1,721,041 research outputs found
On the existence of nanogratings in commercial oxide glasses
Full text linkThe ability to induce nanogratings using a femtosecond laser in common oxide glasses is investigated experimentally. A simple and general viscosity-based approach is subsequently employed to predict their existence in glass
Application and validation of a viscosity approach to the existence of nanogratings in oxide glasses
Full text linkNanogratings are self-organized and sub-wavelength birefringent structures that are formed upon the action of high intensity ultrashort light pulses in the bulk of a transparent material. They have found interest in optics/photonics, microfluidics, optical data storage or sensing applications. However, the ability to successfully imprint 3-dimensional (3D) nanogratings in silicate glasses is a strong function of the glass composition. In this work, we investigate the role of glass viscosity on the ability to induce these nanogratings. We first study the nanogratings formation window in an energy-repetition rate laser parameter landscape for five common oxide glasses: SiO2 (Suprasil), GeO2, and Schott glasses AF32, Borofloat, and BK7. Secondly, and based on previous work, we define a domain of existence of the nanogratings using viscosity-based arguments. The lower limit corresponds to a temperature at which the viscosity is ~106.6 Pa⋅s, where nanocavitation of the glass occurs, forming the nanopores that compose the nanogratings. An upper temperature limit, set for a viscosity value of ~103.0 Pa⋅s, relates to either collapse or growth of the nanopores, resulting in the erasure of the nanopores, hence the nanogratings. The experimental results agree with the predictions made by this viscosity approach and literature data. This work opens the door to future glass viscosity engineering to maximize 3D nanogratings imprinting
On the Formation of Nanogratings in Commercial Oxide Glasses by Femtosecond Laser Direct Writing
Full text linkNanogratings (NGs) are self-assembled subwavelength and birefringent nanostructures created by femtosecond laser direct writing (FLDW) in glass, which are of high interest for photonics, sensing, five-dimensional (5D) optical data storage, or microfluidics applications. In this work, NG formation windows were investigated in nine commercial glasses and as a function of glass viscosity and chemical composition. The NG windows were studied in an energy—frequency laser parameter landscape and characterized by polarizing optical microscopy and scanning electron microscopy (SEM). Pure silica glass (Suprasil) exhibits the largest NG window, whereas alkali borosilicate glasses (7059 and BK7) present the smallest one. Moreover, the NG formation windows progressively reduced in the following order: ULE, GeO2, B33, AF32, and Eagle XG. The NG formation window in glasses was found to decrease with the increase of alkali and alkaline earth content and was correlated to the temperature dependence of the viscosity in these glasses. This work provides guidelines to the formation of NGs in commercial oxide glasses by FLDW
Tunability of form birefringence induced by femtosecond laser irradiation in anion-doped silica glass
No full textForm birefringence originating from self‐assembly of the bulk nanograting structures in silica glass with various anion dopants (OH, Cl and F) was induced by the femtosecond laser pulses. Despite the almost similar nanostructure, the photo‐induced birefringence can be changed by the anion dopants in glass. Larger birefringence can be induced in silica glass doped with higher Cl ion concentration. Even if F‐doped silica glass indicates lower thermal stability, its lifetime could be evaluated to be at least several billion years
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Ultrafast Laser Direct Writing Nanogratings and their Engineering in Transparent Materials
Full text linkFemtosecond laser direct writing is a powerful technique for fabricating micro-nano devices as it can modify the interior of transparent optical materials in a spatially selective manner through nonlinear multi-photon absorption. In this context, laser-induced nanogratings, i.e., a sub-wavelength assembly of nanolayers (approximate to 20 nm in width, approximate to 200 nm period), are ultrashort self-organized structures created by light in the bulk of transparent materials. These have been intensively explored over the last two decades opening a novel era of micro photonic devices due to their unique physicochemical properties, like orientable form birefringence, anisotropic light scattering, highly selective chemical etching, optical chirality, and extraordinary thermal stability. This review provides a throughout overview of the advances in this field, specifically focused on the formation of nanogratings, optical properties that can be exploited in various transparent solids, and the related main applications. Also, the fundamental characteristics, formation mechanism, tuning methods of nanogratings are reviewed
