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Review of Scientific Instruments

Issue 6 • Date Jun 1992

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Displaying Results 1 - 25 of 50
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Cooled submillimeter Fourier transform spectrometer flown on a rocket

    Page(s): 3249 - 3260
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    A detailed description is given of a liquid‐helium‐cooled. Fourier transform spectrometer recently flown on a rocket. The instrument was used to make new precise measurements of the spectrum of the cosmic background radiation in the wave number range 2–30 cm-1, as reported by H. P. Gush, M. Halpern, and E. Wishnow [Phys. Rev. Lett. 65, 537 (1990)]. View full abstract»

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  • Time‐resolved Fourier transform spectroscopy with 0.25 cm-1 spectral and ≪10-7 s time resolution in the visible region

    Page(s): 3261 - 3267
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    The development of a new time‐resolved Fourier transform spectrometer that is capable of 0.25 cm-1 spectral resolution and better than 10-7 s temporal resolution in the visible is reported. The time‐resolved capability of the spectrometer is achieved by coupling a step‐scan interferometer to a transient digitizer/laser system. The operation of the spectrometer is described in detail, and scattered light and laser‐induced fluorescence spectra from an I2 gas cell are presented to demonstrate the temporal and spectral resolution of the spectrometer. View full abstract»

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  • Application of a sine transform method to experiments of single‐photon‐decay spectroscopy: Single exponential decay signals

    Page(s): 3268 - 3273
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    In this article we present as an experiment in single‐photon‐decay spectroscopy an alternative method to that based on the measurement of the probability distribution function, Pf(t), of the time intervals for the time of arrival of the first photon after the excitation pulse. We propose the measurement of the sine transform of Pf(t), which gives a maximum when the fluorescence signal is of the single exponential decay type. The existence of this maximum allows us to determine very accurately the value of the decay constant using a number of measurements which is lower than that required to establish a Pf(t) that is accurate enough to draw the same conclusions. A theoretical model of the error is studied and is compared by means of a computer simulation with the usual method of measuring Pf(t). An experiment is performed using a TMMC crystal to verify the validity of the theoretical predictions and of the simulation results. View full abstract»

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  • Simultaneous spectral and temporal resolution in a single photon counting technique

    Page(s): 3274 - 3279
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    We have demonstrated the performance of a position‐sensitive and time‐resolved photon counting system based on a microchannel plate photodetector with a delay‐line anode, in combination with a picosecond laser source and two‐channel fast timing technique. A spatial resolution of 220 μm and a temporal resolution of 500 ps were achieved. Examples of two‐dimensional, both spectrally and temporally resolved molecular emission spectra are presented. The results obtained clearly show the method to be suitable for those spectroscopic applications that require an extremely high sensitivity and multichannel spectral analysis with picosecond time resolution. View full abstract»

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  • New vapor phase spontaneous Raman spectrometer

    Page(s): 3280 - 3284
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    A highly sensitive, spontaneous Raman spectrometer designed for the study of vapors and other low‐density samples is discussed. The high sensitivity is achieved by means of the novel combination of a multipass light cell and a high‐temperature gasdynamic focusing system. A complete description of the apparatus is given, along with the results of a sensitivity test in ambient air, as well as results demonstrating gasdynamic focusing of a vapor and Raman transitions in such a sample. View full abstract»

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  • Hyper‐Rayleigh scattering in solution

    Page(s): 3285 - 3289
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    The experimental setup for the implementation of a new technique to determine the hyperpolarizability of nonlinear optical molecules in solution is presented. The new technique, hyper‐Rayleigh scattering in solution [K. Clays and A. Persoons, Phys. Rev. Lett. 66, 2980 (1991)], has the advantage over the electric‐field‐induced second‐harmonic generation technique that the dipole moment μ and the second hyperpolarizability γ do not have to be independently determined to obtain the first hyperpolarizability β. No electric field is needed to lower the intrinsic symmetry of the isotropic solution, leading to a simpler cell design and a simpler local field factor. The internal reference method, when applicable, completely eliminates the local field factor. With the technique presented, values of the first hyperpolarizability β of 23×10-30 esu for para‐nitroaniline (PNA), 105×10-30 esu for 4‐methoxy‐4’‐nitrostilbene (MONS), and 95×10-30 esu for 4‐hydroxy‐4’‐nitrostilbene (HONS) dissolved in chloroform have been obtained. View full abstract»

