Thèses sur le sujet « Interactions laser-matière – Propriétés optiques »
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Mansour, Yehia. « Études théorique et expérimentale de la formation des nanoparticules métalliques par ablation laser en milieu liquide. Modélisations des propriétés optiques et thermiques de l'interaction Laser-Nanoparticules ». Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0283.
Texte intégralNoble metal nanoparticles (NPs) are the site of a surface plasmon resonance phenomenon resulting from the collective oscillation of their conduction electrons under the effect of an electromagnetic wave. In the case of gold and silver NPs, the resonant frequency is in the visible range, which gives these plasmonic NPs unique optical properties. In particular, the position and intensity of the plasmon resonance depend on their size, shape (aspect ratio) and the index of the host medium. The possible applications require pure samples and mono-dispersed distribution. The chemical synthesis of NPs allows the shape and size of NPs to be controlled. However, it requires the use of stabilizing agents, which lead to surface contamination by synthetic residues. To limit this disadvantage, the physical technique of laser ablation in a liquid medium is a promising alternative, which, however, suffers from a lack of control over the shape and size of the NPs produced. The shape and size of NPs produced by liquid laser ablation (ALML) are closely related to the three essential steps of the process: Target / laser interaction; Mass transport; Laser / NPs interaction suspended in the liquid. In order to understand the mechanisms governing each of these stages, it is necessary to study them separately. In this work, we focused on the mechanisms of interaction between the laser beam and the NPs suspended in the liquid. Depending on the energy density absorbed by the suspended NPs, they undergo fragmentation or remodeling. We then studied the mechanisms behind the phenomenon of fragmentation. The evolution of the shape distribution of NPs during NP fragmentation was studied by developing an original and quantitative technique of in-situ optical spectroscopy. And, the evolution of the volume fraction of NPs during their preparation by ALML by in-situ optical spectroscopy is obtained and analyzed. In parallel with the experimental work, we have developed theoretical models for understanding the mechanisms of formation of metallic nanoparticles by laser ablation in a liquid medium. A modest study on the modeling of optical and thermal properties of the Laser-Nanoparticle interaction is discussed in this thesis. A modified Takami thermal model named MTM was also presented. Its important utility has been demonstrated for mechanisms for the interpretation of the mechanisms of laser-NPs interaction
Ursu, Cristian. « Caractérisation par méthodes optiques et électriques du plasma produit par ablation laser ». Thesis, Lille 1, 2010. http://www.theses.fr/2010LIL10005/document.
Texte intégralThe transient plasmas generated by high-fluence laser ablation are complex phenomena involving multiple processes, as optical radiation absorption by the matter, temperature increase and phase transitions generated by the energy transfer, expanding gas hydrodynamics, electrical interactions between the charged particles, or the interaction of the laser radiation with the generated plasma. A most complete understanding of this phenomenon is therefore necessary from the fundamental point of view, but also for characterizing the behavior of high technological potential materials under intense irradiation. We have developed a multi-diagnostic approach, based on optical and electrical techniques: fast ICCD camera imaging, space- and time-resolved optical emission spectroscopy, diode laser absorption spectroscopy, Langmuir probe. These techniques have been used to characterize plasmas generated by nanosecond laser ablation of various samples, from simple Al and Cu metals, to more complicated ceramics, chalcogenide glasses or ferromagnetics. The main results have been the observation of the plasma splitting in two structures and the kinetic and energetic characterization of their constituents. These results present fundamental (development of a fractal hydrodynamic model) and applied (erosion of dielectric walls in space plasma thrusters, pulsed laser deposition of thin films) interest
Brust, Matthias. « Propriétés rhéologiques des globules rouges ». Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00952780.
Texte intégralKouriba, Timothé. « Propriétés optiques de microstructures à base de nanofils métalliques ». Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENY084/document.
