Table of contents

This review considers features of the design and development of stabilized lasers and discusses the specification of frequency stability and reproducibility in terms of the Allan variance. The more important stabilization schemes which have recently been employed, particularly with visible lasers, are discussed. The saturated absorption stabilized laser, which has achieved a frequency stability and reproducibility of better than one part in 10¹⁰, is described, and finally both contemporary and future applications are discussed.

When cutting small discs from bulk specimens prior to preparation for transmission electron microscopy it is usual to fix the specimen to the spark cutter with a conducting adhesive. An alternative method using a simple vacuum device is proposed.

The design and construction of a straining stage with load measuring facilities, which permits microscopic examination of a specimen while being strained, is described.

An improved design for a precise superconducting DC ratio transformer is described in which DC ratios with accuracies better than 0.01 ppm have been achieved.

The instrument described gives a visual display of the voltage- current characteristic of any two-terminal device. The forward and reverse applied voltage excursions are independently variable from 0 to 15 V. The forward and reverse current scales are independently variable from 0-250 mA full scale. The circuitry is arranged so that the whole area of the display screen can be used for any combination of the four variables displayed.

The cell described is used for measuring dark and light current through thin organic crystals and similar specimens and for studying the charge carrier injection into these materials from the electrolytes which provide the electrical contacts with the specimens. The cell can be used with degassed solutions.

A torsion pendulum is described which has a low instrumental decrement ( delta <4*10^-5). The temperature of the specimen can be varied between 80 and 1150 K in two stages. Tensile or torsion deformation of the specimen in vacuum can be exerted in situ.

A simple integrated circuit array is described which performs a cyclical reading of memory address in a random way.

The vapour pressure P_A to be measured is compared with the known equilibrium vapour pressure P_B of some reference liquid. A cartesian differential manometer is used to adjust automatically the temperature of the reference liquid so as to give P_A=P_B. The required vapour pressure is then obtained by measuring the temperature of the reference liquid.

A probe holder is described which can transmit tilting and rectilinear motion to a vacuum system from the outside with added vacuum safety while moving the probe. It consists of a spherical part which can rotate within a two-section housing. Rectilinear motion is obtained with a piston ring seal through this sphere. Thus the probe is movable within a cone angle of 34 degrees . The probe holder can be used with vacuum systems for plasma research as well as with coating units for various possible applications and it can be machined easily with a lathe.

A simple, low cost vibrating sample magnetometer is described, performing very sensitive measurements on thin magnetic films. The resolution of the apparatus is about 0.1 nA m², i.e. the contribution of monoatomic layer in a saturated Ni film of 25 mm².

A new opto-electronic system for ellipsometry, based on laser interferometric principles and capable of giving the relevant information at a high rate (down to 30 ms per Delta , psi pair), is described. The method requires no compensator and may become increasingly important as tunable lasers and wide-range transmitting polarizers become available. Its possible application, in the future, as a sensitive and powerful infrared spectroscopic technique based on phase information is mentioned.

A modulated molecular beam mass spectrometer has been developed to measure the concentration of unstable species produced in a fast gas phase chemical reaction. The molecular beam was formed by allowing a portion of the reacting gas to leak through a sampling slit into a three-stage differentially pumped vacuum system. The beam was modulated by an electromagnetic chopper and analysed using a quadrupole mass spectrometer.

A metal target of 50 mm diameter which can be cooled to 3 K and rotated about two perpendicular axes in a high vacuum system has been designed for use in an aerodynamic molecular beam apparatus. The problems of a compact low heat support for the target, and a means of rotating the target that does not interfere with molecules which are incident on or scattered from the target at glancing angles, have been overcome.

In dynamic adiabatic calorimetry, the heat exchange between the calorimeter and its surroundings has been measured from room temperature to 800 degrees C, and the effects of heating method, atmosphere, heating rate and heat content of the sample upon the heat leakage are discussed. From these measurements, it is concluded that the necessary conditions for absolute measurement are that the heat leakage be minimal and constant. This may be achieved by using external heating of the sample and controlling the heating rate.

