Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2006. / Trebino, Rick, Committee Chair ; First, Phillip, Committee Member ; Ralph, Stephen, Committee Member ; Kennedy, Brian, Committee Member ; Buck, John, Committee Member.

Thesis (Ph. D.)--University of Oregon, 2005. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 166-173). Also available for download via the World Wide Web; free to University of Oregon users.

Vários experimentos têm demonstrado que pulsos ultra curtos no domínio de subpicossegundos promovem uma combinação de efeitos termomecânicos que superam algumas das objeções ao uso de um laser como instrumento removedor. Usando os parâmetros apropriados de operação, lasers com pulsos ultra curtos podem se comportar melhor do que instrumentos convencionais, incluindo alguns dos lasers pulsados comercialmente já disponíveis na Odontologia. A exploração e otimização nos parâmetros dos lasers disponíveis podem promover a remoção de certas objeções ao amplo uso dos lasers. O uso de lasers de pulsos ultra-curtos para ablação de dentes previne o superaquecimento e é uma alternativa para a remoção mecânica de material; além de minimizar o volume desse material removido. Através de estudos morfológicos e químicos, são apresentadas as características de interação laser pulsado - tecido duro dental, com relação a sua largura de pulso - nano ou picossegundos. O objetivo principal é dar início a um novo sistema para ablação de esmalte e dentina humanos: o laser de Nd:YAG no regime de picossegundos. A eficiência da ablação com laser através de um regime de picossegundos minimiza a destruição do material adjacente devido a formação de plasma e ataque. Isso previne a geração excessiva de ondas de choque e promove uma considerável diminuição nos efeitos mecânicos. A diminuição das ondas de choque provavelmente também poderá reduzir a vibração e conseqüentemente a sensação de dor, se aplicado clinicamente. Apesar da baixa taxa de ablação, os resultados mostram a real possibilidade para usar um sistema laser comercial relativamente simples para pulsos em picossegundos que poderia promover a Dentística Operatória Puntual e Seletiva, em outras palavras, seria possível tratar apenas o tecido alterado com seletividade e sem remover tecido sadio ou mesmo promover danos aos tecidos ao redor. Na maioria dos experimentos aqui apresentados, o laser de pulso ultra-curtos apresentou aumento na proporção Ca/P, melhorando a resistência química da superfície irradiada. Além disso, os cortes precisos resultam em superfícies mais lisas, que é importante para prevenir a colonização do biofilme. Outros estudos in vitro são necessários, mudando os parâmetros de energia e simulando situações clínicas para propor o uso efetivo desse sistema in vivo, mas, de fato, o sistema laser em picossegundos pode melhorar a qualidade da Dentística Operatória num futuro breve. / In several already demonstrated experiments, ultrashort laser pulses on the subpicosecond range have been shown to produce a strong thermo-mechanical effect, in several different situations. Even been out side dentistry, the general aspects of subpicosecond pulses interaction with matter are of broad applications on can be used as general references. This strong thermo-mechanical effect has created objections toward the use of such lasers as a material removal too1. On the other hand, using the appropriated parameters of operation, ultra short laser pulses of subnanosecond duration could present better performance than conventional lasers operating at nanosecond regime in several aspects. Through chemical and morphological studies, they are presented the main features from interaction between pulsed laser and dental hard tissue, considering pulse width - nano or picosecond pulse. The main objective is starting to use a new system to ablate human enamel and dentin: Nd:YAG picosecond laser system. Efficient laser ablation in the picosecond regime minimizes destruction of adjacent material due to a plasma formation and etching. This avoids an excessive generation of shock waves and promotes a considerable decrease in mechanical effects. The decreasing of shock waves also reduces vibration and consequently the sensation of pain, if clinically used. Despite the small ablation rate, our results show the real possibility to use a relative simple commercial laser system for picosecond pulses to be use effectively in Dentistry. The real clinical use of a picosecond laser system could promote the Punctual and Selective Operative Dentistry, in other words, we could treat just the decayed tissue with selectivity without remove sound tissue or even promote damage to tissues around. Besides, the precise cuts maybe give us a smoother surface, which is important to prevent biofilm colonization. We need to evaluate more in vitro studies, changing parameters and simulating clinical situations to propose the effective use of this system in vivo, but in fact, we believe that the picosecond laser system can improve the quality of Operative Dentistry in a brief future.

