Sol-gel derived ionic copper-doped microstructured optical fiber: a potential selective ultraviolet radiation dosimeter

International audienceWe report the fabrication and characterization of a photonic crystal fiber (PCF) having a sol-gel core doped with ionic copper. Optical measurements demonstrate that the ionic copper is preserved in the silica glass all along the preparation steps up to fiber drawing. The photoluminescence results clearly show that such an ionic copper-doped fiber constitutes a potential candidate for UV-C (200-280 nm) radiation dosimetry. Indeed, the Cu+-related visible photoluminescence of the fiber shows a linear response to 244 nm light excitation measured for an irradiation power up to 2.7 mW at least on the Cu-doped PCF core. Moreover, this response was found to be fully reversible within the measurement accuracy of this study ( ± 1%), underlying the remarkable stability of copper in the Cu+ oxidation state within the pure silica core prepared by a sol-gel route. This reversibility offers possibilities for the achievement of reusable real-time optical fiber UV-C dosimeters

In situ synthesis of highly crystalline Tb-doped YAG nanophosphor using the mesopores of silica monolith as template

International audienceThis report describes the first synthesis of a highly crystalline YAG:Tb nanophosphor inside the pores of a mesoporous silica monolith (MSM). A simple wet impregnation procedure using a YAG:Tb sol and a MSM platform prepared by a sol–gel method was adopted to prepare highly homogeneous MSM–YAG:Tb luminescent composites. The morphological, structural and luminescence properties of in situ generated YAG:Tb nanocrystals, investigated using XRD, TEM, HRTEM, EDS, FTIR, nitrogen gas sorption and photoluminescence measurements, were compared to those of the bulk YAG:Tb phosphor. The specific surface area and the pore volume of the MSM host material were found to be lower when YAG:Tb nanoparticles were grown in the pores of the MSM material. The particle diameter of the nano-sized YAG:Tb phosphor was estimated to be about 23 nm. The MSM–YAG:Tb composite exhibited a strong green fluorescence emission with the characteristic main emission band of Tb3+ located at 548 nm. The prepared composite also showed a shorter photoluminescence (PL) lifetime and excitation bands shifted to lower wavelengths compared to the neat YAG:Tb phosphor. The as-prepared MSM–YAG:Tb material could be integrated into optoelectronic devices and holds good potential to be applied in decorative lightin

Coherent beam combining with an ultrafast multicore Yb-doped fiber amplifier

International audienceActive coherent beam combination using a 7-non-coupled core,polarization maintaining, air-clad, Yb-doped fiber is demonstrated as amonolithic and compact power-scaling concept for ultrafast fiber lasers. Amicrolens array matched to the multicore fiber and an active phasecontroller composed of a spatial light modulator applying a stochasticparallel gradient descent algorithm are utilized to perform coherentcombining in the tiled aperture geometry. The mitigation of nonlineareffects at a pulse energy of 8.9 μJ and duration of 860 fs is experimentallyverified at a repetition rate of 100 kHz. The experimental combiningefficiency results in a far field central lobe carrying 49% of the total power,compared to an ideal value of 76%. This efficiency is primarily limited bygroup delay differences between cores which is identified as the maindrawback of the system. Minimizing these group delay issues, e.g. by usingshort and straight rod-type multicore fibers, should allow a practical powerscaling solution for femtosecond fiber systems

Radiation Response of OFDR Distributed Sensors Based on Microstructured Pure Silica Optical Fibers

Temperature sensors based on microstructured pure silica optical fibers are investigated by OFDR and RIA performed during X-ray irradiation up to 50kGy dose. The results evidence that the temperature measures are poorly influenced by irradiation (the error being less than 0.3°C). Such a radiation tolerance is relevant for the use of these Rayleigh based sensors in harsh environments

Optical Frequency Domain Reflectometer Distributed Sensing Using Microstructured Pure Silica Optical Fibers Under Radiations

We investigated the capability of micro-structured optical fibers to develop multi-functional, remotely-controlled, Optical Frequency Domain Reflectometry (OFDR) distributed fiber based sensors to monitor temperature in nuclear power plants or high energy physics facilities. As pure-silica-core fibers are amongst the most radiation resistant waveguides, we characterized the response of two fibers with the same microstructure, one possessing a core elaborated with F300 Heraeus rod representing the state-of-the art for such fiber technology and one innovative sample based on pure sol-gel silica. Our measurements reveal that the Xray radiations do not affect the capacity of the OFDR sensing using these fibers to monitor the temperature up to 1 MGy dose whereas the sensing distance remains affected by RIA phenomena

Plastic strain accommodation and acoustic emission during melting of embedded particles

Melting point phenomena of micron-sized indium particles embedded in an aluminum matrix were studied by means of acoustic emission. The acoustic energy measured during melting increased with indium content. Acoustic emission during the melting transformation suggests a dislocation generation mechanism to accommodate the 2.5% volume strain required for melting of the embedded particles. A geometrically necessary increase in dislocation density of 4.1 x 10^13 m^-2 was calculated for the 17 wt% indium composition.Comment: 4 pages, 3 figures, 1 tabl

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Préparation et caractérisation de matériaux hybrides organostanniques nanostructures

Deux familles de nouveaux précurseurs bis(tripropynylstannylés) de matériaux hydrides organostanniques ont été préparées. L'hydrolyse par voie sol-gel des précurseurs à espaceur linéaire (1ére famille) conduit à des hybrides nanostructurés spontanément en plans d'oxyde (Sn-O-Sn) séparés par les espaceurs organiques. Les conditions d'hydrolyse (microémulsion ou milieu biphasique) n'influent pas sur cette organisation. L'hydrolyse des précurseurs à chaînes latérales (2ème famille) conduit à des hybrides dont l'organisation, différente de celle des hybrides issus des précurseurs de la première famille, dépend de la longueur des chaînes latérales et du nombre de noyaux aromatiques séparant les deux centres métalliques. La croissance des particules d'hybride, limitée par les vitesses de condensation, a lieu dans la phase aqueuse de la microémulsion et dépend de la la nature de l'espaceur organique. La pyrolyse des hybrides de la 1ère famille sous oxygène conduit à des poudres de dioxyde d'étain dont les propriétés de cristallinité et de texture dépendent de la nature de l'éspaceur et de la température du traitement thermique. La calcination sous air de films minces hybrides à espaceur butylique conduit à du dioxyde d'étain cristallisé dans une phase cubique métastable.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF