Table of contents

The development of integrated electronic circuitry has generated closely related ideas for complete systems which process signals at optical frequencies. The design and performance of individual components are already well documented and current progress is toward integrated optical devices. The initial production methods for individual components are not necessarily suitable for complete circuits but it is suggested that the technique of ion implantation may have general application and solve many of the problems. The advantages of accurate dopant levels, excellent spatial control and the ability to profile refractive index or electro-optic properties, whilst maintaining the sample at a chosen temperature, are very attractive. Examples are considered for a range of materials including GaAs, LiNbO₃ and LiTaO₃ which are currently at the centre of interest in integrated optics.

A modification of the traditional Toepler pump design is described which improves its safety and versatility.

A solid state ionization current comparator is described in detail and the design parameters are discussed. The circuit operation of this instrument depends on direct amplification of the ionization chamber current and on instantaneous electronic computation of the quotient of the measuring chamber current and reference chamber current. Three forms of output may be produced: numerical, analogue and binary coded decimal. The comparator is intended for application in photon and electron dosimetry in both twin- and single-chamber modes as well as for dosimetry requiring high detection sensitivity. The instrument is particularly well suited for measuring beam data in a form needed by computer treatment planning systems, or for drawing isodoses using the decrement lines principle.

A compact atmospheric pressure CO₂ laser utilizing a double-discharge technique has been constructed and operated at moderate repetition rates. Output powers of 30 W have been obtained at pulse repetition frequencies of 100 Hz, corresponding to an output of 300 mJ/pulse. With the addition of small amounts of H₂ and CO to the He-CO₂-N₂ gas mixture, sealed operational lifetimes exceeding 2*10⁶ pulses have been obtained. In operation in the sealed configuration, the output energy is reduced to 250 mJ/pulse at pulse repetition frequencies of 40-50 pulses/s.

Circuitry is described for a simple automatic tracking system to be used with a sample-and-hold amplifier. The gate of this amplifier is driven in order to follow the maximum of any selected pulse. Results of ultrasonic attenuation measurements in liquids are given.

It is shown that in the classical method using a potential difference amplifier with a low-capacity Kelvin vibrating capacitor, one actually performs a short-circuit current measurement. It is proposed to use a current amplifier for suppressing the effect of input capacity.

A low-cost instrument for digitizing chart records is described. Recorder deflection is measured by passing a needle through the chart recorder trace to make contact with one of an array of conductors. The position of the contact along the array is determined by electronic scanning and is presented on a visible display. The Y digitizer has a maximum sensitivity of 0.5% of the full-scale movement. Digitizing in the time direction is determined photoelectrically by counting the number of sprocket holes on one side of the chart. The maximum sensitivity is determined by the sprocket hole spacing.

A simple aid to the indexing of electron diffraction patterns from multicomponent systems is described. An example of the method, which uses slide rule scales, is also given.

Details of design and construction of a variable-temperature cryostat for magnetic circular dichroism (MCD) spectroscopy are described. The main feature is the possibility of measuring variable-temperature spectra using an electromagnet as the field of source, without diminishing the magnetic field strength or inducing any strain in the optical windows of the cryostat.

A variable-gain electronic circuit is described that can be used as a divider or, more specifically, to provide swept gain. A signal V₁ is divided by a control potential V₂: the quotient V₀ and the signal V₁ are isolated from other potentials by an optical link between a light emitting diode and a photoconductive cell. The circuit has been used to provide exponentially increasing gain to compensate for the attenuation of echoes in an acoustic ranging system.

A highly stabilized magnet power supply system is described for magnetic resonance/susceptibility instrumentation, which is capable of providing a current of 0-5 A into a 40 Omega magnet coil together with linear current sweep facilities. This system can easily be adopted for magnets of any resistance. The DC drift is about 1 part in 10⁵ per hour and low-frequency peak-to-peak noise is less than 1 part in 10⁶. Long-term (1 h) nonlinearity in sweep is less than 1%.

Details are given of an item of purpose-built hardware which has been integrated into an automatic data collection system for an X-ray diffractometer. The complete system enables both the investigation time and the volume of data collected to be reduced but does not affect the overall reproducibility. Although the use of the device is described with reference to the collection of X-ray diffraction data it is considered likely that the device could be applied to the collection of any similar types of data where a scanning procedure is involved.

A cryostat is described that is designed to measure changes in the contact potential difference between a normal metal and a superconductor as the superconductor passes through the transition temperature. The Kelvin-Zisman technique is used and the vibrating plate is driven with a commercially produced vibrator. Changes in contact potential of 0.2 mV can be detected.

