Browsing by Subject "Optics"
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Item Barium Titanate Nanoparticles as Exogenous Contrast Agents in Second Harmonic Optical Coherence Tomography(2013-05-06) Pearson, Jeremy TI propose and demonstrate a method by which barium titanate nanoparticle clusters can be used as exogenous contrast agents in Second Harmonic Optical Coherence Tomography imaging systems to localize and highlight desired regions of tissue. SH-OCT has previously been used to identify collagen within OCT images. However, SH-OCT signals from collagen are highly susceptible to inferior reflector artifacts because most of the second harmonic generated light is forward scattered. Second harmonic generating nanoparticle clusters exhibit high scattering properties, which can give them the advantage of backscattering a large quantity of second harmonic light while attenuating the forward scattered light. In this research project, a mathematical model is proposed in which the backward to forward scattering ratio of second harmonic generated light from nanoparticle layers is exponentially proportional to the thickness of the layer. This model was supported by measurements of the backward to forward scattering ratio of second harmonic light in barium titanate nanoparticles layers. This indicates that nanoparticle clusters can be designed and manufactured with the proper thickness so that they generate a large second harmonic signal without creating inferior reflector artifacts.Item Controlling infrared radiation with subwavelength metamaterials and silicon carbide(2011-05) Neuner, Burton Hamilton; Shvets, G.; Fink, Manfred; Florin, Ernst-Ludwig; Yao, Zhen; Zhang, XiaojingThe control and manipulation of infrared (IR) radiation beyond the capabilities of natural materials using silicon carbide (SiC), metamaterials, or a combination thereof, is presented. Control is first demonstrated using SiC, a polar crystal that exhibits a dielectric permittivity less than zero in the mid-IR range, through the excitation of tightly confined surface phonon-polaritons (SPPs), thus enabling a multitude of applications not possible with conventional dielectrics. Optimal, or critical coupling to SPPs is explored in SiC films through Otto-configuration attenuated total reflection. One practical application based on Otto-coupled SPPs is presented: IR refractive index sensing is shown for three pL-scale fluid analytes. It is then demonstrated that when two SiC films are brought to a few-micron separation, IR radiation can excite surface modes that possess phase velocities near the speed of light, a property required for efficient table-top particle accelerators. Metamaterials are engineered with subwavelength structure and possess optical properties not found in nature. Two such metamaterials will be introduced: metal films perforated with arrays of rectangular holes display the ability to control IR light polarization through spoof surface plasmon excitation, and metal/dielectric multilayers patterned with subwavelength-pitch corrugations display frequency-tunable, wide-angle, perfect IR absorption. Two experiments, which have implications in polarization control and thermal emission, combine the benefits of SiC with those of metamaterials: extraordinary optical transmission and absorption are observed in SiC hole arrays, and the design of individual SiC antennas permits the control of the bulk metamaterial responses of impedance and absorption/emission. Finally, a new optical beamline based on Fourier transform IR spectroscopy was designed, built, characterized, and implemented, serving as the major experimental objective of this dissertation. The novel beamline, which confines radiation to a 200-micron diameter and enables angle-dependent IR spectroscopy, was verified using multiple metamaterial structures.Item Development of Advanced Optics and High Resolution Instrumentation for Mass Spectrometry Based Proteomics(2010-01-14) Sherrod, Stacy D.Imaging mass spectrometry (MS) analysis allows scientists the ability to obtain spatial and chemical information of analytes on a wide variety of surfaces. The ability to image biological analytes is an important tool in many areas of life science research, including: the ability to map pharmaceutical drugs in targeted tissue, to spatially determine the expression profile of specific proteins in healthy vs. diseased tissue states, and to rapidly interrogate biomolecular microarrays. However, there are several avenues for improving the imaging MS experiment for biological samples. Three significant directions this work addresses include: (1) reducing chemical noise and increasing analyte identification by developing sample preparation methodologies, (2) improving the analytical figures of merit (i.e., spatial resolution, analysis time) by implementing a spatially dynamic optical system, and (3) increasing both mass spectral resolution and ion detection sensitivity by modifying a commercial time-of-flight (TOF) MS. Firstly, sample methodology schemes presented in these studies consist of obtaining both ?top-down? and ?bottom-up? information. In that, both intact mass and peptide mass fingerprinting data can be obtained to increase protein identification. This sample methodology was optimized on protein microarrays in preparation for bio tissue