HAL Portal IOGS (nstitut d'Optique Graduate School)
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Interface optique, magnétisme et supraconductivité : vers la manipulation d’un spin unique avec un vortex d’Abrikosov
No full textAbrikosov vortices are the most compact magnetic objects in superconductors, with a size of a few tens to a few hundreds of nanometers. These flux tubes, which penetrate type II superconductors (such as Niobium), carry a quantum of flux h/2e and provide a natural basis for building digital electronics with robust, non-volatile operation, as well as developing compatible cryogenic memories. Nevertheless, in an era of globalized information distribution, it seems appropriate to envisage systems capable of interfacing superconducting electronics with optically accessible registers. Our group having recently demonstrated the ability to manipulate single flux quanta with a laser beam, as simply as with optical tweezers, this thesis aims at exploring the interplay between an optically manipulated individual Abrikosov vortex and a single sold-state spin present in a quantum nano-emitter such as a color center in diamond. Using fluorescence microscopy techniques at cryogenic temperatures, we study the photophysical properties of single defect centers in diamond such as the Silicon-Vacancy or Nitrogen-Vacancy center and develop non-invasive superconducting electronics photonic probing tools. For individual Silicon-Vacancy centers hosted in nanosized diamonds, we unravel that a large proportion of centers show giant blue Lamb-shifts of their emission lines, owing to enhanced vacuum field interactions in such confined dielectric nanostructures. A phonon-bottleneck effect is additionally evidenced in these systems, supporting that phonon-mediated spin-relaxation between the ground state orbital branches should vanish in nanometric-sized nanodiamonds, thus allowing extended spin coherence lifetimes without resorting to ultra-low temperatures for spin coherent manipulations. Concerning superconductors, we first address the fundamental optical limitations of vortex magneto-optical imaging by coupling the indicator on its substrate to a high-index solid immersion lens. Using the Weierstrass geometry, we achieve magneto-optical imaging of single vortices with apparent diameters less than 600 nm. Second, we develop an easy-to-implement minimally invasive photonic technique allowing for accurate and treatment-free analysis of Josephson transport properties and demonstrate fast and accurate determination of the Josephson critical current in single planar junction systems. We extend this approach to Josephson supercurrents imaging, providing representation of Josephson vortex states in such systems, with ~450 nm precision. Lastly, preliminary results on probing Abrikosov vortices in Niobium with single Nitrogen-Vacancy centers are discussed in view of designing a photonic-superconductor interface.Les vortex d'Abrikosov sont les objets magnétiques les plus compacts, avec une taille de quelques dizaines à quelques centaines de nanomètres. Ces tubes de flux pénétrant les supraconducteurs de type II (tel que le Niobium) et portant un quantum de flux magnétique h/2e, fournissent une base naturelle pour la construction d'une électronique numérique au fonctionnement robuste et non volatile, ainsi que pour le développement de mémoires supraconductrices. Néanmoins, à l'ère de la distribution mondialisée de l'information, il semble approprié d'envisager des systèmes capables d'interfacer l'électronique supraconductrice avec des systèmes optiquement accessibles. Notre groupe ayant récemment démontré la capacité de manipuler des quanta de flux individuels avec un faisceau laser, aussi simplement qu'avec une pince optique, cette thèse vise à explorer l'interaction entre un vortex d'Abrikosov manipulé optiquement et un spin unique présent dans un nano-émetteur quantique tel qu'un centre de couleur du diamant. En utilisant des techniques de microscopie de fluorescence à des températures cryogéniques, nous étudions les propriétés photophysiques des défauts individuels du diamant tels que les centres Silicium-lacune ou Azote-lacune, et nous développons des outils photoniques non invasifs pour sonder les propriétés de briques élémentaires d'électronique supraconductrice comme les jonctions de Josephson. Dans le cas de centres Silicium-lacune individuels contenus dans des diamants de taille nanométrique, nous découvrons qu'une majorité présentent des décalages géants de Lamb vers le bleu de leurs raies d'émission, en raison d'interactions accrues avec les modes électromagnétiques du vide dans de telles nanostructures diélectriques confinées. La preuve d'un effet de goulot d'étranglement de phonons est également rapportée dans ces systèmes, ce qui confirme que la relaxation de spin médiée par les phonons entre les branches orbitales de l'état fondamental devrait disparaître dans les nanodiamants de taille nanométrique. Cela permettant ainsi d'allonger les temps de cohérence de