Optimization of the Energy Deposition in Glasses with Temporally-Shaped Femtosecond Laser Pulses

International audienceBulk machining of glasses with femtosecond laser pulses enables the fabrication of embedded optical functions. Due to the nonlinear character of the laser-matter interaction, structural modifications can occur within the focal region. To reach a full control of the process, ways of controlling the deposition of the laser energy inside the material have to be unveiled. From static and time-resolved pictures of bulk-excitation of a-SiO2 and borosilicate glass, we show that particular laser temporal shapes such as picosecond sequences can better confine the energy deposition than the femtosecond sequence by reducing the propagation artifacts

Time-Resolved Observation of Energy Deposition in Fused Silica by Ultrashort Laser Pulses in Single and Cumulative Regime

International audienceWhen femtosecond laser pulses are focused in the bulk of transparent materials (glasses), deposition of energy on a restricted volume can occur owing to the non linear character of the laser matter interaction. As a consequence, the possibility to generate micrometer-sized structural modifications arises. Those local changes are often associated with a minute variation in the refractive index which, when positive, enables the fabrication of light guiding components in three dimensions through simple laser translation. Although the first corresponding experimental demonstration approaches fifteen years of age, the complete picture of the dynamics and the proc- esses leading to the local refractive index changes has still to be drawn to reach an optimal control of the laser-induced modification process. In this report, the laser-dielectric interaction is followed on an ultrashort time scale with the help of a unique time-resolved side-imaging technique allow- ing for absorption and phase contrast detection. Experimental observation of an absorptive elec- tronic cloud in the first moments of the interaction along with the launch of a pressure wave after a few ns is reported. These physical objects are shown to be reliable indicators of the success of the energy transfer to the lattice which largely depends on the pulse temporal envelope

Ultrafast Laser Processing using Optimized Spatial Beam Control

Writing the so-called ’HDR’ manuscript (standing for the french ’Habilitation à Diriger la Recherche’) is a somewhat frightening exercise. It is naturally difficult to look back and try to summarize years of research and collaborations. More delicate is to present the advances in the frame of the most recent scientific and technological results while trying to correctly describe the state of the art. Anticipating the next developments of a fast-evolving field of research such as ultrafast laser machining is not an easier task either. However, this step appears to be indispensable in a researcher’s career when the time comes to choose the next research efforts to be conducted. I would like here to use once and only once the famous sentence that this manuscript is written "to the best of my knowledge", hoping this will excuse any short-comings and mistakes in describing the state of the art of ultrafast laser micro machining and how my work stands in this international context. Let me clarify straight away the unclear expression "my work". Behind this, one has to realize that this involve far more than what my brain alone could have ever produce, even under the most efficient drugs. Indeed, a very large group of people including patient and passionate PhD supervisors and co-supervisors, friendly and hard-working colleagues, long-suffering PhD students and postdocs altogether with an enthusiastic and caring community has to be recognized here. I also want to add on the list the many people from other scientific and research communities. It is puzzling how multi disciplinary approaches can bring together the right people at the right moment, creating the appropriate frame for breakthroughs and innovative work. I will try to give some examples of this fact that I had the chance to notice during my career. Ultrafast laser pulses have also this unique property to trigger a deep curiosity in anyone who comes to deal with them. Sometimes appearing as a magical solution’ but still being in competition with much more experienced and mastered processes, this short wavepackets of light have not ceased to surprise the world and find more and more applications, not to mention here the 2018’s Nobel Prize recognizing as a major breakthrough the possibility to amplify these pulses. I hope that this manuscript, with the efforts made to render the reading accessible and the concepts easily understandable, can trigger such interest to the largest possible audience

Mise en forme spatio-temporelle d’impulsions laser ultracourtes pour la fonctionnalisation dans le volume de matériaux transparents

