Introduction: This thesis is an account of the design, construction and testing of a particle accelerator which represents a minor variation on the now-familiar theme of the tandem van de Graaff. The machine has been very briefly described elsewhere (Naylor 1968).

This thesis investigates the properties of an atomic system exhibiting a giant Kerr nonlinearity. The atomic energy level scheme involves four energy levels. A three level A subsystem in the atom exhibits the effect of electromagnetically induced transparency (EIT), reducing the spontaneous emission noise. The fourth level leads to an ac-Stark shift of the ground state, which in turn leads to a giant, noiseless Kerr nonlinearity. Two different environments are explored. First, a system comprising of large number of atoms in an optical cavity is analysed. Detailed aspects of noise reduction in this system are investigated. In particular, strong squeezing in the quadrature in phase with the field driving the cavity mode is found, if the effective coupling of light to the atoms is strong. However, the linewidth of the predicted squeezing is found to be very narrow. This is attributed to a very steep linear susceptibility of the atomic medium. Since the widening of the squeezing window is possible only for weaker effective coupling, in turn reducing the squeezing level, a different environment is proposed. This involves a single four level atom, strongly coupled to the cavity mode. In such a strongly coupled system, the most appropriate approach is found to be that formulated in terms of polaritons – composite excitations of the 'atom-cavity molecule'. Adopting the polariton approach, nonclassical correlations in the field leaving the cavity are investigated. Strong photon antibunching is found and the effect of photon blockade predicted and described. The photon blockade effect can also be found in a system comprised of a two level atom coupled to the cavity mode, if the external driving is tuned to one of the vacuum Rabi resonances. A comparison between the two schemes is performed, and it is found that the four level scheme exhibits much better photon blockade. The reason for this is quantum interference between secondary transitions in the dressed states picture. Destructive interference cancels the transitions that would otherwise introduce a second photon into the system, hence producing a more robust photon blockade. All of these results are valid in the regime where external driving is weak. If the external driving strength is increased, the photon statistics (as measured by the zero-delay second order correlation function) changes from strong antibunching to strong bunching, over a relatively narrow range of driving strengths. The occurrence of this change can again be attributed to quantum interference. It is shown that the interference effect prevents the excitation of the composite system by a second photon, but not excitation by a two-photon transition (following the first excitation). Therefore, the third excitation manifold is excited, which then decays back to the first manifold in a two photon cascade. This two photon cascade is the source of correlated photon pairs causing an increase in the second order correlation function. The dynamics of forward scattering of light is presented, and nonclassical behaviour of the delay dependence of correlation function ('overshoots' and 'undershoots') is discussed. For the analytical treatment of this system, a method based on the polariton approach is devised, which includes the treatment of driving and damping. It is shown that this method is ideally suited to the analysis of strongly coupled systems, where only a few photons contribute to the dynamics.

The proton polarization in the 3He(d,p)4He reaction induced by unpolarized deuterons has been measured at deuteron lab. energies of 2.0, 2.8, 3.9 and 6.0MeV for 20 angles between 0° and 150° (c.m.). Statistical uncertainties are typically ± 0.01. The measurements were made with a proton polarimeter in which the left-right asymmetry of scattering at 60° (lab.) in 4He is determined. The polarimeter employs "venetian-blind" collimation of the protons by conical vanes and 75 cm2 plastic scintillator detectors. Four detectors are included for use in polarization transfer experiments. For 10.5 MeV protons and a helium pressure of 250 p.s.i. the target thickness is 3 MeV and the efficiency per detector per unpolarized proton incident is 10-4. For each polarimeter detector a triple coincidence with a 15 ns resolving time was required with two scintillator transmission detectors preceding the polarimeter. Spectra of random coincidences were accumulated simultaneously and subtracted. Asymmetries resulting from polarimeter-target misalignment and other geometrical effects are discussed. All results quoted are geometric means of pairs of measurements for 180° rotation of the polarimeter and are also arithmetic means of such measurements to left and right of the 3He target. The absolute analyzing power is estimated by computer simulation of trajectories to be -0.638 ± 0.020 for protons entering at 10.3 MeV. The product of polarization and cross section is fitted to an expansion of first-order associated Legendre polynomials using these results and earlier measurements. Only four terms are required except at 6.0MeV where a fifth is necessary. The energy dependence of these coefficients suggests resonances in 5Li at deuteron energies of 60MeV (odd coefficients) and 7.5 MeV (even coefficients) in agreement with results for the polarized-beam analyzing powers(1). Comparison of the results with vector-polarized-beam (1) and polarized-target(2) analyzing powers shows no evidence for the postulated simple relations(3) based on DWBA cal calculations. Comparison of the results with recent measurements of the neutron polarization in the mirror reaction(4) shows no significant differences. The theory of angular correlations in charged particle reactions is developed and used to calculate outgoing nucleon polarizations. Expressions are given for polarization transfer coefficients. These coefficients are evaluated in terms of the T-matrix elements for the interference of various channels with the dominant S-wave, JΠ = 3+/2 channel in 3He(d,p)4He at the 0.43 MeV resonance. Two experiments to measure combinations of these elements are discussed. (1) Gruebler, W. et al., 1971, Nucl. Phys. Al76, 631 (2) Leemann, Ch., W. Gruebler et al., 1971, in Polarization Phenomena in Nuclear Reactions (University of Wisconsin Press), p. 548 (3) Tanifuji,M. and K. Yazaki, 1968, Prog. Theor. Phys. 40, 1023 (4) Mutchler, G.S., W.B. Broste and J.E. Simmons, 1971, Phys. Rev. C3, 1031

