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- Title
- PREDICTING SURFACE SCATTER USING A LINEAR SYSTEMS FORMULATION OF NON-PARAXIAL SCALAR DIFFRACTION.
- Creator
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Krywonos, Andrey, Harvey, James, University of Central Florida
- Abstract / Description
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Scattering effects from rough surfaces are non-paraxial diffraction phenomena resulting from random phase variations in the reflected wavefront. The ability to predict these effects is important in a variety of applications including x-ray and EUV imaging, the design of stray light rejection systems, and reflection modeling for rendering realistic scenes and animations of physical objects in computer graphics. Rayleigh-Rice (small perturbation method) and Beckmann-Kirchoff (Kirchhoff...
Show moreScattering effects from rough surfaces are non-paraxial diffraction phenomena resulting from random phase variations in the reflected wavefront. The ability to predict these effects is important in a variety of applications including x-ray and EUV imaging, the design of stray light rejection systems, and reflection modeling for rendering realistic scenes and animations of physical objects in computer graphics. Rayleigh-Rice (small perturbation method) and Beckmann-Kirchoff (Kirchhoff approximation) theories are commonly used to predict surface scatter effects. In addition, Harvey and Shack developed a linear systems formulation of surface scatter phenomena in which the scattering behavior is characterized by a surface transfer function. This treatment provided insight and understanding not readily gleaned from the two previous theories, and has been incorporated into a variety of computer software packages (ASAP, Zemax, Tracepro). However, smooth surface and paraxial approximations have severely limited the range of applicability of each of the above theoretical treatments. In this dissertation, a linear systems formulation of non-paraxial scalar diffraction theory is first developed and then applied to sinusoidal phase gratings, resulting in diffraction efficiency predictions far more accurate than those provided by classical scalar theories. The application of the theory to these gratings was motivated by the fact that rough surfaces are frequently modeled as a superposition of sinusoidal surfaces of different amplitudes, periods, and orientations. The application of the non-paraxial scalar diffraction theory to surface scatter phenomena resulted first in a modified Beckmann-Kirchhoff surface scattering model, then a generalized Harvey-Shack theory, both of which produce accurate results for rougher surfaces than the Rayleigh-Rice theory and for larger incident and scattering angles than the classical Beckmann-Kirchhoff theory. These new developments enable the analysis and simplify the understanding of wide-angle scattering behavior from rough surfaces illuminated at large incident angles. In addition, they provide an improved BRDF (Bidirectional Reflectance Distribution Function) model, particularly for the smooth surface inverse scattering problem of determining surface power spectral density (PSD) curves from BRDF measurements.
Show less - Date Issued
- 2006
- Identifier
- CFE0001446, ucf:47055
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001446
- Title
- MONOLITHIC INTEGRATION OF DUAL OPTICAL ELEMENTS ON HIGH POWER SEMICONDUCTOR LASERS.
- Creator
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vaissie, laurent, Johnson, Eric, University of Central Florida
- Abstract / Description
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This dissertation investigates the monolithic integration of dual optical elements on high power semiconductor lasers for emission around 980nm wavelength. In the proposed configuration, light is coupled out of the AlGaAs/GaAs waveguide by a low reflectivity grating coupler towards the substrate where a second monolithic optical element is integrated to improve the device performance or functionality. A fabrication process based on electron beam lithography and plasma etching was developed to...
Show moreThis dissertation investigates the monolithic integration of dual optical elements on high power semiconductor lasers for emission around 980nm wavelength. In the proposed configuration, light is coupled out of the AlGaAs/GaAs waveguide by a low reflectivity grating coupler towards the substrate where a second monolithic optical element is integrated to improve the device performance or functionality. A fabrication process based on electron beam lithography and plasma etching was developed to control the grating coupler duty cycle and shape. The near-field intensity profile outcoupled by the grating is modeled using a combination of finite-difference time domain (FDTD) analysis of the nonuniform grating and a self-consistent model of the broad area active region. Improvement of the near-field intensity profile in good agreement with the FDTD model is demonstrated by varying the duty cycle from 20% to 55% and including the aspect ratio dependent etching (ARDE) for sub-micron features. The grating diffraction efficiency is estimated to be higher than 95% using a detailed analysis of the losses mechanisms of the device. The grating reflectivity is estimated to be as low as 2.10-4. The low reflectivity of the light extraction process is shown to increase the device efficiency and efficiently suppress lasing oscillations if both cleaved facets are replaced by grating couplers to produce 1.5W QCW with 11nm bandwidth into a single spot a few mm above the device. Peak power in excess of 30W without visible COMD is achieved in this case. Having optimized, the light extraction process, we demonstrate the integration of three different optical functions on the substrate of the surface-emitting laser. First, a 40 level refractive microlens milled using focused ion beam shows a twofold reduction of the full-width half maximum 1mm above the device, showing potential for monolithic integration of coupling optics on the wafer. We then show that differential quantum efficiency of 65%, the highest reported for a grating-coupled device, can be achieved by lowering the substrate reflectivity using a 200nm period tapered subwavelength grating that has a grating wavevector oriented parallel to the electric field polarization. The low reflectivity structure shows trapezoidal sidewall profiles obtained using a soft mask erosion technique in a single etching step. Finally, we demonstrate that, unlike typical methods reported so far for in-plane beam-shaping of laser diodes, the integration of a beam-splitting element on the device substrate does not affect the device efficiency. The proposed device configuration can be tailored to satisfy a wide range of applications including high power pump lasers, superluminescent diodes, or optical amplifiers applications.
Show less - Date Issued
- 2004
- Identifier
- CFE0000223, ucf:46253
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000223
- Title
- ACCELERATING OPTICAL AIRY BEAMS.
- Creator
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Siviloglou, Georgios, CHRISTODOULIDES, DEMETRIOS, University of Central Florida
- Abstract / Description
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Over the years, non-spreading or non-diffracting wave configurations have been systematically investigated in optics. Perhaps the best known example of a diffraction-free optical wave is the so-called Bessel beam, first suggested and observed by Durnin et al. This work sparked considerable theoretical and experimental activity and paved the way toward the discovery of other interesting non-diffracting solutions. In 1979 Berry and Balazs made an important observation within the context of...
