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The generation of single CO2 laser pulses, having sub-nanosecond rise and fall time, is described. The duration of these pulses is controlled in the range 0.83 to 100ns and their peak power is of the order of 1 MW. For the generation of these pulses, a double-discharge TEA CO2 laser has been used, in conjunction with an electro-optical shutter. A telescopic CO2 laser amplifier has been employed to amplify the nanosecond pulses to 1 GW power levels. The design and operational characteristics of this device are presented and the effective elimination of associated problems is discussed. The effect of organic vapour additives on the performance of this oscillator-amplifier system is investigated. Experimental evidence is presented indicating an increased efficiency in the amplification of multi-line - as opposed to single line - nanosecond pulses. A novel method for single longitudinal mode operation of pulsed TEA CO2 lasers - incorporating the use of two unstable coupled resonators - has been developed. The powers thereby achieved are in excess of 30 MW.

In this thesis, the problem of the metrology of optical surfaces is examined. The need for accurate metrology is established with regard to optical wavefronts reflecting or refracting at the surfaces of optical components. Optical interferometry is identified as the most useful analytical tool for surface metrology by virtue of its high precision and accuracy. Accordingly the theory of interferometry is briefly presented. The application of the theory to the interferometric instruments is shown together with measuring configurations for the various optical surfaces commonly encountered. An extensive overview of the techniques used to evaluate data from interferometric measurements is given with particular emphasis on precision phase measuring methods. Most interferometric measurements of surfaces aremade relative to a reference surface of high quality. Where the accuracy of the surface to be measured is comparable to, or better than, that of the reference surface, an absolute measurement technique is required in order to give meaningful results. A review is given of the existing methods for the absolute measurement of nominally flat and spherical surfaces and the shortcomings of these methods. A new algorithm for the absolute testing of flat surfaces is developed, based on relative measurements of pairs from a population of three test flats in a number of positional combinations. The new method has a number of potential advantages over those previously described, particularly since it yields information about the flats over their entire surfaces on a square grid of points. The implementation of the new method on a Zygo Mark IV interferometer is described together with experimental results using both synthesized and actualexperimental data. Suggestions for improvements to the method and its implementation are made. A speculative study of other possible techniques for absolute flatness measurement is presented, including the possible application of the Ritchey-Common test, point diffraction interferometry, phase conjugation and profilometry. A full and up to date survey of the pertinent literature is given throughout the thesis.

This thesis has two themes. Firstly, it concerns the original application of holographic beam shaping, employed through the methods associated with optical manipulation, to three microscopic fields of research. Secondly, it studies the optical trapping of aerosol droplets through experimentation and computational modelling. The aims are to not only provide an account of the work carried out but also a base for future researchers and students. Chapter 1 provides an introduction to the field of optical manipulation and the relevance of my studies. Chapter 2 outlines the construction of an optical tweezers which is the basis of advanced experimental work described in later chapters. It also overviews how optical tweezers operate and are quantified. In chapter 3 I describe how beam shaping is implemented for my investigations with a spatial light modulator and phase-only holograms. I detail the algorithms and software written before discussing their performance and finally the optimisation of the apparatus. Chapter 4 describes three original applications of beam shaping, including the trapping and coagulation of multiple aerosols, the manipulation of filamentous fungi hyphal tips and novel digital microfluidic operations using thermocapillary forces. I also lay down preliminary results for observing orbital angular acceleration using beams carrying orbital angular momentum. To study single optically trapped aerosols I use two methods. Firstly, their Brownian motion is investigated through sub diffraction limit position detection. Unique results in optical tweezers are shown with liquid droplets behaving as under-damped Brownian oscillators. Through these studies I demonstrate a new technique for sizing trapped aerosols, with significant advantages over current methods. I also show that the droplets can be be parametrically excited which can result in trap failure. Secondly, in chapter 6, I use a theoretical model to describe the forces imparted to a trapped droplet. I extend current theories to include the effects of a three medium focal region to accurately describe airborne optical traps. The work qualitatively explains the phenomena observed experimentally. The work contained here leaves much scope for future investigations, for which I provide an overview in chapter 7.

Optical tweezers have become an invaluable tool for measuring and exerting forces in the pico-Newton regime. Force measurements have in the past concentrated on using only one trapped particle as a probe, partly due to the difficulties in tracking more than one par- ticle at high enough frame rate. Recent advances in video camera technology allow the collection of images at several kHz. However, there has been little use of high-speed cameras in optical tweezers, partly due to data management problems and affordability. This the- sis presents seven experiments carried out during my PhD involving the use of several different high-speed cameras. Chapter 3 presents the use of a CMOS high-speed camera with in- tegrated particle tracking built by Durham Smart Imaging. The camera was used in a Shack-Hartmann sensor setup to determine rapidly and non-ambiguously the sign and magnitude of the orbital angular momentum of a helically-phased beam light beam, as an alternative to interferometric techniques. Chapter 4 presents a di- rect comparison of a CCD high-speed video camera with a quadrant photodiode to track particle position. Particle tracking was possible at high enough accuracy and bandwidth to allow convenient trap calibration by thermal analysis. Chapter 5 reports an investigation of the resulting change in trap stiffness during the update of trap positions in holographic optical tweezers. Chapter 6 presents the re- sults from using a high-speed camera to successfully track multiple particles in a microfluidic channel to measure the viscosity at sev- eral points simultaneously. The last three chapters investigate the hydrodynamic interactions between trapped particles under different conditions and comparisons were made with theory.

