Neste trabalho foi investigado o controle do processo de fluorescência excitada por absorção de dois fótons no polímero conjugado MEH-PPV, utilizando um sistema de formatação espectral da fase dos pulsos ultracurtos. Para tal estudo, foi utilizado um oscilador laser de Ti:Safira (15 fs, ~ 800 nm e largura de banda de 60 nm). Através de dois distintos métodos de formatação, observa-se a influência destes no processo de fotodegradação do MEHPPV, inferido pela diminuição da intensidade do sinal de fluorescência. No primeiro método de formatação, é estudada a influência de diferentes chirps impostos aos pulsos no processo de fluorescência do MEH-PPV. Observa-se uma menor taxa de fotodegradação para pulsos com maiores chirps, independente do sinal, em comparação a pulsos no limite de transformada. Esse efeito foi relacionado ao acréscimo na duração temporal dos pulsos com chirp, com consequente diminuição da intensidade. Numa segunda etapa, através do uso de um espelho deformável, a fase espectral do pulso é formatada usando uma máscara de fase senoidal. Neste caso, a intensidade de fluorescência foi modulada em aproximadamente 25%, num claro processo de controle coerente, sem nenhuma diferença apreciável no processo de fotodegradação. Desta forma, técnicas de controle coerente com formatação espectral da fase poderiam ser utilizadas para modular a intensidade do sinal de fluorescência no MEH-PPV, sem detrimento ao processo fotodegradativo. / In this work we studied the control of two-photon excited fluorescence in the conjugated polymer MEH-PPV, using pulse-shaping techniques to manipulate the pulse spectral phase. The experiments were carried out with a Ti:sapphire laser oscillator (15 fs, ~ 800 nm and 60 nm of bandwidth). We investigated the influence of two distinct pulse-shaping methods in the MEH-PPV photodegradation, inferred by the decrease in the fluorescence intensity. In the first method, we studied the effect of different pulse chirps on the MEH-PPV fluorescence. A smaller photodegradation rate was observed for pulses with higher chirps, independently of its sing, in comparison with pulses close to the Fourier Transform limit. This effect was attributed to the increase in the pulse duration for chirped pulses, and consequent decrease in the pulse intensity. In a second stage, we modulate the pulse spectral phase by employing a senoidal phase mask though a deformable mirror. In this case, a 25% modulation in the fluorescence intensity was determined, whereas no considerable effect was observed in the photodegradation. In this way, coherent control techniques employing spectral phase pulse-shaping could be used to modulate MEH-PPV fluorescence, without any negative effect to its photodegradation.

This thesis explores the generation and the coherence properties of Raman frequency combs that are initiated from vacuum fluctuations using hydrogen-filled hollow-core photonic crystal fibre (HC-PCF). The motivation is to explore a novel route for generating attosecond pulses and waveform synthesis. To this end, work has been undertaken in the design and fabrication of HC-PCF, in the generation of Raman comb with a compact set-up and finally in an experimental demonstration of the mutual coherence between the comb spectral components. Here, the well-established photonic bandgap (PBG) HC-PCF is further developed. Surface mode spectral positions are controlled by chemical etching technique, and a single piece of fibre with two robust bandgaps is fabricated. Furthermore, the second established class of HC-PCF; namely large-pitch Kagome-lattice HC-PCF, has experienced challenging developments. This led to the fabrication of a hypocycloid-core seven-cell Kagome HC-PCF with comparable attenuation value to that of PBG HC-PCF while offering much larger bandwidth. Using the fabricated HC-PCF, different Raman frequency comb systems are developed. In addition to the previously-generated multi-octave Raman frequency comb from a large 1064 nm Nd:YAG Q-switch laser, several more compact version of Raman comb sources have been developed, including one whose lines lay in the visible and UV for applications in forensics and biomedicine. The Raman frequency comb generated inside a length of hydrogen-filled HC-PCF is further investigated by studying the coherence of the Raman lines. Despite of vacuum-fluctuation-initiation, it is demonstrated that the comb has self- and mutualcoherence properties within each single shot, bringing thus the possibility of generating attosecond pulses with non-classical properties.

