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Quantum computation will unlock a new class of computational complexity, allowing us to solve previously unsolvable problems, and understand previously unconscionable phenomena. A quantum computer must exert precise control over complex quantum systems, on a truly massive scale. It must freely wield entanglement- the ethereal connection between quantum particles-to operate. Photons, particles of light, have obvious use in the transmission of quantum information, but could also process it; their manipulation is aided by a millennium of human experience with optics. This thesis describes how to build a photonic quantum computer from the ground up, and applies today's most scalable optical technology-silicon integrated optics-to construct the first integrated devices which can produce photons and wield their entanglement. I detail the nonlinear process used to produce photons, spontaneous four-wave mixing, as well as the silicon optical technology used to control them. I demonstrate, via four experiments, a massive scaling-up of silicon quantum photonics. Finally, I provide a glimpse of possible technological routes towards universal quantum computation with photons.

Photolithography is an optical and chemical process for the patterning of commonly at substrates with shapes which are useful for electronics and a number of other applications. Holography, in its most general sense, is the manipulation of the coherent properties of an optical wave-front to produce two or three dimensional light patterns. A combination of holography and photolithography therefore allows for the patterning of three dimensional substrates by exploiting the coherence of an optical source. The work in this thesis approaches an optical optimisation methodology centered around the iterative algorithms derived from the Gerchberg-Saxton algorithm. This allows the design of holograms which, in turn, allows the patterning of three dimensional surfaces. The system parameters for the design of two and three dimensional light patterns in this methodology are examined. Simulations and practical optical examples are provided throughout with some application-focused demonstrations. The result is an understanding of an iterative optimisation approach within the context of lithography, and an implementation and methodology for achieving three dimensional patterns.

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The interaction of intense laser pulses with solid targets has shown great promise in recent years as a source of coherent, sub-femtosecond bursts of extreme-ultraviolet radiation, via various high harmonic generation mechanisms. For applications in ultrafast science, the temporal and spatial characteristics of these pulses must be carefully understood and controlled. In this thesis, nanometer-scale foil targets are investigated as a target type for these high harmonic generation processes. Here, the first reported experimental observations of high harmonic generation in reflection from nanofoils in a normal incidence geometry are presented. The intensity of the harmonics is observed to depend strongly on target thickness. In particular, the thinnest (- 5 nm) targets showed no harmonic emission, but their intensity increased with foil thickness up to a plateau at -300 nm. This dependence is investigated and explained using particle-in-cell simulations. High harmonic generation in the forward direction from laser-nanofoil interactions at normal incidence is also investigated in this thesis. Experimental observations of harmonic spectra, presented here and previously in the literature, show the appearance of even-numbered harmonics, though conventional models and 1-dimensional simulations suggest that only odd orders should be present. Their appearance is investigated and explained here using 2-dimensional particle-in-cell simulations. This thesis also presents experimental results which suggest that harmonic generation in the forward direction from nanofoils can be controlled by modifying the ellipticity of the driving laser pulse, such that the intensity of harmonics decreases when the driving pulse is made more circular. Finally, this thesis investigates the use of driving pulses with time-dependent ellipticity, in order to confine the high harmonic generation mechanism to a small temporal window, and to achieve an isolated attosecond pulse

Studies of the electric discharge and its application for the excitation of high power gas lasers The electric discharge has been studied in static and fast flow gases at gas pressures between 50 mb and 1 b over a range of current of between 10 mA and 1. 5 A representative of its application to the excitation of high power gas lasers. The investigations have shown that the glow to arc transition is a cathode phenomenon which may oscillate between a glow and arc discharge at the transition current. The oscillation appears to be inherent where neither the glowKor the arc is stable at the transition current. The glow to arc transition has no effect on the positive column characteristics. The contraction of the positive column and the decrease in its voltage gradient as the current is increased appeared to be related to the thermal conductivity of the gas which indicates that the formation of streamers in the discharge column in a fast gas flow is a local constriction due to thermal instabilities. The mu1tiple electric discharge has been investigated and analysed and compared with an equivalent single electric discharge. The investigation showed that the coalesced part of the column has the same characteristics of a single discharge column with the same current and the discharge column coalesces so as to operate at the minimum voltage which supports the Steenbeck minimum principle. A mathematical model was established for the coalescence of the multiple discharge based on Steenbeck' s minimum principle which has been demonstrated experimentally by applying an external magnetic field to the discharge column. The behaviour of the positive column in a fast gas flow was investigated and mathematical models were established for the contraction of the positive column by the shear stress force due to the flow profile of the gas flow in the laminar and turbulent flow regimes using gas injection nozzles to demonstrate the effect of the flow profile on the contraction of the discharge column and a diffusing injection nozzle has been proposed as the optimum design. An injection nozzle-electrode was designed and tested by replacing the original cylindrical injection nozzle-electrode in a 5 kW C02 laser at a gas pressure of 50 mb. The new nozzle-electrode has resulted in a 50% reduction in the gas mass flow rate.

