Pulsed Frequency Shifted Feedback Laser for Accurate Long Distance Measurements: Beat Order Determination

Long-distance measurements (10 m - 1000 m) with an accuracy of 10-7 is a challenge for many applications. We show that it is achievable with Frequency Shifted Feedback (FSF) laser interferometry technique, provided that the determination of the radio frequency beat order be made without ambiguity and on a time scale compatible with atmospheric applications. Using the pulsed-FSF laser that we developed for laser guide star application, we propose and test, up to 240 m, a simple method for measuring the beat order in real time. The moving-comb and Yatsenko models are also discussed. The first of these models fails to interpret our long-distance interferometry results. We show that the accuracy of long-distance measurements depends primarily on the stabilization of the acoustic frequency of the modulator

Conception, élaboration et intégration d'électrodes transparentes optimisées pour l'extraction des charges dans des dispositifs photovoltaïques.

Les oxydes transparents conducteurs (TCO) ont la rare propriété de concilier haute transparence et conductivité élevée, ce qui en fait des matériaux-clés pour de nombreuses applications requérant des électrodes transparentes comme les cellules photovoltaïques, les diodes organiques et les écrans plats. Avec une résistivité de l'ordre de 10^(-4) ohm.cm et une transmittance de 85% dans le domaine visible, l'oxyde d'indium dopé à l'étain (ITO) est le matériau privilégié. Toutefois, sa fragilité, son instabilité aux procédés plasma et son coût croissant du fait de sa haute teneur en indium sont autant de raisons de rechercher des matériaux alternatifs. Cette thèse a pour but de comprendre les points clefs permettant d'améliorer les performances d'une électrode transparente en oxyde de zinc dopé à l'aluminium (AZO) sur les plans optique, électrique et au niveau des interfaces ; des cellules photovoltaïques en silicium amorphe hydrogéné (a-Si:H) servent de dispositif-test à cette étude. Réalisées par pulvérisation cathodique magnétron sous des conditions de dépôt variées, les couches minces d'AZO obtenues ont une structure microcristalline et, pour des paramètres déterminés, des performances optoélectroniques approchant celles de l'ITO. Un modèle adapté d'après la théorie de Drude a permis de rendre compte du lien entre transparence et conduction et de confirmer la saturation en porteurs du matériau. L'efficacité d'une électrode au sein d'un dispositif dépend également très fortement de l'interface entre celle-ci et l'absorbeur, les porteurs devant être extraits rapidement pour ne pas se recombiner. Quelques voies ont été explorées pour réduire la barrière de potentiel entre le silicium amorphe et l'électrode tout en favorisant l'efficacité optique des cellules. Il ressort que l'insertion d'une couche tampon d'oxyde de titane ou de tungstène permet d'obtenir un gain notable dans les performances des cellules.Because of their unique ability to reconcile high transparency with good electrical conductivity, transparent conductive oxides (TCOs) are key materials in many applications such as organic light-emitting diodes, photovoltaic solar cells or flat displays. With its resistivity of a few 10^(-4)$ ohm.cm and its 85% transmittance in the visible range, Indium Tin Oxide (ITO) dominates the TCO market. Yet, it is brittle, unstable to plasma processes and its cost is rising due to its high indium content, encouraging research on alternative materials. This thesis aims at understanding key points to improve the performance of an aluminum-doped zinc oxide (AZO) transparent electrode on the optical, electrical and interface levels; hydrogenated amorphous silicon (a-Si:H) photovoltaic solar cells serve as a test device in this study. We obtain microcrystalline AZO thin films by magnetron sputtering under various deposition conditions ; for certain parameters, performances are close to ITO. An adapted model after the Drude theory allowed to account for the link between transparency and conduction and to confirm that the material is saturated by charge carriers. The effectiveness of an electrode within a device also strongly depends on its interface with the absorber layer, since the charge carriers have to be rapidely extracted in order to avoid recombination. Some ways have been explored to reduce the potentiel barrier between amorphous silicon and the electrode, still favoring optical efficiency of the cells. It appears that the insertion of a buffer layer of titanium or tungsten oxide enables a sensible improvement in the cells' efficiencies.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

