The continual development of precise timing has always pushed technology forward, and the latest generation of clocks uses electronic transitions within cooled atoms as their frequency reference. For atoms where the clock transition is at an optical frequency an ultra stable laser is used to probe the transition; the construction and development of this laser for use with strontium is the subject of this thesis. The system consists of a laser, an optical cavity and the electronics to lock the laser to the optical cavity. The theoretical component of this thesis looked into the possible materials used to make the optical cavity from and how the optical cavity should be supported to minimize the frequency noise of the laser. A compact external cavity diode laser was constructed and shown to have a linewidth of 26 ±15 kHz. To lock and narrow the linewidth of this laser, two ultra stable optical cavity assemblies were constructed with vibration and thermal stabilisation enclosures. To characterise the laser stability a beat measurement was performed between the two stabilised lasers and a beat note linewidth of 1:37 ± 0:28 Hz was measured. The instability of the beat note was measured; an Allan deviation of 2 x10\(^-\)\(^1\)\(^4\) was obtained between averaging times of 0.2 s and 1 s.

This thesis presents a systematic study on the characterising ultrafast dynamics of photo excited carriers in hydrogenated nano crystalline silicon (nc-Si:H) and porous silicon (PS) materials using the ultrafast optical pump probe spectroscopy approaches. The work involves the ground state optical property detection and optical model simulation, ultrafast time resolved pump probe measurements and pump probe data analysis processes. Applying the novel pump probe detection methods, the study explores the carriers concentration, carriers recombination property, scattering rate and conductivity of photo excited semiconducting nano materials.

This thesis presents a study on microstructural evolutions of an ultrafine-grained (UFG) Al-Cu-Mg alloy processed by high-pressure torsion (HPT). This work aims to develop a physically based hardening model to predict the strength of cluster strengthened UFG ternary alloys, and to reveal the relation between thermodynamics and high strain in severe plastic deformation (SPD). Experiments by means of Vickers hardness, differential scanning calorimetry (DSC), Xray diffraction (XRD), transmission electron microscopy (TEM) and atom probe microscopy (APM) have been carried out to provide the relevant information for the calibration and validation of the models. Analysis of XRD line profile broadening using the Rietveld method and Williamson-Hall method shows that the dislocation density increases significantly due to severe plastic deformation, which contributes to the increase of strength. APM reveals the presence of nanoscale co-clusters and defectsolute clustering. The relation between peak temperature for S phase formation and the equivalent strain for HPT was studied with the aid of a diffusion model. The model suggests that on increasing strain, the exothermic peaks correlated to S precipitation shift to lower temperatures. The model is consistent with the data from DSC thermographs of samples after different number of HPT rotations. In both the strengthening model and the stored energy model, strengthening due to dislocations, grain refinement, co clusters (due to short range order and modulus strengthening) and solute segregation are all incorporated to explain the multiple mechanisms. The models show good correspondences with measured microstructure data, measured hardness and measured enthalpy in DSC. The thermal stability of nanostructures in the Al-Cu-Mg alloy obtained by HPT has been studied during DSC heating processes. A significant increase of crystallite size and a significant decrease of dislocation density are revealed from XRD profile broadening when heat treated up to 210 °C, which correlates with an exothermic peak in DSC thermographs. Clusters are thought to act as obstacles that hinder the movement of dislocations, stabilize the ultrafine microstructures. In single reversal (SR) HPT, the hardness slightly decreases after 1/4 reversal turn; and increases again when the reversal rotations continue to increase. This phenomenon is thought to be due to the geometrically necessary dislocation (GND) density which decreases during the inverse straining. This study introduces concepts of the solute-defect complexes and the multiple local interaction energies between solute and dislocations to explain the strengthening mechanisms. The understanding of the HPT processing and microstructural modification has been enhanced through construction of models.

