Les processus physico-chimiques se produisant au sein des nanoparticules que sont les boîtes quantiques semiconductrices (QDs) sont à l'origine d'une nouvelle classe de sondes fluorescentes trouvant des applications en catalyse, en reconnaissance moléculaire et en imagerie. Le confinement quantique des électrons aux sein de ces objets luminescents, qui donne lieu à leur structure excitonique si particulière, permet de tirer simultanément profit de leurs propriétés optiques d'absorption et d'émission dans la gamme spectrale visible, et ce, dans le but de faciliter la détection et l’identification des espèces chimiques situées dans leur environnement proche. Dans ce contexte, nous nous sommes intéressés à des QDs de 3 à 4 nm de diamètre, composées d’un alliage ternaire de cadmium, de tellure et de soufre, et fonctionnalisées par des ligands mercaptocarboxyliques. De manière à déterminer l’ensemble de leurs propriétés structurales, chimiques et optoélectroniques, nous les avons tout d’abord caractérisées à l’état de solutions colloïdales par diverses techniques expérimentales : microscopie électronique, zêta-métrie, analyse par diffusion dynamique de la lumière, spectroscopies de rayons X, d’absorption UV-visible et d’émission de fluorescence. Ceci nous a permis de déduire la composition chimique des nanocristaux, leur structure cristalline, leur taille, leur dispersion en taille, la composition chimique de leurs ligands, les énergies propres de leurs états électroniques, leur moments dipolaires de transition et leur section efficace d’absorption. Fort de ces connaissances, nous avons pu développer un modèle analytique pour calculer la susceptibilité diélectrique des QDs et extraire de cette manière leur fonction de réponse linéaire, véritable carte d’identité optoélectronique. Nous avons ensuite optimisé la conception par voie chimique d’interfaces composées de QDs et de différentes espèces moléculaires organiques, dépôts réalisés sous forme de monocouches ou de films épais sur des substrats solides plans de silicium, de verre et de fluorure de calcium fonctionnalisés par des organosilanes. Ces interfaces substrat/QDs/molécules ont alors été étudiées par spectroscopie linéaire d’absorption UV-visible et par spectroscopie optique non-linéaire de génération de fréquence-somme (SFG). La première nous a permis de déterminer la densité superficielle des QDs déposés et d’en caractériser la stabilité temporelle, et la seconde, qui combine deux lasers visible et infrarouge, d’identifier la signature vibrationnelle des ligands recouvrant les QDs. Grâce à ces échantillons, nous avons alors montré par spectroscopie SFG deux couleurs l’existence d’un couplage vibroélectronique entre les QDs et leur environnement moléculaire. En particulier, nous avons démontré que l’amplitude de vibration des modes moléculaires associés aux ligands des QDs et aux organosilanes greffés sur les substrats est maximale lorsque les QDs sont eux-mêmes stimulés par la lumière visible dans leur premier état excitonique. Cette démonstration expérimentale s’accompagne par ailleurs d’une démonstration théorique : en utilisant les diagrammes de Feynman dans l’espace des fréquences imaginaires de Matsubara, nous avons déterminé l’expression analytique de la susceptibilité non-linéaire d’ordre 2 du complexe QD/molécule. Nous avons alors vérifié que l’hypothèse d’un couplage dipolaire entre QDs et molécules menait à une modélisation de la réponse vibrationnelle SFG compatible avec les mesures expérimentales. De cette manière, l’existence d’un couplage vibroélectronique de nature dipolaire entre boîtes quantiques et molécules est attesté. / The different physico-chemical processes occurring within semiconductor quantum dots (QDs) give rise to a new class of fluorescent probes and a wide range of applications in catalysis, molecular recognition and imaging. Within these luminescent nanoparticles, the quantum confinement of electrons, which leads to their very special excitonic structure, allows us to benefit from