VASAO: visible all sky adaptive optics: a new adaptive optics concept for CFHT

International audienceVASAO is an ambitious project that explores new conceptual direction in the field of astronomical adaptive optics. In the era of 8 meter and larger telescopes, and their instrument costs and telescope time pressure, there is a natural niche for such ground-breaking conceptual development in the 4 meter class telescope. The aim of VASAO is to provide diffraction limited imaging in the visible with 100% sky coverage; the challenge (but potential rewards) arises from the simultaneity of these requirements. To this end, CFHT is conducting a feasibility study based on the polychromatic guide star concept (Foy et al., 1995 [4]) coupled with a high order curvature AO system, presented in this paper. A number of experiments have been started (or carried out) to study the challenges and limits of the techniques involved in an operational setting; these include the FlyEyes detector, and a polychromatic tip-tilt test on natural stars. Because such a project straddles such a fine line between facility instrument and experimental facility, careful thought has to be given to the balance between modes of operations and potential astrophysical targets

Polychromatic guide star: feasibility study

International audienceAdaptive optics at astronomical telescopes aims at correcting in real time the phase corrugations of incoming wavefronts caused by the turbulent atmosphere, as early proposed by Babcock. Measuring the phase errors requires a bright source located within the isoplanatic patch of the program source. The probability that such a reference source exists is a function of the wavelength, of the required image quality (Strehl ratio), of the turbulence optical properties, and of the direction of the observation. It turns out that the sky coverage is disastrously low in particular in the visible wavelength range where, unfortunately, the gain in spatial resolution brought by adaptive optics is the largest. Foy and Labeyrie have proposed to overcome this difficulty by creating an artificial point source in the sky in the direction of the observation relying on the backscattered light due to a laser beam. This laser guide star (hereinafter referred to as LGS) can be bright enough to allow us to accurately measure the wavefront phase errors, except for two modes which are the piston (not relevant in this case) and the tilt. Pilkington has emphasized that the round trip time of the laser beam to the mesosphere, where the LGS is most often formed, is significantly shorter than the typical tilt coherence time; then the inverse-return-of-light principle causes deflections of the outgoing and the ingoing beams to cancel. The apparent direction of the LGS is independent of the tilt. Therefore the tilt cannot be measured only from the LGS. Until now, the way to overcome this difficulty has been to use a natural guide star to sense the tilt. Although the tilt is sensed through the entire telescope pupil, one cannot use a faint source because $APEX 90% of the variance of the phase error is in the tilt. Therefore, correcting the tilt requires a higher accuracy of the measurements than for higher orders of the wavefront. Hence current adaptive optics devices coupled with a LGS face low sky coverage. Several methods have been proposed to get a partial sky coverage for the tilt. The only one providing us with a full sky coverage is the polychromatic LGS (hereafter referred to as PLGS). We present here a progress report of the R&D; program Etoile Laser Polychromatique et Optique Adaptative (ELP-OA) carried out in France to develop the PLGS concept. After a short recall of the principles of the PLGS, we will review the goal of ELP-OA and the steps to get over to bring it into play. We finally shortly described the effort in Europe to develop the LGS

