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Review of Scientific Instruments

Issue 9 • Date Sep 1996

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Displaying Results 1 - 25 of 251
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • A practical direct current discharge helium absorption cell for laser frequency locking at 1083 nm

    Page(s): 3003 - 3004
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    We report the construction of a low pressure (∼0.5 Torr) helium direct current discharge cell to lock a 1083 nm InGaAs diode laser to the 2 3S–2 3P transition in helium using saturated absorption spectroscopy. The direct current discharge cell has the advantage of being radio frequency noise free. © 1996 American Institute of Physics. View full abstract»

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  • High‐resolution electric‐field‐induced second‐harmonic generation with ultrafast Ti:sapphire laser

    Page(s): 3005 - 3009
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    The technique of electric‐field‐induced second‐harmonic generation (EFISHG) has been extended by use of a femtosecond, quasi‐cw laser pump source. The effects of ultrashort pulse widths on the coherent EFISHG process have been examined and the analysis procedure used for nanosecond pulse EFISHG measurements is found to be suitable for femtosecond measurements in off‐resonant regions. A convenient method for measurement of the group velocity mismatch between the fundamental and second‐harmonic pulses in solutions has also been developed to accurately describe the femtosecond EFISHG process. Phase‐sensitive detection of the modulated second‐harmonic signals results in improvements in accuracy and sensitivity over existing nanosecond pulse experiments. This has been demonstrated with a measurement of Γ(-2ω; ω, ω, 0) of an organic molecule, 4‐nitroanisole. © 1996 American Institute of Physics. View full abstract»

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  • Nanosecond time‐resolved circular dichroism measurements using an upconverted Ti:sapphire laser

    Page(s): 3010 - 3016
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    Several years ago a time‐resolved circular dichroism technique for the far ultraviolet spectral region with submicrosecond (10-7 s) time resolution was developed using a xenon flash lamp probe source for measurements of circular dichroism (CD) signals. Recent improvements in Ti:sapphire lasers, providing the ability to frequency‐convert the fundamental outputs to produce second, third, and fourth harmonic pulses, allow single wavelength measurements of CD with nanosecond (10-9 s) time resolution over a broad spectral region (205–910 nm). This provides a powerful technique to study fast biophysical phenomena such as protein folding processes. In this article, the methodology and preliminary application of this new technique are presented. © 1996 American Institute of Physics. View full abstract»

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  • High‐resolution surface sensing device using Bragg diffraction from multiplexed holograms in photorefractive crystal

    Page(s): 3017 - 3020
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    A novel high‐resolution surface sensing device is developed and demonstrated, which utilizes Bragg diffraction from the volume holograms in the photorefractive BaTiO3 crystal. In this device, the angular information of a surface is obtained as a diffraction pattern from the multiplexed holograms stored in the crystal. The resolution of this device is as high as submilliradian due to the Bragg selectivity. Additionally, a new method of surface structure comparison between two samples is also demonstrated using this device, which is applicable to the nondestructive surface inspection of optical components. © 1996 American Institute of Physics. View full abstract»

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  • Performance of a high‐resolution, synchrotron‐based, small‐angle x‐ray scattering instrument

    Page(s): 3021 - 3034
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    We describe the construction and performance of a small‐angle x‐ray scattering (SAXS) instrument which we have used on several beam lines at the National Synchrotron Light Source. The analyzer crystal was a channel cut Si(1,1,1) designed for use at λ=1.54 Å with a measured efficiency of 60% and an angular resolution full width at half maximum of 0.001°. In the case of strongly scattering samples (i.e., powders), momentum transfer q between 1×10-4 Å≪q≪0.1 Å-1 could be studied with over eight decades of dynamic intensity range. We demonstrate the versatility of this instrument by performing scattering experiments on a variety of spherical latex samples spanning the size range from 50 to 800 nm, liquid crystal samples with sharp, asymmetrical Bragg peaks, and metal clusters with sizes less than 10 nm. Small‐angle x‐ray scattering data for the larger polystyrene samples is compared with light scattering data and theoretical structure factors, and the relative roles of instrument smearing, sample polydispersity, and interparticle interference are elucidated. In the case of the liquid crystal samples, the high resolution of the instrument allows structural features to be observed that were previously obscured by the instrumental resolution in other small‐angle neutron and synchroton‐based Kratky camera data taken on the same samples. © 1996 American Institute of Physics. View full abstract»

