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Hussain, Mallik Mohd RaihanNonlinear Electromagnetic Radiation from Metal-Insulator-Metal Tunnel Junctions
Master of Science (M.S.), University of Dayton, 2017, Electro-Optics
Our goal was to experimentally detect nonlinear electromagnetic (EM) radiation (in the far field) from a metal-insulator-metal (MIM) tunnel junction where the insulator thickness lies in the nanometer to subnanometer range and the metals in the junction are coupled to the electromagnetic field of incident photons. The radiation from an MIM junction originated from the photon-induced tunneling current passing through it. The phenomenon is elegantly described by photon-assisted-tunneling (PAT) theory that introduces transfer Hamiltonians in the uncoupled (when two metals are at infinite distance from each other) system Hamiltonian. This theory predicts the contribution of additional conductivity terms in the MIM interface (due to tunneling inside the junction) and ushered the development of quantum conductivity theory (QCT), as a consequence. In this thesis, we reviewed QCT from the perspective of many-body formulation and designed careful experiments to detect the nonlinear electromagnetic radiation from MIM junctions that can be attributed to photon-assisted tunneling of electrons. In our experiment, first, an insulator layer was put on the metal surface using atomic layer deposition (ALD) technique. The number of layers were varied to produce MI samples with different insulator thickness in the subnanometer range. Then, we set the background signal strength by measuring the second harmonic (SH) and third harmonic (TH) signal due to the bulk material and the surface of metal-insulator (MI) interface. Next, we spin-coated the MI sample with Au nanospheres (diameter ~ 10 nm) to construct MIM interfaces and measured SH and TH signals from them again. Without any bias voltage across the MIM, QCT predicts an increase in TH signal only. Experimentally, we observed an increase in TH signal strength. The increase was modest which is partially attributed to the fact that we could not reliably produce MIM samples with subnanometer insulator thickness and uniform coverage. We intend to improve the surface coverage and uniformity of the insulator layer, in future, and measure SH and TH from the improved samples. Detection of such radiation would support QCT and validate the extension of transfer Hamiltonian approach from the realm of superconducting tunnel junctions to normal MIM tunnel junctions.

Committee:

Joseph Haus, Ph.D. (Committee Chair); Andrew Sarangan, Ph.D. (Committee Member); Imad Agha, Ph.D. (Committee Member)

Subjects:

Electromagnetics; Nanoscience; Nanotechnology; Optics; Quantum Physics

Keywords:

tunnel junction; metal-insulator-metal; MIM; nonlinear radiation from MIM; transfer Hamiltonian; photon-assisted-tunneling; PAT; quantum conductivity coefficient; QCT; Au-Al2O3-Au; atomic layer deposition on metal; ALD on metal; metal-insulator; MI

Yang, ZhijunIncoherent Imaging in the Presence of Atmospheric Turbulence and Refractivity
Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Electro-Optics
Atmospheric turbulence, associated with its refractive-index inhomogeneities (refractivity), may severely affect long range incoherent images formation. Example of this impact includes image blurring, motion, warping and anisotropic geometrical distortions. Currently, the effects of turbulence and refractivity on image formation are considered as being mutually independent and analysed separately using the Fresnel diffraction (wave-optics) and geometrical optics (ray tracing) approaches, respectively. Such independent treatment of turbulence and refractivity effects have certain limitations. Atmospheric refractivity may result in significant deviations of optical wave propagation direction. This effect is commonly referred as the ray bending which, in turn, may lead to a change in turbulence characteristics such as the refractive index structure parameter Cn2 that is commonly considered as a function of altitude h above the ground. Correspondingly, optical wave refraction, especially in extended-range imaging scenarios, could affect the turbulence-induced optical aberrations. In this work, we analyze the incoherent image formation in atmosphere in the presence of both atmospheric turbulence and refractivity using numerical simulations based on the brightness function (BF) technique. Using the BF technique, the incoherent imaging system modulation transfer function (MTF) estimation is performed via direct numerical analysis of visibility of sine-test patterns of different spatial frequencies. The test patterns are assumed to be imaged through a volume medium with turbulence and refractivity-induced refractive index inhomogeneities. The major effects observed in numerical simulations, include the spatial frequency shift between frequency of a sine-test object and its image, and spatial non-uniformity of the sine-pattern image distortion which is referred as the refractivity-induced image anisoplanatism. Both effects depend on the location and strength of the localized refractive index structure with respect to the imaging (wave propagation) geometry. The MTFs corresponding to distributed (volume) turbulence with and without atmospheric refractivity are also compared. Next, the joint impact of atmospheric turbulence and inverse temperature layer (ITL) on optical mirage formation is analyzed. The dependency of both desert- (superior) and ocean-type (inferior) mirage image formation on ITL characteristics (temperature inversion and location of the ITL) have been studied. The impact of atmospheric turbulence strength on mirage image qualities is also analyzed. Finally, a numerical analysis is conducted to study the impact of localized refractive index inomogeneites on image quality. It is shown that image quality strongly depends on atmospheric turbulence strength and locations along the optical path. To characterize this impact, two metrics are proposed and developed to measure the image quality as a function of turbulence strength and location. The impact of inverse temperature layer on the developed image quality metrics are also studied.

Committee:

Mikhail Vorontsov (Advisor); Partha Banerjee (Committee Member); Edward Watson (Committee Member); Steven Fiorino (Committee Member)

Subjects:

Atmospheric Sciences; Engineering; Optics

Keywords:

incoherent imaging; atmospheric turbulence; refractivity; modulation transfer function; optical mirage

Hagee, Daniel RBaseball Temporal Seam Recognition Study
Master of Science, The Ohio State University, 2016, Vision Science
It is believed that baseball batters utilize seam recognition to gather information about baseball pitches. However, batters only have a limited amount of time to decide whether they should swing the bat. It is established that there are temporal constraints on visual acuity. Therefore, the purpose of this study was to investigate whether subjects can effectively determine seam orientation patterns in a comparable amount of time as batters face in real-life scenarios. Subjects were tested by being seated 36 feet and 1 inch from a drill press with a spinning baseball. Each baseball used had one of three specific orientations. Subjects were asked to describe the stripes on the baseball in a 3 alternative forced choice manner. All subjects completed two trials on differing days. In the first trial, subjects had unlimited viewing time to determine the seam orientation on the baseball. In the second trial, subjects were limited to approximately 286 milliseconds of viewing time using a two aperture system. All subjects used monocular viewing in this experiment. It was found that with unlimited viewing time, subjects correctly determined the seam orientation 52.06% of the time. With limited viewing time subjects only responded correctly 37.62% of the time. This produced a significant difference (p=0.015) between unlimited viewing time and limited viewing time. Because subjects’ performance did not meet expectations in the temporal constraint study, monocular and binocular seam recognition performance was compared in a second study. Testing for this was performed in a similar fashion to the first study. On one day, subjects had unlimited viewing time under binocular conditions. On the other day subjects had unlimited viewing time under monocular conditions. Subjects responded correctly on 74.29% of presentations under monocular conditions and 76.03% of presentations under binocular conditions. There was no significant difference in performance (p=0.522) between binocular and monocular viewing. Temporal constraints resulted in a 40% reduction in the subjects' ability to accurately determine seam number and location. On the other hand, seam recognition was similar for monocular and binocular viewing.