analysis. Other work consists of optimizing novel sample preparation strategies for hydrated solid-supported lipid bilayer studies. Sample methods incorporating nanomaterials for laser desorption/ionization illustrate the ability to perform selective ionization of specific analytes. Specifically, our results suggest that silver nanoparticles facilitate the selective ionization of olefin containing species (e.g., steroids, vitamins). Secondly, an advanced optical design incorporating a spatially dynamic optical scheme allows for laser beam expansion, homogenization, collimation, shaping, and imaging. This spatially dynamic optical system allows user defined beam shapes, decreases analysis times associated with mechanical movement of the sample stage, and is capable of increasing the MS limits of detection by simultaneously irradiating multiple spots. Lastly, new data acquisition strategies (multiple anode detection schemes) were incorporated into a commercial time-of-flight mass spectrometer to increase both sensitivity and resolution in a matrix assisted laser desorption/ionization mass spectrometer. The utility of this technique can be applied to many different samples, where high mass spectral resolution allows for increased mass measurement accuracy.Item Experimental demonstration of new optical properties in hybrid nanostructures(2015-12) Hartsfield, Thomas Murray; Li, Elaine; Bengtson, Roger; Shih, Chih-Kang; Sitz, Greg; Wang, ZhengIn this dissertation, I present experimental investigation of the optical properties of nanoscale systems composed of both metallic and semiconductor components. Metallic nanostructures may act as resonant cavities for conduction electrons, allowing drastic electromagnetic field enhancement and the concentration of these surface plasmon field modes into tiny volumes. Semiconductor quantum dot emitters demonstrate desirable and broadly tunable optical properties due to the quantized nature of their internal electron states. When paired together, the absorption, emission, optical gain, and internal energy decay pathways of the quantum dot as well as the scattering of the cavity may be strongly modified. This work focuses on the optical properties of two such model hybrid nanostructure systems. Of the many studies of plasmonic cavities, relatively few investigate the influence of a quantum dot on the scattering of the plasmonic cavity itself. The main experimental challenge lies in the difficulty of placing an absorber or emitter at the desired position: the very virtue of the small mode volume of a plasmonic cavity demands precise spatial emitter placement. We will study the simplest plasmonic cavity, a single metal nanoparticle and a single quantum dot. We assembled a hybrid nanostructure using a nanomanipulation “nano-golfing” technique and demonstrated for the first time that the state of a single quantum dot can resonantly control the scattering of a vastly larger plasmonic cavity, manifested as a Fano resonance. A device of this design could potentially be used as a photon source capable of outputting photons of classical or quantum statistics on demand. We then turn to the optical properties of the emitter element of a hybrid nanostructure. We measured the ability of an atomically smooth Ag film to influence the optical properties of a quantum dot. This novel system has been shown to produce more uniform emitter-plasmon coupling and a greater product of excitation and radiative decay rates than possible with traditional systems relying upon rough metal films. Applications utilizing coupling between metallic films and quantum emitters could see benefit from high quality atomically smooth films as demonstrated by our studies.Item Holographic Representations of Optical Systems.(Texas Tech University, 1975-05) Deen, Lewis MonroeNot Available.Item Instrumentation to Measure the Backscattering Coefficient bb for Arbitrary Phase Functions(2011-10-21) Haubrich, DavidThe backscattering coefficient bb is one of the inherent optical properties of natural waters which means that it is independent of the ambient light field in the water. As such, it plays a central role in many problems of optical oceanography and is used in the characterization of natural waters. Essentially, any measurement that involves sending a beam of light into water must account for all inherent backscattering. Some of the applications that rely on the precise knowledge of the backscattering coefficient include studies of suspended particle distributions, optical bathymetry, and remote sensing. Many sources contribute to the backscattering, among them any suspended particles, air bubbles, and the water molecules themselves. Due to the importance of precise measurements and the ease with which water samples can be contaminated, an instrument to determine directly and quickly the backscattering coefficient in situ is highly desirable. We present such an instrument in both theory and experiment. We explain the theory behind our instrument and based on measurements made in the laboratory we demonstrate that our prototype shows the predicted behavior. We present data for increased extinction in the water, and show how measuring the extinction and taking it into account improves the quality of our measurements. We present calibration data obtained from three different particle