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The goal of this dissertation is to study the photophysics of suspensions of colloidal C₆₀ particles to determine if their nonlinear optical (NLO) response is superior in any way to benchmark NLO materials such as molecular solutions of C₆₀ and carbon black suspensions (CBS). C₆₀ in molecular form is known to exhibit strong reverse saturable absorption (RSA) and it is posited that colloidal particles composed of many C₆₀ molecules would maintain some degree of RSA behavior upon association, although some quenching is to be expected. CBS is known to have an NLO response that is dominated by nonlinear scattering resulting from a phase change due to heating of the carbon black particles by absorbed energy. Colloidal C₆₀ particles that are many nanometers in diameter are similar to CBS, so it is posited that they would also have a nonlinear scattering mechanism contributing to their NLO response. Three samples of C₆₀ colloids are characterized by several techniques, along with two carbon black suspensions and one molecular solution of C₆₀. Transmission electron microscopy is used to determine morphology. Femtosecond pump-probe spectroscopy is used to determine the absorption spectrum and the relaxation kinetics of the first excited singlet state. Nanosecond laser flash photolysis is used to determine the absorption spectrum and the relaxation kinetics of the first excited triplet state. Z-scan is used to determine triplet-triplet absorption cross-sections. An experiment is performed to determine the percentage of the input energy that is transmitted, scattered, or absorbed by each sample. Computer modeling is performed to compare the experimental results to theory. Results show that all materials that exhibit nonlinear scattering have a constant extinction coefficient in the nonlinear regime, implying a characteristic size for the scattering centers that is independent of input energy. Quenching processes in C₆₀ colloids are found to be morphology dependent, with more crystalline structures resulting in stronger quenching and less RSA. C₆₀ colloids with stronger RSA are found to result in less nonlinear scattering than strongly quenched colloids. Highly crystalline C₆₀ colloids were shown to have a stronger NLO response than the benchmark materials at medium to high energies.

Neste trabalho são estudadas algumas propriedades ópticas de tetrâmeros de anilina em solução, usando o dimetil sulfóxido (DMSO) como solvente. Os espectros de absorção e emissão permitiram uma determinação aproximada dos níveis de energia do tetrâmero. Para a caracterização das propriedades ópticas não lineares foram utilizadas as técnicas de varredura-Z resolvida em freqüência e com trem de pulsos. Com a primeira foram determinados os parâmetros térmicos relacionados ao solvente, enquanto que com a segunda foram caracterizadas as não linearidades eletrônicas associadas aos estados excitados das moléculas. Além disso, foi possível obter a dinâmica das não linearidades presentes nas soluções, que apresentam um processo acumulativo relacionado à formação de uma lente térmica induzida pelo perfil gaussiano do laser. / This work reports on the optical properties of aniline tetramers in dimethyl sulfoxide (DMSO) solutions. Absorption and emission spectra allowed a rough estimate of the energy levels of the aniline tetramers. Nonlinear optical properties were studied with the frequency resolved Z-scan technique and with the Z-scan technique with pulse trains. The former determined the thermal parameters of the solvent, while the latter characterized electronic nonlinearities associated to molecular excited states. Moreover, we could analyze the dynamics of the optical nonlinearities and verify the presence of an accumulative process related to thermal lensing.

Neste trabalho são estudadas algumas propriedades ópticas de tetrâmeros de anilina em solução, usando o dimetil sulfóxido (DMSO) como solvente. Os espectros de absorção e emissão permitiram uma determinação aproximada dos níveis de energia do tetrâmero. Para a caracterização das propriedades ópticas não lineares foram utilizadas as técnicas de varredura-Z resolvida em freqüência e com trem de pulsos. Com a primeira foram determinados os parâmetros térmicos relacionados ao solvente, enquanto que com a segunda foram caracterizadas as não linearidades eletrônicas associadas aos estados excitados das moléculas. Além disso, foi possível obter a dinâmica das não linearidades presentes nas soluções, que apresentam um processo acumulativo relacionado à formação de uma lente térmica induzida pelo perfil gaussiano do laser. / This work reports on the optical properties of aniline tetramers in dimethyl sulfoxide (DMSO) solutions. Absorption and emission spectra allowed a rough estimate of the energy levels of the aniline tetramers. Nonlinear optical properties were studied with the frequency resolved Z-scan technique and with the Z-scan technique with pulse trains. The former determined the thermal parameters of the solvent, while the latter characterized electronic nonlinearities associated to molecular excited states. Moreover, we could analyze the dynamics of the optical nonlinearities and verify the presence of an accumulative process related to thermal lensing.

