In this thesis novel methods for the laser cooling of quantum systems are presented. The use of quantum interference allows for the tailored cancelation of heating processes, so that an approximation to a cooling operator is possible that does not rely on the rotating wave approximation. This makes these schemes considerably faster and more efficient than existing ground state cooling methods, and allow for a significant relaxation of current experimental constraints. Several approaches are investigated in different systems. On the one hand, a special laser configuration, applicable to trapped ions, atoms or cantilevers, generates a double dark state that eliminates both the blue sideband and the carrier transition. As a consequence, vanishing phonon occupation up to first order in the perturbative expansion is achieved. Underlying this scheme is a combined action of two cooling schemes which makes the proposal very stable under parameter fluctuations. Its suitability as a cooling scheme for several ions in a trap or for a cloud of atoms in a dipole trap is shown. On the other hand, a pulsed cooling scheme for optomechanical systems is presented. It can be implemented for both strongly and weakly coupled optomechanical systems in both weakly and highly dissipative cavities. Its underlying mechanism is based on interferometric control of optomechanical interactions, and its efficiency is demonstrated with pulse sequences that are obtained by using methods from optimal control. Finally, it is shown how this pulsed method can be combined with continuous measurement to drive mechanical oscillators to highly squeezed steady states. Its mechanism relies on the modification of the dissipation and measurement terms, which drive the system towards a specific quadrature eigenstate. The scheme is robust to measurement inefficiencies and works also with highly dissipative cavities, which makes it accessible to implementation with state of the art technology.

This thesis looks at the effects that electron-ion Coulomb collisions have on fast electron transport in solid density plasma. The study of the fast electrons generated in ultra-high intensity laser-plasma interactions is important due to their envisioned use in the fast ignition approach to inertial confinement fusion. Collisions have been added to the particle-in-cell (PIC) code EPOCH in order to study the propagation of fast electron beams in various solid density targets. By using a collisional PIC model several of the assumptions used in previous studies are not required. The code solves the full Maxwell equations (including the displacement current), does not require assumptions of Ohm’s law and of Spitzer resistivity and does not require the background distributions to be Maxwellian. The thesis begins with summaries of the background theory and of the previous work performed in this area. The PIC method is then discussed and the way in which collisions were added to EPOCH is outlined. The results from several collisional PIC simulations with different target Z values are then discussed and com- pared to both collisionless PIC simulation results and hybrid simulation results. The effects of collisions have then been examined by looking into numerous aspects of the simulations that have been performed. Firstly, the generation of fields within the plasma and the subsequent filamentation of the fast electron beam are examined. The effects that the collisions have on the electron distributions within the plasma are then investigated with particular attention given to the divergence of the fast electrons, the energy and momentum distributions of the electrons and the background temperatures within the plasma. Finally, the results of the simulations are used to assess the accuracy of the Spitzer resistivity approximation that is used in hybrid codes.

This thesis presents work on the development of a compact adaptive optics ophthalmoscope to visualize microscopic details of the human fovea. Conventional ophthalmoscopes currently employed in retinal imaging for diagnostic purposes help to detect disorders in real-time; however, their resolution is limited by the optical quality of the last focusing lens, the human eye. In recent years there has been a significant increase in studying retinal alterations, including the complication of non-ophthalmic diseases. In a number of cases, especially for visually impaired and elderly people, when the ocular media become less transparent, fixation is hard for the patients. It is often difficult to repeat the measurements during the usual clinical diagnostic routine; the dynamic changes and imperfection in the optics of the eye also significantly degrade the retinal image quality. In order to resolve cellular level details and hence detect ocular diseases in their infancy, dynamic correction of ocular aberrations is required. Developments in ophthalmoscopy have extended its application to high-resolution imaging using adaptive optics. This technology enables the in-vivo study of finer microscopic structures by dynamically correcting higher-order ocular aberrations. To date, such systems have been large and confined to research laboratory conditions. This thesis investigates the performance of a compact adaptive optics ophthalmoscope built in a cost effective way to provide a diagnostic tool that is more affordable and usable in a general clinical environment. It also highlights some of the problems associated with retinal imaging and discusses the limitations of retinal imaging systems. The results obtained with this system suggest that it is possible to non-invasively detect structural and functional changes of the retina in their early phases of development and enable precise monitoring of the effect of therapies in later clinical research.

