III-nitride semiconductors are the leading material for use in solid state lighting (SSL), with highly efficient blue and white nitride-based light emitting diodes (LEDs) commercially available. However challenges still remain to improve their efficiency. The work in this thesis focuses on the optical and compositional characterisation of InGaN and InAlN alloys, which are widely used as active regions in such light emitters. Composition and luminescence properties of InGaN epilayers with varying growth temperature and hydrogen flow rates are investigated. The measurements revealed that the samples grown with small amounts of hydrogen improved in surface quality, compositional and luminescence homogeneity when compared with samples grown at equivalent temperature. The additional hydrogen did reduce the InN fraction slightly. Investigations of the optical, compositional and structural properties of Ga auto-incorporated InAl(Ga)N epilayers are made. Composition measurements revealed 1 2-28 % of Ga incorporated. The growth parameters and resultant Ga indicated the likely cause is residual Ga coming from the reactor walls and delivery pipes, as by increasing the total flow rate from 8000 sccm to 24000 sccm was seen to suppress the GaN from 28 to 12 %. A broad spectral emission peak was seen, whose energy varied with InN content and not GaN. A large set of InAlN epilayers grown on AlN buffers are studied. Composition measurements revealed a wide range of InN contents from 0.1 % to 25.6 %. The analysis revealed no presence of Ga within the samples. Optical measurements produced broad InAlN luminescence spectra which varied with InN content. The peak energy was found to be 3.46-3.93 eV for InN compositions of 0.7-6.6 %. Analysis suggests this is not bandedge emission due to the low peak energy and very wide FWHMs. Finally, a home built PL mapping system is demonstrated, along with the design and operation challenges. Utilising this mapping system, investigations of InGa N/GaN MQW LED samples grown under different barrier growth methods are made.

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The primary focus of the work presented in this thesis is experimental investigations into microwave surface waves that are supported by various metamaterial geometries. If the patterning of the metamaterial is either resonant or periodic, surface waves that are somewhat analogous to surface-plasmon-polaritons at optical frequencies can be supported at microwave frequencies. The precise form of the texturing strongly influences the surface eigenmodes that can be supported. Two approaches to varying the surface-mode index, the ratio of the phase velocity of the surface wave to the speed of light in vacuum, are employed in order to design two different graded mode index surface wave devices: (i) an omnidirectional absorber that utilises the 'fatal attraction' phenomenon and (ii) a Luneburg lens. The mode index is graded in the former by spatially varying the dielectric environment in the proximity of a metasurface, whereas in the latter, this is achieved by varying the patterning of the metasurface. Both devices are characterised through experiments, with the results compared to the predictions from full wave numerical simulations. In a further study, investigations into surface waves with opposing group and phase velocities (analogous to bulk waves in negative refractive index media) is completed using Sievenpiper `mushroom' geometries with different symmetries. Measured instantaneous electric field maps allow the negative-index phenomenon to be directly visualised through phase sensitive measurements demonstrating that the wave-fronts propagate it towards a near-field point source that is exciting the surface waves. Measurements of the surface mode iso-frequency contours also reflect the negative index character of the surface mode. Patterned metafilms that support coupled microwave surface waves are investigated experimentally. Both a single-layer and a bi-layer of metallic `dumbbell' arrays are shown to be able to support variations of such surface modes. Ultra-thin metafilms that are patterned with variations of the Pendry hole array are also shown to support such surface modes, although the very small thickness means that only the symmetric-in-charge surface mode disperses at microwave frequencies. This surface mode is used to demonstrate the self-collimation of microwave surface waves, with beams of surface waves excited from a point source, the number of which is dependent on the symmetry associated with the metafilm. A graded mode index device is also designed and characterised through experiments by varying the patterning of a metafilm.

This thesis describes interactions between atomic or molecular systems and intense laser fields. Methods for time resolving sub-femtosecond scale Auger-type dynamics in molecules and atoms are discussed. The thesis presents a novel technique for recovering such dynamics by clocking the process with high-harmonic generation. The harmonic generation is driven by an attosecond pump pulse and a long duration, infrared pulse. The technique is then theoretically applied to Auger decay of krypton upon ionisation from the 3d subshell and inner-valence hole dynamics of small molecules. We then examine the extent to which these techniques, which utilise strong fields, can influence the electron dynamics they seek to measure. We describe the coupling between the bound state to a dressed continuum (as opposed to a field-free continuum) and the effect on the Auger decay rate in a sample system is calculated. We then look ahead to possible ways in which the probing strong field may influence the electron dynamics themselves.