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  • An intense, broadband emission spectrum, thyratron‐gated nanosecond light source using a commercially available Xe short‐arc lamp

    Page(s): 3035 - 3038
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    We have developed a thyratron‐gated, high‐intensity nanosecond pulsed lamp using a commercially available Xe short‐arc lamp. A dc voltage higher than 10 kV is applied to the electrode gap through a high‐value resistor. A spark discharge in the electrode gap is generated by the trigger of the thyratron. Intense light pulses as large as 80 W (peak value) of 14–16 ns duration full width at half‐maximum was obtained repetitively from the Xe lamps. This lamp produced broadband emission spectrum (220–600 nm) according to discharge of Xe gas. Because discharge voltage of the pulsed lamp is much higher than that of a conventional dc lamp, a high electron‐temperature pulsed plasma is produced, resulting in enhancement of the UV component of the emitted light. The rich UV light from this lamp can be utilized as an excitation light source in time‐resolved spectroscopy. © 1996 American Institute of Physics. View full abstract»

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  • Experimental instrument for observing angle‐ and frequency‐scanned attenuated total reflection spectra

    Page(s): 3039 - 3043
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    An attenuated total reflection (ATR) instrument for the observation of angle‐ and frequency‐scanned ATR spectra has been constructed. Light characterized by various wave vectors and dispersed into a spectrum has been detected by a charge coupled device camera after reflection from a rotating mirror and a diffraction grating. Two elliptic mirrors and a prism‐sample unit have been set between the rotating mirror and the diffraction grating for the purpose of controlling the light path. The images obtained have been analyzed by a digital image processing system so that angle‐scanned ATR signals are obtained for various wavelengths (500–800 nm). The time required to acquire one image has been 0.7 s in the present system. The dependence of the dielectric constant of a Ag film on wavelength is given here as an example measured by our system. © 1996 American Institute of Physics. View full abstract»

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  • Improving the SOPRA DMDP2000 spectrometer by a Michelson interferometer

    Page(s): 3044 - 3046
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    A new class of multiple dispersion grating spectrometer was commercialized a few years ago (SOPRA DMDP2000). In practice, mechanical tolerances do not let it operate at its very best characteristics. The instrument can be considerably improved by using a simple Michelson interferometer. © 1996 American Institute of Physics. View full abstract»

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  • Simple computer‐controlled scanning for a coherent Stokes Raman scattering spectrometer

    Page(s): 3047 - 3050
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    Synchronous wave number‐shift scanning of a Nd:YAG pumped dye laser and the detection monochromator for a coherent Stokes Raman scattering (CSRS) system were realized using an inexpensive analog to digital board. With this improvement the CSRS spectrometer may be used to scan over a large wave number shift range and/or may be used at relatively high resolution using a photomultiplier tube as the detector. This is especially useful in the probing of luminous systems. © 1996 American Institute of Physics. View full abstract»

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  • A micro‐fluorescent/diffracted x‐ray spectrometer with a micro‐x‐ray beam formed by a fine glass capillary

    Page(s): 3051 - 3064
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    The technique of forming a micro‐x‐ray beam with a fine capillary was studied. It was shown that lightweight materials, such as glass, were suitable for the capillary in terms of their x‐ray refractive indexes. A fine glass capillary with a parabolic cross‐sectional inner wall surface was made. Using the capillary, a fluorescent and diffracted x‐ray spectrometer with a 0.8‐μm‐ϕ x‐ray beam was developed for the analysis of stress, crystal structure, and metal contamination in micro regions of ultra‐large‐scale integration (ULSI) devices. A micro‐focus x‐ray generator with a membrane‐type target was also developed for use with the capillary. The crystal phases of very thin Ti‐silicide fine lines and the strain in Al interconnections of ULSIs were analyzed using the equipment. © 1996 American Institute of Physics. View full abstract»

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  • Sub‐kHz precision voltage‐controlled‐oscillator system for laser frequency control: An application in atom optics

