The drive to produce low cost and efficient solar cells to replace solid state silicon cells has led to the rapid growth of nanotechnology in the PV sector. The extremely thin absorber (ETA) layer solar cell is a device that relies on the use of nanostructured anodes. The very high surface area of the metal oxides enhances the efficiency of the devices by increasing light harvesting in the cell. TiO2 has been the most common material of choice in these cells. However, alternative materials such as composite electrodes ZnO/TiO2, ZnO/SnO2, ZnO/Al2O3 have been considered. These systems also have the ability to improve charge carrier separation and broaden their photoresponse region. In addition to selecting materials with the correct energetics, the morphology of the metal oxide particles plays an important role in these devices. The ability to manipulate the shape, size, and surface to volume ratio of these oxides is critical in influencing the materials chemical, electronic and optical properties. In this thesis the fabrication of composite (ZnO,SnO2) electrodes by aerosol assisted chemical vapor deposition (AACVD) was investigated. By simply varying the Zn:Sn ratio in the precursor solution, a range of (ZnO,SnO2) composite materials along with single phase ZnO and SnO2 has been fabricated. It has been found that the morphology of the deposited electrodes is highly dependent on the Zn content with electrodes with morphologies ranging from nanoplates, to nanocolumns, to highly compact structures have been deposited. The dependence of the Zn content in the deposition solution on the photoelectrochemical (PEC), optoelectronic, photon to electron conversion efficiency (APCE) and photovoltaic characterization was investigated. ETA solar cells with FTO/(ZnO,SnO2)/In2S3/PbS/PEDOT:PSS/Cgraphite/FTO structures were successfully fabricated to demonstrate the suitability of (ZnO,SnO2) anodes in these devices. This work has shown that AACVD is a useful technique for engineering the properties of semiconducting electrodes for PV applications.

Modern tactics for carrying out military and antiterrorist operations calls for the development of a new generation of enhanced portable infrared imagers. The high performance of these imagers relies on the focal plane arrays, which are maintained at cryogenic temperatures using rotary Stirling cryogenic engines. These engines are known as powerful sources of wideband vibration export. For the sake of weight and compactness, the enclosure of the above imager is usually designed in the form of a light metal thin-walled shell, accommodating a directly mounted Infrared Detector Dewar Cooler Assembly. The operation of the device typically leads to an excitation of the inherently lightly damped structural resonances and therefore, to a radiation of the specific acoustic signature capable of compromising the aural stealth of the IR imager. Such a noisy IR imager may be detected from quite a long distance using enhanced sniper detection equipment or even aurally spotted when used in a close proximity to the target. Numerous efforts were taken towards achieving the desired inaudibility level, apparently becoming one of a crucial figure of merit characterizing the portable IR imager. However, even the best examples of modern should-be silent imagers are quite audible from as far as 50 meters. The presented research intends to improve the aural stealth of the portable IR imager by using three different approaches: First, by compliantly mounting the Infrared Detector Dewar Cooler Assembly where the stiffness and damping of the vibration protective pad are optimized for the best acoustical performance without developing excessive line of sight jitter. Secondly, by using the concept of the weak radiator to reshape the enclosure mode shapes, and finally developing a multi-modal distributed dynamic absorber (MMDA) to enhance the absorption of the vibrating structure. The multi-modal characteristic of such a dynamic absorber makes it highly dynamically reactive through a wide frequency range (20 kHz) of excitation. It will be shown that incorporating a MMDA into the vibrating structure will result in ultra range vibration attenuation, making the IR aurally silent.

In this thesis the development of a single pass non-dispersive infrared (NDIR) CO2 gas sensor with a path length of 30mm and with a lowest level CO2 detectivity of 20 ppm is described. A single pass NDIR CO2 sensor was developed in order to better understand the effect of the different sensor components i.e. the infrared source, thermal detector and the interference filter has on the NDIR CO2 gas sensor’s sensing ability for the industrial gas sensing application. . The study of various IR sources, detectors and filters has resulted in developing methodology that can be used for characterising IR sources detectors and filters from an application point of view. The obtained result from such application specific characterisation shows a more realistic measure of the NDIR CO2 sensor’s individual components performance characteristic, than what is quoted by the manufacturer of the IR sources, detectors and filters. The developed characterisation methodology is novel in its own right as such methodology currently to the author’s knowledge does not exist in the available literature. In order to better understand the effect of different infrared (IR) source, detectors and filters four different types of IR sources (microbulb, membrane type source, IR-LED source and ICX 2Dmetallo photonic crystal sources/detector pair), three different type of IR detectors Pyroelectric detectors, Thermopile detectors and 2D-metallo photonic crystal source/detector pair and two interference filters were investigated. A new amplitude modulation (AM) scheme was developed for driving the 2D-metallo photonic crystal device as a detector. This has resulted in an improvement of the 2D-metallo photonic crystal devices detectivity by a factor of 102 compared to the standard / conventional / recommended scheme. Demonstrations of the performance of the developed NDIR CO2 gas sensor are also shown in this thesis.

