In the fifty years since their discovery, the use of laser oscillators and amplifiers has increased to cover a wide range of applications. This thesis develops diode-pumped solid-state (DPSS) lasers for two main applications: industrial processing and remote sensing. The first half of this thesis investigates the development of bounce geometry lasers that can be used to generate high power light sources suitable for industrial processing using diode-pumped Nd:YVO4 laser sources at both 1342nm and 1064nm transitions. The first of these investigations develops bounce geometry configuration Nd:YVO4 laser sources operating at 1342nm. For continuous wave (CW) operation at powers of 15.9W with 30% optical-to-optical efficiency were achieved. For pulsed operation, Q-switching based on an acousto-optic modulator and mode-locking based on nonlinear-mirror mode-locking were demonstrated. To suit a range of different industrial applications, a versatile gain switched laser diode source at a wavelength of 1064nm was developed to have independently adjustable pulse energies, pulse duration and repetition rates. To reach a commercially useful power level, a seed laser was amplified in a master oscillator power amplifier (MOPA) configuration using two ultrahigh-gain Nd:YVO4 bounce amplifiers in series. In a first amplifier (preamplifier), a small-signal gain of ~50dB with good TEM00 beam quality preservation was achieved with 24W pumping while a second power amplifier was used to achieve an average output power of up to ~14W using an input seed power of 188mW. The second part of this thesis develops laser sources for remote sensing applications based on direct diode pumping of Alexandrite lasers in an end-pumping configuration. When compared to Q-switched Nd:YAG lasers, which are typically used for satellite based remote sensing, Alexandrite lasers have the potential to be more efficient and offer more flexible wavelength tunability. Following a broad overview of Alexandrite lasers, this thesis investigates diode-pumped Alexandrite laser performance. To achieve a high average power, a compact laser cavity was built with output power as high as 26.2W and slope efficiency of 49%. This was more than an order of magnitude higher than previously reported from diode pumped Alexandrite lasers. To achieve TEM00 laser output, many extended cavity designs were investigated. Following this, to enhance the laser efficiency, an Alexandrite laser was developed utilizing the unique characteristics of temperature-dependent gain of Alexandrite and the performance from 20-150˚C was characterised. To demonstrate high pulse energies, suitable for remote sensing applications, for the first time, a direct diode pumping Q-switched Alexandrite was demonstrated. A Q-switched output pulse energy of >1mJ at 100Hz pulse repetition rate in TEM00 mode was achieved.

Sensing and imaging at the nanoscale using fluorescence based techniques has advanced the fields of biology and medical science. However there remain shortfalls with currently used fluorescent probes. One such problem is the lack of biologically inert fluorophores which emit in the red regime of the visible spectrum with good brightness. A class of newly developed fluorophores which have shown promise in fitting the required criteria are protein encapsulated gold nanoclusters (AuNCs). They have been shown to be non-toxic, red emitting, long-lived fluorophores however their low brightness has hindered their widespread use. The complexity of protein encapsulated AuNCs' fluorescence mechanism also remains poorly understood. Fluorescence based techniques, Molecular Dynamics simulations and physicochemical characterisation techniques have been employed to uncover important information critical to improving the fluorescence characteristics of protein encapsulated AuNCs. The AuNCs nucleation site within Human Serum Albumin (HSA) has been discovered which will allow for the intelligent modification of the fluorophores with the aim of improving their fluorescence intensity and low quantum yield. The effects of AuNCs on natural protein function have also been studied; indicating that the major drug binding site of HSA is blocked upon AuNCs synthesis. Further studies of the physicochemical changes in HSA upon AuNCs synthesis uncovered that the protein adopts a dimer state which could lead to complications when using as an in vivo sensor. Lysozyme encapsulated AuNCs displayed similar behaviour, forming dimers after AuNCs synthesis. Interestingly, the isoelectric point of this fluorophore was found to be the same as HSA encapsulated AuNCs, suggesting that protein encapsulated AuNCs share common features. Lysozyme encapsulated AuNCs displayed similar adsorption properties as native lysozyme; suggesting that in the future, unmodified AuNCs could be used to observe the formation of lysozyme fibrils which are a major bio-marker for currently incurable brain diseases such as Alzheimer’s and Parkinson’s.

Several groups have demonstrated the potential of the Pockels effect in Cadmium Zinc Telluride (CZT) as a means to detect ionizing radiation. Migrating charge carriers are believed to generate the signal detected via the Pockels effect due to the distortions they create within the electric field, however trapped space charge beneath the cathode has been regularly observed which suggests that the signal amplitude is potentially dominated by a large dose element. In this work, the effects of electric field collapse at the location of charge carrier generation, rather than where space charge builds up, is demonstrated. This confirms the potential to apply the technique for imaging dose rate distributions. Charged coupled device (CCD) images representing the changes in electric field within the crystal were taken and the response to illumination from a collimated 1550 nm 4.5 mW IR laser and irradiation from 150 kVp X-rays measured. The data demonstrates that the signal acquired is a combination of both the local change in the electric field at the location where the carriers are being released/generated and an element caused by them becoming trapped, leading to space charge near the cathode. Whilst the presence of both components has been demonstrated, their time response to an IR pulse measured via a photo-diode is the same (within the 6 ms time limitation of the system). This means that when using a Pockels detection system the average change in field can be considered proportional only to the incident dose rate when working in the millisecond regime. In addition to finding the origins of the detected signal an investigation into the effects of doping a Cadmium Manganese Telluride crystal with vanadium was carried out to see whether the large increases in Pockels constant found in the literature when using doped CZT could be replicated. However, it was found that whilst there is a slight improvement in the constant and hence the sensitivity of the crystals it was not as significant as hoped. A fibre optic Mach-Zehnder interferometer has also been designed and built with the aim of developing further the results from a previous free-space concept demonstrator. In its present condition the effects of environment have been minimised but the detector system struggles with large attenuation losses due to repeated coupling into fibres and is currently not usable, however, increasing the power of the laser and trying to limit even further the free-space elements in the future should remedy this.

