Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 168-173).

The research reported in this thesis is aimed at developing and demonstrating the performance of a p-i-n / vertical cavity enhanced (VCE) photodetector structure with different material compositions of dilute nitride. The tunable selectivity is taken into account during the development in order for the VCE photodetector to be able to perform as a tunable receiver. In the first part, the performance of p-i-n photodetectors with 10 and 20 quantum wells are presented. The 20 quantum well photodetector exhibits the highest ever reported quantum efficiency of 80% at -5V bias for applications at 1.0µm wavelength. However, variation in the absorption’s thickness equates to a trade-off between speed, bandwidth, noise-equivalent-power, and detectivity. A GaInNAs/GaAs VCE photodetector with an internal gain of 1.55 for room temperature operation at 1.3µm wavelength is next demonstrated. This is the first internal gain ever reported using a GaInNAs VCE photodetector with a 5nm FWHM and an overall quantum efficiency of 67%. The proposed VCE photodetector of GaInNAs/GaNAs showed impressive multiplication at a low reverse bias of 0.5V. The internal gain is detected to be 2.45 at -2V bias with a responsivity of 1.63A/W for room temperature operation. The responsivity and gain of the sample can be enhanced by increasing small range of temperature but then suffered from temperature-induced broadening of the full width half maximum (FWHM). Finally, an avalanche VCE photodetector is proposed, where the preliminary outcome shows the current oscillation behaviour under illumination at room temperature operation. The sample produces very low responsivity of 2.15mA/W due to growth problems with the charge layer which affect the electric field in the multiplication region.

The purpose of this study is to investigate student interactions with simulations, and teacher support of those interactions, within naturalistic high school physics classroom settings. This study focuses on data from two lesson sequences that were conducted in several physics classrooms. The lesson sequences were conducted in a whole class discussion format in approximately half of the class sections and in a hands-on-computer small group format in matched class sections. Analysis used a mixed methods approach where: (1) quantitative methods were used to evaluate pre-post data; (2) open coding and selective coding were used for transcript analysis; and (3) comparative case studies were used to consider the quantitative and qualitative data in light of each other and to suggested possible explanations. Although teachers expressed the expectation that the small group students would learn more, no evidence was found in pre-post analysis for an advantage for the small group sections. Instead, a slight trend was observed in favor of the whole class discussion sections, especially for students in the less advanced sections. In seeking to explain these results, qualitative analyses of transcript and videotape data were conducted, revealing that many more episodes of support for interpreting visual elements of the simulations occurred in the whole class setting than in the matched small group discussions; not only teachers, but, at times, students used more visual support moves in the whole class discussion setting. In addition, concepts that had been identified as key were discussed for longer periods of time in the whole class setting than in the matched small group discussions in six of nine matched sets. For one of the lesson sequences, analysis of student work on in-class activity sheets identified no evidence that any of the Honors or College Preparatory students in the small groups had made use in their thinking of the key features of the sophisticated and popular physics simulation they had used, while such evidence was identified in the work of many of the whole class students. Analysis of the whole class discussions revealed a number of creative teaching strategies in use by the teachers that may have helped offset the advantage of hands-on experience with the simulations and animations enjoyed by the small group students. These results suggest that there may exist whole class teaching strategies for promoting at least some of the active thinking and exploration that has been considered to be the strength of small group work, and appear to offer encouragement to teachers who do not have the resources to allow their classes to engage regularly in small group work at the computer. Furthermore, these examples suggest the somewhat surprising possibility that there may be certain instructional situations where there is an advantage to spending at least part of the time with a simulation or animation in a whole class discussion mode.

This thesis is concerned with the detection of surface-breaking defects, such as stress corrosion cracking, using an ultrasonic scanning approach in which a laser source and detector are scanned over the near-field of a defect. Large increases in the amplitude and frequency content of an incident ultrasonic wave are present when either the source or the detector is very close to the defect, leading to a phenomenon known as ultrasonic near-field enhancement. The extent of the ultrasonic enhancement varies with defect characteristics such as defect depth and angle to the surface. Ultrasonic enhancement is observed in both experiment and finite element simulations using Rayleigh waves for both scanning laser detection and scanning laser source methods. The near-field enhancement is shown to vary as a function of the angle of the defect to the horizontal for Rayleigh wave enhancements, allowing the positioning and characterisation of artificial angled defects that are similar to rolling contact fatigue defects in railtrack. The mechanisms behind the near-field enhancement of Rayleigh waves at angled defects are identified, and this aids in the understanding of the behaviour of ultrasound as it interacts with surface-breaking defects. Ultrasonic enhancements are also reported to be present in individual Lamb wave modes for interactions with artificial open-mouthed defects in thin plates, which are similar to the open end of stress corrosion defects. The mechanisms behind both the scanning laser detection and scanning laser source enhancements are identified and used to explain the variation in the enhancement as a function of increasing defect severity. Positioning of these defects is also achieved by identification of the enhancement location. Finally, the scanning laser technique is applied to real stress-driven defects, and both scanning approaches are shown to be capable of detecting partially-closed defects in a variety of sample geometries. The position, geometric alignment and an estimate of the defect depth are obtained for real defects in thin plates, pipework sections and in irregularly shaped engine components.

