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1
Charpin, Pierre-Jean. "Modélisation de l'interaction laser-plasma dans les faisceaux de Bessel femtoseconde". Electronic Thesis or Diss., Bourgogne Franche-Comté, 2024. http://indexation.univ-fcomte.fr/nuxeo/site/esupversions/fe2dc0aa-3386-4ecd-a96f-7f70a3113aa7.
Testo completoAbstract (sommario):
Les impulsions femtoseconde mises en forme de faisceaux de Bessel permettent de créer des nano-plasmas denses dans les diélectriques, menant à la formation de nano-vides à très haut rapport de forme pour des applications dans le domaine de la microélectronique. La modélisation de l'interaction laser-plasma est de prime importance pour comprendre l'évolution spatio-temporelle de la création de plasma et du dépôt d'énergie par l'impulsion laser femtoseconde. Ceci permettra de développer une interaction laser-matière extrêmement efficace dans d'autres géométries et matériaux. La thèse a pour objectif d'adapter des modèles d'ionisation et d'interaction laser plasma, de développer des outils d'analyse d'expériences, pour converger vers un modèle prédictifFemtosecond pulses shaped as Bessel beams create dense nano-plasma in dielectrics, leading to the formation of very high aspect ratio nano-voids for microelectronics applications. The modeling of laser-plasma interaction is very important to understand the spatio-temporal evolution of plasma creation and energy deposition by the femtosecond laser pulse. This will allow the development of highly efficient laser-matter interaction in other geometries and materials. The thesis aims to adapt ionization and plasma laser interaction models, to develop tools for the analysis of experiments, in order to converge towards a predictive model. Translated with www.DeepL.com/Translator (free version)
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Wefers, Marc Michael. "Femtosecond optical pulse shaping and multiple-pulse femtosecond spectroscopy". Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10597.
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Fernández, González Alma. "Chirped pulse oscillators generating microjoule femtosecond pulses at megahertz repetition rate /". [S.l.] : [s.n.], 2007. http://edoc.ub.uni-muenchen.de/archive/00006967.
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Fernández, González Alma. "Chirped Pulse Oscillators: Generating microjoule femtosecond pulses at megahertz repetition rate". Diss., lmu, 2007. http://nbn-resolving.de/urn:nbn:de:bvb:19-69673.
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Belloni, Valeria. "Spatial and temporal pulse shaping for ultrafast laser materials processing". Electronic Thesis or Diss., Bourgogne Franche-Comté, 2023. http://www.theses.fr/2023UBFCD055.
Testo completoAbstract (sommario):
Le traitement par laser ultrarapide a suscité un grand intérêt dans les applications industrielles en raison de sa capacité à réaliser une ablation précise et de haute qualité dans les matériaux. Cependant, les contraintes liées aux lasers, telles que l'énergie des impulsions et les taux de répétition, ont limité son développement, en particulier dans les environnements industriels.Dans ce cadre, la personnalisation des profils spatiaux et temporels des faisceaux laser peut améliorer l'interaction entre le laser et le matériau. Les techniques de mise en forme des faisceaux jouent un rôle crucial dans l'optimisation des performances du traitement des matériaux par laser ultrarapide et permettent d'atteindre des régimes jusqu'alors inaccessibles. Parallèlement, les lasers ultrarapides fonctionnant à des taux de répétition de l'ordre du gigahertz délivrent un nombre d'impulsions par unité de temps nettement plus élevé que les sources laser conventionnelles. La division d'une impulsion en plusieurs sous-impulsions avec un taux de répétition élevé semble être une méthode efficace pour augmenter le taux d'ablation dans le traitement laser.Cette thèse explore la possibilité d'utiliser des systèmes laser ultrarapides avec des taux de répétition de l'ordre du gigahertz, ainsi que des techniques avancées de mise en forme du faisceau pour améliorer le traitement laser ultrarapide. Le faisceau de Bessel est particulièrement utile dans le traitement des matériaux transparents grâce à sa robustesse aux distorsions non linéaires. Un faisceau de Bessel d'ordre élevé est utilisé dans cette thèse pour générer, pour la première fois, des nano piliers positifs avec une seule impulsion laser sur une surface de saphir. En outre, un nouveau système optique de génération de faisceaux de Bessel hautement focalisés a été développé pour étudier de nouvelles possibilités dans le traitement du silicium. Enfin, une source laser de fréquence de répétition allant jusqu’à 15 GHz, a été utilisée pour traiter le silicium. Des résultats prometteurs ont été obtenus en utilisant ce taux de répétition très élevé à la fois avec un faisceau gaussien et avec une mise en forme de faisceau en profil carréUltrafast laser processing has gained significant attention in industrial applications due to its ability to achieve precise and high-quality material ablation. However, laser constraints such as pulse energy and repetition rates have limited the throughput of ultrafast laser processes, especially in industrial settings.In this framework, customizing the spatial and temporal profiles of laser beams can enhance the interaction between the laser and the material. Beam shaping techniques play a crucial role in optimizing the performance of ultrafast laser materials processing and reaching previously inaccessible regimes. In parallel, ultrafast lasers operating at GHz repetition rates deliver a significantly higher number of pulses per unit of time compared to conventional laser sources. Splitting a single pulse into several sub-pulses with high repetition rate seems to be an effective method to increase the ablation rate in laser processing.This thesis explores the possibility of ultrafast laser systems with GHz repetition rates and advanced beam shaping techniques to improve ultrafast laser processing. The Bessel beam is particularly beneficial in processing transparent materials thanks to its robustness to non-linear distortions. A high-order Bessel beam is used in this thesis to generate, for the first time, positive nanopillars with a single laser pulse across the surface of sapphire. In addition, a new setup for highly focused Bessel beams has been developed to investigate new opportunities in silicon processing. Finally, a GHz repetition laser source, in a new regime up to 15 GHz, has been used to process silicon. Promising results were obtained with this very high repetition rate with a Gaussian beam and top-hat beam shaping
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Chin, Roger S. "Femtosecond laser pulse compression". Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/29799.
Testo completoAbstract (sommario):
Once the Spectra-Physics Femtosecond Laser System had arrived, it had to be characterized.
For further pulse compression, various techniques had to be considered. The best of these were chosen considering our needs and limitations.
