Thesis (Ph. D.)--Florida State University, 2003. / Advisor: Dr. Frank Gross, Florida State University, FAMU-FSU College of Engineering, Dept. of Electrical and Computer Engineering. Title and description from dissertation home page (viewed Oct. 3, 2003). Includes bibliographical references.

Swath bathymetry sidescan (SBS) sonar and the angle-of-arrival processing that underlies these systems has the capability to produce much higher resolution three dimensional imagery and bathymetry than traditional beamformed approaches. However, the performance of these high resolution systems is limited by signal-to-noise ratio (SNR) and they are also susceptible to multipath interference. This thesis explores two methods for increasing SNR and mitigating multipath interference for SBS systems. The first, binary coded pulse transmission and pulse compression is shown to increase the SNR and in turn provide reduced angle variance in SBS systems. The second, transmit beamforming, and more specifically steering and shading, is shown to increase both acoustic power in the water and directivity of the transmitted acoustic radiation. The transmit beamforming benefits are achieved by making use of the 8-element linear angle-of-arrival array typical in SBS sonars, but previously not utilized for transmit. Both simulations and real world SBS experiments are devised and conducted and it is shown that in practice pulse compression increases the SNR, and that transmit beamforming increases backscatter intensity and reduces the intensity of interfering multipaths. The improvement in achievable SNR and the reduction in multipath interference provided by the contributions in this thesis further strengthens the importance of SBS systems and angle-of-arrival based processing, as an alternative to beamforming, in underwater three dimensional imaging and mapping. / Graduate / 2015-04-15 / 0544 / 0547 / mark.butowski@gmail.com

High Harmonic Generation (HHG) enables the production of bursts of coherent soft x-rays with attosecond pulse duration. This process arrises from the nonlinear interaction between intense infrared laser pulses and an ionizing gas medium. Soft x-ray photons are used for spectroscopy of inner-shell electron correlation and exchange processes, and the availability of attosecond pulse durations will enable these processes to be resolved on their natural time scales. The maximum or cutoff photon energy in HHG increases with both the intensity as well as the wavelength of the driving laser. It is highly desirable to increase the harmonic cutoff as this will allow for the generation of shorter attosecond pulses, as well as HHG spectroscopy of increasingly energetic electronic transitions. While the harmonic cutoff increases with laser wavelength, there is a corresponding decrease in harmonic yield. The first part of this thesis describes the experimental measurement of the wavelength scaling of HHG efficiency, which we report as lambda^(-6.3) in xenon, and lambda^(-6.5) in krypton. To increase the HHG cutoff, we have developed a 1.8 um source, with stable carrier envelope phase and a pulse duration of <2 optical cycles. The 1.8 um wavelength allowed for a significant increase in the harmonic cutoff compared to equivalent 800 nm sources, while still maintaing reasonable harmonic yield. By focusing this source into neon we have produced 400 eV harmonics that extend into the x-ray water window. In addition to providing a source of photons for a secondary target, the HHG spectrum caries the signature of the electronic structure of the generating medium. In krypton we observed a Cooper minimum at 85 eV, showing that photoionization cross sections can be measured with HHG. Measurements in xenon lead to the first clear observation of electron correlation effects during HHG, which manifest as a broad peak in the HHG spectrum centred at 100 eV. This thesis also describes several improvements to the HHG experiment including the development of an ionization detector for measuring laser intensity, as well as an investigation into the role of laser mode quality on HHG phase matching and efficiency.

