Le choc laser est un procédé de plus en plus répandu qui utilise l’énergie laser pour générer des ondes de choc et inclure des effets mécaniques dans les matériaux ciblés. Lorsque l’énergie laser est absorbée par la cible, un plasma d’interaction est créé à la surface du matériau. Ce plasma, lors de sa détente, génère une onde de choc qui se propage. Les travaux effectués dans le cadre de cette thèse s’inscrivent donc dans une démarche globale de compréhension des phénomènes liés à l’interaction laser-matière. Dans le domaine des ondes de choc générées par laser, on peut distinguer deux procédés : Le traitement de surface par choc laser (LSP - Laser Shock Peening) et le test d’adhérence par choc laser (LASAT - LASer Adhesion Technique). Aujourd’hui la question se pose sur les limitations des procédés de choc par laser et sur les solutions à mettre en place pour pallier à ces limitations. Des idées sur l’amélioration des confinements, comme substitution à l’eau, ou encore l’optimisation des revêtements protecteurs ont été proposées. Par ailleurs, au cours de ces travaux de thèse, l’utilisation de deux impulsions laser a permis, dans le cas du procédé LASAT, l’optimisation de la traction générée aux interfaces des multimatériaux et ainsi de rendre le procédé plus robuste. De plus, dans le cas du procédé LSP, les aspects de rentabilité liés à la cadence de traitement ont été étudiés. Finalement, que ce soit pour les décalages en temps faibles (entre 0 et 1000 ns) ou bien les décalages importants (entre 200µs à 200ms), l’étude des phénomènes liés à l’interaction laser-matière a permis de franchir certaines limitations pour les deux procédés. / The laser shock wave generation is a novel process becoming more and more common. The shock waves are used to generate mechanicals effects in the sample. The laser absorption results in the creation of a plasma at the surface. This plasma during its expansion creates a shock wave propagating through the sample. This work aims to study the various phenomena involved in the laser-matter interaction. In the field of laser generated shock waves, two different processes exist: the Laser Shock Peening (LSP) and the LASer Adhesion Technique (LASAT). The new challenge deals with the limitations of those processes and the solutions to be setting up to improve them. Some ideas concerning the confinement improvement as water substitution or thermal coatings optimization are suggested in this work. Moreover, the use of double delayed laser pulses allows, for LASAT, the location of main tensile stresses near interfaces. However, for LSP, some aspects dealing with the profitability linked to the peening rate are investigated here. Last but not least, whether the very short (0 to 1000 ns) or very long delays (from 200µs to 200ms), the study of the laser-matter interaction phenomena allows to overcome some limitations for both laser shock processes.

Les chocs radiatifs sont des chocs très violents qui sont caractérisés par des températures très élevées. Dans ce type de structure, une grande partie de l’énergie est convertie en rayonnement. Ces chocs sont présents dans de nombreux plasmas astrophysiques, notamment dans le cadre des jets et de l’accrétion stellaires, des restes de supernova etc. Ils peuvent être désormais générés sur terre en utilisant des lasers de grande puissance ce qui permet leur étude à l’interface entre l’astrophysique et la physique des plasmas.Cette thèse présente et discute les résultats d’une expérience réalisées sur l’installation Prague Asterix Laser System. Le choc est généré en focalisant le laser Infrarouge sur une cible de quelques millimètres de long, remplie de xénon à basse pression. Le choc ainsi généré se propage dans le gaz à une vitesse élevée, permettant d’atteindre le régime des chocs dom- inés par le flux radiatif. Nous avons utilisé différents diagnostics pour caractériser le choc, notamment une radiographie éclair, à l’aide d’un laser (Zinc) à 21.2 nm, capable de pénétrer les parties denses du plasma. Un autre important diagnostique consiste à analyser l’émission propre du plasma à l’aide d’une diode rapide.Les résultats expérimentaux montrent pour la première fois, et sans ambiguïté, une structure de choc complète, comprenant le post-choc et le précurseur. Nous avons aussi réalisé différentes mesures de la vitesse des chocs. Les résultats ont été comparés à ceux de simulations numériques, montrant un bon accord avec ces dernières. / Radiative shocks are strong shocks which are characterized by a plasma at high temperatures emitting an important fraction of its energy as radiation. Radiative shocks are found in many astrophysical systems, including stellar accretion shocks, supernovae remnants, jet driven shocks, etc. Recently, radiative shocks have also been produced experimentally using high energy lasers. Thus opening the way to laboratory astrophysics studies of these universal phenomena.In this thesis we discuss the results of an experiment performed on the Prague Asterix Laser System facility. Shocks are generated by focusing the PALS Infrared laser beam on millimetre-scale targets filled with xenon gas at low pressure. The shock that is generated then propagates in the gas with a sufficiently high velocity such that the shock is in a radiative flux dominated regime. We used different diagnostics to characterize these shocks. The two main ones include a radiography of the whole shock structure using sub-nanosecond Zn X-ray laser at 21.2 nm, which is able to penetrate the dense post-shock layer, and a space-and-time resolved plasma self-emission using high speed diodes.The experimental results show, for the first time, an unambiguous shock structure which includes both the post-shock and the precursor, and we also obtained multiple shock velocity measurements from the different diagnostics. The experimental results are compared to simulations, and show good agreement with the numerical results.