The potential of Additive Manufacturing (AM) for microwave and mm-wave applications is increasingly being revealed thanks to recent advancements in research. AM empowers engineers with new capabilities to manufacture complex conformal geometries quicker and at lower costs. It allows, for instance, the embedding of RF front ends into functional structures. In this dissertation, two aspects of AM are explored: (a) The development and characterization of techniques that improve the performance of AM microwave circuits and antennas, and (b) study of complex geometries, such as meshed structures, as an alternative to reduce material usage, cost, and weight of the components. Micro-dispensing of silver paste (CB028) is extensively used in this work as a viable approach for manufacturing microwave planar transmission lines. However, the performance and upper-frequency range of these lines are limited by the cross-sectional shape and electrical conductivity of the printed paste, as well as the achievable minimum feature size which is typically around 100 μm. In this work a picosecond Nd:YAG laser is used to machine slots in a 20-25 μm-thick layer of silver paste (Dupont CB028) that is micro-dispensed on a Rogers RT5870 substrate, producing coplanar waveguide transmission lines with 16-20 μm-wide slots. It is shown that the laser solidifies 2 μm wide region along the edges of the slots, thus significantly increasing the effective conductivity of the film and improving the attenuation constant of the lines. The extracted attenuation constant at 20 GHz for laser machined CB028 is 0.74 dB/cm. CPW resonators and filters show that the effective conductivity is in the range from 10 MS/m to 30 MS/m, which represents a 100x improvement when compared to the values obtained with the exclusive use of micro-dispensing. Another main aspect of this dissertation is the study of meshed structures in coplanar waveguides. For most AM processes the materials utilized for the conductive layer are the most expensive ones; hence, there is value in minimizing the conductor surface area used in a circuit. In this work, the approach of meshed ground coplanar waveguide (MGCPW) is analyzed by simulating, fabricating and measuring a broad set of meshed ground geometry sizes. Furthermore, a physical-mathematical model is presented, which predicts the characteristic impedance and the capacitance per unit length of MGCPW with less than 5.4% error compared to simulated data. A set of filters is designed and fabricated in order to demonstrate the approach. The main parameter affected by meshing the ground plane is the attenuation constant of the waveguide. It is shown that 50% mesh density in the ground plane of a MGCPW line can be used with less than 25% increase in the loss. In contrast, the loss of finite ground coplanar waveguide (FGCPW) can increase by as much as 108% when the ground size is reduced by the same factor (50%). Both 3D printing (micro-dispensing) and traditional printed circuit board manufacturing are used in this work, and most of the propagation characterization is performed at 4 GHz. A meshing technique is also applied to rectangular waveguides, and its effects are studied. It is presented as an option for high power, low loss, but also reduced weight applications. A set of meshed Ku-band waveguides was fabricated using binder jetting 3D printing technology showing that the weight can be reduced by 22% with an increase in loss of only 5%, from 0.019 dB/cm for the solid part to 0.020 dB/cm average across the band with the meshed design. Further weight reduction is possible if higher loss is allowed. To demonstrate the concept, a comparison is made between non-meshed and meshed waveguide 4 pole Chebyshev filters. Finally, the BJ technology is characterized for Ku-Band rectangular waveguide and reflector antenna applications. This technology is characterized using electron beam microscopy (SEM) and energy dispersive spectroscopy (EDS). The RF performance of the 3D printed circuits is benchmarked with Ka-band cavity resonators, waveguide sections, and a filter. An unloaded resonator Q of 616 is achieved, and the average attenuation of the WR-28 waveguide section is 4.3 dB/m. The BJ technology is tested with a meshed parabolic reflector antenna, where the illuminating horn, waveguide feed, and a filter are printed in a single piece. The antenna shows a peak gain of 24.56 dBi at 35 GHz.

