GeV electron bunches accelerated on a centimeter scale device exemplify the extraordinary advances of laser-plasma acceleration. The combination of high charges from optimized injection schemes and intrinsic femtosecond short bunch duration yields kiloampere peak currents. Further enhancing the current while reducing the energy spread will pave the way for future application, e.g. the driver for compact secondary radiation sources such as high-field THz, high-brightness x-ray or gamma-ray sources. One essential key for beam transport to a specific application is an electron bunch with high quality beam parameters such as low energy spread as well as small divergence and spot size. The inherent micrometer size at the plasma exit is typically sufficient for an efficient coupling into a conventional beamline. However, energy spread and beam divergence require optimization before the beam can be transported efficiently. Induced by the high peak current, the beam loading regime can be used in order to achieve optimized beam parameters for beam transport. / In this thesis, the impact of beam loading on the transverse electron dynamic is systematically studied by investigating betatron radiation and electron beam divergence. For this reason, the bubble regime with self-truncated ionization injection (STII) is applied to set up a nanocoulomb-class laser wakefield accelerator. The accelerator is driven by 150TW laser pulses from the DRACO high power laser system. A supersonic gas jet provides a 3mm long acceleration medium with electron densities from 3 × 10^18 cm^−3 to 5 × 10^18 cm^−3. The STII scheme together with the employed setup yields highly reproducible injections with bunch charges of up to 0.5 nC. The recorded betatron radius at the accelerator exit is about one micron and reveals that the beam size stays at the same value. The optimal beam loading, which is observed at around 250 pC to 300 pC, leads to the minimum energy spread of ~40MeV and a 20% smaller divergence. It is demonstrated that an incomplete betatron phase mixing due to the small energy spread can explain the experimentally observed minimum beam divergence.

Les accélérateurs par onde de sillage plasma produites par faisceaux de particules (PWFA) ou par faisceaux laser (LWFA) appartiennent à un nouveau type d’accélérateurs de particules particulièrement prometteur. Ils permettent d’exploiter des champs accélérateurs jusqu’à cent Gigaélectronvolt par mètre alors que les dispositifs conventionnels se limitent à cent Megaélectronvolt par mètre. Dans le schéma d’accélération par onde de sillage plasma, ou par onde de sillage laser, un faisceau de particules ou une impulsion laser se propage dans un plasma et créé une structure accélératrice dans son sillage : c’est une onde de densité électronique à laquelle sont associés des champs électromagnétiques dans le plasma. L’un des principaux résultats de cette thèse a été la démonstration de l’accélération par onde de sillage plasma d’un paquet distinct de positrons. Dans le schéma utilisé, un plasma de Lithium était créé dans un four, et une onde plasma était excitée par un premier paquet de positrons (le drive ou faisceau excitateur) et l’énergie était extraite par un second faisceau (le trailing ou faisceau témoin). Un champ accélérateur de 1,36 GeV/m a ainsi été obtenu durant l’expérience, pour une charge accélérée typique de 40 pC. Nous montrons également ici la possibilité d’utiliser différents régimes d’accélération qui semblent très prometteurs. Par ailleurs, l’accélération de particule par sillage laser permet quant à elle, en partant d’une impulsion laser femtoseconde de produire un faisceau d’électron quasi-monoénergétique d’énergie typique de l’ordre de 200 MeV. Nous présentons les résultats d’une campagne expérimentale d’association de ce schéma d’accélération par sillage laser avec un schéma d’accélération par sillage plasma. Au cours de cette expérience un faisceau d’électrons créé par laser est refocalisé lors d’une interaction dans un second plasma. Une étude des phénomènes associés à cette plateforme hybride LWFA-PWFA est également présentée. Enfin, le schéma hybride LWFA-PWFA est prometteur pour optimiser l’émission de rayonnement X par les électrons du faisceau de particule crée dans l’étage LWFA de la plateforme. Nous présentons dans un dernier temps la première réalisation expérimentale d’un tel schéma et ses résultats prometteurs. / Plasma wakefield accelerators (PWFA) or laser wakefield accelerators (LWFA) are new technologies of particle accelerators that are particularly promising, as they can provide accelerating fields of hundreds of Gigaelectronvolts per meter while conventional facilities are limited to hundreds of Megaelectronvolts per meter. In the Plasma Wakefield Acceleration scheme (PWFA) and the Laser Wakefield Acceleration scheme (LWFA), a bunch of particles or a laser pulse propagates in a gas, creating an accelerating structure in its wake: an electron density wake associated to electromagnetic fields in the plasma. The main achievement of this thesis is the very first demonstration and experimental study in 2016 of the Plasma Wakefield Acceleration of a distinct positron bunch. In the scheme considered in the experiment, a lithium plasma was created in an oven, and a plasma density wave was excited inside it by a first bunch of positrons (the drive bunch) while