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Hornung, Thomas. "Optimal control with ultrashort laser pulses." Diss., lmu, 2002. http://nbn-resolving.de/urn:nbn:de:bvb:19-2963.
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Xu, Bingwei. "Control of multiphoton molecular excitation with shaped femtosecond laser pulses." Diss., Connect to online resource - MSU authorized users, 2008.
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Papastathopoulos, Evangelos. "Adaptive control of electronic excitation utilizing ultrafast laser pulses." Doctoral thesis, [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975015184.
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Walter, Dominik. "Adaptive control of ultrashort laser pulses for high-harmonic generation." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=983790302.
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Deutschmann-Olek, Andreas [Verfasser]. "Modeling and Control of Optical Pulse Amplifiers for Ultra-Short Laser Pulses / Andreas Deutschmann-Olek." Düren : Shaker, 2021. http://d-nb.info/1233547895/34.
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Ren, Qinghua. "Theoretical design of laser pulses for the control of molecular motion." Thesis, University of Bristol, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432731.
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Harper, Matthew R. "Control and measurement of ultrafast pulses for pump/probe-based metrology." Thesis, St Andrews, 2007. http://hdl.handle.net/10023/430.
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Graham, Leigh. "Quantum control of laser induced dynamics of diatomic molecular ions using shaped intense ultrafast laser pulses." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602512.
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The beauty of ultrafast science lies inherently in the ability to induce and image dynamics on a timescale comparable to the fastest nuclear motion, In recent years, a plethora of rich and fascinating phenomena involving the interaction of diatomic molecules with intense femtosecond laser pulse has been unveiled, Such research is motivated by the ambition to understand and optically drive chemical reactions to the highest degree of specificity, In this work, the strategy employed toward achieving this goal relies ., on the interaction of Hydrogenic ions and analytically shaped and well characterized pulses, The ability to manipulate photodissociation dynamics using the instantaneous frequency and temporal profile of pulses shaped with quadratic (ψ") and cubic (ψ’") spectral phase functions was studied, A three-dimensional (3D) momentum imaging technique was used to measure the kinetic energy release (KER) and angular distribution of the dissociation fragments, A significant enhancement in the dissociation probability of non-resonant transitions from the low lying vibrational levels using the sign and magnitude of the applied phase function as a control tool was demonstrated, Furthermore, the tractability of Hydrogenic ions means a mechanistic explanation for these observations can be theoretically determined, Investigating the behavior of ions more complex than H+2 in strong laser fields can present many theoretical and experimental challenges, Laser-induced fragmentation of CD+ was explored using the 3D momentum imaging technique in the longitudinal field imaging mode, The high mass ratio (12:2) hinders the simultaneous measurement of the two constituents, at all angles and kinetic energies, Alternatively, the recently developed longitudinal and transverse field imaging technique was used to perform a piecewise dissociation measurement, This allowed the branching ratio of the dissociation channels to be obtained, Furthermore, the fragmentation channels of CD+ were identified and studied as a function of laser intensity and wavelength,
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Patas, Alexander [Verfasser]. "Control of multiphoton processes by parametrically shaped ultrashort laser pulses / Alexander Patas." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1141678357/34.
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Coughlan, Matthew Anthony. "Controlling Light-Matter Interactions and Spatio-Temporal Properties of Ultrashort Laser Pulses." Diss., Temple University Libraries, 2012. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/186215.
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ChemistryPh.D.
The SPECIFIC method a fast and accurate method for generating shaped femtosecond laser pulses. The femtosecond pulses are user specified from pulse parameters in the temporal domain. The measured spectral and recovered temporal phase and amplitudes from SEA TADPOLE are compared with the theoretical pulse profile from the user specified input. The SPECIFIC method has been shown to be a technique that can generate a diverse array of spectral/temporal phase and amplitude as well as polarization pulse shapes for numerous scientific applications. The spatio -temporal -spectral properties of focusing femtosecond laser pulses are studied for several pulse shapes that are important for non-linear spectroscopic studies. We have shown with scanning SEA TADPOLE that the spatio-spectral phase of focusing double pulse profile changes across the laterally across the beam profile. The spectral features of the sinusoidal spectral phase shaped pulse has been shown to tilt at with a changing angle away from the focus of the lens. Using spatio-spectral coupling, we have shown that multiple spatio-temporal foci can be generated along and perpendicular to the focusing direction of a femtosecond laser pulse. The spatial position of the spatio-temporal foci is controlled optically. Using sinusoidal spectral phase modulated pulse trains fragment ion production from Benzonitrile parent molecule can be controlled. A spectral transmission window perturbed the temporal pulse amplitudes resulting in fragment ion production dependant on spectral window position. The spectral window ion production was shown to also be dependant on temporal phase sequence.
Temple University--Theses
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Saab, Mohamad Yehia. "Photochimie organique guidée par pulses laser : Applications : Benzopyrane et Pyrazine." Thesis, Montpellier 2, 2014. http://www.theses.fr/2014MON20014/document.
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La photo-isomérisation par ouverture de cycle du benzopyrane a été étudiée à l'aide de la méthode MCTDH (Multi-Configuration Time-Dependent Hartree). Nous avons introduit différentes stratégies pour contrôler la conversion du benzopyrane en mérocyanine à l'aide d'impulsions laser. Nous avons utilisé un modèle pour le potentiel électronique à six dimensions développé dans le cadre d'un travail antérieur. Le modèle repose sur une généralisation des Hamiltoniens modèles standards pour les couplages vibroniques et utilise les six coordonnées les plus importantes pour le processus. Le principal objectif est de fournir des stratégies de contrôle qui pourront être utilisées par les expérimentateurs par la suite. Plus précisément, nous avons proposé: (i) une technique de type pompe-sonde pour contrôler la photostabilité, (ii) une stratégie en deux étape avec une préexcitation vibrationnel du système,(iii) une stratégie reposant sur un contrôle par effet Stark induit par un laser non-résonantThe ring-opening photoisomerization of benzopyran, which occurs via a photochemical route involving a conical intersection,has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method (MCTDH). We introduce a mechanistic strategy to control the conversion of benzopyran to merocyanine with laser pulses. We use asix-dimensional model developed in a previous work for the potential energy surfaces (PES) based on an extension of thevibronic-coupling Hamiltonian model (diabatization method by ansatz), which depends on the most active degrees of freedom. The main objective of these quantum dynamics simulations is to provide a set of strategies that could help experimentalists tocontrol the photoreactivity vs. photostability ratio (selectivity). In this work we present:(i) a pump-dump technique used tocontrol the photostability, (ii) a two-step strategy to enhance the reactivity of the system: first, a pure vibrational excitation inthe electronic ground state that prepares the system and, second, an ultraviolet excitation that brings the system to the firstadiabatic electronic state; (iii) finally the effect of a non-resonant pulse (Stark effect) on the dynamics
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Mota, Alessandro Damiani. "Sistema eletrônico de controle para laser amarelo de aplicação oftalmológica com regime de operação contínuo e micro-pulsado." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/18/18152/tde-26042012-100723/.
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Mais recentemente foi proposta uma nova técnica para tratamento de doenças relacionadas à retina humana, utilizando descargas laser na retina com seqüência de pulsos da ordem de 200 \'mü\'s, em substituição ao tratamento convencional que utiliza pulsos longos da ordem de 300 ms. A principal vantagem da nova técnica é a preservação (sem morte celular) do tecido exposto ao laser. Esse trabalho apresenta os mecanismos adotados para o desenvolvimento de um sistema eletrônico de controle de uma cavidade laser em 586 nm, para uso oftalmológico, que objetiva atender o protocolo exigido por essa técnica mais recente. O referido protocolo exige a formação de pulsos rápidos de laser, o que torna vital a velocidade do sistema eletrônico de controle da cavidade laser. Para atender os requisitos do projeto foram implementados dois controladores de corrente em malha fechada PI (Proporcional integrative controller) que trabalham em sincronismo, um controlador de potência óptica em malha fechada PI, e circuitos auxiliares de controle térmico da cavidade laser. Em software foram implementados um PI de potência, com objetivo de tornar a malha de controle estável com o tempo de resposta necessário, e o PI de controle térmico dos elementos da cavidade laser. Os testes realizados do protótipo demonstraram que o sistema de controle atendeu as especificações de projeto, principalmente no que se refere a tempo de resposta do pulso rápido, ponto fundamental na obtenção do protocolo clínico (FastPulse), que esse trabalho objetiva atender. Adicionalmente, o protótipo foi submetido a teste clínico em um paciente, e os resultados demonstraram eficácia no tratamento e ausência de marcas (lesões) na retina.Recently, scientists have proposed a new technique for treating diseases related to the human retina, which is based on retinal laser discharges using pulse sequence around of 200 \'mü\'s, replacing the conventional treatment using long pulses around of 300 ms. The main advantage of the new technique is the conservation (without cell death) of the area exposed to the laser. This work presents the mechanisms adopted for the development of an electronic control system of a laser cavity at 586 nm for ophthalmic use, which aims to meet the protocol required by this recent technique. The protocol requires the formation of rapid pulses of laser, which makes the electronic control system response velocity of the laser cavity vital to the protocol. To meet the project requirements were implemented two current controllers in closed loop PI (proportional integrative controller) working synchronized, an optical power controller in closed loop PI, and auxiliary circuits for temperature control of the laser cavity. Software were implemented for two controls, a PI power, in order to make the control loop stable with the required response time, and a PI thermal control for elements of the laser cavity. Tests showed that the prototype met the design specifications, especially regarding the response time of rapid pulse, key point in obtaining the clinical protocol (FastPulse), that this work aims to meet. Additionally, the prototype was subjected to clinical trial on a patient, and the results demonstrated efficacy and no visible lesions were noticed on retina.
