HAL Portal IOGS (nstitut d'Optique Graduate School)
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FBG-Based Accelerometer With Temperature Compensation for Structural Health Monitoring
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Radiation Induced Refractive Index Change in Optical Fibres Through Rayleigh-OFDR and FBG Techniques
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The water bottle flipping experiment: a quantitative comparison between experiments and numerical simulations
No full textThe water bottle flip experiment is a recreational, non-conventional illustration of the conservation of angular moment. When a bottle partially filled with water is thrown in a rotational motion, water redistributes throughout the bottle, resulting in an increase of moment of inertia and thus to a decrease in angular velocity, which increases the probability of it falling upright on a table as compared with a bottle filled with ice. The investigation of this phenomenom is accessible to undergraduate students and should allow them to gain better understanding of combined translational and rotational motions in classical mechanics. We report a series of detailed experiments that are quantitatively compared with numerical calculations based on a simple theoretical framework in which the water volume is decomposed into thin slices of a rigid body that are subjected to fictitious forces in the non-inertial frame of the spinning bottle. This model also allows us to capture and predict other experimental configurations. Finally, we discuss additionnal counter-intuitive effects that contribute to bottle stabilization on landing
A Theoretical Analysis of the Incremental Counting Ability of LSTM in Finite Precision
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Characterizing microstructures with representative tortuosities
No full textInternational audienceThis paper addresses the numerical characterization of microstructures by the concept of tortuosity. After a brief review of geometric tortuosities, some definitions are considered for a benchmarking analysis. The focus is on the M-tortuosity definition, which is revised by expliciting the link to percolation theory, among other things. This operator fits with the analysis of real samples of materials whatever their complexity. A contribution of this paper is a new formulation of the M-tortuosity , making it generic to many situations. Additionally, the comparison of the various tortuosimetric descriptors, state-of-the-art definitions and M-tortuosity , is proposed by considering several scenarios thanks to stochastic multi-scale models of complex materials. The relationships with porosity, morphological heterogeneity and structural anisotropy are investigated. The results highlight the similarities and differences between the descriptors while attesting that the M-tortuosity is equivalent to the state-of-the-art definitions, for a potential use in diffusion and conductivity analyses. Moreover, the M-tortuosity handles correctly situations where state-of the-art algorithms fail. The anisotropic case highlights some limitations of the state-of-the-art definitions behaving differently according to the given propagation direction. In the case of unknown propagation and irregular piece of materials, the M-tortuosity provides a unique tortuosity value representative of the whole microstructure while detecting the anisotropy. These operators are freely available within the plug im! platform
Identification of early stage liver fibrosis by modifications in the interstitial space diffusive microenvironment using fluorescent single-walled carbon nanotubes
No full textInternational audienceDuring liver fibrosis, recurrent hepatic injuries lead to the accumulation of collagen and other extracellular matrix components in the interstitial space, ultimately disrupting liver functions. Early stages of liver fibrosis may be reversible, but opportunities for diagnosis at these stages are currently limited. Here, we show that the alterations of the interstitial space associated with fibrosis can be probed by tracking individual fluorescent single-walled carbon nanotubes (SWCNTs) diffusing in that space. In a mouse model of early liver fibrosis, we find that nanotubes generally explore elongated areas, whose lengths decrease as the disease progresses, even in regions where histopathological examination does not reveal fibrosis yet. Furthermore, this decrease in nanotube mobility is a purely geometrical effect as the instantaneous nanotube diffusivity stays unmodified. This work establishes the promise of SWCNTs both for diagnosing liver fibrosis at an early stage and for more in-depth studies of the biophysical effects of the disease
Cross-layer analysis of clock glitch fault injection while fetching variable-length instructions
No full textInternational audienceWith the increasing complexity of embedded systems, the use of variable-length instruction sets has become essential, so that higher code density and better performance can be achieved.Security aspects are closely linked, considering the continuous improvement of attack techniques and equipment.Fault injection is among the most interesting and rising physical attack techniques.However, hardware designers and software developers lack accurate fault models to evaluate the vulnerabilities of their designs or codes in the presence of such attacks.In this article, we provide a proper characterization, at instruction set architecture (ISA) level, of several faulty behaviors that are experimentally observed when a processor running a variable-length instruction set is targeted.We include the binary encoding of instructions, and show how the obtained behaviors depend on the alignment in memory.Moreover, we give a deeper insight on previous results from the literature, that were still left unexplained.Additionally, we move downward at system level and consider the register-transfer level (RTL) to perform RTL fault simulation; This enables a better understanding of the faults propagation, validate the inferred fault models at ISA level, and reveal the origin of such faults at microarchitectural level.Finally, applying the given fault models leads us to provide vulnerability analysis on three different implementations of AES
