ALBERT

Notes: A multichannel far-infrared interferometer used on the Joint European Torus (JET) is described. The light source is a 195-μm DCN laser. The instrument is of the Mach–Zehnder type, with a heterodyne detection system. The modulation frequency (100 kHz) is produced by diffraction from a rotating grating. There are six vertical and two oblique channels. The latter rely on retroreflection from mirrors mounted on the vessel wall. Their vibration is compensated by a second wavelength interferometer at 118.8 μm. The various subsystems are described, with emphasis on features necessitated by (a) large path lengths, (b) remote handling requirements, (c) fluctuations in atmospheric humidity, and (d) unmanned automatic operation. Typical measurements, along with real-time and off-line data analysis, are presented. The phase-shift measurement is made with an accuracy of (1)/(20) of a fringe, corresponding to a line-integrated electron density of 5×1017 m−2. Comparison with other electron density diagnostics are shown. The introduction of additional optics allows measurements of the Faraday effect and a determination of the poloidal magnetic field distribution. The signal processing and data analysis are described. Errors introduced by the calibration procedure, birefringence of the probing beams, toroidal field pickup, the flux geometry, and the density profile are considered. The Faraday angle is measured with an accuracy of 5% and a time resolution of 1–10 ms. The poloidal magnetic field is deduced with an accuracy of ±15%.

Notes: A pulse-height-analysis (PHA) technique of soft x rays is applied to Heliotron E experiments. The primary interest of this measurement is the determination of the electron temperature. Since the number of photons measured in a PHA system is extremely restricted owing to a finite processing rate of the system, it is most important to use the full amount of information involved in the spectral data. The statistical estimator from the maximum-likelihood method is efficiently used for this purpose. The estimated temperature is in good coincidence with the temperature by the electron-cyclotron-emission measurement, which is calibrated by the laser Thomson scattering. A check of reliability of the estimated electron temperature is developed from a statistical test of goodness of fit. The identification of impurity lines buried in a thermal spectrum is also discussed in the spectra accumulated through several or several tens of plasma discharges. The line emissions from Si, Cl, Ca, and Ti are identified. A systematic error in the estimated temperature due to the impurity lines is evaluated. The contributions from Cl and Ti cannot be neglected in the temperature estimation from a spectrum accumulated through several currentless ECH plasmas in Heliotron E. A removal of those contributions to the temperature estimation is successfully demonstrated. The electron temperature with several percent uncertainty is obtained by PHA every 10 ms during a Heliotron E discharge.

Notes: An absorption method of soft x ray is applied to Heliotron E plasmas for measurement of the electron temperature. Nitrogen gas is used as an absorber for convenience, owing to its accurate, uniform, and easily controllable density. The general feature of the absorption method for measurement of the electron temperature is discussed using a model with two parameters: the generalized thickness of the absorber and the electron temperature. The energy resolution of this method is not sufficient as a general method for spectral analysis. Hence, it is necessary to assume in advance such a model spectrum as consists of bremsstrahlung, recombination radiation, and impurity line radiation. Since the spectrum is always assumed before the analysis, we should try to find the origins of deformation of the energy spectrum and to correct the contribution. The effect of line emission from impurity ions to the estimated electron temperature is evaluated as a function of the electron temperature and the energy of the line relative to the generalized absorber thickness used in the measurement. An actual spectrum is measured by a pulse-height analysis (PHA) of the soft x ray. The one clear line, from chlorine, is not significant in the present determination of the electron temperature by the absorption method. Another possible line from iron at energy less than 1 keV is included in the analysis. Using a convenient method for determination of local emissivity from a chord-integrated emissivity, the electron temperature is determined from the local emissivity. The observed broad electron-temperature profile might be an artifact due to recombination radiation of the highly ionized ion diffused out of the hot core of the plasma. It is confirmed that the absorption method gives absolute measurement of the electron temperature at the plasma center, when additional information on impurity lines are given by PHA. The estimated temperature is consistent with the PHA measurement. The absorption method combined with PHA provides an easy and inexpensive measurement of the electron temperature compared with a system fully constructed by PHA.

