Magic-sized nanocrystals (MSNs) are nanocrystals with a single size distribution. They have narrow spectral features that do not exhibit inhomogeneous line broadening. This enabled us to analyze homogeneous line broadening of CdSe and CdTe MSNs. In solution, we observed two aggregated configurations of CdSe and CdTe MSNs. Sub-peaks within MSN excitonic peaks were caused by these two aggregated configurations and surface states. A two-dimensional photoluminescence spectrum of a mixture of CdTe 427 nm and 500 nm MSNs gave direct evidence of Förster resonant energy transfer (RET) between the two sizes of MSNs. Normalized experimental overlap between donor emission and acceptor absorption spectra was on the order predicted by theory, confirming that there is sufficient overlap for RET to take place in this system. Additionally, within both aggregated configurations, the two sizes of MSNs were within sufficient distance from one another for RET to occur.

Magic-sized nanocrystals (MSNs) are nanocrystals with a single size distribution. They have narrow spectral features that do not exhibit inhomogeneous line broadening. This enabled us to analyze homogeneous line broadening of CdSe and CdTe MSNs. In solution, we observed two aggregated configurations of CdSe and CdTe MSNs. Sub-peaks within MSN excitonic peaks were caused by these two aggregated configurations and surface states. A two-dimensional photoluminescence spectrum of a mixture of CdTe 427 nm and 500 nm MSNs gave direct evidence of Förster resonant energy transfer (RET) between the two sizes of MSNs. Normalized experimental overlap between donor emission and acceptor absorption spectra was on the order predicted by theory, confirming that there is sufficient overlap for RET to take place in this system. Additionally, within both aggregated configurations, the two sizes of MSNs were within sufficient distance from one another for RET to occur.

The linewidths and line positions of 4I15/2 to 4I13/2 absorption transitions of trivalent erbium in CsCdBr₃ and CaF₂ were measured as a function of temperature from approximately 10 K to 300 K. By comparing the temperature dependence of these transitions with theoretical models of electron-phonon coupling the primary mechanism involved were determined. For Er3+ doped CaF₂ the Raman scattering processes dominated the line broadening, although the single-phonon direct processes were significant enough to drastically alter the values of the Raman scattering electron-phonon coupling constant. In comparison, the Er³⁺ doped CsCdBr₃ had negligible Raman scattering contributing to the line broadening. This is likely due to the exceedingly low Debye temperature and consequently low number of phonons, reducing the likelihood of two-phonon processes relative to single-phonon processes. The results were then analysed in terms of the bond length with the ligands and compared with other studies showing that as the bond length gets shorter the electron-phonon coupling constant associated with Raman scattering is expected to get smaller. To explain the line shifts in CaF₂:Er³⁺ it is necessary to treat the Debye temperature as a parameter. This indicates that the phonon modes causing the line shifts are different from those causing the line broadening, and in most of the cases are vibronic processes rather than Raman processes. In the case of CsCdBr₃:Er³⁺ there is very little difference between the fits using the fixed Debye temperature and a varied Debye temperature in over half of the cases examined. Given the distribution of phonon modes, it is likely that this small difference arises because combinations of these processes are of similar intensity, meaning that a combination of Raman and optical phonon modes are likely causing the line shift.

No description available.

This project aims to determine the solar Mg abundance with two infrared spectral lines: MgI λ10811 and λ10965. Downloaded line data from VALD are updated with modern values for the oscillator strengths and van der Waals damping parameters, the latter obtained through ABO theory. Utilizing SME, the Mg abundances of synthetic spectra are fitted with respect to a solar atlas. The derived abundance for varied turbulence configurations is found to be between logAMg+12 = 7.40–7.52, which is slightly lower than meteoric and 3D-modeled values. Suggested improvements would be to consider the effects of NLTE and line blending.