Texte intégralWe used a novel method of laser photochemistry to fabricate 3D microstructures based on metallic nanowires. Nanowires are obtained by laser photoreduction of metallic salt dissolved in a polymer matrix. The chemical reaction is initiated by the two-photon absorption of a photoreductor only at laser focal point. The geometry of microstructures is obtained by moving laser focal point according to suitable trajectories. In this thesis, we have studied the optical properties of of structures based on silver nanowires. A nanowire that stops a plane wave creates a diffracted field which shows parabolic trajectories of maxima and minima intensities. Calculations based on Rayleigh-Sommerfeld diffraction show that this typical figure corresponds to interferences between the incident plane wave and spherical waves generated at the two nanowire edges. When nanowires are arranged into set of parallel nanowires, spaced by a few microns, their diffracted fields generate intensity distributions similar to those of cylindrical refractive microlenses. In that case interference between the incident wave and the diffracted wave leads to a quadrative phase which is the at origin of focalisation. Manufacturing 2D arrays of nanowires allow to achieve very dense arrays of microlenses (10000x10000 DPI, dots per inch), which are impossible to make with refractive microlenses. The possibility to make 3D geometry permit to manipulate maxima and minima intensity trajectories for new diffractive functions at the microscopic scale. For instance manufacturing nanowires shifted in space leads to a new type of optical microdevice that allows the spatial separation of colors red, green and blue at microscopic scale
Attal, Yoann. « Processeurs atomiques utilisant la propriété de creusement spectral : modélisation et application à l’analyse spectrale radiofréquence large bande sur porteuse optique ». Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS161/document.
Texte intégralThe Spectral Hole Burning property, found in some rare-earth ion-doped crystals at low temperature is particularly relevant for analogic processing of radiofrequency signals. Indeed, it enables processing functions to be programmed in the crystal’s absorption spectrum.Starting with the first demonstrations of a wideband radiofrequency spectrum analyser, we aim at improving its performances, which requires an accurate modelling of the light-matter interaction and all the perturbations arising from the upgrade in TRL (Technology Readiness Level). Therefore, we have developed a model and extended its validity domain to a broad variety of SHB-based protocols.We applied this model on a particular material, namely a Tm³ ⁺:YAG crystal. After measuring experimentally the relevant intrinsic parameters of this crystal, we applied our model to a protocol which is quite similar to the one of the spectrum analyser we aim at optimizing, namely the engraving of wideband spectral gratings. The comparison of our experimental results to the simulations from our model proved its validity.Finally we applied it to the exact case of the radiofrequency spectrum analyser. With the simulations, we determined how to improve its performances, and particularly increase the dynamic range with realistic experimental parameters
Kouriba, Timothe. « Propriétés optiques de microstructures à base de nanofils métalliques ». Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00845919.
Texte intégralBaida, Hatim. « Propriétés optiques et spectroscopie non-linéaire de nanoparticules individuelles ». Phd thesis, Université Claude Bernard - Lyon I, 2010. http://tel.archives-ouvertes.fr/tel-00713129.
Texte intégralGaudry, Jean-Baptiste. « Etude de deux exemples d'interaction non-linéaire d'une onde laser avec la matière : endommagement laser de diélectriques et propriétés optiques non-linéaires de molécules organométalliques en solution ». Bordeaux 1, 2000. http://www.theses.fr/2000BOR10631.
Texte intégralDouti, Dam-Bé Lardja. « Tenue au flux et physique de l'interaction laser/matière dans les couches minces optiques en régime sub-picoseconde ». Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4347/document.
Texte intégralLaser fluence resistance of optical surfaces is a major challenge for the development of high power and short duration pulse lasers. Studies on laser matter interactions show that the damage initiation is the result of highly nonlinear excitation process such as photoionization, impact ionization and electronic avalanche. In this PhD thesis we focused on the study of the damage and the response of materials after this initiation and their dependence with laser parameters, this in order to better understand the complex mechanisms of damage, identify laws of relevant scales for applications, and enable new optical design with higher laser resistance and lifetimes. A multi parametric experimental testing setup was developed for studying laser resistance of optical components. To collect new data on thin film materials damage dependences, which have been less studied in the literature, different experimental studies have been conducted on dielectrics, in coating or bulk form. The study of the dependency of damage with laser wavelength reveals different ranges characterized by the electronic processes occurring during the interaction. We have considered also the effect of multiple pulse irradiations, with different wavelengths and on coatings realized by different technologies. All these experimental results have been discussed with the help of a numerical simulation model we have developed and presented in this thesis. We have also proposed an original method based on optical phase difference measurement for damage characterization and study. We finished with some experiments on the time resolved microscopy measurements and investigations of damage processes
Beaudier, Alexandre. « Etude de l'interaction laser-matière dans les composants optiques en irradiation multiple, en régime nanoseconde et dans l'UV ». Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0334/document.
