Photopolymerization is a technique used to create surface structures or microobjects from a photoresist. This process is started by illuminating the sample with a light of proper wavelength absorbed by the resist. After exposure, the sample is processed according to the type of the photoresist – be it heating, treating with developer or just washing the unaffected monomer with some reagent. Focused femtosecond laser beam with double wavelength can be used in the process. Short pulse length with high photon density starts two-photon absorption localized in the vicinity of focal point. The method resolution is thus increased and details with 1/10 micrometer size can be created. Moreover, very short laser pulse decreases the heat affected zone and the risk of thermal initiation is minimized. Manufacturing of larger structures composed of tiny details with two-photon photopolymerization is time-demanding process. Therefore, we have complemented the optical setup with spatial light modulator (SLM), which splits the incoming laser beam into several beams with holograms dynamically generated by a computer. Polymerization can be thus performed by multiple foci simultaneously which can be used to create separated microparticles or periodical surface structures. Additional speed improvement of the process can be substitution of static configuration, requiring sample replacement after each exposition, with continuous setup using microfluidic channel steadily supplied with photoresist transported to the active region of the sample.

Depuis la première observation de désaimantation ultra-rapide dans des films de Ni soumis à une excitation laser pulsée, on a assisté à un grand intérêt de comprendre l'interaction entre les impulsions laser ultra-courtes et l'aimantation. Ces études ont conduit à la découverte de la commutation toute optique de l'aimantation dans un alliage de film ferrimagnétique en utilisant des impulsions laser femtosecondes. La commutation toute optique permet un renversement de l’aimantation d’un matériau magnétique sans champ magnétique externe. La direction de l'aimantation résultante est donnée par la polarisation circulaire droite ou gauche de la lumière. La manipulation de l'aimantation par un faisceau laser a longtemps été limité à un seul type de matériau, mais ce mécanisme s'est avéré être un phénomène plus général qui s’applique à une grande variété de matériaux ferromagnétiques, y compris des alliages, des empilements et des hétérostructures, ainsi que des hétérostructures ferrimagnétiques synthétiques de terres-rares. Récemment, nous avons observé le même phénomène dans des films ferromagnétiques simples, ouvrant ainsi la voie à une intégration de l'écriture toute optique dans les dispositifs spintroniques. De plus, dans des matériaux de type [Co/Pt] ou [Co/Ni] avec une polarisation de spin élevée et une anisotropie magnétique perpendiculaire contrôlable, un mouvement de parois de domaines induit par un courant polarisé peut être observé dans des pistes magnétiques (couple spin-orbite ou couple de transfert de spin), ce qui présente un grand intérêt pour des applications spintroniques basse consommation et de densité élevée, telles que le concept de mémoire racetrack et la logique magnétique. Cependant, la densité de courant requise pour le mouvement des parois de domaines est encore trop élevée pour permettre la réalisation de dispositifs à faible puissance. Dans ce contexte innovant, la recherche effectuée dans le cadre de ma thèse s’est concentrée sur la manipulation de parois de domaines dans les pistes fabriquées à partir de films minces à forte anisotropie magnétique perpendiculaire en combinant à la fois les effets du courant polarisé et ceux de la commutation toute optique. Différents films minces ont été explorés afin d'étudier les effets combinés optiques dépendant de l'hélicité et des couples spin-orbite ou de transfert de spin sur le mouvement des parois de domaines. Nous avons montré que les parois de domaine peuvent rester piégées sous une hélicité circulaire du laser et dépiégées par une hélicité circulaire opposée, et la densité de courant polarisé seuil peut être considérablement réduite en utilisant un laser femtoseconde. Nos résultats sont prometteurs pour le développement de nouveaux dispositifs photoniques-spintroniques de faible puissance. / Since the first observation of ultrafast demagnetization in Ni films arising from a pulsed laser excitation, there has been a strong interest in understanding the interaction between ultrashort laser pulses and magnetization. These studies have led to the discovery of all-optical switching (AOS) of magnetization in a ferrimagnetic