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Review of Scientific Instruments

Issue 9 • Date Sep 1998

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Displaying Results 1 - 25 of 61
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • A compact rotating-mirror autocorrelator design for femtosecond and picosecond laser pulses

    Page(s): 3099 - 3102
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    An interferometric rapid-scanning autocorrelator employing two antiparallel rotating mirrors in a variable arm is optimized for maximum optical path difference as a function of the separation of the two rotating mirrors. A very compact design (mirror separation≈mirror diameter) is possible without a reduction in the maximum pulse width that can be measured. © 1998 American Institute of Physics. View full abstract»

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  • A velocity interferometer system for any reflector utilizing a short coherence length laser

    Page(s): 3103 - 3105
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    A velocity interferometer system for any reflector, utilizing a laser of coherence length less than the optical path difference (OPD) between the two interferometer arms, is described and tested. In this instrument the laser beam is passed through the interferometer both before and after it is reflected from the target. As a result the coherence length of the laser need only be twice the relatively small distance traveled by the target in the time taken for light to traverse the OPD. Results are presented for a nonspecular target. © 1998 American Institute of Physics. View full abstract»

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  • Soft-x-ray transmission photoelectron spectromicroscopy with the MEPHISTO system

    Page(s): 3106 - 3108
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    We complemented with data taken in transmission mode the recently described tests of the novel spectromicroscope MEPHISTO (Microscope à Emission de Photoélectrons par Illumination Synchrotronique de type Onduleur). Transmitted x rays were converted by a photocathode into photoelectrons, which were subsequently electron-optically processed by the spectromicroscope producing submicron-resolution images. Test images demonstrated excellent contrast. © 1998 American Institute of Physics. View full abstract»

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  • High resolution inelastic x-ray scattering spectrometer at the advanced photon source

    Page(s): 3109 - 3112
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    We have commissioned a new instrument for high resolution inelastic x-ray scattering on the inelastic scattering beamline of the Synchrotron Radiation Instrumentation Collaborative Access Team on sector 3 of the Advanced Photon Source. So far, the instrument is set up at 13.84 keV with a total energy resolution of 7.5 meV and a momentum resolution of ≤0.1 Å-1. We present technical details of the instrument, which includes an in-line monochromator, a focusing mirror, and a focusing analyzer. The performance of the instrument was demonstrated in studies of phonons in diamond and chromium. © 1998 American Institute of Physics. View full abstract»

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  • 5–20 keV laser-induced x-ray generation at 1 kHz from a liquid-jet target

    Page(s): 3113 - 3117
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    We report ultrashort pulse, 1 kHz repetition rate x-ray generation in the 5–20 keV spectral region, induced by the interaction of laser radiation with copper nitrate solution and ethylene glycol liquid-jet targets. The characteristics of the copper nitrate source are relevant for application to time-resolved x-ray diffraction studies as well as for spectroscopic x-ray absorption studies. The x-ray sources were operated uninterrupted for in excess of 5 h with no detectable buildup of debris on the associated optics. The x-ray flux generated by both sources is estimated to be of the order of 106photons s-1 sr-1 in the 5–20 keV region. The spectra have been measured with both a PIN photodiode, and with transmission measurements taken using aluminum filters. We find that the plasma emission has a broadband component attributed to bremsstrahlung emission, with the bulk of the x-ray emission emitted from the chamber lying between 5 and 20 keV for both sources. The copper nitrate emission, however, delivers a dominant emission peak at 9 keV, attributed to the characteristic K emission of copper. © 1998 American Institute of Physics.   View full abstract»

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  • Fast pulsed hollow cathode capillary discharge device

    Page(s): 3118 - 3122
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    A fast pulsed capillary discharge device has been developed and implemented. The device combines the features of a transient hollow cathode discharge with the inherent characteristics of the capillary discharge, to obtain VUV to XUV radiation with ns rise time. The discharge operates in a 0.8 mm inner diameter alumina capillary, at 10–30 kV applied voltage. On axis discharge initiation is assisted by electron beams, which are characteristic of the hollow cathode effect. A short, 5 ns full width at half maximum XUV pulse is produced in association with a ∼1 kA, 5 ns current pulse. © 1998 American Institute of Physics. View full abstract»

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  • Michelson fiberoptic accelerometer

