Browsing by Subject "Interferometry"
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Item A micro-scale universal detector based on backscattering interferometry(Texas Tech University, 2003-05) Wang, ZhanlingAs the current trend in miniaturization of analytical instrument continues, there is an urgent requirement for sensitive, small volume detection methodologies. Refractive index (Rl) detection, affords the generation of a signal for essentially all analyses, further more, the analytical signal is concentration rather than mass sensitive, and the technique is nondestructive. In the first part of this thesis, a universal detector based on backscatter interferometry has been developed to perform nanoliter volume refractive index measurements for on-chip SDS gel electrophoresis of proteins. The on-chip backscattering interferometry (OCIBD) detection system consists of a simple, folded optical train, it is based on the interaction of a laser beam and an etched channel in the shape of half cylinder in a silica plate. The backscattered light from the channel takes on the form of a high contrast interference pattern that contains information related to the bulk properties of the fluid located within the detection volume of 2.32 x 10"^ L. Depending on CE injection method, the positional changes of the interference fringes allow for the quantification of unlabeled proteins at the levels ranging from 17 to 310 attomoles. Separation and detection of 5 label-free proteins was achieved in less than 100 seconds with detection limits ranging from 0.95 picograms (1.1 x 10^-16mol) of Calmodulin to 7.0 picograms (1.0 x 10^-16) of BSA without signal filtering or active thermal control. In the second part of this thesis, an ultra sensitive Dual capillary-Dual bicell (DCDB) MIBD system was also developed. DCDB MIBD system focuses a He-Ne laser through a half wave plate onto the cross section of two capillaries, one for reference and another for sensing analyte. The backscatering fringe patterns were detected with hwo bicell photodetectors. Because the two capillaries are located in identical thermal environment, the difference of the two bicell signals which represent the reference and probing capillary respectively, can cancel out the errors from the thermal drift, which is the major error in MIBD system. Thus gives an accurate detection of the specific signal of analyte without preciously controlling of the environment temperature. The characteristic of this system has been demonstrated by measuring glycerol concentration and real time monitoring protein folding/unfolding when temperature changed in a wild range. It has potential use as a real time nanoliter detector in |j,-HPLC, CE, FIA and scanning micro-calorimetry.Item AFM-based measurement of the mechanical properties of thin polymer films and determination of the optical path length of nearly index-matched cavities(2008-05) Wieland, Christopher F., 1980-; Shih, Chih-KangTwo technologies, immersion and imprint lithography, represent important stepping stones for the development of the next generation of lithography tools. However, although the two approaches offer important advantages, both pose many significant technological challenges that must be overcome before they can be successfully implemented. For imprint lithography, special care must be taken when choosing an etch barrier because studies have indicated that some physical material properties may be size dependent. Additionally, regarding immersion lithography, proper image focus requires that the optical path length between the lens and substrate be maintained during the entire writing process. The work described in this document was undertaken to address the two challenges described above. A new mathematical model was developed and used in conjunction with AFM nano-indentation techniques to measure the elastic modulus of adhesive, thin polymer films as a function of the film thickness. It was found that the elastic modulus of the polymer tested did not change appreciably from the value determined using bulk measurement techniques in the thickness range probed. Additionally, a method for monitoring and controlling the optical path length within the gap of a nearly index-matching cavity based on coherent broadband interference was developed. In this method, the spectrum reflected for a cavity illuminated with a modelocked Ti:Sapphire laser was collected and analyzed using Fourier techniques. It was found that this method could determine the optical path length of the cavity, quickly and accurately enough to control a servo-based feedback system to correct deviations in the optical path length in real time when coupled with special computation techniques that minimized unnecessary operations.Item An on-chip universal detector based on backscattering interferometry(Texas Tech University, 2000-05) Swinney, Kelly ANOt availableItem Deformation