La diffusion Raman est réalisée dans la géométrie inhabituelle de diffusion « en avant » (fonctionnant schématiquement en ‘mode de transmission’) pour explorer la nature et les propriétés des modes phonon-polaritons (polaires) de divers cristaux mixtes A1-xBxC à base de ZnSe. Un aperçu général est recherché en sélectionnant des systèmes qui se rapportent au même composé parent par souci de cohérence - à savoir ZnSe - mais avec différentes structures cristallines, i.e. de type zincblende (cubique : Zn1-xBexSe, ZnSe1-xSx, ZnxCd1-xSe) et de type wurtzite (hexagonal : Zn1-xMgxSe). Les systèmes retenus englobent toute la panoplie des comportements dans le régime de phonons natifs (non polaires) des phonons-polaritons, y compris les déviations sur-diversifiées [1 × (AB), 2 × (AC)] et sous-diversifiées de 1 × (AB, AC) par rapport au type -nominal [1 × (AB), 1 × (AC)], également dénommées multi-mode, 1-mode-mixte et 2-mode, respectivement, dans la classification admise des spectres Raman classiques de cristaux mixtes obtenus dans la géométrie conventionnelle de rétrodiffusion (fonctionnant schématiquement dans en 'mode réflexion'). La modélisation du contour des spectres Raman phonon-polariton obtenus est réalisée dans le cadre de la théorie de la réponse diélectrique linéaire en se basant sur des mesures d’ellipsométrie de l'indice de réfraction, avec des calculs ab initio en appui réalisés sur des motifs d'impureté prototypes dans les limites diluées (x~0,1), pour sécuriser le jeu réduit de paramètres d'entrée qui régissent le comportement phonon de base (non polaire) des cristaux mixtes étudiés. La discussion des spectres Raman obtenus en rétrodiffusion /avant est effectuée dans le cadre du modèle de percolation développé au sein de l’équipe pour une compréhension renouvelée des spectres optiques de vibration des cristaux mixtes. Ce modèle formalise une vision des choses selon laquelle les liaisons chimiques d'une espèce donnée vibrent à des fréquences différentes dans un cristal mixte selon que leur environnement est de même type ou de type différent à l'échelle très locale (des premiers, voire des seconds voisins). [...] / Inelastic Raman scattering is implemented in the unusual (near-)forward scattering geometry (schematically operating in the ‘transmission mode’) to explore the nature and properties of the (polar) phonon-polariton modes of various ZnSe-based A1-xBxC mixed crystals. An overall insight is searched by selecting systems that relate to the same parent compound for the sake of consistency – namely ZnSe – but with different crystal structures, i.e. of the zincblende (cubic: Zn1-xBexSe, ZnSe1-xSx, ZnxCd1-xSe) and wurtzite (hexagonal: Zn1-xMgxSe) types. Most of all, altogether the retained systems span the full variety of behavior in the native (non polar) phonon regime of the phonon-polaritons, including the over-diversified [1×(A−B),2×(A−C)] and sub-diversified 1×(A−B,A−C) deviations with respect to the nominal [1×(A−B),1×(A−C)] type, also referred to as the multi-mode, 1-mixed-mode and 2-mode types, respectively, in the admitted classification of the conventional Raman spectra of mixed crystals taken in the backscattering geometry (schematically operating in the ‘reflection mode’). Fair contour modeling of the obtained phonon-polariton Raman spectra is achieved within the linear dielectric response theory based on ellipsometry measurements of the refractive index and with ab initio calculations in support done on prototypal impurity motifs in both dilute limits (x~0,1), as needed to secure the reduced set of input parameters that govern the native (non polar) phonon mode behavior of the used mixed crystals. The backward/near-forward Raman spectra are discussed within the scope of the so-called percolation model developed within our group for a renewed understanding of the optical vibration spectra of the mixed crystals. This model formalizes a view that the chemical bonds of a given species vibrate at different frequencies in a mixed crystal depending on their like or foreign environment at the very local (first- or second-neighbor) scale. This introduces a generic 1-bond→2-mode phonon behavior for a mixed crystal, presumably a universal one. The main results enunciate as follows. [...]