both their absorption and emission optical properties, with the specific aim of fostering the detection and the identification of the chemical species located in their direct environment. Within this framework, we were interested in 3 to 4-nm-sized QDs composed of ternary alloys of cadmium, telluride and sulfur, and functionalized by mercaptocarboxylic ligands. In order to determine their structural, chemical and optoelectronic properties, we first characterized them thanks to several experimental techniques: electron microscopy, zeta potentiel measurements, dynamic light scattering analysis, X-ray, UV-visible and fluorescence spectroscopies. This enabled us to deduce the chemical composition of the nanocrystals, their crystal structure, size, size-dispersion, the chemical composition of their ligands, the eigenenergies of their electronic states, their transition dipole moments and absorption cross-sections. Given all those results, we succeeded in deriving an analytical model of the QD dielectric susceptibility and extracting in this way their linear response function. Then, we optimized the chemical synthesis of nanostructured interfaces made of QDs and various molecular species through the use of flat solid substrates of silicon, glass and calcium fluoride functionalized with organosilanes. These substrate/QDs/molecules interfaces were studied by linear UV-visible absorption spectroscopy and by sum-frequency generation non-linear optical spectroscopy (SFG). The former allowed us to determine the surface density of the deposited QDs and to characterize their stability over time, while the later, which combines two visible and infrared lasers, enabled us to identify the vibrational signature of the QD ligands. Thanks to those samples probed by two-colour SFG spectroscopy, we therefore shew the existence of a vibroelectronic coupling between QDs and their molecular surroundings. Especially, we demonstrated that the vibration amplitudes associated to the molecular modes of the QD ligands and the organosilanes grafted on the substrates are maximum when the QDs are excited by visible light into their first excitonic state. This experimental demonstration is further supported by theoretical considerations: Feynman diagrams in Matsubara imaginary-time representation were used to determine the analytical expression of the second-order nonlinear susceptibility of the QD/molecule bipartite system. We thus verified that the hypothesis of a dipolar coupling between QDs and molecules resulted in a modeling of the vibrational SFG response which proved to be in complete agreement with the experimental measurements. Thus, we evidenced the existence of a dipolar vibroelectronic coupling between quantum dots and molecules.

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Continuing advances in laser and photonic technology has seen the development of lasers with increasing power and increasingly short pulsewidths, which have become available over an increasing range of wavelengths. As the availability of laser sources grow, so do their applications. To make better use of this improving technology, understanding and controlling laser propagation in free space is critical, as is understanding the interaction between laser light and matter. The need to better control the light obtained from increasingly advanced laser sources leads to the emergence of beam engineering, the systematic understanding and control of light through refractive media and free space. Beam engineering enables control over the beam shape, energy and spectral composition during propagation, which can be achieved through a variety of means. In this dissertation, several methods of beam engineering are investigated. These methods enable improved control over the shape and propagation of laser light. Laser-matter interaction is also investigated, as it provides both a means to control the propagation of pulsed laser light through the atmosphere, and provides a means to generation remote sources of radiation.

