Neste trabalho foi estudada a geração de harmônicos perturbativos por pulsos laser ultracurtos em bicos de gás no vácuo. Os harmônicos foram gerados nas regiões espectrais do UV e VUV e sua geração ocorreu em fluxo de gases nobres. Esta técnica possibilita a produção de luz coerente numa região espectral de interesse considerável para várias aplicações, tais como a espectroscopia resolvida no tempo. Para a geração dos harmônicos foi utilizado um sistema laser amplificado de Ti:Safira que produz pulsos de 25 fs, centrados em 785 nm, a 4 kHz. Estes pulsos ultracurtos são injetados em uma câmara de vácuo, onde são focalizados em um bico de gás. Os harmônicos são selecionados por um monocromador e têm a sua intensidade medida por um cintilador e uma fotomultiplicadora. Buscamos abranger uma visão geral sobre a geração de harmônicos perturbativos em gases, com o objetivo de consolidar um conhecimento teórico e experimental no laboratório. Confeccionamos e comparamos o desempenho de dois sistemas distintos de injeção de gás, o bico metálico e o bico de vidro, que são dispositivos pouco explorados na literatura. Os melhores resultados foram obtidos com o bico de vidro. Pudemos estimar a eficiência de geração dos harmônicos do ponto de vista das propriedades microscópicas e macroscópicas de geração, e foi verificada a conversão de energia do feixe fundamental para a geração dos harmônicos, plasma e outros fenômenos não-lineares em argônio. Geramos até o 9º harmônico em argônio, atingindo a região de 85 nm. Foi estudado o casamento de fase e a dependência da eficiência de geração dos harmônicos com a pressão do gás, potência média do laser, chirp e a posição do foco para o 3º, 5° e 7º harmônicos. Com a variação dos parâmetros, observou-se que é possível sintonizar os harmônicos, e que sua geração compete com outros fenômenos, como a ionização do gás. Adicionalmente, foi observada uma queda da eficiência de geração para alta intensidades, que foi associada à depleção do 1º elétron de valência dos átomos do gás, reduzindo a quantidade de centros geradores dos harmônicos. Além do argônio, foram realizadas medidas em hélio, neônio e criptônio, visando estudar como a eficiência de geração dos harmônicos depende das propriedades eletrônicas do gás. Adicionalmente, esses resultados corroboraram a hipótese da depleção dos elétrons de valência. / In this work the generation of perturbative harmonics by ultrashort laser pulses in gas nozzles in vacuum was studied. The harmonics were generated in the UV and VUV regions and the frequency conversion occurred in flowing gas. This technique ensures the generation of coherent light in a spectral region of interest for various applications, such as ultrafast time-resolved spectroscopy. For the harmonics generation an amplified Ti:Shapphire laser system was used, generating 25 fs pulses, centered at 785 nm, at 4 kHz. These ultrashort pulses are injected into a vacuum chamber, where they are focused on a gas nozzle. The harmonics are selected by a monochromator and their intensity is measured by a scintillator and photomultiplier. We have sought to comprise an overview of the generation of perturbative harmonics in gases, in order to consolidate a theoretical and experimental knowledge in the laboratory. Two distinct gas injection systems were manufactured and had their performances compared, a metallic and a gas nozzle, devices that are poorly explored in literature. The best results were obtained with the glass nozzle. We could estimate the harmonics generation efficiency in argon from the point of view of their macroscopic and microscopic generation properties, and the energy conversion from the fundamental beam to the harmonics was verified, along with plasma creation and other nonlinear phenomena. We generated up to the 9th harmonic in argon, reaching the 85 nm. We studied the phase matching and the dependence of the harmonics generation efficiency with the gas pressure, laser average power, chirp and focus position for the 3rd, 5th and 7th harmonics. By varying the parameters, we observed that it is possible to tune the harmonics wavelengths, and that their generation competes with other nonlinear phenomena, such as the gas ionization. Additionally, a drop in the generation efficiency was observed at high intensities, which was associated to the depletion of the first valence electron in the gas atoms, decreasing the number of harmonic generating centers. In addition to argon, measurements were performed in helium, neon and krypton, aiming to study how the harmonic generation efficiency depends on the electronic properties of the gas. Additionally, these results corroborated the hypothesis of the valence electron depletion.

