HAL Portal IOGS (nstitut d'Optique Graduate School)
Not a member yet
12589 research outputs found
Sort by
Two-Step Femtosecond Laser Ablative strategy for the fabrication of Au-Ni-based and Au-Co-based Nanoparticles with Tunable Plasmonic and Magnetic Behaviors
No full textMagnetic-plasmonic nanoparticles (MP-NPs), combining the localized surface plasmon resonance (LSPR) of noble metals with the magnetic response of transition-metal oxides, represent a versatile class of multifunctional nanomaterials with applications in sensing, catalysis, and biomedicine. However, their structure and properties are highly sensitive to synthesis conditions. Herein, we report a controlled, two-step strategy based on pulsed laser ablation in liquid (PLAL) to synthesize Janus-like Au-Ni-oxides and Au-Co-oxides nanoparticles and investigate the critical influence of ablation sequence on their properties. Comprehensive structural characterization, including XRD, TEM/HRTEM, XPS, and XAS, revealed that the resulting nanostructures are not core-shell but rather Janus-like, consisting of metallic Au, transition-metal oxides, and minor Au-Ni or Au-Co alloy phases. We demonstrate that the ablation order dictates the resulting phase distribution: Au ablated into a pre-existing Ni suspension (Au_in_Ni) produces Au-Ni alloy/NiO interfaces, whereas Ni ablated into a preexisting Au suspension (Ni_in_Au) favors phase-separated Au and NiO domains. Similar trends were observed for the Au-Co systems. The structural differences directly correlate with tunable optical and magnetic behaviors. UV-vis absorption spectroscopy showed that the Au plasmon resonances are broadened and red-shifted in the oxide-rich Au-in-Ni and Au-in-Co systems, but remain sharper and closer to pure Au in the phase-separated Ni-in-Au and Co-in-Au samples. Magnetic measurements at 5 K revealed an exceptionally strong magnetic hardening in the Au-in-Ni sample (Hc= 2130 Oe, Hex= -881 Oe), which surpasses conventional Ni/NiO systems due to robust pinning at the Au-Ni/NiO interfaces. In contrast, the Au-Co systems exhibited lower coercivity (220-571 Oe) and bias fields (-120 to -260 Oe), consistent with the properties of the cobalt oxide phase. These findings highlight that the interplay of oxidation chemistry and ablation sequence governs the structural, optical, and magnetic properties of these bimetallic nanoparticles and demonstrate the unique potential of PLAL for engineering hybrid plasmonic-magnetic heterostructures with tunable exchange anisotropy
Assembling and Modeling Stacked Disordered Metasurfaces
No full textInternational audienceDisordered metasurfaces offer unique properties unattainable with periodic or ordered metasurfaces, notably the absence of deterministic interference effects at specific wavelengths and angles. In this work, we introduce a lithography-free nanofabrication approach to realize cascaded disordered plasmonic metasurfaces with sub-micron total thickness. We experimentally characterize their angle-resolved specular and diffuse reflections using the bidirectional reflection distribution function (BRDF) and develop accurate theoretical models that remain valid even at large incidence angles. These models reveal the intricate interplay between coherent (specular) and incoherent (diffuse) scattering and demonstrate how coherent illumination can strongly influence the perceived color of diffusely scattered light. Exploiting this effect, we realize a centimeter-scale chromo-encryption device whose color changes depending on whether it is viewed under direct or diffuse illumination. Our results lay the groundwork for advanced nanophotonic platforms based on stacked disordered metasurfaces, offering versatile optical functionalities inaccessible with traditional multilayer thin-film technologies or single-layer metasurfaces
Joint despeckling and thermal noise compensation: application to Sentinel-1 images of the Arctic
No full textInternational audienceSynthetic Aperture Radar (SAR) images offer crucial information for studying and monitoring sea ice in the Arctic. Sentinel-1 captures images of the area using an extremely wide swath for reduced revisit time. The backscattered signal from sea ice and open water is often very weak, making it difficult to distinguish from the sensor thermal noise floor. Thermal noise impacts the images by generating a bias and increasing the fluctuations related to speckle phenomenon. Analyzing these images requires both correcting this bias and reducing fluctuations without blurring out the image content. The acquisition of several sub-swaths in a single pass using Terrain Observation with Progressive Scans (TOPS) produces images that exhibit, after compensation for antenna gains, a non-uniform thermal noise floor and strong discontinuities between sub-swaths. Denoising techniques must take these specificities into account to restore the images.This paper introduces a joint approach to remove the thermal noise offset and suppress fluctuations due to speckle and thermal noise. Compensating at once for all these effects largely reduces artifacts at the boundary between sub-swaths. We demonstrate using both numerical simulations and actual Sentinel-1 images that debiased polarimetric reflectivities can be recovered and fluctuations strongly reduced while preserving fine spatial structures
Indirectly LED-pumped Nd:glass: potential for high energy laser facilities
No full textInternational audienceFlashlamp-pumpedNd:glass is used as a power amplifier in many high energy laser facilities. Despite the problems of this old technology, flashlamps are still being considered for the next generation of lasers as diode laser pumping is far from being ready. This work presents an alternative for pumping high energy lasers: LEDs combined with luminescence concentrators. Using a pump head consisting of a green-yellow Ce:LuAG luminescent concentrator pumped by 2240 LEDs, we demonstrate a Nd:glass laser oscillator producing 25 mJ at 1053 nm for an absorbed pump energy of 138 mJ. The small signal gain reaches 1.25 in a single pass despite the short length of the Nd:glass rod (20 mm). These results reveal the potential of indirect LED pumping for Nd:glass amplifiers in high energy lasers.</div
Single-Atom Resolved Collective Spectroscopy of a One-Dimensional Atomic Array