Tapered optical fibres have been manufactured, characterised and studied. These are compact devices made from single-mode optical fibre. A system for producing tapers has been developed, employing flame heating of the optical fibre and computer controlled rotation stages to stretch the fibre in a controlled and repeatable fashion. Subsequently tapered fibres were coated with nanostructured films of materials that change their optical properties in response to an external stimulus. An investigation of the effect of depositing chemically sensitive nano-scale films onto tapered optical fibres has been undertaken. Three different methods of deposition were applied: Langmuir-Blodgett technique, electrostatic-self-assembly and – for the first time - chemical grafting. Six different films of materials were deposited onto tapered fibres: 4-[2-(4-dimethylamino- naphtalen-1-yl)-vinyl]-1-octadecyl-quinolinium iodide (merocyanine dye), calix[4]resorcinarene, bilayers of poly(allyamine hydrochloride) (PAH) and anionic tetrakis(4-sulfophenyl)porphine (TSPP), PAH and cyclodextrine, TiO2 nanoparticles imprinted with ((1-(4-Nitrophenylazo)-2-naphthol (NPAN) compound), polyaniline (PANI). During the deposition process the light was launched into each fibre and the evolution of the transmission spectrum observed. The coated tapers were subsequently investigated for their potential application as chemical sensors: pH, red-ox, ammonia sensors. The response to a stimulus was investigated by immersing the coated tapered fibre in an environment containing the measurand. The properties of these devices were also used in combination other photonics concepts, such as fibre Bragg gratings written in the tapered region of a fiber, under investigation within the Engineering Photonics Group to develop new sensor elements.

Active millimetre-wave imaging systems can be employed in security applications to recognise and identify concealed weapons among clothing. Nevertheless, generated images have some limitations in various aspects. These are primarily related with the high amount of noise present in the system, the poor spatial resolution and the insufficient thermal contrast produced by certain scene components. The main goal of this thesis has been to develop a physical optics modelling of the millimetre-wave image formation (theoretical and computer-based) for the optimization of current millimetre-wave systems. To this etfect, we have implemented a comprehensive millimetre-wave image simulator, which was developed to fulfil the existing gap in the millimetre-wave modelling at the time this system was needed. The major advantage of this innovative system is that it offers low-cost and rapid exploration of the effects of various key parameters of the image formation process. Thus, the optimization is carried out by setting up different im- ager configurations with the simulator and by generating the cor- responding synthetic images for different scenes. The enhanced understanding that these synthetic images provide has enabled the improvement of real millimetre-wave images in terms of thermal contrast or noise. This thesis has contributed in three different areas. First, it provides a theoretical model which includes all the stages of millimetre-wave image formation. Second, it describes the design and implementation of a novel millimetre-wave image simulator, which is capable of generating realistic and mathematically validated images. And third, it reports the exploration of different optimizations that may be carried out within current millimetrewave systems regarding both physical and post-processing aspects.

The aim of the work reported in this thesis was to investigate the physical principles and potential applications of wavefront coding. This technique enables extended depth of field and greatly reduced sensitivity to defocus-related and higher-order aberrations whilst maintaining diffraction-limited resolution in incoherent imaging systems. Wavefront· coding involves the introduction of an asymmetric refractive mask close to the aperture stop so as to encode the image with a specific point spread function that, when combined with decoding of the recorded image, can enable accurate image acquisition even in the presence of aberrations. In practical imaging systems, this enhancement is subject to a range of constraints and limitations which have been neglected in previous works. We show that although-wavefront coding has sometimes been presented as a panacea, it is more realistic to consider it as an additional parameter in the optimisation process. This research explores the trade offs involved in the application of wavefront coding to lowcost imaging systems for use in t,he thermal infrared and visible imaging systems, showing how very useful performance enhancements can be achieved in practical systems. Some of the original contributions of this work include the design of new phase masks, a new understanding of the fundamental physical principles in terms of the decomposition of the optical transfer function, appraisal of the restoration issues (detector sampling, noise amplification and artefacts in the digitally processed image) and the design and manufacture of a wavefront-coded infrared singlet.

No description available.