    Page(s): 3123 - 3126
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    An all fiberoptic accelerometer, based on Michelson interferometry, has been developed theoretically and experimentally. It makes use of an oscillating mass suspended by a transduction fiber in a mass support. The interferometric configuration is formed by a 3 dB single-mode fiberoptic beam splitter, on two distal endfaces of which high-reflectance aluminum films were directly coated and served as reflecting mirrors. An ac phase tracking modulation–demodulation scheme has been employed to process the signal. The performance of a prototype of the accelerometer has been investigated, and the results indicated that the measured frequency spectrum is qualitatively consistent with the theoretical prediction, and the detected output wave forms are also in good agreement with that of the applied simulation signals. In addition, the constraint on the lateral movement of the acceleration-sensitive mass with two specific diaphragms has been experimentally verified, nevertheless, it needs to be optimized further. © 1998 American Institute of Physics. View full abstract»

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  • A simple high pressure flow cell for on-line absorption, Raman, and time resolved laser induced fluorescence spectroscopy in supercritical fluids

    Page(s): 3127 - 3131
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    A versatile spectroscopic flow cell for high pressure liquids and supercritical fluid solutions is described. The cell is capable of being coupled to either standard or fiber optic spectrometers. There are two perpendicular optical paths that are adjustable in length and aperture diameter. The cell has shown it can be used for absorption, emission, or scattering spectroscopy. The design is simple, inexpensive, serviceable, uses conventional materials, and is self aligning. With apertures of 5.7 mm the cell has been tested to pressures up to 500 atm and temperatures up to 90 °C. However, the cell would allow usage at higher temperatures and pressures if desired. © 1998 American Institute of Physics. View full abstract»

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  • An intense atomic hydrogen source with a movable nozzle output

    Page(s): 3132 - 3135
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    The fabrication and operation of a stable and intense source of atomic hydrogen from an easily movable nozzle is described in detail. The source uses a well-known air-cooled, extended cavity microwave source using molecular hydrogen, but conducts the dissociated atoms to the experimental interaction region via inert Teflon “spaghetti” tubing. A resulting collimated beam with a dissociation fraction exceeding 0.8 and with an average number density of atomic hydrogen of 6×1012cm-3 at a distance of 2 mm from the exit of the source is obtained. This source of H is attractive, because it is movable and easily interfaced into beam–beam type experiments. © 1998 American Institute of Physics. View full abstract»

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  • Advances in Stark effect measurements in a molecular beam Fourier transform microwave spectrometer

    Page(s): 3136 - 3141
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    For the first time Stark experiments in a pulsed nozzle Fourier transform microwave spectrometer are successfully performed with the pulsed molecular beam parallel to the resonator axis, together with a new geometry for the Stark electrodes which prevents line broadening due to E-field inhomogeneity. The coaxially oriented beam-resonator arrangement, introduced in the 1990s, is known to provide a considerable improvement in resolution and sensitivity in comparison to the perpendicular geometry, but Stark effect experiments performed in a microwave cavity, using the conventional cubic electrode geometry with this arrangement, suffer from an inhomogeneous field distribution. This gives rise to broadened profiles of the Stark shifted lines and a persistent zero-field line. The linewidth achieved with our new configuration is now close to the typical value found in the absence of a Stark field: less than 10 kHz at 10 GHz half width at half height, which makes the system very suitable for yielding precise values of the dipole moment, a piece of chemical information especially important in understanding both structure and charge distribution of molecular complexes. The performances of the novel design electrodes and the improvements achieved are demonstrated by several examples. © 1998 American Institute of Physics. View full abstract»

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  • Background correction in electron-ion coincidence experiments using a self-optimizing, pseudorandom count generator

    Page(s): 3142 - 3145
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    A technique is described whereby an estimate of the false coincidence signal, suitable for background correction of data acquired in a coincidence experiment, is obtained by using a pseudorandom pulser to generate a stream of “false” start events. The statistical properties of this simulated source are adjusted to mimic those of the real source of electron start events. False ion coincidences with the simulated starts are measured concurrently with the real coincidence signal, with the mean count rate of the pseudorandom pulse source automatically tracking that of the true electron start events. In this manner any long term instrumental drifts during the course of an extended experimental measurement will similarly affect both the real and simulated coincidence data. Subtraction of the simulated background of false coincidences from the real coincidence data then yields an improved estimate of the true coincidence signal. © 1998 American Institute of Physics. View full abstract»