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Jakob, Markus Alexander [Verfasser]. "Generation and Control of Ultrafast 10 um Laser Pulses for Driving Chemical Dynamics / Markus Alexander Jakob." München : Verlag Dr. Hut, 2020. http://d-nb.info/1219475904/34.
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Lomax, Andrew Martin. "Picosecond pulse control using semiconductor laser amplifiers." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333329.
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CORDEIRO, THIAGO da S. "Controle das características geométricas de nanopartículas de prata através da conformação temporal de pulsos ultracurtos utilizando algoritmos genéticos." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10550.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Mančal, Tomáš. "Laser pulse control of dissipative dynamics in molecular systems." [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=968759068.
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Mancal, Tomas. "Laser pulse control of dissipative dynamics in molecular systems." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2002. http://dx.doi.org/10.18452/14895.
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Diese Arbeit wird einer Weiterentwicklung der Dichtematrixtheorie und ihrer Anwendung zum Studium ultraschneller laserpulsinduzierter Dynamik in Molekularsystemen in Wechselwirkung mit einem thermischen Bad gewidmet. Zwei grosse Themenkomplexe werden behandelt. Zuerst werden die sogenannten Gedächtniseffekte diskutiert. Diese folgen aus einer reduzierten Beschreibung des Molekularsystems, in der die Umgebungsfreiheitsgrade eliminiert werden. Im zweiten Teil wird die Laserpulssteuerung der dissipativen Molekulardynamik untersucht. Die theoretische Beschreibung von offenen Quantensystemen führt zu einer zeitlich nicht-lokalen Bewegungsgleichung: Die Zeitentwicklung des Molekularsystems hängt von seiner Vergangenheit ab. In dieser Arbeit wird eine numerische Methode zur Lösung der zeitlich nicht-lokalen Bewegungsgleichung entwickelt und mit einem minimalen Modell eines polyatomaren Moleküls unter dissipativem Einfluss der Umgebung getestet. Eine analytische Lösung der Bewegungsgleichung für den speziellen Fall einer sehr langen Gedächtniszeit wurde hergeleitet. Zur Identifizierung solcher Gedächtniseffekte vergleichen wir diese analytische Lösung mit numerischen Rechnungen inklusive Gedächtnis und mit approximativen Rechnungen, die die zeitliche Nicht-Lokalität vernachlässigen. Für eine Anregung mit einem Laserpuls, der kürzer als die Gedächtniszeit des Systems ist, zeigt das Molekularsystem eine erkennbar unterschiedliche Dynamik als ohne Gedächtniss. Die Gedächtniseffekte werden mit abfallender Laserpulslänge deutlich ausgeprägter. Der zweite Teil der Arbeit konzentriert sich auf die Anwendung der Theorie der Optimalen Kontrolle, um die molekulare Dynamik zu steuern. Aus der Theorie der Optimalen Kontrolle erhält man Laserpulse, die bestimmte Aufgaben erfüllen, z.B. die Besetzung gewünschter vibronischer Niveaus des Molekularsystems oder die Platzierung eines Wellenpakets auf einer vorgegebenen Position auf der molekularen Potentialfläche. Als erstes Beispiel haben wir die Kontrolle des dissipativen fotoinduzierten Elektronentransfers in einem Donator-Brückenmolekül-Akzeptor System betrachtet, wobei wir das Gedächtniss vernachlässigt haben. Die Steuerbarkeit des Elektronentransfers wird diskutiert und der Mechanismus, mit dem sie möglich wird, wird identifiziert. Wir haben festgestellt, dass die Steuerung der Elektronentransferreaktionen selbst unter dem Einfluss von Dissipation möglich ist, obwohl die Kontrollausbeute mit steigender Dissipation drastisch abfällt. In Anwesenheit von Dissipation verändert sich auch der Mechanismus der Steuerung. Die experimentelle Ausführbarkeit der Herstellung des aus der Theorie der Optimalen Kontrolle resultierenden Kontrollpulses wird diskutiert und Methoden werden präsentiert, die die Abschätzung der Effizienz ermöglichen, mit der ein Flussigkristall--Laserpulsformer, wie er heute in Experimenten verwendet wird, den gewünschten Puls erzeugen kann. Um zwischen verschiedenen Kontrollaufgaben zu unterscheiden, wird ein quantitatives Mass eingeführt, das die Komplexität der Kontrollaufgabe charakterisiert. Die Theorie der Optimalen Kontrolle wird auch für Molekularsysteme formuliert, die statische Unordnung zeigen, und wird auf ein Ensemble von Molekülen mit zufälligen Orientierungen angewendet. Zum Schluss wird die Bedeutung der Gedächtnisseffekte für die Steuerung der dissipativen Dynamik diskutiert und die Theorie der Optimalen Kontrolle neu formuliert um eine zeitliche Nicht-Lokalität in der Bewegungsgleichung des Molekularsystems zu berücksichtigen.This work is dedicated to a further development of the density matrix theory and its application to the study of ultrafast laser pulse induced dynamics in molecular systems interacting with a thermal environment. Two topics are considered, first the so-called memory effects are analyzed which result from a reduced description of the molecular system excluding the environmental degrees of freedom. And secondly, the laser pulse control of dissipative molecular dynamics is examined. The theoretical description of open quantum systems results in a time non-local equation of motion so that the evolution of the molecular system depends on its past. In this work a numerical method to solve the time non-local equations of motion has been developed and tested for a minimal model of a polyatomic molecule subject to the dissipative influence of an environment. An analytical solution of the equation of motion for the special case of very long standing memory is also achieved. To identify signatures of such memory effects in general case we compare this analytical solution with numerical calculations involving memory and with approximative computations ignoring time non-locality. For the excitation by a laser pulse shorter than the duration of the memory the molecular systems exhibit noticeably different dynamics than for the absence of the memory. The effects become significantly more pronounced with decreasing laser pulse durations. The second part of the work concentrates on the application of the optimal control theory to guide molecular dynamics. Optimal control theory provides laser pulses which are designed in such a manner to fulfill certain control tasks, e.g. the population of a desired vibrational level of the molecular system or the placement of a wavepacket on a prescribed position on the molecular potential energy surface. As a first example the control of the dissipative photo-induced electron transfer in a donor--bridge--acceptor systems has been particularly considered ignoring the memory. The controllability of the electron transfer has been discussed and the mechanism by which it becomes possible has been identified. We have found the control of electron transfer reactions feasible even under the influence of dissipation although the yield of the control decreases drastically with increasing dissipation. In the presence of dissipation mechanism of the control has been found to change. The feasibility of the reproduction of the control pulses resulting for the optimal control theory in the experiment has been discussed and methods have been presented how to check the efficiency of the reproduction of optimal control pulses by liquid crystal pulse shapers, prevailingly used in modern control experiments. To distinguish different control tasks a quantitative measure has been introduced characterizing complexity of the control task. The optimal control theory has also been formulated for molecular systems showing static disorder and applied on an ensemble of molecules exhibiting random orientations. Finally, the importance of memory effects for the control of dissipative dynamics has been discussed and the optimal control theory has been formulated to account for a time non-locality in the equation of motion for molecular systems.
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Schwarz, Christoph Benjamin [Verfasser], Tobias [Gutachter] Brixner, and Sven [Gutachter] Höfling. "Full vector-field control of femtosecond laser pulses with an improved optical design / Christoph Benjamin Schwarz ; Gutachter: Tobias Brixner, Sven Höfling." Würzburg : Universität Würzburg, 2017. http://d-nb.info/1123957738/34.
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Elghobashi, Nadia. "Theory of using few cycle IR and UV laser pulses to control the orientation and selective dissociation of hydrogen bonded anions." [S.l.] : [s.n.], 2005. http://www.diss.fu-berlin.de/2006/23/index.html.
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Cruz, Vinícius Vaz da. "Dinâmica nuclear dependente do tempo do espalhamento colinear H + HCl sob excitação por pulsos de laser na região do infravermelho." Universidade Federal de Goiás, 2015. http://repositorio.bc.ufg.br/tede/handle/tede/5176.
