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$Absorptive and Refractive Optical Nonlinearities in Organic Molecules and Semiconductors$

Title: Absorptive and Refractive Optical Nonlinearities in Organic Molecules and Semiconductors.
Creator: Peceli, Davorin, Hagan, David, Vanstryland, Eric, Christodoulides, Demetrios, Belfield, Kevin, University of Central Florida
Abstract / Description: The main purpose of this dissertation to investigate photophysical properties, third order nonlinearity and free carrier absorption and refraction in organic materials and semiconductors. Special emphasis of this dissertation is on characterization techniques of molecules with enhanced intersystem crossing rate and study of different approaches of increasing triplet quantum yield in organic molecules. Both linear and nonlinear characterization methods are described. Linear spectroscopic...
Show moreThe main purpose of this dissertation to investigate photophysical properties, third order nonlinearity and free carrier absorption and refraction in organic materials and semiconductors. Special emphasis of this dissertation is on characterization techniques of molecules with enhanced intersystem crossing rate and study of different approaches of increasing triplet quantum yield in organic molecules. Both linear and nonlinear characterization methods are described. Linear spectroscopic characterization includes absorption, fluorescence, quantum yield, anisotropy, and singlet-oxygen generation measurements. Nonlinear characterization, performed by picosecond and femtosecond laser systems (single and double pump-probe and Z-scan measurements), includes measurements of the triplet quantum yields, excited-state absorption, two-photon absorption, nonlinear refraction and singlet and triplet-state lifetimes.The double pump-probe technique is a variant of the standard pump-probe method but uses two pumps instead of one to create two sets of initial conditions for solving the rate equations allowing a unique determination of singlet- and triplet-state absorption parameters and transition rates. The advantages and limitations of the the double pump-probe technique are investigated theoretically and experimentally, and the influences of several experimental parameters on its accuracy are determined. The accuracy with which the double pump-probe technique determines the triplet-state parameters improves when the fraction of the population in the triplet state relative to the ground state is increased. Although increased accuracy is in principle achievable by increasing the pump fluence in the reverse saturable absorption range, it is shown that the DPP is optimized by working in the saturable absorption regime.Two different approaches to increase intersystem crossing rates in polymethine-like molecules are presented: traditional heavy atom substitution and molecular levels engineering. Linear and nonlinear optical properties of a series of polymethine dyes with Br- and Se- atoms substitution, and a series of new squaraine molecules, where one or two oxygen atoms in a squaraine bridge are replaced with sulfur atoms, are investigated. A consequence of the oxygen-to-sulfur substitution in squaraines is the inversion of their lowest lying ??* and n?* states leading to a significant reduction of singlet-triplet energy difference and opening of an additional intersystem channel of relaxation. Experimental studies show that triplet quantum yields for polymethine dyes with heavy-atom substitutions are small (not more than 10%), while for sulfur-containing squaraines these values reach almost unity. Experimental results are in agreement with density functional theory calculations allowing determination of the energy positions, spin-orbital coupling, and electronic configurations of the lowest electronic transitions.For three different semiconductors: GaAs, InP and InAsP two photon absorption, nonlinear refraction and free carrier absorption and refraction spectrums are measured using Z-scan technique. Although two photon absorption spectrum agrees with the shape of theoretical prediction, values measured with picosecond system are off by the factor of two. Nonlinear refraction and free carrier nonlinearities are in relatively good agreement with theory. Theoretical values of the third order nonlinearities in GaAs are additionally confirmed with femtosecond Z-scan measurements. Due to large spectral bandwidth of femtosecond laser, three photon absorption spectrum of GaAs was additionally measured using picosecond Z-scan. Again, spectral shape is in excellent agreement with theory however values of three photon absorption cross sections are larger than theory predicts. ?
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Date Issued: 2013
Identifier: CFE0004735, ucf:49815
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004735

Title: PRESSURE AND TEMPERATURE RESPONSE OF A STIMULI-RESPONSIVE POLYMER PROBED WITH RAMAN MICROSCOPY.
Creator: Cariker, Coleman, Schulte, Alfons, University of Central Florida
Abstract / Description: Poly(N-isopropylacrylamide) (PNIPAM) is a thermo-responsive hydrogel; that is, it is a macromolecule which exists in a hydrated state beneath its lower critical solution temperature (LCST). Polymers such as PNIPAM undergo a phase transition in response to changes in temperature, pressure, pH, salt concentration, and the addition of co-solvents. Previously, visible-light microscopic measurements of the pressure-induced phase transition have been hindered by the lack of a pressurization...
Show morePoly(N-isopropylacrylamide) (PNIPAM) is a thermo-responsive hydrogel; that is, it is a macromolecule which exists in a hydrated state beneath its lower critical solution temperature (LCST). Polymers such as PNIPAM undergo a phase transition in response to changes in temperature, pressure, pH, salt concentration, and the addition of co-solvents. Previously, visible-light microscopic measurements of the pressure-induced phase transition have been hindered by the lack of a pressurization apparatus with the short working distance and optical transmission properties necessary for high resolution microscopy. We employ a high pressure setup which uses a fused silica micro-capillary to contain the sample. Our experiment reveals differences in the spatial evolution of the phase change across the temperature and pressure thresholds, and Raman measurements allude to conformational differences in the evolution of the phase transitions. The Raman peaks positions are in agreement with previous FTIR measurements, and due to a difference in selection rules additional vibrational bands are observed in the Raman spectra.
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Date Issued: 2014
Identifier: CFH0004694, ucf:45246
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004694

