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Review of Scientific Instruments

Issue 1 • Date Jan 2000

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Displaying Results 1 - 25 of 58
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Single-frequency external-cavity tapered diode laser in a double-ended cavity configuration

    Page(s): 1 - 4
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    We achieved stable single-frequency oscillation in an external-cavity tapered diode laser. The external cavity was constructed from a diffraction grating and an output mirror, which were placed, respectively, in the narrow-area side and the broad-area side of the tapered-stripe chip, with collimator lenses on both sides. The best position for the output mirror was a focal point of the output beam along the axis parallel to the diode junction plane, while the beam along the axis perpendicular to the junction plane was collimated by the collimator lens. Continuous frequency tuning of 900 MHz and a linewidth below 1 MHz were obtained. A bistability was observed in the output power around the threshold current after the output mirror was installed. © 2000 American Institute of Physics. View full abstract»

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  • Spectromicroscopy beamline at ELETTRA: Performances achieved at the end of commissioning

    Page(s): 5 - 10
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    In the course of 1998, the Spectromicroscopy beamline at ELETTRA completed commissioning and succeeded in performing its first test experiments. The beamline is designed to perform photoemission experiments with high spatial resolution, which is obtained by focusing the radiation in a small spot on the sample by means of a multilayer-coated Schwarzschild Objective. Three objectives are currently available; these operate at photon energies of 74, 95, and 110 eV. A review is presented of the performances achieved together with an outlook on the future upgrades of the microscope. The smallest achievable spot size is currently 0.5 μm. At present, the limit to the spatial resolution is due to aberrations caused by figure errors of the objective. Typical counting rates in photoemission spectra, for example, on the Au 5d peak, are of the order of 104–105 counts per second with an energy resolution of the order of 100–200 meV. Among the first experiments in which p- and n-type GaAs layers of 0.25 μm thickness were imaged. © 2000 American Institute of Physics. View full abstract»

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  • Feasibility tests of transmission x-ray photoelectron emission microscopy of wet samples

    Page(s): 11 - 14
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    We performed feasibility tests of photoelectron emission spectromicroscopy of wet samples in the water window (285–532 eV) soft x-ray spectral region. Water was successfully confined in an ultrahigh vacuum compatible compartment with x-ray transparent sides. This water cell was placed in the MEPHISTO spectromicroscope in a transmission geometry, and complete x-ray absorption spectra of the water window region were acquired. We also show micrographs of test samples, mounted outside of the compartment, and imaged through the water. This technique can be used to study liquid chemistry and, at least to the micron level, the microstructure of wet samples. Possibilities include cells in water or buffer, proteins in solution, oils of tribological interest, liquid crystals, and other samples not presently accessible to the powerful x-ray photoelectron emission spectromicroscopy technique. © 2000 American Institute of Physics. View full abstract»

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  • Study of a fast ablative capillary discharge dedicated to soft x-ray production

    Page(s): 15 - 19
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    A capillary discharge has been developed to produce pulses of intense soft x-ray radiation of tens of nanoseconds duration. The soft x-ray photons were emitted in a plasma column resulting from polyethylene in capillary wall ablation. The spectrum was dominated by the C IV, C V, and C VI emission lines in the soft x-ray spectral range. The experimental value of the electrical circuit inductance has been measured and compared to the calculated one. The electron temperature was estimated to be higher than 50 eV from the plasma resistivity measurement. The time dependence of the electron density outside the capillary channel has been determined using spectroscopic measurement in the visible range. The time dependence of the electron temperature has been determined from the intensity ratio of C V and C VI emission lines, using a collisional radiative equilibrium code. © 2000 American Institute of Physics. View full abstract»

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  • A compact x-ray beam intensity monitor using gas amplified sample current measurement

    Page(s): 20 - 22
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    Development of a compact beam intensity monitor using gas amplified sample current measurement is described. The monitor can be a powerful tool for x-ray spectroscopy and microscopy when the beam is defined by a small pinhole or slits and when the workspace around the sample is limited. The thickness of the monitor is as small as approximately 3 mm, and the dimension is 10 mm square. The photon flux is monitored by measuring x-ray excited current from an Al foil under atmospheric conditions. Emitted electrons from the Al foil can ionize surrounding air molecules, and the gas amplified current can be measured with the use of a biased grid that prevents created ion pairs from recombination. © 2000 American Institute of Physics. View full abstract»

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  • A method for balancing the paths of a two-photon interferometer

    Page(s): 23 - 26
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    We present and demonstrate a method for balancing the two paths of a two-photon interferometer of the Hong-Ou-Mandel (HOM) variety. This method removes the difficulties of balancing the paths in this type of interferometer where a type-I crystal is used for the generation of the entangled photon pairs. Using this method we show that we are consistently able to balance the ∼2000 mm path lengths in our HOM interferometer on average to within ∼60 μm. © 2000 American Institute of Physics. View full abstract»

