Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 3, 2008) Includes bibliographical references (p. 66-74).

This thesis presents a compact femtosecond laser amplifier design for optical preamplifiers and power amplifiers consist of theoretical perspective, simulations to analyze and optimize beam performance. The propagation through optical media is simulated for every optical component such as mirrors and nonlinear crystal separately and suggested realignment of these components required increasing amplifier performance. Finally Gaussian beam propagation and aberration compensation has been conducted.

Thesis (Ph.D.) - University of St Andrews, March 2007.

In this thesis, the development of a femtosecond Cr⁴⁺:forsterite solid-state laser is described where the mode-locking procedure was initiated using two novel saturable absorbers. One was a GaInNAs quantum-well device and the other a quantum-dot-based saturable absorber. These devices had not previously been exploited for the generation of femtosecond pulses from a solid-state laser but in the course of this project, successful mode-locked laser operation in the femtosecond domain was demonstrated for both devices. When the GaInNAs device was incorporated in the Cr⁴⁺:forsterite laser, transform-limited pulses with durations as short as 62fs were obtained. The performance of this femtosecond laser was significantly superior to that for previous quantum-well based saturable absorbers in the 1300nm spectral region. The dynamics of the device were investigated with the aim of refining subsequent devices and to explore the potential to grow future devices for use at longer wavelengths. At the outset of my research work quantum-dot based saturable absorbers had not be used for the mode locking of solid-state lasers in the femtosecond regime. The work presented in this thesis showed that quantum-dot structures could be exploited very effectively for this purpose. This was initially achieved with the quantum-dot element being inclined at an off-normal incidence within the cavity but experimental assessment together with further development of the device allowed for implementation at normal incidence. Reliable operation of the femtosecond laser was demonstrated very convincingly where transform-limited pulses of 160fs duration were generated. Having developed practical femtosecond Cr⁴⁺:forsterite lasers, the final part of the project research was directed towards exemplar applications for a laser operating in the 1300nm spectral region. These were biophotonics experiments in which assessments of both deep tissue penetration and two-photon chromosome cutting were undertaken. This work confirmed the suitability of the 1300nm laser radiation for propagation through substantial thicknesses of biological tissue (~15cm). The demonstration of highly localised two-photon cutting of Muntjac deer chromosomes also represented a novel result because single-photon absorption could be avoided effectively and the temporal broadening of the femtosecond pulses in the delivery optics arising from group velocity dispersion around 1300nm was minimal.

Este trabalho utilizou pulsos laser ultracurtos para modificar, de forma controlada, as características dimensionais de nanopartículas de prata em solução aquosa. Para atingir este objetivo foram empregados algoritmos genéticos e circuitos microfluídicos. Utilizou-se um conformador temporal de pulsos ultracurtos para criar diversos perfis temporais de pulsos que irradiaram soluções de nanopartículas de prata. Estes perfis temporais foram ajustados em tempo real, visando otimizar o resultado do experimento, quantificada pela diminuição do diâmetro médio das nanopartículas nas soluções irradiadas. Uma vez que cada experimento de minimização do diâmetro das nanopartículas exigiu centenas de medidas, sua realização foi possível em decorrência da utilização de um circuito microfluídico construído especialmente para este trabalho. Neste circuito é possível utilizar pequenas quantidades de amostra, levando a curtos tempos de irradiação e medição, além da evidente economia de amostras. Para a realização deste trabalho foi elaborado e testado um algoritmo genético interfaceado a diversos equipamentos, incluindo um filtro acustóptico dispersivo programável que modifica as características temporais dos pulsos ultracurtos, através da introdução de componentes de fases espectrais nestes pulsos. Utilizando o algoritmo genético e o filtro acustóptico dispersivo programável foram realizados experimentos de encurtamento da duração temporal dos pulsos ultracurtos provenientes do sistema laser, resultando na obtenção de pulsos com durações próximas às limitadas por transformada de Fourier. Além disso, foram realizados experimentos para a otimização do processo evolutivo do algoritmo genético escrito em Labview. Os experimentos de irradiação de soluções de nanopartículas de prata mostraram que, ao conformar a duração dos pulsos utilizados nas irradiações, pôde-se controlar as dimensões destas nanopartículas, diminuindo seu tamanho médio por um fator 2. Esses experimentos caracterizam a irradiação de nanopartículas por lasers de pulsos ultracurtos como uma importante técnica de controle de características de nanopartículas. / This work used ultrashort laser pulses to modify, in a controlled way, the dimensional characteristics of silver nanoparticles in aqueous solution. To reach this goal, genetic algorithm and microfluidic circuits were used. A pulse shaper was used to create different temporal profiles for the ultrashort pulses used to irradiate the silver nanoparticle solutions. These temporal profiles were conformed in real time, aiming to optimize the experiment result, quantified by the decrease of the average diameter of the nanoparticles in the irradiated solutions. Since each nanoparticle diameter minimization experiment demanded hundreds of measurements, its achievement was possible by the use of a microfluidic circuit specially built for this work. This circuit enables the use of small sample quantities, leading to short irradiation and measurement intervals, besides evident sample savings. To make this work possible, a genetic algorithm was created and tested. This genetic algorithm was interfaced to several equipments, including an acustooptic programmable dispersive filter that modifies the ultrashort pulses temporal characteristics by the introduction of spectral phases in the pulses. The genetic algorithm and the acustooptic programmable dispersive filter were used in conjunction in experiments to temporally shorten the ultrashort pulses from the laser system, generating pulses durations close to the Fourier transform limited ones. Besides, experiments were performed with the Labview coded genetic algorithm to optimize its evolutionary process. The silver nanoparticles irradiation experiments showed that the ultrashort pulses temporal conformation allowed the control of these particles dimensions, decreasing its mean size by a factor of 2. These experiments characterize the nanoparticles irradiation by ultrashort pulses as an important technique to control the nanoparticles characteristics.

