HAL Portal IOGS (nstitut d'Optique Graduate School)
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Morphology Determination of Luminescent Carbon Nanotubes by Analytical Super-Resolution Microscopy Approaches
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Tomography of near-field radiative heat exchange between mesoscopic bodies immersed in a thermal bath
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Ferrite Isolators
No full textInternational audienceSignal processing requires specialized functions such as isolators particularly in the microwave range where wave propagation can easily be corrupted. The main applications of isolators as well as their characteristics are described. Some waveguide and planar microwave ferrite devices based on Faraday effect, field displacement, or gyroresonance are then reviewed. For a better understanding of the functioning of such devices, microwave properties of ferrite materials are presented. The ferromagnetic resonance and the resulting nonreciprocal effects are also explained. Finally, recent developments in the use of hard ferrites and in magnetic films technology are discussed
Thulium Holmium co-doped tunable fiber laser
No full textInternational audienceWe report a Tm-Ho co-doped fiber laser with continuous tunability between 1965-2120 nm thanks to a rotating diffraction grating in the laser cavity. It delivers an OSNR of over 60 dB at the central wavelength 2060 nm. The output is linearly polarized with a 0.7% RMS instability. This laser is tailored for spectroscopy of Ho-doped materials
Laser Fault Injection on power off devices
No full textInternational audienceLasers are employed not only for reliability purposes but also for fault injection attacks in order to assess the security of electronic components. Nowadays, laser fault injection attacks represent a significant threat to the security of embedded devices. Numerous state-of-the-art studies, mainly based on Single Event Effects, have investigated the use of lasers to inject faults into an electronic device at run-time.In a recently published paper, we have demonstrated on an experimental basis that it is also possible to perform laser fault injection on an unpowered device. This attack vector is of particular interest due to the persistent nature of the injected faults. Furthermore, it is possible that certain protection mechanisms may also be compromised.Finally, laser injection sensors are unable to detect the attack, as they are active components that only function when the circuit is powered on.In particular, our investigation focused on the Flash non-volatile memory of a widely used off-the-shelf 32-bit microcontroller. We provide an experimental characterization of this phenomenon with a description of the fault model from the physical to the software level for laser-induced faults in NOR Flash memory. We leverage this new laser fault injection method to perform a complete reverse engineering of the mapping between the logical and physical addresses of the Flash memory. The organization of the Flash memory can be retrieved at both the page and bit level
Multi-kW peak power frequency comb MOFPA in nanosecond pulsed regime for lidar applications
No full textInternational audienceRugged laser systems are mandatory for onboard high-altitude lidar wind measurement. We propose a combination of methods to overcome SBS limitation for narrow linewidth pulses (50ns/40kHz) in fibers while being compatible with lidar applications
PROCÉDÉ DE GÉNÉRATION D'UNE PALETTE À UTILISER DANS UN PROCESSUS D'IMPRESSION ET PROCÉDÉ D'IMPRESSION
No full textA method of generating a reduced palette for use in a printing process is disclosed. In the method, a plurality of images (12) obtainable by varying printing parameters of the printing apparatus (100) are printed, and color values of the same are measured. Based on the color values, a clustering is performed to obtain a plurality of clusters (40) having similar color values. For each cluster, one or more representative images (42, 44) are selected to form the palette. In this manner, images (12) with color values both inside a convex hull (22) and on the convex hull (22) can be included in the palette
IMAGERIE ACOUSTO-OPTIQUE DE MILIEUX DIFFUSANTS ÉPAIS AU MOYEN D'UNE SOURCE LASER HAUTE PUISSANCE
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Laser-induced self-organization of nanocomposite films
