A influência das variáveis associadas ao laser como a fluência, o comprimento de onda, e a duração do pulso, assim como as relacionadas às propriedades das amostras, como a distribuição do tamanho das partículas e as características químicas da matriz, foram avaliadas visando à determinação quantitativa de macro- (P, K, Ca, Mg) e micronutrientes (Cu, Fe, Mn, Zn, B) em pastilhas de materiais vegetais por espectrometria de emissão óptica com plasma induzido por laser (LIBS). Os efeitos da distribuição do tamanho das partículas e da fluência do laser foram investigados a partir da análise de amostras peneiradas (150-20 µm) empregando-se um sistema LIBS, em regime temporal de nanossegundos (ns-LIBS), montado com um laser de Nd:YAG a 1064 nm (pulsos de 5 ns e 360 mJ)e um espectrômetro com óptica Echelle e detector ICCD. Observou-se um aumento na sensibilidade e na precisão das medições com a diminuição do tamanho das partículas usadas no preparo das pastilhas, e uma diminuição dos efeitos de matriz causados por diferenças no tamanho das partículas, quando pastilhas preparadas com partículas < 75 µm foram analisadas com pulsos de 50 J cm-2. Verificou-se uma melhora significativa na exatidão das medições de Mg, Fe, Mn e Zn feitas em um conjunto de pastilhas de folhas de cana-de-açúcar (partículas < 75 µm) empregando-se esta fluência. Em uma segunda etapa, observou-se que variações no comprimento de onda do laser de Nd:YAG (1064, 532, 355 e 266 nm) não influenciaram de maneira significativa a precisão e exatidão das medições em pastilhas de folhas de cana-de-açúcar, obtendo-se correlações lineares entre as intensidades dos sinais de emissão e as correspondentes frações de massa dos analitos. Variações no comprimento de onda do laser de Nd:YAG não afetaram a análise de um conjunto heterogêneo de amostras, composto por pastilhas de folhas de plantas de diferentes espécies, como soja, cana-de-açúcar, milho, citros, café, por exemplo, por ns-LIBS. No entanto, diferentemente do observado para o conjunto de pastilhas de folhas de cana-de-açúcar, observou-se, uma baixa correlação (r cal < 0,90) entre as frações de massa de Ca, Mg, P, Cu, Fe, Mn e Zn determinadas por ns-LIBS e os valores de referência, o que demonstra a baixa robustez de ns-LIBS frente às variações na composição química das matrizes. Posteriormente, analisou-se este conjunto heterogêneo de amostras com sistema LIBS, em regime temporal de femtossegundos (fs-LIBS), montado com laser de Ti:Safira (pulsos de 60 fs e 1,65 mJ) e espectrômetro com óptica Czerny-Turner e ICCD. Demonstrou-se que o uso de pulsos em regime de fs proporcionou calibrações e validação menos dependentes da composição química das matrizes. As frações de massa de Ca, Mg, P, Fe e Mn previstas por fs-LIBS foram estatisticamente concordantes com os valores de referência, independentemente do modelo de calibração usado. Além disso, o uso de calibração multivariada melhorou a capacidade preditiva de ns-LIBS, assemelhando-se à de fs-LIBS. Concluiu-se que o emprego de fs-LIBS foi a estratégia mais robusta e que ofereceu maior flexibilidade à variabilidade matricial / The influence of laser properties, such as fluence, wavelength and pulse duration, as well as sample characteristics, such as particle size distribution and chemical matrix composition, was evaluated aiming at the quantitative determination of macro- (P, K, Ca, Mg) and micronutrients (Cu, Fe, Mn, Zn, B) in pellets of plant materials by laser-induced breakdown spectroscopy (LIBS). Firstly, the effects of particle size distribution and laser fluence on the analysis of pellets (test samples) prepared with sieved samples (from 150 to 20 µm apertures) were investigated. Experiments were carried out with a nanosecond LIBS (ns-LIBS) system by using a Q-switched Nd:YAG laser at 1064 nm (5 ns; 360 mJ) and a spectrometer with Echelle optics and intensified charge-coupled device (ICCD) detector. Results indicated that smaller particles yielded to sensitivities\' enhancement and attained better measurements\' precision. Moreover, matrix effects were reduced by analyzing pellets prepared from < 75 ?m sieved fractions and pulses of 50 J cm-2. In addition, there was a significant improvement on accuracy of Mg, Fe, Mn and Zn measurements in a set of test samples of sugarcane leaves by using this fluence. In a second experiment, variations in the Nd:YAG laser wavelength (1064, 532, 355 and 266 nm) did not affect the analysis of test samples of sugarcane leaves, and provided linear correlations between emission signal intensities and corresponding analytes mass fractions. In addition, variations within Nd:YAG laser wavelength did not affect the analysis of a heterogeneous sample set