<p> Novel scalar and full-vectorial mode solvers based on quadratic spline collocation (QSC) method have been developed in MATLAB for optical dielectric waveguide with arbitrary two-dimensional cross-section and refractive index profile.</p> <p> Compared with the conventional finite difference mode solver in the literature and a commercial mode solver, the QSC mode solvers are simple and easy to implement in MATLAB without losing the accuracy of the mode solutions. The scalar mode solver is fast for solving weakly guiding waveguides. Three typical rib waveguides are calculated by the QSC scalar mode solver and compared with the numerical results of a finite difference scalar mode solver in the literature. The full-vectorial mode solver is capable of solving both weakly and strongly guiding waveguides. Typical numerical examples are calculated by the full-vectorial QSC mode solver and the solver is verified by comparing the results to a commercial mode solver.</p> <p> At the end of the thesis, methods of calculating leaky and radiation modes of general dielectric waveguides and possible methods of increasing the accuracy of the QSC mode solvers are proposed.</p> / Thesis / Master of Applied Science (MASc)

Single wavelength ellipsometry measurements at Brewster's angle provide a powerful technique for characterizing ultrathin polymeric films. By conducting the experiments in different ambient media, multiple incident media (MIM) ellipsometry, simultaneous determinations of a film's thickness and refractive index are possible. Poly(tert-butyl acrylate) (PtBA) films serve as a model system for the simultaneous determination of thickness and refractive index (1.45 at 632 nm). Thickness measurements on films of variable thickness agree with X-ray reflectivity results. The method is also applicable to spincoated films where refractive indices of PtBA, polystyrene and poly(methyl methacrylate) are found to agree with literature values within experimental error. Likewise, MIM ellipsometry is utilized to simultaneously obtain the refractive indices and thicknesses of thin films of trimethylsilylcellulose (TMSC), regenerated cellulose, and cellulose nanocrystals where Langmuir-Blodgett (LB) films of TMSC serve as a model system. Ellipsometry measurements not only provide thickness and optical constants of thin films, but can also detect thermally induced structural changes like surface glass transition temperatures (Tg) and layer deformation in LB-films. Understanding the thermal properties of the polymer thin films is crucial for designing nanoscale coatings, where thermal properties are expected to differ from their corresponding bulk properties because of greater fractional free volume in thin films and residual stresses that remain from film preparation. Polyhedral oligomeric silsesquioxane (POSS) derivatives may be useful as a nanofiller in nanocomposite formulations to enhance thermal properties. As a model system, thin films of trisilanolphenyl-POSS (TPP) and two different molar mass PtBA were prepared as blends by Y-type Langmuir-Blodgett film deposition. For comparison, bulk blends were prepared by solution casting and the samples were characterized via differential scanning calorimetry (DSC). Our observations show that surface Tg is depressed relative to bulk Tg and that magnitude of depression is molar mass dependent for pure PtBA films. By adding TPP as a nanofiller both bulk and surface Tg increase. Whereas, bulk Tg shows comparable increases for both molar masses, the increase in surface Tg for higher molar mass PtBA is greater than for lower molar mass PtBA. These studies show that POSS can serve as a model nanofiller for controlling Tg in nanoscale coatings. / Ph. D.

This dissertation describes new methods for measuring surface forces using evanescent waves, and applications to non-DLVO forces. An evanescent wave, generated at a solid-liquid interface, is scattered by AFM tips or particles attached to AFM cantilevers. The scattering of this wave is used to determine absolute separation between surfaces and/or the refractive index as a function of separation in AFM measurements. This technique is known as evanescent wave atomic force microscopy (EW-AFM). The scattering of an evanescent wave by Si3N4 AFM tips is large and decays exponentially with separation from a refractive index boundary. Thus, scattering is a useful method for measuring the separation between a Si3N4 tip and sample. This method has been used to measure the absolute separation between a tip and sample in the presence of an irreversibly adsorbed polymer film. Measurement of the film thickness and time response of the polymer to applied loads has also been studied. These measurements are not possible using current AFM techniques. In addition to measurements in polymer systems, the simple scattering profile from Si3N4 tips was used to re-examine short range hydration forces between hydrophilic surfaces. Results presented in this thesis suggest this force does not depend on the hydrated radius of the ion between glass and silicon nitride. The scattering generated by a Si3N4 tip has also been used to measure the refractive index of bulk fluids and thin films between hydrophobic surfaces. Based on these results, I have shown that a long-range attraction between hydrophobic surfaces is accompanied by an increase in the refractive index between the tip and surface. From this I have concluded that the attractive force, measured in this study, is the result of an increase in the concentration of organic material between surfaces. Finally, I have shown that the scattering profile depends on the material and size of the scattering object. Scattering from silicon nitride tips is exponential with separation. In contrast, the scattering profile from silicon tips, which are similar in size and geometry, is not a simple exponential. The scattering profile of larger spherical particles attached to cantilevers is also not exponential. It is approximately the sum of two exponentials. The functional form of the scattering profile with separation is consistent with the transmission of evanescent light through flat planar films. This result would suggest that a re-examination of the separation-dependence of scattering in TIRM measurements is necessary. / Ph. D.