Electromagnetic acoustic transducers (EMATs) have been used as a non-contact ultrasound approach for detecting and characterising surface defects in aluminium bars and billet. The characterisation was made from understanding the interaction of broadband Rayleigh surface waves with surface crack growing normal or inclined to the sample surface, based on rolling contact fatigue (RCF) cracks in rail tracks. The interaction with normal cracks have been previously reported. For inclined cracks, mode conversion of Rayleigh waves to Lamb-like waves occur in the wedge section formed by the crack, resulting in strong and prominent enhancement in the signal detected. This is confirmed by finite element analysis (FEA) models and Lamb waves arrival times calculation. Signal enhancement from the interaction creates features in B-scan images, and they have been used for initial crack classifications. Then, a number of analyses were performed to estimate the crack inclination, and accurately determine the crack vertical depth. A feature extraction and image classification program based on genetic programming have been developed (through a collaboration work) to perform automated classification on the B-scans. The program produces more than 90% accuracy using the experimental data set. The viability of EMATs to detect and fully characterise narrow cracks have been investigated through experiments using laser interferometer and comparison with EMATs measurements. The results confirmed that narrow cracks can be detected with EMATs, with initial classification (in B-scans) to normal/inclined. However, the depth sizing may not be accurate, and suggestion for better designs of EMATs have been made. FEA models have been used to study the interaction of the Rayleigh waves with branched cracks. Interesting results are observed in terms of Rayleigh waves reflections, which helps to determine the presence of a branch on RCF-like cracks. A method has been proposed for calculating the length of the branch, following a number of analyses.

In this work, some developments in the theory of modelling integrated optical devices are discussed. The theory of the Beam Propagation Method (BPM) to analyse longitudinal optical waveguides is established. The BPM is then formulated and implemented numerically to study both two and three-dimensional optical waveguides using several Finite-Difference (FD) techniques. For the 2-D analysis, comparisons between the performance of the implicit Crank Nicholson (CN), the explicit Real Space (RS) and the Explicit Finite-Difference (EFD) are made through systematic tests on slab waveguide geometries. For three-dimensional applications, two explicit highly-parallel three-dimensional FD-BPMs (the RS and the EFD) have been implemented on two different parallel computers, namely a transputer array (MIMD type) and a Connection Machine (SIMD type). To assess the performance of parallel computers in this context, serial computer codes for the two methods have been implemented and a comparison between the speed of the serial and parallel codes has been made. Large gains in the speed of the parallel FD-BPMs have been obtained compared to the serial implementations; both methods, in their parallel form, can execute, per propagational step, a large problem containing 106 discretisation points in a few seconds. In addition, a comparison between the performance of the transputer array and the Connection Machine in executing the two FD-BPMs has been discussed. To assess and compare the two methods, three different rib waveguides and three different directional couplers have been analysed and the results compared with published results. It has been concluded from testing these methods that the parallel EFD-BPM is more efficient than the parallel RS-BPM. Then, the linear parallel EFD-BPM was extended to model nonlinear second harmonic generation process in three-dimensional waveguides, where the source field is allowed to deplete, using the transputer array and the Connection Machine.

The work described in this thesis is aimed at exploring the possibility of optically integrating an OTDM transmitter operating at 4X10Gb/s on an appropriate substrate. It has been shown that such an OTDM transmitter system could be integrated on III-V semiconductor quantum well (QW) substrates if the design of the substrate, the choice of fabrication techniques and the design of the devices are carefully considered. Suitable device structures for the three main kinds of devices involved in OTDM transmitters, namely light source, optical multiplexers (couplers) and optical modulators, have been discussed. Significant progress regarding these aspects, both theoretical and experimental, has been achieved. In this work, it has been intended to investigate all the devices from the integration point of view. This has been reflected in many aspects in the device design and fabrication process. Integration has always been a very important factor to consider in the determination of substrate material structure, device configuration, waveguide structure and fabrication techniques. As a result, the devices developed in this project are suitable for the proposed purpose of an integrated OTDM transmitter system. Investigation into integration techniques has also been carried out. The most important was to introduce bandgap difference on a semiconductor QW material. IFVD technique is studied and produced some encouraging results such as the extended cavity SRL, which integrates an active section with a passive MMI coupler. Vertically coupled waveguide structures have also been invstigated in an attempt to produce extended cavity lasers. The design considerations of extended cavity lasers employing this waveguide structure have been discussed.

This research presents the study of processing panoramic spherical images for immersive visualisation of real environments and generation of in-between views based on two views acquired. For visualisation based on one spherical image, the surrounding environment is modelled by a unit sphere mapped with the spherical image and the user is then allowed to navigate within the modelled scene. For visualisation based on two spherical images, a view generation algorithm is developed for modelling an indoor manmade environment and new views can be generated at an arbitrary position with respect to the existing two. This allows the scene to be modelled using multiple spherical images and the user to move smoothly from one sphere mapped image to another one by going through in-between sphere mapped images generated.