composed by pellets of leaves from different crops, such as soy, sugarcane, maize, citrus and coffee by ns-LIBS. However, in contrast to previous findings, the univariate calibration models for ns-LIBS presented lower linearity (r cal < 0.90) for Ca, Mg, P, Cu, Fe, Mn and Zn, no matter the laser wavelength used for the analysis. These circumstances reflect the low robustness of ns-LIBS to variations within matrix chemical composition among test samples. Afterwards, test samples from different crops were analyzed by a femtosecond LIBS (fs-LIBS) by using a Ti:Sapphire laser, including a mode-locked oscillator and an ultrafast amplifier (60 fs; 1.65 mJ per pulse), and a spectrometer with Czerny-Turner optics and ICCD. Findings indicated that the pulse duration was a decisive variable for providing accurate quantification of nutrients in different plant species, which present substantial differences in terms of matrix chemical composition. Close agreement between Ca, Mg, P, Fe and Mn mass fractions predicted by fs-LIBS and those determined by ICP OES was evidenced, whatever the modeling approach used. Contrarily, for ns-LIBS analysis of test samples from different crops, only the use of multivariate partial least squares (PLS) regression appears capable for resolving the non-linear transformations of the emission intensities according to the physical mechanisms governing this temporal regime of ablation. Thus, when using multivariate modeling, the figures-of merit reflecting the predictive capabilities of ns-LIBS resemble to those achieved by fs-LIBS. Either way, fs-LIBS is a more robust approach that better offers larger flexibility to the matrix variability

Ce travail de thèse repose sur l’élaboration et l’exploitation d’un banc expérimental dédié à l’étude d’un écoulement cavitant dans un micro-canal, pour des conditions proches de celles de l’injection diesel. Ce banc a été développé dans le but de faire varier différents paramètres, notamment l’état de surface des parois du canal. Plusieurs méthodes optiques (imagerie en transmission, strioscopie et interférométrie) ont été mises en place afin de visualiser l’écoulementet d’en extraire des informations quantitatives. Les images en transmission permettent de visualiser la formation de vapeur dans le canal. Elles sont sensibles au gradient de masse volumique et font ainsi apparaître des couches de cisaillement, des structures turbulentes et des ondes de pression. Leur interprétation est rendue délicate par cette richesse en information et nécessite de recourir aux autres techniques optiques. Il ressort de ce travail que la cavitation se forme dans la couche de cisaillement, sous l’effet combiné de la dépression engendrée par le décollement à l’entrée du canal et de tourbillons générés par des instabilités dans la couche de cisaillement. La confrontation des résultats obtenus à l’aide des différentes techniques optiques, notamment les champs de pression reconstruits à partir des interférogrammes, montre que la zone de formation de la cavitation ne correspond pas à la zone de minimum de pression moyenne de l’écoulement. Il apparaît aussi que certaines bulles de vapeur ont une durée de vie bien supérieure à ce que prévoient les modèles de dynamique de bulles. On suspecte que des fluctuations de pression de l’ordre de 20 bar, associées à la turbulence, contribuent à la prolongation de ces temps de vie. Un algorithme de PIV, appliqué à des couples d’images en transmission, permet de montrer une augmentation importante des fluctuations de vitesse en sortie de canal lorsque les poches de vapeur se développent. Cette augmentation devient plus significative quand les poches atteignent60% de la longueur du canal. L’écoulement cavitant est essentiellement piloté par le nombre de cavitation K. Les conditions d’apparition et de développement de la cavitation ont été quantifiées dans différents canaux, en faisant varier des paramètres géométriques, la pression amont ou la température. L’influence de la hauteur du canal et du rayon de courbure à l’entrée de l’orifice est conforme aux données de la littérature. Une dépendance du nombre de cavitation critique Kcrit à l’apparition de la cavitation au nombre de Reynolds Re est montrée. Enfin, l’influence de l’état de surface des parois a fait l’objet d’une étude spécifique. Cette partie du travail demande probablement à être complétée mais l’état de surface semble avoir une influence sur la cavitation. D’après les cas étudiés au cours de cette thèse, une surface rugueuse ou texturée avec des motifs suffisamment espacés peut retarder l’apparition de la cavitation et une rugosité limitée (jusqu’à Ra = 0,7 μmici) peut favoriser le développement des poches de