A study of the performance of the Nd+3 : POCl3 : ZrCl4 liquid laser system is presented. Its properties are described and compared with those of other neodymium lasers. An evaluation of the potentialities of this system as an actively Q-switched oscillator and as a high power amplifier is made. The generation and amplification of picosecond pulses in neodymium laser systems are reviewed. Frequency shifts in broad band amplifiers have been observed and their effect on the power gain has been investigated.

The optical properties of a selection of crystalline solids have been studied in the far infrared by dispersive Fourier transform spectroscopy. This technique allows both the amplitude and phase to be determined without any approximation. The measurements were performed on a modified Michelson interferometer, in which one of the mirrors is replaced with the sample to obtain the dispersive interferogram. The instrument was improved by replacing the stepper motor drive with a hydraulic piston and a high precision linear bearing. Sampling control was obtained by monitoring the cosine fringes from a secondary laser beam passed down the optic axis. The far infrared amplitude and phase reflection spectra of eight zincblende structure binary semiconductors and two alkaline earth flourides have been measured, in most cases for the first time. Then, by using the equations of Maxwell and Fresnel, the refractive index, absorption index, and the real and imaginary parts of the dielectric response were obtained. From these functions the frequency dependence of the anharmonic self-energy function of the transverse optic mode at the centre of the Brillouin zone was calculated. Features observed in the self-energy functions of the zincblende crystals are attributed to phonon combination bands due to the decay of the lattice resonant mode. These are assigned by critical point analysis with the aid of lattice dynamical models to provide an experimental test of the phonon frequencies. Finally, the amplitude and phase reflectivity of a GaAs-AlGaAs multiple quantum well structure and a GaAs-AlAs super lattice are presented for the first time. In the case of the multiple quantum well structure the results are shown to be in good agreement with calculations based on macroscopic dielectric theory.

Studies have been made of fast timing techniques in various types of positron lifetime spectrometer and of the analysis procedures used for extracting positron lifetime and intensity values. Evaluation is made in terms of their usefulness and reproducibility in high resolution studies of lattice defects and their formation. The optimisation of a Fast-Slow 4-Way Routing Positron Lifetime Spectrometer has been attempted and the results are discussed in terms of changes in important spectrum parameters which have possibly been overlooked on comparative systems. Its viability as a non-destructive testing technique is considered. A Fast-Slow and a Fast-Fast Positron Lifetime Spectrometer have been constructed and studied. The Fast-Fast system has been developed such that it utilises the detector dynode pulses for timing, rather than the conventional anode pulse. By further optimisation of the time-pickoff method, a substantial improvement in the resolution has resulted. The system has been applied to studies of materials in which the defect types, their concentration and their specific trapping rates for positrons, are in question. A study has been made of the uncertainties arising from different approaches to the computer-aided analysis of multi-component decay spectra. Three analysis programs, all in common use, have been investigated and compared. Results are presented that clearly indicate the underlying reason for discrepancies in published positron lifetime data. A temperature study has been made of thermal vacancy creation in polycrystalline indium from 290 to 425 K by observing the variation in the positron trapping rate. Results are discussed in terms of a simple 2-state trapping model although attention has been paid to the question of pre-thermalisation trapping of positrons as the melting point is approached. Values of the monovacancy formation energy, E, are estimated using several types of analysis method for spectra from three sets of similar temperature measurements using the same sample, each made at differing stages of anneal. Differences in trapping rate variation with temperature (and thus in E) is interpreted as a sign of inadequate annealing and this is used to explain the discrepancies between previously published results. The nature of the defects in various types of gallium arsenide single crystal have been investigated by studying the effect of different dopants and their concentrations upon the rate and intensity of positron trapping at room temperature. Positron lifetimes and intensities in e and n°-irradiated samples have been similarly measured. To determine further the characteristics of the defects, an isochronal anneal study was performed using n°-irradiated gallium arsenide over the temperature range 290 to 725 K. This study was combined with infra-red spectroscopy measurements at each anneal stage in an attempt to correlate the variation of specific lifetime component intensities with those of a selection of infra-red spectral peaks whose origin is in question. The high defect concentrations created by the irradiation are shown to give rise to pre-thermalisation trapping of positrons.

