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Review of Scientific Instruments

Issue 8 • Date Aug 1998

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Displaying Results 1 - 25 of 47
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Electrical resistance standards and the quantum Hall effect

    Page(s): 2823 - 2843
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    This review of electrical resistance standards begins with a description of classical standard resistors and their limitations. Methods of comparing resistance are described; these include bridges based on cryogenic current comparators capable of achieving statistical uncertainties approaching one part in 1010 in the measurement of resistance ratios. Such reproducibility is nearly two orders of magnitude smaller than the overall uncertainty of the most accurate determinations of the ohm from its SI definition via the calculable capacitor. The quantum Hall effect can provide an invariable reference standard of resistance linked to the fundamental physical constants. Many factors, however, limit the accuracy of practical realizations of quantized Hall resistance standards. Ultimately, the accuracy of a specific realization must be confirmed by comparison with similar standards; methods for doing this and the resulting agreement are presented. The ac techniques used in the determinations of the SI ohm by means of the calculable capacitor are now being applied to accurately link the quantized Hall resistance to the impedance of standard capacitors and thereby to provide a new reference standard of capacitance. © 1998 American Institute of Physics. View full abstract»

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  • Bragg–Fresnel optics for hard x-ray microscopy: Development of fabrication process and x-ray characterization at the Advanced Photon Source

    Page(s): 2844 - 2848
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    Results are presented on development of processes for fabricating linear and circular Bragg–Fresnel lenses (BFLs) on Si and III–V compound material substrates, and on x-ray characterization of linear BFLs at the Advanced Photon Source (APS). Processes were developed for fabricating long (zone length ≫5 mm) linear BFLs on Si with enhanced capability for focusing high-energy x rays. By stitching together 20 sequentially exposed 400-μm-long linear BFLs, we were able to fabricate 8-mm-long linear BFLs with 0.5-μm finest zone width. BFLs were also fabricated on III–V compound semiconductor substrates GaAs and InP, with improved process control due to the substantially reduced zone thickness required (∼50% less than Si). Reduction of the zone aspect ratio (thickness/width) lessens the demand on the process technology, and may lead to higher lens resolution and pattern transfer accuracy. A process was explored to fabricate BFLs on a GaAs/AlGaAs heterostructure incorporating a built-in “etch stop” layer to ensure uniform zone thickness. Experimental characterization of the focusing properties of a field-stitched 8-mm-long linear BFL on Si (zone aperture=150 μm) was conducted at APS undulator beamline 1-ID-C using 10-keV x rays. Based on measured focal plane intensity distribution, the focus was estimated to be 1.2 μm, comparable to the geometrically demagnified source size of ∼1 μm. Lens efficiency was estimated to be ∼30%. Work is underway to incorporate the BFL-microprobe in x-ray microdiffraction and fluorescence microscopy experiments to study spatially confined complex materials. © 1998 American Institute of Physics. View full abstract»

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  • In situ calibration of a flat-field grazing incidence spectrograph with an x-ray charge-coupled device camera using a transmission grating and a laser-produced plasma for x-ray laser research

    Page(s): 2849 - 2853
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    An in situ calibration experiment of a soft x-ray spectrograph for x-ray laser research has been performed. The calibrated spectrograph was a flat-field grazing incidence spectrometer with an x-ray charge-coupled device camera. The absolute sensitivity of the spectrograph was obtained for the wavelength range from 2.6 to 4.0 nm using a transmission grating spectrograph as a reference spectrograph set along the axial direction of a line-focused laser-produced plasma. The absolute sensitivity determined in this work shows nearly the same value as that deduced from the calibration experiment using synchrotron radiation. © 1998 American Institute of Physics.   View full abstract»

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  • A white-light Michelson interferometer in the visible and near infrared regions

    Page(s): 2854 - 2858
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    A white-light Michelson interferometer in the visible and near infrared regions is described which can obtain the cross-correlation interferogram between the incident light and the transmitted light through samples or optical components. By comparing the autocorrelation interferogram of the incident white light with the cross-correlation interferogram between the incident light and the transmitted light, we can obtain linear response functions of samples or optical components with femtosecond time resolution. Fourier analysis of the interferograms gives also the complex optical constants of the samples without relying on the Kramers–Kronig relation. © 1998 American Institute of Physics. View full abstract»

