Two motives are responsible for the investigation of cosmic rays. Firstly they provide the only source at present availabe of particles with extremely high energy. To study interactions between fundamental particles at energies greater than about 6 x 109 ev. therefore, one must turn to cosmic rays. Interest in geophysics and astrophysics provides the other motive. For example, a theory of the origin of cosmic rays must form an integral part of the astronomer's explnation of the universe. The prob1em of the origin of the cosmic radiation is still looking at satisfactory solution. Further, much information about the physics of the solar system and the earth may be obtained from a world wide distribution of cosmic ray observatories.

Traditionally, growth and morphology studies of bacteria have focused on individual cells. When microbiologists subsequently became interested in bacterial colony growth, they investigated the dynamics of its height as well as those of its diameter. The models they proposed, however, were little more than empirical. In recent decades there has been a shift in focus, as researchers became interested instead in the morphology changes that colonies undergo when exposed to stressful environments such as nutrient and moisture limitation. As a result of this shift, models of colony growth in three dimensions have remained underdeveloped and rudimentary. My first task in this thesis was to assemble a sufficiently comprehensive data set from which diameter, height and cell-number growth trends in colonies could be properly analysed. This was achieved by studying the growth of many colonies of two bacterial species, Serratia marcescens and Esherichia coli, on high-nutrient non-selective agar, over a range of incubation temperatures, over periods ranging from two hours to one week. When graphed and analysed, colony diameter and colony height growth turned out to be most economically described as power-law in time, with exponent < 1. This contrasts with the claims of previous researchers, who had described both growth trends as linear, with diameter switching to a slower yet still linear growth after a certain time, and height growth ceasing altogether. From my results, I proposed a simple conceptual model, an extension of a model developed by Pirt in 1967. My hypothesis was that, in colonies growing on high-nutrient surfaces, diffusion was the dominant factor in colony growth. Ron Keam transformed my conceptual model into a mathematical one, from which I have developed one-dimensional and twodimensional numerical simulations. In all simulations to date, in both one and two dimensions, a power-law growth phase emerges as a consequence of nutrient-controlled growth, preceded by an “accelerating” phase during which colony growth overtakes diffusive processes, and succeeded by a slow transition towards growth cessation as nutrient becomes exhausted. In addition to successful demonstration of the power laws, the model in its final form yields realistic colony profiles and exhibits other features consistent with experimental results reported in the literature. / Whole document restricted, but available by request, use the feedback form to request access.

Ramanscattering and four-wave mixing are two fundamental nonlinear phenomena present in optical fibres with important implications for applications in fields ranging from modern telecommunications networks to biophotonics. This thesis investigates three situations when these two phenomena interact: Firstly we investigate the interplay of multiple four-wave mixing processes using coherent and incoherent pump waves in the presence of Raman scattering. We experimentally demonstrate that despite the requirements of phase-matching conditions it is possible to observe multiple phasematched and non-phasematched four-wave mixing processes. Furthermore we show that an incoherent light wave provided by amplified spontaneous emission noise can act as an effective pump wave for degenerate four-wave mixing. The main part of the thesis is occupied by the investigation of a mode-locked Raman fibre laser. The use of dissipative four-wave mixing for the passive mode-locking technique in combination with Raman scattering as the gain mechanism offers the possibility of achieving ultra-high repetition rates at very high average output powers. We experimentally demonstrate the mode-locked operation of the laser at 500 GHz and achieve an average output power of almost 1 W. Additionally we examine the key limitation of the laser which is supermode noise caused by mode-locking the laser at very high harmonics of the cavity resonance frequency. In order to gain qualitative insight into the influence of supermode noise on the laser dynamics we create a laser model which takes account of supermode noise. Furthermore we design a scheme to reduce supermode noise using additional subcavities, and evaluate the scheme using a lower repetition rate laser. We show that by including the subcavities into the setup the amount of supermode noise can be reduced by at least a factor 100. Lastly we introduce a novel method to measure the noise fluctuations of continuous wave lasers at timescales prohibiting the use of traditional noise measurement techniques. The noise is measured using a technique which transfers the fast noise from the continuous wave laser to a low repetition rate mode-locked laser which can be measured with traditional methods. We demonstrate that a continuous wave Raman fibre laser exhibits ultrafast, high contrast intensity fluctuations at timescales of tens of Gigahertz. This work has led to three publications and six conference presentations.