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This dissertation presents a wavepacket simulation study of the H + HCl collinear reaction when the HCl molecule is initially prepared by an infrared laser pulse in a coherent superposition of vibrational states. A detailed discussion of wavepacket motion, reactive flux and reaction probabilities as function of the superposition state parameters is presented. We apply the flux formalism to derive an analytical expression for the reaction probabilities, which is then used to analyse our numerical simulations. The results show a strong phase dependence of the reaction probabilities, as well as the spatial distribution of the reactant molecules. The full reaction probability surface is computed for two average collision energies, and the enhancement and suppression of the H+HCl!H2+Cl reaction channel is discussed in terms of the surface’s critical points.
Esta dissertação apresenta o estudo por meio de simulações de pacote de ondas das colisões colineares H + HCl quando a molécula de HCl é preparada por pulsos de laser de infravermelho em uma superposição de níveis vibracionais. É feita uma discussão detalhada do movimento do pacote de ondas, fluxo reativo e probabilidades de reação em termos dos parâmetros da superposição de estados. Nós aplicamos o formalismo de fluxo para deduzir uma expressão analítica para as probabilidades de reação, a qual é então utilizada na análise de nossas simulações numéricas. Os resultados mostram uma grande dependência das probabilidades de reação com a fase e com a distribuição espacial das moléculas reagentes. A superfície completa de probabilidade de reação é calculada para duas energias de colisão médias, e as condições de melhora e supressão da reação H+HCl!H2+Cl é discutida em termos dos pontos críticos da superfície.
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Barth, Ingo [Verfasser]. "Quantum control of electron and nuclear circulations, ring currents, and induced magnetic fields in atoms, ions, and molecules by circularly polarized laser pulses / Ingo Barth." Berlin : Freie Universität Berlin, 2009. http://d-nb.info/1023663929/34.
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Wilkenson, Wade F. "A theory for optical wavelength control in short pulse free electron laser oscillators." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA271706.
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Schirrmeister, Dirk. "Zur Theorie photoinduzierter Dynamik offener Molekularsysteme: Kontrolle von Dissipation durch ultrakurze Laser-Pulse." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 1998. http://dx.doi.org/10.18452/14380.
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Zusammenfassung in PostScript In dieser Arbeit wird die photoinduzierte Dynamik offener Molekularsysteme unter dem Einfluß intensiver und ultrakurzer Laserpulse untersucht. Die Anregung eines Moleküls durch einen optischen ultrakurzen Laserpuls führt zu Übergängen zwischen verschiedenen elektronischen Zuständen. Dieser Anregungsprozeß wird begleitet von dissipativen Vorgängen wie Energie-- und Phasenrelaxation. Die Beschreibung dieser photoinduzierten Dynamik erfolgt mit Hilfe der Methode der Dichtematrixtheorie. Dabei zeigt die Ableitung der Quanten--Master--Gleichung im Rahmen des Projektionsoperator--Formalismus, daß die wirkenden äußeren Felder einmal direkt im reversiblen Anteil der Bewegungsgleichung auftreten, aber auch einen indirekten Einfluß über den die Dissipation beschreibenden Dissipations--Superoperator ausüben. In dieser Arbeit wird zum ersten Mal die durch ultrakurze Laserpulse induzierte Feldabhängigkeit des Dissipations--Superoperators berücksichtigt. Im Rahmen der Darstellung der Quanten--Master--Gleichung im Floquetbild kann eine anschauliche Deutung dieses feldabhängigen Effektes gegeben werden: die die Dissipation beschreibende frequenzabhängige Spektraldichte der Umgebungsmoden wird feldabhängig bei verschiedenen Frequenzen abgefragt. Analytische Untersuchungen zum Zwei--Niveau--System zeigen, daß die Feldabhängigkeit dann relevant wird, wenn die Pulslänge vergleichbar ist mit der Zeitskala, auf der die Autokorrelationsfunktion der Umgebungsfreiheitsgrade abklingt. Um den Einfluß auf experimentelle Größen zu untersuchen, wird ein zweifarbiges Pump--Test--Experiment zum Laserfarbstoffmolekül IR 125 betrachtet, bei welchem die spektral und zeitlich aufgelöste Transmission auf einer Femtosekunden-- und Pikosekunden--Zeitskala gemessen wurde. Im Rahmen des Modells einer effektiven Schwingungsmode wird eine Anpassungsrechnung an das Experiment vorgenommen. Dabei wird zunächst die Standard-Redfield-Theorie verwendet, um ein Referenzmodell zu gewinnen. Es gelingt, eine gute Übereinstimmung mit dem Experiment zu erreichen. Die exakte Berücksichtigung des Einflusses der internen Konversion zwischen den angeregten elektronischen Zuständen führt zu einem Anstieg der Transmission innnerhalb einer Pikosekunde. Es ist notwendig, die Dichtematrixgleichungen exakt zu lösen, da eine vergleichende Untersuchung mit Hilfe der nichtlinearen Suszeptibilität dritter Ordnung eine deutliche Abweichung zum exakten Resultat zeigt. Ausgehend vom Referenzfall feldunabhängiger Dissipation wird dann die Feldabhängigkeit der Relaxationsraten bestimmt sowie der Einfluß auf Observablen wie der relativen Transmission untersucht. In Übereinstimmung mit den analytischen Ergebnissen zeigt sich, daß der feldabhängige Effekt am größen ausgeprägt ist, wenn die Pulslänge kleiner als die Korrelationszeit der Umgebungsfreiheitsgrade wird und die wirkenden Felder hinreichend intensiv sind.Damit wird eine Kontrolle von Dissipation möglich. Ein Einfluß des feldabhängigen Effektes auf experimentelle Observablen wird vorhergesagt.abstract in PostScript This thesis investigates the influence of intense and ultrashort laser pulses on the photoinduced dynamics of open molecular systems. The excitation of a molecule by an optical ultrashort laser pulse induces transitions between different electronic states. This excitation process is accompanied by the dissipative processes of energy and vibrational relaxation. This excitation process is described within the method of the density matrix theory. Thereby, the derivation of the quantum master equation in the framework of the projection operator formalism demonstrates that the external fields are present in the reversible part of the equation of motion and also exert an indirect influence by acting on the dissipation superoperator which accounts for dissipation. In this thesis the field--dependency of the dissipation superoperator which is induced by the external fields is considered for the first time. By a representation of the quantum master equation in the Floquet picture, an interpretation of this field--dependent effect can be given: the frequency--dependent spectral density of the environmental modes which describe dissipation is determined at different field--dependent frequencies. Analytical investigations for the two level system demonstrate that the field dependence becomes relevant if the pulse length is comparable with the time scale on which the autocorrelation function of the environmental degrees of freedom decays.To investigate the influence on experimental quantities, a two--color pump--probe experiment for the laser dye molecule IR 125 is considered for which the spectrally and temporally resolved transmission on a femtosecond and picosecond time scale has been measured. Within the model of one effective vibrational mode the experimental data is fitted. The standard Redfield theory is used to provide a reference model. A high degree of concurrence between the theory and the results of the experiment is achieved. The exact treatment of internal conversion between the excited electronic states leads to a rise in transmission within one picosecond. It is necessary to solve the density matrix equations exactly because a comparative investigation with the nonlinear susceptibility of third order leads to a clear viation from the exact result. Starting from the reference case of field--independent dissipation, the field--dependency of the relaxation rates is determined and the influence on observables for example the relative transmission is investigated. The analytical results show that the field--dependent effect is strongest if the pulse length becomes smaller than the correlation time of the environmental modes and if the acting fields are sufficiently strong. Thereby, a control of dissipation becomes possible. An influence of the field--dependent effect on experimental observables is predicted.
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Montgomery, Matthew A. "Understanding adaptive laser pulse-shaping control of two-photon emission and second harmonic generation." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3337186.
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Olle, Vojtech Filip. "Short pulse generation and automated control in quantum well and quantum dot laser diodes." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610420.
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Ruotsalainen, T. (Tarmo). "Integrated receiver channel circuits and structures for a pulsed time-of-flight laser radar." Doctoral thesis, University of Oulu, 1999. http://urn.fi/urn:isbn:9514252160.
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Abstract
This thesis describes the development of integrated structures and circuit implementations for the receiver channel of portable pulsed time-of-flight laser rangefinders for industrial measurement applications where the measurement range is from ∼1 m to ∼100 m to noncooperative targets and the required measurement accuracy is from a few millimetres to a few centimetres. The receiver channel is used to convert the current pulse from a photodetector to a voltage pulse, amplify it, discriminate the timing point and produce an accurately timed logic-level pulse for a time-to-digital converter.
Since the length of the laser pulse, typically 5 ns, is large compared to the required accuracy, a specific point in the pulses has to be discriminated. The amplitude of the input pulses varies widely as a function of measurement range and the reflectivity of the target, typically from 1 to 100 ... 1000, so that the gain of the amplifier channel needs to be controlled and the discrimination scheme should be insensitive to the amplitude variation of the input signal. Furthermore, the amplifier channel should have low noise in order to minimize timing jitter.