Show moreOver the years, non-spreading or non-diffracting wave configurations have been systematically investigated in optics. Perhaps the best known example of a diffraction-free optical wave is the so-called Bessel beam, first suggested and observed by Durnin et al. This work sparked considerable theoretical and experimental activity and paved the way toward the discovery of other interesting non-diffracting solutions. In 1979 Berry and Balazs made an important observation within the context of quantum mechanics: they theoretically demonstrated that the Schrödinger equation describing a free particle can exhibit a non-spreading Airy wavepacket solution. This work remained largely unnoticed in the literature-partly because such wavepackets cannot be readily synthesized in quantum mechanics. In this dissertation we investigate both theoretically and experimentally the acceleration dynamics of non-spreading optical Airy beams in both one- and two-dimensional configurations. We show that this class of finite energy waves can retain their intensity features over several diffraction lengths. The possibility of other physical realizations involving spatio-temporal Airy wavepackets is also considered. As demonstrated in our experiments, these Airy beams can exhibit unusual features such as the ability to remain quasi-diffraction-free over long distances while their intensity features tend to freely accelerate during propagation. We have demonstrated experimentally that optical Airy beams propagating in free space can perform ballistic dynamics akin to those of projectiles moving under the action of gravity. The parabolic trajectories of these beams as well as the motion of their center of gravity were observed in good agreement with theory. Another remarkable property of optical Airy beams is their resilience in amplitude and phase perturbations. We show that this class of waves tends to reform during propagation in spite of the severity of the imposed perturbations. In all occasions the reconstruction of these beams is interpreted through their internal transverse power flow. The robustness of these optical beams in scattering and turbulent environments was also studied. The experimental observation of self-trapped Airy beams in unbiased nonlinear photorefractive media is also reported. This new class of non-local self-localized beams owes its existence to carrier diffusion effects as opposed to self-focusing. These finite energy Airy states exhibit a highly asymmetric intensity profile that is determined by the inherent properties of the nonlinear crystal. In addition, these wavepackets self-bend during propagation at an acceleration rate that is independent of the thermal energy associated with two-wave mixing diffusion photorefractive nonlinearity.
Show less - Date Issued
- 2010
- Identifier
- CFE0003193, ucf:48569
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003193
- Title
- A Diffraction Model for Prediction of Radar Signal Attention by a Rocket Exhaust Plume.
- Creator
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Sphar, Douglas Harrison, Mathews, B.E., Engineering
- Abstract / Description
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Florida Technological University College of Engineering Thesis; This report documents the development of a method of estimating the signal attenuation induced by a rocket exhaust plume. The method is applicable to the early system design phase of high energy solid propellant rockets that produce highly ionized exhaust plumes. The method is based on the premise that when a plume is highly ionized, observed signal levels can be explained by assuming the signal propagates around the plume. A...
Show moreFlorida Technological University College of Engineering Thesis; This report documents the development of a method of estimating the signal attenuation induced by a rocket exhaust plume. The method is applicable to the early system design phase of high energy solid propellant rockets that produce highly ionized exhaust plumes. The method is based on the premise that when a plume is highly ionized, observed signal levels can be explained by assuming the signal propagates around the plume. A simple diffraction at a straight edge model is developed and compared to measured data. The report also provides an overview of exhaust plume electromagnetics and surveys prediction techniques.
Show less - Date Issued
- 1972
- Identifier
- CFR0003481, ucf:53035
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFR0003481
- Title
- DESIGN, ANALYSIS, AND OPTIMIZATION OF DIFFRACTIVE OPTICAL ELEMENTS UNDER HIGH NUMERICAL APERTURE FOCUSING.
- Creator
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Jabbour, Toufic, Kuebler, Stephen, University of Central Florida
- Abstract / Description
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The demand for high optical resolution has brought researchers to explore the use of beam shaping diffractive optical elements (DOEs) for improving performance of high numerical aperture (NA) optical systems. DOEs can be designed to modulate the amplitude, phase and/or polarization of a laser beam such that it focuses into a targeted irradiance distribution, or point spread function (PSF). The focused PSF can be reshaped in both the transverse focal plane and along the optical axis. Optical...
Show moreThe demand for high optical resolution has brought researchers to explore the use of beam shaping diffractive optical elements (DOEs) for improving performance of high numerical aperture (NA) optical systems. DOEs can be designed to modulate the amplitude, phase and/or polarization of a laser beam such that it focuses into a targeted irradiance distribution, or point spread function (PSF). The focused PSF can be reshaped in both the transverse focal plane and along the optical axis. Optical lithography, microscopy and direct laser writing are but a few of the many applications in which a properly designed DOE can significantly improve optical performance of the system. Designing DOEs for use in high-NA applications is complicated by electric field depolarization that occurs with tight focusing. The linear polarization of off-axis rays is tilted upon refraction towards the focal point, generating additional transverse and longitudinal polarization components. These additional field components contribute significantly to the shape of the PSF under tight focusing and cannot be neglected as in scalar diffraction theory. The PSF can be modeled more rigorously using the electromagnetic diffraction integrals derived by Wolf, which account for the full vector character of the field. In this work, optimization algorithms based on vector diffraction theory were developed for designing DOEs that reshape the PSF of a 1.4-NA objective lens. The optimization techniques include simple exhaustive search, iterative optimization (Method of Generalized Projections), and evolutionary computation (Particle Swarm Optimization). DOE designs were obtained that can reshape either the transverse PSF or the irradiance distribution along the optical axis. In one example of transverse beam shaping, all polarization components were simultaneously reshaped so their vector addition generates a focused flat-top square irradiance pattern. Other designs were obtained that can be used to narrow the axial irradiance distribution, giving a focused beam that is superresolved relative to the diffraction limit. In addition to theory, experimental studies were undertaken that include (1) fabricating an axially superresolving DOE, (2) incorporating the DOE into the optical setup, (3) imaging the focused PSF, and (4) measuring aberrations in the objective lens to study how these affect performance of the DOE.
Show less - Date Issued
- 2009
- Identifier
- CFE0002844, ucf:48063
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002844
- Title
- DESIGN AND OPTIMIZATION OF NANO-OPTICAL ELEMENTS BY COUPLING FABRICATION TO OPTICAL BEHAVIOR.
- Creator
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Rumpf, Raymond, Johnson, Eric, University of Central Florida
- Abstract / Description
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Photonic crystals and nanophotonics have received a great deal of attention over the last decade, largely due to improved numerical modeling and advances in fabrication technologies. To this day, fabrication and optical behavior remain decoupled during the design phase and numerous assumptions are made about "perfect" geometry. As research moves from theory to real devices, predicting device behavior based on realistic geometry becomes critical. In this dissertation, a set of numerical tools...
