This thesis deals with the development of automatic methods for nding pulsation events in time series produced by the radars in the SuperDARN network. These methods are then applied to the detection and analysis of pulsation events illustrating the relative usefulness of radar data for the study of global pulsation dynamics. Each of the SuperDARN radars produces 1200 Doppler velocity records every hour. If backscatter is present, and there is a pulsation occurring in the same region as the scatter, the pulsation can be measured as periodic changes in the Doppler velocity of that record. There are over 85 million Doppler velocity data records for 2004. In order to identify pulsations in these data, an automated pulsation nder was developed. All records with signi cant peaks in the FFT spectra were tagged as having a pulsation present. If a record had less than 20% data missing it was termed a clean record as it was suitable for use with the automated pulsation nder. As pulsations can only be observed if there are scatter, an investigation into scatter characteristics are presented. It is shown that the occurrence of clean records is most strongly in uenced by IMF Bz, and the underlying spatial structure of the SuperDARN network. The results for the automated pulsation nder for 2004 are then presented. It was found that the average daily distribution of pulsation events, shown as a function of pulsation frequency, followed 1/f distribution with no distinct peaks. It was also found, however, that the standard deviation of the average showed peaks close to the "magic" frequencies indicating that on average there is more variation at these frequencies that any of the other pulsation frequencies measured. The occurrence of pulsations followed the clean scatter statistics both temporally and directionally telling us that the network is not suited for studying global pulsation dynamics because the variations in scatter dominated any variations in pulsation occurrence. Data from a few events identi ed by the pulsation nder are then presented to illustrate the advantages and disadvantages of using SuperDARN data for pulsation event studies. The events show a pulsation that occurs at its fundamental and third harmonics, an aliased pulsation, a pulsation, interrupted by sounding frequency changes, that shows how ionospheric scatter was tagged as ground scatter and how data from two overlapping pulsations in di erent radars can be merged to give the poloidal and toroidal characteristics of the event. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2009.

The detailed spatial and temporal influence of lightning on precipitation losses from the Earth's radiation belts is not yet well known. The precipitation is mainly due to the pitch angle scattering of electrons by lightning induced whistler mode waves. The World Wide Lightning Location Network (WWLLN) gives continuous real-time global lightning coverage with excellent time resolution. The detection effciency of WWLLN is unfortunately relatively low. This led to the normalisation of WWLLN with reference to Lightning Imaging Sensor (LIS)/Optical Transient Detector (OTD) data. LIS/OTD has very good detection effiency and spatial resolution. However, whereas WWLLN records strokes, LIS/OTD record flashes. Therefore the flash multiplicity had to be taken into account. The normalised WWLLN flash densities were compared to those of the South African Weather Service (SAWS) data, National Lightning Detection Network (NLDN) and the European LINET network. Then the average power per lightning flash was calculated to determine the energy flux incident on the ionosphere. Finally the WWLLN data was transformed to geomagnetic (MAG) coordinates using the Altitude Adapted Corrected Geomagnetic (AACGM) code. By applying absorption curves, the energy flux into the magnetosphere was estimated. These values were then compared to Trimpi produced Whistler-Induced Electron Precipitation (WEP) rates. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2012.

A low-cost Direct Solar Radiation Detector (DSRD) was developed in house in the Department of Physics at the University of KwaZulu-Natal (Westville). A main use of this instrument is to gather solar energy data that are to be used in the design of systems that concentrate and convert solar energy into thermal energy (concentrating solar thermal energy systems). These data are compiled into a database from which the efficiency and potential use of many solar systems can be based. It was required that the detector was fully characterized with respect to spectral range, polar (angular) response and environmental stability. Based on this analysis it was also required to investigate possible ways of improving the detector. An Eppley Normal Incidence Pyrheliometer (NIP) mounted on an Eppley Sun Tracker (ST) was used as a reference instrument. The ST is a power driven tracker with an axis parallel to the Earth's axis of rotation. The NIP and DSRD were mounted together on the tracker in order to correlate their responses and also to calibrate the DSRD. The results indicate that the modified DSRD works better in that it follows the reference instrument. The correlation between the NIP data and the DSRD data is better with the value of correlation factor close to unity and the root mean square error value close to zero. This means that the modifications carried out on the detector have improved the low cost in-house detector and hence the quality of data collected. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2004.

