High harmonic generation (HHG) in solids has two main applications. First, HHG is an all-solid-state source of coherent attosecond very ultraviolet (VUV) radiation. As such, it presents a promising source for attosecond science. The ultimate goal of attosecond science is to make spatially and temporally resolved movies of microscopic processes, such as the making and breaking of molecular bonds. Second, the HHG process itself can be used to spatially and temporally resolve fast processes in the condensed matter phase, such as charge shielding, multi-electron interactions, and the dynamics and decay of collective excitations. The main obstacles to realize these goals are: the very low efficiency of HHG in solids and incomplete understanding of the ultrafast dynamics of the complex many-body processes occurring in the condensed matter phase. The theoretical analysis developed in this thesis promises progress along both directions. First, it is demonstrated that nanoengineering by using lower-dimensional solids can drastically enhance the efficiency of HHG. The effect of quantum confinement on HHG in semiconductor materials is studied by systematically varying the confinement width along one and two directions transverse to the laser polarization. Our analysis shows growth in high harmonic efficiency concurrent with a reduction of ionization. This decrease in ionization comes as a consequence of an increased band gap resulting from the confinement. The increase in harmonic efficiency results from a restriction of wave packet spreading, leading to greater re-collision probability. Consequently, nanoengineering of one and two-dimensional nanosystems may prove to be a viable means to increase harmonic yield and photon energy in semiconductor materials driven by intense laser fields. Thus, it will contribute towards the development of reliable, all-solid-state, small-scale, and laboratory attosecond pulse sources. Second, it is shown that HHG from impurities can be used to tomographically reconstruct impurity orbitals. A quasi-classical three-step model is developed that builds a basis for impurity tomography. HHG from impurities is found to be similar to the high harmonic generation in atomic and molecular gases with the main difference coming from the non-parabolic nature of the bands. This opens a new avenue for strong field atomic and molecular physics in the condensed matter phase and allows many of the processes developed for gas-phase attosecond science to be applied to the condensed matter phase. As a first application, my conceptual study demonstrates the feasibility of tomographic measurement of impurity orbitals. Ultimately, this could result in temporally and spatially resolved measurements of electronic processes in impurities with potential relevance to quantum information sciences, where impurities are prime candidates for realizing qubits and single photon sources. Although scanning tunneling microscope (STMs) can measure electron charge distributions in impurities, measurements are limited to the first few surface layers and ultrafast time resolution is not possible yet. As a result, HHG tomography can add complementary capacities to the study of impurities.

Strong field approximation (SFA) is the most important approximation in the analytical theory of intense laser matter interaction. Based on SFA many analytical theories have been developed such that a broad spectrum of strong field physics phenomena can be described. The central idea of SFA-based theories is to approximate the electron propagation in the continuum by the Gordon-Volkov wavefunction - a well studied analytical solution to the time-dependent Schr\"{o}dinger equation where the electron is driven by the laser field only. This approximation captures some of the essential features of strong-field physics, but at the same time causes several problems in the theory. In this thesis a comprehensive study of the SFA has been presented. We introduce the SFA in both the length gauge and the velocity gauge. The adequacy of SFA has been discussed by comparing the theory to the numerical solution to the time-dependent Schr\"{o}dinger equation (TDSE). The numerical method of solving TDSE is presented as a separate chapter. In order to obtain a better understanding of the applicability of SFA-based theory, we tested the major approximations in the theory by using three different models: the zero-range potential, the hydrogen atom and the hydrogen molecular ion. The accuracy of the method of steepest descent (MSD) and other major approximations in the analytical theory have also been examined. Targeting at the generalization of the SFA-based theories, several extensions and improvements of SFA have been proposed. We will review them in detail and bring them into unity. One of the most successful aspect of the SFA-based theories is to describe and decompose electron dynamics into components such that identification of different physical processes becomes possible. For instance, the direct ionization and non-sequential double ionization bear clear definitions only within the SFA-based framework. The physical interpretation becomes more straight forward due to the fact that there is a close connection between the quantum orbital and classical trajectory. The MSD is a mathematical tool to bridge the quantum orbital and the classical trajectory in an SFA-based theory. We will discuss MSD within a systematic framework so that the higher order asymptotic expansion terms can be obtained in a straight forward way. After gaining substantial understanding of the SFA and the MSD we developed a graphic user interface (GUI) software that is capable of calculating strong field ionization rates, photo-electron spectra and high harmonic generation spectra. The software interface and algorithms have been presented in the thesis. Sample calculations were done and compared with the previously obtained results. In the last chapter of the thesis, we further developed the theory to describe a two-laser ionization scheme where one laser is chosen to be resonantly coupled two real states and the other is a strong few-cycle laser pulse. We demonstrate the periodic dependence of the total ionization on the appearance time of the strong few-cycle laser pulse. In the case of few-cycle pulses with lower intensity, we observed side-bands in the photoelectron spectrum, whose intensity vary periodically with the appearance time of the pulse. We show that our extended theory is able to explain these phenomena adequately.