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Diese Arbeit konzentriert sich auf die Anwendbarkeit eines hochmodernen 100 kHz BB-VSFG-Spektrometers, das kürzlich im SALSA Photonics Lab entwickelt wurde, für die Analyse der Grenzflächenstruktur von Alkylketten, des sie umgebenden Wassers und der Phosphatkopfgruppen von Phospholipidschichten. Zunächst wurden Phospholipid-Doppelschichten, die mehrere Komponenten enthalten, bei Laserwiederholraten von 5, 10, 50 und 100 kHz mit konstanter Pulsenergie untersucht. Die BB-VSFG-Spektren legen nahe, dass die Phospholipid-Doppelschichten während der Messungen ohne wärmeinduzierte Veränderungen stabil waren. Darüber hinaus bot die Erhöhung der Laserwiederholungsrate eine praktikable Möglichkeit, Spektren in kurzen Datenerfassungszeiten zu erhalten, ohne dass das Signal-Rausch-Verhältnis beeinträchtigt wurde. Die extrem kurze Aufnahmezeit von 500 ms, die hohe spektrale Auflösung und alle verwendeten Pulsparameter sorgen dafür, dass bei Messungen unter Umgebungsbedingungen keine thermisch bedingten Photoschäden auftreten. Es wurde eine systematische Untersuchung von ein- und zweikomponentigen Phospholipid-Monoschichten in Abhängigkeit von der Oberflächenspannung und dem Mischungsverhältnis für verschiedene Kombinationen an Polarisationen durchgeführt und die Abhängigkeit der Schwingungsspektren untersucht. Die Struktur von Alkylketten und umgebendem Wasser wurde anhand derselben Modellsystemen analysiert. Bislang nicht beobachtete Schwingungsbanden und Spektren von Monolagen mit geringer Oberflächenbedeckung wurden mit einem bisher nicht erreichten Signal-Rausch-Verhältnis gemessen und beschrieben. Die Struktur von Phospholipid-Monolagen mit identischen Kopfgruppen und unterschiedlichen Ketten wurde analysiert und verglichen. Die Spektren bestätigten die Anwesenheit von Wassermolekülen in der Nähe der Phosphat- und Cholingruppen der Phospholipid-Monolagen. / This thesis focuses on the applicability of a state-of-the-art 100 kHz BB-VSFG spectrometer recently developed at the SALSA Photonics Lab and on the analysis of the interfacial structure of alkyl chains, surrounding water, and the phosphate head groups of phospholipid layers. First, multi-component phospholipid bilayers were studied at laser repetition rates of 5, 10, 50, and 100 kHz at constant pulse energy. The spectra suggest that the phospholipid bilayers were stable during the measurements with no heat-induced distortions. Moreover, an increase in the laser repetition rate provided a feasible route to obtain spectra in short data acquisition times without compromising the signal-to-noise ratio. The extremely short acquisition time of 500 ms, the high spectral resolution, and all applied pulse parameters ensured no thermal induced photodamages occur during the measurements. A systematic study of one- and two-component phospholipid monolayers as a function of surface tension and mixture ratio at different polarization combinations was performed and the dependence of the vibrational spectra was explored. The structure of alkyl chains and surrounding water was analyzed using the same model systems. Vibrational modes that were previously unseen and spectra of monolayers at low surface coverage were reported for the first time with an unprecedented signal-to-noise ratio. The structure of phospholipid monolayers containing identical head groups and different chains was analyzed and compared. The order of the phospholipid molecules as a function of the composition of the monolayers was inferred from the spectral data. The influence of the hydration and/or changes in the orientation of the phosphate group was visible from the spectra as well.

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Diode lasers are a convenient and economical source of near-infrared radiation, which may usefully be applied to a host of different sensitive detection methods; this thesis presents novel extensions of these methods, making use of the favourable characteristics of this type of light source. The first part of this thesis details the development of an optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) apparatus, including the development of the optical system, the sample handling, and the electronics for feedback phase control. A preliminary demonstration of the system is reported, presenting the detection of atmospheric water absorptions close to 1596 nm. Optimisation and application of the OF-CEAS spectrometer are then demonstrated, after which the spectrometer is applied to the sensitive detection of carbon dioxide absorptions suitable as a diagnostic aid in identifying Heliobacter pylori infection. A time-normalised α-min value of 5.8 × 10⁻⁹ cm⁻¹s^1/2 was measured for these spectra. Further optimisation of the system leads to an ultimate detection sensitivity of 1.42 × 10⁻⁹ cm⁻¹s^1/2, measured on absorption transitions in acetylene close to 1532 nm. In order further to characterise the performance of the OF-CEAS system, analogous experiments are presented using