Alternative circuit structures are discussed, the treatment concentrating on the preamplifier, gain control circuitry and timing discriminator, which are the key circuit blocks from the performance point of view. New circuit techniques and structures, such as a fully differential transimpedance preamplifier and a current mode gain control scheme, have been developed. Several circuit implementations for different applications are presented together with experimental results, one of them being a differential BiCMOS receiver channel with a bandwidth of 170 MHz, input referred noise of 6 pA/√Hz
and maximum transimpedance of 260 kW. It has an accuracy of about +/- 7 mm (average of 10000 measurements), taking into account walk error with an input signal range of 1:624 and jitter (3s).
The achievable performance level using integrated circuit technology is comparable or superior to that of the previously developed commercially available discrete component implementations, and the significantly reduced size and power consumption open up new application areas.
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Zeng, Shuo. "Understanding diatomic molecular dynamics triggered by a few-cycle pulse." Diss., Kansas State University, 2015. http://hdl.handle.net/2097/19165.
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Doctor of PhilosophyPhysics
Brett D. Esry
In strong field physics, complex atomic and molecular motions can be triggered and steered by an ultrashort strong field. With a given pulse as an carrier-envelope form, E(t) = E₀(t) cos(ωt + φ), we established our photon-phase formalism to decompose the solution of a time-dependent Schrödinger equation in terms of photons. This formalism is further implemented into a general analysis scheme that allows extract photon information direct from the numerical solution. The φ-dependence of any observables then can be understood universally as an interference effect of different photon channels. With this established, we choose the benchmark system H₂⁺ to numerically study its response to an intense few-cycle pulse. This approach helps us identify electronic, rovibrational transitions in terms of photon channels, allowing one to discuss photons in the strong field phenomena quantitatively. Furthermore, the dissociation pathways are visualized in our numerical calculations, which help predicting the outcome of dissociation. Guided by this photon picture, we explored the dissociation in a linearly polarized pulse of longer wavelengths (compared to the 800 nm of standard Ti:Saphire laser). We successfully identified strong post-pulse alignment of the dissociative fragments and found out that such alignment exists even for heavy molecules. More significant spatial asymmetry is confirmed in the longer wavelength regime, because dissociation is no longer dominated by a single photon process and hence allowed for richer interference. Besides, quantitative comparison between theory and experiment have been conducted seeking beyond the qualitative features. The discrepancy caused by different experimental inputs allows us to examine the assumptions made in the experiment. We also extend numerical studies to the dissociative ionization of H₂ by modeling the ionization.
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Raith, Philipp Nils [Verfasser], and Thomas [Akademischer Betreuer] Pfeifer. "Few-Cycle Multidimensional Laser Control of Attosecond Pulse Generation / Philipp Nils Raith ; Betreuer: Thomas Pfeifer." Heidelberg : Universitätsbibliothek Heidelberg, 2012. http://d-nb.info/1177039893/34.
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Singh, Pooja. "Quantum Coherent Control and Propagation in Lambda System." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849750/.
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Strong coherence in quasi-resonant laser driven system interferes with effective relaxations, resulting in behaviors like, coherent population trapping and Electromagnetically induced transparency. The Raman system can optimize this utilizing excited coherence in the lambda system when exposed to counter- intuitive pump-stokes pulses. The phenomenon can result in complete population transfer between vibrational levels called Stimulated Raman adiabatic passage(STIRAP). STIRAP and CHIRAP have been studied with Gaussian and chirped pulses. The optical propagation effects in dense medium for these phenomenon is studied to calculate the limitations and induced coherences. Further, the effect of rotational levels has been investigated. The molecular vibrational coherence strongly depends on the effect of rotational levels. The change in coherence interaction for ro-vibrational levels are reported and explained. We have considered the effects on the phase of radiation related to rotational mechanical motion of quantum system by taking advantages in ultra strong dispersion medium provided by quantum coherence in lambda system. The enhanced Fizeau effect on a single atom is observed.
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Altinok, Yahya Kemal. "Simulation And Performance Evaluation Of A Fast And High Power Pulsed Laser Diode Driver For Laser Range Finder." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614346/index.pdf.
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Laser Diodes (LDs) are semiconductor coherent lightening devices which are widely used in many fields such as defence, industry, medical and optical communications. They have advantageous characteristics such as having higher electrical-to-optical and optical-to-optical conversion efficiencies from pump source to useful output power when compared to flash lamps, which makes them the best devices to be used in range finding applications.
Optical output power of lasers depends on current through LDs. Therefore, there is a relationship between operating life and work performance of LDs and performance of drive power supply. Even, weak drive current, small fluctuations of drive current can result in much greater fluctuations of optical output power and device parameters which will reduce reliability of LDs.
In this thesis, a hardware for a fast and high power pulsed LD driver is designed for laser range finder and is based on linear current source topology. The driver is capable of providing pulses up to 120A with 250&mus pulse width and frequencies ranging from 20Hz to 40Hz. It provides current pulses for two LD arrays controlled with a proportional-integral (PI) controller and protect LDs against overcurrents and overvoltages. The proposed current control in the thesis reduces current regulation to less than 1% and diminishes overshoots and undershoots to a value less than 1% of steady-state value, which improves safe operation of LDs. Moreover, protection functions proposed in the thesis are able to detect any failure in driver and interrupt LD firing immediately, which guarantees safe operation of LDs.
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Ren, Lan. "Integrated process planning for a hybrid manufacturing system." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2008. http://scholarsmine.mst.edu/thesis/pdf/Ren_09007dcc8046714a.pdf.
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Thesis (Ph. D.)--Missouri University of Science and Technology, 2008.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 18, 2008) Includes bibliographical references.
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Limbach, Christopher M. "Characterization of nanosecond, femtosecond and dual pulse laser energy deposition in air for flow control and diagnostic applications." Thesis, Princeton University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3737448.
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The non-resonant heating of gases by laser irradiation and plasma formation has been under investigation since the development of 100 megawatt peak power, Q-switched, nanosecond pulse duration lasers and the commensurate discovery of laser air sparks. More recently, advances in mode-locking and chirped pulse amplification have led to commercially available 100 gigawatt peak power, femtosecond pulse duration lasers with a rapidly increasing number of applications including remote sensing, laser spectroscopy, aerodynamic flow control, and molecular tagging velocimetry and thermometry diagnostics. This work investigates local energy deposition and gas heating produced by focused, non-resonant, nanosecond and femtosecond laser pulses in the context of flow control and laser diagnostic applications.
Three types of pulse configurations were examined: single nanosecond pulses, single femtosecond pulses and a dual pulse approach whereby a femtosecond pre-ionizing pulse is followed by a nanosecond pulse. For each pulse configuration, optical and laser diagnostic techniques were applied in order to qualitatively and quantitatively measure the plasmadynamic and hydrodynamic processes accompanying laser energy deposition. Time resolved imaging of optical emission from the plasma and excited species was used to qualitatively examine the morphology and decay of the excited gas. Additionally, Thomson scattering and Rayleigh scattering diagnostics were applied towards measurements of electron temperature, electron density, gas temperature and gas density.
Gas heating by nanosecond and dual pulse laser plasmas was found to be considerably more intense than femtosecond plasmas, irrespective of pressure, while the dual pulse approach provided substantially more controllability than nanosecond pulses alone. In comparison, measurements of femtosecond laser heating showed a strong and nonlinearly dependence on focusing strength. With comparable pulse energy, measurements of maximum temperature rise ranged from 50K to 2000K for 500mm and 175mm focal length lenses, respectively. Experiments with various lens and pulse energy combinations indicated an important connection between gas heating and the phenomena of intensity clamping and self-guiding. The long-term behavior of the heated region varied considerably among pulse configurations. However, in each case, the formation of a toroidal vortex could be suppressed or enhanced depending on the variables of pressure, focusing and pulse energy.
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Laurens, Gaétan. "Laser generation of nanoparticles in liquids : new insights on crystal structure control and colloidal stability." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1161/document.