Polychromatic guide star: feasibility study

International audienceAdaptive optics at astronomical telescopes aims at correcting in real time the phase corrugations of incoming wavefronts caused by the turbulent atmosphere, as early proposed by Babcock. Measuring the phase errors requires a bright source located within the isoplanatic patch of the program source. The probability that such a reference source exists is a function of the wavelength, of the required image quality (Strehl ratio), of the turbulence optical properties, and of the direction of the observation. It turns out that the sky coverage is disastrously low in particular in the visible wavelength range where, unfortunately, the gain in spatial resolution brought by adaptive optics is the largest. Foy and Labeyrie have proposed to overcome this difficulty by creating an artificial point source in the sky in the direction of the observation relying on the backscattered light due to a laser beam. This laser guide star (hereinafter referred to as LGS) can be bright enough to allow us to accurately measure the wavefront phase errors, except for two modes which are the piston (not relevant in this case) and the tilt. Pilkington has emphasized that the round trip time of the laser beam to the mesosphere, where the LGS is most often formed, is significantly shorter than the typical tilt coherence time; then the inverse-return-of-light principle causes deflections of the outgoing and the ingoing beams to cancel. The apparent direction of the LGS is independent of the tilt. Therefore the tilt cannot be measured only from the LGS. Until now, the way to overcome this difficulty has been to use a natural guide star to sense the tilt. Although the tilt is sensed through the entire telescope pupil, one cannot use a faint source because $APEX 90% of the variance of the phase error is in the tilt. Therefore, correcting the tilt requires a higher accuracy of the measurements than for higher orders of the wavefront. Hence current adaptive optics devices coupled with a LGS face low sky coverage. Several methods have been proposed to get a partial sky coverage for the tilt. The only one providing us with a full sky coverage is the polychromatic LGS (hereafter referred to as PLGS). We present here a progress report of the R&D; program Etoile Laser Polychromatique et Optique Adaptative (ELP-OA) carried out in France to develop the PLGS concept. After a short recall of the principles of the PLGS, we will review the goal of ELP-OA and the steps to get over to bring it into play. We finally shortly described the effort in Europe to develop the LGS

Molecular dynamics and quantum chaos in small polyatomic molecules (CS_2, C_2H_2) through stimulated-emission pumping experiments and statistical Fourier-transform analysis

International audienceThe experimental study of the quantum properties of polyatomic molecules at high vibrational energy when classical chaos is present (quantum chaos) is discussed. Such a study requires the improvement of both experimental and analytical techniques. Methods by which stimulated-emission pumping spectroscopy and statistical Fourier-transform analysis of spectra can be successfully used to achieve this goal are emphasized. Stimulated-emission pumping and the statistical Fourier transform share the same concept of wave-packet preparation and evolution. This dynamical approach leads to interesting observations in molecular spectra. A numerical model of two coupled Morse oscillators provides information about the physical significance of the correlation hole observed in the Fourier transform of spectra of chaotic molecules. A relevant example in the experimental spectrum of CS2 shows the destabilization of given periodic orbits in a regime of soft chaos. In such a case the destabilizing process starts with Fermi resonances. In CS2 the chaos appears first in a portion of the degree of freedom (symmetric stretching and bending). In C2H2, in contrast, a new periodic orbit appears, corresponding to a new low-frequency mode that emerges from the chaotic bath of C2H2 and that could induce specific chemical reactions

THESE de 3ème CYCLE: Etude de la transition ordre – désordre de NH4Cl par des méthodes d’optique linéaire et non-linéaire : effet électro-optique et génération de la seconde harmonique

