In dieser Arbeit werden die nichtlokalen sowie nichtlinearen Eigenschaften plasmonischer Nanopartikel behandelt, wie sie im hydrodynamischen Modell enthalten sind. Das hydrodynamische Materialmodell stellt eine Erweiterung des Drude Modells dar, in der Korrekturen in der Beschreibung des Elektronenplasmas berücksichtigt werden. Einer ausführlichen Einführung des Materialmodells folgt eine analytische Diskussion der Auswirkungen der Nichtlokalität am Beispiel eines einzelnen Zylinders. Hierbei werden die durch die Nichtlokalität herbeigeführten Frequenzverschiebungen in den Streu- und Absorptionsspektren quantifiziert und asymptotisch behandelt. Des Weiteren wird mit Hilfe einer konformen Abbildung das Problem eines zylindrischen Dimers in der Elektrostatischen Näherung gelöst und die Moden der Struktur bestimmt. Diese Untersuchungen dienen als maßgebliche Grundlage für weiterführende numerische Studien die mit der diskontinuierlichen Galerkin Zeitraummethode durchgeführt werden. Die durch die analytischen Betrachtungen gewonnene Kenntnis der Moden ermöglicht es, im Zusammenhang mit gruppentheoretischen Betrachtungen und numerischen Untersuchungen, rigorose Auswahlregeln für die Anregung der Moden durch lineare und nichtlineare Prozesse aufzustellen. In weiterführenden numerischen Simulationen werden außerdem Strukturen niedrigerer Symmetrie, auf die sich die Auswahlregeln übertragen lassen, untersucht. Zudem werden numerische Studien präsentiert in denen der Einfluss der Nichtlokalität auf Feldüberhöhungen in Dimeren und doppel-resonantes Verhalten (es liegt sowohl bei der Frequenz des eingestrahlten Lichtes als auch bei der zweiten harmonischen eine Resonanz vor) untersucht werden. / This thesis deals with the nonlocal and nonlinear properties of plasmonic nanoparticles, as described by the hydrodynamic model. The hydrodynamic material model represents an extension of the Drude model that contains corrections to the descriptions of the electron plasma. After a thorough derivation of the material model, analytical discussions of nonlocality are presented for the example of a single cylinder. The frequency shifts in the scattering and absorption spectra are quantified and treated asymptotically. Furthermore, by applying a conformal map, the problem of a cylindrical dimer is solved in the electrostatic limit and the modes of the structure are determined. These investigations lay the foundations for numerical investigations which are performed employing the discontinuous Galerkin time domain method. The analytical knowledge of the modes, in conjunction with group theoretical considerations and numerical analysis, enables the formulation of rigorous selection rules for the excitation of modes by linear and nonlinear processes. In further numerical studies, the influence of nonlocality on the field enhancement in dimer structures and double-resonant behavior (a resonance is found at the frequency of the incoming light and at the second harmonic) are investigated.