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L’engouement pour l’originalité des propriétés physiques des nanoparticules s’est accompagné d’un développement de nombreuses méthodes de synthèse depuis un demi siècle. Parmi elles, l’ablation laser en liquide permet de produire des nanoparticules avec des surfaces libres de tout contaminant et ce pour une multitude de combinaisons de matériaux et de solvants. Cependant, la simplicité apparente de cette technique dissimule la complexité des mécanismes physico-chimiques, ce qui entraîne actuellement un manque de contrôle des objets synthétisés. Tout d’abord, nous nous sommes intéressés à la cinétique des bulles pour laquelle les conditionsextrêmes d’ablation laser en liquide présentent des cas originaux de cinétique dans le domaine de la mécanique des fluides. Puis, ce travail de thèse vise à donner de plus amples perspectives quant à une meilleure maîtrise de la structure cristalline des nanoparticules et de la stabilité colloïdale. Une manière plus directe de contrôler la taille, la phase cristalline et la stabilité colloïdale des solutions contenant des nanoparticules est d’ajouter des ligands. Nous avons donc étudié les mécanismes de stabilisation de ces solutions en utilisant des ions qui se complexent aux nanoparticules d’or. Nous avons aussi réussi à synthétiser des nanoparticules de rubis (alumine dopée chrome). La stabilisation de ces nanoparticules dans une phase métastable en utilisant des ligands organiques a été expliquée par une étude théoriqueLaser generation of nanoparticles in liquids : new insights on crystal structure control and colloidal stability The great interest of nanoparticles for their original physical and an chemical properties has been supported by the development of numerous methods of synthesis. In the nineties, laser generation of nanoparticles in liquids appeared, including Pulsed Laser Ablation in Liquids (PLAL). The PLAL technique enables to produce surface free particles for plenty of material and solvent combinations. However, the apparent simplicity of its implementation hides complex physico-chemical mechanisms resulting in a lack of control of the final products. We firstly investigated the dynamics of the laser-generated bubbles for which the PLAL extreme conditions present new studied cases of bubbles dynamics not encountered in the field of fluid mechanics. Then, we aim to bring new insights into better control of the nanoparticles morphology and their colloidal stability. A straight way to tune sizes, crystal structures and the colloidal stability consists in the addition of stabilizing agents. Hence, we investigated the mechanisms of stabilization of colloidal gold using complexing ions. We also succeed to synthesis nano-rubies, i.e. chromium doped corundum alumina nanoparticles, unexpected at nanoscale. The stabilization of the metastable crystal structure using ligands is explained thanks to a comprehensive theoretical approach
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Zahradník, Martin. "Dynamic control of magnetization for spintronic applications studied by magneto-optical methods." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS155/document.
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Deux mécanismes importants reliant la préparation des couches ultraminces d’oxydes magnétiques à leurs propriétés physiques ont été étudiés dans ce travail. En premier lieu, l’influence de la contrainte épitaxiale sur les propriétés magnéto-optiques de la manganite La₂/₃Sr₁/₃MnO₃ (LSMO) a été étudiée. Les couches ultraminces ont été déposées par ablation laser pulsé sur quatre substrats différents, ce qui a fourni différentes valeurs statiques de la contrainte épitaxiale. Les propriétés magnétiques ont été révélées comme se détériorant avec l’augmentation de la contrainte, ce qui était prévisible à cause de la distorsion grandissante de la maille unitaire ainsi qu’à cause de l’effet de la couche magnétiquement inerte. La combinaison de l’ellipsométrie spectroscopique et de la spectroscopie Kerr magnéto-optique a été utilisée afin de déterminer les spectres des éléments diagonaux et non diagonaux du tenseur de permittivité. L’étude des éléments non-diagonaux a confirmé la présence déjà rapportée de deux transitions électroniques dans les spectres de toutes les couches. De plus, elle a révélé une autre transition électronique autour de l’énergie de 4.3 eV, mais seulement dans les spectres des couches déposées avec une contrainte compressive. Nous avons proposé la classification de cette transition comme une transition paramagnétique du champ cristallin Mn t2g → eg. Cette classification a été confortée par des calculs ab initio. Nous avons ainsi montré le rôle clé de la contrainte dans le contrôle des propriétés magnéto-optiques des couches pérovskites ultraminces. En revanche, l’application dynamique de la contrainte par l’utilisation d’une sous-couche piézoélectrique est restée peu concluante. Le transfert de la contrainte entre la sous-couche piézoélectrique et la couche LSMO nécessite des améliorations ultérieures. En second lieu, l’influence de la désorientation du substrat a été étudiée par rapport à la dynamique de l’aimantation dans l’oxyde SrRuO₃ (SRO). Comme attendu, nous avons trouvé qu’un grand angle de désorientation mène à la suppression de la croissance de plusieurs variants cristallographiques du SRO. Au moyen de la microscopie à force magnétique, nous avons montré que la présence de plusieurs variants de SRO mène à l’augmentation de la densité de défauts agissant comme points d’ancrage ou de nucléation pour les domaines magnétiques. Nous avons donc montré que l’emploi d’un substrat vicinal est important pour la fabrication des couches ultraminces de SRO de haute qualité, avec une faible densité de défauts cristallographiques et d’excellentes propriétés magnétiquesTwo important mechanisms in preparation of ultrathin films of magnetic oxides were systematically investigated in this work. First, influence of epitaxial strain on resulting magneto-optical properties of La₂/₃Sr₁/₃MnO₃ (LSMO) ultrathin films was studied. The investigated films were grown by pulsed laser deposition on four different substrates, providing a broad range of induced epitaxial strains. Magnetic properties were found to deteriorate with increasing value of the epitaxial strain, as expected due to the unit cell distortion increasingly deviating from the bulk and effect of the magnetically inert layer. A combination of spectroscopic ellipsometry and magneto-optical Kerr effect spectroscopy was used to determine spectra of the diagonal and off-diagonal elements of permittivity tensor. The off-diagonal elements confirmed presence of two previously reported electronic transitions in spectra of all films. Moreover, they revealed another electronic transition around 4.3 eV only in spectra of films grown under compressive strain. We proposed classification of this transition as crystal field paramagnetic Mn t2g → eg transition, which was further supported by ab initio calculations. A key role of strain in controlling electronic structure of ultrathin perovskite films was demonstrated. Dynamic application of strain via use of piezoelectric underlayer remained inconclusive, requiring further improvement of the strain transfer from the piezoelectric layer into the LSMO. Second, influence of substrate miscut on magnetization dynamics in SrRuO₃ (SRO) was studied. As expected we found that high miscut angle leads to suppression of multi-variant growth. By means of magnetic force microscopy we showed that presence of multiple SRO variants leads to higher density of defects acting as pinning or nucleation sites for the magnetic domains, which consequently results in deterioration of magnetic properties. We demonstrated that use of vicinal substrate with high miscut angle is important for fabrication of high quality SRO ultrathin films with low density of crystallographic defects and excellent magnetic properties
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Pistore, Valentino. "Modelocking of THz quantum cascade lasers : dispersion control and non-linearities." Electronic Thesis or Diss., Sorbonne université, 2019. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2019SORUS302.pdf.
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Les LCQ THz sont aujourd'hui considérés comme une plate-forme prometteuse pour la génération d’impulsions THz intenses et ultracourtes. En raison de leur temps de récupération du gain rapide, le verrouillage en mode passif des LCQ THz s'est jusqu'à présent révélé difficile. Au contraire, le verrouillage de mode actif avec une modulation hyperfréquence a été appliqué avec succès. La durée du pouls a cependant été difficile à réduire malgré des années de recherche. En 2017, notre groupe a généré des impulsions THz de 4ps grâce à l'application d'une structure intégrée (un GTI) visant à réduire la dispersion chromatique. La recherche dans cette thèse commence à partir de ce point. Je présente notamment l'ingénierie de dispersion dans les LCQ THz afin d'obtenir des impulsions très courtes, même à partir de dispositifs à bande relativement étroite. Ceci est réalisé en utilisant des méthodes de modulation actives éprouvées qui peuvent ajuster l’émission de LCQ d’un régime de dispersion élevé à faible. Je montre également que les LCQ THz peuvent présenter une forte modulation d'amplitude de leur profil d'émission et qu'ils peuvent émettre spontanément des impulsions à la suite d'un mécanisme d’auto-verrouillage. En conséquence, cela indique que le temps de récupération de gain rapide n'est pas un facteur limitant pour la génération d'impulsions. Je montre également ce schéma passif dans le cadre des premières démonstrations du verrouillage en mode harmonique de LCQ THz. Enfin, un nouveau phénomène est présenté où les modes d’une LCQ THz peuvent battre ensemble pour générer une émission de micro-ondes dans l’espace libreTHz QCLs are nowadays considered a promising platform for the generation of intense and ultrashort THz pulses. Owing to their fast gain recovery time, passive modelocking of THz QCLs has so far proved to be difficult. On the contrary, active modelocking with a microwave modulation has been successfully applied. The pulse duration, however, has been arduous to reduce despite years of research. In 2017, THz pulses as short as 4ps have been generated by our group with the application of an integrated structure (a GTI) aiming to reduce the chromatic dispersion. The research in this thesis starts from this point.In particular, I present dispersion engineering in THz QCLs in order to obtain very short pulses even from relatively narrow-band devices. This is achieved using proven active modulation methods that can tune the QCL emission from high to low dispersion regimes. I also show that THz QCLs can present a strong amplitude modulation of their emission profile and that they can spontaneously emit pulses as a result of a self-locking mechanism, contrary to the expected frequency modulated response. As a consequence, this indicates that the fast gain recovery time is not a limiting factor for the generation of pulses. I also show this passive self-locking scheme for passive pulse generation in the framework of the first demonstrations of harmonic modelocking of THz QCLs. Finally, a new phenomenon is presented where the modes of a free running THz QCL can beat together to generate free space microwave emission
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Weng, Xiaorong. "Epitaxial CoxNi1-x nanowires in SrTiO3 matrix : growth, structure and control of magnetic anisotropy." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS418.