L'interaction d'impulsions lasers brèves et intenses avec un plasma est une source intéressante d'ions énergétiques. Les travaux effectués au cours de cette thèse s'articulent autour de deux grandes thématiques : la production de protons par laser, et leur utilisation pour le chauffage isochore, avec, pour principal outil d'étude, la simulation à l'aide de codes numériques (cinétique particulaire et hydrodynamique). Dans un premier temps, nous avons étudié le comportement de l'énergie cinétique maximale des protons qu'il est possible d'accélérer avec le mécanisme du Target Normal Sheath Acceleration (TNSA), en régime sub-ps, en fonction de différents paramètres, notamment de la durée d'impulsion laser. Nous avons montré que l'allongement de la durée d'impulsion, à énergie laser constante, est responsable du préchauffage et de la détente du plasma avant l'arrivé du pic d'intensité. Les gradients de densité ainsi produits (face avant et face arrière) peuvent favoriser, ou au contraire pénaliser, le gain en énergie cinétique des protons. Les résultats obtenus ont servi à l'interprétation d'une étude expérimentale réalisée au Laboratoire d'Optique Appliquée. Nos efforts se sont ensuite concentrés sur l'élaboration d'un modèle semi-analytique rendant compte de l'énergie cinétique maximale des protons accélérés par le biais du TNSA. Ce modèle permet de retrouver l'ordre de grandeur des intensités nécessaires, de l'ordre de 6x1021 W/cm², pour atteindre des énergies de proton supérieures à 150 MeV avec des impulsions laser de quelques joules et plusieurs dizaines de fs. Dans la dernière partie de cette thèse, nous nous sommes intéressés à l'utilisation de ces faisceaux de protons pour le chauffage isochore. Nous avons caractérisé, dans un premier temps, les fonctions de distribution produites par des cibles composées d'un substrat lourd (A >> 1) sur la face arrière duquel est déposé un plot d'hydrogène (schéma d'Esirkepov). Ensuite, à partir de simulations hydrodynamiques, nous avons étudié le temps caractéristique de détente de la cible chauffée en modifiant des paramètres tels que la distance à la source de protons, l'intensité et la tache focale du laser, et la densité surfacique du plot. Nous avons enfin étendu cette étude aux cibles cylindriques et nous avons montré qu'il est possible de réduire les effets liés à la divergence naturelle du faisceau de protons et ainsi d'obtenir des températures plus élevées. / The interaction of ultra-high intensity, ultra-short laser pulses with matter is an interesting source of energetic ions. During this work, we studied the production of energetic protons and their application to isochoric heating using kinetics and hydrodynamics code. We first considered the behavior of the maximum proton kinetic energy with the Target Normal Sheath Acceleration (TNSA) mechanism, in the sub-ps interaction regime, as a function of different parameters, especially the laser pulse duration. We showed that stretching the pulse duration, with a constant laser energy, led to the preheating and the expansion of the plasma slab. This expansion can be beneficial or detrimental regarding the maximum proton kinetic energy. The results we obtained helped to explain an experimental study carried out at the Laboratoire d'Optique Appliquée. We then developed a semi-analytical model trying to describe the maximum proton kinetic energy that can be produced in the TNSA regime. The results we obtained can retrieve the minimum intensity, of the order of 6x1021 W/cm², that is required to reach proton energies of 150 MeV with femtosecond, few joules laser pulses. As a final step, we were interested in the use of these proton beams for isochoric heating. We first characterized the proton distribution function produced by targets consisting in an heavy substrate with an hydrogen is deposited at the rear side. By the mean of hydrodynamics simulations, we studied the characteristic expansion time of the heated target by varying several parameters such as the heated sample distance from the proton source, the intensity and focal spot size of the laser, and the areal density of the dot. Finally, we extended the previous study to cylindrical targets and we demonstrated that it is possible to counterbalance the natural divergence of the proton beam and hence, to reach higher temperatures.