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  • High order quarter-wave plates and analysis of the directions of rotation in the circular polarizations

    Page(s): 27 - 31
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    The advent of new research subjects, such as plasmas, optical pumping, and atom cooling, has led to an increased use of quarter-wave plates in order to produce circularly polarized beams with the correct direction of rotation. The recent commercialized quarter-wave plates work in high orders, which leads to a drastic reduction of their pass band. Moreover, the direction of rotation in circular polarization can be affected. The purpose of the present article is to describe new techniques allowing an accurate determination of the optical properties of the used plates. © 2000 American Institute of Physics. View full abstract»

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  • A laser beam analyzer for resonance ionization mass spectrometry studies

    Page(s): 32 - 35
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    We have developed a laser beam analyzer for quantitative studies in resonance ionization experiments. The laser beam profiles, which can be represented as images or as graphs, were used to compute the overlap of a number of laser beams interacting with an atom beam. In our experimental setup, resonance ionization signal was monitored as a function of overlap of laser beams employing the laser beam analyzer developed. The dependence of resonance ionization signal was explained with the help of an interaction model that includes the effects of geometry of the atom beam. © 2000 American Institute of Physics. View full abstract»

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  • Design and performance of an electrospray ionization time-of-flight mass spectrometer

    Page(s): 36 - 41
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    In order to circumvent the limitations of a quadrupole mass filter, which so far has been the most common mass analyzer for use with electrospray ionization, a mass spectrometer coupling electrospray with time-of-flight mass analysis has been constructed. The design of this spectrometer, including a simple electrospray ion source, an atmosphere–vacuum interface without a rf-only quadrupole/multipole that discriminates against low mass ions which can be used for internal calibration, orthogonal extraction, and a reflectron, is presented together with its performance characteristics. A resolving power of 7500 was obtained for the +5 ion of bovine insulin and the detection limit for the same molecule was shown to be 1 f mol. Mass accuracy using a conventional two-point calibration is 60 ppm for internal calibration on low mass ions and better than 100 ppm for external calibration on peptide ions. An improved mass accuracy equal to 10 ppm was achieved using internal three-point calibration on low mass ions naturally present in the spectra. The dynamic range of a single sample was found to be at least 400:1. © 2000 American Institute of Physics. View full abstract»

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  • A molecular beam apparatus for eigenstate-resolved studies of gas-surface reactivity

    Page(s): 42 - 53
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    A new supersonic molecular beam-surface scattering apparatus permits eigenstate-resolved measurements of gas-surface reactivity. Infrared light from a narrow-bandwidth tunable laser intersects a supersonic molecular beam and prepares an ensemble of molecules in a single rotational and vibrational quantum state. The energized molecules, with their well-defined translational, vibrational, and rotational energies, pass into an ultrahigh vacuum chamber and impinge on a single crystal metal surface where their reactivity is quantified. The apparatus provides independent control over translational, vibrational, and rotational degrees of freedom and permits highly detailed studies of gas-surface reactivity. In this article we describe the design and characterization of our apparatus and illustrate its use to study the dissociative chemisorption of methane on Ni(100). © 2000 American Institute of Physics. View full abstract»

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  • Production of bimetallic clusters by a dual-target dual-laser vaporization source

    Page(s): 54 - 58
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    A new dual-target dual-laser vaporization source for the production of binary metallic clusters is presented. Clusters of the type AunXm (X=Al, Fe, Co, Ni) were produced. Excellent control over the mixing process was achieved by varying the delay time between the firing of the two lasers and their energy densities. Having identified these critical parameters, their influence over the production process is shown in detail for the AunAlm system. The production of bimetallic clusters in this source is due to the spatial and temporal overlap of the two laser vaporized materials in the source. © 2000 American Institute of Physics. View full abstract»

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  • A mechanical shutter for light using piezoelectric actuators

    Page(s): 59 - 60
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    The design and performance of a mechanical shutter for laser light based on low voltage piezoelectric transducers is described. By focusing the beam through a pair of piezo-mounted slits, a transmission of 80%, a switching time of 10 μs, and an extinction ratio of 300:1 are obtained. © 2000 American Institute of Physics. View full abstract»

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  • Measurement of electron bunch timing jitter using wakefield analysis

    Page(s): 61 - 65
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    A wakefield is generated when electron bunches pass through discontinuities of beam pipes, such as rf cavities. We analyze the relation between the timing jitter of the bunches and the wakefield. From the analysis we derive a mathematical expression through which the jitter as well as the amplitude fluctuation of the bunches can be obtained by measuring the power spectrum of the wake. A measurement of the bunch jitter using this frequency-domain based wakefield analysis is compared with that measured by a time-domain based sampling oscilloscope. The two measurement results correspond well each other. © 2000 American Institute of Physics. View full abstract»