We use spectroscopy to study infrared optoelectronic inter and intraband semiconductor carrier dynamics. The overall aim of this thesis was to study both III-V and Pb chalcogenide material systems in order to show their future potential use in infrared emitters. The effects of bandstructure engineering have been studied in the output characteristics of mid-IR III-V laser diodes to show which processes (defects, radiative, Auger and phonon) dominate and whether non-radiative processes can be suppressed. A new three-beam pump probe experiment was used to investigate interband recombination directly in passive materials. Experiments on PbSe and theory for non-parabolic near-mirror bands and non-degenerate statistics were in good agreement. Comparisons with HgCdTe showed a reduction in the Auger coefficient of 1-2 orders of magnitude in the PbSe. Using Landau confinement to model spatial confinement in quantum dots (QDs) "phonon bottlenecking" was studied. The results obtained from pump probe and cyclotron resonance saturation measurements showed a clear suppression in the cooling of carriers when Landau level separation was not resonant with LO phonon energy. When a bulk laser diode was placed in a magnetic field to produce a quasi quantum wire device the resulting enhanced differential gain and reduced Auger recombination lowered Ith by 30%. This result showed many peaks in the light output which occurred when the LO phonon energy was a multiple of the Landau level separation. This showed for the first time evidence of the phonon bottleneck in a working laser device. A new technique called time resolved optically detected cyclotron resonance, was used as a precursor to finding the earner dynamics within a spatially confined quantum dot. By moving to the case of a spatial QD using an optically detected intraband resonance it was possible to measure the energy separation interband levels and conduction and valence sublevels within the dot simultaneously. Furthermore this technique has been shown that the inhomogeneous broadening of the photoluminescence spectrum is not purely affected by just size and composition. We suggest that other processes such as state occupancy, In roughing, and exciton binding energies may account for the extra energy.

Les gyromètres laser He-Ne sont des senseurs inertiels dont la fiabilité et la précision sont reconnues depuis le milieu des années 1980. Leur grande sensibilité leur permet de mesurer des vitesses de rotation avec une précision qui atteint 10⁻³ °/ h dans le domaine aéronautique. Cependant, du fait d’un fonctionnement complexe basé sur une physique riche et variée, ses performances sont fortement dépendantes des conditions de fonctionnement et de toute modification du processus de fabrication. Dans ce cas, un travail de modélisation prend tout son sens, puisqu’il permet, outre une compréhension claire et précise des différents phénomènes physiques, un accès à des études paramétriques non envisageables expérimentalement. La modélisation globale du fonctionnement d’un gyrolaser He-Ne a ainsi été l’objectif principal de la collaboration entre la société Sagem (groupe Safran), un des leaders mondiaux dans le domaine des senseurs inertiels, et le Laboratoire de Physique des Gaz et des Plasmas (LPGP). Cette modélisation est « multiphysique » du fait de la diversité des domaines que couvre la physique du gyrolaser (Plasma, Physique Atomique, Lasers). C’est pourquoi nous avons développé trois modèles spécifiquement adaptés à chaque domaine. Le premier décrit la modélisation de la colonne positive du plasma de décharge dans une approche fluide. Ce modèle permet une description quantitative du plasma et l’accès aux grandeurs telles que la densité électronique et la fonction de distribution en énergie des électrons. Ces grandeurs sont les entrées nécessaires au second modèle qui traite la cinétique des états excités du plasma He-Ne. Un modèle collisionnel-radiatif à 1 dimension radiale (1D-CRM) a ainsi été développé. L’aspect 1D se justifie par l’importance des phénomènes de transport d’atomes et de rayonnement pouvant influer sur le profil radial de l’inversion de population du laser. Le transfert radiatif par auto-absorption des transitions radiatives résonantes a notamment été modélisé en résolvant l’équation de Holstein-Biberman à partir d’une méthode Monte-Carlo. Cet aspect constitue un élément majeur de ce travail de thèse. La diffusion des atomes excités du mélange He-Ne a également été prise en compte en résolvant l’équation de diffusion avec différentes conditions au bord à la