Orientadores: Aldário Chrestani Bordonalli, Júlio César Rodrigues Fernandes de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-09-27T13:36:17Z (GMT). No. of bitstreams: 1 Carvalho_LuisHenriqueHeckerde_M.pdf: 8092940 bytes, checksum: da29699f8638d37de27fc0743c89a013 (MD5) Previous issue date: 2014 / Resumo: Uma das alternativas para os sistemas de transmissão óptica de próxima geração é o uso de múltiplos subcanais ópticos densamente multiplexados em frequência (supercanais) com alta eficiência espectral. Supercanais ópticos empregam o processamento paralelo de sinais para alcançar taxas de transmissão além dos limites da eletrônica. Atualmente, as técnicas CO-OFDM e Nyquist WDM são vistas como as principais para a implementação de supercanais ópticos. Neste trabalho, estudam-se abordagens para aumentar a capacidade de transmissão dos sistemas ópticos por meio da realização de supercanais. A implementação em laboratório, análise de desempenho e comparativo entre as técnicas CO-OFDM e Nyquist WDM são realizadas para sistemas operando a 400 Gb/s e 1 Tb/s por canal, com modulação DP-16QAM e eficiências espectrais que chegam a 6 b/s/Hz e acima. Os principais desafios e soluções para a implementação de sistemas de transmissão óptica de próxima geração baseados em supercanais são identificados / Abstract: One of the options for the next generation of optical transmission systems is the use of multiple optical subchannels densely multiplexed in frequency (superchannels) with high spectral efficiency. Optical superchannels employ parallel signal processing to achieve transmission rates beyond the limits of electronics. Currently, CO-OFDM and Nyquist WDM are seen as the main techniques to the implementation of optical superchannels. In this work, different ways to increase the capacity of the current optical systems by the realization of superchannels are studied. The experimental implementation, performance analysis, and comparison between CO-OFDM and Nyquist WDM techniques are performed for systems operating at 400 Gb/s and 1 Tb/s per-channel with DP-16QAM modulation and spectral efficiencies of 6 b/s/Hz and beyond. The main challenges and solutions for the implementation of next generation optical transmission systems based on superchannels are identified / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Fung, Shu Hong = 量子點內自旋弱量度的散粒噪聲相關理論 / 馮書航. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 80-85). / Abstracts in English and Chinese. / Fung, Shu Hong = Liang zi dian nei zi xuan ruo liang du de san li zao sheng xiang guan li lun / Feng Shuhang. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Review on measurement theory --- p.5 / Chapter 2.1 --- Weak measurement --- p.5 / Chapter 2.2 --- POVM formalism --- p.7 / Chapter 2.3 --- Noise spectroscopy --- p.8 / Chapter 3 --- Review on spin decoherence --- p.11 / Chapter 3.1 --- Longitudinal relaxation --- p.12 / Chapter 3.2 --- Transverse relaxation --- p.12 / Chapter 3.3 --- Inhomogeneous broadening --- p.13 / Chapter 3.4 --- Typical relaxation timescales --- p.14 / Chapter 4 --- Proof-of-principle setup --- p.15 / Chapter 4.1 --- Faraday rotation --- p.15 / Chapter 4.2 --- Polarization beam splitter --- p.17 / Chapter 4.3 --- Quantum state of the system --- p.19 / Chapter 5 --- Weak measurement on the spin --- p.22 / Chapter 5.1 --- POVM of measurement --- p.22 / Chapter 5.2 --- POVM of dephasing --- p.25 / Chapter 5.3 --- Interval distribution operator --- p.26 / Chapter 5.4 --- Interval distribution function without dephasing --- p.27 / Chapter 5.5 --- Second order correlation function without dephasing --- p.31 / Chapter 5.6 --- Interval distribution function with dephasing --- p.34 / Chapter 5.7 --- Second order correlation function with dephasing --- p.40 / Chapter 5.8 --- Effect of inhomogeneous broadening on g(2)(t) --- p.42 / Chapter 5.9 --- Third order correlation function --- p.43 / Chapter 5.10 --- Monte Carlo simulation --- p.44 / Chapter 5.11 --- Results and discussion --- p.46 / Chapter 5.11.1 --- Characteristics and implications of g(2)(t) --- p.46 / Chapter 5.11.2 --- "Characteristics and implications of g(3)(t1,t2)" --- p.47 / Chapter 6 --- Interval distribution function with random force models --- p.49 / Chapter 6.1 --- Impact collision model --- p.51 / Chapter 6.2 --- Modified diffusion model --- p.53 / Chapter 6.3 --- Difficulties in the calculation of g(2)(t) --- p.54 / Chapter 6.4 --- Kn as a measured quantity --- p.57 / Chapter 7 --- Conclusion --- p.59 / Chapter A --- Alternative derivation of k and higher order corrections --- p.62 / Chapter B --- Evaluation of integrals in the exponential --- p.70 / Chapter B.1 --- Integral of the form ∫ts + ∫vu --- p.70 / Chapter B.2 --- Integrals of the form ∫ts + ∫vu + ∫yz --- p.72 / Chapter C --- Evaluation of four-click events --- p.74 / Bibliography --- p.76

