Excitation and relaxation dynamics in ultrafast laser irradiated optical glasses

We discuss the dynamics of ultrashort pulsed laser excitation in bulk optical silica-based glasses (fused silica and borosilicate BK7) well-above the permanent modification threshold. We indicate subsequent structural and thermomechanical energy relaxation paths that translate into positive and negative refractive index changes, compression and rarefaction zones. If fast electronic decay occurs at low excitation levels in fused silica via self-trapping of excitons, for carrier densities in the vicinity of the critical value at the incident wavelength, persistent long-living absorptive states indicate the achievement of low viscosity matter states manifesting pressure relaxation, rarefaction, void opening and compaction in the neighboring domains. An intermediate ps-long excited carrier dynamics is observed for BK7 in the range corresponding to structural expansion and rarefaction. The amount of excitation and the strength of the subsequent hydrodynamic evolution is critically dependent on the pulse time envelope, indicative of potential optimization schemes

Saints and lovers: myths of the avant-garde in Michel Georges-Michel's Les Montparnos

This article examines Michel Georges-Michel’s 1924 novel Les Montparnos as a study of the myths circulating around the Montparnasse avant-garde of the 1920s, and their function in relation to art. Key amongst these myths is the idea of art as a religion, according to which avant-garde artists are conceived as secular saints and martyrs. While this notion of artist as saint is strongly present in early-twentieth-century biographies of Van Gogh, Georges-Michel explicitly relates his fictionalized version of Modigliani’s life not to such recent models but rather to the Renaissance masters, and especially to Raphael, a link which is explained in terms of the post-war ‘retour à l’ordre’ in French artistic culture. The novel’s references to Raphael as archetypal painter-lover are also related to its construction of a myth of the artist as virile and sexually prolific, and to its identification of creative and sexual impulses

Analysis of real-time networks with monte carlo methods

Communication networks in embedded systems are ever more large and complex. A better understanding of the dynamics of these networks is necessary to use them at best and lower costs. Todays tools are able to compute upper bounds of end-to-end delays that a packet being sent through the network could suffer. However, in the case of asynchronous networks, those worst end-to-end delay (WEED) cases are rarely observed in practice or through simulations due to the scarce situations that lead to worst case scenarios. A novel approach based on Monte Carlo methods is suggested to study the effects of the asynchrony on the performances

Influence of multiscale and curved structures on the behavior stem cells and macrophages

International audienceOral Influence of multiscale and curved structures on the behavior stem cells and macrophages Vanessa Belaud (a) (b) (c) Stéphane Benayoun (b) Karine Anselme (c) Cyril Mauclair (d) Christophe Donnet (d) (a) Université de Lyon, Labex Manutech size (b) LTDS, Lyon (c) IS2M, Mulhouse (d) LaHC, St-Etienne The direction and motion of cells have a key role in many physiological processes, such as tissue morphogenesis, or embryonic development. These interactions are regulated by the chemical surface properties of the biomaterial and its surface topography. Topographical modifications of surfaces (µm and nm) are known to induce changes in cell shape and adhesion, thereby affecting cell behavior. The control of the cell contact guidance is very promising. Ko and al. have shown that the junction angles, can modulate the motion speed of cells without altering their directionality. Generally speaking, in its environment, the cell is not confronted to structures having strict corners, but to curved structures. Anselme and al. have studied that the influence of curved structures on cell behavior and Laser Induced Periodic Surface Structures (LIPSS) in static mode separately. In this work, the structures which were both curved and multi-scale patterned were designed and their influence on cell behavior was studied. TA6V is one of the most commonly used metallic alloys in biomedical applications. A femtosecond laser was used as a surface texturing technique in order to create multi-scale structures on the TA6V surface: material ablation (30µm) and generation of LIPPS (~600nm). The present work focused on stem and marcrophage cells motion (position, direction and speed) within multi-scaled structures to verify whether the LIPSS has a competitive or a complementary effect on cell movement

Light absorption by surface nanoholes and nanobumps

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Influence des structures curvilignes multi-échelles obtenue par laser femtoseconde sur la migration des cellules

La mission du groupement est de fédérer les connaissances dans les domaines de la mécanique des fluides et matériaux biologiques au sein d'INSIS (sections 09-10-28) en interaction avec la biologie (INSB) et la physique (INP). Il vise à regrouper les chercheurs travaillant dans le domaine de la biomécanique en synergie avec des biologistes et des cliniciens. Une quarantaine d'équipes participent actuellement au GDR. Les problèmes fondamentaux de Modélisation et caractérisation de fluides biologiques en interaction et de Modélisation et caractérisation de matériaux du et pour le vivant ainsi que de leur évolution dynamique sont particulièrement visés. Le GDR travaille aussi en interaction avec le GDR "Réparer l'humain", qui centre ses activités sur le thème de la médecine réparatrice.International audienceInfluence des structures curvilignes multi-échelles obtenue par laser femtoseconde sur la migration des cellule

Investigation and control of ultrafast laser-induced isotropic and anisotropic nanoscale-modulated index patterns in bulk fused silica

Ultrafast laser-induced refractive index changes in a-SiO2 consist, depending on the irradiation conditions, of either positive variations, voids, or regular nanoscale patterns, each of these underlying specific structural transformations. These allow for obtaining a large palette of optical functions ranging from low loss guiding to anisotropic scattering. While briefly reviewing the excitation mechanisms, we spectroscopically interrogate local electronic and structural transformations of the glass in the isotropic index zones and in the regular self-organized nanostructures, indicating bond breaking and matrix oxygen deficiency. A spatial defect segregation marks the material transformation in the different photoinscription regimes. We equally propose a method of real time control of nanogratings formation under the action of ultrashort laser pulse with variable envelopes. Application as polarizing optical devices is discussed. (C) 2013 Optical Society of Americ

Optimization of the energy deposition in glasses with temporally-shaped femtosecond laser pulses

Bulk 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

Influence of pulse repetition rate on morphology and material removal rate of ultrafast laser ablated metallic surfaces

International audienceUltrafast laser ablation is an efficient method for precise micro-machining. Thanks to the recent development of high repetition rate ultrafast lasers, high speed laser scanning of surfaces is more and more employed to generate micro-/nano-surface structures on metals for a vast variety of applications. Issues associated with these lasers are also identified in micro-machining practice. It is commonly believed that, due to possible shielding effects, the conditions of high fluences and high repetition rates compromise an efficient material removal. However, in this study, based on topography and differential weighing evaluations, we report that the material removal rate holds constant even in sub-MHz regime, up to about 20 J/cm 2. The morphology of the post-irradiated surface is found to be determined not only by laser processing conditions but also by the material properties on the other hand. Two trends are experimentally identified in surface laser ablation of Ni, Cu, titanium alloy TA6V and stainless steel 316L: while the former two show a low roughness (Ra below 0.5 μm) at all irradiation conditions , the machining quality of the two later ones degrades rapidly with increasing fluences and repetition rates. In such a scenario, a rugged surface layer of 10-20 μm thickness is formed with the presence of numerous subsurface voids. Microstructural analysis is carried out in order to infer physical transition involved in the micro-machining process. Possible mechanisms accounting for the observation are discussed, especially those related to the electron-phonon coupling, plasma dwelling, and capillary waves. These insights pave the way for tailored, material dependent optimizations of ultrafast laser micro-machining processes