Teses / dissertações sobre o tema "Inhomogeneous spectral line broadening"

A complete stochastic theory of relaxation is developed in terms of a homogeneous equation for the averaged density matrix of a system immersed in a thermal bath. This theory is then used as the basis of a new stochastic approach to the phenomenon of collisional broadening of spectral line shapes. Single photon and multiphoton processes are studied. The features of a line shape are linked by simple expressions to the statistical properties of a stochastic hermitian Hamiltonian. The ordinary line shape predicted by Kubo's approach is generalized. The present approach predicts broadening as well as asymmetry and shift. A representation of line shapes in multiphoton processes by diagrams is also developed.

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.

De nouveaux matériaux inorganiques actifs au laser, dopés avec des ions de thulium et d'holmium, ont été étudiés pour leur potentiel dans les lasers à accord large et ultrarapides fonctionnant dans la gamme spectrale infrarouge à ondes courtes de 2 à 3 μm. Les lasers émettant dans cette gamme spectrale trouvent de nombreuses applications, notamment dans les systèmes de télédétection par laser, la détection de gaz et la médecine. Ils sont utilisés comme systèmes amplificateurs pour la génération d’harmoniques d’ordre élevé, la génération de térahertz, et la conversion ultérieure de fréquence dans la région infrarouge moyen.La présente thèse de doctorat établit des relations entre les propriétés structurelles des matériaux cristallins d'oxydes et de fluorures, sous forme de monocristaux et de céramiques transparentes, et les propriétés spectroscopiques des ions dopants de thulium et d'holmium, ainsi que leurs caractéristiques laser, qui sont essentielles pour le développement des lasers. De plus, les processus physiques sous-jacents à un comportement laser inattendu sont révélés. Cette étude systématique des matériaux laser permet d'identifier les compositions les plus prometteuses pour le développement de lasers à large accordabilité et à impulsions ultracourtes.Cette étude se concentre principalement sur des matériaux présentant un élargissement spectral inhomogène significatif, se traduisant par des spectres d'absorption et d'émission larges et sans structure des ions dopants. Afin de promouvoir cet effet, plusieurs stratégies ont été envisagées, notamment l'agrégation d'ions de terres rares, le désordre de la structure locale, le désordre de composition dans les composés à solution solide et les bandes latérales de phonons résultant des interactions électron-phonon.La formation d'agrégats de thulium et d'holmium dans des cristaux de fluorure de calcium permet une opération laser efficace et à accord large autour de 2,1 μm. Une étude spectroscopique polarisée des propriétés d'émission des ions d'holmium dans des cristaux désordonnés d'aluminate de terres rares met en lumière ses propriétés spectrales à large bande et le rôle de l'émission assistée par multiphonons, qui se produit au-delà des transitions électroniques, dans les émissions laser inattendues observées dans les lasers à verrouillage de modes. Dans les céramiques à solution solide sesquioxyde du système ternaire yttria-lutécia-scandia dopées avec des ions de thulium, il existe une variation forte et presque linéaire de la force du champ cristallin avec la taille moyenne du cation formant l'hôte. Cette relation permet de personnaliser à la fois la position et la largeur de la bande d'émission au-delà de 2 μm en ajustant de manière appropriée la composition de l'hôte. Des opérations laser très efficaces des sesquioxydes dopés au thulium et à l'holmium autour de 2,1 μm et 2,3 μm ont été démontrées
Novel laser-active inorganic materials doped with thulium and holmium ions have been investigated for their potential in broadly tunable and ultrafast lasers operating in the short-wave infrared spectral range of 2 to 3 μm. Lasers emitting within this spectral range find numerous applications, including light detection and ranging systems, gas sensing, medicine. They are used as amplifying systems for high harmonic generation and terahertz generation, and further frequency conversion into the mid-infrared region.The present PhD thesis establishes relationships between the structural properties of oxide and fluoride crystalline materials, in the form of single crystals and transparent ceramics, and the spectroscopic properties of thulium and holmium dopant ions, along with their laser characteristics, which are essential for laser development. Moreover, the physical processes underlying unexpected laser behaviour are revealed. This systematic study of laser materials allows for the identification of the most promising compositions for the development of broadly tunable and ultrashort pulse lasers.This study mainly focuses on materials that exhibit significant inhomogeneous spectral line broadening, resulting in broad and structureless absorption and emission spectra of the dopant ions. In order to promote this effect, several strategies have been considered, including rare-earth ion clustering, local structure disorder, compositional disorder in solid-solution compounds, and phonon-sidebands arising from electron-phonon interactions.The formation of thulium and holmium clusters in calcium fluoride crystals enables efficient and broadly tunable laser operation around 2.1 μm. A polarized spectroscopic study of the emission properties of holmium ions in disordered calcium rare-earth aluminate crystals sheds light on its broadband spectral properties and on the role of multiphonon assisted emission, which occurs beyond electronic transitions, in unexpected laser emissions observed in mode-locked lasers. In solid-solution sesquioxide ceramics of the yttria-lutetia-scandia ternary system doped with thulium ions, there is a strong and nearly linear variation of the crystal-field strength with the mean size of the host-forming cation. This relationship allows for the customization of both the position and width of the emission band above 2 μm by appropriately adjusting the host composition. Highly efficient laser operations of thulium- and holmium-doped sesquioxides around 2.1 μm and 2.3 μm have been demonstrated