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Cette thèse décrit l’étude de l’auto-assemblage de nanofils ferromagnétiques de CoxNi1-x épitaxiés dans une matrice de SrTiO3. Ce système est elaboré par ablation laser pulsé. Profitant du dépôt séquentiel des fils et de la matrice, le diamètre des nanofils est contrôlé dans la gamme de 1,7 à 5,3 nm. En raison du désaccord de paramètre de maille entre les fils et la matrice, les nanofils sont dilatés axialement. Cette déformation décroît lorsque le diamètre des fils augmente, dans la gamme de 2-4%. L'anisotropie magnétique des nanofils résulte de la compétition des anisotropies magnétostatique et magnétoélastique. L'effet magnétostatique favorise un axe d'aimantation facile le long de l'axe des fils. La contribution magnétoélastique introduite par la déformation dépend de la constante de magnétostriction et de la déformation. Elle est uniaxiale, négative pour Ni et positive pour une concentration de Co d'environ 20% et plus. Sous une déformation supérieure à 0,8%, l’anisotropie magnétoélastique prédomine, faisant de l’axe des fils un axe d'aimantation dur pour Ni. Pour les nanofils de CoNi, la grande déformation renforce le caractère facile de l’axe des fils. Il en résulte une augmentation de la température de blocage par rapport à la température ambiante, indiquant une augmentation de la stabilité thermique de l'aimantation. Une étude spectroscopique des moments magnétiques de spin et d'orbite met en évidence le fait que l'anisotropie du moment orbital peut être corrélée à l'anisotropie magnétoélastique. Le contrôle de l'anisotropie magnétique par la déformation ou le diamètre est un bon point de départ pour la construction de structures nanomagnétiques 3DThis thesis describes the study of self-assembled epitaxial ferromagnetic CoxNi1-x nanowires in SrTiO3 matrix. This system is grown by pulsed laser deposition. Taking advantage of the sequential deposition of wires and matrix, the diameter of nanowires is controlled in the 1.7-5.3 nm range. Due to the lattice mismatch between wires and matrix, nanowires are in tensile axial strain. The strain decreases with increasing diameter and is in the 2-4% range. Large strain is thus achieved in this vertically aligned nanocomposite structure. The total magnetic anisotropy of the nanowires reflects the competition of the magnetostatic and magnetoelastic anisotropies. The magnetostatic effect favors an easy magnetization axis along the wire axis. The magnetoelastic contribution introduced by the tensile strain depends on the magnetostriction constant and the strain. It is uniaxial, negative for Ni and positive for Co concentration of about 20% and above. Under a strain larger than 0.8%, the magnetoelastic anisotropy dominates in magnitude the magnetostatic one, leading the wire axis to be a hard magnetization axis for Ni. For CoNi alloy nanowires, the large strain reinforces the easy character of the wire axis. This results in the enhancement of the blocking temperature over room temperature, indicating the increased thermal stability of magnetization. A spectroscopic study of the spin and orbital magnetic moments evidences the fact that the anisotropy of the orbital moment can be correlated with the magnetoelastic anisotropy. The control of the magnetic anisotropy by the strain or the diameter is a good starting point for the construction of 3D nanomagnetic structures
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Zier, Tobias [Verfasser]. "Ab-initio analysis of the structural response of solids after femtosecond-laser-pulse excitation : From understanding towards control / Tobias Zier." Kassel : Universitätsbibliothek Kassel, 2019. http://d-nb.info/1193090164/34.
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Schönenberger, Norbert [Verfasser], Peter [Akademischer Betreuer] Hommelhoff, and Philip [Gutachter] Russell. "Control of free electrons with ultrafast laser pulses:Generation of attosecond electron pulse trains / Norbert Schönenberger ; Gutachter: Philip Russell ; Betreuer: Peter Hommelhoff." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2021. http://d-nb.info/1239898436/34.
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De, Clercq Ludwig Erasmus. "Numerical modelling of the excitation of polyatomic molecules by femtosecond laser beams." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6522.
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Thesis (MSc)--University of Stellenbosch, 2011.ENGLISH ABSTRACT: The selective excitation of an arbitrary vibrational level of a polyatomic molecule, without passage through an intermediary electronic excited state is demonstrated. This was achieved by simulating the interaction of a shaped, femtosecond pulse with one vibrational mode of the molecule. The carrier frequency of the pulse is chosen near resonant to the ground-to- rst-excited vibrational transition of the mode, and the pulse shape is optimized via closed-loop feedback. The simulation concentrates on the rst few vibrationally excited states since the density of states is still low, thus ensuring that the inter-vibrational decoherence time is relatively long compared to the pulse length. While various molecules were investigated this study focuses onUF6 for which detailed spectroscopic data for the v3 vibrational mode is available in literature. A multilevel model was developed and can be adapted for any number of levels. The model reported here was limited to a vibrational quantum number of four. The spectroscopic data included anharmonic splitting as well as forbidden transitions. The effect of rotational levels was not included. A density matrix approach was followed because this will allow for the introduction of dephasing of the coherent excitation via thermalizing collisions with the reservoir, as well as inter-vibrational relaxation. The time evolution of the density matrix is given by the Von Neumann equations.
AFRIKAANSE OPSOMMING: Die selektiewe opwekking van 'n arbitrêre vibrasionele vlak van 'n poliatomies molekule sonder oorgang na 'n intermediëre elektroniese opgewekte toetstand word gedemonstreer. Dit was bereik deur die interaksie te simuleer van 'n gevormde, femtosekonde pulse met een vibrasionele mode van 'n molekule. Die draer frekwensie van die pulse is so gekies dat dit naby resonansie van die grond-tot-eerste-opgewekte vibrasionele oorgang van die mode is, die puls vorm word geoptimeer deur 'n geslote-lus terugvoer. Die simulasie konsentreer op die eerste paar vibrasionele opgewekte toestande, omdat die digtheid van toestande nog steeds laag is, dus verseker dit dat inter-vibrasionele de-koherensie tyd relatief lank is in vergelyking met die puls se lengte. Verskillende molekules was ondersoek vir die studie. Die fokus is op UF6 waarvoor gedetaileerde spektroskopiese data vir die v3 vibrasionele beskikbaar is in die literatuur. 'n Multivlak model was ontwikkel en kan aangepas word vir enige aantal van vlakke. Die model wat hier aangemeld is, is beperk tot die vibrasionele kwantum getal van vier. Die spektroskopiese data het anharmonies splitting so wel as nie toegelaatbare oorgange bevat. Die effek van rotasionele vlakke was nie in berekening geneem nie. 'n Digtheids matriks benadering was gevolg, omdat dit toelaat vir die dekoherensie. Die tyd evolusie van die digtheids matriks word gegee deur die Von Neumann vergelykings.
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Ohnesorge, Alexander. "Bestimmung des Aufmischungsgrades beim Laser-Pulver-Auftragschweißen mittels laserinduzierter Plasmaspektroskopie (LIPS)." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1233310151669-10595.
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Ziel der vorliegenden Arbeit ist die Untersuchung der Methode der Laserinduzierten Plasmaspektroskopie (LIPS) zur Bestimmung des Aufmischungsgrades ([Eta]) in durch Laserstrahl-Präzisionsauftragschweißen (LAP) hergestellten Beschichtungen. Grund- und Zusatzwerkstoff müssen sich hierbei in ihrer Elementzusammensetzung voneinander unterscheiden. Als Substratmaterial diente unlegierter Baustahl, als Zusatzwerkstoff wurde Stellit 21 eingesetzt. [Eta] stellt eine wichtige Qualitätskenngröße dar und kann nach vorheriger Kalibrierung des LIPS-Messsystems sowohl offline als auch online detektiert werden. Der Aufmischungsgrad korreliert mit dem detektierten Emissionslinienverhältnis. Im untersuchten Fall besteht in guter Näherung ein linearer Zusammenhang zwischen beiden Größen. Die Vorteile von LIPS gegenüber anderen Verfahren liegen insbesondere in der berührungslosen Analyse und der entfallenden Probenpräparation. Prinzipiell lässt sich das Vorgehen auf andere Werkstoffsysteme übertragen. Das verwendete LISP-Messsystem kann in den Fertigungsprozess integriert werden und steht als Technologiemodul für eine qualifizierte Überwachung des Aufmischungsgrades beim LAP-Prozess zur Verfügung.
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Ohnesorge, Alexander. "Bestimmung des Aufmischungsgrades beim Laser-Pulver-Auftragschweißen mittels laserinduzierter Plasmaspektroskopie (LIPS)." Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A23904.