film alloy of GdFeCo using femtosecond laser pulses. All-optical switching enables an energy-efficient magnetization reversal of the magnetic material with no external magnetic field, where the direction of the resulting magnetization is given by the right or left circular polarization of the light. The manipulation of magnetization through laser beam has long been restricted to one material, though it turned out to be a more general phenomenon for a variety of ferromagnetic materials, including alloys, multilayers and heterostructures, as well as rare earth free synthetic ferrimagnetic heterostructures. Recently, we have observed the same phenomenon in single ferromagnetic films, thus paving the way for an integration of all-optical writing in spintronic devices. Moreover, in similar materials, like [Co/Pt] or [Co/Ni] with high spin polarization and tunable perpendicular magnetic anisotropy (PMA), efficient current-induced domain wall (DW) motion can be observed in magnetic wires, where spin-orbit torque (SOT) or spin transfer torque (STT) provides a powerful means of manipulating domain walls, which is of great interest for several spintronic applications, such as high-density racetrack memory and magnetic domain wall logic. However, the current density required for domain wall motion is still too high to realize low power devices. This is within this very innovative context that my Ph.D. research has focused on domain wall manipulation in magnetic wires made out of thin film with strong perpendicular magnetic anisotropy combining both spin-polarized current and all-optical switching. Different material structures have been explored, in order to investigate the combined effects of helicity-dependent optical effect and spin-orbit torque or spin transfer torque on domain wall motion in magnetic wires based on these structures. We show that domain wall can remain pinned under one laser circular helicity while depinned by the opposite circular helicity, and the threshold current density can be greatly reduced by using femtosecond laser pulses. Our findings provide novel insights towards the development of low power spintronic-photonic devices.

Cette thèse s’inscrit dans le cadre du développement d’une source laser TW, de cadence élevée, stabilisée en phase, et délivrant des impulsions de quelques cycles optiques pour explorer la physique attoseconde. De telles impulsions contiennent seulement quelques oscillations de l’onde porteuse (durée de 5 fs à une longueur d’onde centrale de 800 nm) et ne sont pas directement disponibles à la sortie d’une source laser femtoseconde classique. Une technique de post-compression efficace pour obtenir de telles impulsions consiste à élargir le spectre des impulsions laser par automodulation de phase dans une fibre creuse remplie de gaz, puis à compenser la phase spectrale introduite avec des miroirs chirpés. Cette technique convient à des impulsions dont l’énergie est inférieure au millijoule. Au-delà, la transmission et la stabilité du compresseur chutent fortement à cause d'effets non linéaires tels que l'autofocalisation et l'ionisation. Pour comprimer des impulsions énergétiques et dont la phase de l’enveloppe est stabilisée par rapport à la porteuse (stabilisation de la CEP), il est possible de diviser l'impulsion initiale en plusieurs répliques d'énergie moindre et de réduire ainsi l'intensité crête en entrée de fibre. Le spectre de chaque réplique est alors élargi indépendamment. Dans le cadre de cette thèse, la combinaison cohérente passive d'impulsions de quelques cycles optiques issues d'une fibre creuse remplie de gaz est démontrée pour la première fois. L'utilisation de lames biréfringentes (calcite) dont l’orientation est soigneusement déterminée permet de générer et combiner des répliques avec une efficacité élevée. Ainsi, dans le cas d’une division en deux répliques, des impulsions stabilisées en phase (CEP), de durée 6 fs et d'énergie 0.6 mJ ont été générées de manière fiable et reproductible. L’étude détaillée de cette technique, aussi bien théorique qu’expérimentale, a permis de mettre en évidence les conditions requises pour générer des impulsions de quelques cycles optiques et présentant un bon contraste temporel. Plus précisément, la phase spectrale relative entre les répliques peut être mesurée à l'aide d'une méthode interférométrique permettant de quantifier les déphasages résiduels dus à la lame qui recombine les répliques, ainsi que ceux induits lors de la propagation dans la fibre par d'éventuels effets de modulation de phase croisée ou d'ionisation. Les effets qui affectent le processus de combinaison des répliques, tels que les modifications