Texte intégralFatigue effects in fused silica have been largely studied in the past years, as this phenomenon is directly linked to the lifetime of high power photonic materials. Indeed, in the UV regime, we observe a decrease of the LIDT (Laser-Induced Damage Threshold) when the number of laser shots increases and this has been attributed for this couple wavelength/material to laser-induced material modifications. Under 266 nm laser irradiation, with nanosecond pulses of constant fluence, we observed that the photoluminescence is modified until damage occurs. Based on this observation, we propose a new representation of the experimental S-on-1 breakdown data which allows predicting the occurrence of material breakdown. This prediction, based on fluorescence signal and not damage statistics (presently widely used) allows consuming fewer sample surface and saving time. To extend the interest of the study to many more applications, we propose an extension of the results at 355 nm. We suppose that damage is caused in our fused silica samples by accumulation of laser-induced modifications under multiple-pulse UV irradiation inducing catastrophic non-linear self-focusing. In order to try to extend the fatigue diagnostic method by fluorescence, we have also realized preliminary tests in well-known non-linear crystals like LBO and KDP
Chouli, Souad. « Structures optiques dissipatives en cavité laser à fibre ». Phd thesis, Université de Bourgogne, 2011. http://tel.archives-ouvertes.fr/tel-00692049.
Texte intégralVialla, Fabien. « Interaction entre les nanotubes de carbone et leur environnement physico-chimique : vers un contrôle des propriétés optiques ». Phd thesis, Université Pierre et Marie Curie - Paris VI, 2014. http://tel.archives-ouvertes.fr/tel-00971753.
Texte intégralDuluc, Maxime. « Étude des propriétés statistiques d'une tache focale laser lissée et de leur influence sur la rétrodiffusion brillouin stimulée ». Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0118/document.
Texte intégralIn the context of inertial confinement fusion (ICF), optical smoothing is a technique used to obtain the most homogeneous laser irradiation possible, by modifying the temporal and spatial coherence properties of the laser beams. The use of optical smoothing is a necessity on high-power lasers such as the Laser Mégajoule (LMJ) to limit the development of parametric instabilities resulting from laser-plasma interaction, and among them, stimulated Brillouin backscattering (SBS). These instabilities lead to target irradiation defects and can also be a source of damage in the optical lines. However, these techniques can lead to other problems in the laser lines, such as the conversion of phase modulation to amplitude modulation (FM-to-AM), which is harmful to the proper conduct of the experiments and can also damage the laser optics.It is therefore a necessity to find a compromise around optical smoothing. The evolution of the smoothing compromise is however complicated because the quantification of gains and losses is very difficult to establish. Thus, as long as quantification is not done, the compromise does not evolve: the laserist always wants less smoothing and the experimentalist always more smoothing, but neither of them can bring enough quantitative elements to tip the balance. This thesis therefore proposes to lay the first groundwork for reaching this compromise for the LMJ, using theoretical and numerical studies.We carefully compare longitudinal (LSSD) and transverse (TSSD) smoothing by spectral dispersion in an ideal smoothing configuration for each case. With 3D codes, we simulated SBS in a gold plasma, typical of ICF experiments and favourable to the development of SBS. We show that, contrary to popular belief, the temporal evolution of SBS shows some differences between the two smoothing schemes. First, the asymptotic values of saturation levels are not quite the same. With a simple description using light rays and the calculation of the SBS gain for each ray, we were able to explain this difference. In addition, the dynamics of SBS are also somewhat different. We have shown that the SBS dynamics is determined by the temporal evolution of the properties of the hot-spots and in particular by the effective interaction length between the Brillouin backscattered light and the hot-spots. This effective interaction length depends on both the longitudinal velocity and the length of the hot-spots. Indeed, the synchronization of the effective interaction lengths of the two smoothing schemes also synchronizes the growth of the backscatter curves before saturation.We also show that it is possible to change the smoothing parameters of the LMJ by illustrating a new way to reduce the FM-to-AM conversion inevitably present in high-power lasers. By splitting the total spectrum usually used by a quadruplet (grouping of 4 beams) into two parts of smaller identical spectra on the left and right beams, the FM-to-AM conversion is significantly reduced from 30% to 5% while maintaining the smoothing performance for SBS. We have also shown that the resulting coherence time of the laser has no effect on the maximum level of SBS achieved. Similarly, the impact of these developments on other instabilities such as stimulated Raman scattering or crossed beam energy transfer will also need to be investigated
Herrmann, Laure. « Polymères confinés dans des mésophases lamellaires lyotropes ». Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-00993471.
Texte intégralMarthe, Jimmy. « Élaboration par projection plasma d'un revêtement bicouche d'alumine réfléchissant et diffusant. Contribution à la compréhension des phénomènes interaction rayonnement/matière ». Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0258/document.
