ALBERT

Notes: We describe here how modern videomicroscopy can be used to enhance the selection of single crystals for x-ray crystallography and provide a permanent record of crystal shape and color. The cost/advantage ratio of this technique is such that we expect it to become a standard practice in the future. © 1997 American Institute of Physics.

Notes: This note describes a newly developed flexible surface-coil-type resonator (FSCR) used for electron paramagnetic resonance (EPR) measurements. A conventional FSCR has used a balanced transmission line made by coaxial lines. The new resonator uses triaxial cable in order to avoid anisotropy of flexure of the transmission line. Experimental results show that the EPR signal measured with the triaxial FSCR is 35% stronger than that measured with the conventional FSCR. © 1997 American Institute of Physics.

Notes: Easy to realize recipes are given to modify a conventional low pressure longitudinally excited Q-switched CO 2 laser by pulsing the electrical discharge. An increase of the peak power of strong laser lines up to a factor of 6 is obtained, as well as laser emission on a considerably larger number of vib–rot transitions. © 1997 American Institute of Physics.

Notes: Particle and energy transport in tokamaks and other toroidal confinement devices is dominated by turbulence generated by flows and gradients. In order to understand and control of this transport, diagnostic instrumentation was developed to study the structure and magnitude of microturbulent processes and to identify the origins of plasma loss. This review will cover the primary instruments that have been developed to measure fluctuating quantities associated with transport: density, δn, temperature, δT, potential, δφ, and magnetic field, δB, and their correlations. The methods discussed are Langmuir probes, heavy ion beam probes, collective and phase scintillation scattering, beam emission and ordinary spectroscopy, reflectometry and enhanced scattering, electron cyclotron emission, and several magnetic methods. The emphasis here will be on techniques applicable to microturbulence whose scale length is greater than the ion cyclotron radius and much less than the minor radius. Limitations and strengths of each method will be described and compared. Techniques will be discussed for estimating fluctuation intensities and wave number spectra or, equivalently, multipoint correlations in radial, poloidal, and toroidal directions. Large scale or magnetohydrodynamic-like plasma oscillations are typically studied with tomographic techniques or external probes and are reviewed elsewhere. © 1997 American Institute of Physics.

Notes: A miniature-cavity realization of the cavity ring-down concept, which permits extension of the technique to spectroscopy of surfaces, thin films, liquids, and, potentially, solids, is explored using a wave-optics model. The novel spectrometer design incorporates a monolithic, total-internal-reflection-ring cavity of regular polygonal geometry with at least one convex facet to induce stability. Evanescent waves generated by total-internal reflection probe absorption by matter in the vicinity of the cavity. Optical radiation enters or exits the resonator by photon tunneling, which permits precise control of input and output coupling. The broadband nature of total-internal reflection circumvents the narrow bandwidth restriction imposed by dielectric mirrors in conventional gas-phase cavity ring-down spectroscopy. Following a general discussion of design criteria, calculations are presented for square and octagonal cavity geometries that quantify intrinsic losses and reveal an optimal cavity size for each geometry. Calculated absorption spectra for the NO3 radical from 450 to 750 nm in a nitric acid solution are presented to demonstrate bandwidth and sensitivity.

Notes: Micrometer-sized nozzles and skimmers made from drawn glass tubes are described and tested for the production of highly monoenergetic He atom beams. Glass nozzles with diameters between 1 μm and 4 μm when operated at He source stagnation pressures of up to 1000 atm provide intense beams with measured speed ratios of S=50–100, in good agreement with the predicted behavior scaled from nozzles with larger openings. Miniature glass skimmers with diameters as small as 3 μm were also successfully tested with conventional 10 μm diameter nozzles. These miniature nozzle-beam sources can be used to greatly reduce the size of present-day He-atom surface-scattering time-of-flight spectrometers and to reduce the number of vacuum stages and the size of vacuum pumps. They also open up new experimental possibilities as illustrated by measurements of the spatial profiles of seeded nozzle beams. © 1997 American Institute of Physics.

Notes: Optical microscopy is an important measurement tool in many industries. This importance is primarily due to the ease-of-use and nondestructive characteristics of optical microscopes. Unfortunately, the far-field optics of conventional microscopes limit their resolution to approximately 200 nm. An imaging technique called near-field microscopy uses a subwavelength aperture to circumvent this limit to obtain images with enhanced resolution without many of the destructive consequences of other techniques. Visible microscopes based on this technique have produced images that demonstrate 10–15 nm resolution. This article describes the extension of these techniques to the infrared regime. A description of an infrared microscope capable of imaging the thermal emissions from micron scale conductors using optical techniques has been given. The microscope has been designed to operate in both the collection mode using an external infrared radiation source and in the self-illumination mode using thermally activated objects. Several infrared images of 2-μm-wide conductors have been provided to demonstrate the resolution capabilities of the microscope. These images clearly show the presence of the conductors and represent a significant increase in resolution over conventional infrared imaging devices. © 1997 American Institute of Physics.

Notes: Under routine source conditions, the optimum nozzle-skimmer distance to achieve maximum molecular beam intensities is within the range of a few millimeters. In cases where double skimming is additionally required, the distance between the skimmers should be kept small in order to sample a sufficiently large solid angle of the beam and hence maintain a good enough intensity. These two facts make it normally difficult to isolate the first from the second expansion chamber using a commercial vacuum gate valve due to the lack of remaining space. This note presents the design of a vacuum-tight valve which allows the aperture of a skimmer to be closed by plugging a needle directly against its internal conical wall. The valve can be driven manually or pneumatically from outside the vacuum chamber. The helium conductance of the valve was measured to be better than 1×10−8 mbar×l×s−1 for a helium partial pressure difference of 1 bar. © 1997 American Institute of Physics.

Notes: The temperature-dependent characteristics of fluorescence of several rare-earth-doped ceramic phosphors has made these materials the focus of a major effort in the field of noncontact thermometry over the past few decades. These "thermographic phosphors," e.g., Y2O3:Eu, have been used for remote measurements of the temperatures of both static and moving surfaces, and have performed many other tasks that standard sensors (thermocouples, thermistors, etc.) cannot. The range of usefulness of this class of materials extends from cryogenic temperatures to those approaching 2000 °C. The instrumentation needed for this type of thermometry has followed many different lines of development, and this evolution has produced a wide variety of both field- and laboratory-grade systems that are now described in the literature. In general, the technique offers high sensitivity ((approximate)0.05 °C), robustness (e.g., stability of the sensor sample in harsh environments), and NIST traceability. In addition, such systems have been successfully adapted to make remotely sensed measurements of pressure, heat flux, shear stress, and strain. In this review, we summarize the physical mechanisms that form the basis for the technique, and then catalog and discuss the instrumentation-related aspects of several different remote thermometry systems that employ thermographic phosphors as the sensors. © 1997 American Institute of Physics.

Notes: A new polarization modulator is presented. It uses two phase-locked identical electro-optic phase modulators at 50 kHz. Thanks to a coupling object introduced between the two phase modulators, the four Stokes parameters of the light beam are independently modulated on the basis of the first and second complex harmonics of the modulation signal. A Mueller matrix ellipsometer (MME) using this new modulation and a multichannel polarimeter are also described. The data processing and the feedback control of Pockels cells is based on a numerical Fourier transform system. It allows one to measure simultaneously, in one modulation period (20 μs), the 16 coefficients of any Mueller matrix. This MME takes advantage of an easy-to-operate calibration method. The high-frequency modulation of the four parameters of the polarization enables low-light-level measurements (without any chopper and lock-in) and presents spectroscopic capabilities. It provides a promising tool for the study of many subjects of growing interest like, for example, rough surfaces treatment or particle characterization. © 1997 American Institute of Physics.

Notes: Contaminant particles peculiar to a type of equipment emanate inside and around a semiconductor, or thin-film-transistor–liquid-crystal-display device fabrication front-end equipment. To analyze such deposition phenomena and implement contamination control measures, it is necessary to observe in situ deposition behavior over a long period. This article describes a measuring instrument for this purpose. Deposition and tearing off of particles or mist take place on the surface of a transparent plate (of glass or quartz) and Mie scattering occurs when a laser beam is irradiated onto the particles or mist from below. The scattered light is detected in situ while the detection signals are accumulated and kept track of. In this instrument, a semiconductor laser with beam focusing optics and an ellipsoidal mirror are integrated into a small, portable unit. The laser beam is scanned onto the glass surface over a maximum area of 250 by 250 mm in one or two dimensions. It is possible to adjust the scanned area, scanning speed, and laser beam diameter. One-spot, fixed irradiation is also possible for detection of particle flow or tearing on the surface. The minimum detectable particle size was about 0.3–0.4 μm for polystyrene latex sphere (PSL) particles deposited on the glass surface with a beam diameter of 35 μm and a scanning speed of 0.3 m/s (0.14 μm for a silicon wafer surface). Two kinds of experiments were carried out by the use of one glass with PSL particles deposited on the surface and another glass on whose surface PSL particles were spouted so they would roll without deposition. By using this instrument, it became clear that the response curve for the rolling of the particles agreed well with the Mie equation, whereas the curve for the deposited particles deviated from the equation, but only in the range of minute particle sizes. Another phenomenon clarified through in situ measurement was that once deposited, real-world particles were subjected to the influence of the down flow of clean air (0.3 m/s), and some were torn off in a time period on the order of hours. A comparison of the real-world particle deposition rate was made between the grounded and ungrounded states using a glass plate with a transparent conductive thin film. An increase in the deposition rate was observed for the ungrounded state, while a remarkable tearing-off rate was seen for the grounded state. © 1997 American Institute of Physics.