Neste trabalho, com objetivo de desenvolvermos dispositivos de limitação óptica, estudamos o processo de absorção de estado excitados em um grupo de tetrapiridil porfirinas com diferentes substituintes centrais (2H+, Zn2+, Ni2+, Cu2+). Para isso utilizamos a técnica de varredura – Z com pulsos de femto e picossegundos bem como com trem de pulsos. Desta forma, determinamos a dinâmica de absorção de estados excitados, para estas moléculas, obtendo parâmetros espectroscópicos tais como tempo de cruzamento intersistema, e as seções de choque de absorção dos primeiros estados excitados singleto e tripleto. Além disso, visando aproveitar os processos ópticos acumulativos de alguns materiais não lineares, em aplicação de limitação óptica, desenvolvemos uma nova geometria óptica denominada de limitador óptico de múltiplas passagens, a qual utiliza dois espelhos esféricos confocais e um espelho plano posicionado paralelamente a linha que une os espelhos esféricos. / In this work, aiming to develop optical limiting devices, we have studied excited state absorption process in a group of tetrapyridyl porphyrins with different central substitutes (2H+, Zn2+, Ni2+, Cu2+). We have employed Z-scan technique with femto and picosecond pulses as well as with pulse trains to determine the excited state absorption dynamics and obtain some spectroscopic parameters like intersystem crossing time and triplet and singlet excited state absorption cross-sections. Moreover, we have developed a new geometry for an optical limiter, named multipass optical limiter. It is formed by two confocal spherical mirrors together with a plane mirror placed in parallel with the line joining them.

Neste trabalho, com objetivo de desenvolvermos dispositivos de limitação óptica, estudamos o processo de absorção de estado excitados em um grupo de tetrapiridil porfirinas com diferentes substituintes centrais (2H+, Zn2+, Ni2+, Cu2+). Para isso utilizamos a técnica de varredura – Z com pulsos de femto e picossegundos bem como com trem de pulsos. Desta forma, determinamos a dinâmica de absorção de estados excitados, para estas moléculas, obtendo parâmetros espectroscópicos tais como tempo de cruzamento intersistema, e as seções de choque de absorção dos primeiros estados excitados singleto e tripleto. Além disso, visando aproveitar os processos ópticos acumulativos de alguns materiais não lineares, em aplicação de limitação óptica, desenvolvemos uma nova geometria óptica denominada de limitador óptico de múltiplas passagens, a qual utiliza dois espelhos esféricos confocais e um espelho plano posicionado paralelamente a linha que une os espelhos esféricos. / In this work, aiming to develop optical limiting devices, we have studied excited state absorption process in a group of tetrapyridyl porphyrins with different central substitutes (2H+, Zn2+, Ni2+, Cu2+). We have employed Z-scan technique with femto and picosecond pulses as well as with pulse trains to determine the excited state absorption dynamics and obtain some spectroscopic parameters like intersystem crossing time and triplet and singlet excited state absorption cross-sections. Moreover, we have developed a new geometry for an optical limiter, named multipass optical limiter. It is formed by two confocal spherical mirrors together with a plane mirror placed in parallel with the line joining them.

Cette étude traite des propriétés optiques non linéaires (NL) du troisième ordre des tétraphénylporphyrines et de certains de ses dérivées métallisées (Zn, Co) dissoutes dans le chlorobenzène. Les solutions ont été exposées à un laser émettant à 1064 nm, 532 nm et 355 nm dans le régime picoseconde ( ≈ 10 ps) en utilisant la méthode D4σ-Z-scan dans un montage 4f ainsi qu’une nouvelle technique appelée Dark-Field Zscan. Cette dernière se révèle être très fiable pour la détermination directe du signal de réfraction non linéaire en présence d’une forte absorption linéaire et/ou non linéaire. Le comportement des coefficients non linéaires a été étudié en fonction de la concentration et de l’intensité laser. La réponse a été attribuée à une susceptibilité effective du 3eme ordre {χ} rsub {eff} rsup {(3)} = {χ} ^ {(1)} : {χ} ^ {(1)} , dominée par un processus en cascade. Il a été mis en évidence que le comportement optique non linéaire des porphyrines dépend fortement du métal incorporé et de la durée des impulsions par rapport aux durées de vie des états excités. Ces résultats démontrent aussi que l’extension des systèmes électroniques π -conjugués accroît les non linéarités du troisième ordre de ces complexes, ce qui devrait être utile à l’élaboration de nouveaux matériaux. Cette propriété se révèle être intéressante pour la synthèse de porphyrines plus complexes avec d’autres substituants. Les effets importants d'absorption et de réfaction NL donnent aux porphyrines un fort potentiel d’utilisation pour la limitation optique, la commutation optique et pour différents autres applications en optique non linéaire. / This study deals with the third-order nonlinear optical properties (NL) of tetraphenylporphyrins and some of its metallic derivatives (Zn, Co) dissolved in chlorobenzene. The solutions were exposed to a laser emitting at 1064 nm, 532 nm and 355 nm in the picosecond regime ( ≈ 10 ps) using D4σ-Z-scan method in a 4f setup and a new technique called Dark-Field Zscan. The latter provides to be very reliable for the direct determination of the nonlinear refractive signal in the presence of a strong linear absorption and / or nonlinear one. The behavior of nonlinear coefficients has been studied as a function of the concentration and laser intensity. The response has been attributed to an effective 3rd order susceptibility, {χ} rsub {eff} rsup {(3)} = {χ} ^ {(1)} : {χ} ^ {(1)} , dominated by a cascading process. It has been demonstrated that the nonlinear optical behavior of porphyrins strongly depends on the metal incorporated and the pulse duration when compared to lifetimes of the excited states. These results also demonstrate that the extension of π- conjugated electronic systems increases the third order nonlinearities of these complexes, which should be useful in the development of new materials. This property appears to be interesting for the synthesis of more complex porphyrins with other substituents. The high impact on the coefficients related to the NL absorption and refraction gives porphyrins great potential of use for applications in optical limiting, optical switching