The three dimensional Monte Carlo radiation transport model McArtim is extended to account for the simulation of the propagation of polarized radiation and the inelastic rotational Raman scattering which is the cause of the so called Ring effect. From the achieved and now sufficient precision of the calculated Ring effect new opportunities in optical absorption spectroscopy arise. In the calculation the method of importance sampling (IS) is applied. Thereby one obtains from an ensemble of Monte Carlo photon trajectories an intensity accounting for the elastic aerosol particle-, Cabannes- and the inelastic rotational Raman scattering (RRS) and simultaneously an intensity, for which Rayleigh scattering is treated as an elastic scattering process. By combining both intensities one obtains the so called filling-in (FI, which quantifies the filling-in of Fraunhofer lines) as a measure for the strength of the Ring effect with the same relative precision as the intensities. The validation of the polarized radiometric quantities and the Ring effect is made by comparison with partially published results of other radiation transport models. Furthermore the concept of discretisation of the optical domain into grid cells is extended by making grid cells arbitrarily joining into so called clusters, i.e. grid cell aggregates. Therewith the program is able to calculate derivatives of radiometrically or spectroscopically accessible quantities, namely the intensities at certain locations in the atmospheric radiation field and the light path integrals of trace gas concentrations associated thereto, i.e. the product of the DOAS (differential optical absorption spectroscopy) method, with respect to optical properties of aerosols and gases in connected spatial regions. The first and second order derivatives are validated through so called self-consistency tests. These derivatives allow the inversion of three dimensional tracegas and aerosol concentration profiles and pave the way down to 3D optical scattered light tomography. If such tomographic inversion scheme is based solely on spectral intensitites the available second order derivatives allows the consideration of the curvature in the cost function and therefore allows implementation of efficient optimisation algorithms. The influence of the instrument function on the spectra is analysed in order to mathematically assess the potential of DOAS to a sufficient degree. It turns out that the detailed knowledge of the instrument function is required for an advanced spectral analysis. Concludingly the mathematical separability of narrow band signatures of absorption and the Ring effect from the relatively broad band influence of the elastic scattering processes on the spectra is demonstrated which corresponds exactly to the DOAS principle. In that procedure the differential signal is obtained by approximately 4 orders of magnitude faster then by the separate modelling with and without narrow band structures. Thereby the fusion of the separated steps DOAS spectral analysis and subsequent radiation transport modeling becomes computationally feasible.:1.1. Radiation Transport Modeling and Atmospheric State Inversion 1.2. Vector RTE Solution Methods 1.3. Scope of the Thesis 1.4. Outline of the Thesis 2.1. General Structure 2.1.1. Chemical Composition of the Gas Phase 2.1.2. The Troposphere, Temperature and Pressure Vertical Structure 2.1.3. The Stratosphere 2.2. Aerosols and Clouds 2.2.1. Classification and Morphology 2.2.2. Water Related Particle Growth and Shrinking Processes 2.2.3. Size Spectra and Modes 3.1. Electromagnetic Waves 3.1.1. Maxwell\''s Equations 3.1.2. Measurement of Electromagnetic Waves 3.1.3. Polarization State of EM Waves 3.1.4. Stokes Vectors 3.2. Scattering and Absorption of EM Waves by Molecules and Particles 3.2.1. General Description of Scattering and Coordinate Systems 3.2.2. Molecular Scattering 3.2.3. Molecular Absorption Processes and Electronic Molecular States 3.2.4. Scattering On Spherical Particles - Mie Theory 3.3. Mathematical Description of Radiation Transport 3.3.1. Radiance and Irradiance 3.3.2. Absorption, Scattering and Extinction Coefficients 3.3.3. Optical Thickness and Transmission 3.3.4. Scattering 3.3.5. Incident (Ir)Radiance 3.3.6. The Black Surface Single Scattering Approximation 3.3.7. Radiative Transfer Equations 4.1. General Monte Carlo Methods 4.1.1. Numerical Integration 4.1.2. Importance Sampling and Zero Variance Estimates 4.1.3. Optimal Sampling 4.1.4. Sampling from Arbitrary