First, the Spectra-Physics Femtosecond Laser System is described and its 616 nm laser pulses are characterized. By using an autocorrelation technique based on the nonlinear optical characteristics of a potassium dihydrogen phosphate (KDP) crystal and assuming a particular intensity pulse shape (such as that described by a symmetric exponential decay), the pulse width (full width at half maximum) could be obtained. Assuming a pulse shape described by a symmetric exponential decay function, the "exponential" pulse width was measured to be 338 ± 6 fs. The nominal average power of the 82-MHz modelocked pulse train was 225 mW. The "exponential" pulse energy was 2.7 nJ with a peak pulse power of 2.8 kW.
Theoretical calculations for fibre grating pulse compression are presented. Experimentally,
I was able to produce 68 ± 1 fs (exponential) pulses at 616 nm. The average power was 55 mW. The "exponential" pulse energy was 0.67 nJ with a peak power of 3.4 kW. The pulse compressor consisted of a 30.8 ±0.5 cm fibre and a grating compressor with the effective grating pair distance of 103.8 ± 1 cm.
Various techniques were considered for further pulse compression. Fibre-grating pulse compression and hybrid mode locking appeared to be the most convenient and least expensive options while yielding moderate results.
The theory of hybrid mode locking is presented. Experimentally, it was determined that with the current laser system tuned to 616 nm, DODCI is better than DQOCI based
on pulse shape, power, stability and expense. The recommended DODCI concentration is 2-3 mmol/l. The shortest "exponential" pulse width was 250 fs. The average power was 185 mW. The exponential pulse energy was 2.3 nJ with a peak pulse power of 2.6 kW.
An attempt to increase the bandwidth of the laser pulse by replacing the one-plate birefringent plate with a pellicle severely limited the tunability of the dye laser and introduces copious noise.
Attempts to reduce group velocity dispersion (responsible for pulse broadening) with a grating compressor was indeterminate, but did result in a slightly better pulse shape. Interferometric autocorrelation is recommended for such a study.
An increase or decrease from the nominal power output of the pulse compressor showed a decrease in pulse compression.Science, Faculty of
Physics and Astronomy, Department of
Graduate
7
Dooley, Patrick W. Corkum Paul B. "Molecular imaging using femtosecond laser pulses". *McMaster only, 2003.
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8
Kafka, Kyle R. P. "Laser-Induced Damage with Femtosecond Pulses". The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483661596059632.
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Chanal, Margaux. "Space-time study of energy deposition with intense infrared laser pulses for controlled modification inside silicon". Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0488/document.
Testo completoAbstract (sommario):
La modification du silicium dans son volume est possible aujourd’hui avec des lasers infrarouges nanosecondes. Néanmoins, le régime d’intérêt pour la modification contrôlée en volume des matériaux transparents correspond aux impulsions femtosecondes. Cependant, aujourd’hui aucune démonstration de modification permanente du volume du Si n’a été réalisée avec une impulsion ultra-brève (100 fs). Pour infirmer ce résultat, nous avons développé des méthodes de microscopie infrarouge ultra-rapides. Tout d’abord, nous étudions le microplasma confiné dans le volume, caractérisé par la génération de porteurs libres par ionisation nonlinéaire du silicium, suivie de la relaxation totale du matériau. Ces observations, couplées à la reconstruction de la propagation du faisceau dans le matériau, démontrent un dépôt d’énergie d’amplitude fortement limitée par des effets nonlinéaires d’absorption et de propagation. Cette analyse a été confirmée par un modèle numérique simulant la propagation nonlinéaire du faisceau femtoseconde. La compréhension de cette limitation a permis de développer de nouvelles configurations expérimentales grâce auxquelles l’endommagement local et permanent du volume du silicium a pu être initié en régime d’impulsions courtesThe modification of bulk-silicon is realized today with infrared nanosecond lasers. However, the interest regime for controlled modifications inside transparent materials is femtosecond pulses. Today, there is no demonstration of a permanent modification in bulk-Si with ultra-short laser pulses (100 fs). To increase our knowledge on the interaction between femtosecond lasers and silicon, we have developedultra-fast infrared microscopy experiments. First, we characterize the microplasma confined inside the bulk, being the generation of free-carriers under nonlinear ionization processes, followed by the complete relaxation of the material. These results, combined with the reconstruction of the beam propagation inside silicon, demonstrate that the energy deposition is strongly limited by nonlinear absorption andpropagation effects. This analysis has been confirmed by a numerical model simulating the nonlinear propagation of the femtosecond pulse. The understanding of this clamping has allowed us the development of new experimental arrangements, leading to the modification of the bulk of Si with short pulses
10
Bowlan, Pamela. "Measuring the spatiotemporal electric". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28188.
Testo completoAbstract (sommario):
Thesis (M. S.)--Physics, Georgia Institute of Technology, 2009.Committee Chair: Rick Trebino; Committee Member: Jennifer Curtis; Committee Member: John Buck; Committee Member: Mike Chapman; Committee Member: Stephen Ralph.
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Bock, Katherine J. "Femtosecond Fiber Lasers". Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23391.
Testo completoAbstract (sommario):
This thesis focuses on research I have done on ytterbium-doped femtosecond fiber lasers. These lasers operate in the near infrared region, lasing at 1030 nm. This wavelength is particularly important in biomedical applications, which includes but is not limited to confocal microscopy and ablation for surgical incisions. Furthermore, fiber lasers are advantageous compared to solid state lasers in terms of their cost, form factor, and ease of use. Solid state lasers still dominate the market due to their comparatively high energy pulses. High energy pulse generation in fiber lasers is hindered by either optical wave breaking or by multipulsing. One of the main challenges for fiber lasers is to overcome these limitations to achieve high energy pulses. The motivation for the work done in this thesis is increasing the output pulse peak power and energy. The main idea of the work is that decreasing the nonlinearity that acts on the pulse inside the cavity will prevent optical wave breaking, and thus will generate higher energy pulses. By increasing the output energy, ytterbium-doped femtosecond fiber lasers can be competitive with solid state lasers which are used commonly in research. Although fiber lasers tend to lack the wavelength tuning ability of solid state lasers, many biomedical applications take advantage of the 1030 µm central wavelength of ytterbium-doped fiber lasers, so the major limiting factor of fiber lasers in this field is simply the output power. By increasing the output energy without resorting to external amplification, the cavity is optimized and cost can remain low and economical. During verification of the main idea, the cavity was examined for possible back-reflections and for components with narrow spectral bandwidths which may have contributed to the presence of multipulsing. Distinct cases of multipulsing, bound pulse and harmonic mode-locking, were observed and recorded as they may be of more interest in the future. The third-order dispersion contribution from the diffraction gratings inside the laser cavity was studied, as it was also considered to be an energy-limiting factor. No significant effect was found as a result of third-order dispersion; however, a region of operation was observed where two different pulse regimes were found at the same values of net cavity group velocity dispersion. Results verify the main idea and indicate that a long length of low-doped gain fiber is preferable to a shorter, more highly doped one. The low-doped fiber in an otherwise equivalent cavity allows the nonlinear phase shift to grow at a slower rate, which results in the pulse achieving a higher peak power before reaching the nonlinear phase shift threshold at which optical wave breaking occurs. For a range of net cavity group velocity dispersion values, the final result is that the low doped fiber generates pulses of approximately twice the value of energy of the highly-doped gain fiber. Two techniques of mode-locking cavities were investigated to achieve this result. The first cavity used NPE mode-locking which masked the results, and the second used a SESAM for mode-locking which gave clear results supporting the hypothesis.
