Table of contents

Reviews nonlinear devices that have been used or are potentially useful for laser frequency measurement in the optical region, extending from the submillimetre to the ultraviolet. The devices are grouped mainly in two classes: point-contact junctions and bulk nonlinear crystals or gases. Their physical principles and limitations are discussed, and attainments when constructed of various materials are listed. Ways of measuring frequencies with them are considered.

A fast transistor driver circuit with rise and decay times <50 ns is described. This driver was developed to be employed in a high-voltage discharge pulser.

A simple inexpensive high power flashlamp and high voltage spark gap have been developed for use in flash photolysis and dye laser apparatus.

Slow disturbances are compensated at the site of an iron-free magnetic lens spectrometer (Jennings 1972) by a servo system driven by a fluxgate magnetometer at a site remote from the spectrometer. To avoid the presence of ferromagnetic material near the spectrometer, a pickup coil 0.20 m in diameter and of approximately 6000 turns (DC resistance 600 Omega : inductance 10 H) is placed near to the spectrometer and detects the disturbances in the vertical magnetic field.

A simple method is described for producing vigorous mechanical agitation of tungsten wire structures while they are being electropolished in a 1% potassium hydroxide solution. The technique enables a high current density to be used and produces a very highly polished surface on tungsten baskets and filaments.

In conditions of steady and pulsatile flow in liquids, cylindrical film probes have been found to possess a directional calibration which can be explained by considering the distribution of the local Nusselt number over the heated film. Under low-frequency pulsatile conditions the probe signal at the flow reversal point can be less than, equal to or greater than the true zero-velocity signal, It is suggested that this discrepancy, which is frequency dependent, is the resultant of swirl around the wire and the conduction of heat to the fluid immediately adjacent to the wire before natural convection can establish a steady state. Within the range of pulsations studied (0-0.24 Hz) the dynamic and steady flow calibrations were coincident at velocities above approximately 3.0 cm s^-1.

A multiple technique UHV chamber has been constructed for simultaneous LEED measurements, line of sight mass spectrometry, and Auger electron spectroscopy by a cylindrical mirror analyser. Semiconductor surfaces can be prepared in situ by molecular beam epitaxy. For this purpose a molecular beam source has been constructed on a small flange of 2³/₄ in (70 mm) outer diameter.

Points out the possibility of using a lens system involving electric and magnetic fields which has been used successfully to image electrons in an oblique electron multiplier array device (Johnson and Hallam 1973). The oblique nature of this crossed field device is useful in eliminating difficulties with irradiation of the surface to be investigated with charged particles or photons.

A simple method is described of improving the visibility of the surface of the melt in a Czochralski crystal grower.

An apparatus has been developed for performing zone solidification under the polarizing microscope. The apparatus has been designed specifically for the oriented crystallisation of polymers, taking into account their susceptibility to degradation and depolymerisation. Temperature gradients of up to 400 degrees C cm^-1 have been obtained, with polymer residence times in the melt being of the order of about one hour.

In electron microprobe investigations of porous materials there are no simple relations between porosity and the signals normally applied (emitted X-rays and backscattered electrons). The absorption of X-rays by a body of constant composition, however, is a simple and well established function of the mass density and thus of the porosity. It is demonstrated how measurements can be performed in a simple way in the electron microprobe where a certain spatial resolution can be obtained by using the electron beam to produce a point-shaped X-ray source. Optimal conditions for the measurements are found and practical arrangements described. The method is suitable for instance for measuring radial density variations in cylindrical, spherical, or similar bodies, the measurements being performed on a plate cut along a centre plane.

With a function generator and a proportional controller, a linear heating-rate controller has been developed. The desired temperature-time curve is obtained as a voltage from the function generator composed of diodes and resistors. It provides a range of heating rate from 3-60 degrees C min^-1. Any arbitrary temperature-time function may be obtained by adjusting the resistors of the function generator.