    Page(s): 3065 - 3069
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    A system design is presented which allows a voltage controlled oscillator (VCO) to be tuned to an arbitrary frequency between 78 and 94 MHz with an accuracy better than 1 kHz (10 ppm). The temperature coefficient is on the order of 1 kHz/K, giving a long‐term stability better than 1 kHz in a controlled environment. The slew rate for frequency switching is ≊10 MHz in 50 μs. The system comprises a computer‐controlled precision voltage source, a spline interpolation of the voltage versus frequency characteristic, and good isolation of the VCO electronics from the subsequent circuitry. It provides an extremely low‐cost alternative to frequency synthesisers. In our application involving the launching of slow atoms at a target, we can achieve atomic velocities as low as 10 cm/s with 1 cm/s precision. © 1996 American Institute of Physics. View full abstract»

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  • Cam‐driven pulsed Laval nozzle with a large optical path length of 50 cm

    Page(s): 3070 - 3072
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    This article describes the design and performance of a pulsed valve developed as a gas source for a 500‐nm‐long supersonic Laval nozzle with a 3‐mm‐wide throat. The valve consists of a plate cam and a valve seat equipped with O‐rings on both the upper and lower faces. The duration of quasi‐steady‐state expansion is measured to be 12 ms at the nozzle throat when the pulsed valve is filled with Ar gas at 100 Torr. © 1996 American Institute of Physics. View full abstract»

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  • Installation of an on‐line Lamb shift spin‐filter polarimeter in the Triangle Universities Nuclear Laboratory atomic beam polarized ion sourcea)

    Page(s): 3073 - 3081
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    An atomic beam polarized ion source, used heavily since 1989 for producing polarized H± and D± beams for experiments between 25 keV and 20 MeV, has been modified to accept a Lamb shift, spin‐filter polarimeter. In this source, polarized ground‐state H or D atoms enter an electron cyclotron resonance ionizer where they are stripped to produce an outgoing positive polarized ion beam. When negative ions are desired, cesium vapor is introduced into a downstream charge‐exchange canal. The polarimeter, based on an atomic physics concept first developed to produce nuclear‐spin‐polarized beams at Los Alamos, is designed to monitor the polarization of 2S1/2 metastable H or D atoms emerging from the cesium canal. Metastable 2S1/2 atoms created by electron pickup in a collision with cesium are ‘‘filtered’’ by the polarimeter according to magnetic substate, as the magnetic field imposed on the polarimeter cavity is tuned between 53 and 61 mT. Photons produced by subsequent quenching of these filtered atoms to their ground state are monitored downstream by a phototube to reveal the magnetic substate population of the incident positive beam. To install the polarimeter cavity and phototube assembly, the existing polarized ion source was lengthened by 30 cm. Installation is complete, and comparisons with calibrated nuclear polarimeters have shown agreement to better than 0.023. Principles of operation, a description of the hardware, measurements for cross calibration, and impressions gained from its use are all presented. © 1996 American Institute of Physics. View full abstract»

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  • A segmented Faraday cup for two‐dimensional representation of the current distribution of an ion beam

    Page(s): 3082 - 3084
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    A Faraday cup with 37 segments has been developed to measure the two‐dimensional current distribution I=f(x,y) and the total beam current of an ion beam. With an overall cross‐sectional area of about 3420 mm2, reproducible current measurements can be carried out down to some nanoamperes. The Faraday cup is used to measure ion beams in an energy range up to 25 keV and beam currents up to 10 mA. The current is determined on the basis of the voltage drop at selected metal film resistors. Initial results confirm good practical applicability in the analysis and adjustment of ion beams. © 1996 American Institute of Physics. View full abstract»

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  • Longitudinal beam emittance monitor for 433 MHz proton linac

    Page(s): 3085 - 3091
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    We have developed a longitudinal emittance monitor for a 7 MeV proton beam provided by the 433 MHz linac at the Institute for Chemical Research, Kyoto University. In the present system, the beam first hits a thin gold target on the beam line, and a fraction of the scattered protons comes into a small cavity. After deflected by a rf electric field in the cavity, the protons finally reach a position sensitive detector (PSD). The PSD gives the information of the energy and position of the individual scattered proton, which enables us to reconstruct the longitudinal distribution of the beam before colliding with the target. The phase and energy resolution of the system are estimated to be 13° and 23 keV full width at half‐maximum, respectively. The longitudinal rms emittance measured was 0.39±0.07 π deg MeV under the nominal operating condition of the linac. © 1996 American Institute of Physics. View full abstract»

