Table of contents

A state-of-the-art review of electron interferometry and interference electron microscopy is given. The various types of interferometry device, interferometers and interference microscopes, which have been proposed and/or constructed are reviewed and commented upon. The electron biprism, by far the most successful interferometry device, is treated in some detail from both the experimental and theoretical (geometric and wave optics) points of view. The applications of electron interferometry are presented with particular reference to off-axis electron holography. Finally the future perspectives are indicated.

The physical principles of low total pressure measurement are presented and the associated specific problems discussed. Low pressure measurement under isotropic conditions is briefly reviewed. Emphasis is placed on the analysis of the conditions of pressure determination in nonisotropic media. The principles underlying the design of instruments for the measurement of the molecular flow in terms of pressure, such as the pressure converter and the beam detector, are presented. Experiments for the study and measurement of the density and distribution of the molecular flux evolved in high vacuum chambers from distributed or localised sources are described. Finally, the techniques for pressure measurement in sealed-off products are reviewed.

A new automatically synchronised system for optical measurements is proposed. The system comprises a monochromator and plotter combined in such a way that provides various regimes of work.

A technique has been developed for the measurement of the linearity of a SQUID system which is used to provide a scale of magnetic flux or current with increments of one flux quantum. SQUID linearity has been determined by using as reference an RF biased Josephson junction voltage source. The linearity of the system over a range of 5*10⁴ flux quanta is of the order of 2*10^-3 flux quanta or 4*10^-8 of the scale range.

A new realisation of the differential method of electrolytic conductivity measurement is reported and an electronic circuit for its use is presented. This method enables the electrode polarisation influence on the measuring accuracy to be considerably reduced.

One of the few crystals available for X-ray spectroscopy in the 1.0 to 1.5 nm band is natural beryl. This report describes work carried out to measure and improve the X-ray characteristics of four samples of the pink form of beryl (morganite) to establish the suitability of its use in the X-ray polychromator (XRP) instrument flown in the NASA Solar Maximum Mission satellite. Surface preparation of beryl crystals by etching in hydrofluoric acid followed by polishing in X-30 syton is shown to bring the rocking curve widths (FWHM) as measured on a two-crystal spectrometer to the near perfect values of 5 arc sec at Cu K alpha (0.154 nm) and 3.3 arc min at Cu L alpha (1.331 nm). In addition the crystals peak reflectivity can be enhanced by a factor eight times that of flat and ground but otherwise untreated crystals.

A new wall shear probe for measurement at flexible walls, such as membranes or arteries is presented. The design is based on commercially available hot-film wall shear probes. Rapid fixation at the membrane and sealing of the probe hole is guaranteed by a cap screw. The membrane is pressed between the screw and a flange. The probe is calibrated in stationary Couette flow by means of a calibration device which was described in an earlier paper (Tillmann and Schlieper, 1979). Application of the probe in an artificial blood pump chamber is demonstrated and first results for the wall shear stress distribution at different sites of the chamber are presented.

The method first suggested by Deschamps (1953) for the determination of the scattering parameters of microwave junctions, is applied to the measurements of dielectric permittivities of liquids. This involves the use of a cell with two windows. Using the appropriate correction formula for these windows, the method permits determination of the permittivity of non-polar liquids with an accuracy better than 0.2%.

A simple spring-loaded, four-contact mount for residual resistance measurements is described. It is suitable for small, rectangular-prism metal samples of the type used in de Haas-van Alphen studies.

In order to avoid reflections of RF power from the probe circuit to the power amplifier, the authors have used a circuit which preserves a constant resistive impedance during the frequency sweep.

Determining the spatial distribution of flux density in magnetic fields is of importance in many areas of research involving magnets. An inexpensive device is described which provides a clear display of relative field intensities at all points along the boundaries of a square region in a magnetic field. This field mapper is useful for determining field homogeneity and for accurately displaying gradients. This device, in conjunction with a storage oscilloscope and an X-Y plotter, allows field mappings to be performed in less than 5 s, and to be continuously repeated. Dynamic studies of time-varying fields are also practicable using this technique. Examples of the use of this system to display linear and nonlinear static and time-varying magnetic field gradients are shown.

A high-power multiple ruby laser recording system has been developed and is described. The system, which produces a train of Q-switched, monochromatic, polarised light pulses of 10 MW power and 20 ns duration, is being used in sequential photography at a speed of 10⁶ frames/second.

A multibit, minicomputer-based digital autocorrelator with a large number of delay channels is described. Due to a novel operating principle, quasi real-time behaviour is achieved at low count rates. Therefore no time is wasted in situations where the time needed for an experiment is most critical. Sample times range from 10 ns to 168 ms, the counting capacity may be set from one to five bits per sample time, the total delay is between 4000 and 760 channels. Signal utilisation and accuracy of the instrument are discussed and compared with an ideal real-time autocorrelator.