In order to understand water quality in the coastal ocean and its effects on human health, the necessity arises to locate the sources of contaminants and track their transport throughout the ocean. Dynamical systems methods are applied to the study of transport of enterococci as an indicator of microbial concentration in the vicinity of Hobie Beach, an urban, subtropical beach in Miami, FL that is used for recreation and bathing on a daily basis. Previous studies on water quality have shown that Hobie Beach has high microbial levels despite having no known point source. To investigate the cause of these high microbial levels, a combination of measured surface drifter trajectories and numerically simulated flows in the vicinity of Hobie Beach is used. The numerically simulated flows are used to identify Lagrangian Coherent Structures (LCSs), which provide a template for transport in the study area. Surface drifter trajectories are shown to be consistent with the simulated flows and the LCS structure. LCSs are then used to explain the persistent water contamination and unusually high concentrations of microbes in the water off of this beach as compared with its neighboring beaches. From the drifter simulations, as well as field experiments, one can see that passive tracers are trapped in the area along the coastline by LCS. The Lagrangian circulation of Hobie Beach, influenced primarily by tide and land geometry causes a high retention rate of water near the shore, and can be used to explain the elevated levels of enterococci in the water.

The effects of vertical confinement on a neutrally-buoyant turbulent round jet discharging from a circular nozzle into quiescent shallow water were investigated. The focus was on identifying changes in the mean flow, turbulence characteristics, and large vortical structures of a horizontal water jet at different degrees of vertical confinement. The confinement resulted from the proximity of a lower solid wall and an upper free surface. The jet exit Reynolds number for all cases was 22,500. The depth of the water layer was the principal parameter. The axial and lateral confinements were negligible. Three different degrees of vertical confinement were investigated in addition to the free jet case. For the confined cases, the water layer depth was 15, 10 and 5 times the jet exit diameter. The centreline of the jet was located midway between the solid wall and the free surface. Particle image velocimetry (PIV) was used to investigate the flow behaviour. Measurements were taken on two orthogonal planes along the jet axis; one parallel and one perpendicular to the free surface. For each case, measurements were taken at three locations downstream of the jet exit where the effects of vertical confinement were expected to be significant. All image pairs were acquired at a frequency of 1 Hz using a 2048  2048 pixel camera. This rate was slow enough that the velocity fields were uncorrelated. At each location, two thousand image pairs were acquired in order to extract statistical information about the behaviour of the flow. <p>After completing the cross-correlation analysis of the PIV images and filtering outliers using a cellular neural network with a variable threshold, the statistical quantities such as mean velocities, turbulence intensities, Reynolds shear stress, centreline velocity decay, centreline turbulence intensities, and spread rate were obtained. The proper orthogonal decomposition (POD) technique was applied to the PIV data using the method of snapshots to expose vortical structures. The number of modes used for the POD reconstruction was selected to recover ~40% of the turbulent kinetic energy. An automated method was employed to identify the position, size, and strength of the vortices by searching for closed streamlines in the POD reconstructed velocity fields. This step was followed by a statistical study to understand the effect of vertical confinement on the frequency of vortex occurrence, size, strength, rotational sense, and preferred locations.