Abstract In this paper, the optical properties of magnetic fluid thin films are studied. We present the experimental observation of optical linear birefringence and dichroism in magnetic fluid thin film induced by crossed magnetic field perpendicular to the direction of light propagation. According to our results, we ascertain that both the magnetic birefringence and dichroism are existed. Besides, we also find that the relations between magnetic field and magneto-optical effects changed with the applied magnetic field intensity.

Cancer is a major public health problem worldwide due to its poor prognosis. Detection of cancer in the earliest stages is crucial for the success of therapeutic strategies to truly cure the disease. Molecular imaging provides the potential to diagnose and image cancers at an asymptomatic stage. In molecular imaging, the nanoparticles are designed to target the cancer cells. Molecular imaging is capable of assessing the molecular processes within the tumors by detecting the accumulated or targeted nanoparticles. However, for most molecular imaging systems, the background signal is a common problem, obscuring signals from specific probes and limiting sensitive detection. A hybrid imaging technique, entitled magneto-photo-acoustic (MPA) imaging, was developed as a non-invasive imaging tool to detect nanoparticles, which are used to target pathologies, with high sensitivity and specificity. Based on dual-contrast of both optical absorption and magnetic susceptibility, MPA imaging can significantly improve the molecular contrast specificity as well as investigate the interaction of nanoparticles with cells. Studies were performed using tissue-mimicking phantoms, ex vivo tissue sample and in vivo animal models of cancer. The results indicate that, coupled with dual-contrast agent, the molecular MPA imaging will allow not only mapping the pathologies located in the body, but also sensing the molecular and physiological processes. / text

This dissertation has been motivated by the increasing application of sensing technologies in structural health monitoring. Many wireless sensor techniques exist for structural health monitoring while a challenge faced is the finite lifetime of batteries. The objective of this dissertation is to develop passive wireless technology to provide early warning of conditions that damage the structure. In this dissertation, sensing mechanism is proposed based on time and frequency domain characteristics of magneto-inductive (MI) waves. Experimental results are also presented to demonstrate the sensing mechanism. MI waves are predominantly magnetic waves that are supported in periodic arrays of magnetically coupled resonators and propagate within a narrow frequency band around the resonant frequency. The array is to be embedded in a structure and different types of transducers can be integrated for different sensing applications. With the onset of structure defect, the transducer introduces an impedance discontinuity that generates reflected MI waves along the array, which are monitored and processed by Smoothed Wigner-Ville distribution (WVD) to extract time-of-flight for frequency components in the narrow passband. The transmission and reflection coefficients of MI waves are also investigated based on the lumped-element circuit model of the array. Based on MI waves travel time, amplitude and group velocity, the position and severity of structure defect are decided. The sensing mechanisms for different distribution of defects are proposed. The validity of the sensing mechanism is examined in experiments. The guided wave testing is implemented in one-dimensional square-shaped printed spiral resonators with Q-factor of 161 at 13.6 MHz. It demonstrates that low MI waves propagation loss is achieved with value of 0.098 dB per element at mid-band with center-to-center distance of half an inch. A pitch-catch measurement system is built to capture traveling MI signal in resonant element and extract group velocity, and a pulse-echo measurement system is designed to monitor reflected MI signal and locate structure discontinuity. In both measurement systems, MI waves are excited with wide bandwidth voltage pulse, and a digitizer is attached to sense the MI signal in a specific resonant element circuit. A baseline signal is obtained from the healthy state to use as reference and comparison with the test case using pitch-catch system. The test signal subtracted from baseline signal infers the structure damage information with time and frequency domain characteristics. It can offer an effective method to estimate the structure discontinuity location, severity and type of damage. The experimental results are consistent with the theoretical predictions. At the end, future directions for the research to integrate with other technologies are suggested. / text

Articial spin ice structures are two-dimensional systems of lithographically fabricated lattices ofelongated ferromagnetic islands, which interact via dipolar interaction. These systems have beenshown to be a suitable playground to study the magnetic, monopole-like, excitations, similar tothose in three-dimensional rare-earth pyrochlores. Therefore, such articial structures can be potentialmaterials for investigations of magnetricity [1]. The investigations of these articial spin icestructures stretches from the direct imaging of the magnetic congurations among the islands to indirectinvestigation methods allowing to determine the phase transitions occurring in such systems. Inthis project, square articial spin ice arrays were investigated employing magneto-optical Kerr eectfor the measurement of the magnetic susceptibility. The susceptibility dependence on temperaturewas measured at dierent frequencies of the applied AC magnetic eld for arrays of the dierentisland spacing and at two dierent incident light directions with the respect to the direction of theislands. A peak shift of the real part of susceptibility, χ', with increasing frequency towards thehigher temperatures was observed. Furthermore, a rough estimation of the relaxation times of themagnetic moments in the islands is given by the analysis of the susceptibility data.