Future generations of gravitational wave detectors will require significant progress in the reduction of all forms of noise affecting the system. One form of noise it is critical to reduce is thermal noise, which can be described as the consequence of the atoms which make up the measurement optics experiencing vibrations because of their non-zero temperature. The dielectric multilayer coatings of the mirror in an interferometric gravitational wave detector are known to contribute significantly to the overall levels of thermal noise. The next generation of gravitational wave detectors may need to use exotic coatings, cryogenic operating temperatures and silicon mirror substrates in an effort to mitigate the effects of thermal noise. Chapter Two describes thermal noise in detail, and introduces the concepts of substrate noise, coating noise, thermoelastic dissipation, mechanical loss and the formulae used to calculate them. Chapter Three describes the current state of research on the factors affecting mechanical loss in dielectric coatings. The technique of probing the structure and dissipation characteristics of materials by assessing the shape and position of the low temperature excess loss feature known as a Debye peak is introduced. The cryogenic mechanical loss measurement apparatus used in Chapters Four, Five and Six is described and characterised. Chapter Four concerns the variation of mechanical loss of ion-beam sputtered silica coatings with temperature and investigates the effects of heat-treatment upon them. The low-temperature Debye peak was found in some modes of a sample heat treated at 300oC and an Arrhenius analysis provided a characteristic energy for the dissipation process of (17.3 ± 2.3)meV. Further heat treatment of silica at 600oC and 800oC appears to narrow the Debye peak, which is thought to be indicative of the narrowing of the distribution of bond angles in the amorphous silica network. Hafnia is investigated as an alternative coating material in Chapter Five. The mechanical loss of hafnia heat-treated at 300oC was measured and two excess loss features were discovered, one below 100K and one above 200K. Electron scattering measurements indicate that this sample may already have developed polycrystalline regions which are known to be connected to high levels of mechanical loss. The mechanical loss of an un-heat-treated hafnia coating is also measured and an extremely low coating loss of 1.87 × 10−5 is found at 20K. Chapter Six describes an experiment to find the mechanical loss of a hydroxycatalysis bond between silicon cantilevers at temperatures between 10K and 300K.This new technique for the measurement of the mechanical loss of bond material produced a minimum upper limit of the bond loss of (0.13 ± 0.03) occurring in the fundamental mode at 80K and upper limit of the bond loss of (0.19 ± 0.07) occurring in the third mode at 15K. Chapter Seven describes the development and testing of a nodal support system to enable cryogenic measurements of cylindrical bulk mirror substrates to be made. The efficacy of the support varied significantly with the frequency of the mode and the cryogenic measurements were partially successful. The major results in this work are the successful measurements of the mechanical loss of amorphous hafnia coatings at low temperatures and the use of a structure made from hydroxy-catalysis bonded silicon cantilevers to obtain an upper limit for the mechanical loss of the bond material. These results may inform technological advances that reduce the level of thermal noise experienced in future gravitational wave detectors.

