Table of contents

Outlines the theory and practical applications of the Fabry-Perot interferometer. In particular, the use of the instrument as a resonator at infrared and microwave frequencies is discussed.

The design and metrological applications of Fabry-Perot resonators in the microwave and millimetre regions of the electromagnetic spectrum are reviewed. The review opens with introductory discussions on open resonator principles and configurations, continues with an analysis of developments in theoretical and empirical resonator characterisation and concludes with a broad survey of recent microwave Fabry-Perot applications. These include dielectric, anisotropy, magnetic resonance, scattering and atmospheric measurements and gas refractometry and spectroscopy. Other applications discussed include quasi-optical filters and diplexers.

Reviews the use of Fabry-Perot interferometers at submillimetre wavelengths. The theory of these interferometers is discussed, and practical limitations on the performance are considered. The authors discuss the development of practical instruments, and the applications in which such instruments have been used for submillimetre wave spectroscopy. They identify some areas in which instrumental improvements are desirable, and suggest some possible developments.

Presents a review of current experimental progress on nonlinear Fabry-Perot interferometry placing particular emphasis on the phenomenon of optical bistability. After a short theoretical introduction outlining physical principles and device uses the authors describe the early experiments on Na, ruby and Kerr media. The most recent experiments on the semiconductors InSb, GaAs and Te constitute the most promising possibilities for practical applications.

The construction of an additional collimator is described which removes asymmetric long wavelength tails from X-ray emission peaks. The resulting spectra can be subjected to deconvolution procedures, based on Fourier analysis, which reduce the broadening due to the primary collimator. The final spectra are very similar, in quality and resolution, to those obtained from double crystal spectrometers.

Describes further developments of the interface unit employed by Shaw et al. (1981) to couple experimental measuring devices to a minicomputer. Since the original system only allowed for three input signals, a four to ten-line decoder has now been used to increase the number of channels available, and additional interface output signals now operate relays to enable programmable range selection for the analogue-to-digital converter. Two channels have also been used for control and now drive either the servo-motor of an automatic traverse gear, or the stepper motor of a pressure scanning valve. The resultant closed-loop control system is thus capable of performing the complete experiment under appropriate software instruction. When necessary the computer clock is employed to control the required time intervals.

The accuracy of ultrasonic velocities of propagation in an anisotropic material is verified, usually, by comparison with those of earlier authors. This practice can be given up, at least in the case of certain systems of crystals, in the light of the rules explained. These rules pave the way to an independent method of ascertaining the reliability of a new technique to determine ultrasonic velocities. The invariancy exhibited by the velocities of propagation in the cases of cubic and trigonal crystals, under certain specified conditions, is the characteristic feature of the rules. Numerical illustrations are given to stress the dependability of the rules.

A new method for calibrating the energy scale of photoelectron spectra, using the He⁺ peak at 24.59 eV, is shown to be satisfactory for both the He I and the He II spectra produced by spectrometers fitted with He I/He II photon sources.

A servo system has been developed for cavity stabilisation of a far infrared HCN laser operating at 337 mu m. It has advantages over previous methods in that accurate temperature control of the laser cavity is not required. The technique should be applicable to other types of far infrared lasers.

The fundamentals of ion motion in electromagnetic fields are reviewed in detail with a special emphasis on electric radio-frequency (RF) fields which are used frequently in dynamic mass spectrometry. Forces and effects on ions in electromagnetic fields which are typically neglected, but which may be important in practical applications are reviewed and discussed for completeness. A method, based on complex variable theory, is developed for finding the potential function of 'ideal multipole electromagnetic fields'. Application of this method for the determination of potential functions and differential equations of ion motion is demonstrated with reference to the electric radio-frequency dipole, quadrupole, hexapole, octupole and decapole fields. This is the first time that these topics have been addressed in one unified and fundamental literature presentation. The results and implications of this preliminary communication and tutorial are of importance in ion physics and dynamic mass spectrometry.

An apparatus is described for the determination of the solubilities of gases in liquids by a method which does not appear to have been applied previously. The method depends on observing the pressure at which a measured amount of the gas is just completely dissolved in a known amount of liquid. The apparatus is a stainless steel vessel and attached cylinder. The gas and liquid are confined above mercury. A few cm³ only of liquid and gas at NTP are required and the method is quick and easy to use in the pressure range 0.1-3.0 MPa and between 0 degrees and 90 degrees C. These ranges could be extended without great difficulty. The objective of the method is convenience rather than high accuracy. Results are repeatable to within +or-2% but the absolute accuracy is lowered to about +or-5% by possible errors in the amounts of liquid and gas actually transferred to the pressure chamber. The method has been tested and found satisfactory by comparing the observed solubilities of oxygen and nitrogen in cyclohexane and methanol with previously published values.