An accurate and relatively simple generator of decaying exponentials is described. It is able to produce three different exponentials and their sum. The initial amplitudes of the exponentials can be adjusted between 0 V and 10 V and their polarity can be inverted. The time constant range is between 1 mu s and 1 s.

A very simple circuit has been developed which permits variation of the current through an electromagnetic lens under the command of an electrically isolated control signal. Control of the power of the electromagnetic lens may be determined by any external variable as long as that variable is capable of being converted into an electrical signal. It is particularly applicable to scanning electron microscopes. Initial development was carried out on a Stereoscan Mk IIA.

The circuitry and the properties of a low-cost preamplifier/discriminator, using monolithic integrated emitter-coupled logic (ECL) circuits, are described. The resolution of input pulse pairs is better than 10 ns with output pulses of constant length. The circuit can be modified to meet special requirements (e.g. speed, output pulse shape).

A simple charge dispensing attachment for flash evaporation is described. A flat strip with a hole in its centre slides under a squarely fitting charge container. Each time the hole passes under the container, a small amount of charge corresponding to the volume of the hole is transferred onto a heated boat. The longitudinal oscillatory movement of the strip can be imparted by an electromagnet or a pulley operated through a Wilson seal.

The program and the interface which are described in this paper allow nuclear longitudinal relaxation time (T₁) measurements in multiline NMR spectra together with the nuclear Overhauser enhancement (NOE) factor. These two quantities are particularly interesting when dealing with ¹³C (or ¹⁵N) FT-NMR. The whole experiment is entirely automatic. Stacked plot as well as numerical results are provided. The operator's role consists only in setting the spectrometer parameters. The present system is implemented on a Bruker HX90 spectrometer interfaced to a Nicolet 1080 computer without disc.

The probe characteristic and the energy distribution function in gas plasmas are measured by a digital electronic apparatus with high speed scanning and a good signal-to-noise ratio. To counteract noise, the apparatus has averaging functions using digital accumulation and multiple scanning. In the multiple scanning, data at each probe voltage step are added in a memory and their average is taken so that low frequency noise may be eliminated.

A digital feedback system for ESR and ENDOR spectrometers is described which allows stabilisation of the ratio of the microwave oscillator frequency to the static magnetic field to one part in 10⁶ to any prescribed value. By use of a voltage-controlled oscillator the field may be swept with the same precision through ranges of a few gauss. Typical applications to precision measurement of lineshape in high-resolution spectra are presented.

The towing tank is described; this consists of a simple trough of water, 4 m in length, with an external model-carrying carriage running along rails on the top of the tank support frame. The carriage is towed by means of wires by an electric motor and gear arrangement which gives a speed range of 1 mm s^-1 to 100 mm s^-1. Background motions in the water of the tank were discovered to be a little greater than 0.2 mm s^-1 even when the tank was housed in a temperature-controlled room. The investigation of these motions and their reduction is described.

The effects of varying the sampling rate, sample size and data rejection criteria have been investigated for a water pipeline configuration in which the flow is characterized by a high Reynolds number and low turbulence intensity. The results show that convergence is obtained with samples greater than 3500 data points and statistical techniques have been used to obtain the mean velocity, turbulence intensity, skewness and flatness factors for a range of Reynolds numbers.

Based on a previously described method (Svarovsky and Svarovska, 1975) of 'analogue deconvolution', a new data analyser was built for particle size distribution measurements by homogeneous sedimentation in a disc centrifuge. A short description of the technique and available instruments for obtaining the data in the form of a sedimentation curve is followed by a summary of the deconvolution method and conclusions made from its testing. The new instrument is then described together with a data recording unit and results of tests with the whole system are shown. The new data analyser is shown to have an accuracy similar to that achieved with a big analogue computer and is now used as a valuable tool for centrifugal data analysis.

A magnetometer has been constructed with which accurate measurements of ferromagnetic magnetocrystalline anisotropy can be made over the temperature range 4K to 300K. The instrument will operate in the confined space inside a superconducting solenoid and measurements can be made by either a rotating sample or a ripple field method. It is shown that for each method the system performance follows that predicted by the phenomenological theory.