Whole document restricted at the request of the author / This thesis examines a number of questions that arise in the process of forecasting and managing the load of an electrical power system, and presents some possible solutions. The study was based on the situation of one New Zealand Supply Authority, which is able to directly control the hot water heater component of its load. To the extent that the data worked with was obtained from this particular electrical system, the solutions found apply specifically to it. However the methods used to determine a model for the hot water heater load channels in response to switching, as well as the pulse filter and short-term load forecasting algorithms developed, are more generally applicable. The digital pulse filter algorithm is an improvement on the traditionally employed method of obtaining frequently updated readings of system load from kWh metering pulses. The hot water heater channel model that was found, enabled a reconstruction of uncontrolled load values from the measured controlled system load values to be undertaken. The ability of various short-term forecasting algorithms of the time series type to predict such load series was then examined. The different methods were designed to incorporate to various extents the features of the load and temperature series, and the effect of temperature on load. Comparisons of the methods' forecasting accuracies then pointed out those load features that it is most important to model in order to obtain better forecasts. (The results were of interest in that they showed that additional model sophistication did not necessarily imply more accurate forecasting algorithm performance.)

The work in this thesis is in the fields of profilometry and Fourier transform spectrometry. Deformation measurement of diffuse objects by phase stepping was achieved by thermal frequency drift in a HeNe laser. The system was easy to construct, required no specialised components, was immune to the effects of piezo-actuator hysteresis, and was capable of producing phase maps in which noise was less than 1/20λ. A method was proposed for measuring absolute surface profile by scanning frequency over the range of a white light source. The coincidence technique of coherence radar was used to measure surface profiles in three dimensions to micron accuracy. Spatial techniques were developed to process the large data set quickly and efficiently. A novel Fourier transform spectrometer was developed to measure the spectrum of narrowband light sources. Heterodyning techniques gave a resolution of 0.01nm with a free spectral range of =2.5nm. The Sagnac common path design afforded immunity to vibration. The mode structure and mode hopping characteristics of a typical laser diode were measured as a function of diode injection current. An improved Fourier transform spectrometer was developed. Based on a Michelson interferometer. The instrument could resolve to 0.013nm over a =3nm free spectral range. Instrument operation was simplified and functionality was extended to non point sources.

Experimental techniques for measuring fluorescence lifetimes were evaluated for the purpose of studying the fluorescence quenching of the biologically important dye ethidium. A synchronously pumped cavity dumped dye laser was used to produce stable high repetition rate picosecond pulses for sample excitation. A system was established for recording nanosecond decay profiles by time correlated single photon counting. A careful investigation of the factors which contribute to the instrumental time jitter enabled an overall impulse response of 600 ps to be achieved. Software was developed for analysing fluorescence decay profiles by the method of convolution and curve fitting and its capability for accurately resolving multiple exponential components was evaluated using simulated data. Some improvement in accuracy was obtained by modifying the Poisson weights used in the curve fitting routine to allow for non-statistical errors, caused primarily by the wavelength dependence of the time response of the single photon counting photomultiplier. Fluorescence polarization effects are discussed. The rotational lifetime of Rhodamine 6G in ethylene glycol was determined by measuring the fluorescence polarization anisotropy decay and the Debye-Stokes-Einstein theory reaffirmed for small molecules at moderate viscosities. The torsional rigidity of DNA can be determined by measuring the depolarization of fluorescence of tightly bound (intercalated) ethidium, and this was not observed to change appreciably when the antitumour drug amsacrine also binds to the DNA. The fluorescence quenching of DNA intercalated ethidium by anticancer drugs was studied by accurately resolving the fluorescence decay profiles into exponential components. The lifetimes and proportions are interpreted in terms of current theories for drug binding and fluorescence quenching mechanisms. The fluorescence quenching behaviour by the antitumour drug amsacrine is consistent with a previously proposed electron transfer mechanism.

Light and atoms couple together via the electromagnetic interaction. The simplest form of this interaction is the electric dipole interaction, and in its quantised form it provides a useful starting point for the investigation of quantum effects in optics. Two examples of quantum noise manipulation of the light field due to interaction with atoms will be presented, as well as an analysis of a simple model for laser cooling of trapped atoms. The first example of quantum noise manipulation is the investigation of a quantum non-demolition measurement scheme based on a three-level atomic system in the ladder configuration. An effective two-level model of the atomic system is used, which enables the inclusion of spontaneous emission noise from the upper atomic level. The system is found to perform well, when detuned far from resonance. The second example is the treatment of squeezing in the intensity difference between two modes coupled by a three-level atomic system in the ladder configuration. The noise correlations are similar to those occurring in the optical parametric oscillator, and give rise to good squeezing when the system is well detuned from the intermediate level. The simple model of laser cooling consists of a single two-level atom with quantised centre-of-mass motion constrained to move in a one-dimensional harmonic potential while interacting with a single-mode classical travelling light field. It is shown that there is an analogy between this model and the Jaynes-Cummings model. This gives rise to interesting coherent effects including quantum collapses and revivals in the atomic inversion. Sideband cooling occurs for this model when the light field is tuned to the atom's first lower vibrational sideband. The strong sideband and Lamb-Dicke perturbation regimes are defined. Analytic results have previously been obtained for the latter regime, but we carry out a numerical investigation of the steady state and time evolution behaviour in the former regime. Differences in the behaviour in the two regimes are discussed. Finally the possibility of observing quantum jumps between trap levels is discussed.

