Table of contents

The SERS 'polarisation flip' method, which can be used to measure the intensity ratio of otherwise inaccessible infrared atomic transitions, is found to suffer from certain intrinsic limitations and sources of error. In particular the intensity ratio for the 7s²S_1/2-7p²P_1/2,3/2 transitions of atomic caesium, as measured previously using this technique, could be in error by as much as a factor of 2.

In order to improve the adhesion of the electrodes which are most often vacuum-evaporated, the surface of the polypropylene film has been subjected to a high-pressure corona discharge at a frequency of the order of 10 kHz or higher. This type of surface treatment is very easily used and does not produce any transformation of the material for short expositions. In certain atmospheres and for longer exposition times, appreciable, and sometimes important, transformations of the dielectric characteristics appear. The evolution of these properties has been studied as a function of various corona discharge parameters, at a frequency of 50 Hz. This frequency, which is low compared with frequencies usually chosen, causes a slowing down of transformations which remains qualitatively identical. In order to establish a correlation between the species created by the discharge, the superficial and volume chemical transformations, and the dielectric properties of the material, several types of measurement were made: multi-internal reflectance (MIR) IR spectroscopy, the tan delta variations as a function of frequency and measurement of dielectric strength.

A new class of ion beam lenses is described. The electrostatic coaxial field between a thin central rod and an outer cylinder is used as the focusing element. MeV ion beams may be focused in 100 mm using kilovolts on the lens. Both diverging and converging electrostatic lenses may be made and the two combined to reduce aberrations. An analysis of particle trajectories through these lenses is given and results for a 400 keV proton beam presented.

The problem of shaping dual offset reflectors, fed by a linearly polarised rotationally symmetric feed horn, to produce a parallel beam over a non-circular aperture with zero cross-polarisation, is considered under the assumptions of geometrical optics. The condition for zero cross-polarisation leads to a partial differential equation, which hitherto has been solved numerically, but is shown here to possess an analytical solution. For uniqueness an additional constraint is put on systems with a plane of symmetry by prescribing the power distribution along the aperture line of symmetry. A suitable choice yields a uniform aperture edge illumination.

Cr and Cu offer the best possibilities of increasing the efficiency of Nd glass lasers. Unfortunately Cu must be discounted as it is pumped in the part of the UV which has to be blocked from the glass to prevent solarisation. Cr to Nd transfer is investigated by various methods. The classical method involving measuring lifetimes is shown to be misleading, at least for this pair of ions. A 45% efficient transfer from Cr to Nd was achieved, resulting in a glass of lower threshold and higher slope efficiency than pure Nd glass. A 35% increase in pumping efficiency was achieved.

Small indentations and scratches can be made in highly brittle materials such as glass or silicon without any associated fracture. It is proposed that this effect, which is usually explained in terms of flaw statistics, is in fact governed by a strain energy criterion which can be defined quantitatively if the tensile field which initiates fracture is known. Using a model of the field of residual stress around an indentation proposed by Swain and Hagan (1976), it is shown that the critical size of indentation for fracture to occur should be about 12(ET/Y²), where E is Young's modulus, Gamma fracture surface energy, and Y the yield stress for plastic flow in uniaxial compression. The critical size parameter is evaluated for silicon.

The dynamic flow characteristics of an electro-hydraulic servo-valve have been determined experimentally using a laser velocimeter. The volume flow rates were predicted from centre-line velocity measurements using a finite difference digital computer analysis of the Navier-Stokes equation adapted for incompressible flow along a tube. The analysis was first verified at low pulsatile system excitation frequencies by making velocity measurements at radial positions across the flow tube and comparing the profile thus generated with that from the computer analysis. The results show that the attenuation in flow amplitude with increasing frequency could not be accounted for by inertia effects alone and could be explained by changes in the contraction coefficient of the valve spool orifice. An expression is given for the change in flow amplitude as a function of the valve non-dimensional inertial loading.

Long plasma columns, in many instances preferable to the positive columns of DC discharges, can be obtained by means of a UHF surface wave propagating along the column. This is possible through the use of a novel wave-launching structure, called a surfatron. The launcher is compact and located on the outside of the dielectric tube containing the plasma. The surfatron is described and analysed in terms of an equivalent circuit theory. Guidelines for its design and operation are given.

Presents a study of the self-focusing and self-defocusing of elliptically shaped Gaussian laser beams in collisional and collisionless plasmas. The non-linear dependence of the dielectric constant inside a collisional plasma is due to inhomogeneous heating of energy carriers and in a collisionless plasma it is due to the ponderomotive force. It is found that the beam gets focused at different points in different planes, exhibiting the effect of astigmatism. In certain power regions considered, the beam either converges or defocuses in both the directions, while in some other regions of the power spectrum one dimension of the beam focuses while the other defocuses. The beam also propagates in an oscillatory waveguide.