Structured photonic materials are typically composed of periodic subwavelength elements where the unit cell geometries can impact the overall optical characteristics of the bulk material. By using micro and nanofabrication technologies it is possible to engineer the electromagnetic properties of structured photonic materials for a given application and create a variety of optical components such as band pass filters and absorbers. Two structured photonic materials that have gained substantial interest in recent years are plasmonic filters and metamaterials which are well suited for optical and terahertz imaging applications, respectively. In addition to imaging applications within individual wavebands, structured photonic materials, such as plasmonic filters and metamaterials, could be hybridised and combined with suitable sensors to create a multi-spectral imaging system capable of imaging at optical and terahertz wavebands simultaneously. These new hybrid structured photonic materials are known as synthetic multi-spectral materials, and their development will be presented in this work. To design synthetic multi-spectral materials it was necessary to optimise the plasmonic filter and metamaterial components independently. This involved electromagnetic simulation studies using finite-difference time-domain techniques, fabrication of the structured materials and characterisation using suitable techniques for the relevant spectral band. It was also necessary to ensure that all structures used the same materials and similar fabrication processing techniques as a means of simplifying hybridisation of the two structures. Plasmonic filters exhibit extraordinary optical transmission due to coupling of light with surface plasmons at a metal-dielectric interface. A 16 colour plasmonic filter set, consisting of triangular hole arrays etched into an aluminium film, was optimised for imaging applications in the visible and near infrared spectral range. Initial work on the integration of synthetic multi-spectral materials with CMOS image sensors was undertaken by developing fabrication processes to integrate plasmonic colour filters with two different CMOS chips. Preliminary results from the characterisation of the optical filters fabricated on to the chips have been presented. The resonant wavelengths of the plasmonic colour filters were then scaled up to infrared wavelengths where it was necessary to consider the role of spoof surface plasmons on the extraordinary optical transmission phenomenon. This led to the fabrication of 8 short wave infrared plasmonic filters. Metamaterial band pass filters consist of a single metal film etched with a periodic complementary electric ring resonator unit cell structure. Metamaterial absorbers consist of an electric ring resonator, separated by a metallic ground layer by a dielectric spacer. In the course of this work, two metamaterial filters and four metamaterial absorbers were designed. The metamaterial structures exhibit resonant characteristics at terahertz frequencies. Three synthetic multi-spectral materials, each consisting of hybrid plasmonic filter and terahertz metamaterial structures, have been simulated, fabricated and characterised. The first synthetic multi-spectral material combines 16 plasmonic filters with a terahertz metamaterial filter and is capable of filtering 15 optical wavelengths and a single near infrared wavelength, whilst simultaneously filtering a single terahertz frequency. The multi-spectral filter demonstrates that it is possible to engineer the optical passband characteristics of a thin metal film over several decades of wavelength using a single electron beam lithography step. The second synthetic multi-spectral material consists of 16 plasmonic filters hybridised with a terahertz metamaterial absorber and can filter 15 optical wavelengths and a single near infrared wavelength whilst simultaneously absorbing a single terahertz frequency. Plasmonic filters and metamaterial absorbers are promising components for use in the development of new optical and terahertz imaging systems, respectively, and therefore the second synthetic multi-spectral material represents a significant step forward in the development of a visible and terahertz multi-spectral camera. The third synthetic multi-spectral material combines 7 plasmonic filters with a low metal fill factor metamaterial absorber, to increase the measured transmission of the plasmonic filter components. The third synthetic multi-spectral material is capable of filtering three optical wavelengths, a single near infrared wavelength, a single short wave infrared wavelength and two mid infrared wavelengths, whilst simultaneously absorbing a single terahertz frequency. Such a synthetic multi-spectral material could aid in the development of a visible, infrared and terahertz multi-spectral camera.

Diffraction in pp collisions contributes approximately 30 % of the inelastic cross section. Its influence on the pseudorapidity density is not well constrained at high energy. A method to estimate the contributing fractions of diffractive events to the inelastic cross section has been developed, and the fractions are measured in the ALICE detector at 900 GeV (7 TeV) to be f\(_D\)=0.278\(\pm\)0.055 (f\(_D\)=0.28\(\pm\)0.054) respectively. These results are compatible with recent ATLAS and ALICE measurements. Bjorken’s energy density relation suggests that, in high multiplicity pp collisions at the LHC, an environment comparable to A-A collisions at RHIC could be produced. Such events are of great interest to the ALICE Collaboration. Constraints on the running conditions have been established for obtaining a high multiplicity pp data sample using the ALICE detector’s multiplicity trigger. A model independent method to separate a multiplicity distribution from ‘pile-up’ contributions has been developed, and used in connection with other findings to establish a suitable threshold for a multiplicity trigger. It has been demonstrated data obtained under these conditions for 3 months can be used to conduct early strangeness analyses with multiplicities of over 5 times the mean. These findings have resulted in over 16 million high multiplicity events being obtained to date.