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Ziel der vorliegenden Arbeit ist die Untersuchung der Methode der Laserinduzierten Plasmaspektroskopie (LIPS) zur Bestimmung des Aufmischungsgrades ([Eta]) in durch Laserstrahl-Präzisionsauftragschweißen (LAP) hergestellten Beschichtungen. Grund- und Zusatzwerkstoff müssen sich hierbei in ihrer Elementzusammensetzung voneinander unterscheiden. Als Substratmaterial diente unlegierter Baustahl, als Zusatzwerkstoff wurde Stellit 21 eingesetzt. [Eta] stellt eine wichtige Qualitätskenngröße dar und kann nach vorheriger Kalibrierung des LIPS-Messsystems sowohl offline als auch online detektiert werden. Der Aufmischungsgrad korreliert mit dem detektierten Emissionslinienverhältnis. Im untersuchten Fall besteht in guter Näherung ein linearer Zusammenhang zwischen beiden Größen. Die Vorteile von LIPS gegenüber anderen Verfahren liegen insbesondere in der berührungslosen Analyse und der entfallenden Probenpräparation. Prinzipiell lässt sich das Vorgehen auf andere Werkstoffsysteme übertragen. Das verwendete LISP-Messsystem kann in den Fertigungsprozess integriert werden und steht als Technologiemodul für eine qualifizierte Überwachung des Aufmischungsgrades beim LAP-Prozess zur Verfügung.
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Bensch, Hauke Magnus [Verfasser]. "Kontrolle der Pulsdynamik in modengekoppelten Hochenergie-Festkörperlasern : Control of the pulse-dynamics of a mode-locked high energy solid state laser / Hauke Magnus Bensch." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2018. http://d-nb.info/1172414513/34.
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Akkal, Elzem. "Control Actuation Systems And Seeker Units Of An Air-to-surface Guided Munition." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1028430/index.pdf.
Full textAbstract:
This thesis proposes a modification to an air to surface guided munition (ASGM) from bang-bang control scheme to continuous control scheme with a little cost. In this respect, time domain system identification analysis is applied to the control actuation system (CAS) of ASGM in order to obtain its mathematical model and controller is designed using pulse width modulation technique. With this modification, canards would be deflected as much as it is commanded to. Seeker signals are also post-processed to obtain the angle between the velocity vector and target line of sight vector. The seeker is modeled using an artificial neural network. Non-linear flight simulation model is built using MATLAB Simulink and obtained seeker and CAS models are integrated to the whole flight simulation model having 6 degrees of freedom. As a flight control unit, fuzzy logic controller is designed, which is a suitable choice if an inertial measurement sensor will not be mounted on the munition. Finally, simulation studies are carried out in order to compare the performance of the &ldquoASGM&rdquo
and &ldquo
improved ASGM&rdquo
and the superiority of the new design is demonstrated.
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Komashko, Aleksey Mikhaylovich. "Laser-material interaction of powerful ultrashort laser pulses /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2003. http://uclibs.org/PID/11984.
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Dooley, Patrick W. Corkum Paul B. "Molecular imaging using femtosecond laser pulses." *McMaster only, 2003.
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Guay, Jean-Michel. "Metal Colorization Using Picosecond Laser Pulses." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/38894.
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In the last few decades, the nanoscale fabrication of metallic structures has demonstrated promising applications in security (e.g. cryptography), photochemistry (e.g. plasmonassisted photo-chemistry), decoration (e.g. colouring), biocompatibility of implants and more. To fabricate such subwavelength nanostructures, we typically resort to the use of several nanolithography techniques that are lengthy and incompatible with large-scale production on complex substrates. For this purpose, we invented an innovative technique for the fast fabrication of nanostructures via the use of a picosecond laser. We used this technique to produce colourful coins for the Royal Canadian Mint which were presented at the World Money Fair in Germany in 2015 as a world rst. To ensure the long-term survival of these plasmonic colours, a new dual-layer passivation technique was conceived based on a atomic deposition process, to meet the commercialisation requirements of our industrial partner. A new burst colouring technology was also invented that allows for the creation of more visually appealing colours. These laser burst colours were also shown to have a high sensing potential and an overall better visual response to the application of the passivation layer.
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Kafka, Kyle R. P. "Laser-Induced Damage with Femtosecond Pulses." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483661596059632.
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Gonon, Benjamin. "Simulations quantiques non-adiabatiques d’un photo-interrupteur moléculaire vers un dialogue expérience-théorie." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTT186/document.
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Cette thèse a pour objet l’étude et le contrôle de la photo-réactivité d’interrupteurs moléculaires, en particulier la photo-isomérisation des spiropyranes. Ce travail théorique a été réalisé en collaboration étroite avec l’équipe expérimentale PFL de l’ICB à Dijon. Des simulations de dynamique quantique non-adiabatique ont été réalisées afin de reproduire et rationaliser les résultats expérimentaux de spectroscopie d’absorption transitoire résolue en temps. Ces expériences ont montré une photo-réactivité ultra-rapide (~ 100 fs) suite à une excitation par une pulse LASER ultra-court. Celle-ci est interprétée comme un mécanisme de conversion interne entre le premier état électronique excité singulet et l’état fondamental via une intersection conique. L’étude théorique a utilisé la réaction d’ouverture de cycle du benzopyrane comme modèle. Les développements réalisés ont porté sur : (1) L’exploration du mécanisme réactionnel et le calcul de surfaces d’énergie potentielle via des méthodes de chimie quantique post-CASSCF perturbatives (XMCQDPT2). Cette analyse a montré des résultats variant fortement par rapport à ceux relevés dans la littérature à des niveaux de calcul moins élevés. (2) Le développement d’un modèle de surfaces d’énergie potentielle électronique par la construction d’un hamiltonien diabatique à partir de données ab initio XMCQDPT2. Du fait de l’importante anharmonicité de l’état électronique fondamental, nous avons mis en place une approche effective en rupture avec les études antérieures. (3) La réalisation de simulations de dynamique quantique non-adiabatique par la méthode MCTDH. Les résultats obtenus sont en très bon accord avec les résultats expérimentaux. L’inclusion explicite du pulse LASER a permis de reproduire et de rationaliser l’effet de contrôle par mise en forme d’impulsion observé expérimentalement. Ce travail a ainsi permis la mise en place d’une collaboration et d’un dialogue théorie/expérience effectifsThis thesis adresses the study and control of the photo-reactivity of molecular switches, here the photo-isomerisation of spiropyrans. This theoretical work has been achieved in close collaboration with the experimental team PFL within the ICB in Dijon. Non-adiabatic quantum dynamics simulations were carried out so as to reproduce and rationalise the experimental results from time-resolved transient absorption spectroscopy. Such experiments have demonstrated ultra-fast photo-reactivity (~ 100 fs) following excitation by an ultra-short LASER pulse. It is interpreted as an internal conversion mechanism between the first singlet excited eletronic state and the ground state via a conical intersection. The theoretical study used the ring-opening reaction of benzopyran as a model. Developments were made regarding: (1) The exploration of the reaction mechanism and the computation of potential energy surfaces with perturbative, post-CASSCF quantum chemistry methods (XMCQDPT2). This investigation showed that results changed significantly compared to those reported in the literature with lower-level calculations. (2) The generation of a diabatic Hamiltonian based on ab initio XMCQDPT2 data. Owing to the significant anharmonicity in the ground electronic state, we designed a new effective approach, quite different from the previous studies. (3) The production of non-adiabatic quantum dynamics simulations using the MCTDH method. The results thus obtained are in excellent agreement with the experimental ones. Including explicitly the LASER pulse allowed us to reproduce and rationalise the action of pulse shaping on control observed in experiments. The present work thus made possible the succesful implementation of a theoretical/experimental collaboration
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Kröner, Dominik (Dr rer nat ). "Analysis and control of light-induced processes in molecules: Electron and nuclear quantum dynamics for aspects of stereoisomerism and spectroscopy." Thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2014/7047/.
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The habilitation thesis covers theoretical investigations on light-induced processes in molecules. The study is focussed on changes of the molecular electronic structure and geometry, caused either by photoexcitation in the event of a spectroscopic analysis, or by a selective control with shaped laser pulses. The applied and developed methods are predominantly based on quantum chemistry as well as on electron and nuclear quantum dynamics, and in parts on molecular dynamics. The studied scientific problems deal with stereoisomerism and the question of how to either switch or distinguish chiral molecules using laser pulses, and with the essentials for the simulation of the spectroscopic response of biochromophores, in order to unravel their photophysics. The accomplished findings not only explain experimental results and extend existing approaches, but also contribute significantly to the basic understanding of the investigated light-driven molecular processes. The main achievements can be divided in three parts:
First, a quantum theory for an enantio- and diastereoselective or, in general, stereoselective laser pulse control was developed and successfully applied to influence the chirality of molecular switches. The proposed axially chiral molecules possess different numbers of "switchable" stable chiral conformations, with one particular switch featuring even a true achiral "off"-state which allows to enantioselectively "turn on" its chirality. Furthermore, surface mounted chiral molecular switches with several well-defined orientations were treated, where a newly devised highly flexible stochastic pulse optimization technique provides high stereoselectivity and efficiency at the same time, even for coupled chirality-changing degrees of freedom. Despite the model character of these studies, the proposed types of chiral molecular switches and, all the more, the developed basic concepts are generally applicable to design laser pulse controlled catalysts for asymmetric synthesis, or to achieve selective changes in the chirality of liquid crystals or in chiroptical nanodevices, implementable in information processing or as data storage.