Committee:

Nicklaus Fogt, O.D., Ph. D. (Advisor); Aaron Zimmerman, O.D., M.S. (Committee Member); GIlbert Pierce, O.D., Ph. D. (Committee Member)

Subjects:

Ophthalmology; Optics

Keywords:

baseball; pitching; seam recognition; seams; temporal constraints; batting

Basunia, MahmudunnabiA Recursive Phase Retrieval Technique Using Transport of Intensity: Reconstruction of Imaged Phase and 3D Surfaces
Doctor of Philosophy (Ph.D.), University of Dayton, 2016, Electrical and Computer Engineering
Transport of intensity is a noninterferometric method to find the phase of an object by recording optical intensities at different distances of propagation. The transport of intensity equation results from the imaginary part of the complex paraxial wave equation and is equivalent to the principle of conservation of energy. The real part of the paraxial wave equation gives the eikonal equation in the presence of diffraction, which can be also termed the transport of phase equation. The amplitude and phase of the optical field must simultaneously satisfy both the real and imaginary parts of the paraxial wave equation during propagation. In this dissertation, it is demonstrated, using illustrative examples, how to exploit this to retrieve the phase through recursive calculations of the phase and intensity. This is achieved using the transport of intensity equation which is solved using standard Fourier transform techniques and the transport of phase equation, which is solved using a Gauss-Seidel iterative method. Examples include calculation of the imaged phase induced through self-phase modulation of a focused laser beam in a liquid, and the imaged phase of light reflected from a surface which yields its 3d surface profile.

Committee:

Partha Banerjee (Advisor); Guru Subramanyam, (Committee Member); Monish Chatterjee, (Committee Member); Youssef Raffoul, (Committee Member)

Subjects:

Electrical Engineering; Optics

Keywords:

TPE, TIE, Transport of Intensity, Transport of Phase, Recursive

Cayayan, Lyndon Mark D.Collective Quantum Jumps of Rydberg Atoms Undergoing Two-Channel Spontaneous Emission
Master of Science, Miami University, 2016, Physics
An analysis is performed on a open quantum system of driven and damped Rydberg atoms. The interactions between Rydberg states are characterized by dipole-dipole energy shifts that give rise to a Rydberg blockade with on-resonant driving, and collective quantum jumps while driving with an off-resonant nonzero detuning. Under fully independent emission the system admits a bistable steady state exhibiting collective quantum jumps, in which quantum fluctuations drive transitions between two bistable values predicted by a quasiclassical mean-field model. When competition between fully independent and fully collective emission is considered in a two-channel emission model, a collective emission enhancement impacts the presence of the quantum jumps by shifting the predicted region of bistability for the system to different values of detuning. It is shown that jumps can be recovered to an extent, but that the bistability is ultimately destroyed under fully collective emission.

Committee:

James Clemens (Advisor); Samir Bali (Committee Member); Stephen Alexander (Committee Member)

Subjects:

Optics; Physics; Quantum Physics; Theoretical Physics

Keywords:

quantum optics, Rydberg atoms, quantum jumps, computational physics, Python, QuTiP, quantum trajectory, bistability, open quantum system, theoretical quantum optics, quantum computer science, superradiance, correlation, Lindblad master equation

Zaidi, Syed Anwar HyderOptical Redox Imaging of Metabolic Activity
Master of Science in Biomedical Engineering (MSBME), Wright State University, 2016, Biomedical Engineering
Fluorescence imaging can be used to determine tissue metabolism, which is an indication of the cellular functionality. Metabolic contrast is useful for the early detection of several medical conditions such as cancer, diabetes, lung diseases etc. This study aims to use fluorescence imaging to quantify NADH and FAD, which are cellular metabolic indicators. A parameter known as Redox ratio, can be used to study metabolic state of several tissue types and disease states. To quantify the Redox ratio, three fluorescence imaging systems were optimized to measure the fluorescence signal from NADH and FAD. The first system was a camera based model suitable for laboratory and clinical settings. The second and third were compact versions of the same instrument. The systems were characterized and brain cancer cells were measured using the camera-based system and the compact model, which resulted in a similar Redox ratio.

Committee:

Ulas Sunar, Ph.D. (Advisor); Jaime Ramirez-Vick, Ph.D. (Committee Member); Debra Mayes, Ph.D. (Committee Member)

Subjects:

Biomedical Engineering; Biomedical Research; Biophysics; Electrical Engineering; Medical Imaging; Optics

Keywords:

Fluorescence imaging; cancer diagnosis; compact devices; wireless devices; optical imaging

Poon, Chien SingEarly Assessment of Burn Severity in Human Tissue with Multi-Wavelength Spatial Frequency Domain Imaging
Master of Science in Biomedical Engineering (MSBME), Wright State University, 2016, Biomedical Engineering
Burn injuries such as thermal burns, which are caused by contact with flames, hot liquids, hot surfaces, and other sources of high heat as well as chemical burns and electrical burns, affects at least 500,000 people in the United States, to which 45,000 of them require medical treatment and 3,500 of them result in death. It has also been reported that in the United States alone, fire results in a death approximately every three hours and an injury every 33 minutes. Early knowledge about burn severity can lead to improved outcome for patients. In this study, the changes in optical properties in human skin following thermal burn injuries were investigated. Human skin removed during body contouring procedures was burned for either 10 or 60 seconds using a metal block placed in boiling water. Multi-wavelength spatial frequency domain imaging (SFDI) measurements were performed on each sample and the optical properties (absorption and scattering parameters) were obtained at each wavelength. Multi-wavelength fitting was used to quantify scattering parameters, and these parameters were compared to histologic assessments of burn severity. Our results indicate substantial changes in optical parameters and changes, which correlate well with respect to burn severity. This study shows the characterization of thermal burn injury on human skin ex vivo by using the optical method of SFDI with high sensitivity and specificity. Due to more challenging conditions of layered skin structures with differing thickness in humans, ongoing work tackles combining high-resolution ultrasound imaging with SFDI for more accurate quantification of optical properties during in vivo clinical studies.