Laser cooled ions in a Penning trap can be isolated from the environment by placing them in vacuum and only interacting with them through optical and RF fields. The number of trapped particles can be varied from a single ion up to thousands. Confinement is provided by a static homogeneous magnetic field and a quadrupole electric potential. In the natural frame of the ions, this appears as a 3D simple harmonic potential. Therefore three dimensional structures can be formed in the absence of any additional RF field which may lead to heating as is the case with RF traps. There are 3N different motional modes for N particles. I present an analysis of the motion of a single particle showing that the energy levels for all three modes are equally spaced. I also describe the interaction between a trapped two level atom and an optical field. During my time in the lab the laser and computer control of the experiment has been significantly improved. In addition, an existing trap was modified to provide greater optical access and fluorescence collection. This allowed the vibrational levels superimposed on the internal states of a single 40Ca+ ion to be resolved via a narrow linewidth, electric quadrupole transition. This is the first observation of magnetron and modified cyclotron sidebands on an optical transition. When more than one calcium ion is laser cooled, and their temperature reduced below 5mK, they form a Coulomb crystal. The locations of the ions minimise the total potential energy which is comprised of the Coulomb repulsion and trap potential. The fluorescence collection optics have been arranged to resolve individual ions in these crystals. Information about the motion of the ions is deduced by comparing photos from the experiment to numerical simulations. Previously, only two ions have ever been aligned along the magnetic field in a Penning trap. I present strings of up to 29 particles and suggest the only limitation, apart from the electrode structure, is the overlap of the laser beams with the ions.

Confocal fluorescence endomicroscopes employ fibre optics along with miniaturised scanning and focussing mechanisms to allow microscopic investigation of remote tissue samples with sub-cellular resolution. For this reason they are widely used in biomedical research, both in clinical studies and in small animal imaging experiments. Fluorescence lifetime imaging microscopy (FLIM) has been shown to provide contrast between normal and unhealthy tissue in several diseases including gastro-intestinal (GI) cancer. As such, there is significant interest in developing instrumentation that will allow endoscopic confocal FLIM as this would permit the in vivo investigation of human GI tissue. This thesis describes the development and use of several instruments and techniques aimed at clinically viable in vivo fluorescence lifetime spectroscopy and confocal endomicroscopy. This research has consisted of two broad branches: the study of the fluorescence signature of healthy and diseased tissue both ex vivo and in vivo; and the development of a novel method for achieving beam scanning in confocal endomicroscopy. Firstly the tissue studies are discussed. This begins with the application of a compact steady-state diffuse reflectance/fluorescence spectrometer and a fibre-optic-coupled time-resolved spectrofluorometer to an in vivo investigation of the spectral signatures of skin cancer. This study – which involved the interrogation of 27 clinically diagnosed lesions – was carried out in collaboration with researchers at Lund University in Sweden and revealed significant differences between healthy and diseased tissue both in terms of fluorescence lifetime and steady state reflectance and fluorescence spectra. Further to this study, work is presented charting the development of a clinically viable spectrometer, which measures time-resolved fluorescence spectra with two excitation wavelengths (375 nm and 435 nm) as well as diffuse reflectance spectra. The entire system is contained within a compact trolley (120 x 70 x 55 cm) for easy transportation and safe use in a clinic. It utilises a fibre optic probe to deliver/collect light that can be inserted into the working channel of a medical endoscope meaning that the system can be used to measure diffuse reflectance and time-resolved fluorescence spectra in the GI tract in vivo. The development and testing of this system are discussed and data are presented from both ex vivo and in vivo studies of GI cancer. The second broad section of this thesis focuses more closely on confocal endomicroscopy. Firstly current methods used in this field are discussed and the sources of several drawbacks are explained. A novel approach to laser scanning endomicroscopy is then presented, which requires no moving parts and can be implemented without the need for any distal scanners or optics. This technique is similar in concept to the use of adaptive optics to focus through turbid media: it utilises a proximal spatial light modulator to correct for phase variations across a fibre imaging bundle and then to encode for arbitrary wavefronts at the distal end of that fibre bundle. Thus, it is possible to realise both focussing and beam scanning at the output of the fibre bundle with no distal components, permitting extremely compact endoscopic probes to be developed. Proof-of-principle results are presented illustrating the imaging capabilities of this novel system as well as simulations showing the achievable resolution and field of view in several feasible endoscopic configurations. Overall, this thesis contains work from two quite different projects both aimed at developing novel optical techniques for clinical diagnostic use in endoscopic procedures. The first is aimed at investigating the temporal and spectral properties of the fluorescence and reflectance signatures of cancer, while the goal of the second is to develop improved confocal endomicroscopes.

