at identifying and determining the physical phenomena which could reduce the accuracy of the electron affinity measurements provided by the photodetachment microscope. The first point deals with the effect of the gradient of the electric field within the interaction zone. It is shown that this effect explains the dispersion of the measurements. We have applied some statistical methods to data taken while following a new acquisition method. Hence, we were able to recommend a new value of the electronic affinity of sulfur with a 2.4 10-7 accuracy, which becomes the most accurately known electron affinity. With similar purposes, a two-colour laser technique has been developed for photodetachment microscopy. It is shown that the superposition of the two resulting interference patterns can be used as a spectral vernier to determine the electron affinity with no a priori knowledge of the applied electric field.We also studied the effect of a residual magnetic field on the interference phase. Using the semi classical theory, some perturbative calculations are realised and show that the interference phase remains unchanged in our experimental conditions. In order to check the reliability of our calculations, we installed magnetic coils capable of creating a magnetic field in all direction of space. No effect on the phase interference was observed.Finally, a preliminary study of photodetachment microscopy with a p wave is described. Using a new sputtering ion source, we obtained classical images, which enable us to measure the electron affinity of gold.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Optomechanical issues in the gravitational wave detector Advanced VIRGO

International audienceThe next generation of the gravitational wave detector VIRGO, namely Advanced VIRGO, will feel an enhancement of optomechanical effects. In fact, it is planned that cavities will be antisymmetrically detuned to compensate symmetry defects between the two arms, which then allows DC detection. In this article, we show that even with slight detuning, the high intra-cavity power stored within the Fabry-Perot cavities makes optical spring effects important enough to constrain the detector adjustment procedure and to limit its sensitivity. Résumé: Dans l'interféromètre, Advanced VIRGO, seconde génération de l'antenne gravitationnelle VIRGO, les effets opto-mécaniques seront d'une importance capitale pour le fonctionnement global du système. En effet, afin de compenser les défauts de symétrie entre les deux bras du Michelson, les cavités optiques devront être désaccordés de manière dissymétrique. Ceci permettra de mettre en place un schéma de détection DC. Dans cet article, on démontre que même dans le cas d'un faible désaccord, la puissance laser intra-cavité rend les effets de ressorts optiques suffisamment importants pour contraindre le contrôle de l'interféromètre et limiter sa sensibilité

Telescope-based cavity for negative ion beam neutralization in future fusion reactors

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Mitigation of Parametric Instability

International audienceA key action for enhancing the sensitivity of gravitational wave (GW) detectors based on laser interferometry is to increase the laser power. However, in such a high-power regime, a nonlinear optomechanical phenomenon called parametric instability (PI) leads to the amplification of the mirrors vibrational modes preventing the detector functioning. Thus this phenomenon limits the detectors maximum power and so its performances. Our group has started an experimental research program aiming at realizing a exible and active mitigation system, based on the radiation pressure applied by an auxiliary laser. A summary on the PI mitigation techniques will be presented, we will explain the working principle of the system that we are implementing and report about the first experimental results

High speed, high power 2D beam steering for mitigation of optomechanical parametric instability in gravitational wave detectors

In this paper we propose a novel strategy to control optomechanical parametric instability (PI) in gravitational wave (GW) detectors, based on radiation pressure. The fast deflection of a high power beam is the key element of our approach. We built a 2D deflection system based on a pair of acousto-optic modulators (AOMs) that combines high rapidity and large scan range. As fast frequency switching configurable AOM driver we used an Universal Software Radio Peripheral (USRP) combined with a high performance personal computer (PC). In this way we demonstrate a 2D beam steering system with flat efficiency over the whole scan range and with a transition time of 50 ns between two arbitrary consecutive deflection positions for a beam power of 3.6 W

High bandwidth frequency lock of a rigid tunable optical cavity

International audienceIn this paper, we present a high bandwidth frequency lock of a rigid tunable Fabry Perot cavity based on a set of lead zirconate titanate (PZT) actuators. The cavity spacer was specifically designed such that the frequency of the first resonance of the whole assembly under PZT excitation is above 35 kHz, thus allowing a servo-loop bandwidth of 13 kHz. It is demonstrated that no significant noise is added by the cavity to the output beam with respect to the input beam over the servo-loop bandwidth. This cavity can be used as a pre-mode cleaner in interferometric gravitational wave detectors such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo

Generation of very high-order high purity Gaussian modes via spatial light modulation

We experimentally demonstrate the conversion of a fundamental $\text{TEM}_{00}$ laser mode at 1064\,nm to higher order Hermite-Gaussian modes (HG) of arbitrary order via a commercially available liquid crystal Spatial Light Modulator (SLM). We particularly studied the $\text{HG}_{5,5}/\text{HG}_{10,10}/\text{HG}_{15,15}$ modes. A two-mirror plano-spherical cavity filters the higher-order modes spatially. We analyze the cleaned modes via a three-mirror diagnosis cavity and measure a mode purity of 96/93/78\% and a conversion efficiency of 6.6\%/3.7\%/1.7\% respectively. The generated high-purity Hermite-Gaussian modes can be employed for the mitigation of mirror thermal noise in optical cavities for both optical clocks and gravitational wave (GW) detectors. HG modes are then converted into high order LG modes which can be of particular interest in cold atom physics