Notes: The development of in vivo electron paramagnetic resonance spectrometers has generated a need for a better method of inductive coupling between a microwave resonator and a transmission line. We describe here an approach, based on introducing an additional impedance transformer between a coupling loop and the transmission line. This additional transformer decreases (by a factor of 20) the resonance frequency shift that occurs during adjustment of the coupling. The calculated optimal length is slightly greater than a quarter of the wavelength of the electromagnetic waves. Experimental measurements of the return loss for the matching circuit has shown the validity of the calculations and the usefulness of the proposed theoretical model. © 1997 American Institute of Physics.

Notes: A signal generator is described that provides two oscillations of "almost" incommensurate frequencies, along with their sum and difference frequency. There is no phase drift between the outputs since all signals are generated from a single master clock. The concept is based on Fibonacci approximands to the golden mean. Technical implementation requires ordinary digital frequency dividers and a single phase-locked-loop frequency multiplier. Applications are measurements of weak nonlinearities in "almost linear" transfer functions. © 1997 American Institute of Physics.

Notes: Single headed three dimensional (3D) laser Doppler velocimetry (LDV) geometries generally rely upon the use of three Doppler difference channels, inclined at differing angles with respect to the mechanical axes of the probe. The transformation between the nonorthogonal measurement coordinate system and the Cartesian system can result in large errors in the calculated velocities. A theoretical analysis of the geometrically induced uncertainties in measurements produced by four single headed 3D LDV configurations is presented. These considerations have lead to the development of a single headed fiber optic 3D LDV probe based on the use of two Doppler difference channels to directly measure the transverse velocity components, and a reference beam channel to measure the on axis velocity component. The f/4 probe head has a working distance of 200 mm, designed to operate within the constraints of the limited optical access available in turbomachinery applications. © 1997 American Institute of Physics.

Notes: The formation of adducts resulting from interactions between protein ions and residual gases in an electrospray ionization ion trap/time-of-flight mass spectrometer is reported. This instrument utilizes diffusion pumps to achieve high vacuum, and we found that when silicon based diffusion pump fluids were used, characteristic adduct peaks appeared in the mass spectra. These adduct peaks were not detected, however, when a polyphenyl ether (Santovac 5) was used as the diffusion pump fluid. In switching the diffusion pump fluid to Santovac 5, a rigorous cleaning procedure capable of removing residual silicon pump fluid from the instrument was a critical step. This cleaning procedure can also be used for routine cleaning of the ion trap and other source components. © 1997 American Institute of Physics.

Notes: An accelerometer adaptor, for near field shock wave measurements, is described for applications in which the mounting structure undergoes elasto-plastic deformation. It is of simple construction, light, easy to install and remains attached on the mounting surface during relatively large deformations. The design overcomes the possibility of the accelerometer being projected from the mounting plate, which results from mounting directly on a plate surface. It was successfully employed for measuring peak accelerations up to 100 000 g. © 1997 American Institute of Physics.

Notes: It is shown that a simple rectangular filter is a good approximation to Wein's optimal filter for improving the signal-to-noise ratio in a typical modulated reflectance spectroscopy experiment. This enables one to obtain identical information from data recorded with much smaller time constants for data averaging and therefore faster scan speeds. The limitations of this method are also discussed. © 1997 American Institute of Physics.

Notes: Measurement of the lattice functions was carried out in the storage ring for the light source. The measurement includes β, dispersion functions, phase advances, tunes, momentum compaction, chromaticities, and linear coupling. Two methods were used for the β measurement; a quadrupole-tweaking method and a method using a sensitivity matrix. Using the sensitivity-matrix method gives additional information on the phase between monitors and correctors, as well as the fractional part of the tunes. The linear-coupling constant was obtained by driving the tunes across the coupling resonance and measuring the minimum tune separation. It is also shown that by using four skew-quadrupole circuits, the coupling constant can be varied arbitrarily. In this article, a detailed method for the lattice-function measurement is presented, and the result applied to the storage ring of the Pohang Light Source is given. The measured results are compared with the design values and shown to be in good agreement. © 1997 American Institute of Physics.

Notes: A hot filament can be used as a simple, reliable, and inexpensive sensor to measure quantitatively ppm-level concentrations of oxidizing species present in high-purity nitrogen. A coiled tungsten filament of a 1 W signal lamp acts as a sensing element, which, by high-temperature reaction with O2 and H2O, forms volatile oxides. The resulting decrease in filament diameter and rise in filament resistance is monitored by measuring the current at constant voltage. The sensor's response is linear with the O2 concentration over an extended range of "burn-down" and is relatively insensitive to the gas velocity. The reaction appears to be rate limited by the diffusion of oxygen along its concentration gradient toward the filament. The sensor's sensitivity, operated in nitrogen at Ufil=6.3 V, is determined to S=21 ppm O2/(mA/min). © 1997 American Institute of Physics.

Notes: The understanding of radon migration in the earth's crust is important in many applications, such as radiation protection in residential buildings, uranium ore prospecting, or earthquake prediction. Recent studies also show correlations of radon exhalation with short-periodic rock stresses induced by tidal forces. The borehole radon sensor presented can be used to investigate subsurface radon migration in situ. It is capable of measuring the concentration of both radon and thoron in air with a time resolution of less than an hour and a detection limit of approximately 1 Bq m−3, even in volumes as small as 100 ml. The sensor is fully automated and can be calibrated in situ. © 1997 American Institute of Physics.

Notes: We have developed a novel digital feedback scheme of distance control via shear-force measurement in the near-field scanning optical microscope. Using simple comparators, full digital control is achieved. In this new scheme, the probe tip stops at a reference point as it approaches the sample and then draws back when the scanning piezoelectric tube executes lateral translation of the sample by one step. The resulting feedback motion is similar to tapping at each point, which removes the feedback oscillation and the hysteresis effect in the conventional analog feedback scheme. Because the control program monitors the tip position at each step and there is no settling time of the feedback, the scanning speed can be improved without oscillation and tip–sample collision. © 1997 American Institute of Physics.

Notes: We designed and constructed a low energy focused ion beam apparatus for direct deposition. The optical properties of our lens system were calculated to obtain its optimum shape and arrangement for a low energy (50–100 eV) and fine focused (〈1 μm) ion beams. We evaluated magnification, chromatic aberration, and spherical aberration. Using the apparatus based on our design, we deposited a focused ion beam and deduced the beam diameter from linewidth measurement of the deposited film. The diameter of 50–200 eV Au+ beams could be tuned between 0.4–7 μm corresponding to beam currents of 40 pA–10 nA. The current density was constant at about 30 mA/ cm2. At lower currents, the minimum beam diameter was limited to 0.35 μm. These experimental results agree with calculated results qualitatively, but quantitative differences exist. Assumptions, based on Ga+ ion sources, seem to cause the differences. If we adopt our measured energy dispersion (30 eV) and angular current density (10 μA/sr) and assume the virtual source size to be 0.13 μm, the measured beam diameter and current density can be reproduced by calculation. Ways to reduce beam diameter and increase current density are discussed. © 1997 American Institute of Physics.

Notes: We describe a new apparatus for magnetic confinement of a pure ion plasma, with laser diagnostics to measure test particle transport across the magnetic field. In addition to the axisymmetric trapping potential, rotating electrostatic wall perturbation is used to counteract the plasma loss processes, giving steady-state ion confinement for weeks. Electronic spin polarization of the ion ground states is used to label the test particles; this spin orientation is controlled by direct optical pumping. The laser-induced fluorescence (LIF) technique is used to nondestructively measure the ion velocity distribution; and an absolute calibration of the charge density is obtained from the LIF measurement of the plasma rotation velocity. Two new technological improvements compatible with ultrahigh vacuum systems have been used: a semirigid Teflon insulated coaxial cable has low microphonic noise, and an antireflective coating is used to reduce reflection of ultraviolet light inside the vacuum chamber. © 1997 American Institute of Physics.

Notes: A one-sided very-high-temperature guarded hot plate has been built to measure thermal conductivity of monolithic ceramics, ceramic composites, thermal barrier coatings, functional graded materials, and high-temperature metal alloys. It is an absolute, steady-state measurement device with an operational temperature range of 400–1400 K. Measurements are made in an atmosphere of low-pressure helium. Specimens examined in this apparatus are 70 mm in diameter, with thicknesses ranging between 1 and 8 mm. Optimal specimen thermal conductivities fall in the range of 0.5–30 W/(mK). Internal heated components are composed entirely of high-purity aluminum oxide, boron nitride, beryllium oxide, and fibrous alumina insulation board. Pure nickel and thermocouple-grade platinum-based alloys are the only metals used in the system. Apparatus design, modeling, and operation are described, along with the methods of data analysis that are unique to this system. An analysis of measurement uncertainty yields a combined measurement uncertainty of ±5%. Experimental measurements on several materials are presented to illustrate the precision and bias of the apparatus.