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Gabolde, Pablo. "Measurements of the spatio-temporal profiles of femtosecond laser pulses". Diss., Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-06272007-101312/.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2008.Trebino, Rick, Committee Chair ; Kennedy, Brian, Committee Member ; Kuzmich, Alex, Committee Member ; Curtis, Jennifer, Committee Member ; Buck, John, Committee Member.
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Williams, John Arthur Robert. "An investigation of femtosecond optical pulse generation". Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46608.
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Paye, Malini. "Femtosecond pulse generation in solid-state lasers". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/38019.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (leaves 181-193).
by Malini Paye.
Ph.D.
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Takayanagi, Jun, Norihiko Nishizawa, Hiroyuki Nagai, Makoto Yoshida e Toshio Goto. "Generation of high-power femtosecond pulse and octave-spanning ultrabroad supercontinuum using all-fiber system". IEEE, 2005. http://hdl.handle.net/2237/6770.
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Jeandet, Antoine. "Spatio-temporal characterization of femtosecond laser pulses using self-referenced Fourier transform spectroscopy Spatio-temporal structure of a petawatt femtosecond laser beam Controlling the velocity of a femtosecond laser pulse using refractive lenses". Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS089.
Testo completoAbstract (sommario):
La technologie actuelle des lasers ultrabrefs permet de délivrer des impulsions d'une énergie de quelques dizaines de joules dont la durée est de l'ordre de la dizaine de femtosecondes. Focaliser fortement de telles impulsions permet d'obtenir des valeurs d'éclairement considérables, qui sont notamment utilisées pour générer des faisceaux de particules relativistes. Le bon fonctionnement des lasers de ultra-haute intensité nécessite un excellent contrôle des propriétés du faisceau en tout point de la chaîne d'amplification. Développer un tel niveau de contrôle exige de pouvoir mesurer les imperfections temporelles et spatiales des impulsions avec une très grande précision. Cependant, les instruments de mesure utilisés jusqu'à présent négligent un aspect important de la structure des impulsions lasers, qui est lié aux couplages spatio-temporels. Ces derniers représentent une classe particulière d'imperfections, dont l'influence sur les expériences d'ultra-haute intensité a longtemps été négligée. Les rares instruments capables de mesurer ces défauts spécifiques sont pour la plupart inadaptés à la caractérisation de faisceaux de haute énergie. Le travail présenté dans cette thèse a porté sur l'instrument TERMITES, qui permet la caractérisation totale d'impulsions ultrabrèves, ainsi que leur restitution en trois dimensions. TERMITES est une technique auto-référencée qui est basée sur la spectroscopie par transformée de Fourier résolue spatialement. Une première partie de la thèse présente l'étude détaillée et l'optimisation de l'instrument TERMITES. Dans un deuxième temps, différents systèmes laser sont caractérisés grâce à cet instrument, permettant ainsi d'établir la première revue expérimentale des différentes origines de couplages spatio-temporels dans les lasers ultrabrefsCurrent ultrashort laser technology makes it possible to generate pulses lasting a few tens of femtoseconds, with energies of up to tens of joules. Strongly focusing such pulses produces ultra-intense fields that are notably used to generate relativistic particle beams. Proper operation of ultra-intense laser facilities requires to control the temporal and spatial properties of ultrashort pulses. Until now, measurement devices used for this purpose have neglected an important aspect of ultrashort pulses structure, which is linked to spatio-temporal couplings. Spatio-temporal couplings are a particular kind of defects in ultrashort pulses, of which the influence on ultra-intense experiments has been largely overlooked until recently. The rare instruments capable of measuring spatio-temporal couplings are hardly scalable to high-energy laser beams. This thesis is dedicated to TERMITES, a device for the full characterization of ultrashort laser beam, which is used to provide their three dimensional shape in space and time. TERMITES is a self-referenced technique based on spatially-resolved Fourier-Transform Spectroscopy. The first part of this work presents the detailed study of TERMITES, as well as the optimization of its design. Multiple laser systems are then characterized using the instrument. The obtained results are used to establish the first experimental review of spatio-temporal couplings origins in ultrashort lasers
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Erny, Christian. "Femtosecond Mid-IR chirped pulse optical parametric amplifier /". Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=18065.
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Krampert, Gerhard. "Femtosecond quantum control and adaptive polarization pulse shaping". Doctoral thesis, [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=97440814X.
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Quarterman, Adrian Hugh. "Femtosecond pulse generation in surface-emitting semiconductor lasers". Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/72535/.
Testo completoAbstract (sommario):
In this thesis I report significant advances towards the goal of stable ultrashort pulse generation in mode-locked optically pumped vertical external-cavity surface-emitting lasers (VECSELs). Continuous wave VECSELs were first designed as a type of semiconductor laser capable of producing high output power in near transform-limited beams. Optical pumping allows the output power of the device to be increased simply by increasing the pumped area of the sample, and an external cavity forces the laser into single transverse mode operation. VECSELs’ external cavities also allow for the insertion of semiconductor saturable absorber mirrors (SESAMs) for modelocking. Mode-locked VECSELs have surpassed the performance of other types of mode-locked semiconductor laser, with modelocking via the optical Stark effect allowing VECSELs to produce sub-picosecond pulses in transform-limited beams, at power levels up to 100 mW and at GHz repetition rates. The work presented in this thesis describes recent progress in reducing the durations of VECSEL pulses to below 100 fs. At these pulse durations, gain saturation forces the laser oscillator to enter a dynamic regime never before seen in semiconductor lasers, which is also investigated here. In addition, the timing jitter of a VECSEL mode-locked using the optical Stark effect is characterised for the first time, and a versatile frequency-divider-based active stabilisation technique is demonstrated. Finally, the fabrication of carbon nanotube based saturable absorbers for VECSEL modelocking via solution processing is investigated.
