Search

LASERIX est une plateforme de l’IJClab sur le campus de l’Université Paris Saclay. Le laser est une chaîne CPA de niveau 50 TW à 10 Hz. Des thématiques de recherche en rapport avec la physique des deux infinis sont menées en parallèle avec une vocation affirmée d’ouverture à la formation. Nous présentons un panorama sur les sources XUV de lumière structurée, l’accélération laser plasma et des études prospectives sur l’étude des propriétés du vide soumis à un champ électromagnétique ultra-intense.

[EN]Structured light in the short-wavelength regime opens exciting avenues for the study of ultrafast spin and electronic dynamics. Here, we demonstrate theoretically and experimentally the generation of vector-vortex beams (VVB) in the extreme ultraviolet through high-order harmonic generation (HHG). The up-conversion of VVB, which are spatially tailored in their spin and orbital angular momentum, is ruled by the conservation of the topological Pancharatnam charge in HHG. Despite the complex propagation of the driving beam, high-harmonic VVB are robustly generated with smooth propagation properties. Remarkably, we find out that the conversion efficiency of high-harmonic VVB increases with the driving topological charge. Our work opens the possibility to synthesize attosecond helical structures with spatially varying polarization, a unique tool to probe spatiotemporal dynamics in inhomogeneous media or polarization-dependent systems., European Research Council (851201); Ministerio de Ciencia de Innovación y Universidades, Agencia Estatal de Investigación and European Social Fund (PID2019-106910GB-I00, RYC-2017-22745); Junta de Castilla y León and FEDER Funds (SA287P18); Université Paris-Saclay (2012-0333T-OASIS, 50110000724-OPTX, PhOM REC-2019-074-MAOHAm); Conseil Régional, Île-de-France (501100003990); Barcelona Supercomputing Center (FI-2020-3-0013).

We report temporal coherence measurement of solid-target plasma-based soft X-ray laser (XRL) in amplified spontaneous emission (ASE) mode. By changing the XRL pumping angle, we generate lasing at two-times higher electron density than the routine condition. A relatively shorter coherence time at a higher pumping angle indicates a clear spectral signature of higher electron density in the gain region. We probe the amplification dynamics of XRL in routine, and high electron density conditions to confirm gain-duration reduction resulting from ionization gating in the latter case. We also present recent results on the seeding of a vortex beam carrying orbital angular momentum (OAM) in XRL plasma. A small part of the high topological charge extreme ultraviolet (EUV) vortex is injected in XRL. These preliminary results suggest that the vortex seed indeed can be efficiently amplified. In the end, we propose a pathway towards the seeding of the complete vortex beam and wavefront characterization of the amplified beam.

Quantum electrodynamics predicts that the vacuum must behave as a nonlinear optical medium: the speed of light should be modified when the vacuum is stressed by intense electromagnetic fields. This optical phenomenon has not yet been observed. The DeLLight (deflection of light by light) experiment aims to observe the optically induced index change of vacuum, a nonlinear effect which has never been explored. The experiment is installed in the LASERIX facility at IJCLab, which delivers ultrashort intense laser pulses (2.5 J per pulse, each of 30 fs duration, with a 10 Hz repetition rate). The proposal is to measure the refraction of a probe laser pulse when crossing a transverse vacuum index gradient, produced by a very intense pump pulse. The refraction induces a transverse shift in the intensity profile of the probe, whose signal is amplified by a Sagnac interferometer. In this article we describe the experimental method and setup, and present the complete theoretical calculations for the expected signal. With a minimum waist at focus of $5\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{m}$ (corresponding to a maximum intensity of $\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{4pt}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$), and with the nonlinear vacuum index derived from QED, the expected refraction angle is 0.13 prad. First results of the interferometer prototype are presented. It is shown that an extinction factor $\mathcal{F}=0.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ (corresponding to a signal amplification factor of 250) and a spatial resolution ${\ensuremath{\sigma}}_{y}=10\phantom{\rule{4pt}{0ex}}\mathrm{nm}$ are achievable. The expected signal is then about 15 pm, and could be observed at a 5-sigma confidence level with about one month of collected data.

