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In this thesis, three advanced experiments based on laser spectroscopy are introduced for the first time which address several experimental topics for trace gas analysis. The implementation of a diode laser based gas phase Raman detector is introduced, capable of parts per million (ppm) detection limits. The spectrometer features a low power laser diode (10 mW) which is enhanced by power build up in an optical cavity. This new technique is characterised by recording spectra of N2, O2, H2, CH4 and benzene. A second advanced laser based spectroscopy technique for trace gas detection, mid infrared cavity enhanced resonant photoacoustic spectroscopy (mid-IR CERPAS) is set up and characterised. This scheme uses optical cavity power build-up, optical feedback stabilisation and resonant photoacoustics. A single-mode continuous wave quantum cascade laser is coupled to a three mirror V-shape optical cavity. Gas phase species absorbing in the mid-IR are detected using the photoacoustic (PA) technique. Mid-IR CERPAS was characterised by measuring acetylene (limit of detection 50 ppt) and nitromethane (0.8 ppb). The mid-IR CERPAS equipment was also used to detect explosives’ vapours; TNT (1.2 and 5.5 ppb), 2, 4-DNT (7 ppb), TATP (4 ppb) and explosives’ taggants such as DMNB (11 ppb). Significant interferences from ambient water in lab air are observed and are overcome. Normalized noise-equivalent absorption coefficients are determined as » 6 x 10-10 cm-1 s1/2 (1 s integration time) and 6 x 10-11 cm-1 s1/2 W (1 s integration time and 1 W laser power). Finally, a near infrared Herriott cell enhanced resonant photoacoustic spectroscopy spectrometer is set up and characterised. This scheme uses enhancement from the absorption pathlength by a multipass Herriott cell and detection of the gas phase species by resonant photoacoustics, Herriott cell enhanced resonant photoacoustics, HERPAS. A single-mode continuous wave near infrared external cavity diode laser is coupled to a Herriott cell. Absorbing gas phase species are detected using the photoacoustic (PA) technique which was characterised by measuring acetylene (150 ppb detection limit at 100 ms integration time). HERPAS was extended to measure several toxic industrial gases including hydrogen sulfide, ammonia and carbon monoxide. Normalized noise-equivalent absorption coefficients are determined for H2S as » 5.3 x 10-9 cm-1 s1/2 (1 s integration time) and 1.6 x 10-10 cm-1 s1/2 W (1 s integration time and 1 W laser power). These three novel advanced spectroscopic techniques allow the detection of IR-inactive and IR- active gas phased species with great sensitivities and selectivity and improve significantly current capabilities for trace gas phase detection.

Since industrial devices create power dissipation in the form of heat created as a by-product, which can have a negative effect on their performance, certain temperature limit constraints are required for almost all these applications to work within suitable conditions. That is, these engineering devices might fail in some way if these limitations are surpassed by overheating. In all the related industries, inexorable increases in power densities are driving innovation in heat exchange techniques. Furthermore, electronic devices are becoming smaller at the same time as their thermal power generation increases. Thus, heat sinks can be applied for cooling critical components in many important applications ranging from aero-engines and nuclear reactors to computers, data centre server racks and other microelectronic devices. The most common cooling technique for heat dissipation for thermal control of electronics is air cooling. Reduced cost, simplicity of design, the easy availability of air, and increased reliability are the main benefits of this cooling method. Heat sinks with a fan/blower are commonly used for air-cooled devices as a forced convection heat transfer. An amount of heat is dissipated from the heat source to environmental air utilising a heat sink as a heat exchanger, which is a vital practice employed in air-cooling systems. This transfer mechanism is easy, simple and leads to reduced cost and increased reliability, and pinned heat sinks are more beneficial than plate fin heat sinks. The main interest of this study is to investigate the benefits of using perforated, slotted, and notched pinned heat sinks with different configurations to reduce CPU temperature and fan power consumption to overcome the pressure drop and maximise a heat transfer rate through the heat sink. An experimental heat sink with multiple perforations is designed and fabricated, and parameter studies of the effect of this perforated pin fin design on heat transfer and pressure drops across the heat sinks are undertaken, to compare it to solid pinned heat sinks without perforations. Experimental data is found to agree well with predictions from a CFD model for the conjugate heat transfer and turbulent airflow model into the cooling air stream. The validated CFD model is used to carry out a parametric study of the influence of the number and positioning of circular perforations, and slotted/notched pinned heat sinks. Then, the multi-objective optimum pinned heat sink designs are tested to obtain CPU temperature and fan power consumption as lowest as possible through the heat sink. In addition, the limitations in application of pinned heat sinks based on the pin density and applied heat flux are reported for active air-cooling electronic systems. An overview of the findings indicates that the CPU temperature, the fan power consumption, and the heat transfer rate in terms of Nusselt number are enhanced with the number of pin perforations and slotted/notched pinned heat sinks, while the locations of the pin perforations are much less influential. These benefits arise due to not only the increased surface area but also to the heat transfer enhancement near the perforations through the formation of localised air jets. Finally, the perforated heat sinks will be lighter in weight compared with solid pinned heat sinks.

