An J=1→J=1 atomic system in Samarium with incident laser resonant radiation has been investigated. A linearly polarized laser at 686nm excites atoms from the level 4ƒ[superscript]66s[superscript]2 [superscript]7F[subscript]1 to a excited level 4ƒ[superscript]66s6p [superscript]9F[subscript]1 via the process of optical pumping. When an external magnetic field is applied to the atom-laser interaction and the decay fluorescence collected, a level-crossing profile appears. Theoretical predictions of the level-crossing profile can be made using spherically irreducible tensors to describe the density matrix which take advantage of the symmetry of the atomic system. By comparing theory with experimental data, a discussion is made of the various parameters and external factors that can affect this system, which show that Doppler broadening is the major influence. An additional investigation is made into the evolution of the J=1→J=1 atomic system with increasing laser exposure. Comparisons of the experimental data with theoretical predictions are made by analyzing the FWHM of the overall level-crossing profile, the FWHM of the dip about B = 0 and the relative depth of the dip. By charting the progress of these parameters with increasing laser exposure, it can be seen that the theory and experimental data agree qualitatively. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1320338 / Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2008

In the current transmission systems, the transmission capacity is still not enough. The information bandwidth of the optical fiber communication system is limited by the optical amplifier bandwidth, and more efficient use of the bandwidth is a very important issue. Therefore, the amplitude and phase shift keying (APSK) is one attractive method of multi-bit per symbol modulation scheme to improve the spectral efficiency, and it can effectively increase the transmission capacity. To improve the capacity and the spectral efficiency, the advanced modulation format is effective, and the coherent detection scheme is also effective. However, an optical phase-locked loop (PLL) to lock the local oscillator (LO) phase and the signal phase required for the homodyne detection is still difficult to realize and it makes the receiver circuit complicated. Using the digital coherent receiver, the optical carrier phase information can be recovered by means of the digital signal processing (DSP), and this scheme enables to eliminate the optical PLL circuit by the phase estimation algorithm through the DSP. The stored data can be offline processed by using the MATLAB program. This master thesis is focusing on studying the transmission performance of the APSK format using the DSP in the digital coherent receiver. 497km transmission experiment has been conducted. Subsequently, the stored data are offline processed by the algorithms of the DSP. Then, the APSK performances between back-to-back and 497km transmission are compared.

The coherent optical fiber communication technology is attracting significant attentions in the world, because it can realize the spectrally efficient transmission system. One major difference between 1980¡¦s and the latest coherent technology is the utilization of the digital signal processing (DSP). In 1980¡¦s the optical phase locked loop (OPLL) was required to realize the homodyne detection, and it was significantly difficult to realize. The latest coherent technology utilizes the DSP in place of the OPLL to realize the homodyne detection, and it is much easier than the OPLL. The real-time realization of the DSP is still a problem. Because the DSP uses software to process the signal, it needs an extreme calculation power for the high-speed communication system. People always utilize the field programmable gate array (FPGA) to realize the real-time DSP, but the cost of the FPGA is too expensive for the commercial system at this moment. This master thesis intend to utilize commercially available personal computer (PC) contained a GPU calculation board to replace FPGA. It can reduce the cost of the coherent receiver. Also, this receiver is defined by the software rather than the hardware. It means that we can realize a flexible receiver defined by the software.

Coherent nonlinear effects such as Electromagnetically Induced Transparency (EIT), Coherent Population Trapping (CPT), and Slow light are studied in thermal Rb vapor by both continuous and pulsed laser fields. This work primarily includes three parts: (I) mode-locked rubidium laser and its applications (II) enhanced coupling between optical and sound waves in the forward direction via ultra-slow light (III) optical steering via ultra-slow light in rubidium vapor. In part(I), I describe the construction and study of a mode-locked rubidium laser operating at the Rb D1 line using an active mode-locking technique inside the laser cavity. The mode-locked laser field is used to observe coherent effects in a dense rubidium gas. In part(II), I experimentally demonstrate enhanced acoustic-optic coupling that occurs when the velocity of sound is close to the group velocity of light. Dragging of the light by effective motion of the gas in a Rb cell is the origin of enhanced coupling. Good agreement between theory and experiment is found. In part(III), I experimentally demonstrate optical beam deflection in coherently driven rubidium vapor due to the steep refraction index profile in the region of EIT.