Committee:

Ulas Sunar, Ph.D. (Committee Chair); Ping He, Ph.D. (Committee Member); Jeffrey Travers, M.D. Ph.D. (Committee Member)

Subjects:

Biomedical Engineering; Biomedical Research; Biophysics; Cellular Biology; Engineering; Medical Imaging; Optics; Physics

Keywords:

Optical Imaging; Medical Imaging; burn wound assessment; diagnosis; fluorescence; multispectral imaging; optical properties; quantitative assessment; skin burn; spatial frequency domain imaging; system; tissue scattering; wounds

Thota, Venkata Ramana KumarTunable Optical Phenomena and Carrier Recombination Dynamics in III-V Semiconductor Nanostructures
Doctor of Philosophy (PhD), Ohio University, 2016, Physics and Astronomy (Arts and Sciences)
Semiconductor nanostructures such as quantum dots, quantum wires and quantum wells have gained significant attention in the scientific community due to their peculiar properties, which arise from the quantum confinement of charge carriers. In such systems, confinement plays key role and governs the emission spectra. With the advancements in growth techniques, which enable the fabrication of these nanostructured devices with great precision down to the atomic scale, it is intriguing to study and observe quantum mechanical effects through light-matter interactions and new physics governed by the confinement, size, shape and alloy composition. The goal is to reduce the size of semiconductor bulk material to few nanometers, which in turn localizes the charge carriers inside these structures such that the spin associated with them is used to carry and process information within ultra-short time scales. The main focus of this dissertation is the optical studies of quantum dot molecule (QDM) systems. A system where the electrons can tunnel between the two dots leading to observable tunneling effects. The emission spectra of such system has been demonstrated to have both intradot transitions (electron-hole pair residing in the same dot) and interdot transitions (electron-hole pair participating in the recombination origin from different dots). In such a system, it is possible to apply electric field such that the wavefunction associated with the charge carriers can be tuned to an extent of delocalizing between the two dots. This forms the first project of this dissertation, which addresses the origin of the fine structure splitting in the exciton-biexciton cascade. Moreover, we also show how this fine structure can be tuned in the quantum dot molecule system with the application of electric field along the growth direction. This is demonstrated through high resolution polarization dependent photoluminescence spectroscopy on a single QDM, which was described in great detail by H. Ramirez (et al.) and also experimentally observed by N. Skold (et al.) for a fixed barrier thickness. However, we measured the strength of FSS as a function of barrier thickness in the strong tunneling regime. The results are discussed in chapter 4. The second project is carried out with an intention to generate entangled photon pairs from molecular states found in the emission spectra of a single QDM: A pair of photons, which reveals the information associated with the intrinsic property (polarization for example) of the other photon simultaneously and spontaneously when a measurement has been performed in either one of the two. The exciton-biexciton cascade not only has intradot transitions but the photoluminescence spectra also depicts interdot transitions, realizing the molecular nature of the system. Since the charge carriers are localized in different dots, the wavefunction overlap between the two is also reduced significantly. It is with this goal of enhancing the intensity of interdot or indirect transitions between the molecular biexciton-indirect exciton that we performed two color photoluminescence excitation studies and the results are discussed in chapter 5. Thirdly, the continuous creation of electron-hole pairs through photoexcitation leads to some local electric field effects, which arises due to the ionization of charge carriers inside the device structure. The advantage of the interdot transition in the emission spectra is the large Quantum Confined Stark Effect (QCSE) associated with it. This interdot QCSE is over an order of magnitude larger than for the intradot or direct transition and varies linearly with the applied electric field. By making use of the interdot exciton as a sensitive probe, the effects of optically generated electric field as a function of time are measured experimentally. Both rise time and fall time of the optically generated electric field as a function of excitation wavelength and applied field are studied in detail. The results are presented in chapter 6. Finally, carrier recombination dynamics in rare-earth doped nanostructures are measured by using ultrafast spectroscopy. Carrier dynamics in InGaN:Yb3+ nanowires and InGaN/GaN-Eu3+ superlattices are measured by frequency doubling the excitation laser, and the effects of implantation of rare-earth ions into the host material have been investigated. The results from the experimental measurements are presented in chapters 7 & 8. These experimental findings might help to understand the challenges associated with these nanostructured materials in the applications of quantum information processing, single photon emitters, and to integrate them into existing optoelectronic devices.

Committee:

Eric A. Stinaff, Prof. (Advisor); Sergio E. Ulloa, Prof. (Committee Member); Arthur R. Smith, Prof. (Committee Member); Wojciech M. Jadwisienczak, Prof. (Committee Member)

Subjects:

Condensed Matter Physics; Materials Science; Nanoscience; Nanotechnology; Optics; Physics; Quantum Physics; Solid State Physics

Keywords:

Quantum Dots; Quantum Dot Molecules; Light-Matter Interactions; Photoluminescence Excitation; III-V Semiconductor Nanostructures; Tunable Fine Structure Splitting; Time-Resolved Photoluminescence Measurements; Carrier Dynamics in III-V Nanostructures;

Krug, Sarah ElaineDigital Phase Correction of a Partially Coherent Sparse Aperture System
Master of Science (M.S.), University of Dayton, 2015, Electro-Optics
Sparse aperture image synthesis requires proper phasing between sub-apertures. Phasing can be difficult due to hardware misalignments, atmospheric turbulence, and many other causes of optical path differences (OPD). Common synthesis techniques include incoherent and coherent methods. Incoherent methods utilize passive illumination and adaptive optics while coherent methods rely on active illumination and phase reconstruction approaches such as phase retrieval or spatial heterodyne. In this thesis, we present a partially coherent technique with the capability to use either active or passive illumination to digitally correct for piston phase errors. This technique requires an anamorphic pupil relay system and a piston correction algorithm. The anamorphic pupil relay causes two closely spaced sub-apertures in the entrance pupil to appear to be shifted further apart in the exit pupil. Analytic and numerical wave optics models demonstrate the effectiveness of this relay system, matching with experimental results. An analytic model shows that the higher frequency terms are equivalent to scaled cross-correlations of the two sub-apertures, which are shifted due to the anamorphic separation. The constant shifts due to the separation are found experimentally using a registration algorithm with a calibration target. The cross-correlations are dependent on the piston phase errors between sub-apertures. We show that a piston correction algorithm can be used to shift the cross-correlations to their original positions dictated by the entrance pupil, multiply a cross-correlation with the complex conjugate of the auto-correlation, use the summation of this product to calculate the piston, and correct the phase error in each cross-correlation before recombining them with the auto-correlation. Examples show diffraction limited results for both simulated and experimental images that are supported by analytical, numerical, and experimental analysis of the system’s modulation transfer function (MTF). In addition, analysis of the piston for multiple wavelengths reveals two effects of bandwidth on the system. First, the impact of a constant spatial separation resulting in different spatial frequency shifts for different wavelengths, referred to as field dependent contrast (FDC), is addressed. Second, the inverse relationship between the bandwidth of the system and OPD tolerances is shown. In future research, diffraction gratings could eliminate the FDC so that partially coherent illumination with a small enough system bandwidth could relax OPD requirements for the sparse aperture array.