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  • Depth profile of implanted species with a detector telescope

    Page(s): 3092 - 3094
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    Conventional elastic recoil detection analysis (ERDA) is considered to be an ideal nondestructive technique for depth profiling of implanted species of light mass elements in a material. The present work shows that it can lead to inaccurate misleading results in the cases where the implanted sample has surface impurity of nearby light mass element. It is also shown that the detector telescope behind the stopper foil in ERDA allows accurate profiling of implanted specimen as well as surface impurities simultaneously. © 1996 American Institute of Physics. View full abstract»

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  • Vacuum arc trigger systems based on E×B discharges

    Page(s): 3095 - 3098
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    Triggering systems for vacuum arc plasma sources and ion sources have been developed that make use of a gaseous trigger discharge in a strong magnetic field. Two kinds of trigger discharge configurations have been explored, a Penning discharge and a magnetron discharge. The approach works reliably for low gas pressure in the vacuum arc environment and for long periods of operation between required maintenance: pressures in the mid‐10-6 Torr range and for ≳106 pulses. © 1996 American Institute of Physics. View full abstract»

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  • Active trajectory control for a heavy ion beam probe on the compact helical system

    Page(s): 3099 - 3107
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    A 200 keV heavy ion beam probe (HIBP) on the compact helical system heliotron/torsatron uses a newly proposed method in order to control complicated beam trajectories in nonaxisymmetrical devices. As a result, the HIBP has successfully measured potential profiles of the toroidal helical plasma. This article will describe the results of the potential profile measurements, together with the HIBP system and procedures to realize the method. © 1996 American Institute of Physics. View full abstract»

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  • A submillimeter polychromator for plasma spectroscopy

    Page(s): 3108 - 3116
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    A 12‐channel grating polychromator for the measurement of electron cyclotron emission on the Frascati tokamak upgrade (FTU) has been built. Three gratings can be exchanged remotely, to allow the instrument to cover three different spectral ranges (between 200 and 600 GHz) which correspond to the second harmonic of electron cyclotron emission for tokamak magnetic fields of 4, 6, and 8 T. Three sets of low‐pass filters, whose cut‐off frequencies are optimized for each grating, are used to cut the high diffraction orders. In order to exchange the filters together with the grating it was necessary to integrate the groups of filters with the polychromator itself. This has been done reducing the grating sizes and assembling them all closely on a moveable structure. The exchange of gratings and filters can be performed remotely via computer in few seconds without any lost of the alignment. InSb cryogenic hot‐electron bolometers are used as detectors. The cryostat hold‐time is more than 30 days. Spectral resolution λ/δλ is about 40 corresponding to a spatial resolution of δR≊2.3 cm. The minimum detectable temperature is about 10 eV at 20 kHz bandwidth. The spatial structure and temporal evolution of several kinds of fast temperature perturbations (as the ones due to magnetohydrodynamic activity, temperature fall during pellet injection and plasma disruption) have been measured on FTU by means of this diagnostic system. © 1996 American Institute of Physics. View full abstract»

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  • An extension to laser‐induced fluorescence measures multiple velocity components simultaneously

    Page(s): 3117 - 3121
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    An extension to laser‐induced fluorescence is presented. The new technique, called intermodulated optical tagging, can be used to measure multidimensional velocity distribution functions directly as well as to tag ions in two velocity and three spatial coordinates. The first application makes the technique a possible replacement for tomography, the second makes it useful for heretofore difficult transport measurements. Application to velocity‐space transport perpendicular to the magnetic field is discussed for a quiescent plasma. © 1996 American Institute of Physics. View full abstract»

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  • Design and operation of the pellet charge exchange diagnostic for measurement of energetic confined α particles and tritons on the Tokamak Fusion Test Reactor