Distributions 4.2. Path Generation or Collision Density Estimation 4.2.1. Discretization of the Optical Domain into Cells and Clusters 4.2.2. RTE Integral Form 4.2.3. Formal Solution of the IRTE 4.2.4. Overview on Monte Carlo RTE Solution Algorithms 4.2.5. Crude Monte Carlo 4.2.6. Sequential Importance Sampling (SIS) or Path Generation 4.3. Importance Sampling in Monte Carlo SIS Radiative Transfer 4.3.1. Weights for Alternate Kernels 4.3.2. Weights in the Calculation of RTE Functional Estimates 4.3.3. Application of IS to Mie Phase Functions Scatter Angle Sampling 5.1. Radiances, Intensities and the Reciprocity Theorem 5.1.1. Scalar Radiance Estimates 5.1.2. Backward Monte Carlo Scalar Radiance 5.1.3. Vector Radiances 5.2. Radiance Derivatives 5.2.1. Variables for Radiance Derivatives 5.3. Validation of Functionals 5.3.1. Validation of Vector Radiances 5.3.2. Validation of Radiance Derivatives 6.1. A Simply Structured Instrument Forward Model 6.2. Pure Atmospheric Spectra and Absorption 6.2.1. Direct Light Spectra 6.2.2. Scattered Sun Light Spectra 6.3. (D)OAS from the Perspective of Radiative Transfer Modeling 6.3.1. (Rest) Signatures of Weakly Absorbing Gases 6.3.2. Spectroscopic Measurements and Standard DOAS 6.4. DOAS Analysis Summary 6.4.1. DSCD Retrieval 6.4.2. Inversion 7.1. RRS-Modified RTE 7.1.1. RRS Cross Sections for Scattering out and into a Wavelength 7.1.2. Modification of the RTE Loss and Source Terms 7.2. Intensity Estimates Considering Rotational Raman Scattering 7.2.1. RRS in the Path Sampling Procedure 7.2.2. Adjoint RRS Correction Weights 7.2.3. Local Estimates of Intensities with RRS 7.2.4. Intensity Estimates 7.3. Ring Spectra 7.3.1. Elastic Biasing of the Local Estimates 7.3.2. Cumulative Weights and Local Estimates 7.3.3. Test of the Elastic Biasing 7.4. Validation 7.4.1. Comparison to an Analytic Single Scattering Code 7.4.2. Single Scattering Model Including Rotational Raman Scattering 7.4.3. Multiple Scattering Model Comparison 7.4.4. Comparison with A Measurement 7.4.5. Validation of Approximate Methods For Ring Effect Modeling 7.5. Summary and Discussion 8.1. Status and Summary 8.1.1. Ring-Effect and Absorption Corrected Radiances 8.1.2. Derivatives of Radiometric Quantities Accessible Through Spectroscopy 8.1.3. Polarization 8.1.4. Time Integrated Sensitivities for 3D UV/vis/NIR Remote Sensing 8.2. Outlook A.1. Zero Variance Estimates A.2. Free Path Length Sampling in a Homogeneous Medium A.3. Cumulative Differential Scatter Cross Sections A.3.1. Cardanic formulas A.3.2. Rayleigh and Raman Phase Functions A.3.3. Henyey-Greenstein Model A.3.4. Legendre Polynomial Phase Function Model A.3.5. Table Methods A.4. Greens Function in the Derivation of the IRTE A.5. Source Code For Stokes Vector Transformation Plot B.1. 1st Order Derivatives B.2. 2nd Order Derivatives B.3. Hessian of Integrals Depending on Many Variables C.1. Slit Function f Derivatives C.2. Signal Sn Derivatives C.3. Chi Square Spline Fitting C.3.1. Constrained Non-Linear Least Square Problem C.3.2. Spline Fitting C.3.3. Jacobians and Hessian

The transformation of the vibrational spectrum of Cu2Zn(Sn1−xGex)S4 single crystals over the entire composition range (0 ≤ x ≤ 1) is studied experimentally by low-temperature Raman scattering and photoluminescence spectroscopies, as well as theoretically in the framework of density functional theory (DFT). It is shown that unlike “classic” mixed binary II–VI and III–V compounds, which are characterized by either one- or two-mode behavior of spectra transformation upon composition variation, the vibrational modes of the quaternary semiconductor Cu2Zn(Sn1−xGex)S4 exhibit both types of behavior within the same alloy system. DFT calculations reveal that the two-mode transformation is in fact observed for the vibrational modes, which possess a very small dispersion across the Brillouin zone, that is typical for a molecular crystal. These modes are due to the “breathing” motion of sulfur within GeS4 and SnS4 tetrahedra. The effects of structural (positional) disorder of mixed crystals are analyzed based on Raman scattering as well as photoluminescence results. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Die vorliegende Dissertation befasst sich mit der Anwendung und Weiterentwicklung der CARS -Mikroskopie (CARS, (Coherent anti-Stokes Raman scattering)) zur Lokalisierung von Wirkstoffen in Zellen. Aufgrund einer C-Deuterierung dieser Wirkstoffe werden diese intrinsisch markiert und lassen sich nicht-invasiv mit Hilfe Raman-basierter Mikrospektroskopietechniken von Zellbestandteilen unterscheiden. Diese Arbeit widmet sich der für biomedizinische Anwendungen zu geringen Sensitivität und zu hohen Komplexität des experimentellen Aufbaus für CARS-Mikroskopie. Auf der Anwendungsseite wurdenzunächst mittels quantitativer Raman- und CARS- Mikroskopie die Detektionsgrenzen C-deuterierter Stoffe bestimmt. Anhand von mit deuterierter Fettsäure inkubierter Makrophagen wurde chemischer Kontrast in Zellen qualitativ gezeigt. Die Weiterentwicklung des experimentellen Aufbaus erfolgte durch den Einsatz von Impulsformern. Diese können das Anregungslicht in Amplitude und Phase formen und somit den Schwingungskontrast optimieren und den experimentellen Aufbau vereinfachen. Verwendet wurden dabei sowohl ein spatial light modulator (SLM) als auch ein akustooptischer Modulator (AOM), die in dieser Arbeit miteinander verglichen werden. Mit Hilfe einer photonischen Kristallfaser als spektral breite Lichtquelle und des AOM als spektraler Filter konnte der Aufbau vereinfacht und ein Schema zur Implementierung von Quasi-Multiplex CARS-Mikroskopie aufgebaut werden, welches ein schnelles Schalten zwischen verschiedenen bildgebenden Raman-Banden erlaubt. Die automatisierte Optimierung des Schwingungskontrasts erfolgte schließlich durch den Einsatz des SLM, der mit Hilfe eines selbstlernenden Algorithmus den Schwingungskontrast von CARS-Bildern um bis zu 160 % verbessern konnte.

<p dir="ltr">The objective of this research is to advance the development and application of laser diagnostics in gas phase medium, which ranges from atmospheric non-reacting flows to turbulent reacting flows in high-pressure, high-temperature environments. Laser diagnostic techniques are powerful tools for non-intrusive and in-situ measurements of important chemical parameters, such as temperature, pressure, and species mole fractions, in harsh environments. These measurements significantly advance the knowledge across various research disciplines, such as combustion dynamics, chemical kinetics, and molecular spectroscopy. In this thesis, detailed theoretical models and experimental analysis are presented for three different techniques: 1. Chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering (CPP fs CARS); 2. Two-color polarization spectroscopy (TCPS); 3. Ultrafast-laser-absorption-spectroscopy (ULAS). The first chapter provides a brief survey of laser diagnostics, including both linear and nonlinear methods. The motivations behind the three studies covered in this dissertation are also discussed. </p><p dir="ltr">In the second chapter, single-shot CPP fs CARS thermometry is developed for the hydrogen molecule at 5 kHz. The results are divided into two parts. The first part concentrates on the development of H₂ CPP fs CARS thermometry for high-pressure and high-temperature conditions. The second part demonstrates the application of H₂ CPP fs CARS in a model rocket combustor at pressures up to 70 bar. In the first part, H₂ fs CARS thermometry was performed in Hencken burner flames up to 2300 K, as well as in a heated gas-cell at temperatures up to 1000 K. It was observed that the H₂ fs CARS spectra are highly sensitive to the pump and Stokes chirp. Chirp typically originates from optical components such as windows and polarizers. As a result, the pump delay is modeled to provide a shift to the Raman excitation efficiency curve. With the updated theoretical model, excellent agreement was found between the simulated and experimental spectra. The averaged error and precision are 2.8% and 2.3%, respectively. In addition, the spectral phase and pump delay determined from the experimental spectra closely align with the theoretical predictions. It is also found that pressure does not have significant effects on the H₂ fs CARS spectra up to 50 bar at 1000 K. The collision model provides excellent agreement with the experiment. This allows the use of low-pressure laser parameters for high-pressure thermometry measurements. In the second part, spatially resolved H₂ temperature was measured in a rocket chamber at pressures up to 70 bar. This is the first demonstration of fs CARS thermometry inside a high-pressure rocket combustor. These results highlight the potential of using H₂ CPP fs CARS thermometry to provide quantitative data in high-pressure experiments for the study of combustion dynamics and model validation efforts at application relevant operating conditions.