Committee:

David Rabb, Ph. D (Advisor); Matthew Dierking, Ph. D (Committee Member); Edward Watson, Ph. D (Committee Member)

Subjects:

Electrical Engineering; Optics; Physics; Remote Sensing

Keywords:

digital phasing; partially coherent; computational imaging; passive aperture synthesis; adaptive optics; sparse aperture imaging

Jackson, Richard AramA Preliminary Study of Pump/Probe Angular Dependence of Zeeman Electromagnetically Induced Transparency
Master of Science, Miami University, 2015, Physics
This thesis outlines my work to determine the dependence of Zeeman Electromagnetically Induced Transparency (EIT) on the relative angle between the pump and probe beams. We report initial measurements of Zeeman EIT and EIA using a simple arrangement in which the Zeeman sublevels are scanned around fixed pump and probe frequencies. We introduce improvements in magnetic field uniformity and measure EIT/EIA feature lineshape vs. pump/probe angle. Next, we outline our progress on performing Zeeman EIT/EIA experiments in the traditional format, i.e. scanning the probe frequency while holding the pump frequency fixed, which is more amenable to theoretical modeling.

Committee:

Samir Bali (Advisor); Perry Rice (Committee Member); James Clemens (Committee Member)

Subjects:

Electromagnetics; Experiments; Optics; Physics; Quantum Physics

Keywords:

Electromagnetically Induced Transparency; Zeeman effect; anglular displacement; vapor cells; warm atoms; quantum optics

Chen, HongweiOptical Beam Scanning Using Potassium Tantalate Niobate
Master of Science (M.S.), University of Dayton, 2015, Electro-Optics
This thesis aims to study the characteristics of the one-dimensional optical scanner made of Potassium Tantalate Niobate [KTa1-xNbxO3] (KTN) based on electro-optic (EO) effect and space-charge-controlled electrical condition. A large deflection angle of 11.28° full range is achieved by applying a relatively low voltage ±250V to a 1.0-mm-thick KTN crystal with a short interaction length of 3.2mm. In theory, the electrical conduction is carried by the electrons injected from the Ohmic contact of the electrodes. The injected electrons induce the space-charge effect and the electrical field becomes non-uniform while the electrical field has a square root dependence on the distance from the cathode. Consequently, a linearly graded refractive index is induced and the optical beam is cumulatively deflected as it propagates through the crystal. Deflection angle, deflection efficiency, resolution and frequency response are characterized. A thermistor is also utilized because that the temperature of KTN crystal has to be controlled around 44.2°C.

Committee:

Qiwen Zhan (Committee Chair); Joseph Haus (Committee Member); Partha Banerjee (Committee Member)

Subjects:

Electrical Engineering; Optics

Park, ChangKyooDevelopment of Precise Femtosecond Laser Micromachining Processes for Metals and Electrospun Nanofibers
Doctor of Philosophy, The Ohio State University, 2015, Materials Science and Engineering
Femtosecond pulse lasers have proven to be versatile for micro-scale ablation of a variety of materials with high quality machining due to minimal residual stress, heat affected zone, and melting. In addition, femtosecond laser is one of the non-cleanroom techniques that does not require masking, chemical reagents, and multiple steps. This simple and convenient micromachining technique enables machining of various materials in 3-dimensional geometry. However, some factors such as optical scattering, beam shape, and debris accumulation hinder the high quality of ablation. In this dissertation, femtosecond laser was employed for the micromachining of electrospun nanofibers and metals. Optimization of a process for the high quality femtosecond laser machining was investigated. Femtosecond laser and electrospun poly(e-caprolactone) (PCL) nanofibers mesh interaction was analyzed by optical property measurements and the optical absorption and scattering coefficients were estimated. The specific energy required for ablating a unit volume of pure PCL nanofibers and polydimethylsiloxane-poly(e-caprolactone) (PDMS-PCL) core-shell nanofibers was measured. Material inherent optical properties including the ablation threshold fluence and the incubation coefficient of PDMS and PCL were estimated. Circular grooves were fabricated on aluminum, stainless steel 316, and Stellite 6 and circular disks were successfully machined from a thick section of Stellite. The tapered cross-section was detected from the Stellite disk and the tapering was minimized by varying pulse energy during ablation process. Moreover, a novel debris removal technique based on DC-dielectrophoresis (DEP) force was used to machine the linear and circular grooves on aluminum and the ablation depth and precision were compared with the gas jet debris removal technique.

Committee:

Dave Farson (Advisor); John Lannutti (Committee Member); Antonio Ramirez (Committee Member)

Subjects:

Materials Science; Metallurgy; Optics; Polymers

Keywords:

Femtosecond laser, Ablation, Metal, Polymer, Electrospun nanofiber, Scattering, Tapering, Debris removal, DC-dielectrophoresis

Cheng, HsienHuiHIGH EFFICIENCY DOUBLE TWIST PANCHARATNAM PHASE OPTICAL BEAM DEFLECTORS
PHD, Kent State University, 2015, College of Arts and Sciences / Department of Chemical Physics
We demonstrate a camera combined with a large angle non-mechanical image steering device based on primary a Pancharatnam phase device. The device consists of primary Pancharatnam phase beam deflectors and liquid crystal polarization rotators (LCPRs). The image steering device can change the view direction of a camera to ±30° and ±10° while the image quality using this device is only slightly degraded at large angles. We explore the diffraction efficiency limit of double twist Pancharatnam phase deflectors (DTPPD) with large deflection angles. We show that a Pancharatnam phase device with a dual twist structure can deflect light up to 60 degrees with nearly perfect efficiency. This was beyond the limits previous thought for these types of devices. In this dissertation we consider the range of parameters that will allow for high efficiency and show results for a structure that demonstrates up to 80 degree deflection. We then explore the light propagation through these devices to point out interesting intensity variations in the deflected mode of light as it traverses the deflecting layer. Finally, we offer that a key to understanding the efficiency of these devices, is not the typical parameters important for traditional diffractive devices, but is the control of the polarization state of light. Liquid crystal polarization rotators (LCPRs) are another key component in digital image steering devices. To extend fast response LCPRs from switchers to display applications, we propose and demonstrate a fast response liquid crystal (LC) variable optical retarder, or attenuator with several transmission levels. The fast response LC optical device consists of dual pi-cells. The device is designed so that the transition between any two states is controlled by the application of an increased voltage level, rather than by applying a lower level. This design offers transition times in the range of 10s of microseconds between any transmission states. The combination of the high efficiency Pancharatnam phase device and the high speed polarization rotators allow for an ultra-compact, high quality, non-mechanical optical image steering system.