vapeur. / This PhD study is based on the design and use of an experimental set-up dedicated to the study of a cavitating flow in a micro-channel in conditions close to Diesel injection. The experimental set-up has been designed so that different parameters may vary, in particular channel wall roughness. Several optical systems (backlit imaging, Schlieren imaging and interferometry) have been developed in order to visualize the flow and get quantitative data.Backlit images make it possible to visualize vapor formation in the channel. They are sensitive to density gradients and therefore show shear layers, turbulent structures as well as pressure waves. Since they are rich in information, it is tricky to interpret them and the use of other optical methods is required.This study shows that cavitation appears in the shear layer due to the combined effect of the depression induced by flow detachment at the channel inlet and vortexes caused by instabilities in the shear layer. The comparison of the results obtained from the different optical systems – in particular the pressure fields rebuilt from interferograms – indicates that cavitation does not appear where flow pressure is the lowest in average.It is noticed that some vapor bubbles have a life expectancy much higher than predicted by bubble dynamics models. It is thought that pressure variations of about 20 bar, associated to turbulence, may play a role in this phenomenon.A PIV algorithm applied to couples of backlit images shows that velocity fluctuations largely increase at the channel outlet when vapor cavities develop. The increase gets more significant when cavities are 60 % the channel length.The cavitating flow is mainly dependent on the cavitation number K. The conditions of cavitation inception and development have been quantified in different channels, and geometrical parameters, upstream pressure or temperature have varied. The influence of channel height and radius inlet on cavitation is in line with the literature. At cavitation inception, it is shown that the critical cavitation number Kcrit is dependent on Reynolds number Re. Finally, the influence of wall roughness has been the subject of a specific study. Although it would need to be further investigated, roughness seems to have an influence on cavitation. The samples used during this PhD work suggest that roughness or patterns sufficiently spaced out may delay cavitation inception, and limited roughness (up to Ra = 0.7 μm here) may enhance vapor cavity development.

In this thesis, experimental studies are reported of ultrafast dynamics and third order optical nonlinear coefficients of carbon nanotubes, and time resolved coherent phonon dynamics of semiconductors and rare earth titanates. The thesis is divided into three parts. The first part presents (i) general introduction to theoretical background on nonlinear optical susceptibility and time resolved studies, and systems studied (chapter 1) and (ii) experimental techniques (chapter 2). The second part of the thesis deals with the measurements of third order nonlinear susceptibilities and ultrafast dynamics of single and double walled carbon nanotubes (chapter 3). The third part contains coherent phonon dynamics in semiconductors, Te (chapter 4), Bi2Te3 (chapter 5), and ZnTe (chapter 6) and spin-frustrated rare earth titanate insulators (chapter 7). Chapter 1: This chapter is a general introduction to the thesis. The chapter is divided into two parts: (i) light-matter interaction, and (ii) systems studied. Under light-matter interaction, we describe the required theoretical and conceptual background of nonlinear optical susceptibilities and time resolved carrier and phonon dynamics. In the next part, a brief summary of details of the systems studied, that include carbon nanotubes (single and double walled), semiconductors (Te, Bi2Te3 and ZnTe) and insulating spin-frustrated rare earth titanates (Gd2Ti2O7, Dy2Ti2O7 and Tb2Ti2O7), are presented. Chapter 2: Details of the ultrafast laser systems (femtosecond oscillator and amplifier), pulse width measurements and ultrafast experimental pump-probe and z-scan techniques, used in this thesis are given in this chapter. Chapter 3: Here the experimental results on the measurements of third order optical nonlinearity and ultrafast dynamics of single and double walled carbon nanotubes are presented. The chapter starts with a general overview of optical switching followed by known ultrafast dynamics and nonlinear studies on carbon nanotubes. In the next section, our theoretical modelling of nonlinear absorption and refraction in the limit of saturable absorption is described. The final two sections depict our results on single and double