Second, laser-driven electron wavepacket dynamics based on ab initio calculations, namely time-dependent configuration interaction, was extended by the explicit inclusion of magnetic field-magnetic dipole interactions for the simulation of the qualitative and quantitative distinction of enantiomers in mass spectrometry by means of circularly polarized ultrashort laser pulses. The developed approach not only allows to explain the origin of the experimentally observed influence of the pulse duration on the detected circular dichroism in the ion yield, but also to predict laser pulse parameters for an optimal distinction of enantiomers by ultrashort shaped laser pulses. Moreover, these investigations in combination with the previous ones provide a fundamental understanding of the relevance of electric and magnetic interactions between linearly or non-linearly polarized laser pulses and (pro-)chiral molecules for either control by enantioselective excitation or distinction by enantiospecific excitation.
Third, for selected light-sensitive biological systems of central importance, like e.g. antenna complexes of photosynthesis, simulations of processes which take place during and after photoexcitation of their chromophores were performed, in order to explain experimental (spectroscopic) findings as well as to understand the underlying photophysical and photochemical principles. In particular, aspects of normal mode mixing due to geometrical changes upon photoexcitation and their impact on (time-dependent) vibronic and resonance Raman spectra, as well as on intramolecular energy redistribution were addressed. In order to explain unresolved experimental findings, a simulation program for the calculation of vibronic and resonance Raman spectra, accounting for changes in both vibrational frequencies and normal modes, was created based on a time-dependent formalism. In addition, the influence of the biochemical environment on the electronic structure of the chromophores was studied by electrostatic interactions and mechanical embedding using hybrid quantum-classical methods. Environmental effects were found to be of importance, in particular, for the excitonic coupling of chromophores in light-harvesting complex II. Although the simulations for such highly complex systems are still restricted by various approximations, the improved approaches and obtained results have proven to be important contributions for a better understanding of light-induced processes in biosystems which also adds to efforts of their artificial reproduction.Die Habilitationsschrift behandelt theoretische Untersuchungen von durch Licht ausgelösten Prozessen in Molekülen. Der Schwerpunkt liegt dabei auf Veränderungen in der Elektronenstruktur und der Geometrie der Moleküle, die durch Bestrahlung mit Licht entweder bei einer spektroskopischen Untersuchung oder bei gezielter Kontrolle durch geformte Laserpulse herbeigeführt werden. Um die dabei auftretende Elektronen- und Kerndynamik zu simulieren, wurden vornehmlich quantentheoretische Methoden eingesetzt und weiterentwickelt. Die wissenschaftlichen Fragestellungen beschäftigen sich mit dem gezielten Verändern und dem Erkennen der räumlichen Struktur von Molekülen ohne Drehspiegelachse, der sog. molekularen Chiralität, sowie mit durch Licht eingeleiteten Prozessen in biologisch relevanten Pigmenten auf sehr kurzen Zeitskalen. Die entwickelten Ansätze und gewonnenen Erkenntnisse lassen sich drei Haupterfolge unterteilen: Erstens gelang die Entwicklung einer generellen Kontrolltheorie für das Ein- und Umschalten von molekularer Chiralität mit geformten Laserpulsen. Dabei wird die räumliche Struktur der vorgeschlagenen molekularen Schalter zwischen ihren stabilen sog. stereoisomeren Formen selektiv geändert, was sich auf ihre optischen und chemischen Eigenschaften auswirkt. Für komplexere Bedingungen, wie z.B. auf einer Oberfläche verankerten molekularen Schaltern verschiedener Orientierung, wurde eine neue Pulsoptimierungsmethode basierend auf Wahrscheinlichkeiten und Statistik entwickelt. Solche laserpulskontrollierten chiralen molekularen Schalter hofft man u.a. in der Nanotechnologie zum Einsatz zu bringen, wo sie z.B. als Informationsspeicher dienen könnten. Zweitens konnte geklärt werden, welche die wesentlichen Einflüsse sind, die das Erkennen von sog. Enantiomeren, das sind spiegelbildliche Moleküle von entgegengesetzter Chiralität, nach Ionisierung durch ultrakurze zirkular polarisierte Laserpulse ermöglichen. Diese Form des sog. Zirkulardichroismus in der Ionenausbeute erlaubt die quantitative und qualitative Unterscheidung von Enantiomeren in der Massenspektrometrie. Durch Simulation der Elektronendynamik während der Laseranregung konnte u.a. erstmals gezeigt werden, dass neben der Zirkularpolarisation der Laserpulse vor allem die schwachen magnetischen Wechselwirkungen für die Unterscheidung entscheidend sind. Drittens wurden die Spektren von in der Natur vorkommenden Pigmenten simuliert, welche u.a. an wichtigen biologischen Funktionen, wie dem Sammeln von Sonnenenergie für die Photosynthese, beteiligt sind. Die Lichtanregung führt dabei zu einer Veränderung der Elektronenstruktur und Geometrie der Pigmente, wobei letzteres wichtige Konsequenzen für die Verteilung der Energie auf die spektroskopisch beobachteten Molekülschwingungen mit sich bringen. Auch der wichtige Einfluss der biochemischen Umgebung auf die Elektronenstruktur der Pigmente bzw. den Energietransfer zwischen solchen wurde untersucht. Neben der Klärung experimenteller Ergebnisse ermöglichen die Untersuchungen neue Einblicke in die fundamentalen Prozesse kurz nach der Lichtanregung -- Erkenntnisse, die auch für die technische Nachahmung der biologischen Funktionen von Bedeutung sein können.
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Loeser, Markus. "Diode-Pumped High-Energy Laser Amplifiers for Ultrashort Laser Pulses." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-232571.
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The ultrashort chirped pulse amplification (CPA) laser technology opens the path to high intensities of 10^21 W/cm² and above in the laser focus. Such intensities allow laser-matter interaction in the relativistic intensity regime. Direct diode-pumped ultrashort solid-state lasers combine high-energy, high-power and efficient amplification together, which are the main advantages compared to flashlamp-pumped high-energy laser systems based on titanium-doped sapphire. Development within recent years in the field of laser diodes makes them more and more attractive in terms of total costs, compactness and lifetime.
This work is dedicated to the Petawatt, ENergy-Efficient Laser for Optical Plasma Experiments (PENELOPE) project, a fully and directly diode-pumped laser system under development at the Helmholtz–Zentrum Dresden – Rossendorf (HZDR), aiming at 150 fs long pulses with energies of up to 150 J at repetition rates of up to 1 Hz. The focus of this thesis lies on the spectral and width manipulation of the front-end amplifiers, trivalent ytterbium-doped calcium fluoride (Yb3+:CaF2) as gain material as well as the pump source for the final two main amplifiers of the PENELOPE laser system. Here, all crucial design parameters were investigated and a further successful scaling of the laser system to its target values was shown.
Gain narrowing is the dominant process for spectral bandwidth reduction during the amplification at the high-gain front-end amplifiers. Active or passive spectral gain control
filter can be used to counteract this effect. A pulse duration of 121 fs was achieved by using a passive spectral attenuation inside a regenerative amplifier, which corresponds to an improvement by a factor of almost 2 compared to the start of this work. A proof-of-concept experiment showed the capability of the pre-shaping approach. A spectral bandwidth of 20nm was transferred through the first multipass amplifier at a total gain of 300. Finally, the predicted output spectrum calculated by a numerical model of the final amplifier stages was in a good agreement with the experimental results.
The spectroscopic properties of Yb3+:CaF2 matches the constraints for ultrashort laser pulse amplification and direct diode pumping. Pumping close to the zero phonon line at 976nm is preferable compared to 940nm as the pump intensity saturation is significantly lower. A broad gain cross section of up to 50nm is achievable for typical inversion levels. Furthermore, moderate cryogenic temperatures (above 200K) can be used to improve the amplification performance of Yb3+:CaF2. The optical quality of the doped crystals currently available on the market is sufficient to build amplifiers in the hundred joule range.
The designed pump source for the last two amplifiers is based on two side pumping in a double pass configuration. However, this concept requires the necessity of brightness conservation for the installed laser diodes. Therefore, a fully relay imaging setup (4f optical system) along the optical path from the stacks to the gain material including the global beam homogenization was developed in a novel approach.
Beside these major parts the amplifier architecture and relay imaging telescopes as well as temporal intensity contrast (TIC) was investigated. An all reflective concept for the relay imaging amplifiers and telescopes was selected, which results in several advantages especially an achromatic behavior and low B-Integral. The TIC of the front-end was improved, as the pre- and postpulses due to the plane-parallel active-mirror was eliminated by wedging the gain medium.