This thesis describes an investigation into the potential of coupled-cavity semiconductor lasers for bio-sensing applications. This has involved the design and development of a fabrication process for a novel micro-fluidic coupled-cavity laser sensor. The efficiency of the etched inner laser facets of this device have been identified as a key determinant of the device behaviour. The multi-section gain characterization technique has been used to measure the efficiency of these facets to be η = 0.48 ± 0.13. Perturbation of the optical coupling between the two laser sections of the device can induce a wavelength shift in the laser output of Δλ = 20 ± 5 Å. This wavelength change is attributed to the difference in the threshold gain requirements of the coupled-cavity and individual cavity modes of the device. A multi-mode travelling wave rate equation model has been used to predict that the size of this effect can be maximized by optimizing the cavity lengths of the device. For the AlGaInP quantum well material used in this work the coupling effect is maximized by using the shortest cavity lengths possible that can still achieve laser action. The utility of including a segmented contact system to the coupled-cavity design has also been investigated. This modification enables wavelength tuning via the gain lever effect and self-pulsation through saturable absorption. A wavelength tuning range of Δλ = 1.2 ± 0.2 nm has been measured for a single cavity laser with a segmented contact length ratio of 4:1. This tuning behaviour has been attributed to the carrier density dependence of the net modal gain peak. Rate equation modelling has been used to interpret the self-pulsation behaviour of the segmented contact device and to demonstrate how optical pumping of a saturable absorber can increase the sensitivity of the coupled-cavity device.

This work reports an investigation of the interaction of ultrashort laser pulses with a graphite surface. Time-of-flight experiments were conducted with a 100 fs laser system, then 13 fs laser pulses at 800 nm wavelength were used for photoelectron spectroscopy studies. Multi-shots and single-shot laser pulse regimes have shown the existence of two mechanisms involved in the ablation of graphite: at low laser fluence, a non-thermal physical process known as Coulomb explosion (CE) is responsible for the ultrafast removal of particles. At high laser fluence, a thermal process, called plasma generation and characterized by a liquid-carbon phase initiated by the laser pulse, takes place and is believed to be at the origin of the ejection of particles. On the other hand, results from 13 fs laser pulses give rise to unusual high kinetic energy photoelectron around 20 eV that cannot be explained by the multiphoton ionization process but by tunnel and/or above barrier ionization (ABI). This unexpected result at such low intensities (10¹⁰ < I(W/cm²) <10¹²) is interpreted as a roughening of the surface by the laser pulse that leads to photon-plasmon coupling, then an enhancement of the local electric surface field enough to make possible electrons tunneling through the potential barrier or even to escape directly (ABI) into the vacuum.

The HERMES experiment was a forward angle spectrometer on the HERA storage ring at DESY, Hamburg, Germany. HERMES successfully increased understanding of the “spin puzzle”, the spin structure of the nucleon, by providing high precision measurements of ∆Σ in the Quark Parton Model, the fraction of the spin carried by the current quarks. Following the link of another piece of the puzzle, the orbital angular momentum of quarks and gluons, to the Generalised Parton Distribution (GPD) theoretical framework, HERMES focused on measurements of the Deeply Virtual Compton Scattering (DVCS) process. These measurements are sensitive to GPDs, allowing further experimental constraints to be made on the components of nucleon spin. In the Winter shutdown period 2005-2006 HERMES was upgraded with a Recoil Detector in the target region. This allowed the experiment to make exclusive measurements of the DVCS process for the first time, reducing background and increasing the resolution of various kinematic variables. The method for reconstructing particle tracks in the inhomogeneous magnetic field is investigated here. DVCS off a deuterium target is measured with all available data prior to the installation of the Recoil Detector. A comparison is made to currently available models of spin-1/2 GPDs. This analysis has been approved for publication by the HERMES collaboration. The data is further employed in an investigation of a model dependent constraint of the total angular momentum of up and down quarks in the nucleon.