Notes: The brief note describes diverse aspects of the technique used for rhenium plating the hot plate used for contact ionization of barium in a Q plasma source. The rhenium plating optimizes the probability of barium ionization. Special care has to be taken in order to deposit a uniform layer of rhenium, for this purpose a slow rotation is given to the plate during deposition.

Notes: The simultaneous photon-counting and wavelength scanning by IBM compatible computers is described. Real-time photon counting is accomplished using the EG&G Ortec ACE-MCS interface board while the monochromator scan is simultaneously driven by a DCC5 multifunction counter-timer interface board. Count rates of up to 100 MHz are achieved.

Notes: We have developed new types of ion-optical systems having larger solid angles (i.e., collecting power) and flexibility than many existing designs. They use relatively simple axially symmetric elements, namely solenoids, axial magnetic dipoles, and radial electric field lenses. The systems can focus, with good optical properties, energetic ions in the range of tens of keV up to tens of MeV kinetic energy and are capable of operating in nondispersive, achromatic modes. The key elements for the latter are new types of defocusing magnetic and electrostatic correction lenses. The lens systems have applications in any existing devices used to collect and focus energetic ions (including electrons). Typical devices are: mass spectrometers, leak detectors and gas analyzers, ion sources, accelerators and ion implantation systems, nuclear particle spectrometers, electron microscopes, ion microprobes, and ion-beam lenses for cancer therapy.

Notes: An electron spectrograph is described that covers electron energies from 400 eV to 200 keV with an energy resolution of 10%. This overlaps the range of electrostatic deflection devices at low energy and solid state detectors at high energy. The spectrograph uses magnetic deflection of the electrons to achieve energy separation and images the full range of energies on a single plane. The magnetic circuit uses the fringing field of two axially located magnets to attain the large energy range. Six separate electron beams can be dispersed in the field, each entering the circuit from a different angle. This is a particular advantage when measuring plasma electron three-dimensional velocity distributions. The angular response of the instrument is particularly favorable and the stray magnetic field is sufficiently low to meet spacecraft requirements. Compared with electrostatic deflection devices, the spectrograph is particularly advantageous for measuring high energy electron plasma velocity distribution functions with fast time resolution at modest energy resolution.

Notes: A simple source chamber is described which enables the introduction of laser-generated, vacuum ultraviolet (VUV) radiation below 102 nm into most existing photoelectron and photoion spectrometers. A long capillary light guide provides a conductance barrier between the VUV source and experimental chambers, and also provides a small, well-collimated VUV beam at the interaction region. A platinum photodiode is found to provide a useful measure of the VUV intensity with minimal interference from the unconverted UV light. The performance and capabilities of the source are demonstrated by several applications using photoelectron spectroscopy.

Notes: A parallel-plate refractometer has been developed which can be used to measure the refractive index of liquid and solid films with an accuracy of 0.4%. The refractometer, which is a modification of the Pfund single-plate refractometer, provides the ability to measure film thicknesses which range between 0.1 and several millimeters.

Notes: A device for rapid-tuning cw, Q-switched lasers for a CO2 heterodyne detection lidar is presented. It is shown that it is possible to utilize galvanometer-driven mirrors to rapidly switch wavelengths over randomly selected lasing transitions in the 9–11 μm portion of the spectrum. Both a transmitter and a local oscillator are simultaneously switched between transitions while still achieving the frequency stability typically required for a coherent lidar system.

Notes: A gating circuit is described which provides a cutoff efficiency of approximately 99% by pulsing the first dynode of an RCA C31034 type linear-focused photomultiplier by only 18 V. This is accomplished by utilizing a local minimum in the photomultiplier gain which occurs immediately before the sharp turn-on point. The circuit achieves the requirements of fast turn-on, variable gating duration, and minimal switching transients. The technique is especially suited to photon-counting applications in which stability of the anode baseline voltage is critical.