the OF-CEAS setup and a standard diode-laser cavity-enhanced absorption spectroscopy (CEAS) apparatus. Detection is carried out on the P(6) line of the ν₁ + ν₃ vibrational band of the mixed isotopologue of acetylene, ¹²-C¹³-CH₂. Direct comparison is made between the sensitivities of the two methods, and in light of this the suitability of each technique for detection in different environments is considered. The well-characterised and consistent frequency scale which is inherent to the OF-CEAS technique is then applied to a line shape analysis for the presented absorption spectra. Pressure-broadening coefficients are determined for selected absorptions in the ν₁ + ν₃ band of acetylene. In spite of the low resolution associated with this technique, this accurate frequency scaling allows observation of subtle line shape effects such as Dicke collisional narrowing using the data presented in Chapter 3 for the R(60) line in the 3ν₁ + ν₃ vibrational band of CO₂. These effects are quantified through use of a Galatry fit to each absorption spectrum. The statistical significance associated with the use of such a model, and the physical meaning of the results, are examined and discussed. An alternative strategy for increasing the sensitivity of a diode-laser-based gas monitoring technique lies in moving detection to the mid-infrared region, where the absorption cross-sections are generally larger. With this motivation, difference frequency generation is presented, to produce radiation close to 3.5 µm which is then applied to a series of different enhanced spectroscopy techniques. The optimal sensitivity, of 32 ppb NO2 at 45 Torr total sample pressure, was achieved using wavelength modulation spectroscopy. The different techniques are compared and possible improvements to them are put forward. Finally, proof-of-principle work is presented seeking to combine the enhanced circulating power associated with the optical-feedback-locked techniques and non-linear optical techniques to move detection to a more favourable spectral region. Light close to 429 nm is generated by second harmonic generation in a crystal of potassium niobate, with resonance-enhancement afforded by a feedback V-cavity of the sort employed in OF-CEAS. The potential of such a system for diode-laser-based generation of blue and ultraviolet light is demonstrated and discussed, along with improvements that might be implemented to increase the efficiency of the system.

Monolayers of the cationic surfactant hexadecyltrimethylammonium halide (CTAX, where X = F¯, Cl¯, Br¯, and I¯) have been studied at the air-water and oilwater interfaces. At the air-water interface, the effects of the halide counterion and the addition of counterion were investigated. Sum-frequency spectroscopy (SFS), ellipsometry, and surface tensiometry indicated that the counterion changed the efficiency and effectiveness of the surfactant, both decreasing in the order of Br¯> Cl¯>F¯. The addition of salt in the form of 0.1 M KX was found to reduce the cmc but had little effect on the limiting area per molecule attained at the cmc, which increased from 44 Ų for CTAB to 65 Ų for CTAC and ca. 94 Ų for CTAF. Neither SFS nor ellipsometry provided any firm evidence for specific effects of the halide ions on the structure of the surfactant monolayers. For CTAB monolayers in the absence of excess electrolyte, the effect of area per molecule on the sum-frequency (SF) spectra was studied. Mixed monolayers of CTAB and tetradecane at the air-water interface exhibit a first-order phase transition from a conformationally disordered to a conformationally ordered state as the temperature is lowered. The phase transition occurs ca. 11 °C above the bulk melting point of tetradecane. A new experimental arrangement is described for acquiring SF spectra from surfactants at the oil-water interface. The key features of this approach are the stabilisation of a thin oil film between a sapphire prism and an aqueous phase, and the use of total internal reflection to enhance the total signal and discriminate against signals from other interfaces in the system. With this new methodology, the first SF vibrational spectra of surfactant monolayers at an alkane-water interface were obtained. Surface tensiometry was used to characterise the monolayers further. The structure of CTAB monolayers at the hexadecane-water interface was determined by SFS and compared with monolayers of CTAB at the air-water interface. At low concentrations, CTAB/hexadecane showed the expected features in the C-H stretching region, characteristic of a conformationally disordered monolayer. As the bulk concentration approached the critical micelle concentration, the spectra changed to one characteristic of a more ordered, upright conformation. Ellipsometric measurements supported this conclusion. This qualitative structural change is not observed in analogous monolayers at the air-water interface or CCl₄-water interface, or in surfactant solutions in contact with a hydrophobic solid surface.