    Page(s): 3122 - 3135
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    Radially resolved energy and density distributions of the confined α particles in D–T experiments on the Tokamak Fusion Test Reactor (TFTR) are being measured with the pellet charge exchange (PCX) diagnostic. Other energetic ion species can be detected as well, such as tritons produced in D–D plasmas and H, He3, or tritium rf‐driven minority ion tails. The ablation cloud formed by injected low‐Z impurity pellets provides the neutralization target for this active charge exchange technique. Because the cloud neutralization efficiency is uncertain, the PCX diagnostic is not absolutely calibrated so only relative density profiles are obtained. A mass and energy resolving E‖B neutral particle analyzer (NPA) is used which has eight energy channels covering the energy range of 0.3–3.7 MeV for α particles with energy resolution ranging from 5.8% to 11.3% and a spatial resolution of ∼5 cm. The PCX diagnostic views deeply trapped ions in a narrow pitch angle range around a mean value of v‖/v=-0.048±10-3. For D–T operation, the NPA was shielded by a polyethylene–lead enclosure providing 100× attenuation of ambient γ radiation and 14 MeV neutrons. The PCX diagnostic technique and its application on TFTR are described in detail. © 1996 American Institute of Physics. View full abstract»

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  • Cold‐cathode, pulsed‐power plasma discharge switch

    Page(s): 3136 - 3148
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    CROSSATRONTMmodulator switches are cold‐cathode, grid‐controlled, plasma‐discharge devices that are used for thyratron and hard‐tube replacement in high‐voltage, pulsed‐power applications. CROSSATRON modulator switches have been used to produce square pulses of up to 100 kV and 1000 A, and CROSSATRON laser‐discharge switches have switched peak discharge currents of up to 10 kA at 40 kV. The major advantage that CROSSATRON switches offer over other plasma switches is a rapid deionization time that permits high pulse‐repetition frequencies (103 to 106 pulses per second depending on the application), and a long life associated with the cold‐cathode plasma production mechanism. Compared to hard tubes, CROSSATRON switches have a relatively low forward voltage drop (500 V), the ability to close and open up to 1 kA of peak current, and lower grid‐drive power requirements. In this article, we describe the physical mechanisms for how the switch works based on simple models and experimental data. The design of CROSSATRON switches is explained, and characteristic performance in closing and opening applications is described and explained. © 1996 American Institute of Physics. View full abstract»

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  • Novel capillary pulse viscometer for non‐Newtonian fluids

    Page(s): 3149 - 3157
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    This article describes the design and principle of operation of an unsteady‐state capillary pulse viscometer for measuring the rheology of non‐Newtonian fluids at elevated pressures and elevated temperatures. The relevant equations for the flow of a power‐law fluid in a capillary tube under a transient pressure gradient that decays at a rate proportional to the fluid flux in the tube are derived. The viscometer does not require a pump to generate a steady flow and is relatively simple and cheap to manufacture. Only a small amount of the test fluid is required and it is comparatively faster than other steady‐state atmospheric pressure viscometers. Furthermore, the viscosity of the test fluid is measured over a range of shear rates with each run. The pressure decay across the capillary tube is recorded, and the apparent viscosity is calculated as a function of shear rate from the relevant flow equations. The viscometer has been used to measure the viscosity of polymer solutions over a wide range of concentrations [250–2500 parts per million by weight (wppm)] and the results compared with data using a steady‐state commercial viscometer. The accuracy of the instrument is comparable to or better than that of other types of viscometers. © 1996 American Institute of Physics. View full abstract»

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  • Poiseuille geometry shear flow apparatus for small‐angle scattering experiments

    Page(s): 3158 - 3163
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    A new apparatus to investigate the structure of fluids under Poiseuille shear flow using small‐angle neutron or light scattering techniques is described. Important features of the design include low sample volumes, area average shear rates of up to 5000 s-1, accurate temperature control over the range of 10–125 °C, and the ability to study the development of flow‐induced alignment phenomena. Small‐angle neutron scattering data are presented for two example systems: the well‐characterized surfactant system C16E6/D2O, used to contrast the effects of Poiseuille and Couette flow, and the block copolymer Synperonic P‐85/D2O system. © 1996 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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Meet Our Editors

Editor
Albert T. Macrander
Argonne National Laboratory