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  • Imaging spectrometer based on an acousto-optic tunable filter

    Page(s): 2859 - 2867
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    This article describes an imaging spectrometer developed for remote sensing applications. The instrument consists of an acousto-optic tunable filter (AOTF), a high sensitive charged coupled device camera and optic lens. The selected AOTF was designed to have a large entrance aperture and to diffract light between 600 and 900 nm with a high spectral resolution. The signal was digitized by the camera and acquired with a developed WINDOWS executable software which drives the instrument. The spectrometer has been operated in a classical mode and in an imaging mode for its evaluation. In the imaging mode, images including different types of targets were acquired in reflection and transmission mode and were used to investigate image homogeneity, spatial resolution, chromatic and geometric aberrations, sensitivity and reliability. Spectra have been extracted from images and were successfully compared with spectra from the same sample area obtained with classical nonimaging spectrometers. This confirms the ability of this instrument to clear up many problems in surface analysis, particularly in the case of laboratory and field measurements used in remote sensing studies. © 1998 American Institute of Physics. View full abstract»

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  • A simple technique for investigating whispering gallery modes in optical fibers

    Page(s): 2868 - 2870
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    A simple technique for investigating whispering gallery modes in optical fibers is described. Unlike the conventional technique of winding a fiber around a mandrel, a bent fiber is produced simply by inserting it inside a commercial glass tube. The fiber naturally assumes a semicircular shape at the bend. It is shown that the loss spectrum due to whispering gallery modes is insensitive to small variations in the glass tube diameter. The glass tube with the bent fiber inside is used to fabricate a rugged interferometric temperature sensor which can be moved around even during measurements. Application of the technique for quality control is also demonstrated by measuring the variation of fiber buffer properties along the length of fiber. © 1998 American Institute of Physics. View full abstract»

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  • Measurement system for optical Kerr effect induced by continuous wave laser

    Page(s): 2871 - 2874
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    An experimental technique was developed for studying the optical Kerr effect induced by a cw Ar+ laser with 500 mW output. A Pockels cell was used for modulating the pump laser so that the polarization changed periodically between the vertical and horizontal plane. The dielectric anisotropy thus induced in a sample liquid was probed in the ellipsometry with a He–Ne laser. The system was applied to nitrobenzene and p-n-hexyl p-cyanobiphenyl (6CB), a nematogen in the isotropic phase. The observed birefringence showed a linear dependence on the pump laser intensity and the gradient yielded the Kerr constant: B=5.75×10-14V-2 m at 30 °C in nitrobenzene and B=6.72×10-12(T-T*)-1V-2 m in 6CB, T* being the virtual transition temperature to the nematic phase. This technique can be used for investigating the relaxation of molecular orientation in frequency domain. © 1998 American Institute of Physics. View full abstract»

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  • Advances in the transient dc photocurrent technique for excited state dipole moment measurements

    Page(s): 2875 - 2887
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    Recent advances in the transient dc photocurrent technique for measuring excited state dipole moments, developed in our group, are discussed. A variety of approaches with detailed analyses of their advantages and disadvantages including cell design, circuit construction tricks, the data acquisition procedure, calibration, and the theoretical treatment of different conditions, are presented. Sensitivity, time resolution limitations, and newly developed features, such as the signal’s dependence on light polarization as well as charge separation at interfaces are outlined. Dipole moments of a few molecules (diphenylcyclopropenone, bianthryl, dimethylaminonitrostilbene, Coumarin 153, and fluoroprobe) suitable for calibration purpose are reported—some of them for the first time. © 1998 American Institute of Physics. View full abstract»

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  • A peristaltic injection nozzle for collinear laser and molecular beams

    Page(s): 2888 - 2891
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    A novel gas nozzle design that allows for collinear laser and molecular beams is described. Unlike conventional nozzles that open and close to limit the gas flow into a vacuum chamber, this nozzle opens to release a small volume of gas into the chamber. Gas pulses of 300 μs duration and 65±5 μs opening times have been obtained. When room-temperature H2 is used as the source gas, the rotational temperature was found to be 175±12 K, whereas when room-temperature D2 was used, the rotational temperature was found to be 104±7 K. The collinear optical and molecular beam path provided in this design may be useful in photodissociation experiments, the study of atomic and molecular collisions, Rydberg state lifetime measurements, and vacuum ultraviolet generation by nonlinear mixing in gases. © 1998 American Institute of Physics. View full abstract»