Experiments on regular two dimensional waves breaking over an artificial sand bar were conducted in a glass walled flume to facilitate an investigation of the hydrodynamic processes that evolve in the surf zone. The instantaneous time averaged velocities and the velocity flow fields have been measured using digital video imaging and analysis techniques. The instantaneous velocity flow fields were then processed, resulting in the phase-ensemble-averaged velocities, time averaged velocities and energy and momentum fluxes. The time averaged velocities above the trough level have been found to be much higher than those below. After wave breaking, kinetic energy and momentum flux are shown to increase, reaching a peak value and decreasing thereafter. An estimate of the relative density of the fluid in the wave crests was obtained by comparing the forward and reverse velocity fluxes. Other surf zone physical parameters such as the free surface displacements, wave heights across the flume and potential energies have been derived from the resistive wave gauge measurements. A spectral analysis of the water level time series was conducted and the energy growth in each spectral component was examined. It was noticed that there is a transfer of energy from the primary frequency of the wave maker to higher harmonics. Also, wave breaking has little effect on the amplitudes of the harmonic components. The roller and aeration areas were also computed. Two methods of estimating the roller area have been explored and these are the analysis of the wave gauge measurements of the surface elevation and the analysis of the video images. There was agreement between the results obtained and those published in the literature. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2005.

Pulsed lasers have a wide range of applications in industry, medicine and for scientific research. Many of these devices are expensive and have delicate optics. The nitrogen laser is robust and inexpensive to build and maintain. A short review of the experimental nitrogen lasers is given. A major part of this thesis covers work on increasing the energy output (from30 µJ to 0.3 mJ). The one design of nitrogen laser consists of a pc board etched on the sides and at the centre for the laser discharge. The separated sections are rectangular in shape. However, in the new design the discharge section of the nitrogen laser has a parabolic shape and an inclined laser channel was used instead of a horizontal one to observe the effect on the energy output. Parameters such as the distance between the top and bottom plates, the area of the bottom plate, the area of the parabola and the flow velocity of nitrogen were varied. Both nitrogen gas and cold nitrogen vapour were used as the lasing medium. The substitution of vapour for gas increased the energy 2 fold. Liquid nitrogen was tried unsuccessfully as the medium in the discharge channel. Two large lasers were built giving increased laser energy. A multilayer nitrogen laser was also built increasing the output by a factor of 2.5. The multilayer idea was also tried on the large lasers. The multilayer laser behaves like a small capacitor bank, discharging in parallel into the laser channel. The low pressure electrodes which were used on the large parabolic laser consisted of a pair of flat copper electrodes enclosed in a plexiglass housing and the latter being connected to a vacuum pump. The effect of using the low pressure electrodes on the laser energy output was investigated. Three nitrogen lasers made of aluminium foil were also constructed where transparencies and mylar were used as the dielectric insulator. In addition, a multilayer parabolic N2 laser was made using the same materials. A water wave simulation experiment of the parabolic laser was done which showed that due to the parabolic form, circular waves are converted into planes wave. The spark gap which acts as a fast nanosecond switch must be precisely located at the focus of the parabola. Otherwise the laser does not lase. Michelson Interferometry was carried out to measure the coherence length of the laser Which was found to be longer than that mentioned in the literature. The improved parabolic nitrogen laser was used to obtain fringes in a Mach Zehnder experiment. The laser is now being used by the Durban laser group as a diagnostic tool to measure the refractive index of the gas lens created in a Colliding Shock wire experiment. Carbon dioxide lasers have numerous industrial applications. The Laser group at the Atomic Energy Corporation(AEC), Pretoria are looking into possible industrial applications such as carbon isotope separation, paint-stripping and de-rusting. The author spent sometime at the centre to investigate how the beam quality and energy output of the laser can be improved since a near gaussian profile is very important for many applications. The carbon dioxide laser system basically consists of an oscillator and two amplifiers in series. Measurements of the beam parameters (waist size, pulse shape, divergence angle) along different sections of the laser chain were taken. The laser beam was double passed through one of the amplifiers to observe the effect on the energy output. Burn patterns at several places were taken to observe the beam profile. An investigation into the optical energy losses along the laser chain was made. A device called the Three Element Detector invented by the Laser Group, AEC, was also used to analyse the laser beams. / Thesis (M.Sc.)-University of Natal, Durban, 1999.

