Master of Science / Department of Physics / Matthias Kling / This thesis consists of two major parts. The first part concerns studies of the orientation dependence of the ionization of diatomic molecules in intense, femtosecond two-color laser fields. The second part is about studies on the ionization mechanisms of the C[subscript]6[subscript]0 molecule in femtosecond near-infrared and ultraviolet laser fields. In the first part, experimental and theoretical results on the asymmetric ion emission of the heteronuclear molecules CO and NO in two-color laser fields are discussed. The two-color fields, which can be tailored by a relative phase, are used to ionize and dissociate CO and NO molecules, both of which are molecules with small polarizabilities. The resulting C[superscript]+, C[superscript]2[superscript]+, N[superscript]+ and O[superscript]+ ions are detected by a velocity map imaging (VMI) setup. The photoelectrons from above-threshold ionization (ATI) of Xe are studied under such a two-color field to assign the phase. For both CO and NO we find that enhanced ionization occurs when the molecule is oriented with the electric field pointing from the C or N atom toward the O atom. This is in agreement with the molecular orbital Ammosov-Delone-Krainov (MO-ADK) theory and the Stark-corrected strong-field-approximation (SFA) calculations. The second part is devoted to the investigation of the ionization mechanism of neutral C[subscript]6[subscript]0 molecules with 30 fs laser pulses at about 800 nm and with 50 fs pulses at about 400 nm. The angular distributions of photoelectrons are measured utilizing VMI. Measurements under different intensities are carried out for the two wavelengths. In our work, thermal electron emission is highly suppressed by the use of short pulses. For near-infrared excitation, photoelectron angular distributions (PADs) that contain six lobes are observed for low energy electrons. This behavior is different from studies for longer pulses of about 120 fs [1]. Further analysis indicates that the PADs might originate from single photon ionization of a super atomic molecular orbital (SAMO), however, a detailed assignment requires further theoretical work. The PADs for the ultraviolet excitation show very similar structures to earlier results [1]. For the near-infrared excitation, we have carried out studies as a function of the chirp of the pulses and find effects on photoelectron spectra and on PADs, which are tentatively explained by sequential multiphoton ionization via “doorway” states.

L’Industrie actuelle demande des produits à haute valeur ajoutée offrant des nouvelles fonctions à moindre coût. Parmi les fonctions on peut citer la coloration de surface, le noircissement de surface, la réduction des frottements, la génération de surface anti-réflexion, anti-bactérienne, superhydrophobe ou anti-formation de glace. Les surfaces fonctionnelles présentes dans la nature nous indiquent que ces propriétés uniques sont possibles par des texturations de surface à l’échelle micro et nanométrique adéquates.Parallèlement à cela, la technologie laser révolutionne le champ des possibles en termes de texturation de surface et permet de reproduire ces fonctions inspirées du monde du vivant en modifiant la morphologie et la chimie de surface. Néanmoins, le développement et le déploiement de telles techniques de texturation laser au niveau industriel nécessite la levée de trois verrous. Le premier est de connecter les propriétés macroscopiques (couleur, résistance mécanique, stabilité chimique, vieillissement) et la morphologie de surface aux échelles nano et microscopiques. Le second d’acquérir une parfaite maîtrise de la morphologie de surface à ces échelles. Le troisième est la transposition du procédé développé en laboratoire en procédé industriel adapté aux traitements de grandes surfaces avec des temps de cycles les plus courts possibles. Nous avons étudié plusieurs techniques de texturation de surface à l’échelle submicronique par laser femtoseconde. Ainsi des « ripples » de quelques dizaines de nanomètres ont être réalisées par laser UV. L’irradiation avec double impulsion apporte une capacité supplémentaire dans le contrôle de la morphologie de surface finale. Différents types de structures, avec différentes symétries, ont ainsi été produites en jouant sur le délai entre les deux impulsions. Des structures LIPSS homogènes triangulaires ou carrées ont été obtenues pour des délais inférieurs à 5 ps et 500 ps respectivement. Des paramètres opératoires, en particulier la fluence et la polarisation, ont été identifiés comme jouant un rôle majeur dans les caractéristiques de la morphologie de surface finale. Des expériences complémentaires ont montré que des résultats similaires peuvent être obtenus en utilisant des cristaux biréfringents pour générer des délais courts. Nous avons également exploré la possibilité d’utiliser des trains d’impulsions uniques pour produire des texturations de surface de dimensions caractéristiques supérieures allant de quelques microns à plusieurs dizaines de microns en faisant varier de manière systématique la fluence, la dose énergétique et le