Laser à fibres Tm : Ho de haute puissance à femtoseconde à 2050 nm
No full textThe chirped pulse amplification (CPA) technique was developed to power scale the pulsesfrom mode-locked oscillators as the pulse energy was not sufficient to target applicationssuch as strong field physics and particle acceleration. Since its development in 1985 ithas been applied in a wide variety of commercially available laser systems and ultra-highpower laser facilities. The technique allows to circumvent the accumulation of non-linearphase which hampers pulse compression and allows to maintain the fluence of the pulsesbelow the laser induced damage thresholds (LIDT) of components. In this thesis wedevelop CPA laser systems operating at 2.05μm wavelengths with high average powerand high energy starting from the development of the seed laser up to the design andimplementation of the pulse stretcher, amplifiers and pulse compressor.In the first section of the thesis we introduce the physics background and phenomenarequired for understanding the chirped pulse amplification technique and the developmentof the seed laser. This includes dispersion, self-phase modulation and Raman scattering.In the second section of the thesis we present the development of an all-fiber polarizationmaintaining laser tunable over 170nm, from 1880nm up to 2050nm via Ramansoliton self-frequency shift (SSFS). The system is based on exclusively commercially availablestandard fibers. We have characterised the laser in terms of power, spectrum andpulse duration and we have included a post-compression stage that relies on non-lineareffects to reach the sub-100 fs duration across the whole tunability range. Simulations ofthe soliton post-compression shows the versatility of the laser which allows to customisethe pulse duration over a spectral range or for a particular wavelength. We believe thatthe laser is a versatile and robust alternative to Tm and Tm:Ho oscillators.In the third section we have tested the tunable laser in a wide variety of stretchingand compression architectures suitable for CPA. We have investigated fibers and chirpedvolume Bragg gratings (CVBG) as pulse stretching devices and grating pairs and CVBGsas pulse compressors. We discuss how to dimension a stretching-compressor pair takinginto account the non-linear phase and gain narrowing effect that takes place during pulseamplification and how to evaluate the stretching-compressor performance. Two differentchirped pulse amplification laser systems have been designed and presented, the first onetargets broadband fs pulses with high average power and the second system targets highenergetic ps pulses. The non-mature technology in the 2μm spectral region and the weakavailability of suitable stretching devices hinders pulse compression at this wavelength.In the last section of the thesis we investigated the performance of Tm:Ho co-dopedfibers in amplification configuration. We discuss the main challenges of these fibers includingthe cross-relaxation effects, the availability of pump sources which gives rise totwo main pumping schemes: diode pumping and in-band pumping and the limitations interms of fiber size. We tested Tm:Ho doped fibers, including LMA for narrowband andbroadband pulse amplification.La technique d’amplification à dérive de fréquence "chirped pulse amplification" (CPA)a été développée pour augmenter la puissance des impulsions issues d’oscillateurs à verrouillage de mode, car l’énergie des impulsions n’étaient pas suffisantes pour des applications telles que la physique des champs forts et l’accélération de particules. Depuis son développement en 1985, elle a été utilisée dans une grande variété de systèmes laser industriels et dans des installations laser à ultra-haute puissance. Cette technique permet d’une part de s’affranchir de l’accumulation de phase non linéaire qui entrave la compression d’impulsions et d’autre part de maintenir la fluence des impulsions en dessous des seuils de dommages induits par laser aux composants. Dans cette thèse, nous développons des systèmes laser CPA à la longueurs d’onde de 2.05μm avec une puissance moyenne élevée et une énergie élevée, en commençant par le développement du laser à 2050nm jusqu’à la conception et la mise en oeuvre de l’étireur, des amplificateurs et du compresseur d’impulsions.Dans la première section de la thèse, nous introduisons les principaux concepts de physique et les phénomènes nécessaires à la compréhension de la technique d’amplification par dérive de fréquence et au développement du laser à fibre à 2050nm. Cela inclut la dispersion, l'automodulation de phase et la diffusion Raman.Dans la deuxième section de la thèse, nous présentons le développement d’un laser entièrement fibré à maintien de polarisation et accordable sur plus de 170nm, de 1880nmà 2050nm, via le phénomene de décalage de fréquence solitonique (Raman soliton selffrequencyshift, SSFS). Notre systéme est basé