Este trabalho investigou a fotodegradação do corante Rodamina-B com o auxílio do catalisador semicondutor Dióxido de Titânio, utilizando como fonte de irradiação pulsos de 40 fs gerados por um sistema laser de Titânio - Safira. Os pulsos laser foram formatados espectralmente (modulação senoidal), gerando trens de pulsos cuja separação foi escolhida para ser ressonante com um modo Raman intenso do catalisador. A fotodegradação da Rodamina-B foi monitorada através de medidas de fluorescência excitada via absorção de dois fótons. Não observamos fotodegradação do corante mediante a irradiação com pulsos ultracurtos, mesmo na presença do catalisador, tanto para o pulso de menor duração alcançada quanto para os trens de pulsos com diferentes separações temporais. Contudo, observamos uma diminuição no espalhamento da luz de excitação devido às nanopartículas de Dióxido de Titânio. Este processo foi estudado com mais detalhes, tendo sido analisada a influência da formatação espectral senoidal no resultado da medida. A relação entre a irradiação com pulsos de femtossegundos e a quebra de aglomerados de nanopartículas foi intuída a partir dos resultados obtidos, sendo fortalecida por medidas de microscopia eletrônica de varredura de um filme das amostras. / This work investigated the photodegradation of Rhodamine-B assisted by Titanium Dioxide semiconductor catalyst, using as irradiation source a Ti:Sapphire laser system delivering 40 fs pulses. The laser pulses were spectrally shaped (sinusoidal modulation), generating pulse trains whose separation was chosen to be resonant with an intense catalysts Raman mode. The Rh-B photodegradation was monitored by two photon excited fluorescence measurements. We have not observed dye photodegradation by the ultrashort pulses irradiation, in the absence of the catalyst, neither with the shortest pulse obtained, nor with pulse trains. Nevertheless, we observed a decrease in the excitation light scattering due to the Titanium Dioxide nanoparticles. Such process was studied by analyzing the influence of sinusoidal spectral phase mask in the signal. The results indicate a relationship between femtosecond pulse irradiation and the breaking of nanoparticles clusters, which was also corroborated by scanning electron microscopy measurements.

Neste trabalho foi estudada a geração de harmônicos perturbativos por pulsos laser ultracurtos em bicos de gás no vácuo. Os harmônicos foram gerados nas regiões espectrais do UV e VUV e sua geração ocorreu em fluxo de gases nobres. Esta técnica possibilita a produção de luz coerente numa região espectral de interesse considerável para várias aplicações, tais como a espectroscopia resolvida no tempo. Para a geração dos harmônicos foi utilizado um sistema laser amplificado de Ti:Safira que produz pulsos de 25 fs, centrados em 785 nm, a 4 kHz. Estes pulsos ultracurtos são injetados em uma câmara de vácuo, onde são focalizados em um bico de gás. Os harmônicos são selecionados por um monocromador e têm a sua intensidade medida por um cintilador e uma fotomultiplicadora. Buscamos abranger uma visão geral sobre a geração de harmônicos perturbativos em gases, com o objetivo de consolidar um conhecimento teórico e experimental no laboratório. Confeccionamos e comparamos o desempenho de dois sistemas distintos de injeção de gás, o bico metálico e o bico de vidro, que são dispositivos pouco explorados na literatura. Os melhores resultados foram obtidos com o bico de vidro. Pudemos estimar a eficiência de geração dos harmônicos do ponto de vista das propriedades microscópicas e macroscópicas de geração, e foi verificada a conversão de energia do feixe fundamental para a geração dos harmônicos, plasma e outros fenômenos não-lineares em argônio. Geramos até o 9º harmônico em argônio, atingindo a região de 85 nm. Foi estudado o casamento de fase e a dependência da eficiência de geração dos harmônicos com a pressão do gás, potência média do laser, chirp e a posição do foco para o 3º, 5° e 7º harmônicos. Com a variação dos parâmetros, observou-se que é possível sintonizar os harmônicos, e que sua geração