The ultrashort chirped pulse amplification (CPA) laser technology opens the path to high intensities of 10^21 W/cm² and above in the laser focus. Such intensities allow laser-matter interaction in the relativistic intensity regime. Direct diode-pumped ultrashort solid-state lasers combine high-energy, high-power and efficient amplification together, which are the main advantages compared to flashlamp-pumped high-energy laser systems based on titanium-doped sapphire. Development within recent years in the field of laser diodes makes them more and more attractive in terms of total costs, compactness and lifetime. This work is dedicated to the Petawatt, ENergy-Efficient Laser for Optical Plasma Experiments (PENELOPE) project, a fully and directly diode-pumped laser system under development at the Helmholtz–Zentrum Dresden – Rossendorf (HZDR), aiming at 150 fs long pulses with energies of up to 150 J at repetition rates of up to 1 Hz. The focus of this thesis lies on the spectral and width manipulation of the front-end amplifiers, trivalent ytterbium-doped calcium fluoride (Yb3+:CaF2) as gain material as well as the pump source for the final two main amplifiers of the PENELOPE laser system. Here, all crucial design parameters were investigated and a further successful scaling of the laser system to its target values was shown. Gain narrowing is the dominant process for spectral bandwidth reduction during the amplification at the high-gain front-end amplifiers. Active or passive spectral gain control filter can be used to counteract this effect. A pulse duration of 121 fs was achieved by using a passive spectral attenuation inside a regenerative amplifier, which corresponds to an improvement by a factor of almost 2 compared to the start of this work. A proof-of-concept experiment showed the capability of the pre-shaping approach. A spectral bandwidth of 20nm was transferred through the first multipass amplifier at a total gain of 300. Finally, the predicted output spectrum calculated by a numerical model of the final amplifier stages was in a good agreement with the experimental results. The spectroscopic properties of Yb3+:CaF2 matches the constraints for ultrashort laser pulse amplification and direct diode pumping. Pumping close to the zero phonon line at 976nm is preferable compared to 940nm as the pump intensity saturation is significantly lower. A broad gain cross section of up to 50nm is achievable for typical inversion levels. Furthermore, moderate cryogenic temperatures (above 200K) can be used to improve the amplification performance of Yb3+:CaF2. The optical quality of the doped crystals currently available on the market is sufficient to build amplifiers in the hundred joule range. The designed pump source for the last two amplifiers is based on two side pumping in a double pass configuration. However, this concept requires the necessity of brightness conservation for the installed laser diodes. Therefore, a fully relay imaging setup (4f optical system) along the optical path from the stacks to the gain material including the global beam homogenization was developed in a novel approach. Beside these major parts the amplifier architecture and relay imaging telescopes as well as temporal intensity contrast (TIC) was investigated. An all reflective concept for the relay imaging amplifiers and telescopes was selected, which results in several advantages especially an achromatic behavior and low B-Integral. The TIC of the front-end was improved, as the pre- and postpulses due to the plane-parallel active-mirror was eliminated by wedging the gain medium.