Este trabalho utilizou pulsos laser ultracurtos para modificar, de forma controlada, as características dimensionais de nanopartículas de prata em solução aquosa. Para atingir este objetivo foram empregados algoritmos genéticos e circuitos microfluídicos. Utilizou-se um conformador temporal de pulsos ultracurtos para criar diversos perfis temporais de pulsos que irradiaram soluções de nanopartículas de prata. Estes perfis temporais foram ajustados em tempo real, visando otimizar o resultado do experimento, quantificada pela diminuição do diâmetro médio das nanopartículas nas soluções irradiadas. Uma vez que cada experimento de minimização do diâmetro das nanopartículas exigiu centenas de medidas, sua realização foi possível em decorrência da utilização de um circuito microfluídico construído especialmente para este trabalho. Neste circuito é possível utilizar pequenas quantidades de amostra, levando a curtos tempos de irradiação e medição, além da evidente economia de amostras. Para a realização deste trabalho foi elaborado e testado um algoritmo genético interfaceado a diversos equipamentos, incluindo um filtro acustóptico dispersivo programável que modifica as características temporais dos pulsos ultracurtos, através da introdução de componentes de fases espectrais nestes pulsos. Utilizando o algoritmo genético e o filtro acustóptico dispersivo programável foram realizados experimentos de encurtamento da duração temporal dos pulsos ultracurtos provenientes do sistema laser, resultando na obtenção de pulsos com durações próximas às limitadas por transformada de Fourier. Além disso, foram realizados experimentos para a otimização do processo evolutivo do algoritmo genético escrito em Labview. Os experimentos de irradiação de soluções de nanopartículas de prata mostraram que, ao conformar a duração dos pulsos utilizados nas irradiações, pôde-se controlar as dimensões destas nanopartículas, diminuindo seu tamanho médio por um fator 2. Esses experimentos caracterizam a irradiação de nanopartículas por lasers de pulsos ultracurtos como uma importante técnica de controle de características de nanopartículas. / This work used ultrashort laser pulses to modify, in a controlled way, the dimensional characteristics of silver nanoparticles in aqueous solution. To reach this goal, genetic algorithm and microfluidic circuits were used. A pulse shaper was used to create different temporal profiles for the ultrashort pulses used to irradiate the silver nanoparticle solutions. These temporal profiles were conformed in real time, aiming to optimize the experiment result, quantified by the decrease of the average diameter of the nanoparticles in the irradiated solutions. Since each nanoparticle diameter minimization experiment demanded hundreds of measurements, its achievement was possible by the use of a microfluidic circuit specially built for this work. This circuit enables the use of small sample quantities, leading to short irradiation and measurement intervals, besides evident sample savings. To make this work possible, a genetic algorithm was created and tested. This genetic algorithm was interfaced to several equipments, including an acustooptic programmable dispersive filter that modifies the ultrashort pulses temporal characteristics by the introduction of spectral phases in the pulses. The genetic algorithm and the acustooptic programmable dispersive filter were used in conjunction in experiments to temporally shorten the ultrashort pulses from the laser system, generating pulses durations close to the Fourier transform limited ones. Besides, experiments were performed with the Labview coded genetic algorithm to optimize its evolutionary process. The silver nanoparticles irradiation experiments showed that the ultrashort pulses temporal conformation allowed the control of these particles dimensions, decreasing its mean size by a factor of 2. These experiments characterize the nanoparticles irradiation by ultrashort pulses as an important technique to control the nanoparticles characteristics.

Technologies laser pour l’élaboration de matériaux carbonés pour microsystèmes analytiques environnementaux. Pas de résumé en français fourni / Amorphous carbon nitride (a-CzN) material has attractor much attention in research and development. Recently, it has become a more promising electrode material than conventional carbon based electrodes in electrochemical and biosensor applications. Nitrogen containing amorphous carbon (a-C:N) thin films have been synthesized by femtosecond pulsed laser deposition (fs-PLD) coupled with plasma assistance through Direct Current (DC) bias power supply. During the deposition process, various nitrogen pressures (0 to 50 Pa) and DC bias (0 to -350 V) were used in order to explore a wide range of nitrogen content into the film. The structure and chemical composition of the films have been studied by using Multi-wavelength (MW) Roman spectroscopy, electron energy-loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTBM). The surface morphology has been studied by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Increasing the nitrogen pressure or adding a DC bias induced an increase of the N content, up to 28 at.%. Nitrogen content increase induces a higher sp2 character of the film. However DC bias has been found to increase the film structmal disorder, which was detrimental to the electrochemical properties. Indeed the electrochemical measurern-ts, investigated by cyclic voltammetry (CV), demonstrated that the a-CzNfilms show better electron transfer kinetics, reversibility and excellent reproducibility than the pure a-C films. Electrochemical grafting from diazoniurn salts was successfully achieved on this film, with a surface coverage of covalently bonded molecules close to the dense packed monolayer of ferrocene