Lasers which operate at both high average power and energy are in demand for a wide range of applications such as materials processing, directed energy and EUV generation. Presented in this dissertation is a high-power 1 μm ytterbium-based hybrid laser system with temporally tailored pulse shaping capability and up to 62 mJ pulses, with the expectation the system can scale to higher pulse energies. This hybrid system consists of a low power fiber seed and pre-amplifier, and a solid state thin-disk regenerative amplifier. This system has been designed to generate high power temporally tailored pulses on the nanosecond time scale. Temporal tailoring and spectral control are performed in the low power fiber portion of the system with the high pulse energy being generated in the regenerative amplifier. The seed system consists of a 1030 nm fiber-coupled diode, which is transmitted through a Mach-Zehnder-type modulator in order to temporally vary the pulse shape. Typical pulses are 20-30 ns in duration and have energies of ~0.2 nJ from the modulator. These are amplified in a fiber pre-amplifier stage to ~100 nJ before being used to seed the free-space Yb:YAG thin-disk regenerative amplifier. Output pulses have maximum demonstrated pulse energies of 62 mJ with 20 ns pulse after ~250 passes in the cavity. The effects of thermal distortion in laser and passive optical materials are also. Generally the development of high power and high energy lasers is limited by thermal management strategies, as thermally-induced distortions can degrade laser performance and potentially cause catastrophic damage. Novel materials, such as optical ceramics, can be used to mitigate thermal distortions; however, thorough analysis is required to optimize their fabrication and minimize thermal distortions. iv Using a Shack-Hartmann wavefront sensor (SHWFS), it is possible to analyze the distortion induced in passive and doped optical elements by high power lasers. For example, the thin-disk used in the regenerative amplifier is examined in-situ during CW operation (up to 2 kW CW pump power). Additionally, passive oxide-based optical materials and Yb:YAG optical ceramics are also examined by pumping at 2 and 1 μm respectively to induce thermal distortions which are analyzed with the SHWFS. This method has been developed as a diagnostic for the relative assessment of material quality, and to grade differences in ceramic laser materials associated with differences in manufacturing processes and/or the presence of impurities. In summation, this dissertation presents a high energy 1 μm laser system which is novel in its combination of energy level and temporal tailoring, and an analysis of thermal distortions relevant to the development of high power laser systems.

Ce travail explore le contrôle de la composition et la cinétique du panache d’ablation laser en régime ultrabref par mise en forme temporelle des impulsions laser femtoseconde. L’objectif est l’optimisation du dépôt de couches minces et de nanoparticules. Le chapitre 1 est une synthèse de la littérature sur le dépôt de couches minces par ablation laser femtoseconde, en particulier de films de Diamond-Like Carbon et de nanoparticules. L’influence de la mise en forme temporelle du laser sur les mécanismes d’ablation est développée, ainsi que le diagnostic du panache d’ablation. Le chapitre 2 présente les dispositifs expérimentaux de mise en forme temporelle et de diagnostic du panache d’ablation par spectroscopie d’émission résolue en temps et espace et spectroscopie d’extinction. Le chapitre 3 rapporte l’impact de l’utilisation d’impulsions doubles et élargies sur les panaches de l’aluminium et du bore. L’augmentation de la composante ionique du plasma d’aluminium est expliquée au travers de simulations hydrodynamiques. Dans le chapitre 4, différentes formes temporelles sont employées pour l’ablation du graphite et le dépôt de couches de Diamond-Like Carbon. Le contrôle de la cinétique du panache est atteint en peuplant plus ou moins ses différentes composantes de vitesse : molécules, atomes et ions. Si la structure du Diamond-Like Carbon déposé n’est pas affectée, une amélioration de la surface des couches est observée. Le chapitre 5 montre l’efficacité et la sensibilité de la spectroscopie d’extinction optique pour la mesure in situ de la distribution en taille des nanoparticules métalliques dans le panache d’ablation laser femtoseconde / This work explores the control of ultrafast laser ablation plume composition and kinetics by temporal shaping of femtosecond laser pulses. The goal is the optimization of thin films and nanoparticles deposition. Chapter 1 is a synthesis of the literature on femtosecond laser deposition of thin films. The focus is on Diamond-Like Carbon films and nanoparticles. The impact of laser temporal pulse shaping on the ablation mechanisms is developed. Ablation plume diagnostic methods are detailed. Chapter 2 describes the experimental setup for temporal pulse shaping and plasma diagnostic. The latter is done through space and time-resolved optical emission spectroscopy and extinction spectroscopy. Chapter 3 reports on the impact of doubles pulses and long pulses on aluminium and boron ablation plumes. Ion yield enhancement in aluminium ablation plasma is explained through hydrodynamics simulations. In chapter 4, various temporal pulse shapes are used for graphite ablation and Diamond-Like Carbon thin films deposition. The control of the plume kinetics is reached by selectively populating the various plume speed components: molecules, atoms, ions. Even though the deposited Diamond-Like Carbon structure is unaffected, it has been observed an improvement of the thin films surface. Chapter 5 shows the efficiency and sensitivity of optical extinction spectroscopy for in situ measurement of nanoparticles size distribution in femtosecond laser ablation plumes