Nonlinear magneto-optical effects, originated from atomic coherence, are studied both theoretically and experimentally in thermal Rb vapor. The analytical description of the fundamental properties of coherent media are based on the simplified three- and four-level systems, and then verified using numerical simulations and experimental measurements. In particular, we analyze the modification of the long-lived atomic coherence due to various physical effects, such as reabsorption of spontaneous radiation, collisions with a buffer gas atoms, etc. We also discuss the importance of the high-order nonlinearities in the description of the polarization rotation for the elliptically polarized light. The effect of self-rotation of the elliptical polarization is also analyzed. Practical applications of nonlinear magneto-optical effects are considered in precision metrology and magnetometery, and for the generation of non-classical states of electromagnetic field.

This thesis provides a summary of the laser system constructed in the Quantum Degenerate Gases Laboratory for laser cooling and trapping of 85/87Rband 6Li as well as of experiments that have been pursued in our lab to date. The first chapter provides an overview of the experimental focus of the QDG lab. The second and third chapters provide the fundamental theory behind laser cooling and trapping. The fourth chapter provides details of the laser system. The fifth chapter describes an experiment performed on the subject of dual-injection, performed in collaboration with Dr. James Booth of the British Columbia Institute of Technology (BCIT) involving the dual-injection of a single slave amplifier. The last chapter describes the progress made on the experimental setup needed for the study of Feshbach resonances between 85/87Rb and 6Li and the photoassociative formation of molecules.

There is strong interest in the use of small low-cost highly sensitive magnetic field sensors for applications (such as small memory and biomedical devices) requiring weak field measurements. Among weak-field sensors, the magneto-impedance (MI) sensor has demonstrated an absolute resolution on the order of 10-11 T. The MI effect is a sensitive realignment of a periodic magnetization in response to an external magnetic field within small ferromagnetic structures. However, design of MI sensors has relied primarily on trial and error experimental methods along with decoupled models that separate the micromagnetic and classical electromagnetic equations describing the MI effect. To offer a basis for more cost-effective designs, this thesis research presentation begins with a general formulation describing MI sensors, which relaxes assumptions commonly made leading to decoupling. The coupled set of nonlinear equations is solved numerically using an efficient meshless method in a point collocation formulation. For the problem considered, the chosen method is shown to offer advantages over alternative methods including the finite element method. In the case of time, projection methods are used to stabilize the time discretization algorithm while quasi-Newton methods (nonlinear solver) are shown to be more computationally efficient, as well. Specifically, solutions for two MI sensor element geometries are presented, which were validated against published experimental data. While the examples illustrated here are for MI sensors, the approach presented can also be extended to other weak-field sensors like fluxgate and Hall effect sensors.

Highly sensitive magneto-optical techniques have been used to investigate weak linear and nonlinear optical absorption mechanisms in p- and n-type InSb. As a result, new absorption processes involving both impurities and free carriers have been identified and studied in detail. For p-InSb, magneto-optical spectra has been obtained over a wide range of temperatures and photon energies. The spectra obtained at higher sample temperatures are seen to result from combined-resonance transitions of free holes between heavy-and light-hole Landau levels, while bound-hole transitions between ground heavy-hole-like and excited light-hole-like acceptor states are observed at lower temperatures. Analysis of the combined-resonance data along with extensive intra-conduction band and two-photon interband data using a modified Pidgeon and Brown 8X8 energy band model has allowed the determination of a single set of band parameters for InSb that quantitatively describes these different sets of data. In addition, a ground state binding energy of 8.1 meV for Cd acceptors and 42.5 meV for Au acceptors has been extracted from the analysis of the bound-hole spectra. For n-lnSb, photo-Hall techniques have been developed and used to study both resonant impurity and two-photon magneto-absorption (TPMA) processes in detail. As a result, LO-phonon-assisted impurity cyclotron resonance harmonic (LOICRH) transitions from the shallow Te donor level have been observed for the first time. In addition, transitions from deep levels are also observed in the photo-Hall signal obtained at sample temperatures greater than 20K. Both time-resolved and intensity-dependent measurements on impurity and TPMA processes are reported and the results compared directly with the predictions of rate equations describing the photoexcited carrier dynamics. These investigations have yielded important information about the optical properties of n-InSb; e.g. impurity and two-photon absorption coefficients, photo-excited carrier lifetimes, and recombination rates.