Notes: Using our dedicated Auger depth profiling device (applying a grazing angle of incidence 84° and low ion energy 1 keV of Ar and specimen rotation), we could detect a thin oxide layer buried by about a 180 nm thick layer. Due to the good depth resolution achieved, the oxide layer could be localized to the interface. The oxide layer thickness was determined for two independent specimens to be about 2 and 3 ML. © 1997 American Institute of Physics.

Notes: We introduce a materials science tool for investigating refractory solids and melts: the electrostatic containerless processing system (ESCAPES). ESCAPES maintains refractory specimens of materials in a pristine state by levitating and heating them in a vacuum chamber, thereby avoiding the contaminating influences of container walls and ambient gases. ESCAPES is designed for the investigation of thermophysical properties, phase equilibria, metastable phase formation, undercooling and nucleation, time–temperature–transformation diagrams, and other aspects of materials processing. ESCAPES incorporates several design improvements over prior electrostatic levitation technology. It has an informative and responsive computer control system. It has separate light sources for heating and charging, which prevents runaway discharging. Both the heating and charging light sources are narrow band, which allows the use of optical pyrometry and other diagnostics at all times throughout processing. Heat is provided to the levitated specimens by a 50 W Nd:YAG laser operating at 1.064 μm. A deuterium arc lamp charges the specimen through photoelectric emission. ESCAPES can heat metals, ceramics, and semiconductors to temperatures exceeding 2300 K; specimens range in size from 1 to 3 mm diam. This article describes the design, capabilities, and applications of ESCAPES, focusing on improvements over prior electrostatic levitation technology. © 1997 American Institute of Physics.

Notes: This article reports the update in the design of a microwave spectrometer for measuring concentrations of ethylene oxide gas during sterilization. The specificity of the measurement (absorption line at 23.134 GHz) using the spectrometer has been found to be virtually 100%. A great number of calibrations have been conducted in the range of concentrations 100% to 40% of ethylene oxide gas at intervals of −10% in order to determine the accuracy of the spectrometer. It was found that the maximum standard deviation from the regression curve was 1.2% full scale (0%–100%). A mathematical model based on a diffusion equation has been developed and was used to interpret the real time measurement data during sterilization. Numerical simulation using this model has demonstrated that it is possible to predict the dynamic distributions of ethylene oxide concentration within the load being sterilized. © 1997 American Institute of Physics.

Notes: In the case of semiconductor diodes, the temperature range over which the temperature dependence of the forward voltage is linear, can be increased by lowering the operating current along with the increase of the sensitivity (dVf/dT) which is found to vary logarithmically with I. The temperature and current dependence of forward voltage Vf can be explained by using the theory of the p-n junction. The capacitance-voltage (C−V) measurements of p-n junctions are carried out at different temperatures and are discussed in light of the theory of the p-n junction. The band gap Eg, estimated from Vf−T measurement, is found to be ∼1.17 eV, whereas it is found to be 1.189 eV from C−V measurement. © 1997 American Institute of Physics.

Notes: We describe a pulsed single-mode dye laser whose output characteristics satisfy the stringent requirements of coherent control experiments. This simple, low cost laser exhibits 1.6× transform-limited frequency performance with a single-shot linewidth of 58 MHz, and a time averaged linewidth of 240 MHz. The spatial mode is nearly Gaussian and has a beam quality parameterM2=1.2. We modified the pulse shape using saturable absorption in the dye amplifier. The resultant pulses are temporally smooth and have a duration of approximately 20 ns. © 1997 American Institute of Physics.

Notes: We describe a fast and convenient method of high precision size and refractive index determination of electrodynamically levitated microdroplets using Fraunhofer diffraction. The diffraction data were obtained with a 16-bit, unintensified charge coupled device (CCD) camera, and converted into angle-resolved elastic scattering intensity patterns by means of a carefully determined set of transformation parameters. The angular scattering patterns were analyzed without any a priori estimate of the droplet size and only a nominal estimate ((approximate)2%) of the refractive index. Experimental angular scattering patterns were fit to calculated patterns from Mie theory using a graded step-size and scaling algorithm and optimized with respect to both droplet diameter and refractive index (real part only) with a precision of ≤3 parts in 104 and 1 part in 103, respectively. Potential application to quantitative fluorescence and Raman spectroscopy, as well as mixture analysis in microdroplets is discussed. © 1997 American Institute of Physics.

Notes: A powerful, compact, and repetitive flash x-ray system based on a cable transformer technology powered by ceramic capacitors in a Blumlein-like configuration has been developed. Open circuit voltages in excess of 100 kV can be achieved while commutation occurs at low voltage (〈20 kV). The x-ray emission from a low impedance x-ray diode with a hollow cathode configuration was observed under a wide range of experimental conditions. The critical parameters limiting the flash x-ray performances are mainly the pressure in the x-ray diode and the anode–cathode space. This true table top device is able to produce doses up to 1 R per shot, measured at the output window, of x-rays between 5 and 100 keV. The pulse widths were about 20 ns and the maximum repetition rate was about 60 Hz. Operation is possible in air or in other gases (He, Ne, Ar, Kr, Xe, H2, N2) at pressures varying from 10−3 mbar for xenon to about 1 mbar for helium. © 1997 American Institute of Physics.

Notes: A new reflectron time-of-flight mass spectrometer with a cylindrical electrostatic mirror instead of the usual plane reflector is described. When it is mounted at right angles to the direction of an incoming molecular beam, this system automatically compensates for the transverse drift of the ions in the spectrometer due to their initial velocity parallel to the molecular beam direction. As a consequence, ions of any mass can be collected onto the detector, whatever their initial transverse velocity is. The mass range accessible in a single scan with our cylindrical reflectron is thus strongly increased as compared to the case of a usual plane reflectron. This article presents the general design of our cylindrical reflectron. A detailed description of the apparatus is given and its performances are illustrated on selected examples. Cluster mass spectra extending over a very wide size range are presented. A mass resolution of about 4000 is achieved in mass spectra of laser photoionized aluminum clusters. Moreover, the cylindrical geometry of the reflector gives rise to focusing properties onto the detector, which could be interesting in view of collection efficiency improvement. © 1997 American Institute of Physics.

Notes: An optical interferometric proximeter system (IPS) for measuring thrust and impulse bit of pulsed electric thrusters was developed. Unlike existing thrust stands, the IPS-based thrust stand offers the advantage of a single system that can yield electromagnetic interference-free, high accuracy (〈2% error) thrust measurements within a very wide range of impulses (100 μN s to above 10 N s) covering the impulse range of all known pulsed plasma thrusters. In addition to pulsed thrusters, the IPS is theoretically shown to be capable of measuring steady-state thrust values as low as 20 μN for microthrusters such as the field emission electric propulsion thruster. The IPS-based thrust stand relies on measuring the dynamic response of a swinging arm using a two-sensor laser interferometer with 10 nm position accuracy. The wide application of the thrust stand is demonstrated with thrust measurements of an ablative pulsed plasma thruster and a quasi-steady magnetoplasmadynamic thruster. © 1997 American Institute of Physics.

Notes: The results of bench tests performed on a new method of combined interferometry/polarimetry for the magnetic-field reconstruction of tokamak plasmas is presented. In particular, the sensitivity obtained in the polarimetric measurement shows the feasibility of Faraday rotation determination approaching a precision of ±0.2°. The method is based on an optically pumped far-infrared laser with a rotating polarization where both the interferometric and polarimetric information is determined from phase measurements. Specific sources that introduce disturbances in the optical arrangement and that can limit the attainment of the polarimetric precision, mentioned above, are discussed. © 1997 American Institute of Physics.

Notes: Modern charge-coupled-device (CCD) detectors can achieve peak quantum efficiencies of 90%, compared with less than 10% for the photocathode of an electron multiplier. We report on laboratory tests of examples of these two detector technologies to evaluate their relative performance for precision Doppler spectroscopy of laboratory plasmas. The tests reveal that the accuracy of the Doppler width and shift measurements improves with the square root of the photoelectron flux, and thus as the square root of the detector quantum efficiency. An analytic estimate of the performance of these two types of detectors confirms the square root dependence on photoelectron flux but also highlights the importance of other noise sources that could be important under different conditions. The gain of the electron multiplier system can be reduced to the level of 10 photon-electrons per ADC count before there is any reduction in the accuracy of the estimation of fitted parameters. © 1997 American Institute of Physics.

Notes: An imaging instrument for measuring the 2D distribution of both free radicals and protons in a single sample was developed. A common resonator was designed for this instrument that can resonate at an L-band electron spin resonance (ESR) frequency or a HF (27.7 MHz) proton nuclear magnetic resonance (NMR) frequency. This resonator enabled construction of a simple detection block for the instrument. Because the detection processes of ESR and NMR are similar, many components, including the main magnet, magnetic-field modulation coils, field gradient coils, electrical circuits, data acquisition system, computer for reconstructing images, and most of the software were shared by these two systems. By using this instrument, both ESR and NMR images of the head of a live rat were successfully produced. The free radical distribution could be positioned by superimposing the ESR image on the NMR image. © 1997 American Institute of Physics.