Study and 3D texturing of optical glasses by femtosecond laser for infrared applications
No full textDe nombreuses recherches sont aujourd'hui menées afin de miniaturiser et simplifier les caméras infrarouges dans le but de les intégrer à de petits porteurs tels que des micro drones. L'objectif est de fonctionnaliser des composants habituellement inutilisables en conception optique tels que les filtres ainsi que de mieux corriger les aberrations optiques. Dans ce cadre, la texturation par laser femtoseconde permet de créer des gradients d'indice de réfraction à l'intérieur de la matière. La flexibilité de la technique pourrait permettre la fabrication de composants optiques non-conventionnels. Dans ce contexte, nous avons étudié la méthode de la texturation par laser femtoseconde afin de créer des lentilles à gradient d'indice dans quatre matériaux spécifiques et dans le but de simplifier des caméras infrarouges. Trois types de lentilles à gradient d'indice ont été modélisées : une lentille boule à gradient d'indice sphérique permettant de corriger les aberrations optiques, une lentille plate à gradient d'indice de petit diamètre permettant de simplifier une caméra dans le LWIR et une lentille de Fresnel plate à gradient d'indice permettant de simplifier une caméra cryogénique dans le MWIR. Les lentilles plates ont ensuite été fabriquées et partiellement caractérisées. Cette étude a ainsi permis de montrer la capacité de la texturation par laser femtoseconde à fabriquer des optiques à gradient d'indice.Miniaturizing and simplifying infrared optical systems is a research area of great interest nowadays in order to integrate them into small carriers such as micro-UAVs. The objective is to functionalize components usually unusable in optical design such as filters and to better correct optical aberrations. In this context, femtosecond laser writing allows to create a gradient index inside the material. The flexibility of the technique could allow the fabrication of unconventional optical components. In this context, we have studied the femtosecond laser writing method to create gradient index lenses in four specific materials for the purpose of simplifying infrared cameras. Three types of gradient index lenses were modeled: a spherical gradient index ball lens to correct optical aberrations, a small diameter gradient index flat lens to simplify a camera in the LWIR, and a gradient index flat Fresnel lens to simplify a cryogenic camera in the MWIR. The flat lenses were then fabricated and partially characterized. This study has shown the ability of femtosecond laser texturing to fabricate gradient index optics
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Mécanismes de formation et effacement des nanoréseaux dans les verres d'oxyde par écriture directe laser femtoseconde
No full textLes nanoréseaux sont les plus petites structures « auto-organisées » jamais créées par la lumière dans le volume d'un matériau transparent. Ils ont été observés pour la première fois en 2003 à l'intérieur d'un verre de silice, et induits au moyen d'une irradiation par laser femtoseconde (fs). Ils ont suscité un grand intérêt ces dernières années en raison de propriétés particulières. Ils sont biréfringents, avec un axe neutre orientable dans l'espace grâce à la polarisation du laser fs. Ils peuvent également induire une biréfringence circulaire et un dichroïsme, présentent une stabilité thermique extraordinaire, et permettent une attaque chimique hautement sélective. En conséquence, ces nanostructures suscitent un intérêt dans des domaines tel quel le stockage optique de données, les dispositifs optiques biréfringents 2D ou 3D, les capteurs en environnement extrême, la microfluidique, etc. Ces nanoréseaux sont constitués d'un assemblage de couches nanoporeuses principalement observées dans la silice et les verres riches en silice. Plusieurs travaux ont pu mettre en évidence l'effet des propriétés physiques du verre (température de ramolissement, diffusivité thermique, etc.) sur leur processus de formation et d'effacement au cours de l'irradiation. En outre, l'importance de comprendre les mécanismes de formation réside dans la capacité de les produire de manière contrôlée, ainsi que d'acquérir une compréhension fondamentale plus approfondie des interactions complexes lumière-matière. Cette compréhension permettrait une généralisation dans tout type de verres optiques. Dans ce contexte, l'objectif de cette thèse est de mettre en évidence le lien entre la composition chimique des verres et la fenêtre d'inscription des nanoréseaux. De plus, nous sommes intéressés à mieux comprendre les mécanismes de formation et d'effacement des nanoréseaux pendant l'irradiation, afin de contrôler les propriétés optiques anisotropes associées à ces transformations (signe, amplitude, orientation, pertes associées). Premièrement, nous discutons de l'impact de la viscosité du verre