Table of contents

A measuring apparatus that was originally developed for measurements of the coefficient of linear thermal expansion and Young's modulus of thin specimens has been improved in order to measure both the thermal expansivity and thermoelasticity of monofibre specimens. The apparatus is composed of a rolling-ball slide mechanism, an optical heterodyne laser interferometer and a high-temperature vacuum furnace. Four kinds of high-strength organic monofibre specimens, the minimum diameter of which is about 10 mu m, were investigated in the temperature range between room temperature and 300 degrees C. The estimated accuracies in the determination of the thermal expansivity and thermoelasticity of the fibres were about +or-5% and +or-10% respectively at a 95% confidence level.

Theoretical and experimental investigation of the frequency response of fine wires is presented over a temperature range where radiative effects can no longer be neglected. In these conditions, the response of fine wires can be characterised both by a convective and a radiative time constant. In the case of 20 mu m and 50 mu m diameter Pt wires over the temperature range 300 K<T<1500 K in air flows, the radiative time constant is always found to be greater than the convective time constant.

The accuracy of conductance measurements performed with the help of phase-sensitive detectors is analysed. Appreciable measuring errors can be induced by the electrical system, the phase shifter and the detectors, especially when the loss tangent of the capacitor is low.

The I-V characteristics as a function of temperature of sintered NdBa₂Cu₃O_{7- delta} are investigated using a microcomputer for control, data capture and data analysis. The variation of the critical current with temperature is determined. By applying the theory of weak links in superconductors, a value of 63 meV is obtained for the energy gap in the material at 0 K.

The problem of attaining high power efficiency, that is high Fabry factor (G-factor) for a split-coil system of uniform current density, is investigated numerically. The dependence of G-factor on the parameters length, cross section and spacing is shown graphically. The significance of this study from the point of view of design and analysis is discussed.

Fresnel's equations reduce to a very simple form for an incident angle of 45 degrees . Using this fact, a simple apparatus has been devised to measure the ratio of specularly scattered s- and p-polarised light incident on a solid and hence its refractive index. The apparatus is controlled by a microcomputer and is very low cost. It employs a single polarising element and a minimum of other optical components. It is therefore potentially an instrument which can measure the refractive index of solids with an extremely high accuracy. The errors associated with the system are analysed and discussed and the means by which its accuracy can be improved are indicated.

A broadly tunable CW colour-centre laser spectrometer is described. The tuning mechanism and the problems for broad-band continuous single-mode tuning (about 50 cm^-1 in two hours) are discussed. Calibrating and scanning of a laser is obtained by a 68000-VME-Bus microcomputer system (Eltec, Eurocom 3), while the frequency calibration and evaluation is done by an 80286 personal computer (Hewlett Packard, Vectra). Some structures for comfortable data processing of spectral files from continuously tunable lasers are presented. Measurements of frequency stability and the linearity of the tuning behaviour show that the spectrometer can be used routinely for Doppler-limited spectroscopy (minimum step width 10 MHz) of molecular transitions.

A simple high-eigenfrequency scanning tunnelling microscope (STM) with atomic resolution is described. A small tube of piezoelectric ceramic is used as the scanner unit. Long-term drift is suppressed to first order using a compact construction of axial symmetry in combination with a thermal drift compensation in the z direction. The instrument is designed also for cryogenic applications and may be operated in conjunction with a personal computer.

The design and performance of a solid-state angle-resolved photoemission (ARP) spectrometer is described. The electron energy analyser is based on a 180 degrees hemispherical electrostatic deflector, the design being optimised for energy resolution and sensitivity. Using He I (h nu =21.2 eV) excited ARP spectra of the Cu(001) M Tamm state, the empirically determined energy resolution is found to approach the theoretical limit. With the current choice of defining apertures the theoretical limit (for the Tamm state) is 14 meV, and the angular resolution is +or-2 degrees . The observation of previously unresolved thermal effects on the intensity, inverse lifetime and binding energy of the Tamm state feature illustrates a typical application of the instrument.

A multi-detector telescope has started functioning at Gulmarg, India, to study cosmic gamma-ray sources at photon energies beyond 10¹² eV, through the mode of atmospheric Cerenkov radiation. The authors describe the instrumentation details of the Gulmarg telescope and also present an account of the telescope performance under actual observation conditions. An estimate of the telescope sensitivity, in terms of the minimum observation time required to detect a statistically significant signal from several representative gamma -ray sources, is also given.

A rangefinding technique has been developed, which is based on the phase change of the received signal with respect to the transmitted signal. The phase shift is caused by the finite transit time taken for the wave to travel from the transmitter to the receiver. The displacement is calculated by measuring the phase shift at three different frequencies. The signal with the longest wavelength enables a large displacement to be approximately measured, and the shortest wavelength provides the required high resolution and accuracy. The final value of the displacement is calculated from the phase information of the three signals. The signals are transmitted by amplitude modulation so that only a single ultrasonic transducer is required to transmit all three frequencies. The rangefinder is intended for applications where low cost and high accuracy are essential.

A simple method is described for investigation of the mass sensitive areas of quartz crystal mass sensors.

A rotating substrate holder for use in thin-film deposition systems with base pressures down to 10^-8 Torr is described. The principal advantages are the inexpensive and simple construction, the ease of controlling the temperature of the growing samples and the possibility of making electrical studies of the growing film during deposition.

A copper vapour laser is described which uses in situ formation of copper halide by a flowing mixture of halogen and inert gas. The discharge is confined by copper segments which also act as the copper reservoir.