International audience; Optische Strahlen mit Orbital Angular Momentum (OAM) sind ein sehr aktives Forschungsfeld für ihre prospektiven Anwendungen, insbesondere bei kurzen Wellenlängen. Wir betrachten hier solche Strahlen, die durch hochharmonische Erzeugung (HHG) in einem seltenen Gas erzeugt werden, und analysieren die Charakterisierung ihrer Hochladungs-Wirbelstruktur durch einen EUV (Extreme UltraViolet) Hartmann-Wellenfrontsensor. Wir zeigen, dass solche HHG-Strahlen in der Regel aus einer Reihe von zahlreichen Vortex-Modi bestehen. Die Empfindlichkeit der Intensität und Phase des HHG-Strahls auf die infraroten (IR) Laseraberrationen wird mit einem deformierbaren Spiegel untersucht.; Optical beams carrying Orbital Angular Momentum (OAM) are a very active field of research for their prospective applications, especially at short wavelengths. We consider here such beams produced through high-harmonic generation (HHG) in a rare gas and analyze the characterization of their high charge vortex structure by an EUV (Extreme UltraViolet) Hartmann wavefront sensor. We show that such HHG beams are generally composed of a set of numerous vortex modes. The sensitivity of the intensity and phase of the HHG beam to the infrared (IR) laser aberrations is investigated using a deformable mirror.; Les faisceaux optiques portant un Moment Angulaire Orbital (OAM) font l'objet de recherches très actives,en raison de l'intérêt de leurs applications potentielles, particulièrement à courtes longueurs d'onde. Nous nous intéressons ici à des faisceaux produits par Génération d'Harmoniques d'Ordre Elevé (HOE) dans un gaz rare, et analysons la structure du vortex de haute charge grâce à la caractérisation complète obtenue par un capteur de front d'onde de type Hartmann dans l'Extrême UltraViolet (EUV). Nous montrons que ces faisceaux HOE sont généralement constitués d'un ensemble de nombreux modes de vortex. Un miroir déformable nous permet d'étudier la sensibilité de l'éclairement et de la phase du faisceau HOE vis à vis des aberrations du laser infrarouge (IR).

We demonstrate for the first time, to the best of our knowledge, the ability of extreme ultraviolet (XUV) Hartmann wavefront sensors to characterize high charge vortex beams produced by high-order harmonic generation up to the order of 25. We also show that phase matched absorption limited high harmonic generation is able to maintain the high charge vortex structure of the XUV beam even in a rather long (1 cm) generation medium.

10.18429/JACoW-IPAC2018-TUPML079; International audience; We present a start to end (s2e) simulation of the Laser-plasma Wakefield Accelerator (LPWA) foreseen as the ESCULAP project. We use a photo injector to produce a 5MeV 10pC electron bunch with a duration of ~ 1 ps RMS, it is boosted to 10MeV by a S-band cavity and then compressed to 74 fs RMS (30 fs FWHM) by a magnetic compression chicane (dogleg). After the dogleg, a quadrupole doublet and a triplet are utilized to match the Twiss parameters before injecting into the subsequent plasma wakefield. A 40 TW laser is used to excite plasma wakefield in the 10 cm plasma cell. An optimized configuration has been determined yielding at the plasma exit an electron beam at 180 MeV with energy spread of ~ 4.2%, an angular divergence of 0.6 mrad and a duration of 4 fs.

We present theoretical and numerical studies of longitudinal compression and transverse matching of electron bunch before injecting into the Laser–plasma Wake Field Accelerator (LWFA) foreseen at the ESCULAP project in ORSAY. Longitudinal compression is performed with a dogleg chicane, the chicane is designed based on theory of beam optics, beam dynamics in dogleg is studied with ImpactT (Martin Dohlus and Torsten Limberg, 2004) and cross checked with CSRtrack (Qiang and Steve Lidia, 2006), both 3D space charge (SC) and coherent synchrotron radiation (CSR) effects are included. Simulation results show that the energy chirp at the dogleg entrance should be smaller than the nominal optic design value, in order to compensate the negative energy chirp increase caused by longitudinal SC, while CSR can be ignored in our case. With an optimized configuration, the electron bunch ( ∼ 10 MeV, 10 pC) is compressed from 0.9 ps RMS to 70 fs RMS (53 fs FWHM), with a peak current of 152 A. Transverse matching is realized with a doublet and a triplet, they are matched with Madx and the electron bunch is tracked with ImpactT, simulation results show little difference with the nominal design values, that is due to the SC effect. Finally, by simply adjusting the quadrupole strength, a preliminary optimized configuration has been achieved, that matches the Courant–Snyder (C–S) parameters to α x = 0 . 01 , α y = − 0 . 02 , β x = 0 . 014 m , β y = 0 . 012 m at the plasma entrance.

We present numerical simulations results on the injection and acceleration of a 10 MeV, 10 pC electrons beam in a plasma wave generated in a gas cell by a 2J, 45 fs laser beam . This modeling is related to the ESCULAP project in which the electrons accelerated by the PHIL photo-injector is injected in a gas cell irradiated by the laser beam of the LASERIX system. Extensive modeling of the experiment was performed in order to determine optimal parameters of the laser plasma configurations. This was done with the newly developed numerical code WakeTraj . We propose a configuration that benefits of a highly compressed electron bunch and for which the injected electron beam can be efficiently coupled to the plasma wave and accelerated up to 140 MeV, with an energy spread lower than 5%.

International audience; We present the status of optical field ionization soft X-ray lasers. The amplifying medium is generated by focusing a high-energy circularly polarized 30-fs 10-Hz Ti: sapphire laser system in a gaseous medium. Using xenon or krypton, strong laser emission at 41.8 and 32.8 nm, respectively, has been observed. After presenting the basis of the physics, we present recent characterization of the sources as well as dramatic improvement of their performances using the waveguiding technique.