This thesis presents the simulated optical design of a fully LED-based solar simulator. The work focuses on the spectral mismatch, the spatial uniformity acquired with direct light and the spectral uniformity. The proposed LED solar simulator has an illuminated area of 32cm x 32cm and can characterise medium size photovoltaic devices under variable light intensities and variable output spectra. The spectral range covered is between 350nm and 1300nm which offers the capability of characterising various different PV technologies. The spectral match classification is A+ for the 400nm-1100nm spectral range and B for the 350nm-1300nm spectral range. The spatial non-uniformity of irradiance is also A+ across the illuminated area. The temporal stability of LEDs can easily reach class A as proven by previous work in the group and is not examined here. An automated LED selection methodology that optimises the spectral mismatch was developed to replace the trial and error method usually employed. The algorithm created accommodates a more accurate selection of the most appropriate LED wavelengths in order to represent the solar spectrum even more closely than before and improve the uncertainties caused by the spectral mismatch. A genetic algorithm and the chi-squared error criterion were used to create the automated methodology applying a minimisation technique. This technique helps the user choose from a wide variety of LEDs available on the market, determine the wavelengths and the number of LEDs per wavelength needed to accurately represent the AM1.5G solar spectrum and other spectra and provides a cost-effective and straightforward solution. The solution chosen for this project involves 24 different wavelengths. A direct beam approach was followed regarding the collimation of light to account for the measurement errors introduced by the frequent overestimation of the current due to the unpredicted reflections caused by diffuse light. Extended simulations of different optics were performed to determine the best layout that offers good directionality and satisfactory non-uniformity of irradiance and light collection efficiency. Total internal reflectors of 13.5mm diameter proved to be the most appropriate primary optics with the highest collection efficiency. An imaging homogeniser was chosen as secondary optics for its capability to mix the light and achieve low levels of non-uniformity of irradiance. The spatial non-uniformity of irradiance achieved with 612 LEDs is 0.29% across the 32cm x 32cm illuminated area and the irradiance is equal to 1316 W/m2 assuming 1W LEDs. The hexagonal placement set-up was used for the placement of the LEDs since it results in the lowest non-uniformity and it is the best option for keeping the lamp size compact. An optical engineering software called FRED was used for ray-tracing individual optics. Due to the time and computational demands of the simulations a different approach needed to be found for overlaying the irradiance profiles of hundreds or even thousands optical elements. An algorithm was developed in Matlab that takes into consideration the geometry of each case and calculates the final irradiance profile. A placement methodology that accounts for the spectral uniformity on the illuminated target was also developed. It was shown that placing the LEDs randomly does not offer enough spectral mixing and is therefore problematic as it introduces an unexpected source of measurement uncertainty. The influence of spectral non-uniformity varies for different photovoltaic technologies due to their variable spectral responses. Thus, a placement methodology using a genetic algorithm was developed to optimise the positioning of the LEDs. As a result the highest spectral non-uniformity drops from almost 5% to 1.46% and the measurement uncertainty is reduced significantly since an improvement of up to 1.8% is noted in the current density non-uniformity.