compete com outros fenômenos, como a ionização do gás. Adicionalmente, foi observada uma queda da eficiência de geração para alta intensidades, que foi associada à depleção do 1º elétron de valência dos átomos do gás, reduzindo a quantidade de centros geradores dos harmônicos. Além do argônio, foram realizadas medidas em hélio, neônio e criptônio, visando estudar como a eficiência de geração dos harmônicos depende das propriedades eletrônicas do gás. Adicionalmente, esses resultados corroboraram a hipótese da depleção dos elétrons de valência. / In this work the generation of perturbative harmonics by ultrashort laser pulses in gas nozzles in vacuum was studied. The harmonics were generated in the UV and VUV regions and the frequency conversion occurred in flowing gas. This technique ensures the generation of coherent light in a spectral region of interest for various applications, such as ultrafast time-resolved spectroscopy. For the harmonics generation an amplified Ti:Shapphire laser system was used, generating 25 fs pulses, centered at 785 nm, at 4 kHz. These ultrashort pulses are injected into a vacuum chamber, where they are focused on a gas nozzle. The harmonics are selected by a monochromator and their intensity is measured by a scintillator and photomultiplier. We have sought to comprise an overview of the generation of perturbative harmonics in gases, in order to consolidate a theoretical and experimental knowledge in the laboratory. Two distinct gas injection systems were manufactured and had their performances compared, a metallic and a gas nozzle, devices that are poorly explored in literature. The best results were obtained with the glass nozzle. We could estimate the harmonics generation efficiency in argon from the point of view of their macroscopic and microscopic generation properties, and the energy conversion from the fundamental beam to the harmonics was verified, along with plasma creation and other nonlinear phenomena. We generated up to the 9th harmonic in argon, reaching the 85 nm. We studied the phase matching and the dependence of the harmonics generation efficiency with the gas pressure, laser average power, chirp and focus position for the 3rd, 5th and 7th harmonics. By varying the parameters, we observed that it is possible to tune the harmonics wavelengths, and that their generation competes with other nonlinear phenomena, such as the gas ionization. Additionally, a drop in the generation efficiency was observed at high intensities, which was associated to the depletion of the first valence electron in the gas atoms, decreasing the number of harmonic generating centers. In addition to argon, measurements were performed in helium, neon and krypton, aiming to study how the harmonic generation efficiency depends on the electronic properties of the gas. Additionally, these results corroborated the hypothesis of the valence electron depletion.

Rapidly developing areas of high field physics, generation of high order harmonics or isolated attosecond pulses, require high peak power few-cycle pulse sources. Optical parametric chirped pulse amplification (OPCPA) has shown potential to satisfy these requirements and at present OPCPA is the leading technology for high energy few-cycle pulse table-top systems. The main objectives of this thesis were to investigate optical parametric amplification of broadband seed pulses in femtosecond and picosecond regimes, to develop and optimize a compact TW-scale OPCPA system intended for various applications in areas of high-field physics. In this thesis the main concept of such system is discussed, advantages and disadvantages of proposed approach are analyzed, the setup is compared to other world known systems. In this thesis an original approach for power scaling of regenerative amplifier by implementing several active elements in prolonged resonator has been proposed and investigated. Femtosecond pulse amplification in dual active element Yb:KGW regenerative amplifier has been demonstrated, resulting in boost of average output power to 30 W. Broad bandwidth pulse generation, parametric amplification