Une technique couramment employée pour développer les sources de paires de photons corrélés indispensables au domaine des télécommunications quantiques repose sur le processus non linéaire de mélange à quatre ondes, qui peut avoir lieu directement dans le cœur d’une fibre optique. Cette architecture fibrée permet de s’adapter au mieux aux besoins des réseaux de communications quantiques (en particulier en minimisant les pertes par couplage lors de la connexion de la source aux autres composants du réseau). L’utilisation d’une fibre microstructurée plutôt que d’une fibre de silice conventionnelle permet d’ajuster les propriétés de dispersion de la fibre et d’optimiser l’efficacité du processus non linéaire. Cependant, les sources fibrées usuelles, à cœur de silice, présentent une limitation majeure : leur pureté quantique est fortement dégradée par la diffusion Raman spontanée, qui survient elle aussi dans le cœur en silice de la fibre. Pour s’affranchir de ce problème, notre idée est de remplacer le cœur en silice par un cœur liquide, en utilisant une fibre microstructurée à cœur creux rempli d’un liquide non linéaire. Nos recherches nous ont ainsi conduits à faire la première démonstration expérimentale de génération de paires de photons corrélés dans une fibre à cœur liquide, et à montrer que, grâce aux propriétés Raman particulières des liquides (dont le spectre Raman se présente en général sous la forme de raies très fines), il était possible de réduire de plusieurs ordres de grandeur le niveau de diffusion Raman spontanée dans la source. Ce travail ouvre donc la voie au développement de sources de paires de photons corrélés fibrées de très haute qualité quantique. / Quantum telecommunication technologies rely on correlated photon pair sources, which are often based on the third-order nonlinear process of spontaneous four-wave mixing in silica-core photonic crystal fibres. A fibred architecture is advantageous because it minimizes the coupling losses between the optical source and the other components of quantum communication networks. Moreover, using a photonic crystal fibre rather than a conventional silica fibre offers the possibility of improving the photon generation (thanks to a small effective core area) and extending the wavelength coverage (thanks to dispersion management through the microstructuration design). However, the performances of silica-core photonic crystal fibre sources are limited in terms of quantum purity, because of the ubiquitous spontaneous Raman scattering process, which is a source of uncorrelated broadband noise photons in silica. We propose an original solution to this Raman problem by replacing the silica core by a liquid core, thanks to a hollow-core photonic crystal fibre filled with a nonlinear liquid. We actually performed the first experimental demonstration of the generation of correlated photon pairs in a liquid-core fibre, and demonstrated that, thanks to the specific Raman properties of liquids (which usually exhibit thin-line Raman spectra), it is possible to reduce the Raman noise level by several orders of magnitude. This work opens the way for the development of high quantum quality correlated photon pair fibred sources.

The Phase Change Memories (PCM) based on chalcogenide glasses are being considered recently as a possible replacement for conventional Non Volatile Random Access Memories (NVRAM). The main advantages of chalcogenide phase change memories are their direct write/overwrite capability, lower voltages of operation, large write/erase cycles, easiness to integrate with logic, etc. The phase change random access memories work on the principle of memory switching exhibited by chalcogenide glasses during which a local structural change (between amorphous and crystalline states) occurs due to an applied electric field. The development of newer phase change materials for NVRAM applications is based on synthesizing newer glass compositions and investigating their electrical switching characteristics by applying current/voltage pulses of different waveforms. The thermal studies on chalcogenide glasses which provide information about thermal stability, glass forming ability, etc., are also important while selecting a chalcogenide glass for PCM applications. The present thesis work deals with electrical switching and thermal studies on certain silicon based ternary telluride glasses (As-Te-Si, Ge-Te-Si and Al-Te-Si). The effect of network topological thresholds on the composition dependence of switching voltages and thermal parameters such as glass transition temperature, specific heat capacity, non-reversing enthalpy, etc., of these glasses has been investigated. The first chapter of the thesis provides an introduction to various properties of chalcogenide glasses, including