This thesis presents the investigations of femtosecond laser machining on three different dielectric materials, namely quartz, sapphire and diamond. The laser micromachining experiments were performed with a Titanium:Sapphire solid state laser with a repetition rate of 1 kHz, centered at a wavelength of 800 nm and pulse duration of 150-200 femtoseconds (fs). A 5x microscope objective for surface micromachining and a 50x microscope objective for subsurface micromachining. The 50x microscope objective was used to obtain a smaller spot size and a shorter confocal parameter. The purpose of this research was to study the interaction between the femtosecond laser pulses and quartz, sapphire and diamond which have bandgap energies of 8.4 eV (λ=148 nm), 9.9 eV (125 nm), and c)· diamond 5.5 eV (225 nm) respectively. Since the photon energy of the laser was below the wide bandgap energies of the aforementioned dielectrics, the materials were essentially transparent to the incident laser. In order to study the behavior of the dielectric materials under femtosecond laser irradiation, several experiments with varying type and number of pulses (N) were performed, such as single pulse ablation, plural pulse ablation (N ≤ 100 pulses), multiple pulse ablation (N ≤ 100 pulses), and continuous lines micromachining on the surface and in the sub-surface of materials were performed. The features, damage, and structural changes introduced by femtosecond laser irradiation on the materials studied were characterized through examination of both the plan and cross-section views. The characterization process was carried out using optical microscopy (operated in the Nomarski mode), scanning electron microscopy, focused ion beam, atomic force microscopy, and transmission electron microscopy. The laser micromachining demonstrated distinct behaviors of the three wide bandgap materials. Quartz was very prone to cracking and showed nearwavelength alternating crystalline and amorphous sub-structure with the orientation parallel with respect to the electric field direction. Sapphire showed sub-wavelength ripples formation in lower fluences. Finally, diamond showed a strong tendency for ripples formation from near- to sub-wavelength spacing with the orientation of the ripples perpendicular and parallel with respect to electric field polarization. / Thesis / Master of Applied Science (MASc)

A description of several experiments carried out to study the existence of evanescent waves behind totally reflecting dielectric surfaces is given in this thesis. Chapter I describes the experimental apparatus used to generate and measure the electromagnetic radiation. A detailed description of the construction of the radiating horns used and the casting of a plastic prism is also given. Chapters II and III give the results of two experiments in the region behind a totally reflecting face of the plastic prism and similar effects noted behind a lucite semicylinder with its plane face towards the source of radiation. Near field diffraction patterns of this cylinder with its plane face towards the source, away from the source, and parallel to the axis of radiation are also given. The above three cases are compared with results obtained by coating the semicylinder with aluminum foil. / Thesis / Master of Science (MSc)

Success in geotechnical analysis, design, and construction invariably requires that we have proper knowledge and understanding of (1) the strength, (2) the fluid flow properties, and (3) the stress-deformation behavior of the earth materials. These important engineering properties are primarily determined by the components and structure of a soil, which also dictate the soil's responses in an electromagnetic field. As a nondestructive technique, the electromagnetic property measurement offers a promising approach to characterize earth materials and identify the effects of changes in environments. However, despite many investigations in the last several decades, the relationship between the frequency-dependent electromagnetic properties of soils and their components and structure are still not well understood. Hence, estimation of engineering properties of a soil in a quantitative way from electromagnetic measurements can be uncertain. In this research several tasks have been accomplished: (1) Development of a physically based model that provides a means of investigating the coupled effects of important polarization mechanisms on soil electromagnetic properties, and a means of relating the electromagnetic properties of a soil to its fines content, clay mineralogy, anisotropy, degree of flocculation and pore fluid chemistry; (2) Proposal of a practically applicable method to determine the volumetric water content, specific surface area and pore fluid salt concentration simultaneously from the dielectric spectrum; (3) Deduction of the wide-frequency electromagnetic properties of a soil by measuring its responses to a step pulse voltage using time domain reflectometry (TDR); (4) Establishment of the relationships between the specific surface area and compressibility, residual shear strength and hydraulic conductivity. This study establishes a framework for quantifying soil engineering properties from their electromagnetic properties. If properly determined and interpreted, the electromagnetic properties can also provide insights into the causes of soil property changes over time and can be very useful in studying the effects of biological factors in geotechnical engineering, a field that may offer great potential for future advances. / Ph. D.