Swath bathymetry sidescan (SBS) sonar and the angle-of-arrival processing that underlies these systems has the capability to produce much higher resolution three dimensional imagery and bathymetry than traditional beamformed approaches. However, the performance of these high resolution systems is limited by signal-to-noise ratio (SNR) and they are also susceptible to multipath interference. This thesis explores two methods for increasing SNR and mitigating multipath interference for SBS systems. The first, binary coded pulse transmission and pulse compression is shown to increase the SNR and in turn provide reduced angle variance in SBS systems. The second, transmit beamforming, and more specifically steering and shading, is shown to increase both acoustic power in the water and directivity of the transmitted acoustic radiation. The transmit beamforming benefits are achieved by making use of the 8-element linear angle-of-arrival array typical in SBS sonars, but previously not utilized for transmit. Both simulations and real world SBS experiments are devised and conducted and it is shown that in practice pulse compression increases the SNR, and that transmit beamforming increases backscatter intensity and reduces the intensity of interfering multipaths. The improvement in achievable SNR and the reduction in multipath interference provided by the contributions in this thesis further strengthens the importance of SBS systems and angle-of-arrival based processing, as an alternative to beamforming, in underwater three dimensional imaging and mapping. / Graduate / 0544 / 0547 / mark.butowski@gmail.com

High Harmonic Generation (HHG) enables the production of bursts of coherent soft x-rays with attosecond pulse duration. This process arrises from the nonlinear interaction between intense infrared laser pulses and an ionizing gas medium. Soft x-ray photons are used for spectroscopy of inner-shell electron correlation and exchange processes, and the availability of attosecond pulse durations will enable these processes to be resolved on their natural time scales. The maximum or cutoff photon energy in HHG increases with both the intensity as well as the wavelength of the driving laser. It is highly desirable to increase the harmonic cutoff as this will allow for the generation of shorter attosecond pulses, as well as HHG spectroscopy of increasingly energetic electronic transitions. While the harmonic cutoff increases with laser wavelength, there is a corresponding decrease in harmonic yield. The first part of this thesis describes the experimental measurement of the wavelength scaling of HHG efficiency, which we report as lambda^(-6.3) in xenon, and lambda^(-6.5) in krypton. To increase the HHG cutoff, we have developed a 1.8 um source, with stable carrier envelope phase and a pulse duration of <2 optical cycles. The 1.8 um wavelength allowed for a significant increase in the harmonic cutoff compared to equivalent 800 nm sources, while still maintaing reasonable harmonic yield. By focusing this source into neon we have produced 400 eV harmonics that extend into the x-ray water window. In addition to providing a source of photons for a secondary target, the HHG spectrum caries the signature of the electronic structure of the generating medium. In krypton we observed a Cooper minimum at 85 eV, showing that photoionization cross sections can be measured with HHG. Measurements in xenon lead to the first clear observation of electron correlation effects during HHG, which manifest as a broad peak in the HHG spectrum centred at 100 eV. This thesis also describes several improvements to the HHG experiment including the development of an ionization detector for measuring laser intensity, as well as an investigation into the role of laser mode quality on HHG phase matching and efficiency.

The aim of this thesis was introducing the options of conversion between OTDM and WDM technologies. Since this issue is rather extensive, first of all the principle of optical transmission system is described. One chapter presents the effects influencing the optical transmissions. Material absorption, linear and nonlinear scattering and bending losses are mentioned in terms of fiber losses, followed by description of waveguide, chromatic and polarization-mode dispersion of optical fibers. Last part of the chapter presents nonlinear effects, including self-phase modulation, cross-phase modulation and four-wave mixing. The practical part of the thesis deals with multichannel systems. The principles of frequency, space a hybrid multiplexing are explained. Multichannel systems with optical time domain multiplexing and waveguide multiplexing are described in detail and compared. The elements of the transmission chain of multiplex, such as different types of lasers, detectors, modulators, optical amplifiers, splitters, couplers, MUX and DEMUX are discussed. The next part of the thesis was aimed at suggesting the model of mutual conversion between OTDM and WDM systems. First of all, the previously performed experiments concerning the conversion between OTDM and WTM were evaluated. Then the model of OTDM/WDM/OTDM conversion was designed, with explanation of its parts and their function. The general recommendations for practical implementation were are also included. Due to the limited amount of time reserved for access to the simulation program Optsim, the simulations were performed only for certain parts of the proposed conversion model. At the end of the thesis, the proposed model is evaluated.