sizes representing differently shaped volume scattering functions. Based on these measurements we demonstrate that our prototype has the necessary resolution to measure the backscattering coefficient bb over the whole range found in natural waters. We discuss potential improvements that should be made for a commercial version of the instrument.Item An investigation of the physical parameters of young stellar objects(2011-12) Deen, Casey Patrick; Jaffe, D. T.; Lacy, John; Sneden, Chris; Scalo, John; Johns-Krull, Christopher; Evans, Neal J.Studies of the temporal evolution of young stars and their associated properties rely upon the ability of astronomers to determine ages and masses of objects in different evolutionary states. The best method for determining the age and mass of a young stellar object is to place the object on the Hertzsprung-Russell (HR) diagram and to compare to theoretical evolutionary tracks. Accurate ages allow the investigation of the temporal evolution of properties associated with stellar youth (accretion rates, X-ray activity, circumstellar excess, etc...). One property intimately linked with stellar youth is the presence (or absence) of an optically thick primordial circumstellar disk. Objects in "young" star forming regions are more likely to show evidence for a disk than objects in "older" clusters. Within a single cluster, the picture is not as clear. There exist objects in very young clusters (~1 Myr) which show no evidence for circumstellar disks, and there exist objects in very old clusters (~10 Myr), which show evidence for robust disks, suggesting a variable other than stellar age is driving the evolution of the disks. To investigate whether these outliers are due to age spreads, initial conditions, or simply appear anomalous due to erroneous age determinations, we must determine better placements in the HR diagram by carefully transforming observable quantities (spectral type and apparent magnitude) into the quantities necessary for comparison evolutionary models (effective temperature and luminosity). In the Ophiuchus star forming region, I investigate whether or not objects with disks are younger than disk-less objects. I find no difference in the ages of the two populations, but the systematic and random uncertainties are large enough to mask all but the largest age differences. In the hope of better determining the physical parameters of young stellar objects, I embark on a spectral synthesis campaign to produce comparison synthetic spectra which account for the effects of magnetic fields. This requires the modification of the MOOG spectral synthesis program to handle the full Stokes vector treatment for polarized radiation through a magnetized medium. I create a grid of synthetic spectra covering ranges in effective temperature, surface gravity, and average magnetic field strength relevant for studies of young stellar objects, and develop a Chi-squared minimization routine to determine the best fit synthetic spectrum for a given observed spectrum at an arbitrary resolving power. This grid of synthetic spectra will be an invaluable complement to future near infrared, large band-pass, high-resolving power spectrographs (i.e. IGRINS). In addition to these observational and theoretical attempts to reduce systematic errors, I also helped to develop a suite of silicon and KRS-5 grisms for use in the FORCAST instrument, a mid infrared camera on the SOFIA telescope. These grisms will afford the imaging instrument a mid infrared spectroscopic capability at wavelengths normally inaccessible from the ground. I also report on my work to help write FG Widget, the quick-look reduction software package developed to support grism observations.Item Micro/nano fabrication of polymeric materials by DMD-based micro-stereolithography and photothermal imprinting(2006) Lu, Yi; Chen, ShaochenItem Optical methods for microscopic particle size measurement(Texas Tech University, 1997-12) Kustov, Vadim MichailovichNot availableItem Optical power concentrations on aligned and misaligned receivers in solar gridiron power systems(Texas Tech University, 1978-08) Leung, HipsumA powerful strategy, the ROSA approach, has been developed for calculation of optical power concentrations produced by solar collectors. The ROSA method is yery general and can be applied to concentrators and receivers of any geometrical shape. In addition, the method can be used for light from a source of finite extent undergoing any number of multiple reflections on the collector mirror. The work presented here is applied to optical concentrations on a conical receiver suspended in a spherical segment collector as appropriate for a Solar Gridiron Power System. Optical power concentrations on both aligned and misaligned receivers are described for various solar inclinations. A simplified approach for calculating azimuthally averaged power concentrations on a perfectly aligned receiver is also presented.Item Single-stage large-angle beam steering optical phased array on silicon nanomembrane(2010-05) Kwong, David Nien; Chen, Ray T.; Bank, Seth R.In this paper, we present the results of the design and fabrication of a 12 channel nano-membrane-based optical phased array that allows for large angle beam steering operating at wavelength=1.55µm. Our device is fabricated on silicon-on-insulator using standard CMOS process. By implementing unequally spaced waveguide array elements, we can relax the half-wavelength spacing requirement for large angle beam steering, thereby avoiding the optical coupling between adjacent waveguides and reducing the side-lobe-level of the array radiation pattern. 