taux de répétition du laser. La comparaison de résultats expérimentaux avec ceux issus de simulation nous avons mis en évidence le rôle majeur de l’accumulation thermique sur les dimensions caractéristiques des structures générées par laser. Par ailleurs, nous avons démontré la capacité du procédé à produire de texturations sub-longueurs d’onde, homogènes, sur des surfaces supérieures à 1 cm², avec des lasers ayant des taux de répétitions allant jusqu’à 10 MHz et des systèmes de positionnement innovants. Des nano-rugosités de surface ainsi produites affichent des propriétés de super hydrophobicité. A titre d’exemple, nous avons atteint un temps de texturation de l’ordre de 1 min/cm², soit 60 fois inférieurs à ce que nous obtenions en début des travaux. Enfin, nous avons démontré un temps de 9 s/cm² pour le noircissement de surface.Ces travaux de recherche, mettant à profit des sources laser et des équipements de déflection optique de dernière génération, apportent une contribution significative dans la compréhension des mécanismes d’une part, et dans la capacité à contrôler et à produire de telles texturations sur des grandes surfaces d’autre part. Ils devraient favoriser une dissémination rapide de ces technologies de texturation laser dans l’industrie. / Current industrial markets demand highly value-added products offering new features at a low-cost. Among the most desired functionalities are surface colouring and blackening, anti-icing, anti-biofouling, wear reduction and anti-reflectivity. Laser surface processing holds a virtually endless potential in surface functionalization since it can generate versatile surface properties by modifying surface morphology and chemistry. Nevertheless, developing functional surfaces for implementation in the industry requires action on three levels. The first is to connect the macro-scale surface properties (colour, mechanical resistance, chemical stability, ageing) and the micro & nano-scale morphology. The second is to increase the level of control over the laser induced morphology in the near micron and submicron scale. The third is to upscale the lab-developed process both in terms of processed area and cycle time. Functional textures found in nature can be used as a guideline for connecting the surface texture with the surface property. It is well established that different textures can enable different functionalities. Nevertheless, the level of control of the laser induced morphology has to be improved significantly in order to allow one to mimic nature’s examples. Increase of control requires an in-deep understanding of the physical mechanisms that lead to nanostructure formation. To this end, we carry out a comprehensive parametric study of fs processing on stainless steel. The impact of wavelength, overlap, fluence, dose, repetition rate, polarization and interpulse delay in the induced morphology was investigated.We investigate several techniques to achieve controlled laser structuring in the submicron regime. Ripples of a few tens of nanometres were obtained with a UV laser. Double pulses were employed to further control the submicron structures. Structures of different size and symmetry were obtained in different delays underlining the key role of the interpulse delay (Δτ). Homogeneous triangular and square 2D-LIPSS were obtained for Δτ smaller than 5 ps and 500 ps, respectively. Process parameters and particularly fluence and polarization were found to play also a role in the laser induced feature characteristics. In a complementary set of experiments, we show that similar results can be obtained for small delays with a robust setup of birefringent crystals. In the above micron regime, trains of single pulses were employed for controlling the surface morphology. Fluence, dose and repetition rate, were varied to show a systematic variation of spikes in the range of tens of micrometers. Combining our experimental results with simulation data we underline the key role of heat accumulation on the structures size. Finally, we proposed an upscaling strategy showing the possibility to exploit repetition rates up to 10 MHz for laser texturing.In the upscaling part, areas much larger than the spot size were textured homogenously using high repetition rate laser and innovative laser positioning systems. Nanometric ripples induced by UV laser act as a subwavelength grating. Laser induced nano roughness exhibits superhydrophobic properties. Uniform distribution of well-defined, sub-wavelength, 2D-LIPSS was successfully generated over ~1 cm2. The final surface exhibits multiple axis iridescence giving a holographic effect. Employing a 10 MHz laser surface was textured at a rate of ~ 1 min/cm2 almost 60 times faster compared to our starting point. Lastly, surface blackening was achieved at a rate of ~ 9 sec/cm2.In conclusion, valuable data were provided both in surface functionalization, in understanding and controlling of laser induced structuring and in upscaling a lab developed process. We believe that our results open the way for exploiting fs laser texturing in everyday applications employing up to date laser sources and positioning systems.