Notes: A new optical method using a Pockels device is developed to simultaneously measure two directional components of an electric field. In this method, an output light beam from a Pockels device is split into two beams and then each of the beams is transmitted through a polarizing plate whose polarization direction is different, depending on the measured field component. The relation between two measured field components and the required polarization direction of the polarizing plate is theoretically derived for representative materials of the Pockels device and is also examined experimentally. A field sensor is made on the basis of this new idea and is used to investigate a nonuniform electric field. An electric field changing spatially by 20% per centimeter can be measured with an accuracy of 5% using the Pockels sensor. The sensor is successfully applied to measure an impulse electric field between a sphere-to-sphere gap.

Notes: Using two commercially available hot-wire X probes, a conventional measurement technique, and the evaluation method described here, the magnitude of the time-averaged velocity vector and the magnitudes of the Reynolds normal stress components as well as the magnitudes and signs of the Reynolds shear stress components can be determined. The evaluation method employs as a basis the spatial directional sensitivity of hot-wire probes and involves the squaring of the anemometer's output signal. Furthermore, the region of applicability of this method is discussed.

Notes: The TEXTDB data base organizes the analyzed experimental data from the TEXT experiment so as to aid in understanding the physics of a complete discharge. The data base was constructed using a commercial relational data base. The relational model provided a flexible structure for organizing data from many different diagnostics into a unified description of the plasma discharge.

Notes: This article deals with the determination of the magnitude and sign of the three components of the instantaneous velocity vector from the output signals of a triple-sensor hot-wire probe. All three sensors lie in the same plane with a given angular orientation. Measurements with this triple probe are performed with the wire plane inclined at an angle of about 45° to the main transport direction of the fluid, thus ensuring high sensitivity of the probe and the determination of the three components of the instantaneous velocity of the flow in magnitude and sense. Furthermore, the region of applicability and the accuracy of the values of the flow parameters of the method are discussed.

Notes: A microprocessor-controlled system has been developed to automatically scan tissue culture dishes in order to detect and locate fluorescently labeled cell colonies for subsequent cloning. An X-Y recorder mechanism moves an 80-mm-diam dish in a raster scan through a stationary laser beam adjacent to a photomultiplier tube equipped with an emission filter. Front-end electronics processes the PMT signal to screen out small-scale fluorescent artifacts of selectable size (e.g., 〈0.2 mm). Appropriate signals are input to the computer which then interrupts the raster scan to perform a limited fine scan of the dish to accurately localize the fluorescent spot position. An additional artifact test using a different filter is then performed. The underside of the dish is scribed at the location of spots that pass this test. Using fluorescein as a label, fluorescence as low as 25% above intrinsic cell background fluorescence can be detected. The fluorescence signal level threshhold can be set (e.g., 70% above intrinsic cell background) to within an accuracy of approximately 15% of intrinsic cell background fluorescence, and the system will reliably find colonies with a signal exceeding that level. With the above typical values, the number of false positives is typically less than five per dish and the time to completely scan an 80-mm-diam tissue culture dish is 2–4 min.

Notes: This paper describes an x-ray K-edge subtraction television system for noninvasive angiography utilizing synchrotron radiation. The phantom, including contrast material (iodine), is irradiated by monochromatized dual-energy x-ray flux, alternately, using a high speed monochromator. The monochromator consists of a silicon crystal plate vibrating at 15 Hz so that the phantom is irradiated by the x-ray flux of 150 eV above and below the K-edge photon energy of iodine, 15 times per second. As an x-ray detector, TV cameras optically coupled to an x-ray image intensifier are used and the video signal is processed to display the subtraction image of pairs of successive images in real time. This system was fully implemented and moving phantoms were examined. Both the time interval between the energy change and the exposure time of each image has been shortened to 2 ms.