This thesis presents measurements of the photon asymmetry polarisation observable for the γd→K⁺Λ and γd→K⁺Σ⁰ reactions from the bound proton in deuterium. The data were collected in the summer of 2007 at the Thomas Jefferson National Accelerator Facility in Newport-News, Virginia, using a linearly polarised photon beam in the energy range 1.3 to 2.3 GeV. The aim of the experiment was to investigate the validity of the quasifree approximation of a bound nucleon in deuterium. This analysis focusses on the proton and by directly comparing results from this analysis to those from previous similar analyses on the free proton, this issue is addressed. Ultimately, this will allow reliable results to be extracted from analyses of channels on the bound neutron in deuterium. The photon asymmetry is found to be positive for the entire kinematic range for both channels with indications of some structure above centre-of-mass energies of 1.8 GeV. The K⁺Λ results are compared to measurements from the free proton produced with similar kinematics. Also included in the comparison are model predictions from the Kaon-MAID isobaric model which includes the established ****S₁₁(1650), ***P₁₁(1710) and ****P₁₃(1720) resonances and uses various Born terms to describe the background. Comparison to the free proton results gave good agreement with the majority of the quasifree measurements being comparable to those from the free proton. There was however seen to be some indication of a systematic overestimation of the results in one kinematic region. The model gives reasonable agreement with the data, with some evidence for a role to be played by the missing D₁₃(1900) resonance. For the K⁺Σ⁰ results, the same comparison was made with free proton results and the Kaon-MAID model, this time with the inclusion of the **S₃₁(1900) and ****P₃₁(1910) resonances. No missing states were considered in this calculation and the agreement with the results was not as good as that of the K⁺Λ channel. Comparison to measurements from the free proton produced similarly good results as were found with the K⁺Λ results but this time with no obvious indication of any systematic discrepancy. Overall, the agreement between the quasifree and the free predictions was found to be quite good and will lend weight to future analyses from the bound neutron in deuterium by allowing a quasifree approximation to be assumed prima facie.

This thesis presents measurements of isolated photon production in deep inelastic ep scattering made with the ZEUS detector at HERA using an integrated luminosity of 320 pb-1. Measurements were made in the isolated-photon transverse-energy and pseudorapidity ranges 4 < E_T < 15 GeV and -0.7 < eta < 0.9 for exchanged photon virtualities, Q^2, in the range 10 < Q^2 < 350 GeV^2 and for invariant masses of the hadronic system W_X > 5 GeV. Differential cross sections are presented for inclusive isolated photon production as functions of Q^2, x, E_T and eta. Leading-logarithm parton-shower Monte Carlo simulations and perturbative QCD predictions give a reasonable description of the data over most of the kinematic range. To increase the precision of the measurement, a study was undertaken to improve the Monte Carlo description of electromagnetic showering in the ZEUS calorimeter. This utilised isolated electromagnetic clusters from ZEUS data to which Monte Carlo event samples with varying parameters for electromagnetic showering were fitted. These improvements have been adopted in the standard ZEUS detector simulation and were also shown to improve electron identification. For the main isolated photon analysis a range of methodologies for photon clustering and identification, isolation and signal extraction were investigated and the optimal methods were chosen. As a result of these refinements and the improved electromagnetic shower modelling, the systematic errors decreased significantly, typically by a factor of three when compared to the same phase space in the previous ZEUS publication. In addition the luminosity was increased threefold and the phase space was expanded. These two improvements brought about a factor three reduction in statistical uncertainty.

A study has been made of the influence of impurities on the flow stress of melt-grown magnesium oxide single crystals. The state of dispersion of the transition metal impurities chosen -iron, titanium 9 vanadium and chromium - was varied by heat treatment at temperatures up to 2,000oC in different environments? and the associated changes in flow stress measured at room temperature Evidence for impurity redistribution in each case was derived from an application of optical and microwave absorption techniques, combined with direct microstructural observations by electron microscopy a A good correlation has been found between the experimentally observed flow stress and the calculated strengthening by dispersed obstacles identified by these methods. In as-grown crystals the principal defects influencing the flow stress are considered to be in the form of impurity-vacancy pairs and anion-cation vacancy pairs, and it is these defects which govern the initial annealing behaviour. Additional evidence to substantiate these conclusions has been provided by measurements of the temperature dependence of the flow stress, and the recovery of neutron irradiation damage in doped crystals. During low temperature anneals in air vacancy clustering and collapse as dislocation loops has been observed, and correlated with an initial plastic softening behaviour. Impurity oxidation also takes place under these conditions9 leading to an increased concentration of impurity vacancy pairs, and subsequently to the formation of a spinel precipitate dispersion. An explanation for the flow stress variations at low temperatures for long ageing times is proposed in terms of a precipitation hardeninq-overageing behaviour in which precipitates are undeformed in the initial stages of yielding As a result of the high nucleation rate in the supersaturated vacancy environment existing in as-grown crystals, a significant hardening is produced, even for low volume fractions of precipitates In many cases the particle dispersion corresponding to the flow stress maximum has been found to be unresolvable. Nevertheless, a correlation of the flow stress calculated on the basis of an Orowan mechanism with the experimentally observed flow stress is possible by evaluating the precipitate volume fractions indirectly from the E.P.R. and optical results. The particle radii calculated in this way are in good agreement with the observed microstructure over the annealing ranges considered. At elevated temperatures in air the flow stress has been found to be modified by interstitial oxygen diffusion. The centre responsible for the flow stress peak in these conditions is considered to be in the form of an interstitial oxygen ion trapped at an impurity site.