The pulse compression scheme implemented on the Imaging Wind and Rain Air-borne Profiler (IWRAP) is described. Developed at the UMASS Microwave Remote Sensing Laboratory (MIRSL), IWRAP is a dual-band (C and Ku) conically scanning Doppler scatterometer designed to map the atmospheric boundary layer wind fields, ocean surface wind fields, and precipitation within tropical cyclones. IWRAP has previously been deployed using a pulsed transmit waveform with a peak transmit power of 80 watts. This limits the average transmit power and sensitivity for the system which affects the more distant range gates (especially at Ku-band). As a result, IWRAP could operate only at lower altitudes (approx. 5000 ft) causing safety concerns and limiting the missions for which it can be deployed. Increasing sensitivity was achieved by converting IWRAP to a pulse compression radar system. Pulse compression is a technique that combines the increased energy of a longer pulse with the high resolution of a short pulse by implementing a frequency modulated (FM) “chirped” transmit waveform. This method requires advanced signal processing, in which the received signal is passed through a filter to compress the pulse on the receiving end. A system with various chirp/filtering schemes as well as a new control system which UMASS has recently developed will be discussed in this thesis.

Le positionnement d'un engin sous-marin s'appuie sur des systèmes dits "acoustiques". Ces derniers renseignent la position relative de l'engin immergé par rapport au navire support. Les performances de ces systèmes sont définies en termes de limite de portée et de précision. Le principe de ces systèmes repose sur les notions de distance-métrie et de goniométrie, qui s'appuient toutes deux sur l'estimation du temps de propagation et donc de la date d'arrivée du signal utile. Cela est classiquement réalisé par une opération de Compression d'Impulsion. Cette technique qui est largement utilisée dans les domaines du SONAR, RADAR et imagerie bio-médicale, repose sur une application sous-optimale du Filtrage Adapté. En effet, le Filtrage Adapté est une technique d’estimation ou de détection optimale lorsque le bruit et blanc et gaussien et lorsque le signal utile est déterministe, c’est-à-dire que le signal reçu est bien connu. Cependant, il est bien connu que dans le monde sous-marin, le bruit n’est pas blanc, et pas toujours gaussien. Aussi, le signal utile étant déformé soit par le milieu de propagation soit par des phénomènes physiques tels que l’effet Doppler, celui-ci n’est pas déterministe. On peut alors considérer que le bruit est coloré et que le signal utile est une réalisation d’un processus aléatoire. Ainsi, en vue d’étendre les hypothèse d’application de la Compression d’Impulsion classique, nous proposons de construire une nouvelle forme de Compression d’Impulsion basée sur l’utilisation du Filtrage Adapté Stochastique. En effet, ce dernier est une extension naturelle du Filtrage Adapté pour des bruits colorés et des signaux déterministes. Toutefois, le Filtrage Adapté Stochastique suppose que les signaux sont stationnaires au second ordre. Or, cela n’est pas toujours le cas pour le bruit en milieu marin, et cela n’est jamais le cas pour un signal modulé en fréquence tel que ceux utilisés par les systèmes de positionnement acoustiques. Ainsi, nous proposons une nouvelle technique de Compression d’Impulsion alliant les qualités du Filtrage Adapté Stochastique et celle des techniques Temps-Fréquence. Ces dernières, et en particulier la transformée de Wigner-Ville, permettent de contourner l’hypothèse de stationnarité imposée par le Filtrage Adapté Stochastique. D’autre part, en vue de contrer l’apparition d’interférences générées par ces techniques, nous développons ici une approche par « décomposition atomique » sur une base de DCT. Ainsi donc, ces trois années de thèse, ont donné naissance à de nouvelles méthodes de Compression d'Impulsion qui permettent d'améliorer les performances des systèmes de positionnement sous-marin. / The underwater vehicules positioning is based on acoustic systems. These systems provide us the relative position of the immersed submarine to the carrier ship. The systems performances are defined in terms of precision and slant range. The positioning systems use concepts like distance measurement and goniometry, both based on the Time Of Arrival estimation of the useful signal, which is classically performed by a Pulse Compression. This technique, widely applied on SONAR, RADAR and bio-medical imaging, is a sub-optimal application of the Matched Filtering. After these three years of work, we had obtained new methods of Pulse Compression that allow to improve the performances of the acoustic positioning systems. These new techniques are based on an expension of the application assumptions of the Pulse Compression to reach, as well as possible, the optimality.