Oil is placed on a flat vertical surface and flows down under gravity. Theory shows that the oil should take up a parabolic profile, the square of the thickness being directly proportional to the viscosity and inversely proportional to the time from the start of flow. This suggests a method of viscosity measurement which has a number of potential advantages. The paper gives interferometric measurements of oil films showing that, except near the upper edge of the film, the theory is accurately followed. Comparisons with a U-tube viscometer show discrepancies, probably arising from lack of temperature control and other inadequacies in the apparatus. An optical technique suitable for practical implementation of the method is suggested.

A direct method of measuring optical density by a linear relation to an indicating voltage has been developed by combining the law of absorptivity of light in a medium with the photovoltaic relationship of a barrier layer cell. Temperature compensation has been obtained by using two similar photovoltaic cells differentially, but with a single beam of light, resulting in considerable simplicity of the optical system. The upper limit of measurable D is about 7 while the lower range may be extended to values less than 0.01. A meter adjusted for full-scale reading for D=2 has been found to read consistently within an accuracy of 2% over the entire range of 2 to 0.01.

A method of retrieving velocity probability distributions from photon correlograms of laser anemometer signals using a fast Fourier transform is described. Mean velocity, turbulence and higher-order moments may be obtained with sufficient accuracy for most engineering applications.

The authors describe the design of a simple and novel travelling-wave-type pulsing system suitable for transverse discharge excitation of high-power UV gas lasers. The pulsers have been used to excite high-pressure nitrogen lasers at 337.1 nm with effective inversion lifetimes of <or approximately=1 ns. The beam powers exceed 2 MW.

A new method is described for measuring the tensile strength of weak powder compacts by applying stress to a vertical powder test piece, formed and supported by the glass and metal surfaces of a split cell. Tension is applied by slowly stretching a long vertical spring to which the upper powder support is attached, until brittle fracture occurs at the unsupported waist of the test piece. Tensile strength is calculated from the spring elongation at fracture. The instrument is designed to measure tensile strengths in the range 10-2000 N m^-2 at temperatures up to 200 degrees C. There are two modes of operation for separate or joint determination of shear and tensile properties. The ability to function in the presence of high electric fields (up to 2 kV mm^-1) is an additional feature of the equipment.

A four-quadrant photodiode detector was used in an automatic system for tracking convoluted bright lines produced on a screen by back-projection. Error signals from the detector amplifier were processed by a small analogue computer which controlled the detector movement by the action of stepping motors. The detector did not need to be rotated while following the line. Tracking accuracies of the order +or-0.3 mm have been achieved while recording digital data by this method from test curves of width 1.5 mm.

Light scattering experiments in the critical region require the temperature of the scattering cell to be constant within +or-10^-3 degrees C over a period of about two days. For temperatures up to about 200 degrees C this can be achieved by placing the whole cell configuration into a liquid thermostatic medium. At higher temperatures, when vacuum thermostats have to be used, a different design of the cell configuration is required. It was found to be most convenient to divide the cell volume into two parts: the scattering cell inside the vacuum thermostat and a regulating cell in a separate thermostat at room temperature. The cells are connected by a thin-walled stainless steel tube of small bore. Thus the density of the substance inside the scattering cell can be varied without interfering with the temperature regulation of the vacuum thermostat.

Two microwave cavities operating at 2450 MHz for producing and maintaining plasmas are described. They have been tested in nitrogen, argon and hydrogen. Cavity I can be used for discharges in nitrogen between 30 mu Torr and 230 Torr, in hydrogen between 30 mu Torr and 640 Torr and in argon between 30 mu Torr and 990 Torr. Cavity II with the same gases can be used between 30 mu Torr and 500 Torr, between 30 mu Torr and 760 Torr, and between 30 mu Torr and 1500 Torr. No experiment has been made at a pressure lower than 30 mu Torr. Cavity I is very easy to handle and the stability of its discharge makes it an attractive source of free radicals to initiate chemiluminescences in kinetic studies.