monitoring using scanning synthetic aperture radar interferometry(2009-05) Gudipati, Krishna Vikas, 1979-; Buckley, Sean M.This dissertation provides the first demonstration of scanning synthetic aperture radar (ScanSAR) advanced interferometry processing for measuring surface deformation. ScanSAR data are synthesized from ERS-1/2 stripmap SAR images over known deformation in Phoenix, Arizona. The strategy is to construct a burst pattern similar to Envisat ScanSAR data and to create a realistic variable-burst synchronization scenario in which any image pair has at least 50% burst overlap. The Small Baseline Subsets technique is applied to the synthesized data to demonstrate ScanSAR time series analysis for a scenario generally conducive for interferometry. The same processing approach is employed with the stripmap data to validate the results. The differences in ScanSAR and stripmap velocities have a mean and standard deviation of 0.02±0.02 cm/year. 96.3% and 99.1% of the velocity differences are within ±0.1 cm/year and ±0.2 cm/year, respectively. The RMS deviations between the ScanSAR and stripmap displacement estimates are 0.40±0.30 cm. 68.5% and 94.6% of the differences are within ±0.5 cm and ±1.0 cm, respectively. The Permanent Scatterer (PS) technique also is adapted and applied to the synthesized data to demonstrate the presence of PS in ScanSAR data. The atmospheric and nonlinear motion phase derived from a PS analysis of stripmap data are removed from the ScanSAR interferograms. Even for this idealized scenario, the final PS identification yields fewer ScanSAR PS (10 PS/km²) than the stripmap PS results (312 PS/km² or 15.6 PS/km² at the ScanSAR pixel resolution). Based on the calculated likelihood of finding multiple stripmap PS within a ScanSAR pixel, it is concluded that the ScanSAR single scatterer PS model is flawed. A model is introduced that considers multiple PS within a ScanSAR pixel. The search for two PS per pixel yields 120 PS/km². The ScanSAR and stripmap PS velocity differences mean is zero and standard deviation is 0.02 cm/year. However, while the differences between the ScanSAR and stripmap PS DEM error estimates are zero-mean, they have a 7-meter standard deviation. One possible explanation for this relatively large deviation is the differencing of the wrong ScanSAR and stripmap PS as the result of a misalignment between the ScanSAR and stripmap images.Item Estimating high resolution atmospheric phase screens from differential InSAR measurements(2010-05) Yang, Dochul; Buckley, Sean M.; Tapley, Byron D.; Schutz, Bob E.; Lightsey, Glenn; Wilson, Clark R.Atmospheric artifacts superimposed on interferometric synthetic aperture radar (InSAR) measurements have the potential to greatly impede the accurate estimation of deformation signals. The research presented in this dissertation demonstrates a novel InSAR time series algorithm, called HiRAPS algorithm, for effectively estimating high resolution atmospheric phase screens (APS) from differential InSAR measurements. In summary, the HiRAPS algorithm utilizes short time span differential interferograms and rearranges components of existing advanced InSAR techniques to identify a higher density of scatterers used to create the APS. The improved scatterer density allows one to estimate high spatial frequency atmospheric signals not recovered from existing InSAR time series techniques. The HiRAPS algorithm was tested with simulated and actual data, which contain phase contributions from linear and nonlinear deformation, topographic height errors, and atmospheric artifacts. Simulated differential interferograms were generated to have the same spatial and temporal baselines as the actual differential interferograms formed from RADARSAT-1 data over Phoenix, Arizona. The APS superimposed on simulated differential interferograms were then estimated and compared to simulated APS. The root mean square error (RMSE) between the estimated and simulated APS was calculated to qualitatively assess the different values obtained. The RMSE was 0.26 radians when utilizing the HiRAPS algorithm, compared to an RMSE value of 0.39 radians using an implementation of the permanent scatterer (PS) algorithm. The HiRAPS algorithm also showed its applicability for estimating high spatial frequency atmospheric signals for actual data. Sixty-six SAR images, starting from October 5, 2002 and spanning 5 years, were processed for this research. The APS pixel density obtained using the HiRAPS algorithm was 253 pixels per square kilometer, compared to 14 pixels per square kilometer utilizing the PS algorithm. The APS superimposed on the differential interferograms were estimated with both the proposed and PS algorithms. High resolution APS were estimated with the HiRAPS algorithm, whereas only low resolution APS were obtained with the PS algorithm. After estimating and removing estimated APS, the phase