In this thesis methods of accurately and reproducibly measuring intestinal content and transverse relaxation to study the fate of food in the gastrointestinal tract are reported. In addition to this a technique for measuring relaxation parameters in the brain at ultra-high field is also investigated. Several methods can be used when quantifying the fate of food through the gastrointestinal tract; there are many factors that can be measured using MRI and these are discussed along with other non-MRI techniques. In this work a method for quantifying small bowel water content (SBWC) is optimised and validated for use at 3.0 T and a technique for measuring T2 in the abdomen is developed and optimised called T2-prepared balanced turbo field echo (T2-prep bTFE). These two methods are then used, in conjunction with other established MRI techniques, to study the fate of food in the gastrointestinal tract from the stomach all the way through to the colon. A hybrid gradient echo-spin echo (GESSE) sequence is also investigated and optimised for measuring T2 and T2* simultaneously in the brain at 7.0 T. This sequence is also proved to have applications in the liver at lower field strengths. The GESSE sequence is used to measure the first T2 values in deep grey structures in the brain at 7.0 T. In this work cross-field (1.5, 3.0 and 7.0 T) variations in T2 are studied. Also differences in T2 and T2* are measured in the brain to determine variations between white matter tracts and to ascertain any effects of Parkinson’s disease on deep grey matter structures.

Determining a scattering medium's absorption and scattering coefficients from measurements of the light reflected or transmitted from the medium is a common problem in various fields. The aim of this thesis was to calculate the errors in the determined coefficients using different combinations of light "metrics" such as reflectance and mean flight time under realistic noise conditions, as a result of which the optimum metric combination could be found. This was investigated by the forward modelling of various metrics of detected light from a semi-infinite, homogeneous medium using the Diffusion Approximation. The normalised intensity and cumulants of the light's temporal point spread function (TPSF), were investigated as possible metrics and their form over a range of optical coefficients corresponding to in vivo human tissue described fully. These metrics were then used to provide simultaneous equations from which the medium's scattering and absorption coefficients could be calculated. Errors in the metrics will propagate through to errors in the determined coefficients and a general method to calculate the extent of this propagation was described. To simulate realistic metric errors, a typical streak camera (Hamamatsu C5680) was modelled to determine its effect on the measurements of the metrics. Using this model, "error maps" showing the expected error in each metric's value over the range of absorption and scattering coefficients were produced. These were then applied to the general error analysis method. In full-field detection mode, it was shown that the combination of normalised intensity and first cumulant gave the most accurate answer for the medium's coefficients, while for spatially resolved detection, various combinations of reflectance and the mean time of flight were found to be the optimum metric pairs under different conditions. Finally, a method of using the known characteristics (either from modelling or experiment) of a detector such as the streak camera to improve the accuracy of the determined coefficients was described.

Z-contrast imaging, using a high-angle annular dark field detector, can be used to characterise III-V heterostructures. GaAs/AlAs heterostructures were grown using MBE and prepared for TEM using a cross-sectional method. SuperSTEM 1 was used to investigate both the GaAs-on-AlAs and the AlAs-on-GaAs interfaces as a function of specimen thickness. The analysis of the images showed that the apparent interface widths varied with thickness in an unexpected manner. The measured GaAs-on-AlAs interface widths remained constant with thickness while the AlAs-on-GaAs interface widths increased. Furthermore, the apparent width of the GaAs layer increased with increasing thickness. The actual interfacial width can be a result of either surface stepping during MBE growth or inter-diffusion of the Type-3 atoms. To assist the interpretation of these results, a series of interfacial models were created and explored using a modified version of the frozen phonon multislice simulation. The models consisted of terraced, vicinal and diffused interfaces. The model results indicate that a diffuse interface can be used to describe the characteristics observed in the experimental images. However, probe scattering from the interfacial region can be counter intuitive. A systematic study of these effects is presented outlining complications that can occur when interpreting interfacial structures using HAADF imaging.

A statistical combination of the low mass search channels for the Standard Model (SM) Higgs boson at the ATLAS Experiment is presented. It is found that with 1 inverse femtobarn of ATLAS data, the SM Higgs can be excluded between 130 GeV and 190 GeV, at or above the 95% Confidence Level. In the presence of signal, a 5σ observation is expected between 125 GeV and 185 GeV for 10 inverse femtobarns of data. The effect of systematic uncertainties on the discovery and exclusion sensitivities are presented. The discovery potential of the Higgs plus associated top decay mode of the SM Higgs is assessed and the discovery sensitivity is found to be 1.5σ for 30 inverse femtobarns. It is shown that the use of a neural network can improve the exclusion potential of this search mode by a factor 3, increasing the SM cross-section excluded at 95% CL, with 1 inverse femtobarn of expected ATLAS data, from 14.6 to 4.6σ. A study of ATLAS particle identification efficiencies is also presented. A tool which applies these efficiencies to the output of the ATLAS fast simulation tool, ATLFast, has been developed. It is shown for isolated electrons from a top-antitop sample that application of the electron identification efficiency improves the agreement between the fast and full simulation from ±10% to ±5%.