</p><p dir="ltr">The third chapter presents the development of a TCPS system for the study of the NO (<i>A</i>²Σ⁺-<i>X</i>²Π) state-to-state collision dynamics with He, Ar, and N₂. Two sets of TCPS spectra for 1% NO, diluted in different buffer gases at 295 K and 1 atm, were obtained with the pump beam tuned to the R₁₁(11.5) and ^OP₁₂(1.5) transitions. The probe was scanned while the pump beam was tuned to the line center. Collision induced transitions were observed in the spectra as the probe scanned over transitions that were not coupled with the pump frequency. The strength and structure of the collision induced transitions in the TCPS spectra were compared between the three colliding partners. Theoretical TCPS spectra, calculated by solving the density matrix formulation of the time-dependent Schrödinger wave equation, were compared with the experimental spectra. A collision model based on the modified exponential-gap law was used to model the rotational level-to-rotational level collision dynamics. An unique aspect of this work is that the collisional transfer from an initial to a final Zeeman state was modeled based on the difference in the cosine of the rotational quantum number <i>J</i> projection angle with the z-axis for the two Zeeman states. Rotational energy transfer rates and Zeeman state collisional dynamics were varied to obtain good agreement between theory and experiment for the two different TCPS pump transitions and for the three different buffer gases. One key finding, in agreement with quasi-classical trajectory calculations, is that the spin-rotation changing transition rate in the <i>A</i>²Σ⁺ level of NO is almost zero for rotational quantum numbers ≥ 8. It was necessary to set this rate to near zero to obtain agreement with the TCPS spectra. </p><p dir="ltr">The fourth chapter presents the development and application of a broadband ULAS technique operating in the mid-infrared for simultaneous measurements of temperature, methane (CH₄), and propane (C₃H₈) mole fractions. Single-shot measurements targeting the C-H stretch fundamental vibration bands of CH₄ and C₃H₈ near 3.3 μm were acquired in both a heated gas cell up to ~650 K and laminar diffusion flames at 5 kHz. The average temperature error is 0.6%. The average species mole fraction error are 5.4% for CH₄, and 9.9% for C₃H₈. This demonstrates that ULAS is capable of providing high-fidelity hydrocarbon-based thermometry and simultaneous measurements of both large and small hydrocarbons in combustion gases. </p>

No description available.

No description available.

<p dir="ltr">In recent years, nanosecond repetitively pulsed (NRP) plasma discharges have garnered significant interest due to their rapid generation of reactive excited-state species, reactive radicals, and localized heat release within nanosecond (ns) timescale. To effectively harness these plasmas for altering system-level thermal and chemical behavior, a thorough understanding of their governing physics is crucial. This knowledge enables the development of predictive plasma kinetic models for tailoring NRP plasmas to specific applications. However, achieving this requires high-fidelity experimental data to validate models and deepen our understanding of fundamental plasma physics. Advancing experimental spectroscopy and laser diagnostics methods is essential for probing such temporally highly dynamic and optically complex nonequilibrium environments. This includes developing novel <i>test platforms</i>, conducting <i>fundamental research</i> to address existing knowledge gaps, and constructing custom <i>ultrafast laser architectures</i> for probing plasma properties. </p><p dir="ltr">The pioneering development of Streak-based <i>test platform</i> in the diagnostics field of nanosecond pulsed plasmas and its successful application towards inferring the underlying ultrafast spatio-temporal evolution of nanosecond pulsed plasma discharges with an unprecedented time-resolution as short as ~25 ps is presented for the first time. Spectrally filtered, 1D line-imaging of nanosecond pulsed plasma discharges in a single-shot, jitter-free, continuously sweeping manner is obtained, and differences in discharge dynamics of air and N2 plasma environments are studied. Successive <i>test platform</i> advancement includes spectrally resolved Streak-spectroscopy measurements of thermal regime-transition evolution from early-nonequilibrium to local-thermal-equilibrium (LTE) to attain time-resolved quantitative insights into N2(C) state rotational/vibrational nonequilibrium temperatures, electron temperature/density, and