Texte intégralThis study deals with the manufacturing of reflecting and scattering coatings by plasma spraying process. By the selection of operating parameters and the control of the coatings microstructure, the first part of this work presents the elaboration of a micro/nanostructured bilayer material in alumina with a reflectance up to 90 % in the near UV-Visible range of wavelength. The feasibility of larger pieces (0.25m2) is demonstrated and the different characterizations for inserting the material in the Laser MegaJoule are performed. In a second part, from characterizations of the microstructure (by SEM, Hg Porosimetry, USAXS) and the chemical composition (DRX, X fluorescence), the improvement of the reflectance in the near-UV thanks to the nanostructured layer is explained, on the one hand, by the less absorbing crystallographic phase and, on the other hand, by the smaller and numerous pores. Moreover, the characterization of the radiation properties by the Radiation Transfer Equation inversion brings new elements for understanding the phenomena during radiation/porous media interaction and to determine the spatial repartition of the scattering radiation. The aim of the last part is to set up the different tools which are necessary to compute simulations of plasma-sprayed coatings optical behavior. From the microstructure analysis, a tridimensional numerical representation of each layer is suggested. The resolution of Maxwell equations is performed by FDTD (Finite Difference Time Domain) method. The model is validated and some first simulations are realized
Tahan, Gilles. « Étude des assemblages collés sous choc - Propriétés mécaniques après choc laser ». Thesis, Brest, École nationale supérieure de techniques avancées Bretagne, 2018. http://www.theses.fr/2018ENTA0014.
Texte intégralThe study presented follows on from the work carried out during different projects in different laboratories concerning the development of a laser shock adhesion test. The goal is to develop a method for evaluating the mechanical properties after laser impact of a bonded assembly. It will therefore not be a question of evaluating a level of adhesion using laser shock, but of considering and evaluating the possible influence of a laser shock on the mechanical properties of an assembly. This study therefore only concerns healthy assemblies, the mechanical properties of which should be evaluated before and after impact, for different amplitudes in the usual pressure range of the LASAT method (LASer Adhesion Test). This characterization of assemblies involves the choice of a method suitable for adhesive joints, capable of taking into account the specificities linked to the geometry of the substrate, but also of generating a desired stress field. The method adopted is the ARCAN mechanical test, capable of evaluating the resistance of a bonded assembly under quasi-static stresses, in tension, in shear or mixed. In addition, the ARCAN test allows the identification of behavioral laws of adhesive joints. Likewise, it is possible to characterize the composite lamellae in their out-of-plane behavior. This work was carried out at Institut de Recherche Dupuy de Lôme (IRDL), on ENSTA Bretagne site (Brest), in partnership with Engie Ineo whose activity, the construction of radomes in composite materials, is concerned with questions of control of bonded assemblies. This work was also the occasion of a collaboration with the CEA DAM DIF which made available ESTHER laser - material interaction simulation code
Klaime, Kamil. « Laser à blocage de modes à base de boîtes quantiques InAs/InP pour les télécommunications optiques ». Phd thesis, INSA de Rennes, 2013. http://tel.archives-ouvertes.fr/tel-00905711.
Texte intégralElbouaanani, Lalla Kenza. « Contribution à l'étude des propriétés structurales et magnétiques de phosphates et silicophosphates de fer ». Nancy 1, 2000. http://www.theses.fr/2000NAN10023.