Title: Random Transformations of Optical Fields and Applications.
Creator: Kohlgraf-Owens, Thomas, Dogariu, Aristide, Saleh, Bahaa, Schulzgen, Axel, Tamasan, Alexandru, University of Central Florida
Abstract / Description: The interaction of optical waves with material systems often results in complex, seemingly random fields. In many cases, the interaction, while complicated, is both linear and deterministic.This dissertation focuses on the possible inverse problems associated with the determination of either the excitation field or the scattering system. The scattered field can be thought of as a massive sampling and mixing of the excitation field. This dissertation will show how such complicated sampling...
Show moreThe interaction of optical waves with material systems often results in complex, seemingly random fields. In many cases, the interaction, while complicated, is both linear and deterministic.This dissertation focuses on the possible inverse problems associated with the determination of either the excitation field or the scattering system. The scattered field can be thought of as a massive sampling and mixing of the excitation field. This dissertation will show how such complicated sampling functions can be characterized and how the corresponding scattering medium can then be used as an optical device such as a lens, polarimeter, or spectrometer.Another class of inverse problems deals with extracting information about the material system from changes in the scattered field. This dissertation includes a novel technique, based on dynamic light scattering, that allows for a full polarimetric measurement of the scattered light using a reference field with controllable polarization. Another technique relates to imaging the reflectivity of a target that is being randomly illuminated. We demonstrate that a method based on the correlation between the integrated scattered intensity and the corresponding illumination intensity distribution can prove superior to standard imaging microscopy at low-light levels.
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Date Issued: 2012
Identifier: CFE0004786, ucf:49746
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004786

Title: RAMAN SPECTROSCOPY OF GLASSESWITH HIGH AND BROAD RAMAN GAIN IN THE BOSON PEAK REGION.
Creator: Guo, Yu, Schulte, Alfons, University of Central Florida
Abstract / Description: This thesis investigates Raman spectra of novel glasses and their correlation with structure for Raman gain applications. Raman gain for all-optical amplification by fibers depends significantly on the cross section for spontaneous Raman scattering allowing to compare signal strength and spectral coverage. We also investigate the relationship between glass structure and the Boson peak (enhancement of the low-frequency vibrational density of states) and report new inelastic neutron scattering...
Show moreThis thesis investigates Raman spectra of novel glasses and their correlation with structure for Raman gain applications. Raman gain for all-optical amplification by fibers depends significantly on the cross section for spontaneous Raman scattering allowing to compare signal strength and spectral coverage. We also investigate the relationship between glass structure and the Boson peak (enhancement of the low-frequency vibrational density of states) and report new inelastic neutron scattering spectra for niobium-phosphate glasses. Polarization resolved Raman spectra of glasses based on tellurite and phosphate formers have been measured from 6 – 1500 cm-1 using an excitation wavelength of 514 nm. The Tellurite glasses exhibit Raman Spectra at least 10 times more intense, are more spectrally uniform and possess spectral bandwidths more than a factor of two wider than fused silica. Assignments of the vibrational bands are presented and the compositional dependence of the spectra is discussed with respect to the molecular structure. Significantly high Boson peaks were found in the frequency range from 30-100 cm-1. The Raman gain curves were calculated from the polarized spontaneous Raman spectra. In particular, they show broad and flat band in the low frequency region (50-400 cm-1) suggesting that these glasses may be useful for Raman gain applications extending to very low frequencies. The inelastic neutron scattering spectra of the niobium-phosphate glasses display a pronounced low-frequency enhancement of the vibrational density of states. By averaging over the full accessible wavevector range we obtain an approximate spectral distribution of the vibrational modes. Through direct comparison with the Raman spectra we determine the Raman coupling function which shows a linear behavior near the Boson peak maximum. Possible mechanisms contributing to the low frequency Raman band such as disorder-induced irregular vibrational states are discussed.
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Date Issued: 2006
Identifier: CFE0001322, ucf:47021
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001322

Title: In Actu Et In Silicio: Linear and Nonlinear Photophysical Characterization of a Novel Europium Complex, and Incorporating Computational Calculations in the Analysis of Novel Organic Compounds.
Creator: Woodward, Adam, Belfield, Kevin, Campiglia, Andres, Harper, James, Frazer, Andrew, Cheng, Zixi, University of Central Florida
Abstract / Description: Despite not being a tangible substance, light is becoming an increasingly valuable tool in numerous areas of science and technology: the use of laser excitation of a fluorescent probe can generate incredibly detailed images of cellular structures without the need for large amounts of dissection; new types of solar cells are being produced using organic dyes to harvest light; computer data can be stored by inducing a chemical change in a compound through irradiation with light. However, before...
Show moreDespite not being a tangible substance, light is becoming an increasingly valuable tool in numerous areas of science and technology: the use of laser excitation of a fluorescent probe can generate incredibly detailed images of cellular structures without the need for large amounts of dissection; new types of solar cells are being produced using organic dyes to harvest light; computer data can be stored by inducing a chemical change in a compound through irradiation with light. However, before any of these materials can be applied in such a way, their properties must first be analyzed for them to be deemed viable.The focus of this dissertation is the photophysical characterization, linear and nonlinear, of a several novel organic compounds, and a europium complex, as well as using quantum chemical calculation techniques to understand some of the phenomena that are witnessed and begin to develop predictive capability. The nonlinear characterization of compounds utilizes wavelengths outside of their linear absorption range, where a focused beam can achieve the same excitation as one at half the wavelength, though this effect has a quadratic dependence on power.The potential for nonlinear excitation, or two-photon absorption (2PA), is becoming of increasing interest and importance for organic chromophores. Exciting only a small volume of material at a focal point makes it possible to nondestructively image samples in 3-dimensions, record data in multiple layers, and fabricate intricate structures through photopolymerization reactions.Lanthanides such as europium are known to exhibit sharp emission bands when excited, typically through an antenna effect due to the low probability of achieving direct excitation. This emission is long-lived, and through gating systems can readily be separated from background noise and autofluorescence (often observed in biological samples) that have much shorter lifetimes. Thus, one of the foci of this dissertation is the photophysical investigation of a series of novel lanthanide complexes, with particular attention to a europium complex.
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Date Issued: 2014
Identifier: CFE0005908, ucf:50891
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005908

