HAL Portal IOGS (nstitut d'Optique Graduate School)
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Capteur optique d’hydrogène à bascule énergétique pour la détection à faible seuil
No full textInternational audienceles challenges impliqués dans la transition énergétique actuelle mettent en avant l’hydrogène comme un vecteur énergétique prometteur pouvant répondre aux futurs enjeux privilégiant des émissions bas carbone. Cependant, la fabrication, le transport, et l’utilisation de gaz d’hydrogène présentent un danger se manifestant par un caractère explosif suite à un faible intervalle de combustion compris entre 4 et 75 % de concentration dans l’air [1]. Couplée à un risque de fuite élevé dû à une grande perméabilité [2], la détection précise et rapide de l’hydrogène est alors cruciale pour garantir la sécurité et la viabilité de son utilisation.C’est dans ce contexte que le projet CAPTHY, porté par le laboratoire Hubert Curien de Saint-Étienne et l’Institut Pascal d’Aubière, financé par la Région Auvergne Rhône-Alpes, développe des capteurs optiques pour la détection d’hydrogène à faible seuil basé sur le principe de la bascule énergétique. Ce phénomène, d’ordre plasmonique, est excité par une diode laser (850 nm) au travers d’un réseau métallique d’or profond (> 100 nm) recouvert d’une fine couche de palladium de quelque nanomètre (15 nm). Il en résulte la diffraction de deux ordres, l’ordre 0 et -1, où leur oscillation énergétique angulaire illustrée en figure 1.a, est réalisée par l’intermédiaire de plasmons de surface propagatifs et co-propagatifs qui permettent un transfert d’énergie entre ces deux ordres. Ces oscillations conduisent à l’apparition de deux points de croisement θ_1^(WP) et θ_2^(WP) .La grande interaction entre l’hydrogène et le palladium induit une forte modification des propriétés optiques, conduisant aux translations angulaires locales des deux points de croisements (figure 1a), permettant d’estimer la concentration d’hydrogène par une simple mesure différentielle optique normalisée η. Comme illustrée en figure 1 b, une excellente répétabilité est observée pour des concentrations d’hydrogène comprises entre 500 et 1000 ppm. Couplé à une faible limite de détection de 1,91 ppm déduite de la figure 1c, le système révèle des performances prometteuses pour une utilisation en milieu sous faible concentration d’hydrogène. De par sa simplicité et son potentiel de miniaturisation, ce type de capteur se montre prometteur pour la détection d’hydrogène à faible seuil de l’ordre du ppm pour des applications industriel ou médical [3–7]
Impact of a Self-Autonomous Evaluation Station and Personalized Training Algorithm on Quality of Life and Physical Capacities in Sedentary Adults: Randomized Controlled Trial
No full textInternational audienceBackground Physical inactivity is a major risk factor for noncommunicable diseases and a leading cause of premature death. The World Health Organization (WHO) recommends at least 150 minutes of moderate intensity physical activity (PA) weekly, regardless of age, gender, or personal habits. However, in both sports performance and clinical settings, personalized training (PT) regimens have shown superior efficacy over general guidelines. Objective We hypothesized that an automatic PT program, informed by initial physical evaluations, would increase overall quality of life, quality of sleep, and physical capabilities and reduce fatigue and depression compared with adherence to WHO recommendations. Methods This 5-month, randomized, single-blinded controlled trial involved 112 sedentary or minimally active participants, divided randomly into PT and free training (FT) groups. Physical capabilities and subjective measures such as quality of life, sleep, depression, and fatigue were evaluated for both groups. After 1 month, both groups were asked to perform 150 minutes of PA per week for 4 months; the PT group could either follow a “virtual coach” on a mobile app to follow some personalized PA or do what they would like, while the FT group was to follow the general PA recommendations of the WHO. Results We did not find any group×time interaction for PA duration or intensity, physical qualities, and subjective measures. However, considering both groups together, there was a significant pretest and posttest time effect for duration of PA (18.2 vs 24.5 min/d of PA; P<.001), intensity (2.36 vs 3.11; P<.001), and workload (46.8 vs 80.5; P<.001). Almost all physical qualities were increased pretest and posttest (ie, estimated VO2max 26.8 vs 29 mL min–1 kg–1; P<.001; flexibility 25.9 vs 26.9 