Spelling suggestions: "subject:"attosecond pulse"" "subject:"attoseconde pulse""
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Ultra-intense laser-plasma interaction for applied and fundamental physicsGonoskov, Arkady January 2013 (has links)
Rapid progress in ultra-intense laser technology has resulted in intensity levels surpassing 1022 W/cm2, reaching the highest possible density of electromagnetic energy amongst all controlled sources available in the laboratory. During recent decades, fast growth in available intensity has stimulated numerous studies based on the use of high intensity lasers as a unique tool for the initiation of nonlinear behavior in various basic systems: first molecules and atoms, then plasma resulting from the ionization of gases and solids, and, finally, pure vacuum. Apart from their fundamental importance, these studies reveal various mechanisms for the conversion of a laser pulse's energy into other forms, opening up new possibilities for generating beams of energetic particles and radiation with tailored properties. In particular, the cheapness and compactness of laser based sources of energetic protons are expected to make a revolution in medicine and industry. In this thesis we study nonlinear phenomena in the process of laser radiation interacting with plasmas of ionized targets. We develop advanced numerical tools and use them for the simulation of laser-plasma interactions in various configurations relating to both current and proposed experiments. Phenomenological analysis of numerical results helps us to reveal several new effects, understand the physics behind them and develop related theoretical models capable of making general conclusions and predictions. We develop target designs to use studied effects for charged particle acceleration and for the generation of attosecond pulses of unprecedented intensity. Finally, we analyze prospects for experimental activity at the upcoming international high intensity laser facilities and uncover a basic effect of anomalous radiative trapping, which opens up new possibilities for fundamental science.
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From few-cycle femtosecond pulse to single attosecond pulse-controlling and tracking electron dynamics with attosecond precisionWang, He January 1900 (has links)
Doctor of Philosophy / Department of Physics / Zenghu Chang / The few-cycle femtosecond laser pulse has proved itself to be a powerful tool for controlling the electron dynamics inside atoms and molecules. By applying such few-cycle pulses as a driving field, single isolated attosecond pulses can be produced through the high-order harmonic generation process, which provide a novel tool for capturing the real time electron motion. The first part of the thesis is devoted to the state of the art few-cycle near infrared (NIR) laser pulse development, which includes absolute phase control (carrier-envelope phase stabilization), amplitude control (power stabilization), and relative phase control (pulse compression and shaping). Then the double optical gating (DOG) method for generating single attosecond pulses and the attosecond streaking experiment for characterizing such pulses are presented. Various experimental limitations in the attosecond streaking measurement are illustrated through simulation. Finally by using the single attosecond pulses generated by DOG, an attosecond transient absorption experiment is performed to study the autoionization process of argon. When the delay between a few-cycle NIR pulse and a single attosecond XUV pulse is scanned, the Fano resonance shapes of the argon autoionizing states are modified by the NIR pulse, which shows the direct observation and control of electron-electron correlation in the temporal domain.
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Basis sets for light-matter interaction: from static coherent states to moving GaussiansEidi, Mohammad Reza 06 October 2022 (has links)
This thesis develops a computationally efficient way of employing Gaussian wave packets to study laser-induced electron dynamics in atomic and molecular systems by directly solving the time-dependent Schrödinger equation (TDSE). First, we investigate charge migration (treating the nuclei classically), high-order harmonic generation (HHG), and single-isolated attosecond pulse generation in the Hydrogen molecular ion subjected to intense laser fields in a different range of frequencies with a basis of static coherent states (SCS). Then, seeking for a smarter way of constructing and guiding a minimal set of time-dependent basis functions, we introduce a fast and accurate approach for optimizing s-type Gaussian type orbitals (GTOs) and apply it to calculate electronic states of different 1D and 3D time-independent systems. Finally, we apply our optimization approach to time-dependent problems. With our approach we obtain excellent agreement with the exact results for HHG spectra of the 1D Hydrogen atom and molecular ion exposed to intense laser fields, which is not possible even with a much larger basis of static s-type GTOs. / Diese Arbeit sucht nach einem computereffizienten Ansatz für die Verwendung von Gaußschen Wellenpaketen zur Untersuchung der Quantenelektronendynamik in atomaren und molekularen laserinduzierten Systemen durch direkte Lösung der zeitabhängigen Schrödingergleichung (TDSE). Beginnend mit statischen kohärenten Zuständen (SCS) untersuchen wir die Ladungsmigration (wobei wir die Kerne klassisch behandeln), die Erzeugung von Oberwellen höherer Ordnung (HHG) und die Erzeugung von isolierten Attosekundenimpulsen im 3D-Wasserstoffmolekül-Ion \ih, das intensiven Laserfeldern in einem unterschiedlichen Frequenzbereich ausgesetzt ist. Auf der Suche nach einer intelligenteren Methode zur Konstruktion und Führung eines minimalen Satzes von Basisfunktionen stellen wir einen schnellen und genauen Ansatz zur Optimierung von Gauß-Orbitalen (GTOs) vom s-Typ vor und wenden ihn erfolgreich zur Berechnung gewünschter elektronischer Zustände verschiedener 1D- und 3D-Quantensysteme an. Letztendlich erweitern wir unseren Optimierungsansatz auf zeitabhängige Szenarien. Wir demonstrieren, wie diese Methode eine ausgezeichnete Übereinstimmung mit den exakten Ergebnissen in den HHG-Spektren des 1D-Wasserstoffatoms und des 1D-\ih, die intensiven Laserfeldern ausgesetzt sind, erzielt, wo die nicht optimierten s-Typ GTOs nicht übereinstimmen, selbst nach den ersten paar Harmonien im Plateaubereich.
