Fonctionnalisation de surface par laser ultrarapide et mise en œuvre pour les applications industrielles : planification de trajectoire basée sur la vision par ordinateur

International audienceThe unique laser-matter interaction pathway in the ultrafast regime opens up many key potential applications in biology, electronics, optics, and beyond. However, upscaling local laser texturing on large and freeform surfaces remains a challenge for the deployment of the technology at an industrial level. In this concern, path planning appears as a crucial preliminary step to succeed in an accurate and fast process. In the present work, we develop a methodology delivering an optimal scan path from a 3D point cloud on the surface to be laser treated. It can be implemented for any laser scanner embedded in a mobile head. The scan path is here defined by the sequence of target points centered in a 3D mesh adapted to the surface curvature, and calculated with surface normal, to obtain the positioning of the laser head in space for laser texturing the mesh cells, successively.L’interaction laser-matière en régime ultrarapide ouvre des perspectives clés dans de nombreuses applications en biologie, en électronique, en optique et au-delà. Cependant, la mise à l’échelle de la texturation laser locale sur de grandes surfaces de forme libre reste un défi pour le déploiement de la technologie au niveau industriel. Dans cette perspective, la planification du parcours de la tête laser apparaît comme une étape préliminaire cruciale pour réussir une texturation précise et rapide. Dans ces travaux, nous développons une méthodologie fournissant un chemin de balayage optimal à partir d'un nuage de points 3D de la surface à traiter au laser. Il peut être mis en œuvre pour tout scanner laser embarqué dans une tête mobile. Le chemin de balayage est ici défini par la séquence de points cibles centrés dans un maillage 3D adapté à la courbure de la surface, et calculé avec la normale à la surface. Il donne ainsi les positions de la tête laser dans l'espace et les cellules de maillage à texturer, séquentiellement

Laser Textured Black Silicon Solar Cells with Improved Efficiencies

International Conference on Intelligent Materials and Mechanical Engineering (MEE 2011), Guangzhou, PEOPLES R CHINA, SEP 24-25, 2011International audienceFemtosecond laser irradiation of silicon has been used for improving light absorption at its surface. In this work we demonstrate the successful implementation of femtosecond laser texturisation to enhance light absorption at Si solar cell surface. In order to adapt this technology into solar industry, the texturisation process is carried out in air ambient. The microstructure similar to what has been produced in vacuum can be made in air by using appropriate laser conditions. The texturised surface shows excellent optical properties with a reflectivity down to 7% without crystalline orientation dependence. Junction formation and metallisation proceeded after texturisation. Suns-Voc measurements are performed to evaluate the cell performance and decent electrical characteristics have been achieved

Advanced ultrafast laser Bessel beam for hybrid machining in metallic materials

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Ultrafast Cylindrical Vector Beams for Improved Energy Feedthrough and Low Roughness Surface Ablation of Metals

The use of ultrafast cylindrical vector vortex beams in laser–matter interactions permits new ablation features to be harnessed from inhomogeneous distributions of polarization and beam geometry. As a consequence, the ablation process can yield higher ablation efficiency compared with conventional Gaussian beams. These beams prevent surface quality degradation during the ablative processes. When processing stainless steel and titanium, the average surface roughness obtained by deploying the cylindrical vector is up to 94% lower than the Gaussian case, and the processing efficiency is 80% higher

Nondestructive inspection of surface nanostructuring using label-free optical super-resolution imaging

International audienceAbstract Ultrafast laser processing can induce surface nanostructurating (SNS) in most materials with dimensions close to the irradiation laser wavelength. In-situ SNS characterization could be key for laser parameter’s fine-tuning, essential for the generation of complex and/or hybrid nanostructures. Laser Induced Periodic Surface Structures (LIPSS) created in the ultra-violet (UV) range generate the most fascinating effects. They are however highly challenging to characterize in a non-destructive manner since their dimensions can be as small as 100 nm. Conventional optical imaging methods are indeed limited by diffraction to a resolution of $$\approx 150$$ ≈ 150 nm. Although optical super-resolution techniques can go beyond the diffraction limit, which in theory allows the visualization of LIPSS, most super-resolution methods require the presence of small probes (such as fluorophores) which modifies the sample and is usually incompatible with a direct surface inspection. In this paper, we demonstrate that a modified label-free Confocal Reflectance Microscope (CRM) in a photon reassignment regime (also called re-scan microscopy) can detect sub-diffraction limit LIPSS. SNS generated on a titanium sample irradiated with a $$\lambda =257$$ λ = 257 nm femtosecond UV-laser were characterized with nanostructuring period ranging from 105 to 172 nm. Our label-free, non-destructive optical surface inspection was done at 180 \upmu μ m $$^2$$ 2 /s, and the results are compared with commercial SEM showing the metrological efficiency of our approach

Edge isolation using ultra-short pulse laser materials with a top-hat beam profile

