Les propriétés optiques des nanoparticules métalliques, caractérisées par l'existence d'une résonance plasmon de surface (SPR) dans le domaine visible, sont aujourd'hui couramment utilisées afin de détecter et de caractériser des espèces chimiques, en solution ou déposées sur des substrats (dans les capteurs par exemple). Dans ce travail, j'ai optimisé la réalisation puis la caractérisation physico-chimique et optique d'interfaces composées de nanoparticules d'or d'environ 15 nm de diamètre sur des substrats de silicium et de verre fonctionnalisés par des silanes, à l'aide de méthodes d'optique linéaire et non linéaire. La spectroscopie UV-visible en réflexion et transmission, couplée aux microscopies électronique et à force atomique, et aidée par la modélisation, m'a permis de corréler les propriétés optiques des particules à leur densité locale sur la surface. La spectroscopie optique non linéaire par génération de fréquence somme (SFG) permet de sonder la chimie de surface des particules et du substrat ainsi que de tirer parti de l'amplification locale des processus optiques par excitation de la SPR. Après avoir montré qu'elle amplifie effectivement des signaux SFG moléculaires peu intenses de la couche de silanes, j'ai révélé la présence dans la couche organique de greffage de groupements méthyles résultant d'une réaction de silanisation incomplète, démontré le lien entre la stabilité temporelle chimique et plasmonique des interfaces et l'irradiation laser, caractérisé finement la qualité de fonctionnalisation des particules par des thiols et montré la relation de proportionnalité entre réponses optiques linéaire et non linéaire en surface. Finalement, j'ai étudié directement le processus d'amplification de la SFG par le couplage à la SPR en réalisant une spectroscopie à deux dimensions infrarouge et visible. J'ai montré que ce couplage est mesurable même sur de petites particules déposées, et qu'il se produit dans la zone spectrale d'existence du plasmon de surface (du vert au rouge). La comparaison avec une surface plane de platine et d'or m'a permis d'extraire de façon fine des facteurs d'amplification, qui correspondent à ce que prédit une modélisation simple de la plasmonique en jeu dans ces interfaces. / Optical properties of metallic nanoparticles, exhibiting a surface plasmon resonance (SPR) in the visible range, are nowadays extensively used to detect and characterize chemical entities, either in solution or deposited on substrates (e.g. sensors). In this work, I have optimized the creation of interfaces composed of 15nm in diameter gold nanoparticles on silicon and glass substrates after functionnalization by silanes, and their chemical and optical characterization by linear and nonlinear optical methods. I have used UV-visible spectroscopy in reflexion and transmission geometries, coupled to electronic and atomic force microscopies, with the help of optical simulations, to correlate the optical properties of the particles to their local density at the surface. Nonlinear sum frequency generation spectroscopy is able to probe the surface chemistry of both the particles and the substrate, through a local amplification of optical processes due to the excitation of the SPR. After showing that the latter does indeed amplify the low intensity molecular SFG signals from the silane layer, I have revealed the presence, in the organic layer, of unreacted methyl groups arising from an incomplete silanization, evidenced the link between plasmonic and chemical stability in time and laser irradiation, finely assessed the quality of surface functionnalization of the particles by thiols, and established the linear relationship between linear and nonlinear optical responses at the surface. Finally, I have directly studied the amplification process itself by coupling to the SPR through two dimension spectroscopic studies in the visible and infrared ranges. I have shown that the coupling is indeed measurable, even on small deposited particles, and that it happens in the spectral zone where the surface plasmon exists (from green to red). A comparison to flat platinum and gold surfaces leads to a fine estimation of amplification factors, which correspond to the predictions of a simple model for the plasmonic processes at stake at such interfaces.