the energy deposited in the plasma was extracted by a second bunch (the trailing bunch). An accelerating field of 1.36 GeV/m was reached during the experiment, for a typical accelerated charge of 40 pC. In the present manuscript is also reported the feasibility of several regimes of acceleration, which opens promising prospects for plasma wakefield accelerator staging and future colliders. Furthermore, this thesis also reports the progresses made regarding a new scheme: the use of a LWFA-produced electron beam to drive plasma waves in a gas jet. In this second experimental study, an electron beam created by laser-plasma interaction is refocused by particle bunch-plasma interaction in a second gas jet. A study of the physical phenomena associated to this hybrid LWFA-PWFA platform is reported. Last, the hybrid LWFA-PWFA scheme is also promising in order to enhance the X-ray emission by the LWFA electron beam produced in the first stage of the platform. In the last chapter of this thesis is reported the first experimental realization of this last scheme, and its promising results are discussed.

Une impulsion laser ultra-courte et ultra-intense se propageant dans un gaz de faible densité est capable d'accélérer une partie des électrons de ce gaz à des énergies relativistes, de l'ordre de quelques centaines de MeV, sur des distances de seulement quelques millimètres. Pendant leur accélération et dû à leur mouvement transverse, ces électrons émettent de plus un rayonnement X fortement collimaté et dirigé vers l'avant appelé rayonnement bétatron. Les caractéristiques de cette source la rendent intéressante pour son utilisation en imagerie à ultra-haute résolution.Dans ce manuscrit, nous explorons trois axes de travail autour de cette source à l'aide de simulations réalisées avec les codes Particle-In-Cell CALDER et CALDER-Circ. Nous commençons ainsi par étudier la création d'une source bétatron avec des impulsions laser de durée picoseconde et d'énergie kilojoule, donc plus longues et plus puissantes que celles habituellement utilisées par la communauté. Nous montrons que malgré les paramètres inhabituels de ces impulsions lasers il est toujours possibles de générer des sources X, et ce dans deux régimes différents.Ensuite, afin de comprendre une partie des différences généralement observées entre expériences et simulations, nous montrons dans une autre étude que l'utilisation dans les simulations de profils lasers réalistes au lieu de profils parfaitement Gaussiens dégrade fortement les performances de l'accélérateur laser-plasma et de la source bétatron. De plus, ceci conduit à un meilleur accord qualitatif et quantitatif avec l'expérience.Enfin nous explorons plusieurs techniques pour augmenter l'émission X basées sur une manipulation des profils de plasmas utilisés pour l'accélération. Nous trouvons que l'utilisation d'un gradient transverse ou d'une marche de densité conduisent tous deux à une augmentation de l'amplitude du mouvement transverse des électrons, et donc de l'énergie émise par la source bétatron. Alternativement, nous montrons que cet objectif peut-être atteint par la transition d'un régime de sillage laser vers un régime d'accélération par sillage plasma induit par une augmentation de la densité. L'accélération des électrons est optimisée dans le premier régime, tandis que l'émission X est fortement favorisée dans le second. / An ultra-short and ultra-intense laser pulse propagating in a low-density gas can accelerate in its wake a part of the electrons ionized from the gas to relativistic energies of a few hundreds of MeV over distances of a few millimeters only. During their acceleration, as a consequence of their transverse motion, these electrons emit strongly collimated X-rays in the forward direction, which are called betatron radiations. The characteristics of this source turn it into an interesting tool for high-resolution imagery.In this thesis, we explore three different axis to work on this source using simulations on the Particles-In-Cells codes CALDER and CALDER-Circ. We first study the creation of a betatron X-ray source with kilojoule and picosecond laser pulses, for which duration and energy are then much higher than usual in this domain. In spite of the unusual laser parameters, we show that X-ray sources can still be generated, furthermore in two different regimes.In a second study, the generally observed discrepancies between experiments and simulations are investigated. We show that the use of realistic laser profiles instead of Gaussian ones in the simulations strongly degrades the performances of the laser-plasma accelerator and of the betatron source. Additionally, this leads to a better qualitative and quantitative agreement with the experiment.Finally, with the aim of improving the X-ray emission, we explore several techniques based on the manipulation of the plasma density profile used for acceleration. We find that both the use of a transverse gradient and of a density step increases the amplitude of the electrons transverse motions, and then increases the radiated energy. Alternatively, we show that this goal can also be achieved through the transition from a laser wakefield regime to a plasma wakefield regime induced by an increase of the density. The laser wakefield optimizes the electron acceleration whereas the plasma wakefield favours the X-ray emission.