Neste trabalho foram estudadas as propriedades morfológicas, estruturais e magnéticas de nanoestruturas de Fe crescidas em Si(111) vicinal. A análise de superfície foi feita usando microscopia de força atômica e microscopia de tunelamento, e as medidas de caracterização estrutural, por espectroscopia de absorção de raios-X. As propriedades magnéticas foram investigadas usando dois métodos distintos: efeito Kerr magneto-óptico e magnetômetro de força de gradiente alternado. Os substratos foram preparados quimicamente com uma solução NH4F e caracterizados por microscopia de força atômica. As análises morfológicas das superfícies permitiram classificá-las em dois grupos: Si(111)- monoatômicos e Si(111)-poliatômicos. Filmes finos de ferro de 1.5, 3, 6 e 12 nm foram crescidos sobre eles. A análise das superfícies indicou dois modos diferentes de crescimento do ferro; o sistema Fe(x)Si(111)-monoatômico resulta em grãos de ferro aleatoriamente distribuídos, e o sistema Fe(x)Si(111)-poliatômico em nanogrãos de ferro alongados na direção perpendicular aos degraus, auto-organizados. Particularmente no filme Fe(3 nm)/Si(111)-poliatômico, ao redor de metade dos grãos estão alinhados ao longo da direção [110] , ou seja, paralelo aos degraus. O padrão de nanogrãos de ferro alongados orientados perpendicular aos degraus foi interpretado com uma conseqüência da anisotropia induzida durante o processo de deposição e a topologia do substrato Si(111)-poliatômico. Uma forte relação entre a morfologia e a resposta magnética dos filmes foi encontrada. Um modelo fenomenológico foi utilizado para interpretar os dados experimentais da magnetização, e uma excelente concordância entre as curvas experimentais e calculadas foi obtida.

Submitted by Marcio Filho (marcio.kleber@ufba.br) on 2017-06-09T13:11:51Z No. of bitstreams: 1 Dissertação - Tiago Torres - Final.pdf: 3067345 bytes, checksum: 1842568e20cde36ba7250ab0f179b3d0 (MD5) / Approved for entry into archive by Vanessa Reis (vanessa.jamile@ufba.br) on 2017-06-16T14:05:42Z (GMT) No. of bitstreams: 1 Dissertação - Tiago Torres - Final.pdf: 3067345 bytes, checksum: 1842568e20cde36ba7250ab0f179b3d0 (MD5) / Made available in DSpace on 2017-06-16T14:05:42Z (GMT). No. of bitstreams: 1 Dissertação - Tiago Torres - Final.pdf: 3067345 bytes, checksum: 1842568e20cde36ba7250ab0f179b3d0 (MD5) / Este trabalho tem como objetivo apresentar uma proposta para o controle de um sistema de suspensão veicular semiativo utilizando um amortecedor magneto-reológico e um controlador baseado na técnica de controle preditivo baseado em modelo (MPC – Model-Predictive Control). O princípio de funcionamento dos amortecedores magnetoreológicos é evidenciado e o modelo de Bouc-Wen modificado é utilizado no trabalho. O controlador MPC é projetado para produzir a força ideal a ser utilizada pelo amortecedor, assegurando que a magnitude das forças calculadas pela lei de controle satisfaça às restrições físicas de passividade do amortecedor. A tensão requerida para o amortecedor MR produzir a força de controle estimada pelo controlador MPC é calculada por um algoritmo de controle clipped-optimal. Um modelo matemático não linear de um quarto de veículo com 2 graus de liberdade é utilizado e o desempenho do controle MPC proposto para o sistema de suspensão semiativa é investigado através de simulações numéricas e comparado com o desempenho do controlador LQR. Realiza-se a análise do desempenho dos controladores considerando excitações de estrada com perfil rampa, lombada, buraco e senoidal. Os resultados das simulações demonstram que o controle MPC proposto com malha de controle interna reduz as oscilações na carroceria, mantendo os níveis de aceleração abaixo dos considerados desconfortáveis pela norma BS 6841 (1987), contribuindo para o conforto dos passageiros. Também contribui com o aumento da segurança do veículo e melhora sua dirigibilidade, reduzindo o deslocamento vertical do conjunto eixo e roda e o espaço de trabalho do amortecedor. Além disso, o MPC mostra-se mais eficiente, reduzindo o consumo de energia pelo amortecedor.