Title: Spectral Study of Asteroids and Laboratory Simulated Asteroid Organics.
Creator: Hargrove, Kelsey, Colwell, Joshua, Fernandez, Yan, Britt, Daniel, Kelley, Michael, University of Central Florida
Abstract / Description: We investigate the spectra of asteroids at near- and mid-infrared wavelengths. In 2010 and 2011 we reported the detection of 3 ?m and 3.2-3.6 ?m signatures on (24) Themis and (65) Cybele indicative of water-ice and complex organics [1] [2] [3]. We further probed other primitive asteroids in the Cybele dynamical group and Themis family, finding diversity in the shape of their 3 ?m [4] [5] [6] and 10 ?m spectral features [4]. These differences indicated mineralogical and compositional...
Show moreWe investigate the spectra of asteroids at near- and mid-infrared wavelengths. In 2010 and 2011 we reported the detection of 3 ?m and 3.2-3.6 ?m signatures on (24) Themis and (65) Cybele indicative of water-ice and complex organics [1] [2] [3]. We further probed other primitive asteroids in the Cybele dynamical group and Themis family, finding diversity in the shape of their 3 ?m [4] [5] [6] and 10 ?m spectral features [4]. These differences indicated mineralogical and compositional variations within these asteroid populations. Also in the mid-infrared region we studied a larger population of asteroids belonging to the Bus C, D, and S taxanomic classes to understand the relationship between any mineralogy and hydration inferred in the visible and near- infrared with the shape, strength, and slope of the 10 ?m emission. We have discovered that at least 3 of the main Bus taxanomic groups (Cs, Ds, and Ss as defined by their visible spectra) clearly cluster into 3 statistically distinct groups based on their 8-13 ?m spectra. Additionally we have attempted to simulate in a laboratory the possible organic compounds we have detected on two asteroids, using various mixtures containing aromatic and aliphatic hydrocarbons. We find that asteroid (24) Themis and (65) Cybele have ?CH2/?CH3 and NCH2/NCH3 ratios similar to our 3- methylpentane, propane, and hexane residues, suggesting that the organics on these asteroids may be short chained and/or highly branched. The ?CH2/?CH3 and NCH2/NCH3 for asteroid(24)Themis are most consistent with the DISM, and some carbonaceous chondrites. The band centers of the C-H stretch absorptions indicate that both asteroids may have aliphatic carriers chemically bonded to electronegative groups (i.e. aromatics), and some that are not. We also detect a 3.45 ?m feature in the spectra of both asteroids that is present in several dense molecular clouds. Our results suggest an interstellar origin for the organics on (24) Themis, and likely (65) Cybele. The differences in the organics of Themis and Cybele are likely related to variations in thermal processing, irradiation and/or formation region in the solar nebula.
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Date Issued: 2015
Identifier: CFE0005624, ucf:50201
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005624

Title: A NOVEL SETUP FOR HIGH-PRESSURE RAMAN SPECTROSCOPY UNDER A MICROSCOPE.
Creator: Oakeson, Thomas, Schulte, Alfons, University of Central Florida
Abstract / Description: Functional properties of biological molecules and cells are affected by environmental parameters such as temperature and pressure. While Raman spectroscopy provides an intrinsic probe of molecular structural changes, the incorporation of a microscope enables studies of minuscule amounts of biological compounds with spatial resolution on a micron scale. We have developed a novel setup which combines a Raman microscope and a high pressure cell. A micro-capillary made out of fused silica...
Show moreFunctional properties of biological molecules and cells are affected by environmental parameters such as temperature and pressure. While Raman spectroscopy provides an intrinsic probe of molecular structural changes, the incorporation of a microscope enables studies of minuscule amounts of biological compounds with spatial resolution on a micron scale. We have developed a novel setup which combines a Raman microscope and a high pressure cell. A micro-capillary made out of fused silica simultaneously serves as the supporting body and the optical window of the pressure cell. The cell has been tested over the pressure range from 0.1 to 4 kbar. Raman spectra of less than 100 nanoliter amount of amino acid and protein solutions have been measured in the micro-capillary high pressure cell. It is also demonstrated that the setup is well suited for spectrally resolved fluorescence measurements at variable pressure.
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Date Issued: 2007
Identifier: CFE0001683, ucf:47208
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001683

Title: Interplay of Molecular and Nanoscale Behaviors in Biological Soft Matter.
Creator: Ciaffone, Nicholas, Tetard, Laurene, Kang, Hyeran, Santra, Swadeshmukul, University of Central Florida
Abstract / Description: The complexity of biological soft matter at the sub-micrometer level is fundamentally correlated to the functionalities at the larger scale. Reflecting the level of heterogeneities in the properties of systems remains challenging when probing small scales, due to the mismatch between the area surveyed with the tools offering nanoscale resolution, such as atomic force microscopy (AFM), and the scale of natural variations inherent to biology. Hence, to understand the physiological and...
Show moreThe complexity of biological soft matter at the sub-micrometer level is fundamentally correlated to the functionalities at the larger scale. Reflecting the level of heterogeneities in the properties of systems remains challenging when probing small scales, due to the mismatch between the area surveyed with the tools offering nanoscale resolution, such as atomic force microscopy (AFM), and the scale of natural variations inherent to biology. Hence, to understand the physiological and mechanical alterations that occur within a single cell relative to a cell population, a multiscale approach is necessary. In this work we show that it is possible to observe molecular, chemical and physical alterations in both plant and human cells with a multiscale approach. Biophysical and biochemical traits of cell populations are studied with Fourier Transform infrared spectroscopy (FTIR) and in turn, guide higher resolution discovery with Raman spectroscopy and nanoscale infrared spectroscopy using AFM (NanoIR) to access finer details. We illustrate this with three examples of biological soft matter systems: 1) a preliminary study of cellular interactions with naturally occurring vehicles applicable to human health, 2) a qualitative examination of antibiotics and new pesticide treatments in food crop systems, and 3) a fundamental investigation of the deconstruction mechanisms of plant cells during pre-treatments in preparation for biofuel production.
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Date Issued: 2018
Identifier: CFE0007395, ucf:52058
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007395