The principles of operation of the different classes of silicon photodiodes are given together with a discussion of the importance of various parameters when using the diodes for measuring the power and energy of short laser pulses. A theoretical analysis is made of the speed of response and maximum linear current to be expected from a photodiode of known area, thickness and bulk sensitivity for various bias voltage, pulse lengths and wavelengths.

The sensitivity of a grazing incidence grating spectrograph has been derived from measurements of the absolute efficiency of the diffracting element, a Bausch and Lomb catalogue grating, and of the response of the recording emulsion, Ilford Q2 and Kodak Kodirex. Results are presented for wavelengths between 8 and 44 AA, obtained as K-line emissions from electron-bombarded targets, incident on the grating at an angle of 88 degrees .

For pt. I see ibid., vol.6, no.9, 854 (1973). A grazing incidence spectrograph has been calibrated for absolute intensity at several points in the wavelength range 25-33 AA by the method of branching ratios, using line pairs such as C VI (1-7) 25.83 AA, (6-7) 3434 AA which are observed in a laser-produced carbon plasma. Experimental results are presented for Ilford Q2 emulsion, used with a 2 m, 600 grooves/mm, gold-coated, catalogue grating, at an angle of incidence of 88 degrees , and agreement is found with a second calibration based on X-ray K-line emission from a standard source.

An analysis instrument for continuous and specific detection of phosphorylated hydrocarbons has been developed. The operating principle is flame ionization- flame emission combined in a hydrogen flame. Due to a geometric arrangement that optically shields the photomultiplier tube from the main part of the flame and by a narrow bandpass interference filter for spectral isolation of the phosphorus emission at 526 nm, it was possible to detect organophosphorus compounds specifically. By means of cooling baffles and a light conducting rod of quartz, the temperature of the photomultiplier tube and the interference filter could be kept at room temperature, which gave a low noise level and a good background stability.

A new optical method for measuring the velocity of sound has been investigated; it is based essentially on optical heterodyne detection techniques using a pair of ultrasonic light modulators of slightly different frequency. A light beating signal can be easily generated from the frequency difference between these modulators if signal and reference light waves obtained from the first order dual diffraction spectrum are photomixed with each other. The only optical components are the two modulators, and their alignment is not critical to the generation of a stable beating signal. Since the beating signal includes the sound velocity in each modulator in its phase factor, the sound velocity is immediately measured by making use of a conventional electronic phasemeter.

An apparatus is described for automatically collecting and storing optical transmission data from the vacuum ultraviolet spectral region. A sample positioning apparatus which has been used in a study of the optical transmission properties of thin solid films is described together with the modifications which were made to a commercial monochromator in the development of the automated system. The transmission spectra of fused quartz and polyethylene samples are presented to demonstrate the performance of the system.

The design of a new mass spectrometer for the study of positive and negative ions in flames burning at low pressure is described. The performance of the instrument, the requirements of the ion inlet system with reference to peak shape of the mass spectra obtained are discussed.

The design and performance of a segmented aluminium laser tube with O-ring insulation is described. The cathode is a plasma jet.

A six-nozzle plug air gauge has been developed to measure diametral creep of tubular specimens of 23 mm internal diameter for distances up to 7.5 m within a nuclear reactor. The progressive changes made to the air gauging system to increase range, improve reproducibility and decrease response time are described. The present system can measure up to a difference of 0.65 mm between the diameters of the gauge head and that of the tube being measured.

A system is described which has been built to control the density of the gas in a soft X-ray proportional counter to within +or-0.5% of the desired value when making astrophysical observations from a sounding rocket.

An investigation into the operating characteristics of a double discharge TEA CO₂ laser is presented, the object of which is to optimize the available focused power density. The existence of an operating regime of enhanced peak power but degraded energy is noted and qualitatively explained.