Die vorliegende Arbeit widmet sich der Untersuchung von 4 Modellsystemen der Oberflächenforschung. Die verwendeten experimentellen Methoden sind Summenfrequenzerzeugungsspekroskopie (SFG), Thermische Desorptionsspektroskopie (TDS), Beugung niederenergetischer Elektronen (LEED), Augerelektronenspektroskopie (AES), Infrarotadsorptionsspektrokopie (IRAS) und Rastertunnelmikroskopie (STM). Durch die Verwendung von SFG waren Messungen bis zu 50 mbar möglich. Die untersuchten Systeme sind: CO auf Pt(111), Wasser auf Ag(001) und MgO/Ag(001), CO auf Au/MgO/Ag(001) und CO auf Au-Pd/MgO/Ag(001). Bei den Messungen von CO auf Pt(111) tritt unter bestimmten Druck- und Temperaturbedingungen eine bisher nicht näher untersuchte Doppelpeakstruktur auf, die genauer charakterisiert wurde. Die Untersuchungen von Wasser auf MgO/Ag(001) und Ag(001) zeigen, dass sich auf MgO/Ag(001) zuerst eine Monolage Wasser mit einer darauffolgenden Multilage ausbildet, wohingegen es auf Ag(001) von Beginn an in einer Multilagenschicht wächst. Die Monolage kann unter der Multilage gemessen werden und einige Resonanzen identifiziert werden. Für Au/MgO/Ag(001) zeigte sich mittels STM eine Abhängigkeit des Au-Wachstums von der Schichtdicke, die allerdings nicht spektroskopisch in Erscheinung tritt. Bei den Messungen an gemischten Au-Pd-Teilchen auf MgO/Ag(001) zeigen sich Unterschiede im Adsorptionsverhalten zwischen reinen Metallteilchen und gemischten Teilchen, die auf eine Wechselwirkung zwischen den beiden Metallen zurückzuführen ist. Nach Heizschritten auf 600 K reichern sich die Au-Atome im Mantel des Teilchens an, das Pd bildet den Kern. Die Ergebnisse aller Messungen werden unter Berücksichtigung neuer Veröffentlichungen diskutiert. / This thesis focuses on 4 different model systems of surface science. The experimental techniques used for the measurements include sum frequency generation (SFG), thermal desorption spectroscopy (TDS), low energy electron diffraction (LEED), Auger electron spectroscopy (AES), infrared adsorption spectrosocopy (IRAS) and scanning tunneling microscopy (STM). By using SFG, measurements could be performed up to a pressure of 50 mbar. The systems under investigation were: CO on Pt(111), water on Ag(001) and on MgO/Ag(001), CO on Au/MgO/Ag(001), and CO on Au-Pd/MgO/Ag(001). The system of CO on Pt(111) exhibits a two peak-pattern under certain pressure and temperature conditions which has not been studied so far. Various experiments helped to elucidate the origin of this distinct behaviour. The measurements of water on Ag(001) and MgO/Ag(001) show that on MgO, water first adsorbs as a monolayer with a following multilayer, whereas on Ag(001) it adsorbs as a multilayer from the beginning. The monolayer can be studied below the multilayer and some resonances can be identified. For the case of Au/MgO/Ag(001), STM shows that the growth mode of Au depends on the thickness of the supporting MgO film, which can not be seen with spectroscopic methods. For mixed Au-Pd particles on MgO/Ag(001) a clear difference in the adsorption behaviour between pure metal particles and mixed particles can be seen, which is explained by an interaction between these metals. Annealing the mixed particles to 600 K leads to a segregation of the metals, where the Au atoms diffuse to the shell and the Pd atoms make up the core. The results of all these measurements are discussed in the light of recent publications.