Table of contents

This paper reviews some of the integrated optical devices being developed for use either as a part of or as a complete laser system for optical radar, space communication, pollution detection and data processing. An introduction to optical waveguides and fabrication techniques is included.

The authors have developed an accurate, counterbalanced, vertical-pushrod, vacuum dilatometer constructed primarily of brass, with a sampling force that can be reduced to less than 0.5 g. A special measuring loop confines distortion to quartz parts making sample measurement easier. Using this dilatometer they have reproduced the expansion characteristics of an Fe standard of the National Bureau of Standards to +or-0.5% in length up to a temperature of 1473K. The measurement loop in the instrument is designed to include a quartz tube and pushrod, and a linear variable differential transformer.

The response of a superconducting chopper amplifier system has been calculated with a view towards optimum sensitivity. A chopper operable between 2 and 4K and with sample resistance up to 0.5 m Omega has been constructed. The best noise level (5 pV peak-to-peak for a 1 s integration time) could only be obtained with a bath of superfluid helium. Noise is discussed with reference to a particular circuit.

Describes a gas-pressure-operated shutter interfaced to a Sloan 1000 digital thickness monitor which is suitable for operation under ultra-high vacuum. The shutter is used to control the thickness of metallic thin films during deposition. The mechanical motion in the system was achieved by varying the gas pressure in two tubes, each being connected to a stainless-steel welded-diaphragm bellows (normal length 16 mm, diameter 12 mm).

A live-fringe holographic technique is described which allows the visualisation of gas flow inside a lamp envelope. Incandescent ribbon-filament lamps are investigated using this technique, which shows instabilities in the gas flow, which in turn lead to fluctuations in the light output from the lamps. Use of a thermoplastic recording material facilitates live-fringe investigation, allowing real-time observation, and in situ development of the holograms.

The Collette torsion pendulum with torsion wires of the same material and dimension is considered. The use of the pendulum is restricted to a certain range of the ratio rho identical to f_t/f₁, depending on the value of internal friction for the specimen; here f_t and f₁ are the frequencies of the total system and a pendulum of the Ke type with the upper torsion wire.

Apparatus is described which is capable of measuring forces in the range 10^-4-10^-2 N with a response time of the order of a millisecond. The use of piezoresistive strain-gauge transducers extends the response to DC. The noise level of less than 10^-5 N is achieved with the aid of a simple but effective antivibration, screened enclosure. Application to dynamic meniscus rise measurements illustrates the capabilities of the system.

A technique of digital averaging is applied to the measurement of nitrogen spectra obtained from a low-light-level electron-beam-excited source. Results of analysis to determine the number of samples needed to yield a given precision and the transfer function of the system are presented. The technique has been shown to improve significantly the quality of spectra obtained from a low-density wind tunnel facility.

Experimental arrangements are described which have enabled the following measurements to be made without siphoning liquid helium into a cryostat: capacitance and loss with a transformer bridge from 4.2 to 350K (4.2-50K accurately and also 25-350K less accurately but more rapidly); and loss only at 4.2K from 10 kHz to 10 MHz.

A switching noise thermometer incorporating a series-resonant filter between the sensor and reference resistors and the amplifier stages is described. The first-order dependence of the temperature measurement on the magnitudes of the sensor and reference resistances and also on the magnitude of any stray capacitance is thereby removed. The DC voltage developed across a shot-noise diode load (the reference resistor) gives a direct measurement of the difference between the absolute temperatures of the sensor and reference resistors. The configuration enables noise signal bandwidths of 0.5 MHz to be used, allowing temperatures to be measured with a statistical uncertainty of 0.2% with a 1 s measurement time. FETS are incorporated at the input of the system in place of the conventional electromechanical switches.

A digital minicomputer has been interfaced with a scanning electron microscope, and programmed to control the excitations of the objective lens and the stigmator of the microscope. The electron beam is scanned by a digital scan generator and the digitised video signal is used for computations. To focus the microscope, a parameter related to the 'sharpness' of the image is maximised, and to set the stigmator, the directional information in the above- and below-focus images is used.

A vibration-insensitive 633 nm He-Ne laser interferometer for the measurement of plasma electron densities is described. This instrument is a Michelson interferometer with the reference arm located parallel to the test arm so that spurious fringes resulting from mechanical vibration of the optical components are minimised, allowing a resolution of 0.1 fringe to be achieved. A rotating glass plate in the reference arm was used where necessary to determine the sign of the electron density change. The performance of this interferometer is compared with that of a CO₂ laser interferometer.

An improved low-energy electron spectrometer using concentric hemispheres with a grid retarding field is presented. Emphasis is given to the means by which a triple-cylinder electrostatic lens, with the middle potential higher than the outer potentials, can perform a preselection. This improves simultaneously the collection efficiency and the intrinsic signal-to-noise ratio of the spectrometer. The operating mode of both the input lens and hemispheres is invariable over the energy range 0-1500 eV. The comparison of Auger transition probabilities is therefore possible. The variations of the relative collection efficiency and instrumental broadening as functions of the detection energy inside the deflectors are shown on characteristic curves. Good-quality Auger spectra of molybdenum and silicon carbide are given as examples on the electron distribution curves N(E)=f(E), obtained with a very small current density (10^-3 A cm^-2) at relatively low primary energy (1500 eV).

Measurements with two laser anemometer arrangements are reported and demonstrate the influence of particle velocity on the amplitude and visibility of the signal at the output from the photomultipliers. Physical arguments are provided to explain the measured results and to permit their interpolation and extrapolation. The dependence of signal amplitude and visibility on particle velocity implies a bias effect in the measurement of velocity and particle diameter; this can be minimised, but not removed, by the use of frequency shifting and an appropriate photodetector.

The design concepts, constructional details and performance of a pair of recently developed iodine-stabilised lasers are discussed. The effect of parameters such as iodine cell temperature and pressure and modulation amplitude on the performance of these lasers has been investigated. It has been found that the size of the absorption features normally used for the stabilisation increases rapidly with temperature (at constant pressure) while the width of the features decreases slightly. This enhancement in the signal-to-noise ratios and gradient of the absorption features results in significantly improved stability. Unfortunately, the reproducibility is adversely affected by temperature shifts. The lasers have a reproducibility of about 2 parts in 10¹¹ and a stability of 4 parts in 10¹³ over a 400 s sampling period.

A gas gun is described which enables a projectile of novel design containing a steel rod to be accelerated to a maximum velocity of 37 m s^-1 in a distance of just over 1 m. On impact with a loading bar a stress pulse is produced of ideal trapezoidal shape with a duration of 70 mu s and an amplitude which can be accurately controlled up to a maximum of 700 MPa. The gun differs from conventional systems in that instead of being of narrow bore operating under high driving-gas pressures it uses a wide-bore evacuated tube with atmospheric driving pressure. This enables the system to be much more compact, as well as being simpler and safer to operate.

Presents an electrical pulse excitation method for determination of the dynamic error of a thin-wire resistance thermometer. If the system being measured works cyclically in the steady-state and sharp electrical pulses are applied to the thermometer, the dynamical error and the correction factors can be evaluated by determining the mean value of the thermometer signal. An experiment to verify the practical application of this method was carried out, and measurement results are presented.

The effect of high magnetic fields (up to 18.4T) on germanium, platinum and carbon resistance thermometers and SrTiO₃ capacitive thermometers has been investigated in the temperature range from 2-87K. Figures are presented which allow a crude estimate of the real temperature if these thermometers are read under high-field conditions.

A simple method is suggested for stabilising the pump frequency independently of the FIR laser gas.