Beam-chopping in the scanning electron microscope (SEM) by electrostatic deflection over an aperture is examined in some detail. The chopping aperture used is the final aperture image and the beam is of finite diameter. The required deflection angle to cut off the beam and the apparent movement of the spot due to the deflection in chopping are obtained for the cases of the deflection structure placed between the gun and the top lens and between the gun and the other lens.

The main part of the apparatus for Langmuir film deposition is its dipping and raising device which can affect the quality of films. A new mechanism, attractively simple in both its operational principle and construction, is described for up and down strokes of the slide across the monolayer-covered surface. The slide attached to the cylinder of an inverted, conventional glass syringe (clinical) moves downwards due to the hydrostatic pressure of water and moves up when the latter is sucked out. The key points of the mechanism are the use of an incompressible liquid instead of compressible gas, negligible frictional variations and hence uniformity of the driving force, and speed control as low as 0.1 mm s^-1 or better. In addition, it does not involve the design and precise fabrication of either a PTFE guide tube or the piston, as described in an earlier method. A demountable PTFE trough and some experimental results on Langmuir films obtained using the equipment are also discussed.

The design, construction and operation of a cylindrical geometry electron bombardment heat source are described and discussed. The assembly has generated a heat flux of 30 MW m^-2 on the inner surface of a 25 mm bore tube and 20 MW m^-2 on the outer surface (38 mm diameter) over a length of 42 mm. These power densities were limited by the rating of an existing power supply and cooling circuit. The cathode is positioned concentrically on the axis of the anode so that heat transfer through the anode (test section) wall is radially outwards. The device using this arrangement may be used for high-flux heat transfer studies which are of particular interest in the nuclear power field.

An experiment previously reported in a letter to Nature by Jennison and Davies (1974) has been improved and is now capable of detecting a frequency shift of two parts in 10¹⁸. The experiment shows that light is reflected from a transversely moving mirror without change in frequency to better than 0.2% of (v/c)² where v is the velocity of the mirror and c is the velocity of light. The result is in agreement with the correct application of the theory of special relativity to the problem (as reported by Ashworth and Davies (1976)) in contrast to the results predicted by certain authors (Ditchburn (1952), Gerharz (1964), Dashchuk (1969)) who predicted a change in frequency of second order in v/c for light reflected from a transversely moving mirror. The technique has other applications and is therefore reported in greater detail in this paper.

In this paper an improved optical method of determining the mutual diffusion coefficient as a function of concentration is presented. Measurements for carbon tetrachloride-ethyl alcohol and carbon tetrachloride-benzene mixtures are reported. The values of D obtained by this method are compared with those obtained by interferometric and diaphragm cell methods.

The spectrometer uses a single tunnel diode to generate and detect oscillations in a marginal oscillator circuit. It can be operated at helium temperatures and, though the sensitivity is not remarkable, it is more than adequate for many purposes. The main advantages of the circuit apart from its simplicity, small size, low dissipation and cost are its ability to work in a hitherto rather inaccessible frequency range and the fidelity of its response to complex resonance lines. An analysis of the circuit is presented and compared with experiment, and constructional details are given.

A normal incidence Wadsworth-type monochromator is described which is suitable for use with a UHV electron spectrometer and for employing a synchrotron radiation source. The optical and practical issues to be resolved when designing an instrument to work with a synchrotron source are discussed in a general way. One of the principal problems associated with using a continuum source is the presence of second- and higher-order radiation in the output of monochromators. A method is presented by which the amount of second-order radiation can be determined by means of a simple photo-yield measurement. A second grating monochromator is thus unnecessary.

At the H C Orsted Institute the multiprogrammed medium-size RC4000 computer is used for time sharing and batch and process control. The advent of cheap microprocessors has opened new ways for building controllers for this type of computer. It is shown that using a microcomputer as a slave computer can cut the resource demands in an on-line plotting system considerably and that the microcomputer can handle time-critical problems in process control of experiments without losing the advantages of using a multiprogrammed computer. The programs to the microcomputer are assembled on the 4000 and loaded directly into the microcomputer memory.

A large cold chamber has been developed for experiments on ice near its melting point. Temperature control is achieved by maintaining a three-phase two-component equilibrium temperature in a bath surrounding the experimental space. The proportion of ice and water is controlled continuously by using changes in system volume to switch refrigerant pumps. This enables the temperature to be controlled to +or-0.01 C. The equilibrium temperature is varied by using a solution instead of air-saturated deionized water.