The work described in this thesis is aimed at the exploring the possibility of optically integrating multi-bandgap energy devices on appropriate semiconductor substrates, using the technology of quantum well intermixing. A novel quantum well intermixing technique, based on sputtering process induced disordering (SID), has been developed for the first time, addressing multi-bandgap active device integration. Using this technique, blue shifts have been precisely tuned from 0 nm to over 160 nm for the InGaAs/AlInGaAs and from 0 nm to 100 nm for the InGaAs/InGaAsP MQW systems. Assessment of post-process material characteristics has shown that good electrical and optical qualities were maintained in the bandgap widened regions of both the InGaAs/AlInGaAs and InGaAs/InGaAsP material systems. This novel technique has been used to create multi-wavelength light sources that are of potential application in WDM systems and 2x2 crosspoint optical integrated switches. The expected performance has been achieved. A reactive ion etching process, using CH4/H2 etching gas, has been investigated, particularly for effective etching in the InGaAs/AlInGaAs MQW system. A 'standard' process for the InGaAs/AlInGaAs material system has been developed, based on experimental research. Modelling and design of 3-dB MMI couplers have been carried out. An improved Ti/Si02 mask for reactive ion etching has been successfully employed to ensure the waveguide profiles of fabricated MMI couplers meet the design specification, especially regarding the lateral profiles of the MMI section. Characterisation has shown the waveguide profile is close to the design requirement (side wall angle is of 81±2°). The principle operation of the so-called terahertz optical asymmetric demultiplexer has been qualitatively described and the design of a Mach-Zehnder interferometer (MZI) type demultiplexer has been carried out. Three kinds of MZI demultiplexers with different geometric structures have been fabricated using SID technique. Assessment of the devices has been carried out, including the operation of semiconductor amplifier, propagation loss of the device, etc.

The work presented in this thesis is an investigation which aims to quantitatively characterise the physical microstructure, magnetic structure and micromagnetic behaviour of nanostructured thin films for magnetic recording and spintronics application. The nanostructures in the present work involve continuous and patterned thin films. Chapters 1, 2, and 3 present the overview backgrounds directly relevant to the work. Chapter 4 focuses on vortex structure in magnetic nanodots. The results confirm that the behaviour of the vortex can be modified by changing the edge geometry of the dots. It is demonstrated a practical method to determine the out-of-plane component of the vortex core with high accuracy and speed. Additionally in-plane curling magnetisation of the vortex is also mapped by reconstructing the electron phase using the transport-of-intensity equation. However this method is susceptible to spurious low spatial frequency and this aspect is explored to show limitations of the method. Chapter 5 deals with the characterisation of magnetic structure in nanoconstrictions intended to trap domain walls (DWs) in the nanoconstrictions. A structure was fabricated with two micron-sized pads as the sources for creation of DWs. A DW can be driven to be pinned at the nanoconstriction resulting in a change of magnetoresistance due to the contribution of the DW to the resistance of the device. The magnetisation configuration around the constriction is studied during the reversal process. It is apparent that that understanding the magnetisation rotation around the constriction and into the pads is the key to the magnetoresistance measurements and the DW resistance is part of this process. Evidences of DW compression at the nanoconstriction were noted. In Chapter 6 the investigation of the physical structure and micromagnetism of CoIr film is described. A hexagonal crystal structure with a [0001] texture normal to the film plane was characterised. Weak anisotropy is observed in the film denoted by a complex reversal on the hard axis due to incoherent rotation of magnetic moments. The film exhibits typical soft magnetic behaviour it merits compared to other soft materials are discussed in light of the results obtained here. Chapter 7 concludes with a discussion of the outcomes of the present thesis. Additionally possible directions for future research in topics discussed in this thesis are proposed.

Photoproduction of mesons provides an excellent means by which to study the proton excitation spectrum. The existence and properties of some nucleon resonances are well established, but many more are still debated, meriting much theoretical and experimental attention. The proximity and widths of such excited states result in difficulties in separating contributions from individual resonances. However, the S_11(1535) is the only state in the second resonance region to couple strongly to an Nη final state. Consequently, η production provides clean selection of this S_11 intermediate state, for incident photons in the energy range 700 to 1400MeV. The S_11(1535) is a well-established resonance, but its composition is a contentious topic, requiring further experimental data to distinguish between competing theories. The MAMI electron accelerator was upgraded in 2006 to increase its maximum beam energy from 885 to 1508MeV. The A2 collaboration use tagged Bremsstrahlung to produce the necessary photons for photoproduction experiments. The upgrade granted access to the second resonance region of the proton excitation spectrum, which covers the centre-of-mass energy range 1.3 < W < 1.6GeV. This exceeds the η production threshold of W = 1485MeV (Eγ = 707MeV) and encompasses the full width of the S_11(1535). For exclusive measurements of η photoproduction, a reasonably precise knowledge of the incident photon energy is required. This is provided for the A2 collaboration by the Glasgow Photon Tagging Spectrometer (the “tagger”). The upgrade of MAMI necessitated the corresponding upgrade of the tagger. The work of this thesis included assisting in the upgrade and calibration of the tagger before using the completed spectrometer in the measurement of differential cross-sections of η photoproduction on the proton from threshold to 1403MeV incident photon energy. The agreement of this analysis with previous experiments demonstrates the success of both upgrade and calibration.