The discharge is operated in oxygen with a 1 cm gap between a positive point and a plane at a pressure near 300 Torr. The discharge has been found to have a behaviour similar to that in atmospheric air. By introducing traces of hydrogen it has been possible to study the H_alpha and H_beta lines broadening which is mainly connected to the Stark effect. However, due to the presence of a macroscopic field the usual theory does not apply, i.e. it is shown that the Stark profile is related to the electron current density j rather than to the electron density N_e. The current density j is derived and from total current i a characteristic radius r₀ of the filamentary discharge is obtained. A value of the macroscopic field F_e is then determined from a numerical simulation of the discharge, leading in turn to the electron density. All these measurements are time resolved and are given as a function of time during the glow-to-arc transition. Typical values are j approximately 3*10³ A cm^-2, r₀ approximately 20 mu m, N_e approximately 10¹⁵ cm^-3. Some indications concerning the primary streamer, the nature of the discharge plasma and the glow to arc transition are derived from these measurements.

The martensitic transformation in a beta phase, Cu=12 wt.% Al alloy was studied by three different techniques; acoustic emission (AE), electrical resistivity (R), and electron microscopy. By changing the heat treatment it was possible to change the size of the ordered domains, and consequently both AE ringdown counting (N) and the hardness number (H) of the martensite were strongly increased, H and N were found to be related by the equation N=(0.042H-12.28)*10⁶ counts. Amplitude analysis of the AE bursts showed that increasing the size of the ordered domains increases the amplitude of bursts and the number of ringdown counts, while the number of bursts is constant since the number and average size of plates are the same, as shown from transmission electron micrographs.

Thin films have been grown on the cubic, dodecahedral and octahedral faces of rock salt by vacuum evaporation, at 10^-6 and 10^-10 Torr, of Gd, Tb, Dy, Er and Ho, and their structures have been examined by electron microscopy and diffraction. Conditions have been established for the epitaxial growth of the rare-earth dihydride films in the thickness range up to approximately 25 nm. Between 25 and 20 nm a mixed phase of FCC dihydride and HCP metal is formed, and above 90 nm the films are substantially metallic. Reflection electron diffraction and hydrogen annealing experiments suggest that the formation of the dihydride may be influenced by adsorbed hydrogen on the substrates.

The doping of gallium phosphide by the in-diffusion of nickel gives rise to extensive whisker growth on the semiconductor surface.

The electrification of lithium fluoride crystals by plastic deformation is studied experimentally. It is shown that this phenomenon is explicable starting from the notion of the intrinsic charge of solid insulators.

A formal solution is obtained for the potential and current distribution in a rectangular crystal sample with parallel electrodes on its upper surface. Explicit formulae are derived for the case where the crystal is infinitely long, the electrode width is greater than about twice the crystal thickness, and the electrode spacing is greater than about four times the crystal thickness. Application to the measurement of resistivity using a two-point probe method is given, and working formulae derived.

Current peaks due to transient SCLC were observed both in high-density polyethylene (HD-PE) and in oxidised HD-PE in the temperature range 50-90 degrees C. From the time at which the current peak occurs, carrier mobilities ranging from 10^-11 to 10^-9 cm² V^-1 s^-1 were obtained. The mobility values obtained agree well with those evaluated from surface-charge decay measurements. They strongly depend upon applied field and temperature. The charge carriers have a much lower mobility in oxidised HD-PE than in non-oxidised HD-PE. This is attributed to the introduction of deep traps by the oxidation.

The authors have investigated the electrical response of structures consisting of an interdigitated electrode pattern printed on a dielectric substrate, by measuring the complex admittance over a frequency range 2-10⁴ Hz. Substrates investigated were CoO, alumina, single-crystal sapphire, BeO and gypsum (CaSO₄.3H₂O). They found that carefully cleaned substrates (except for gypsum) showed no measurable change in electrical properties when a solvent film was adsorbed on the surface, but when mobile ions were introduced on to the dielectric surfaces, adsorbed films of some solvents produced large changes in the surface electrical properties. Solvents studied included water, methanol, ethanol, propanol, benzene, hexane, toluene and aniline. The data support the conclusions that changes in the surface electrical properties are due to hydration of adsorbed ions when a solvent film is adsorbed on the dielectric.

The magnetic birefringence of various samples of Fe₃O₄ ferrofluids with particle sizes in the range of approximately 8.5-18.5 nm has been measured in field strengths of 5*10^-4 to 5*10^-1 T. For all the samples it has been found that in low fields the birefringence varies as the square of the field strength, indicating a classical behaviour of the particles. The size of the particles and the width of the particle size distribution curve have been estimated from an analysis of the variation of the birefringence with the applied magnetic field; the results obtained are in good agreement with results obtained from electron microscope and magnetic susceptibility measurements.