Strong field approximation (SFA) is the most important approximation in the analytical theory of intense laser matter interaction. Based on SFA many analytical theories have been developed such that a broad spectrum of strong field physics phenomena can be described. The central idea of SFA-based theories is to approximate the electron propagation in the continuum by the Gordon-Volkov wavefunction - a well studied analytical solution to the time-dependent Schr\"{o}dinger equation where the electron is driven by the laser field only. This approximation captures some of the essential features of strong-field physics, but at the same time causes several problems in the theory. In this thesis a comprehensive study of the SFA has been presented. We introduce the SFA in both the length gauge and the velocity gauge. The adequacy of SFA has been discussed by comparing the theory to the numerical solution to the time-dependent Schr\"{o}dinger equation (TDSE). The numerical method of solving TDSE is presented as a separate chapter. In order to obtain a better understanding of the applicability of SFA-based theory, we tested the major approximations in the theory by using three different models: the zero-range potential, the hydrogen atom and the hydrogen molecular ion. The accuracy of the method of steepest descent (MSD) and other major approximations in the analytical theory have also been examined. Targeting at the generalization of the SFA-based theories, several extensions and improvements of SFA have been proposed. We will review them in detail and bring them into unity. One of the most successful aspect of the SFA-based theories is to describe and decompose electron dynamics into components such that identification of different physical processes becomes possible. For instance, the direct ionization and non-sequential double ionization bear clear definitions only within the SFA-based framework. The physical interpretation becomes more straight forward due to the fact that there is a close connection between the quantum orbital and classical trajectory. The MSD is a mathematical tool to bridge the quantum orbital and the classical trajectory in an SFA-based theory. We will discuss MSD within a systematic framework so that the higher order asymptotic expansion terms can be obtained in a straight forward way. After gaining substantial understanding of the SFA and the MSD we developed a graphic user interface (GUI) software that is capable of calculating strong field ionization rates, photo-electron spectra and high harmonic generation spectra. The software interface and algorithms have been presented in the thesis. Sample calculations were done and compared with the previously obtained results. In the last chapter of the thesis, we further developed the theory to describe a two-laser ionization scheme where one laser is chosen to be resonantly coupled two real states and the other is a strong few-cycle laser pulse. We demonstrate the periodic dependence of the total ionization on the appearance time of the strong few-cycle laser pulse. In the case of few-cycle pulses with lower intensity, we observed side-bands in the photoelectron spectrum, whose intensity vary periodically with the appearance time of the pulse. We show that our extended theory is able to explain these phenomena adequately.