The object of this thesis is to extend the current tables for two useful quantities when calculatingcollisional broadening, the cross-section of interaction and the velocity parameter.These quantities, which have hitherto been tabulated for lower states, have now been calculatedfor higher lying states and are used in the ABO - model for spectral line broadening.Having larger tables for these values enables broadening calculations for more spectral linesand this thesis shows examples of calculations which beneted from this. During the calculationsof the tables some unexpected behaviour in the distribution of values arose whichhas not been seen previously. This could point to an unknown underlying mechanism.

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.

Etude systématique des coefficients d'élargissement par collisions des raies infrarouge et Raman de dioxyde de carbone perturbé par dioxyde de carbone, eau, diazote et dioxygène. Les résultats obtenus dans la gamme de température 300-3000 K sont utiles pour modéliser les transferts radiatifs en particulier dans les systèmes de combustion, et pour les diagnostics infrarouge et Raman.

Un code de calcul raie par raie des propriétés radiatives de mélanges gazeux hétérogènes et anisothermes CO2, H2O, CO, N2, o a été construit a partir de données spectroscopiques, applicable de 300 à 2500 K de 0,1 à 50 ATM, et dans tout le domaine infrarouge. Réalisation d'un montage de mesure de la transitivité d'un gaz a température élevée

Ispitivana je zavisnost brzine fronta udarnih talasa u T-cevi od više parametara. Izvršeno je povezivanje ICCD kamere sa spektrometrom. Ispitane su karakteristike celokupnog sistema i izvršena je njegova optimizacija i kalibracija. Izmerene su Štarkove poluširine 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.
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.

Etude expérimentale et théorique de l'élargissement par effet Stark de raies d'argon ionisé. Etude expérimentale des différents paramètres physiques de l'arc TIG utilisé. Mesure des largeurs de raies. Calcul numérique des largeurs en théorie semi-classique à l'aide de l'approximation impact. Comparaison critique des différents résultats

Pour expliquer le deplacement et l'elargissement du pic compton,lorsque l'energie du photon est voisine de l'energie de liaison de l'electron, il est necessaire d'introduire non seulement la liaison et le mouvement de l'electron, mais aussi le recul du mnoyau. On donne un calcul relativiste de la valeur quadratique moyenne de l'impulsion de l'electron et une expression generale des fonctions d'onde radiales. Pour le calcul analytique covariant de l'element de matrice ou utilise un propagateur pour un electron lie dans le schema de furry et determine la secton efficace, sans aucune integration