The optical properties of a selection of layered semiconductor samples have been studied in the far-infrared by reflection dispersive Fourier transform spectroscopy (DFTS) and attenuated total reflection (ATR) spectroscopy in DFTS the reference mirror in a two-beam Michelson interferometer is replaced with the sample to obtain a dispersive interferogram. This technique allows both the amplitude and phase to be measured directly. The amplitude and phase reflectivities of a variety of epitaxial layers (including a GaAs/AlAs superlattice)on GaAs substrates are presented. The measurements on the epitaxial layers are in good agreement with theoretical results obtained using standard multilayer opticalcalculations. ATR spectroscopy, which permits the study of nonradiative transitions, has been used for the first time tostudy surface phonon-polar itons on a GaAs/AlxGa-xAs multiple quantum well (MQW) structure, as well as a CdTe epitaxial layer deposited on a GaAs substrate. Both P- and S-polarised measurements have been made with a far infrared FT spectrometer fitted with an ATR stage at the output port. In the MQW sample, the experimental results are compared with theoretical calculations derived by treating the MQW structure as an effective uniaxial dielectric medium. The measured and theoretical results are in excellent agreement both qualitatively and quantitatively. Surface phonon-polaritons are observed in P-polarisation but only bulk modes are seen in S-polarisation as predicted by theoretical calculation. For the CdTe epitaxial sample, surface phonon-polaritons are observed by ATR in P-polarisation in the CdTe reststrahl region. In S-polarisation, a sharp guided wave is observed in the GaAs reststrahl region. The results for both polarisations are in good agreement with calculations.

The far infrared optical properties and complex dielectric response functions of two alkali halide crystals (CsT and KI) and two III-V compound semiconductor crystals (InAs and InP) have been studied using the technique of dispersive Fourier transform spectroscopy. The values of the transverse optic and longitudinal optic phonon frequencies at wave vector q=0 determined from these results agree quite well with published values, and the dielectric functions were used to calculate the imaginary parts of the an harmonic self-energies (oj,V) of the q=0 transverse optic modes. These are the first reported measurements on Csl by dispersive Fourier transform spectroscopy, and reasonable agreement is obtained between the frequencies of measured features in (oj,V ) and published two-phonon frequencies. In the case of KI the present measurements have been made at a higher resolution than any reported previously, and they provide a sensitive test of the validity of various theoretical calculations available in publications. Also, in the case of KI some two-phonon difference bands have been observed and assigned in the, spectrum of (oj,V) for the first time. No measurements of the optical constants of InP in the far infrared region using this technique have been reported before, and, for both In Lambdas and InP, these are the first reported experimental determinations of the imaginary part of the frequency dependent damping function. A number of features in the spectra of (oj 'V ) for In Lambdas and InP are revealed and attributed to two-phonon decay processes with the aid of a critical point analysis based on published data for these materials. Since the performance of the dispersive reflection interferometer was limited by the specimen size a prototype focused beam interferometer was constructed, and its performance has been demonstrated by recording a water vapour absorption spectrum at a resolution of 2 cm using end mirrors 5mm in diameter.

Recent advances in the field of non-linear optical phenomena are reviewed in which particular reference is made to those effects induced within liquid media. Several aspects of this field of study were experimentally investigated. In particular, direct quantitative examinations were made of the intensity dependent refractive index modulations (associated with the phenomena of stimulated light scattering) induced in both absorbing and non-absorbing liquids by the intense light fields from a pulsed ruby laser. A probe technique, which facilitated both spatial and temporal analyses of this induced non-linearity, was developed, in which the output from a continuous argon ion laser was Bragg reflected off the induced structure within the liquid. The experimental and theoretical results are shown to be consistent and values for the thermal relaxation time of liquids are determined. Qualitative aspects of the non-linear phenomena of self trapping and de-focusing of laser light are considered with particular emphasis placed on the effects of self-bending and the interaction of self-trapped light beams. Studies were conducted into the effect of intense laser light on saturable absorbers. The intensity dependent blue fluorescence observed from these absorbers when excited by ruby laser light resulted from excited state absorption to the second singlet state. The intensity dependence also indicated the power density required to saturate the first excited singlet state for each dye. A similar fluorescence due to two photon absorption was observed in certain solvents. The residual population inversion characteristics of ruby were examined using a stimulated light scattering feedback technique. The results of these investigations are shown to be in qualitative agreement with current theories.