Ce manuscrit de thèse s'articule autour de l'étude de l'interaction entre des impulsions lumineuses ultra brèves et des atomes ainsi que des molécules polyatomiques et chirales en phase gazeuse. En utilisant des techniques développées en physique attoseconde ainsi qu'en femtochimie, notre objectif général est de parvenir à une meilleure compréhension des dynamiques ultrarapides photoinduites dans la matière. Pour ce faire, nous avons développé des sources de lumière à ultra brèves dans le proche infrarouge et l’infrarouge moyen, qui ont été utilisées pour construire une source de rayons X dans la fenêtre de l’eau, basée surla génération d'harmoniques d’ordre élevé (GHOE), ainsi que pour l’étude de nouveaux canaux de GHOE impliquant des états hautement excités (Rydberg). Cette dernière étude a démontré une émission harmonique via l'ionisation depuis des états de Rydberg et la recombinaison radiative sur l'état fondamental, attirant ainsi notre intérêt pour le rôle des états de Rydberg en physique des champs forts. Cela nous a conduit à étudier la décroissance libre de l’induction XUV de paquets d'ondes électroniques comme une nouvelle technique de spectroscopie 2D. De plus, nous avons découvert que l'interaction entre un laser intense et un atome préparé dans une superposition cohérente d'états électroniques peut conduire à la génération de lignes hyper-Raman concomitantes avec la GHOE standard. Ce mécanisme avait été prédit lors des premiers calculs théoriques de GHOE, mais n'avait jamais été démontré expérimentalement. Par la suite, nous nous sommes intéressé à l’étude de systèmes moléculaires, dans lesquelles une excitation électronique induite par la lumière peut déclencher des dynamiques nucléaires. Nous avons étudié la photo isomérisation non-adiabatique de l’acétylène cationique en vinylidène cationique ainsi que le contrôle cohérent de la localisation électronique lors de la photodissociation de H2+. La simplicité de ces systèmes moléculaires a permis la comparaison des résultats expérimentaux avec des calculs théoriques de pointe,révélant l'importance du couplage entre les degrés de liberté nucléaires et électroniques lors de dynamiques moléculaires photoinduites.Un autre pilier majeur de cette thèse est l'étude de l'ionisation de molécules chirales avec des impulsions chirales. On sait depuis les années 70 que l'ionisation d'un ensemble de molécules chirales aléatoirement orientées, en utilisant une impulsion polarisée circulairement, conduit à une forte asymétrie avant-arrière dans le nombre de photoélectrons émis, selon l'axe de propagation de la lumière (DichroismeCirculaire de Photoélectron, DCPE). Avant cette thèse, le DCPE a été largement étudié à l’aide du rayonnement synchrotron (ionisation à un photon) et a récemment été démontré avec des lasers femtoseconde, via des schémas d'ionisation multiphotonique. Dans cette thèse, nous avons montré que le DCPE est un effet universel, c'est-à-dire qu'il émerge dans tous les régimes d'ionisation: l'ionisation àun photon, l'ionisation à multiphonique, l'ionisation au-dessus du seuil ainsi que l’ionisation par effet tunnel. Ensuite, nous avons démontré que la combinaison d’approches standard de femtochimie et du DCPE peuvent être utilisées pour suivre des dynamique de molécules chirales photoexcitées. En utilisant des approches expérimentales similaires, avec des séquences d'impulsions ayant des états de polarisation contre-intuitifs, nous avons démontré un nouvel effet chiroptique, appelé Dichroïsme Circulaire de Photoexcitation (DCPX), qui est décrit par un courant électronique directionnel et chirosensible, lorsque plusieurs niveaux sont peuplés de manière cohérente avec de la lumière chirale. Enfin, nous avons introduit une perspective temporelle à la photoionisation chirale en mesurant l'asymétrie avant arrièredes retards de photoionisation dans les molécules chirales photoionisées par des impulsions lumineuses chirales. / This thesis manuscript is articulated around the investigation of the interaction between ultrashort light pulses and gas-phase atoms, polyatomic and chiral molecules. Using the toolboxes developed in attosecond and strong-field physics as well as in femtochemistry, our general goal is to reach a better understanding of subtle effects underlying ultrafast light-induced dynamics in matter.To do so, we developed cutting-edge near-infrared and mid-infrared few-cycle light sources, which were used to build a water-window soft-X-ray source based on high order harmonic generation (HHG), as well as to study new HHG channels involving highly-excited (Rydberg) states. The latter study revealed a delayed HHG emission from the ionization of Rydberg states and radiative recombination onto the electronicground state, triggering our interest in the role of Rydberg