The thesis focuses on the asteroseismology of main sequence B-type stars, particularly β Cephei and Be stars. Photometric observations of these stars were analysed in order to detect stellar oscillations. The photometric data analysed in this thesis were collected using the Solar Mass Ejection Imager (SMEI). The analysis initially focussed on known β Cephei stars, to refine information on previously detected frequencies and detect further oscillations. A survey was then conducted using data from the SMEI instrument to search for further β Cephei stars. The results from this survey were analysed, and individual stars were examined in more detail which may possibly be β Cephei like. Due to the long duration of light curves obtained with the SMEI instrument, stellar oscillations can be analysed for evidence of amplitude and phase change. This type of analysis was completed on two Be stars, Achernar and \(\zeta\) Oph, and significant amplitude changes in the oscillations of both of these stars were detected. There is evidence that the amplitude variations may be linked with the outburst events that occur on Be stars, and therefore this analysis may be used to help solve the puzzle of the Be phenomenon.

The work outlined in this thesis focuses on the development and fabrication of metasurfaces for manipulating electromagnetic waves, with the potential for applications in imaging and holography. Metasurfaces are the Two-Dimensional counterpart of metamaterials, which are artificial materials used to invoke electromagnetic phenomena, not readily found in nature, through the use of periodic arrays of subwavelength ‘meta-atoms’. Although they are a new and developing field, they have already secured a foothold as a meaningful and worthwhile focus of research, due to their straight-forward means of investigating fundamental physics, both theoretically and experimentally - owing to the simplicity of fabrication - whilst also being of great benefit to the realisation of novel optical technologies for real-world purposes. The main objective for the complete manipulation of light is being able to control, preferably simultaneously, the polarisation state, the amplitude, and the phase of electromagnetic waves. The work carried out in this thesis aims to satisfy these criteria, with a primary focus on the use of Geometric phase, or Pancharatnam-Berry phase. The first-principles designs are then used to realise proof-of-concept devices, capable of Circular Conversion Dichroism; broadband simultaneous control of phase and amplitude; and a high-efficiency, broadband, high-resolution hologram in the visible-to-infrared.

The sensitivity of the next generation of interferometric gravitational wave detectors will be limited in part by thermal noises of the optics. It has been proposed that using higher-order Laguerre-Gauss (LG) beams in the interferometers can reduce this noise. This thesis documents progress made in assessing the compatibility of higher-order LG beam technology with the existing precision interferometry framework used in the gravitational wave detector community. A numerical investigation was made into techniques for generating higher-order LG modes with a phase modulating surface. The optimal conditions for mode conversion were determined using fast Fourier transform (FFT) simulations, and predictions were made for the mode purity achievable with this method. Table-top experiments performed at Birmingham demonstrated the generation of higher-order LG modes using a spatial light modulator, and showed for the first time the feedback control of an optical cavity on resonance for higher-order LG modes. An increase in the purity of LG\(_{33}\) modes from 51% to over 99% upon transmission through the cavity was shown. Investigations were carried out at the Glasgow 10m prototype detector into the performance of the LG\(_{33}\) mode in a suspended 10m cavity, providing useful insights into the compatibility of LG modes with larger scale interferometers.

This thesis starts by reviewing superconductivity in one-dimension where fluctuations cause a loss of supercurrent due to an intrinsic resistance. Solved via the Ginzburg-Landau equations, the theory of thermally activated phase slips given by Langer and Ambegaokar is outlined. In turn this leads to the investigation of superconductivity via a microscopic approach, in particular the quasi-classic green’s functions of Eilenberger. The Eilenberger equations are derived and considered in the dirty and weakly anisotropic limits which provides a simple derivation of the Ginzburg-Landau equations near the transition temperature. This prompts an extended derivation which includes the non-linear terms normally removed in deriving the Ginzburg-Landau equations. This is required for calculating effects at temperatures below the transition temperature. These quasi-classic equations of weakly anisotropic superconductors are first written for arbitrary temperature and impurity concentration then limited to the pure and dirty cases. The latter being simplified to zero temperature and solved in the context of thermally activated phase slips.