Intense and stable laser operation with Ni-like Zr and Ag was demonstrated at pump energies between 2 J and 5 J energy from the PHELIX pre-amplifier section. A novel single mirror focusing scheme for the TCE x-ray laser (XRL) has been successfully implemented by the LIXAM/MBI/GSI collaboration under different pump geometries. This shows potential for an extension to shorter XRL wavelength. Generation of high quality XRL beams for XRL spectroscopy of highly charged ions is an important issue within the scientific program of PHELIX. Long range perspective is the study of nuclear properties of radioactive isotopes within the FAIR project.

In very intense electromagnetic fields, the vacuum refractive index is expected to be modified due to nonlinear quantum electrodynamics (QED) properties. Several experimental tests using high intensity lasers have been proposed to observe electromagnetic nonlinearities in vacuum, such as the diffraction or the reflection of intense laser pulses. We propose a new approach which consists in observing the refraction, i.e. the rotation of the waveplanes of a probe laser pulse crossing a transverse vacuum index gradient. The latter is produced by the interaction of two very intense and ultra short laser pulses, used as pump pulses. At the maximum of the index gradient, the refraction angle of the probe pulse is estimated to be $0.2 \times (\frac{w_0}{10 \mathrm{\mu m}})^{-3} \times \frac{I}{1 \mathrm{J}}$~picoradians, where $I$ is the total energy of the two pump pulses and $w_0$ is the minimum waist (fwhm) at the interaction area. Assuming the most intense laser pulses attainable by the LASERIX facility ($I = 25$~J, 30~fs fwhm duration, 800~nm central wavelength) and assuming a minimum waist of $w=10 \mathrm{\mu m}$ (fwhm) (corresponding to an intensity of the order of $10^{21}$~W/cm$^2$), the expected maximum refraction angle is about 5~picoradians. An experimental setup, using a Sagnac interferometer, is proposed to perform this measurement., Comment: Accepted for publication in Eur. Phys. Journal D

We report the preliminary result of the application of the collisional Ne-like soft x-ray laser as radiation source to induce DNA damage. The goal of this experiment was a test bed study of the damage yields induced by soft x-ray radiation in dried plasmid DNA sample. The saturated Ne-like soft x-ray laser available at the PALS facility, delivering several millijoules in a single 100 ps pulse at 21.2 nm was used to irradiate two different plasmids: pSPl 89 and pBS. The study is centered on the dose effect leading to single and double strand break in DNA.

International audience; Synchrotrons have for decades provided invaluable sources of soft X-rays, the application of which has led to significant progress in many areas of science and technology. But future applications of soft X-rays—in structural biology, for example—anticipate the need for pulses with much shorter duration (femtoseconds) and much higher energy (millijoules) than those delivered by synchrotrons. Soft X-ray free-electron lasers1 should fulfil these requirements but will be limited in number; the pressure on beamtime is therefore likely to be considerable. Laser-driven soft X-ray sources offer a comparatively inexpensive and widely available alternative, but have encountered practical bottlenecks in the quest for high intensities. Here we establish and characterize a soft X-ray laser chain that shows how these bottlenecks can in principle be overcome. By combining the high optical quality available from high-harmonic laser sources (as a seed beam) with a highly energetic soft X-ray laser plasma amplifier, we produce a tabletop soft X-ray femtosecond laser operating at 10 Hz and exhibiting full saturation, high energy, high coherence and full polarization. This technique should be readily applicable on all existing laser-driven soft X-ray facilities.

International audience; Nous avons utilisé une technique récente de mesure d'impulsions ultra-courtes afin d'étudier la dynamique de l'ionisation et la propagation dans un milieu gazeux. Nous présentons les mesures de variation de l'intensité, de la phase temporelle et du spectre d'une impulsion laser intense (10^16W/cm^2), ultracourte (35 fs) après son interaction avec un milieu gazeux. Les variations de l'indice de réfraction du plasma sont rapides et modifient la structure spatiale et temporelle de l'impulsion lors de sa propagation dans le gaz. Ces variations d'intensité et de phase temporelles peuvent être utilisées pour connaitre la dyriamique de l'interaction laser-plasma. En particulier, cette expérience permet de mettre en évidencc les effets sur la génération d'un milieu de gain pour le laser X de type OFI (Optical Field Ionization).

We show that a significant enhancement of the photon flux produced by high harmonic generation can be obtained through guided configuration at high laser intensity largely above the saturation intensity. We identify two regimes. At low pressure, we observe an intense second plateau in the high harmonic spectrum in argon. At relatively high pressure, complex interplay between strongly time-dependent ionization processes and propagation effects leads to important spectral broadening without loss of spectral brightness. We show that the relevant parameter for this physical process is the product of laser peak power by gas pressure. We compare source performances with high harmonic generation using a gas jet in loose focusing geometry and conclude that the source developed is a good candidate for injection devices such as seeded soft x-ray lasers or free electron lasers in the soft x-ray range.