This dissertation consists of two main sections. The first is a review of laser resonators using spherical mirrors, and incorporates a physical optics numerical model of a Fabry-Perot laser resonator without gain. The output of this model, which includes spot sizes, loss, and transverse mode formation, is compared to the parameters calculated using published analytical results. This comparison serves as a verification of the numerical methods used, as well as a frame of reference for the model of a Porro prism resonator which follows in the second section. The second section proposes a new method for analysing Porro prism resonators. The analysis incorporates both geometric as well as physical optics concepts, with the prisms modelled as rotating elements with amplitude and phase distortions. This yields expressions for the orientation of the loss at the apex of each prism, and as well as the number of petals in the “petal-pattern” beam structure commonly observed from Porro prism lasers. These expressions are included in a numerical model, which is first used to verify the development of the characteristic petal-pattern. Next, the numerical model is used to investigate the development of the beam structure, in both time and space, in crossed Porro resonators with a range of Fresnel numbers and stability parameters. This leads to some new insight into the transverse modes of these lasers. / Thesis (M.Sc.)-University of KwaZulu Natal, Westville, 2008.

The purpose of this thesis was to investigate certain factors important for the operation of a high repetition rate continuously tunable CO2 laser. The tuning range of specific importance for this research program was the R30 region within the ten micron band, since this frequency is of great importance for the laser isotope separation of uranium. This research program focused on: (i) Lowering the pressure at which viable continuous tunability could be achieved. {ii)Resonator design and analysis. {iii)Investigating the feasibility of using water capacitors in a high repetition rate laser system. A theoretical as well as an experimental investigation was done into the use of CO2 isotopes to lower the pressure at which continuous tunability in the R30, ten micron band could be achieved. A theoretical analysis was done into the use of a three mirror resonator with an etalon and a grating to ensure single longitudinal mode tuning in the R30 region. Such a resonator was designed and experimental results obtained were compared with those predicted by the theoretical analysis. A study was done into the use of water as a dielectric medium in a high repetition rate pulse power supply. A mathematical model, describing the electric breakdown of water,was developed. This was compared with published experimental results. Certain parameters important for the design of a water capacitor were experimentally measured. These include the intrinsic time constant,dielectric constant and resistivity of the water. A design proposal as well as a comparison between a water capacitor and other capacitor technologies are presented. / Thesis (M.Sc.)-University of Natal, Durban, 1990.

No abstract available. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Nowadays, the information society that presides the everyday life is dependent on the communication industry to facilitate unintelligible data transfers between authenticated parties. Human desire to communicate secretly since the beginnings of the civilisation. Methods of secret communication were developed by many ancient societies, including those of Mesopotamia, Egypt, India, China and Japan, but details regarding the origins of cryptology, i.e. the science and art of secure communication, remain unknown. Secure communication as well as the protection of sensitive data against unauthorised eavesdropping are inevitably important. For example, the device, used for communication between military commanders, consisted of a tapered baton around which was wrapped a spiral strip of parchment or leather containing the message. The key is a random sequence of 0’s and 1’s, and therefore the resulting cryptogram, i.e. the plaintext plus the key, is also random and completely scrambled unless one knows the key. Indeed, Shannon proved that if the key is secret, the same length as the message, truly random, and never reused, then the one-time pad is unbreakable. All one-time pads suffer from serious practical drawback, known as the key distribution problem. The key itself must be established between the sender and the receiver by means of a very secure channel for example a very secure telephone line, a private meeting or hand-delivery by a trusted courrier. Even if a secure channel is available, this security can never be truly guaranteed, a fondamental problem remains because any classical private channel can be monitored passively without the sender or receiver knowing that the eavesdropping has taken place. Since all information, including cryptographic keys, is encoded in measurable physical properties of some object or signal, classical theory leaves open the possibility of passive eavesdropping, because in principle it allows the eavesdropper to measure physical properties without disturbing them. This is not the case in quantum theory, which forms the basis for quantum cryptography. Modern cryptographic practice rests on the use of one-way functions which are easy to evaluate in the forward direction but infeasible to compute in the reverse direction without additional information. For example, multiplying large prime numbers can be done in a time that is a polynomial function of their size, but finding the prime factors of the product is believed to require exponential time. Factoring the product of two large prime numbers can be accomplished in polynomial time on a quantum computer. However, the advancement of computing power and the advent of the quantum computer together with the vulnerability of this scheme to mathematical progress have prompted the introduction of quantum cryptography which process through the laws of quantum mechanics, ensures provably secure data transfers. The use of physical mechanisms for cryptography is well known in quantum cryptography, based on the combinations of concept from quantum mechanics and information theory, i.e. the impossibility of cloning quantum information. The Heisenberg’s uncertainty principle is exploited to designe an unconditionally secure quantum communications schemes. Quantum cryptography mades enormous progress in the technology of quantum optics, optical fibers and free space optical communication. It can be used over a classical communications channel providing a physical protection to individual bits of information as well as a hardware implemented solution. The implementation of this theoretical concept requires much practical innovation for transparent deployment into current cryptographic solutions. The theory of quantum cryptography as well as its potential relevance and the application of prototype system at the University of KwaZulu-Natal are described and the phenomenon of single-photon interference is used to perform quantum cryptography over an optical communications link. The method of BB84 (a quantum key distribution protocol that works with qubits which are two-dimensional) is presented to solve the problem of key distribution between two parties. Theoretically, BB84 is secured under certain conditions. The practical of id 3000 Clavis (quantum key distribution system) over installed terrestrial cables of distances 13,08 km at Cato Manor in Durban between Central Application Office and Minicipal original Office buildings and 15.6 km in Pinetown between Pinetown Civic Center and Pinetown Clinic buildings is the proof that the solution to the key distribution problem is given by quantum cryptography. The experiments in this work are the practical real quantum key distribution that produces the key which can be shared between two parties at the distances enunciated above. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2009.