For controlled heating of metal microcrystals up to the melting point, the end of the field emitter tips are bombarded by an electron beam (8 keV, 400 mu A, 200 mu m beam diameter). To measure local temperatures on small areas down to 2 mu m diameter a special one-wavelength micropyrometer was built. Using an optical microscope, an image of the glowing tip was projected on to a screen outside the vacuum chamber. The screen has a movable hole behind which a one-wavelength filter and a photomultiplier are placed to measure local radiant intensities. The relative temperatures are obtained from Wien's law, and are absolutely calibrated by a thermocouple spot-welded on the emitter shank. Local relative temperatures and temperature gradients for a tungsten emitter are measured in the range between 2800K and 3650K, with an error and a stability better than 10K. For absolute temperatures the error is 50K when no evaporation occurs.

A method of determining the three main instrumental factors in an X-ray powder diffractometer is described, the factors being the receiving slit width b_c, the projected width of the X-ray tube focal spot b_t, and the divergence of the X-rays in the focal plane gamma . The method is based on the calculation of the minimum distortion of the diffraction peak assuming that the integrated intensity of the diffracted beam remains constant. The following optimal ratios between the instrumental factors were obtained: gamma degrees =66.8 square root b_c/R tan theta and b_c approximately= square root (0.2+b_f)b_f (where R is the radius of the goniometer circle). The application of these equations to the powder diffractometer with Bragg-Brentano geometry is discussed.

The spectrometer uses an array of 50 pyroelectric detectors etched from a PVF₂ sheet in the precise positions for the various lines in the P and R branches of the CO₂ spectrum. The detectors are accessed in sequence to give a bar chart display of the spectrum. Compared to the conventional spectrum analyser (using a phosphor screen for CW or a graphite screen for pulsed lasers) the instrument gives a substantial advantage in sensitivity with a noise equivalent power of 100 mu W for CW or 200 nJ for pulsed. The dynamic range is 3000:1, enabling the detection of weak satellite lines, while a digital store allows monitoring of each shot of an inconsistent but low repetition rate laser.

In the attempt to provide reliable experimental data for comparison of different methods for electron-polarisation analysis, an efficient analyser based on low-energy Mott scattering has been built and tested. By increasing the solid angle of each of the two detecting channels to about 0.2 sr, an efficiency of 4*10^-5 at 15 eV was obtained; a further increase of this figure of merit is to be expected by improving the target system. The device is much more compact than a high-energy Mott analyser and its efficiency is almost comparable to that obtained by high-energy Mott scattering or low energy electron diffraction.

Describes an apparatus to obtain low temperature electroreflectance spectra of the E₁ transition of uniaxially stressed indium up to 5.6*10⁸ P_a InSb, in high magnetic field.

A simple, constant stress viscometer without bearing is described. The rotating part consists of a ferromagnetic disc which floats on the liquid. It is driven and centred by a fast rotating magnetic field. The shear stress can be varied continuously between 5*10^-5 and 0.5 Pa by changing the distance between the disc and the rotating magnet.

A new method based on a modified laser interferometric anemometer principle is presented. The new optical system provides a measurement volume of almost constant intensity modulated by fringes and crossed by two dark bands. The particle behaviour inside such a measurement volume is discussed and formulae for the determination of the velocity vector module and its direction are obtained. In the case of large particles a correction for the particle diameter is performed. The particle sizing is based on the analysis of the wave amplitudes of the photomultiplier signal. The accuracy and validation rate are discussed and experimental results obtained with real particulate flow are presented.

A device for the hydrostatic loading of a two-dimensional photoelastic model is described and its application in a study of the stresses in saddle-supported, liquid-filled, cylindrical vessels is outlined. The loading technique will permit an adequate solution to many three-dimensional hydrostatic loading problems or provide a time-saving and cost-saving preliminary to a comprehensive three-dimensional study.

Mechanical and electrical details, together with performance tests, are presented for a double container 0.032 m³ thermostat for use in the temperature range 0-30 degrees C. The control system uses a precision thermistor to give a stability of <or=+or-4 mK over a period of 14 days. The short-term stability over several hours was better than +or-1.5 mK, the limit of the temperature measuring system used during tests.

Diverse materials and techniques of illumination have been proposed for the cross wires in guiding and micrometric eyepieces. A brief historical review of the design problem is given, together with a new solution implemented on the Radcliffe Telescope at the University of London Observatory.

A novel velocity filter for ion beams of low energy is described which is easily constructed and which operates at ion energies of less than 20 eV. The filter behavior was studied by both computer simulation and experiment, with good agreement between the two methods. The velocity is selected by the frequency of a small radio-frequency voltage and hence contact potential errors are avoided. The velocity resolution is a function of the RF amplitude and so is easily adjusted. The normal operating resolution is about 7% full width half maximum (velocity) at all energies.