The influence on Nickel-like Molybdenum soft-x-ray laser performance and stability of a low energy laser prepulse arriving prior to the main laser pumping pulses is experimentally investigated. A promising regime for 10 Hz operation has been observed. A four times increase in soft-x-ray laser operation time with a same target surface is demonstrated. This soft-x-ray laser operation mode corresponds to an optimum delay between the prepulse and the main pulses and to a prepulse energy greater than 20 mJ. We also show that this regime is not associated with a weaker degradation of the target or any reduced ablation rate. Therefore the role of preplasma density gradient in this effect is discussed.

Un article est recemment paru dans le journal “Nature Physics” sous le nom “Laser-driven amplification of soft X-rays by parametric stimulated emission in neutral gases” [1]. Suite a l’observation experimentale de la croissance exponentielle du signal harmonique en fonction de la pression de gaz, les auteurs annoncent que seule une nouvelle theorie qu’ils appellent “XPA” pour (X-ray parametric amplification) permet d’expliquer le resultat. Or dans ce qui suit nous montrons qu’une etude detaillee de l’accord de phase dans le cadre de la theorie classique de la generation d’harmoniques d’ordres eleves permet de reproduire parfaitement et d’expliquer la croissance exponentielle du signal harmonique en fonction de la pression par l’augmentation de la longueur de coherence due a la dispersion atomique.

LASERIX is a french high-repetition rate laser facility devoted to the realisation of performed XUV laser sources and their use for applications. In this paper we describe the present status and the perspectives of use of LASERIX in the high-repetition rate configuration and the high-Energy one.

International audience; We present what we believe to be the first measurement of the spectral properties of a soft x-ray laser seeded by a high-order harmonic beam. Using an interferometric method, the spectral profile of a seeded Ni-like krypton soft x-ray laser (32.8 nm) generated by optical field ionization has been experimentally determined, and the shortest possible pulse duration has been deduced. The source exhibits a Voigt spectral profile with an FWHM of 3.1±0.3 mÅ, leading to a Fourier-transform pulse duration of 4.7 ps. This value is comparable with the upper limit of the soft x-ray pulse duration determined by experimentally investigating the gain dynamics, from which we conclude that the source has reached the Fourier limit. The measured bandwidth is in good agreement with the predictions of a radiative transfer code, including gain line narrowing and saturation rebroadening.

Proposed as satellite-based weapons during the 1980s, X-ray lasing was for a long time only achieved with enormous amounts of pump energy in either nuclear explosions or at kilojoule-class laser installations. During the last few years a tremendous development was achieved, most visible in the realisation of the FEL lasers at DESY and SLAC. As important for a wider applicability is the enormous reduction in pump energy for laser pumped plasma X-ray lasers, which now brings such devices into the range of applications for diagnostics and spectroscopy even in smaller laboratories. Main developments were the transient excitation scheme and the optimized pumping concepts. This paper concentrates on developments at the GSI Helmholtzcenter at Darmstadt aiming towards reliable X-ray laser sources in the range from 50 to several 100 eV. The main driving forces for the laser development at GSI are the possible application for the spectroscopy of Li-like ions in the storage ring ESR and the future storage ring NESR at FAIR, and the interest in novel plasma diagnostics.

Resume. The LASERIX facility provides coherent and short soft x-ray beams for scientific applications. The beams are generated through high intensity laser interaction with matter using two different schemes, plasma based soft x-ray lasers, and high order laser harmonic generation. We describe in this communication the present status of the facility. The experimental setup composed of a terawatt titanium-sapphire laser and of different IR/XUV conversion devices is briefly described. The LASERIX beamtime has been recently opened to external users. We present two typical experiments performed in that context with the facility. The first one is dedicated to the fundamental study of the plasma based soft x-ray laser, whereas the second uses the existing beam to study irradiation induced damages in DNA samples. The future evolution of the facility, including enhancement of the laser energy is finally presented.

Caracterisation spatio-temporelle d’un laser XUV injecte J.-P. Goddet1, S. Sebban1, O. Guilbaud2, G. Maynard3, B. Cros3, J. Gautier1, Ph. Zeitoun1, C. Valentin1, F. Tissandier1, T. Marchenko1, G. Lambert1, D. Benredjem2, A. Boudaa3, A. Klisnick2, D. Ros2, S. Kazamias2, K. Cassou2,3, J. Habib2, G. Jamelot2, J.-C. Lagron2, D. Joyeux4, S. De Rossi4, D. Phalippou4, F. Delmotte4, M.F. Ravet4, A. Calisti5, T. Mocek6, M. Kozlova6 et K. Jakubczak6

International audience; A soft x-ray laser from Ni-like Mo, pumped in grazing incidence (GRIP), is analyzed with regard to high repetition rate operation. Reliable lasing is obtained, but with significant energy fluctuations attributed mainly to beam pointing jitter from the pump laser. Two modes of operation are compared: continuously moving target and stationary target. With a moving target the soft X-ray output is constant on average, whereas the repeated use of the same target position leads to a pulse energy which increases for several tens of shots. This effect might be caused by improved guiding of the pump laser in the formed groove and the removal, through laser ablation, of the oxide layer on the target surface.

