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Sensing in scattering environments, such as fog and dust, poses a serious challenge for all optical systems and is important for many critical surveillance applications. The use of polarized light, specifically circularly polarized light, has shown great promise for improving detection range and sensing in highly scattering, real-world environments. While the potential impact to application is significant, the optical science and sensing community lacks data on broad wavelength and environmental parameters where circularly polarized light outperforms linearly polarized light, increasing detection range and signal persistence. In this dissertation I quantify, through simulation and experimental results, the advantage of circularly polarized light in laboratory and real-world scattering environments - focusing on circularly polarized light's superior persistence in these environments. I present new and unique contributions to the study of polarized light in both isotropic (Rayleigh regime) and forward-scattering environments, showing circular polarization's superior persistence increases detection range for real-world environments over broad wavelength and particle size regimes. Utilizing polarization-tracking Monte Carlo simulations for varying particle size, wavelength, and refractive index, I quantify when circular polarization outperforms linear polarization in maintaining the illuminating polarization state for large optical thicknesses, persisting to longer ranges. I identify many real-world environments with particle sizes of radiation fog, advection fog, and Sahara dust where circular polarization outperforms linear polarization over broad wavelength ranges in the infrared spectrum. This enhancement with circular polarization can be exploited to improve sensing range and target detection in obscurant environments that are important in many critical surveillance applications. Conversely, I also identify a few environmental configurations where linear polarization outperforms circular polarization. However, circular polarization's response is generally larger and over broader wavelength ranges in the infrared regime for real-world scattering environments. Experiments were conducted for both 1) isotopically-scattering (Rayleigh regime) environments and 2) forward-scattering environments using polystyrene microspheres with well-defined diameters. These measurements demonstrated that in the forward-scattering environments, circular polarization persists through increasing optical thickness better than linear polarization. Variations in persistence were investigated as a function of collection geometry, angular field of view, and collection area. Persistence for both linear and circular polarization was found to be more susceptible to collection geometry, specifically increased collection area, in the isotropically-scattering (Rayleigh regime) environment. Similarly, linear polarization in the forward-scattering environments is dependent upon changes in collection geometry. Significantly, circular polarization's response is nearly unaffected by variations of both field of view and collection area for the forward-scattering environments. Circular polarization proves to be not only generally better in persistence but also more tolerant of variations in angular collection and collection area compared to linear polarization, making it ideal and flexible for use in optical sensing systems in scattering environments. Finally, I present simulation results that show the evolution of linear and circularly polarized light as it scatters throughout both isotropic (Rayleigh regime) and forward-scattering environments as a function of scattering event. Circularly polarized light persists through a larger number of scattering events longer than linearly polarized light for all forward-scattering environments; but not for scattering in the Rayleigh regime. Circular polarization's increased persistence occurs for both forward and backscattered light. The evolution of the polarization states as they propagate through the various environments are illustrated on the Poincaré sphere after successive scattering events. This work displays individual scattering events as well as a cumulative, measureable result, in an intuitive manner. Throughout this dissertation I quantify the polarization persistence and memory of circularly polarized light in real-world scattering environments over broad wavelength, particle size, and collection-geometry parameter spaces; and for the first time, detail the evolution and modification of both circularly and linearly polarized states through isotropic and forward-scattering environments. These results show how circular polarization can extend range and sensing capability in surveillance sensing applications in real-world scattering environments.

