Pulse shaping is the technique which controls the ultra-short pulse shape, and it became of great technological interest because of its potential applications in laser pulse compression, digital communications, microscopy etc. We demonstrate the idea of pulse-shaping technique and pulse propagation with low energy losses in a resonant linear absorbing medium. This thesis presents the results of a study of the propagation of Gaussian and hyperbolic secant ultrashort chirped and chirp-free pulses in homogeneously and inhomogeneously broadened resonant linear absorbers. Changes to the pulse shape and energy loss factor are presented as the pulse propagates in the absorber. The Fast Fourier method is used to numerically determine both the normalized intensity profile and the pulse spectrum. Our results show that, for pulse durations shorter than the relaxation time, chirped pulses in absorbing media obey the area theorem, with their shape changing with the propagation distance. Simulation results of the spectra of chirped pulses clearly show the burning of a spectral ’hole’ as the pulse propagates, with the pulse energy pushed away towards the wings. When compared to chirp-free pulses, chirped pulses reshape faster and develop wings in their tail due to initial phase modulation. Simulation results of the energy loss factor show that chirped pulses propagating in resonant linear absorbers sustain less energy losses than do chirp-free pulses. A comparison of chirped secant and Gaussian pulses shows that secant pulses propagate with lower energy losses. Analytic solutions are presented for long-distance asymptotic expressions of initial rms spectral bandwidth as well as for the attenuation factor of chirped Gaussian pulses. These analytical results are in agreement with numerical simulations. The comparison of energy losses of short chirped Gaussian pulses and long pulses of any profile in linear absorbers is also discussed in the thesis.

Coherent control of laser induced processes is based on the quantum interference among multiple excitation pathways. Progress in the field has been fueled by advances in pulse shaping techniques, allowing modulation of phase and amplitude across the bandwidth of ultra short pulses. This dissertation makes use of coherent control technique for the optimization of two-photon fluorescence (TPF) and its applications in selective excitation for biomedical imaging. Different physical processes, e.g. TPF, second harmonic generation (SHG) and their ratios (e.g. TPF/SHG) were optimized by using feedback control pulse shaping technique with an evolutionary algorithm. Various nonlinear effects, e.g. filamentation, intensity clamping and white light generation were studied using two-photon fluorescence and Z-scan technique with different dyes and biomarkers. Simultaneous measurements of different nonlinear effects were performed. Novel methods were proposed and implemented to obtain two-photon excitation characteristics in intensity-resolved manner. Understanding of these nonlinear effects can give new solution to the issues of spatial resolution and molecular contrast for cellular and tissue imaging.

Temporal pulse shaping based on integrated Bragg gratings is investigated in this work to achieve arbitrary output waveforms. The grating structure is simulated based on the sidewall-etching geometry in an AlGaAs platform. The inverse scattering employin the Gel'fan-Levithan-Marchenko theorem and the layer peeling method provides a tool to determine grating structures from a desired spectral reflection response. Simulations of pulse shaping considered flat-top and triangular pulses as well as one-to-one and one-to-many pulse shaping. The suggested grating profiles revealed a compromise between performance and grating length. The integrated grating, a few hundred microns in length, could generate flat-top pulses with pulse durations as short as 500 fs with rise/fall times of 200 fs; the results are comparable to previous work in free-space optics and fiber optics. The theories and the devised algorithms could serve as a design station for advanced grating devices for, but not restricted to, optical pulse shaping.

Temporal pulse shaping based on integrated Bragg gratings is investigated in this work to achieve arbitrary output waveforms. The grating structure is simulated based on the sidewall-etching geometry in an AlGaAs platform. The inverse scattering employin the Gel'fan-Levithan-Marchenko theorem and the layer peeling method provides a tool to determine grating structures from a desired spectral reflection response. Simulations of pulse shaping considered flat-top and triangular pulses as well as one-to-one and one-to-many pulse shaping. The suggested grating profiles revealed a compromise between performance and grating length. The integrated grating, a few hundred microns in length, could generate flat-top pulses with pulse durations as short as 500 fs with rise/fall times of 200 fs; the results are comparable to previous work in free-space optics and fiber optics. The theories and the devised algorithms could serve as a design station for advanced grating devices for, but not restricted to, optical pulse shaping.

Genetic algorithm is often used to find the global optimum in a multi-dimensional search problem. Inspired by the natural evolution process, this algorithm employs three reproduction strategies -- cloning, crossover and mutation -- combined with selection, to improve the population as the evolution progresses from generation to generation. Femtosecond laser pulse tailoring, with the use of a pulse shaper, has become an important technology which enables applications in femtochemistry, micromachining and surgery, nonlinear microscopy, and telecommunications. Since a particular pulse shape corresponds to a point in a highly-dimensional parameter space, genetic algorithm is a popular technique for optimal pulse shape control in femtosecond laser experiments. We use genetic algorithm to optimize third harmonic generation (THG), and investigate various pulse shaper options. We test our setup by running the experiment with varied initial conditions and study factors that affect convergence of the algorithm to the optimal pulse shape. Our next step is to use the same setup to control coherent anti-Stocks Raman scattering. The results show that the THG signal has been enhanced.

This thesis utilized pulse shaping technology to study chirp response of SSBR and attempt to analyze contribution of SSBR in mode-locked process. A home-made pulse shaping system (based on 4f scheme) with Freezing algorithm and Gerchberg-Saton algorithm was demonstrated. A normal dispersion at nonabsorbable wavelength and an anomalous dispersion around absorbable wavelength region in SSBR were obtained. Meanwhile, a Kramers-Kronig relation like behavior of pulse depression/broadening ratio in the strained multiple quantum well was observed and also refer to that pulse starting force is stronger at short wavelength. Decrease of pulse compression with increasing power of negative chirp incident pulse was characterized. Unclear power dependence for positive chirp case was also performed. These could be due to competition of band-filling and pump dump process. In addition, higher reflectivity and tendency of lower saturation fluence of SSBR for negative chirp incident pulse were observed.

