This thesis employs molecular quantum electrodynamical theory to analyse the interactions between light and matter for four main processes. The first to be considered is Raman scattering, where the effect of the electrodynamic environment for the centre of spectroscopic interest is considered. This is achieved by engaging a retarded dipole-dipole interaction between the centre and a neighbouring molecule. Physically, this is explained by a virtual photon between the pair of centres. The results predict characteristic new lines on the Raman spectrum, for the species, arising from the engagement of selection rules not limited to those of a two-photon process. The second process, is hyper-Rayleigh scattering, in which a single multipolar coupling is considered in place of the more familiar electric dipole. This modification to the theory subverts the standard selection rules for a three-photon process, which can allow for second-harmonic emission to be generated by a centre of high symmetry, such as a centrosymmetric molecule. The third process offers another means of subverting the standard selection rules for second-harmonic generation, namely by incorporating six-wave mixing. First, the general mechanism is developed and pertinent results are expressed for the widely-deployed depolarisation ratio. Following this, structured light is considered and by utilising orbital angular momentum (OAM) conservation arguments, the pair of harmonic photons are found to display quantum entanglement. Moreover, the relative magnitudes of the possible emissions are found to correspond directly to that of the binomial coefficients. This thesis concludes with a family of novel structures capable of directly generating OAM light. This work exploits symmetry characteristics for a delocalised excitonic structure that can allow for a more complex multipolar emission than that of any isolated centres. The phase of the exciton is shown to display an azimuthal phase progression, a vortex feature most commonly associated with Laguerre-Gaussian light.

No description available.

Ferroelectric materials have established themselves as indispensable in key applications such as piezoelectric transducers and energy storage devices. While the use of ferroelectrics in these fields dates back more than 50 years, little progress has been made to extend applications of ferroelectrics into new fields. To a large extend the observed slow progress is not caused by a lack of potential applications, but to by the inherent complexity associated with a structural phase transition, combined with strong coupling of polarisation, strain and temperature, and the strong modification of the phenomena by material defects. This thesis takes a look at prospective applications in energy storage for pulse power applications, solid state cooling and non-volatile random access memory and identifies key issues that need to be resolved. The thesis delivers time-domain based approaches to determine ferroelectric switching behaviour of bulk materials and thin films down to sub-ns time scales. The approach permitted study of how information written to a ferroelectric memory decays as a result of multiple non-destructive read operations. Furthermore simultaneous direct measurements of temperature and ferroelectric switching established a direct link between the retarded switching phenomenon observed in ferroelectrics and temperature changes brought by the electrocaloric effect. By comparison with analytical models and numerical simulation a large localised temperature change on the scale of individual domains is postulated. It implies a much larger coupling between switching and local temperature than has been previously considered. In extension of the model the frequency dependence of polarisation fatigue under bipolar conditions is explained by the occurrence of large temperature gradients in the material.

One way countries around the world are increasing the proportion of renewable fuels for electricity generation is to convert coal fired power stations to co-fired (biomass/coal fired) or converting coal fired power stations to burn only biomass fuels. This however has led to measurement challenges monitoring the complex multi-phase flow of the pulverised fuels entering the furnace due to the complex shape of biomass particles. To meet these measurement challenges a novel electrostatic sensor array and piezoelectric sensor array have been developed. The electrostatic sensor array consists of an array of electrostatic electrode pairs that span the diameter of the pipe. Consequently the electrostatic sensor array is capable of determining the particle velocity and concentration profiles as well as detecting specific flow regimes such as roping. The piezoelectric impact sensor array consists of an array of piezoelectric individual impact sensors that span the diameter of the pipe. The piezoelectric sensor array is capable of determining the particle concentration and size distribution profiles. Experimentation has been carried out on laboratory scale pneumatic conveying systems using a variety of materials such as coal, biomass, coal/biomass blends and plastic shot. Experiments using the electrostatic sensor array have shown that it is indeed capable of determining the particle velocity and concentration profiles in both dilute developed and undeveloped flows. Analysis of the standard deviation of the velocity profiles as well as the correlation coefficient profiles have indicated that parts of the pipe cross section have a more stable flow compared to others. Data obtained through on-line and off-line experimentation using the piezoelectric sensor array has shown that through selective frequency filtering of the impact signal particle size can be determined assuming the particle velocity and the mechanical properties of the conveyed pulverised materials are known. By using a threshold voltage to determine when an impact has occurred on each element of the piezoelectric sensor array the particle concentration profile has been determined. The concentration profiles measured by the piezoelectric sensor array were verified using the electrostatic sensor array.