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  • Transverse Kerr magneto‐optic measurements with a rotating analyzer ellipsometer

    Page(s): 3290 - 3292
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    The use of a rotating analyzer ellipsometer is proposed to measure the spectral variation of the transverse Kerr magneto‐optic effect. A low inductance coil is placed close to the sample in such a way that an alternating magnetic field is applied in the plane of the sample and perpendicular to the plane of incidence. First the quantities ψ and Δ are measured in the conventional way. For the magneto‐optic effect the magnetization is varied at a high frequency. The analyzer and polarizer are fixed at specified angles while the magneto‐optic signal is measured with a lock‐in detector. The data are used to determine the real and imaginary parts of the magneto‐optic coefficients and their relative sign. It is shown how to calculate from this measurement the value of the off‐diagonal elements of the dielectric tensor. View full abstract»

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  • A far‐infrared spectrometer based on cyclotron resonance emission sources

    Page(s): 3293 - 3297
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    Practical realization of the spectrometer based on the cyclotron emission sources is presented. It is shown that it can be used for transmission measurements in the range from 35 to 110 cm-1 with resolution up to 1.3 cm-1. Performances of the spectrometer are demonstrated by its application to the studies of impurity and free‐electron states in two‐dimensional structures. View full abstract»

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  • Silicon photodiode detector for a glancing‐emergence‐angle EXAFS technique

    Page(s): 3298 - 3302
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    We have constructed a silicon photodiode detector for use with a glancing‐emergence‐angle (GEA) geometry useful for obtaining fluorescence EXAFS spectra from thick specimens with concentrated absorbing species. We present a description of the detector and the results of tests, including dark‐noise tests, EXAFS spectra from a standard sample, and a comparison to an ion chamber also in the GEA configuration. Data obtained from the two detectors are comparable in quality, making the diode detector a preferable choice for this application due to factors such as simplicity of construction and compact size. The diodes also have potential for significant further improvement in the quality of the signal due to their high quantum efficiency if the dark noise can be reduced. We present suggestions for achieving this in future generations of the detector. View full abstract»

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  • A diamond anvil cell for high‐pressure NMR investigations

    Page(s): 3303 - 3306
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    A diamond anvil cell suitable for high‐pressure NMR experiments in a cryostat is described. Inside a rhenium gasket pressures up to 8.3 GPa could be generated. With this apparatus the pressure dependence of the Knight shift and of the self‐diffusion coefficient in metallic lithium and sodium has been measured (as published elsewhere). View full abstract»

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  • High‐pressure NMR probes for the in situ investigation of gas/liquid reactions

    Page(s): 3307 - 3310
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    Three different types of nuclear magnetic resonance (NMR) probes have been developed for investigating multiple phase (gas/liquid) reactions in situ at ambient and high pressure. Versions requiring only minimal modifications of existing NMR probes, low volume probes, and high precision flow systems have been optimized for specific boundary conditions. Pressures ranging from 1 to 20 bar have been successfully applied. The arrangements are especially attractive for the in situ investigations of homogeneous hydrogenation reactions displaying nuclear spin polarization. View full abstract»

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  • Rangefinder with fast multiple range capability

    Page(s): 3311 - 3316
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    A rangefinder is described that uses the propagation time of a beam of infrared radiation to measure distances of up to 120 m with errors of less than 50 μm. The instrument is capable of measuring up to five different distances per second by directing an amplitude modulated infrared beam to a retroreflector located at the far end of each path. The instrument is being tested with the expectation that such a system could be used to make precise and rapid measurements on a large radio telescope. Such measurements would be used to adjust the shape of the telescope reflector surface to correct for thermal and gravitational deformations taking place during astronomical observations. It is possible that the measuring system could be extended to relate the positions of certain moving parts of the structure to a reference system fixed in the ground, thus opening the possibility of making corrections to the telescope pointing. View full abstract»

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  • Picosecond response of photon‐drag detectors for the 10‐μm wavelength range

    Page(s): 3317 - 3320
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    The response times of nonresonant p‐Ge detectors and of resonant photon‐drag detectors made from AlxGa1-xAs/GaAs multiquantum well systems are measured with intense 300‐ps optical pulses of 10‐μm wavelength generated with the aid of an improved laser system based on optical free induction decay. A response time limited by the oscilloscope‐amplifier bandwidth is reached with the quantum well systems. Their response time is shorter than that of a p‐Ge photon‐drag detector. The light‐pulse traveling time limits the performance of the large p‐Ge photon‐drag detectors. View full abstract»