La modification du silicium dans son volume est possible aujourd’hui avec des lasers infrarouges nanosecondes. Néanmoins, le régime d’intérêt pour la modification contrôlée en volume des matériaux transparents correspond aux impulsions femtosecondes. Cependant, aujourd’hui aucune démonstration de modification permanente du volume du Si n’a été réalisée avec une impulsion ultra-brève (100 fs). Pour infirmer ce résultat, nous avons développé des méthodes de microscopie infrarouge ultra-rapides. Tout d’abord, nous étudions le microplasma confiné dans le volume, caractérisé par la génération de porteurs libres par ionisation nonlinéaire du silicium, suivie de la relaxation totale du matériau. Ces observations, couplées à la reconstruction de la propagation du faisceau dans le matériau, démontrent un dépôt d’énergie d’amplitude fortement limitée par des effets nonlinéaires d’absorption et de propagation. Cette analyse a été confirmée par un modèle numérique simulant la propagation nonlinéaire du faisceau femtoseconde. La compréhension de cette limitation a permis de développer de nouvelles configurations expérimentales grâce auxquelles l’endommagement local et permanent du volume du silicium a pu être initié en régime d’impulsions courtes. / The modification of bulk-silicon is realized today with infrared nanosecond lasers. However, the interest regime for controlled modifications inside transparent materials is femtosecond pulses. Today, there is no demonstration of a permanent modification in bulk-Si with ultra-short laser pulses (100 fs). To increase our knowledge on the interaction between femtosecond lasers and silicon, we have developedultra-fast infrared microscopy experiments. First, we characterize the microplasma confined inside the bulk, being the generation of free-carriers under nonlinear ionization processes, followed by the complete relaxation of the material. These results, combined with the reconstruction of the beam propagation inside silicon, demonstrate that the energy deposition is strongly limited by nonlinear absorption andpropagation effects. This analysis has been confirmed by a numerical model simulating the nonlinear propagation of the femtosecond pulse. The understanding of this clamping has allowed us the development of new experimental arrangements, leading to the modification of the bulk of Si with short pulses.

A primeira etapa do projeto foi realizar testes para usinagem controlada e otimizada de vidro ótico de borosilicato (BK7) por laser de femtossegundos. Parâmetros como energia, pulsos sobrepostos e a variação da posição focal foram investigados para controle da taxa de remoção do material e extensão da cratera ablacionada. Especial atenção foi dada à condição física e topográfica da superfície resultante da usinagem para torná-la menos rugosa e evitar a retenção de reagentes que possam contaminar e alterar as reações pretendidas. Microcanais, microválvulas, microbombas, misturadores, microrreatores, aquecedores e outros componentes foram desenvolvidos para compor sistemas microfluídicos. Os microcanais construídos sobre a superfície de vidro BK7 vedados por uma lâmina de polidimetilsiloxano (PDMS) são a base dos sistemas microfluídicos. O controle de fluxo de reagentes é feito por miniválvulas pneumáticas controladas por um microcontrolador Arduino através de uma plataforma Labview. Este trabalho mostra os componentes desenvolvidos e dois sistemas microfluídicos criados. O primeiro contém um circuito capaz de replicar ensaios imunoenzimáticos (ELISA) com um custo muito menor de insumos. O segundo é um sistema para a produção de nanocristais fluorescentes de NaYF4 especialmente utilizados como marcadores em imagens de sistemas biológicos. / The first stage of the project was to perform tests for controlled and optimized machining of borosilicate optical glass (BK7) by femtosecond laser. Parameters such as energy, number of overlapped pulses, and the focal position variation were investigated for a better extraction of material. Microchannels, microvalves, micropumps, mixers, reactors, heaters and other components were developed to compose applied microfluidic systems. Microchannels built on the surface of BK7 glass sealed by a polydimethylsiloxane (PDMS) sheet form the basis of the microfluidic circuits. The reagents flow control is done by pneumatic mini-valves controlled by an Arduino microcontroller through a Labview platform. This work shows the components developed and two microfluidic systems created. The first contains a microfluidic circuit capable of replicating enzyme-linked immunosorbent assays (ELISA) with a much lower cost of materials. The second has a microfluidic circuit for the production of NaYF4 fluorescent nanocrystals specially used as markers in images of biologic systems.