states in strong-field physics. This led us to investigate the laser-induced XUV Free Induced Decay from electronic wave packets as a new background-free 2D spectroscopic technique.More over, we have found out that strong-field interaction with a well prepared coherent superposition of electronic states led to the generation of hyper-Ramanlines concomitant with standard high-order harmonics. These spectral features were predicted in the early-days theoretical calculations of HHG but had never been reported experimentally.After these experiments in rare gas atoms, we moved to molecular targets, in whichlight-induced electronic excitation can trigger nuclear dynamics. Using simple benchmark molecules, we have studied dynamics involving the participation of both nuclear and electronic degrees of freedom: first, we studied the ultrafast non adiabatic photoisomerization of the acetylene cation into vinylidene cation, andsecond, we investigated the coherent control of electron localization during molecular photodissociation of H2+. The simplicity of these molecular targets enabled the comparison of the experimental results with state-of-the-art theoretical calculations,revealing the importance of the coupling between nuclear and electronic degrees of freedom in photoinduced molecular dynamics.The other major pillar of this thesis is the study of ionization of chiral molecules usingchiral light pulses. It has been known since the 70s that the ionization from an ensemble of randomly oriented chiral molecules, using circularly polarized light pulse,leads to a strong forward-backward asymmetry in the number of emitted photoelectrons, along the light propagation axis (Photoelectron Circular Dichroism,PECD). Prior to this thesis, PECD was widely studied at synchrotron facilities (single photonionization) and had recently been demonstrated using table-top lasers in resonant-enhanced multiphoton ionization schemes. In this thesis, we have shownthat PECD is a universal effect, i.e. that it emerges in all ionization regimes, from single photon ionization, to few-photon ionization, to above-threshold ionization, up to the tunneling ionization regime. This bridges the gap between chiral photoionizationand strong-field physics. Next, we have shown how the combination of standard femtochemistry approaches and PECD can be used to follow the dynamics of photoexcited chiral molecules using time-resolved PECD. Using similar experimental approaches, but by using pulse sequences with counter-intuitive polarization states,we have demonstrated a novel electric dipolar chiroptical effect, called Photoexcitation Circular Dichroism (PXCD), which emerges as a directional and chirosensitive electron current when multiple excited bound states of chiral molecules are coherently populated with chiral light. Last, we introduced a time-domain perspective on chiral photoionization by measuring the forward-backward asymmetry of photoionization delays in chiral molecules photoionized by chiral light pulses. Our work thus carried chiral-sensitive studies down to the femtosecond and attosecond ranges.

Depuis une vingtaine d’années, la physique attoseconde, via le phénomène de génération d’harmoniques d’ordres élevés (HHG), a permis de nombreuses avancées dans la compréhension des phénomènes de dynamique ultra-rapide. Les lasers femtoseconde émettant des impulsions de fortes énergies et de durées de quelques cycles optiques sont les outils indispensables à cette physique. De plus, la phase entre la porteuse et l’enveloppe (CEP) des impulsions doit être contrôlée. Récemment les lasers basés sur les fibres dopées ytterbium ont permis de transposer les expériences d’HHG à haute cadence. La stabilisation de la CEP pour ce type de systèmes constitue la brique manquante au développement de sources à haute cadence pleinement compatibles avec ces applications. Cette thèse a été consacrée à la stabilisation CEP d’un laser à fibre dopée ytterbium pour une application à la génération de rayonnement cohérent dans l’XUV à fort flux de photon. Dans la première partie nous présentons l’architecture d’une source à un taux de répétition de 100 kHz stable en CEP émettant des impulsions de 30 microjoules et 96 fs. Ce système constitue une preuve de principe pour les futures sources haute énergie. La stabilisation de CEP est assurée par une architecture hybride composée d’un injecteur stabilisé passivement suivi d’un amplificateur de puissance stabilisé activement. Un bruit résiduel de CEP inférieur à 400 mrad est obtenu dans différentes configurations, de la mesure courte durée (1 s) tir à tir jusqu’à la mesure sur une heure de fonctionnement. Dans la seconde partie nous présentons la mise au point d’une ligne HHG XUV optimisée à 13 nm sur les paramètres d’un laser à fibre, pour des