Silicon photonics has gained more popularity in the last decade stimulated by a series of recent breakthroughs and attractive potential applications in the integrated-optics. One of the great challenges is to modify the silicon lattice so as to enhance the light emission properties. Moreover, by referring to Moore’s Law, there are concerns of the increase in interconnect time delay which can surpass the switching time if the gate length in transistors are continued to scale down. By implementing the silicon optical emitter on the integrated circuit, it will eliminate this major problem thus enhancing the performance and speed of the computer. This work will focus on researching the point defect especially the G-centre in silicon as a potential technique to emit coherent light from silicon. We have investigated and presented a new approach to incorporate high levels of the emissive G-centre peaking sharply at 1280 nm by implanting carbon and protons into the silicon lattice. Significantly this technique utilizes fully ULSI technology compatible processes such as ion implantation and high temperature annealing. Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM) techniques were used along with the photoluminescence measurement to correlate the optical and structural properties of the G-centre formed by the carbon implantation and high energy ion irradiation. The analysis reveals that the silicon interstitials generated after proton irradiation are an essential factor in forming the G-centre complex. We have also introduced the dislocation engineering technique into the silicon lattice with the G-centre complexes. The results are promising and with optimization of the technique to introduce the dislocation loops into the G-centre technique, the temperature quenching problem often related to the optically active point-defect centre, may be solved. Electroluminescence (EL) measurements were carried out after the fabrication of the LED devices. Results from the sample with the G-centre luminescence is the most crucial as it shows that by using the proposed technique in this research, luminescence from silicon is indeed possible when electrically pumped. This is an essential key result for the future research of the optically active point-defect especially the G-centre towards the possibility of an electrically pumped, efficient silicon laser.

Composite repairs are often used for damaged structures in order to recover the mechanical properties of the original structure. During service, there is the possibility that damage will occur in the repaired region and hence it would be useful to be able to monitor such repairs. This research investigates the use of chirped fibre Bragg grating (CFBG) sensors to monitor the development of fatigue damage initiation and growth in the repaired region of three different repair systems, i.e. glass fibre reinforced polymer (GFRP)-to-GFRP scarf repair, GFRP-to-GFRP patch repair and a GFRP patch repair to an aluminium panel. All of these repairs were investigated using a combination of experimental testing and theoretical predictions using finite-element analysis and optical prediction software. For each repair system, the CFBG sensor was embedded in the bond-line during the repair fabrication and the transparency of the GFRP material enabled damage to be observed and recorded. The work began by fatigue loading the GFRP-to-GFRP scarf repair coupon under 4-point bending. The CFBG sensor was embedded in the tensile side of the repair. For this system, the growth of the bond-line cracks could be detected but an accurate determination of the extent of damage was not possible. This was mostly due to the geometry of the scarf repair which led to a high degree of complexity in the interpretation of the data. There was good agreement between the trend of the changes in the spectra in the comparisons of the experimental results and finite-element/optical modelling, although the experimental spectra showed smaller changes than were produced by the modelling. The second repair system investigated was the GFRP-to-GFRP patch repair which was tested in the same way as the scarf repair system. An asymmetric repair was fabricated with the patch being bonded on the tensile face of the coupon. Here, it can be said that growth of the bond-line cracks can be detected using CFBG sensors, and an accurate determination of the current length of the cracks from the spectra was achieved. A explanation of the shift of the low-wavelength end of the spectrum changes with increasing crack growth was provided in terms of strain field change caused by the bond-line cracks. There was good agreement in the comparisons of the experimental results and finite-element/optical modelling. Finally, the third repair system investigated was the patch repair of an aluminium panel which was fatigue loaded in tension. Prior to repair, the aluminium panel was notched at the centre in order to promote crack initiation. Again, an asymmetric repair was fabricated. It can be concluded from the results that the embedded sensor could clearly detect the approach of a fatigue crack and indicate when the crack had passed the location of the sensor. Again, there was good agreement in the comparisons of the experimental results and finite-element/optical modelling. The work has shown that CFBG sensors can be used to monitor damage development in various types of repairs and can give an indication of damage initiation for all of the cases investigated. However, where there is significant geometrical complexity to the repair, as in the case of a scarf repair, detailed interpretation of the spectra in order to extract information on damage growth is much more difficult.