spin sans avoir recours à des températures ultra-basses. En ce qui concerne les supraconducteurs, nous nous attaquons tout d'abord aux limitations optiques fondamentales de l'imagerie magnéto-optique par vortex en couplant l'indicateur sur son substrat à une lentille à immersion solide. En utilisant la géométrie de Weierstrass, nous obtenons une imagerie magnéto-optique avec des diamètres apparents de vortex uniques inférieurs à 600 nm. Deuxièmement, nous développons une technique photonique peu invasive et facile à mettre en œuvre, permettant une analyse précise et directe des propriétés de transport Josephson. Ainsi, nous démontrons une détermination rapide et précise du courant critique Josephson dans des systèmes à jonction planaire unique. Nous étendons cette approche à l'imagerie des supercourants Josephson, en fournissant une représentation des états de vortex Josephson dans ces systèmes, avec une précision de ~450 nm. Enfin, des résultats préliminaires sur l'étude des vortex d'Abrikosov dans le Niobium avec des centres individuels Azote-lacune sont discutés dans la perspective du développement d'une interface photonique-supraconducteur
Dual-Comb generation in III-V semiconductor laser: Transverse modes versus modeless cavities
No full textInternational audienceDual frequency-combs have been relevant for applications such as spectroscopy [1], Many methods are used to generate dual-combs like polarization multiplexing [2] or wavelength/space multiplexing [3,4]. We demonstrated two passively mode-locked dual-comb configurations in a single Vertical External-Cavity SurfaceEmitting Laser (VECSEL) using a InGaAs/GaAs based optically-pumped gain mirror (1/2-VCSEL) and a fast Semiconductor Saturable Absorber Mirror (SESAM) for an emission at 1.06µm with a pulse width of 5ps at 1GHz repetition rate
Synthesis and Modeling of Alloy Nanoparticles
No full textInternational audienceNanoalloys, which are composed of two or more elements interacting through metallic bonds, are a wide class of nanostructures occupying a focal point of research across a diverse range of sectors. [1] This is due to their versatile applications and unique physicochemical properties, critically depending on the precise control over composition and structure. [2-4] In energy, they play a fundamental role in the development of fuel cells, batteries, and solar cells by enhancing energy conversion and storage efficiencies. Environmental science leverages nanoalloys for pollution control, such as CO2 reduction and catalytic water treatment. In medicine and healthcare, they are exploited for imaging, targeted drug delivery, and biosensing technologies.Additionally, they have a consolidated role in materials science, particularly in the synthesis of novel coatings, sensors, and lightweight yet durable materials. Magnetism, quantum technologies and fine chemicals production are only some of the other sectors where nanoalloys received great attention and contributed to the most recent advancements.The synthesis, modeling and investigation of alloy nanoparticles bring together transversal competences from physics, chemistry and materials science, both from the theoretical and experimental perspective.ChemPhysChem is a natural forum for the dissemination of scientific results concerning nanoalloys, as showcased through this special collection which includes the most relevant contributions appeared in the last four years.The catalytic properties of multielement nanoparticles are better investigated in their most ideal configuration, that is without any coating or capping layer. [5,6] For this reason, new synthetic techniques such as laser assisted synthesis in liquid [7-9] are being increasingly exploited for the production of surface-clean alloy nanocrystals, in addition to traditional routes such as sputtering, [10] impregnation followed by calcination, [11] chemical reduction, [12] or electrodeposition. [13] For instance, catalytic CO oxidation, [10] </div
Online X-ray radiation induced attenuation of RPL Dosimeters: Dose rate dependence at high doses
No full textInternational audienc
Radiation and Temperature Effects on Carbon- and Aluminum-Coated Optical Fibers
No full textInternational audienc
Femtosecond Laser Fabrication of Plasmonic-Magnetic Ni-Au Nanoparticles with Enhanced Magnetic Properties
No full textInternational audienceBimetallic nanoparticles, particularly Ni-Au, exhibit unique magneto-optical properties that can be fine-tuned through careful control of their morphology and composition. Femtosecond lasers have shown great promise in achieving these modifications. Specifically, Ni-Au nanoparticles demonstrate enhanced mixing and alloying under rapid heating, resulting in the formation of nanocomposites with diverse sizes, shapes, and compositions. The catalytic properties of the considered nanoparticles have also been extensively studied, with findings suggesting that their improved catalytic performance may arise from the incorporation of Ni into the gold surface, as well as from surface lattice relaxation and subsurface misfit defects.In this study, we investigate the mechanisms underlying laser-induced synthesis of Ni-Au nanoparticles through both experimental and numerical approaches. Ni and Au nanoparticles were produced via femtosecond laser ablation in liquids, with the choice of solvent, such as water or ethanol, significantly influencing the outcomes. To gain deeper insights into the processes involved, detailed atomistic simulations were conducted, revealing the conditions that favor size reduction and enhance the magnetic properties of these nanoparticles