1D beam steering of tranverse-electric polarized single mode light is designed to be achieved thermo-optically through the use of thin film metal phase shifters.Item Study of applications of second harmonic generation(2011-05) Prem, Adrienne Marie; Downer, Michael Coffin; Sitz, Greg O.Two applications of second harmonic generation (SHG), a nonlinear optical technique, are studied. First, Fresnel factors are used with a bond model to describe SHG from vicinal silicon at five incidence angles: 7.5°, 22°, 30°, 45°, and 52°. Second, a prototype apparatus for applying SHG to enhance imaging capabilities of optical coherence tomography, a microscopy technique used in many biological fields, is briefly described.Item Study of microfluidic measurement techniques using novel optical imaging diagnostics(Texas A&M University, 2007-04-25) Park, JaesungNovel microscale velocity and temperature measurement techniques were studied based on confocal laser scanning microscopy (CLSM) and optical serial sectioning microscopy (OSSM). Two microscopic measurement systems were developed, 1) a CLSM micro particle image velocimetry (PIV) system with a dual Nipkow disk confocal unit (CSU-10), a CW argon-ion laser and an upright microscope, and 2) an OSSM micro- particle tracking velocimetry (PTV) system with an epi-fluorescence microscope and a non-designed specimen to make a three-dimensional (3-D) diffraction particle image. The CLSM micro-PIV system shows a unique optical slicing capability allowing true depth-wise resolved vector field mapping. A comparative study is presented between the CLSM micro-PIV and a conventional epi-fluorescence micro-PIV. Both have been applied to the creeping Poiseuille flows in two different microtubes of 99-????m (Re = 0.00275) and 516-????m ID diameters (Re = 0.021). The CLSM micro-PIV consistently shows significantly improved particle image contrasts, the definition of "optical slicing" and measured flow vector fields more accurately agreeing with predictions based on the Poiseuille flow fields, compared to the conventional micro-PIV. The OSSM micro-PTV technique is applied for a 3-D vector field mapping in a microscopic flow and a Brownian motion tracking of nanoparticles. This technique modifies OSSM system for a micro-fluidic experiment, and the imaging system captures a diffracted particle image having numerous circular fringes instead of an in-focus particle image. The 3-D particle tracking is based on a correlation between the 3-D diffraction pattern of a particle and the defocus distance from a focal plane. A computational program is invented for the OSSM micro-PTV, and provides a 3-D velocity vector field with a spatial resolution of 5.16 ????m. In addition, a concept of nonintrusive thermometry is presented based on the correlation of the Brownian motion of suspended nanoparticles with the surrounding fluid temperature. Detection of fully three-dimensional Brownian motion is possible by the use of the OSSM, and the measured value of mean square displacement (MSD) is compared fairly well with Einstein's predictions.Item Temperature dependent refractive index of lipid tissue by optical coherence tomography imaging(2011-05) Lim, Hyunji; Milner, Thomas E.; Tunnell, JamesTemperature dependent optical properties of lipid tissue verify critical information of tissue dynamics which can be applied to tissue treatment and diagnosis of various pathological features. Current methods of treating lipid rich tissues via heating are associated with post operation complications. Recent studies shows potential of lipid rich tissue removal by cooling. For monitoring cooling procedure and physical and chemical changes in lipid tissue, temperature dependent optical properties in subzero cooling need to be verified. This study designed heat transfer system estimating heat flux by cooling and programmed codes for image and data processing to obtain refractive indices of rodent subcutaneous lipid tissue. Phase transition of lipid tissue was observed and finally verified temperature dependent refractive index coefficient of lipid tissue from 24°C to -10°C.Item Terawatt Raman laser system for two-color laser plasma interactions(2014-08) Sanders, James Christopher; Downer, Michael CoffinIn some high-field laser-plasma experiments, it is advantageous to accompany the main high-energy (~1 J) laser with a second high-energy pulse (~0.1 J) which has been frequency-shifted by ~10-20%. Such a pulse-pair would have a low walk-off velocity while remaining spectrally distinct for use in two-color pump-probe experiments. Moreover, by shifting the second pulse by ~plasma frequency, it is theoretically possible to exercise some amount of control over a variety of laser-plasma instabilities, including forward Raman scattering, electromagnetic cascading, and relativistic self-focusing. Alternatively, the two pulses may be counter-propagated so that the collide in the plasma and create a slowly-propagating beatwave which can be used to inject electrons into a laser wakefield accelerator. The