A series of picosecond excite-probe experiments was performed on various concentrations of aqueous and ethanolic solutions of rhodamine B in order to determine the existence of dimerization in those solutions. The goals of the research presented in this dissertation were twofold. Initially, various techniques of time-resolved spectroscopy were to be employed to further characterize the ground and excited-state molecular properties of the aqueous RB dimer. The information obtained, and the techniques developed in that study would then be utilized in an effort to secure evidence which would support or refute the claims of rhodamine B dimerization in an ethanolic solution.

by Chan Lai Yin Simon. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references. / Chapter Chapter 1: --- Introduction / Chapter 1.1 --- Background --- p.1-2 / Chapter 1.2 --- Properties of the InGaAsP quaternary alloy on InP substrate --- p.2 / Chapter 1.2.1 --- Physical Properties of In1-xGaxASyP1-y on InP substrate --- p.3-4 / Chapter 1.2.2 --- Optical Properties of In1-xGaxASyP1-y on InP substrate --- p.4-7 / Chapter 1.2.3 --- Nonlinear Optical Property of InGaAsP --- p.7-9 / Chapter 1.3 --- Fabrication of InGaAsP/InP rib waveguide / Chapter 1.3.1 --- Epitaxial Growth of In1-xGaxASyP1-y on InP substrate by MOCVD --- p.9 / Chapter 1.3.2 --- Etching of the five layer In1-xGaxASyP1-y slab waveguide --- p.9-12 / Chapter 1.4 --- Overview of the thesis --- p.12-13 / References --- p.13-15 / Chapter Chapter 2: --- Modal analysis of the single mode III-V semiconductor waveguidesin multi-layer rib structure by Effective Index Method / Chapter 2.1 --- Introduction --- p.16-17 / Chapter 2.2 --- Modal analysis of the rib waveguides --- p.17-27 / Chapter 2.3 --- Optical Confinement in rib waveguide --- p.28-30 / Chapter 2.4 --- Conclusions and discussions --- p.30-31 / References --- p.31-33 / Chapter Chapter 3: --- Ultrashort Pulsewidth Measurement Part I / Chapter 3.1 --- Introduction --- p.34 / Chapter 3.2 --- Pulsewidth measurement by streak camera --- p.34-37 / Chapter 3.3 --- Pulsewidth measurement by nonlinear autocorrelation --- p.37-40 / Chapter 3.3.1 --- Second Harmonic Generation Autocorrelator --- p.40-43 / Chapter 3.3.2 --- Two Photon Fluorescence Autocorrelator --- p.43-44 / Chapter 3.4 --- Two Photon Absorption Waveguide Autocorrelator --- p.45 / Chapter 3.4.1 --- TPA theory --- p.45-48 / Chapter 3.4.2 --- Autocorrelation Measurement by TPA in InGaAsP Waveguide --- p.48-51 / Chapter 3.4.3 --- The Estimated performance of the TPA Waveguide Autocorrelator --- p.52 / References --- p.52-57 / Chapter Chapter 4: --- Ultrashort Pulsewidth Measurement Part II: High Sensitivity Two Photon Absorption InGaAsP Waveguide Autocorrelator for Low Power Pulsewidth Measurement of 1.55μm Waveguide Pulses / Chapter 4.1 --- Introduction --- p.58-60 / Chapter 4.2 --- Waveguide structures --- p.60 / Chapter 4.3 --- Practical Implementation of the TPA Waveguide Autocorrelator / Chapter 4.3.1 --- Mirror arrangement for the delay system --- p.61 -63 / Chapter 4.3.2 --- Alignment and Coupling of the InGaAsP/InP Waveguide --- p.63-64 / Chapter 4.3.3 --- TPA photocurrent detection --- p.64-65 / Chapter 4.4 --- Experimental results --- p.65-67 / Chapter 4.4.1 --- Pulsewidth measurement of the TPA InGaAsP waveguide autocorrelator --- p.67-71 / Chapter 4.4.2 --- Spectral analysis by the TPA InGaAsP waveguide autocorrelator --- p.71 -73 / Chapter 4.5 --- Conclusions and discussions --- p.73-75 / References --- p.75-78 / Chapter Chapter 5: --- Picosecond Pulses Generation by Colliding-Pulse Mode-locking of a Fabry-Perot Laser Diode with an Intra-cavity Gradual Degradation Defect / Chapter 5.1 --- Introduction --- p.79-80 / Chapter 5.2 --- Gain-switching --- p.80-84 / Chapter 5.3 --- Colliding Pulse Mode-locking --- p.84-85 / Chapter 5.3.1 --- Degradation of diode laser --- p.85-86 / Chapter 5.3.2 --- CPM Theory --- p.86-89 / Chapter 5.3.3 --- Experimental results --- p.89-92 / Chapter 5.4 --- Conclusions and discussions --- p.92-93 / References --- p.94-98 / Chapter Chapter 6: --- Conclusions / Chapter 6.1 --- Summary of the Research / Chapter 6.1.1 --- Theoretical Results --- p.99-100 / Chapter 6.1.2 --- Experimental Results --- p.101-104 / Chapter 6.2 --- Future Development / Chapter 6.2.1 --- Improvement of the TPA InGaAsP waveguide autocorrelator --- p.105 / Chapter 6.2.2 --- Future development of III-V semiconductor waveguides --- p.105-107 / References --- p.107-108 / Appendix --- p.109-121