<p>The results showed that the structure of the flow underwent significant changes because of the vertical confinement. The axial velocity profiles in the vertical plane become almost uniform over the entire depth with a mild peak below the centreline of the jet for the shallowest case, while the axial velocity profiles in the horizontal plane are Gaussian but narrower than the free jet profile. The mean vertical and horizontal velocity profiles show that fluid is drawn from the sides of the jet to its centreline and then diverted upward and downward from the jet axis. The decay rate of the mean centreline velocity becomes slower at downstream locations and the jet width becomes narrower in the horizontal mid-plane compared to the free jet case. The mixing efficiency of the fluid in the vertical plane is significantly inhibited by the confinement while there is a slight effect in the horizontal plane. Also, with increasing vertical confinement, the wall jet characteristics become more dominant. Investigation of the coherent structures revealed that at intermediate distances from the exit the population of vortical structures of either rotational sense is almost identical for all vortex sizes. At downstream locations in the vertical plane, this distribution is changed by the vertical confinement which causes a significant increase in the number of small clockwise vortices. In addition, it was observed that, as the confinement increases, the total number of vortical structures decreases and their sizes increase. This is evidence of the pairing process. Moreover, with increasing confinement the circulation decreases as the flow proceeds downstream on the vertical plane with a corresponding increase in the horizontal plane. This behaviour is consistent with the turbulence intensity results.

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.

Engineering and Physical Science Research Council (EPSRC) / This thesis describes the development of the two-frequency Planar Doppler Velocimetry (2n-PDV) flow measurement technique. This is modification of the Planar Doppler Velocimetry (PDV) technique that allows the measurement of up to three components of the flow velocity across a plane defined by a laser light sheet. The 2n-PDV technique reduces the number of components required to a single CCD camera and iodine cell from the two CCDs in conventional PDV. This removes the error sources associated with the misalignment of the two camera images and polarisation effects due to the beam splitters used in conventional PDV. The construction of a single velocity component 2n-PDV system is described and measurements made on the velocity field of a rotating disc and an axisymmetric air jet. The system was then modified to make 3D velocity measurements using coherent imaging fibre bundles to port multiple views to a single detector head. A method of approximately doubling the sensitivity of the technique was demonstrated using the measurements made on the velocity field of the rotating disc and was shown to reduce the error level in the final orthogonal velocity components by ~40 to 50%. Error levels of between 1.5ms-1 and 3.1ms-1 depending upon observation direction are demonstrated for a velocity field of ±34ms-1. The factors that will influence the selection of a viewing configuration when making 3D PDV measurements are then investigated with the aid of a computer model. The influence of the observation direction, the magnitude of the flow velocity, and the transformation to orthogonal velocity components are discussed. A new method using additional data in this transformation is presented and experimental results calculated using four-measured velocity components are compared to those found conventionally, using only three components. The inclusion of additional data is shown to reduce the final error levels by up to 25%.