Nous avons mis en place un dispositif de microscopie par génération de somme de fréquences optiques pour étudier les milieux isotropes chiraux. Ce dispositif a tout d'abord été validé en utilisant la molécule chirale de bi-2-naphtol en solution liquide et en milieu sol-gel. Nous avons établi les conditions expérimentales permettant de limiter les phénomènes de blanchiment par absorption biphotonique du chromophore. Nous avons ensuite entrepris une étude des polymères de coordination chiraux élaborés à partir de l'auto-assemblage de ligands organiques chiraux et d'ions métalliques en solution. Nous avons mesuré un signal SFG chiral apparaissant lors du séchage de films de polymères et de complexes de coordination chiraux. Nous démontrons ainsi que la technique de microscopie SFG spécifique des milieux isotropes chiraux permet de détecter le processus de coordination des polymères de coordination chiraux en phase condensée et de suivre l'établissement de la phase solide. / We have built a set-up to perform sum frequency generation (SFG) microscopy in order to study isotropic chiral media. This set-up was first validated with molecules of bi-2-naphthol in liquid solution and sol-gel matrices. We have established the experimental conditions to limit the bleaching phenomena of the chromophore by two-photon absorption. Next, we have conducted a study of chiral coordination polymers produced through the self-assembly of chiral organic ligands and metal ions in solutions. We have measured a chiral SFG signal developing while films of chiral coordination polymers and complexes are drying. Thus we show that SFG microscopy specific to isotropic chiral media makes it possible to detect the coordination process of chiral coordination polymers in the condensed phase and monitor the establishment of the solid phase.

No description available.

While the development of bright pulses produced in free space devices can be found in a large set of applications and research equipment all over the world. The production of dark pulses in a free-space device has not been shown prior to this work. In this work a method of producing free space mode-locked laser in a straight laser cavity using intra-cavity loss induced by periodic nonlinear interactions mediated by a mode-locked source. We are able to show the existence of a dark pulse propagating inside of the cavity. An extensive analysis of the generation of the dark pulse is made using a homemade cross correlator. A symmetric dark pulse with a 10 ps width is achieved with a 90% modulation depth. This work will be used in a continued project involving passive two-color pulse synchronization. / Framtagningen av ljusa pulser i kristall baserade lasrar finns i en stor utsträckning av tillämpningar inom forskning och industri. Utvecklandet av mörkpulskällor i kristall baserade kaviteter har till vår kunskap inte tagits fram. I detta arbete presenteras en metod att utveckla en modlåst mörkpuls laser i en rak kavitet som utnyttjar intrakavitär förlust som periodiskt induceras av en ickelinjär interaktion som styrs av en ljus modlåst källa. Vi kan visa att en mörk puls propagerar inuti kaviteten. En utförlig analys och experiment med hjälp av en hemagjord korskorrelator belyser hur den mörka pulsen kan formas. En symmetrisk mörk puls formas med en 10 ps bredd och över 90 % modulations djup. Detta arbete kommer användas i ett framtida projekt inom passiv tvåfärgs puls synkronisation.

Important aspects of adhesion occur at interfaces, including structures that may be different from those in the bulk materials. However, probing the orientation of molecules in functional adhesives poses a significant challenge because adhesive molecules are always located at a buried interface. The limited penetration depth of surface-specific analysis prohibits the study of buried interfaces using those techniques. The large quantity of bulk molecules relative to the adhesive molecules interacting at the interface results in the bulk signal swamping out adhesive signal in bulk analysis techniques. An interface-specific technique is required to study functional adhesives. One such technique that has shown promise in recent years is Vibrational sum frequency generation (VSFG) spectroscopy. This technique is useful for studying interactions that occur at surfaces and interfaces because it selectively probes regions of broken inversion symmetry. Despite the ability of VSFG to isolate signal from a buried interface, a non-resonant signal that is produced simultaneously with the resonant signal corrupts the vibrational data of interest and greatly impedes reliable analysis of VSFG spectra. Over the last several years, researchers have experimentally removed non-resonant signal by delaying the upconverting pulse with respect to the initial excitation. Obtaining reliable results from VSFG data depends upon complete removal of non-resonant signal. However, complete removal of non-resonant signal presents a challenge because it can be present in spectra even when the indicators of non-resonant signal are absent. By taking advantage of polarization selection rules for VSFG and the differing symmetry of an azimuthally isotropic film and an azimuthally non-isotropic substrate, spectra containing non-resonant signal can be easily identified. These and other advances in VSFG methodology have enabled the study of surface and interfacial systems of interest. In a study of the effects of plasma treatment on polystyrene thin films, plasma exposure was found to affect not only the free surface but also portions of the sub-surface polymer, challenging previous assumptions that plasma effects are constrained to the free surfaces of materials. The next step is to use VSFG to study functional adhesives under known amounts of applied stress. An apparatus is in place to simultaneously collect VSFG spectra during mechanical testing of a functional adhesive, and in preliminary studies, an increase in VSFG non-resonant signal has been observed when a pulling force is applied to the adhesive bond.

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No description available.

