Table of contents

The fibre optic gyroscope (FOG) offers the potential of a low cost, high performance strap down inertial navigational instrument. In this article, the principles of the FOG are reviewed and the factors which limit the performance of the system are discussed. The basic Sagnac interferometer is shown to be susceptible to polarisation effects, optically induced nonlinearities and both spatial and temporal coherence within the optical source and within the passive gyroscope optics. However, with due attention to these phenomena, a high performance instrument is feasible. An assessment of the applications role of this instrument is presented together with some speculations on the required technological developments to produce the instrument.

A principal survey of holographic techniques is presented and the following applications are considered: holographic interferometry, optical filtering, computer holography, multiplex holography, holographic storage, and holographic optical elements.

Microsampling valves of new design were developed in glass or metal forms. The valves are suitable for sampling minute quantities of gases and can be used for sampling in gas mixture streams. The valves were used to produce gas streams of a time-programmable concentration.

Two types of microdoublebalance have been developed which allow the independent measurement of two perpendicular forces, such as pressure and weight, at the same time. The first type, a balance with a strained suspension, shows a strong temperature dependence of the zero point of the read out of weight and pressure. Therefore the second construction with a point bearing has been developed. Compared with the first version the resolution is increased and the zero-point drift decreased. The resolution in both directions was around 10^-8 g; details of its construction are described and the calibration process is reported.

A method for observing surface Raman spectra in solids is proposed and realised. The waveguiding properties of a curved surface are used for this purpose. In this way surface spectra of synthetic alpha quartz were obtained.

A dither stabilisation system is described in which the laser pulses are synchronised to the frequency dither. The required circuitry is very simply constructed using gated sample-hold amplifiers. For a miniature TEA laser operating on 10P(18) a stability of better than +or-3 MHz is achieved over 5 hours 100 MHz from line centre.

High-degree linearity in the magnetic field gradients has been considered essential in order to reconstruct an accurate NMR image from projections. Here, for the first time, the effects of nonlinear gradients on the reconstructed NMR images are analysed in detail. It is found that the gradient nonlinearities cause geometric distortions on the image. The image can be fully recovered from the distortions, provided that the spatial distributions of the field generated from each set of gradient coils are known. Computer programs are used to stimulate an imaging experiment under nonlinear gradients, and demonstrate the techniques of restoring the distorted image. After the restoration, the image gives accurate geometry and intensity information, but, unlike imaging under linear gradients, the spatial resolution is not uniform nor isotropic.

The positions of four equiradial circular coils, arranged coaxially to generate a maximum volume of uniform magnetic field, were found to depend on the level of uniformity required. Dimensions of four new coil arrangements are given that allow a current (turns) ratio of 9/4, and that produce larger working volumes, for field variations in the range 10^-3 to 10^-6, than the original system due to Barker (1949).

The construction and the design equations of a resonator for low frequency ESR spectroscopy are described. The resonator consists of a thin wall split ring which can be designed for a particular frequency by careful choice of the ring inductance and the gap capacitance. The design equations have been obtained on the basis of a very simple equivalent circuit which takes into account the resonator parameters and the coupling of the resonator with the microwave bridge. Prototypes have been built for frequencies between 1 and 4 GHz but resonators for lower or higher frequencies can be easily constructed. At a frequency of 2.1 GHz, a power level of 10 mW and using an aqueous sample a sensitivity of 8*10¹¹ spins/Gauss has been obtained. This sensitivity compares favourably with that of an X band spectrometer in the case of aqueous samples.

Bimodal cavities were found to give a Faraday rotation in a magnetic field, arising from the Hall effect in the cavity walls, which seriously limited the application of this technique to low-mobility materials. Methods of reducing the empty cavity signals are described, and new results are reported for biological materials which differ from earlier published values. In particular, no support can be adduced for earlier views on band conduction in the mitochondrial electron transfer system.

By using the method of diabatic passage, the authors have developed a spin flipper which allows a rapid and convenient reversal of the atomic spins. The spin flipper was tested with a polarised lithium atomic beam by analysing the atomic beam polarisation with the help of a second spin-flip region and a sextupole magnet. The reversal efficiency was measured to be 0.98 which is in agreement with the calculation. The flipper is especially useful in low-energy electron-atom crossed-beam collision studies. The experimental arrangement used also allows a precise determination of the atomic beam polarisation.