It is well known that the ionosphere is not a uniform and homogeneous medium. For many years studies have been made of ionospheric irregularities down to sizes of less than 1 km; some of which are associated with periodic motion caused by gravity waves, others, with turbulence phenomena. The effect of these ionospheric disturbances on conventional high-frequency radio communication links is an important study, and extends back to almost the beginning of ionospheric investigations. It is now recognised, in fact, that the Ionosphere behaves as an irregular reflector which imposes fluctuations on initially plane wavefronts as they, emerge from the medium.

Introduction: This thesis is an account of the design, construction and testing of a particle accelerator which represents a minor variation on the now-familiar theme of the tandem van de Graaff. The machine has been very briefly described elsewhere (Naylor 1968).

This thesis investigates the properties of an atomic system exhibiting a giant Kerr nonlinearity. The atomic energy level scheme involves four energy levels. A three level A subsystem in the atom exhibits the effect of electromagnetically induced transparency (EIT), reducing the spontaneous emission noise. The fourth level leads to an ac-Stark shift of the ground state, which in turn leads to a giant, noiseless Kerr nonlinearity. Two different environments are explored. First, a system comprising of large number of atoms in an optical cavity is analysed. Detailed aspects of noise reduction in this system are investigated. In particular, strong squeezing in the quadrature in phase with the field driving the cavity mode is found, if the effective coupling of light to the atoms is strong. However, the linewidth of the predicted squeezing is found to be very narrow. This is attributed to a very steep linear susceptibility of the atomic medium. Since the widening of the squeezing window is possible only for weaker effective coupling, in turn reducing the squeezing level, a different environment is proposed. This involves a single four level atom, strongly coupled to the cavity mode. In such a strongly coupled system, the most appropriate approach is found to be that formulated in terms of polaritons – composite excitations of the 'atom-cavity molecule'. Adopting the polariton approach, nonclassical correlations in the field leaving the cavity are investigated. Strong photon antibunching is found and the effect of photon blockade predicted and described. The photon blockade effect can also be found in a system comprised of a two level atom coupled to the cavity mode, if the external driving is tuned to one of the vacuum Rabi resonances. A comparison between the two schemes is performed, and it is found that the four level scheme exhibits much better photon blockade. The reason for this is quantum interference between secondary transitions in the dressed states picture. Destructive interference cancels the transitions that would otherwise introduce a second photon into the system, hence producing a more robust photon blockade. All of these results are valid in the regime where external driving is weak. If the external driving strength is increased, the photon statistics (as measured by the zero-delay second order correlation function) changes from strong antibunching to strong bunching, over a relatively narrow range of driving strengths. The occurrence of this change can again be attributed to quantum interference. It is shown that the interference effect prevents the excitation of the composite system by a second photon, but not excitation by a two-photon transition (following the first excitation). Therefore, the third excitation manifold is excited, which then decays back to the first manifold in a two photon cascade. This two photon cascade is the source of correlated photon pairs causing an increase in the second order correlation function. The dynamics of forward scattering of light is presented, and nonclassical behaviour of the delay dependence of correlation function ('overshoots' and 'undershoots') is discussed. For the analytical treatment of this system, a method based on the polariton approach is devised, which includes the treatment of driving and damping. It is shown that this method is ideally suited to the analysis of strongly coupled systems, where only a few photons contribute to the dynamics.