Committee:

Philip Bos, J. (Advisor); Hiroshi Yokoyama (Committee Member); Lian-Chy Chien (Committee Member); Deng-Ke Yang (Committee Member); Achintya Bhowmik (Committee Member); James Gleeson, T. (Committee Member); Mark Manley (Committee Chair)

Subjects:

Optics; Physics

Keywords:

Liquid Crystal Device, Pancharatnam Phase, Photoaligment, Polarization Grating, Fast Response Display

Wang, ShiyiEngineering Electromagnetic Wave Properties Using Subwavelength Antennas Structures
Doctor of Philosophy (Ph.D.), University of Dayton, 2015, Electro-Optics
With extraordinary properties, generation of complex electromagnetic field based on novel subwavelength antennas structures has attracted great attentions in many areas of modern nano science and technology, such as compact RF sensors, micro-wave receivers and nano-antenna-based optical/IR devices. This dissertation is mainly composed of two parts. For the first part, the idea of plasmonic localization in optical range is transferred and utilized for generating confined fields with high enhancement in RF range. A subwavelength modified bowtie antenna in RF range is designed for generating strong broadband field enhancement in its extended feed gap. The strongly enhanced RF field within the gap can be applied to directly modulate guided optical wave propagating in a waveguide, which enables to realize indirect RF signal sensing through photonic methods. Systematic exploration for modified bowtie antennas and its substrate effect has been given in this part. In the second part, the RF antenna design idea is extended to infrared and optical range based on antenna scaling theory specific for this spectrum. Both transmission and reflection types of metasurface structures have been designed and proposed to obtain optical needle field with a flat-top longitudinal intensity of depth of focus 5λ. With fine adjustment of different nano-antenna structures, both of the metasurfaces enable to generate complex vectorial field with spatial radial polarization, whose amplitude modulation range covers 0.07 to 1 with binary phase control. Then the scattered field can be tightly focused by a high numerical aperture (NA) lens in order to generate longitudinally polarized flat-top field along propagation direction. By exploring the subwavelength antennas’ mechanism and connections between different frequency regions, this dissertation is expected to provide general guidance for design and characterization of next-generation subwavelength antennas structures with extraordinary electromagnetic wave properties.

Committee:

Qiwen Zhan, PhD (Committee Chair); Partha Banerjee, PhD (Committee Member); Andrew Sarangan, PhD (Committee Member); Imad Agha, PhD (Committee Member)

Subjects:

Electromagnetics; Engineering; Experiments; Nanoscience; Nanotechnology; Optics

Keywords:

Subwavelength antennas; vectorial light; meta-surface; nano structures; full wave control; optical needle field

Zamani, Hamidreza3C-SiC Multimode Microdisk Resonators and Self-Sustained Oscillators with Optical Transduction
Doctor of Philosophy, Case Western Reserve University, 2015, EECS - Electrical Engineering
These days, sensor chips in very small form factors are ubiquitous. In this dissertation, I explain my efforts and achievements in proposing the first center-clamped 3C-SiC RF microdisk resonators with out-of-plane vibration as a candidate for future resonant sensing applications. First, nanomachining of 3C-SiC material using Focused Ion Beam (FIB) to find sputtering yield and lateral deformations for many different FIB conditions as well different patterns (and scales), is investigated accompanied by SRIM simulations. Then, I report theoretical analysis, fabrication and measurement of (center-clamped) RF multi-mode micromechanical resonators based upon vibrating circular disks made of a ~500nm thin SiC epilayer grown on single crystal Si. The fabrication method - composed of FIB sputtering and HNA etching - has been used for the first time and the vibration resonance peaks (in frequency spectrum) are detected through laser-interferometry measurements. A ~40µm-diameter SiC disk with a slender (~800nm) anchor exhibits more than a dozen flexural modes between ~2MHz¿20MHz with quality factors (Q’s) of ~1000¿4000. Two other disks with diameters of ~40µm and ~30µm, and wide anchors (~20µm and ~10.3µm, respectively) have their set of major flexural peaks (associated with modes of zero-circular nodes) between 15¿19MHz with Q’s of ~500¿2500. This dissertation then describes the efforts to achieve an improved self-sustained oscillator based on such resonators. First, a theory-inspired method is developed for design of electrostatically-transduced MEMS/NEMS referenced Pierce oscillators to improve phase noise (by increasing motional inductance and thus motional resistance) while also addressing oscillation start-up and other specifications e.g. frequency detuning and power consumption. Finally, the laser-based optical transduction scheme is used to make self-sustained oscillators from microdisk resonators. Laser actuation is very compatible with 3C-SiC material and the targeted application of sensing in harsh-environments and very immune to the undesired circuit loading effects and power handling inefficiencies of other transductions. The oscillator is analyzed by behavioral simulations and also measured with a home-built setup. The transduction with the microdisk resonator is via interferometry-based sensing and laser-based optical actuation. The measured phase noise of such oscillator shows a noticeable improvement of the effective Q (~2.3) over that of the open-loop microdisk resonators.

Committee:

Philip X.-L. Feng (Advisor); Philip X.-L. Feng (Committee Chair); Christian Zorman (Committee Member); Pirouz Pirouz (Committee Member); Francis L. Merat (Committee Member); Soumyajit Mandal (Committee Member)

Subjects:

Electrical Engineering; Materials Science; Mechanical Engineering; Optics; Physics

Keywords:

3C-SiC, Microdisk, resonator, self-sustained oscillator, optical transduction, Pierce oscillator, Focused Ion Beam, FIB, AFM, Phase Noise

Ni, ChuanEffects of Different Wetting Layers on the Growth of Smooth Ultra-thin Silver Thin Films
Master of Science (M.S.), University of Dayton, 2014, Electro-Optics
Ultra-thin silver films (thickness below 10 nm) are of great interest as optical coatings in low emissive windows and plasmonic devices. However, producing these films has been a continuing challenge because of their tendency to form clusters rather than smooth contiguous thin films. In this work we have studied the effects of Cu, Ge and ZnS as wetting layers to achieve ultra-smooth ultra-thin silver films. The silver films (5 nm) were grown by RF sputter deposition on silicon and glass substrates using a few monolayers of the different wetting materials. SEM imaging was used to characterize the surface properties such as island formation and roughness of the films. And the optical properties, such as reflection and transmission, were measured to identify the optical impact of the different wetting layers. Then, a multi-layer silver based structure, low emissive coating was designed. The low emissive coating combines high transmittance over most visible spectrum and high reflectance over infrared spectrum. Such kind of coating is utilized as highly transparent in the visible and heat-reflective coating for the purpose of energy saving. The designed coatings were fabricated and their performances were evaluated. The comparison between the samples with different wetting layers shows that the designs with Cu wetting layer which has similar optical properties to silver produces the best overall performance. In the absence of a wetting layer, the measured optical spectra shows a significant departure from the model prediction, which we attribute primarily to the formation of silver film clusters.