Notes: The possible integration of a recently fabricated high-purity silicon radiation-sensor array into experimental-instrumentation systems currently being developed for digital-subtraction angiography (DSA) procedures conducted with synchrotron radiation is discussed. In order to motivate the intended application of the sensor, the medical-imaging techniques of conventional coronary angiography and DSA are briefly reviewed followed by a summary of the different system and detector designs currently in use.

Notes: A linear x-ray gas position sensitive detector with delay line readout has been constructed. The detector is described, characterized, and used for detecting x-ray diffraction patterns from polycrystals.

Notes: Transient heat generation by absorption of x-ray and far-infrared beams was successfully detected by a photoacoustic detection method. The photoacoustic detectors of solid and gas phase for x rays and of solid materials for far-infrared light are shown together with its instrumentation. The x-ray photoacoustic signal showed a linear dependence on the ring current and ionization chamber current, both of which are the measure of the photon flux. Typical examples of photoacoustic signals were shown, and their characteristics were briefly discussed in relation to the physicochemical properties of the samples. The potential use of this detection method is discussed.

Notes: We have developed a current-to-frequency converter which is designed to be used with electron multipliers whose anodes are raised to high voltages. It has three sensitivity scales: 10 fC/Hz, 100 fC/Hz, and 1 pC/Hz, with 6.7 decades of dynamic range in each scale. We show that this technique has the high signal-to-noise ratio required for use with electron detectors such as channel plate multipliers and channel electron multipliers.

Notes: The photon counting method is proposed for the field of A(ring) x-ray diffraction. For this purpose, a new memory device was developed. The photon distribution and the photon autocorrelation were measured, and high-intensity sources such as the rotating anode generator and the Photon Factory were characterized. It has been shown that the method is useful to investigate time-dependent phenomena on the time scale down to 10 μs.

Notes: To assess the ability of the high-speed K-edge energy subtraction system which was made at beamline 8C of Photon Factory, Tsukuba, we performed an animal experiment. Rabbits were used for the intravenous K-edge subtraction angiography. In this paper, the actual images of the artery obtained by this system, are demonstrated. The high-speed K-edge subtraction system consisted of movable silicon (111) monocrystals, II–ITV, and digital memory system. Image processing was performed by 68000-IP computer. The monochromatic x-ray beam size was 50×60 mm. Photon energy above and below iodine K edge was changed within 16 ms and 32 frames of images were obtained sequentially. The rabbits were anaesthetized by phenobarbital and a 5F catheter was inserted into inferior vena cava via the femoral vein. 1.5 ml/kg of contrast material (Conlaxin H) was injected at the rate of 0.5 ml/kg/s. TV images were obtained 3 s after the starting point of injection. By using this system, the clear K-edge subtracted images were obtained sequentially as a conventional DSA system. The quality of the images were better than that obtained by DSA. The dynamical blood flow was analyzed, and the best arterial image could be selected from the sequential images. The structures of aortic arch, common carotid arteries, right subclavian artery, and internal thoracic artery were obtained at the chest. Both common carotid arteries and vertebral arteries were recorded at the neck. The diameter of about 0.3–0.4 mm artery could be clearly revealed. The high-speed K-edge subtraction system demonstrates the very sharp arterial images clearly and dynamically.