The benefits of applying microwave energy to material processing techniques have been well documented and studied. The potential benefits over conventional oven heating include faster processing times, more uniform heating, more consistent product quality, and the possibility of precise control. The actual implementation of microwave technology has been lacking and the benefits have gone largely unrealized. This is due in part to the temperature dependence of the dielectric loss of many industrial materials such as ceramics and polymers. These materials absorb more microwave energy as they heat, creating uncontrollable heating, often called 'thermal runaway'. The focus of this research is to address this challenge. The work described here is an experimental program for the microwave processing of specific ceramic rods and polymer tows. The objective of the program is to study the thermal runaway effect, and to provide data which will be used to verify numerical models. Accurate test data are essential to the development of precise, comprehensive models that can be used in applicator design and heating control strategies for thermal runaway materials. The experimental program explores the difficulties of microwave heating and offers solutions to more efficient systems. Successful measurements of power loss and control of thermal runaway are detailed for mullite, alumina, and nylon. / Master of Science

The prime result has been the development of an experimental procedure for producing a definite dielectric effect when water is added to an acetone solution of cellulose nitrate. This effect depends not only on the purity, dryness and concentration of the cellulose nitrate, but also on the average degree of polymerization. This last dependency is shown in Figure V, and its theoretical aspects will be discussed in the next section. The discontinuity at the precipitation region is a general effect, not depending on such extreme conditions. / M.S.

Periodic gratings in waveguides act as frequency selective mirrors making them very useful as spectral filters for wavelength division multiplexing applications and as end mirrors for narrow linewidth lasers. A study of the spectral characteristics of both single and double gratings in planar dielectric waveguides is presented. The analysis of light propagation in a planar dielectric waveguide with sinusoidal boundary perturbations is carried out using coupled-mode theory. Power reflection and transmission coefficients are calculated for single gratings as well as two gratings of the same period and depth but arbitrary lengths and separated by a specified distance. The spectral response is examined for several cases. The influence of grating period, depth, and length in the single-grating case as well as separation of the gratings in the case of a double grating is investigated. Numerical results for example cases are presented. The results of this study are valuable for designing grating devices which are becoming increasingly attractive to broadband fiber-optic communication systems. / Master of Science

Neste trabalho foi desenvolvido um dispositivo, denominado forno de indução eletromagnética (FIE), que permite trabalhar em altas temperaturas ~ 1900oC e com vácuo dinâmico equivalente a uma pressão parcial de oxigênio PO2 ~ 10-10 atm. Durante os experimentos de calibração do FIE, foram estudadas amostras de um composto binário de Y2O3 com 3% em mol de ZrO2, cujo pó foi obtido por mistura de óxidos. As amostras foram conformadas por prensagem uniaxial de 50 MPa, seguida de prensagem isostática a 350 MPa por 10 minutos e submetidas à sinterização em temperaturas superiores a 1800oC, resultando em transparência superior a 60% para comprimentos de onda em torno de 800 nm. Posteriormente, um composto quaternário de BaTi0.85Zr0.15O3 foi produzido por mistura de óxidos e calcinação a 1200oC. As amostras foram então conformadas seguindo a mesma metodologia da Y2O3, posteriormente sinterizadas entre 1250oC a 1400oC, com patamares de 1 h e 3 h. As amostras preparadas no FIE foram submetidas a uma pressão parcial de oxigênio de ~ 10-7 atm, enquanto outro conjunto de amostras foi sinterizado em um forno elétrico convencional (FEC) com atmosfera aberta para comparação. Foram realizadas caracterizações microestruturais aplicando-se as técnicas de difração de raios X, BET, EDX, microscopia eletrônica de varredura, além de caracterização elétrica por espectroscopia de impedância. Destas caracterizações verificou-se a obtenção de partículas do pó de BaTi0.85Zr0.15O3 com tamanho médio de 110 nm. O tamanho médio dos grãos nas microestruturas variou entre 4 e 30 &microm nas amostras fabricadas em FEC, enquanto nas amostras fabricadas em FIE o tamanho foi em torno de 250 nm. Para as amostras feitas no FEC, a resposta dielétrica dos grãos evidenciou o cumprimento da lei de Curie-Weiss conforme o modelamento bricklayer feito no programa Zview, porém foi observada anomalia dielétrica para medidas de permissividade em temperaturas maiores do que 96oC. O material feito no FIE não apresentou comportamento ferroelétrico no intervalo de temperatura estudado de -243 - 137oC, mas foi evidenciado um comportamento típico de material varistor. Considerando a relação entre as propriedades macro e microscópicas no modelo bricklayer, a ferroeletricidade e a variação da anomalia dielétrica são discutidas em função do tamanho de grãos para as amostras feitas no FEC. Com base no modelo de Pike para varistores, o comportamento varistor do material feito no FIE é discutido em função dos defeitos causados pela baixa pressão parcial de oxigênio ~ 10-7 atm. / In this work it has been developed a device, called electromagnetic induction furnace (EIF), which allow us to work at high temperatures ~ 1900oC and under dynamic vacuum equivalent to partial pressure of oxygen PO2 ~ 10-10 atm. During the calibration experiments of the EIF, it was studied a binary compound of Y2O3 with 3 mol% of ZrO2 which was obtained by mixing oxides. The samples were processed by uniaxial pressing 50 MPa followed by isostatic pressing at 350 MPa for 10 minutes and submitted to sintering at temperatures above 1800 oC, resulting in transparency greater than 60% for wavelengths around 800 nm. After, a quaternary compound of BaTi0.85Zr0.15O was produced by mixing oxides and calcination at 1200 oC. Then the samples were shaped according to the same methodology of the Y2O3 subsequently sintered between 1250oC to 1400 oC, with 1 h and 3 h baseline. The samples prepared in the EIF were submitted to oxygen partial pressure of ~ 10-7 atm, while another samples set was sintered in a conventional electric furnace (CEF) with open atmosphere for comparison. Microstructural characterizations were performed by applying the techniques of X-ray diffraction, BET, EDS, SEM, and electrical characterization by impedance spectroscopy. In these characterizations were obtained powder particles of BaTi0.85Zr0.15O3 with an average size of 110 nm. The average grain size in the microstructures ranged between 4 and 30 &microm in the samples fabricated in CEF, but in the samples manufactured in EIF the size has been around 250 nm. For samples made in the CEF, the dielectric response of the grains showed the fulfillment of the Curie-Weiss law according to the bricklayer model made in the Zview program, but was observed dielectric anomaly on measurements of permittivity at temperatures higher than 96 oC. The material made in EIF does not showed ferroelectric behavior in the studied temperature range -243 - 137 oC, but was shown a typical behavior of varistor material. Considering the relationship between macroscopic and microscopic properties in the bricklayer model, the ferroelectricity and the dielectric anomaly variation are discussed at function of the grain size for samples made in CEF. Based on the model of Pike for varistors, the varistor behavior of the material made in EIF is discussed in terms of defects caused by low oxygen partial pressure ~ 10-7 atm.