Coated nanoparticles (CNP) are core-shell particles consisting of differing layers of epsilon positive (EP) and epsilon negative (ENG) materials. The juxtaposition of these EP and ENG materials can lead to the possibility of coupling incident plane waves to surface plasmon resonances (SPR) for particles even highly subwavelength in size. We introduce standard models of the permittivities of the noble metals used in these CNPs, and propose corrections to them based on experimental data when their sizes are extremely small. Mie theory is the solution to plane wave scattering by spheres and we extend the solution here to spheres consisting of an arbitrary number of layers. We discuss the resonance behaviors of passive CNPs with an emphasis on how the Coated nanoparticles (CNP) are core-shell particles consisting of differing layers of epsilon positive (EP) and epsilon negative (ENG) materials. The juxtaposition of these EP and ENG materials can lead to the possibility of coupling incident plane waves to surface plasmon resonances (SPR) for particles even highly subwavelength in size. We introduce standard models of the permittivities of the noble metals used in these CNPs, and propose corrections to them based on experimental data when their sizes are extremely small. Mie theory is the solution to plane wave scattering by spheres and we extend the solution here to spheres consisting of an arbitrary number of layers. We discuss the resonance behaviors of passive CNPs with an emphasis on how the resonance wavelength can be tuned by controlling the material properties and radii of the various layers in the configuration. It is demonstrated that these passive CNPs have scattering cross sections much larger than their geometrical size, but their resonance strengths are attenuated because of the inherent losses in the metals. To overcome this limitation, we show how the introduction of active material into the CNPs can not only overcome these losses, but can actually lead to an amplification of the scattering of the incident field. We report several optimized active CNP designs, including ones based on quantum dot gain media and study their performance characteristics with particular attention to the effect of the location of the gain material on the performance of these designs. We investigate the ability to control the scattered field directivity of the CNPs in both their far- and near-field regions and propose designs with minimal backscattering and those emulating macroscopic nanojets. We compare data generated by initial efforts to experimentally prepare CNPs and compare against analytical and numerical simulation results. Finally, we suggest a variety of interesting future research directions. resonance wavelength can be tuned by controlling the material properties and radii of the various layers in the configuration. It is demonstrated that these passive CNPs have scattering cross sections much larger than their geometrical size, but their resonance strengths are attenuated because of the inherent losses in the metals. To overcome this limitation, we show how the introduction of active material into the CNPs can not only overcome these losses, but can actually lead to an amplification of the scattering of the incident field. We report several optimized active CNP designs, including ones based on quantum dot gain media and study their performance characteristics with particular attention to the effect of the location of the gain material on the performance of these designs. We investigate the ability to control the scattered field directivity of the CNPs in both their far- and near-field regions and propose designs with minimal backscattering and those emulating macroscopic nanojets. We compare data generated by initial efforts to experimentally prepare CNPs and compare against analytical and numerical simulation results. Finally, we suggest a variety of interesting future research directions

Surface plasmon resonance has become a widely investigated phenomenon in the past few years. Initially descriptive of light interactions with metallic films, research has branched out to encompass the nanoparticles as well. Generation of the maximum surface plasmon resonance for nanostructures is based on the resonance condition that the oscillatory behavior of the 'free' electrons on the surface of the particle become equivalent to the frequency of the excitation light; for films this required a specific geometry. Metallic nanoparticles have also interested researchers because of their unique optical properties. Depending on the metal, observations of quenching as well as fluorescence enhancement have been reported. Based on the phenomenon of surface plasmon resonance as well as the properties of metallic nanoparticles, this research reports the interaction of gold and silver nanoparticles in an aqueous dye solution. Our research is the basis for developing an optical sensor used for water