HAL Portal IOGS (nstitut d'Optique Graduate School)
Not a member yet
12589 research outputs found
Sort by
Estimation of 5-ALA-induced PpIX concentration in fluorescence spectroscopy for Improving glioma classification using symbolic Monte-Carlo
No full textInternational audienc
Theory of Photoluminescence by Metallic Structures
No full textInternational audienceLight emission by metals at room temperature is quenched by fast relaxation processes. Nevertheless, Mooradian reported in 1969 the observation of photoluminescence by metals pumped by a laser. While this phenomenon is currently at the heart of many promising applications, it is still poorly understood. In this work, we report a theory which reproduces quantitatively previously published experimental data of photoluminescence by metallic nanoparticles. We first provide a general formula that relates the emitted power for a frequency, direction and polarization state to a sum over all transitions involving matrix elements, electronic distribution of all bands and Green’s tensors. We then consider the case of intraband recombination and derive a closed-form expression of the emitted power depending only on macroscopic quantities. This formula, which is a generalization of Kirchhoff’s law, answers many of the open questions related to intraband photoluminescence. © 2024 American Chemical Society
Vers les dosimètres à fibre optiques pour les applications dans les milieux spatiaux
No full textLong-term space missions aimed at pushing the boundaries of humanity are becoming increasingly concrete. Space is no longer reserved solely for international and national programs but is also becoming a preferred venue for projects and concepts from commercial companies, driving each actor to innovate and leading to a variety of space programs. Among the major difficulties in achieving these ambitions, human health safety remains essential, and ionizing radiation is considered a regular health risk. While the radiation environment in space could be described as a vast array of primary particles covering a wide range of energies, it threatens the integrity of living beings, materials, and components in various ways. To mitigate the potential risks associated with radiation, systems and crews must be informed of the radiation risk and be able to react promptly. A robust dosimeter, providing real-time measurements of dose rates, can help anticipate solar events with appropriate reactions. The Lumina dosimeter has demonstrated the capabilities of optical fibers for these dosimetry challenges by exploiting the phenomenon of radiation-induced attenuation. The detection of singular events such as passages through the South Atlantic Anomaly or the consequences of solar flares attests to the achieved performance. Lumina remains a first prototype that still has some limitations. Nevertheless, these can be overcome with suitable technical solutions. All the tools necessary for an improved version, a Lumina 2.0, are now available.Les missions spatiales à long terme prévues pour repousser les limites de l’humanité deviennent de plus en plus concrètes. L'espace n'est plus réservé uniquement aux programmes internationaux et nationaux, mais devient également un lieu privilégié pour les projets et concepts des entreprises commerciales, poussant chaque acteur à innover et conduisant à une variété de programmes spatiaux. Parmi les principales difficultés pour réaliser ces ambitions, la sécurité de la santé humaine reste essentielle et les rayonnements ionisants sont considérés comme un risque sanitaire régulier. Alors que l'environnement de rayonnement dans l'espace pourrait être décrit comme un vaste éventail de particules primaires couvrant une large gamme d'énergies, il menace de différentes manières l'intégrité des êtres vivants, des matériaux et des composants. Pour atténuer les risques potentiels associés aux radiations, les systèmes et les équipages doivent être informés du risque de rayonnement et être capables de réagir promptement. Un dosimètre robuste, fournissant des mesures en temps réel des débits de dose, peut aider à anticiper les événements solaires avec les réactions appropriées. Le dosimètre Lumina a permis de démontrer les capacités des fibres optiques pour ces problématiques de dosimétrie en exploitant le phénomène d’atténuation induite par radiation. Les détections d’événements singuliers tels que les passages dans l’anomalie de l'Atlantique Sud ou les conséquences d’éruptions solaires témoignent des performances atteintes. Lumina reste un premier prototype qui conserve encore quelques limitations. Néanmoins, ces dernières peuvent être surmontées avec les solutions techniques adaptées. Tous les outils nécessaires pour une version améliorée, une Lumina 2.0, sont désormais à disposition
Driven-dissipative phase separation in free-space atomic ensembles