stability of APS-free differential interferograms was examined by identifying the permanent scatterers (PS). The final density of identified PS obtained with the HiRAPS algorithm was 453 PS per square kilometer, whereas the density of detected PS using the generic PS algorithm was 381 PS per square kilometer. The maximum difference in the deformation time series between the HiRAPS algorithm and the PS algorithm was less than 6 mm. However, the HiRAPS algorithm resulted in less apparent noise in the time series than the PS algorithm due to the precise estimation of APS.Item Experimental studies of high energy density silicon using ultra-fast lasers(2007) Grigsby, Will Robert, 1978-; Ditmire, Todd R.Understanding material behavior under extreme conditions is an important area of research in physics and material science. One method to study the behavior of materials under these conditions is to drive a strong shock wave through a material and watch its response. In many cases the material response is complicated by phase transitions such as lattice restructuring (Barker 1975; Mabire and Hereil 2000; Swift, Tierney et al. 2005) and melting (Asay 1975; Elias, Chapron et al. 1988; Werdiger, Eliezer et al. 1999; Mabire and Hereil 2000; Swift, Tierney et al. 2005). To study these dynamics we are using lasers in high time resolution pump-probe experiments to develop a real time diagnostic on the phase of a shocked material. This technique enables probing of the entire phase history of a material as it shock compresses and releases. In addition to linear reflectivity and ultra-fast 2D displacement interferometry, we developed a melting diagnostics based on the non-linear optical technique of third harmonic generation (THG) using a circularly polarized laser pulse. This diagnostic resolves the less than 300 fs melting transition of laser excited Si and GaAs, and it also detects a response in shock compressed silicon. Our results show that Si remains crystalline during compression of an elastic 100 kbar shock wave. Results from Si shocked to higher pressures (> 300 kbar) indicate a decrease in THG, suggesting some level of disordering or unexplained phase change.Item Impact of surface conditioning of large area electrodes on the dielectric strength of water(Texas Tech University, 2004-08) Wetz, David A.Due to water's high dielectric constant, 6r = 81, there is considerable interest in breakdown phenomena in water, particularly as an insulator and/or switching media in pulsed power systems. In numerous research efforts conducted over the last several decades, it has been documented that electrical breakdown in water is initiated from localized field enhancements on the electrode surface caused from asperities or microprotrusions on the electiode surface. The research conducted here attempts to determine the impact of electiode surface conditions on the holdoff voltage of a water gap. In this document, experimental results are presented on the impact electrode material and surface treatment has on the dielectric strength of water. A 4mm water gap was tested under pulsed conditions with pulse widths greater than 1 /is, peak electric fields over 1 MV/cm and peak currents over 20 kA. Stainless steel electrodes machined with a Bruce profile and an effective area of 5cm^ were tested with surface roughnesses ranging from .34 /.im to 1.41 /xm. Results comparing electiodes that have additionally been electropohshed are compared to those without an additional tieatinent. These various surface tieatments remove microprotrusions from the electiode surface and reduce localized field enhancements. It is believed that this technique will minimize the number of breakdown initiation points, thereby, increasing tiie dielectiic stiength. Results are given on the degree to which each finish improves the dielectiic stiength of water.Item Microwave diagnostics on a railgun plasma(Texas Tech University, 1996-12) Grant, Gregory T.This thesis describes microwave interferometry measurements on the High Energy Railgun Apparatus (HERA) at Texas Tech University. Chapter I discusses railguns in general, basic railgun theory, and problems encountered whh railguns. The physical railgun system is described and illustrated as well as the timing and firing system, and the data acquishion system. Chapter II contains a general discussion of interferometry, a detailed discussion of the microwave interferometer used on the HERA railgun, and a discussion and analysis of the expected signal from the detector of the HERA interferometer. Chapter III discusses the acquishon of the experimental data. It describes how the interferometer was "zeroed" before each shot and shows how attenuation and reflection of the interferometer microwave probing beam played a role in the collection of the data. This chapter also describes techniques which could be used to cut down on microwave reflections at