Notes: During the last years attempts have been underway at several synchrotron radiation laboratories1–4 to employ the abrupt change of absorption at the iodine K edge (33.17 keV) to the imaging of coronary arteries. The subtraction of two images taken with photon energies just above and below the edge strongly surpresses background contrast like bone and soft tissue and allows for amplification of iodinated structure contrast. At HASYLAB, for these studies, a beamline at a bending magnet was only available until 1987. At this beamline the system NIKOS I was tested to obtain information on its essential components like monochromator and detector by in-vivo investigations of dogs.The basic feature which differs from the approaches in other laboratoriesis simultaneous registration of two stationary beams in a two-line detector without any beam switching. Based on the experience with this system during the last year all its components have been improved and changed to dimensions capable of taking a 12-cm-wide image of the human heart. At present the new system NIKOS II is under testing at the new wiggler beamline HARWI. The new monochromator comprises two pairs of a thin Si Laue case crystal and a Ge Bragg crystal, each, with inherent focussing of the beam to a horizontal line focus of about 0.5 mm height and 12 cm width. The advantage of the Laue crystals which are optimized in thickness (30 μm) for maximum reflectivity, is the low heat absorption and the full use of the white beam in the production of two monochromatic beams. The crystals are cooled in a stream of helium. Compared to the NIKOS I version5 the detector was changed in the following points: The two detection lines are enlarged to 125 mm width and the phosphor at the entrance is exchangeable to be either made of powderlike Gd2O2S:Tb or of single crystals like CdWO4 or CaF2:Eu separated by thin walls for optimum spatial resolution. The numerical aperture of the glass fiber optics guiding the light via image intensifiers to the photodiode arrays is higher. The gain of the intensifiers is raised to 1000.Now two photodiode arrays are needed for the simultaneous readout of the two entrance lines. The readout time is halved by reading the odd and even number diodes by two ADCs per array. All these measures will increase the detective quantum efficiency from 0.2 to 0.6. The performance of the new system will be tested again by investigations of dogs before moving to investigations on humans, expected at the end of this year.

Notes: When detecting x-ray images by solid-state semiconductor imagers (charge-coupled devices, photodiode arrays) there arise specific distortions caused by the diffusion of minority photogenerated carriers in the semiconductor substrate. The mode and scale of the diffusion and, accordingly, of distortions which arise are determined by properties of both the detector and the image. In this paper, some aspects of the diffusion are experimentally studied and the results obtained are interpreted on the basis of a theoretical model obtained in definite approximations. The result of the theoretical model is presented as the Fourier transfer function of the time and spatial frequencies, normalized over the quantum efficiency. This function incorporates the following parameters: the diffusion length and diffusion factor for minority carriers, the depth of the depletion regions of sensitive cells, the thickness of the epitaxial layer (or the single-crystal substrate), the linear absorption coefficient of radiation for a semiconductor material, and the angle of incidence of the radiation on the device surface. For the corresponding point-spread function, among the properties illustrated experimentally are the peculiarity providing a good geometrical resolution, the formation of a "stepped'' profile at the grazing incidence, the formation of the "halo'' of the scattered charge. The results of the x-ray and optic measurements have also shown that diffusion from the passive (peripheral) regions, which determines, to a considerable extent, the applicability of linear imagers (lines) in high-resolution systems, contributes appreciably to the distortions. The authors have considered some ways of diminishing the distortions which are accessible to experimenters: diaphragming and oblique incidence of the radiation, and an increase of the depths of the depletion regions of the cells. In addition, the authors dwell briefly upon the influence of the diffusion on the quantum noise and the effect of spectra superimposition, the contribution of x-ray fluorescence and the photoelectron range to the distortions. As an illustration, the possibility of utilizing solid-state imaging detectors to x-ray tomography systems has been evaluated.

