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This thesis is about investigation of untapered and tapered fibre transmission properties by experimentation and simulation. Tapered fibre fabricated from commercial products and custom fibre from Bath University was investigated including different fibre type, taper length, and taper ratios. Simulations of untapered and tapered fibre by consideration of geometrical optics using Zemax are presented and compared to electromagnetic waveguide simulations using COMSOL. In addition, the impact of modal noise in tapered fibre is investigated, especially graded-index tapers, by quantifying macro- and micro-bending loss. Moreover, the fabrication of build-inhouse connector tapered fibre is introduced as a robust and cost-saving tool for spectrograph link. Lastly, a tapered fibre is tested with a compact EXOplanet high-resolution SPECtrograph (EXOhSPEC) of the University of Hertfordshire using Tungsten and ThAr lamps. Although the cladding light is detected clearly in custom graded-index taper, the light throughput in EXOhSPEC is improved. Overall these results indicate the potential for reasonable fibre-fed spectrograph performance using a 'single tapered fibre'.

Key to the safe operation of nuclear reactors is the understanding of materials degradation due to neutron damage. Ion implantation is often used as a surrogate for nutron damage when screening nuclear candidate materials. Ion implantation results in a thin damage layer, the mechanical properties of which are often difficult to determine. In this study a micromechanical test regime is developed in a model material, 6H single crystal silicon carbide (SiC). This test technique is then applied to gold ion irradiated zirconium nitride (ZrN). Micromechanical test samples are often prepared using a focused ion beam. However, ion beam milling has the potential to damage the crystal structure of a material and introduce residual stress. Therefore, a range of cutting strategies were used to assess the effects of focused ion beam cutting on the modulus and strength of SiC cantilevers. The effects of sample size were also explored. Gallium ion milling resulted in amorphisation of the surface of the SiC crystal micro cantilevers. The thickness of the amorphous zone was then reduced using low voltage cleaning. Low voltage cleaning did not, however, result in increased mechanical performance as other unintended consequences such as cantilever edge rounding occurred. SiC exhibited a plastic deformation threshold of around 0.3 × 0.3 µm but did not exhibit a significant size effect. Nanoindentation was used as a benchmark test to compare to the mechanical properties gathered during micro bend testing. Under indentation conditions, a size effect was identified in hardness and modulus but not in fracture toughness. Modulus results from indentation, and micro bend testing was comparable when ion damage was accounted for. Hot pressed ZrN samples were ion implanted with gold ions. Microstructural characterisation, nanoindentation and micromechanical tests were performed in the ion implanted zone. Microstructural characterisation identified a dual phase microstructure consisting of ZrN and Zr2ON2. The implanted layer consisted of implanted gold ions followed by a network of dislocations centred around a depth of 1.20 µm. High-resolution electron backscatter diffraction (HR-EBSD) identified that tensile surface stresses and compressive subsurface stress had been introduced. Nanoindentation linked ion implantation to increased hardness and no modification in modulus. Micromechanical testing indicated a reduction in modulus and strength. This work highlighted the need to understand sample size effect and ion damage on micro mechanical tests if they are to be used for screening nuclear materials.