spectral lifetime dynamics. </p><p dir="ltr">Ultrafast laser-based progression includes detailed <i>fundamental</i> investigation of higher-order optical nonlinearity perturbations of fs-EFISH by considering of – self-phase modulation induced spectral characteristic of fs-EFISH signal, calibration mapping during-below-and-beyond optical breakdown regime, optical Kerr effect consequences, impact of femtosecond (fs) laser seeding on the noninvasiveness of fs-EFISH, and spectral emission characteristics of fs laser filaments. To infer N2(X) state nonequilibrium of NRP pulsed plasmas, two hybrid fs/ps ro-vibrational coherent anti-Stokes Raman scattering (CARS) <i>ultrafast laser architectures</i> are developed. First architecture, single-laser-solution, reduces system’s energy budget by ~3 mJ/pulse for generating narrowband (~21 ps), high-energy (~420 μJ/pulse), 532 nm probe pulses through incorporation of custom built visible fs optical parametric amplifier (OPA) coupled with an Nd:YAG power amplifier module. The second architecture, two-laser-solution, improves system’s robustness through the development of a 1 kHz, 532 nm, high-energy (~600 μJ/pulse), low-jitter (<1 ps), narrowband (~27 ps), master-oscillator-power-amplification (MOPA) based picosecond probe pulse laser time-synchronized with fs master-oscillator. Single-shot, hybrid fs/ps narrowband ro-vibrational CARS demonstration in a combusting flame up to temperatures of ~2400 K is demonstrated. Experimental ro-vibrational CARS investigation includes polarization based nonresonant background suppression and demonstration of preferential Raman coherence excitation shift, a temperature sensitivity enhancing strategy for vibrationally hot mediums like nanosecond pulsed plasmas. Lastly, an ultrafast pulse-friendly optically accessible vacuum cell is designed and fabricated for controlled experiments of NRP fs/ps CARS. Special care is taken to prevent self-focusing and spectral-temporal chirp of fs CARS beams while maintaining Gaussian focusing beam caustic.</p>

Ce mémoire porte sur la mise au point de plateforme microfluidique couplée à la microscopie Raman confocale, utilisée dans des conditions d’excitation de la diffusion Raman (diffusion Raman exaltée de surface), dans le but d’obtenir une détection de très haute sensibilité d’espèces moléculaires sous écoulement dans des canaux de dimensions micrométriques. Ce travail a pour ambition de démontrer la faisabilité d’un couplage microscopie Raman/microfluidique en vue de la caractérisation in-situ et locale, des espèces et des réactions mises en jeu dans les fluides en écoulement dans les microcanaux. Nous avons utilisé un microcanal de géométrie T, fabriqué par lithographie douce, dans lequel sont injectées, à vitesse constante, des nanoparticules métalliques d’or ou d’argent dans une des deux branches du canal et une solution de pyridine ou de péfloxacine dans l’autre branche. La laminarité et la stationnarité du processus nous ont permis de cartographier la zone de mélange et de mettre en évidence l’exaltation du signal de diffusion Raman de la pyridine et de la péfloxacine, obtenue grâce aux nanoparticules métalliques, dans cette zone d’interdiffusion. L’enregistrement successif de la bande d’absorption des nanoparticules d’argent (bande plasmon) et du signal de diffusion Raman de la péfloxacine, en écoulement dans un microcanal, nous a permis d’établir un lien entre la morphologie des nanostructures métalliques, et plus précisément l’état d’agrégation des nanoparticules d’argent, et l’exaltation du signal Raman de la péfloxacine observé. Nous avons alors modifié la géométrie du canal afin d’y introduire une solution d’électrolyte (NaCl et NaNO3) et de modifier localement la charge de surface des colloïdes d’argent en écoulement. Nous avons ainsi confirmé que la modification de l’état d’agrégation des nanoparticules d’argent, induite par l’ajout contrôlé de solutions d’électrolytes, permet d’amplifier le signal SERS de la péfloxacine et d’optimiser la détection en microfluidique. Enfin, nous avons développé une seconde approche qui consistait à mettre en place une structuration métallisée des parois d’un microcanal. Nous avons ainsi démontré que la fonctionnalisation chimique de surface via un organosilane (APTES) permettait de tapisser le canal avec des nanoparticules d’argent et d’amplifier le signal Raman des espèces en écoulement dans ce même microcanal. / This thesis focuses on the development of a microfluidic platform coupled with confocal