des états de polarisation des répliques ou bien les interactions non linéaires entre les répliques, sont analysés en détail. Une méthode est proposée pour minimiser ces effets, même dans le cas plus critique de la division et combinaison d'impulsions à quatre répliques. / The framework of this thesis is the design and development of a TW-class, high-repetition rate, CEP-stabilized, few-cycle laser system devoted to attosecond physics. Few-cycle pulses includes only a few oscillations of the carrier wave (duration about 5 fs for 800nm central wavelength) and are not directly available at the output of typical femtosecond sources. One of the most popular techniques used for producing such pulses with high spatial quality is nonlinear spectral broadening in a gas-filled hollow-core fiber followed by temporal compression with chirped mirrors. However, as the input pulse energy approaches the milliJoule level, both the transmission and stability of hollow fiber compressors rapidly drop with the onset of self-focusing and ionization. A way of overcoming this limitation is to divide the input pulse into several lower energy replicas that can be subsequently recombined after independent spectral broadening in the fiber. In this thesis, the passive coherent combining of millijoule energy laser pulses down to few-cycle duration in a gas-filled hollow fiber is demonstrated for the first time. High combining efficiency is achieved by using carefully oriented calcite plates for temporal pulse division and recombination. Carrier-envelope phase (CEP)- stable, 6-fs, 800-nm pulses with more than 0.6 mJ energy were routinely generated in the case of twofold division and recombination. A detailed theoretical and experimental analysis of this temporal multiplexing technique is proposed to explain the conditions required for producing few-cycle pulses with high fidelity. In particular, an interferometric method for measuring the relative spectral phase between two replicas is demonstrated. This gives a measure of the phase mismatch in the combining plate, as well as that induced by eventual cross-phase modulation or ionization during propagation in the fiber. The effects degrading the combining process, as polarization change or nonlinear interactions between pulse replicas are analyzed in details. A method is proposed to overcome these limitations, even in the critical case of fourfold pulse division and combination.

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Integrated quantum photonic circuits have gained increasing interest in the field of quantum information, due to their compactness, the intrinsic stability and the potential scalability. Photons are the promising candidate for quantum information processing. Among all the optical platforms, femtosecond-laser waveguide writing technique has shown the extraordinary versatility in producing different components of a complete quantum system. In the last decade, femtosecond-laser writing has greatly expanded its applications in quantum technology. The aim of this thesis is to study and optimize the fundamental optical devices for integrated quantum circuits using femtosecond-laser waveguide writing technique. We investigate relevant theory of optical waveguides, the methods to fabricate and characterize laser-written waveguides in glass. In this work, we demonstrate the femtosecond-laser writing of integrated devices including Mach-Zehnder interferometer and path-encoded CNOT quantum gate. These devices can further serve as building blocks to produce complete integrated quantum system. / Integrerade kvantfotoniska kretsar har fått ett ökande intresse inom området kvantinformation, på grund av deras kompakthet, den inneboende stabiliteten och den potentiella skalbarheten. Fotoner är den lovande kandidaten för bearbetning av kvantinformation. Bland alla optiska plattformar har femtosekund-laservågledarskrivteknik visat den extraordinära mångsidigheten i att producera olika komponenter i ett komplett kvantsystem. Under det senaste decenniet har femtosekundlaserskrivning kraftigt utökat sina tillämpningar inom kvantteknologi. Syftet med denna avhandling är att studera och optimera de grundläggande optiska enheterna för integrerade kvantkretsar med hjälp av femtosekund-laservågledarskrivteknik. Vi undersöker relevant teori om optiska vågledare, metoderna för att tillverka och karakterisera laserskrivna vågledare i glas. I detta arbete demonstrerar vi femtosekundlaserskrivning av integrerade enheter inklusive Mach-Zehnder-interferometer och vägkodad CNOT-kvantgrind. Dessa enheter kan vidare fungera som byggstenar för att producera kompletta integrerade kvantsystem.

