Thesis (M. Sc.)--University of Manitoba, 1995. / Includes bibliographical references.

Thesis (Ph.D.) - University of St Andrews, November 2009. / Restricted until 5th November 2011.

Thesis (Ph. D.)--University of Florida, 1985. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 185-193).

Thesis (Ph. D.)--Oregon Graduate Center, 1985.

This thesis is concerned with the design and development of compact, all-solid-state femtosecond pulse lasers with low pump power requirements. A number of directly-diode- pumped laser systems based on the gain materials Cr3:LiSrGaF6 (chromium-doped lithium strontium aluminium fluoride) and Cr3:LiSrGaF6 (chromium-doped lithium strontium gallium fluoride) pumped with AlGaInP laser diodes are described. The motivation behind this work was the development of portable, low-noise and lower cost ultrashort pulse lasers for a number of low-power applications such as the characterisation of electron-optical streak camera systems. The investigation into the modelocking of lasers with modest intracavity powers was also an important challenge. The achievement of a battery-powered, compact and efficient laser system represents an excellent outcome for this research programme. Major consideration is given to the key factors that determine both the cw and modelocking thresholds of an ultrashort-pulse laser. In particular, the reduction of intracavity optical losses by designing the laser to operate with fewer cavity elements, the optimisation of second-order and higher-order dispersion for efficient modelocked operation and the inclusion of a semiconductor saturable absorber mirror for increased stability are discussed. This has enabled pump thresholds to be reduced to a level permitting, for the first time, the use of diffraction-limited, narrow-stripe laser diodes for efficient, low-power optical pumping. A number of laser oscillators with novel cavity designs and progressively lower pump thresholds are described. Pulses as short as 57 fs and average output powers as high as 9 mW for only 80 mW of incident pump power are reported for a battery powered femtosecond Cr:LiSAF laser. This represents an overall electrical-to-optical conversion efficiency of approximately 1% which is excellent for a femtosecond pulse laser system. In addition, the amplitude and phase noise performance is shown to be exceptionally good and is believed to be the best yet reported for this type of ultrashort pulse laser. The design and demonstration of highly compact, ultrashort-pulse lasers incorporating novel resonator configurations and simplified dispersion compensation schemes are then described. These lasers produced sub-ps pulses at cavity frequencies as high as 450 MHz.

This thesis describes the development of an intracavity frequency doubled dye laser from a commercial Spectra-Physics 380D single frequency ring dye laser, and the application of this system to a number of spectroscopic studies in discharges. Evaluation of the stability of the laser cavity is carried out, by computer calculation, in order to optimise the optical component set used in the frequency doubled dye laser. Using an ADA (ammonium dihydrogen arsenate) crystal, 17 mW of continuous wave ultra-violet, tunable over the range 292-302 nm, has been produced. The linewidth, when the laser is stabilised, is about 500 kHz in the UV. The CW UV output has been used to measure helium triplet (23S) metastable densities in a positive column discharge as a function of pressure (1-8 Torr) and current (2.5-80 mA). A maximum density of 10x10¹² cm-3 is measured for a pressure of 2 Torr and current of 60mA. The measured metastable densities are used in a rate equation analysis to extract values of the rate coefficient for distraction (by collisions with electrons) of the 23S metastables (1.6x10^-8 cm3s-1 for p = 2 Torr). A study of the optogalvanic signal generated when irradiating a neon positive column discharge with laser light of wavelength 588.2 nm, corresponding to the ls5-2p2 transition, is carried out. The signal is found to change sign as the dye laser power is increased, for some discharge conditions. Spatial studies of the optogalvanic signal in conjunction with absorption and emission studies are carried out to investigate the evolution of the population densities of levels connected to the 1s5 and 2p2 levels. A rate equation model is developed which demonstrates the importance of the 1s3 population density in explaining the observed sign reversal. A high resolution study of two transitions in the UV, in the tungsten spectrum, is presented. The even isotope splittings and the hyperfine splitting between the two strongest hyperfine components on transitions at 294.4 nm and 294.7 nm have been resolved by saturated absorption spectroscopy. From centre of gravity considerations the hyperfine splittings of the three levels involved in the two transitions have been predicted as 1630 MHz for the7s3 level, -506 MHz for the 3692 level and 225 MHz for the 3683 level. A simple wavemeter using a corner-cube Michelson interferometer is described. Digital counting circuits to provide a direct reading of either the fundamental or second harmonic wavelength have been designed and constructed. Wavelength readings accurate to 1 part in 106 are achieved.