Raman microscopy, used in excitation conditions of Raman scattering (Surface enhanced Raman scattering, SERS) in order to gain in the detection sensitivity of molecular species flowing in channels of micrometer dimensions. This work aims to demonstrate the feasibility of coupling Raman microscopy / microfluidics for the in situ and local characterization of species and reactions taking place in the fluid flowing in microchannels. We used a T-shaped microchannel, made by soft lithography, in which gold or silver nanoparticles injected at constant speed, in one of the two branches of the channel and a solution of pyridine or pefloxacin in the other one. The laminar flow and the stationarity of the process allowed us to map the mixing zone and highlight the enhancement of the Raman signal of pyridine and pefloxacin, due to the metallic nanoparticles, in the interdiffusion zone. The recording of the both absorption band of the silver nanoparticles (plasmon band) and the Raman signal of pefloxacin, flowing in microchannel, allowed us to establish a link between the shape of the metallic nanostructure, and more precisely the silver nanoparticle aggregation state, and the enhancement of the Raman signal of pefloxacin observed. We then changed the channel geometry to introduce an electrolyte solution (NaCl and NaNO3) and locally modify the surface charge of the colloids. We have put in evidence that the change of the silver nanoparticle aggregation state, induced by the controlled addition of electrolyte solutions, could amplify the SERS signal of pefloxacin and thus optimizing the detection in microfluidics. At last, we established second a approach that consists in the metallic structuring of microchannel walls. This has shown that the surface chemical functionalization through organosilanes (APTES) allowed the pasting of the channel with silver nanoparticles, thus amplifying the Raman signal of the species flowing within the same microchannel.

Diese Arbeit befasst sich mit der theoretischen Beschreibung nichtlinearer optischer Phänomene in Hinblick auf das (numerische) unstetige Galerkin-Zeitraumverfahren. Insbesondere werden zwei Materialmodelle behandelt: das hydrodynamische Modell für Metalle und das Modell für Raman-aktive Materialien. Im ersten Teil der Arbeit wird das hydordynamische Modell für Metalle unter Verwendung eines störungstheoretischen Ansatzes behandelt. Insbesondere wird dieser Ansatz genutzt, um die nichtlinearen optischen Effekte, Erzeugung zweiter Harmonischer und Summenfrequenzerzeugung, mit Hilfe des unstetigen Galerkin-Verfahrens zu studieren. In diesem Zusammenhang wird demonstriert, wie das optische Signal zweiter Ordnung von Nanoantennen optimiert werden kann. Hierzu wird ein hier erarbeitetes Schema für die Abstimmung des eingestrahten Lichtes angewandt. Zudem führt eine intelligente Wahl des Antennendesigns zu einem optimierten Signal. Im zweiten Teil dieser Arbeit wird das Modell für Raman-aktive Dielektrika behandelt. Genauer wird die nichtlineare Antwort dritter Ordnung für stimulierte Raman-Streuung hergeleitet. Diese wird dazu genutzt, um ein System aus Hilfsdifferentialgleichungen für das unstetige Galerkin-Verfahren zu konstruieren. Die Ergebnisse des erweiterten numerischen Verfahrens werden im Anschluss gezeigt und diskutiert. / This thesis is concerned with the theoretical description of nonlinear optical phenomena with regards to the (numerical) discontinuous Galerkin time-domain (DGTD) method. It deals with two different material models: the hydrodynamic model for metals and the model for Raman-active dielectrics. In the first part, we review the hydrodynamic model for metals, where we apply a perturbative approach to the model. We use this approach to calculate the second-order nonlinear optical effects of second-harmonic generation and sum-frequency generation using the DGTD method. In this context, we will see how to optimize the second-order response of plasmonic nanoantennas by applying a deliberate tuning scheme for the optical excitations as well as by choosing an intelligent nanoantenna design. In the second part, we examine the material model for Raman-active dielectrics. In particular, we see how to derive the third-order nonlinear response by which one can describe the process of stimulated Raman scattering. We show how to incorporate this third-order response into the DGTD scheme yielding a novel set of auxiliary differential equations. Finally, we demonstrate the workings of the modified numerical scheme.