A study of a Plasma Focus device by optical diagnostic techniques based on plasma refractivity is reported. The device produces at the axis of symmetry of its coaxial electrodes a transient dense plasma filament, of density ≳ 10¹⁹ electrons cm-3 and electron temperature ~2.5keV, by a focusing mechanism. A review of earlier experimental and theoretical studies of the Plasma Focus permits a detailed description of the four principal phases of the discharge. The principles of showdowgraphy, schlieren photography and inter-ferometry and their application to plasma diagnostics are discussed in detail. It is shown that in the present study the plasma refractivity is mainly due to free electrons. The Plasma Focus used in the study is described and the experimental details of using the diagnostic techniques are discussed. A shutter has been developed to produce a pulse of duration one nanosecond from a Q-switched ruby laser and is used to obtain good temporal resolution of the transient plasma. The refractivity studies lead to a detailed understanding of the PIasma Focus. Interferometry provides the time dependence of the plasmaelectron-density profile, permitting calculation of the time-dependent plasma line-density and the focusing efficiency. Multiple-expo sure shadowgrams lead to values of the velocity and acceleration of the plasma boundary, the dense-filament lifetime and the growth rates of plasma instabilities. An ion temperature is deduced from the damping of acceleration-driven instabilities. The significance of the results from these original studies is discussed. They are compared with the results from other measurements on the Plasma Focus and with the results of a numerical fluid code. The limitations of the optical techniques used are considered and improvements are suggested. Future studies of the Plasma Focus based on these improved techniques are proposed.

The far infrared optical properties of a selection of binary semiconductors have been studied by the technique of dispersive Fourier transform spectroscopy. A commercial modular Michelson interferometer has been rebuilt in a single pass dispersive mode for this work. The performance of the instrument has been substantially improved by mounting the moving mirror on a pneumatically controlled precision linear slide to provide a smooth travel. The interferogram was sampled internally by monitoring the interference fringes derived from a secondary He-Ne laser channel. Precision alignment maximises the throughput signal enabling a relatively small specimen to be studied. Direct measurements of the amplitude and phase transmission spectra of GaP, GaAs, InSb, InAs and ZnSe have been performed at room temperature and 100K for the first time. The single-pass configuration has enabled new optical constant data to be obtained accurately on either side of the reststrahlen band. In most cases, these are the first reported results at the two temperatures. In each case the absorption coefficient and the complex dielectric response functions have also been calculated. Prominent features in the spectra are assigned as phonon-combination bands with the aid of critical point phonon frequencies derived from a lattice dynamical model. The magnitude of the imaginary part of the anharmonic self-energy function of the zone-centre transverse optical phonon required to account fully for the observed absorption has been estimated. The results give a clear indication of the range of validity of the anharmonic mechanism and the onset of lattice absorption due to non linear terms in the dipole moment expansion.

This thesis is concerned with the investigation, both numerically and experimentally of novel electrostatic lenses. The properties of a five-element lens are described. This lens allows the variation of the magnification of an image of fixed position with fixed overall energy, and can be therefore considered a 'zoom' lens. This lens can also be constrained so that it is afocal and the separation between any pair of conjugate points is constant, and therefore independent of V5/V1, with the magnification related very simply to V5/V1. A numerical technique involving matrix multiplication is used to compute the properties of the five-element lens from the tabulated properties of two-element lenses. Manipulation of the calculated data revealed that it is possible to define two 'universal' curves to summarise its properties. The calculated lens properties are compared with those previously obtained by experiment, (Heddle and Papadovassilakis 1984). The aberration behaviour of a five-element lens was investigated. In particular, the dependence of the spherical aberration coefficient Cson V3/V1 where V5/V1 = 1, and V2/V1 = V4/V5. Cs was also investigated for a number of afocal lenses. Finally, Cs was investigated for the lens where V5/V1 = V3/V1 = 1, V2/V1 is the variable and V4/V3. This lens was found to have a minimum value for the product MAG x Cs, therefore, optimum values of V2/V1 and the magnification exist for this lens. The values for Cs obtained by experiment are compared with those calculated by my supervisor Professor Heddle using the Bessel Function Expansion Method, and the Fox-Goodwin Method. Finally, the properties of a three-element lens constructed from 31 discs electrically insulated from each other, and sandwiched between two ordinary cylindrical elements was investigated. Voltages were applied to this lens so that it simulated a three-element lens with a 'movable' centre element of variable length. The obtained experimental properties are also compared with those calculated by Professor Heddle.

This thesis is concerned with an experimental study of a novel microwave oscillator which is based on quasi-optic principles rather than more conventional closed cavity techniques. A quasi-optic open cavity resonator is used in order to combine and stabilize the frequency of many solid state source modules. At mm wavelengths, the small physical size of the open resonator, (127 mm diameter mirrors at Q-band) enables the fabrication of medium power oscillators with dimensions suitable for integration within a practical system. A self-oscillating microstrip patch antenna, mounted conformally with the resonator mirror surface, is developed as the basic source module. A suitable method of coupling many of these modules efficiently to a beam mode supported by the open resonator is discussed, together with the dependence of the preferred active cavity mode upon the array geometry. Initial experimental investigations have been undertaken at J-Band (12-18 GHz) yielding techniques that have been successfully applied at Q-Band (26 - 40 GHz).