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  • Experimental methods in radioactive ion-beam target/ion source development and characterization

    Page(s): 2892 - 2897
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    We have developed off-line experimental techniques and apparatuses that permit direct measurement of effusive-flow delay times and ionization efficiencies for nearly any chemically reactive element in high-temperature target/ion sources (TIS) commonly used for on-line radioactive ion-beam (RIB) generation. The apparatuses include a hot Ta valve for effusive-flow delay-time measurements, a cooled molecular injection system for determination of ionization efficiencies, and a gas flow measurement/control system for introducing very low, well-defined molecular flows into the TIS. Measurements are performed on a test stand using molecular feed compounds containing stable complements of the radioactive nuclei of interest delivered to the TIS at flow rates commensurate with on-line RIB generation. In this article, the general techniques are described and effusive-flow delay times and ionization efficiency measurements are reported for fluorine in an electron-beam plasma target/ion source developed for RIB generation and operated in both positive- and negative-ion extraction modes. © 1998 American Institute of Physics. View full abstract»

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  • Saturation of multiplication mechanism in silicon avalanche photodiodes used for single electron detection

    Page(s): 2898 - 2901
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    We have examined the multiplication factor of silicon avalanche photodiodes designed for fast timing detection of monoenergetic electrons. The multiplication mechanism was found to be saturated. The highly concentrated space charge generated by a primary electron causes the saturation. This was confirmed by a Monte Carlo simulation of electron trajectories in silicon and an experiment exploiting a subpicosecond laser pulse with a variable illuminating spot size to simulate an electron bombardment. © 1998 American Institute of Physics. View full abstract»

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  • The dynamic properties of the preset count digital rate meter algorithms

    Page(s): 2902 - 2908
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    The exact analytical expressions for the response times of the preset count moving average and exponential digital rate meter algorithms to sudden changes of count rate have been obtained. Generalized concepts of the response time equivalence and steady-state statistical fluctuations equivalence allowed a detailed comparison of the two classes of digital rate meter algorithms. The conditions for complete equivalence, i.e., equal both response times and steady-state statistical fluctuations for the two classes of algorithms have been identified. The similarities and differences between the preset time and preset count digital rate meter algorithms are indicated. © 1998 American Institute of Physics. View full abstract»

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  • A new method of finding the pole profile in quadrupole magnets for obtaining high field quality

    Page(s): 2909 - 2911
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    The field quality in quadrupole magnets depends mainly on the pole profile. One often uses a circular pole of optimized radius to reduce the field errors. Hyperbolic profiles which are modified at the pole edges are also used. In the design of these magnets one first chooses a profile and then calculates the error harmonics. Here we have described a new method in which we choose the error harmonics first and then find the profile thus ensuring that the field quality is good. The method can also be applied to other multipole magnets. © 1998 American Institute of Physics. View full abstract»

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  • Gas-coupled laser acoustic detection at ultrasonic and audio frequencies

    Page(s): 2912 - 2917
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    Airborne acoustic waves have been detected by a laser-beam deflection technique in both the ultrasonic and audio frequency ranges. For ultrasonic applications, a probe beam is directed parallel to the surface of a sample. Ultrasonic waves in the solid are detected when an acoustic wave is radiated from the surface into the ambient air, where the density variations cause a beam deflection. Gas-coupled laser acoustic detection (GCLAD) has been used to record well-resolved through-transmission and surface-acoustic wave forms in various materials. GCLAD has also been incorporated into a C-scanning system where it has been used to image subsurface flaws in graphite/polymer composite panels. Because the laser beam is not reflected from the sample surface, the technique is not dependent upon the surface optical properties of the material under investigation. It is particularly useful for testing graphite/polymer composites and other materials with rough surfaces. The beam-deflection technique has been tested quantitatively in the kHz frequency range by passing a probe beam through a cylindrical resonator. The acoustic spectrum of the resonator was measured from 4 to 13.5 kHz by scanning the frequency of a source and recording the acoustic field with both a microphone and the beam-deflection system. The acoustic fields of the lower-frequency modes are well known and enable both qualitative and quantitative tests of the beam-deflection technique. Measurements on the lowest-frequency plane-wave mode were used for absolute calibration of the microphone. The noise level of the beam-deflection measurements at 4.3 kHz was found to be 0.05 nrad (rms), corresponding to an acoustic pressure of 0.005 Pa (rms). © 1998 American Institute of Physics. View full abstract»