applications à l’imagerie par diffraction cohérente. / In the last two decades, attosecond physics, based on the high harmonic generation (HHG) phenomenon, has allowed a better understanding of ultrafast dynamics in the microcosm. High-energy few-cycles carrier-envelope phase (CEP) stabilized sources are the main enabling tools for this physics. Recently, temporally compressed Ytterbium-doped fiber amplifiers have been successfully used as high XUV photon flux HHG drivers. CEP stabilization of these sources would ensure their full compatibility with attoscience. The thesis is devoted to the CEP stabilization of a high repetition rate Yb-doped fiber femtosecond source, for high XUV photon flux beamline applications. In the first part, we present the architecture of such a source at 100 kHz repetition rate delivering 30 microjoules 96 fs CEP-stable pulses. It constitutes a test bench for future energy-scaled few-cycle sources. The CEP stabilization is ensured in a hybrid architecture including a passively stabilized frontend followed by an actively stabilized power amplifier. A residual CEP noise <400 mrad is measured using various setups, including a shot-to-shot measurement over 1 s and a long-term stability over 1 h. In the second part, we discuss the design of a high flux HHG beamline optimized for a future generation of fiber-based driver at 13 nm for applications to coherent diffraction imaging.

No description available.

High harmonic generation (HHG) is a process that occurs when an intense laser interacts with a material and generates new frequencies of light. HHG has many practical applications, namely as a spectroscopy technique and source for high frequency light and attosecond pulses. While HHG has been done extensively in gases, HHG in solids is a relatively new field. Solids are appealing as an HHG medium as they require much simpler equipment and are subsequently much more compact, and thus may have a variety of applications previously inaccessible to gas-phase HHG. However, the generation mechanism of HHG in solids has not been fully characterized yet, as the processes behind HHG in gases and solids are not synonymous. Here, we study the influence of polarization, symmetry, and setup geometry on HHG in solids. We study the propagation effects in a transmission geometry setup and use Jones calculus to counteract the polarization change from propagation. We compare these results to a reflection geometry setup, which naturally does not have propagation effects, to determine the validity of the polarization correction technique. We also look at the electric field symmetry dependence on HHG through the manipulation of the laser electric field with a two-color interferometer. The impact of symmetry dependence and propagation effects both contribute to a better understanding of the HHG process in solids.

Lors de la focalisation d’un laser femtoseconde ultra-intense [I>10¹⁶W/cm²] sur une cible solide, dès le début de l’impulsion le champ laser est suffisant pour totalement ioniser la surface de la cible. Le reste de l’impulsion est ensuite réfléchi dans la direction spéculaire par le plasma dense ainsi créé : c’est un miroir plasma. Le champ laser ultra-intense peut accélérer les électrons au sein du plasma à des vitesses relativistes. Certains sont éjectés vers le vide et ces miroirs plasmas sont ainsi des sources de faisceaux d’électrons énergétiques. De plus, ils rayonnent dans l’extrême ultra-violet (XUV) à chaque période laser, ce qui se traduit par de la génération d’harmoniques d’ordre élevé de la pulsation laser. L’objectif de cette thèse est de mieux comprendre l’interaction laser-plasma sur miroirs plasmas à l’aide de la caractérisation de ces deux observables physiques qui en sont issues : les faisceaux d’électrons relativistes et les faisceaux d’harmoniques d’ordre élevé. Une première partie traite de la mesure des faisceaux harmoniques. Du fait des conditions physiques extrêmes d’interaction, la détection ne peut se faire qu’à une distance macroscopique de la cible. Ainsi la caractérisation des propriétés angulaires de ces faisceaux (réalisée en fonction des conditions d’interaction au cours de travaux précédents) ne fournit que des informations partielles sur l’interaction en elle-même. La ptychographie, une technique de mesure par diffraction cohérente où une sonde est diffractée par un objet, est ici transposée à la génération d’harmoniques sur miroirs plasmas grâce à la micro-structuration optique du plasma à la surface de la cible. Les champs sources harmoniques sont ainsi reconstruits en amplitude et en phase spatiales directement dans le plan cible. Grâce à ces mesures dans différentes conditions d’interaction, des modèles théoriques analytiques d’interaction en régime non relativiste [I<10¹⁸W/cm²] et