International audience; We report the near-field imaging characterization of a 10 Hz Ni-like 18.9 nm molybdenum soft-x-ray laser pumped in a grazing incidence pumping (GRIP) geometry with a table-top laser driver. We investigate the effect of varying the GRIP angle on the spatial behavior of the soft-x-ray laser source. After multiparameter optimization, we were able to find conditions to generate routinely a high-repetition-rate soft-x-ray laser with an energy level of up to 3 μJ/pulse and to 6×1017 photons/s/mm2/mrad2/(0.1% bandwidth) average brightness and 1×1028 photons/s/mm2/mrad2/(0.1% bandwidth) peak brightness.

International audience; A novel multilayer mirror was designed and fabricated based on a recently developed three-material technology aimed both at reaching reflectivities of about 20% and at controlling dispersion over a bandwidth covering photon energies between 35 and 50 eV. The spectral phase upon reflection was retrieved by measuring interferences in a two-color ionization process using high-order harmonics produced from a titanium: sapphire laser. We demonstrate the feasibility of designing and characterizing phase-controlled broadband optics in the extreme-ultraviolet domain, which should facilitate the manipulation of attosecond pulses for applications.

International audience; Au LOA, nous avons réalisé la première chaîne d'amplification laser fonctionnant dans la gamme spectrale XUV. La chaîne est constituée d'une source, d'un relais d'image et d'un amplificateur. La source de génération d'harmoniques d'ordre élevé avait de bonnes qualités optiques, tandis que l'amplificateur produit intrinsèquement des impulsions de forte énergie. Afin de garder les qualités optiques de la source durant l'amplification, le laser X était pompé par ionisation par effet de champs dans un gaz neutre. La métrologie de ce laser X injecté a permis de mesurer une énergie de sortie de 0.7 µJ et un haut degré de cohérence et de polarisation. La durée de l'impulsion a été estimée à 500 fs. On peut espérer atteindre un éclairement de 1.5x10^16 Wcm^-2 en focalisant le faisceau.

International audience; Afin de contrôler la génération d'harmoniques d'ordre élevé dans des conditions optimisées, nous avons réalisé des expériences préliminaires de contrôle spectral et spatial du laser infrarouge. Nous avons démontré la possibilité de modifier la longueur d'onde des harmoniques grâce à la modification de la phase spectrale du laser infrarouge par un modulateur acousto-optique « Dazzler ». Nous montrons que cette méthode permet d'obtenir un spectre plus large et un flux de photon intégré beaucoup plus important qu'en utilisant une simple modification de la dérive de fréquence du laser. Nous présentons également les premiers résultats de mise en forme de la tache focale du laser par optique adaptative, et l'effet de ce contrôle spatial sur la génération d‘harmoniques.

International audience; We give on overview of recent advances in collisionally pumped optical field-ionization soft X-ray lasers developed at LOA. Saturated amplification has been achieved on the 5d-5p transition in Xe^8+ at 41.8 nm, and on the 4d-4p transition in Kr^8+ at 32.8 nm. We demonstrate a significant increase of the energy output from the Xe^8+ laser driven within two types of wave-guide. Finally, we present results of a pioneering work aimed to set up and characterize the first true soft X-ray laser chain.

International audience; Nous présentons des résultats expérimentaux de spectre d'harmoniques anormales d'ordre élevé générées à basse intensité laser (2 10^13 W/cm^2) dans l'argon. Ce spectre ne peut pas être expliqué par le modèle classique à trois étapes qui prédit les caractéristique du spectre . Les ordres observés dans notre mesure vont bien au delà de la limite de la coupure donnée par l'intensité du laser dans le milieu gazeux. De plus, nous n'observons pas les ordres très bas. Nous présentons une étude systématique de ces spectres, ainsi que des simulations numériques issues de la résolution de l'équation de Schrödinger dépendante du temps.

International audience; We use a train of sub-200 attosecond extreme ultraviolet (XUV) pulses with energies just above the ionization threshold in argon to create a train of temporally localized electron wave packets. We study the energy transfer from a strong infrared (IR) laser field to the ionized electrons as a function of the delay between the XUV and IR fields. When the wave packets are born at the zero crossings of the IR field, a significant amount of energy (∼20 eV) is transferred from the field to the electrons. This results in dramatically enhanced above-threshold ionization in conditions where the IR field alone does not induce any significant ionization. Because both the energy and duration of the wave packets can be varied independently of the IR laser, they are valuable tools for studying and controlling strong-field processes.