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Rahimiangolkhandani, Mitra. "Interaction of Structured Femtosecond Light Pulses with Matter". Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42334.
Testo completoAbstract (sommario):
Physics and potential applications of femtosecond laser pulses interacting with matter have captured interest in various fields, such as nonlinear optics, laser micromachining, integrated optics, and solar cell technologies. On the one hand, such ultrashort intense pulses make them practical elegant tools to be utilized for direct structuring of materials with high accuracy and numerous potential applications. On the other hand, studying the fundamental aspects and nonlinear nature of such interactions opens new remarkable venues for various unique investigations. In recent years, the emerging topic of structured light (also known as twisted or optical vortex light), i.e., a beam of light with a twisted wave-front that can carry orbital angular momentum (OAM), has attracted the attention of many researchers working in the field of light-matter interaction. Such beams offer various applications from classical and quantum communication to imaging, micro/nano-manipulation, and modification of fundamental processes involved in light-matter interactions, e.g., absorption and emission. Nevertheless, the fabrication of complex structures, controlled modification, and achieving a high spatial resolution in material processing still remain in the spotlight. Moreover, the fundamental role of orbital angular momentum in the nonlinear absorption of materials, particularly in solids, has yet remained a subject of debate. Addressing these points was the main motive behind this dissertation. To accomplish this objective and investigate new aspects of structured light-matter interaction, I conducted various experiments, the results of which are presented in this work. The general idea was to study the interaction of femtosecond laser radiation, having a structured phase and polarization, with the matter in two aspects: (i) surface morphology modification and (ii) nonlinear absorption of solids. In this regard, I studied surface processing of crystalline silicon and CVD diamond with femtosecond laser vortex pulses generated by a birefringent phase-plate, known as q-plate, in single and multiple pulse irradiation regimes, respectively. The characterization of the modified region was performed using optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). I demonstrated that upon irradiation of a single vortex pulse on silicon, a nano-cone structure is formed within the ablated crater, whose height was independent of the helicity of the twisted light. However, for a linearly polarized vortex pulse, the height of the nano-cone decreases at higher pulse energies. The dynamics of nano-cone formation and the role of polarization were also investigated by simulating the mass transport function in this process. Moreover, using superimposed vortex beams, we fabricated complex patterns containing several nano-cones, by single-shot irradiation on the silicon surface. My experimental results offer an ability to actively control and manipulate material, in terms of the nanocones position, in two dimensions with an ultra-high resolution. I further proceeded with our experiments in the multiple pulse regime on a diamond target. By irradiation of a high number of superimposed vortex pulses, I was able to imprint complex polarization states of structured light on the target surface in the form of periodic nano-ripples. This procedure enabled us to not only generate spatially varying nano-gratings but also directly visualize and study very complex states of polarization. Besides these surface structuring, I carried out experimental studies to investigate the response of bulk material to an incident circularly polarized vortex beam that carries orbital angular momentum. The experimental results reveal, for the first time, that such an interaction can produce a differential absorption that gives rise to helical dichroism. We demonstrate that this response is sensitive to the handedness and degree of the twist in the incident vortex beam. Such a dichroism effect may be attributed to the excitation of dipole-forbidden atomic transitions, e.g., electric quadrupole transitions. However, this explanation is not absolute and remains open to further research and investigations.
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Hort, Ondřej. "High harmonic generation with high energy femtosecond pulses". Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0097/document.
Testo completoAbstract (sommario):
Nous présentons nos travaux sur la génération d’harmoniques élevée (HHG) avec des impulsions térawatt femtosecondes. Nous avons effectué l’HHG avec les impulsions fondamentales de haute énergie et caractérisé l’émission de XUV spatialement et spectralement de manière monocoup et nous avons observé plusieurs structures dans le champ lointain. Ces structures sont très robustes et reproductibles et ont été observés dans de nombreux types de gaz et des géométries de génération. Sans caractérisation monocoup spatiale et spectrale les structures ne sont pas visibles. Nous avons développé des simulations simples pour identifier ces structures et nous avons pu observer des structures similaires. Nous les avons identifiés comme étant liées à la cohérence spatiale de la source XUV et la diffraction dans le champ lointain. Dans le champ proche, la phase et l’amplitude harmonique évoluent spatialement et temporellement et leurs profils sont fortement modulés. Ces profils modulés diffractent et créent des spectres structurés dans le champ lointain. Nous avons observé que la propagation dans un milieu générateur fin a peu d’influence sur les structures. Nous démontrons une mise en forme spatiale de l’impulsion fondamentale via l’optique adaptative et leur avantage pour HHG. Une optique adaptative nous permet d’avoir un faisceau à profil de phase régulier. Un tel faisceau est utilisé pour HHG avec un faisceau de grand diamètre et contrôle du faisceau XUV est démontrée. Nous avons développé une technique de post-compression de haute énergie, et nous avons obtenu des impulsionsde 10 fs et 10 mJ dans un profil quasi gaussien. La technique repose sur l’automodulation de phase induite par l’ionisation et est compatible avec des impulsions niveau TW de haute énergie. Nous avons effectué des HHG avec ces impulsions et obtenu des spectres XUV quasi continu avec des structures spatiales et spectrales. Nous avons effectué des simulations simples etdes simulations de SFA et nous avons observé des structures similaires même sans prendre en compte la propagation dans le milieuWe present our work on high harmonic generation with TW femtosecond pulses. We performed HHG with high energy femtosecond pulses and characterize the generated XUV emission spatially and spectrally at the single-shot basis and we observed many structures in spatially resolved XUV spectra in the far field. Those structures are very robust and reproducible and have been observed in many different gases and generation geometries. Without spatial and spectral characterization on the single-shot basis the structures are not visible. We developed simple simulations to identify those structures and we observed similar structures as experimentally. We identified them as a result of spatial coherence of the XUV source and the diffraction to the far field. In the near field, the harmonic amplitude and phase are spatially and temporally dependent and their profiles are strongly modulated. Such modulated profiles diffract to structured spatially resolved spectra in the far field. We observed that propagation of the XUV in the generating medium has little influence on the structures. We demonstrate spatial shaping of the driving pulses via adaptive optics and their advantage for HHG. An adaptive optics allows us to have the driving beam of regular spatial profile and phase even out of focus. Such a beam is used for HHG with a large diameter driving beam and control of the XUV beam is demonstrated. We developed a high energy TW post-compression technique and we obtained pulses of 10 fs and 10 mJ in a quasi-Gaussian spatial profile. The technique is based on ionization-inducedself-phase-modulation and is compatible with high energy TW level pulses. We performed HHG with such TW pulses and obtained XUV quasi-continuum spectra with spectral and spatial structures. We performed simple simulations and SFAsimulations and we observed similar structures even without considering the XUV propagation in the medium
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Kornaszewski, Lukasz. "Novel sources of near- and mid-infrared femtosecond pulses for applications in gas sensing, pulse shaping and material processing". Thesis, Heriot-Watt University, 2008. http://hdl.handle.net/10399/2224.