O desenvolvimento de sistemas laser com pulsos ultracurtos trouxe a possibilidade de usinagem de estruturas muito pequenas em praticamente qualquer tipo de material. Neste trabalho foi dada continuidade a estudos já iniciados no Centro de Lasers e Aplicações (CLA) com os materiais dielétricos, introduzindo a largura temporal dos pulsos laser como mais uma variável e utilizando os conhecimentos adquiridos para a determinação de limiares de ablação e parâmetros de incubação em alguns metais como: aço AISI 1045, aço inoxidável VI138, cobre eletrolítico e molibdênio. A ausência de calor no processo de ablação dos metais torna-se muito difícil, pois a criação de uma camada de íons é muito prejudicada pela mobilidade eletrônica ao seu redor. Assim a ablação de metais com pulsos ultracurtos, tem como principal mecanismo a explosão de fase associada a outros processos que também contribuem na ablação, porém em menor escala, como a explosão coulombiana e a fusão ultrarrápida. Além disso, propriedades como a constante de acoplamento elétron-fônon e a condutividade térmica assumem um papel importante e devem ser levadas em conta na investigação do processo de ablação dos metais. Este trabalho possibilitou a obtenção de parâmetros de operação nos quais o calor transferido para a rede é minimizado, possibilitando a microusinagem de precisão e alterações controladas na morfologia da superfície de diversos metais. Os resultados propiciaram assim condições para novos desenvolvimentos e aplicações práticas de usinagem com pulsos ultracurtos. / The development of laser systems with ultrashort pulses brought the possibility of machining very small structures in virtually any type of material. In this work was continued the studies already started in Lasers and Applications Center (CLA), with dielectric materials, introducing temporal width of the laser pulses as another variable, and using the knowledge acquired to determine ablation threshold and incubation parameters of some metals such as AISI 1045 steel, VI 138 stainless steel, electrolytic copper and molybdenum. The absence of heat in the ablation process of metals is much more difficult since the creation of a layer of ions is greatly impaired by electronic mobility in its vicinity. Hence, the ablation process for metals with ultrashort pulses, has, as main mechanism, the phase explosion associated with other processes that also contribute in the process, but on a smaller scale, such as Coulomb explosion and ultrafast fusion. Moreover, properties such as electron-phonon coupling constant and thermal conductivity play an important role and should be taken into account in investigating the process of ablation of metals. This study made it possible to obtain operation parameter where the heat transferred to the lattice is minimized, enabling precision micromachining and controlled changes in the morphology of the surface of metals. The results provided conditions for new developments and real machining applications with ultrashort pulses.