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  • Measurements of the thermodynamic equation of state via the pressure dependence of thermophysical properties of air by a thermal-wave resonant cavity

    Page(s): 2918 - 2923
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    The thermodynamic equation of state for ambient air was investigated by means of a thermal-wave resonant cavity in the pressure range between 40 and 760 Torr and at ambient, or near-ambient, temperature conditions. The pressure dependencies of the thermal diffusivity, conductivity, effusivity, and thermal-wave-source infrared emissivity were measured. The experimental results were found to be consistent with the ideal gas law for air in the foregoing pressure and temperature range. It was observed that the thermal diffusivity of air increases linearly with decreasing cavity pressure. The experimental curves obtained from the four channels (amplitude, phase, in-phase, and quadrature) of the thermal-wave signal-demodulating lock-in amplifier were fitted to thermal-wave resonant cavity theory, and the thermal conductivity and effusivity of the air in the cavity were also calculated as functions of pressure. Within the experimental error range, the thermal conductivity was found to be independent of pressure and equal to (28.9±0.2)×10-3W/m K at 309–310 K. The thermal effusivity of air exhibited a linear increase with increasing pressure at approximately constant ambient temperature. In addition, the infrared emissivity of the resistively heated Cr–Ni thermal-wave thin-film strip source (cavity wall) was measured as a function of the source rms voltage at several pressures. The obtained values, ranging from 0.094 to 0.108, showed that the emissivity decreases with decreasing cavity pressure. © 1998 American Institute of Physics.   View full abstract»

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  • Characterization of erbium-doped intrinsic optical fiber sensor probes at high temperatures

    Page(s): 2924 - 2929
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    The use of rare-earth-doped fibers for high temperature measurement has shown considerable promise. In this work, studies of the key characteristics of the performance of Er-doped fiber-based thermometer probes using the fluorescence decay time technique were carried out. Results showed the effects of fluorescence intensity as a function of doped fiber length and temporal and dopant concentration features of the probes. Annealing effects were seen to occur, and a satisfactory stable performance at up to 1100 °C was reported from this material, yielding improvement on results obtained with Nd-based systems. © 1998 American Institute of Physics. View full abstract»

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  • Determination of local high temperature excursion in an intrinsic doped fiber fluorescence-based sensor

    Page(s): 2930 - 2934
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    A fluorescence-based intrinsic doped fiber temperature sensing system for determining local extremes of high temperatures has been demonstrated in this work. Data on this temperature rise are analyzed using a mathematical relationship, based on a correlation coefficient ratio scheme, to relate to the reduced fluorescence decay time information thus associated with the hot part of the fiber. In schemes incorporating this mathematical analysis, two separate sensor configurations have been demonstrated, one of which is to use short, single lengths of fiber spliced into a network and the other a long single length of doped fiber, using both Nd and Er doped fiber materials. The results show that the correlation coefficient ratio, R, will deviate from and be smaller than unity with the increase of the temperature of the localized region where the heat is applied, providing the mechanism for a simple high temperature excursion detection system. © 1998 American Institute of Physics. View full abstract»

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  • Optimal operating conditions of the impulse diode thermometer

    Page(s): 2935 - 2938
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    Statistical analysis of experimental results obtained by implementing an impulse diode thermometer with a sensor at constant temperature yields the dependence of relative error in determining the voltage across the diode–sensor ends upon the voltages which figure as parameters. Very good agreement of the experimental results with analytically obtained estimates completely confirms both applied methods. In such a way uniquely determined operating conditions of the impulse diode thermometer with maximal resolution and minimal error are obtained. © 1998 American Institute of Physics. View full abstract»

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  • Design and validation of guarded hot plate instruments for measuring heat flow between evacuated plane-parallel glass surfaces