Notes: An optical device called a multichannel collimator (MCC) was developed to rapidly perform an angle-dispersive diffraction using a multi-anvil press (MAP) with synchrotron radiation. The MCC consists of multiple channels of collimators in a radial alignment. This eliminates diffraction from the materials surrounding the sample so that we can obtain high-quality diffraction from samples in a MAP using an imaging plate. We have installed a MCC system on a MAP named MAX90 at the Photon Factory, National Laboratory for High Energy Physics. Performance of the MCC has been satisfactorily evaluated, and diffraction patterns of liquid sodium and liquid gallium under 4.8 GPa have been successfully obtained using this system. © 1997 American Institute of Physics.

Notes: A sputtering deposition system has been developed to grow high-quality superconductor/insulator multilayers specifically for use in fabricating vertically stacked Josephson junctions. A unique feature of the design is the computer control of all parameters involved in the repetitive deposition of multilayers. The computer is interfaced with stepper motors that position the substrate, and shutter wheels. Additional computer controlled stepper motors allow in situ changing of up to five contact masks. The computer is also interfaced to a gas flowmeter that controls the partial pressure of the inert and reactive sputtering gases. High-quality, reproducible multilayer films have been produced and are described. Stacked Josephson junctions have been patterned with the multilayer films and some of their electrical characteristics are presented. © 1997 American Institute of Physics.

Notes: A fast broadband pyrometer with a spatial resolution of 2 μm and an accuracy of 10% in temperature is described plus a calibration method suitable for liquid metals. The time resolution of temperature measurements is limited by the electronics rise time (3.5 ns) to 14 ns (10%–90% rise time) of a temperature change because of the nonlinear relation between electronic signal and temperature. The pyrometer was applied to determine the temperature of melts produced by focused nanosecond laser pulses in gold and iron films. Measured heating rates (1010–1011 K/s) and peak temperatures (3000 K) are correctly reproduced by numerical simulations for gold, but theoretical peak temperatures in iron were 1000 K in excess. The low actual temperature in iron can be explained by native oxides, decomposing during the laser pulse and thus dissipating energy. This effect may cause considerable differences between computed and actual temperatures during laser processing of thin metal films with unstable impurities. © 1997 American Institute of Physics.

Notes: A novel technique is developed to measure quantitatively the adhesion strength of metallizations deposited on substrates such as silicon. Electrostatic adhesion testing employs electrostatic forces to generate delaminating stresses in thin metallic films. The interfacial adhesion strength is readily calculated from the electrode geometry and the applied electrostatic field at failure. Unlike other adhesion tests, this technique does not require any mechanical contact and is virtually independent of the plastic deformation of the film. Furthermore, this test provides direct strength measurements as opposed to work or energy of adhesion measurements obtained by the common peel test. The adhesion strengths of several metallizations (Cu, Al) are characterized using the electrostatic technique. The distribution of stress-at-failure data follows Weibull failure statistics. Field emission scanning electron microscopy reveals that the films are delaminated in a microblister-type mode. It is shown that electrostatic adhesion testing is effective in providing quantitative values for the adhesion strengths and failure probabilities of thin-film metallizations. © 1997 American Institute of Physics.

Notes: Infrared imaging of CO in combustion environments is made difficult by cross-talk effects due to the high emission of CO2. A new method for discriminating CO emission, to be implemented in thermal cameras, is proposed. This method is based on a new family of infrared multilayer filters, denominated solid-state Fabry–Pérot (SSFP) filters. The design and spectral parameters of these filters are developed on the basis of the optical properties of the multilayers and substrate, and specific designs for CO imaging are presented. The application of this method to CO emission imaging in a flame is described, as an illustration of the wide range of applicability of SSFP filters in the detection and imaging of gases with a regularly spaced fine structure emission spectrum. © 1997 American Institute of Physics.

Notes: A simple but useful technique for feedback stabilization and modulation of diode lasers is described. The interposition of an optoelectronic coupler between laser diode and feedback amplifier allowed safe circuitry together with good linearity and relatively high speed. © 1997 American Institute of Physics.

Notes: We describe a new rotational accelerometer exhibiting excellent rotational acceleration sensitivity of 2–3×10−9 rad s−2/(square root of)Hz for frequencies below 2 Hz and increasing as the square of frequency for frequencies higher than 2 Hz. The sensitivity to horizontal linear accelerations and static tilts is 60 dB less than its rotational sensitivity. The accelerometer has been used to characterize the seismic ground tilt spectrum. Measurements of the performance of the device and of the seismic rotational spectrum are presented. © 1997 American Institute of Physics.

Notes: A research instrument has been designed, fabricated, and tested that produces ∼25–100 μm diameter, liquid xenon droplets on demand at variable repetition rates of 1–100 Hz. Drops have been produced with low spatial dispersion which allows consistent interception by a high power laser beam to produce x-rays for advanced lithography systems. Experimental sequences of up to 42 min in length have been conducted at 30 Hz, producing over 75 000 xenon drops. This technology allows significant debris reduction from the laser-target interaction. The mass-limited, cryogenic droplets are vaporized, producing no fragments, and the resulting gas can be collected preferentially on a cold surface for later recycling. © 1997 American Institute of Physics.

Notes: This article describes the distribution of absorption doses and spectrum shift of synchrotron x-ray traversing materials. The analytical approximations of the universal function of the synchrotron power spectrum was found. From this analytical approach, the penetration doses and the high-pass window effect were estimated for materials of low atomic numbers. The result can be generally applied to the deep x-ray lithography. © 1997 American Institute of Physics.

Notes: A modular differential interference contrast microscope combined with laser interferometry has been designed and constructed to detect nm-scale displacements of microscopic beads with a root mean square noise less than 0.4 nm. The unique feature of our system lies in its capability of preserving the nm-scale detection sensitivity down to a low-frequency region of a few Hz. The modularized design ensures the system is accessible to further modifications as frequently required by various biological experiments such as employing multiple laser traps to manipulate rod-shaped samples. © 1997 American Institute of Physics.

Notes: A new type of pulse transformer has been developed as a substitute for a Marx generator. In the transformer amorphous metallic cores are utilized with windings of cylindrical conductors. As a result, low leakage inductance is realized with high breakdown strength. The coupling coefficient of the transformer is estimated to be more than 0.99. By using the transformer of winding ratio of 1:3, a Blumlein pulse forming line of capacitance 20 nF is successfully charged up to 270 kV by using a capacitor bank of 240 nF, 90 kV. High speed charging of charging time=250 ns is realized with high efficiency of energy transfer (energy transfer efficiency from the capacitor bank to the pulse forming line was evaluated to be 76%). © 1997 American Institute of Physics.

Notes: In time correlated photon counting, the picosecond resolution offered by the reduced transit time spread of ultrafast microchannel plate (MCP) photomultipliers is fully exploited only if all other timing jitter contributions are minimized. With the ultrashort signals of MCP detectors, the commercially available circuit modules do not provide true constant fraction triggering (CFT) operation. The residual amplitude dependent time walk therefore sets the actual limit to the obtained time resolution. A new CFT scheme has been devised for obtaining true constant fraction triggering. A circuit has been accordingly developed and tested. The time walk is reduced to less than 8 ps for a 1:14 dynamic of the input signal (pulse amplitudes from 100 mV to 1.4 V) and to less than 25 ps for a 1:20 dynamic (from 70 mV to 1.4 V). It is shown that such a performance makes it possible to exploit in actual experiments the 20 ps intrinsic resolution of the fastest available MCP detectors. © 1997 American Institute of Physics.

Notes: This article presents a review of techniques and instrumentation for using x rays and synchrotron radiation in high-pressure experiments. The review focuses on x-ray diffraction experiments using diamond anvil cells. After a brief introductory passage, details about diamond anvil cells, large volume apparatus, pressure measurement, and simultaneous high-temperature and high-pressure instrumentation are provided, with adequate references to these topics. A section on adapting x-ray methods for use with high-pressure apparatus lists the problems encountered. Examples of studies are presented using energy dispersive diffraction, angle dispersive diffraction, infrared spectroscopy, x-ray absorption spectroscopy, and single-crystal techniques. The current trend indicates that energy dispersive diffraction, so far the mainstay of high-pressure powder diffraction with synchrotron sources, has lost some ground to angle dispersive diffraction, due to advances in instrumentation in the latter method. © 1997 American Institute of Physics.

Notes: A new fast scan submillimeter spectroscopic technique (FASSST) has been developed which uses a voltage tunable backward wave oscillator (BWO) as a primary source of radiation, but which uses fast scan (∼105 Doppler limited resolution elements/s) and optical calibration methods rather than the more traditional phase or frequency lock techniques. Among its attributes are (1) absolute frequency calibration to ∼1/10 of a Doppler limited gaseous absorption linewidth (〈0.1 MHz, 0.000 003 cm−1), (2) high sensitivity, and (3) the ability to measure many thousands of lines/s. Key elements which make this system possible include the excellent short term spectral purity of the broadly (∼100 GHz) tunable BWO; a very low noise, rapidly scannable high voltage power supply; fast data acquisition; and software capable of automated calibration and spectral line measurement. In addition to the unique spectroscopic power of the FASSST system, its implementation is simple enough that it has the prospect of impacting a wide range of scientific problems. © 1997 American Institute of Physics.