Testo completoAbstract (sommario):
In this thesis the design, construction process and the performance of two femtosecond optical parametric oscillators and one second–harmonic generation femtosecond pulse shaper is described. One oscillator was applied to gas sensing while potential applications of other devices are outlined. ATi:sapphire oscillator was used to pump a periodically–poled lithium niobate– based optical parametric oscillator. This signal–resonant device was configured to produce broadband idler pulses tunable in the range of 2.7–3.4 μm. This wavelength coverage was matched to the ν3 optical absorption band of methane, and Fourier–transform spectroscopy of a CH4:N2 mixture was implemented by employing a mid–IR silica photonic bandgap fibre simultaneously as a gas cell and an optical waveguide. Methane sensing below a 1% concentration was demonstrated and the main limiting factors were identified and improvements suggested. Another optical parametric oscillator was demonstrated which was pumped by a commercial Yb:fibre master oscillator/power amplifier system and was based on a periodically–poled lithium niobate crystal. The signal was tunable between 1.42–1.57 μm and was intended as a source for a subsequent project for waveguide writing in silicon. The oscillator was a novel long–cavity device operating at 15 MHz. The 130 nJ pump pulse energies allowed for 21 nJ signal pulses at a pump power of 2 W. The performance of the oscillator was characterised via temporal and spectral measurements and the next steps of its development are outlined. Finally a pulse shaper based on second harmonic generation in a grating– engineered periodically–poled lithium niobate crystal was demonstrated. Pulses from a 1.53 μm femtosecond Er:fibre laser were compressed and then used as the input to the shaper. The performance of the shaper was tested by performing cross–correlation frequency–resolved optical gating measurements on the output second harmonic pulses and this confirmed the successful creation of multiple pulses and other tailored shapes including square and chirped pulses, agreeing well with theoretical calculations.
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Wright, Peter. "Generation, Characterization and Application of the 3rd and 4th Harmonics of a Ti:sapphire Femtosecond Laser". Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/20628.
Testo completoAbstract (sommario):
Femtosecond time-resolved photoelectron spectroscopy (fsTRPES) experiments have been used to study the photoelectron energy spectra of simple molecules since the 1980’s. Analysis of these spectra provides information about the ultrafast internal conversion dynamics of the parent ions. However, ultraviolet pulses must be used for these pump-probe experiments in order to ionize the molecules. Since current solid state lasers, such as the Ti:sapphire laser, typically produce pulses centered at 800nm, it is necessary to generate UV pulses with nonlinear frequency mixing techniques. I therefore constructed an optical setup to generate the 3rd and 4th harmonics, at 266.7nm and 200nm, respectively, of a Ti:sapphire (Ti:sa) chirped-pulse amplified (CPA) laser system that produces 35fs pulses centered at 800nm. Thin Beta-Barium Borate (β-BaB2O4 or BBO) crystals were chosen to achieve a compromise between short pulse durations and reasonable conversion efficiencies, since ultrashort pulses are quite susceptible to broadening from group velocity dispersion (GVD).
Output energies of around 11μJ and 230nJ were measured for the 266.7nm and 200nm pulses, respectively. The transform limits of the 3rd and 4th harmonic pulse lengths were calculated from their measured spectral widths. We found that the 266.7nm bandwidth was large enough to support sub-30fs pulses, and due to cutting at the lower-wavelength end of the 200nm spectrum, we calculated an upper limit of 38fs. The pulses were compressed with pairs of CaF2 prisms to compensate for dispersion introduced by transmissive optics. Two-photon absorption (TPA) intensity autocorrelations revealed fully compressed pulse lengths of 36 ± 2 fs and 42 ± 4 fs for the 3rd and 4th harmonics, respectively.
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Henderson, Gordon George. "Femtosecond laser studies of fullerenes and nanotubes". Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7737.
Testo completoAbstract (sommario):
This work concerns the interaction of intense, ultrashort laser pulses with fullerenes and carbon nanotubes. This includes the excitation and ionisation dynamics of gas phase fullerenes and the response of carbon nanotubes to intense ultrashort laser pulses. When ionising C60 with laser pulses of duration between 50 fs up to a few hundred fs, the ionisation mechanism has been proposed to be thermal in nature, with the electronic subsystem ‘hot’ and the vibrational system ‘cold’ at the time of ionisation. Recent results show an anisotropy in the photoelectron angular distribution which may suggest more direct mechanisms at work. Velocity-Map Imaging photoelectron spectroscopy results are presented for the ionisation of C60 and C70 at various wavelengths, pulse durations and intensities and the results are compared to theoretical models. The results are described well by a thermal ionisation mechanism in which a significant number of electrons are emitted during the laser pulse. Electrons may gain a momentum ‘kick’ from the electric field of the laser which results in an anisotropy in the photoelectron angular distributions. Peaks are observed, superimposed on the thermal background, in the photoelectron kinetic energy spectra of fullerenes ionised by ultrashort laser pulses which were previously assigned as Rydberg peaks. Photoelectron angular distributions of these peaks are presented for C60 and C70 ionised with laser pulses of various wavelengths. The binding energies and anisotropy parameters fitted to the peaks suggest that they are due to the population and one-photon ionisation of superatom molecular orbitals (SAMOs). The results rule out a direct multiphoton population mechanism for these states and show many similarities with Rydberg fingerprint spectroscopy. The fusion of carbon nanotubes has been observed under high energy electron beams and fullerene molecules have been shown to fuse together after irradiation with ultrashort laser pulses. Results are presented for experiments where fusion of carbon nanotubes with ultrashort laser pulses was attempted. Thin carbon nanotube films are analysed via Raman spectroscopy after irradiation by single laser pulses. A number of low frequency radial breathing mode peaks were observed which suggest that fusion may have taken place at certain areas of the sample.