    Page(s): 2939 - 2947
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    This article discusses the design and construction of guarded hot plate instruments for measuring the heat flow through an evacuated space between plane-parallel glass surfaces. In this structure, the insulating region is surrounded by two pieces of relatively highly conducting material. High resolution measurements of heat flow using these instruments therefore requires the detection of quite small temperature differences (10-4K) between the metering piece and the guard. The instruments are calibrated, and the linearity evaluated, by measuring radiative heat transfer through the evacuated space between uncoated soda lime glass sheets; this is because this heat flow can be calculated to high accuracy from the infrared optical properties of the glass. The level of parasitic heat flow in the instruments is estimated by measuring radiative heat flow between glass surfaces coated with very low emittance layers, such as evaporated gold. These instruments operate over a range of temperatures from 0 to about 70 °C. It is shown that the heat flow between evacuated glass surfaces can be measured with these instruments to high resolution (∼10 μW) and high accuracy (∼1%) over an area of ∼1 cm2. The departures from linearity, and the level of parasitic heat flow, are within the measurement resolution. For a temperature difference across the sample of 20 K, the measurement resolution corresponds to an uncertainty in the thermal conductance of the sample of ∼0.005 W m-2 K-1. © 1998 American Institute of Physics. View full abstract»

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  • Vapor volume fraction, flow regime, and vapor velocity inference using fluid conductivity measurements

    Page(s): 2948 - 2955
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    An array of conductivity sensors is presented that infers the vapor volume fraction, flow regime, and vapor velocity in a two-phase flow. The frequency response of the sensors is up to 40 Hz, which allows for dynamic signal processing to ascertain flow characteristics additional to the time average vapor volume fraction, such as the vapor velocity and flow regime. The sensor array, associated driving circuitry, and signal processing techniques are presented, and the performance of the array is evaluated for an air–water flow at one atmosphere and a steam water flow at 0.095 MPa. © 1998 American Institute of Physics. View full abstract»

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  • A confocal fiber-coupled single-lens theta microscope

    Page(s): 2956 - 2963
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    A confocal theta microscope using a single water-immersion objective lens is described. The system is based on the Zeiss Axioplan universal microscope, such that the illumination light is coupled into, and the detected light out of, the microscope optics via optical fibers attached to the reflector slider of the microscope. Conventional wide-field, laser-scanning confocal, confocal theta, and 4Pi-confocal theta microscopy modes are available with the system. As the design can be easily adapted to other microscopes, objective lenses, and wavelengths, it allows confocal theta techniques to be implemented in many standard systems. The design constraints and specifications for the microscope are given, as well as a demonstration of its performance. © 1998 American Institute of Physics.   View full abstract»

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  • A scanning transmission x-ray microscope for materials science spectromicroscopy at the advanced light source

    Page(s): 2964 - 2973
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    Design and performance of a scanning transmission x-ray microscope (STXM) at the Advanced Light Source is described. This instrument makes use of a high brightness undulator beamline and extends the STXM technique to new areas of research. After 2.5 years of development it is now an operational tool for research in polymer science, environmental chemistry, and magnetic materials. © 1998 American Institute of Physics. View full abstract»

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  • Description of an x-ray microscope with 30 nm resolution

    Page(s): 2974 - 2977
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    The Aarhus x-ray microscope has been in operation for some years and has evolved into a scientific user facility, the activities of which include a wide range of applications. A technical description of the microscope is given with emphasis on problems that have general character for high precision instrumentation and soft x-ray equipment. © 1998 American Institute of Physics. View full abstract»

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  • Numerical removal of ring artifacts in microtomography

    Page(s): 2978 - 2980
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    Defective and insufficient calibrated detector elements introduce ring or half-circle artifacts in microtomographic image reconstructions. A computationally efficient numerical filter is presented which suppresses these defects by taking advantage of the particular appearance of ring artifacts in the Fourier transforms of the recorded sinograms. The performance of the filter is demonstrated on experimental data taken with high-energy synchrotron radiation in phase-contrast (outline) mode. © 1998 American Institute of Physics. View full abstract»

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Aims & Scope

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

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Editor
Albert T. Macrander
Argonne National Laboratory