surface du capillaire.A partir des populations et des taux cinétiques de peuplement et dépeuplement calculés par 1D-CRM, l’amplification laser dans la cavité a été modélisée dans le cadre d’une approche Maxwell-Bloch à 2 niveaux (NADIA) en incluant la saturation inhomogène du gain c’est-à-dire en tenant compte de la vitesse des atomes émetteurs dans la direction de propagation des faisceaux lasers. La cinétique de NADIA a été optimisée et les processus de transports dans l’espace des phases ont également été implémentés. Ce modèle a été utilisé pour étudier les performances du gyrolaser liées au milieu amplificateur et pour dériver les paramètres physiques nécessaires au développement d’un simulateur du gyrolaser.Dans ce simulateur, un modèle physique simplifié dérivé de NADIA, a été couplé à des modules « systèmes » dans le but de reproduire en sortie le signal opérationnel d’un gyrolaser. Ceci nous a permis de réaliser des études paramétriques sur les grandeurs caractérisant les performances d’un gyrolaser notamment le biais dynamique et le Random-Walk. Nous montrons en particulier que les performances de notre simulateur sont en bon accord avec celles observées en conditions opérationnelles. De plus, nos résultats montrent que ce simulateur est également un outil puissant pour l’analyse de données expérimentales. / Ring laser gyros (RLG) are inertial sensors whose reliability and accuracy have been recognised since the mid-1980s. Their high sensitivity enables them to measure angular velocity with an accuracy of 10⁻³ °/ h in aeronautics. However, because of a complex functioning based on a rich and varied physics, their performances are highly dependent on the working conditions and on any modification in the manufacturing process. In this case, a numerical modelling is pertinent since it allows both a clear understanding of the ring laser physics and parametric studies which are not experimentally feasible. The global modelling of a He-Ne RLG has been the main objective of the collaboration between Sagem (Safran group), which is one of the world leader in the inertial sensors field, and the Gas and Plasma Physics Laboratory (LPGP).This modelling is “multi-physics” since RLG physics involves several disciplines (plasma, atomic and laser physics). Therefore we have developed three models specifically adapted to each field. The first one describes the modelling of the positive column of the glow discharge following a fluid approach. This model allows a quantitative description of the plasma and gives access to fundamental quantities like the electron density or the electron energy distribution function. These quantities are the required inputs for the second model which treats the kinetics of the excited states inside the He-Ne plasma. For this, a collisional-radiative model in a radial geometry (1D-CRM) has been developed. The radial geometry is justified by the importance of the transport processes of atoms and radiations which can influence the radial profile of the population inversion. Notably, the radiative transfer by self-absorption of the resonant radiative transitions has been modelled by solving the Holstein-Biberman equation by a Monte-Carlo method. This aspect is a major component of this PhD work. Diffusion of excited atoms inside the plasma has also been taken into account by solving the diffusion equation with different boundary conditions at the capillary surface. From the populations and the kinetic rates computed by 1D-CRM, the laser amplification inside the cavity has been modelled using a two-level Maxwell-Bloch approach (NADIA) taking into account the inhomogeneous gain saturation, which means to consider the thermal speed of the atoms in the direction of propagation of the laser beams. The kinetics of NADIA has been optimized and transport processes in the phase space have also been implemented. This model has been used to study the performances of the RLG linked to the amplifying medium and to derive the physical parameters needed for the development of a simulator.Concerning this simulator, a simplified physical model from NADIA has been coupled to system modules in order to reproduce the operating signal of a RLG. This allows to conduct parametric studies on the quantities defining the RLG performance in particular the dynamic bias and the so-called “Random Walk”. We showed notably that the results of our simulator are in good agreement with experimental measurements in operating conditions. Moreover, our results show that this simulator is a powerful tool for analysing experimental data.