dielectric interfaces on the railgun bore. Chapter IV is a detailed analysis of the shot data. This analysis includes a figure for each shot of interest and a table to describe the shot condhions. It also provides calculations and observations based upon the observed waveforms. These calculations are shown for the HERA railgun first whh a 1.8 cm square bore, and then with a 1 cm round bore. Chapter IV also gives resuhs and conclusions of this research. Trends in the data are pointed out and speculations about the significance of these trends are given. Conclusions are drawn and final remarks and recommendations are made.Item Optimal Maneuvers for Distributed Aperture Imaging Systems(2012-10-19) Fitch, DanielleInterest in space-borne, distributed multi-aperture interferometric systems is driven by a need for continuously sustained imaging with high resolution. Amplitude interferometry systems measure the Fourier components of the image corresponding to the wave vectors (locations in the so-called u-v plane) that are proportional to the relative positions of the apertures. Imaging to specified resolution demands measurement of the Fourier components with adequate signal-to-noise ratio over the interior of a disk in the u-v plane (the resolution disk). In this paper we concentrate on the case in which interferometric measurements are made while the apertures are changing their relative positions. This work discusses heuristic maneuvers and strategies for a system of two space-borne telescopes to cover the frequency plane while optimizing a cost function that includes both a measure of image quality and propulsive effort. The current study is motivated by previous research in which the optimization problem was formulated and the first-order necessary conditions (FONC) derived. The earlier work obtained short time horizon solutions to the FONC for various simple situations, but the complexity of the integro-differential equations for optimal maneuvering have heretofore prevented solution for an optimal maneuver for the entirety of the imaging process. In place of a direct attack on the FONC, the present work investigates various heuristic approaches to minimizing the cost function in the discretized state and discretized time domains in a hexagonal coordinate system. Using three classes of coverage rules, experimentation with a variety of maneuver strategies involving two apertures has led to a number of time-optimal or fuel-optimal solutions based on the initial conditions of the spacecraft. This thesis shows that an optimal maneuver can be determined from the starting positions of the spacecraft and that a self-spiral class of motion seems to be the most beneficial for long term strategies. Future work may focus on strategies for interferometric systems with more than two apertures and with a finer mesh of the hexagonal coordinate system.Item Phase Retrieval with Application to Intensity Correlation Interferometers(2012-10-24) Trahan, Russell 1987-As astronomers and astrophysicists seek to view ever-increasingly distant celestial objects, the desired angular resolution of telescopes is constantly being increased. Classical optics, however, has shown a proportional relationship between the size of an optical telescope and the possible angular resolution. Experience has also shown that prohibitive cost accompanies large optical systems. With these limitations on classical optical systems and with the drastic increase in computational power over the past decade, intensity correlation interferometry (ICI) has seen renewed interest since the 1950?s and 60?s when it was initially conceived by Hanbury Brown and Twiss. Intensity correlation interferometry has the advantage of less stringent equipment precision and less equipment cost when compared to most other forms of interferometry. ICI is thus attractive as a solution to the desire for high angular resolution imaging especially in space based imaging systems. Optical interferometry works by gathering information about the Fourier transform of the geometry of an optical source. An ICI system, however, can only detect the magnitude of the Fourier components. The phase of the Fourier components must be recovered through some computational means and typically some a priori knowledge of the optical source. This thesis gives the physics and mathematical basis of the intensity correlation interferometer. Since the ICI system cannot detect the phase of an optical source's Fourier transform, some known methods for recovering the phase information are discussed. The primary method of interest here is the error-reduction algorithm by Gerchberg-Saxton which was adapted by Fienup to phase retrieval. This algorithm works by using known qualities of the image as constraints; however, sometimes it can be difficult to know what these constraints are supposed to be. A method of adaptively discovering these constraints