International audience; Nous présentons une étude complète de l'influence de la diaphragmation du faisceau infrarouge sur la génération d'harmoniques d'ordres élevés. Nous avons mesuré l'efficacité de conversion obtenue dans différents gaz et pour différentes énergies laser en fonction de l'ouverture du diaphragme. Les courbes ainsi déduites présentent un caractère assez général : le maximum d'efficacité de conversion se détache nettement des valeurs obtenues pour des ouvertures de diaphragme trop importantes : un facteur 25 d'amélioration est obtenu entre le cas sans diaphragmation et le cas optimal. Une simulation basée sur un code uni-dimensionnel de calcul d'accord de phase dépendant du temps permet de reproduire fidèlement les résultats expérimentaux. Nous pouvons ainsi conclure que l'ouverture optimale du diaphragme est celle qui réalise le meilleur compromis entre la géométrie focale dont découle l'accord de phase (qui aurait tendance à favoriser des diaphragmes fermés) et l'amplitude et la phase du dipôle harmonique (qui sont favorisées par des diaphragnies ouverts).

A new compact scheme for a double-stage seeded x-ray laser is demonstrated. This laser is offering greatly improved beam quality and brilliance making it a useful tool for applications.

International audience; Experimental results of a two-stage Ni-like Ag soft X-ray laser operated in a seed-amplifier configuration are presented. Both targets were pumped applying the double-pulse grazing incidence technique with intrinsic travelling wave excitation. The injection of the seed X-ray laser into the amplifier target was realized by a spherical mirror. The results show amplification of the seed X-ray laser and allow for a direct measurement of the gain lifetime. The experimental configuration is suitable for providing valuable input for computational simulations. (C) 2012 Optical Society of America

The quest for a compact X-ray laser has long been a major objective of laser science. Several schemes using optical undulators are currently considered, in order to trigger the amplification of backscattered radiation, in Compton or inverse Compton regime [37, 38]. We have proposed a new concept of compact XFEL based on a combination between the physics of free electron lasers, of laser-plasma interactions, and of nonlinearoptics [39]. In this thesis, we study the necessary steps to trigger a X-ray laser during the interaction between a free relativistic electron bunch and an optical lattice created by the interference of two intense transverse laser pulses. For this purpose I developed a particular traking code dubbed RELIC. RELIC allowed us to study the dynamics and injection process of a bunch of relativistic electrons into the optical lattice [50]. Thanksto RELIC, we distinguished several interaction regimes depending on the relativistic electron bunch parameters, and on those of the optical lattice and its geometry. These studies are applied to the X ray amplification and supported by PIC simulations. RELIC also allowed us to model and analyze the first experiment conducted in october 2015 on the ”Salle Jaune” laser facility at LOA. This first experiment was very important tovalidate our theoretical models, and should prove to be an essential milestone for the development of a Raman X-ray free electron laser. [52]., L’obtention d’un Laser à Électrons Libres X (LEL-X) compact est un objectif majeur pour le développement des lasers. Plusieurs schémas prometteurs de LEL-X ont été proposés en utilisant à la fois l’accélération d’électrons dans les plasmas et des onduleurs optiques en régime Compton ou Compton inverse [37, 38]. Nous avons proposé un nouveau concept de LEL-X compact baptisé Raman XFEL [39], en combinant la physique des LEL en régime Compton, des lasers XUV conventionnels basés sur l’interaction laser-plasma, et de l’optique non-linéaire. Nous étudions dans cette thèse les étapes préalables pour déclencher un effet laser à rayons X lors de l’interaction entre un paquet d’électronslibres relativistes et un réseau optique créé par l’interférence transverse de deux impulsions laser intenses. Dans cet objectif j’ai développé un code particulaire baptisé RELIC. Les études menées avec le code RELIC nous ont permis d’étudier la dynamique d’électrons relativistes et les processus d’injection du paquet d’électrons dans le réseau optique [50]. Grâce à RELIC, nous avons distingué de nouveaux régimes d’interaction [51] en fonction des paramètres du paquet d’électrons, ainsi que de la géométrie du réseau optique. Ces études ont été appliquées à l’amplification du rayonnement X et appuyées par des simulations PIC. RELIC a également permis de modéliser et d’analyser la première expérience réalisée en octobre 2015 sur l’installation laser ’Salle Jaune’ au Laboratoire d’Optique Appliquée (LOA). Cette première expérience a été une étape très importante pour la validation des modèles théoriques, et pour la réalisation future d’un laser à électrons libre X Raman [52].