The mixing behaviour of viscous solutions in a stopped-flow spectrometer has been investigated. Complete mixing is shown to occur within 10 ms of the stoppage of the flow provided that a sufficiently high driving pressure is employed and the viscosity of the solutions does not exceed 18 mPa s. Reactions in solutions of such viscosity with half-lives down to 7 ms can be satisfactorily followed.

Gain factors of an EMI 9603B particle multiplier having oxidized Ag-Mg dynodes (98.5% Ag) were investigated for three singly charged alkali ions, K⁺, Na⁺ and Li⁺, in the energy range 1-6 keV by considering the ratio of currents at the anode of the multiplier and at an efficient Faraday cup placed in front of the particle multiplier. From curves of ion velocity against gain factor, kinetically induced electron emission was inferred; almost equal threshold velocities for secondary electron emission for Ag by K⁺, Na⁺ and Li⁺ ions were measured at 6.1*10⁴, 6.4*10⁴ and 6.9*10⁴ m s^-1 respectively. Results also show that the gain factor exhibits a linear dependence on the velocity of the ion and that the slope of the secondary electron emission curve is proportional to the square root of the ion mass.

An oil film is placed on a surface over which gas is flowing, and moves under the influence of skin friction. The skin friction meter to be described makes use of the fact that, at time t after the start of the flow with skin friction tau , the thickness y of oil of viscosity mu at a point x close downstream of the leading edge is y= mu x/ tau t. A laser beam focused at position x, reflects partly from the oil surface and partly from the metal substrate. The reflected beams are focused on a photocell and the pen recorder output gives an interferometric record of y against t. To permit accurate setting of the position x, a second laser beam is used which is set at the upstream oil edge, x=0. The results obtained show good agreement with theory, repeatability and consistency. The meter can be used with any polished metal surface, whether flat or curved, and provides versatile and potentially accurate method for skin friction measurement.

The monochromators used in spectrofluorometers typically behave as filters with a triangular-shaped intensity transmission spectrum, with the bandpass value referring to the width of the triangular spectrum at half the maximum intensity. The effects of the shape of the waveband upon the reflectance and fluorescence measurements made with the spectrofluorometer are discussed from a geometric point of view, particularly in relation to subsequent colorimetric calculations.

Describes the construction and operation of a retarding field energy analyser intended to measure the distribution of both beam and plasma electrons in a high-power beam-plasma system. The analyser has been tested in an axial magnetic field up to 0.2 T, applying retarding voltages up to 10 kV. The paper is devoted to a review of problems and their solutions met in the design of such an energy analyser.

By improving the system for control of iodine vapour pressure with molecular sieves in a positive-column He-I₂ discharge, it has been possible to construct a stable sealed-off He-I⁺ laser device for the visible region. It has a total laser power of 20-30 mW for five visible lines, and a lifetime longer than 1000 h. Details of the construction and operation of the practical He-I⁺ laser are reported. The characteristics of the laser power are also described.

A variable-temperature X-ray diffraction camera, primarily intended for the study of liquid crystal phases, is described. This camera enables the diffraction pattern to be recorded continuously on a reciprocating film whilst the temperature is repeatedly increased and decreased (linearly with time). Diffraction patterns may therefore be recorded under conditions where the rate of change of temperature is comparable with that encountered in thermal analysis. The camera operates over a temperature range of 20-300 degrees C, and temperature spans of up to 115 degrees C (each with ten rates of temperature change from 3 to 180 degrees C h^-1) may be selected within this range. The sample temperature may be controlled to within +or-¹/₂ degrees C, remains linear with film position and is directly measurable to within +or-2 degrees C over the entire temperature range.

This paper describes the development of a vest-pocket miniature general purpose (type S2A) sound-level meter. The readout indicator consists of 16 sequentially illuminated LEDS graduated in steps of 1 dB. Some salient features are wide dynamic range (over 90 dB), low power consumption (90 mW) and true RMS detection (crest factor of 5). The instrument has an AC output of 3 V peak-to-peak at full scale and an internal 'A' weighted circuit with manual 'fast' and 'slow' response selection. The overall physical dimensions are 140 mm*33 min*17 mm and the weight is 160 g with batteries.

Unlike techniques involving plates and rings, cylindrical rods, with or without detachment, have not been widely used to determine interfacial tensions. Clarke (1976) has described a balance for use with a method of employing rods without detachment. Experimental conditions for the success of his method, and for the use of the balance with other methods, are described.