When a high-energy (MeV) atom or neutron collides with an atom in a solid, a region of radiation damage is formed. The intruding atom may cause a large number of atoms to leave their lattice sites with low energies (keV) in a collision cascade. Alternatively, it may cause a single lattice atom to be removed from its crystal lattice site and travel large distances without undergoing any further atomic collisions/scatterings in a process known as channelling. Any moving atom may lose energy via collisions with other atoms or by the excitation of electrons. The microstructural evolution of the irradiated material depends on the rate at which the damaged region cools, which in turn depends on the rate at which electrons are excited and carry energy away. Since silicon is a semiconductor with a band gap of 1.1 eV, it is normally assumed that the rate of excitation of electrons by atoms with low kinetic energies (< 100 eV) is negligible. However, the atomic kinetic energy threshold required for electronic excitation is not understood. This thesis uses large-scale quantum mechanical simulations to investigate how a moving atom loses energy to the electrons in a crystal of silicon. It is possible to calculate the energy transfer from a channelling atom to the host material's electrons using time-dependent density functional theory (TDDFT) and we have done so. However, these highly accurate calculations are computationally expensive and cannot be used to study very large systems. Hence, we also use a less accurate method called time-dependent tight binding (TDTB). We show that TDTB and TDDFT simulations of channelling in small silicon systems are in good qualitative agreement and use the cheaper TDTB method to investigate finite-size effects. We also investigate how an atom oscillating around its lattice site transfers energy to the crystal's electrons. To understand the complex behaviour of the electronic energy transfer, we utilise non-adiabatic perturbation theory. Our simulations and the perturbative analysis both show that the presence of a gap state with a time-dependent energy eigenvalue allows electronic excitations for very low energy (eV) channelling atoms.

When a quantum system interacts with many other quantum mechanical objects, the behaviour of the system is strongly affected; this is referred to as an open quantum system (OQS). Since the inception of quantum theory the development of OQSs has been synonymous with realistic descriptions of quantum mechanical models. With recent activity in the advancement of quantum technologies, there has been vested interest in manipulating OQSs. Therefore understanding and controlling environmental effects, by structuring environments, has become an important field. The method of choice for tackling OQSs is the master equation approach, which requires approximations and doesn't allow direct assessment of the environment. This thesis tackles the issues of OQSs with an unorthodox method; we employ a series of coupled quantum harmonic oscillators to simulate an OQS. This permits the use of the covariance matrix technique which allows us to avoid approximations and analyse the environment modes. We investigate the Markov approximation and Rotating-Wave approximation (RWA), which are commonly used in the field. By considering four OQS models, we study an entanglement-based non-Markovian behaviour (NMB) quantifier (ENMBQ). The relevance of detuning, coupling strength and bath structures in determining the amount of NMB is noted. A brief study of the factors that affect a fidelity-based NMB quantifier is also conducted. We also analyse the effect on the ENMBQ if the terms excluded by the RWA are included in the models. Finally, an examination of the applicability of the RWA in the presence of strong coupling is undertaken in a three oscillator model. The fidelity-based analysis utilised could allow one to ascertain when and if the RWA can be applied to a model of interest, including OQSs. The knowledge within, and the methodology used throughout this thesis, could arm researchers with insights to control the flow of quantum information in their systems.

This thesis contains a report on the development of a new type of confocal microscope. The microscope aims to allow the user to be able to determine the three dimensional orientation of single fluorescent emitters. The microscope has at its heart a binary spatial light modulator that allows us to control the excitation electric field in the pupil of the microscope objective. This allows us to exploit the fact that the excitation of, and emission from, a single fluorescent emitter is polarisation and orientation dependent. By changing the field in the excitation pupil we can generate a set of images that when taken together can be analysed to find the emitter orientation. We show that the microscope allows us to resolve the orientation of single fluorescent molecules and nitrogen vacancy centres in nanodiamond. We designed the microscope from scratch using extensive mathematical modelling techniques. We anticipate that these models will be useful to other researchers. One example is that our model of the polarisation distortions introduced during scanning is relevant to any galvanometer-based scanning system. We also developed a full model of a confocal microscope that includes the dipole-like nature of many samples. We use this to calculate, amongst other things, the optical sectioning properties of confocal microscopes. This allows us to validate previous models that ignored polarisation distortions of high numerical aperture lenses and also to make calculations where previous models would have been inadequate, for example in calculating the sectioning strength of sheets of aligned dipoles. As well as developing numerical models, we invented a new method for controlling the polarisation of light using a binary spatial light modulator. This work has applications in materials science, and industrial applications.