That neutrinos have mass and mix is now well established experimentally. Measurements of the properties of neutrinos from both natural and man-made sources have measured the large mixing angles and mass squared differences. In order to fully understand the nature of the neutrino, and ultimately the lepton sector, a number of measurements remain to be made. The Neutrino Factory would produce an intense beam of muon neutrino (muon antineutrino) and electron antineutrino (electron neutrino) from the decay of muons creating an intense flux of neutrinos. Such a facility would be capable of constraining the already measured mixing parameters to unprecedented accuracy while achieving sensitivity to the measurement of the third mixing angle and leptonic CP violating phase unrivaled by other facilities. The golden channel is characterised by the observation of a primary muon of the opposite charge to that decaying at the source, however, since this signal is subdominant the large data sample of correct sign muons have the potential to produce backgrounds to the desired signal channel and as such understanding the cross-sections to high accuracy enables a far better understanding of the response of the detector. Making these measurements requires the optimisation of all aspects of the detectors used for the measurement of the interaction properties as well as those which search for the appearance of neutrino flavours not present at the source. Pixellated silicon detectors are capable of high resolution three dimensional track reconstruction and vertexing. In studying active pixel sensors (APS) it was sought to understand the feasibility of commercially available technology to perform vertexing at a detector positioned within 1~km of the neutrino factory source. Using such technology at this near detector would improve significantly the ability of the experiment to constrain the cross-sections of neutrinos. These measurements would be particularly important in understanding neutrino induced charm production since the decays, in particular of charged D mesons, can produce penetrating muons with the potential to confuse the extraction of the appearance of muon neutrino (muon antineutrino). The capability to observe the impact parameter of the decaying meson significantly improves the accuracy of any measurement of the charm production cross-section. A Magnetised Iron Neutrino Detector (MIND) of large mass (50-100 ktonne) has been studied as the far detector where high suppression of the beam inherent backgrounds can be achieved due to the powerful suppression of hadronic particles in iron. Particular focus has been given to the introduction of a realistic reconstruction of the signal and analysis which optimises the signal efficiency below 5 GeV which has been identified by theoretical studies as key to the accurate measurement of the oscillation parameters down to low values. Studies of this detector have led to the extraction of the expected response of the detector to both golden channel signals and demonstration of the power of such an analysis to the measurement of the remaining oscillation parameters. Using minimal assumptions in the digitization of the simulated signal, the reconstruction and analysis of a large data-set of neutrino interactions, including deep-inelastic scattering (DIS), quasi-elastic scattering (QEL) and resonant pion production (RES), in MIND has led to the extraction of response matrices predicting signal efficiency for both muon neutrino and muon antineutrino appearance with thresholds between 2-3 GeV while suppressing key beam inherent backgrounds to at or below the 10^-4 level. Such a response has been shown to open the possiblity of sensitivity to the measurement of leptonic CP violation through the measurement of the mixing complex phase delta down to theta13 of order 0.2 degrees for maximal violation and to most possible values from theta13 of order 1 degrees. Sensitivity to the measurement of theta13 and to the determination of the true mass hierarchy is maintained down to theta13 of order 0.25 degrees.

The work in this thesis is focused on characterisation and evaluation of two classes of science grade imaging radiation detectors. The first class is Monolithic Active Pixel Sensors (MAPS). The advances in CMOS fabrication technologies over the last four decades allowed MAPS to compete with Charge-Coupled Devices (CCD) in many applications. The technology also provides relatively inexpensive ways to tailor design to suit specific application needs. It is important to understand performance capabilities of new sensor designs through characterisation and optimisation of readout parameters. In this work three MAPSs were characterised. The first one - HEPAPS4 - designed for charged particle detection, with the potential technology application in the vertex detector for the International Linear Collider. The noise of the sensor was measured to be 35±5 e, which agrees well with simulated data. The dark current was found to be 175 pA/cm2. The SNR performance for minimum ionising particles detection was demonstrated to be 40. The sensor was also evaluated for indirect detection of thermal and fast neutrons using lithium and polyethylene converters. The technology performed well in such an application with an estimated fast neutron detection efficiency of ~0.01%. The second sensor characterised – Vanilla MAPS – was designed to evaluate new techniques for fast readout, small noise and reduced image lag. The system was capable to readout 150 full frames (520x520 pixels) per second; the sensor showed 14±4 e noise and decreased image lag. The dark current was found to be ~50 pA/cm2. The back-thinned version of the sensor demonstrated dramatic improvement in quantum efficiency from 0% to 20% at 220 nm. The third device is parametric sensor eLeNA. It features 14 test structure designed to evaluated noise reduction architectures. The most promising structures showed temporal noise values as low as 6 e and 20 e fixed pattern noise. Medipix as an example of the second class of imaging detectors - hybrid pixel detectors - was evaluated in two applications. It was used as the core element of the ATLAS radiation background monitoring system. The sensors were covered with neutron converters, which extended the number of radiation types that can be detected. X-ray calibration was performed, showing excellent tolerance of all 18 devices characterised. Detection efficiencies were estimated to be ~1% for thermal and ~0.1% for fast neutrons. The second application of Medipix was mass spectrometry. The detector was place in the focal plane of a prototype mass spectrometer. 2D representation of data allowed focusing correction of the ion beam. The system was capable to detect ions in the range of 5-25 keV. The detector characterisation with broad range of ions (from Cu to Pb) showed very good abundance agreement with table data.

The influence of various dopants on the properties and local structure of glass samples was explored and a quantitative determination of the structural changes in the network as the dopant concentration was varied was achieved using 27Al, 29Si, 33S MAS NMR. Findings showed that silver- and copper-doping of phosphate based glass gave rise to unexpected connectivity between the phosphate units most likely due to some phase separation creating a different composition to that intended in the majority glass. This emphasises the importance of a careful and systematic approach to sample manufacture in achieving high sample stabilities, leading to a good degree of predictability in both structure and properties. Lanthanum and yttrium ions, despite their huge difference in ionic size, showed very little difference in their effect upon the phosphate coordination in the glass samples as they remain outside the phosphate network, cross-linking between the terminal oxygen atoms. The aluminium ions however, showed evidence of behaving in both a cross-linking manner and in a network forming, tetrahedral role and it appears energetically favourable for them to avoid any Al-O-Al linkage, hence resulting in the formation of AlO4 rather than exceeding the AlO5 or AlO6 quantities that would lead to this. The sulphur NMR looks to be a very promising method for future use in understanding sulphur speciation in glasses.