The authors report direct measurements of the amplitude modulation of de Haas-van Alphen waveforms caused by magnetic interaction between two different dHvA frequencies in an inhomogeneous magnetic field. Experiments are carried out on a pure Au single crystal, oriented with H parallel to the (111) direction, at 2.0 K and 36.1 kG.

Measurement of diffusion constants using NMR usually requires the generation of a large, known, linear magnetic field gradient. The design and construction of two sets of coils providing orthogonal gradients are outlined. Their measured performance is shown, and applications and limitations to 'pulsed' diffusion experiments are discussed.

A method has been devised for the simple yet accurate determination of the magnetization coercive force of soft magnetic steels. Measurements made on five samples having coercivities in the range 55-550 A m^-1 showed good agreement with the values obtained in the NPL compensated permeameter.

The thickness of a rapidly moving, wavy film of water can be continuously measured and recorded using a probe, which consists of two surface-mounted parallel conductors across which a high frequency AC signal is applied. A theory is given which allows prediction of the electrical conductance of the probe as a function of the film thickness and shows how the useful range of particular probe designs can be assessed. The theory, which can be applied to probes in either flat or curved surfaces, also includes the effect of a step change in the film thickness, so that the resolution of the probe may be predicted.

Pulse nuclear magnetic resonance is a good alternative to the slow, laborious dilatometer technique for determining the solid/ liquid ratio in partially crystallized fats and has some advantages over wide-line NMR. A processing unit is described which has the advantage that it displays directly the solid fat content on a digital voltmeter. Accepting a standard deviation of 0.6%, as is the case with the dilatometer technique, the solid fat content can be measured in 4 s.

If two hot wires are kept at different but constant temperatures by Joule heating, the difference between the squared voltages across two wires can give information concerning the velocity of an air flow. The electronic circuit and operating procedure for this are simple. With this technique velocity fluctuations up to 300 Hz have been successfully decoupled from temperature fluctuations in a heated wake. The limitation on the frequency is due to spatial inhomogeneity of the flow field.

The conventional scintillator-photomultiplier tube detector of a Stereoscan microscope was replaced by a split silicon detector, and a suitable AC coupled amplifier developed. By this means, two signals A and B were produced, both being formed by backscattered electrons. This detector was developed specifically for the metallographic examination of flat surfaces.

Many methods of measuring the out-of-roundness of nominally circular components or holes have been based, for convenience, upon some form of graphical assessment in which the inspector uses a pair of compasses, a rule and a good measure of subjective judgement. This has changed in recent years with the introduction of methods which can be implemented in an analogue or digital form and which are based normally on a best-fit circle rather than on zonal methods. The author justifies the use of a limacon reference line for roundness measuring instruments and goes on to develop a general expression which enables reference lines to be fitted to components having partial arcs or discontinuous circumferences very often met with in industry. It therefore allows for the first time the meaningful objective assessment of the out-of-roundness or roughness of such parts.

A modulated mass spectrometer for use in ion bombardment work such as sputtering and radiation damage is presented. The instrument incorporates an oscillating electron beam ionizer of simple geometry but high ionization and extraction efficiencies. Advantages offered are widely variable resolution, versatility in application and high sensitivity.

A stopped-flow apparatus for the study of fast reactions in solution is described. Its special features are that it permits accurate temperature control, that the flow system is chemically inert, and that flexible light-guides are employed in the optical system. When the absorbance change on reaction is 0.02, the ratio of signal change to noise under optimum conditions is around 500 and the rate constant can be determined with an accuracy of a few per cent. The temperature range so far used is -10 to +55 degrees C.

The author points out that a very simple and usually much more effective method is to subject the lamp to a dose from a common photographic electronic flashgun. The high intensity of the photons over the full visible waveband is ample to ionize even the most stubborn RF lamp.