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Sarmani, Abdul Rahman. "Yb-doped femtosecond lasers and their frequency doubling". Thesis, St Andrews, 2008. http://hdl.handle.net/10023/781.
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Holzwarth, Ronald. "Measuring the frequency of light using femtosecond laser pulses". [S.l.] : [s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=96303006X.
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Zeidler, Dirk. "Coherent control of molecular dynamics with shaped femtosecond pulses". [S.l.] : [s.n.], 2001. http://edoc.ub.uni-muenchen.de/archive/00000236.
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Borowiec, Andrzej Haugen Harold Kristen. "Ablation and micromachining of INP with femtosecond laser pulses /". *McMaster only, 2004.
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Zeidler, Dirk. "Coherent Control of Molecular Dynamics with Shaped Femtosecond Pulses". Diss., lmu, 2002. http://nbn-resolving.de/urn:nbn:de:bvb:19-2367.
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Holzwarth, Ronald. "Measuring the Frequency of Light using Femtosecond Laser Pulses". Diss., lmu, 2001. http://nbn-resolving.de/urn:nbn:de:bvb:19-3214.
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Alshehri, Ali. "Micro and Nanostructuring of Polymers by Femtosecond Laser Pulses". Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35356.
Testo completoAbstract (sommario):
Micro/Nanostructuring of polymers by femtosecond pulses is of extreme importance because it drives applications in photonics and biomedicine. A femtosecond pulse, with an intensity of ∼ 10^13 W/cm^2, is capable of causing an optical breakdown and inducing permanent modification in the material. With such high intensity, and considering the fact that polymers possess high band gaps, the interaction nature is completely nonlinear, and the material can be modified locally on the surface and in bulk. The irradiated regions exhibit fluorescence, and they display new wetting properties as a consequence of the optical breakdown of a material. The optical breakdown can be investigated by studying the nonlinear absorption. In this thesis, we discuss the nonlinear absorption of fs-laser pulses inside polymers using transmission measurements. We show a step– function–like behaviour of the transmission, dropping abruptly to ∼ 20% at the optical breakdown threshold with a ∼ 40 % reduction in the band gap. Utilizing spectroscopy, we show that the laser-modified regions contain randomly distributed nanoclusters. The presence of localized nanoclusters is responsible for exhibiting fluorescence, within ∼ 10 µm3 for a single pulse. This feature was exploited to demonstrate high-density data storage in Polymethyl methacrylate (PMMA) without any special material preparation. We demonstrate up to 20 layers of embedded data that can be stored in a standard 120 mm disc. Storage capacity of 0.2 TBytes/disc can be achieved by adjusting read laser parameters. Besides the fluorescence capability induced in the bulk of polymers, the hydrophilicity shown by the fs–laser modified surface is utilized to study selective cell growth on the micro-structured Polydimethylsiloxane (PDMS) surface. We show that the C2C12 cells and rabbit anti-mouse protein attach preferentially to the modified regions when the surface is modified with low pulse energies. However, in the high pulse energy regime, the laser-modified regions exhibit superhydrophobicity inhibiting cell adhesion.
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Badger, Antony Daniel. "Transport in dense plasmas produced by femtosecond laser pulses". Thesis, University of Essex, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361032.
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Brahms, Malte Christian. "Few-femtosecond deep-UV pulses for transient-absorption experiments". Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/63816.
Testo completoAbstract (sommario):
In this thesis I describe the development, implementation and characterisation of a source of wavelength-tunable few-femtosecond laser pulses in the deep ultraviolet spectral region for use in time-resolved experiments. I also propose and model an extension of this source capable of simultaneously generating a single-cycle driving pulse for extreme nonlinear optics as well as a few-femtosecond ultraviolet pulse. Building on advances in the field of femtochemistry, ultrafast science is moving towards ever shorter timescales and more complex systems. One of the key building blocks for the next generation of experiments studying ultrafast dynamics in molecules will be the availability of few-femtosecond pulses to directly address electronic resonances whose corresponding photon energy lies in the vacuum and deep ultraviolet spectral regions. By harnessing the capabilities of soliton self-compression in novel micro-structured waveguides, we have generated pulses in the deep ultraviolet with energies of hundreds of nanojoules. The delivery of these pulses to an experiment as well as the measurement of their temporal profile pose significant challenges due to the dispersive properties of optical materials in the ultraviolet. We have developed an in-vacuum device for ultrafast pulse characterisation, and by directly coupling the waveguide to vacuum we were able to measure distortion-free pulses with durations below 10 fs at a range of different central wavelengths. Numerical modelling of a scaled-up version of the apparatus shows that the self-compressed driving pulse in the ultraviolet pulse generation process can maintain its shape when delivered directly to vacuum. The single-cycle pulse duration makes it an ideal driver for extreme nonlinear optics and the generation of isolated attosecond pulses in the soft X-ray spectral region.
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Anderson, Patrick. "High-order harmonic generation with self-compressed femtosecond pulses". Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/375102/.
Testo completoAbstract (sommario):
Here, a state-of-the-art model is developed that can predict both the evolution of an intense laser pulse propagating through a gas-filled fibre, and the extreme ultraviolet field that it generates. This model is first used to discover a new mechanism for compressing energetic laser pulses to few cycle durations within short gas-filled fibres at pressures where high-order harmonic generation is routinely performed. Next, the fibre design is optimised for enhanced phase-matching using the model. Once fabricated and integrated into the source characterisation apparatus, the conversion efficiency at 30-40 nm is found to be almost an order of magnitude higher than comparable sources. Preliminary simulations also predict that isolated attosecond pulses may emerge from the fibre if parameters are carefully tuned. Additionally, a 13.5 nm source is developed in an extended gas cell geometry. Filters suitable for this wavelength are tested and a single harmonic is then selected and brought to a focus. This apparatus is now being used by the wider scientific community to image test objects and biological samples.
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Mitchell, Robert Andrew III. "Understanding Femtosecond-Pulse Laser Damage through Fundamental Physics Simulations". The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440411512.
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Austin, Drake Ross. "Semiconductor Surface Modification using Mid-Infrared, Femtosecond Laser Pulses". The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu150324882632046.
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Centurion, Martin Psaltis Demetri. "Study of the nonlinear propagation of femtosecond laser pulses /". Diss., Pasadena, Calif. : California Institute of Technology, 2005. http://resolver.caltech.edu/CaltechETD:etd-05262005-174627.