their applications in phase change memories. The fundamental aspects of amorphous solids such as glass formation, glass transition, etc., are presented. Further, the concepts of rigidity percolation and self organization in glassy networks and the influence of local structural effects on the properties of glassy chalcogenides are discussed. Also, a brief history of evolution of phase change memories is presented. The second chapter deals with the experimental techniques employed in this thesis work; for sample preparation and for electrical switching studies, Alternating Differential Scanning Calorimetry (ADSC), Raman spectroscopy, NMR spectroscopy, etc. The third chapter discusses the electrical switching and thermal studies on As30Te70-xSix (2 ≤ x ≤ 22) and As40Te60-xSix (2 ≤ x ≤ 17) glasses. The composition dependence of electrical switching voltage (VT) and thermal parameters such as glass transition temperature (Tg), crystallization temperature (Tc), thermal stability (Tc-Tg), etc., reveals the occurrence of extended rigidity percolation and chemical thresholds in As30Te70-xSix and As40Te60-xSix glasses. Chapter 4 presents the electrical switching and thermal studies on Ge15Te85-xSix glasses (2 ≤ x ≤ 12). These glasses have been found to exhibit memory type electrical switching. While Ge15Te85-xSix glasses with x ≤ 5 exhibit a normal electrical switching, an unstable behavior is seen in the I-V characteristics of Ge15Te85-xSix glasses with x > 5 during the transition to ON state. Further, the switching voltage (VT) and initial resistance (R) are found to increase with addition of Si, exhibiting a change in slope at the rigidity percolation threshold of the Ge15Te85-xSix system. The ADSC studies on these glasses indicate the presence of an extended stiffness transition and a thermally reversing window in Ge15Te85-xSix in the composition range of 2 ≤ x ≤ 6. The fifth chapter deals with electrical switching investigations, thermal and structural studies on Al15Te85-xSix glasses (2 ≤ x ≤ 12). These glasses have been found to exhibit two crystallization reactions (Tc1 and Tc2) for compositions with x < 8 and a single stage crystallization is seen for compositions above x = 8. Also, a trough is seen in the composition dependence of non-reversing enthalpy (ΔHNR), based on which it is proposed that there is a thermally reversing window in Al15Te85-xSix glasses in the composition range 4 ≤ x ≤ 8. Further, Al15Te85-xSix glasses are found to exhibit a threshold type electrical switching at ON state currents less than 2 mA. The start and the end of the thermally reversing window seen in the thermal studies are exemplified by a kink and saturation in the composition dependence of switching voltages respectively. 27Al Solid State NMR measurements reveal that in Al15Te85-xSix glasses, Al atoms reside in 4-fold as well as 6-fold coordinated environments. Unlike in Al-As-Te glasses, there is no correlation seen between the composition dependence of the fraction of 4-fold and 6-fold coordinated aluminum atoms and the switching behavior of Al-Te-Si samples. Chapter 6 provides a comparison of the properties of the three glassy systems studied (As-Te-Si, Ge-Te-Si and Al-Te-Si), made to identify the system better suited for phase change memory applications. It is found that the Ge-Te-Si glassy system has better electrical/thermal properties for phase change memory applications. The seventh chapter describes easily reversible SET-RESET processes in Ge15Te83Si2 glass which is a promising candidate for phase change memory applications. This sample exhibits memory switching at a comparatively low threshold electric field (Eth) of 7.3 kV/cm. The SET and RESET processes have been achieved with 1 mA triangular current pulse for the SET process and 1 mA rectangle pulse (of 10 msec width) for RESET operation respectively. Further, a self-resetting effect is seen in this material upon excitation with a saw-tooth/square pulse. About 6.5x104 SET-RESET cycles have been achieved without any damage to the device. In chapter 8, results of in-situ Raman scattering studies on the structural changes occurring during the SET and RESET processes in Ge15Te83Si2 sample, are presented. It is found that the degree of disorder in the glass is reduced from OFF to SET state. The local structure of the sample under RESET condition is similar to that in the OFF state. The Raman results are found to be consistent with the switching results which indicate that the Ge15Te83Si2 glass can be SET and RESET easily. Further, Electron Microscopic studies on switched samples indicate the formation of nanometer sized particles of cSiTe2. A summary of the results obtained and the scope for future work are included in the chapter 9 of the thesis.

No description available.

Depuis leur avènement, les fibres à cristal photonique à cœur creux ont prouvé leur capacité à convertir des fréquences avec une haute efficacité, notamment en jouant sur le phénomène de diffusion Raman stimulée. Dans le cadre d’un contrat CIFRE entre la société GLOphotonics et l’institut de recherche Xlim, ce projet de thèse a consisté à développer ces fibres afin d’améliorer leurs performances optiques pour cibler deux voies d’applications: une industrielle pour proposer un laser compact multi-ligne dans le visible et dans l’UV et une seconde plus fondamentale pour réaliser un synthétiseur d’onde optique. L’amélioration de ces performances repose sur l’exacerbation de l’inhibition du couplage entre le mode du coeur d’air et les modes de silice de la gaine. Pour cela deux types de micro-structures ont été explorées à savoir une maille Kagomé et une maille tubulaire. Plusieurs fibres ont été alors fabriquées démontrant des performances records sur toute une gamme de longueurs d’onde (8,5 dB/km à 1 µm, 7,7 dB/km à 750 nm, 13,8 dB/ km à 549 nm, et autour de 70 dB/km à 355 nm). Concernant la fonctionnalisation de ces fibres, des micro-capsules photoniques ont été conçues et réalisées permettant à la fois de palier au problème de la perméabilité de la silice au gaz (stabilité de la conversion dépassant 12 mois) et de démontrer une conversion de 26 lignes dans le visible. Un produit industriel nommé CombLas a alors été produit puis appliqué à une étude de cytométrie en flux pour étudier l’influence du taux de répétition du laser de pompe. Ce produit a également été étendu à la gamme spectrale de l’UV avec la génération de 24 lignes entre 225-400 nm. Enfin, des travaux plus fondamentaux ont été réalisés consistant à développer un synthétiseur d’onde optique à base de génération Raman dans ces fibres creuses. Une nouvelle dynamique a été observée démontrant le piégeage de molécules d’hydrogène par un réseau optique auto-assemblé de puits de potentiel ultra-profonds et nanométriques. Cela permis de générer un régime Lamb-Dicke de la diffusion Raman stimulée. Des signatures sub-Doppler usuellement vues dans les atomes froids ont été mesurées avec des largeurs de bandes plus étroites de plus de 5 ordres de grandeurs par rapport à ce qui est prédit dans la littérature. Finalement, cette largeur de bande a été optimisée d’un ordre de grandeur en jouant sur la longueur de la fibre et la pression de l’hydrogène. / Since their advent, hollow-core photonic crystal fibers have proved to be highly efficient for frequency conversion, especially via by playing with stimulated Raman scattering. Within the frame work of a CIFRE contract between the firm GLOphotonics and the Xlim research institute, this thesis project has consisted in developing these fibers to enhance their optical performances, in order to target two different field of applications: an industrial one to offer a a compact multi-line laser in the visible and UV and a second more fundamental one to realize a optical wave synthesizer. The amelioration of these performances relies on the exacerbation of the inhibition of the coupling between the air core mode and the silica cladding modes. Two types of micro-structures have been explored, a Kagomé and a tubular lattice. Several fibers have been fabricated demonstrating record performances on all a wavelength range (8.5 dB/km at 1 µm, 7.7 dB/km at 750 nm, 13.8 dB/km at 549 nm, and around 70 dB/km at 355 nm). Concerning the functionalization of the fibers, photonic micro-cells have been designed and realized enabling to overcome the problem the permeability of silica to gas (conversion stability over 12 months) and demonstrate a conversion to 26 lines in the visible. An industrial product coined CombLas has been made and used for flow cytometry in order to study the influence of the repetition rate of the pump laser. This product has also been extended to the UV range with 24 lines generated between 225-400 nm. Also, more fundamental research has been realized consisting in developing an optical wave synthesizer based on Raman generation in hollow core fibres where a new dynamic has been observed demonstrating the trapping of hydrogen molecules by an auto-assembled optical lattice of ultra-deep and nano-metric potential wells. This configuration has enabled to generate a Lamb-Dicke regime of stimulated Raman scattering. Sub-Doppler signatures usually found in cold atoms have been measured with linewidths narrower than 5 orders of magnitude than what is predicted in the literature. Finally, this linewidth has been optmised of an order of magnitude by plaing on the length of the fiber and the pressure of hydrogen.