walled carbon nanotubes. These studies indicate that double walled carbon nanotubes are best candidates for ultrafast optical switching. Chapter 4: This chapter presents temperature and pump fluence dependent femtosecond time resolved reflectivity measurements on tellurium. The chapter starts with an overview of previous pump-probe reflectivity studies at room temperature on tellurium followed by our results. A totally symmetric A1 coherent phonon at 3.6 THz responsible for the oscillations in the reflectivity data is observed to be strongly positively chirped (i.e, phonon time period decreases at longer pump-probe delay times) with increasing photoexcited carrier density, more so at lower temperatures. We show for the first time that the temperature dependence of the coherent phonon frequency is anomalous (i.e, increasing with increasing temperature) at high photoexcited carrier density due to electron-phonon interaction. At the highest photoexcited carrier densities of ~ 1.4 x 1021cm-3 and the sample temperature of 3K, the lattice displacement of the coherent phonon mode is estimated to be as high as ~ 0.24 Å. Numerical simulations based on coupled effects of optical absorption and carrier diffusion reveal that the diffusion of carriers dominates the non-oscillatory electronic part of the time-resolved reflectivity. Finally, using the pump-probe experiments at low carrier density of 6 x 1018 cm-3, we separate the phonon anharmonicity to obtain the electron-phonon coupling contribution to the phonon frequency and linewidth. Chapter 5: This chapter begins with a introduction of previous ultrafast studies at room temperature on Bi2Te3 and then presents our results on the temperature dependent high pump fluence time resolved reflectivity measurements on Bi2Te3. The time resolved reflectivity data shows two coherently generated totally symmetric A1g modes at 1.85 THz and 3.6 THz at 296K which blue shift to 1.9 THz and 4.02 THz, respectively at 3K. At high photoexcited carrier density of ~ 1.7 x 1021cm-3, the phonon mode at 4.02 THz is two orders of magnitude higher positively chirped than the lower frequency mode at 1.9 THz. The chirp parameter, β is shown to vary inversely with temperature. The time evolution of these modes is studied using continuous wavelet transform of the time-resolved reflectivity data. The analysis shows that the build up time for the two coherent phonons is different. Chapter 6: This chapter starts with a general introduction on various as pects of ZnTe to be used in generation and detection of THz followed by our results on influence of carriers and sample temperature on coherent phonon and polariton generation in ZnTe. Combination of femtosecond Kerr, two photon absorption and impulsive stimulated Raman scattering experiments have been carried out to investigate the effect of pulse energy and crystal temperature on the generation of coherent polaritons and phonons in < 110 > cut ZnTe single crystals of three different resistivities. We demonstrate that the effect of two-photon induced free carriers on the creation of both the polaritons and phonons is largest at 4K where the free carrier lifetime is enhanced. Further, the temperature dependant impulsive stimulated Raman scattering on high and low purity ZnTe crystals allows us to unambiguously assign the phonon mode at 3.5 THz to the longitudinal acoustic mode at X-point in the Brillouin zone, LA(X) in contrast to the assignment as two-phonon process in earlier studies. Chapter 7: This chapter starts with an introduction on previous Raman studies on the pyrochlore systems accompanied by our results on the generation of coherent optical phonons in spin frustrated pyrochlore single crystals Dy2Ti2O7, Gd2Ti2O7 and Tb2Ti2O7 and their behavior as a function of sample temperature from 296K to 4K. At 4K, two coherent phonons are observed at 5.3 THz (5.0 THz) and ~ 9.3 THz (9.4 THz) for Dy2Ti2O7 (Gd2Ti2O7) whereas three coherent phonons are generated at ~ 4.8 THz, 8.6 THz and 9.6 THz for Tb2Ti2O7. In the case of spin-ice Dy2Ti2O7, a clear discontinuity is observed in the linewidths of both the coherent phonons as well as in the phase of low energy coherent phonon mode, indicating a subtle structural change as also suggested by Raman studies. In comparison, such changes are not seen in the coherent phonons of Gd2Ti2O7, and Tb2Ti2O7. Another important observation is the phase difference of ‘π’ between the modes in all the samples, thus suggesting that the driving forces behind the generation of these modes are different in nature unlike a purely impulsive or displacive mechanism. Chapter 8: This chapter summarizes our results reported in this thesis and gives future directions.