No description available.

This thesis reports on the design, construction and implementation of a moving-trap Zeeman decelerator which uses 3D magnetic traps to guide and decelerate paramagnetic particles from a supersonic beam. The decelera- tor will ultimately be used in a quantum simulator device, where a system of strongly-interacting quantum particles, where their interactions can be tuned, is formed using polar molecules. The decelerator is a potential load- ing stage for a molecular magneto-optical trap (MOT), where high densities of molecules can be cooled down to the sub milliKelvin temperatures. The molecules can then be further cooled sympathetically with laser-cooled atoms into the microKelvin regime, allowing their trapping in an optical lattice. This thesis mainly describes the design, construction, and implementation of the decelerator. The technicalities of the beam machine, the decelerator coils, and the driving electronics are described in detail. A homebuilt fast- ionisation gauge (FIG) detector allows the characterisation and optimisation of pulsed beams produced by a cryogenically cooled pulsed valve. We produce supersonic beams of metastable argon atoms (Ar*), made by the electronic excitation of the atoms using a homebuilt pulsed electric discharge assembly, stabilised by a hot filament. This enables the discharge to operate more stably at voltages as low as 400 V and at discharge pulse durations as short as 20 μs, which combine to create a cold packet of Ar* atoms. An optimised slow beam of Ar* with a measured velocity of 306±8 m/s and a translational temperature of 4 K is formed. The decelerator has a detection chamber that allows different means of detecting atoms and molecules: michrochannel- plate (MCP), single-pass laser-induced fluorescence (LIF), cavity-enhanced laser-induced fluorescence (CELIF), and a quadrupole mass spectrometer (QMS) with the ability to photo-ionise. We demonstrate that the CELIF detection technique, which combines a cavity ring-down (CRD) setup and a LIF setup, using a standard UV pulsed dye laser, can be an effective detection method for molecules with fluorescence lifetimes on the order of hundreds of nanoseconds. Using CELIF, we measure the absolute density of SD radicals in a pulsed supersonic jet down to the limit-of-detection of 105 cm−3. In the 0.002 cm3 probe volume, this corresponds to ca. 200 molecules, and the quantum-noise-limited absorption coefficient is αmin = 7.9 × 10−11 cm−1 in 200 s of acquisition time. The biggest advantage of this type of decelerator is in the fact that the para- magnetic atoms are confined in all three dimensions continuously throughout the length of the decelerator. We present our proof-of-principle experimen- tal results where we demonstrate, using a single deceleration stage with a length of 123mm, the manipulation of Ar* atoms in the 3P2 metastable state using 3D magnetic fields, and using continuously modulated magnetic fields which produce a travelling potential. It is successfully shown that the Ar* signal intensity is greatly increased, nearly by a factor two by using a 290mm long quadrupole magnetic guide which provides transverse confine- ment of the atoms. With the addition of the decelerator coils, magnetic confinement along the longitudinal beam axis is achieved, forming 3D-traps. The 3D-guiding of the low-field-seeking states of 3P2 state of Ar* is carried out at constant velocities ranging from 320 m/s up to 400 m/s along a single decelerator module. The longitudinal temperatures were ∼500mK. While attempting the deceleration of the traps, though no real deceleration was observed for this short decelerator length, the fields did show a manipulation effect. This gives us the confidence that with a longer decelerator, we will see very prominent bunching. The work presented in this thesis is a major step forward in the demon- stration of an efficient Zeeman decelerator which can bring large numbers of molecules to low velocities. It will be an ideal loading step for a molecular MOT where high densities of molecules can be cooled down to the sub mil- liKelvin temperatures. A beam of CaF molecules from a buffer gas source, starting at an initial velocity of 150m/s, could be decelerate to a standstill using a 1 m long decelerator. This would only require eight decelerator mod- ules. Aside from its use as a loading step for a molecular MOT, for building a quantum simulator device, this new type of decelerator can be used for various applications. One of these is in cold chemistry. The methyl radi- cal is one of the most important and fundamental intermediates in chemical reactions. With regards to magnetic deceleration, the methyl radical has a similar magnetic-moment-to-mass ratio to argon, so with an appropriate choice of a seed gas we should be able reproduce the results we have so far with argon and demonstrate deceleration of our first molecule.