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  • Polarization lifetime near an induced depolarizing resonance

    Page(s): 3146 - 3148
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    The time dependence of the polarization of a stored proton beam was measured near an induced depolarizing resonance. The resonance was created by a magnetic field which oscillated along the beam axis. The distance to the resonance was varied by changing the frequency of the oscillating field. The resonance was approached from either side and the time dependence of the polarization was found to be symmetric with respect to the resonance, and in agreement with an earlier measurement that involved an intrinsic depolarizing resonance. © 1998 American Institute of Physics. View full abstract»

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  • Parameters of the discharge plasma of surface-plasma H- ion sources

    Page(s): 3149 - 3154
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    The plasma of a high-current hydrogen–cesium glow discharge of planotron and Penning H- ion sources was studied with the use of spectroscopic methods. The elemental and charge compositions of the plasma were determined. The temperature of hydrogen atoms was determined and the electron density was estimated. The density variation of hydrogen atoms, cesium atoms, and molybdenum atoms (electrode material) and cesium ions during the discharge pulse with the space resolution along two coordinates was observed. Blocking up of cesium atoms and ions and molybdenum atoms near the cathode surface was found. The radiation energy of the discharge plasma was measured within the visible spectral range. © 1998 American Institute of Physics. View full abstract»

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  • Background measurement with constant detector geometry in positronium three quanta annihilation experiments

    Page(s): 3155 - 3158
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    In experiments on positronium annihilation in three photons, the background rate of triple-coincident events is usually measured by performing a separate counting run, in which one of the detectors is moved out of the three quanta annihilation plane. A thorough analysis shows that this approach can entail systematic errors and we suggest an alternative procedure. By employing a few auxiliary coincidence modules, the new approach avoids the necessity of a further dedicated counting run with modified detector geometry. Experimental results confirm the viability and accuracy of the method. © 1998 American Institute of Physics. View full abstract»

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  • Natural crystals selection process for neutron diffraction applications

    Page(s): 3159 - 3164
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    This work aims to show a selection process for natural crystals that considers the major characteristics and performance as gratings for neutron monochromators using the neutron diffraction technique. A total of 19 crystals have been selected and classified regarding their adequacy for use as neutron diffraction devices. Applying special criteria, method and the rocking curve technique, the measurements have been performed and the theoretically available values compared with the experimental results, obtained directly from a neutron diffractometer in operation at the IEA-R1 (5 MW) nuclear research reactor. The choice for natural crystals, expanding the operational range of the neutron diffraction instruments, is related with the purpose of getting monochromatic neutron sources suitable for the applications. The neutron has proved to be the most powerful microscopic testing particle in condensed matter studies and in many other areas of application. © 1998 American Institute of Physics. View full abstract»

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  • Diagnostic method for radial electric fields in Tokamaks by the observation of ripple-trapped ions

    Page(s): 3165 - 3175
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    Weakly collisional ions trapped in the toroidal field ripples at the outer plasma edge of a Tokamak can be prevented from escaping the plasma due to grad B drift by a counteracting radial electric field. This leads to an increase in the density of ripple-trapped ions, which can be monitored by the analysis of charge exchange neutrals. The minimum radial electric field Er necessary to confine ions with energy E and charge q (q=-1: charge of the electron) is Er=-E/(q×R), where R is the major radius at the measuring point. Slowing-down ions from neutral injection are usually in the right energy range to be sufficiently collisionless in the plasma edge and show confinement by radial electric fields in the range of tens of kV/m. The density of banana ions is almost unaffected by the radial electric field indicating that the change in the fluxes of ripple-trapped ions is, indeed, caused by the radial electric field and not by direct changes in plasma parameters. Single particle calculations for real ASDEX Upgrade geometry and magnetic fields but with an assumed electric field profile give a rule of thumb estimate of the electric field strength. They also make plausible the reason why the charge exchange flux may react in less than 100 μs to an abrupt onset of a radial electric field with a halfwidth of at least the Larmor diameter of the particles in question and thus make this measurement an interesting tool for the investigation of the edge radial electric field. © 1998 American Institute of Physics. View full abstract»

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  • A novel electro-optical probe to diagnose plasma uniformity