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Post compression d'impulsions intenses ultra-brèves et mise en forme spatiale pour la génération d'impulsions attosecondes intenses / Post compression of high energy ultra-short pulses and spatial shaping of intense laser beams for generation of intense attosecond pulsesDubrouil, Antoine 28 October 2011 (has links)
La génération d'harmoniques d'ordre élevé en milieu gazeux est un phénomène habituellement décrit par un modèle à trois étapes : sous l'effet d'un champ laser intense, un atome (ou une molécule) est ionisé par effet tunnel. L'électron éjecté est accéléré dans le champ laser, puis il se recombine sur son ion parent en émettant un photon XUV. Ce rayonnement XUV, émis sous la forme d'impulsions attosecondes (1 as = 10-18 s), est un outil idéal pour sonder la structure électronique des atomes ou des molécules, avec une résolution temporelle de l'ordre de l'attoseconde. Néanmoins, l'intensité de ce rayonnement n'est en général pas suffisante pour induire des effets non-linéaires (transitions à deux photons).Au cours des travaux réalisés pendant cette thèse, nous avons développé une source harmonique capable de produire un rayonnement XUV intense qui doit permettre d'accéder à la physique non-linéaire dans cette gamme de longueur d'onde. Pour parvenir à ces résultats, un travail important sur les impulsions infrarouges génératrices a été nécessaire, aussi bien dans le domaine spatial que dans le domaine temporel. Une technique de mise en forme spatiale de faisceaux laser intenses a donc été développée, ainsi qu'une technique de post compression adaptée aux impulsions laser intenses. Ce travail de thèse se divise donc en trois étapes : - Le développement de la source harmonique haute énergie et des diagnostics associés. Cette source est basée sur l'utilisation d'une chaîne laser Titane-Saphir qui délivre des impulsions de 150 mJ pour des durées de 40 fs à une cadence de 10 Hz. De bonnes conditions d'optimisation ont été obtenues, donnant lieu à des impulsions XUV dont l'énergie est de l'ordre du µJ lors de la génération dans l'argon.- Le développement d'une technique de mise en forme spatiale adaptée aux faisceaux laser intenses et à la génération d'harmoniques. Le dispositif est basé sur une optique en réflexion et sur les interférences à deux faisceaux. Il permet de produire, dans la région focale, des faisceaux dont le profil d'intensité est radialement constant (faisceaux flat top) et ainsi d'apporter un contrôle supplémentaire sur la génération d'harmoniques d'ordre élevé.- Le développement d'une technique de post compression en propagation guidée basée sur l'élargissement spectral induit par ionisation. Cette technique est adaptée pour des impulsions intenses (3.5 TW) et permet de produire des impulsions de puissance crête supérieure au Térawatt dans le domaine sub-10 fs. Cette technique fournit donc une source unique pour la génération d'harmoniques d'ordre élevé.Ces deux approches ont été testées et validées pour la génération d'harmoniques d'ordre élevé, et les résultats obtenus ouvrent d'intéressantes perspectives telles que la génération d'impulsions attosecondes isolées de haute énergie (> 100 nJ). / The generation of high order harmonics in a gaseous medium is a phenomenon conveniently described by a three steps model : subject to a strong laser field irradiation, an atom (or molecule) can undergo a tunneling ionization. The ejected electron is accelerated in the laser field and recombine on its parent ion leading to the emission of an XUV photon. The XUV radiation can be emitted as attosecond pulses (1 as = 10-18 s), and it is then an ideal tool to probe the electronic structure of atoms or molecules which require the highest time resolution. However, the intensity of this radiation is usually not sufficient to induce non-linear processes (two-photon transitions).In the frame of this work, we have developed a harmonic source capable of producing an intense XUV radiation to access non-linear physics in this wavelength domain.To achieve these results, significant work on the infrared generating pulses was necessary, both in the spatial and temporal domain. We have developed a technique for spatial shaping of intense laser beams, and a post compression technique fitted to high energy pulses.This thesis is therefore divided into three parts:- The development of an high energy harmonic source and related diagnostics. We use a Ti: sapphire laser system for this source which delivers 40-fs pulses up to an energy of 150 mJ at 10 Hz repetition rate. Good optimization conditions were obtained, leading to XUV pulse energies of the order of μJ in the case of generation in argon.- The development of a spatial shaping technique adapted to intense laser beams and to harmonic generation. The device is based on reflection optics and the interferences of two beams. It can produce, in the focal region, beams with a radially constant intensity over a large volume (flat top beams) and thus provide additional control of the harmonics generating process.- The development of a post compression technique in guided geometry based on the ionization induced spectral broadening. This technique is suitable for intense pulses (3.5 TW) and produces pulses above the terawatt level in the 10-fs range. This technique therefore provides a unique source for harmonic generation.These two approaches have been tested and validated for high order harmonics generation, and the results open interesting perspectives such as the generation of isolated attosecond pulses of high energy (> 100 nJ).
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