Notes: This paper presents closed form equations based on a modification of those originally derived by Paros and Weisbord in 1965, for the mechanical compliance of a simple monolithic flexure hinge of elliptic cross section, the geometry of which is determined by the ratio ε of the major and minor axes. It is shown that these equations converge at ε=1 to the Paros and Weisbord equations for a hinge of circular section and at ε ⇒∞ to the equations predicted from simple beam bending theory for the compliance of a cantilever beam. These equations are then assessed by comparison with results from finite element analysis over a range of geometries typical of many hinge designs. Based on the finite element analysis, stress concentration factors for the elliptical hinge are also presented. As a further verification of these equations, a number of elliptical hinges were manufactured on a CNC milling machine. Experimental data were produced by applying a bending moment using dead weight loading and measuring subsequent angular deflections with a laser interferometer. In general, it was found that predictions for the compliance of elliptical hinges are likely to be within 12% for a range of geometries with the ratio βx (=t/2ax) between 0.06 and 0.2 and for values of ε between 1 and 10. © 1997 American Institute of Physics.

Notes: We have built an apparatus to study the viscoelastic response and measure the complex shear moduli of Langmuir monolayers as functions of the frequency and amplitude of the applied sinusoidal shear strain. A rotor is placed in contact with the monolayer and suspended by a torsion wire; a coil attached to the rotor carries a direct current. The voltage induced in this coil by a high-frequency external magnetic field is used to measure the angle of rotation with an accuracy of ∼0.005°. A low-frequency external magnetic field is used to drive the rotor into forced oscillations at the desired frequency (1 mHz–1 Hz), or the rotor may oscillate freely with the "natural" frequency variable over the range 0.01–3 Hz using a static external magnetic field. The apparatus has a large dynamic range for shear modulus measurement (∼5×10−3–103 dyn/cm), achieved by using the free oscillation (ring-down) method for films with low shear moduli (∼5×10−3–1 dyn/cm), and the forced oscillation method for films with higher shear moduli (∼1–103 dyn/cm). We have found that the complex shear modulus G of heneicosanoic acid Langmuir monolayers depends on the applied strain except at very low amplitudes. We also present sample data showing the frequency dependence of G. © 1997 American Institute of Physics.

Notes: The finite element method was employed to calculate the correction factors for the measurement of sheet resistivity of a square sample with a square four-point probe. This method is simpler than methods of image and conformal transformation, and can be used for calculating the correction factors for four-point resistivity measurement of an arbitrarily shaped sample with an arbitrary four-probe array. © 1997 American Institute of Physics.

Notes: The design and operation of a high temperature gas aggregation source, capable of in situ deposition of mass-selected atomic clusters of transition metals onto a substrate in an ultrahigh vacuum chamber, is described. Mass-selection is achieved by an ultrahigh mass quadrupole filter operating at masses up to 3×104 amu. © 1997 American Institute of Physics.

Notes: We report on the use of recently developed spin-polarized electron sources with very high polarization for electron spectroscopy. In particular we present data of spin-resolved inverse photoemission from Fe(100) films excited by polarized electrons produced by a strained GaAsP negative electron affinity photocathode. This highly polarized source (beam polarization P=65%) allows a direct and almost complete decoupling of the majority and minority empty states in Fe(100), much better than the standard GaAs sources (P=20%–30%). The preparation and characterization of the strained photocathode is also discussed. © 1997 American Institute of Physics.

Notes: We report on our investigation into the development of electrostatic mirror based charged particle analyzers for space plasma physics experimentation. For this work, we tested an elliptical mirror analyzer which was designed to provide a wide, 2-dimensional field of view with high throughput and good angular resolution. Measurements with an ion beam demonstrated 2° full width at half-maximum angular resolution over a 16×16° field of view (FOV) and 4° resolution over a 40×40° FOV for an optical system with a linear dimension (entrance aperture to the particle detector) of 20 cm. The energy resolution is variable, similar in operation to a retarding-potential-analyzer or a modulated grid Faraday cup, with a geometric factor of 3.2×10−3 cm2 str ΔE/E for an energy resolution setting of 10%. © 1997 American Institute of Physics.

Notes: Design and operation of two simple capacitive transducer systems are described here. The first design uses a spring for the air-gap variations of a capacitor, while the second one employs a cantilever steel beam as a restoring element in a capacitive transducing arrangement. The reported setup makes it possible to detect mass changes of the order of 0.1 g in a 250 g range. A comparison has been made between the results of two sensors, and the second design shows a better performance in terms of repeatability, linearity, and sensitivity. It has a repeatability of better than 4% for this range of operation. This device is suitable for mass measurements of medium resolution and dynamic range and has the advantage of simplicity in design and construction. © 1997 American Institute of Physics.

Notes: A low cost, low power compact optical correlator is demonstrated. It operates interchangeably in the matched-filter or joint-transform configurations. The active medium is a high diffraction efficiency photorefractive host–guest polymer system. Successful image correlation has been achieved. © 1997 American Institute of Physics.

Notes: A modified feed-forward control system has been operated at the Brookhaven Accelerator Test Facility to control the phase and amplitude of two high power klystron rf systems used to power a photocathode rf gun and a traveling wave electron linac. The changes to the control algorithm include an improved handling of cross coupling between the amplitude and the phase channels, an improved calibration routine that allows for changes in the matrix elements due to the variable base-line and improved filtering. The modifications to the software include modularity, portability, and user-friendliness. Improvements to the hardware include a linearized phase and amplitude controller with dc biasing for an improved dynamic range. The feed-forward system can handle nonlinear and noninstantaneous systems. With simultaneous regulation of two channels, the phase and the amplitude fluctuations over a time span of more than 3 μS were reduced to less than ±0.2° and ±0.2%, from the initial ±2.7° and ±1.8%, respectively. © 1997 American Institute of Physics.

Notes: We report on the application of the vacuum photodiode to detect vacuum ultraviolet (VUV) radiation emitted from the Saha Institute of Nuclear Physics (SINP) Tokamak. It is simple to fabricate and provides broadband spectral response in the VUV and ultrasoft x ray (10 eV–1 keV). In our design, a stainless steel photocathode is used, which has a response identical to tungsten in the wavelength range 100–1200 Å. Its surface is passivated, to minimize contamination and monolayer deposition, by electropolishing it. Some representative experimental results illustrating the range of applicability are presented with special emphasis on its performance in disruptive shots. © 1997 American Institute of Physics.

Notes: The design, fabrication, and characterization of a 2.3 kJ plasma focus device with negative inner electrode are discussed. The purpose of the design was to initiate research in and study of plasma dynamics, nuclear reactions, and neutron emission mechanisms at the university. Also the device will be used to teach and demonstrate plasma phenomena at the postgraduate level and to perform experiments with inverted polarity to examine different operating regimes with nonstandard gases. It is hoped that in the long run the research work will help find a solution to the polarity riddle of plasma focus devices. When the system was operated with spectrographic argon as the filling gas, the best focus was obtained at a pressure range of 0.1–1.25 Torr. With nitrogen as the filling gas, the best focus was obtained at pressures between 0.1 and 1.25 Torr. Air gave the best focus at a pressure range of 0.5–1.5 Torr. The observed good focus action is attributed to the small inner electrode length (this reduces the amount of anode material ablated into the current sheath) and tapering of the inner electrode. Positive z-directed electrons contribute to the temperature and further ionization of the plasma gas during focusing. The performance of the device compares quite well with other known devices. © 1997 American Institute of Physics.

Notes: Although classical electrostatic plasma probes can provide detailed information regarding electrons and ions, these devices rely on charge-carrying particles both for energy filtering and for detection. Neutral particles are transparent to such diagnostics. In light of this a new probe design was developed to provide a measurement of the neutral particle flux component of a flowing plasma. The simple design adopted for this probe utilizes a set of electrostatic retarding grids to remove the charged particles from the flow. The neutral particles are sensed within the tube of an off-the-shelf hot cathode ionization gauge. Additionally, by varying the potential on the retarding grids, this same probe configuration can be used to measure the ion energy distribution. Preliminary data from this probe were taken in the exhaust plume of a Hall-current accelerator designed for space propulsion. This probe was found to be a very simple, accurate diagnostic tool for such use. By using this probe in combination with interrelated diagnostics the spatial distribution of energetic charge exchange neutrals was quantified in the plume of an SPT-100 thruster. © 1997 American Institute of Physics.