During the last decades, the continuing need for faster and smaller sensors has indeed triggered the rapid growth of more sophisticated technologies. This has led to the development of new optical-based sensors, able to detect and measure different phenomena using light. Furthermore, material processing technologies and micro fabrication methods have exponentially advanced, allowing engineers and scientists to develop new and more complex sensors on optical fibers platforms; specifically attractive for life science and biomedical research. All these substantial developments have brought biosensors to a point where multifunctionality is needed, this has led to envision the "Lab-on-Fiber" concept. Which promotes the integration of different sensing components into a single platform, an optical fiber. In this work, an integrated system with non-conventional polymer optical fibers and their further surface modification has been developed. With these different approaches, electrodes, hollow channels and plasmonic nanostructures can be incorporated into a single optical fiber-based sensor, allowing for both electrical and optical sensing with the capabilities of tuning and signal enhancement thanks to the metallic nanostructures. Different fiber substrates can be designed and modified in order to satisfy multiple requirements for a wide variety of applications. / MS

Laser-based photo-thermal therapies can provide minimally-invasive treatment of cancers. Their effectiveness is limited by light penetration depth in tissue due to its highly scattering properties. The highly disordered refractive index distribution in tissue leads to multiple-scattering of incident light. It has been hypothesized that mechanical compression has a great potential to enhance the capabilities of laser therapy by inducing localized water transport, decreasing the refractive index mismatch, and decreasing the scattering coefficient of tissue. To better understand this process, we investigated the refractive index change of ex-vivo dog skin during mechanical compression using a swept-source optical coherence tomography (OCT) device built in our lab. The Lorentz-Lorenz rule of mixtures was applied to evaluate the water and protein weight fraction of tissue simultaneously. Results show that the refractive index of skin increased from 1.38 to 1.52 during compression and water content decreased about 60%-70% when the skin sample was compressed by 70%. In addition, we conducted compression experiments on human finger, palm, back of hand, and front of forearm in vivo. OCT images of these skin sites before and after compression by 1 minute were compared. Optical thickness of epidermis and light penetration depth in the dermis were measured. The extended Huygens-Fresnel model was applied to measure the scattering coefficient μs of skin specimens. μs of skin was measured to be about 10-17 mm-1 before compression and decreased 60%-80% after compression, which increases the averaged light intensity by 2-7 dB and almost doubles light penetration depth in dermis. It is quite significant in laser therapies especially for treating epithelia cancers which originate at 1-2 mm beneath the tissue surface. In the OCT imaging of skin dehydration experiment, we conclude that dehydration is an important mechanism of mechanical clearing. / Master of Science