In the past decade, ultrashort laser sources have had a decisive impact on material processing for photonic applications. The technique is usually restricted to the elemental association of an ultrashort source with a focusing lens. It is thus limited in the achievable bulk modifications. Accompanying studies of material modifications in space and time, we propose here that automated spatio-temporal tailoring of the laser pulses is an efficient manner to overcome these limitations. More precisely, we demonstrate the generation of multiple processing foci for synchronous photomachining of multiple devices in the bulk. Thus, we report on the parallel photowriting of waveguides, light couplers, light dividers in 2D/3D in fused silica glass. We show that the domain of photowriting can be extended to deep focusing. We indicate that this can be achieved by wavefront shaping or temporal profile tailoring conducted by an evolutionary optimization loop. We also have unveiled a singular interaction regime where regular structuring takes place before the focal region. For the first time, the dynamics of the energy coupling to the glassy matrix is evaluated for various temporal pulse profiles. Enhanced energy confinement in the case of picosecond pulses is confirmed by characterization of the transient electronic gas and of the subsequent pressure. These pump-probe studies were carried out with a self-build time-resolved microscopy system with temporally shaped pump irradiation. We also developed a new method based on the Drude model to differentiate the electronic and matrix contributions to the contrast of the microscopy images.L’arrivée des sources lasers ultracourtes a bouleversé le domaine de la micro-structuration pour l’optique intégrée. Le plus souvent, le procédé se résume à l’utilisation d’une lentille de focalisation sur le trajet du faisceau laser. Cette méthode souffre de limitations intrinsèques sur la vitesse d’usinage et sur le spectre des modifications accessibles. Nous montrons dans ce mémoire que la mise en forme spatio-temporelle des impulsions lasers ultracourtes répond efficacement à ces défis. En particulier, nous indiquons la possibilité de multiplier le nombre de spots lasers pour la fabrication simultanée de plusieurs composants optiques, en répondant ainsi au besoin de rapidité. Cette avancée majeure est illustrée par la photoinscription en parallèle de guides, de diviseurs, de coupleurs ainsi que de démultiplexeurs de lumière en 2Det 3D dans la silice. Il est également reporté ici que le domaine de photoinscription peut être élargi à la focalisation profonde dans les matériaux grâce à la modulation du front d’onde ainsi que la mise en forme temporelle de l’impulsion permettant de préserver la densité d’énergie déposée. Le couplage d’énergie vers le matériau transparent en fonction de divers profils d’impulsions est étudié à l’échelle femtoseconde. La caractérisation du gaz d’électrons libres ainsi que de l’onde de pression nous permet de mettre en évidence l’efficacité des impulsions picosecondes `a déposer l’énergie de manière plus confinée dans différents verres. Ces études sont conduites sur un système de microscopie de type pompe-sonde permettant de mettre en forme l’irradiation pompe

Ultrafast laser spatial beam shaping using an optically addressed liquid crystal optical valve

International audienc

Ultrafast Laser Processing using Optimized Spatial Beam Control

Writing the so-called ’HDR’ manuscript (standing for the french ’Habilitation à Diriger la Recherche’) is a somewhat frightening exercise. It is naturally difficult to look back and try to summarize years of research and collaborations. More delicate is to present the advances in the frame of the most recent scientific and technological results while trying to correctly describe the state of the art. Anticipating the next developments of a fast-evolving field of research such as ultrafast laser machining is not an easier task either. However, this step appears to be indispensable in a researcher’s career when the time comes to choose the next research efforts to be conducted. I would like here to use once and only once the famous sentence that this manuscript is written "to the best of my knowledge", hoping this will excuse any short-comings and mistakes in describing the state of the art of ultrafast laser micro machining and how my work stands in this international context. Let me clarify straight away the unclear expression "my work". Behind this, one has to realize that this involve far more than what my brain alone could have ever produce, even under the most efficient drugs. Indeed, a very large group of people including patient and passionate PhD supervisors and co-supervisors, friendly and hard-working colleagues, long-suffering PhD students and postdocs altogether with an enthusiastic and caring community has to be recognized here. I also want to add on the list the many people from other scientific and research communities. It is puzzling how multi disciplinary approaches can bring together the right people at the right moment, creating the appropriate frame for breakthroughs and innovative work. I will try to give some examples of this fact that I had the chance to notice during my career. Ultrafast laser pulses have also this unique property to trigger a deep curiosity in anyone who comes to deal with them. Sometimes appearing as a magical solution’ but still being in competition with much more experienced and mastered processes, this short wavepackets of light have not ceased to surprise the world and find more and more applications, not to mention here the 2018’s Nobel Prize recognizing as a major breakthrough the possibility to amplify these pulses. I hope that this manuscript, with the efforts made to render the reading accessible and the concepts easily understandable, can trigger such interest to the largest possible audience

Mise en forme spatio-temporelle d’impulsions laser ultracourtes pour la fonctionnalisation dans le volume de matériaux transparents