Notes: Measured figures (linearity, avalanche gain, frequency response, and noise) of the avalanche photodiodes (APD) detectors used on the FTU Thomson scattering system (FTU-TS) are reported. This investigation on the APD figures is motivated by the necessity of knowing their values over a wide range of input signals, and also of checking the validity of McIntyre model of APD noise, since using this model the experimental signal-to-noise ratio is calculated. From the noise analysis, a method of optimization of the detection system sensitivity is derived, leading to the optimization of the signal-to-noise ratio over the entire FTU-TS system. © 1997 American Institute of Physics.

Notes: A high sensitivity, high bandwidth, two-color interferometer (1064 and 532 nm) has been tested on the Hawk pulsed power generator at the Naval Research Laboratory. The phase resolution is 10−5 waves with a rise time of 3 ns, a new capability for diagnosing plasmas, and neutrals in pulsed power experiments. The two-color feature is used to distinguish phase shifts from free (plasma) electrons and bound (neutral and ion) electrons. Simultaneous electron and neutral density measurements were demonstrated in a plasma opening switch (POS) experiment. The ability to measure small phase shifts with fast rise time were demonstrated in a plasma filled diode experiment. The high sensitivity and vibration isolation enable neutral gas distribution measurements from supersonic nozzles used in plasma radiation source experiments. Examples of these measurements and future applications are described. © 1997 American Institute of Physics.

Notes: The Wendelstein 7-X experiment is a concept test for properties of reactor relevant plasmas in advanced stellarators. Prominent features include a modular superconducting coil assembly, a fivefold toroidal symmetry, and a helical magnetic axis. Due to the optimization process, W7-X is characterized by a vacuum magnetic field configuration with smooth magnetic surfaces, improved equilibrium properties with a weak dependence of rotational transform and shear on the plasma pressure β, good magneto-hydrodynamic stability properties due to magnetic well stabilization, reduced neoclassical transport losses and negligible bootstrap current in the long mean-free-path regime, good collisionless α-particle confinement in an equivalent reactor, and, as a technical aspect, good feasibility of the superconducting modular coils. W7-X will be heated by continuous electron cyclotron resonance heating and pulsed neutral beam injection and ion cyclotron resonance heating. The envisaged parameters are Te≤10 keV, Ti≤6 keV central densities ≤3×1020 m−3 with an averaged 〈β〉≤5%. Despite the complicated geometrical structure, all basic diagnostics are compatible with W7-X. Generally, diagnostic methods and applications in a stellarator are not different from those in tokamaks. However, special efforts are being made to equip the experiment with those diagnostics necessary to measure the quantities directly related with the optimization of the machine: the verification of the predicted magnetic topology and characterization of the configuration throughout the entire parameter range, the identification of equilibrium and stability, and the determination of the confinement properties. The article describes the strategy developed which assures that the detailed measurement needs of the W7-X experimental program can be met. © 1997 American Institute of Physics.

Notes: New diagnostics have been developed to address key divertor physics questions, including: target plate heat flux reduction by radiation, basic edge transport issues, and plasma wall interactions (PWIs) such as erosion. A system of diagnostics measures the target plate heat flux (imaging ir thermography) and particle flux (probes, pressure and Penning gauges, and visible emission arrays). Recently, Te, ne, and Pe (electron pressure) have been measured in two-dimensions (2D) with divertor Thomson Scattering. During radiative divertor operation Te is less than 2 eV, indicating that new atomic processes are important. Langmuir probes measure higher Te in some cases. In addition, the measured Pe near the separatrix at the target plate is lower than the midplane pressure, implying radial momentum transport. Bolometer arrays, inverted with reconstruction algorithms, provide the two-dimensional core and divertor radiation profiles. Spectroscopic measurements identify the radiating species and provide information on impurity transport; both absolute chordal measurements and tomographic reconstructions of images are used. Either intrinsic carbon or an inert species (e.g., injected Ne) are usually observed, and absolute particle inventories are obtained. Computer codes are both benchmarked with the experimental data and provide important consistency checks. Several techniques are used to measure fundamental plasma transport and fluctuations, including probes and reflectometry. PWI issues are studied with in situ coupons and insertable samples (DiMES). Representative divertor results from DIII-D with references to results on other tokamaks will be presented. © 1997 American Institute of Physics.

Notes: An inversion technique has been developed to calculate local poloidal rotation velocities of impurity ions from line-integrated measurements of an extended emission source in a tokamak plasma. This technique can recover radial spatial resolution that is lost due to the curvature of the field lines. With charge exchange emission from neutral beams, it can be used to obtain poloidal velocity profiles across the entire minor radius of the plasma without requiring restricted neutral beam height to localize the emission. The technique consists of two Abel-like matrix inversions to obtain the emissivity and the velocity-weighted emissivity from which the velocity is obtained. Use of the neutral beams breaks the assumed symmetry, but knowledge of the beam deposition and geometry allow analogous matrices to be generated. The inversion technique is demonstrated with a simulation of a poloidal rotation diagnostic for the TFTR tokamak with tangential neutral beams with a height of 80 cm. Two opposing vertical views are required to handle effects of the charge exchange cross section, which can cause apparent velocities greatly in excess of expected poloidal velocities. The simulated errors due to the inversion process are about 1.5 km/s near the plasma center. © 1997 American Institute of Physics.

Notes: A simple, compact, low temperature scanning tunneling microscope system is described which can easily be incorporated into pre-existing ultrahigh vacuum chambers designed around a centrally located sample. Cooling is achieved by the transfer of a cryogenic fluid from an external commercial Dewar to the bottom of a cold finger, where the sample and a beetle-type microscope are mounted. Details of the microscope operation with liquid nitrogen are given. © 1997 American Institute of Physics.

Notes: A new and stable scanning tunneling microscope (STM) system has been constructed for the investigation of thin organic films in air. The STM unit is made of Macor, which is machinable ceramic and has a small thermal expansion coefficient and a high mechanical stiffness. Three-dimensional coarse position adjustment (within 3 μm) is carried out using five stacked piezoelectric transducers (PZTs). A cross-type configuration is used to prevent the thermal effect of the x- and y-direction displacement mechanism. In order to achieve high resolution, x-, y-, and z-direction displacements are performed using a tube-type PZT. The z direction of the tube PZT has a high mechanical resonant frequency of 24.4 kHz. Therefore, this STM unit is mechanically rigid, and allows stable operation under mechanical disturbances (sound and mechanical vibration). Moreover, this STM unit can be controlled for 24 h or longer by using an ordinary operational amplifier, because thermal effects are compensated. The STM system can also be used to obtain information on the spatially resolved local tunneling barrier height, which is sensitive to the chemical structure of the sample. The capabilities of this newly designed STM are demonstrated with experiments investigating the morphology and tunneling barrier height of stearic acid thin films on indium-tin-oxide substrates. © 1997 American Institute of Physics.

Notes: Linear thermal expansivities, α, have been obtained from 1 to 300 K for a sample of Stycast 2850FT epoxy that initially was cured at room temperature (X1), and then at 95 °C (X2). Heat capacities, Cp, were measured from 1 to 95 K for X2. The α's for X1 and X2 are roughly equal to and twice that of copper near room temperature, but differ by as much as 10% at low temperature. The α's approach those for copper near 100 K, but have a much smaller temperature dependence at lower temperatures. The different shapes of the α(T) and Cp(T) relations give a Grüneisen parameter, Γ, which decreases from 1.2 at 10 K to 0.5 at 95 K. Both α and Cp show apparent changes in lattice properties near 4.5 K, and a low temperature anomaly (Γ=3.5) that is characteristic of amorphous solids. Sample relaxation (shortening) effects from 300 K to 110 K were more serious for X2 than for X1. Because of differences related to the curing procedure, these data should be used only semiquantitatively in the design of experiments in which Stycast 2850FT will be used as a construction material. Possible Stycast-related problems with a capacitance dilatometer are discussed. © 1997 American Institute of Physics.

Notes: A skin motion imaging system with two modes of operation, diffusive and specular reflections, was developed. The system consists of image capturing and processing elements. Using optical flow analyses of skin motion at the wrist, we have detected successfully a blood pulsation signal that concurs with the electrocardiogram. The signal provides information not only about blood pulsation, but also about blood circulation and the biomechanical properties of the skin. This system may have other applications in the future, such as noncontact blood pulsation detection and evaluation of the biomechanical properties of skin, for example. © 1997 American Institute of Physics.

Notes: High pressures are often measured using the resistance of Manganin wires. However, the pressure coefficient of resistance is known to depend on temperature. We have measured this temperature dependence by comparing the output from a Manganin gauge with that of a well calibrated Zeranin gauge and determined a correction factor which enables us to measure the pressure at any temperature between 150 and 300 K with a temperature dependent error well below 0.5%. © 1997 American Institute of Physics.

Notes: The potential use of a free electron laser (FEL) amplifier as a diagnostic tool for relativistic electron beams is investigated. It is in fact shown that a simple relation exists between electron bunch length, energy spread, and the gain of a FEL resonant amplification. It is also discussed how the beam qualities can be derived from an actual experimental configuration. Finally, the possibility of combining the present methods to other techniques, like nondestructive diagnosis with short undulators, is also analyzed. © 1997 American Institute of Physics.