Ce présent travail de thèse porte sur l’étude du potentiel d’un traitement de surface par laser femtoseconde comme étape de substitution aux traitements réalisés actuellement lors de la métallisation de polymère. Pour cela, l’étude des modifications chimiques et morphologiques induites par traitement laser femtoseconde ainsi que leurs influences respectives sur les propriétés d’adhérences et de mouillabilités de la surface polypropylène sont présentées. Une revue bibliographique met en évidence la faisabilité d’une modification contrôlée de la surface du polypropylène après traitement laser femtoseconde. De plus, ces modifications engendrent une évolution démontrée des propriétés de mouillage qui peuvent répondre à certaines demandes industrielles. Après traitement laser femtoseconde, la surface traitée répond de différentes manières à la sollicitation en fonction de ses propriétés intrinsèques. Les expériences d’impacts localisés et de surfaces nous ont conduits à observer trois stades de modifications topographiques pour les conditions étudiées : un phénomène d’incubation, d’accumulation et d’ablation. Ce dernier a fait l’objet d’une étude plus approfondie. De manière générale, on observe deux régimes d’ablation linéaires pour l’ensemble des densités de puissance étudiées lorsque l’on étudie la profondeur d’ablation en fonction du nombre d’impulsion et le volume d’ablation en fonction de la densité de puissance cumulée. Enfin, nous montrons que les liaisons présentes en surface après traitement sont dépendantes de deux facteurs ; la densité de puissance cumulée utilisée et l’environnement de travail. Sachant que les modifications topographiques obtenues sont de types multi-échelles, les résultats ont été analysés sur la base des modèles de Wenzel (1936) et de Cassie-Baxter (1944) relatifs à la théorie du mouillage de surfaces rugueuses. Les résultats expérimentaux et leurs corrélations avec les paramètres de rugosités 3D calculés à différentes échelles ont été traités par une analyse statistique. On observe alors un comportement mixte avec un contact intime de la goutte sur les sommets des aspérités (modèle de Wenzel) et un contact hétérogène (airpolypropylène) à une échelle mésoscopique (état « fakir » décrit par le modèle de Cassie-Baxter). Toutefois, la situation où la goute repose sur le sommet des structures (CB) n’est pas toujours stable. Nous avons étudié la transition de l’état CB à l’état W par des expériences d’évaporation. On observe que cette transition est fortement dépendante de la chimie de surface dont la contribution est prépondérante sur les propriétés d’adhérence métal/PP. En contrôlant cette propriété, il est alors possible de répondre à une problématique industrielle de galvanoplastie (adhérence augmenté par le traitement laser) ou d’électroformage (adhérence faible permettant une réplication de bonne qualité des motifs). / This work presents the potential of a femtosecond laser surface treatment as an alternative step of pretreatments during the metallization of polymer. To do this, the study of chemical and morphological modification induced by femtosecond laser treatment and their respective influences on the properties of adhesion and wettability of polypropylene surface are presented. A literature review highlights the feasibility of a controlled surface modification after femtosecond laser treatment of polypropylene (PP). In addition, it is known that these modifications changes the wetting properties and can be used to meet industrial applications development. After femtosecond laser treatment, the treated surface responds to the solicitation with different morphological comportment according to its intrinsic properties. Experiences of localized impacts and surfaces us to observe three stages of topographic changes to the conditions studied: an incubation phenomenon of accumulation and ablation. The ablation phenomenon is further study. Generally, two linear ablation regime is observed for all power densities examined when considering the depth of ablation as a function of the pulse number and the ablation volume according to the accumulated power density. Finally, we show that the bonds present on the surface after treatment are dependent on two factors: the accumulated power density used and the working environment. Knowing that topographic obtained is multi-scales, the results were analyzed on the basis of models Wenzel (W)(1936) and Cassie–Baxter (CB) (1944) which explain the theory of wetting of rough surfaces. The experimental results and their correlations with 3D roughness parameters calculated at different scales were treated by statistical analysis. We observe a mixed model behavior with intimate contact of the drop on the tops of the asperities (Wenzel model) and a heterogeneous contact (air - PP) in a mesoscopic scale (state " fakir " described by the Cassie -Baxter model). However, this situation where the drop sits on the top of asperities (CB) is not always the most stable. We have studied the transition between the CB state and the W state by evaporation experiments. It is observed that this transition is strongly dependent on the surface chemistry whose contribution is much greater than the adhesion properties metal / PP. If controlling this property, it is possible to obtain two industrial applications: electroplating (increased adhesion by laser treatment) or electroforming (low adherence to replicate the topography).