This thesis is concerned with the generation of picosecond pulses and their propagation through both resonant and non-resonant media. This was achieved by constructing a passively modelocked Erbium doped fibre laser (EDFL) which was used to study pulse propagation through sections of standard communications grade optical fibre, dispersion shifted optical fibre, and also through an Erbium doped fibre amplifier (EDFA) module. The EDFL produced a train of ˜2 psec pulses at 4 MHz, tunable over the erbium gain band ( 1520 - 1570 nm). The laser was constructed from commercially available components and had the property of stability combined with low pump power requirements to produce ˜50 Watt peak power pulses. The laser cavity geometry included a nonlinear optical loop mirror, which has the property of efficiently switching high peak power pulses, and allowed pulsed operation without the aid of any high-speed electronics. An EDFA module of identical geometry to that used in the laser was also constructed, and this was probed using the pulses from the EDFL. The traditional temporal and spectral measurements were found to be inadequate to allow a complete description of the pulse amplification process to be developed. To overcome this problem the technique of frequency resolved optical gating (FROG) was applied for the first time to optical fibre research, and allowed an indirect measurement of the electric field of the pulse. This complete description of the pulse was used in a numerical model to describe pulse propagation in an optical fibre. Fundamental propagation terms in the model were treated as free parameters in a minimisation scheme, which could be determined for a fibre under examination. This technique was shown to be accurate when used to examine pulse propagation through both standard and dispersion shifted optical fibre. A comprehensive numerical model was developed for the EDFA, and it was apparent from this model that a pulse propagating through an optimised EDFA encounters an atomic inversion distribution which is a strong function of distance along the amplifying fibre. It was also shown from the experimental results that the EDFA exhibited resonant dispersion, which is characteristic for propagation through an atomic medium on resonance.

An investigation has been carried out into the operation of a mode-locked argon laser at a wavelength of 514.5 nm and a repetition rate of 76.8 MHz. The characteristics of the pulses from the laser have been found to depend on the intra-cavity power level in the laser, and at average intra-cavity power levels exceeding 4 W, the pulses from the laser have a duration of typically 35 psec accompanied by a characteristic double-peaked spectrum with a spectral width of 13 GHz These pulse durations are approximately three times shorter than expected based on the inhomogeneously broadened transition bandwidth of 4 GHz. The dependence of the pulse characteristics on the intra-cavity power level has been explained by a model of pulse propagation where the coherent coupling between the pulse and the atomic polarisation in the laser gain medium is included. Detailed examination of the pulse structure reveals the presence of afterpulses that have a typical intensity two orders of magnitude lower than the main pulse. These afterpulses are interpreted as ringing arising from coherent Rabi-type oscillation of the atomic polarisation associated with the circulating pulse in the laser. Numerical simulations of the mode-locked laser have also been developed based on the fully coherent Maxwell-Bloch equations, and the results from the simulations reproduce well the experimentally observed variation in pulse characteristics. Based on results from the simulations, the short pulses observed at high intra-cavity powers are interpreted as the superfluorescent π –pulse solutions predicted in the long distant limit of pulse propagation in a swept-gain amplifying medium. The laser operation has also been studied in a mode-locked cavity dumped configuration. In this case the combination of the coherent mode-locking processes described above with the cavity dumped operation at a repetition rate of 3.8 MHz results in the observation of stable pulses with peak power of 1.6 kW.

The development of a mobility spectrometer which yields a complete spectrum every 25 seconds is described. The spectrometer uses a Differential Gerdien Chamber of the First Order with 8 collecting electrodes, giving a set of 8 "electrode charges" corresponding to each observed spectrum. A Least Squares iteration is used to fit the parameters of a function which describes the complete mobility spectrum. The spectrum function's parameters can be fitted reliably with standard deviations of 3% or better. The spectrometer was used for observations of temporal variations in the atmospheric ion mobility spectrum at Auckland. These show a clear diurnal variation, and demonstrate that the spectrum can change significantly in an interval of 100 seconds. Atmospheric polar conductivities calculated from the mobility spectrum (which agreed well with independently measured conductivities) indicate that large ions can contribute as much as 40% of the total conductivity.