This thesis involves a structural and spectroscopic investigation of the electroluminescent polymer poly(9,9-dioctylfluorene), F8T2, and its copolymers poly(9,9-dioctyl)fluorene, PFO, and poly(9,9-dioctylfluorene-alt-benzothiadiazole), F8BT. Small angle neutron scattering (SANS) studies have shown that the three polymers take up very rigid, rod-like conformations in toluene and chloroform solutions. Aggregation effects of F8T2 in toluene were studied over 16 hours with a sheet-like aggregate structure suggested. Light-scattering (LS) measurements were used to investigate the molecular weight, backbone conformation on different length scales, coil size and the effect of chain aggregation in different solvents, and at different temperatures of the three polymers. Again, the polymers appear to be very rigid, with precise molecular weights and radii of gyrations found. F8T2 was extensively studied using optical absorption, photoluminescent (PL) emission, PL quantum efficiency (PLQE) and PL lifetime measurements of solutions and films deposited from them. Strong PL quenching effects were seen which have been attributed to interchain interactions at concentrations around 0.01 mg/ml, self-absorption effects dominate at higher concentrations above ~0.1 mg/ml. Large spectral changes were seen due to solvent choice, aggregation effects and thermal dissolution histories. Deposited films were also investigated with temperature dependent PL, which allowed some thermal transition temperatures to be found, atomic force microscopy and as bottom-gate/top-contact organic field-effect transistors. Synchrotron Grazing Incidence Wide-Angle X-ray scattering (GIWAXS) studies were conducted on films deposited on flat substrates and polyimide alignment layers, as well as annealed within an in-situ vapour cell. F8T2 was found to be a poor scatterer of X-rays but F8BT appears to stack with a vertical interchain distance of 4.4 Å, with an interchain seperation of 5.8 Å due to sidechains. Other copolymers of F8T2, poly[2,7-(9,9-dihexylfluorene)-alt-bithiophene] F6T2, and SC005 were found to be good candidates for GIWAXS study. Thermally treated PFO was very well indexed, with clear changes seen due to vapour exposure in situ. Chapter 1 discusses vital, general concepts used to describe electro-conductive polymers, as well as a thorough review of the background of organic semiconductor characterisation. Further relevant details are covered in each results chapter. Chapter 2 describes and defines the polymer samples and processing methods used throughout this thesis. The experimental techniques used are described in detail, as are the polymers involved and sample fabrication methods. In Chapter 3 small-angle neutron scattering undertaken at RAL is discussed, with results shown from F8T2 in various solvents, as well as studies of F8BT and PFO. Chapter 4 covers both the results of multi-angle light scattering on F8T2 and other polyfluorenes in a variety of solvents. The effect of the passage of time of dissolved polymer solutions is investigated, along with size and molecular weight characteristics in different solvents. SAXS results from F8T2 solutions are also briefly discussed. In Chapter 5 a broad variety of spectroscopic investigations of F8T2 are discussed, both in solution and as thin-films. The effects of thermal treatments on thin-films are studied, including DSC results and the consequences on the electrical properties of thermal and solvent annealing on field-effect transistors. In Chapter 6 the results from a GIWAXS study on aligned and non-aligned thin-films of PFO and three co-polymers are shown. Unit cell size parameters are determined, and the effect of exposing PFO thin-films to solvent vapour is studied.

Granular materials can consume large amounts of kinetic energy through deformation of their inherently complex meso-structure. Little is understood about what effect the geometrical variations such as particle size and shape have on their response to shock loading. With this in mind, this thesis attempts to measure the effects that particle size has on the compaction curve of brittle granular materials. Three monodisperse and one polydisperse samples of soda-lime glass microspheres were chosen for this study. A quartz sand was also investigated to determine if the microspheres were a sufficient analogue whilst additionally introducing morphological differences. Beds of these materials were subjected to quasi-static loading therefore measuring the stress-density compaction response. Post-loading analysis of the samples revealed a strong dependence on particle size and morphology. The macro-scale shock compaction responses of the granular samples were measured using plate impact techniques and piezo-resistive stress gauge diagnostics. Similar trends were observed in the quasi-static loading behaviour. Smaller particles appeared to have higher strength in the macroscale which, due to scaling effects at boundaries, contradicted trends from meso-scopic fracture tests. It was concluded that beds composed of smaller, spherical particles show the greatest resistance to shock and quasi-static compaction. For convenience, a single Hugoniot relationship is typically used to represent the shock response of granular materials. This assumption was challenged in this thesis. Identical incident shock loading produced different loading states with a changing bed thickness. The terminal loading states varied considerably with bed thickness in the samples of larger microspheres. The majority of this variation was due to dispersion within the initial portion of the wave. The study concludes that particle size has a significant effect on the shock response of granular materials if the particle geometry is suited to inducing a total-fracture particle densification mechanism.

