Diode-pumped alexandrite laser development and vortex mode generation

This thesis is focussed on two aspects of solid-state laser development: optimising and understanding diode-pumped Alexandrite laser performance, and a new laser cavity design for vortex mode generation. Due to its broad wavelength tunability (700nm to 858nm) and excellent physical properties, Alexandrite has a wide range of potential applications from remote sensing to quantum optics. Recent advances in red laser diode-pumping has enabled high power and efficient laser operation. In this work a continuous-wave analytical model of end-pumped Alexandrite lasers was developed and applied to experimental systems. This helped to achieve a record diode-pumped slope efficiency of 54% with 1.2W of output power. A record shortest wavelength (714nm) and broadest tuning range (104nm) was obtained through optimising the crystal temperature between 8 °C and 105 °C. Investigation and new measurements of the properties of Alexandrite gave rules applicable in general to optimising these lasers, along with assessing the fundamental limits to Alexandrite laser efficiency. Optical vortex laser beams have attracted considerable attention from their wide range of applications that cover many areas of science, from optical communications to laser machining to microscopic laser manipulation. Directly generating them from a laser has advantages due to the pure and high power modes that can be generated. In this work an anti-resonant ring was proposed and used to couple two lasers through a shared gain medium. Using one cavity to control the output of the other, first order vortex Laguerre-Gaussian modes of power 9.0W from 24W of input power with high quality (M² = 2.1) were obtained, which had controllable and pure handedness. A second order vortex mode with 4.3W of power was also created. This vortex generation geometry could be applied to any solid-state laser gain medium, which would enable vortex generation across the electromagnetic spectrum.Open Acces

The Validity and Timing of the ABR Core Exam

The American Board of Radiology's (ABR) new Core Exam is not working, at least not as well as it needs to. Having helped to prepare candidates (RG), studied for and taken the exam (WK), and talked with hundreds of candidates who have taken the exam (RG and WK), we believe that that one aspect of the exam, its validity, can be significantly enhanced. Just as we expect candidates for board certification and practicing radiologists to measure up to the high standards, so we should subject the board exam to continuous scrutiny, seeking opportunities to rectify errors and enhance the exam's overall quality, with a view to better promoting excellence in radiology practice and the care of patients. Here we focus on two exam parameters: validity and timing

Anatomy of a failure: how we knew when our design went wrong, and what we learned from it

In this paper, we describe the failure of a novel sensor-based system intended to evoke user interpretation and appropriation in domestic settings. We contrast participants' interactions in this case study with those observed during more successful deployments to identify 'symptoms of failure' under four themes: engagement, reference, accommodation, and surprise and insight. These themes provide a set of sensitivities or orientations that may complement traditional task-based approaches to evaluation as well as the more open-ended ones we describe here. Our system showed symptoms of failure under each of these themes. We examine the reasons for this at three levels: problems particular to the specific design hypothesis; problems relevant for input-output mapping more generally; and problems in the design process we used. We conclude by noting that, although interpretive systems such as the one we describe here may succeed in a myriad of different ways, it is reassuring to know that they can also fail, and fail incontrovertibly, yet instructively

Form and Movement in Domestic Networked Systems

It is increasingly desirable for electronic artefacts in the home to be grouped as sets, sharing data and properties across a network. A range of strategies can be used by a designer to explore the value and use of the systems for users, in particular through the properties of form and dynamic behaviours, including visual output and movement. This paper focuses on a range recent work which exploits rich behaviour and novel forms to highlight opportunities for user engagement in the home

Open Access Issues and Potential Solutions Workshop

This report provides a summary of the discussion and findings of the Open Access Issues and Potential Solutions workshop held as part of the End-to-End Project. The workshop was highly interactive and feedback received indicated it was extremely valuable, stimulating a useful exchange of ideas

Fat Necrosis of the Breast: A Pictorial Review of the Mammographic, Ultrasound, CT, and MRI Findings with Histopathologic Correlation

Fat necrosis of the breast is a challenging diagnosis due to the various appearances on mammography, ultrasound, CT, PET-CT, and MRI. Although mammography is more specific, ultrasound is a very important tool in making the diagnosis of fat necrosis. MRI has a wide spectrum of findings for fat necrosis and the appearance is the result of the amount of the inflammatory reaction, the amount of liquefied fat, and the degree of fibrosis. While CT and PET-CT are not first line imaging examinations for the diagnosis of breast cancer or fat necrosis, they are frequently performed in the surveillance and staging of disease. Knowledge of how fat necrosis presents on these additional imaging techniques is important to prevent misinterpretation of the imaging findings. Gross and microscopic appearances of fat necrosis depend on the age of the lesion; the histologic examination of fat necrosis is usually straightforward. Knowledge of the variable appearances of fat necrosis on a vast array of imaging modalities will enhance a radiologist's accuracy in the analysis and interpretation of fat necrosis versus other diagnoses