Show morePhotonic crystals and nanophotonics have received a great deal of attention over the last decade, largely due to improved numerical modeling and advances in fabrication technologies. To this day, fabrication and optical behavior remain decoupled during the design phase and numerous assumptions are made about "perfect" geometry. As research moves from theory to real devices, predicting device behavior based on realistic geometry becomes critical. In this dissertation, a set of numerical tools was developed to model micro and nano fabrication processes. They were combined with equally capable tools to model optical performance of the simulated structures. Using these tools, it was predicted and demonstrated that 3D nanostructures may be formed on a standard mask aligner. A space-variant photonic crystal filter was designed and optimized based on a simple fabrication method of etching holes through hetero-structured substrates. It was found that hole taper limited their optical performance and a method was developed to compensate. A method was developed to tune the spectral response of guided-mode resonance filters at the time of fabrication using models of etching and deposition. Autocloning was modeled and shown that it could be used to form extremely high aspect ratio structures to improve performance of form-birefringent devices. Finally, the numerical tools were applied to metallic photonic crystal devices.
Show less - Date Issued
- 2006
- Identifier
- CFE0001159, ucf:46849
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001159
- Title
- Engineering and Application of Ultrafast Laser Pulses and Filamentation in Air.
- Creator
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Barbieri, Nicholas, Richardson, Martin, University of Central Florida
- Abstract / Description
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Continuing advances in laser and photonic technology has seen the development of lasers with increasing power and increasingly short pulsewidths, which have become available over an increasing range of wavelengths. As the availability of laser sources grow, so do their applications. To make better use of this improving technology, understanding and controlling laser propagation in free space is critical, as is understanding the interaction between laser light and matter.The need to better...
Show moreContinuing advances in laser and photonic technology has seen the development of lasers with increasing power and increasingly short pulsewidths, which have become available over an increasing range of wavelengths. As the availability of laser sources grow, so do their applications. To make better use of this improving technology, understanding and controlling laser propagation in free space is critical, as is understanding the interaction between laser light and matter.The need to better control the light obtained from increasingly advanced laser sources leads to the emergence of beam engineering, the systematic understanding and control of light through refractive media and free space. Beam engineering enables control over the beam shape, energy and spectral composition during propagation, which can be achieved through a variety of means. In this dissertation, several methods of beam engineering are investigated. These methods enable improved control over the shape and propagation of laser light. Laser-matter interaction is also investigated, as it provides both a means to control the propagation of pulsed laser light through the atmosphere, and provides a means to generation remote sources of radiation.
Show less - Date Issued
- 2013
- Identifier
- CFE0004650, ucf:49881
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004650
- Title
- LOW TEMPERATURE NITIFE SHAPE MEMORY ALLOYS: ACTUATOR ENGINEERING AND INVESTIGATION OF DEFORMATION MECHANISMS USING IN SITU NEUTRON DIFFRACTION AT LOS ALAMOS NATIONAL LABORATORY.
- Creator
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Krishnan, Vinu, Vaidyanathan, Raj, University of Central Florida
- Abstract / Description
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Shape memory alloys are incorporated as actuator elements due to their inherent ability to sense a change in temperature and actuate against external loads by undergoing a shape change as a result of a temperature-induced phase transformation. The cubic so-called austenite to the trigonal so-called R-phase transformation in NiTiFe shape memory alloys offers a practical temperature range for actuator operation at low temperatures, as it exhibits a narrow temperature-hysteresis with a desirable...
Show moreShape memory alloys are incorporated as actuator elements due to their inherent ability to sense a change in temperature and actuate against external loads by undergoing a shape change as a result of a temperature-induced phase transformation. The cubic so-called austenite to the trigonal so-called R-phase transformation in NiTiFe shape memory alloys offers a practical temperature range for actuator operation at low temperatures, as it exhibits a narrow temperature-hysteresis with a desirable fatigue response. Overall, this work is an investigation of selected science and engineering aspects of low temperature NiTiFe shape memory alloys. The scientific study was performed using in situ neutron diffraction measurements at the newly developed low temperature loading capability on the Spectrometer for Materials Research at Temperature and Stress (SMARTS) at Los Alamos National Laboratory and encompasses three aspects of the behavior of Ni46.8Ti50Fe3.2 at 92 K (the lowest steady state temperature attainable with the capability). First, in order to study deformation mechanisms in the R-phase in NiTiFe, measurements were performed at a constant temperature of 92 K under external loading. Second, with the objective of examining NiTiFe in one-time, high-stroke, actuator applications (such as in safety valves), a NiTiFe sample was strained to approximately 5% (the R-phase was transformed to B19' phase in the process) at 92 K and subsequently heated to full strain recovery under a load. Third, with the objective of examining NiTiFe in cyclic, low-stroke, actuator applications (such as in cryogenic thermal switches), a NiTiFe sample was strained to 1% at 92 K and subsequently heated to full strain recovery under load. Neutron diffraction spectra were recorded at selected time and stress intervals during these experiments. The spectra were subsequently used to obtain quantitative information related to the phase-specific strain, texture and phase fraction evolution using the Rietveld technique. The mechanical characterization of NiTiFe alloys using the cryogenic capability at SMARTS provided considerable insight into the mechanisms of phase transformation and twinning at cryogenic temperatures. Both mechanisms contribute to shape memory and pseudoelasticity phenomena. Three phases (R, B19' and B33 phases) were found to coexist at 92 K in the unloaded condition (nominal holding stress of 8 MPa). For the first time the elastic modulus of R-phase was reported from neutron diffraction experiments. Furthermore, for the first time a base-centered orthorhombic (B33) martensitic phase was identified experimentally in a NiTi-based shape memory alloy. The orthorhombic B33 phase has been theoretically predicted in NiTi from density function theory (DFT) calculations but hitherto has never been observed experimentally. The orthorhombic B33 phase was observed while observing shifting of a peak (identified to be B33) between the R and B19' peaks in the diffraction spectra collected during loading. Given the existing ambiguity in the published literature as to whether the trigonal R-phase belongs to the P3 or P space groups, Rietveld analyses were separately carried out incorporating the symmetries associated with both space groups and the impact of this choice evaluated. The constrained recovery of the B19' phase to the R-phase recorded approximately 4% strain recovery between 150 K and 170 K, with half of that recovery occurring between 160 K and 162 K. Additionally, the aforementioned research methodology developed for Ni46.8Ti50Fe3.2 shape memory alloys was applied to experiments performed on a new high temperature Ni29.5Ti50.5Pd20 shape memory alloys. The engineering aspect focused on the development of (i) a NiTiFe based thermal conduction switch that minimized the heat gradient across the shape memory actuator element, (ii) a NiTiFe based thermal conduction switch that incorporated the actuator element in the form of helical springs, and (iii) a NiTi based release mechanism. Patents are being filed for all the three shape memory actuators developed as a part of this work. This work was supported by grants from SRI, NASA (NAG3-2751) and NSF (CAREER DMR-0239512) to UCF. Additionally, this work benefited from the use of the Lujan Center at the Los Alamos Neutron Science Center, funded by the United States Department of Energy, Office of Basic Energy Sciences, under Contract No. W-7405-ENG-36.