is presented, and its performance is evaluated in the presence of noise. Additionally, an algorithm is presented to adapt to the presence of noise in the Fourier modulus data. Finally, the effects of the initial condition of the error-reduction algorithm are shown and a method of mitigating its effect by averaging several independent solutions together is shown.Item Radar interferometry measurement of land subsidence(2000-08) Buckley, Sean Monroe, 1970-; Tapley, Byron D.Item The impact packaged device planarity has on insertion loss in a DMD based optical networking system(Texas Tech University, 2003-12) Spain, James DThis paper will effectively show whether or not packaged die planarity has an impact on optical system insertion loss and also determine whether or not the die attach systems compromises system performance criteria due to reduced packaged die planarity. A new and important application for Texas Instruments Incorporated Digital Micromirror Device (DMD^M) is in optical switching where it can play a role in dynamic network reconfiguration and signal grooming in the DWDM technology. Using the DMD™ will help the Dense Wavelength Division Multiplexing (DWDM) technology reach a high number of wavelengths in the optical fiber, thus increasing the overall bandwidth of the optical fiber. To obtain this goal, many parameters must be considered. One key performance parameter in this application is insertion loss. Insertion loss is the light power that is lost going from one optical fiber to another as it passes through key optical components. In this work, the impact of device planarity on insertion loss for a particular system configuration is investigated. Calculating the radius of curvature from the topography of the packaged die will enable the user to determine the mathematical approximation of the impact of planarity on insertion loss. Interferometric data obtained by measuring the packaged devices are used to create a simple model for the optical performance. The insertion loss of the DMDTM in a generic fiber optic system can be estimated. The distributions of two different die attach systems are compared from an optical performance perspective.Item Time reversal and plane-wave decomposition in seismic interferometry, inversion and imaging(2012-12) Tao, Yi, active 2012; Sen, Mrinal K.This thesis concerns the study of time reversal and plane-wave decomposition in various geophysical applications. Time reversal is a key step in seismic interferometry, reverse time migration and full waveform inversion. The plane-wave transform, also known as the tau-p transform or slant-stack, can separate waves based on their ray parameters or their emergence angles at the surface. I propose a new approach to retrieve virtual full-wave seismic responses from crosscorrelating recorded seismic data in the plane-wave domain. Unlike a traditional approach where the correlogram is obtained from crosscorrelating recorded data, which contains the full range of ray parameters, this method directly chooses common ray parameters to cancel overlapping ray paths. Thus, it can sometime avoid spurious arrivals when the acquisition requirement of seismic interferometry is not strictly met. I demonstrate the method with synthetic examples and an ocean bottom seismometer data example. I show a multi-scale application of plane-wave based full waveform inversion (FWI) with the aid of frequency domain forward modeling. FWI uses the two-way wave-equation to produce high-resolution velocity models for seismic imaging. This technique is implemented by an adjoint-state approach, which viii involves a time-reversal propagation of the residual wavefield at receivers, similar to seismic interferometry. With a plane-wave transformed gather, we can decompose the data by ray parameters and iteratively update the velocity model with selected ray parameters. This encoding approach can significantly reduce the number of shots and receivers required in gradient and Hessian calculations. Borrowing the idea of minimizing different data residual norms in FWI, I study the effect of different scaling methods to the receiver wavefield in the reverse time migration. I show that this type of scaling is able to significantly suppress outliers compared to conventional algorithms. I also show that scaling by its absolute norm generally produces better results than other approaches. I propose a robust stochastic time-lapse seismic inversion strategy with an application of monitoring Cranfield CO2 injection site. This workflow involves two steps. The first step is the baseline inversion using a hybrid starting model that combines a fractal prior and the low-frequency prior from well log data. The second step is to use a double-difference inversion scheme to focus on the local areas where time-lapse changes have occurred. Synthetic data and field data show the effectiveness of this method.