International Conference on Intelligent Materials and Mechanical Engineering (MEE 2011), Guangzhou, PEOPLES R CHINA, SEP 24-25, 2011International audienceLaser grooving is an existing industrial solution for solar cell junction isolation. However there is still plenty room to improve this process. Potential approach includes choosing proper laser wavelength, tuning laser pulse width and laser focus beam profile, etc. We have recently investigated laser edge isolation of crystalline silicon solar cells using an ultra-short pulse laser. In this study we carried out isolation test using the same laser with a top-hat beam profile. A comparative study between isolation using top-hat and Gaussian is launched. The geometry of laser scribed grooves and the electrical performance of the cells are characterised. More homogenous ablation and material removal are achieved using top-hat hence the dopants from the isolation groove area are eliminated efficiently. The results from I-V characterisation confirm that more efficient isolation process and better isolation quality can be achieved using top-hat

Ultra-short Laser Surface Functionalization: from Modeling to Bioengineering

International audienceFemtosecond laser texturing allows one to produce various surface relief ranging from nano- and micro ones to much more complex multi-scale pattern. In this context, the main advantages of using ultra-short laser pulses are known to be in a reduction of thermal effects, of debris, and of the surface contamination. Additionally, combinations of laser-induced micro- and nano- reliefs have strong capacities to alternate cell-surface interactions and even to guide cell behavior. Despite previously demonstrated link of cell behavior with wetting properties, the definition of the best laser treatment condition remains challenging. In particular, the difficulty arises from the change in surface wettability with time after laser treatment, but also due to annealing, sterilization, ultra-sound or cold plasma treatment. The reasons for these changes are not yet well understood. For this, femtosecond laser irradiation of titanium-based surfaces is used. As a result, multi-scale textures are produced with high precision. A series of simulations were also performed to determine the properties of these surfaces. Their wetting properties were tested and the capacities to guide stem cells were evaluated. Several templates with different sizes and motifs have been tested. In addition, human stem cell cultures (HSC) have been cultivated on several structured surfaces. The results reveal that HSCs preferentially place their nuclei in the pits with a diameter about the cell size, while the cell were looking for the hydrophilic areas for the attachment of their periphery. As a result, wetting maps can serve to predict cellular behavior. To better understand the involved mechanisms, wetting tests were performed for several surface reliefs and the results were compared to the results of our modeling. The obtained results are particular helpful in bioengineering, for cellular tests, for the treatment of various prosthesis, as well as of dental implants

Investigation of structural effects induced by LIPSS formation with a HR-EBSD approach

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Contrôle non destructif de nanostructurations de surface par imagerie de super-résolution optique sans marque

Ultrafast laser processing can induce surface nanostructurating (SNS) in most materials with dimensions close to the irradiation laser wavelength. In-situ SNS characterization could be key for laser parameter's fine-tuning, essential for the generation of complex and/or hybrid nanostructures. Laser Induced Periodic Surface Structures (LIPSS) created in the ultraviolet (UV) range generate the most fascinating effects. They are however highly challenging to characterize in a non-destructive manner since their dimensions can be as small as 100 nm. Conventional optical imaging methods are indeed limited by diffraction to a resolution of ≈ 150 nm. Although optical super-resolution techniques can go beyond the diffraction limit, which in theory allows the visualization of LIPSS, most super-resolution methods require the presence of small probes (such as fluorophores) which modifies the sample and is usually incompatible with a direct surface inspection. In this paper, we demonstrate that a modified label-free Confocal Reflectance Microscope (CRM) in a photon reassignment regime (also called re-scan microscopy) can detect sub-diffraction limit LIPSS. SNS generated on a titanium sample irradiated with a λ =257 nm femtosecond UV-laser were characterized with nanostructuring period ranging from 105 nm to 172 nm. Our label-free, non-destructive optical surface inspection was done at 180µm²/s, and the results are compared with commercial SEM showing the metrological efficiency of our approach.L'interaction entre un laser ultrarapide et une objet peut induire une nanostructuration de surface (NSS) dans la plupart des matériaux, avec des dimensions proches de la longueur d'onde du laser d'irradiation. La caractérisation de NSS in-situ pourrait être la clé permettant un réglage fin des paramètres lasers, essentiel pour la génération de nanostructures complexes et/ou hybrides. Les structures de surface périodiques induites par laser (LIPSS) générées par une illumination ultraviolette (UV) génèrent les effets les plus fascinants. Ils sont cependant très difficiles à caractériser de manière non destructive puisque leurs dimensions descendre à 100 nm. Les méthodes d'imagerie optique classiques sont en effet limitées par la diffraction à une résolution de ≈ 150 nm. Bien que les techniques de super-résolution optique puissent aller au-delà de la limite de diffraction, ce qui permet en théorie la visualisation de LIPSS, la plupart des méthodes de super-résolution nécessitent la présence de petites sondes (comme des fluorophores) qui modifient l'échantillon et sont généralement incompatibles avec une imagerie directe des surfaces. Dans cet article, nous démontrons qu'un microscope confocale en réflectance sans marquage (CRM) dans un régime de réallocation de photons (également appelé microscopie de re-scan) peut détecter des LIPSS spis la limite de diffraction. Les NSS générées sur un échantillon de titane irradié avec un laser UV femtoseconde λ = 257 nm ont été caractérisés avec une période de nanostructuration allant de 105 nm à 172 nm. Notre inspection de surface optique sans marquage et non destructive a été effectuée à 180 µm²/s, et les résultats sont comparés avec un MEB commercial montrant l'efficacité métrologique de notre approche