Show less - Date Issued
- 2007
- Identifier
- CFE0001934, ucf:47437
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001934
- Title
- MICRO-OPTIC-SPECTRAL-SPATIAL-ELEMENTS (MOSSE).
- Creator
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Mehta, Alok, Johnson, Eric, University of Central Florida
- Abstract / Description
-
Over a wide range of applications, optical systems have utilized conventional optics in order to provide the ability to engineer the properties of incident infra-red fields in terms of the transmitted field spectral, spatial, amplitude, phase, and polarization characteristics. These micro/nano-optical elements that provide specific optical functionality can be categorized into subcategories of refractive, diffractive, multi-layer thin film dichroics, 3-D photonic crystals, and polarization...
Show moreOver a wide range of applications, optical systems have utilized conventional optics in order to provide the ability to engineer the properties of incident infra-red fields in terms of the transmitted field spectral, spatial, amplitude, phase, and polarization characteristics. These micro/nano-optical elements that provide specific optical functionality can be categorized into subcategories of refractive, diffractive, multi-layer thin film dichroics, 3-D photonic crystals, and polarization gratings. The feasibility of fabrication, functionality, and level of integration which these elements can be used in an optical system differentiate which elements are more compatible with certain systems than others. With enabling technologies emerging allowing for a wider range of options when it comes to lithographic nano/micro-patterning, dielectric growth, and transfer etching capabilities, optical elements that combine functionalities of conventional optical elements can be realized. Within this one class of optical elements, it is possible to design and fabricate components capable of tailoring the spectral, spatial, amplitude, phase, and polarization characteristics of desired fields at different locations within an optical system. Optical transmission filters, polarization converting elements, and spectrally selective reflecting components have been investigated over the course of this dissertation and have been coined MOSSE,' which is an acronym for micro-optic-spectral-spatial-elements. Each component is developed and fabricated on a wafer scale where the thin film deposition, lithographic exposure, and transfer etching stages are decoupled from each other and performed in a sequential format. This facilitates the ability to spatially vary the optical characteristics of the different MOSSE structures across the surface of the wafer itself.
Show less - Date Issued
- 2007
- Identifier
- CFE0001962, ucf:47457
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001962
- Title
- FEMTOSECOND LASER WRITTEN VOLUMETRIC DIFFRACTIVE OPTICAL ELEMENTS AND THEIR APPLICATIONS.
- Creator
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Choi, Jiyeon, Richardson, Martin, University of Central Florida
- Abstract / Description
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Since the first demonstration of femtosecond laser written waveguides in 1996, femtosecond laser direct writing (FLDW) has been providing a versatile means to fabricate embedded 3-D microstructures in transparent materials. The key mechanisms are nonlinear absorption processes that occur when a laser beam is tightly focused into a material and the intensity of the focused beam reaches the range creating enough free electrons to induce structural modification. One of the most useful features...
Show moreSince the first demonstration of femtosecond laser written waveguides in 1996, femtosecond laser direct writing (FLDW) has been providing a versatile means to fabricate embedded 3-D microstructures in transparent materials. The key mechanisms are nonlinear absorption processes that occur when a laser beam is tightly focused into a material and the intensity of the focused beam reaches the range creating enough free electrons to induce structural modification. One of the most useful features that can be exploited in fabricating photonic structures is the refractive index change which results from the localized energy deposition. The laser processing system for FLDW can be realized as a compact, desktop station, implemented by a laser source, a 3-D stage and focusing optics. Thus, FLDW can be readily adopted for the fabrication of the photonic devices. For instance, it has been widely employed in various areas of photonic device fabrication such as active and passive waveguides, couplers, gratings, opto-fluidics and similar applications. This dissertation describes the use of FLDW towards the fabrication of custom designed diffractive optical elements (DOE's). These are important micro-optical elements that are building blocks in integrated optical devices including on-chip sensors and systems. The fabrication and characterization of laser direct written DOEs in different glass materials is investigated. The design and performance of a range of DOE's is described, especially, laser-written embedded Fresnel zone plates and linear gratings. Their diffractive efficiency as a function of the fabrication parameters is discussed and an optimized fabrication process is realized. The potential of the micro-DOEs and their integration shown in this dissertation will impact on the fabrication of future on-chip devices involving customized DOEs that will serve great flexibility and multi-functional capability on sensing, imaging and beam shaping.
Show less - Date Issued
- 2009
- Identifier
- CFE0002958, ucf:47984
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002958
- Title
- ULTRASHORT LASER PULSE INTERACTION WITH PHOTO-THERMO-REFRACTIVE GLASS.
- Creator
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Siiman, Leo, Glebov, Leonid, University of Central Florida
- Abstract / Description
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Photo-thermo-refractive (PTR) glass is an ideal photosensitive material for recording phase volume holograms. It is a homogeneous multi-component silicate glass that demonstrates all the advantages of optical glass: thermal stability, high laser damage threshold, and a wide transparency range. Moreover the ability to record phase patterns (i.e. spatial refractive index variations) into PTR glass has resulted in the fabrication of volume holograms with diffraction efficiency greater than 99%....
Show morePhoto-thermo-refractive (PTR) glass is an ideal photosensitive material for recording phase volume holograms. It is a homogeneous multi-component silicate glass that demonstrates all the advantages of optical glass: thermal stability, high laser damage threshold, and a wide transparency range. Moreover the ability to record phase patterns (i.e. spatial refractive index variations) into PTR glass has resulted in the fabrication of volume holograms with diffraction efficiency greater than 99%. The conventional method of recording a hologram in PTR glass relies on exposure to continuous-wave ultraviolet laser radiation. In this dissertation the interaction between infrared ultrashort laser pulses and PTR glass is studied. It is shown that photosensitivity in PTR glass can be extended from the UV region to longer wavelengths (near-infrared) by exposure to ultrashort laser pulses. It is found that there exists a focusing geometry and laser pulse intensity interval for which photoionization and refractive index change in PTR glass after thermal development occur without laser-induced optical damage. Photoionization of PTR glass by IR ultrashort laser pulses is explained in terms of strong electric field ionization. This phenomenon is used to fabricate phase optical elements in PTR glass. The interaction between ultrashort laser pulses and volume holograms in PTR glass is studied in two laser intensity regimes. At intensities below ~10^12 W/cm^2 properties such as diffraction efficiency, angular divergence, selectivity, and pulse front tilt are shown to agree with the theory of linear diffraction for broad spectral width lasers. A volume grating pair arrangement is shown to correct the laser pulse distortions arising from pulse front tilt and angular divergence. At higher intensities of irradiation, nonlinear generation and diffraction of third harmonic is observed for three types of interactions: sum-frequency generation, front-surface THG generation, and THG due to phase-matching with a grating formed by modulation of the nonlinear refractive index of PTR glass.