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

La microfabrication 3D par laser dans les matériaux à faible bande interdite néces- sitera l’utilisation d’impulsions intenses dans l’infrarouge proche et moyen. Cette étude expérimentale se concentre sur les spécificités de la physique d’ionisation nonlinéaire dans la gamme de longueur d’onde de 1300-2200nm. Contrairement aux semiconducteurs, l’ab- sorption nonlinéaire mesurée dans les diélectriques est indépendante de la longueur d’onde révélant ainsi l’importance accrue de l’ionisation par effet tunnel avec ces longueurs d’onde. Nous étudions également les rendements et les seuils d’ionisation multiphotonique et ava- lanche dans le silicium intrinsèque et dopé N. Les résultats couplés à l’observation des ma- tériaux irradiés montrent que les propriétés intrinsèques des semiconducteurs empêchent un dépôt d’énergie suffisamment confiné pour viser directement des applications de modifica- tion locale. Ce travail illustre les possibilités de micro-usinage laser 3D dans les diélectriques et les défis de l’extension de cette technique aux semiconducteurs. / 3D laser microfabrication inside narrow gap solids like silicon will require the use of long wavelength intense pulses. This experimental study concentrates on the specificity of the nonlinear ionization physics with tightly focused femtosecond laser beams over a wa- velength range of 1300-2200nm. The measured nonlinear absorption is independent of the wavelength in dielectrics revealing the increased importance of tunnel ionization with long wavelength. This can open up an alternative to pulse shortening toward ultraprecision op- tical breakdown in dielectrics. Using n-doped silicon, we study the multiphoton-avalanche absorption yields and thresholds inside semiconductors. Also observations of the irradia- ted materials reveal that the intrinsic properties of semiconductors prevent efficient direct energy deposition in the bulk for applications. This work illustrates opportunities for 3D laser micromachining in dielectrics and challenges for its extension to semiconductors.

Sa conductivité électronique ou encore sa transparence optique sont autant de propriétés physico-chimiques singulières du graphène qui expliquent le nombre accru de méthodes d’exfoliation de précurseurs graphitiques développées pour l’obtention de ce matériau. Pour palier à l’utilisation d’un oxyde de graphite/graphène caractérisé par une chimie de surface mal maitrisée, des graphites fluorés, de cristallinité mais aussi de concentration en fluor variables, ont été préparés par fluoration de graphite sous fluor moléculaire pur après optimisation des paramètres. Les précurseurs, que ce soit par fluoration dynamique ou statique, ainsi obtenus ont été caractérisés finement : diffraction des rayons X, spectroscopies IR et Raman et leur texture sondée par Microscopie Electronique à Balayage et à Transmission. Suite à cela, trois méthodes d’exfoliation ont été mises en place, basées sur des mécanismes différents : i) une exfoliation par choc thermique, déjà connue mais dont les mécanismes de décomposition ont été affinés dans cette étude, ii) une exfoliation en voie liquide, avec l’utilisation pour la première fois d’un graphite fluoré pour la synthèse de graphène fluoré multi feuillets par voie électrochimique pulsée, et enfin iii) une méthode originale, peu conventionnelle, basée sur l’interaction laser femtoseconde/graphite hautement fluoré pour induire des mécanismes de réduction contrôlée, et surtout d’exfoliation de la matrice. Ces méthodes ont permis de mettre en évidence l’intérêt de la présence de fluor dans la course actuelle pour la synthèse de graphène, et ont montré l’obtention de matériaux graphéniques,possédant une fonction résiduelle fluorée intéressante pour certaines applications. / Its electronic conductivity or its optical transparency are unequaled physicochemicalproperties of graphene which explain the increased number of exfoliation methods based ongraphitic precursors to obtain this material. To overcome the use of a graphite/graphene oxidecharacterized by a poorly controlled surface chemistry, graphite fluorides, with variablecrystallinity and also fluorine concentration, were prepared by fluorination of graphite under puremolecular fluorine atmosphere after optimization of the process parameters. The obtainedprecursors, whether by dynamic or static fluorination, were characterized : X-Ray diffraction, FTIRand Raman spectroscopies for the structure, and their texture probed by Scanning andTransmission Electron Microscopy. After that, three methods of exfoliation were developed, basedon different mechanisms: i) a thermal shock, already known but decomposition mechanisms wererefined in this study, ii) an exfoliation within liquid medium by pulsed electrochemical treatment,using for the first time a fluorinated graphite for the synthesis of few-layered fluorinated grapheneand finally iii) an unconventional method, based on the interaction between femtosecond laser andhighly fluorinated graphite to induce mechanisms like controlled reduction, and especially for thisstudy exfoliation of the matrix. These methods have permit to highlight the interest of fluorine inthe current race for the synthesis of graphene, and have shown the production of graphenematerials, having an interesting fluorinated residual functionalization for some applications.