The interaction of an intense laser pulse of short duration with a rare gas induces a highly non-linear polarization in the XUV spectral range: the high order harmonics. Due to the specific properties of the harmonic radiation and its applications, this issue is particularly rich and fertile. The efficient production of high order harmonics is based both on the non-linear response of the single atom and on collective behavior.The principle of the research presented in this thesis is the understanding and control of phase matching or quasi-phase matching in the presence of substantial ionization in the generating gas. In this context, we show the importance of the coherence length on the phase matching in High harmonic generation. We study its dependence on laser focusing, pressure but also its time dependence related to ionization. Moreover, experiments and simulations aim at extending harmonic spectra towards shorter wavelengths, a spectral range for which the X Ray Laser is emitted. This will give access to a source with complementary characteristics as regards to X-ray lasers. This source shall be developed in parallel on the LASERIX station or injected in soft X-ray laser amplifiers., L'interaction d'une impulsion laser intense (~10¹⁴ W /cm²) et de courte durée (femtoseconde) avec un gaz rare induit une polarisation hautement non-linéaire dans le domaine spectral XUV; les harmoniques d'ordre élevés. En raison des propriétés spécifiques du rayonnement harmonique et de ses applications, cette thématique est particulièrement riche et fertile. La production efficace d'harmoniques d'ordres élevés repose à la fois sur la réponse non-linéaire de l'atome unique et un comportement collectif.Le fil directeur des études présentées dans cette thèse est la compréhension et le contrôle de l'accord de phase ou du quasi accord de phase en présence d'une ionisation substantielle du gaz générateur. Dans ce contexte, nous montrons l'importance de la longueur de cohérence sur l'accord de phase en génération d'harmoniques. Nous étudions sa dépendance en fonction de la focalisation du laser, de la pression mais aussi sa dépendance temporelle liée à l'ionisation, effet que nous avons mis en évidence lorsqu'on a cherché à optimiser une double impulsion harmonique. Le travail de développement, sur la station LASERIX, de la source à double impulsion harmonique générée à partir d'un même milieu gazeux et avec un délai picoseconde variable est présenté. Cette source possède un véritable potentiel d'applications scientifiques, injectée dans un milieu amplificateur plasma qu'on appelle laser X, la double impulsion permettra de sonder la réponse temporelle de ce type de milieu. Par ailleurs, des expériences et des simulations menées sur la génération d'harmoniques en propagation guidée visent ainsi à étendre les spectres harmoniques vers les courtes longueurs d'ondes, zone spectrale pour laquelle le laser X à plasmas est émis. Ceci donnera l'accès à une source offrant des caractéristiques complémentaires des lasers X, sources développées en parallèle sur la station LASERIX.

Chirality is a geometric property that characterizes objects that cannot be superposed on their mirror image. Our hands are an emblematic example of this, since they exist in two different forms, right and left. While chirality is observed at all scales in the universe, it plays a particularly important role in chemistry. A chiral molecule and its mirror image can react differently with their environment and be therapeutic or toxic. These effects obviously have immense repercussions on the animal and plant kingdom. It then becomes clear that it is essential to study precisely the dynamics of chiral chemical reactions.In this thesis, we studied the ultrafast dynamics of chiral molecules by laser sources of femtosecond duration (10⁻¹⁵s). Molecular chirality is generally difficult to detect, so we have used a recent technique, circular photoelectron dichroism (PECD), to generate a very important chiral signal. We have thus observed ultrafast molecular dynamics at the attosecond scale (10⁻¹⁸s), and highlighted relaxation and ionization dynamics never observed before.In parallel to these time-resolved studies, we have developed several experiments using a new high repetition rate, high mean power Yb fiber laser. We have developed a new method, by extending the PECD, that has allowed us to measure the composition of chiral samples quickly and accurately. Finally, we have developed an ultra-short XUV beamline with very high brightness (∽2mW). This source, coupled with a photoelectron and photoion coincidence detector, will be used to study chiral recognition mechanisms.; La chiralité est une propriété géométrique caractérisant les objets qui ne sont pas superposables à leur image dans un miroir. Nos mains en sont un exemple emblématique, puisqu’elles existent sous deux formes différentes droite et gauche. Si la chiralité s'observe à toutes les échelles de l'univers, elle joue un rôle particulièrement important en chimie. Une molécule chirale et son image miroir peuvent réagir différemment avec leur environnement et être thérapeutiques ou toxiques. Ces effets ont évidemment d'immenses répercussions sur le règne animal et végétal. Il apparaît alors clairement qu'il est essentiel d’étudier précisément les dynamiques des réactions chimiques chirales.Dans cette thèse, nous avons étudié les dynamiques ultrarapides de molécules chirales par des sources lasers de durée femtosecondes)(10⁻¹⁵s). La chiralité moléculaire étant généralement difficile à détecter, nous avons ici utilisé une technique récente, le dichroïsme circulaire de photoélectrons (PECD) qui permet de générer un signal chiral très important. Nous avons ainsi observé des dynamiques moléculaires ultrarapides jusqu'à l'échelle attoseconde (10⁻¹⁸s), et mis en avant des dynamiques de relaxation et d'ionisation encore jamais observées.Parallèlement à ces études résolues en temps, nous avons développé plusieurs expériences employant une nouvelle source laser Yb fibrée à haute cadence et grande puissance moyenne. Nous avons développé une nouvelle méthode, par extension du PECD, qui nous a permis de mesurer la compositions d'échantillons chiraux rapidement avec une grande précision. Enfin, nous avons développé une ligne de lumière XUV ultrabrève de très haute brillance (∽2mW). Cette source, couplée à un détecteur de photoélectrons et photoions en coïncidence, servira à étudier les mécanismes de reconnaissance chirale.