cm; P=.049; lower limb isometric forces 328 vs 347 N m; P=.002; reaction time 0.680 vs 0.633 s; P<.001; power output on cyclo-ergometer 7.63 vs 7.82 W; P<.003; and balance for the left and right leg 215 vs 163 mm2; P<.003 and 186 vs 162 mm2; P=.048, respectively). Finally, still considering the PT and FT groups together, there were significant pretest to posttest improvements in the mental component of quality of life using the 12-item Short Form Health Survey (41.9 vs 46.0; P<.006), well-being using the Warwick-Edinburgh Mental Well-Being Scale (48.3 vs 51.7; P<.002), depression using the Center for Epidemiologic Studies Depression Scale (15.5 vs 11.5; P=.02), and fatigue using the Functional Assessment of Chronic Illness Therapy–Fatigue (37.1 vs 39.5; P=.048). Conclusions The individualized training was not more effective than the general recommendations. A slight increase in PA (from 18 to 24 min/d) in sedentary or poorly active people is enough for a significant increase in physical capabilities and a significant improvement in quality of life, well-being, depression, and fatigue. Trial Registration ClinicalTrials.gov NCT04998266; https://clinicaltrials.gov/study/NCT0499826
Collage direct - Assemblage sans adhésif pour environnements extrêmes
No full textInternational audienceThis article deals with the direct bonding method, also known as molecular adhesion, by revealing the phenomena and mechanisms that enable adhesion without glue. It focuses on the cases of silica and silicon, as these are the materials that have been most extensively studied and physically best understood to date. The fundamental issues that allow spontaneous adhesion in terms of surface quality (roughness), coverage and cleanliness are detailed in the first part. Methods for characterising adhesion forces during assembly and adhesion during disassembly are then reviewed. Finally, the physico-chemical mechanisms of adhesion and the treatments that can be used to improve the durability of assemblies are described.Cet article traite de la méthode de collage direct encore nommée adhésion moléculaire en dévoilant les phénomènes et les mécanismes qui permettent d’adhérer sans colle. Il s’intéresse aux cas de la silice et du silicium, car ce sont les matériaux les plus étudiés et physiquement les mieux compris à ce jour. Les points fondamentaux qui autorisent l’adhésion spontanée en termes de qualité (rugosités, planéités), de recouvrement et de propreté des surfaces sont détaillés dans une première partie. Puis les méthodes de caractérisation des forces d’adhésion lors du collage, et de l’adhérence, lors du désassemblage sont explorées. Enfin, les mécanismes physico-chimiques de l’adhérence et les traitements permettant de renforcer la tenue des assemblages sont décrites
Optical constants of magnetron sputtered aluminum in the range 17–1300 eV with improved accuracy and ultrahigh resolution in the L absorption edge region
No full textInternational audienceThis work determines a new set of EUV/x-ray optical constants for aluminum (Al), one of the most important materials in science and technology. Absolute photoabsorption (transmittance) measurements in the 17-1300 eV spectral range were performed on freestanding Al films protected by carbon (C) layers, to prevent oxidation. The dispersive portion of the refractive index was obtained via the Kramers-Kronig transformation. Our data provide significant improvements in accuracy compared to previously tabulated values and reveal fine structure in the Al L 1 and L 2,3 regions, with photon energy step sizes as small as 0.02 eV. The implications of this work in the successful realization of EUV/x-ray instruments and in the validation of atomic and molecular physics models, are also discussed
Two‐photon Dye‐Based Fluorogenic Organic Nanoparticles as Intracellular Thiols Sensors
No full textInternational audienceAbstract Optical bioimaging is an ever‐growing field that benefits both from the fast progress of optical instrumentation and modalities, and from the development of light‐emitting probes. The efficacy of molecular fluorescent dyes is crucial, yet hindered by limited brightness and hydrophilicity. Addressing these challenges, self‐stabilized fluorogenic organic nanoparticles only made of pure dyes ( d FONs) are introduced in this work. Comprising thiol‐sensitive fluorogenic chromophores, these d FONs exhibit enhanced brightness exclusively in the presence of biological thiols, notably glutathione, overcoming the need for water‐solubilizing moieties. Importantly, these nanoparticles demonstrate large fluorescence and one‐ and two‐photon brightness, enabling sensitive bioimaging of intracellular thiols at micromolar concentrations. Notably, only the pristine fluorogenic nanoparticles can penetrate the cells and does not require to wash the cells before imaging, emphasizing their unique role as dye carriers, fluorogenic probes and ease of use. This work highlights the transformative potential of d FONs in advancing optical bioimaging, paving the way for the use of d FONs not just as tracers, but also now as biosensors and ultimately in the future as biomarkers