Show less - Date Issued
- 2008
- Identifier
- CFE0002349, ucf:47804
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002349
- Title
- Liquid crystal phase modulation for beam steering and near-eye displays.
- Creator
-
Lee, Yun Han, Wu, Shintson, Moharam, Jim, Likamwa, Patrick, Dong, Yajie, University of Central Florida
- Abstract / Description
-
Liquid crystal spatial phase modulator plays an important role in laser beam steering, wave-front shaping and correction, optical communication, optical computation and holography. One fundamental limitation lays in the response time of liquid crystal reorientation. To achieve fast response time, polymer-network liquid crystals are therefore proposed. By incorporating polymer network in a liquid crystal host, the response time can be reduced by a factor of 100. However, the polymer network...
Show moreLiquid crystal spatial phase modulator plays an important role in laser beam steering, wave-front shaping and correction, optical communication, optical computation and holography. One fundamental limitation lays in the response time of liquid crystal reorientation. To achieve fast response time, polymer-network liquid crystals are therefore proposed. By incorporating polymer network in a liquid crystal host, the response time can be reduced by a factor of 100. However, the polymer network introduces hysteresis, light scattering, and high voltage. The motivation for a fast-response liquid crystal phase modulator will be discussed in the first chapter. In the second chapter, we introduce our discovery that by modifying the polymer network structure with C12A, the hysteresis from the network can be eliminated, while keeping response time at the same order. In the third chapter, we introduce a new route toward fast response time. Instead of randomly generated network, we propose to utilize two-photon-polymerization method to create well-defined polymer scaffold. By introducing polymer scaffold, we demonstrated a 7-fold faster response in comparison with traditional phase modulators, while hysteresis, scattering, and high driving voltage are all eliminated. In the fourth chapter, we introduce phase modulation based on Pancharatnam-Berry (PB) phase principle. In this type of phase modulation, the defect at 2? phase reset in conventional phase modulators can be avoided. Therefore, a higher optical quality can be achieved, making them suitable for display and imaging applications. We demonstrated a fast PB lens with response time less than 1 ms, and using which we realized the first PB lens-based additive light field display to generate true (monocular) 3D content with computationally rendered images. In chapter five, we demonstrate the resolution enhancement based on pixel-shifting of fast PB gratings. By synchronizing display content with shifting pixels, we demonstrated ~2x enhanced resolution and significantly reduced screen-door artifact.In chapter six, we report our discovery of reflective polarization volume gratings (PVGs) based on self-organized liquid crystal helix. We achieved a large deflection angle ((>)50(&)deg; in glass), high diffraction efficiency ((>)95%), and unique polarization selectivity (distinction ratio (>) 100:1). A system integrating PB optical elements is described in chapter seven.Finally, we will summarize our major accomplishments in chapter eight.
Show less - Date Issued
- 2018
- Identifier
- CFE0007760, ucf:52389
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007760
- Title
- Saturn's Rings: Measuring Particle Size Distributions Using Cassini UVIS Occultation Data.
- Creator
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Becker, Tracy, Colwell, Joshua, Fernandez, Yan, Campins, Humberto, Showalter, Mark, Klemm, Richard, University of Central Florida
- Abstract / Description
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Since its arrival to Saturn in 2004, the Cassini spacecraft has utilized its suite of sophisticated instruments to further our understanding of the Saturnian ring system. We analyze occultation data from Cassini's Ultraviolet Imaging Spectrograph (UVIS) in order to measure the particle size distribution and place limits on the minimum particle sizes in Saturn's rings.Throughout the ring system, particle accretion is countered by collisional and tidal disruption and Keplerian shear. Therefore,...
Show moreSince its arrival to Saturn in 2004, the Cassini spacecraft has utilized its suite of sophisticated instruments to further our understanding of the Saturnian ring system. We analyze occultation data from Cassini's Ultraviolet Imaging Spectrograph (UVIS) in order to measure the particle size distribution and place limits on the minimum particle sizes in Saturn's rings.Throughout the ring system, particle accretion is countered by collisional and tidal disruption and Keplerian shear. Therefore, the particle size distribution of the rings is continually evolving. The presence of sub-centimeter particles, which have short lifetimes due to these processes, is indicative of ongoing dynamics in the rings. Sub-centimeter-sized particles efficiently diffract light at ultraviolet wavelengths, and thus produce signatures of diffraction in the occultation data. The shape and intensity of the diffraction signatures are indicative of the sizes of the particles that produce them. The UVIS wavelength bandpass, 51.2 - 180 nm, contains the shortest wavelengths of the Cassini instruments, making it most sensitive to the smallest particles in the rings. We have developed a computational model that reconstructs the geometry of a UVIS observation and produces a synthetic diffraction signal for a given truncated power-law particle size distribution, which we compare with the observed signal. We implement this model for two sets of observations: (1) diffraction spikes at sharp ring edges during stellar occultations and (2) the light curve due to attenuated and diffracted sunlight by particles in Saturn's F ring during solar occultations. Near sharp ring edges, ring particles can diffract light such that there is a measurable increase in the signal of an unocculted star exterior to the ring. In Saturn's A ring, diffracted light can augment the stellar signal by up to 6% and can be detected tens of kilometers radially beyond the edge. The radial profile of the diffraction signal is dependent on the size distribution of the particle population near the ring edge. These diffraction signals are observed at sharp edges throughout Saturn's rings, although in this work we focus on diffraction at the outer edge of Saturn's A ring and at the edges of the Encke Gap. We find an overall steepening of the power-law size distribution and a decrease in the minimum particle size at the outer edge of the A ring when compared with the Encke Gap edges. This suggests that interparticle collisions caused by satellite perturbations in the region result in more shedding of regolith or fragmentation of particles in the outermost parts of the A ring. We rule out any significant population of sub-millimeter-sized particles in Saturn's A ring, placing a lower limitation of 1-mm on the minimum particle size in the ring.We also model the light curves produced as Saturn's F ring occults the Sun. We consider both the attenuated signal and the light diffracted by the particles in the ring during the occultation. Five of the eleven solar occultations analyzed show a clear signature of diffracted light that surpasses the unocculted solar signal. This includes a misaligned solar occultation that placed most of the solar disk outside of the instrument's field of view, reducing the solar signal by 97.5% and resulting in the serendipitous detection of diffracted light. We measure a large variation in the the size distribution of the particles that fill the broad, ~500 km region surrounding the F ring core. We find that smaller particles ((<) 50 micrometers) are present during solar occultations for which diffraction was detected, and place a lower limit on the minimum particle size of 100 micrometers for occultations during which diffraction was not detected. A comparison with images of the F ring observed by the Cassini Imaging Science Subsystem near the times of the occultations reveals that the detections of small particles in the UVIS data correspond with locations of collisional events in the F ring. This implies that collisions within the F ring core replenish the sub-millimeter-sized dust in the 500-km region that encompasses the F ring core.