Lee Ka-lun. / "September 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

In the last decade, there has been tremendous progress in the field of ultrashort-pulse measurement. However, this effort has focused mostly on the temporal behavior of 100-fs, 800-nm ultrashort pulse, ignoring other pulse lengths, wavelengths, and the very common space-time couplings or so called spatio-temporal distortions. In this thesis work, I do an extensive study of spatio-temporal distortions and their measurement using Frequency Resolved Optical Gating (FROG) and its relatives. I clarify some ambiguities in the descriptions of these effects in the existing theory and establish a more general description of such distortions in ultrashort pulses. I also extend these measurement techniques to different wavelengths and pulse lengths. Specifically, I develop measurement devices for few-cycle NIR pulses, weak and narrowband fiber laser pulses, long (several-ps) NIR pulses, and visible pulses from NOPAs.

We have used ultrafast optics, primarily focused on the nonlinear processes of Polarization Gating and of Optical Parametric Amplification, one for measurement and the other for imaging purposes. For measurement, we have demonstrated a robust method of measurement to simultaneously measure both optical pulses used in a pump-probe type configuration. We refer to this method of pulse measurement as Double Blind Polarization Gating FROG. We have demonstrated this single-shot method for measuring two unknown pulses using one device. In addition to pulse measurement, we have demonstrated the processes of Optical Parametric Amplification (OPA) applicability to imaging of complex objects. We have done this where the Fourier transform plane is used during the interaction. We have amplified and wavelength converted a complex image. We observe a gain of ~100, and, although our images were averaged over many shots, we used a single-shot geometry, capable of true single-shot OPA imaging. To our knowledge, this is the first Fourier-plane OPA imaging of more than a single spatial-frequency component of an image. We observe more than 30 distinct spatial frequency components in both our amplified image and our wavelength shifted image. We have demonstrated all-optical spatial filtering for these complex images. We have demonstrated that direct Fourier filtering of spatial features is possible by using a shaped pump beam. We can isolate certain portions of the image simply by rotating the crystal.

The dynamics of atomic scale structures during structural change can be studied by Ultrafast Electron Diffraction (UED). The time resolution needed to reveal the fastest dynamics is 100 fs. Sub-angstrom structural resolution becomes possible with 1-1000 pC of charge necessary for diffraction pattern analysis during subtle structural changes. This combination of requirements cannot currently be realized due to the space-charge temporal broadening inherent to bunches of electrons of high fluence and short temporal duration. Simulations show that the incorporation of a specially designed Radio-Frequncy (RF) cavity into the UED apparatus removes this technical limitation. The RF cavity reverses the near linear position-momentum distribution of the temporally broadened electron bunch, causing the bunch to recompress itself as it propagates. It is found that our proposed method allows for sub-100 fs bunches with maximum charge of 0.6 pC, almost 3 orders of magnitude improvement over today's state of the art.