An experimental investigation of collisions between supersonic plasma jets with metal foils and head-on collisions of two jets will be presented. The jets are produced by ablation of thin aluminium foils driven by 1.4MA, 250ns current pulse in a radial foil Z-pinch configuration. The jets propagate with velocity of 50-100km/s, showing a high degree of collimation (opening angle 2 [degrees] to 5 [degrees]) and are radiatively cooled (cooling time << hydrodynamic times). Collisions of the jets with foils, as well as inter-jet collisions, create a system of strong shocks both in the central dense part of the jet and in the lower density halo plasma which surrounds the jet and moves with the same speed. The formed shock features are sustained for 300ns, and are diagnosed with laser interferometry, optical and XUV imaging, and Thomson scattering diagnostics. Interpretation of the results indicates that dynamically significant magnetic fields are present in the system, balancing the ram pressure of the flow and supporting extended stationary shock structures. The results are relevant to the studies of astrophysical phenomena in the laboratory, in particular internal shocks in jets from young stars, accretion shocks, and for the understanding of magnetised high energy density plasma flows.

This thesis presents the results of a study into the design and characterisation of optically pumped organic semiconductor lasers for hybrid organic/inorganic applications. The study involves a detailed investigation into a broad range of materials including conjugated polymers and monodisperse oligomer molecules with emissions spanning the visible spectrum. To make viable electrically pumped organic semiconductor lasers using a hybrid system, it is essential that their lasing thresholds are reduced as far as possible. The optical properties of two main families of oligomer and one conjugated polymer are investigated and the effect of their conjugation on stimulated emission discussed. Gain measurements based on one oligomer and the polymer are performed to assess the reliability of current gain extraction techniques and a new variant of an existing gain extraction experiment introduced. A second oligomer was optically- pumped to illustrate the phenomenon of random lasers and explicitly show how modes can develop in different ways depending on how their optical pump source is varied. Lasers based on the green-emitting polymer were optically-pumped and wavelength tuning of their emission was demonstrated by altering both the grating duty cycle and the polymer film thickness allowing us to tune the wavelength to a region with a lower lasing threshold. Finally, first imaged optical pump experiments using micro-LED arrays were performed. Micro-LED emission was imaged to replicate optimum pump conditions.

The Z-accelerator at Sandia National Laboratories (SNL), is a high-current pulsed power machine used to drive a range of high energy density physics (HEDP) experiments [1]. To achieve peak currents of >20MA, in a rise time of ~100ns, the current is split over four levels of transmission line, before being added in parallel in a double-post-hole convolute (DPHC) and delivered to the load through a single inner magnetically insulated transmission line (MITL). The electric field on the cathode electrode, >107Vm-1, drives the desorption and ionisation of neutral contaminants to form a plasma from which electrons are emitted into the anode-cathode (a-k) gap. The current addition path in the DPHC forms magnetic 'null' regions, across which electrons are lost to the anode, shunting current from the inner MITL and load. In experiment, current losses of >10% have been measured within the convolute; this reduces the power delivered to the load, negatively impacting the load performance, as well as complicating the prediction of the Poynting flux used to drive detailed magneto-hydrodynamic (MHD) simulations [2, 3]. In this thesis we develop 3-dimensional (3D) Particle-in-Cell (PIC) and hybrid fluid-PIC computer models to simulate the plasma evolution in the DPHC and inner MITL. The expected experimental current loss at peak current was matched in simulations where Hydrogen plasma was injected from the cathode elec- trode at a rate of 0.0075mlns-1 (1ml=1015cm-2), with an initial temperature of 3eV. The simulated current loss was driven by plasma penetrating the downstream side of the anode posts, reducing the effective a-k gap spacing and enhancing electron losses to the anode. The current loss at early time (<10MA), was matched in simulations where space-charge-limited (SCL) electron emission was allowed directly from the cathode; to match the loss over the entire current pulse, a delay model is motivated. Here, plasma injection was delayed after the start of SCL emission, based on realistic plasma expansion velocities of ~3cmμs-1. The PIC model, which was necessary to accurately simulate the kinetic behaviour of the lower density plasma and charged particle sheaths, was computationally intensive such that the spatial resolutions achieved in the 3D simulations were relatively poor. With the aim of reducing the computational overhead, allowing finer spatial resolutions to be accessed, we investigate the applicability of hybrid techniques to simulating the cathode plasma in the convolute. Our PIC model was both implemented in the resistive MHD code, Gorgon, where part of the plasma was modelled in the single fluid approximation, and extended to include an inertial two-fluid description of the plasma. The hybrid models were applied to the DPHC simulations, the results from which are used to motivate a three component model; here, the densest part of the convolute plasma is modelled using the single fluid MHD approximation, transitioning to a fully kinetic PIC description of the lower density plasma and charged particle sheaths, linked by a two-fluid description.