[ES] La difusión de la luz es un fenómeno ubicuo con implicaciones significativas en gran variedad de disciplinas. Mientras que la mayoría de los estudios de difusión se centran en la extinción u otras mediciones relacionadas con la amplitud, la fase de la onda difusa contiene información importante que puede ser aprovechada para múltiples propósitos. Aunque pocas técnicas de caracterización son adecuadas para esta tarea, la espectroscopía de terahercios (THz) es una técnica coherente que permite esto en un amplio rango de frecuencias con propiedades cuasi ópticas. Para lograrlo, estudiaremos y mejoraremos la metodología existente de pulsos de THz aumentando la velocidad de adquisición de espectros de alta resolución mediante la combinación de diversas técnicas para el muestreo de retardo. Esta tesis aborda la investigación de luz difusa con tecnología de THz para dos desarrollos principales. El primero es un método de caracterización del tamaño de partículas resuelto espectralmente utilizando medidas de extinción y de índice de refracción (IR). Al resolver el problema inverso de luz difusa, se puede obtener una gran información de las propiedades geométricas y químicas de las partículas. Este método tradicionalmente ha empleado solo de datos de extinción del medio heterogéneo. Demostramos que se puede lograr una mejora neta en la reconstrucción de la distribución del tamaño de partícula al combinar datos de extinción con datos de IR. Dado que las mediciones se encuentran en un rango de frecuencia limitado, obtener el IR a partir de relaciones de Kramers-Kronig (KK) no puede sustituir su medición directa utilizando técnicas coherentes. Una razón adicional por la cual las relaciones de KK pueden no ser útiles es que, en el caso de una partícula con una densidad óptica menor que el fondo, el IR efectivo complejo no sigue relaciones de dispersión convencionales. El estudio de este fenómeno y la interpretación de las implicaciones causales que surgen son el foco de la última parte de esta tesis, junto con su posible aplicación para el diseño de ondas con contenido espectral arbitrario. Finalmente, se discuten las conclusiones y las líneas futuras de trabajo derivadas de nuestros hallazgos. / [CA] La difusió de la llum és un fenomen ubic amb implicacions significatives en una gran varietat de disciplines. Mentre que la majoria dels estudis de difusió se centren en l'extinció o altres mesures relacionades amb l'amplitud, la fase de l'ona difusa conté informació important que es pot aprofitar per a múltiples propòsits. Encara que poques tècniques de caracterització són adequades per a aquesta tasca, l'espectroscòpia de teraherços (THz) és una tècnica coherent que permet això en un ampli rang de freqüències amb propietats quasi òptiques. Per a aconseguir-ho, estudiarem i millorem la metodologia existent de polsos de THz augmentant la velocitat d'adquisició d'espectres d'alta resolució mitjançant la combinació de diverses tècniques per al mostreig de retard. Aquesta tesi aborda la investigació de la llum difusa amb tecnologia de THz per a dos desenvolupaments principals. El primer és un mètode de caracterització de la mida de partícules resolt espectralment utilitzant mesures d'extinció i d'índex de refracció (IR). En resoldre el problema invers de llum difusa, es pot obtenir una gran informació sobre les propietats geomètriques i químiques de les partícules. Aquest mètode tradicionalment ha emprat només dades d'extinció del medi heterogeni. Demostrem que es pot aconseguir una millora neta en la reconstrucció de la distribució de la mida de partícula en combinar dades d'extinció amb dades d'IR. Donat que les mesures es troben en un rang de freqüència limitat, obtenir l'IR a partir de relacions de Kramers-Kronig (KK) no pot substituir la seua mesura directa utilitzant tècniques coherents. Una raó addicional per la qual les relacions de KK poden no ser útils és que, en el cas d'una partícula amb una densitat òptica menor que el fons, l'IR efectiu complex no segueix relacions de dispersió convencionals. L'estudi d'aquest fenomen i la interpretació de les implicacions causals que sorgeixen són el focus de la darrera part d'aquesta tesi, juntament amb la seua possible aplicació per al disseny d'ones amb contingut espectral arbitrari. Finalment, es discuteixen les conclusions i les línies futures de treball derivades dels nostres descobriments. / [EN] Light scattering is a ubiquitous phenomenon with significant implications across various disciplines. While most scattering studies focus on extinction or other amplitude-related measurements, the phase of the scattered wave holds important information that can be harnessed for a multitude of purposes. However, while few characterization techniques are suited for this task, terahertz (THz) spectroscopy is a coherent technique that permits this across a wide range of frequencies with quasi-optical properties. To accomplish this, we will study and improve the existing methodology of pulsed THz by increasing the speed of acquisition of high-resolution spectra with a combination of existing delay sampling techniques. This thesis approaches light scattering research with THz technology for two main developments. The first one is a spectrally resolved particle size characterization method using extinction and refractive index (RI) measurement. By solving the inverse scattering problem, great insight into the geometric and chemical properties of the particles can be gained. This method has traditionally relied only on extinction data from the heterogeneous medium. We demonstrate that a net improvement in the reconstruction of the particle size distribution can be made by combining extinction with RI datasets. Since the measurements are in a limited frequency range, obtaining the RI from Kramers-Kronig (KK) relations cannot substitute for its direct measurement using coherent techniques. One additional reason why KK relations may not be of use is that, for the case of a particle with lower optical density than the background, the measured complex effective RI does not follow conventional dispersion relations. The study of this phenomenon and the interpretation of the causal implications that arise are the subject of the last part of this thesis, along with its possible application to the arbitrary shaping of spectral wave features. Ultimately, the conclusions and future lines of work derived from our findings are discussed. / This thesis has been developed under grant FPI ACIF-2018-163 by GVA, project PID2019-111339GBI00 and project PDC2021-121597-I00 by MCIN/AEI / Báez Chorro, MÁ. (2024). Study of the Complex Spectral Response of Scattering Media with Terahertz Spectroscopy [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/205586

The complex refractive index is reported at room temperature for CdxZn1_xO thin film alloys for Cd composition up to 0.16. The CdxZn1_xO epilayers were grown by molecular-beam epitaxy on smooth ZnO/GaN/sapphire lattice templates. Transmission spectra were recorded by spectrophotometry in the 350-800nm wavelength range. The refractive index and extinction coefficient were derived by an evolutionary algorithm, which optimizes the Sellmeier and Forouhi-Bloomer dispersion models by a least-squares fitting to the experimental data.