This thesis presents work in the area of mesh generation for large scale and complex computational simulation. The work covers two areas of great interest within the field of mesh generation; anisotropic mesh generation and parallel large scale mesh generation. Examples of anisotropic Delaunay mesh generation are presented with application to fluid dynamics and computational electromagnetic scattering simulations. Results are shown with reference to simulation accuracy and computational efficiency. Research into parallel mesh generation is presented and a method of parallel Delaunay mesh generation suitable for use on distributed and shared memory parallel computers is described. Results are shown with reference to computational efficiency, memory usage and finale mesh quality. Examples of meshes generated in parallel are shown for both computational fluid dynamics simulations on simple aeronautical geometries to full aircraft and computational electromagnetic scattering simulations on full aircraft. The meshes range in size from a few thousand tetrahedral elements to a mesh for a computational electromagnetic simulation containing approximately one billion tetrahedral elements.

This study explores and describes the interface properties of various high-k materials deposited on the Ge substrate. Deposition/ growth of these material films has been achieved using multiple techniques such as atomic layer deposition (ALD), molecular beam epitaxy and thermal growth. High dielectrics (k) materials based on metal (4d and 5d) such as Y2O3, ZrO2, HfO2, Ta2O5, and from the lanthanide series, La2O3 and Tm2O3 were deposited on germanium and characterized to find out interface quality and band offset between Ge substrate and the oxides. Additionally, Al2O3 was considered, both as an interface barrier layer and as a high –k layer. Material and interface characterization was done using atomic force microscopy (AFM), capacitance-voltage (C-V), current-voltage (I-V), Variable Angle Spectral Ellipsometry (VASE), X-Ray diffraction (XRD), and X-ray photoelectron Spectroscopy (XPS) including the post growth micro-structural and compositional analysis using high resolution transmission electron microscope (HRTEM). Various physical and electrical studies were performed based on the above mentioned characterization techniques. The high-k material/Ge interface has been studied systematically using XPS and VASE characterization, considering the effects of temperature and thickness during deposition. Two germanium interface engineering methods were developed and discussed: (i) germanate formation using La2O3 and Y2O3, and (ii) using Al2O3 and Tm2O3 as barrier layers, and S passivation for Ta2O5 films. Based on the physical and electrical characterization carried out in this work, Ge interface engineering using rare-earth material inclusion happens to be a promising route to fabricate Ge CMOS devices with high performance. This statement is supported by the fact that these high-k materials provide a defect free interface and reduce the possibility of unstable GeOx formation at the interface, hence improving the interface quality. Post deposition annealing effects on Tm2O3 has been analysed using XPS and VUV-VASE. The stack prepared for the purpose was of EOT (equivalent oxide thickness) ~5 nm Tm2O3/epi-Ge/Si. Study with Tm2O3 presented 3 main findings, i) Valence band offset estimation using Kraut’s method was consistent within the experimental error, and found to be 3.05 ± 0.2 eV, ii) the VBO for thermal GeO2/Ge stack was found to be matching with the recently reported value by Toriumi’s group. The value of conduction band offset was estimated to be higher than 1 eV, indicating the favorability of GeO2 as a passivation layer for Ge, iii) the reactivity of Tm2O3 on Ge was found to be even lower than that of Si, indicating the possibility of a desirable interface. This thesis further explores the use of hafnia and alumina with Sulphur (S) passivated and un-passivated Ge samples. For this purpose HfO2/Ge and Al2O3/Ge stacks were prepared using ALD technique. It was observed that using H2O with O plasma, reduces the purge time and gives low carbon incorporation from metals. Hence O plasma and H2O were used as oxidizing agents and the interface properties were studied systematically, which is a new contribution by this work. Further the effects of adding TiO2 contents to HfO2 layer on interface properties were studied, using Al2O3 (0.3 nm) as surface passivation. In this work the achieved EOT of HfO2 with the controlled introduction of TiO2 was ~ 1.3 nm, giving a leakage current as low as10-7 A/cm-2 at ±1 V, which is in the acceptable limits. Finally, Ta2O5 films were characterized on Ge for band line up with respect to Ge. The deposition of the films was done by ALD technique at 250 °C. The analysis was done on both S passivated and un-passivated samples. The band line up parameters were estimated using XPS and it was observed that the valence band offset for S passivated sample was 2.67 eV whereas it was 2.84 eV for un-passivated Ge sample. Ta2O5 reflected a band gap of 4.44 eV (estimated from the energy loss spectrum of O1 s core level) for a 20 nm thick film deposited by ALD. Hence this thesis will cover the high-k materials and their application as a gate oxide and also the passivation layer for Ge substrates for Ge CMOS devices.