No full textInternational audienceLaser technology has become a pivotal tool for engineering materials at the nanoscale to achieve specific optical properties. In particular, metal-dielectric nanocomposite thin films present a unique opportunity for manipulation via laser-induced mechanisms. These mechanisms, which can be applied over large areas, allow for the precise control of the material's statistical properties through various physico-chemical processes.Our nanocomposite films consist of Ag nanoparticles embedded in a TiO2 matrix. When exposed to laser irradiation, these nanoparticles can undergo significant transformations. The laser energy can reshape, resize, and reorder nanoparticles through self-organization mechanisms that operate over areas as wide as the laser beam size with sub-wavelength periods.1 This reorganization is driven by the laser ability to locally heat the material, promoting atomic mobility, growth and coalescence mechanisms, and the excitation of surface or guided modes propagating parallel to the surface plane. The high temperature rise can also result in a phase change in the crystal structure of the dielectric matrix and modify its thickness.Continuous wave (cw), femtosecond (fs), and nanosecond (ns) pulse laser beams each interact with the material in distinct ways. From a thermal point of view, cw lasers exhibit the most surprising behaviour with a maximum temperature rise in the material increasing when decreasing the deposited energy.2 The behaviour results from the interplay between optically and thermally activated mechanisms. Fs and ns lasers deliver energy in short, intense pulses that can lead to rapid, localized heating and cooling cycles. These cycles are advantageous for inducing specific changes without overheating the entire film, thus preserving the integrity of the nanocomposite and the substrate.3 Self-organization mechanisms are observed for all types of lasers. They are triggered by the excitation, by scattering at Ag nanoparticles, of optical modes propagating parallel to the surface plane (Figure 1). Irrespective of the excited mode, the period of the resulting self-organized structures is determined by the period of the interference pattern arising from the superposition of the incident wave and the wave propagating along the surface.3 The period is thus a fraction of the laser wavelength where the fraction is the effective refractive index of the excited optical mode. The orientation of the nanostructure is related to the nature of the excited optical mode, which sets the condition for the positive feedback loop that initiates the self-enhanced growth of a periodic structure. The experimental results will highlight the presence of two types of structures resulting from the direct laser processing of the nanocomposite films.The resulting modifications have a direct impact on the optical properties of the films.4,5 These tailored optical properties are especially useful for producing visual effects that are not only striking but also extremely difficult to replicate, making them ideal for security applications. By utilizing nanostructured patterns produced by laser, one can create secure images that are integral to anti-counterfeiting measures. Such images, often used in security printing, contain features that are visible only under specific lighting conditions or viewing angles.The diffractive and dichroic properties of these nanostructures are also investigated. Recent advancements have shown that full-color images can be drawn on these films using pulsed lasers, a technique that offers tremendous potential for security printing.6 These images can incorporate microscopic details and color changes that are virtually impossible to duplicate without access to the same highly specialized laser technology.In conclusion, the ability of lasers to modify materials at the nanoscale presents a significant opportunity for developing new materials with customized properties. The intricate interplay of physical and chemical mechanisms activated by laser irradiation enables the precise tuning of optical characteristics, making this technology indispensable in fields ranging from security printing to advanced optical devices. As research continues to evolve, the potential applications of laser-modified materials are bound to expand, opening up new frontiers in material science and nanotechnology.References1.Z. Liu, T. Epicier, Y. Lefkir, G. Vitrant, N. Destouches, J. Microsc. 2017, 266 (1), 60-68.2.H. Ma, S. Bakhti, A. Rudenko, F. Vocanson, D. S. Slaughter, N. Destouches, T. Itina, J. Phys. Chem. C 2019, 123, 25898−25907.3.Z. Liu, J. Siegel, M. Garcia-Lechuga, T. Epicier, Y. Lefkir, S. Reynaud, M. Bugnet, F. Vocanson, J. Solis, G. Vitrant, N. Destouches, ACS Nano 2017, 11 (5), 5031–5040. 4.N. Destouches, N. Sharma, M. Vangheluwe, N. Dalloz, F. Vocanson, M. Bugnet, M. Hébert, J. Siegel , Adv. Func. Mater. 2021, 31, 2010430.5.N. Dalloz, V. D. Le, M. Hébert, B. Eles, M. A. Flores Figueroa, C. Hubert, H. Ma, N. Sharma, F. Vocanson, S. Ayala, N. Destouches, Adv. Mater. 2022, 34, 2104054.6.V. D. Le, B. Eles, N. Dalloz, M. A. Flores Figueroa, F. Vocanson, C. Hubert, N. Destouches, ACS Appl. Opt. Mater. 2024 , 2, 3, 373–385
Simulation of LQG control with Pyramid wavefront Sensor: preparation of PAPYRUS implementation
No full textInternational audienceThe PAPYRUS demonstrator is designed to test Pyramid WFSs and methods for SCAO before the advent of ELT. An LQG controller should be soon implemented. We present here first simulation results preparing on-sky implementation