No description available.

This thesis reports on the development of two, conceptually different, holographic measurement systems for the study of three-dimensional displacement and velocity fields. The first approach reported in this thesis is an intensity correlation-based holographic velocimetry system that employs a reference-multiplexed, off-axis geometry for determining velocity directions using the cross-correlation technique, and a stereo camera geometry for determining three-dimensional fluid velocity fields. The pulsed-laser recording system produces three-dimensional particle images with resolution, signal-to- noise ratio, accuracy and derived velocity fields that are comparable to high-quality two-dimensional photographic PIV (particle image velocimetry). The high image resolution is accomplished by using low f-number optics, a fringe-stabilized processing chemistry, and a phase conjugate play-back geometry that compensates for aberrations in the imaging system. This holographic velocimetry system is then used to successfully measure the volumetric, three-dimensional velocity field of an air nozzle jet flow. In this experiment, more than five million three-dimensional velocity vectors are successfully identified within a single hologram result.

Underwater optics is a subject area with many applications from vision to remote sensing. Most have traditionally suffered from a limited range capability, despite advances in compact laser sources and beam steering technology. One reason for this is a lack of fundamental data concerning the propagation characteristics of high-power cw and pulsed beams through turbid media at the distances required. This project was designed to address that shortcoming by investigating two non-linear effects of high-power lasers underwater: thermal lensing and stimulated Raman scattering (SRS). A novel test facility was designed and attenuation measurements made at pathlengths up to 27m, using an array of mirrors, with argon ion (4.5W, 514.5nm) and Nd:YAG (140mJ, 532nm) lasers.

The analysis of aerosols was one of the first direct applications of holography and illustrates the advantage of in-line holography over photographic or direct observation methods. The diffracted light waves from an illuminated sample volume are made to interfere with a phase related reference wave and the resulting hologram can be used to produce a real, magnified, three-dimensional image of the original sample volume. It therefore provides a unique approach to the in-situ analysis of dynamic particle fields. However, although the technique has many important applications, its usefulness has been limited by the quality of the reconstructed image. The choice of recording materials and processing methods and their contribution to the image quality, has been investigated. This has resulted in improved images from both phase and absorption holograms. By direct analysis of the reconstructed image, the size, shape, orientation and velocity of individual droplets or particles is obtained. The technique has been used to determine the droplet size distribution from several agricultural spray devices and in this context has been compared to some of the major existing sizing systems. In addition, in-line holography has been applied to the study of droplet behaviour near cotton leaf surfaces. The effect of parameters such as droplet size and wind speed on the impaction efficiency was investigated to determine the optimum droplet size for specific spraying conditions. Finally, the technique has been applied to problems of concentration studies, the measurement of natural spore velocities and the conditions governing ligament formation from rotary atomisers.

The aim of this project has been to improve the visual quality of holograms by improving the quality of commercially available photographic recording materials and their associated photochemical processing. This aim has been achieved by carefully considering all aspects of processing stages and applying them to the very high resolution images encountered in holography.

No description available.

Red-emitting quantum well (QW) 630nm laser diodes have many potential applications in industry and medicine. The main profiteers would be in areas such as the development of critical memory, barcode readers and in the treatment of cancer. The limitation of the low inherent band offsets of the materials used to create such devices, gives rise to a high percentage of electron leakage via thermal activation in the QW active region. However, implementation of Multiquantum Barrier (MQB) into the p-type cladding region of the device enhances the effective conduction band discontinuity, thus increasing the reflection probability of carriers back into the device active region, consequently elevating output power of the laser device. A study of (Al[0.7].Ga[0.3])[0.5]ln[0.5]P/(Al[0.3]Ga[0.7])[0.5]ln[0.5]P (barrier/well) MQB has been investigated as a feasible material structure to enhance electron confinement within laser diodes in the 630nm regime. The structure was optimised theoretically based on the Gamma-X transport mechanisms, using an effective mass approximation and the transfer matrix technique. To accurately model such structures it is important to include possible distortion to the conduction band profiles induced by the different positions of the Fermi level with respect to the vacuum level. Thus, a dual-band device simulator was developed to model the band bending features, of both the Gamma and X minima. This novel simulator simultaneously solves the constituent expressions making up the drift-diffusion equation set, which is then solved iteratively with Schrodinger's equation to yield a self-consistent solution. Using these two simulation models a novel MQB structure is proposed which inhibits electron transmission across it in both the Gamma and X bands. Subsequently, this MQB structure predicts a theoretical effective enhancements of 50% the height of the intrinsic conduction band offset.