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The thesis is divided into three parts. The first part of the thesis describes the design and development of two prototypes of an ultra-low phase noise 3.8GHz dielectric resonator oscillator. The first prototype included vibration measurements with a reasonable phase noise measurements developed for Selex-ES. The phase noise for the first 3.8GHz oscillator is -117 dBc/Hz at 1kHz offset and -150 dBc/Hz at 10kHz offset. The second prototype was the improved modular yet compact oscillator was then developed which demonstrated a significantly improved phase noise performance of -125.6 dBc/Hz at 1kHz offset and -153 dBc/Hz at 10kHz offset which is the lowest noise reported in the literature in this frequency band using a ceramic dielectric resonator. In the second part of the thesis, a design and measurement of a high Q broad tuning aperiodic Bragg resonator operating at 10GHz is described. The resonator utilises an aperiodic arrangement of non (λg/4) low loss alumina plates (ℰr=9.75, loss tangent of ~1 to 2 ×10-5) mounted in a cylindrical metal waveguide. The insertion loss, S21, varied from -3.9 dB to -6.4 dB while the unloaded Q varies from 81,650 to 61,020 over the tuning range of 100MHz (1%). In the third part of the thesis, simulation, design and measurement of a low noise Bragg resonator oscillator operating at 10GHz is presented. The oscillators demonstrated a phase noise of -153 dBc/Hz at 10kHz offset and -123 dBc/Hz at 1kHz offset for an unloaded Q of 190,000. To achieve these results extensive optimization of different transistors with different power level and noise figure has taken place.

Current thermosonic flip chip bonding technologies are adversely affected by chip-to-substrate co-planarity errors and bump/pad height variations which can lead to uneven bonding strength and, in extreme cases, chip cratering. This has limited the industrial uptake of thermosonic flip chip assembly. The aim of the research reported here was to explore the use of laser-generated ultrasound as an alternative ultrasound source in flip chip bonding. The research was motivated by the idea that, with greater control over the distribution of ultrasonic energy applied over the bonding interface, it should be possible to compensate for and mitigate the above effects. The main objective of this research work was to establish a working flip-chip bonding process using laser induced ultrasonic vibration. Initially, a literature review on current flip-chip bonding methods and laser ultrasonic methods was carried out. This suggested that confined laser ablation would be the most appropriate technique for generating strong ultrasonic vibration. Next, through modelling and simulation, an investigation was carried out to determine the suitable parameters and methods to be implemented during the experimental stage, including the pressure pulse amplitude, cavity width (irradiance spot size) and type of sacrificial material. Additional investigations were also carried out to explore the effect of applying different materials in generating ultrasonic vibration and also to show the effect of applying multiple pressure pulses simultaneously. In the experimental phase, a custom bonding rig was developed and used to explore the parameter space for thermosonic bonding on polymer substrates using ultrasound generated by a diode-pumped solid-state laser (355 nm wavelength). Initial experiments showed unstable bond strength due to the accumulation of heat which resulted in the appearance of an unwanted glue-like substance at the bonding interface. However, this issue was overcome through careful choice of process parameters combined with the introduction of off-axis laser irradiation. A process for bonding dummy test chips to flexible substrates was successfully established, and in the best case a die shear strength of 9.3 gf/bump was achieved.