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Wilson, Philip Trent. "Second harmonic generation spectroscopy using broad bandwidth femtosecond pulses /". Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
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Mlejnek, Michal 1965. "Intense femtosecond pulse interaction with transparent and absorbing medium". Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/288895.
Testo completoAbstract (sommario):
The work reported in this dissertation represents an investigation into some aspects of resonant and nonresonant light-matter interaction as experienced by femtosecond optical pulses. We look at the role of plasma generation via multi-photon ionization in the arrest of the 2-D collapse of femtosecond pulses governed by the nonlinear Schrodinger equation. First we studied the exciting new area of anomalous long-distance propagation of femtosecond optical pulses in the atmosphere. Our simulations do not support the existence of a stable pulse propagating through the air, but rather a dynamical picture involving several collapse events emerges. This investigation led us to consider the question of the role of pressure on the pulse propagation in gases. The pressure dependence of the collapse in Argon is discussed next, and we make the connection between the results obtained in crystals on one hand, and low-density gases on the other. An interesting behavior is observed for pressures at which the Kerr nonlinearity and plasma-induced defocusing are of the same order. Next, we investigate second harmonic generation of femtosecond pulses at the boundary of a nonlinear medium using the full vector Maxwell equations and simple phenomenological constitutive relations. We observe the initial pulse to split in time into two ultrashort pulses in the case of phase-mismatch. This phenomenon should be readily measured experimentally. The effect of low-frequency material dispersion and a possibility of "one-hump" pulsed solution is discussed. Finally, in the last chapter we investigate the resonant coupling of light to a semiconductor which is sensitive to the field polarization, using a many-body model for electronic structure. Pump-probe type experiments with copropagating, cross-polarized beams are considered, and we demonstrate theoretically the existence of an oscillating signal at twice the optical frequency in the probe transmission measurements. Our results show that the change of the interaction among the carriers leads to a phase shift of the oscillation pattern. We also know that such interaction depends on the intensity of light: The Coulomb screening is changed. Thus the phase shift contains information about the microscopic interaction among the carriers.
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Remy, Quentin. "Ultrafast spin dynamics and transport in magnetic metallic heterostructures". Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0191.
Testo completoAbstract (sommario):
Le contrôle de l'aimantation, et donc du spin, aux échelles de temps ultra courtes, est un sujet d'importance fondamentale pour l'élaboration de systèmes qui peuvent stocker de l'information beaucoup plus rapidement. La possibilité d'écrire de l'information avec des pulses laser femtoseconde sur des métaux magnétiques tels que GdFeCo ou MnRuGa en quelques picosecondes fut une étape conséquente pour pouvoir réaliser ce progrès technologique. Cependant, le renversement de l'aimantation observé dans ces matériaux après les avoir irradié avec un unique pulse laser, appelé retournement tout optique indépendant de l'hélicité (AO-HIS pour {All Optical Helicity Independent Switching} en anglais), est toujours limité à une petite catégorie de matériaux ferrimagnétiques et sa description physique n'est toujours pas entièrement comprise. Dans cette thèse, nous étudions l'AO-HIS dans des films minces composés d'une ou deux couches d'alliages de GdFeCo de différentes compositions. Nous montrons que ces couches génèrent des courants de spin qui peuvent modifier l'AO-HIS de ces matériaux. En particulier, nous montrons qu'il est possible d'utiliser ces courants de spin pour renverser l'aimantation des différentes multicouches ferromagnétiques, avec un seul pulse laser femtoseconde, qui ne subiraient qu'une désaimantation et ne se retourneraient donc pas autrement. En changeant la composition de l'alliage de GdFeCo et la température de Curie du matériau ferromagnétique, nous pouvons modifier l'énergie nécessaire pour engendrer le renversement magnétique de la multicouche ferromagnétique avec un pulse de lumière. De plus, nous montrons que l'AO-HIS de l'alliage de GdFeCo n'est en réalité pas nécessaire ainsi que l'illumination directe de la couche ferromagnétique par la lumière laser. Il est donc possible de retourner l'aimantation d'un matériau ferromagnétique en utilisant uniquement des courants ultra courts de chaleur et de spin qui sont créés par la désaimantation ultra rapide partielle de l'alliage de GdFeCo et transportés jusqu'à la couche ferromagnétique via une couche de cuivre. Ces expériences sont comprises grâce à un modèle de transport semi classique dans un système contenant des électrons, des phonons et des spins quantiques et qui est basé sur l'échange de moment cinétique entre des spins localisés et itinérants. Enfin, nous avons mesuré la dynamique du renversement de l'aimantation de ce système ferromagnétique. Nous montrons que ce retournement se passe en moins d'une picoseconde, ce qui est le retournement d'aimantation le plus rapide jamais observé. Nous montrons que le courant de spin provenant de l'alliage de GdFeCo à un pouvoir réfrigérant sur l'aimantation, déjà visible en moins d'une picoseconde, et qui peut augmenter l'aimantation transitoire du système jusqu'à trente pourcents. Ces résultats sont également compris dans le cadre de notre modèle de transport de chaleur et de moment cinétiqueThe control of magnetization, and thus spin, at the shortest timescale, is a fundamental subject for the development of faster data storage devices. The capability to encode information with femtosecond laser pulses on magnetic metals such as GdFeCo or MnRuGa within a few picoseconds was a significant step towards the realization of such a technology. However, the reversal of magnetization observed in these materials upon a single laser pulse irradiation, called All Optical Helicity Independent Switching (AO-HIS), is still limited to a small class of ferrimagnetic materials and its physical mechanism is not completely understood.In this work, we study AO-HIS in magnetic thin films composed of a single or two GdFeCo layers with different alloy compositions. We show that these layers generate spin currents that can affect the AO-HIS of these materials. In particular, we can use such spin currents to reverse the magnetization of various ferromagnetic multilayers, with a single femtosecond laser pulse, which would otherwise only demagnetize and never switch. Playing with the GdFeCo alloy concentration and the ferromagnetic multilayer Curie temperature, we can tune the energy required to observe single shot reversal of the ferromagnet. In addition, we show that neither AO-HIS of the GdFeCo layer is actually required nor direct light illumination of the ferromagnetic multilayer. It is then possible to reverse the magnetization of ferromagnets using only ultrashort heat and spin currents which are generated by the partial ultrafast demagnetization of GdFeCo and transported via a thick metallic copper spacer. These experimental results were successfully understood using semiclassical transport equations for electrons, phonons and quantum spins based on exchange of angular momentum between localized and itinerant spins.Finally, we were able to measure the dynamics of the ferromagnetic multilayer magnetization reversal which is shown to happen in less than a picosecond, being the fastest magnetization reversal ever observed. The action of the external spin current is shown to have an ultrafast cooling effect on the spin which is visible at the sub-picosecond timescale and which can enhance the transient magnetization by up to thirty percent. These results are also understood using our model of heat and angular momentum transport
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Gil, Villalba Abel. "Single shot ablation of monolayer graphene by spatially shaped femtosecond laser pulses". Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCD028/document.