by Wai Ho Mow. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 116-124). / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Spread Spectrum Technique --- p.2 / Chapter 1.1.1 --- Pulse Compression Radars --- p.3 / Chapter 1.1.2 --- Spread Spectrum Multiple Access Systems --- p.6 / Chapter 1.2 --- Definitions and Notations --- p.8 / Chapter 1.3 --- Organization of this Thesis --- p.12 / Chapter 2 --- Lower Bounds on Correlation of Sequences --- p.15 / Chapter 2.1 --- Welch's Lower Bounds and Sarwate's Generalization --- p.16 / Chapter 2.2 --- A New Construction and Bounds on Odd Correlation --- p.23 / Chapter 2.3 --- Known Sequence Sets Touching the Correlation Bounds --- p.26 / Chapter 2.4 --- Remarks on Other Bounds --- p.27 / Chapter 3 --- Perfect Polyphase Sequences: A Unified Approach --- p.29 / Chapter 3.1 --- Generalized Bent Functions and Perfect Polyphase Sequences --- p.30 / Chapter 3.2 --- The General Construction of Chung and Kumar --- p.32 / Chapter 3.3 --- Classification of Known Constructions ...........； --- p.34 / Chapter 3.4 --- A Unified Construction --- p.39 / Chapter 3.5 --- Desired Properties of Sequences --- p.41 / Chapter 3.6 --- Proof of the Main Theorem --- p.45 / Chapter 3.7 --- Counting the Number of Perfect Polyphase Sequences --- p.49 / Chapter 3.8 --- Results of Exhaustive Searches --- p.53 / Chapter 3.9 --- A New Conjecture and Its Implications --- p.55 / Chapter 3.10 --- Sets of Perfect Polyphase Sequences --- p.58 / Chapter 4 --- Aperiodic Autocorrelation of Generalized P3/P4 Codes --- p.61 / Chapter 4.1 --- Some Famous Polyphase Pulse Compression Codes --- p.62 / Chapter 4.2 --- Generalized P3/P4 Codes --- p.65 / Chapter 4.3 --- Asymptotic Peak-to-Side-Peak Ratio --- p.66 / Chapter 4.4 --- Lower Bounds on Peak-to-Side-Peak Ratio --- p.67 / Chapter 4.5 --- Even-Odd Transformation and Phase Alphabet --- p.70 / Chapter 5 --- Upper Bounds on Partial Exponential Sums --- p.77 / Chapter 5.1 --- Gauss-like Exponential Sums --- p.77 / Chapter 5.1.1 --- Background --- p.79 / Chapter 5.1.2 --- Symmetry of gL(m) and hL(m) --- p.80 / Chapter 5.1.3 --- Characterization on the First Quarter of gL(m) --- p.83 / Chapter 5.1.4 --- Characterization on the First Quarter of hL(m) --- p.90 / Chapter 5.1.5 --- Bounds on the Diameters of GL(m) and HL(m) --- p.94 / Chapter 5.2 --- More General Exponential Sums --- p.98 / Chapter 5.2.1 --- A Result of van der Corput --- p.99 / Chapter 6 --- McEliece's Open Problem on Minimax Aperiodic Correlation --- p.102 / Chapter 6.1 --- Statement of the Problem --- p.102 / Chapter 6.2 --- A Set of Two Sequences --- p.105 / Chapter 6.3 --- A Set of K Sequences --- p.110 / Chapter 7 --- Conclusion --- p.113 / Bibliography --- p.124