Show less - Date Issued
- 2016
- Identifier
- CFE0006073, ucf:50940
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006073
- Title
- Multi-axial Thermomechanical Characterization of Shape Memory Alloys for Improved Stability.
- Creator
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Nicholson, Douglas, Vaidyanathan, Raj, Kumar, Ranganathan, Chen, Ruey-Hung, University of Central Florida
- Abstract / Description
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Shape recovery in shape memory alloys (SMAs) occurs against external stress by means of a reversible thermoelastic solid state phase transformation typically between so-called austenite, martensite and R-phases. The ability to do work enables their use as high-force actuators in automotive and aerospace applications while superelastic NiTi is of interest in biomedical devices such as stents. Both R-phase and martensite can detwin, reorient and undergo a thermal or stress induced...
Show moreShape recovery in shape memory alloys (SMAs) occurs against external stress by means of a reversible thermoelastic solid state phase transformation typically between so-called austenite, martensite and R-phases. The ability to do work enables their use as high-force actuators in automotive and aerospace applications while superelastic NiTi is of interest in biomedical devices such as stents. Both R-phase and martensite can detwin, reorient and undergo a thermal or stress induced transformation. For these reasons, it is difficult from ordinary macroscopic measurements to decouple elastic and inelastic contributions (from their respective phases) from the overall deformation. In situ neutron diffraction is ideally suited to probing these microstructural and micromechanical changes while they occur under external stress fields. Despite SMAs typically operating under multi-axial stress states in applications, most previous in situ neutron diffraction based investigations on SMAs have been limited to homogenous stress states as a result of uniaxial loading. The current investigation spatially maps thermoelastic deformation mechanisms during heating and uniaxial/torsional loading of shape memory and superelastic NiTi by recourse to in situ neutron diffraction, performed at Oak Ridge and Los Alamos National Laboratories. SMA spring actuators were also used to experimentally validate the ability of a recently developed model to predict the evolutionary deformation response under multi-axial loading conditions.By recourse to in situ neutron diffraction, martensite variants were tracked during isothermal, isobaric, and isostrain loading in shape memory NiTi. Results show variants were equivalent for the corresponding strain and more importantly, the reversibility and equivalency was immediately evident in variants that were first selected isobarically but then reoriented to a near random self-accommodated structure by isothermal deformation. Variants selected isothermally were not significantly affected by a subsequent thermal cycle under constant strain. During uniaxial/torsional loading and heating, thermoelastic deformation mechanisms in non-uniform states of stress in superelastic NiTi were spatially mapped. The preferred selection of R-phase variants by reorientation and detwinning processes were equivalent for the corresponding strain (in tension and compression) and was reversed by isothermal loading. The variants selected were consistent between uniaxial and torsional loading when the principal stress directions of the stress state were considered (for the crystallographic directions considered here). The similarity in general behavior between uniaxial and torsional loading, in spite of the implicit heterogeneous stress state associated with torsional loading, pointed to the ability of the reversible thermoelastic transformation to accommodate both stress and strain mismatch associated with deformation.Overall, various thermomechanical combinations of heating and loading sequences yielded the same final texture (preferred selection of variants), which highlighted the ability to take different paths yet still obtain the desired response while minimizing irrecoverable deformation mechanisms. These paths have implications for minimizing the number of cycles required to train an SMA, which limits the amount of work required for stabilizing their evolutionary response thereby increasing the fatigue life and overall durability of the SMA. This finding is valuable to the aerospace and medical device industries where SMAs find current application.
Show less - Date Issued
- 2017
- Identifier
- CFE0006952, ucf:51676
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006952
- Title
- Load Transfer in an Isolated Particle Embedded within an Epoxy Matrix.
- Creator
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Durnberg, Erik, Raghavan, Seetha, Gou, Jihua, Bai, Yuanli, University of Central Florida
- Abstract / Description
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Particulate composites are widely used in many aerospace applications such as protective coatings, adhesives, or structural members of a body and their mechanical properties and behavior have gained increasing significance. The addition of modifiers such as alumina generally leads to improved mechanical properties. This addition also enables the non-invasive study of the load transfer between the particle and the matrix. Understanding the load transfer between the particulate and the matrix...
Show moreParticulate composites are widely used in many aerospace applications such as protective coatings, adhesives, or structural members of a body and their mechanical properties and behavior have gained increasing significance. The addition of modifiers such as alumina generally leads to improved mechanical properties. This addition also enables the non-invasive study of the load transfer between the particle and the matrix. Understanding the load transfer between the particulate and the matrix material is the first step to understanding the behavior and mechanical properties of the composite as a whole. In this work, samples with an isolated alumina particle embedded in an epoxy matrix were created to replicate the ideal assumptions for many particulate mechanics models. In separate experiments, both photo stimulated luminescent spectroscopy (PSLS) and synchrotron radiation were used to collect the spectral emission and diffraction rings, respectively, from the mechanically loaded samples. The PSLS data and XRD data are shown to be in qualitative agreement that as particle size is increased, the load transferred to the particle also increased for the range of particle sizes tested. This trend of increasing load transfer with increasing particle size is compared with the classical Eshelby model. Results from this work provide experimental insight into the load transfer properties of particulate composites and can serve to experimentally validate the theoretical load transfer models that currently exist.
Show less - Date Issued
- 2014
- Identifier
- CFE0005326, ucf:50535
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005326
- Title
- In-situ synchrotron studies of turbine blade thermal barrier coatings under extreme environments.