No full textInternational audienceOrdered atomic arrays feature an enhanced collective optical response compared to random atomic ensembles due to constructive interference in resonant dipole-dipole interactions. One consequence of this is the existence of a large shift of the transition with respect to the bare atomic frequency. In the linear optics regime (low light intensity), one observes a spectroscopic shift of the Lorentzian atomic line often called the collective Lamb shift. For stronger driving, many excitations are present in the system rendering the calculation of this shift theoretically challenging, but its understanding is important for instance when performing Ramsey spectroscopy in optical clocks. Here we report on the study of the collective optical response of a one-dimensional array of 30 dysprosium atoms. We drive the atoms on the narrow intercombination transition isolating a two-level system, and measure the atomic state with single-shot state readout using a broad transition. In the linear optics regime, we measure the shift of the resonance in steady state due to dipole interactions, and measure how this shift depends on the interatomic distance. We further resolve at the single atom level how the excitation is distributed over the array. Then, on the same transition we perform Ramsey spectroscopy i.e., away from the linear regime. We observe a time-dependent shift, that allows us to draw the connection between the collective Lamb shift observed in the linear optics regime and in the large-excitation case
Collagen-Based Gut-on-Chip for in vitro modeling of intestinal barrier function and host-pathogen interactions
No full textAbstract The human intestine, characterized by its villi and crypt structures, plays a critical role in nutrient absorption, barrier function, and host defense. However, traditional in-vitro models employing synthetic membranes like polydimethylsiloxane (PDMS) and polycarbonate (PC) often fail to accurately replicate the complex physiological environment of the intestine. To address this limitation, we developed a gut-on-chip, incorporating a porous collagen type I membrane, to better mimic the natural extracellular matrix (ECM) and create a more physiologically relevant in vitro system. Thin, porous collagen type I membranes were fabricated and characterized by linear close contact profilometry to determine their thickness, which closely approximated the in vivo intestinal basement membrane. Caco-2 cells cultured within the device exhibited the formation of villi-like structures, tight junction formation, and mucin production, demonstrating successful differentiation and functional barrier formation on the collagen membrane. We investigated the device’s capacity to model host-pathogen interactions by infecting the cell layer with Candida albicans . Confocal microscopy revealed hyphal invasion of the epithelial cells, and permeability assays demonstrated increased layer permeability following infection, highlighting the device’s ability to replicate infection processes and their impact on barrier integrity. This gut-on-chip, by integrating physiological membrane and replicating key structural and functional aspects of the intestine, offers a promising platform for studying intestinal physiology and host-pathogen dynamics
Ppb detection level’s hydrogen sensor using a SPR grating in the triggered switching configuration
No full textInternational audienceAn optical plasmonic hydrogen sensor is proposed, based on what we believe to be a novel configuration named plasmon-triggered switching. This configuration, involving two propagative orders diffracted by a deep metallic grating combined to a hydrogen-sensitive layer, is capable of measuring hydrogen concentrations. The two diffracted orders enable a differential measurement, which estimates a change of refractive index through evolution of the relative diffraction efficiency of each order at fixed wavelength and fixed angle, while cancelling any drift of the input laser source and other disturbances and allowing both a high sensitivity and a very low limit of detection (LOD). Experimental results, using a simple implementation involving one laser and two detectors, demonstrate a LOD without any signal post-processing, below 0.2 ppm (2.10 −5 % Vol) in filtered air, are in good agreement with simulations and exhibit very good repeatability. The proposed setup represents a very promising, compact and cost-efficient approach to real-time hydrogen sensing using a thin H 2 sensitive and selective palladium thin layer deposited on a gold grating for highly sensitive plasmon coupling
Contrôle du port de la ceinture de sécurité par imagerie polarimétrique
No full textInternational audienc
Thin layer deposition of TiO2 and PMMA on optical micro or nano fibers for nonlinear optics
No full textInternational audienceOver the last twenty years, silica optical tapered micro or nanofibers (called ONF in the following) have been widely exploited for a large range of potential applications in several areas of research for their original properties of light propagation. The high confinement of the optical mode in the uniform part and the presence of a strong evanescent field near the surface make them devices of choice for nonlinear applications. In this paper we study the coating of ONF with nonlinear materials to expand further the possibilities offered by these devices. Two materials are chosen for the coatings, Titanium Dioxyde (TiO2) and Polymethyl Metacrylate (PMMA). Two processes have been developed for the coatings. Firstly, Atomic Layer Deposition has enabled to deposit controlled thin layers of TiO2 of several tens of nm on an ONF having a diameter of 1 μm with very low additional losses (0.5 dB). Secondly, we have realized a multiple layer deposition process to deposit PMMA layers on ONF. With this technique we were able to reach thicknesses of about 100 nm on ONF diameters as small as 1 μm. The encapsulation of a coated tapered fiber in silicone has been conducted, resulting in minimal additional losses, showing great promises from such a treatment. These initial experimental proofs of concept open the way for further experiments in nonlinear optics using functionalized ONF. Potential applications include the development of Raman converters within the evanescent field of the optical propagating mode, as well as experiments that necessitate precise control of phase matching