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La microscopie électronique et la diffraction d’électrons ont permis de comprendre l’organisation des atomes au sein de la matière. En utilisant une source courte temporellement, il devient possible de mesurer les déplacements atomiques ou les modifications de la distribution électronique dans des matériaux. A ce jour, les sources ultra-brèves pour les expériences de diffraction d’électrons ne permettent pas d’atteindre une résolution temporelle inférieure à la centaine de femtosecondes (fs). Les accélérateurs laser-plasma sont de bons candidats pour atteindre une résolution temporelle de l’ordre de la femtoseconde. De plus, ces accélérateurs peuvent fonctionner à haut taux de répétition, permettant d’accumuler un grand nombre de données.Dans cette thèse, un accélérateur laser-plasma fonctionnant au kHz a été développé et construit. Cette source accélère des électrons à une énergie de 100 keV environ à partir d’impulsions laser d’énergie 3 mJ et de durée 25 fs. La physique de l’accélération a été étudiée, démontrant entre autres l’effet du front d’onde laser sur la distribution transverse des électrons.Les premières expériences de diffraction avec ce type de sources ont été réalisées. Une expérience de preuve de principe a montré que la qualité de la source est suffisante pour obtenir de belles images de diffraction sur des feuilles d’or et de silicium. Dans un second temps, la dynamique structurelle d’un échantillon de Silicium a été étudiée avec une résolution temporelle de quelques picosecondes, démontrant le potentiel de ce type de sources.Pour augmenter la résolution temporelle à sub-10 fs, il est nécessaire d’accélérer les électrons à des énergies relativistes de quelques MeV. Une étude numérique a montré que l’on peut accélérer des paquets d’électrons ultra-courts grâce à des impulsions laser de 5 mJ et 5 fs. Il serait alors possible d’atteindre une résolution temporelle de l’ordre de la femtoseconde. Finalement, une expérience de post-compression des impulsions laser due à l’ionisation d’un gaz a été réalisée. La durée du laser a pu être réduite d’un facteur deux, et l’homogénéité de ce processus a été étudiée expérimentalement et numériquement. / Electronic microscopy and electron diffraction allowed the understanding of the organization of atoms in matter. Using a temporally short source, one can measure atomic displacements or modifications of the electronic distribution in matter. To date, the best temporal resolution for time resolved diffraction experiments is of the order of a hundred femtoseconds (fs). Laser-plasma accelerators are good candidates to reach the femtosecond temporal resolution in electron diffraction experiments. Moreover, these accelerators can operate at a high repetition rate, allowing the accumulation of a large amount of data.In this thesis, a laser-plasma accelerator operating at the kHz repetition rate was developed and built. This source generate electron bunches at 100 keV from 3 mJ and 25 fs laser pulses. The physics of the acceleration has been studied, and the effect of the laser wavefront on the electron transverse distribution has been demonstrated.The first electron diffraction experiments with such a source have been realized. An experiment, which was a proof of concept, showed that the quality of the source permits to record nice diffraction patterns on gold and silicium foils. In a second experiment, the structural dynamics of a silicium sample has been studied with a temporal resolution of the order of a few picoseconds.The electron bunches must be accelerated to relativistic energies, at a few MeV, to reach a sub-10 fs temporal resolution. A numerical study showed that ultra-short electron bunches can be accelerated using 5 fs and 5 mJ laser pulses. A temporal resolution of the order of the femtosecond could be reached using such bunches for electron diffraction experiments. Finally, an experiment of the ionization-induced compression of the laser pulses has been realized. The pulse duration was shorten by a factor of 2, and the homogeneity of the process has been studied experimentally and numerically.