<p>Orthogonal Frequency Division Multiplexing (OFDM) is well known as an efficient technology for wireless communications and is widely used in many of the current and upcoming wireless and wireline communication standards. However, it has some intrinsic drawbacks, e.g., sensitivity to the inter-carrier interference (ICI) and high peak-to-average power ratio (PAPR). Additionally, the cyclic prefix (CP) is not spectrum efficient and fails when the channel delay spread exceeds the length of CP, which will result in inter-symbol interference (ISI). In order to combat or alleviate these drawbacks various techniques have been proposed, which can be categorised into two main classes: techniques that keep the structure of OFDM and meanwhile increase the system robustness or re-organise the symbol streams on each sub-carrier, and techniques that increase the ISI/ICI immunity by adopting well designed pulse shapes and/or resorting to general system lattices. The latter class are coined as Generalised FDM (GFDM) throughout this thesis to distinguish with the former class.</p><p>To enable seamless handover and efficient usage of spectrum and energy, GFDM is expected to dynamically adopt pulse shapes that are optimal in doubly (time and frequency) dispersive fading channels. This is however not an easy task as the method of optimal pulse shape adaptation is still unclear, let alone efficient implementationmethods. Besides, performance of GFDM highly depends on the channel estimation quality, which is not straightforward in GFDM systems.</p><p>This thesis addresses, among many other aspects of GFDM systems, measures of the time frequency localisation (TFL) property, pulse shape adaptation strategy, performance evaluation and channel estimation.  We first provide a comparative study of state-of-the-art GFDM technologies and a brief overview of the TFL functions and parameters which will be used frequently in later analysis and discussion. A framework for GFDM pulse shape optimisation is formulated targeting at minimising the combined ISI/ICI over doubly dispersive channels. We also propose a practical adaptation strategy utilising the extended Gaussian functions (EGF) and discuss the trade-off between performance and complexity.  One realisation under the umbrella of GFDM, namely OFDM/OQAM, is intensively studied and an efficient implementation method by direct discretisation of the continuous time model has been proposed.  Besides, a theoretical framework for a novel preamble-based channel estimation method has been presented and a new preamble sequence with higher gain is identified. Under the framework, an optimal pulse shape dependent preamble structure together with a suboptimal but pulse shape independent preamble structure have been proposed and evaluated in the context of OFDM/OQAM.</p>

The purpose of this investigation was to provide quality dynamic strength properties for a solid grade severe-weather (SW) brick material and to illustrate the need for careful evaluation of the strain-rate effects on geomaterials. A split Hopkinson pressure bar (SHPB) was used to perform a series of tests on specimens from a solid grade SW brick to determine the mechanical response of this material at high strain-rates. Both classical and modified SHPB tests were performed. The results from the classical SHPB tests provided evidence that modifications to the SHPB are necessary when testing geomaterials such as brick. To modify the SHPB, a small copper disk was placed at the impact end of the SHPB incident bar to increase the rise time of the initial pulse. The material response from the modified SHPB tests provided an average compressive strength of 104 MPa, which resulted in a dynamic increase factor of 1.42.

The effects of microcracking on the mechanical properties of Salem limestone were investigated in three phases: introduction of quantifiable levels of microcracks by thermal treating, mechanical testing of limestone samples with varying levels of microcracks, and modification of a numerical model to incorporate the measured effects. This work demonstrated that this approach is useful for examination of the effects of microcracking on quasi-brittle materials and can be used to improve the predictive capabilities of material models. Thermal treating was found to consistently induce quantifiable levels of microcracks in Salem limestone. Sonic wave velocities indicated that the induced microstructural changes were a function of the maximum temperature. The wave velocities showed little variability demonstrating the effectiveness of the approach for inducing consistent levels of microcracking. X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis confirmed that no composition changes occurred for the temperature range of interest. Computed tomography scanning, scanning electron microscopy, and optical microscopy (OM) were used to observe microstructural changes caused by the heat treatments. OM analysis was the primary method used in the microcrack characterization and yielding qualitative and quantitative data. OM images showed an increase in grain boundary and intragranular cracking with increasing maximum heat treatment temperatures. Stereological evaluation provided microcrack data indicating that microcrack density increased as function of the maximum heat treatment temperatures. Mechanical testing was performed to characterize the mechanical response of the intact and damaged limestone. Quasi-static tests included uniaxial compression, triaxial compression, hydrostatic compression, and uniaxial strain / constant volume tests. Microcracking did not affect the limestone’s strength at pressures greater than 10 MPa. Dynamic tests were performed using a modified split Hopkinson pressure bar. Microcracking did not have an effect on the dynamic strength of the limestone. The results of the mechanical tests were used to modify the HJC model. Modifications were made to account for shear modulus degradation and failure surface changes. The original and modified HJC models were used in a numerical analysis of the mechanical tests performed in this work. The modified HJC provided better results for damaged material when compared with the quasi-static and dynamic experiments.

International Telemetering Conference Proceedings / October 27-30, 1997 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The most bandwidth-efficient communication methods are imperative to cope with the congested frequency bands. Pulse Shaping methods have excellent effects on narrowing bandwidth and increasing band utilization. The position of the baseband filters for the pulse shaping is crucial. Filters after the modulator will have non-constant envelope and before the modulator will have constant envelope. These two types have different effects on narrowing the bandwidth and producing bit errors. The constant envelope 8 PSK is used throughout the simulations and is compared with the non-constant envelope results. This work provides simulation results of spectrum analysis and measure of bit errors produced by pulse shaping in an AWGN channel.