POLSAR2POLSAR: A SEMI-SUPERVISED DESPECKLING ALGORITHM FOR POLARIMETRIC SAR IMAGES
No full textInternational audiencePolarimetric Synthetic Aperture Radar (PolSAR) imagery is a valuable tool for Earth observation. This imaging technique finds wide application in various fields, including agriculture, forestry, geology, and disaster monitoring. However, due to the inherent presence of speckle noise, filtering is often necessary to improve the interpretability and reliability of PolSAR data. The effectiveness of a speckle filter is measured by its ability to attenuate fluctuations without introducing artifacts or degrading spatial and polarimetric information. Recent advancements in this domain leverage the power of deep learning. These approaches adopt a supervised learning strategy, which requires a large amount of speckle-free images that are costly to produce. In contrast, this paper presents PolSAR2PolSAR, a semi-supervised learning strategy that only requires, from the sensor under consideration, pairs of noisy images of the same location and acquired in the same configuration (same incidence angle and mode as during the revisit of the satellite on its orbit). Our approach applies to a wide range of sensors. Experiments on Radarsat-2 and RCM data demonstrate the capacity of the proposed method to effectively reduce speckle noise and retrieve fine details. The code of the trained models is made freely available at https://gitlab.telecom-paris.fr/ring/polsar2polsar. The repository additionally contains a model fine-tuned on SLC PolSAR images from NASA's UAVSAR sensor.</div
Quantum Nanoscopy and Optical Control: From Single Molecules to Entangled Pairs
No full textInternational audienc
Oxidation and laser synthesis of Ni nanoparticles: an atomistic analysis
No full textApplied Physics A, Collection: Laser-Matter Interaction for Life and Society: Fundamental Mechanisms and Emerging ApplicationsInternational audienceNickel nanoparticles (NiNPs) exhibit unique magnetic and chemical properties that make them attractive for applications in catalysis, sensing, and nanotechnology. In this study, reactive molecular dynamics simulations were used to investigate the oxidation behavior of NiNPs in oxygen-rich environments, focusing on the roles of particle size, temperature, and pulsed thermal excitation. The results reveal that oxidation proceeds via a surface-limited mechanism, with reaction rates increasing systematically with nanoparticle diameter and temperature. Simulated pulsed heating, designed to mimic femtosecond laser excitation, significantly enhances oxidation by inducing transient high-temperature conditions that promote irreversible surface reactions. These findings provide fundamental insight into the size-and temperature-dependent oxidation dynamics of NiNPs and underscore the importance of laser-induced thermal histories in controlling their reactivity during laser-based processing or synthesis
Letter of Intent: AICE -- 100m Atom Interferometer Experiment at CERN
No full textInternational audienceWe propose an O(100)m Atom Interferometer (AI) experiment -- AICE -- to be installed against a wall of the PX46 access shaft to the LHC. This experiment would probe unexplored ranges of the possible couplings of bosonic ultralight dark matter (ULDM) to atomic constituents and undertake a pioneering search for gravitational waves (GWs) at frequencies intermediate between those to which existing and planned experiments are sensitive, among other fundamental physics studies. A conceptual feasibility study showed that this AI experiment could be isolated from the LHC by installing a shielding wall in the TX46 gallery, and surveyed issues related to the proximity of the LHC machine, finding no technical obstacles. A detailed technical implementation study has shown that the preparatory civil-engineering work, installation of bespoke radiation shielding, deployment of access-control systems and safety alarms, and installation of an elevator platform could be carried out during LS3, allowing installation and operation of the AICE detector to proceed during Run 4 without impacting HL-LHC operation. These studies have established that PX46 is a uniquely promising location for an AI experiment. We foresee that, if the CERN management encourages this Letter of Intent, a significant fraction of the Terrestrial Very Long Baseline Atom Interferometer (TVLBAI) Proto-Collaboration may wish to contribute to AICE