This thesis examines second-order optical nonlinear wave mixing processes in domain-disordered quasi-phase matching waveguides and evaluates their potential use in compact, monolithically integrated wavelength conversion devices. The devices are based on a GaAs/AlGaAs superlattice-core waveguide structure with an improved design over previous generations. Quantum-well intermixing by ion-implantation is used to create the quasi-phase matching gratings in which the nonlinear susceptibility is periodically suppressed. Photoluminescence experiments showed a large band gap energy blue shift around 70 nm after intermixing. Measured two-photon absorption coefficients showed a significant polarization dependence and suppression of up to 80% after intermixing. Similar polarization dependencies and suppression were observed in three-photon absorption and nonlinear refraction. Advanced modeling of second-harmonic generation showed reductions of over 50% in efficiency due to linear losses alone. Self-phase modulation was found to be the dominant parasitic nonlinear effect on the conversion efficiency, with reductions of over 60%. Simulations of group velocity mismatch showed modest reductions in efficiency of less than 10%. Experiments on second-harmonic generation showed improvements in efficiency over previous generations due to low linear loss and improved intermixing. The improvements permitted demonstration of continuous wave second-harmonic generation for the first time in such structures with output power exceeding 1 µW. Also, Type-II phase matching was demonstrated for the first time. Saturation was observed as the power was increased, which, as predicted, was the result of self-phase modulation when using 2 ps pulses. By using 20 ps pulses instead, saturation effects were avoided. Thermo-optically induced bistability was observed in continuous wave experiments. Difference frequency generation was demonstrated with wavelengths from the optical C-band being converted to the L- and U-bands with continuous waves. Conversion for Type-I phase matching was demonstrated over 20 nm with signal and idler wavelengths being separated by over 100 nm. Type-II phase matched conversion was also observed. Using the experimental data for analysis, self-pumped conversion devices were found to require external amplification to reach practical output powers. Threshold pump powers for optical parametric oscillators were calculated to be impractically large. Proposed improvements to the device design are predicted to allow more practical operation of integrated conversion devices based on quasi-phase matching superlattice waveguides.

This thesis reports work extending the scope of a recently developed gas sensing technique, multi-mode absorption spectroscopy (MUMAS). The ability of MUMAS to simultaneously detect multiple species from a mixture is demonstrated for the first time. The technique is subsequently extended to mid-infrared wavelengths, realising large gains in sensitivity. A solid-state, multi-mode laser has been developed to provide a high-performance comb source for use with MUMAS. This in-house constructed, diode-pumped, Er/Yb:glass laser operates on 10 longitudinal modes, separated by 18 GHz and centred close to 1565 nm. The extensive development and prototyping work leading to this final laser design is described. Multi-species detection with MUMAS is reported for the first time, thus demonstrating the ability of this technique to perform multi-gas sensing using a single laser and simple detection scheme. The previously described Er/Yb multi-mode laser was used to record MUMAS signals from a sample containing CO, C₂H₂, and N₂O. The components of the mixture were detected simultaneously by identifying multiple transitions in each of the species. Temperature- and pressure-dependent modelled spectral fits to the data were used to determine the partial pressures of each species in the mixture with an uncertainty better than +/-2%. Multi-mode radiation has been successfully generated at 3.3 μm using quasi phase matched difference frequency generation (QPM-DFG). A mid-infrared laser comb was produced by optically mixing the near-infrared, multi-mode comb produced by the previously developed Er/Yb:glass laser with the single-mode output of a Nd:YAG laser operating at 1064 nm. This multi-frequency laser source was characterised to verify performance, and subsequently used to perform proof-of-principle MUMAS measurements on the strong transitions found in this spectral region. Spectra were recorded of NH₃ and CH₄ both individually and as components of a mixture. A minimum detection level for this system was determined to be 4.3 μbar m^-1 for CH₄, a sensitivity increase of 300 over similar measurements performed in the near-IR.