treatment centers as an alarm mechanism. Due to the inefficiency of the fluorophore used in similar optodes, sufficient fluorescence was not obtained. With the addition of the nanoparticles, we hoped to observe the transfer of energy from the nanoparticle to the fluorophore to increase the overall intensity, thereby creating a sufficient signal. Using the excitation theories discovered by Raman, Mie, and Forster and Dexter as our foundation, we mixed a strongly fluorescent dye with gold nanoparticles and aagain with silver nanoparticles. After taken measurements via fluorescence spectroscopy, absorption spectroscopy, and photoluminescence excitation, we observed that the silver nanoparticles seemed to enhance the fluorescence of the dye while the gold nanoparticles quenched the fluorescence. / Master of Science

Aerosols of nitrate solutions were irradiated in the presence of radical scavengers in an attempt to measure the yield of hydroxyl radical in both the aqueous phase and the gas phase. Carbon monoxide, benzoic acid, benzene and cyclohexane were used as scavengers to trap hydroxyl radical. The products from the reaction of these scavengers with hydroxyl radical were analysed with High Performance Liquid Chromatography and mass spectrometry. The radiant flux in the chamber was measured via ferrioxalate actinometry, both with bulk liquid and aerosol droplets. Many quantitative results were obtained but several anomalies were found. This suggests that Mie theory is not capable of predicting rates of photochemical reactions within droplets.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2014-08-19T14:30:36Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertacao_Jose Carlos Campello Lopes Jr.pdf: 3551367 bytes, checksum: fc027437d4c362a01703752003b22515 (MD5) / Made available in DSpace on 2014-08-19T14:30:37Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertacao_Jose Carlos Campello Lopes Jr.pdf: 3551367 bytes, checksum: fc027437d4c362a01703752003b22515 (MD5) Previous issue date: 2010-05-17 / In this work we investigated, theoretically and experimentally, the magneto-optical properties of a magnetic fluid consisting of core-shell nanoparticles, where the core is made of magnetite, while the shell is silver. The theoretical model used was based on Mie s theory, under the electrostatic approximation, i.e. for nanoparticles with diameters much less than the incident wavelength (lambda). A Clausius-Mosotti for a core-shell system was used to calculate the electrical susceptibility of the core-shell nanoparticle for equals to 632 nm. The susceptibility was shown to be strongly dependent on the core diameter and the shell thickness. Nevertheless, a maximum value of 7.20 (greater than isolated nanoparticles of silver, which has 0 = 4.30, or magnetite with 0 = 1.47) was obtained for a fraction f, defined as f = (Dcore/Dcore−shell)3, equal to 0.36. This result suggest that there exist an ideal fraction f for nanocomposites with enhanced optical properties. In order to compare our theoretical results with experimental data a core-shell magnetic fluid was synthesized on the Institute of Chemistry of UFG by the group of Dr. Em´ılia Celma de Oliveira Lima. The nanoparticles were suspended in water at fisiological pH and recovered by a double layer of lauric acid (dodecanoic acid). The nanoparticles were characterized by X-ray diffraction, high resolution electron transmission, energy dispersive X-ray spectroscopy, and vibrating sample magnetometer. The Sturges method was used to obtain the nanoparticle diameter histogram. The data revealed the existence of a bimodal nanoparticle distribution. Both distributions were curve fitted using a lognormal function. The modal diameter of one of them was 9.24 ± 0.03 nm with a dispersity of 0.27 ± 0.02, while for the other one we found a modal diameter of 23.0 ± 0.2 nm with disperisty 0.2 ± 0.1. The energy dispersive X-ray spectroscopy confirmed the existence of magnetite and silver only for larger particle diameters, while the lower ones only magnetite was found. From the experimental analysis we confirmed the synthesis of a magnetic fluid containing 10% of core-shell nanoparticles. Magnetization data was used to estimate the magnetic particle volume fraction. The magneto-optical properties were obtained using a magnetotransmissivity technique, where the polarizer and analyser axis are positioned on the magnetic field direction. The sample containing 10% of core-shell nanoparticles, with a total particle volume fraction of 0.18%, had shown an extinction of light of 100% for a magnetic field of only 500 Oe, while a magnetic fluid with 100% of core nanoparticles, at a similar particle concentration (0.15%), had shown a 50% extinction of light at the same field range. The magnetotransmissivity data were curve fitted with a theoretical model containing only two parameters, one related to the electrical susceptibility and the other to the