By utilising a CW mode-locked Nd:YAG pump laser an experimental study of self-phase modulation (SPM) and stimulated Raman scattering (SRS) in single mode optical fibres has been conducted. The dependence of the spectral broadening due to SPM upon the launched optical power was observed to obey a linear relationship in agreement with a simple theory. A deviation from this occurred for high input powers due to the onset of stimulated Raman scattering which caused a preferential depletion of the leading edge of the pump pulse and an increased spectral broadening to the long wavelength side of the spectrum. The pulses exiting the fibre were then compressed using a pair of holographic diffraction gratings, which were able to compensate for the linear part of the frequency chirp imposed on the pulse by SPM and the 1.06 ?m pulses were reduced in duration from ~ 100 ps to approximately 4 ps by this method. By making use of Raman generation in the fibre, a synchronously pumped fibre Raman oscillator was constructed. This enabled the generation of frequency tunable (1.07 - 1.12 ?m) near infrared pulses by the method of time dispersion tuning. By incorporating two fibre grating reflectors onto the ends of the optical fibre, an all-fibre device was constructed having the potential advantages of compactness and stability. The generation of mode-locked pulses around the 1.5 jim wavelength region was accomplished with the use of a colour centre laser based upon a stabilised F2+ centre in NaC1 or a thallium centre in KCl. Both of these lasers were examined, although to date the poor quality of our NaC1 laser crystals has meant that most of the work reported here was performed with KC1:T1. This laser produced pulses of ? 20 ps duration, tunable over 1.45 - 1.55 ?m with average powers ? 200 mW. A simple experiment to observe soliton propagation of these pulses in an optical fibre was conducted and this compressed the pulses to ? 0.8 ps, although this does not represent the optimum compression that could be achieved. Using nonlinear pulse propagation in an optical fibre, the mode-locked characteristics of the colour centre laser were dramatically improved with the duration of the pulses from the laser being reduced to ? 200 fs. This enhancement was achieved by the use of a nonlinear external cavity containing the optical fibre, which reinjected the pulses back into the main laser cavity, with an increased spectral bandwidth due to SPM. It was initially thought that the explanation to this effect was due to soliton formation within the control cavity, however experimental evidence is presented here which shows that the mode-locking enhancement phenomena is in fact quite general and does not rely on dispersion in the control cavity.

Recent advances in the development of high power short pulse laser systems has opened a new regime of laser plasma interactions for study. The thesis is presented in two parts. In Part I, we consider the implications of these high power laser pulses for the interaction with a uniform underdense plasma, with particular regard to plasma-based accelerators. We present a scheme for the resonant excitation of large electrostatic Wakefields in these plasmas using a train of ultra-intense laser pulses. We also present an analysis of the resonant mechanism of this excitation based on consideration of phase space trajectories. In Part II, we consider the transition from linear Resonance Absorption to nonlinear absorption processes in a linear electron density profile as the intensity of the incident radiation increases and the scale length of the density profile decreases. We find that the electron motion excited by an electrostatic field exhibits some extremely complicated dynamics with bifurcations to period doubling and chaotic motion as the strength of the driving field is increased or the density scale length is decreased. We also present some results obtained from particle simulations of these interactions.