relativiste [I>10¹⁸W/cm²] développés précédemment sont validés expérimentalement. Une seconde partie de cette thèse est consacrée à l’étude expérimentale des propriétés angulaires et en énergie des faisceaux d’électrons relativistes issus des miroirs plasmas. Une étude théorique et numérique, permet de prouver que ces mesures sont la première observation claire de l’accélération d’électrons relativistes par laser dans le vide (VLA). Enfin, l’étude simultanée des efficacités de génération des faisceaux d’électrons et d’harmoniques montre une corrélation nette entre les deux processus en régime relativiste. / When focusing an ultra-intense femtosecond laser pulse [I>10¹⁶W/cm²] onto a solid target, this target is ionized at the very beginning of the laser pulse. The resulting dense plasma then reflects the laser in the specular direction: it is a plasma mirror. The ultra-intense laser field can accelerate electrons within the plasma at relativistic speeds. Some are ejected towards the vacuum and these plasma mirrors are therefore sources of relativistic electron beams. Moreover, at each optical cycle they radiate in the form of extreme ultraviolet light, resulting in the generation of high-order harmonics of the laser frequency (HHG). The objective of this PhD is to understand laser-plasma interaction though the characterization of high-order harmonics and relativistic electron beams generated from plasma mirrors. The first part deals with harmonic beam measurement. Due to the extreme physical conditions during the interaction, detection can only be performed at macroscopic distance from target. Thus, the characterization of the harmonic beams’ angular properties (carried out as a function of interaction conditions in previous works) only provides partial information on the interaction itself. A technique of coherent diffraction imaging, named ptychography, which consists of diffracting a probe onto an object, is transposed to HHG on plasma mirrors by optically micro-structuring the plasma on a target surface. Harmonic fields are then reconstructed spatially in amplitude and phase directly in the target plane. Thanks to this measurement in different interaction conditions, previously developed theoretical analytical models in non-relativistic regime [I<10¹⁸W/cm²] and relativistic regime [I>10¹⁸W/cm²] are experimentally validated. The second part of the PhD is dedicated to the experimental characterization of angular and spectral properties of relativistic electron beams. A theoretical and numerical study shows that this constitutes the first clear observation of vacuum laser acceleration (VLA). Finally, a simultaneous study of harmonic and electron signals highlights a strong correlation between both processes in the relativistic regime.

No description available.

The curiosity of researchers to find novel characteristics and properties of matter constantly pushes for the development of instrumentation based on X-radiation. I present in this thesis techniques for electron spectroscopy based on developments of X-ray sources both in time structure and energy. One part describes a laser driven High-Harmonic Generation source and the application of an off-plane grating monochromator with additional beamlines and spectrometers. In initial experiments, the source is capable of producing harmonics between the 13th and 23rd of the fundamental laser 800 nm wavelength. The intensity in the 19th harmonic, after monochromatization, was measured to be above 1.2·1010 photons/second with a repetition rate of 5 kHz.  The development of a chopper system synchronized to the bunch clock of an electron storage ring is also presented. The system can be used to adjust the repetition rate of a synchrotron radiation beam to values between 10 and 120 kHz, or for the modulation of continuous sources. The application of the system to both time of flight spectroscopy and laser pump X-ray probe spectroscopy is shown. It was possible to measure triple ionization of Kr and in applied studies the valence band of a laser excited dye-sensitized solar cell interface. The combination of the latter technique with transient absorption measurements is proposed. The organic molecule maleic anhydride (MA) and its binding configuration to the three anatase TiO2 crystals (101), (100), (001) has been investigated by means of Xray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine structure Spectroscopy (NEXAFS). The results provide information on the binding configuration to the 101 crystal. High Kinetic Energy Photoelectron Spectroscopy was used to investigate multilayers of complexes of iron, ruthenium and osmium. The benefit of hard X-rays for ex-situ prepared samples is demonstrated together with the application of resonant valence band measurements to these molecules.