Notes: A new digital correlator was developed. The one-bit-clipped digital correlator used so far is simple and sensitive enough to detect one photon. The clipping circuits, however, tend to distort the temporal characteristics. In order to alleviate the distortion, we extended the clipping points of counters and multipliers to two bits and three bits, respectively. The novel correlator has the dynamic range ten times wider than that of one-bit-clipped correlator. Here we report the 130 channel correlator that uses seven chips of field programmable gate array. © 1997 American Institute of Physics.

Notes: A double-beam Ti:sapphire laser photolysis system has been constructed for measurements of the subpicosecond transient absorption spectra by a pump-probe method. Although the spectroscopic characteristics tested for the practical availability are satisfactory enough, the transient absorption spectrum thus obtained exhibits an artificial time-dependent spectral change owing to the group velocity dispersion of the probing light pulse. Hence, its wavelength-dependent arrival time to the sample cell is determined utilizing the optical Kerr effect induced in carbon tetrachloride and the true transient absorption spectrum (the corrected spectrum) at a given delay-line setting is calculated by a microcomputer using a great number of uncorrected transient absorption spectra obtained at different delay-line settings. Interestingly, the corrected singlet-singlet absorption band (band C with a lifetime of 0.8 ps) obtained for the lowest excited singlet state of 9-nitroanthracene in cyclohexane really shifts with time. This can be interpreted in terms of the wide wavelength-range superposition of band C and an absorption band which increases and then decreases with rise and decay times of 0.8 and 1.8 ps, respectively; the latter band is ascribed to the absorption of 9-nitrite (or its precursor) or that of a higher excited triplet state of 9-nitroanthracene. By 400 nm biphotonic excitation of the neat solvents (cyclohexane and n-heptane), furthermore, population of their higher excited singlet states with a very short lifetime of 0.4 ps can be seen. © 1997 American Institute of Physics.

Notes: A difficult part of the analysis of the neutron collimator data is the distinction between contributions from DD and DT neutrons. This is important for the majority of TFTR discharges, which use neutral deuterium heating beams and relatively small amounts of tritium. At present, the DT-neutron contribution is determined from a comparison of the chord-integrated neutron collimator data with measurements of the DT-neutron source strength from general wide-angle detectors, using an iterative computational method. A more satisfactory solution should be obtained with detectors that measure the contributions from DD and DT neutrons, and gamma radiation, directly. Pulse-shaping techniques are insufficient, since the detectors in the neutron collimator are operated in current mode. The presently used data analysis is described and the concept of a new multilayered plastic detector that makes use of the differences in the attenuation of the various radiation components is presented. The dimensions of the detector are based on calculations of the attenuation for the expected neutron energy spectrum. © 1997 American Institute of Physics.

Notes: Active feedback control of the current profile, requiring real-time determination of the current profile parameters, is envisioned for tokamaks operating in enhanced confinement regimes. The distribution of toroidal current in a tokamak is now routinely evaluated based on external (magnetic probes, flux loops) and internal (motional Stark effect) measurements of the poloidal magnetic field. However, the analysis involves reconstruction of magnetohydrodynamic equilibrium and is too intensive computationally to be performed in real time. In the present study, a neural network is used to provide a mapping from the magnetic measurements (internal and external) to selected parameters of the safety factor profile. The single-pass, feedforward calculation of output of a trained neural network is very fast, making this approach particularly suitable for real-time applications. The network was trained on a large set of simulated equilibrium data for the DIII-D tokamak. The database encompasses a large variety of current profiles including the hollow current profiles important for reversed central shear operation. The parameters of safety factor profile (a quantity related to the current profile through the magnetic field tilt angle) estimated by the neural network include central safety factor, q0, minimum value of q, qmin, and the location of qmin. Very good performance of the trained neural network both for simulated test data and for experimental datais demonstrated. © 1997 American Institute of Physics.

Notes: A novel thermoreflectance technique has been developed for noncontact temperature measurements using laser light incident at large angles on solid materials and devices. The method involves measuring the differential reflectance from a polarization modulated laser beam. The polarization differential reflectance technique is demonstrated on single-crystal Si wafers and on a polycrystalline carbon thin film over a temperature range of 20–60 °C. The method is shown to be an extremely sensitive temperature probe for near grazing angle measurements, which could be useful for monitoring the surface temperature of closely stacked silicon wafers used in batch processing in the microelectronics industry. © 1997 American Institute of Physics.

Notes: Since the discovery of photosensitivity in optical fibers there has been great interest in the fabrication of Bragg gratings within the core of a fiber. The ability to inscribe intracore Bragg gratings in these photosensitive fibers has revolutionized the field of telecommunications and optical fiber based sensor technology. Over the last few years, the number of researchers investigating fundamental, as well as application aspects of these gratings has increased dramatically. This article reviews the technology of Bragg gratings in optical fibers. It introduces the phenomenon of photosensitivity in optical fibers, examines the properties of Bragg gratings, and presents some of the important developments in devices and applications. The most common fabrication techniques (interferometric, phase mask, and point by point) are examined in detail with reference to the advantages and the disadvantages in utilizing them for inscribing Bragg gratings. Reflectivity, bandwidth, temperature, and strain sensitivity of the Bragg reflectors are examined and novel and special Bragg grating structures such as chirped gratings, blazed gratings, phase-shifted gratings, and superimposed multiple gratings are discussed. A formalism for calculating the spectral response of Bragg grating structures is described. Finally, devices and applications for telecommunication and fiber-optic sensors are described, and the impact of this technology on the future of the above areas is discussed. © 1997 American Institute of Physics.

Notes: A novel scheme combining interferometer and refractometer for simultaneous plasma density and plasma density gradient measurements is described. The scheme employs a ribbon laser beam obtained from one-dimensional laser beam expansion by a pair of cylindrical lenses. This beam shape allows measurements at several spatial locations simultaneously. The beam deflection measurements give additional important information on the spatial distribution of plasma density gradient in the direction perpendicular to the major axis of the expanded beam. Fast pin photodiodes are used as light detectors for temporal resolution better than 1 ns. The high power (700 mW) of the argon ion laser allows 0.1° phase resolution and simultaneously 0.1 mrad refractional deflection angle resolution. © 1997 American Institute of Physics.

Notes: We summarize the problem of measuring an ultrashort laser pulse and describe in detail a technique that completely characterizes a pulse in time: frequency-resolved optical gating. Emphasis is placed on the choice of experimental beam geometry and the implementation of the iterative phase-retrieval algorithm that together yield an accurate measurement of the pulse time-dependent intensity and phase over a wide range of circumstances. We compare several commonly used beam geometries, displaying sample traces for each and showing where each is appropriate, and we give a detailed description of the pulse-retrieval algorithm for each of these cases. © 1997 American Institute of Physics.

Notes: We describe a rapid-scanning modified Mach–Zehnder interferometer suitable for use in femtosecond pump–probe or dichroism spectroscopy with self-mode-locked titanium–sapphire oscillators. A galvanometer-type rapid-scanning translation stage is employed in the pump arm of the interferometer. The intensity or polarization of the pump beam is modulated by a fused-silica photoelastic modulator employed as a half-wave retarder. The detection system exploits the rapid-scanning stage and photoelastic modulator by combining phase-sensitive detection with transient digitization. The system we describe permits pump–probe or dichroism spectroscopy to be conducted without temporal distortion of the laser pulses used in the experiment, with high scan-to-scan reproducibility, and with all of the previously noted advantages of rapid-scanning methods in terms of sensitivity. The approach is especially well suited for use with pulse-picked or cavity-dumped sources, which are often required to be operated at moderate pulse-repetition rates in order to avoid artifacts from sample heating or from long-lived intermediates. © 1997 American Institute of Physics.

Notes: The development of new types of sophisticated soft x-ray sources requires the knowledge of their emission characteristics such as photon flux, spectral distribution, and size of the radiation source. Calibrated spectrographs for the soft x-ray region are needed to determine these properties. The components of a soft x-ray spectrograph consisting of a pinhole gold transmission grating and a charge coupled device (CCD) camera are calibrated at the radiometry laboratory of the Physikalisch-Technische Bundesanstalt using the synchrotron radiation facility BESSY. Two different kinds of CCD-based photon detectors (one thinned and back illuminated, one coated with a phosphorous layer) are compared with regard to their sensitivities in the spectral range between 50 eV and 1.7 keV. The results obtained for the thinned CCD are compared with theoretical calculations of the sensitivity. © 1997 American Institute of Physics.

Notes: We have used a white light continuum generated with ultrashort laser pulses from a Ti:sapphire laser system as the radiation source for second-harmonic generation measurements. The white light continuum provides easily tuned radiation for experiments requiring a range of wavelengths. Despite the small coherence length of the radiation, parametric processes, such as second-harmonic generation, are possible with this source. In particular, surface second-harmonic generation using the white light continuum is reasonable because the extent of the interface is much smaller than the coherence length of the radiation. We demonstrate second-harmonic generation from a gold surface and show that surface second-harmonic generation using the white light continuum can be used to measure absorption spectroscopy of molecules adsorbed to surfaces via resonance enhancement of the surface second-harmonic signals. © 1997 American Institute of Physics.