The subject of this thesis is the design and development of a unified set up for femtosecond transient absorption and ultrafast Raman loss spectroscopy and demonstrate its potential in capturing the ultrafast photophysical and photochemical processes with excellent time and frequency resolution. Ultrafast spectroscopy has been serving as a powerful tool for understanding the structural dynamical properties of molecules in the condensed and gas phase. The advent of ultrashort pulses with their high peak power enables the laser spectroscopic community to study molecular reaction dynamics and photophysics that happen at extremely short timescales, ranging from picosecond to femtosecond. These processes can be measured with extremely high time resolution, which helps to resolve the under-lying molecular process. But in order to understand the global mechanism of the underlying molecular processes, we have to resolve the nuclear dynamics with the proper frequency resolution. However, achieving both, time and frequency resolutions simultaneously is not possible according to the Heisenberg uncertainty principle. Later, this limitation was overcome by femtosecond stimulated Raman spectroscopy (FSRS), a third order non-linear Raman spectroscopy. In this thesis we introduced the ultrafast Raman loss spectroscopic (URLS) technique which is analogous to FSRS, offering the modern ultrafast community to resolve molecular processes with better signal-to-noise ratio along with proper time and frequency resolution. We demonstrate the experimental procedure including the single shot detection scheme to measure whitelight background, ground state Ra-man, transient absorption and transient Raman in shot-to-shot detection fashion. URLS has been applied to understand the excited state planarization dynamics of 1,4-bis(phenylethynyl)benzene (BPEB) in different solvents. In addition, excitation wavelength dependent conformational reorganization dynamics of different sub-sets of thermally activated ground state population of BPEB are also discussed. Using the same techniques along with femtosecond transient absorption, we demonstrate the ultrafast vibrational energy transfer and the role of coherent oscillations of low frequency vibrations on the solution phase photo-isomerization of trans-stilbene from an optically excited state. The effects of solvents on the coherent nuclear motion are also discussed in the context of reaction rates. 2

Fundação de Amparo a Pesquisa do Estado de Minas Gerais / In this work, Zn1-xAxTe (A = Mn, Co) diluted magnetic semiconductors (DMS) nanocrystal (NCs) were successfully grown in the P2O5 ZnO Al2O3 BaO PbO glass system synthesized by the method of Fusion-Nucleation, after subjecting to appropriate thermal annealing. Various experimental techniques were used in this study in order to get a comprehensive understanding of the optical, morphological, structural and magnetic properties these NCs. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) images revealed the size of both of Zn1-xMnxTe and Zn1-xCoxTe NCs. From the vibrating sample magnetometer (VSM) technique, there was growth behavior of magnetization and magnetic susceptibility as a function of the Mn concentration in the samples containing Zn1-xMnxTe NCs. At lower Mn concentrations, the sp electrons of ZnTe host semiconductor interact with the d electrons of Mn2+ ions, resulting in the sp-d exchange interaction, which causes a small increase in susceptibility. At higher Mn concentrations, the d-d exchange interaction between Mn atoms dominates over the sp-d exchange interaction, resulting in an abrupt increase in susceptibility. The EPR spectra, in addition to prove the results exhibited the well-known sextet hyperfine lines of Mn2+ ions, since samples with low Mn concentrations revealed the presence of Mn2+ ions within and near the surface of the ZnTe NCs. From the optical absorption spectra (OA) and photoluminescence (PL), analyzed on the basis of crystal field theory (CFT) as well as of the diffraction X-ray (XRD), Raman scattering (RS) and electron microscopy transmission (TEM) techniques, the substitutional incorporation of Mn2+ ions was confirmed up to its solubility limit (x = 0.100) ZnTe NCs. Above this concentration, can observe the formation of manganese oxide NCs such as MnO and MnO2, since the nucleation rate for the formation of these NCs is greater than that of Zn1-xMnxTe NCs, at high concentrations. Furthermore, from the PL spectra, it was found that it is possible to tune the emission of energy related to transition 4T1(4G) &#8594; 6A1(6S) of Mn2+ ions, of the spectral orange region to the near infrared, depending on Mn concentration. This is possible due to the variation of the local crystal field, where these ions are inserted. From the OA spectra, analyzed on the basis of CFT, it showed that Co2+ ions are substitutionally incorporated in tetrahedral sites of ZnTe NCs, due to its characteristics transitions in visible and near infrared spectral region. This evidence has been enhanced from MFM images, since NCs doped with magnetic ions, magnetically respond when induced by the magnetization of the probe. / Neste trabalho, nanocristais semicondutores magnéticos diluídos (SMD) de Zn1-xAxTe (A = Mn; Co) foram crescidos com sucesso no sistema vítreo P2O5 ZnO Al2O3 BaO PbO, sintetizado pelo método de Fusão-Nucleação, após submetê-lo a tratamento térmico apropriado. Várias técnicas experimentais foram utilizadas neste estudo a fim de obter um entendimento compreensivo das propriedades ópticas, morfológicas, estruturais e magnéticas desses NCs. Imagens de microscopia eletrônica de transmissão (MET) e microscopia de força atômica (MFA) revelaram o tamanho tanto de NCs de Zn1-xMnxTe quanto de Zn1-xCoxTe. A partir da técnica de magnetometria de amostra vibrante (MAV), verificou-se o crescimento