The work presented in this thesis is centred on the generation of superimposed optical fields which each carry orbital angular momentum (OAM) and the development of OAM measurement techniques. Optical fields which carry OAM have found applications ranging from optical tweezing to quantum cryptography. Due to the fact that they offer a potentially infinite-dimensional state space, much interest has been generated in the measurement of OAM in optical fields, in order for higher-dimensional quantum information processing to be realised. In this study we generate superpositions of higher-order Bessel beams and show that even though we can create a field which carries no overall OAM, we can still witness an angular rotation in the intensity profile of the beam. We also develop two new OAM measurement techniques: (1) a robust odd-even-OAM interferometer and (2) a method to measure the OAM density of an optical field by means of a single spatial light modulator (SLM). In the first chapter we give an overview of the literature regarding optical OAM, followed by the derivation of the Helmholtz wave equation from Maxwell’s equations. We illustrate that helically-phased beams, having a phase factor of exp(ilθ), possess a well-defined OAM. Definitions for the fundamental Gaussian mode, as well as two OAM-carrying modes: Laguerre-Gaussian (LG) and Bessel-Gaussian (BG) modes are also given. Since a majority of this thesis involves generating superimposed OAM fields as well as the measurement of OAM, chapter 2 contains detailed discussions on the optical components used to generate and measure OAM. In section 2.9 we present one of our contributions to the field of OAM-measurement, which involves a stable Dove-prism embedded Mach-Zehnder interferometer, capable of sorting 41 OAM states into odd and even ports with a contrast ranging from 92% to 61%. We implement the Dove prism embedded Mach-Zehnder interferometer to mimic an amplitude damping channel for OAM states in chapter 3. Our device is useful in modelling a ‘lossy’ environment for OAM states. In chapter 4 we develop a new technique for the generation of superimposed Bessel beams through the use of a single digital hologram and theoretically and experimentally show that even though the superimposed Bessel beams can be constructed to produce no overall OAM, a rotation in the beam’s intensity profile is still present, as the field propagates. This rotation is due to the differing longitudinal wave-vectors present in the field and we make quantitative, experimental measurements of the angular rotation rates, which are in very good agreement with our theoretical predictions. We also show that the far-field of these superimposed Bessel beams, exhibit no rotation in their intensity profile and we offer a theoretical explanation for this occurrence. In chapter 5, we adapt our technique for generating superimposed Bessel beams to create non-diffracting speckle fields, which are known to possess optical vortices, and show that by controlling the standard deviation of the phase distribution within the digital hologram, we are able to control the evolution of the non-diffracting speckle field into a non-diffracting zero-order Bessel beam. Our final chapter contains a novel technique for the measurement of the OAM density of optical fields, by implementing two optical components: an SLM and a lens. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.