No description available.

This dissertation presents a fibre-optic sensing approach to provide continuous measurements of CO2 concentration at discrete points under typical conditions of geological CO2 storage. Carbon capture and storage is considered to have potential for a large-scale reduction in CO2 emissions in a relatively short period of time while other solutions to replace fossil fuels are being investigated. One significant drawback of carbon capture and storage is the possibility of long-term CO2 leakage. Therefore, the development of reliable technology for monitoring, verification, and accounting of geological CO2 storage is critical to fulfill safety regulations and achieve public acceptance. The major limitations of current technology include relatively low resolutions, high costs, and the lack of continuous monitoring for long periods of time. To address these limitations, two types of fibre-optic sensors are investigated, namely long period gratings and Mach-Zehnder interferometers. The sensing principle for CO2 detection is based on the sensitivity of these sensors to the refractive index of the medium that surrounds the fibre. Fibre-optic sensors are attractive for downhole applications due to the possibility of fabricating inexpensive high resolution devices that are able to operate in harsh environments over long periods of time. This dissertation focuses on increasing the refractive index sensitivity of long period gratings and Mach-Zehnder interferometers by applying coatings that have a high refractive index. The dip-coating method is used to coat long period gratings with polystyrene, and the sensitivity at low refractive indices is increased by tuning coating thickness. The results show that long period gratings coated with polystyrene are able to detect CO2 in gaseous and aqueous media. This work reports the first measurement of CO2 dissolution in water at high pressure with a fibre-optic sensor. Additionally, atomic layer deposition is investigated to coat long period gratings and Mach-Zehnder interferometers with hafnium oxide. The study of this coating technique aims to address the main limitation of the dip-coating method: the challenge to achieve precise control over coating thickness. The results show that atomic layer deposition is suitable to maximize the sensitivity of long period gratings and Mach-Zehnder interferometers at a target refractive index. / Graduate / 0548 / 0752 / 0799 / luismelo@uvic.ca

Jusqu’à récemment, la plupart des applications des arcs électriques mettaient en oeuvre les propriétés du coeur de la colonne, un effort particulier a donc été effectué pour développer des méthodes de caractérisation de ces zones dont la température moyenne est de l’ordre de 10000 K. Avec le développement de la plasma-chimie, le diagnostic des zones périphériques d’arcs et des décharges hors équilibre est devenu un enjeu primordial. Les méthodes de mesure classiques sont mal adaptées pour cette tâche ; le but du travail présenté dans cette thèse se résume donc au développement et à la validation de techniques de diagnostic adaptées à ces zones, dont la température cinétique n’excède pas 8000 K. Deux méthodes innovantes basées sur l’indice de réfraction, l’ombroscopie quantitative et la déflectométrie moirée, ont été étudiées en détails. Les résultats théoriques ainsi que le traitement des données obtenues ont été validés sur un jet de plasma laminaire d’argon, un modèle parfait de zone périphérique. Pour sonder les décharges hors équilibre, l’utilisation du spectre UV de OH a été aussi envisagée. À cette occasion, un programme de simulation de spectre moléculaire a été développé. L’étude des spectres synthétiques obtenus a permis de mettre au point des méthodes de mesure simples de la température rotationnelle et vibrationnelle pour une large gamme de résolution. Une des méthodes développées a été mise en œuvre sur une décharge à faible intensité de courant. On montre que les résultats obtenus par spectroscopie moléculaire sur le radical OH sont très proches de ceux obtenus à l’aide d’une simulation. / Until recently, most of electrical arcs applications were dealing with the properties of the centre of the plasma column, a large number of works was then done to develop diagnostic techniques dedicated to those area where the mean temperature is about 10000 K. With the emergence of plasma chemistery, the diagnostic of arc’s peripheral areas and un-equilibrium discharges become a goal of prime importance. Classical diagnostic techniques are not adapted to those objects where the maximum temperature is around 8000 K; the principal aim of this work was to develop and check diagnostic techniques. Two inovating techniques based on refractive index, the quantitative shadowgraphy and the moiré deflectometry were studied extensively and checked on a laminar plasma jet, a perfect model of arc’s peripheral area. To probe unequilibrium discharge, the use of UV OH spectrum was considered. At this occasion, a spectrum simulation software was written. The study of synthetic spectra lead to the creation of simple measurement methods of rotationnal and vibrationnal OH temperature for a large range of resolution. Those methods was checked on a low power electric discharge. It can be shown that result from molecular spectroscopy are close to those obtained by simulation.