Thesis advisor: Michael J. Naughton / Surface plasmon polaritons (SPPs) are hybridized quasiparticles of photons and electron density waves. They are confined to propagate along metal-dielectric interfaces, and decay exponentially along the direction perpendicular to the interfaces. In the past two decades, SPPs have drawn intensive attention and undergone rapid development due to their potential for application in a vast range of fields, including but not limited to subwavelength imaging, biochemical/biomedical sensing, enhanced light trapping for solar cells, and plasmonic logic gates. These applications utilize the following intrinsic properties of SPPs: (1) the wavelength of SPPs is shorter (and can be much shorter) than that of free photons with the same frequency; (2) the local electric field intensity associated with SPPs can be orders of magnitude larger than that of free photons; and (3) SPPs are bound to metal surfaces, and are thus easily modulated by the geometry of those surfaces. Here, we present studies on SPPs along metal surfaces with novel structures, including the following: (1) SPP standing waves formed along circular metal surfaces that lead to a "plasmonic halo" effect; (2) directional reflectionless conversion between free photons and SPPs in asymmetric metal-insulator-metal arrays; and (3) broadband absorbance enhancement of embedded metallic nanopatterns in a photovoltaic absorber layer. These works may prove useful for new schemes for SPP generation, plasmon-photon modulation, ultrasensitive dielectric/bio sensing, and high efficiency thin film solar cells. / Thesis (PhD) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Desenvolveu-se um sistema para medir a constante dielétrica complexa de amostras dielétricas, de construção simples, versátil e de baixo custo. A medida é feita aplicando-se uma tensão senoidal e fazendo-se a aquisição do sinal aplicado e do sinal da resposta elétrica (carga elétrica). Emprega-se uma placa A/D para a aquisição de dados com taxa de amostragem de 100 Ksamples/seg e através da transformada de Fourier discreta destes sinais determina-se a impedância complexa da amostra, a partir da qual calcula-se a constante dielétrica complexa. A placa utilizada e o circuito de medida da carga elétrica introduzem defasagens indesejáveis nos sinais, cujas correções são feitas através de programa no computador usado para aquisição dos sinais. O sistema mostra um desempenho similar àqueles dos equipamentos comerciais para freqüências no intervalo de 0,1H.z a 1KHz, sendo testado com componentes resistivos e capacitivos e posteriormente em amostras de Teflon FEP, poli(fluoreto de vinilideno) e seus copolímeros com trifluoretileno. O sistema também foi utilizado para medir o deslocamento elétrico nos polímeros ferroelétricos sob a aplicação de campos elevados. Neste caso determinaram-se as curvas de histerese dielétrica e os deslocamentos de primeira, segunda e terceira ordem. / A low cost and a simple experimental system for measuring the complex dielectric constant of dielectric samples were developed. Measurements were performed measuring the electric charge response resulting from the application of a sinusoidal voltage. The system was based on an A/D acquisition board with sampling rate of 100 Ksamples/sec. The complex impedance was calculated using the discrete Fourier transform from which the complex dielectric constant was found. The phase differences introduced by the A/D board and the amplifiers circuits were connected by software. The setup showed that the results are comparable to that ones obtained with commercial impedance analyzers in the range of frequencies between 0.1 Hz and 1 KHz. Such measurements were obtained using resistors and/or capacitors and also using samples of Teflon FEP, PVDF and its copolymers with trifluorethylene. The setup was also capable to measure the electric displacement in ferroelectric polymers submitted to high fields. Hysteresis loops and the nonlinear electric displacement of first, second and third order were measured.

Thesis (Elec.E)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Includes bibliographical references. / by Huan Lim Lee. / Elec.E