A terapia fotodinâmica (TFD) é uma promissora técnica para o tratamento de câncer e de outras patologias. O tratamento baseia-se na ação de uma fonte de luz com o agente fotossensibilizador (FS) e o oxigênio molecular presente nas células, gerando espécies reativas de oxigênio que causam a morte celular. Uma das limitações atuais da técnica é a penetração da luz no tecido biológico. Entre os fotossensibilizadores mais empregados, estão os derivados de hematoporfirina, que são excitados da região do vermelho do espectro eletromagnético. Fotossensibilizadores vêm sendo desenvolvidos para iluminação com comprimentos de onda maiores, com o potencial de aumentar a profundidade de penetração e em conseqüência, o volume tecidual tratado. Outra opção para aumentar o volume tecidual de resposta utilizando derivados de hematoporfirina é a utilização de fontes de luz pulsada que, em comparação com a contínua, vem apresentado resultados significativos no estudo da TFD. Neste estudo, foi realizada a fotodegradação in vitro do fotossensibilizador comercial Photogem® (Moscou, Rússia) com tempos variando entre 0 e 40 minutos. Como fonte de luz contínua foi utilizado um laser de diodo (Eagle Heron Quantum Tech, Brasil), e como fonte de luz pulsada, foi utilizado um laser em regime de femtossegundos emitindo em 630 nm, 1 kHz, pulso < 70 fs (Ti:Sapphire Libra-S, Opera-VIS Coherent, USA). Para a coleta dos dados, foi utilizado um sistema de espectroscopia por fluorescência portátil composto por um espectrometro USB 2000, um laptop e sonda em Y para excitação e coleta da fluorescência do FS. Também foi realizada a TFD em fígados normais de ratos. Foram utilizados 18 animais, pesando entre 180 e 250g. Os animais foram divididos em 2 grupos. Ambos os grupos receberam 1,5 mg/kg de FS, e após 30 minutos foram iluminados com dose de energia de 150 J/cm2 e intensidade de 74 mW/cm2. Também foi realizado o estudo da penetração da luz utilizando macerado de figado de rato, e o mapeamento térmico durante a TFD com a fonte de luz CW e o laser pulsado. O estudo da taxa de fotodegradação do FS nos mostrou uma maior eficiência da fonte de luz pulsada para a degradação da molécula de Photogem®, enquanto que a taxa de degradação para o CW foi 6 vezes menor. O macerado mostrou que o coeficiente de penetração da luz CW e a luz pulsado são praticamente os mesmos, o que sustenta a análise com a intensidade média. O estudo in vivo mostra, através de uma análise histológica do perfil de necrose, que a fonte de luz pulsada alcança uma profundidade de necrose cerca de 2 vezes maior, em comparação com a fonte em regime contínuo, além de um melhor resultado em uma avaliação qualitativa da morfologia da região de necrose. Isto está relacionado com a alta intensidade dos pulsos emitidos pela fonte de luz pulsada com o tecido e o FS presente, promovendo o aumento na profundidade de necrose. / Photodynamic therapy (PDT) is a useful technique for the treatment of cancer lesions and other diseases. The treatment is based on the interaction of light with a photosensitizer agent (PS) and with molecular oxygen that is present in cells, which generates reactive oxygen species that promote cell death. One of the limitation factors of this technique is limited light penetration in biological tissue. Hematoporphyrin derivatives are among the most used photosensitizers. They are excited on the red region of the electromagnetic spectrum. New photosensitizers has been developed for the use with longer wavelengths, potentializing the increase of penetration depth and, hence, the volume of treated tissue. Another option to increase the volume of responding tissue in PDT studies is to use pulsed light sources, which has presented satisfactory results when compared to continuous (CW) light sources. In this study, in vitro photodegradation of Photogem® (commercial photosensitizer, Moscow, Russia) was performed, during irradiation times between 0 and 40 minutes. A diode laser (Eagle Heron Quantum Tech, Brazil) was used as CW light source, and a femtosecond laser (Ti:Sapphire Libra-S, Opera-VIS Coherent, USA) emitting in 630 nm (1 kHz, < 70 fs pulse) was used as a pulsed light source. Data collection was performed using a portable fluorescence spectroscopy system, including a spectrometer USB 2000 (Ocean Optics®, Palo Alto, CA), a laptop and a Y-type optical fiber probe for PS fluorescence excitation and collection. Photodynamic response was investigated in eighteen animals, weighting between 180 g and 250 g, which were divided in two groups. Both groups received 1.5 mg/kg of body mass of PS, and after thirty minutes were irradiated with light dose of 150 J/cm2 and 74 mW/cm2 for fluence rate. Light penetration was also investigated using rat liver macerate, and thermal monitoring during PDT as well, for both pulsed and CW light sources. The photodegradation rate study allowed us to observe a greater efficiency in Photogem® molecules degradation for the pulsed light source. For the CW irradiation, the degradation rate was 6 times lower. Macerate study showed that light penetration coefficient values for CW and pulsed were similar, which corroborates with the average intensity analysis. The depth of necrosis histological analysis showed that the pulsed light source allows depth of necrosis to be about 2x deeper when compared to CW source. Additionally, the pulsed source showed a better result in the qualitative evaluation of necrotic tissue morphology. This is related to the high intensity of the pulses emitted from the pulsed light source on the photosensitized tissue, promoting an increase in depth of necrosis.