da magnetização e o comportamento da susceptibilidade magnética, em função da concentração de Mn, em amostras contendo NCs de Zn1-xMnxTe. Em baixas concentrações de Mn, os elétrons sp do semicondutor hospedeiro ZnTe, interagem com os elétrons d dos íons Mn2+, resultando na interação de troca sp-d, que provoca um pequeno aumento na susceptibilidade magnética. Já, em concentrações mais elevadas de Mn, a interação de troca d-d entre átomos de Mn domina a interação de troca sp-d, o que resulta em um aumento abrupto da susceptibilidade. Os espectros RPE, além de comprovar esses resultados, exibiram o bem conhecido sexteto de linhas hiperfinas de íons Mn2+, uma vez que amostras com baixas concentrações de Mn revelaram a presença de íons Mn2+ no interior e próximos à superfície dos NCs de ZnTe. A partir dos espectros de absorção óptica (AO) e fotoluminescência (FL), analisados com base na teoria do campo cristalino (TCC), bem como das técnicas de difração de raios-X (DRX), espalhamento Raman (ER) e microscopia eletrônica de transmissão (MET), confirmou-se a incorporação substitucional de íons Mn2+ até seu limite de solubilidade nominal (x = 0,100) em NCs de ZnTe. Acima dessa concentração, observa-se a formação de NCs de óxido de manganês, tais como MnO e MnO2, uma vez que a taxa de nucleação para a formação desses NCs é maior que a de NCs de Zn1-xMnxTe, em altas concentrações. Além disso, a partir dos espectros FL, verificou-se que é possível sintonizar a energia de emissão relacionada à transição 4T1(4G) &#8594; 6A1(6S) de íons Mn2+, da região espectral laranja ao infravermelho próximo, em função da concentração de Mn. Isso é possível devido à variação do campo cristalino local, onde esses íons estão inseridos. A partir dos espectros AO, analisados com base na TCC, evidenciou-se que íons Co2+ são incorporados substitucionalmente em sítios tetraédricos de NCs de ZnTe, devido às suas transições características na região espectral do visível e infravermelho próximo. Essa evidência foi reforçada a partir de imagens de MFM, uma vez que os NCs, dopados com íons magnéticos, respondem magneticamente quando induzidos pela magnetização da sonda. / Doutor em Física

The primary purpose of this study was to investigate the combination of experimental and computational methods in the search for reproducible colloidal surface-enhanced Raman scattering of pharmaceutical compounds. In the search for optimal experimental conditions for colloidal surface-enhance Raman scattering, the amphipathic β-blocker propranolol was used as the target molecule. Fractional factorial designs of experiments were performed and a multiobjective evolutionary algorithm was used to find acceptable solutions, from the results, that were Pareto ranked. The multiobjective evolutionary algorithm suggested solutions outside of the fractional factorial design and the experiments were then performed in the laboratory. The results observed from the suggested solutions agreed with the solutions that were found on the Pareto front. One of the experimental conditions observed on the Pareto front was then used to determine the practical limit of detection of propranolol. The experimental conditions that were chosen for the limit of detection took into account reproducibility and enhancement, the two most important parameters for analytical detection using surface-enhanced Raman scattering. The principal conclusion to this study was that the combination of computational and experimental methods can reduce the need for experiments by > 96% and then selecting solutions from the Pareto front improved limit of detection by a factor of 24.5 when it was compared to the previously reported limit of detection for propranolol. Using the same experimental conditions that were used for the limit of detection, these experiments were extended to plasma spiked with propranolol in order to test detection of this pharmaceutical in biofluids. Concentrations of propranolol were prepared using plasma as the solvent and measured for detection using colloidal surface-enhanced Raman scattering. Detection was determined as <130 ng/mL, within physiological concentrations, previously achieved using separation techniques. The second part of this thesis also involved a combination of experimental and computational methods. Raman optical activity was utilized to investigate secondary structure of amino acids and diamino acid peptides in combination with density functional theory calculations. Amino acids are important biological molecules that have vital functions in the biological system. They have been recognized as neurotransmitters and implicated in neurodegenerative diseases. Raman and Raman optical activity experimental results were compared to determine site-specific acetylation, marker bands for constitutional isomers and identification of functional groups that interact with the solvent. The experimental spectra were then compared to those from the density functional theory calculations. The results indicated that; constitutional isomers cannot be distinguished from the Raman spectra but can be distinguished from the Raman optical activity spectra, site-specific acetylation can be identified from the Raman spectra, however, Raman optical activity provides more structural information in relation to acetylation. When the results were compared to the density functional theory calculations for the diamino acid peptides the results agreed reasonably well, however, agreement was not as good for the monoamino acids because diamino acid peptides support fewer conformations due to the peptide bond whereas monoamino acids can adopt a far greater number of conformations. Combined computational and experimental techniques have developed the ability to detect and characterize biomedical compounds, a significant move in the advancement of Raman spectroscopies.

