The work described in this thesis details the development of mid-infrared waveguide laser sources created through the fabrication of waveguide structures in Cr2+: ZnSe using ultrafast laser inscription (ULI). Current quantum cascade laser (QCL) technology in the 2 – 5 μm region offer compact and robust sources suited to use outside the laboratory but the technology does not offer the high average powers, >100 mW, and wide tuneability, 2 – 3.3 μm of Cr2+: ZnSe laser sources. The development of a Cr2+: ZnSe waveguide laser source provides an environmentally robust product with access to powers and tuneable ranges greater than that provided by QCL systems. The first phase of the investigation produced the first successful refractive index modification of ZnSe using ULI. Both positive and negative refractive index changes were achieved and utilised to fabricate a range of waveguides in ZnSe and Cr2+: ZnSe. Low loss near-infrared waveguides were demonstrated through exploitation of the positive refractive index change. Low loss mid-infrared depressed cladding waveguides were subsequently demonstrated utilising the negative refractive index change. These waveguides were characterised at wavelengths of 1928, 2300 and 3390 nm as representative of pump and signal wavelengths in Cr2+: ZnSe laser systems. Finally, the newly fabricated Cr2+: ZnSe waveguides were constructed into waveguide laser cavities and pumped with a thulium fibre laser source operating at 1928 nm. Laser operation is demonstrated in both waveguides devices at wavelengths of 2573 and 2486 nm with a maximum achieved output power of 285 mW and a slope efficiency of 45%. Furthermore, a tuneable laser source is constructed in the Littman-Metcalf configuration exhibiting a maximum tuning range of 510 nm, 2330-2840 nm, with output powers exceeding 25 mW across the full range. These waveguide laser devices offer an environmentally robust and compact source in the 2 – 3 μm region with improvements upon maximum power and tuneability ranges in current quantum cascade laser sources. The waveguide laser sources reported open the door to products offering the robust nature of QCL sources with the higher powers and 2 – 3 μm tuneability associated with current bulk Cr2+: ZnSe laser systems.

Femtosecond Laser DirectWriting has emerged as a key enabling technology for realising miniaturised biophotonic applications offering clear advantages over competing soft-lithography, ion-exchange and sol-gel based fabrication techniques. Waveguide writing and selective etching with three-dimensional design flexibility allows the development of innovative and unprecedented optofluidic architectures using this technology. The work embodied in this thesis focuses on utilising the advantages offered by direct laser writing in fabricating integrated miniaturised devices tailored for biological analysis. The first application presented customised the selective etching phenomenon in fused silica by tailoring the femtosecond pulse properties during the writing process. A device with an embedded network of microchannels with a significant difference in aspect-ratio was fabricated, which was subsequently applied in achieving the high-throughput label-free sorting of mammalian cells based on cytoskeletal deformability. Analysis on the device output cell population revealed minimal effect of the device on cell viability. The second application incorporated an embedded microchannel in fused silica with a monolithically integrated near-infrared optical waveguide. This optofluidic device implemented the thermally sensitive emission spectrum of semiconductor nanocrystals in undertaking remote thermometry of the localised microchannel environment illuminated by the waveguide. Aspects relating to changing the wavelength of illumination from the waveguide were analysed. The effect of incorporating carbon nanotubes as efficient heaters within the microchannel was investigated. Spatio-thermal imaging of the microchannel illuminated by the waveguide revealed the thermal effects to extend over distances appreciably longer than the waveguide cross-section. On the material side of direct laser writing, ultra-high selective etching is demonstrated in the well-known laser crystal Nd:YAG. This work presents Nd:YAG as a material with the potential to develop next-generation optofluidic devices.

This thesis investigates the technology of luminescent down-shifting (LDS) of light for improving the short-wavelength response and efficiency of photovoltaic (PV) modules. A critical literature review of previously published work is presented identifying the opportunity to include the luminescent species in the encapsulation layer of certain PV technologies. A range of luminescent materials and mixtures thereof were tested in ethylene vinyl acetate (EVA) host. They all exhibited very high luminescent efficiencies and did not impair the transmittance of the encapsulant. LDS EVA sheets were used to encapsulate multi-crystalline silicon (mc-Si) and chalcopyrite (CIGS) solar cells. An increase in short-λ external quantum efficiency of up to 25 % was achieved for mc-Si devices. For CIGS, the increase was up to 25 % and 40 % for 50-nm- and 100-nm-thick buffers respectively. The overall efficiency of mc-Si devices was improved by 0.2 % in the best case and gains of up to 0.2 mA / cm2 and 0.6 mA / cm2 were achieved for 50-nm- and 100-nm-thick buffer CIGS devices. LDS offers the additional benefit of device colouration, which can encourage the further uptake of PV in applications where colour is a desirable property.