No full text16 pages and 9 figures in the main text + 2 pages and 2 figures in the AppendixThe driven Dicke model, wherein an ensemble of atoms is driven by an external field and undergoes collective spontaneous emission due to coupling to a leaky cavity mode, is a paradigmatic example of a system exhibiting a driven-dissipative phase transition as a function of driving strength. Recently, a similar phenomenon was experimentally observed, not in a cavity setting, but rather in a free-space atomic ensemble. The reason why similar behavior should emerge in free space is not obvious, as the system interacts with a continuum of optical modes, which encodes light propagation effects. Here, we present and solve a simple model to explain the behavior of the free-space system, based on the one-dimensional Maxwell-Bloch equations. On one hand, we show that a free-space ensemble at a low optical depth can exhibit similar behavior as the cavity system, as spatial propagation effects are negligible. On the other hand, in the thermodynamic limit of large atom number, we show that certain observables such as the transmittance or the atomic excited population exhibit non-analytic behavior as a function of the driving intensity, reminiscent of a phase transition. However, a closer analysis reveals that the atomic properties are highly inhomogeneous in space, and based on this we argue that the free-space system does not undergo a phase transition but rather a ``phase separation", roughly speaking, between saturated and unsaturated regions
Overview of the Infrared Radiation Responses of Telecom-grade Single Mode Optical Fibers
No full textInternational audienc
Mechanisms of laser-based synthesis and modifications of nanomaterials
No full textInternational audienceAbstractLasers are known to be extremely versatile tools suitable both for the synthesis and modifications of numerous nanomaterials with unique and extremely interesting optical properties suitable for a wide range of applications in various fields ranging from optics and photonics to medical applications. Efficient control over these processes is still challenging and often requires numerical simulations because of the complex interplay of many physical and chemical processes involved that depend on the combination of both material properties and laser parameters. To simulate these processes, multi-physical modeling should be used including electromagnetic, thermal, mechanical, and chemical effects taking place at several time and space scales. Depending on the experimental conditions, nanoparticles can be formed, grow, aggregate, or on the contrary decay, so that a set of transient variations often take place, particularly when multi-pulse laser irradiation is applied. In the case of short and ultra-short laser pulses, strongly non-linear and time-dependent processes play a role involving not only ionization but also phase transitions, acoustic vibrations, shock waves, as well as void formation, and cavitation. If a considerable energy is released in a very short time, firstly aggregates decay, then nanoparticles are fragmented. Here, based on numerical calculations, the roles of several above-mentioned effects are analyzed. The performed simulations can be used for a better understanding of laser interactions with nanoobjects
Radiation Monitoring with Radiosensitive Pure-Silica Core Ultra-Low Loss Optical Fiber
No full textInternational audienc
Participation à la table ronde : Pourquoi soutenir les communs numériques dans l’éducation ?
No full textInternational audienc
5-ALA induced PpIX fluorescence spectroscopy in neurosurgery: a review
No full textInternational audienceThe review begins with an overview of the fundamental principles/physics underlying light, fluorescence, and other light-matter interactions in biological tissues. It then focuses on 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX) fluorescence spectroscopy methods used in neurosurgery (e.g., intensity, time-resolved) and in so doing, describe their specific features (e.g., hardware requirements, main processing methods) as well as their strengths and limitations. Finally, we review current clinical applications and future directions of 5-ALA-induced protoporphyrin IX (PpIX) fluorescence spectroscopy in neurosurgery
Trois images en une : comment la nanophotonique révolutionne le concept d’image imprimée
No full textInternational audienceLe traitement par laser de films photosensibles contenant des nanoparticules métalliques permet de produire de manière contrôlée des centaines de milliers de nanostructures, affichant chacune une palette de couleurs variées suivant l’angle de vue et d’éclairage. Un choix judicieux parmi ces nanostructures permet d’afficher différentes images au même endroit d’un support, une révolution dans le domaine de l’impression qui intéresse l’industrie des documents sécurisés