Title: A Multisystem Approach for the Characterization of Bacteria for Sustainable Agriculture.
Creator: Lee, Briana, Tetard, Laurene, Kang, Hyeran, Mason, Chase, University of Central Florida
Abstract / Description: The chemical, physical, and biological properties of bacteria developing resistance have been explored in animal based bacteria while plant bacteria have been largely neglected. Thus, the ability to probe changes in stiffness, adhesion, binding interactions and molecular traits of bacteria causing plant diseases is of great interest to develop a new generation of more potent, yet sustainable, pesticides. Our study aims to investigate the physical and chemical properties of bacterial systems,...
Show moreThe chemical, physical, and biological properties of bacteria developing resistance have been explored in animal based bacteria while plant bacteria have been largely neglected. Thus, the ability to probe changes in stiffness, adhesion, binding interactions and molecular traits of bacteria causing plant diseases is of great interest to develop a new generation of more potent, yet sustainable, pesticides. Our study aims to investigate the physical and chemical properties of bacterial systems, in particular their cell walls. Building upon this fundamental understanding of the cells, we also investigate the physicochemical responses associated to multivalent nanoparticle-based bactericide treatments on bacterial systems identified as pathogens in plant diseases. Here our efforts focus on developing a protocol for the fundamental understanding of Xanthomonas perforans, a strain known for causing bacterial spot in tomatoes and causing close to 50% losses in production. To support the design and accelerate the development of pesticides and treatments against this disease, we evaluate the changes bacteria undergo in the presence of the treatment. Using a silica nanoparticle-based treatment designed with a shell containing multivalent copper and quaternary ammonium, we compare bacteria pre- and post-treatment with infrared spectroscopy, atomic force microscopy (AFM)-based techniques, and TIRF microscopy. Statistical data analysis enables the identification of attributes that can potentially serve as markers to track the bacterial responses to the treatment in the future. Finally, we will discuss the exciting implications of this work, such as potential clues for the development of more potent treatments for resistant bacteria.
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Date Issued: 2018
Identifier: CFE0007038, ucf:52005
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007038

Title: Enhancing CNT Composites with Raman Spectroscopy.
Creator: Freihofer, Gregory, Raghavan, Seetha, Gou, Jihua, Zhai, Lei, University of Central Florida
Abstract / Description: Carbon Nanotubes (CNTs) have been the subject of intense research for their potential to improve a variety of material properties when developed as nano-composites. This research aims to address the challenges that limit the ability to transfer the outstanding nano-scale properties of CNTs to bulk nano-composites through Raman characterization.These studies relate the vibrational modes to microstructural characterization of CNT composites including stress, interface behavior, and defects. The...
Show moreCarbon Nanotubes (CNTs) have been the subject of intense research for their potential to improve a variety of material properties when developed as nano-composites. This research aims to address the challenges that limit the ability to transfer the outstanding nano-scale properties of CNTs to bulk nano-composites through Raman characterization.These studies relate the vibrational modes to microstructural characterization of CNT composites including stress, interface behavior, and defects. The formulation of a new fitting procedure using the pseudo-Voigt function is presented and shown to minimizethe uncertainty of characteristics within the Raman G and D doublet. Methods for optimization of manufacturing processes using the Raman characterization are presentedfor selected applications in a polymer multiwalled nanotube (MWNT) composite andlaser-sintered ceramic-MWNT composite. In the first application, the evolution of theMWNT microstructure throughout a functionalization and processing of the polymer-MWNT composite was monitored using the G peak position and D/G intensity ratio.Processing parameters for laser sintering of the ceramic-MWNT composites were optimized by obtaining maximum downshift in stress sensitive G-band peak position, whilekeeping disorder sensitive D/G integrated intensity ratio to a minimum. Advanced Raman techniques, utilizing multiple wavelengths, were used to show that higher excitationenergies are less sensitive to double resonance Raman effects. This reduces their ininfluence and allows the microstructural strain in CNT composites to be probed more accurately. The use of these techniques could be applied to optimize any processing parameters in the manufacturing of CNT composites to achieve enhanced properties.
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Date Issued: 2011
Identifier: CFE0004110, ucf:49098
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004110