This project is in collaboration with the Hydro-Quebec Research Institute (IREQ) and the Canadian Centre for Electron Microscopy (CCEM) on the mechanical test performance of miniature-scale micro-tensile specimens. The objective of the thesis project is to create an efficient and reliable fabrication route for producing micro-tensile specimens and to validate the accuracy of a newly custom-built micro-tensile bench at IREQ. The fabrication techniques developed and outlined in this thesis use the underlying fundamental physical mechanisms of secondary electron microscopy (SEM), focused-ion beam (FIB), and the femtosecond (fs)-laser machining for producing optimal quality micro-tensile specimens. The mechanical testing of the specimens is geared towards studying the localized deformation occurring in the microstructure when the size of the specimen only limits a number of grains and grain boundaries in order to target the specific detailed measurement of the mechanical behaviour of individual grains and interfaces. The goal for creating an optimal fabrication route for micro-tensile specimens is to carry out micro-mechanical testing of the primary turbine steels of 415 martensitic stainless steel used in the manufacture of Francis turbine components at Hydro-Quebec. The mechanical testing of single phase and interphase interface 415 steel micro-tensile specimens are considered building blocks to developing digital twin models of the steel microstructure. The experimental data from the mechanical tests would be fed into the crystal plasticity finite element models (CPFEM) that are currently being developed by researchers at IREQ. With the development of digital twin models, engineers at IREQ would be able to predict crack initiation at the microstructure level (prior to crack propagation into macro-scale cracks) by observing the evolution of the grain’s crystallographic orientation and morphology, as well as deformation mechanisms such as martensite formation and twinning produced from localized induced strains in the microstructure. In addition, self-organized dislocation processes such as dislocation nucleation and dislocation escape through the free surface can also be studied using the CPFEM models for size-limited mechanical deformation behaviour of miniature-scale mechanical test specimens. The fabrication routes studied in this thesis project use the combination of the fs-laser and plasma focused ion beam (PFIB) to machine the micro-tensile specimens. (100) single crystal copper was the ideal material chosen to validate the accuracy of the micro-tensile bench and quality of the fs-laser-machined tensile specimens, due to its ductile nature and well-characterized properties studied in literature. A mechanical size effect was studied for single crystal copper specimens with different gauge thicknesses. It was observed from the micro-tension testing that the strength of the specimens increased with decreasing gauge thickness occurring in the size-limited tensile gauges. In addition, it was determined there was negligible differences in the size effect seen between the PFIB-machined copper micro-tensile specimens and the fs-laser-machined micro-tensile specimens, demonstrating that the fs-laser is a reliable machining route for the micro-tensile specimens. X-ray computed tomography was used to validate the correct geometry of the machined gauge section produced from an innovative gauge thinning method adopted from IREQ’s research collaborator, Dr. Robert Wheeler. As well, finite-element analysis (FEA) was performed to determine the deformation behaviour under both linear-elastic and non-linear elastoplastic conditions of (100) copper and 415 steel models simulated in pure tension, prior to the fabrication of the micro-tensile specimens, respectively. Furthermore, significant progress has been made towards targeting martensite grains in the 415-steel microstructure using electron backscattered diffraction (EBSD) analysis to produce single crystal and interphase interface micro-tensile specimens. A workflow towards grain targeting using EBSD analysis has been developed, as well as for the relocation of grains using reference fiducial marks for future fabrication of the single crystal and interphase interface 415 micro-tensile specimens. / Thesis / Master of Applied Science (MASc) / Hydro-Quebec is an energy utilities company that operates the design of Francis hydro-turbines to supply hydroelectric power across the province of Quebec. The hydro-turbines have an expected service life of 70 years. Unfortunately, the turbines can get replaced by new ones prior to reaching half of its service life, due to the development of severe fatigue crack growth in the primary components of the turbines. A solution proposed by the researchers at the Hydro-Quebec Research Institute (IREQ) is to determine a linkage between the turbine’s steel’s microstructure and the mechanical behaviour of the turbine steels. Deformation of the material starts at the microstructure level, where dislocations glide through the material lattice, causing both reversible (elastic) and irreversible (plastic) deformation. Therefore, a solution was proposed by the researchers at IREQ to create computational models of the steel microstructure to predict the deformation of the steel’s microstructure. Being able to predict the deformation mechanisms through the simulation models of the microstructures allows for engineers at Hydro-Quebec to schedule regular maintenance of the turbines more efficiently and provide metallurgists the knowledge on what is occurring at the microstructure level and what can be done to improve the chemical and physical composition of the steel. To develop the digital twin models, experimental data must be collected through mechanical testing of miniature mechanical test specimens of the turbine steels. The mechanical properties of the single phases and interphase interface specimens are fed into the models as building blocks to building a microstructure map of the turbine steels. Micro-tension testing of micro-tensile specimen provides direct information about the material’s mechanical properties. In this work, a reliable and efficient fabrication route for micro-tensile specimens was developed for the purpose of extracting mechanical properties of single phase and interphase interface turbine steel specimens using focused ion beam (FIB) and femtosecond laser machining.