Le besoin d'une très grande précision lors du traitement des matériaux par laser a fortement encouragé le développement des études de l'effet des impulsions ultra brèves pour la structuration des matériaux à une échelle micro et nano métrique. Une diffusion d'énergie minimale et une forte non linéarité de l'interaction permet un important confinement énergétique à des échelles les plus petites possibles. La possibilité d'introduire des changements de phases rapides et même de créer de nouveaux états de matière ayant des propriétés optimisées et des fonctions améliorées donne aux impulsions ultra brèves de sérieux arguments pour être utilisées dans des dispositifs très précis de transformation et de structuration des matériaux. L'étude de ces mécanismes de structuration et, en particulier, de leurs caractéristiques dynamiques, est une clé pour l'optimisation de l'interaction laser-matière suivant de nombreux critères utiles pour les procédés laser : efficacité, précision, qualité. Ce mémoire synthétise les travaux de l'auteur sur l'étude statique et dynamique du dépôt d'énergie ultra rapide, avec application aux procédés laser. La connaissance de la réponse dynamique des matériaux après irradiation laser ultra brève montre que les temps de relaxation pilotent l'interaction lumière-matière. Il est alors possible d'adapter l'énergie déposée à la réponse du matériau en utilisant les toutes récentes techniques de mise en forme spatio temporelle de faisceaux. Un couplage optimal de l'énergie donne la possibilité d'orienter la réponse du matériau vers un résultat recherché, offrant une grande flexibilité de contrôle des procédés et, sans doute, la première étape du développement de procédés « intelligents ».

Broadband spectral content is required to support ultrashort pulses. However this broadband content is subject to dispersion and hence the pulse duration of corresponding ultrashort pulses may be stretched accordingly. I used a commercially-available adaptive ultrashort pulse shaper featuring multiphoton intrapulse interference phase scan technology to characterise and compensate for the dispersion of the optical system in situ and conducted experimental and theoretical studies in various inter-linked topics relating to the light-matter interaction. Firstly, I examined the role of broadband ultrashort pulses in novel light-matter interacting systems involving optically co-trapped particle systems in which inter-particle light scattering occurs between optically-bound particles. Secondly, I delivered dispersion-compensated broadband ultrashort pulses in a dispersive microscope system to investigate the role of pulse duration in a biological light-matter interaction involving laser-induced cell membrane permeabilisation through linear and nonlinear optical absorption. Finally, I examined some of the propagation characteristics of broadband ultrashort pulse propagation using a computer-controlled spatial light modulator. The propagation characteristics of ultrashort pulses is of paramount importance for defining the light-matter interaction in systems. The ability to control ultrashort pulse propagation by using adaptive dispersion compensation enables chirp-free ultrashort pulses to be used in experiments requiring the shortest possible pulses for a specified spectral bandwidth. Ultrashort pulsed beams may be configured to provide high peak intensities over long propagation lengths, for example, using novel beam shapes such as Bessel-type beams, which has applications in biological light-matter interactions including phototransfection based on laser-induced cell membrane permeabilisation. The need for precise positioning of the beam focus on the cell membrane becomes less strenuous by virtue of the spatial properties of the Bessel beam. Dispersion compensation can be used to control the temporal properties of ultrashort pulses thus permitting, for example, a high peak intensity to be maintained along the length of a Bessel beam, thereby reducing the pulse energy required to permeabilise the cell membrane and potentially reduce damage therein.