The results of an experimental study into the third order nonlinear optical properties of chalcogenide glasses at a wavelength of 1550 nm are presented. Of the glasses investigated glass gallium lanthanum sulphide (GLS) was found to have an optical Kerr nonlinearity approximately 70 times higher than silica. Additionally the upper limit of GLS nonlinear absorption coefficient was measured to be over an order of magnitude smaller than the other chalcogenide glasses analysed. GLS was subsequently chosen as the host material for waveguide fabrication via ultrafast laser inscription. Near and mid infrared singlemode waveguide structures were successfully fabricated and their nonlinear guiding properties investigated. These investigations led to the generation of a supercontinuum from a singlemode waveguide that spanned over 3000 nm throughout the mid wavelength infrared spectral region. Studies into the contributing mechanisms of supercontinuum generation are presented in work conducted in silica based photonic crystal fibres with the extent of the supercontinuum generation being limited by the transmission range of silica. An investigation into saturable absorption effects in single walled carbon nanotubes is also presented. This study identified that for field irradiances on the order of 9.5×1013 W/m2 the contribution of multi-photon absorption exceeded that of saturable absorption.

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This thesis considers the calculation of phase from sets of phase contrast and defocused images. An improvement to phase contrast imaging is developed that combines three phase contrast images. This method results in a reduction in the phase error by a factor of up to 20 in comparison to using a single image. Additionally the method offers the potential for optimisation and the extension to an arbitrary number of images. Phase diversity using defocused images is considered in more depth where the intensity transport equation is used to calculate the phase. First a Green's function approach to solving this equation was considered. One of the Green's functions stated in the literature is shown to be incorrect, the other two are shown to be correct both giving equivalent phase estimates. A further improvement is made to this method by removing the singularities in the phase calculation process. As an alternative to the Green's function solution a Fourier transform approach is also considered. A complete solution to the intensity transport equation is derived with inclusion of the boundary conditions. This completes the method incompletely described in the literature. Through simulation, generic key factors are identified for the potential optimisation of experimental and numerical process to improve the estimated phase. Determining 3D structural information of an object from the phase calculated in a single plane is considered using an iterative process. It is shown that this process is limited but can be used, in some cases, to generate an approximate representation of the object.

Several types of pupil modulation have been reported to decrease the aberration variance of the modulation-transfer-function (MTF) in aberration-tolerant hybrid optical-digital imaging systems. It is common to enforce restorability constraints on the MTF, requiring trade of aberration-tolerance and noise-gain. In this thesis, instead of optimising specific MTF characteristics, the expected imaging-error of the joint design is minimised directly. This method is used to compare commonly used phase-modulation functions. The analysis shows how optimal imaging performance is obtained using moderate phasemodulation, and more importantly, it shows the relative merits of different functions. It is shown that the technique is readily integrable with off-the-shelf optical design software, which is demonstrated with the optimisation of a wide-angle reflective system with significant off-axis aberrations. The imaging error can also be minimised for amplitudeonly masks. It is shown that phase aberrations in an imaging system can be mitigated using binary amplitude masks. This offers a low-cost, transmission-mode alternative to phase correction as used in active and adaptive optics. More efficient masks can be obtained by the optimisation of the imaging fidelity.

The three state contact process is the modi cation of the contact process at rate in which rst infections occur at rate instead. Chapters 2 and 3 consider the three state contact process on (graphs that have as set of sites) the integers with nearest neighbours interaction (that is, edges are placed among sites at Euclidean distance one apart). Results in Chapter 2 are meant to illustrate regularity of the growth of the process under the assumption that , that is, reverse immunization. While in Chapter 3 two results regarding the convergence rates of the process are given. Chapter 4 is concerned with the i.i.d. behaviour of the right endpoint of contact processes on the integers with symmetric, translation invariant interaction. Finally, Chapter 5 is concerned with two monotonicity properties of the three state contact process.

The ability to detect infrared photons is increasingly important in many elds of scienti c endeavour, including astronomy, the life sciences and quantum information science. Improvements in detector performance are urgently required. The Superconducting Nanowire Single-Photon Detector (SNSPD/SSPD) is an emerging single-photon detector technology o ering broadband sensitivity, negligible dark counts and picosecond timing resolution. SNSPDs have the potential to outperform conventional semiconductor-based photon-counting technologies, provided the di culties of low temperature operation can be overcome. This thesis describes how these important challenges have been addressed, enabling the SNSPDs to be used in new applications. A multichannel SNSPD system based on a closed-cycle refrigerator has been constructed and tested. E cient optical coupling has been achieved via carefully aligned optical bre. Fibre-coupled SNSPDs based on (i) NbN on MgO substrates and (ii) NbTiN on oxidised Si substrates have been studied. The latter give enhanced performance at telecom wavelengths, exploiting the re ection from the Si=SiO2 interface. Currently, the detector system houses four NbTiN SNSPDs with average detection e ciency >20% at 1310 nm wavelength. We have employed SNSPDs in the characterisation of quantum waveguide circuits, opening the pathway to operating this promising platform for optical quantum computing for the first time at telecom wavelengths.