and compression to transform limited values were analyzed both numerically and experimentally. White light continuum generation in bulk material for broadband seed formation, its further optical parametric amplification in noncollinear scheme were investigated and Yb:KGW driven... [to full text] / Stiprių laukų fizikos srities tyrimams, aukštų eilių harmonikų ir pavienių atosekundinių impulsų generavimui, yra reikalingos kompaktiškos teravatų smailinės galios kelių optinių ciklų išvadinių impulsų lazerinės sistemos. Optinis parametrinis „čirpuotų“ impulsų stiprinimas yra vienas pagrindinių metodų leidžiančiu pasiekti šiems taikymams reikalingus lazerinių sistemų parametrus. Šios disertacijos darbo tikslas – ištirti femtosekundinės ir pikosekundinės trukmės impulsų stiprinimą optiniuose parametriniuose stiprintuvuose užkratui naudojant ypač plataus spektro signalą, bei sukurti ir optimizuoti čirpuotų impulsų parametrinio stiprinimo sistemą, užtikrinančią patikimą teravatų smailinės galios impulsų formavimą. Disertacijoje aptariama bendra tokios sistemos architektūra, nagrinėjami privalumai ir trūkumai, palyginama su kitomis pasaulyje egzistuojančiomis sistemomis. Šiame darbe pasiūlytas ir ištirtas lazerių vidutinės išvadinės galios didinimo metodas, naudojant kelis aktyviuosius elementus viename rezonatoriuje, ir pademonstruotas femtosekundinių impulsų stiprinimas šio metodo pagrindu sukonstruotame dviejų Yb:KGW aktyvių elementų regeneratyviniame stiprintuve, tokiu būdu padidinant lazerio išvadinę galią iki 30 W. Darbo metu sukonstruota bei ištirta Yb:KGW femtosekundiniu lazeriu kaupinamos baltos šviesos kontinuumo generavimo ir nekolinearaus kaupinimo optinio parametrinio stiprinimo sistema, kurios išvadinių impulsų energiją siekia 20 mikrodžiaulių, o impulsai... [toliau žr. visą tekstą]

Este trabalho investigou a fotodegradação do corante Rodamina-B com o auxílio do catalisador semicondutor Dióxido de Titânio, utilizando como fonte de irradiação pulsos de 40 fs gerados por um sistema laser de Titânio - Safira. Os pulsos laser foram formatados espectralmente (modulação senoidal), gerando trens de pulsos cuja separação foi escolhida para ser ressonante com um modo Raman intenso do catalisador. A fotodegradação da Rodamina-B foi monitorada através de medidas de fluorescência excitada via absorção de dois fótons. Não observamos fotodegradação do corante mediante a irradiação com pulsos ultracurtos, mesmo na presença do catalisador, tanto para o pulso de menor duração alcançada quanto para os trens de pulsos com diferentes separações temporais. Contudo, observamos uma diminuição no espalhamento da luz de excitação devido às nanopartículas de Dióxido de Titânio. Este processo foi estudado com mais detalhes, tendo sido analisada a influência da formatação espectral senoidal no resultado da medida. A relação entre a irradiação com pulsos de femtossegundos e a quebra de aglomerados de nanopartículas foi intuída a partir dos resultados obtidos, sendo fortalecida por medidas de microscopia eletrônica de varredura de um filme das amostras. / This work investigated the photodegradation of Rhodamine-B assisted by Titanium Dioxide semiconductor catalyst, using as irradiation source a Ti:Sapphire laser system delivering 40 fs pulses. The laser pulses were spectrally shaped (sinusoidal modulation), generating pulse trains whose separation was chosen to be resonant with an intense catalysts Raman mode. The Rh-B photodegradation was monitored by two photon excited fluorescence measurements. We have not observed dye photodegradation by the ultrashort pulses irradiation, in the absence of the catalyst, neither with the shortest pulse obtained, nor with pulse trains. Nevertheless, we observed a decrease in the excitation light scattering due to the Titanium Dioxide nanoparticles. Such process was studied by analyzing the influence of sinusoidal spectral phase mask in the signal. The results indicate a relationship between femtosecond pulse irradiation and the breaking of nanoparticles clusters, which was also corroborated by scanning electron microscopy measurements.