Estudos em interfaces são importantes para o completo entendimento de muitos processos em química, física e biologia. Esses sistemas são governados principalmente pelas propriedades interfaciais dos materiais. Nas duas últimas décadas, o desenvolvimento de novos métodos experimentais melhorou o nosso entendimento das propriedades interfaciais. O advento de uma série de técnicas de espectroscopia a laser baseadas em óptica não linear e o desenvolvimento das técnicas de microscopia por ponta de prova, possibilitaram estudos antes inimagináveis em superfícies e interfaces. Entre as técnicas de espectroscopia não linear, destacamos a espectroscopia por Geração de Soma de Frequências (espectroscopia SFG). Essa técnica foi desenvolvida por Shen et al. em 1987 e, desde então, é aplicada a muitos estudos em superfícies e interfaces. A espectroscopia SFG pode fornecer informações sobre a natureza química por meio do espectro vibracional e sobre o ordenamento médio das moléculas em uma única monocamada. O sinal SFG só pode ser gerado em meios não centrossimétricos, isso inclui superfícies ou interfaces entre meios centrossimétricos, onde há quebra da simetria de inversão. A combinação da espectroscopia SFG com a microscopia óptica tem sido proposta como uma nova técnica experimental para obter imagens em interfaces com sensibilidade química pelo espectro vibracional e contraste pela orientação e ordenamento das moléculas. Neste trabalho, apresentamos o desenvolvimento, construção e caracterização de um Microscópio SFG (MSFG). Esse MSFG foi especialmente projetado para estudos em superfícies ou interfaces tanto líquidas quanto sólidas. Testes iniciais de desempenho do MSFG foram realizados na interface líquido/ar da solução binária água/acetonitrila (H2O⁄CH3CN). Foram obtidas imagens do sinal SFG ressonante com o estiramento simétrico do grupo metil (CH3) da acetonitrila na interface líquido⁄ar da solução binária. Variando a fração molar da acetonitrila na solução entre 4% e 20% observamos a dependência da intensidade do sinal SFG na interface em função da fração molar de acetonitrila no volume do líquido. Testes também foram feitos em filmes Langmuir-Blodgett multicamada de ácido esteárico (CH3(CH2)16COOH). Obtivemos a espectromicroscopia SFG na ressonância dos grupos CH2 e CH3 do ácido graxo. Pelas diferenças entre os espectros SFG das regiões ordenadas e desordenadas, a espectromicroscopia revelou distribuições microscópicas do ordenamento das cadeias alquila que formam o filme. A sensibilidade da detecção do sinal SFG foi caracterizada e revelou a possibilidade de obter imagens na superfície da água em menos de um minuto. A caracterização óptica e os testes nas interfaces líquido⁄ar e sólido⁄ar demonstraram a completa capacidade do MSFG como ferramenta para investigar qualquer superfície ou interface, seja essa líquida ou sólida. / Interface studies are important for the complete understanding of many processes in chemistry, physics and biology. These systems are mainly governed by the interfacial properties of the materials. In the last two decades, the development of new experimental methods improved our understanding of interfacial properties. The advent of a host of laser spectroscopy techniques based on nonlinear optics and the development of the scanning probe microscopy techniques, opened up unimaginable possibilities of studies at surfaces and interfaces. Among these nonlinear spectroscopies we turned our attention to Sum Frequency Generation spectroscopy (SFG spectroscopy). This technique was developed by Shen et al. in 1987 and, since then, it has been applied to many studies of surfaces and interfaces. SFG spectroscopy can provide information about the chemical nature by the vibrational spectra and about the average of molecular ordering in a single monolayer. The SFG signal only can be generated in a noncentrossymetric media, this includes surfaces or interfaces between centrossymetric media, where there is a broken in the inversion symmetry. The combination of SFG spectroscopy with optical microscopy has been proposed as a novel experimental technique to obtain images at interfaces with chemical sensitivity by the vibrational spectra as well as contrast by the ordering and orientation of the molecules. In this work we present the development, construction and characterization of an SFG Microscope (SFGM). This SFGM was specially designed to perform studies on surfaces or interfaces of liquids and solids. Initial SFGM performance tests were performed at the liquid/air interface of the water/acetonitrile (H2O/CH3CN) binary solution. The images of the SFG signal were acquired on the resonance of the methyl group (CH3) of acetonitrile present at the liquid⁄air interface of the binary solution. By varying the molar fraction of acetonitrile in the solution between 4% and 20% we observed the dependency of the SFG signal intensity as a function the acetonitrile bulk mole fraction. We also performed tests in multi-layered Langmuir-Blodgett films of stearic acid (CH3(CH2)16COOH). We obtained the SFG spectromicroscopy in the resonance of CH2 and CH3 groups of the fatty acid. By the differences between the SFG spectra of ordered and disordered regions, the spectromicroscopy revealed microscopic distribution of the conformational ordering in the alkyl chains that composes the film. The sensitivity of the SFG microscope was characterized and it was shown that images could be acquired at the water surface in less than one minute. The optical characterization and the performed tests at the liquid/air and solid/air interfaces demonstrated the full capabilities of the SFGM as a tool for investigations in any liquid or solid interface.