A new high-performance electrostatic charged particle energy analyser has been developed with the purpose of combining all the diverse advantages of the currently available types of spectrometer into a single instrument. This paper indicates how the instrument evolved directly from the requirements of the design specification. The resulting device acts as a bandpass filter and consists of a retarding grid section, followed by an energetically dispersing region formed by a continuously decelerating, focusing field. Design aims, basic theory, construction and experimental evaluation are presented. Important performance parameters of the new design are its high signal-to-noise ratio, characterised by a high transmission (15%) and low spurious signal collection; high available energy resolution (0.03% FWHM); electrical adjustment of bandwidth; and comparative insensitivity to source position and external magnetic field. Capability to produce high-quality Auger spectra is demonstrated, emphasising the advantages of trade-off between spectral resolution and sensitivity.

A simple method of obtaining accurately calibrated resolved fluorescence spectra of pulsed laser excited sources is described. A microprocessor data collection system has been constructed to record these signals.

An apparatus is described for measuring the linear birefringence and linear dichroism induced in liquids or dispersions by an applied magnetic field. The apparatus uses a vibrating beam phase modulator and conventional optical and electro-optical components. It is capable of measuring Delta n' (the real part of the complex birefringence Delta n) down to about 10^-12 and Delta n" (the imaginary part of Delta n) down to about 10^-10. Results are given for liquids of very small Cotton-Mouton constant, hitherto unmeasurable, and very dilute colloidal dispersions. Dust removal from sample liquids is shown to be of major importance for weakly birefringent or dichroic samples.

Design and operational characteristics of a line source with very high intensity in the vacuum UV are described. The source generates rare-gas resonance radiation in a low-pressure, cold-cathode, DC glow discharge up to 200 mA. The windowless lamp is differentially pumped and can be installed inside a vacuum chamber. During operation it is water cooled and can be mildly baked because it contains metal seals only. In a light beam of 2.5 mm diameter the photon flux for the strongest HeI and NeI emission line has been measured to be nearly 10¹³s^-1and one order of magnitude less for the strongest HeII, NeII and ArI lines. The photon intensities obtained are compared with values from the literature. The lamp has been used to investigate atomic and molecular photoionisation simultaneously resolved with respect to photon and electron energy, electron emission angle, and spin. To show the performance, angular-distribution results of photoelectron intensities for nitrogen molecules (X² Sigma _g⁺, A² Pi _u, B² Sigma _u⁺) at 58.43 nm are presented.

In all the synchrotron X-ray beam lines, one of the major experimental problems is due to the 'glitches' that distort the monochromatised radiation. In principle, if the X-ray absorption measuring apparatus were linear, such distortion should be compensated. In practice this is not always so because of many frequency experimental inaccuracies. The authors analyse the most important of these, and suggest the correct procedure to avoid them.

Low light level imaging is possible using a standard TV camera with a video recorder, if the integration properties of the vidicon tubes or CCDs are exploited. Only a simple additional electronic circuit is necessary. The field of application is for static or slowly variable images, the integration time being about equal to the sampling period. Analogue image display and computer acquisition is performed off-line using the standard video signal from the video recorder.

The distinguishing feature of the equipment is a magnetically levitated Archimedian bob. The silica bob with the sample is contained in a sealed glass cell which is suspended from an automatic balance. Different types of cell are described for liquid and vapour density measurement. Also included in the equipment is a well-tried liquid density apparatus which employs a magnetically controlled float and from which the levitated-bob method was developed. Results are given for density measurements to near-critical temperatures of samples of propan-2-ol (vapour only) and benzene. The vapour measurements are prejudiced by slowness of equilibration between liquid and vapour at lower temperatures, and by an unidentified factor producing low results. Nevertheless the general self-consistency and reproducibility of the results indicates the effectiveness of the method.

The authors have constructed a thermally insulated box-shaped enclosure of approximate (1*1*0.8) m internal dimensions to carry out precision measurements at room temperature. The design of the enclosure is based on the solution of the heat conduction equation by a finite-difference approximation method. Temperature measurements carried out inside the enclosure in consecutive periods of eleven days over a four-month interval show that the stability obtained lies within +or-0.5 mK h^-1 and the gradients are less than 50 mu K mm^-1. The power spectrum analysis, via a fast Fourier transform (FFT) technique, shows the still significant components inside the insulating enclosure.