formation of self-organized nanostructures in the colloid. The mean agglomerate size (nanoparticles forming linear chains) had changed from 2.09 to 3.36 for a particle volume fraction increasing from 0.06% to 0.18%. Using the estimative of the double layer lenght of lauric acid, approximately 2 nm, and analyzing the magnetotransmissivity data for several particle concentrations, we were able to obtain the fraction f of core-shell nanoparticles of 0.17. This result, together with TEM data, allowed us to calculate the core diameter of the core-shell nanoparticle as 13 nm. Indeed such result suggest that in order to be suscessful in coating the nanoparticle with the shell element one might need monodisperse-like nanoparticle systems. / Neste trabalho investigamos, teorica e experimentalmente, as propriedades magneto-´opticas de um fluido magn´etico constitu´ıdo de nanopart´ıculas core-shell (caro¸co-casca), em que o caro¸co ´e feito de magnetita e a casca de prata. O modelo te´orico utilizado baseou-se no modelo de Mie, dentro da aproxima¸c ao eletrost ´atica, que consiste no caso em que o di ametro das nanopart´ıculas ´e muito menor que o comprimento de onda da luz incidente ( ). Uma rela¸c ao de Claussius-Mossotti para o sistema core-shell foi utilizada para o c´alculo da susceptilidade el´etrica da nanopart´ıcula core-shell para lambda=632 nm. A susceptilidade el´etrica do nanocomposto foi fortemente dependente do di ametro do caro¸co e da espessura da casca. Entretanto atinge um valor m´aximo de 7,20 (maior que o de uma nanopart´ıcula de prata com 0 = 4, 30 ou de magnetita 0 = 1, 47) para uma fra¸c ao f, definida como f = (Dcore/Dcore−shell)3, igual a 0,36. Este resultado sugere que existe uma fra¸c ao ideal entre os materiais que proporciona ao nanocomposto resposta m´axima `as propriedades ´opticas. No intuito de comparar nossos resultados te´oricos com dados experimentais, um fluido magn´etico core-shell foi sintetizado no Instituto de Qu´ımica da UFG pelo grupo da Profa. Dra. Em´ılia Celma de Oliveira Lima. As nanopart´ıculas foram suspensas em ´agua em pH fisiol´ogico e recobertas por uma dupla camada de ´acido la´urico (´acido dodecan´oico). As nanopart´ıculas foram caracterizadas por difra¸c ao de raios-X (DRX), microscopia eletr onica de transmiss ao de alta resolu¸c ao (HR-TEM), espectrometria de energia dispersiva de raios-X (EDS) e magnetometria de amostra vibrante (VSM).O m´etodo de Sturges foi utilizado para montar o histograma dos di ametros das nanopart´ıculas. Os dados revelaram a exist encia de uma distribui¸c ao bimodal. Ambas distribui¸c oes foram ajustadas considerando uma distribui¸c ao do tipo lognormal. O di ametro modal de uma delas foi de 9.24 ± 0.03 nm com uma dispers ao de 0.27 ± 0.02, enquanto que para a outra distribui¸c ao foi encontrado um di ametro modal de 23.0 ± 0.2 nm e dispers ao 0.2 ± 0.1. A espectrometria de energia dispersiva confirmou a presen¸ca de magnetita e prata, em quantidades significativas, somente nas part´ıculas de maior di ametro, enquanto nas de menor di ametro foi confirmado a exist encia apenas de magnetita. A partir destas an´alises foi confirmada a s´ıntese de um fluido magn´etico contendo 10 % das nanopart´ıculas do tipo core-chell . Dados de magnetiza¸c ao foram obtidos para estimar a fra¸c ao volum´etrica de nanopart´ıculas magn´eticas. Medidas das propriedades magneto-´opticas foram feitas utilizando a t´ecnica de magnetotransmissividade com polarizador e analisador orientados na dire¸c ao do campo magn´etico aplicado. Amostra contendo10% de suas nanopart´ıculas do tipo core-shell , com uma fra¸c ao volum´etrica total de apenas 0,18%, apresentou uma extin¸c ao da luz de 100% a um campo de apenas 500 Oe, enquanto que uma amostra com 100% de nanopart´ıculas do tipo core , em concentra¸c ao semelhante (0,15%), apresentou uma extin¸c ao de 50% na mesma faixa de campo magn´etico. Os dados de magnetotransmissividade foram ajustados considerando um modelo contendo apenas 2 par ametros, estando um deles relacionado a susceptibilidade el´etrica e outro a forma¸c ao de estruturas auto-organizadas no col´oide. O tamanho m´edio de aglomerados (nanopart´ıculas formando uma cadeia linear) variou de 2.09 para 3.36 para uma fra¸c ao volum´etrica crescendo de 0,06% para 0,18%. Usando dados da literatura acerca da estimativa do comprimento da dupla camada de ´acido la´urico, como sendo de aproximadamente 2 nm, e analisando os dados de magnetotransmissividade para diversas concentra¸c oes de nanopart´ıculas, foi poss´ıvel obter a fra¸c ao f das nanopart´ıculas core-shell como sendo de 0,17. Este resultado, conjuntamente com os dados de TEM, permitiu concluir que o di ametro do caro¸co na nanopart´ıcula core-shell ´e de 13 nm. Este resultado ´e interessante tecnologicamente, pois sugere que, para se obter sucesso no recobrimento de nanopart´ıculas, seja necess´ario, ou ao menos importante, utilizar amostras com baixa dispers ao de di ametros.