design, characeterization, and performance of a hybrid chirped-pulse Raman amplifier (CPRA)/Ti-Sapphire amplifier are reported and discussed. This hybrid system allows for the generation of a high-energy (>200 mJ), broadband (15-20 nm bandwidth FWHM), short duration (>100 fs duration) laser sideband. When amplified and compressed, the Raman beam's power exceeds 1 TW. This sideband is combined with the primary laser system to create a bi-color terawatt laser system which is capable of performing two-color high-field experiments. This two-color capability can be added to any commercial terawatt laser system without compromising the energy, duration or beam quality of the primary system. Preliminary two-color laser-plasma experiments are also discussed.Item Ultra-precise manipulation and assembly of nanoparticles using three fundamental optical forces(2012-12) Demergis, Vassili; Florin, Ernst-Ludwig; Shubeita, George T; Fink, Manfred; Makarov, Dmitrii E; Korgel, Brian AThe invention of the laser in 1960 opened the door for a myriad of studies on the interactions between light and matter. Eventually it was shown that highly focused laser beams could be used to con fine and manipulate matter in a controlled way, and these instruments were known as optical traps. However, challenges remain as there is a delicate balance between object size, precision of control, laser power, and temperature that must be satisfied. In Part I of this dissertation, I describe the development of two optical trapping instruments which substantially extend the allowed parameter ranges. Both instruments utilize a standing wave optical field to generate strong optical gradient forces while minimizing the optical scattering forces, thus dramatically improving trapping efficiency. One instrument uses a cylinder lens to extend the trapping region into a line focus, rather than a point focus, thereby confining objects to 1D motion. By translation of the cylinder lens, lateral scattering forces can be generated to transport objects along the 1D trapping volume, and these scattering forces can be controlled independently of the optical gradient forces. The second instrument uses a collimated beam to generate wide, planar trapping regions which can con fine nanoparticles to 2D motion. In Part II, I use these instruments to provide the first quantitative measurements of the optical binding interaction between nanoparticles. I show that the optical binding force can be over 20 times stronger than the optical gradient force generated in typical optical traps, and I map out the 2D optical binding energy landscape between a pair of gold nanoparticles. I show how this ultra-strong optical binding leads to the self-assembly of multiple nanoparticles into larger contactless clusters of well de ned geometry. I nally show that these clusters have a geometry dependent coupling to the external optical field.Item Ultrafast third-harmonic generation from nanostructured optical thin films and interfaces(2006) Stoker, David Stevens; Keto, John W.Optical harmonic generation from nanostructured thin films and interfaces was investigated experimentally and theoretically. Sample materials were large band gap optical semiconductors (AlN/GaN), rare earth oxides (NdAlO3), and noble metals (Ag). They were examined as solids, nanoparticles, and as hybrid nanocomposites. The goal of the project was to create and characterize high susceptibility, third-order (third-harmonic) materials that relied on nanostructure for an enhanced response. Laser ablation of a microparticle aerosol (LAMA) was used to produce these materials. Two routes to nanostructured materials were investigated. In the first method, a microparticle aerosol, composed of a small concentration of metal or semiconductor, and a larger amount of glass microparticles, was ablated by a focused excimer laser, and the resultant nanoparticle aerosol was supersonically deposited and sintered. In the second method, a monolayer of silver nanoparticles was deposited by LAMA, and this film was further processed by pulsed laser deposition (PLD) of either a passive glass or active matrix material. Better optical quality was found in the hybrid LAMA/PLD materials. Many optical properties were required for characterization: linear transmission and absorption spectroscopy of plasmon resonances, second-harmonic generation (SHG) for field-enhancement analysis, and fluorescence spectroscopy and fluorescence lifetime experiments provided preliminary data for third-harmonic generation studies. The third-harmonic generation experiments were performed using an ultrafast laser system, and modeling the ultrafast dynamics of harmonic generation showed that pulse breakup occurs in the third-harmonic field. Interfaces were found to produce the harmonics, through cooperative group-velocity and phase mismatching. This uniquely ultrafast effect allowed for z-scan measurements to be simplified and for focusing effects to be eliminated. Using frequency-domain interferometry allowed for the measurement of the absolute phase of a third-harmonic pulse, and for an accurate determination of the third-order susceptibility of AlN. Finally, enhancement of second- and third- harmonic generation in PLD-coated Ag nanoparticle films was found to depend both on the material microstructure and the fundamental laser intensity.