This thesis reports the effects of ultrashort laser pulse irradiation of various materials. The morphology after irradiation was examined using several microscopy techniques. Emphasis was placed on the identification of crystallographic changes and the analysis of laser-induced periodic surface structures. Grooves were machined in silicon by translating the target under the focused laser beam. The resulting depths were measured as a function of pulse energy, translation speed, and number of consecutive passes, for 800 and 400nm wavelength irradiation. The wall morphology and a corrugation along the bottom of the grooves were characterized. Various polarization configurations relative to the translation direction were compared. Such characterizations are relevant for the practical application of femtosecond laser micromachining. Silicon and gallium phosphide exhibited periodic structures after irradiation using photon energies less than the bandgap energy, with periods as small as ~20% of the irradiation wavelength. The significantly sub-wavelength periodic structures had a shallow profile on silicon, appearing as fine lines or grids of protrusions and depressions. On gallium phosphide, the surface evolved into planar-like structures with a large aspect ratio, possessing crystalline centers coated with amorphous material. These investigations, along with additional experiments, would help identify the precise physical origins of the short-period structures. On silicon and germanium, the target crystal orientation was shown to affect the formation of certain morphological features. For multiple-pulse irradiation, the (100) and (111) surface orientations exhibited significantly different tendencies for large conical structure formation. A thin layer of defected material coated the conical structures, with some defects present within the periodic structures. The different crystalline orientations did not affect periodic structuring. Cross-sectional transmission electron microscopy of silicon after irradiation by single pulses revealed amorphous material and dislocations in the bulk for sufficiently high pulse fluences. On a sample consisting of a metal layer on thermally-grown oxide on silicon, a range of pulse fluences was found which removed the metal layer without observed thinning of the oxide layer. Within this fluence range, above a particular fluence substantial defects were formed in the underlying silicon. Although ultrashort pulse irradiation of materials is frequently considered to be 'damage-free', attention should be paid to sub-surface modifications not evident from surface imaging. For the drilling of holes in copper foils, the pulse duration did not strongly affect the final morphology for durations under several picoseconds. A photodiode below the foil during drilling recorded transmitted light, indicating the number of pulses required for penetration under a variety of conditions, and characterizing hole evolution during drilling. Periodic surface structuring on the walls of holes depended on the irradiation atmosphere, pulse duration, and laser polarization. These measurements provide insight into the physical processes of material modification, and for the selection of irradiation parameters in practical applications. / Thesis / Doctor of Philosophy (PhD)

Transparent conductive oxides (TCOs) are used in solar cells not only to extract photogenerated carriers but also to allow sunlight to reach the photoactive material. Therefore, controlling the electrical and optical properties of such oxides is crucial for the optimization of the efficiency of solar cells. Herein, direct laser interference patterning (DLIP) method is used to control the surface morphology, optical and electrical properties of fluorine-doped tin oxide (FTO) by applying femtosecond laser pulses. The topography characterization reveals periodic line-like microstructures with a period of 3.0 μm and average heights between 20 and 185 nm, depending on the applied laser fluence levels. Laser-induced periodic surface structures are observed on the valleys of the texture aligned perpendicularly to the laser radiation polarization. A relative increase in the average total and diffuse optical transmittance up to 5% and 500%, respectively, is obtained in the 400–800 nm spectral range as a consequence of the generated micro- and nanostructures. Calculations of two figures of merit suggest that the texturing of FTO might enhance the efficiency of solar cells, in particular dye-sensitized (DSSCs). The findings of this study confirm that DLIP is a convenient technique for structuring electrodes for highly efficient optoelectronic devices.

Ce travail de thèse est consacré au développement de sources lasers femtosecondes à haute cadence, de forte puissancemoyenne (>10 W) avec des énergies supérieures à 100 μJ. Ce type de sources est primordial pour le développementd’applications industrielles variées (micro-usinage athermique, chirurgie oculaire, …) ainsi qu’en recherchefondamentale pour l’étude de l’interaction laser matière.Après un chapitre d’introduction sur l’état de l’art des chaînes lasers de forte puissance moyenne à base de matériauxdopés ytterbium, la réalisation d’une chaîne laser de forte puissance moyenne compacte à base de fibre photoniquemicrostructurée à large aire modale sera présentée. Il sera notamment démontré les principales limitations en termed’énergie et de puissance moyenne. D’une part, le fort confinement de l’impulsion lumineuse dans le coeur de la fibrefavorise l’accumulation d’effets non-linéaires lors de l’amplification et détériore la qualité de l’impulsion. D’autrepart, en raison du diamètre de coeur important (> 70 μm) choisit pour lutter contre l’effet précèdent, le guidage dumode fondamental TEM00 de ces fibres est très critique et