A simple automatic power-supply using a bidirectional thyristor and a phase-control circuit was developed to operate a titanium sublimation pump (TSP) in a long-term performance without any troublesome adjustment. It can operate TSP either at constant voltage or at constant current to the filament. To avoid the fracture of the Ti filament due to the thermal stress or the structural change of Ti, it can also keep the filament at any elevated temperature during the off-cycle of TSP.

Implementation of a new NMR imaging technique has lead to the introduction of new instrumentation in imaging machines. The authors describe magnetic field gradient drivers and microprocessor control circuits which have increased the versatility of the system. The performance of the imaging method and improved resolution whole body images are discussed.

An inductive sensor or penetrographic sensing device has been applied directly to a hardness tester for the detection of the indenter axial velocity under various conditions for the loading-unloading cycle. The device has not been used previously in this type of application. The sensor under consideration is capable of detecting very low velocities, giving information on the mechanism of the indentation on solid materials. Technical data and the performance of the device are also discussed.

The problems involved in accurately measuring the phase distribution in low megahertz ultrasonic fields are discussed. Two measurement techniques are described, one using continuous waves and the other using tonebursts. Preliminary measurement results, using both techniques, on the field radiated by a 2 MHz circular source are presented and show good agreement.

A wide band dielectric frequency domain spectrometer is described. The system is based on a computer controlled sampling oscilloscope, which is used as the amplitude and phase measuring unit. It is shown how the transmission method can be used to cover the whole frequency range from the MHz region to the upper limit of 18 GHz. As illustrative examples the dielectric spectra of benzyl alcohol, chlorobenzene and water have been studied.

A scanning instrument to measure the optical profile of a high-power neutral beam is described. The instrument is capable of both spectral and spatial resolution of Doppler-shifted Balmer-alpha radiation from the beam. To interpret the line-integral data from the scanner a theoretical model giving both the three-dimensional beam particle density and expected (line-integral) optical profiles is presented. By fitting empirical light profiles to experimental data, it is shown how information on beam divergence, beam steering, uniformity and hydrogenic species ratios can be obtained.

A high resolution voltage to frequency type digitiser is described, suitable for recording secondary electron spectra with sufficient resolution to allow the shape of Auger features and electron loss features to be determined directly. The digitiser has an amplitude resolution of 10000 and it takes approximately 2-3 min to record a spectrum of 250 data points. The performance of the digitiser is demonstrated with some results for a clean Ag(111) surface.

A design is presented for a stable liquid helium cooled 430 MHz preamplifier, using a GaAs MESFET, with a 3 dB bandwidth of 35 MHz. Changes in device parameters with temperature are considered. Accurate matching is achieved by the use of GaAs varactor diodes and may be optimised in situ by controlling the bias voltages. The expected improvements in performance from both the increase in transconductance, and the decrease in the level of the Johnson noise sources is observed. By this technique the authors have achieved a noise temperature T_N<or approximately=10K with a single stage gain of 19 dB. The output power for 1 dB gain compression is +7 dB m.

A half-meter Johann spectrometer for the measurement of low-intensity alloy valence bands in the low keV region is described. The instrument is of novel mechanical design and incorporates fully automatic control of all functions. Sample results are included to illustrate the instrumental performance.

A new instrument to enable cheesemakers to decide on the optimum time for cutting the curd by continuously monitoring the development of ridigity is described. A transmitter/receiver probe immersed in the milk after rennetting measures the ability of the curd gel to transmit a low frequency pressure wave (0.07 kPa at 0.02 Hz). The results are recorded as a series of voltage peaks on a chart, peak voltage representing curd rigidity. The repeatability of the instrument was assessed in the laboratory and showed that the amplitude of traces 40 min from rennetting had a coefficient of variation of 2.6% about the mean amplitude at that time. A brief summary of results obtained during preliminary trials in cheesemaking indicates that the instrument has considerable potential in the cheese factory and would be most useful for fundamental gel studies in the laboratory.

Describes an interface which produces a significant enhancement of a digital correlator. With the interface fitted, completely remote operation using a PET microcomputer is possible, as well as on-line data acquisition and processing.