zIncubascope: long-term quantitative imaging of multi-cellular assemblies inside an incubator
No full textRecent advances in bioengineering have made it possible to develop increasingly complex biological systems to recapitulate organ functions as closely as possible in vitro . Monitoring the assembly and growth of multi-cellular aggregates, micro-tissues or organoids and extracting quantitative information is a crucial but challenging task required to decipher the underlying morphogenetic mechanisms. We present here an imaging platform designed to be accommodated inside an incubator which provides high-throughput monitoring of cell assemblies over days and weeks. We exemplify the capabilities of our system by investigating human induced pluripotent stem cells (hiPSCs) enclosed in spherical capsules, hiPSCs in tubular capsules and yeast cells in spherical capsules. Combined with a customized pipeline of image analysis, our solution provides insight into the impact of confinement on the morphogenesis of these self-organized systems
Métasurfaces incandescentes : un tutoriel
No full textInternational audienceIncandescence has long been the most popular source of light, despite a number of limitations in terms of efficiency, polarization, and coherence. In the last twenty years, it has been shown that most of these limitations can be overcome by taking advantage of the advances in nanophotonics. In this paper, we provide a tutorial presentation of the field with emphasis on the fundamental principles used to control the properties of thermal radiation in the far field. We introduce several figures of merit and list some directions for future work.L'incandescence a longtemps été la source de lumière la plus populaire malgré un certain nombre de limitations en termes d'efficacité, de polarisation et de cohérence. Au cours de la dernière décennie, le sujet a fait l'objet d'une recherche active. Dans cet article, nous fournissons une présentation tutorielle du domaine en mettant l'accent sur les principes fondamentaux utilisés pour contrôler les propriétés de l'émission de lumière. Nous présentons plusieurs figures de mérite et énumérons quelques orientations pour les travaux futurs
Study of self-heated tapered silica microfibers by laser in air
No full textInternational audienceWe present measurements of the temperature of optical microfibers self-heated by a cw laser emitting at 1.48 μm. The experimental method we have implemented is simple and enables to perform for the first time to our knowledge spatially distributed measurements along the tapers and the microfiber part. Temperature rise of more than 20 °C is measured for moderate powers (200 mW) and relatively large radii (1.45 μm). The results are confronted to a numerical model we have developed and enable to determine range of values for the couple thermal transfer coefficient/surface absorption coefficient
Semiconductor optical amplifiers as an optical arbitrary waveform generator for high-energy laser systems
No full textInternational audienceA simple and straightforward technique is presented as a novel temporally controllable front-end for nanosecond very-high energy laser systems. It is based on an original utilization of a semiconductor optical amplifier (SOA) used as an intensity modulator. The essential characteristics of the component are analyzed in order to evaluate potential limitations. Various parameters of interest for standard operation are displayed, demonstrating its usability and its effectiveness. We demonstrate arbitrary and controllable pulse temporal profiles with duration ranging from 1 nanosecond to 100 nanoseconds and a temporal precision of 1.1 ns. A high extinction ratio is also achieved ensuring a modulation contrast up to 53 dB. The SOA is then integrated into an existing operating system in an ultra-compact, reliable all-fibered system. It is used to seed a 2*200 J laser system, exhibiting excellent performance, and validating its usability under operation conditions without any detrimental effects