L’arrivée des sources lasers ultracourtes a bouleversé le domaine de la micro-structuration pour l’optique intégrée. Le plus souvent, le procédé se résume à l’utilisation d’une lentille de focalisation sur le trajet du faisceau laser. Cette méthode souffre de limitations intrinsèques sur la vitesse d’usinage et sur le spectre des modifications accessibles. Nous montrons dans ce mémoire que la mise en forme spatio-temporelle des impulsions lasers ultracourtes répond efficacement à ces défis. En particulier, nous indiquons la possibilité de multiplier le nombre de spots lasers pour la fabrication simultanée de plusieurs composants optiques, en répondant ainsi au besoin de rapidité. Cette avancée majeure est illustrée par la photoinscription en parallèle de guides, de diviseurs, de coupleurs ainsi que de démultiplexeurs de lumière en 2Det 3D dans la silice. Il est également reporté ici que le domaine de photoinscription peut être élargi à la focalisation profonde dans les matériaux grâce à la modulation du front d’onde ainsi que la mise en forme temporelle de l’impulsion permettant de préserver la densité d’énergie déposée. Le couplage d’énergie vers le matériau transparent en fonction de divers profils d’impulsions est étudié à l’échelle femtoseconde. La caractérisation du gaz d’électrons libres ainsi que de l’onde de pression nous permet de mettre en évidence l’efficacité des impulsions picosecondes `a déposer l’énergie de manière plus confinée dans différents verres. Ces études sont conduites sur un système de microscopie de type pompe-sonde permettant de mettre en forme l’irradiation pompe.In the past decade, ultrashort laser sources have had a decisive impact on material processing for photonic applications. The technique is usually restricted to the elemental association of an ultrashort source with a focusing lens. It is thus limited in the achievable bulk modifications. Accompanying studies of material modifications in space and time, we propose here that automated spatio-temporal tailoring of the laser pulses is an efficient manner to overcome these limitations. More precisely, we demonstrate the generation of multiple processing foci for synchronous photomachining of multiple devices in the bulk. Thus, we report on the parallel photowriting of waveguides, light couplers, light dividers in 2D/3D in fused silica glass. We show that the domain of photowriting can be extended to deep focusing. We indicate that this can be achieved by wavefront shaping or temporal profile tailoring conducted by an evolutionary optimization loop. We also have unveiled a singular interaction regime where regular structuring takes place before the focal region. For the first time, the dynamics of the energy coupling to the glassy matrix is evaluated for various temporal pulse profiles. Enhanced energy confinement in the case of picosecond pulses is confirmed by characterization of the transient electronic gas and of the subsequent pressure. These pump-probe studies were carried out with a self-build time-resolved microscopy system with temporally shaped pump irradiation. We also developed a new method based on the Drude model to differentiate the electronic and matrix contributions to the contrast of the microscopy images

Ultrafast laser beam tailoring for efficient surface and bulk processing

International audienceUltrafast laser beam tailoring for efficient surface and bulk processin

Ultrafast laser processing with optimized wavefront modulation by liquid crystral based spatial light modulators

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Photoinscription par laser à impulsions ultrabrèves pour des systèmes optiques 3D

International audienceUltrafast laser photoinscription experienced strong development fueled by its capability to confine energy in micro-domains of arbitrary geometries. This locally modifies the material structure, changing the refractive index design and lays down the concept of three-dimensional modifications for novel and efficient optical functions. We discuss the physical mechanisms of photoinscription, outlining the possibility of refractive index engineering. Subsequently we present different irradiation geometries for photoinscription and pinpoint their potential to generate photonic systems in 3D. Finally we indicate a range of application domains, from telecom to optofluidics and astrophotonics.La photoinscription par laser à impulsions ultracourtes a connu un fort développement du fait de sa capacité à confiner l'énergie à l'échelle micrométrique. La structure du matériau irradié peut ainsi être modulée spatialement en 3D pour réaliser des fonctions optiques innovantes en volume. Cet article aborde les mécanismes physiques de la photoinscription et les possibilités liées au contrôle local de l'indice de réfraction. Différentes stratégies de photoinscription sont ensuite discutées, ainsi que le potentiel pour générer des composants photoniques en 3D. Divers domaines d'applications sont considérés, des télécommunications à l'astrophotonique, en passant par l'optofluidique