Testo completoAbstract (sommario):
Depuis sa découverte expérimentale en 2004, le graphène a émergé comme un matériau potentiel pour les technologies de nouvelle génération. Le graphène était le premier matériau 2D produit et l’intérêt et qu’il suscite provient de ses remarquables propriétés: il possède d’importants coefficients de mobilité électronique et de conductivité thermique, il est également le matériau le plus solide et léger connu. Pour permettre le développement d’applications à l’ échelle industrielle, des technologies de structuration à l’ échelle submicronique sont nécessaires.Cette thèse se concentre sur l’exploration de l’ablation par laser femtoseconde en tant que technique de structuration rapide et peu coûteuse de structuré graphène obtenu par technique CVD (Chemical Vapor Deposition). L’utilisation d’impulsions laser ultra brèves est a priori intéressante en raison de la capacité des impulsions laser ultra brèves à déposer au sein des matériaux une quantité élevée d’ énergie dans un volume extrêmement confiné.Nous avons réalisé un ensemble d’expériences à partir de faisceaux non-diffractants pour caractériser les paramètres requis pour contrôler l’ablation à l’ échelle sub-micronique. Nous avons déterminé les caractéristiques de l’ablation en régime mono-coup pour le graphène CVD, tels que le seuil d’ablation et la probabilité d’ablation. Pour cela, nous avons développé une nouvelle technique de mesure indépendante du seuil indépendante de la taille de la zone ablatée. Nous avons ainsi pu mettre en évidence un écart par rapport au modèle classique d’ablation, l’effet des différents substrats diélectriques, ainsi que le rôle des joints de grain.Nos résultats montrent que l’ablation mono-coup par impulsion femtoseconde est une technique efficace pour des structures au-delà d’une taille caractéristique de 1 _m, mais en dessous de cette dimension, de nouvelles stratégies d’illuminations se révèlent encore nécessairesSince its isolation in 2004, graphene has emerged has a potential material for next generation technologies.Graphene was the first truly 2D material produced. The interest in this material is due to its outstandingproperties: graphene is the lightest and strongest material known. It has a large electronic mobility andthermal conductivity. To enable the development of technological applications at industrial scale, fast patterningtechniques, operable at sub-micron scale are needed.This thesis focuses on the requirement of a fast, easily reconfigurable, low cost method to pattern graphene.The aim of our research is to determine the possibilities and constraints of ultrafast laser ablation of CVDgraphene at sub-micron scale. Using ultrafast laser to pattern graphene layers is interesting due to the abilityof femtosecond laser pulses to accurately depositing a high energy density in confined regions.We performed a set of experiments using non-diffractive shaped-beams to characterize the parametersrequired to control laser material processing at such small scale. We determined laser patterningcharacteristics on CVD monolayer graphene such as the ablation threshold and the ablation probability. To thisaim, we have developed a novel technique to measure ablation threshold that is independent of the ablated sizeand reported unexpected deviation from the threshold model, we also investigated the influence of differentdielectric substrates and the effect of the presence of graphene grain boundaries. From our experimentalresults we conclude that direct single shot laser patterning is a very effective method to pattern features above 1 µm, but below this dimension, novel illumination strategies are needed
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Ju, Heongkyu. "Photon-number squeezing of femtosecond optical pulses in nonlinear media". Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249632.
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Ueffing, Moritz [Verfasser], e Ferenc [Akademischer Betreuer] Krausz. "Direct amplification of femtosecond pulses / Moritz Ueffing ; Betreuer: Ferenc Krausz". München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2018. http://d-nb.info/1159506523/34.
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Campbell, Stuart. "Advances in femtosecond pulse laser micromachining and index waveguide inscription". Thesis, Heriot-Watt University, 2007. http://hdl.handle.net/10399/67.
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Suresh, M. "Neutral and ionic atoms and molecules in femtosecond laser pulses". Thesis, Queen's University Belfast, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421008.
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Gouveia, Neto Artur da Silva. "Femtosecond pulse generation and propagation in single-mode optical fibres". Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47085.
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Kauer, Matthias. "Ultrafast dynamics and propagation of femtosecond pulses in semiconductor lasers". Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621970.
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McCracken, Richard A. "Femtosecond optical parametric oscillator frequency combs for coherent pulse synthesis". Thesis, Heriot-Watt University, 2013. http://hdl.handle.net/10399/2702.
Testo completoAbstract (sommario):
Coherent pulse synthesis takes as its objective the piecewise assembly of a sequence of identical broadband pulses from two or more mutually-coherent sequences of narrowband pulses. The requirements for pulse synthesis are that the parent pulses share the same repetition frequency, are phase coherent and have low mutual timing jitter over the required observation time. The work carried out in this thesis explored the requirements for broadband coherent pulse synthesis between the multiple visible outputs of a synchronously pumped femtosecond optical parametric oscillator. A femtosecond Ti:sapphire laser was characterised and used to pump a PPKTP-based OPO that produced a number of second-harmonic and sum-frequency mixing outputs across the visible region. Using a novel lock-to-zero CEO stabilisation technique, broadband phase coherence was established between all the pulses on the optical bench, producing the broadest zero-offset frequency comb to date. Employing a common optical path for all the pulses provided common-mode rejection of noise, ensuring less than 150 attoseconds of timing jitter between the pulses over a 1 second observation window. The parent pulses were compressed and their relative delays altered in a quasi-common path prism delay line, allowing pulse synthesis at a desired reference plane.
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Salzmann, Wenzel. "Photoassociation and coherent control of ultracold molecules by femtosecond pulses". [S.l. : s.n.], 2007.
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Xu, Bingwei. "Control of multiphoton molecular excitation with shaped femtosecond laser pulses". Diss., Connect to online resource - MSU authorized users, 2008.
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