Title: Synchrotron based infrared microspectroscopy of carbonaceous chondrites.
Creator: Yesiltas, Mehmet, Peale, Robert, Fernandez, Yan, Britt, Daniel, Reach, William, University of Central Florida
Abstract / Description: Relationships between organic molecules and inorganic minerals are investigated in five carbonaceous chondrites, Northwest Africa 852 (CR2), Tagish Lake (C2-ungroupped), Orgueil (CI1), Sutter's Mill (CM), and Murchison (CM2), with micron spatial resolution using synchrotron-based imaging micro-FTIR spectroscopy. Correlations based on absorption strength for various constituents are determined using statistical correlation analysis. Silicate band is found to be positively correlated with...
Show moreRelationships between organic molecules and inorganic minerals are investigated in five carbonaceous chondrites, Northwest Africa 852 (CR2), Tagish Lake (C2-ungroupped), Orgueil (CI1), Sutter's Mill (CM), and Murchison (CM2), with micron spatial resolution using synchrotron-based imaging micro-FTIR spectroscopy. Correlations based on absorption strength for various constituents are determined using statistical correlation analysis. Silicate band is found to be positively correlated with stretching modes of aliphatic hydrocarbons in NWA 852 and Tagish Lake. The former is highly correlated with the hydration band in all meteorites. Negative correlation is observed between water+organics and carbonate bands in all meteorites. Two dimensional infrared maps for NWA 852 and Orgueil show that carbonates are spatially separated from water+organic combination, silicates, OH, and CH distributions. Overlapping of the latter three in NWA 852 and Tagish Lake suggests a possible catalytic role of phyllosilicates in the formation of organics. Additionally, spectroscopic analyses on Sutter's Mill meteorite fragments present multiple distinct mineralogies. Spatial and spectral evidences on this regolith breccia suggest mixing of multiple parent bodies. Ratios of asymmetric CH2 and CH3 band strengths for NWA 852, Tagish Lake, and Sutter's Mill are similar to the average ratio of interplanetary dust particles and Wild 2 cometary dust particles, however significantly exceeds that of interstellar medium objects and several aqueously altered carbonaceous chondrites such as Orgueil. This suggests distinct formation regions and/or parent body processing of organics for these meteorites. Our infrared spectro-microtomography measurements on Murchison meteorite, representing the first such measurement on any kind of meteorite, comprise of three-dimensional reconstructions of specific molecular functional groups for understanding the spatial distributions of these groups.
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Date Issued: 2015
Identifier: CFE0006061, ucf:50966
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006061

Title: Non-Dispersive Infrared (NDIR) Gas Sensor Utilizing Light-Emitting-Diodes Suitable for Applications Demanding Low-Power and Lightweight Instruments.
Creator: Thurmond, Kyle, Vasu Sumathi, Subith, Kassab, Alain, Kapat, Jayanta, University of Central Florida
Abstract / Description: Gas sensors that are low-power, light-weight, and rugged, while also remaining low-cost, have considerable appeal to areas from automotive to space flight. There are increasing demands for higher efficient vehicles with lower emissions in order meet regulations that are meant to mitigate or lessen the effects of climate change. An affordable, fast response sensor that can measure transient carbon monoxide (CO) and carbon dioxide (CO2) has broad application which can lead to more efficient,...
Show moreGas sensors that are low-power, light-weight, and rugged, while also remaining low-cost, have considerable appeal to areas from automotive to space flight. There are increasing demands for higher efficient vehicles with lower emissions in order meet regulations that are meant to mitigate or lessen the effects of climate change. An affordable, fast response sensor that can measure transient carbon monoxide (CO) and carbon dioxide (CO2) has broad application which can lead to more efficient, fuel flexible engines and regulations of harmful emissions. With compact, economical, low-power sensors that are able to continually monitor gases that are characteristic of burning materials, a distributed sensor array could be implemented on space vehicles that would allow early detection of fires, gas leaks, or other critical events. With careful selection of targeted gases, it may be possible to identify the material that is burning or smoldering, better informing the crew so that they may respond and prioritize high emergency events. Further applications may include fuel/ hazardous gas leak detection on space vehicles and atmospheric constituent sensor for portable life support systems (PLSS) used by astronauts in extra vehicular activity (EVA). Non-dispersive infrared (NDIR) sensors are attractive due to their simplicity and low-cost; and by using light-emitting-diodes (LEDs) in this approach, power efficient, light-weight, and stable gas sensors can be developed to meet these needs.This thesis discusses a sensor that was developed for simultaneous, time resolved measurements of carbon monoxide (CO) and carbon dioxide (CO2). This sensor utilizes low-cost and compact light emitting diodes (LEDs) that emit in the 3-5?m wavelength range. Light emission of LEDs is spectrally broader and more spatially divergent compared to that of lasers, which presented many design challenges. Optical design studies addressed some of the non-ideal characteristics of the LED emissions. Measurements of CO and CO2 were conducted using their fundamental absorption bands centered at 4.7?m and 4.3?m, respectively, while a 3.6?m reference LED was used to account for scattering losses (e.g., due to soot, window deposits, etc.) common to the three measurement LEDs. Instrument validation and calibration was performed using a laboratory flow cell and bottled-gas mixtures. The sensor was able to detect CO2 and CO concentration changes as small as 30 ppm and 400 ppm, respectively. Because of the many control and monitor species with infra-red absorption features, which can be measured using the strategy described, this work demonstrates proof of concept for a wider range of fast (250Hz) and low cost sensors for gas measurement and process monitoring.
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Date Issued: 2016
Identifier: CFE0006190, ucf:51091
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006190

Title: Quantitative Line Assignment in Optical Emission Spectroscopy.
Creator: Chappell, Jessica, Baudelet, Matthieu, Hernandez, Florencio, Campiglia, Andres, Ni, Liqiang, Sigman, Michael, University of Central Florida
Abstract / Description: Quantitative elemental analysis using Optical Emission Spectroscopy (OES) starts with a high level of confidence in spectral line assignment from reference databases. Spectral interferences caused by instrumental and line broadening decrease the resolution of OES spectra creating uncertainty in the elemental profile of a sample for the first time. An approach has been developed to quantify spectral interferences for individual line assignment in OES. The algorithm calculates a statistical...
Show moreQuantitative elemental analysis using Optical Emission Spectroscopy (OES) starts with a high level of confidence in spectral line assignment from reference databases. Spectral interferences caused by instrumental and line broadening decrease the resolution of OES spectra creating uncertainty in the elemental profile of a sample for the first time. An approach has been developed to quantify spectral interferences for individual line assignment in OES. The algorithm calculates a statistical interference factor (SIF) that combines a physical understanding of plasma emission with a Bayesian analysis of the OES spectrum. It can be used on a single optical spectrum and still address individual lines. Contrary to current methods, quantification of the uncertainty in elemental profiles of OES, leads to more accurate results, higher reliability and validation of the method. The SIF algorithm was evaluated for Laser-Induced Breakdown Spectroscopy (LIBS) on samples with increasing complexity: from silicon to nickel spiked alumina to NIST standards (600 glass series and nickel-chromium alloy). The influence of the user's knowledge of the sample composition was studied and showed that for the majority of spectral lines this information is not changing the line assignment for simple compositions. Nonetheless, the amount of interference could change with this information, as expected. Variance of the SIF results for NIST glass standard was evaluated by the chi-square hypothesis test of variance showing that the results of the SIF algorithm are very reproducible.
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Date Issued: 2018
Identifier: CFE0007564, ucf:52575
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007564