An ultra-low-load penetration hardness tester which operates at loads of up to 3 mN with a resolution of 10 mu N is described. It is capable of producing a continuous record of the penetration depth of the indenter and the resolution of the depth measurement is estimated to be 5 nm. A hardness value is deduced from the applied load and the penetration depth, which may be less than 0.1 mu m. The ability of the machine to obtain information on on-load hardness, off-load hardness, elasticity, adhesion and load-dependent effects is demonstrated. The authors describe a study of the properties of a soft metal (indium) and thereby show how the types of measurement obtained are related to conventional microhardness measurements.

Describes a system for accurate specific heat measurements of solid samples with masses of the order of 10^-6 kg with automatic stepwise temperature regulation and data read-out in the range from 2-380K and with the ability to apply a uniaxial pressure using an AC technique. The system has great flexibility in temperature regulation and selection of frequency of heating. The temperature steps can be varied from 1 mK to 1K. The time intervals between successive measurements may be from a few seconds to several hours. In particular, the system is well suited for measurements at solid-state phase transitions and has been tested largely in this connection. Uniaxial pressure up to 10⁸ Pa has been applied. The absolute accuracy of specific heat measurements is about +or-5%, but the relative accuracy is typically 0.1%. Since the system is intended for the study of phase transitions, the latter number is of greater importance.

A simple and robust torque magnetometer which has a wide sensitivity range, from 10^-6 to 0.2 N m, is described. The design is based on that of Aldenkamp et al. (1960) but uses a modified mutual inductance method for measurement of angular displacement which in conjunction with a lock-in amplifier provides a direct reading of torque. This output is fed, together with a voltage proportional to magnet angle, to an on-line microcomputer, Fourier analysis of the torque curve, including a shearing correction takes approximately one minute following the complete input of data. The instrument is suitable for work down to liquid helium temperatures and up to about 450K.

A device for the measuring of the complex permittivity in the 0.1 MHz-300 MHz range is presented. It is a resonant system on which we can easily fit the measurement cells of the laboratory used in the 1 Hz-4 GHz range. This device allows us to measure the loss angle of materials down to 0.4*10^-3. After the description of the mechanical and electronic parts of the device, the authors give the calibration method used to obtain the real and imaginary components of the electric permittivity. Finally, they report the results of dielectric measurements performed with this device for a liquid crystal and a synthetic zeolite. Automatic data processing by means of a computer increases the rapidity of measurement and decreases the number of manual operations.

A survey is given of the theoretical background for designing multi-terminal capacitor sensors of several types, suitable for control of every physical quantity that can be related with the change in position of two carriers, covered with electrodes. Previously published investigations of capacitor sensors, are briefly mentioned, and a description of the capacitance bridge used and the results of investigations of a multi-terminal capacitor test model are given. The main conclusion is that the capacitor sensors described can be used in cases where reliability and sensitivity of laser interferometry and strain gauge measurements fail.

Describes a technique which uses pulsed dye laser excitation and piezoelectric ceramic detection to obtain photoacoustic spectra of solids at temperatures down to 4.2K. It shows how the PAS signal is dependent upon the Gruneisen parameter and demonstrates good experimental agreement with theory.

For pt.II see ibid., vol.13, p.763 (1980). The imaging performance of a proximity-focused imaging photon detector using microchannel plate (MCP) intensifiers, and a resistive anode is determined by four major factors. These are: the electron optics of the biplanar lens formed by the photocathode and MCP, with a gap of between 300 mu m and 1 mm; the random walk process of intensification within a triple-MCP (Z-plate) intensifier; the noise factor of the anode and the preamplifiers, and the errors of the main signal processing electronics. A device with a 1.0 mm photocathode to MCP gap and a potential difference of about 250V across this gap, and a 'linear' resistive anode read-out system, shows a point spread function with a full width half maximum (FWHM) of 86 mu m. Consideration of the potential improvements which would materially affect resolution indicate that about 30 mu m FWHM is achievable, corresponding to a limiting resolution of 34 line pairs per mm, at 3% modulation.

A pulse processing system for randomly distributed pulse streams is described which incorporates two independent filters discriminating against correlated noise. One acts against noise bursts, the other detects and identifies the frequency of any regular pulse trains. Both filters are automatically adjusted by an internal microprocessor which monitors their performance. The microprocessor also counts and presents data on the accepted pulses forming a complete and versatile pulse counting system.