Neste trabalho foi utilizado o método de regressão do diâmetro para a medida do limiar de ablação nos materiais Suprasil, BK7, Safira e Ti:Safira por pulsos de femtossegundos. Através de medidas dos limiares de ablação para pulsos únicos e pulsos sobrepostos, quantificou-se o parâmetro de incubação para cada dielétrico. Essas medidas preliminares serviram para validação do método denominado Diagonal Scan ou D-scan. Para tanto, o método D-scan teve seu formalismo expandido o que possibilitou a quantificação da sobreposição de pulsos durante o seu uso. A simplicidade e rapidez do método D-scan permitiram que o limiar de ablação no BK7 fosse medido para diferentes larguras temporais e sobreposições. O limiar de ablação para pulsos únicos em função da largura temporal dos pulsos foi comparado com uma simulação teórica. A partir do conhecimento do parâmetro de incubação desenvolveu-se uma metodologia de usinagem em dielétricos que considera a sobreposição de pulsos durante a ablação. Isso permitiu a fabricação de microcanais para uso em microfluídica em BK7. / In this study, the diameter regression method was used to measure the ablation threshold of Suprasil, BK7, Sapphire and Ti: Sapphire by femtosecond pulses. Through measurements of the ablation thresholds for single and overlapping pulses, the incubation parameter for each dielectric was quantified. These preliminary steps were used to validate the method called Diagonal Scan or D-scan. This was made possible by expanding the D-scan formalism, which allowed the quantification of overlapping pulses during its use. The simplicity of the D-scan method allowed the ablation threshold measurement in BK7 for different temporal widths and overlaps. The ablation threshold for single pulse for different temporal width was compared with a theoretical simulation. From the knowledge of the parameter of incubation, a methodology that considers dielectric machining overlapping pulses during ablation was developed. This allowed the manufacture of microchannels on BK7 for microfluidics.

Neste trabalho foi estudada a geração de harmônicos perturbativos por pulsos laser ultracurtos em bicos de gás no vácuo. Os harmônicos foram gerados nas regiões espectrais do UV e VUV e sua geração ocorreu em fluxo de gases nobres. Esta técnica possibilita a produção de luz coerente numa região espectral de interesse considerável para várias aplicações, tais como a espectroscopia resolvida no tempo. Para a geração dos harmônicos foi utilizado um sistema laser amplificado de Ti:Safira que produz pulsos de 25 fs, centrados em 785 nm, a 4 kHz. Estes pulsos ultracurtos são injetados em uma câmara de vácuo, onde são focalizados em um bico de gás. Os harmônicos são selecionados por um monocromador e têm a sua intensidade medida por um cintilador e uma fotomultiplicadora. Buscamos abranger uma visão geral sobre a geração de harmônicos perturbativos em gases, com o objetivo de consolidar um conhecimento teórico e experimental no laboratório. Confeccionamos e comparamos o desempenho de dois sistemas distintos de injeção de gás, o bico metálico e o bico de vidro, que são dispositivos pouco explorados na literatura. Os melhores resultados foram obtidos com o bico de vidro. Pudemos estimar a eficiência de geração dos harmônicos do ponto de vista das propriedades microscópicas e macroscópicas de geração, e foi verificada a conversão de energia do feixe fundamental para a geração dos harmônicos, plasma e outros fenômenos não-lineares em argônio. Geramos até o 9º harmônico em argônio, atingindo a região de 85 nm. Foi estudado o casamento de fase e a dependência da eficiência de geração dos harmônicos com a pressão do gás, potência média do laser, chirp e a posição do foco para o 3º, 5° e 7º harmônicos. Com a variação dos parâmetros, observou-se que é possível sintonizar os harmônicos, e que sua geração compete com outros fenômenos, como a ionização do gás. Adicionalmente, foi observada uma queda da eficiência de geração para alta intensidades, que foi associada à depleção do 1º elétron de valência dos átomos do gás, reduzindo a quantidade de centros geradores dos harmônicos. Além do argônio, foram realizadas medidas em hélio, neônio e criptônio, visando estudar como a eficiência de geração dos harmônicos depende das propriedades eletrônicas do gás. Adicionalmente, esses resultados corroboraram a hipótese da depleção dos elétrons de valência. / In this work the generation of perturbative harmonics by ultrashort laser pulses in gas nozzles in vacuum was studied. The