Orientador: Daniel Pereira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-21T14:25:47Z (GMT). No. of bitstreams: 1 Viscovini_RonaldoCelso_M.pdf: 1535704 bytes, checksum: fa0145803f25ac853ae133c9d7ef1d84 (MD5) Previous issue date: 1996 / Resumo: Neste trabalho realizamos, pela primeira vez, o bombeamento óptico da molécula de 13CD3OD utilizando um laser guia de ondas de CO2 de grande sintonizabilidade (290MHz). Com o bombeamento sistemático em 38 linhas das bandas 10R e 10P deste laser, realizamos um estudo de espectroscopia fotoacústica onde pudemos discriminar 69 transições de absorção, associadas ao modo vibracional de estiramento CO do 13CD3OD. Orientados pelos dados fotoacústicos, conseguimos a geração, nesta molécula, de 46 novas linhas laser no infravermelho longíquo (IVL ), que foram caracterizadas quanto ao comprimento de onda, dessintonia, pressão ideal, polaridade e intensidade relativas. A maioria dessas linhas apresentou grande dessintonia, tendo sido possível observá-las devido ao uso do laser de CO2 em guia de ondas. Utilizando-se do modelo torso-roto-vibracional para o 13CD3OD e de constantes moleculares por nós estimadas, pudemos fazer a proposição dos números quânticos ("assignments") de 12 transições laser IVL, trabalho inédito para esta molécula / Abstract: In this work we have done, for the first time, the optical pumping of the 13CD30D. molecule using a CO2 waveguide laser of large tunability (290MHz). By systematically pumping 38 lines from the 10R and 10P branches, we have identified 69 absorption transitions by optoacoustic spectroscopy, associated with the CO stretch Oriented by optoacoustic data we obtain, with this molecule, the generation of 46 new laser lines in the far infrared (FIR) region, which were characterized with respect to their wavelength, offset, ideal working pressure, relative polarity and relative intensity. Most of these lines showed high offset, the observation of which was only possible by using the CO2 waveguide laser. Using the torso-roto-vibrational model for the 13CD30D molecule and the molecular constants estimated by us, we were able to assign quantum numbers to 12 FIR laser transitions, an unpublished work for this molecule / Mestrado / Física / Mestre em Física

Orientadores: Evandro Conforti, Marek Osinski / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-07-22T11:58:31Z (GMT). No. of bitstreams: 1 Leal_AntonioAndrade_D.pdf: 8063861 bytes, checksum: 2b4259cd6d8a16557482afd54970146e (MD5) Previous issue date: 1997 / Resumo: Neste trabalho são elaborados modelos teóricos que visam permitir a análise, compreensão e prevenção d auto-aquecimento em lasers de emissão superficial com cavidade vertical (VCSELs). Um modelo teórico incorporando o efeito da profundidade de penetração do campo nos espelhos é desenvolvido. Este formalismo é usado no estudo do comportamento de limiar de oscilação do laser e do efeito exercido sobre o mesmo pela temperatura de meio ativo. São desenvolvidos modelos simples para o cálculo da resistência térmica de VCSELs de emissão pelo topo, empregando o conceito de condutividade térmica efetiva. Também, apresenta-se um método de cálculo de resistência térmica de VCSELs, no qual o fluxo anisotrópico de calor no interior de cada camada componente da estrutura do laser é considerado / Abstract: In this work, models were developed aiming to allow the analysis, understanding and prevention of self-heating in vertical-Cavity Surface-Emitting Lasers (VCSELs). A model, including the effect of the field penetration depth in the mirror, was developed. This approach was used to study the threshold behavior and the influence of active region temperature on it. Simple approaches to calculate the thermal resistance of top emitting VCSELs were developed using the concept of effective thermal conductivity. Also, a method to calculate the thermal resistance of VCSELs, in which the anisotropic heat flux inside each layer is considered, is presented. / Doutorado / Doutor em Engenharia Elétrica