This thesis consists of two parts. In part I we consider a discrepancy in the derivation of the electromagnetic self force for a point charge. The self force is given by the Abraham-von Laue vector, which consists of the radiation reaction term proportional to the 4-acceleration, and the Schott term proportional to the 4-jerk. In the point charge framework the self force can be defined as an integral of the Lienard-Wiechert stress 3-forms over a suitably defined worldtube. In order to define such a worldtube it is necessary to identify a map which associates a unique point along the worldline of the source with every field point of the worldline. One choice of map is the Dirac time, which gives rise to a spacelike displacement vector field and a Dirac tube with spacelike caps. Another choice is the retarded time, which gives rise to a null displacement vector field and a Bhabha tube with null caps. In previous calculations which use the Dirac time the integration yields the complete self force, however in previous calculations which use the retarded time the integration produces only the radiation reaction term and the Schott term is absent. We show in this thesis that the Schott term may be obtained using a null displacement vector providing certain conditions are realized. Part II comprises an investigation into a problem in accelerator physics. In a high energy accelerator the cross-section of the beampipe is not continuous and there exist geometric discontinuities such as collimators and cavities. When a relativistic bunch of particles passes such a discontinuity the field generated by a leading charge can interact with the wall and consequently affect the motion of trailing charges. The fields acting on the trailing charges are known as (geometric) wakefields. We model a bunch of particles as a one dimensional continuum of point charges and by calculating the accumulated Lienard-Wiechert fields we address the possibility of reducing wakefields at a collimator interface by altering the path of the beam prior to collimation. This approach is facilitated by the highly relativistic regime in which lepton accelerators operate, where the Coulomb field given from the Lienard-Wiechert potential is highly collimated in the direction of motion. It will be seen that the potential reduction depends upon the ratio of the bunch length to the width of the collimator aperture as well as the relativistic factor and path of the beam. Given that the aperture of the collimator is generally on the order of millimetres we will see that for very short bunches, on the order of hundredths of a picosecond, a significant reduction is achieved.

This thesis considers aspects of nonlinear electromagnetism and the eects of spin under the in uence of extreme elds. Born-Infeld-like theories are studied in the context of possible slow light experiments. Maximum amplitude plasma waves are considered as a possible testing ground for nonlinear electrodynamics with regards to electron energy gain. Finally the eects of the coupling between the electromagnetic eld and the spin of a relativistic classical particle are considered via a new derivation of the relativistic Stern-Gerlach and Thomas- Bargmann-Michel-Telegdi equations. These equations are then paired with the Nakano-Tulczyjew condition and, as the Stern-Gerlach-type terms in the equations of motion are most prominent in a eld with a high eld gradient, the impact of spin is investigated in the context of a maximum amplitude plasma wave.