Title: Development of laser spectroscopy for elemental and molecular analysis.
Creator: Liu, Yuan, Richardson, Martin, Vanstryland, Eric, Bass, Michael, Sigman, Michael, University of Central Florida
Abstract / Description: Laser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy are still growing analytical and sensing spectroscopic techniques. They significantly reduce the time and labor cost in analysis with simplified instrumentation, and lead to minimal or no sample damage. In this dissertation, fundamental studies to improve LIBS analytical performance were performed and its fusion with Raman into one single sensor was explored.On the fundamental side, Thomson scattering was reported for the...
Show moreLaser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy are still growing analytical and sensing spectroscopic techniques. They significantly reduce the time and labor cost in analysis with simplified instrumentation, and lead to minimal or no sample damage. In this dissertation, fundamental studies to improve LIBS analytical performance were performed and its fusion with Raman into one single sensor was explored.On the fundamental side, Thomson scattering was reported for the first time to simultaneously measure the electron density and temperature of laser plasmas from a solid aluminum target at atmospheric pressure. Comparison between electron and excitation temperatures brought insights into the verification of local thermodynamic equilibrium condition in laser plasmas.To enhance LIBS emission, Microwave-Assisted LIBS (MA-LIBS) was developed and characterized. In MA-LIBS, a microwave field extends the emission lifetime of the plasma and stronger time integrated signal is obtained. Experimental results showed sensitivity improvement (more than 20-fold) and extension of the analytical range (down to a few tens of ppm) for the detection of copper traces in soil samples. Finally, laser spectroscopy systems that can perform both LIBS and Raman analysis were developed. Such systems provide two types of complimentary information (-) elemental composition from LIBS and structural information from Raman. Two novel approaches were reported for the first time for LIBS-Raman sensor fusion: (i) an Ultra-Violet system which combines Resonant Raman signal enhancement and high ablation efficiency from UV radiation, and (ii) a Ti:Sapphire laser based NIR system which reduces the fluorescence interference in Raman and takes advantage of femtosecond ablation for LIBS.
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Date Issued: 2013
Identifier: CFE0005105, ucf:50729
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005105

Title: HIGH GAIN / BROADBAND OXIDE GLASSES FOR NEXT GENERATION RAMAN AMPLIFIERS.
Creator: Rivero, Clara, Stegeman, George, University of Central Florida
Abstract / Description: Interest in Raman amplification has undergone a revival due to the rapidly increasing bandwidth requirements for communications transmission, both for long haul and local area networks, and recent developments in the telecom fiber industry and diode laser technology. In contrast to rare earth doped fiber amplifiers, for which the range of wavelengths is fixed and limited, Raman gain bandwidths are larger and the operating wavelength is fixed only by the pump wavelength and the bandwidth of...
Show moreInterest in Raman amplification has undergone a revival due to the rapidly increasing bandwidth requirements for communications transmission, both for long haul and local area networks, and recent developments in the telecom fiber industry and diode laser technology. In contrast to rare earth doped fiber amplifiers, for which the range of wavelengths is fixed and limited, Raman gain bandwidths are larger and the operating wavelength is fixed only by the pump wavelength and the bandwidth of the Raman active medium. In this context, glasses are the material of choice for this application due to their relatively broad spectral response, and ability of making them into optical fiber. This dissertation summarizes findings on different oxide-based glasses that have been synthesized and characterized for their potential application as Raman gain media. Two main glass families were investigated: phosphate-based glass matrices for broadband Raman gain application and TeO2-based glasses for high Raman gain amplification. A phosphate network was preferred for the broadband application since the phosphate Raman active modes can provide amplification above 1000 cm-1, whilst TeO2-based glasses were selected for the high gain application due to their enhanced nonlinearities and polarizabilities among the other oxide-based network formers. The results summarized in this dissertation show that phosphate-based glasses can provide Raman amplification bandwidths of up to 40 THz, an improvement of almost 5 times the bandwidth of SiO2. On the other hand, tellurite-based glasses appear to be promising candidates for high gain discrete Raman applications, providing peak Raman gain coefficients of up to 50 times higher than SiO2, at 1064 nm. Although, visible spontaneous Raman scattering cross-section measurement is the most frequently used tool for estimating the strength and spectral distribution of Raman gain in materials, especially glasses, there are some issues that one needs to be aware when conducting these measurements near the absorption band edge of the material. This led to the detection of an inherent frequency-dispersion in the Raman susceptibility and a resonant enhancement phenomenon when measurements were conducted near the absorption edge of the material.
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Date Issued: 2005
Identifier: CFE0000752, ucf:46554
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000752