devient sensible à la charge thermique interne à la fibre.Cette source laser a été utilisée dans le cas de deux applications bien spécifiques : le perçage de plaques d’acierépaisses pour une finalité de déminage (relatif au cadre du financement de cette thèse par la Direction Générale del’Armement) et à la génération d’harmoniques d’ordres élevées à très haute cadence (relatif au domaine d’expertisedu CELIA). Ces deux applications sont traitées au cours du troisième chapitre.A la vue des limitations observées et afin de disposer de chaînes lasers plus énergétiques et offrant des duréesd’impulsions encore plus courtes, une nouvelles architecture d’amplification a été proposée : le pompage fortebrillance de matériaux dopés Ytterbium. Ce concept présenté dans le dernier chapitre utilise le développement desources fibrées monomodes continues émettant à 976 nm. Cette architecture d’amplification a été utilisée afin deréaliser d’une part un oscillateur sub-70 fs et de forte puissance moyenne (>2,3 W) à une cadence de 73 MHz etd’autre part : un amplificateur type « booster » à fort gain. Deux expériences qui ont été réalisées avec des cristauxd’Yb:CaF2. Ce matériaux présente en effet l’avantage d’avoir un très large spectre d’émission (>60 nm) propice à lagénération et amplification d’impulsions femtosecondes mais aussi d’être « compatible » avec les chaînes de trèsforte puissance grâce à sa très bonne conductivité thermique. / This work concerns the development of high repetition rate femtosecond lasers with high average power (>10 W)and energies in excess of 100 μJ. Such lasers are paramount for the development of new industrial applications(athermal micro-drilling, eye surgery, ...) and for fundamental research on high repetition rate laser matter interactionstudies.After a brief introduction and the state of the art summary on high-average power femtosecond laser with ytterbiumdoped materials, a compact high-average power femtosecond laser with a large mode area microstructured rod typeamplifier will be presented. It will browse the main limitations in terms of energy and average power. Limitationsare mainly due to the strong confinement of the electric field propagating in the fibre core leading to non-linear effectsaccumulated during the amplification. On the other hand, for larger core diameter (> 70 μm), the fundamental modeguiding (TEM00) is very weak and thus very sensitive to the internal thermal load of the fibre.This laser source has been used in two specific applications: athermal drilling of thick stainless steel plate for mineclearing(an application of interest for the Direction Générale de l’Armement) and High order Harmonics Generationat high repetition rate (related to CELIA activities). These two applications are presented in the third chapter.In order to stretch the limits and generate more energetic and a shorter pulse, a new amplification scheme has beenproposed, namely high brightness optical pumping of ytterbium doped materials. This concept presented in the lastchapter benefits from the development of high average power single-mode fibre lasers source emitting at 976 nm.This amplification scheme allowed us to realize a high average power Kerr-lens oscillator delivering pulses with apulse duration below than 70 fs and an average power of 2.3W at a repetition rate of 73 MHz. In a second phase, wealso developed a « booster » amplifier with a high single- pass-gain. These two results have been obtained by usingYb-doped CaF2 crystals. This material presents the advantage to have a very broad emission bandwidth (> 60nm)suitable to generate and amplify femtosecond pulses and to be compatible with high average power laser due to hisvery good thermal conductivity.

Recently, laser light sources of different regimes have emerged as an essential tool in the biophotonics research area. Classic applications include, for example: manipulating single cells and their subcellular organelles, sorting cells in microfluidic channels and the cytoplasmic delivery of both genetic and non-genetic matter of varying sizes into mammalian cells. In this thesis several new findings specifically in the optical cell sorting as well as in the photo-transfection study fields are presented. In my optical cell sorting and guiding investigations, a new technique for enhancing the dielectric contrast of mammalian cells, which is a result of cells naturally engulfing polymer microspheres from their environment, is introduced. I explore how these intracellular dielectric tags influence the scattering and gradient forces upon these cells from an externally applied optical field. I show that intracellular polymer microspheres can serve as highly directional optical scatterers and that the scattering force can enable sorting through axial guiding onto laminin coated glass coverslips upon which the selected cells adhere. Following this, I report on transient photo-transfection of mammalian cells including neuroblastomas (rat/mouse and human), embryonic kidney, Chinese hamster ovary as well as pluripotent stem cells using a tightly focused titanium sapphire femtosecond pulsed laser beam spot. These investigations permitted advanced biological studies in femtosecond laser transfection: firstly, the influence of cell passage number on the transfection efficiency; secondly, the possibility to enhance the transfection efficiency via whole culture treatments of cells thereby, synchronizing them at the mitotic (M phase) as well as the synthesis phases (S phase) of the cell cycle; thirdly, this methodology can activate the up-regulation of the protective heat shock protein 70 (hsp70). Finally, I show that this novel technology can also be used to transfect mouse embryonic stem (mES) cell colonies and the ability of differentiating these cells into the extraembryonic endoderm.