<p>The redistribution of incident light into scattered fields ultimately limits the ability to image into biological media. However, these scattered fields also contain information about the structure and distribution of protein complexes, organelles, cells and whole tissues that can be used to assess the health of tissue or to enhance imaging contrast by excluding confounding signals. The interpretation of scattered fields depends on a detailed understanding of the scattering process as well as sophisticated measurement systems. In this work, the development of new instruments based on low coherence interferometry (LCI) is presented in order to perform precise, depth-resolved measurements of scattered fields. Combined with LCI, the application of new light scattering models based on both analytic and numerical methods is presented in order to interpret scattered field measurements in terms of scatterer geometry and tissue health. </p><p>The first portion of this work discusses the application of a new light scattering model to the measurement recorded with an existing technique, Angle Resolved Low Coherence Interferometry (a/LCI). In the a/LCI technique, biological samples are interrogated with collimated light and the energy per scattering angle at each depth in the volume is recorded interferometrically. A light scattering model is then used to invert the scattering measurements and measure the geometry of cell nuclei. A new light scattering model is presented that can recover information about the size, refractive index, and for the first time, shape of cell nuclei. This model is validated and then applied to the study of cell biology in a series of experiments measuring cell swelling, cell deformation, and finally detecting the onset of apoptosis.</p><p>The second portion of this work introduces an improved version of a/LCI based on two dimension angle resolved measurement (2D a/LCI) and Fourier domain low coherence interferometry (FD-LCI). Several systems are presenting for high speed and polarization-resolved measurements of scattered fields. An improved light scattering model based on fully polarization and solid angle resolved measurements is presented, and then efficiently implemented using distributed computing techniques. The combined system is validated with phantoms and is shown to be able to uniquely determine the size and shape of scattering particles using a single measurement.</p><p>The third portion of this work develops the use of angle-resolved interferometry for imaging through highly scattering media by exploiting the tendency of scatterers to forward scatter light. A new interferometers is developed that can image through very large numbers of scattering events with acceptable resolution. A computational model capable of reproducing experimental measurements is developed and used to understand the performance of the technique.</p><p>The final portion of the work develops a method for processing 2D angle resolved measurements using optical autocorrelation. In this method, measurements over a range of angles are fused into a single depth scan that incorporates the component of scattered light only from certain spatial scales. The utility of the technique is demonstrated using a gene knockout model of retinal degeneration in mice. Optical autocorrelation is shown to be a potentially useful biomarker of tissue disease.</p> / Dissertation

The pseudo-spectral time domain (PSTD) and discrete dipole approximation (DDA) are two of the most popular methods to model the single-scattering properties of ice crystals and aerosols. Both methods solve for Maxwell’s equations. The PSTD method uses a Fourier pseudo-spectral method and a finite-difference method to compute the spatial and temporal derivatives of electromagnetic fields. The DDA method uses an electromagnetic integral equation in the frequency domain to calculate the single-scattering properties. We used a spherical model for this study because the analytical solution was given by the Lorenz-Mie theory. Previous studies have found that at refractive indices between 1.2 and 1.5, PSTD computed the single-scattering properties of spherical particles faster for large size parameters, while DDA was more computationally efficient at small size parameters; however, these previous studies did not consider absorptive cases. The purpose of this study was to expand the range of refractive indices to include absorptive cases and to determine which method was more efficient for computing the single-scattering properties of atmospheric particles within set criteria. The PSTD and DDA methods were systematically assessed in this study for 31 different realistic complex refractive indices. Similar to the previous studies, it was found that PSTD was more efficient than DDA for particles with large size parameters. The results in this study were consistent with the previous studies for non-absorptive to moderately absorptive particles. However, for strongly absorptive cases, DDA was more efficient than PSTD at all size parameters for the absorptive particles. It was also determined that the efficiencies of the two methods were dependent on both the real and imaginary parts of the complex refractive index. The significance of this study was to improve our understanding of the capabilities of the PSTD and DDA methods for computing single-scattering properties.

With the rapid development of the industry all over the world, the consumption of fossil fuel of human activities has reached an extremely high level which result in an incredible dust emission level nowadays. As one of the major environment challenges today, dust pollution has become a vital issue that the human beings have to face and resolve.    To tackle the dust pollution problem, a reliable measurement of the dust concentration level is essential. In recent years, methods with different principles are used to detect the dust concentration have been developed. The methods developed based on the scattering principle and the extinction principle for dust concentration measurement have a series of virtues such as high measurement speed, excellent precision and can be useful for real time monitoring.    This thesis reviewed the popular theories that are applied in the field which are light scattering (Mie theory) and light extinction (Lambert-beer theory). Matlab simulation is used to verify the possibility of the determined physical quantities related to the concentration measurement in the theory analysis. A new method using the ratio of scattering intensity and extinction intensity is discussed in this thesis providing a more accurate result eliminating the drawbacks of the scattering method and the extinction method.