    Page(s): 3176 - 3180
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    A novel electro-optical probe (EOP) has been developed to characterize the spatial uniformity of various plasma parameters. Spatially resolved electron density and energy distribution function, neutral and charged particle densities, as well as ion flow velocity are determined by the EOP. The design of the EOP combines a Mach probe, back-to-back charge collectors, and a collimated optical fiber. The light collection angle of the optical fiber is limited by recessing the fiber in a ceramic tube. The line-of-sight integration length of the plasma emission is bounded by the charge collector disk. A spatial resolution of 2.4 cm is obtained by the present design of the EOP. The ion flow velocity perpendicular to the charge collector surface is determined by the ratio of the ion saturation currents of the two counter facing charge collectors. Localized actinometry, that combines spatially resolved optical emission spectra and electron energy distribution functions, is used to determine the density of atomic chlorine and fluorine radicals. The spatial distribution is obtained by scanning the EOP across the plasma volume. © 1998 American Institute of Physics. View full abstract»

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  • Versatile millimeter-wave interferometer with two frequencies in the divertor region of JT-60U

    Page(s): 3181 - 3185
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    A millimeter-wave interferometer having a capability of concomitant electron temperature measurement, based on the electron cyclotron absorption (ECA) technique, has been developed for divertor diagnostics in JT-60U. Three lines of sight, which pass through the X point horizontally, the inboard divertor and the outboard divertor, are chosen. Two transmitter/receiver units with frequencies of 217 and 183 GHz are employed in order to eliminate the spurious vibration effect using a two color scheme. The two independent units are also arranged to enable two sight line measurements without the vibration compensation. Furthermore, these units allow us to apply the simultaneous ECA diagnostic. Due to the complexity of the transmission line inside the tokamak, the insertion loss is as large as 65 dB. However, the interferometer system can be operated with the signal-to-noise (S/N) ratio of about 20 dB due to the low equivalent input noise of -90 dB m. The measurements performed for several types of the JT-60U discharges indicate the feasibility of the system and the rapid reduction of the electron density near the X point at the high confinement mode transition is first demonstrated. © 1998 American Institute of Physics. View full abstract»

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  • Imaging of laser produced plasma at 1.43 keV using Fresnel zone plate and Bragg–Fresnel lens

    Page(s): 3186 - 3193
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    X-ray imaging of plasmas with a resolution on the order of 1 μm could not be achieved with pinholes because the light flux on the detector would be too low. We tested two different types of diffractive lenses derived from the circular grating based on the Fresnel zones. Compared to pinholes, they can have an equivalent diameter of about 100 μm with a resolution of about 1 μm. The two kinds of devices tested were: (1) a transmission phase Fresnel zone lens (PFZL) associated with a multilayer mirror; (2) a reflective Bragg–Fresnel lens (BFL) which combines a multilayer mirror and the grating. The PFZL works at normal incidence by transmission; an additional mirror is used to reflect only a small bandwidth within the spectrum; the angle of reflection of the multilayer of the imaging beam on the mirror is set as to adjust the center of the useful bandwidth. The BFL works at fixed grazing incidence and we only use an off-axis part of the BFL in order to avoid the illumination of the detector by zeroth order diffracted light. We computed the spatial response of both devices and found that the aberrations were very low within an object field of 100 μm for the BFL device and 1 mm for the PFZL device. Their theoretical resolution is given by the width of their last zone: below 0.1 μm for the BFL device and 0.4 μm for the PFZL device. We also made images of plasma with both devices and using back-lighted grids, we obtained a resolution on the order of 4–5 μm. In the discussion, we try to explain the difference between the theoretical and experimental results. © 1998 American Institute of Physics. View full abstract»

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  • Production and acceleration of tracer encapsulated solid pellets for particle transport diagnostics

    Page(s): 3194 - 3198
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    A new method for producing a tracer-encapsulated solid pellet (TESPEL) has been developed for a local deposition of the tracer ions in the core plasma and an accurate measurement of the particle transport. The method allows manufacturing of TESPELs in the form of polystyrene shells containing lithium hydride inside as a tracer. The TESPEL acceleration has been successfully performed and photos of the pellets in flight confirmed the TESPEL integrity. For the pellets with diameter 300–400 μm and wall thickness 40–50 μm the pellet fragility becomes insignificant. Calculation of the TESPEL ablation rate has showed that the achieved pellet velocities and sizes are appropriate for the injection into a medium size plasma. It was proposed to fractionate the tracer contents in order to provide better localization of the deposited tracer ions in the plasma. The data obtained in these experiments have proved that injection of the TESPEL made from the plastic shells can be a promising tool for the particle transport diagnostics.© 1998 American Institute of Physics. View full abstract»