Historically, much scientific work has been performed with two optical systems - the telescope and the microscope. Although Galileo was probably not the first to invent the refracting telescope, his rapid development of the instrument from 1609 results in his association as the father of the telescope today. Certainly he was the first human to view the giant moons of the planet Jupiter - Io, Ganymede, Callisto and Europa - and thus dare to venture our world was not the centre of the universe, and save our race from another thousand years of mysticism. A year later, in 1610, Galileo invented the microscope and this led to the new field of science called 'microscopy' to open up the previously unsuspected world of the ultra small. Tiny life forms no larger than a pinhead were revealed, and with instrumental improvements by later scientists the existance of bacteria proven. This discovery prompted the sterilisation of surgical equipment taken for granted today, saving countless millions of lives since then through freedom from bacterial infection. It is beyond doubt that the new world opened by the invention of the microscope inspired the scientists of that time to seek yet greater magnification and sharper images, to delve deeper into this tiny world. Yet technical improvement in the design of the microscope wase hampered by the lack of a proper theory of image formation. Not until the late nineteenth century, when ABBE and RAYLEIGH provided the foundations of the present day diffraction theory of imaging was the microcope properly understood. The work of this thesis has its roots in the developments of the early twentieth century microscopists. For many years they had observed tiny, transparent organisms and sought ways to improve the visibility of these creatures so that their nature might better be understood. The problem was solved by F.Zernike in 1935 (1, 425 for ref.) when he considered the way the organisms altered the phase of the illuminating light field. By the correct positioning of a thin phase-plate in the back focal plane of the microscope lens, Zernike demonstrated that optical thickness variations of the organism may be rendered visible as intensity variations. In this thesis , the light distribution in the back focal plane of such a lens that results from a transparent object is analysed in detail. From the expression derived by Zernike to explain the operating principle of his invention, we evaluate alternative formulations of the problem and proceed to a full analytical expression for the light field . Though mathematically awkward, it is shown the expression is not unworkable and several useful results are derived. In place of a microscope the study is based on imaging in a modern image processing bench, the physical principles involved being identical. Zernike introduced the idea of image modification through the use of a basic form of phase filter. The second half of this thesis develops this idea to show the use of much more intricate phase filters, which may be used to 'recognise' particular objects. Filter design is followed by experimental results on a special type of phase object, the programmeable Spatial Light Modulator.

Sensors incorporating zirconia electrolytes have been widely used for monitoring oxygen concentration and the air-to-fuel ratio of combustion systems. The aim of this work was to investigate the extension of this technology to other gases and to gas mixtures. Initial work was done on single zirconia. discs with porous metal electrodes on each face. Platinum, silver and gold electrodes were tested in controlled Atmospheres at temperatures between 300*C and 850*C. It was shown, as expected, that in 02/N2 mixtures electrode activity/conductance decreased as oxygen concentration and temperature were reduced. In CO/CO2/N, 2 atmospheres reproducibility was poor. Interestingly, an increase in electrode conductance of 1-2 orders of magnitude was observed as the temperature was reduced through around 700*C which does not appear to have previously been reported. Is is thought to be related to the corrresponding change in the thermodynamic stability of CO at this temperature, ie 2CO ; ==t C1 + C02. Zirconia pump-gauges with small enclosed volume (< Imm3) and laser drilled diffusion holes were constructed with the novel addition of reference electrodes. These were operated with current-interruption circuitry and rapid subsequent data aquisition. This enabled, for the first time, the overvoltage due to charge transfer on the internal pumping electrode to be isolated: interesting behaviour was revealed. The overvoltage increased as oxygen-containing gases were, reduced and then. in the case of NO, decreased as the reduction reached completion. The gauge EMF remained remarkably stable while NO was being reduced. Reduction of S02 was shown to generate electronic conductivity in the yttria-stabilised zirconia. A potentially important result was obtained when operating a sensor in CO/CO2/02/N2 mixtures where there was sufficient 02 present to oxidise all the CO present to C02. With the application of zero pumping current the gauge EMF showed a substantial, non-zero, value. It was suspected that a mixed potential developed on the external electrode while the diffusion hole prevented its formation on the internal electrode. Based upon'the results obtained, two sensor designs are proposed. The first is a lean-bum combustion sensor eliminating the possibility of an ambiguous response in rich- and lean-bum conditions. By reducing the activity of the external pumping electrode while maintaining a highly active internal pumping electrode the response in rich-bum conditions would be insignificant while the response in leanbum conditions would be maintained. The second design concerns multi-gas sensing; it is based upon previous designs but the need for minimising electrochemical leakage was pinpointed by this work. Because overvoltages on the internal electrodes were shown to reach high values electrode activitity should be high and a gauge cell should be incorporated to provide information about the oxygen partial pressure within the sensor. If operated by sweeping the voltage applied it was shown that because of the slow electrode response the sweep rate would need to be less than 0.2mV/s. Consequently, it is proposed that an array of sensors operating at a range of fixed pump voltages would greatly reduce the response time. A computer-controlled apparatus was built with which to perform the experimental work. The apparatus controlled the furnace temperature, gas mixing apparatus and a potentiolstat/gaivanostat. The latter was purpose built so that all current and voltage ranges could be selected by the computer and current interruption performed automatically. Using software written in Turbo Pascal the apparatus was capable of performing a wide range of tests, unattended over periods of months.

No description available.