The vibrational wave-packet dynamics of diatomic rubidium molecules (Rb2) in triplet states formed on the surface of superfluid helium nanodroplets is investigated both experimentally and theoretically. Detailed comparison of experimental femtosecond pump–probe spectra with dissipative quantum dynamics simulations reveals that vibrational relaxation is the main source of dephasing. The rate constant for vibrational relaxation in the first excited triplet state 13Σ+g is found to be constant γ ≈ 0.5 ns−1 for the lowest vibrational levels v [less, similar] 15 and to increase sharply when exciting to higher energies. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

<p>Ultrafast laser-based diagnostic techniques are powerful tools for the detailed understanding of highly dynamic combustion chemistry and physics. The ultrashort pulses provide unprecedented temporal resolution along with high peak power for broad spectral range−ideal for nonlinear signal generation at high repetition rate−with applications including next-generation combustors for gas turbines, plasma-assisted combustion, hypersonic flows and rotating detonation engines. The current work focuses on advancing (i) femtosecond (fs) two-photon laser-induced fluorescence, and (ii) hybrid femtosecond/picosecond vibrational and rotational coherent anti-Stokes Raman scattering (fs/ps RCARS and VCARS) to higher pressures for the first time. </p><p>Quantitative single-laser-shot kHz-rate concentration measurements of key atomic (O-atom) and molecular (CO) species is presented using femtosecond two-photon laser-induced fluorescence (TP-LIF) for a range of equivalence ratios and pressures in diffusion flames. A multitude of signal-interfering sources and loss mechanisms−relevant to high-pressure fs TP-LIF applications−are also quantified up to 20 atm to ensure high accuracy. The pressure scaling of interferences take into account degradation, attenuation and wave-front distortion of the excitation laser pulse; collisional quenching and pressure dependent transition line-broadening and shifting; photolytic interferences; multi-photon ionization; stimulated emission; and radiation trapping. </p><p>Hybrid fs/ps VCARS of N₂ is reported for interference-free temperature measurement at 1300-2300 K in high-pressure, laminar diffusion flames up to 10 atm. A time asymmetric probe pulse allowed for detection of spectrally resolved CARS signals at probe delays as early as ~200-300 fs while being independent of collisions for the full range of pressures and temperatures. Limits of collisional independence, accuracy and precision of the measurement is explored at various probe-pulse delays, pressures and temperatures. </p><p> </p><p>Additionally, a novel all diode-pumped Nd:YAG amplifier design is presented for generation of time-synchronized ps-probe pulses for hybrid fs/ps RCARS of N₂. High-energy, nearly transform-limited, single-mode, chirp-free ps probe-pulses are generated at variable pulsewidths. The detailed architecture and characterization of the laser is presented. kHz-rate RCARS thermometry is presented up to 2400 K. Excellent spatial, spectral, and temporal beam quality allowed for fitting the theoretical spectra with a simple Gaussian model for the probe pulse with temperature accuracies of 1-2%. </p> <p><br></p>