This thesis investigates the use of high-power lasers for synchrotron radiation sources with high brilliance, from the EUV to the hard X-ray spectral range. Hereby lasers accelerate electrons by laser-wakefield acceleration (LWFA), act as optical undulators, or both. Experimental evidence shows for the first time that LWFA electron bunches are shorter than the driving laser and have a length scale comparable to the plasma wavelength. Furthermore, a first proof of principle experiment demonstrates that LWFA electrons can be exploited to generate undulator radiation. Building upon these experimental findings, as well as extensive numerical simulations of Thomson scattering, the theoretical foundations of a novel interaction geometry for laser-matter interaction are developed. This new method is very general and when tailored towards relativistically moving targets not being limited by the focusability (Rayleigh length) of the laser, while it does not require a waveguide. In a theoretical investigation of Thomson scattering, the optical analogue of undulator radiation, the limits of Thomson sources in scaling towards higher peak brilliances are highlighted. This leads to a novel method for generating brilliant, highly tunable X-ray sources, which is highly energy efficient by circumventing the laser Rayleigh limit through a novel traveling-wave Thomson scattering (TWTS) geometry. This new method suggests increases in X-ray photon yields of 2-3 orders of magnitudes using existing lasers and a way towards efficient, optical undulators to drive a free-electron laser. The results presented here extend far beyond the scope of this work. The possibility to use lasers as particle accelerators, as well as optical undulators, leads to very compact and energy efficient synchrotron sources. The resulting monoenergetic radiation of high brilliance in a range from extreme ultraviolet (EUV) to hard X-ray radiation is of fundamental importance for basic research, medical applications, material and life sciences and is going to significantly contribute to a new generation of radiation sources and free-electron lasers (FELs).

Die vorliegende Arbeit beschäftigt sich in Experiment und Theorie mit Laser-Plasma beschleunigten Elektronen und optischen Undulatoren zur Erzeugung von brillianter Synchrotronstrahlung. Zum ersten Mal wird experimentell nachgewießen, dass laserbeschleunigte Elektronenpulse kürzer als 30 fs sind. Ferner werden solche Elektronenpulse erstmalig in einem Demonstrationsexperiment durch einen magnetischen Undulator als Synchrotronstrahlenquelle genutzt. Aufbauend auf diesen experimentellen Erkenntnissen, sowie umfangreichen numerischen Simulationen zur Thomsonstreuung, werden die theoretischen Grundlagen einer neuartigen Interaktionsgeometrie für Laser-Materie Wechselwirkungen entwickelt. Diese neue, in der Anwendbarkeit sehr allgemeine Methode basiert auf raum-zeitlicher Laserpulsformung durch nichtlineare Winkeldispersion wie diese durch VLS- (varied-line spacing) Gitter erzeugt werden kann und hat den Vorteil nicht durch die Fokussierbarkeit des Lasers (Rayleighlänge) begrenzt zu sein. Zusammen mit laserbeschleunigten Elektronen ermöglicht dieser traveling-wave Thomson scattering (TWTS) benannte Ansatz neuartige, nur auf optischer Technologie basierende Synchrotronstrahlenquellen mit Zentimeter bis Meter langen optische Undulatoren. Die hierbei mit existierenden Lasern erzielbaren Brillianzen übersteigen diese bestehender Thomsonquellen-Designs um 2-3 Größenordnungen. Die hier vorgestellten Ergebnisse weisen weit über die Grenzen der vorliegenden Arbeit hinaus. Die Möglichkeit Laser als Teilchenbeschleuniger und auch optischen Undulator zu verwenden führt zu bauartbedingt sehr kompakten und energieeffizienten Synchrotronstrahlungsquellen. Die hieraus resultierende monochromatische Strahlung hoher Brillianz in einem Wellenlängenbereich von extremen ultraviolett (EUV) zu harten Röntgenstrahlen ist für die Grundlagenforschung, medizinische Anwendungen, Material- und Lebenswissenschaften von fundamentaler Bedeutung und wird maßgeblich zu einer neuen Generation ultrakurzer Strahlungsquellen und freien Elektronenlasern (FELs) beitragen. / This thesis investigates the use of