- Creator
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Knipe, Kevin, Raghavan, Seetha, Gordon, Ali, Kapat, Jayanta, Sohn, Yongho, University of Central Florida
- Abstract / Description
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Thermal Barrier Coatings have been used for decades to impose a thermal gradient between the hot combustion gases and the underlying superalloy substrate in engine turbine blades. Yttria Stabilized Zirconia (YSZ) is an industry standard high temperature ceramic for turbine applications. The protective coating is adhered to the substrate using a nickel based alloy bond coat. Through exposure to high temperature, a Thermally Grown Oxide (TGO) layer develops at the bond coat-YSZ interface. Large...
Show moreThermal Barrier Coatings have been used for decades to impose a thermal gradient between the hot combustion gases and the underlying superalloy substrate in engine turbine blades. Yttria Stabilized Zirconia (YSZ) is an industry standard high temperature ceramic for turbine applications. The protective coating is adhered to the substrate using a nickel based alloy bond coat. Through exposure to high temperature, a Thermally Grown Oxide (TGO) layer develops at the bond coat-YSZ interface. Large residual stresses develop in these layers due to thermal expansion mismatch that occurs during cool down from high temperature spraying and cyclic operating conditions. Despite their standard use, much is to be determined as to how these residual stresses are linked to the various failure modes. This study developed techniques to monitor the strain and stress in these internal layers during thermal gradient and mechanical conditions representing operating conditions. The thermal gradient is applied across the coating thickness of the tubular samples from infrared heating of the outer coating and forced air internal cooling of the substrate. While thermal and mechanical loading conditions are applied, 2-dimensional diffraction measurements are taken using the high-energy Synchrotron X-Rays and analyzed to provide high-resolution depth-resolved strain. This study will include fatigue comparisons through use of samples, which are both 'as-coated' as well as aged to various stages in a TBC lifespan. Studies reveal that variations in thermal gradients and mechanical loads create corresponding trends in depth resolved strains with the largest effects displayed at or near the bond coat/TBC interface. Single cycles as well as experiments targeting thermal gradient and mechanical effects were conducted to capture these trends. Inelastic behavior such as creep was observed and quantified for the different layers at high temperatures. From these studies more accurate lifespan predictions, material behaviors, and causes of failure modes can be determined. The work further develops measurement and analysis techniques for diffraction measurements in internal layers on a coated tubular sample which can be used by various industries to analyze similar geometries with different applications.
Show less - Date Issued
- 2014
- Identifier
- CFE0005640, ucf:50206
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005640
- Title
- Scandia and ceria stabilized zirconia based electrolytes and anodes for intermediate temperature solid oxide fuel cells: Manufacturing and properties.
- Creator
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Chen, Yan, Orlovskaya, Nina, An, Linan, Chen, Quanfang, Sohn, Yongho, Raghavan, Seetha, Huang, Xinyu, University of Central Florida
- Abstract / Description
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Scandia and ceria stabilized zirconia (10 mol% Sc2O3 (-) 1 mol% CeO2 (-) ZrO2, SCSZ) has superior ionic conductivity in the intermediate temperature range for the operation of solid oxide fuel cells, but it does not exhibit good phase stability in comparison with yttria stabilized zirconia (8 mol% Y2O3 (-) ZrO2, YSZ). To maintain high ionic conductivity and improve the stability of the electrolyte, layered structures with YSZ outer layers and SCSZ inner layers were designed, along with the...
Show moreScandia and ceria stabilized zirconia (10 mol% Sc2O3 (-) 1 mol% CeO2 (-) ZrO2, SCSZ) has superior ionic conductivity in the intermediate temperature range for the operation of solid oxide fuel cells, but it does not exhibit good phase stability in comparison with yttria stabilized zirconia (8 mol% Y2O3 (-) ZrO2, YSZ). To maintain high ionic conductivity and improve the stability of the electrolyte, layered structures with YSZ outer layers and SCSZ inner layers were designed, along with the referential electrolytes containing pure SCSZ or YSZ. The electrolytes were manufactured by tape casting, laminating, and pressureless sintering techniques. After sintering, while the thickness of YSZ outer layers remained constant at ~30 ?m, the thickness of inner layers of SCSZ for the 3-, 4- and 6-layer designs varied at ~30, ~60 and ~120 ?m, respectively. Selected characterizations were employed to study the structure, morphology, impurity content and the density of the electrolytes. Furthermore, in situ X-ray diffraction, neutron diffraction and Raman scattering were carried out to study the phase transition and lattice distortion during long-term annealing at 350 (&)deg;C and 275 (&)deg;C for SCSZ and YSZ, respectively, where the dynamic damping occurred when Young's modulus was measured.In YSZ/SCSZ electrolytes, thermal residual stresses and strains were generated due to the mismatch of coefficients of thermal expansion from each layer of different compositions. They could be adjusted by varying the thickness ratios of each layer in different designs of laminates. The theoretical residual stresses have been calculated for different thickness ratios. The effect of thermal residual stress on the biaxial flexural strength was studied in layered electrolytes. The biaxial flexure tests of electrolytes with various layered designs were performed using a ring-on-ring method at both room temperature and 800 (&)deg;C. The maximum principal stress during fracture indicated an increase of flexural strength in the electrolytes with layered structure at both temperatures in comparison with the electrolytes without compositional gradient. Such an increase of strength is the result of the existence of residual compressive stresses in the outer YSZ layer. In addition, Weibull statistics of the strength values were built for the layered electrolytes tested at room temperature, and the effect of thermal residual stresses on Weibull distribution was established. The calculation of residual stress present at the outer layers was verified. The high ionic conductivity was maintained with layered electrolyte designs in the intermediate temperature range. It was also established that the ionic conductivity of layered electrolytes exhibited 7% (-) 11% improvement at 800 (&)deg;C due to the stress/strain effects, and the largest improvements in a certain electrolyte was found to nearly coincide with the largest residual compressive strain in the outer YSZ layer.In addition to the study of layered electrolytes, mechanical properties of porous Ni/SCSZ cermet were studied. The anode materials were reduced by 65 wt% NiO (-) 35 wt% SCSZ (N65) and 50 wt% NiO (-) 50 wt% SCSZ (N50) porous ceramics in the forming gas. Young's modulus as well as strength and fracture toughness of non-reduced and reduced anodes has been measured, both at room and high temperatures. High temperature experiments were performed in the reducing environment of forming gas. It was shown that while at 700 (&)deg;C and 800 (&)deg;C the anode specimens exhibited purely brittle deformation, a brittle-to-ductile transition occurred at 800 (-) 900 (&)deg;C, and the anode deformed plastically at 900 (&)deg;C. Fractography of the anode specimens were studied to identify the fracture modes of the anodes tested at different temperatures.
Show less - Date Issued
- 2013
- Identifier
- CFE0005090, ucf:50750
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005090
- Title
- ADDITIVE LITHOGRAPHY FABRICATION AND INTEGRATION OF MICRO OPTICS.