Un plasma a forte correlation est constitue par une lame mince de cesium vaporise entre 900 et 1500**(o)c sous une pression totale d'argon variant jusqu'a 110 bars. Le parametre de non idealite de ce plasma est compris entre 1 et 5. Le cesium a ete choisi pour son tres faible potentiel d'ionisation, une polarisabilite atomique elevee et le point critique ( 1651**(o)c, 92 bars) le plus bas parmi les metaux alcalins. Par transmission optique, on mesure, autour du premier doublet de resonance (8943-8521 a**(o)) des coefficients d'absorption compris entre 0,3 et 0,6mu m**(-1) et des elargissements de raies variant entre 10 et 90 a**(o) quand temperature et pression augmentent

Etude experimentale, a l'aide d'un spectrometre a reseau a haute resolution, des intensites et des parametres d'elargissement par o::(2) et n::(2), entre 296 et 198 k pour co::(2). Deduction des facteurs d'interaction rovibrationnelle de co::(2) a partir des intensites et du coefficient de variation thermique des parametres d'elargissement ( equiv. A 0,72). Calcul de l'elargissement par effet de pression, resultant des interactions collisionnelles entre molecules, a partir de modele semi-classiques pour tester les potentiels et les valeurs des parametres utilises pour les calculer: importance instable des forces a courte et moyenne portee dans l'elargissement des raies de co::(2) par o::(2) et n::(2) et des raies auto-perturbees de j eleve pour co::(2) et n::(2)o, au moyen des theories d'anderson-tsao-curnutte et de robert-bonamy; role de l'interaction entre translation et rotation, qui semblerait devoir etre prise en compte

L'etude des populations des quasiparticules (excitons, polaritons, etc. ), des durees de vie de leurs etats fondamentals et excites est faite par mesures de transmission induite et de gain a l'aide d'une technique "pompe et sonde". L'elargissement asymetrique de la raie d'absorption excitonique est explique par les collisions elastiques entre excitons. Les variations de l'indice de refraction sont expliquees par la dynamique des polaritons de type photonique

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.

This thesis presents a spectroscopic study of the 7F0 ---t5D0 transition of Eu3+ in EuC13 ·6H2 0, which is used to evaluate the potential performance of a quantum com­ puting system implemented in EuCla·6H2 0 and, more generally, in stoichiometric rare earth crystals. EuC13 ·6H2 0 has one of the narrowest optical inhomogeneous linewidths of any solid but this linewidth is shown to be still much larger than that required for practical quantum computing in a rare earth crystal. To assess the possibility of reducing the linwidth, the contributions of isotopic impurities to both the optical linewidth and line structure were investigated, and ligand isotopes were identified as a major source of both inhomogeneous broadening and structure on the optical transition, suggesting that the linewidth could be substantially reduced by isotopi­ cally purifying EuC13 ·6H20. The effect of ligand isotopes on the optical lifetime and coherence time was also investigated. It was found that fully deuterating the crystal to EuC13·6D20 substantially improves both the lifetime and coherence time. The satellite lines formed in the optical spectrum of a rare earth crystal when it is doped with another rare earth are proposed as qubits. A crucial step in char­ acterising EuCla ·6H20 for quantum computing is associating these satellite lines in EuC13 ·6H2 0 with crystallographic sites. A new method for associating sites with lines, which works for low symmetry crystals such as EuC13·6H20, is presented. This method involves modelling the splitting of the ground state hyperfine levels caused by the magnetic dipole-dipole interaction between a Kramers dopant and the Eu3+ ion. Using this method, most of the outer satellite lines in rare earth doped EuCla·6H2 0 were assigned to crystallographic sites. It has been proposed that the electronic interactions between these satellite lines be used to enact two-qubit gates in a rare earth quantum computer. These interac­ tions were measured between a number of different satellite lines using a new two­ laser spectral holeburning technique. Interactions of up to 46.081±0.005 MHz were observed, and this was the first time that electronic interactions between weakly coupled rare earth ions had been measured. The two most common interactions identified between rare earth ions in solids are electric dipole-dipole and exchange, but the observed interactions are stronger than expected from a electric dipole-dipole model and occur at too large a distance to be superexchange. It is shown that the development of a moderate-sized quantum processor, one with more than 10 qubits, in a stoichiometric rare earth crystal is feasible provided that the optical inhomogeneous linewidth is reduced below 1MHz. Demonstrations of three or four qubit devices should be possible using existing materials.