In this joint thesis, performed between the French Institute CENBG (Bordeaux) and the Canadian Institute INRS (Varennes), laser driven ion acceleration and an application of the beams are studied. The first part, carried out at CENBG and on the PICO2000 laser facility of the LULI laboratory, studies both experimentally and using numerical particle-in-cell (PIC) simulations, the interaction of a high power infrared laser with a high density gas target. The second part, performed at ALLS laser facility of the EMT-INRS institute, investigates the utilization of laser generated beams for elementary analysis of various materials and artifacts. In this work, firstly the characteristics of the two lasers, the experimental configurations, and the different employed particle diagnostics (Thomson parabolas, radiochromic films, etc.) employed are introduced.In the first part, a detailed study of the supersonic high density gas jets which have been used as targets at LULI is presented, from their conceptual design using fluid dynamics simulations, up to the characterization of their density profiles using Mach-Zehnder interferometry. Other optical methods such as strioscopy have been implemented to control the dynamics of the gas jet and thus define the optimal instant to perform the laser shot. The spectra obtained in different interaction conditions are presented, showing maximum energies of up to 6 MeV for protons and 16 MeV for Helium ions in the laser direction. Numerical simulations carried out with the PIC code PICLS are presented and used to discuss the different structures seen in the spectra and the underlying acceleration mechanisms.The second part presents an experiment using laser based sources generated by the ALLS laser to perform a material analysis by the Particle-induced X-ray emission (PIXE) and X-ray fluorescence (XRF) techniques. Proton and X-ray beams produced by the interaction of the laser with Aluminum, Copper and Gold targets were used to make these analyzes. The relative importance of XRF or PIXE is studied depending on the nature of the particle production target. Several spectra obtained for different materials are presented and discussed. The dual contribution of both processes is analyzed and indicates that a combination improves the retrieval of constituents in materials and allows for volumetric analysis up to tens of microns on cm^2 large areas, up to a detection threshold of ppms., Cette thèse en cotutelle entre la France et le Canada étudie l’accélération d’ions dans l’interaction laser-plasma. La première partie, réalisée au CENBG et sur l’installation PICO2000 du laboratoire LULI à l'École Polytechnique de Palaiseau, présente des études expérimentales, complétées par des simulations numériques de type Particle-In-Cell, portant sur l’accélération d’ions dans l'interaction d'un laser infrarouge de haute puissance avec une cible gazeuse de haute densité. La seconde, réalisée avec le laser ALLS de l’institut EMT INRS, concerne le développement d'une application des faisceaux génerés par laser pour l’analyse élémentaire d’échantillons. Dans le manuscrit, les caractéristiques des deux lasers, des différents diagnostics de particules et d’X utilisés (paraboles de Thomson, films radiochromiques, CCD...) ainsi que les configurations expérimentales sont décrites.Les jets de gaz denses supersoniques utilisés comme cibles d'interaction laser au LULI, sont présentés en détail; depuis leur conception grâce à des simulations de dynamique des fluides, jusqu’à la caractérisation de leurs profils de densité par interférométrie Mach Zehnder. D'autres méthodes optiques comme la strioscopie ont été mises en œuvre pour contrôler la dynamique du jet de gaz et définir l’instant optimal pour effectuer le tir laser. Les spectres obtenus dans differentes conditions d’interaction sont présentés. Ils montrent, dans la direction du laser, des énergies maximales allant jusqu’à 6 MeV pour les protons et 16 MeV pour les ions hélium. Des simulations numériques effectuées avec le code PICLS sont utilisées pour discuter les différentes structures observées dans les spectres et les mécanismes d’interaction sous jacents.Des faisceaux de protons et d’X générés par le laser ALLS dans l’interaction avec des cibles solides d’aluminium, de cuivre et d’or ont été utilisés pour effectuer des analyses de matériaux par les méthodes Particle-induced X-ray emission (PIXE) et X-ray fluorescence (XRF). L’importance relative des deux techniques, XRF et PIXE, est étudiée en fonction de la nature de la cible d’interaction. Les deux diagnostics peuvent être implémentés simultanément ou individuellement, en changeant simplement la cible d'interaction. La double contribution des deux processus améliore l’identification des constituants des matériaux et permet une analyse volumétrique jusqu'à des dizaines de microns et sur de grandes surfaces (~cm2) jusqu'à un seuil de détection de quelques ppms.