exclusivement sur des fibres disponibles commercialement. Nous avons caractérisé le laser en termes de puissance, de spectre et de durée d’impulsion, et nous avons inclus une étape de post-compression qui repose sur des effets non linéaires pour atteindre une durée inférieure à 100 fs sur toute la plage d' accordabilité. Les simulations sur la post-compression de solitons montrent la polyvalence du laser, qui permet de personnaliser la durée de l’impulsion sur une plage spectrale donnée, ou alternativement à une longueur d’onde particulière.Dans la troisième section, nous avons testé le laser accordable dans une grande variété d’architectures d’étirement et de compression adaptées au CPA. Nous avons examiné les fibres et les réseaux de Bragg en volume étiré (CVBG) en tant que dispositifs d’étirement d’impulsions, ainsi que les paires de réseaux de diffraction et les CVBG en tant que compresseurs d’impulsions. Nous discutons la manière de dimensionner une paire d’étireur compresseuren tenant compte de la phase non linéaire et de l’effet de rétrécissement du gain qui se produit pendant l’amplification d’impulsions, ainsi que de l’évaluation des performances de l’étireur-compresseur. Deux systèmes laser d’amplification à dérive de fréquence ont été conçus et présentés, le premier visant des impulsions fs à large bande avec une puissance moyenne élevée, et le second système visant des impulsions ps à haute énergie. La technologie peu mature dans la région spectrale de 2μm et la faible disponibilité de dispositifs d’étirement adaptés entravent la compression d’impulsions à cette longueur d’onde.Dans la dernière section de la thèse, nous avons étudié les performances des fibres co-dopées Tm:Ho en configuration d’amplification. Nous discutons des principaux défis de ces fibres, notamment les effets de transfert d’énergie, la disponibilité des sources de pompage qui donnent lieu à deux schémas de pompage principaux : le pompage par diode et le pompage intra-bande, ainsi que les limitations en termes de taille de fibre. Nous avons testé les fibres dopées Tm:Ho, y compris les fibres à coeur large pour l’amplification d’impulsions à bande étroite et à large bande
β -rays induced displacement damage on epitaxial 4H-SiC revealed by exciton recombination
No full textInternational audienceOne of the most interesting wide-bandgap semiconductor is 4H-SiC that has an indirect wide-bandgap of 3.3 eV. This material holds great potential to develop power devices that find applications in the field of high-voltage and high-temperature electronics and harsh environments. In this study, we employed complementary noninvasive characterization techniques, including micro-Raman, optical absorption, steady-state, and time-resolved photoluminescence spectroscopy, to investigate the characteristics of a 12 μm thick epitaxial layer of 4H-SiC grown on 4H-SiC. Furthermore, we explored the impact of ionizing radiation on this material, utilizing β-rays and two x-ray sources. The doses are in the range of 1–100 kGy for electrons with energy of 2.5 MeV, 16 kGy for the first x-ray source (an x-ray tube with a W target operating at an anode bias voltage of 28 kV), and 100 kGy for the second x-ray source (an x-ray tube with a W target operating at an anode bias voltage of 100 kV). When exposed to the electron beam, the excitonic band at 3.2 eV exhibits a reduction in its lifetime as the deposited dose increases. In particular, in samples characterized by a greater amount of native defects, both extended and point defects, this effect becomes evident at lower deposited doses. Conversely, in the samples subjected to x-ray irradiation, these effects are not observed. These findings indicate that electron beam irradiation triggers the formation of defects associated with atomic displacement. Ultimately, we have examined the impact of thermal treatments in air, ranging from 100 to 900 °C, to investigate the recovery characteristics of 4H-SiC
Quantitative mapping of transient thermodynamic states in ultrafast laser nanostructuring of quartz
No full textInternational audienceUnderstanding material structural reaction to light is of utmost importance to advance processing resolution in ultrafast laser volume structuring into the nanoscale. Selective thermodynamic pathways are required to quench energy transport in the most rapid manner and to confine the process to nm lengths, bypassing optical resolution. Quantifying material dynamics under confinement, with in-situ access to transient local temperature and density parameters, becomes thus key in understanding the process. We report in-situ reconstruction of thermodynamic states over the entire matter relaxation path in bulkα-quartz irradiated by ultrafast non-diffractive laser beams using time-resolved qualitative and quantitative optical phase microscopy. Thermooptic dynamics indicate rapid spatially-confined crystalline-to-amorphous transition to a hot dense fused silica form. Densification exceeds 20% and the matrix temperature rises to more than 2000 K in the first ns. This structural state relaxes in hundreds of ns. The dispersion design of the optical beam to ps durations increases the spatial confinement and triggers an extreme nanostructuring process based on nanocavitation that occurs within the amorphizing material, where the low-viscosity phase lowers the mechanical requirements for the process. Processing feature scales of less than a tenth of the optical wavelengthare obtained in the volume. This allows for structural and morphological nanoscale material features under 3D confinement that can engineer optical materials