Committee:

Andrew Sarangan (Advisor); Joseph Haus (Committee Member); Imad Agha (Committee Member)

Subjects:

Nanotechnology; Optics

Keywords:

ultra-thin film; Ag film; wetting layer; low emissive coating

Moghaddas, Mohamad AminComparison of Computational Modeling of Precision Glass Molding of Infrared Lenses
Master of Science, The Ohio State University, 2014, Industrial and Systems Engineering
Over the past decades Precision Glass Molding (PGM) technology has been used to manufacture high-quality infrared lenses with surfaces ranging from simple conics to complex aspheric. Since most of the infrared lenses utilize chalcogenide glasses including germanium, which is expensive as a raw material, the use of near net shape process like Precision Glass Molding Process as a cost effective process to eliminate material waste is necessary. In this case, Finite Element Analysis (FEM) is a tool that can simulate the PGM process and help designers to predict the appropriate mold geometry that can form the desire surface lens profile. This tool can also anticipate residual stress of the molded lens that can result in an inhomogeneous refractive index that directly affects the optical performance of the lens. As can be seen in the market, there is a lot of commercial FE software like ABAQUS, MSC MARC, ANSIS, DEFORM, and etc., that can be used to simulate the PGM process that each has its own advantages and disadvantages. In this case, a fair evaluation of software would be helpful for FEM users. This thesis starts with an understanding of glass properties as a fundamental to establish a model by FE software. To have an understanding of glass behavior, glass properties like glass viscoelasticity, glass viscosity and glass transition temperature and other related glass properties should be studied. The study of manufacturing process of an infrared lens by using a commercial glass molding machine, GP-10000HT, is the second step to figure out all the details of a real precision glass molding process that help us to provide a simulation that makes a better prediction of glass molding process. By having a good understanding of material properties as well as manufacturing process of glass molding process, the numerical modeling of PGM process by using two commercial FE software, MSC MARC and ABAQUS, is another approach of this thesis. These two numerical modeling are designed with the same condition to help us evaluate and compare these two software at a fair situation. The simulation results that consist of molded glass geometry as well as residual von Mises stress, show that the maximum geometry (center thickness and diameter) deviation of 8 and 6 microns for MSC MARC and ABAQUS, respectively. In the last chapter of this thesis, the simulation results, obtained by MSC MARC and ABAQUS, are evaluated based on seven parameters which are Overall dimensions, curvature of upper and lower molded glass, residual stress at each step software capability to introduce material properties, calculation Time, visualization capability, and being user-friendly. According to this evaluation, both software are able to have a good prediction of the final geometry of the lens as well as the residual stress, but ABAQUS because of its ability to converge to the solution in shorter time, better visualization and also being user-friendly would be preferred. MSC MAC has also a built-in module to introduce the Narayanaswamy model to describe the structural relaxation behavior of the glass, which is not available in ABAQUS. This disadvantage of ABAQUS can be easily covered by running appropriate code that could be write in software like C++ or FORTRAN.

Committee:

Allen Yi (Advisor)

Subjects:

Engineering; Optics

Keywords:

Aspherical lens, lenses,precision glass molding, finite element method, chalcogenide glasses, molded infrared optics, viscosity, glass viscoelasticity, Glass transition temperature,ABAQUS, MSC MARC,

Rollakanti, Kishore ReddyProtoporphyrin IX Fluorescence for Enhanced Photodynamic Diagnosis and Photodynamic Therapy in Murine Models of Skin and Breast Cancer
Doctor of Engineering, Cleveland State University, 2015, Washkewicz College of Engineering
Protoporphyrin IX (PpIX) is a photosensitizing agent derived from aminolevulinic acid. PpIX accumulates specifically within target cancer cells, where it fluoresces and produces cytotoxic reactive oxygen species. Our aims were to employ PpIX fluorescence to detect squamous cell carcinoma (SCC) of the skin (Photodynamic diagnosis, PDD), and to improve treatment efficacy (Photodynamic therapy, PDT) for basal cell carcinoma (BCC) and cutaneous breast cancer. Hyperspectral imaging and a spectrometer based dosimeter system were used to detect very early SCC in UVB-irradiated murine skin, using PpIX fluorescence. Regarding PDT, we showed that low non-toxic doses of vitamin D, given before ALA application, increase tumor specific PpIX accumulation and sensitize BCC and breast cancer cells to ALA-PDT. These optical imaging methods and the combination therapy regimen (vitamin D and ALA-PDT) are promising tools for effective management of skin and breast cancer.

Committee:

Edward Maytin, PhD (Committee Chair); Sridhar Ungarala, PhD (Committee Member); John Turner, PhD (Committee Member); Judith Drazba, PhD (Committee Member); Anand Ramamurthi, PhD (Committee Member)

Subjects:

Biomedical Engineering; Biomedical Research; Engineering; Medical Imaging; Optics

Keywords:

Aminolevulinic acid; Protoporphyrin IX; Photodynamic therapy; Photodynamic Diagnosis; IVIS, basal cell carcinoma; squamous cell carcinoma; breast cancer; vitamin D; differentiation

Dolasinski, Brian DavidNonlinear systems for frequency conversion from IR to RF
Doctor of Philosophy (Ph.D.), University of Dayton, 2014, Electro-Optics
The objective of this dissertation is to evaluate and develop novel sources for tunable narrowband IR generation, tunable narrowband THz generation, and ultra-wideband RF generation to be used in possible non-destructive evaluation systems. Initially a periodically poled Lithium Niobate (PPLN) based optical parametric amplifier (OPA) is designed using a double-pass configuration where a small part of the pump is used on the first pass to generate a signal, which is reflected and filtered by an off-axis etalon. The portion of the pump that is not phase matched on the first pass is retro-reflected back into the PPLN crystal and is co-aligned with the narrow bandwidth filtered signal and amplified. We demonstrate that the system is tunable in the 1.4 µm -1.6 µm signal range with a linewidth of 5.4 GHz. Next the outputs of seeded, dual periodically poled lithium niobate (PPLN) optical parametric amplifiers (OPA) are combined in the nonlinear crystal 4-dimthylamino-N-methyl-4-stilbazolium-tosylate (DAST) to produce a widely tunable narrowband THz source via difference frequency generation (DFG). We have demonstrated that this novel configuration enables the system to be seamlessly tuned, without mode-hops, from 1.2 THz to 26.3 THz with a minimum bandwidth of 3.1 GHz. The bandwidth of the source was measured by using the THz transmission spectrum of water vapor lines over a 3-meter path length. By selecting of the DFG pump wavelength to be at 1380 nm and the signal wavelength to tune over a range from 1380 nm to 1570 nm, we produced several maxima in the output THz spectrum that was dependent on the phase matching ability of the DAST crystal and the efficiency of our pyro-electric detector. Due to the effects of dispersive phase matching, filter absorption of the THz waves, and two-photon absorption multiple band gaps in the overall spectrum occur and are discussed. Employing the dual generator scheme, we have obtained THz images at several locations in the spectrum using an infrared camera that runs at a rate of 35 frames per second. We have demonstrated the ability to image 2 THz to 26 THz both in static and in real time conditions. We will present images of carbon fibers illuminated at different THz frequencies. Lastly, microwave generation was demonstrated by ultrafast photo-excitation experiments to induce non-equilibrium quasi-particle relaxation. Using a laser with a pulse energy of 1 mJ and a pulse duration greater than 120 fs (808 nm wavelength) incident on a charged, superconducting YBa_2 Cu_2 O_(7-d) (YBCO) thin film ring, the photo-response was measured with a series of microwave antennas. From the observed nanosecond response time of the transient pulse, we extracted the frequency spectrum in the GHz regime that was dependent on the incident beam diameter, pulse duration, power, and the physical structure of the YBCO thin film.