STUDY OF THE TRANSFORMATION USING THE POCKELS EFFECT AND THE GENERATION OF SECOND HARMONIC USING A LASER BEAM; VIEWING AREAS OF THE DOMAIN STRUCTURE AND PHASE CO-EXISTENCE BETWEEN ORDERED AND DISORDED PHASES; DESCRIPTION OF CRYSTAL DEFECTS (DISLOCATIONS) BY PHOTO-CHEMICAL ATTACK AND THE ROLE OF SUCH DEFECTS IN THE VICINITY OF THE TRANSFORMATION BY SMALL ANGLES OPTICAL-DISTRIBUTION DIFUSION; COMPARISON OF RESULTS TO BIBLIOGRAPHIC DATA; DESCRIPTION OF A MODEL TO EXPLAIN THE GERMINATION PROCESS OF ORDERED PHASE IN CONNECTION WITH THE CRYSTAL DEFECTS; DISCUSSION OF ORDER PARAMETRER MEASUREMENT WITH THE THEORY OF LANDAU AND CRITICAL EXPONANT; PRELIMINARY EXPERIENCE UNDER PRESSURE.ETUDE DE CETTE TRANSFORMATION EN UTILISANT L'EFFET POCKELS ET LA GENERATION DU SECOND HARMONIQUE, A L'AIDE D'UN FAISCEAU LASER ; VISUALISATION DE LA STRUCTURE EN DOMAINES ET DE LA STRUCTURE DE COEXISTENCE DES PHASES ORDONNEE ET DESORDONNEE. DESCRIPTION DES DEFAUTS CRISTALLINS (DISLOCATIONS) PAR ATTAQUE CHIMIQUE ET PHOTOELASTICITE ET ROLE DE CES DEFAUTS DANS L'APPARITION DE L'HETEROPHASE AU VOISINAGE DE LA TRANSFORMATION PAR DIFFUSION OPTIQUE AUX PETITS ANGLES ; COMPARAISON DES RESULTATS AUX DONNEES BIBLIOGRAPHIQUES; DESCRIPTION D'UN MODELE POUR EXPLIQUER LE PROCESSUS DE GERMINATION DE LA PHASE ORDONNEE EN LIAISON AVEC LES DEFAUTS CRISTALLINS; DISCUSSION DES MESURES DU PARAMETRE D'ORDRE A L'AIDE DE LA THEORIE DE LANDAU ET D'UN EXPOSANT CRITIQUE ; EXPERIENCES PRELIMINAIRES SOUS PRESSION

THESE D'ETAT: Étude des interactions hyperfines dans les molécules diatomiques homo-nucléaires: application à l’Iode et au Brome

This work presents a detailed theoretical and experimental study of hyperfine interactions in homonuclear diatomic molecules. The establishment of relations that govern made appeal to symmetry considerations and leads to a general expression of the hyperfine matrix element between any two electronic states. Two situations are particularly considered: predissociation and especially the neighborhood of a dissociation limit where the value of the matrix element can be obtained by ab-initio calculations from the corresponding atomic parameters. The experimental study focused on iodine and bromine: used techniques (dye laser, supersonic jet, computer based data acquisition) will have demonstrated their effectiveness. The existence of a hyperfine predissociation in the Br2 molecule superimposed on the gyroscopic predissociation, has been demonstrated for the first time. A detailed study of the hyperfine structure of vibratinnels levels (v ', J') of the electronic state 127I2 B near the dissociation limit (2P1 / 2 - 2P3 / 2) allowed the observe, around the vibrational v '= 77, hyperfine perturbation of the ungerade B state by a state of symmetry gerade: this is the first time direct evidence of such u-g symmetry breaking by hyperfine interaction which has long been suspected.Ce travail présente une étude théorique et expérimentale détaillée des interactions hyperfines dans les molécules diatomiques homonucléaires. L’établissement des relations qui les régissent fait un large appel aux considérations de symétrie et conduit à une expression générale de l’élément de matrice hyperfin entre deux états électroniques quelconques. Deux situations sont particulièrement considérées : la prédissociation et surtout le voisinage d’une limite de dissociation où la valeur de cet élément de matrice peut s’obtenir par un calcul ab-initio à partir des paramètres atomiques correspondants. L’étude expérimentale a porté sur l’iode et le brome : les techniques employées (laser à colorant, jet supersonique, acquisition de données sur micro-ordinateur) y ont fait la preuve de leur efficacité. L’existence d’une prédissociation hyperfine dans la molécule Br2, superposée à la prédissociation gyroscopique, a ainsi pu être démontrée pour la première fois. Une étude détaillée de la structure hyperfine des niveaux vibratinnels (v’, J’) de l’état électronique B de 127I2 près de la limite de dissociation 2P1/2 – 2P3/2 a d’autre part permis d’observer, aux alentours du vibrationnel v’=77, une perturbation hyperfine de l’état B (ungerade) par un état de symétrie gerade : il s’agit là de la première mise en évidence directe d’une telle brisure de symétrie u-g par interaction hyperfines, soupçonnée depuis longtemps