Les sources lasers femtosecondes sont utilisées dans grand nombre d’applications (industrielles, médicales, de recherche fondamentale) avec un besoin croissant d’impulsions très énergétiques à haut taux de répétition. Bien que la technologie Ti:Saphir fournisse des impulsions PetaWatt, son taux de répétition s’avère limité. Une alternative est l’utilisation de la technologie fibrée. Cependant, l’énergie extractible d’une seule fibre est intrinsèquement limitée.Une solution prometteuse est alors de réaliser une combinaison de fibres (jusqu’à plus de 10 000 fibres pour l’accélération de particules). La combinaison de fibres par méthode interférométrique (avec un record de 64 fibres combinées en régime continu) a prouvé qu’elle était un excellent candidat pour la combinaison d’un grand nombre de fibres.La collaboration XCAN entre l’Ecole Polytechnique et Thales, vise à réaliser un démonstrateur de combinaison cohérente de 61 fibres amplifiées en régime femtoseconde. Les travaux menés au cours de cette thèse s’inscrivent dans ce projet.Dans un premier temps, afin d’étudier les points durs inhérents au régime femtoseconde tout en s’affranchissant des difficultés liées à l’amplification, la méthode interférométique en régime femtoseconde a été étudiée sur un démonstrateur passif, c’est-à-dire sans amplification, de 19 fibres. Une fois la méthode de mise en phase validée celle-ci a pu être testée avec succès sur le démonstrateur avec amplification du projet XCAN.Nous présentons également les travaux menés afin d’augmenter un paramètre clé des systèmes de combinaison de faisceaux à savoir : l’efficacité de combinaison du système laser. Pour cela, nous avons réalisé une mise en forme de faisceaux issus des fibres de la tête optique. Cette mise en forme, gaussien vers super-gaussien, est réalisée à l’aide de deux réseaux de lames de phase dont nous présenterons le calcul des profils asphériques. Afin de valider expérimentalement nos simulations et après réalisation des lames de phase nous avons pu tester celles-ci sur le démonstrateur passif, démontrant une augmentation de 14 %.Les travaux présentés dans ce manuscrit présentent ainsi les premiers par vers la réalisation d’une nouvelle architecture laser massivement parallèle, capable de délivrer à la fois une haute puissance crête et une haute puissance moyenne. / Femtosecond fiber sources are used in a large number of applications (industrial, medical, fundamental physics) with a growing need in high energy pulses at high repetion rate. Although Ti: Saphirre technology provides energies up to PetaWatt, its repetion rate is low (up to 1 Hz). An alternative is to use an amplified fiber. However, the extractable energy of a single fiber is intrinsically limited.A solution is then to combine several fibers (up to 10 000 fibers for particle acceleration). Coherent beam combining of fibers with an interferometric method (with a record of 64 fibers combined in the cw regime) has proven to be an excellent candidate to combine a large number of fibers.The XCAN project, a collaboration between l'Ecole polytechnique and Thales, aims to realize a demonstrator of 61 fibers coherently combined in the femtosecond regime.The works presented in this thesis are part of this project.In order to study the hard points inherent to the femtosecond regime and to free from the amplification issues, the interferometric method has been implemented on a passive demonstrator, meaning without amplification, of 19 fibers. Once the interferometric method validated, it has been succesfully tested on the amplified XCAN demonstrator.We present also the works done to increase a key parameter of beam combining systems : the combining efficiency. To do this, we have realized a beam shaping of the fiber array output beams. This beam shaping, gaussian to super-gaussian, is done with two arrays of phase plates. The aspherical profiles calculation is described. In order to validate our simulations we have tested the phase plates on the passive demonstrator by getting an increase of 14 %.The works presented in this manuscript are the first steps towards a new massively parallel laser architecture, able to provide both high peak power and high average power.

In the presented thesis the topic of femtosecond pulse dispersion and methods of characterizing pulse profile are briefly introduced. Then, a functionality of a spatial light modulator is described. The spatial light modulator was used in an experimental scheme called the pulse shaper, which allowed independent amplitude and phase modulation of pulses. Duration and dispersion of pulses was measured by two methods called MIIPS and PICASO. MIIPS was also used for a reconstruction of a spectral phase of pulses. The autocorrelator was constructed on a design of the Mach-Zehnder interferometer. The duration of the shortest measured pulse (13.3 ± 0.5) fs was retrieved from measured interferometric autocorrelations by PICASO. Furthermore, theoretical dependence of pulse duration on the group delay dispersion was confirmed for pulses shorter than 120 fs. The group velocity dispersion was measured for fused silica windows and for a pair of diffraction gratings in the pulse shaper. Both values confirmed theoretical expectations.