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Experimental investigations of the optical properties of InGaN/GaN quantum dots are presented. A pulsed laser is used to perform time-integrated and time-resolved microphotoluminescence, photoluminescence excitation, and polarisation-resolved spectroscopy of single InGaN quantum dots under a non-linear excitation regime. The first micro-photoluminescence results from InGaN/GaN quantum dots grown on a non-polar crystal plane (11^-<sub style='position: relative;left: -.4em;'>2</sub>0) are presented. Time-resolved studies reveal an order of magnitude increase in the oscillator strength of the exciton transition when compared to InGaN quantum dots grown on the polar (0001) plane, suggesting a significantly reduced internal electric field in non-polar InGaN quantum dots. Polarisation resolved spectroscopy of non-polar InGaN quantum dots reveals 100% linearly polarised emission for many quantum dots. For quantum dot emissions with a polarisation degree less than unity, a fine structure splitting between two orthogonal polarisation axes can be resolved in an optical setup with a simple top-down excitation geometry. A statistical investigation into the origins of spectral diffusion in polar InGaN quantum dots is presented, and spectral diffusion is attributed to charge carriers trapped at threading dislocations, and itinerant and trapped carriers in the underlying quantum well layer which forms during the growth procedure. Incorporating quantum dots into the intrinsic region of a p-i-n diode structure and applying a reverse bias is suggested as a method to reduce spectral diffusion. Coherent control of the excited state exciton in a non-polar InGaN quantum dot is experimentally demonstrated by observation of Rabi rotation between the excited state exciton and the crystal ground state. The exciton ground state photoluminescence is used as an indirect measurement of the excited state population.

The purpose of this research was, in order to forestall future failures of foresight, to provoke those responsible for risk governance into new ways of thinking through a greater exposure to and understanding of the body of existing academic knowledge. The research, which focused on the scholarship of application, synthesised the existing knowledge into a ―coherent whole‖ in order to assess its practical utility and to examine what is to be learnt about existing knowledge by trying to use it in practice. The findings are in two parts. The first focuses on how one ―thinks about thinking‖ about an issue. Early work identified three issues that were seen as being central to the understanding of risk governance. The first is the concept of risk itself, the second is to question whether there is a single paradigm used and the third is what is meant by the term ―risk indicator‖. A ―coherent whole‖, structured around seven-dimensions, was created from the range of definitions used within existing literature. No single paradigm was found to be used when discussing risk issues. Three paradigms were identified and labelled ―Line‖, ―Circle‖ and ―Dot‖. It was concluded that Risk Indicators were used to performance manage risk mitigation barriers rather than as a mechanism by which organisations may identify emerging risks. The second focus was the synthesis of academic work relevant to risk governance. It produced a list of statements which encapsulated the concerns of previous writers on this subject. The research then operationalised the issues as questions, which were seen to have practical utility. The elements of the ―coherent whole‖ suggest a way to provide access into the original research. The research suggests that it is unlikely that practitioners would wish to access the original research in its academic format. Further work therefore needs to be done to present the original work in a format that is more digestible to the practitioner community if it is to be used effectively. The results of this research are considered to be preliminary. No claim is being made that these questions are definitive. The research is however addressing an area which is of concern to those in practice and has not been previously examined.