high-power lasers for synchrotron radiation sources with high brilliance, from the EUV to the hard X-ray spectral range. Hereby lasers accelerate electrons by laser-wakefield acceleration (LWFA), act as optical undulators, or both. Experimental evidence shows for the first time that LWFA electron bunches are shorter than the driving laser and have a length scale comparable to the plasma wavelength. Furthermore, a first proof of principle experiment demonstrates that LWFA electrons can be exploited to generate undulator radiation. Building upon these experimental findings, as well as extensive numerical simulations of Thomson scattering, the theoretical foundations of a novel interaction geometry for laser-matter interaction are developed. This new method is very general and when tailored towards relativistically moving targets not being limited by the focusability (Rayleigh length) of the laser, while it does not require a waveguide. In a theoretical investigation of Thomson scattering, the optical analogue of undulator radiation, the limits of Thomson sources in scaling towards higher peak brilliances are highlighted. This leads to a novel method for generating brilliant, highly tunable X-ray sources, which is highly energy efficient by circumventing the laser Rayleigh limit through a novel traveling-wave Thomson scattering (TWTS) geometry. This new method suggests increases in X-ray photon yields of 2-3 orders of magnitudes using existing lasers and a way towards efficient, optical undulators to drive a free-electron laser. The results presented here extend far beyond the scope of this work. The possibility to use lasers as particle accelerators, as well as optical undulators, leads to very compact and energy efficient synchrotron sources. The resulting monoenergetic radiation of high brilliance in a range from extreme ultraviolet (EUV) to hard X-ray radiation is of fundamental importance for basic research, medical applications, material and life sciences and is going to significantly contribute to a new generation of radiation sources and free-electron lasers (FELs).

This thesis investigates the use of high-power lasers for synchrotron radiation sources with high brilliance, from the EUV to the hard X-ray spectral range. Hereby lasers accelerate electrons by laser-wakefield acceleration (LWFA), act as optical undulators, or both. Experimental evidence shows for the first time that LWFA electron bunches are shorter than the driving laser and have a length scale comparable to the plasma wavelength. Furthermore, a first proof of principle experiment demonstrates that LWFA electrons can be exploited to generate undulator radiation. Building upon these experimental findings, as well as extensive numerical simulations of Thomson scattering, the theoretical foundations of a novel interaction geometry for laser-matter interaction are developed. This new method is very general and when tailored towards relativistically moving targets not being limited by the focusability (Rayleigh length) of the laser, while it does not require a waveguide. In a theoretical investigation of Thomson scattering, the optical analogue of undulator radiation, the limits of Thomson sources in scaling towards higher peak brilliances are highlighted. This leads to a novel method for generating brilliant, highly tunable X-ray sources, which is highly energy efficient by circumventing the laser Rayleigh limit through a novel traveling-wave Thomson scattering (TWTS) geometry. This new method suggests increases in X-ray photon yields of 2-3 orders of magnitudes using existing lasers and a way towards efficient, optical undulators to drive a free-electron laser. The results presented here extend far beyond the scope of this work. The possibility to use lasers as particle accelerators, as well as optical undulators, leads to very compact and energy efficient synchrotron sources. The resulting monoenergetic radiation of high brilliance in a range from extreme ultraviolet (EUV) to hard X-ray radiation is of fundamental importance for basic research, medical applications, material and life sciences and is going to significantly contribute to a new generation of radiation sources and free-electron lasers (FELs).