During the past decades, the development of laser technology has produced pulses with increasingly higher peak intensities. These can now be made such that their strength rivals, and even exceeds, the atomic potential at the typical distance of an electron from the nucleus. To understand the induced dynamics, one can not rely on perturbative methods and must instead try to get as close to the full machinery of quantum mechanics as practically possible. With increasing field strength, many exotic interactions such as magnetic, relativistic and higher order electric effects may start to play a significant role. To keep a problem tractable, only those effects that play a non-negligible role should be accounted for. In order to do this, a clear notion of their relative importance as a function of the pulse properties is needed.  In this thesis I study the interaction between atomic hydrogen and super-intense laser pulses, with the specific aim to contribute to the knowledge of the relative importance of different effects. I solve the time-dependent Schrödinger and Dirac equations, and compare the results to reveal relativistic effects. High order electromagnetic multipole effects are accounted for by including spatial variation in the laser pulse. The interaction is first described using minimal coupling. The spatial part of the pulse is accounted for by a series expansion of the vector potential and convergence with respect to the number of expansion terms is carefully checked. A significantly higher demand on the spatial description is found in the relativistic case, and its origin is explained. As a response to this demanding convergence behavior, an alternative interaction form for the relativistic case has been developed and presented. As a guide mark for relativistic effects, I use the classical concept of quiver velocity, vquiv, which is the peak velocity of a free electron in the polarization direction of a monochromatic electromagnetic plane wave that interacts with the electron. Relativistic effects are expected when vquiv reaches a substantial fraction of the speed of light c, and in this thesis I consider cases up to vquiv=0.19c. For the present cases, relativistic effects are found to emerge around vquiv=0.16c .

The ultrashort chirped pulse amplification (CPA) laser technology opens the path to high intensities of 10^21 W/cm² and above in the laser focus. Such intensities allow laser-matter interaction in the relativistic intensity regime. Direct diode-pumped ultrashort solid-state lasers combine high-energy, high-power and efficient amplification together, which are the main advantages compared to flashlamp-pumped high-energy laser systems based on titanium-doped sapphire. Development within recent years in the field of laser diodes makes them more and more attractive in terms of total costs, compactness and lifetime. This work is dedicated to the Petawatt, ENergy-Efficient Laser for Optical Plasma Experiments (PENELOPE) project, a fully and directly diode-pumped laser system under development at the Helmholtz–Zentrum Dresden – Rossendorf (HZDR), aiming at 150 fs long pulses with energies of up to 150 J at repetition rates of up to 1 Hz. The focus of this thesis lies on the spectral and width manipulation of the front-end amplifiers, trivalent ytterbium-doped calcium fluoride (Yb3+:CaF2) as gain material as well as the pump source for the final two main amplifiers of the PENELOPE laser system. Here, all crucial design parameters were investigated and a further successful scaling of the laser system to its target values was shown. Gain narrowing is the dominant process for spectral bandwidth reduction during the amplification at the high-gain front-end amplifiers. Active or passive spectral gain control filter can be used to counteract this effect. A pulse duration of 121 fs was achieved by using a passive spectral attenuation inside a regenerative amplifier, which corresponds to an improvement by a factor of almost 2 compared to the start of this work. A proof-of-concept experiment showed the capability of the pre-shaping approach. A spectral bandwidth of 20nm was transferred through the first multipass amplifier at a total gain of 300. Finally, the predicted output spectrum calculated by a numerical model of the final amplifier stages was in a good agreement with the experimental results. The spectroscopic properties of Yb3+:CaF2 matches the constraints for ultrashort laser pulse amplification and direct diode pumping. Pumping close to the zero phonon line at 976nm is preferable compared to 940nm as the pump intensity saturation is significantly lower. A broad gain cross section of up to 50nm is achievable for typical inversion levels. Furthermore, moderate cryogenic temperatures (above 200K) can be used to improve the amplification performance of Yb3+:CaF2. The optical quality of the doped crystals currently available on the market is sufficient to build amplifiers in the hundred joule range. The designed pump source for the last two amplifiers is based on two side pumping in a double pass configuration. However, this concept requires the necessity of brightness conservation for the installed laser diodes. Therefore, a fully relay imaging setup (4f optical system) along the optical path from the stacks to the gain material including the global beam homogenization was developed in a novel approach. Beside these major parts the amplifier architecture and relay imaging telescopes as well as temporal intensity contrast (TIC) was investigated. An all reflective concept for the relay imaging amplifiers and telescopes was selected, which results in several advantages especially an achromatic behavior and low B-Integral. The TIC of the front-end was improved, as the pre- and postpulses due to the plane-parallel active-mirror was eliminated by wedging the gain medium.