The nanoscale morphology of the active layer in organic photovoltaic devices is critical to their performance. Blend morphologies can be manipulated by using a variety of additives, co-solvents and by thermal annealing. However, one crucial issue for any organic photovoltaic device is operational lifetime, which is largely dictated by changes in the active layer morphology. Such changes may be due to reordering of the polymer material, or diffusion and aggregation of fullerene derivatives to a more thermodynamically stable state. This reordered structure can potentially have detrimental effect by losses in interfacial surface area and an increase in exciton recombination. Many novel polymers are designed without this consideration and may be susceptible to this type of degradation. Herein, we explore a variety of approaches to stabilise the blend morphology, principally by the incorporation of various reaction functionalities onto the polymer backbone. The three main areas which have been investigated are; varying of acceptor strengths, chain end modifications with various crosslinking chemistries and thermally cleavable leaving groups. Firstly, poly(dithienogermole-benzothiadiazole) analogues are synthesised to investigate how changes to the acceptor strength of the D-A co-polymers will affect the bulk heterojunction morphology and polymer performance. Then the synthesis and functionalisation of benzotriazole in poly(cyclopentadithiophene-benzotriazole) with alkyl bromine crosslinking groups and thienopyrroledione in poly(dithienogermole-thienopyrroledione), with both alkyl bromide & alkyl oxetane crosslinking groups was investigated. Further studies will investigate the effects on material and optoelectronic properties as well as device performance in OPV and suitability of additives with crosslinking. Lastly, we explore the incorporation of thermal cleavable BOC groups on thienopyrroledione, in poly(cyclopentadithiophene-thienopyrroledione), the deprotection of Boc in polymeric materials and its effects on material and optoelectronic properties.

The design and testing of an ultrasonic time of ight Mach number probe for use in the bypass duct of an aircraft gas turbine is presented. Analysis of the time and frequency domain behaviour of the type of thickness mode transducers selected for use in the probe, and the effects of beam profile and attenuation on the transmitted ultrasonic wave in a owing medium are also covered and extended. The results of this analysis are implemented in a computer model which is used to aid in the design of various parts of the probe. Experimental assessment of the transducers designed for the probe is presented together with the results of tests on the performance of the selected probe configuration. A digital signal processing system to control the probe and compensate for the poor signal to noise ratio of the received signal is developed together with analogue circuitry to interface this system to the transducers. A novel method of compensating for the beam sweep encountered at the Mach numbers to b measured using 'ski-ramps' is then developed and implemented. Results from the final configuration including the ski-ramps is then presented.

Ptychography aims to completely revolutionise imaging in visible light, X-rays and Electron wavelengths by providing a robust platform for sub-Nyquist high-resolution real-time imaging. This thesis explores the framework of the very promising implementation of ptychography called the Ptychographic Iterative Engine (PIE). The PIE algorithm provides an elegant solution to the phase problem that facilitates recovery of complex representations of both the illuminating wave and the object of interest. The aim of this thesis is to present work done on the study of the machinery behind the PIE algorithm. This thesis formulates the solution provided by the PIE algorithm in reciprocal space; this shows the exact minimisation routine implemented by the PIE update function and provides a unified framework for quantifying the performance of the PIE algorithm. This work is timely because it highlights aspects of the PIE algorithm that permits practical implementation of bandwidth extrapolation of a specimen from a small detector and demonstrates the uniqueness of the corresponding solution provided by the PIE algorithm. This thesis also presents a viable scheme that utilises the redundancy of the ptychographic dataset to greatly reduce the sampling requirement on the detector; thus optimising the dataset size employed in real-time high-resolution reconstruction of the specimen over a wide field of view.

This thesis explores the realization of low facet reflectivity using self-aligned stripe buried waveguide configuration and its implementation in optoelectronic devices such as superluminescent diodes (SLDs) and semiconductor optical amplifiers (SOAs). I explored the development of the buried waveguide in AlGaAs/GaAs material system ,since its first presentation in 1974 by Tsukada, in order to identify the problems associated with this technology. A novel window-faceted structure is demonstrated. The experimental measurements demonstrated effective reflectivity <10-14 as a result of both divergence and absorption within these window-like regions (i.e. not transparent). Its implementation to suppress lasing in tilted and normal-to-facet waveguide SLDs was thoroughly investigated in chapters 3 and 4. In the tilted devices, ~40mW output power with spectral modulation depth < 2% is demonstrated. In the latter types of SLDs, up to 16mW output power with <5% spectral modulation depth was recorded, which is the highest power demonstrated for such configurations. The performance of the two types of devices was measured without the application of anti-reflective coatings on the rear facet, which makes them inherently broadband. By incorporating a windowed facet at each end of a waveguide I could realize an SOA with window structured facet. Promising results were demonstrated in this configuration including 33dB gain and <6dB noise figure, which are comparable to the state-of-the-art. A trial was held to extend the concept of absorptive rear window to visible wavelengths available in the GaInP/AlGaInP material system. Problems associated with such devices were explored briefly and two solutions are suggested. Simulations were performed to realize design of an optimized device. Unfortunately, the experimental implementation of the design was not successful but suggestions for strategies to overcome these problems are discussed.