Texte intégralStructural and magnetic properties of iron phosphates and silicophosphates have been investigated. The compounds have been characterised by X-ray and neutron diffraction as well as magnetization measurements and Mössbauer spectroscopy. The crystallographic structure of C-Fe(PO3)3 shows that Fe3+ ions are in isolated octahedra, related by infinite cbains of PO4 tetrahedra. This compound is antiferromagnetic below 10 K, in spite of an average distance Fe-Fe higher than 5,5 A, showing the occurence of Fe-O-P-O-Fe superexchange interactions. In Fe4(P2O1)3, the arrangement of FeO6 octahedra in face-sharing Fe2O9 dimers, , yields strong antiferromagnetic Fe3+-Fe3+ direct interactions, which dominates in respect to the frustrated Fe-O-P-O-Fe superexchange interactions. Fe2P2O7 is characterised by a bidimensionnel stacking of iron atoms as deformed Kagomé network. The FeO6 octahedra are connected by P2O7 units. The structural and magnetic studies agree with the coexistence of two Fe2 + sublattices, ordering below TN = 18 K. At 2 K, within the layers, the dominating Fe2+_Fe2+ interactions are ferromagnetic along the chains, and antiferromagnetic between the chains. The evidence of a threshold field in the magnetization curve confirms a low dimensionality magnetic character. An incommensurate magnetic structure is proposed in the 11-18 K range, probably related to the existence of frustrated interactions. In the silicophosphates, FeO6 octahedra are connected orny via PO4 tetrahedra. For the ferric FeP3SiO11 and Fe3P5SiO19 compounds, the appearance of silicon in the three-dimensional networks seems to be favored by the formation of "Si2P6O25" units. The magnetic behaviour of Fe3P5SiO19 is similar to Fe4(P2O7)3, the dominating interactions are AF within Fe2O9 dimers. Fe2SiP4O14 presents, like Fe2P2O7, layers of FeO6 octahedra sharing edges. However, Fe2SiP4O14 is paramagnetic until 1. 3 K due to unfavourable overlapping via two PO4 and a SiO4 groups. The characterization of these new silicophosphates compounds open new prospects for a better understanding of the poorly explored Fe-P-Si-O system
Vallobra, Pierre. « Effects of interfacial interactions on optical switching in magnetic heterostructures ». Thesis, Université de Lorraine, 2019. http://www.theses.fr/2019LORR0015/document.
Texte intégralDuring the last 20 years, nanomagnetism has attracted a growing interest in the scientific community due to its multiple applications for magnetic memories. At the nanometer scale, many of the properties of the magnetic materials arise from their interfaces with other materials (magnetic or non-magnetic). This explains the omnipresence of heterostructures composed of several layers of thicknesses in the range of the nanometer in the field of nanomagnetism. In the heterostructures we study, those interfacial properties are the exchange bias, the Dzyaloshinskii-Moriya interaction, the perpendicular magnetic anisotropy and the interlayer exchange between two ferromagnetic layers. First we study the modification of the exchange bias field in a [Pt/Co]xN/IrMn bilayer when we expose it to laser pulses of a femtosecond circularly polarized light. We demonstrate that the final exchange bias field after laser pulses results from the magnetic configuration of the [Pt/Co]xN multilayer. We then study the conditions required for a helicity-dependent all optical switching of a synthetic ferromagnetic material composed of a CoFeB /Pt /CoFeB and a Co ferromagnetic layers coupled antiferromagnetically and conclude that the key factors that drive the switching of the total magnetization are the Curie temperatures of both layers. We focused also on the field-driven propagation of Néel domain walls of the same chirality stabilized by the Dzyaloshinskii-Moriya interaction in [Pt/Co/Ni]xN multilayers. We finally demonstrated the possibility to generate skyrmionic bubbles with the femtosecond laser
Raulin-Woznica, Katarzyna. « Étude du dopage par des ions actifs et des nanoparticules semi-conductrices de matériaux sol-gel pour l'optique : interaction dopant-matrice et croissance localisée de nanoparticules par irradiation laser ». Thesis, Lille 1, 2008. http://www.theses.fr/2008LIL10100/document.
Texte intégralThis work concerns the elaboration by sol-gel process and the characterization of porous SiO2 xerogels doped with active ions and/or with semiconducting nanoparticles of CdS. The aim of the study was to contribute to the comprehension of the doping effects on structural and optical properties of the final material. We showed by Raman spectroscopy and nitrogen absorption-desorption that the insertion of active ions, such as Cd2+, Pb2+ or Eu3+, changes the kinetics and the mechanisms of the gelation and densification of the network of SiO2. The choices of the pH and of the concentration of the doping ion have distinct effects on the kinetics. This study was completed by emission spectroscopy using Eu3+ ion as luminescent probe to describe the environment of this ion in the porous matrix. The SiO2 xerogels were post-doped with CdS nanoparticles. The post-doping technique consists in the diffusion of an aqueous solution containing cadmium and sulphur precursors in the porous matrix. The nanoparticles crystallize in situ by heat treatment. The nanoparticle size and their emission properties were determined by UVvisible absorption as well as emission and excitation spectroscopies. The results showed the influence on optical properties of trap levels introduced by the surface defects of nanoparticles and an enhancement of the Eu3+ emission in SiO2 xerogel co-doped with CdS :Eu3+. A second method for the formation of CdS nanoparticles was used. CdS microstructures were created locally by pulsed laser irradiation of sol-gel matrices containing the CdS precursors
Ghadimi, nassiri Mikaël. « Mise en forme topologique large-bande de la lumière ». Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0187/document.