Committee:

Joseph Haus (Committee Chair)

Subjects:

Optics

Keywords:

nonlinear parametric process; difference frequency generation; optical parametric amplifier; DAST THz wave generation; THz DFG; PPLN OPA; etalon OPA; CMC THz evaluation; CMC THz imaging; CMC laser line scan

Gillespie, Shane MatthewCharacterizing Phase Noise for Beam Steering Devices
Master of Science (M.S.), University of Dayton, 2014, Electro-Optics
In this thesis we assemble a type of Mach-Zehnder interferometer to measure the complex signal after passage through a device under test placed in one arm. The signal's phase is extracted from the complex signal dataset and is analyzed to study the phase noise added due to the device. We are studying a liquid crystal beam steering system, which is a combination of two optical devices; the first is a variable liquid crystal half-waveplate and the second is a liquid crystal phase grating. The variable liquid crystal waveplate is the active element that has voltages applied to achieve a specific birefringence, whereas the liquid crystal phase grating is a passive device. For the beam steering devices of interest the liquid crystal phase grating is passive and therefore unlikely to impart appreciable amounts of phase noise, so the focus of this research was on the potential phase noise due to variable liquid crystal waveplate. The phase noise using the variable liquid crystal waveplate is measured in three operational states: a non-energized off state, an energized state having zero-phase change,and an energized state with voltage set for a half-wave phase change. We examine the phase spectrum |Φ(ƒ)|2, obtained from the frequency analysis of the temporal phase. A comparison is made between the phase noise spectrums in several cases: pre-device insertion to a post-device insertion of the variable liquid crystal waveplate for the three different states. We examine the signal spectrum over frequencies spanning the range from 1 Hz to 107 Hz and tentatively conclude that the active devices add little additional noise to the system. Further data is needed to solidify this conclusion given the data being analyzed is from one data capture, and the system required readjustment between captures, and we observe a drift of the noise floor.

Committee:

Joseph Haus, Ph.D. (Committee Chair); Paul McManamon, Ph.D. (Committee Member); Tim Finegan (Committee Member); David Rabb (Committee Member)

Subjects:

Military Studies; Optics; Technology

Keywords:

phase noise; beam steering; liquid crystal polarization gratings; mach zehnder; interferometry; polarization IQ;

Chen, LiHybrid Silicon and Lithium Niobate Integrated Photonics
Doctor of Philosophy, The Ohio State University, 2015, Electrical and Computer Engineering
A hybrid silicon and lithium noibate (LiNbO3) material system is developed to combine the high index contrast of silicon and the second order susceptibility of lithium niobate. Ion-sliced single crystalline LiNbO3 thin film is bonded to silicon-on-insulator (SOI) waveguides via Benzocyclobutene (BCB) as the top cladding. The LiNbO3 thin films are patterned to achieve desired size, shape and crystal orientations. Integrated electrodes are integrated to confine electric fields to the LiNbO3 thin film. Empowered by the linear electro-optic effect of LiNbO3, compact chip-scale hybrid Si/LiNbO3 integrated photonic devices are enabled on the SOI platform, including radio-frequency electric field sensors, tunable optical filters, high speed electro-optical modulators for optical interconnects, and high linearity modulators for analog optical links. Compact and metal-free electric field sensors based on indirect bonding of z-cut ion-sliced LiNbO3 thin film to silicon microrings are demonstrated. The demonstrated sensitivity to electric fields is 4.5 V m-1Hz-1/2 at 1.86 GHz. Tunable optical filters based on hybrid Si/LiNbO3 microring resonators with integrated electrodes are also demonstrated with a tunability of 12.5 pm/V, which is over an order of magnitude greater than electrode-free designs. By integrating metal thin film electrode and utilizing silicon as an optically transparent electrode, voltage induced electric fields in the LiNbO3 are enhanced. We also presented low power compensation of thermal drift of resonance wavelengths in hybrid Si/LiNbO3 ring resonators. A capacitive geometry and low thermal sensitivity result in the compensation of 17 oC of temperature variation using tuning powers at sub-nanowatt levels. The method establishes a route for stabilizing high quality factor resonators in chip-scale integrated photonics subject to temperature variations. Gigahertz speed hybrid Si/LiNbO3 electro-optical microring modulators are enabled by optimizing the RC time constant of the biasing electrodes. Fabricated devices exhibit a resonance tuning of 3.3 pm/V and a small-signal electrical-to-optical 3 dB bandwidth of 5 GHz. Digital modulation with an extinction ratio greater than 3 dB is demonstrated up to 9 Gb/s. High-speed and low tuning power chip-scale modulators that exploit the high-index contrast of silicon with the second order susceptibility of lithium niobate are envisioned. An alternative design with x-cut LiNbO3 thin films on silicon racetrack resoantors enables compact highly linear integrated optical modulator for high spectral free dynamic range (SFDR) analog optical links. The measured third order intermodulation distortion SFDR is 98.1 dB·Hz2/3 at 1 GHz and 87.6 dB·Hz2/3 at 10 GHz. The demonstrated SFDR is over an order of magnitude greater than silicon ring modulators based on the plasma dispersion effect, and is comparable to commercial LiNbO3 Mach-Zehnder interferometer modulators, but with a footprint three orders of magnitude smaller. The hybrid Si/LiNbO3 photonic platform is promising for applications in optical interconnections, microwave photonics, optical computing and sensing. More broadly, empowering silicon with second-order susceptibility opens a suite of nonlinear optic applications to the chip scale.