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  • Torsion cantilever as magnetic torque sensor

    Page(s): 3199 - 3203
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    A macroscopic cantilever for capacitive torque magnetometry has been developed and tested. It is based on torsion arms in order to obtain better damping against external vibrations than with ordinary cantilevers of similar size but anchored on one side. Microfabricated out of silicon-on-insulator wafers by deep reactive ion etching, the sensor consists of a long (14 mm) and thin (40 μm) cantilever with two capacitive plates, anchored at its center to a rigid frame by two torsion bars having a rectangular cross section (80×40 μm2). By comparing the theoretical and experimental resonance frequencies in three different oscillation modes, we show that the elastic properties of the torque sensor can be evaluated with good accuracy. Calibrations performed with a piece of Fe2O3 audiotape and a cylindrical NdFeB magnet yield a torque sensitivity better than 5×10-13N m under optimized conditions. This device can also be used as a sensitive Gauss meter to detect magnetic fields down to 10 nT. © 1998 American Institute of Physics. View full abstract»

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  • An alternative approach to vector vibrating sample magnetometer detection coil setup

    Page(s): 3204 - 3209
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    Vector vibrating sample magnetometers (VSMs) can present problems with respect to angular dependent calibration and positional dependency when they are used for measurements on thin film samples, which have dimensions comparable to or larger than the sample–coil distances. The problems are due to the fact that in conventional VSMs the sample is rotating with respect to the coils, when performing angular dependent measurements. In this article a solution is presented based on a setup of VSM detection coils, whose position is linked to that of the sample. Together with a newly designed sample holder, the above mentioned problems are prevented or reduced. The vector detection coil system shows a relatively small error in the determination of the magnetization vector (±1% in the absolute value and ±0.6° in the angle). Furthermore, it has a relatively small positional dependency (1% per mm) combined with a sufficient sensitivity (1 nA m2 or 1 μemu at 10 s time constant) and a capability of using samples up to 10×10 mm2. The improved sample holder for thin film measurements reduces positional problems while, at the same time, reducing the background signals of the holder (to 10 pA m2 per kA/m or 7.958×10-10emu/Oe). © 1998 American Institute of Physics. View full abstract»

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  • Thulium-doped intrinsic fiber optic sensor for high temperature measurements (≫1100 °C)

    Page(s): 3210 - 3214
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    The need to achieve higher temperature performance from fluorescence-based optical thermometers has prompted the investigation of a range of rare-earth doped materials. In this work, results are presented on the use of a thulium-doped fiber-based system. The performance of the thermometer is presented, and stable measurements at temperatures up to 1250 °C are reported using the fluorescence lifetime approach. © 1998 American Institute of Physics. View full abstract»

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  • Optical fiber velocimetry: A technique for measuring velocity in two-dimensional flows

    Page(s): 3215 - 3222
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    In this article we describe a new technique, optical fiber velocimetry (OFV), to instantaneously measure two components of velocity at a point in freely suspended flowing liquid films. The technique relies on the measurement of displacements of an optical fiber tip which is coupled to the flowing film. The deflection of the fiber tip is proportional to the velocity and it behaves as a simple harmonic oscillator. Thus the low frequency response of the fiber gives direct measurements of the flow velocity. A statistical test using data acquired simultaneously by the fiber and by a laser Doppler velocimeter shows good agreement between the two techniques. Velocity power spectra measured in the wake of a von Karman street and in two-dimensional (2D) grid turbulence using the OFV also compare favorably with the laser Doppler velocimeter. The OFV technique is simple and robust, allowing it to be used in a wide variety of flows that have strong 2D characteristics. New prospects of using multiple fibers to measure circulation and velocity correlations at several separated spatial points are discussed. © 1998 American Institute of Physics. View full abstract»

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Review of Scientific Instruments, published by the American Institute of Physics, is devoted to scientific instruments, apparatus, and techniques.

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Albert T. Macrander
Argonne National Laboratory