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  • The use of magnetic fields in a partial-coaxial microwave cavity holey-plate ion source

    Page(s): 66 - 69
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    A low-pressure and high-density microwave ion source created and sustained by evanescent waves emitted from a holey plate, and using permanent magnet multicusp fields, has been studied. This source is called a holey-plate ion source. Microwave power at 2.45 GHz is supplied from a coaxial cavity and then converted into an evanescent mode through the use of a holey plate. This source can produce low-pressure and high-density plasma using an octopole magnetic field. The ion current densities are in excess of 4.8 mA/cm2 at an extraction voltage of 3 kV, an argon gas pressure of 0.3 Pa in the plasma chamber, and an input microwave power of 80 W. An 18-mm-diam ion beam is extracted and accelerated from the ion source. © 2000 American Institute of Physics. View full abstract»

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  • Sapphire filter thickness optimization in neutron scattering instruments

    Page(s): 70 - 73
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    The present work is concerned with the optimization of the sapphire fast neutron filter thickness used in neutron diffraction instruments. The optimization is based on maximization of the slow neutron transmission, minimization of the fast neutron transmission, and also taking into consideration the neutron background at the vicinity of an instrument. Scattering properties of the sapphire in the fast and slow neutron regions are discussed. © 2000 American Institute of Physics. View full abstract»

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  • Ultrafast frequency sweep heterodyne reflectometer on the Tore Supra tokamak

    Page(s): 74 - 81
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    A new O-mode dual frequency heterodyne reflectometer has been installed on Tore Supra [Tore Supra Team, Fusion Technol. 29, 417 (1996)] and it has greatly improved the phase determination due to its high dynamic heterodyne detection and ultrafast sweep capabilities (10 μs) provided by its solid state source HTO. This system operates with O-mode electric field polarization in the range of 26–36 GHz and has been designed for density profile measurements. The reflectometer launches two frequencies separated by 320 MHz simultaneously into the plasma. Heterodyne detection improves the dynamics up to 60 dB, and is associated with a sin/cos detection to allow separate analysis of the amplitude and phase of each reflected signal of both probing waves. Therefore, to calculate the density profile, the group delay can be defined in two different ways: (i) from the derivative of the absolute phase of one of the two probing waves or (ii) by calculating the phase difference between the two probing waves. We explain how ultrafast sweep operations (down to 10 μs) significantly reduce the influence of plasma turbulence on the phase measurements. We also point out the importance of carefully filtering the signal detected in order to keep only information coming from the reflection at the cutoff and get rid of parasitic reflections. It is shown that the phase difference technique does not completely remove fluctuations such as long radial correlation magnetohydrodynamic perturbations. The density profiles determined by the heterodyne reflectometer are in good agreement with the measurements from the other diagnostics of Tore Supra. © 2000 American Institute of Physics. View full abstract»

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  • Eight-channel x-ray spectrometer for 0.2–1.5 keV energy range with high time and energy resolution

    Page(s): 82 - 87
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    An eight-channel soft x-ray spectrometer has been developed, manufactured, and calibrated. Each channel consists of a calibrated bandpass filter, multilayer mirror, and vacuum x-ray diode. The accuracy of channel sensitivity calibration is ≤ 15%. The time resolution of the spectrometer is Δt≈150 ps and energy resolution is E/ΔE≥20. © 2000 American Institute of Physics. View full abstract»

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  • An imaging spectrometer with a convex crystal for pulsed x rays in plasma experiments

    Page(s): 88 - 92
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    An imaging spectrometer with a convex rubidium acid phthalate (RbAP) crystal is designed and examined. Using the ray tracing technique based on the kinematical theory of diffraction, resolution power, dispersion, linearity, spatial resolution and dynamic range of the monochromatic image are discussed. Broadening by a rocking curve is also taken into account. Performance of the spectrometer is successfully examined using the so-called hot spots as the soft x-ray source which are generated in the pinched plasma by the plasma focus facility with an additional gas puff. © 2000 American Institute of Physics. View full abstract»

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  • Properties of a differential pressure pseudospark device