Committee:

Ronald Reano (Advisor); Joel Johnson (Committee Member); Fernando Teixeira (Committee Member); Gregory Lafyatis (Committee Member)

Subjects:

Electrical Engineering; Electromagnetics; Nanotechnology; Optics

Keywords:

silicon photonics; integrated optics devices; electro-optical devices; sensors; waveguides; resonators; optical modulators; optical interconnects; microwave photonics; hybrid photonics; integrated optics materials; lithium niobate; micro-fabrication;

Wang, JunxinNanoimprint Fabrication of Wire-grid Polarizers Using Deep-UV Interference Lithography
Master of Science (M.S.), University of Dayton, 2014, Electro-Optics
Wire-grid polarizers in the visible and near-IR spectra have a number of interesting applications in imaging because they can be made in pixel-sizes and at different orientations. They are most easily fabricated by lift-off lithography, but this reduces the wire thickness resulting in low aspect ratios and the poor polarizer extinction ratios. Alternative methods such as the damascene process have also proven to be difficult. In this thesis, we demonstrate a nanoimprint technique where a polymer film on glass is used as the substrate for imprinting the grooves, followed by metallization. A high resolution 220nm periodic stamp, with feature sizes of the order of 100nm, is fabricated on silicon using deep-UV (266nm) interference lithography and directional plasma etching. The interference lithography process was developed and optimized for the fabrication of these nanostructures. This nanostructure is transferred onto a patternable epoxy (SU-8) using vacuum thermo-compression and in-situ UV exposure. SU-8 was chosen because it is optically clear and easily imprinted. A new in-situ UV illumination system was designed and built for the imprint. The imprinted structure also enables a unique glancing angle deposition method that is much easier for the fabrication of wire grids than lift-off or damascene. A polarizer extinction ratio of 90 was measured at 1064nm wavelength. In this thesis we will show the results from these processes, including process details, SEM images and performance data.

Committee:

Andrew Sarangan (Committee Chair); Imad Agha (Committee Member); Jay Mathews (Committee Member)

Subjects:

Nanotechnology; Optics

Van Hook, Richard L.A Comparison of Monocular Camera Calibration Techniques
Master of Science in Computer Engineering (MSCE), Wright State University, 2014, Computer Engineering
Extensive use of visible electro-optical (visEO) cameras for machine vision techniques shows that most camera systems produce distorted imagery. This thesis investigates and compares several of the most common techniques for correcting the distortions based on a pinhole camera model. The methods being examined include a common chessboard pattern based on (Sturm 1999), (Z. Zhang 1999), and (Z. Zhang 2000), as well as two "circleboard" patterns based on (Heikkila 2000). Additionally, camera models from the visual structure from motion (VSFM) software (Wu n.d.) are used. By comparing reprojection error from similar data sets, it can be shown that the asymmetric circleboard performs the best. Finally, a software tool is presented to assist researchers with the procedure for calibration using a well-known fiducial.

Committee:

Kuldip Rattan, Ph.D. (Advisor); Juan Vasquez, Ph.D. (Committee Member); Thomas Wischgoll, Ph.D. (Committee Member)

Subjects:

Computer Engineering; Computer Science; Optics; Scientific Imaging

Keywords:

Calibration; Reprojection Error; Visual Structure from Motion; OpenCV; calibration patterns

Borshch, VolodymyrNanosecond Electric Modification of Order Parameters
PHD, Kent State University, 2014, College of Arts and Sciences / Department of Chemical Physics
In this Dissertation, we study a nanosecond electro-optic response of a nematic liquid crystal in a geometry where an applied electric field E modifies the tensor order parameter but does not change the orientation of the optic axis (director ). We use nematics with negative dielectric anisotropy with the electric field applied perpendicularly to . The field changes the dielectric tensor at optical frequencies (optic tensor), due to the following mechanisms: (a) nanosecond creation of biaxial orientational order; (b) uniaxial modification of the orientational order that occurs over the timescales of tens of nanoseconds, and (c) quenching of director fluctuations with a wide range of characteristic times up to milliseconds. We develop a model to describe the dynamics of all three mechanisms. We design the experimental conditions to selectively suppress the contributions from the quenching of director fluctuations (c) and from the biaxial order effect (a) and thus, separate the contributions of the three mechanisms in the electro-optic response. As a result, the experimental data can be well fitted with the model parameters. The analysis provides a rather detailed physical picture of how the liquid crystal responds to a strong electric field, E ~ 108 V/m, on a timescale of nanoseconds. This work provides a useful guide in the current search of the biaxial nematic phase. Namely, the temperature dependence of the biaxial susceptibility allows one to estimate the temperature of the potential uniaxial-to-biaxial phase transition. An analysis of the quenching of director fluctuations indicates that on a timescale of nanoseconds, the classic model with constant viscoelastic material parameters might reach its limit of validity. The effect of nanosecond electric modification of the order parameter (NEMOP) can be used in applications in which one needs to achieve ultrafast (nanosecond) changes of optical characteristics, such as birefringence.

Committee:

Oleg Lavrentovich, DSc (Advisor); Sergij Shiyanovskii, DSc (Advisor)

Subjects:

Condensed Matter Physics; Experiments; Materials Science; Optics; Physics

Keywords:

Liquid Crystals; electro-optics; nanoseconds; Liquid Crystal Displays; dielectric anisotropy; nematic; dynamics; ultrafast switching; soft matter;uniaxial; biaxial; order parameter; fluctuations; birefringence;

Cui, ZiruoWet Etching Optical Fibers to Sub-micron Diameters for Sensing Application
Master of Science (M.S.), University of Dayton, 2014, Electro-Optics
In this thesis we explore a novel technique to fabricate sub-micron diameter tapered fibers for sensor applications. Physically the light propagating in a tapered fiber has an evanescent field that extends into the medium surrounding the fiber containing an analyte. A sub-micron diameter taper can expels most the electromagnetic energy into the medium thus increasing the sensitivity of the measurement. The tapering process we develop enables us to have precise control over the final diameter of the taped fiber's waist. The tapered single mode fiber sensors (TSMFs) are fabricated using a two-step procedure. First, a single mode fiber is tapered to about 10 microns using Vytran Glass Processing System. Second, we etch the TSMFs with 6:1 buffered HF solution to a controlled sub-micron size. During the etching process we monitor the fiber's progress by measuring the transmittance characteristics. The in situ measurements are made by connecting a laser at one fiber end and using a photodetector to measure the transmittance at the other end. We find a temporal modulation of the transmittance during the etching process, which is due to the changes in the propagation constants of the fiber modes. The details of this device are described and its optical properties are examined in this thesis. To better understand the transmission characteristics recorded in the experiment we develop a simulation of the optical power propagating through the tapered fiber to calculate the transmitted power. We apply a Beam Propagation Method (BPM) to simulate the light wave passing through the tapered fiber sensor. We numerically analyze the transmittance characteristics of the beam oscillating inside the TSMFs. Our simulations are applied to validate the experimental results.

Committee:

Joseph Haus, Ph.D. (Committee Chair); Peter Powers, Ph.D. (Advisor); Partha Banerjee, Ph.D. (Committee Member)

Subjects:

Optics

Keywords:

Tapered single-mode fiber sensor;Wet etching;Sensitivity;Beam Propagation Method

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