Notes: A compact high pressure cell and its control environment designed for small- and wide-angle x-ray scattering experiments under hydrostatic pressure up to 3000 bar and temperatures between −20 °C and +80 °C are described. With this system x-ray scattering experiments can be performed at constant pressure and temperature with a conventional laboratory x-ray source and it can be easily modified to carry out time resolved pressure jump studies at synchrotron radiation sources. The computer-aided pressure adjustment has a calibrated accuracy of ±0.5%, and temperature is computer-controlled to a precision of ±0.05 °C. The instrument has been designed to investigate systems of biological interest, especially lipid-water dispersions, but it is equally possible to measure highly viscous or solid samples. The performance is illustrated by a pressure dependent small- and wide-angle x-ray scattering study of a phospholipid-water dispersion at constant temperature. © 1997 American Institute of Physics.

Notes: The Q factors of violin modes for wires of various materials have been measured in order to determine which would be most suitable for use in the suspension of test masses in the initial laser interferometer gravitational wave observatory (LIGO) interferometers. A "guitar" type apparatus was employed to measure violin mode Qs, and losses due to clamping and other practical sources were successfully suppressed below the level of intrinsic wire losses. Steel music wire was found to give the highest extrapolated Q factors under LIGO conditions among the wires we tested. This extrapolated Q sets a target for the LIGO suspension which can be attained if all the losses other than the intrinsic wire loss are successfully suppressed. The measured Qs for the steel, tungsten, and titanium wire, which were approximately frequency independent for the first two to three modes, were found to be roughly proportional to the square root of the tension in the wire. This is consistent with the theory of violin mode losses due to frequency-independent intrinsic wire losses. © 1997 American Institute of Physics.

Notes: Standard spark gaps have lower time limits of gap recovery when testing with high repetition rate impulses and in high-current high-voltage multiple impulse testing. More important, they are not suitable for the generation of opposite-polarity successive impulses using conventional capacitive-type generation techniques. In this article, an improved design incorporating two rotating spark gaps is described. The new spark gap was used to test ZnO surge arresters with two successive impulses of currents up to 5 kA and voltages up to 50 kV. Time intervals as low as 10 ms were achieved between the two impulses. Both similar and opposite polarity tests were carried out successfully. © 1997 American Institute of Physics.

Notes: A laser Doppler velocimeter employing a CO2 laser has been developed by using its optogalvanic effect. A change in the electric impedance of a discharge, induced by mixing of a returned wave with an originally existing wave inside the cavity, is employed to detect the Doppler frequency shift. We found that a Doppler frequency shift as much as 60 kHz was detected, and also a good linear relationship between the velocity and the Doppler frequency shift was obtained. © 1997 American Institute of Physics.

Notes: The microphone technique has been applied to the study of laser ablation of a silicon target. The momentum flux of silicon atoms generated by laser ablation at 266 nm was detected both at high vacuum and at background gas conditions. The response of the microphone to an atomic pulse of a few μs was in agreement with theoretical expectations. The magnitude of the microphone signal increased linearly with laser fluence. A pulsed valve was adopted to also compare the response of the microphone at longer pulse durations. © 1997 American Institute of Physics.

Notes: The design of a device for the simultaneous application of uniaxial stress and hydrostatic pressure is presented. Shown in detail is the design of the part that applies the uniaxial force to the sample and first results of the simultaneous application of uniaxial stress and hydrostatic pressure to a semiconductor laser. © 1997 American Institute of Physics.

Notes: We report on several complementary methods for improving the stability of a free running diode laser. We were primarily concerned with: (a) the construction of a stable power supply to reduce the main frequency and rf noise, and (b) long term drift of the laser frequency, for which we have developed a lock-in amplifier to be combined with a simple proportional-integrating circuit. While we have kept everything simple and inexpensive to construct, the stability is comparable with that of far more expensive, commercially available systems. Development and testing of our stabilization scheme was done on the distributed Bragg reflector diode lasers for use in a range of atomic collision and atom optics experiments, but it is applicable to all diode lasers, and can be used in a large range of atomic physics experiments. © 1997 American Institute of Physics.

Notes: One of the promising radiation detection devices for various practical applications is the series-connected superconducting tunnel junction (STJ) detector. In this article, interesting topics of the detectors are described since our previous work: e.g., more than two order higher detection efficiency compared with single STJ detectors, high count rate detection, and position resolution. Detectors were cooled to 0.35–0.4 K by means of a convenient 3He cryostat. The 5.9 and 6.5 keV x rays from 55Fe are separated by a detector specially designed for x-ray detection. The possible count rate of the series-junction detector estimated from the shaping-time constant applied in the measurements is high, e.g., over 104 counts per second. A series-junction detector equipped with a position sensing mechanism has shown a position resolution of about 35 μm in a sensing area with a radius of 1.1 mm. The position resolution of series junctions improves the energy resolution. A new type series-connected STJ detector is also proposed, i.e., the dispersed multitrap series-junction detector, for further improvement of detection efficiency and energy resolution. © 1997 American Institute of Physics.

Notes: A new thermal, supersonic cluster source for the investigation of binary metal cluster formation at thermodynamically well-defined expansion conditions is described. The source consists of two separately heatable cartridges. A first cartridge can be heated up to 1220 K and the second high temperature cartridge reaches maximal temperatures of 1800 K. A temperature difference of 1000 K between the two cartridges can be maintained for at least 3 h. Clustering occurs upon supersonic expansion from a conical nozzle. This cluster source has two main applications: (a) the generation of mixed metal clusters and (b) the investigation of pure metal clusters at various expansion conditions. The performance and applications of this source are illustrated by presenting results of the heterocluster formation of mixed sodium/gold and sodium/silver heteroexpansions. In addition, the influence of the oven parameters on the internal temperatures of the generated clusters is illustrated with the example of Na2. © 1997 American Institute of Physics.

Notes: A formula including correction due to change of beam injection angle is derived for measurements of beam energy using parallel plate energy analyzers. The formula is mainly aimed for potential measurements in high temperature plasma with heavy ion beam probes, and an example is presented to demonstrate the usage of the formula. © 1997 American Institute of Physics.

Notes: A superconducting quantum interference device magnetometer system designed for low field static and dynamic susceptibility measurements is described. Magnetic shields reduce the residual field in the sample space to about 0.04 A/m (0.5 mOe). A highly stable dc magnetic field is generated by a small superconducting solenoid working in the persistent mode. The temperature control system yields a resolution better than 10 μK in the range of 30–100 K. Combining ac susceptibility and dc magnetic relaxation measurements, the system allows dynamic susceptibility studies in a time window ranging from 3×10−6to 106 s. The sensitivity of the system is 10−12 Am2 (10−9 emu). © 1997 American Institute of Physics.

Notes: A simple silicon two-dimensional (2D) flow sensor for the measurement of both flow direction and speed is described. By integrating two couples of silicon spreading-resistance temperature (SRT) sensors in two perpendicular directions on the surface of a silicon chip, this sensor can detect flow speed and flow direction φ in a full range of 360°. Experimental results confirm theoretical analysis that the output of the sensor increases with the square root of the flow velocity, and the outputs in the two perpendicular directions are proportional to sin φ and cos φ, respectively. The effects of sensor layout are also discussed. With complete oxide isolation for the SRT sensors, the flow sensor could achieve higher sensitivity by operating above the intrinsic temperature of silicon (∼150 °C), or could be used to detect fluid flow at a temperature as high as 300 °C. © 1997 American Institute of Physics.

Notes: We present a new design of a low-temperature ultrahigh-vacuum (UHV) scanning tunneling microscope setup with a combination of a solenoid and a split-pair magnet. The scanning tunneling microscope can be operated at temperatures down to 8 K and in a rotatable magnetic field of up to 1 T. Magnetic fields of up to 7 T perpendicular and 2 T parallel to the sample surface can be applied. The UHV part of the system allows in situ preparation and low energy electron diffraction/Auger analysis of samples. First topographic and spectroscopic measurements on p-InAs(110) are presented. © 1997 American Institute of Physics.

Notes: Research into the high velocity impact of materials has necessitated the setting up of a new facility at the Royal Military College of Science. A light-gas gun and flash x-ray system were acquired to meet the research objectives. In this article, the light-gas gun and auxiliary equipment are described. Modifications were made to the facility to ensure the safety of personnel during a gas gun and flash x-ray firing. An analysis was carried out to select operating parameters within the maximum safe loading condition of the gas gun. The work met the safety and operational objectives, and suggestions for future work are made. © 1997 American Institute of Physics.

Notes: A review of the perturbation theory to calculate the wave propagation constant for a waveguide containing a plasma cylinder of small radius on its axis is presented. The wave propagation constant is important for implementing some diagnostic techniques. In the present paper, this constant for a column of a cold, magnetoactive plasma of small radius is calculated, assuming that the distribution of electron density in the plasma is a parabolic function of the radius, and it is shown that this result simplifies the determination of the average plasma density. Moreover, it is shown that for the particular case of an H11 mode, the result obtained at the electron cyclotron resonance, can be used to gauge the waveguide as well as to describe a simplified model of the plasma heating in an electron cyclotron resonance plasma source. © 1997 American Institute of Physics.