CD containing a copy of the thesis, software and extra documentation is held with print copy. / Nuclear Magnetic Resonance (NMR) is a relatively complex technique and normally requires expensive equipment. However, with advances in computing, electronics and permanent magnet technologies, NMR is becoming more feasible as a non-invasive tool for industry. The strength of NMR is its ability to probe at the molecular level and hence gain information about molecular structure, organisation, abundance and orientation. This thesis describes the development of an instrumentation platform technology that is compact and therefore portable. It has been produced to aid the development of NMR based tools or sensors for research and industry and will lead to a series of low cost, portable NMR systems for the non-destructive testing of materials such as polymer composites, rubber, timber, bricks and concrete. The instrumentation is largely electronics based and consists of a series of modules that can be interconnected to produce a solution. The first of two main modules is called the system core. What is common to all NMR applications is the generation of precisely timed signals, the capturing of signals and the processing/display of data. This has been implemented by developing a general purpose Digital Signal Processor (DSP) based instrumentation and control module that uses a Universal Serial Bus interface to communicate with a host computer. A graphical user interface is provided by an application running under Windows® XP. The second main module is a radio frequency transceiver that has been developed using digital receiver technology. The signals, after some amplification, are digitized with a 14-bit, 62.5MH.z analogue to digital converter. The sampled signal is then mixed digitally with synthesized sine and cosine functions to generate lower frequency quadrature outputs which are then digitally filtered and decimated before being passed onto the DSP for further processing and storage. A direct digital synthesizer with an analogue output is used to generate any required excitation signals. All synthesizers have phase and frequency hopping capabilities and are phase locked to each other and the DSP. The system was designed to interface to a range of NMR probes. The type of probe is determined by the intended application and each probe has specific requirements such as the type of radio frequency power amplifier, duplexer and preamplifier needed. This results in a number of instrumentation variations and a modular instrument enclosure was used to cater for these variations. The instrument was first configured for an NMR probe called the NMR-MOUSE. Tests were performed with this probe to verify the correct operation and performance of the instrument. The instrument was then reconfigured for a new probe called the NMR-MOLE and further testing was performed. This probe was still undergoing development and had not been previously tested. Finally, a dedicated compact instrument measuring 360 x 240 x 55 mm and weighing 3.6 kg was developed for the NMR-MOUSE probe.

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In this thesis we present three different aspects of spin and spin-dependent transport properties in novel materials. Spurred by the prospect of spintronic devices, which use the spin degree of freedom of electrons instead of, or combined with, the charge degree of freedom, we analyse the spin properties of quantum wires, organic conducting polymers and sheets of graphene. First, we examine a quantum wire that is embedded in a two dimensional electron gas. We consider the Rashba spin-orbit coupling, and include the effect of interaction between the conduction electrons. We construct an analytically solvable low-energy theory for the wire, and explore the interaction between two magnetic impurities in the wire. We find that both the spin-orbit coupling and the electron-electron interaction have an effect on the magnetic interaction, and find the magnetic interaction to be tunable by an electric field. Next, we study an organic conducting polymer, which is contacted to magnetised ferromagnetic leads. In semiconducting organic polymers the current is transported by spinful polarons and spinless bipolarons. We simulate the transport through the system, including both types of charge carriers, and find the current to be insensitive to the presence of bipolarons. In addition, we find the bipolaron density to depend on the relative magnetisation of the ferromagnetic contacts. This constitutes an optical way of measuring the spin accumulation in conducting polymers. Finally, we investigate the optical conductivity of graphene. Symmetry arguments indicate the existence of two kinds of spin-orbit coupling in the two dimensional lattice, but there is no consensus about the actual strength of these couplings. We calculated the microwave optical conductivity of graphene including both possible spin-orbit interactions. We find the low frequency dependence of the optical conductivity to have a unique imprint of the spin-orbit couplings. This opens a possibility to experimentally determine both couplings separately.