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  • Photoionization mass spectrometer with a microscope laser desorption source

    Page(s): 3321 - 3325
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    An apparatus is been described in which laser desorption, separate laser ionization, mass spectrometry, and microscopy are combined. An UV waveguide laser is focused on a sample, which is mounted on translation stages in vacuum. Desorbed neutral molecules are ionized above the surface by a second laser, and ions are extracted into a reflectron time of flight mass spectrometer. A spatial resolution of 1 μm is demonstrated, with a mass resolution of 2000 and a detection efficiency of 10-4. View full abstract»

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  • Vibration isolation analysis for a scanning tunneling microscope

    Page(s): 3326 - 3329
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    We analyze the efficiency of a vibration isolation system (VIS) for a scanning tunneling microscope as a function of the different parameters involved. The VIS consists of a stack of several metallic plates, separated by rubber elements with known properties. We show three‐dimensional graphs obtained for different values of parameters such as rigidity (spring) constant (K), damping constant (C), mass (M), and the number of stages (n). Analyzing the K dependence of the position of the main peaks, we find a parabolic behavior when the damping constant is small, with a slight deviation for larger values. View full abstract»

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  • Atomic force microscopy using ZnO whisker tip

    Page(s): 3330 - 3332
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    We have developed an atomic force microscope (AFM) using a zinc oxide (ZnO) whisker crystal as a probing tip. The ZnO whisker crystal is tetrapodal in shape, with each leg having a length of 5–30 μm, a radius of curvature less than 10 nm, and a cone half angle of 1°–2°. Polyimide thin films rubbed with cloths as liquid‐crystal aligning films were employed for AFM imaging. Due to the needle shape of the probing tip, the AFM was able to resolve the tiny grooves (3–5 nm deep, 60–80 nm apart) on these films more clearly than that using a conventional pyramidal tip. The new AFM will be available for precise evaluation of surfaces on which fine structures are microfabricated in nanometer scale. View full abstract»

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  • Spin‐polarized electron gun for electron spectroscopies

    Page(s): 3333 - 3338
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    A spin‐polarized electron gun for electron spectroscopies is described in detail. The gun consists of an electron source based on a negative electron affinity GaAs photocathode coupled to an appropriate transport electron optics. The gun has been designed with the aid of ray‐tracing analysis and then accurately tested. It produces a transversely polarized (P0∼27%) electron beam at variable energy with a small spot size and angular spread (less than 2 mm and 5°, respectively). Such performances are attained up to sample currents as high as 10 μA for the whole beam energy range (8–50 eV). As an application we present data on spin‐dependent absorbed current spectroscopy from bcc Fe films epitaxially grown on Ag(100). View full abstract»

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  • Chromatic aberration of three‐cylinder electrostatic lenses

    Page(s): 3339 - 3345
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    Accurate calculations of the axial chromatic aberration coefficients of geometrically symmetric three‐cylinder tripotential electrostatic lenses are presented for two different center electrode lengths. This is an extension of the first‐order properties and the third‐order spherical aberration coefficients published by Harting and Read. View full abstract»

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  • Real‐time computer‐optimized electron coincidence spectrometer

    Page(s): 3346 - 3351
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    An electron coincidence spectrometer utilizing real‐time optimization and control by a standard IBM 80286 personal computer is described. Details of the system hardware and software are presented together with a description of the optimization routine adopted for maintaining the tuning of the spectrometer and data acquisition. Data collected by the computer‐controlled spectrometer for (e,2e) coincidence experiments are also presented. View full abstract»

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  • Instrumentation for gas electron diffraction employing a pulsed electron beam synchronous with photoexcitation

    Page(s): 3352 - 3358
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    A novel instrument is described capable of recording gas electron diffraction (GED) patterns of excited molecular states or transient species with pulsed electron beams. The system incorporates (1) a pulsed optical beam for electronic excitation of materials under study, (2) a synchronously pulsed source of 30–50 keV electrons in a space‐charge‐limited beam, (3) necessary vacuum environment and sample‐handling capabilities, and (4) detection and signal processing equipment using an on‐line procedure developed at the University of Arkansas. Data obtained for several test gases demonstrate successful operation of the instrument. The 193 nm laser photofragmentation of carbon disulfide, CS2, is described in detail. In agreement with a recent time‐of‐flight mass spectrometric study of the same process, carbon monosulfide was observed as the reaction product. This study is the first quantitatively successful joint exercise of on‐line multichannel GED data recording and a stroboscopic electron source. The method is expected to be generally useful in determining the structures of excited molecular states or reactive species, and it may enable studies of time‐dependent phenomena. The current time resolution is ∼20 ns. View full abstract»