harmonics were generated in the UV and VUV regions and the frequency conversion occurred in flowing gas. This technique ensures the generation of coherent light in a spectral region of interest for various applications, such as ultrafast time-resolved spectroscopy. For the harmonics generation an amplified Ti:Shapphire laser system was used, generating 25 fs pulses, centered at 785 nm, at 4 kHz. These ultrashort pulses are injected into a vacuum chamber, where they are focused on a gas nozzle. The harmonics are selected by a monochromator and their intensity is measured by a scintillator and photomultiplier. We have sought to comprise an overview of the generation of perturbative harmonics in gases, in order to consolidate a theoretical and experimental knowledge in the laboratory. Two distinct gas injection systems were manufactured and had their performances compared, a metallic and a gas nozzle, devices that are poorly explored in literature. The best results were obtained with the glass nozzle. We could estimate the harmonics generation efficiency in argon from the point of view of their macroscopic and microscopic generation properties, and the energy conversion from the fundamental beam to the harmonics was verified, along with plasma creation and other nonlinear phenomena. We generated up to the 9th harmonic in argon, reaching the 85 nm. We studied the phase matching and the dependence of the harmonics generation efficiency with the gas pressure, laser average power, chirp and focus position for the 3rd, 5th and 7th harmonics. By varying the parameters, we observed that it is possible to tune the harmonics wavelengths, and that their generation competes with other nonlinear phenomena, such as the gas ionization. Additionally, a drop in the generation efficiency was observed at high intensities, which was associated to the depletion of the first valence electron in the gas atoms, decreasing the number of harmonic generating centers. In addition to argon, measurements were performed in helium, neon and krypton, aiming to study how the harmonic generation efficiency depends on the electronic properties of the gas. Additionally, these results corroborated the hypothesis of the valence electron depletion.

Este trabalho investigou a fotodegradação do corante Rodamina-B com o auxílio do catalisador semicondutor Dióxido de Titânio, utilizando como fonte de irradiação pulsos de 40 fs gerados por um sistema laser de Titânio - Safira. Os pulsos laser foram formatados espectralmente (modulação senoidal), gerando trens de pulsos cuja separação foi escolhida para ser ressonante com um modo Raman intenso do catalisador. A fotodegradação da Rodamina-B foi monitorada através de medidas de fluorescência excitada via absorção de dois fótons. Não observamos fotodegradação do corante mediante a irradiação com pulsos ultracurtos, mesmo na presença do catalisador, tanto para o pulso de menor duração alcançada quanto para os trens de pulsos com diferentes separações temporais. Contudo, observamos uma diminuição no espalhamento da luz de excitação devido às nanopartículas de Dióxido de Titânio. Este processo foi estudado com mais detalhes, tendo sido analisada a influência da formatação espectral senoidal no resultado da medida. A relação entre a irradiação com pulsos de femtossegundos e a quebra de aglomerados de nanopartículas foi intuída a partir dos resultados obtidos, sendo fortalecida por medidas de microscopia eletrônica de varredura de um filme das amostras. / This work investigated the photodegradation of Rhodamine-B assisted by Titanium Dioxide semiconductor catalyst, using as irradiation source a Ti:Sapphire laser system delivering 40 fs pulses. The laser pulses were spectrally shaped (sinusoidal modulation), generating pulse trains whose separation was chosen to be resonant with an intense catalysts Raman mode. The Rh-B photodegradation was monitored by two photon excited fluorescence measurements. We have not observed dye photodegradation by the ultrashort pulses irradiation, in the absence of the catalyst, neither with the shortest pulse obtained, nor with pulse trains. Nevertheless, we observed a decrease in the excitation light scattering due to the Titanium Dioxide nanoparticles. Such process was studied by analyzing the influence of sinusoidal spectral phase mask in the signal. The results indicate a relationship between femtosecond pulse irradiation and the breaking of nanoparticles clusters, which was also corroborated by scanning electron microscopy measurements.