Die vorliegende Arbeit beschäftigt sich in Experiment und Theorie mit Laser-Plasma beschleunigten Elektronen und optischen Undulatoren zur Erzeugung von brillianter Synchrotronstrahlung. Zum ersten Mal wird experimentell nachgewießen, dass laserbeschleunigte Elektronenpulse kürzer als 30 fs sind. Ferner werden solche Elektronenpulse erstmalig in einem Demonstrationsexperiment durch einen magnetischen Undulator als Synchrotronstrahlenquelle genutzt. Aufbauend auf diesen experimentellen Erkenntnissen, sowie umfangreichen numerischen Simulationen zur Thomsonstreuung, werden die theoretischen Grundlagen einer neuartigen Interaktionsgeometrie für Laser-Materie Wechselwirkungen entwickelt. Diese neue, in der Anwendbarkeit sehr allgemeine Methode basiert auf raum-zeitlicher Laserpulsformung durch nichtlineare Winkeldispersion wie diese durch VLS- (varied-line spacing) Gitter erzeugt werden kann und hat den Vorteil nicht durch die Fokussierbarkeit des Lasers (Rayleighlänge) begrenzt zu sein. Zusammen mit laserbeschleunigten Elektronen ermöglicht dieser traveling-wave Thomson scattering (TWTS) benannte Ansatz neuartige, nur auf optischer Technologie basierende Synchrotronstrahlenquellen mit Zentimeter bis Meter langen optische Undulatoren. Die hierbei mit existierenden Lasern erzielbaren Brillianzen übersteigen diese bestehender Thomsonquellen-Designs um 2-3 Größenordnungen. Die hier vorgestellten Ergebnisse weisen weit über die Grenzen der vorliegenden Arbeit hinaus. Die Möglichkeit Laser als Teilchenbeschleuniger und auch optischen Undulator zu verwenden führt zu bauartbedingt sehr kompakten und energieeffizienten Synchrotronstrahlungsquellen. Die hieraus resultierende monochromatische Strahlung hoher Brillianz in einem Wellenlängenbereich von extremen ultraviolett (EUV) zu harten Röntgenstrahlen ist für die Grundlagenforschung, medizinische Anwendungen, Material- und Lebenswissenschaften von fundamentaler Bedeutung und wird maßgeblich zu einer neuen Generation ultrakurzer Strahlungsquellen und freien Elektronenlasern (FELs) beitragen. / This thesis investigates the use of high-power lasers for synchrotron radiation sources with high brilliance, from the EUV to the hard X-ray spectral range. Hereby lasers accelerate electrons by laser-wakefield acceleration (LWFA), act as optical undulators, or both. Experimental evidence shows for the first time that LWFA electron bunches are shorter than the driving laser and have a length scale comparable to the plasma wavelength. Furthermore, a first proof of principle experiment demonstrates that LWFA electrons can be exploited to generate undulator radiation. Building upon these experimental findings, as well as extensive numerical simulations of Thomson scattering, the theoretical foundations of a novel interaction geometry for laser-matter interaction are developed. This new method is very general and when tailored towards relativistically moving targets not being limited by the focusability (Rayleigh length) of the laser, while it does not require a waveguide. In a theoretical investigation of Thomson scattering, the optical analogue of undulator radiation, the limits of Thomson sources in scaling towards higher peak brilliances are highlighted. This leads to a novel method for generating brilliant, highly tunable X-ray sources, which is highly energy efficient by circumventing the laser Rayleigh limit through a novel traveling-wave Thomson scattering (TWTS) geometry. This new method suggests increases in X-ray photon yields of 2-3 orders of magnitudes using existing lasers and a way towards efficient, optical undulators to drive a free-electron laser. The results presented here extend far beyond the scope of this work. The possibility to use lasers as particle accelerators, as well as optical undulators, leads to very compact and energy efficient synchrotron sources. The resulting monoenergetic radiation of high brilliance in a range from extreme ultraviolet (EUV) to hard X-ray radiation is of fundamental importance for basic research, medical applications, material and life sciences and is going to significantly contribute to a new generation of radiation sources and free-electron lasers (FELs).