Micro/Nanostructuring of polymers by femtosecond pulses is of extreme importance because it drives applications in photonics and biomedicine. A femtosecond pulse, with an intensity of ∼ 10^13 W/cm^2, is capable of causing an optical breakdown and inducing permanent modification in the material. With such high intensity, and considering the fact that polymers possess high band gaps, the interaction nature is completely nonlinear, and the material can be modified locally on the surface and in bulk. The irradiated regions exhibit fluorescence, and they display new wetting properties as a consequence of the optical breakdown of a material. The optical breakdown can be investigated by studying the nonlinear absorption. In this thesis, we discuss the nonlinear absorption of fs-laser pulses inside polymers using transmission measurements. We show a step– function–like behaviour of the transmission, dropping abruptly to ∼ 20% at the optical breakdown threshold with a ∼ 40 % reduction in the band gap. Utilizing spectroscopy, we show that the laser-modified regions contain randomly distributed nanoclusters. The presence of localized nanoclusters is responsible for exhibiting fluorescence, within ∼ 10 µm3 for a single pulse. This feature was exploited to demonstrate high-density data storage in Polymethyl methacrylate (PMMA) without any special material preparation. We demonstrate up to 20 layers of embedded data that can be stored in a standard 120 mm disc. Storage capacity of 0.2 TBytes/disc can be achieved by adjusting read laser parameters. Besides the fluorescence capability induced in the bulk of polymers, the hydrophilicity shown by the fs–laser modified surface is utilized to study selective cell growth on the micro-structured Polydimethylsiloxane (PDMS) surface. We show that the C2C12 cells and rabbit anti-mouse protein attach preferentially to the modified regions when the surface is modified with low pulse energies. However, in the high pulse energy regime, the laser-modified regions exhibit superhydrophobicity inhibiting cell adhesion.

L’endommagement laser est le résultat d’une interaction laser-matière qui se traduit par une dégradation physique des optiques, entraînant une détérioration de leur fonction optique. C'est un des facteurs limitant le développement des lasers de puissance et de leurs applications. Dans les matériaux diélectriques et en régime femtoseconde, ce phénomène repose sur des processus non linéaires et dépend des propriétés intrinsèques du matériau, contrairement au régime nanoseconde. Un banc d'endommagement laser femtoseconde a été développé et appliqué à l'étude du comportement des couches minces diélectriques. Le caractère déterministe de l'endommagement femtoseconde a été confirmé sur les substrats et les couches minces. Nous montrons de plus que les couches minces sont le siège d’effets transitoires, capables d’affecter le seuil d’endommagement, lorsque la densité d’électrons libres atteint une valeur critique. Un modèle dynamique a été développé afin de prendre en compte ces effets. Son efficacité à prédire l’évolution du seuil d’endommagement en fonction de la durée de l’impulsion a été démontrée expérimentalement. Les tests d’endommagement menés sur des monocouches HfO2 montrent une dépendance du seuil d’endommagement avec la technique de dépôt. Par ailleurs le comportement linéaire du seuil d’endommagement en fonction de la largeur de bande interdite a été confirmé pour les oxydes purs. Enfin nous présentons la première étude exhaustive sur la tenue au flux de mixtures d'oxydes, menée en collaboration avec le centre laser de l’Université de Vilnius, Lituanie et le Laser Zentrum Hannover LZH, Allemagne. / The laser damage is the result of a laser-matter interaction leading to the physical degradation of the optics, causing a deterioration of their optical function. This is one factor limiting the development of high power lasers and their applications. In dielectric materials and sub-picosecond regime, this phenomenon is based on non-linear processes and depends on the intrinsic properties of the material, as opposed to the nanosecond regime. A bench dedicated to the measurement of laser damage threshold has been developed and applied to study the behavior of optical dielectric thin films at 1030nm. The deterministic nature of sub-picosecond damage was evidenced on the substrates and thin films. A predictive model based on photo-ionisation and avalanche effects was developed for interpretation of the measurements. This model is specific to the case of multilayer optical effects since interference effects and transient response of the films are taken into account. Its effectiveness in predicting the evolution of the damage threshold as a function of pulse duration on HfO2 films. Moreover, the linear behavior of the damage threshold with the band gap has been experimentally observed for oxide materials and described by the model. Finally we present the first exhaustive study on the optical resistance of oxides mixtures, conducted in collaboration with the University of Vilnius, Lithuania, and the Laser Zentrum Hannover LZH, Germany.