Notes: Since the early 1980s a tandem system consisting of an electrostatically focused image intensifier and an image vidicon has found extensive applications to visualization of the images formed by weak fluxes of x radiation. We present the result of measurements of some parameters of this complex linear video signal shaper (LVSS). The test x-ray image—x-ray lines dispersed in space by a single-crystal diffraction scheme (the projections of the linear focus of an x-ray tube) is directed onto a commercial one-stage image intensifier with electrostatic image focusing whose fiber-optics input window is covered by a luminophor to convert x radiation to light. The outlet of the image intensifier is fiber-optically coupled to the input fiber glass window of the commercial image vidicon (silicon intensifier target tube with intensifier section). The measurements performed on the device for absolute calibration of x-ray imaging detectors and x-ray counters (see the report at this Conference) have shown that the use of this LVSS permits one to record threshold flux densities of monoenergetic photons which are more than one order of magnitude lower than with the use of the image vidicon alone. Measurements of the dependence of the threshold flux density on the photon energy have been made. For example, for 8 keV (Cukα), when using gadolinium oxysulphide as the luminophor the threshold flux density is 20 times lower than for the image vidicon alone, and achieves 105 cm−2 s−1. At such a high sensitivity, detection of small-scale details of images with low brightness and contrast requires taking account of the noise of the radiation being detected, which is caused by the fluctuations of the photon flux. This LVSS visualizes light flashes caused by single hard x-ray photons and β particles which are incident upon the luminophor settled on the inlet window of the image intensifier. Both the x-ray images of the test objects and the luminescent flashes caused by photons and fast electrons are represented in digital form (see the report on multiframe digitization x-ray images at this Conference).

Notes: Using monochromatic synchrotron radiation and a high resolution x-ray sensing pickup tube as a two-dimensional detector, we have improved the spatial resolution of x-ray computed tomographic (CT) images. A quantitative elemental analysis was made based on the difference between two CT images measured just above and below an element's absorption edge energy. The developed CT imaging system has been used to observe nondestructive fine structures, such as cracks, in a ceramic material. High resolution of 10 μm was obtained. The differential CT value, which was seen as the shading intensity in the differential CT image, was proportional to the concentration of the specific element.

Notes: The performance of a system for quantitave microtomography with synchrotron radiation is described with regard to the spatial resolving power. The experimental setup consists of a double-crystal monochromator, a monitor in front of a sample stage and a line scan detector which is built up of two photodiode arrays (Reticon RL1024SF), which are cooled by Peltier elements to increase the dynamic range. We present the modulation transfer function of the detector and several monitor configurations. So far a spatial resolution of 100 μm has been achieved.

Notes: Recent developments of a high-precision diffractometer for multiple crystal arrangement at the Photon Factory is described. New x-ray optics for topography using this diffractometer are shown, including plane-wave topography, ultraplane wave topography and equilattice-spacing mapping topography.

Notes: A versatile environmental facility for in situ x-ray topographic (white radiation) investigations of the perfection of nearly perfect single crystals is described. The system is built to UHV standards and can be optimized to investigate the defect structure in many materials at variable pressure and temperature. High quality data have been obtained with this facility during the decomposition of nickel sulphate hexahydrate and calcite. In the former case, in contradiction to what has previously been believed, the results clearly show that dislocations are not involved in the nucleation of the reaction process.

Notes: In many cases the fluorescence EXAFS signal is contaminated with fluorescence from nearby elements. If this fluorescence is of lower energy than the element of interest, x-ray filters are not effective. One method for dealing with this problem is the double fluorescence method described by Wong and Rao. This paper describes an improved version of this double fluorescence scheme that greatly improves its efficiency. Data are presented for a sample of 1/2% Hf in Ni3 Al, and 1.6% CuO in NiO. When standard fluorescence is used, both signals are almost completely obscured by the (approximately-equal-to)100× larger Ni K fluorescence signal. With the double fluorescence detector the Hf L3 and Cu K-edge signals are clearly observed, and good spectra can be obtained in about an hour.

Notes: An improved method for light scattering from acoustic phonons in small, low-symmetry solids is described. This instrumentation greatly facilitates the determination of elastic constants in highly anisotropic materials. Elastic scattering can be greatly reduced so that weaker phonon modes can be observed. Errors associated with the determination of the polarization directions of an anisotropic material are minimized by considering crystal optics.

Notes: A double beam laser interferometer is built up to study high-frequency piezoelectric and electrostrictive strains. The system is capable of resolving a displacement of 10−2 A(ring) using lock-in detection and measuring the strain all the way to the piezoelectric resonance frequencies using a digital oscilloscope for detection. The interference of sample bending to the detected signal is effectively avoided.