Femtosekundenaufgelöste Ramanspektroskopie ist ein leistungsfähiges Werkzeug, um die Schwingungsentwicklung eines angeregten Chromophors in Echtzeit zu studieren. In dieser Arbeit wurde ein durchstimmbares Ramanspektrometer mit 10 cm-1 spektraler und 50--100 fs zeitlicher Auflösung entwickelt und für eine Anwendung auf flavinbasierte Photorezeptoren optimiert. Es wird der Einfluß der Resonanzbedingungen auf das transientes Ramanspektrum charakterisiert. Die Dynamik des angeregten Zustandes wird zuerst für den Modellphotoschalter Stilben untersucht, ausgehend sowohl vom cis-, als auch vom trans-Isomer. Intensitätsabnahme, spektrale Verschiebung und Bandenverschmälerung liefern Einblicke in die Schwingungsrelaxation des angeregten Chromophors. Wellenpaketbewegung und anharmonische Kopplung werden als Oszillationen beobachtet. Für das "Mutter"-Cyanin 1,1''-Diethyl-2,2''-pyridocyaniniodid wird die Isomerisierung bis in den Grundzustand verfolgt. Ramanspektren des Franck-Condon-Zustandes, des intermediär gebildeten heissen Grundzustandes und der Isomerisierungsprodukte werden erhalten. Als Grundlage für Experimente an Flavoproteinen werden die Eigenschaften des angeregten Flavinchromophors in Lösung untersucht. Transiente Absorptions- und Fluoreszenzexperimente weisen auf den Einfluss dynamischer polarer Solvatation hin. Es werden Ramanspektren des angeregten Zustandes von Flavin aufgenommen und die Schwingungsbanden zugeordnet. Populationsverminderung durch den Ramanimpuls wird als potentielles Artefakt in zeitaufgelösten Messungen identifiziert; der Effekt wird aber auch genutzt, um Wellenpaketbewegung im angeregten Zustand zu markieren. Die Photorezeptormutanten BlrB-L66F und Slr1694-Y8F werden mit transienter Absorption studiert. Dabei wird die Bildung des Signalzustandes und Flavinreduktion durch ein Tryptophan beobachtet. Die Anwendung des entwickelten Ramanspektrometers auf biologische Proben wird in einem ersten Experiment an Glucose Oxidase demonstriert. / Femtosecond stimulated Raman spectroscopy is a powerful tool that allows to study the structural relaxation of an excited chromophore directly in time. In this work a tunable Raman spectrometer with 10 cm-1 spectral and 50-100 fs temporal resolution was developed, and the technique was advanced towards applications to flavin-based proteins. With this device the influence of resonance conditions on the transient Raman spectrum is characterized. Excited-state dynamics is first investigated for the model photoswitch stilbene, starting from both the cis and the trans isomers. Decay, spectral shift, and narrowing of individual bands provide insight into the vibrational relaxation of the excited chromophore. Wavepacket motion and anharmonic coupling is seen as oscillations. Isomerization is followed to the ground state for the "parent" cyanine 1,1''-diethyl-2,2''-pyrido cyanine iodide. From a global analysis, Raman spectra for the Franck-Condon region, the intermediately populated hot ground state, and the isomerization products are obtained. As a basis for experiments on flavoproteins, the excited-state properties of the pure flavin chromophore are studied in solution. Transient absorption and fluorescence experiments suggest an influence of dynamic polar solvation on the electronic properties of the excited state. Raman spectra from the flavin excited state are recorded and the vibrational bands assigned. Population depletion by the Raman pulse is identified as a potential artefact, but the effect is also used to mark wavepacket motion in the excited state. The photoreceptor mutants BlrB-L66F and Slr1694-Y8F are studied by transient absorption; signaling state formation and flavin reduction by a semiconserved tryptophan are seen, respectively. The application of femtosecond Raman spectroscopy to biological samples is demonstrated in a first experiment on glucose oxidase.