    Page(s): 93 - 99
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    A differential pressure pseudospark device is developed to produce a discharge at a pressure of 10-4mbar near the anode. This pressure range is two orders in magnitude lower than conventional pseudospark devices. In this device a pressure gradient is maintained between the cathode and the anode by providing a gas flow through the discharge column. The pressure gradient helps in shifting the Paschen curve more towards the left in comparison to the conventional case. The empirical relationship V∝(p2dD)-2, valid without a gas flow, is not applicable when the pressure difference between the cathode and the anode is over two orders in magnitude. Self-biasing collector technique reveals the presence of energetic electrons (0.4–1.2 keV) present in the plasma downstream of the anode. The nature of this plasma at two distinct pressure ranges of operation of the device shows marked difference in properties. A qualitative discussion is presented that explains the possible discharge mechanism in this device. © 2000 American Institute of Physics. View full abstract»

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  • Analysis of dopant concentration effects in praseodymium-based fluorescent fiber optic temperature sensors

    Page(s): 100 - 103
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    An analysis of concentration effects in praseodymium-doped glasses used as the sensor element of several fiber optic temperature sensors has been performed. Results show the dependence of a range of relevant parameters on concentration, and the determination of concentration-independent parameters used in the design of effective probe sensor elements with both doped and co-doped rare earth materials. Low concentrations of Pr3+, commensurate with an acceptable signal-to-noise ratio in the optical system, are preferable for the design of the most effective optical fiber fluorescence sensors based upon this species. © 2000 American Institute of Physics. View full abstract»

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  • Strain and temperature effects on erbium-doped fiber for decay-time based sensing

    Page(s): 104 - 108
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    An experimental investigation into the strain and temperature sensitivity of the fluorescence decay time in commercial erbium-doped optical fiber has been carried out. Results show that a strain effect on the performance of temperature-based sensors using such fiber is larger than that for neodymium-doped fiber, but a little smaller than is seen in similar ytterbium-doped material. For the materials studied, the relative change in lifetime ranges from about 5×10-7 (for Yb) to 14×10-7 (for Nd) μЄ-1 and the associated error in the temperature measurement ranges from 1.8×10-3 (for Nd) to 6.1×10-3KμЄ-1 for the Yb sample used. The application to simultaneous strain and temperature monitoring is discussed. © 2000 American Institute of Physics. View full abstract»

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  • A four-point constant-current/temperature controlled circuit for anemometric applications

    Page(s): 109 - 112
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    A four-point constant-current/temperature controlled circuit is an electronic system for supplying a resistance measuring sensor in two modes of operation: either in constant-current or in constant-temperature mode. This circuit is destined for anemometric applications. It is new nonbridge, four-point constant-current/temperature anemometer circuit. Separation of current and voltage leads of the sensor makes it possible to eliminate the effects of leads’ resistance on the preset value of sensor supply parameters. In such a circuit no cable adjustment is required. The value of sensor current or its resistance is set with digital signals. This article presents the design of the original measuring circuit and its principle of operation. Design of measuring circuit based on those principles is also presented. Attention is also given to its applications. The most important advantages of the new circuit are: both constant-current or constant-temperature modes of operation are available, precise digital control of sensor current or resistance can be performed, and four-point sensor operation in both modes is possible. It enables high-precision laboratory anemometric measurements, especially under the conditions of low sensor resistance, low overheat ratio range, and long sensor supply cables. © 2000 American Institute of Physics. View full abstract»

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  • Visible light scattering to measure small scale turbulence

    Page(s): 113 - 117
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    A laser scattering optical bench using ionized argon laser was set up to study the small scales of turbulence. Scales between 200 and 10 μm are resolved. The signal being proportional to the Fourier transform of the density fluctuations, heterodyne detection is used to recover its real and imaginary parts. The optical and electronic facilities are described in detail. The minimum density fluctuations for a signal-to-noise ratio greater than 1 is assessed. Using an acoustic wave, the spatial bandpass filter of the Fourier transform is demonstrated. A sample of recorded signals on a turbulent air jet is shown and the dependence of their intensity on the analyzing wave vector is discussed. The frequency spectra are shown to reflect the temperature and the pressure fluctuations. One can thus measure the flow and sound speed. © 2000 American Institute of Physics. View full abstract»

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  • Characterization of an open-loop controlled scanning stage using a knife edge optical technique

    Page(s): 118 - 123
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    Our experimental confocal microscope project required the construction of a high performance scanning stage. In order to understand the scanning stage behavior we modeled each axis of motion as a damped harmonic oscillator, and measured its mechanical response using an optical knife edge technique. In order to maximize the scan stage accuracy and performance we used the characterization results of the stage to implement first order correction for such influences as the mass, the damping, and the stiffness of the springs of the scanning stage. We show that the stage can be driven over a range of frequencies and motion wave forms, without inducing primary resonant response, and this results in an improved quality of the confocal images. We have constructed a novel scanning motion incorporating the corrected results. The linearity of motion was found to be better than with a ramp or sine wave driving voltage, enabling an order of magnitude increase in speed of acquisition. © 2000 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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Editor
Albert T. Macrander
Argonne National Laboratory