sur leur existence à l'aide de l'équation de Rayleigh-Plesset. Il est établi que la viscosité est une propriété clé à considérer, et proposons un domaine d'existence des nanoréseaux grâce à une approche basée cette dernière, en faisant une série d'hypothèses sur les conditions de confinement thermique et de pression pendant l'irradiation. L'étude de la fenêtre d'existence dans un paysage taux de répétition - énergie d'impulsion pour un grand nombre de verres d'oxyde (commerciaux et réalisés en laboratoire), valide l'approche proposée, où la fenêtre théorique est bien corrélée à son équivalent expérimental. Ensuite, nous analysons la nanostructure interne des nanoréseaux par des techniques d'imagerie en microscopie électronique à haute résolution, rendant ainsi compte de leur formation à l'intérieur de la silice. Ces investigations à l'échelle nanométrique révèlent que leur structure intrinsèque est composée de nanopores aplatis, façonnés en nanoplans, régulièrement espacés et orientés perpendiculairement à la polarisation du laser. Ces couches nanoporeuses sont organisées par la lumière sous des effets thermomécaniques via un processus de nanocavitation assisté par le plasma. D'après les observations obtenues par des expériences de recuit en conditions isochrones, l'effacement des nanopores créés lors de l'irradiation laser est également fortement lié à la dépendance de la viscosité du verre à la température. Finalement cet effacement peut être prédit pour un processus temps-température quelconque. Ainsi, il devient possible de d'anticiper la durée de vie des nanoréseaux dans différents verres commerciaux, étendant ainsi notre travail bien au-delà de la silice.Nanogratings are the smallest "self-organized" structures ever created by light inside transparent materials. They were observed for the first time in 2003 inside silica glass and induced by femtosecond (fs) laser irradiation. They have drawn considerable attention over the last decades due to their unique properties. They are birefringent, with a neutral axis orientable in space through light polarization, can induce dichroism or circular birefringence, exhibit excellent thermal stability and a highly selective chemical etching. Consequently, they have shown promise in technological areas, including optical data storage, 2D/3D birefringent optical devices, sensing in harsh environments, microfluidics, etc. These nanogratings are composed of nanoporous layers, mostly observed in silica and silicate glasses. A series of works have shed light on the role played by physical glass properties (softening temperature, thermal diffusivity, etc.) on their formation and erasure during the laser writing process. Moreover, the understanding of formation mechanism directly impacts the ability to inscribe nanogratings in a controlled way, as well as improve the fundamental physics and chemistry at play during complex light-matter interaction. This understanding could thus be generalized to all optical glasses, and in this context the main objective of this work is to decipher the relationship between glass composition and nanogratings formation window. Additionally, better control of the anisotropic properties associated with fs laser induced modifications (sign, amplitude, orientation, losses) is possible, provided the nanogratings formation and erasure mechanisms are well understood. In this thesis, we first discuss the effect of glass viscosity on nanogratings existence using the Rayleigh-Plesset equation. It is established that viscosity is a key property to consider, and we propose a related approach to determine a theoretical temperature domain of their existence provided a series of assumptions are satisfied (thermal confinement and associated pressure induced). The latter approach is experimentally validated using a large number of oxide glasses (commercial and laboratory ones) by investigating the nanogratings processing window in a repetition rate - pulse energy landscape. Following this work, the internal structuring of the nanogratings inside silica is investigated by high resolution electron microscopy techniques. Observations at the nanoscale reveal that nanoplanes are intrinsically made of regularly spaced nanoplanes, oriented perpendicular to the light polarization, and where oblate nanopores line up to form the nanoplanes. These nanoporous layers are organized by light through thermomecanical solicitations and assisted by a plasma mediated nanocavitation process. Under isochronal thermal annealing experiments, the erasure of nanopores created during the laser irradiation is strongly correlated to the temperature dependence of the glass viscosity. Finally, such an erasure can be predicted for any time-temperature process, provided the hypothesis remains valid. It becomes possible to anticipate and model nanogratings lifetime in many commercial glasses and extending it well beyond silica glass
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