This thesis is concerned with coherent effects in high resolution mid-infrared gas phase spectroscopy using quantum cascade lasers (QCLs). An introductory chapter explains the importance of QCLs as radiation sources in the mid-infrared region of the spectrum and goes on to detail their development and structure. A discussion of coherent effects in spectroscopy follows, leading into the second chapter which discusses the theories relevant to the experimental sections of the thesis. In chapter 2 the theory underpinning direct and velocity selective, Doppler-free spectroscopy is discussed and a density matrix formalism is followed to derive the equations of motion that govern coherent excitation effects in two-level systems. In the final part of the chapter this treatment is extended to three-level systems. The equations derived in this chapter form the basis of quantitative interpretations of the phenomena observed in experimental data and presented in the remainder of the thesis. In chapter 3 the characterisation of a high power, narrow linewidth QCL is carried out. This laser is then used to perform direct and sub-Doppler resolution spectroscopy on NO, demonstrating non-linear absorption at high laser intensities and providing a measurement of the laser linewidth in the limit of slow frequency tuning. As the slow tuning rate increases, evidence of coherent transient effects is presented and density matrix theory used to model this behaviour. The data presented include the first observations of asymmetric Lamb dips and the onset of rapid passage oscillations from a Lamb dip. Pump-probe experiments on NO, utilising two cw QCLs are presented in chapter 4. The high level of velocity selection afforded by QCL excitation leads to coherent transient signals at far lower probe scan rates than previously reported. The effect of altering both the scan rate and the gas pressure and the importance of hyperfine structure are presented. A radio frequency noise source applied to one of the lasers is shown to broaden the laser linewidth, leading to rapid dephasing. A two-colour polarisation spectroscopy experiment is also presented which allows the measurement of both the absorption and the Doppler-free dispersion signals and the three-level density matrix formalism presented at the end of chapter 2 used to model the non-linear response of the system. The final chapter details the use of an acousto-optic modulator to create a pulse of mid-IR light using a cw QCL and the application of this to time resolved pump-probe spectroscopy. This capability suggests the prospect of achieving coherent population transfer by stimulated Raman adiabatic passage (STIRAP) using two such pulses. Simulations based on a simple three-level model and including Zeeman coherences are presented, which take the measured properties of the lasers used in this thesis as inputs to predict the potential population transfer achievable in NO as well as providing useful information about the angular momentum polarisation of the excited molecules. An experimental realisation of STIRAP would require the lasers to be stabilised, and so the final part of the chapter details experimental attempts to achieve stabilisation of an external cavity QCL, and suggests future avenues for improved implementation.

Student Number : 9804484F MSc dissertation - School of Statistics and Acturial Science - Faculty of Science / This dissertation conducts a comprehensive and up to date review of measures of component and module importance within monotone systems, where it is assumed that components work independent of each other. The dissertation traces the development of these important measures from the initial definition of Birnbaum importance right through to the definition of Meng's criticality importance. Furthermore, the dissertation draws a distinction between time independent measures and time dependent measures (such as the Barlow-Proschan measures). The dissertation demonstrates how such measures may be implemented in analysing the importance of components within the monotone systems by evaluating these measures for a well known bridge structure example. This evaluation also reveals how each defined measure can be compared to each other. In conclusion, the dissertation describes how these measures can be extended to non-monotone systems or systems with dependent components.

Esta dissertação descreve o movimento quântico de uma partícula numa barreira de potencial parabólica, condicionalmente este sistema é chamado de oscilador invertido. Determinamos estados quânticos semiclássicos como família de estados coerentes generalizados (ECG), sendo construídos através da adaptação do trabalho de Malkin e Man´ko, determinando-se um operador que seja integral do movimento, parametrizado por algumas constantes e reconhecido como operador de aniquilação, cujos auto-estados tem características dos estados comprimidos. Discutimos suas propriedades e observamos que é possível comparar ECG do oscilador invertido com ECG da partícula livre e oscilador harmônico obtidos na literatura. Também é feito um estudo do movimento puramente quântico (tunelamento) nas barreiras de potenciais do oscilador invertido e oscilador invertido truncado, por meio das soluções estacionárias exatas e aproximadas (JWKB), comparando os resultados obtidos em cada situação. / This dissertation describes the motion of a particle in a quantum potential barrier parabolic, this system is conditionally called inverted oscillator. Determined quantum states semi-classics like family generalized coherent states (GCS), being constructed by adapting work Malkin\'s and Man\'ko, determining an operator who is integral of the motion, parameterized for some constants and recognized as annihilation operator, whose eigenstates have characteristics of squeezed states. We discuss its properties and note that it is possible to compare the GCS of inverted oscillator with GCS the particle free and harmonic oscillator obtained in the literature. Also made a study of the movement purely quantum (tunneling) in the barriers potential inverted oscillator and truncated inverted oscillator by means of exact and approximate stationary solutions (JWKB), comparing the results obtained in each situation.