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  • Ion temperature measurements in tokamak plasmas by Rutherford scattering

    Page(s): 3359 - 3368
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    A Rutherford scattering diagnostic has been applied at the TEXTOR tokamak to obtain spatially and temporally resolved information on the temperature of the bulk ions in the plasma. In the experimental setup, a helium atomic beam (30‐keV, 12‐mA equivalent current) passes vertically through the plasma core. A small part of the injected atoms is scattered elastically by the thermally moving plasma ions. The ion temperature in the scattering volume can be determined from the broadening of the energy spectrum of the scattered particles. Energy analysis of the scattered atoms is performed by a mass‐selective time‐of‐flight analyzer detecting the particles at an observation angle which is selectable between 3° and 8°. Coincidence techniques have been successfully applied in this detector for rejection of background events triggered by detections of neutrons and gamma radiation. Ion temperature profiles were measured on a shot‐to‐shot basis by shifting the cross section of the diagnostic beam and the observational volume of the analyzer through the plasma. The ion temperatures measured in ohmic deuterium plasmas were found to be in reasonable agreement with those obtained from passive neutral particle analysis. Up to now, ion temperatures have been measured throughout the complete discharge with an accuracy of 8% and a time and space resolution of 100 ms and 0.10 m at a scattering angle of 7°. Deuteron density profiles could be deduced from the scattering yield measured at different radial positions in the plasma. The ratio of the isotopes, hydrogen and deuterium, was determined from their separate contributions to the spectrum of helium particles scattered on hydrogen and deuterium. Although theoretical predictions showed that the majority of the probing helium atoms loses one of its electrons during the elastic scattering process on multiply charged carbon and oxygen ions, contributions from impurit- ies to the observed experimental spectrum are shown to appear dominant for impure plasmas. View full abstract»

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  • A combined Thomson–Rayleigh scattering diagnostic using an intensified photodiode array

    Page(s): 3369 - 3377
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    A combined Thomson–Rayleigh scattering device is discussed. It consists of a Nd:YAG laser as a light source in combination with a multichannel detection technique consisting of a gated light amplifier in combination with an optical multichannel analyzer. Special attention is focused on the analysis of the measured spectra. Including convolution methods and taking into account weak coherent effects increases the dynamic range and the accuracy of the measured electron density ne and temperature Te and neutral particle density n0. Accuracies of 1%–4% for ne, 2%–6% for Te, and 10%–50% for n0 depending on the plasma condition are obtained. The dynamic range for ne is 7×1017–1021 m-3, for n0 is 1020–1023 m-3 and for Te is 1000–50 000 K. View full abstract»

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  • Cryostat to provide a solid deuterium layer in a plastic shell for the Gekko XII glass laser system

    Page(s): 3378 - 3383
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    A system to provide a liquid or solid deuterium shell target with a plastic ablator for laser implosion experiments was developed. The system is capable of filling a plastic capsule with deuterium gas of 11 MPa at room temperature at the firing position in the target chamber. Then, the target is cooled down to a cryogenic temperature to form a uniform liquid or solid fuel layer inside without exposing it to the atmosphere. Details of the system, tensile strength of polystyrene shells at low temperature, and the residual vapor pressure in the central void of the target at the laser irradiation are described. View full abstract»

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  • Small diameter nozzle plasma arc as a processing tool

    Page(s): 3384 - 3388
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    High‐power‐density plasma arc equipment with a small diameter nozzle of 0.1–0.3 mm has been developed, which produces power density of about 104 W/mm2 at the exit of the nozzle. The density is comparable to those produced by electron and laser beams. In the present article, development procedure, power density on the target surface, and processing capability in comparison to the conventional electron and laser beams are described. The power density as the processing heat source depends on the kind of processing. The apparent power density in cutting is of the order of 104 W/mm2; on the other hand, that in surface hardening is of the order of 102 W/mm2. The processing capability for causing melting such as cutting and welding does not depend on the working distance, which is defined as the distance between the torch and target material; furthermore, the deviation of the torch from the correct position does not affect the processing capability. The equipment developed is suitable for an automated production system because high precision position control of the torch is not required. 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