<p>Ispitivana je zavisnost brzine fronta udarnih talasa u T-cevi od vi&scaron;e parametara. Izvr&scaron;eno je povezivanje ICCD kamere sa spektrometrom. Ispitane su karakteristike celokupnog sistema i izvr&scaron;ena je njegova optimizacija i kalibracija. Izmerene su &Scaron;tarkove polu&scaron;irine 45 spektralnih linija OII, 13 spektralnih linija Si II i 14 spektralnih linija Si III. Dobijene vrednosti su upoređene sa vrednostima koje se mogu naći u literature, kao i sa teorijskim vrednostima. Urađena je detaljna analiza rezultata iz ovog rada kao i svih dostupnih prethodno dobijenih eksperimentalnih podataka.</p> / <p>The dependence of shock front velocity on different parameters was examined. The ICCD camera was mounted on the spectrometer. The characteristics of the whole system were examined and the system was optimized and calibrated. The Stark halfwidths of 45 O II spectral lines, 13 Si II spectral lines and 14 Si III spectral lines were measured. The obtained values were compared with the data available in the literature, as well as with theoretical values. A detailed analysis of both the experimental results given in this dissertation and previously published experimental data was done.</p>

Analyzing stellar spectra plays a big role in understanding the evolution of our galaxy. Having good data for spectral line properties is very important when analyzing these spectra. One part of the Gaia-ESO public spectroscopic survey (GES) is to gather data for spectral line properties from stellar spectra. The scope of this project is to study one of these properties, the spectral line width caused by collisional broadening by hydrogen. Collisional broadening by hydrogen occurs when a hydrogen atom collides with a particle. The goal of this project is to successfully calculate the collisional spectral line broadening of iron lines where new data is missing from the GES using modern quantum mechanical calculations. These calculations are done using the ABO theory, which is more advanced than previously established theory.A table of Fe-I (Neutral iron) spectral lines without collisional broadening data in the GES has been provided. Using the ABO theory and the accompanying ABO cross section calculator code, estimates of collisional broadening by hydrogen have been calculated for these lines. The new calculations predict that the line width of the spectral lines are typically twice as large compared to older estimates calculated using simpler theory. This new data can be expected to improve stellar spectrum analysis in the Gaia-ESO survey spectra. / Analys av stjärnspektran spelar en stor roll i vår förståelse av vintergatans utveckling. Att ha bra data för spektrallinjers egenskaper är oerhört viktigt vid analys av dessa spektran. En del i Gaia-ESO public spectroscopic survey (GES) är att samla in data för dessa spektrallinjers egenskaper ur stjärnspektran. Omfattningen av detta projekt innefattar att titta närmare på en av dessa egenskaper, spektrallinjebreddning orsakad av kollisionsbreddning av väte. Kollisionsbreddning av väte uppstår när en väteatom kolliderar med en annan partikel. Målet med projektet är att med framgång beräkna kollisionsbreddningen av spektrallinjer från järn där ny data saknas ur GES genom att använda moderna kvantmekaniska beräkningar. Dessa beräkningar är gjorda med den så kallade ABO-teorin, vilken är mer avancerad än tidigare etablerade teorier. En tabell med Fe-I (neutralt järn) spektrallinjer utan kollisionsbreddningsdata i GES har tillhandahållits. Med hjälp av ABO-teorin och den medföljande ABO-tvärsnittsräknar-koden har beräkningar av kollisionsbreddning med väte utförts för dessa linjer. De nya beräkningarna förutser att spektrallinjernas bredd blir typiskt två gånger så stor jämfört med de äldre beräkningarna gjorda med enklare teori. Denna nya data kan förväntas att förbättra analysen av stjärnspektrum ur Gaia-ESO kartläggningen.

Le présent travail de thèse a porté sur l’étude expérimentale et théorique de signatures spectroscopiques de molécules atmosphériques clés: CO2 et CH3D. 11 a été divise en partie expérimentale, consacrée aux mesures a haute pression des spectres IR CO2, et a la partie théorique, a. savoir le calcul des largeurs de ligne de collision pour CH3D perturbé par divers gaz. Dans la première partie, j'ai présenté des mesures &absorption de CO2 a haute pression a température ambiance dans l'intervalle spectral 600-9650 cm (sondes dans des études d’atmosphère planétaire) pour deux raisons principales: fournit des données exactes et étendues et suivre l’évolution de effets de "line-mixing" avec des variations graduelles de pression. Dans la deuxième partie, j'ai présenté des calculs semi-classiques des coefficients d'élargissement de CH3D -N2 (-H2) en utilisant le modèle de trajectoire exacte dans les bandes v3 parallèles et perpendiculaires vs, v6 de CH3D ---N2 ainsi que dans la bande v3 parallèle de CH3D -142 pour de grands intervalles les de nombres quantiques de rotation requis pour les bases de données spectroscopiques. / Present Ph.D work has focused on experimental and theoretical studying of spectroscopic signatures of key atmospheric molecules: CO2 and CH3D. It was divided into experimental part, devoted to high-pressure measurements of IR CO2 spectra, and theoretical part, namely calculation of collisional line-widths for CH3D perturbed by various gases. In the first part, I reported room-temperature high-pressure CO2 absorption measurements in the spectral interval 600-9650 cm-1 (probed in planetary atmosphere studies) with the double goals: to provide accurate and extensive data and to trace evolution of the line-mixing effects with gradual pressure variations. In the second part, I presented semi-classical calculations of CH3D-N2 and -142 line-broadening coefficients using exact trajectory model in the parallel v3 and perpendicular vs, v6 bands of CH3D-N2 as well as in the parallel v3 band of CH3D-112 for large intervals of rotational quantum numbers required for spectroscopic databases.