Pour un grand nombre d'applications, les sources laser impulsionnelles femtoseconde (fs) doivent fournir des puissances toujours plus importantes. En régime impulsionnel, on recherche d'une part une forte puissance crête par impulsion, et d'autre part une forte puissance moyenne, c'est à dire un taux de répétition élevé. Parmi les technologies existantes, les amplificateurs à fibre optique dopée ytterbium présentent de nombreux avantages pour l'obtention de fortes puissances moyennes, cependant le fort confinement des faisceaux dans la fibre sur de grandes longueurs d'interaction induit inévitablement des effets non-linéaires, et limite ainsi la puissance crête accessible. Nous avons étudié lors de cette thèse la combinaison cohérente d'impulsions fs appliquée aux systèmes fibrés.Ayant déjà fait ses preuves dans les régimes d'amplification continu et nanoseconde, la combinaison cohérente de faisceaux (dite combinaison spatiale) permet de diviser une seule et unique source en N voies indépendantes, disposées en parallèle et incluant chacune un amplificateur. Les faisceaux amplifiés sont ensuite recombinés en espace libre en un seul et unique faisceau, qui contient toute la puissance des N amplificateurs sans accumuler les effets non-linéaires. Cette architecture permet théoriquement de monter d'un facteur N le niveau de puissance crête issu des systèmes d'amplification fibrés. Au cours de cette thèse, nous avons démontré la compatibilité et l'efficacité de cette méthode en régime d'amplification fs avec deux amplificateurs, selon différents procédés. Les expériences démontrent d'excellentes efficacités de combinaison ainsi qu'une très bonne préservation des caractéristiques temporelles et spatiales initiales de la source. Les procédés de combinaison cohérente nécessitent cependant un accord de phase entre différents amplificateurs stable dans le temps, assuré en premier lieu par une boucle de rétroaction. Nous avons poursuivi notre étude en concevant une architecture totalement passive, permettant une implémentation plus simple d'un système de combinaison à deux faisceaux sans asservissement électronique. Enfin, une méthode passive de combinaison cohérente dans le domaine temporel est étudiée et caractérisée dans le domaine fs, et implémentée simultanément avec la méthode passive de combinaison spatiale proposée précédemment. Ces expériences démontrent la validité et la variété des concepts proposés, ainsi que leurs nombreuses perspectives pour les systèmes d'amplification fs fibrés. / Applications addressed by femtosecond (fs) laser sources are requiring increasing pulse energies and increasing average powers. Ytterbium-doped fiber amplifiers are excellent candidates to generate high average powers at high repetition rates, but present strong disadvantages in terms of peak power. Indeed, the tight confinement of the beam over long interaction length induces nonlinear effects at high peak-powers that affect the overall performances of fiber systems. This work describes coherent combining methods that can be used to scale the performances of femtosecond laser sources.Coherent beam combining has been widely used in CW regime and more recently in the nanosecond range. It consists in splitting a single seed into N beam replicas, amplified each by independent amplifiers in parallel. Their respective outputs are combined in free space into one single beam that carries the power of the N amplifiers without cumulating nonlinearities. This architecture allows scaling both peak and average powers of the amplification systems. We have studied and demonstrated the efficiency of active coherent beam combining in the fs regime with two fiber amplifiers, which are peak-power limited. The experiments show the preservation of the temporal/spectral/spatial properties of the combined pulses, with high combination efficiencies.Coherent beam combining methods require phase-matching between all the beams to combine. This is usually achieved by an active feedback loop on each amplifier along with a phase detection scheme. We demonstrate that a Sagnac interferometer can be used to ensure perfect and stable phase-matching over time, which considerably simplifies the setup. Finally, another passive combining method known as divided-pulse amplification, acting in the temporal domain, is studied and demonstrated in the fs regime. It is coupled with the passive spatial combining method described above to scale the number of pulse divisions. All these experiments show the compatibility of coherent combining concepts in the fs regime and provide new opportunities for fiber amplifier systems.