La génération d’impulsions courtes d’ondes acoustiques de surface est étudiée, en s’inspirant du principe de l’amplification des impulsions chirpées qui est utilisée pour la génération d’impulsions laser ultrabrèves. La compression temporelle des impulsions est généralement réalisée à l’aide d’éléments dispersifs. Dans ce travail, un transducteur à ondes acoustiques de surface pouvant émettre des impulsions brèves est utilisé comme élément dispersif. Une étude comparative des transducteurs à peignes interdigités chirpés est menée avec un modèle du premier ordre et un modèle dit de matrice mixte. Des dispositifs à ondes acoustiques de surface sont conçus et réalisés à partir des résultats de simulation numérique. La façon de distribuer la période dans le transducteur est étudiée. L’apparition de bandes interdites dues aux réflexions internes dans le transducteur chirpé et son effet sur l’émission directionnelle des ondes surface sont en particulier observées et étudiées.Un interféromètre optique différentiel dans le domaine temporel et stabilisé est ensuite proposé afin de caractériser les impulsions brèves. Le transducteur à ondes acoustiques de surface est placé à l’extérieur de l’interféromètre. Des expériences sont conduites avec un transducteur à peignes interdigités chirpé ayant une bande opérationnelle couvrant la gamme de fréquences 200 MHz – 400 MHz et produisant des impulsions de 10 ns avec un déplacement hors-plan maximal de 36 nm. La réponse interférométrique est comparée à une mesure électrique directe obtenue à l’aide d’un transducteur de réception large bande ; une bonne correspondance des deux mesures est observée. Les influences de la différence de chemin optique dans l’interféromètre et du choix du point d’observation sur la surface sont discutées. La compression de l’impulsion le long du transducteur chirpé est observée expérimentalement.Finalement, une étude comparative de différents filtres de compression temporelle est présentée, dans l’objectif d’obtenir des impulsions optimales à la fois courtes temporellement et de forte intensité, pour un élément dispersif donné. Le filtre inverse est identifié comme le plus efficace et nous permet de produire les impulsions de plus grande amplitude. Afin d’optimiser la compression de l’impulsion pour les dispositifs fabriqués, des expériences sont conduites pour trouver les courbes de compromis optimal dans chaque cas de modulation de la période du transducteur. / Generation of short pulses with surface acoustic waves (SAW) is studied, in analogy with the principle of chirped pulse amplification (CPA) used to produce ultrashort laser pulses. Temporal compression of pulses is generally achieved with dispersive elements. A SAW transducer emitting short SAW pulses is used as a dispersive element in this work. A comparative study of chirped inter digital transducers (CIDTs) using the first order model and the p-matrix model is presented. SAW devices are designed and fabricated using the simulation results and the effect of the varying pitch of the CIDts on the response is studied. Appearance of band gaps due to internal reflections within the CIDts and its effect on the directionality of the CIDTs are in particular found and studied.A stabilized time-domain differential optical interferometer is then proposed in order to characterize short pulses, with the surface acoustic wave (SAW) sample placed outside the interferometer. Experiments are conducted with surface acoustic waves excited by a chirped inter-digital transducer on a piezoelectric lithium niobate substrate having an operational bandwidth covering the 200 MHz – 400 MHz frequency range and producing 10 ns pulses with 36 nm maximum out-of-plane displacement. The interferometric response is compared with a direct electrical measurement obtained with a receiving wide bandwidth inter-digital transducer and good correspondence is observed. The effects of varying the path difference of the interferometer and the measurement position on the surface are discussed. Pulse compression along the chirped inter-digital transducer is observed experimentally.Finally, a comparative study of different filter designs for generating short pulses is presented with an objective to find a design to produce the optimal pulse which is short in width and high in amplitude, for a given dispersive element. The inverse filter is found to be the most efficient as it produces a short pulse with the highest amplitude. To optimize the pulse compression for the fabricated devices, experiments are conducted to find the optimal trade-off curve for each chirp case.