Texte intégralToday, several beam shaping tools are available, some of them commercially, but most of themare designed for only one working wavelength. This thesis aims to develop several experimentalapproaches for broadband topological beam shaping of light. After the presentation of the state ofthe art, our work focuses on vortex shaping of polychromatic beam exploiting the spin-orbitinteraction of light. Concretely, we report the development of four techniques to modulate the socalledgeometric phase of polychromatic light fields. First, we describe anisotropic reflection frominterfaces that involves at least one uniaxial crystal. We identify a refractive index matchingcriterion enabling highly pure broadband phase control. Then we discuss the use of circularBragg reflection phenomenon inherent to the optics of cholesteric liquid crystals. This propertyallows the selective reflection of circularly polarized light over a bandgap while the reflected fieldacquires a geometric phase. These properties are exploited to design, fabricate and characterizestructured mirrors reflecting Laguerre-Gauss optical modes to a good approximation. The last twosolutions consist of vortex beam shaping using inhomogeneous anisotropic planar opticalelements, namely, topological defects that spontaneously appear in homeotropic nematic liquidcrystal films characterized by negative dielectric anisotropy. The first option is based on using twodefects in series while the other is based of parallel processing using an array of independentlycontrolled topological defects, each of them being dedicated to process distinct spectralchannels. The latter approach can be viewed as a spatial light modulator whose pixels areinhomogeneous and potential applications are proposed in the field of super-resolution opticalimaging and spatio-temporal beam shaping of ultrashort pulses
Massabeau, Sylvain. « Optical and electronic properties of graphene quantum dots in the Terahertz spectral range ». Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS445.
Texte intégralThe goal of the present thesis is to explore the electronic and optical properties of graphene quantum dots (GQDs) in the THz spectral range. Using tight-binding modelling, we first calculate the energy levels of GQDs of diameters ranging from 6 to 50 nm and analyse the different nature of these energy states. We further calculate their coupling to low energy photons and determine the absorption probability spectra in the THz spectral range. We finally explore how the size, temperature and doping of the GQDs affect their absorption spectra. Secondly, we focus on the experimental investigation of the optical properties of GQDs at THz frequencies, using THz time-domain spectroscopy. Multilayer epitaxial graphene (MEG) samples are probed and then nanostructured in 107 GQDs arrays. We show that the THz response of GQDs with diameters of few tens of nm is mainly characterised by a deep absorption around 6 THz at low and room temperature. These original outcomes are supported by the theoretical analysis and are strongly different from what is observed in MEG. Finally, we study the electronic transport properties of a single GQD in the Coulomb-blockade regime. A single GQD, made of exfoliated graphene encapsulated with hBN layers, is inserted within single electron transistor coupled to a bow-tie THz antenna. Dark transport measurements in the GQD-based transistors show Coulomb blockade regime and excited states of the GQD. Finally, we provide the photoresponse of the GQD in the Coulomb blockade regime under incoherent THz illumination. These results open very exciting perspectives for the development of GQD-based devices for THz photonic applications such as THz lasers
Chopinaud, Aurélien. « Atomes et vortex optiques : conversion de moments orbitaux de lumière en utilisant la transition à deux photons 5S-5D du rubidium ». Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS155/document.
Texte intégralThe orbital angular momentum of light (OAM) is a quantized quantity arising from the azimuthal phase carried by optical vortices and is well-known for quantum technology applications. Its set of values is theoretically infinite.In this context this thesis experimentally study the conversion of optical vortices in a rubidium vapor through the 5S₁/₂ − 5D₅/₂ stimulated Raman transition. When the atoms are illuminated with laser beams at 780 nm and 776 nm they generate two coherent light beams at 5,23 μm and 420 nm. We investigate the blue light when one laser or both are optical vortices, in particular Laguerre-Gaussian modes. In a first part we show that if the laser at 776 nm carries an OAM the blue light is an optical vortex with an OAM which respects azimutal and Gouy phase matchings. We further show that the conversion is efficient on a large set of OAM from -50 to +50, that the efficiency is governed by the product of the input laser intensities and that the blue light behaves like a pure Laguerre-Gaussian mode. In a second part we demonstrate the conversion of a vortex superposition or a pair of coaxial vortices and that the OAM of the emitted light obeys the conservation rule of total OAM. For each studied case we propose a four wave mixing model establishing selection rules for the conversion process. This work opens possibilities towards OAM conversion using higher atomic levels