Notes: We describe a method for measuring the internal friction of solids at low temperatures. Our design uses a composite oscillator vibrating in torsion at 100 kHz. The oscillator makes good thermal contact to the cryostat while maintaining a low background loss of Q−1(approximately-equal-to)2×10−6 at 2 K. The usefulness of the design is demonstrated by data for BaF2 and a-SiO2 from 2 to 300 K.

Notes: A pneumatic-based, hydrogen isotope pellet injector that was developed at the Oak Ridge National Laboratory (ORNL) has been used in recent plasma fueling experiments on the Joint European Torus (JET). The injector consists of three independent machine-gun-like mechanisms (nominal pellet sizes of 2.7, 4.0, and 6.0 mm in diameter) and features repetitive operation (1–5 Hz) for quasi-steady-state conditions (〉10 s). An extensive set of injector diagnostics permits evaluation of parameters for each pellet shot, including speed, mass, and integrity. Pellet speeds range from 1.0 to 1.5 km/s. Over 3700 pellets have been fired with the equipment at JET, with about 1500 pellets shot for plasma fueling experiments. In recent experiments, the system performance has been outstanding, including excellent reproducibility in pellet speed and mass, and a reliability of 〉98% in delivery of pellets to the plasma.

Notes: The magnetic susceptibility, χ, at 295 K of a wide variety of common laboratory construction materials has been carefully measured. Only materials with well-characterized compositions are included in the final data. Materials such as Cu alloys and filled epoxies showing ferromagneticlike saturation behavior are listed with the recognition that workers will probably want to use these with great caution in precision experiments where magnetic effects may be a source of error. Susceptibility values are given for over 30 materials for which χ values are not available in the literature and which exhibit χ independent of H.

Notes: Single photon avalanche diodes (SPADs) are avalanche photodiodes specifically designed for reverse bias operation above the breakdown voltage and used for detecting single optical photons. A new silicon epitaxial device structure was designed to give improved timing performance with respect to previous SPADs. Extensive tests were carried out in order to establish the timing resolution of the device in time correlated photon counting (TCPC). The timing resolution of the SPAD in terms of its full-width at half-maximum (FWHM) contribution to the overall instrumental response width is 20 ps with the detector cooled to −65 °C, and 28 ps at room temperature. This is the highest resolution so far reported for solid-state single-photon detectors. In vacuum tubes, comparable results are obtained only with special microchannel-plate photomultipliers (MCP-PMT). Results from time-resolved photoluminescence measurements in GaAs demonstrate the power of the TCPC technique when used with the new SPAD detector. With the excellent timing resolution of the SPAD and the well-known advantages of TCPC systems (high sensitivity, linearity, etc.), various applications are foreseen in areas so far dominated by streak cameras.

Notes: A high-sensitivity high-spatial-resolution eddy-current apparatus has been set up for contactless conductivity measurements on Si and HgCdTe. The inductive sensitivity limit has been demonstrated, on Si slices, to a very low σt (product of conductivity and thickness) of 0.0004 Ω−1 and the spatial resolution was shown to be about 4 mm, both a threefold improvement over past published results. HgCdTe bulk slices and epitaxial films have been measured over a wide range of σt from 0.001 to 1 Ω−1 at 77 K. The conductivity mapping measurements on HgCdTe material were also demonstrated for the first time. The sensitivity of eddy-current probes consisting of miniature commercial rf coils were shown to be not only temperature independent, but also very stable after repeated thermal cyclings between 300 and 77 K. This feature makes the eddy-current method an ideal technique for routine contactless conductivity measurements on HgCdTe material at 77 K. We also show that both the sensitivity and the spatial resolution of eddy-current probes can be explained quantitatively by a simple theory which treats coils as magnetic dipoles.