- Creator
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Pitchumani, Mahesh, Johnson, Eric, University of Central Florida
- Abstract / Description
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Optical elements are the fundamental components in photonic systems and are used to transform an input optical beam into a desired beam profile or to couple the input beam into waveguides, fibers, or other optical systems or devices. Macroscopic optical elements are easily fabricated using grinding and polishing techniques, but few methods exist for inexpensive fabrication of micro optical elements. In this work we present an innovative technique termed Additive Lithography that makes use of...
Show moreOptical elements are the fundamental components in photonic systems and are used to transform an input optical beam into a desired beam profile or to couple the input beam into waveguides, fibers, or other optical systems or devices. Macroscopic optical elements are easily fabricated using grinding and polishing techniques, but few methods exist for inexpensive fabrication of micro optical elements. In this work we present an innovative technique termed Additive Lithography that makes use of binary masks and controlled partial exposures to sculpt photoresist into the desired optical surface relief profile. We explore various masking schemes for fabricating a variety of optical elements with unprecedented flexibility and precision. These masking schemes used in conjunction with the additive lithographic method allows us to carefully control the photoresist exposure and reflow processes for fabricating complex aspheric lens elements, including aspheric elements whose fabrication often proves highly problematic. It will be demonstrated that employing additive lithography for volume sculpting followed by controlled reflow can also allow us to fabricate refractive beam shaping elements. Finally we will discuss the dry etching techniques used to transfer these optical elements into the glass substrate. Thus the additive lithography technique will be demonstrated as an inexpensive, high throughput and efficient process in the fabrication of micro optical elements.
Show less - Date Issued
- 2006
- Identifier
- CFE0000914, ucf:46761
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000914
- Title
- Non-Hermitian and Space-Time Mode Management.
- Creator
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Nye, Nicholas, Christodoulides, Demetrios, Khajavikhan, Mercedeh, Abouraddy, Ayman, Kaup, David, University of Central Florida
- Abstract / Description
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In the last few years, optics has witnessed the emergence of two fields namely metasurfaces and parity-time (PT) symmetry. Optical metasurfaces are engineered structures that provide unique responses to electromagnetic waves, absent in natural materials. On the other hand, PT symmetry has emerged from quantum mechanics, when a new class of non-Hermitian Hamiltonian quantum systems was shown to have real eigenvalues. In this work, we demonstrate how PT-symmetric diffractive structures are...
Show moreIn the last few years, optics has witnessed the emergence of two fields namely metasurfaces and parity-time (PT) symmetry. Optical metasurfaces are engineered structures that provide unique responses to electromagnetic waves, absent in natural materials. On the other hand, PT symmetry has emerged from quantum mechanics, when a new class of non-Hermitian Hamiltonian quantum systems was shown to have real eigenvalues. In this work, we demonstrate how PT-symmetric diffractive structures are capable of eliminating diffraction orders in specific directions, while maintaining/enhancing the remaining orders. In the second part of this work, we emphasize on supersymmetry (SUSY) and its applications in optics. Even though the full ramification of SUSY in high-energy physics is still a matter of debate that awaits experimental validation, supersymmetric techniques have already found their way into low-energy physics. In this work, we apply certain isospectral techniques in order to achieve single mode lasing in multi-element waveguide systems, where multimode chaotic emission is expected. In the third part of this dissertation, we emphasize on dynamically reconfigurable nanoparticle platforms. By exploiting the dielectrophoresis effect, we demonstrate how controllable lasing can be achieved in random photonic arrangements. Although this work focuses on the case of controlling random lasers, we expect that the proposed nanoparticle architecture can incorporate heterogeneous materials of a wide range of optical functionalities, including gain, scattering, plasmonic resonance, and nonlinearity. In the last part of the dissertation, we demonstrate the capability of synthesizing space-time (ST) wave packets, based on new propagation-invariant elementary solutions of the wave equation identified through a complexification of the spatial and temporal degrees of freedom. By establishing the connection between ST propagation-invariant pulses and tilted-pulse-front pulses, a path is opened to exploiting the unique attributes of such wave packets both in nonlinear and quantum optics.
Show less - Date Issued
- 2019
- Identifier
- CFE0007896, ucf:52780
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007896
- Title
- Growth and doping of MoS2 thin films for electronic and optoelectronic applications.
- Creator
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Abouelkhair, Hussain, Peale, Robert, Kaden, William, Stolbov, Sergey, Coffey, Kevin, University of Central Florida
- Abstract / Description
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MoS2 high absorption coefficient, high mobility, mechanical flexibility, and chemical inertness is very promising for many electronic and optoelectronic applications. The growth of high-quality MoS2 by a scalable and doping compatible method is still lacking. Therefore, the suitable dopants for MoS2 are not fully explored yet. This dissertation consists mainly of four main studies. The first study is on the growth of MoS2 thin films by atmospheric pressure chemical vapor deposition. Scanning...
Show moreMoS2 high absorption coefficient, high mobility, mechanical flexibility, and chemical inertness is very promising for many electronic and optoelectronic applications. The growth of high-quality MoS2 by a scalable and doping compatible method is still lacking. Therefore, the suitable dopants for MoS2 are not fully explored yet. This dissertation consists mainly of four main studies. The first study is on the growth of MoS2 thin films by atmospheric pressure chemical vapor deposition. Scanning electron microscope images revealed the growth of microdomes of MoS2 on top of a smooth MoS2 film. These microdomes are very promising as a broadband omnidirectional light trap for light harvesting applications. The second study is on the growth of MoS2 thin films by low pressure chemical vapor deposition (LPCVD). Control of sulfur vapor flow is essential for the growth of a pure phase of MoS2. Turning off sulfur vapor flow during the cooling cycle at 700 (&)#186;C leads to the growth of highly textured MoS2 with a Hall mobility of 20 cm2/Vs. The third study was on the growth of Ti-doped MoS2 thin films by LPCVD. The successful doping was confirmed by Hall effect measurement and secondary ion mass spectrometry (SIMS). Different growth temperatures from 1000 to 700 ? were studied. Ti act as a donor in MoS2. The fourth study is on fluorine-doped SnO2 (FTO) which has many technological applications including solar cells and transistors. FTO was grown by an aqueous-spray-based method. The main objective was to compare the actual against the nominal concentration of fluorine using SIMS. The concentration of fluorine in the grown films is lower than the concentration of fluorine in the aqueous solution.?
Show less - Date Issued
- 2017
- Identifier
- CFE0006847, ucf:51767
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006847