Title: DESIGN AND IMPLEMENTATION OF AN EMISSION SPECTROSCOPY DIAGNOSTIC IN A HIGH-PRESSURE STRAND BURNER FOR THE STUDY OF SOLID PROPELLANT COMBUSTION.
Creator: Arvanetes, Jason, Petersen, Eric, University of Central Florida
Abstract / Description: The application of emission spectroscopy to monitor combustion products of solid rocket propellant combustion can potentially yield valuable data about reactions occurring within the volatile environment of a strand burner. This information can be applied in the solid rocket propellant industry. The current study details the implementation of a compact spectrometer and fiber optic cable to investigate the visible emission generated from three variations of solid propellants. The grating was...
Show moreThe application of emission spectroscopy to monitor combustion products of solid rocket propellant combustion can potentially yield valuable data about reactions occurring within the volatile environment of a strand burner. This information can be applied in the solid rocket propellant industry. The current study details the implementation of a compact spectrometer and fiber optic cable to investigate the visible emission generated from three variations of solid propellants. The grating was blazed for a wavelength range from 200 to 800 nm, and the spectrometer system provides time resolutions on the order of 1 millisecond. One propellant formula contained a fine aluminum powder, acting as a fuel, mixed with ammonium perchlorate (AP), an oxidizer. The powders were held together with Hydroxyl-Terminated-Polybutadiene (HTPB), a hydrocarbon polymer that is solidified using a curative after all components are homogeneously mixed. The other two propellants did not contain aluminum, but rather relied on the HTPB as a fuel source. The propellants without aluminum differed in that one contained a bimodal mix of AP. Utilizing smaller particle sizes within solid propellants yields greater surface area contact between oxidizer and fuel, which ultimately promotes faster burning. Each propellant was combusted in a controlled, non-reactive environment at a range of pressures between 250 and 2000 psi. The data allow for accurate burning rate calculations as well as an opportunity to analyze the combustion region through the emission spectroscopy diagnostic. It is shown that the new diagnostic identifies the differences between the aluminized and non-aluminized propellants through the appearance of aluminum oxide emission bands. Anomalies during a burn are also verified through the optical emission spectral data collected.
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Date Issued: 2006
Identifier: CFE0000971, ucf:46694
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000971

Title: NONDESTRUCTIVE EVALUATION OF THERMAL BARRIER COATINGS WITH THERMAL WAVE IMAGING AND PHOTOSTIMULATED LUMINESCENCE SPECTROSCOPY.
Creator: Franke, Barbara, Sohn, Yong-ho, University of Central Florida
Abstract / Description: Gas Turbine manufacturers strive for increased operating temperatures of gas turbine engines to improve efficiency and performance. One method of increasing the temperature beyond material limits is by applying thermal barrier coatings (TBCs) to hot section components. TBCs provide a thermal gradient between the hot gases and metallic substrate, and allow an increase in turbine inlet temperatures of 100-150ºC. However, spallation of TBCs can cause catastrophic failure of turbine engines...
Show moreGas Turbine manufacturers strive for increased operating temperatures of gas turbine engines to improve efficiency and performance. One method of increasing the temperature beyond material limits is by applying thermal barrier coatings (TBCs) to hot section components. TBCs provide a thermal gradient between the hot gases and metallic substrate, and allow an increase in turbine inlet temperatures of 100-150ºC. However, spallation of TBCs can cause catastrophic failure of turbine engines by incipient melting of the substrate. To prevent such an occurrence, non-destructive evaluation (NDE) techniques are critical for quality control, health monitoring, and life assessment of TBCs. Two techniques in development for this purpose are thermal wave imaging (TWI) and photostimulated luminescence (PL) spectroscopy. TWI is a promising NDE technique with the ability to detect integrity and thickness of TBCs. In this study, TWI was employed as an NDE technique to examine as-coated TBCs with varying thicknesses, and thermally-cycled TBCs for initiation and progression of subcritical-subsurface damage as a function of thermal cycling. TWI and thermal response amplitude were correlated to the microstructural characteristics and damage progression of TBCs based on phenomenological expressions of thermal diffusion. The TBC specimens examined consisted of air plasma sprayed ZrO2 - 7wt.% Y2O3 on NiCoCrAlY bond coats with Haynes 230 superalloy substrate. As-coated specimens of varying thicknesses were evaluated by TWI to examine its applicability as a thickness measurement tool. It was found that heat dissipation through the TBC following pulsed excitation by xenon flash lamps initially followed the 1-D law of conduction and deviated from it as a function of thickness and time. The deviation resulted from quick dissipation of heat into the conductive metallic substrate. Therefore, with calibration, TWI can be used as a tool for YSZ thickness measurements of APS TBCs in the as-coated condition for quality control measures. Specimens of uniform thickness were evaluated as a function of thermal cyclic oxidation for subcritical-subsurface damage detection. Thermal cycling was carried out in air with 30-minute heat-up, 10-hour dwell at 1150°C, 30-minute air-quench and 1-hour hold at room temperature. During thermal cycling, TBC specimens were evaluated non-destructively by TWI at room temperature every 10 to 20 thermal cycles, and selected specimens were removed from thermal cycling for microstructural analysis by scanning electron microscopy (SEM). Higher thermal response amplitude associated with disrupted heat transfer was observed where localized spallation at or near the YSZ/TGO interface occurred. The health of the TBC was monitored by a rise in thermal response amplitude which may indicate a coalescence of microcracks to a detectable level. PL has been developed to measure stress, and detect subsurface damage and polymorphic transformation within the thermally grown oxide (TGO) of TBCs. PL was employed in this study as an NDE technique for TBCs to correlate subsurface damage as a function of thermal cyclic oxidation. The TBCs consisted of ZrO2 – 7 wt.% Y2O3 applied by electron beam physical vapor deposition with an as-coated (Ni,Pt)Al bond coat on a CMSX-4 superalloy substrate. Specimens were thermally cycled with a 10 minute ramp to a peak temperature of 1121°C, 40 minute hold at peak temperature, and 10 minute forced air quench. The TBCs were periodically removed from thermal cycling for NDE using PL until failure. Two specimens were removed from thermal oxidation after 10% and 70% of the average lifetime for microstructural analysis by SEM. During initial thermal cycling, metastable phases and polymorphic transformations of the Al2O3 scale were examined by PL. The polymorphic transformation from a metastable phase to equilibrium a-Al2O3 was detected. Since metastable phases are thought to be detrimental to coating lifetime, detection of these phases by PL can be used as a quality control tool. Nearing end-of-life, relief of the TGO from the compressive residual stress arising from thermal expansion mismatch was detected with PL and confirmed with microstructural analysis that revealed damage initiation (e.g. microcracking within the TGO scale parallel to the interfaces.) Rise in luminescence near the R-line frequency for polycrystalline a-Al2O3 without any residual stress (i.e. n = 14402 cm-1 and n = 14432 cm-1) corresponded to regions where cracked TGO was adhered to YSZ and not exposed to compressive stresses from thermal expansion mismatch upon cooling.
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Date Issued: 2005
Identifier: CFE0000717, ucf:46613
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000717

