This thesis reports on experimental and numerical investigations of the collective response of electrons and ions to the interaction of ultra-intense (10²⁰ Wcm⁻²) laser with ultra-thin (nanometre scale) foils undergoing expansion and relativistic induced transparency. The onset of this relativistic mechanism is also characterised and studied in detail. This new insight into relativistic transparency is an important step towards optical control of charged particle dynamics in laser driven dense plasma sources and in its potential applications; including ion and radiation source development. The experimental and numerical investigations exploring the onset and the underpinning physics of the relativistic transparency have focused on its dependency on the target areal density, laser intensity and polarisation. The results show a maximum laser transmission for the thinnest targets investigated, which decreases exponentially with increasing target thickness. The same trend is obtained for linearly and circularly polarised laser light. However, for a given target thickness, the linear polarisation case exhibits a significantly higher transmission fraction, with respect to the circular polarisation case, due to additional electron heating and expansion. Moreover, it is shown that for the thinnest targets, once they become relativistically transparent, the transmitted light fraction increases rapidly as the laser intensity increases. The increasing rate is shown to be more pronounced in the thinnest targets investigated. This is diagnosed by measurement of both the fundamental and second harmonic wavelengths. An alternative approach, based on numerical measurement of the critical surface velocity, asa function of time, for various target thickness, and comparing it with corresponding analytical models is also proposed. The onset of relativistic induced transparency is found to curb the radiation pressure effciency of the charged particle acceleration mechanism. Investigations of the collective response of electrons in ultra-thin foils undergoing transparency show that a 'relativistic plasma aperture' is generated by intense laser light in this regime, resulting in the fundamental optical phenomenon of diffraction. It is numerically found that the plasma electrons collectively respond to the resulting laser near-field diffraction pattern, resulting in a beam of energetic electrons with spatial-intensity distribution, related to this diffraction structure, which can be controlled by variation of the laser pulse parameters,and in turn the onset of relativistic transparency. Additionally, it is shown that static electron beam, and induced magnetic field, structures can be made to rotate at fixed or variable angular frequencies depending on the degree of ellipticity in the laser polarisation. The predicted electron beam distributions using the 'relativistic plasma aperture' concept are verified experimentally. Understanding the collective response of plasma electrons to transparency and how this affects the subsequent acceleration of ions is highly important to the interpretation of experiments exploring ion acceleration employing ultra-thin foils. Control of this collective electron motion, and thus the resultant electrostatic fields, could enable unprecedented control over the spatial-intensity distribution of laser-driven ion acceleration. The results presented in this thesis show that in ultra-thin foils undergoing transparency the electron dynamics are mapped onto the beam of protons accelerated via strong charge-separation-induced electrostatic fields. It is demonstrated that the degree of ellipticity of the laser polarisation defines the spatial-intensity distribution of the proton beam profile and can therefore be used to control it. This demonstration of dynamic optical control of structures within the spatial-intensity distribution of the beam of laser accelerated ions opens a new route to optimising the properties of these promising ion sources.

Flame Assisted Chemical Vapour Deposition (FACVD) is an inexpensive and robust method of producing a wide range of metal and metal-oxide films. The work presented shows this method's ability to deposit durable, semi-transparent anti- microbial films which show large reductions in the number of colony forming units (99% in just 15 minutes, 100% in 60 minutes) of Escherichia Coli and Staphylococcus Aureus using just 55 ^mol silver per m2 of substrate. A further focus of this work is on the production of transparent conducting oxides. A series of experiments based on complex factorial design is presented which allows for the optimum properties of a conducting, transparent film of SnC>2 to be presented. Intrinsically doped indium oxide films with sheet resistance 250 Q per square, neodymium oxide films and zinc oxide films with preferential growth orientation have also been deposited. The ineffectiveness of FACVD to extrinsically dope metal oxide films was studied and the conclusion was reached that the gas-phase driven nature of the chemical reactions allows for preferential nucleation of one oxide over another. Finally, work is presented on the flow considerations of the FACVD process. A method is shown to achieve the optimum flow conditions for each particular precursor used and previous workers' theories are tested on the gas-phase breakdown of particulates and shown to be inadequate with a new theory of gas-phase flow being argued.

A range of theoretical studies regarding the static and dynamic behaviour of smectic liquid crystals will be presented. The thesis is mainly concerned with the smectic A phase as modelled by the continuum theory of Stewart, though a working knowledge of the smectic C phase, modelled using the Leslie-Stewart-Nakagawa continuum theory, proves necessary. In Chapter 3, reductions of Stewart's theory by appeal to certain physically motivated assumptions upon the smectic and the flow pattern to which it is subjected are outlined. The linear stability of each of the resultant systems is then analysed. Chapter 4 presents the derivation of a "lubrication-type" theory based on one of these resultant systems of equations, which is then analysed in general terms before being applied to the problem of flow past a finite obstacle. Chapter 5 presents an investigation of a shear wave incident at a planar boundary between an isotropic elastic solid and a smectic A liquid crystal. The behaviour of the wave upon reflection and refraction at the interface is established, as is the response of the smectic; a comparison with the smectic C case as considered by Gill and Leslie concludes the chapter. Finally, Chapter 6 discusses the static configuration of a smectic A liquid crystalin the presence of an isolated edge dislocation. After constructing the energy density to fourth order, we first recover the results of previous investigations by assuming the director and layer normal always coincide, in addition to examining a perturbation to a known solution. We then relax the constraint director-layer normal equivalence, obtaining exact solutions for the smectic's configuration for a quadratic energy density and deriving equilibrium equations for special cases for the fourth order formulation.

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The object of the work was to investigate whether the relaxation time of a polar molecule in solution in a non-polar solvent is controlled by the viscosity of the solution (as is implied by Debye's theory) or by a mutual viscosity which is a measure of the solute solvent interactions. Measurements have been made on viscosity, density, refractive index, complex permittivity at a wavelength of 3.33 cm of polar and non-polar mixtures. The non-polar liquids used were benzene and carbon tetrachloride and the polar ones were chloroform, chlorobenzene and t-butylchloride. The measured permittivity and loss together with refractive index values were used to calculate the relaxation times at different concentrations of the liquid mixtures. The mutual viscosity values were determined from the density, solution, solvent and solute viscosities, for the benzene solutions the temperature range used was 10°C to 60°C and for the carbon tetrachloride solutions it was -10°C to 40°C. The results were analysed as functions of temperature and also as concentration. The relaxation times, solution viscosities and the complex viscosity terms all behave as expected when studied as functions of temperature, that is, all these terms decrease with the increase of temperature. The ratios were (within experimental error) both constant with change of temperature which make it impossible to discriminate between the two theories (eta, the solution viscosity, and e, is the viscosity term taking into account the mutual viscosity). The results when studied as functions of concentration seemed to indicate that there is no direct dependence of relaxation time on the viscous properties of the liquid mixtures

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