A new calculation following traditional methods is proposed for deducing optical constants and thickness from the fringe pattern of the transmission spectrum of a thin transparent dielectric film surrounded by non-absorbing media. The particular interest of this method, apart from its easiness, is that it makes a directly programmable calculation possible; the accuracy is of the same order as for the iteration method.

An anemometer which was developed for indoor climate research has been modified in order to get the same shape of calibration curve for each anemometer. Experiments in a wind tunnel showed that this was the case for more than 80% of a test series of the modified anemometers. The time constant has increased but is still acceptable. Calibration curves and time constants could be predicted by calculation with reasonable accuracy. Some influence of dust particles on the instrument was noticed.

A direction-sensitive two-component laser Doppler anemometer is described. The basic element in this system is a rotating radial diffraction grating functioning both as a beam splitter and as a frequency shifter. Two different arrangements are discussed. One arrangement gives two non-orthogonal velocity components from which the on-axis velocity component could be derived. The second arrangement directly gives two orthogonal velocity components perpendicular to the optical axis. Experimental results are reported from measurements of the orbital velocities below artificially generated surface waves in a water flume.

Fluorimeters based on phase sensitive amplification cannot reject fast components such as scattered light or fluorescence in the case of phosphorescence measurements. Using a fast electrical switching function between photomultiplier and lock-in amplifier allows the recording of the slow decaying component only, in a very convenient manner ('electrical' phosphoroscope). Lifetime measurements for the slow decaying component are made possible.

A low energy electron gun is used to discharge insulating specimens during observation with a scanning electron microscope. The apparatus includes essentially the gun, an optical microscope, a supplementary grid before the electron detector, and a video signal chopper. Either topographic, chemical, crystallographic or potential contrasts can be observed with a high energy (30 keV) electron probe; observation of insulators under deformation is possible.

Scale gratings longer than 10-12 in. are often required for measuring linear displacement over long distances, e.g. numerical control of machine tools. The production of such large single gratings is by no means a simple task. A simple method is described for joining two or more identical amplitude gratings (photographic gratings), produced on a glass base. The method is found satisfactory for gratings of moderate pitch, 1000-2500 lines per inch (lpi), which is the usual requirement for machine tool control systems.

Colour reversal film (High Speed Ektachrome ASA 160) has been used as the recording medium for emission line spectra in an attempt to facilitate visual estimation of the relative intensities of lines. Moderate overexposure of this film appears as a colour change, and the colour of a line can therefore be used as a measure of its intensity. The molecular spectrum is recorded on the same film as a series of calibration spectra of white light of different exposure times. The colour of a molecular line is matched to the same colour at the same wavelength in the calibration spectra, and the exposure time of the matched calibration is a measure of the line intensity.

Discusses the removal of microscopic surface reticulation from the gelatin emulsion of the photographic plates of bleached-silver phase holograms. The perfect index match for the emulsion surface is provided by gelatin. Therefore, during the final water wash the emulsion surface of the hologram is pressed against another photographic plate from which all silver bromide grains and anti-halation dyes have been removed. The surfaces are bonded permanently by being warmed at 40 degrees C for a few minutes in an oven. This method, of covering the hologram by a clear-gelatin-covered wet plate is also applied in a modified wet exposure technique.

Extends the discussion of escape peaks and internal silicon fluorescence presented by Reed and Ware (see ibid., vol.5, no.6, p.582 (1972)) to the case where the surface of the lithium-drifted silicon detector is not normal to the direction of the incident X-rays. This oblique geometry is used in several SEM and microprobe instruments. It is found that the effect on the escape peak of a change in geometry is not trivial. An equation is derived for the size of the SiK alpha internal fluorescence peak as a function of the X-ray angle of incidence. It is noted, however, that contamination from silicon-containing vacuum oils or greases may obscure the contribution from internal fluorescence.