The effects of vertical confinement on a neutrally-buoyant turbulent round jet discharging from a circular nozzle into quiescent shallow water were investigated. The focus was on identifying changes in the mean flow, turbulence characteristics, and large vortical structures of a horizontal water jet at different degrees of vertical confinement. The confinement resulted from the proximity of a lower solid wall and an upper free surface. The jet exit Reynolds number for all cases was 22,500. The depth of the water layer was the principal parameter. The axial and lateral confinements were negligible. Three different degrees of vertical confinement were investigated in addition to the free jet case. For the confined cases, the water layer depth was 15, 10 and 5 times the jet exit diameter. The centreline of the jet was located midway between the solid wall and the free surface. Particle image velocimetry (PIV) was used to investigate the flow behaviour. Measurements were taken on two orthogonal planes along the jet axis; one parallel and one perpendicular to the free surface. For each case, measurements were taken at three locations downstream of the jet exit where the effects of vertical confinement were expected to be significant. All image pairs were acquired at a frequency of 1 Hz using a 2048  2048 pixel camera. This rate was slow enough that the velocity fields were uncorrelated. At each location, two thousand image pairs were acquired in order to extract statistical information about the behaviour of the flow. <p>After completing the cross-correlation analysis of the PIV images and filtering outliers using a cellular neural network with a variable threshold, the statistical quantities such as mean velocities, turbulence intensities, Reynolds shear stress, centreline velocity decay, centreline turbulence intensities, and spread rate were obtained. The proper orthogonal decomposition (POD) technique was applied to the PIV data using the method of snapshots to expose vortical structures. The number of modes used for the POD reconstruction was selected to recover ~40% of the turbulent kinetic energy. An automated method was employed to identify the position, size, and strength of the vortices by searching for closed streamlines in the POD reconstructed velocity fields. This step was followed by a statistical study to understand the effect of vertical confinement on the frequency of vortex occurrence, size, strength, rotational sense, and preferred locations.<p>The results showed that the structure of the flow underwent significant changes because of the vertical confinement. The axial velocity profiles in the vertical plane become almost uniform over the entire depth with a mild peak below the centreline of the jet for the shallowest case, while the axial velocity profiles in the horizontal plane are Gaussian but narrower than the free jet profile. The mean vertical and horizontal velocity profiles show that fluid is drawn from the sides of the jet to its centreline and then diverted upward and downward from the jet axis. The decay rate of the mean centreline velocity becomes slower at downstream locations and the jet width becomes narrower in the horizontal mid-plane compared to the free jet case. The mixing efficiency of the fluid in the vertical plane is significantly inhibited by the confinement while there is a slight effect in the horizontal plane. Also, with increasing vertical confinement, the wall jet characteristics become more dominant. Investigation of the coherent structures revealed that at intermediate distances from the exit the population of vortical structures of either rotational sense is almost identical for all vortex sizes. At downstream locations in the vertical plane, this distribution is changed by the vertical confinement which causes a significant increase in the number of small clockwise vortices. In addition, it was observed that, as the confinement increases, the total number of vortical structures decreases and their sizes increase. This is evidence of the pairing process. Moreover, with increasing confinement the circulation decreases as the flow proceeds downstream on the vertical plane with a corresponding increase in the horizontal plane. This behaviour is consistent with the turbulence intensity results.

In the current transmission system, the information bandwidth of the optical fiber communication system is limited by optical amplifier bandwidth, and more efficient use of bandwidth is a very important issue. Amplitude and phase shift keying (APSK) is an advanced modulation scheme to improve the spectral efficiency and can effectively increase the transmission capacity. Certainly, APSK format has a good potential for development. This master thesis is focusing on that to study the transmission performance of the APSK format using digital coherent receiver. As the extinction ratio (ER) of the amplitude shift keying (ASK) signal affects the performances of the ASK signal and phase shift keying (PSK) signal simultaneously, the effect of the ER on the APSK transmission performance was studied. The APSK format has the trade-off between the performances of both the ASK signal and the PSK signal through the ER of the ASK signal. To overcome this issue, a method named zero-nulling method had been proposed, and this method solved the trade-off issue properly. At first, the amendment is to modify the digital coherent receiver program, confirmed that the digital coherent receiver program can correctly resolve APSK signal. Second, in this master thesis, I set up a 500km long optical fiber to measure the transmission performance under APSK format, and try to use recirculating loop system to further increase the transmission distance to several thousand kilometers. Finally, by further modify the receiver program to achieve APSK modulation of the zero-nulling method, and can prove its feasibility.