The thesis deals with the development and characterization of new light sources, which are mandatory for applications in atomic and molecular spectroscopy, medical and biological imaging or industrial production. For that purpose, the employment of interactions of high intensity ultra-short laser pulses with gaseous media offers a rich variety of physical effects which can be exploited. The effects are characterized by a nonlinear dependency on the present light fields. Therefore, accurate modeling of the nonlinearities of the gas is crucial. In general, the nonlinearities are due to the electronic response of the gas atoms to the light field and one distinguishes between the response of bound and ionized electrons. The first part investigates laser pulse self compression, where the consideration of a purely bound electron response is sufficient. We apply an exotic setup with an negative Kerr nonlinearity in order to avoid spatial collapse of the beam on the cost of dealing with an highly dispersive nonlinearity. Analytical analysis and numerical simulations prove the possibility of laser pulse compression in such setups and reveals a new compression scheme, where the usually disturbing dispersion of the nonlinaerity is responsible for compression. Dealing with tera-Hertz generation by focusing an ionizing two-color laser pulse into gas, the second part exploits a medium nonlinearity caused by ionized electrons. We reveal in a mixed analytical and numerical analysis the underlying physical mechanism for THz generation: ionized electrons build up a current, which radiates. Thereby, the the two-color nature of the input laser is crucial for the emitted radiation to be in the tera-Hertz range. Combining this physical model with a pulse propagation equation allows us to achieve remarkable agreement with experimental measurements. Finally, the third part deals with nonlinearities from bound as well from ionized electrons on a fundamental level. We advance beyond phenomenological models for responses of bound and ionized electrons and quantum mechanically model the interaction of an ultra-short laser pulse with a gas. Already the simplest case of one dimensional hydrogen reveals basic features. For low intensities, the Kerr nonlinearity excellently describes the response of bound electrons. For increasing intensity, ionization becomes important and the response from ionized electrons is the governing one for high intensities. This quantum mechanical correct modeling allows us to explain saturation and change of sing of the nonlinear refractive index and to deduce suited approximate models for optical nonlinearities.

No description available.

La matière dense et tiède (WDM) est un régime caractérisé par une densité proche du solide pour une température avoisinant celle de Fermi. Pour étudier cet état de la matière, dans cette thèse, une expérience d'interférométrie dans le domaine des fréquences est mise en place afin de mesurer la phase et la réflectivité - dans les deux directions de polarisation S et P - d'une onde sonde en réflexion sur un échantillon chauffé de manière très brève par une impulsion laser ultra-courte (sub-100fs). Il est alors porté dans un état hors-équilibre. Une méthode basée sur les mesures de réflectivité est mise en place pour contrôler la forme de l'interface entre le vide et la matière chauffée. Pour des fluences laser de l'ordre de 1 J/cm2, l'hydrodynamique d'un échantillon chauffé est étudiée par la mesure du déplacement de la surface et comparée au code hydrodynamique à deux températures ESTHER. Ensuite, la fonction diélectrique à 800 nm et 400 nm est déduite des mesures expérimentales et certaines quantités en sont extraites comme la densité électronique, la température électronique et les fréquences de collision en régime WDM. Elles sont par la suite comparées avec des modèles couramment utilisés. / The Warm Dense Matter (WDM) regime is characterised by a density close to the solid density and an electron temperature close to the Fermi temperature. In this work, the nonequilibrium Warm Dense Matter is studied during the solid to liquid phase transition induced by an ultra short laser interacting with a solid. A 30 femtoseconds time resolution pump-probe experiment (FDI) is set up, yielding to the measurement of the heated sample complex reflectivity for both S and P polarisation.We have determined a criterion based on the measured reflectivities, which permits to control the interface shape of the probed matter. For pump laser fluences around 1 J/cm2, the hydrodynamics of the heated matter is studied and experimental results are compared to the two-temperatures code ESTHER. Furthermore, the evolution of the dielectric function at 800 nm and 400 nm is inferred from our measurements on a sub-picosecond time-scale. Within the Drude-Lorentz model for the conduction electrons, the dielectric function yields information such as ionisation state, electronic temperature and electron collision frequency.

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.