Title: DEVELOPMENT AND VALIDATION OF AN ABSORPTION SENSOR FOR TIME-RESOLVED MEASUREMENTS OF CO AND CO2.
Creator: Thurmond, Kyle, Vasu, Subith, University of Central Florida
Abstract / Description: A sensor was developed for simultaneous measurements of carbon monoxide and carbon dioxide fluctuations in internal combustion engine exhaust gases. This sensor utilizes low-cost and compact LEDs that emit in the 3-5[mu] wavelength range which are more appropriate for practical applications than the more traditionally used lasers. An affordable, fast response sensor that can measure these gases has broad application that can lead to more efficient, fuel flexible engines and regulations of...
Show moreA sensor was developed for simultaneous measurements of carbon monoxide and carbon dioxide fluctuations in internal combustion engine exhaust gases. This sensor utilizes low-cost and compact LEDs that emit in the 3-5[mu] wavelength range which are more appropriate for practical applications than the more traditionally used lasers. An affordable, fast response sensor that can measure these gases has broad application that can lead to more efficient, fuel flexible engines and regulations of harmful emissions. LEDs have a more spectrally broad and diverging emission than lasers which presented many design challenges. The optical design software ZEMAX was utilized to overcome these challenges. CO and CO2 LED measurements are conducted in their fundamental bands centered at 4.7[mu] and 4.3[mu], respectively, while a reference LED at 3.6[mu] is used as a reference for H2O. Tests were carried out using a simple flow cell for validation and calibration of the instrument. The sensor was able to see 0.1% changes in CO2 and about 0.3% changes CO. No interference between CO and CO2 was observed.
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Date Issued: 2013
Identifier: CFH0004529, ucf:45192
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004529

Title: MICRO-RAMAN SPECTROSCOPY OF CARBONACEOUS CHONDRITE METEORITES.
Creator: Habach, Asmail, Schulte, Alfons, University of Central Florida
Abstract / Description: Analyzing the constituents of meteorites has played an important role in forming the contemporary theories of solar system evolution, planets formation, and stellar evolution. Meteorites are often a complex mixture of common rock forming silicates, such as olivines and pyroxenes, with a range of exotic species including hydrated silicates, and in some cases organic compounds. We used Micro-Raman spectroscopy to analyze the compositions of three carbonaceous chondrites: NWA852, Murchison and...
Show moreAnalyzing the constituents of meteorites has played an important role in forming the contemporary theories of solar system evolution, planets formation, and stellar evolution. Meteorites are often a complex mixture of common rock forming silicates, such as olivines and pyroxenes, with a range of exotic species including hydrated silicates, and in some cases organic compounds. We used Micro-Raman spectroscopy to analyze the compositions of three carbonaceous chondrites: NWA852, Murchison and Allende. Raman spectra were measured using laser sources with different excitation wavelengths: HeNe 633 nm and Nd:YAG 532 nm. We were able to detect 9 minerals in NWA852, 3 minerals in Murchison and 4 minerals in Allende. Some of these minerals like pyrite in NWA852 and magnetite in NWA852 and Murchison provide evidence for potential previous organic life. Other minerals like ringwoodite in Allende and lizardite in NWA852 reveal information about previous astrophysical and geological events experienced by the meteorites. The detection of graphite in the Murchison and Allende reveals information about the microstructure of these meteorites.
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Date Issued: 2014
Identifier: CFH0004710, ucf:45396
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004710

Title: RESONANT ANISOTROPIC EMISSION IN RABBITT SPECTROSCOPY.
Creator: Ghomashi, Bejan M, Argenti, Luca, Douguet, Nicolas, University of Central Florida
Abstract / Description: A variant of RABBITT pump-probe spectroscopy in which the attosecond pulse train comprises both even and odd harmonics of the fundamental IR probe frequency is explored to measure time-resolved photoelectron emission in systems that exhibit autoionizing states. It is shown that the group delay of both one-photon and two-photon resonant transitions is directly encoded in the energy-resolved photoelectron anisotropy as a function of the pump-probe time-delay. This principle is illustrated for a...
Show moreA variant of RABBITT pump-probe spectroscopy in which the attosecond pulse train comprises both even and odd harmonics of the fundamental IR probe frequency is explored to measure time-resolved photoelectron emission in systems that exhibit autoionizing states. It is shown that the group delay of both one-photon and two-photon resonant transitions is directly encoded in the energy-resolved photoelectron anisotropy as a function of the pump-probe time-delay. This principle is illustrated for a 1D model with symmetric zero-range potentials that supports both bound states and shape-resonances. The model is studied using both perturbation theory and solving the time-dependent Schodinger equation on a grid. Moreover, we study the case of a realistic atomic system, helium. In both cases, we demonstrate faithful reconstruction of the phase information for resonant photoemission.
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Date Issued: 2018
Identifier: CFH2000451, ucf:45703
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH2000451

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