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Review of Scientific Instruments

Issue 5 • Date May 2009

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Displaying Results 1 - 25 of 67
  • Issue Cover

    Page(s): c1
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  • Issue Table of Contents

    Page(s): toc1
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  • Acousto-optic modulator based frequency stabilized diode laser system for atom trapping

    Page(s): 053101 - 053101-4
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    We report on an inexpensive commercial laser diode stabilized to the D2-line in rubidium using a simple scheme. The linewidth was reduced to 1.3 MHz without an external cavity, making it suitable for laser cooling and trapping. The system is very robust and the laser frequency can be changed rapidly (within 51 μs) while the laser remains in lock. The frequency of the locked laser drifts less than 850 kHz peak-to-peak over 25 h. We demonstrate laser cooling and trapping using our system. View full abstract»

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  • Tapered optical fibers as tools for probing magneto-optical trap characteristics

    Page(s): 053102 - 053102-5
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    We present a novel technique for measuring the characteristics of a magneto-optical trap (MOT) for cold atoms by monitoring the spontaneous emission from trapped atoms coupled into the guided mode of a tapered optical nanofiber. We show that the nanofiber is highly sensitive to very small numbers of atoms close to its surface. The size and shape of the MOT, determined by translating the cold atom cloud across the tapered fiber, is in excellent agreement with measurements obtained using the conventional method of fluorescence imaging using a charge coupled device camera. The coupling of atomic fluorescence into the tapered fiber also allows us to monitor the loading and lifetime of the trap. The results are compared to those achieved by focusing the MOT fluorescence onto a photodiode and it was seen that the tapered fiber gives slightly longer loading and lifetime measurements due to the sensitivity of the fiber, even when very few atoms are present. View full abstract»

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  • Analysis and calibration of absorptive images of Bose–Einstein condensate at nonzero temperatures

    Page(s): 053103 - 053103-7
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    We describe the method allowing quantitative interpretation of absorptive images of mixtures of Bose–Einstein condensate and thermal atoms which reduces possible systematic errors associated with evaluation of the contribution of each fraction and eliminates arbitrariness of most of the previous approaches. By using known temperature dependence of the BEC fraction, the analysis allows precise calibration of the fitting results. The developed method is verified in two different measurements and compares well with theoretical calculations and with measurements performed by another group. View full abstract»

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  • Toward real-time charged-particle image reconstruction using polar onion-peeling

    Page(s): 053104 - 053104-7
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    A method to reconstruct full three-dimensional photofragment distributions from their two-dimensional (2D) projection onto a detection plane is presented, for processes in which the expanding Newton sphere has cylindrical symmetry around an axis parallel to the projection plane. The method is based on: (1) onion-peeling in polar coordinates [Zhao etal, Rev. Sci. Instrum. 73, 3044 (2002)] in which the contribution to the 2D projection from events outside the plane bisecting the Newton sphere are subtracted in polar coordinates at incrementally decreasing radii; and (2) ideas borrowed from the basis set expansion (pBASEX) method in polar coordinates [Garcia etal, Rev. Sci. Instrum. 75, 4989 (2004)], which we use to generate 2D projections at each incremental radius for the subtraction. Our method is as good as the pBASEX method in terms of accuracy, is devoid of centerline noise common to reconstruction methods employing Cartesian coordinates; and it is computationally cheap allowing images to be reconstructed as they are being acquired in a typical imaging experiment. View full abstract»

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  • Cold-target recoil-ion momentum spectroscopy for diagnostics of high harmonics of the extreme-ultraviolet free-electron laser light source at SPring-8

    Page(s): 053105 - 053105-4
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    We have developed a cold-target recoil-ion momentum spectroscopy apparatus dedicated to the experiments using the extreme-ultraviolet light pulses at the free-electron laser facility, SPring-8 Compact SASE Source test accelerator, in Japan and used it to measure spatial distributions of fundamental, second, and third harmonics at the end station. View full abstract»

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  • Lensless Fourier transform digital holographic interferometer for diffusivity measurement of miscible transparent liquids

    Page(s): 053106 - 053106-6
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    Lensless Fourier transform digital holographic technique is applied for measurement of diffusion in miscible transparent liquid solutions. The phase information at two time instances and a synthetic plane wavefront is used to determine the diffusion coefficient. The experiment was conducted to measure the diffusion coefficient of aqueous solution of NaCl in water. The measured values of diffusion coefficient deviates approximately 1.06% from the values given in literature. View full abstract»

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  • Measurement of small birefringence and loss in a nonlinear single-mode waveguide

    Page(s): 053107 - 053107-6
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    We design and fabricate a birefringent semiconductor waveguide for application to nonlinear photonics, demonstrating that it is possible to engineer a small birefringence into such a device using multiple core layers. We also demonstrate a simple technique to accurately determine small waveguide birefringence using a differential measurement, present useful methods for coupling light into and out of the device, and make estimates of coupling and linear device losses. View full abstract»

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  • Characterizing the detection system nonlinearity, internal inelastic background, and transmission function of an electron spectrometer for use in x-ray photoelectron spectroscopy

    Page(s): 053108 - 053108-7
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    We present a method for removing spectrometer specific contributions to x-ray photoelectron spectroscopy data. We consider the degree of linearity of the detection system, the strength of the internal analyzer inelastic background, and finally determine the spectrometer’s transmission function. The procedures presented here are performed on a SPECS Phoibos 150 hemispherical analyzer with a two-dimensional detection system, but are applicable to a wide variety of different electron spectrometers. The spectrometer’s detection system is found to deviate from linear behavior by a few percent over the whole intensity range studied. The size of the analyzer internal inelastic scattering has been measured, and we find that it can normally be neglected at large pass energies or high kinetic energies for most types of analysis (contributing less than 1% at 100 eV pass energy). Finally, we measure the transmission function of the analyzer and lens system for a variety of different settings with the preceding corrections applied, and find that the form of the transmission function is dependent on small changes in the system’s settings. View full abstract»

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  • A versatile fiber-optic coupled system for sensitive optical spectroscopy in strong ambient light

    Page(s): 053109 - 053109-4
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    In this work we describe design and use of a fiber-optic based optical system for the spectroscopic studies on the samples under the presence of strong ambient light. The system is tested to monitor absorption, emission, and picosecond-resolved fluorescence transients simultaneously with a time interval of 500 ms for several hours on a biologically important sample (vitamin B2) under strong UV light. An efficient stray-light rejection ratio of the setup is achieved by the confocal geometry of the excitation and detection channels. It is demonstrated using this setup that even low optical signal from a liquid sample under strong UV-exposure for the picosecond-resolved fluorescence transient measurement can reliably be detected by ultrasensitive microchannel plate photomultiplier tube solid state detector. The kinetics of photodeterioration of vitamin B2 measured using our setup is consistent with that reported in the literature. Our present studies also justify the usage of tungsten light than the fluorescent light for the healthy preservation of food with vitamin B2. View full abstract»

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  • Simplified ultrafast pulse shaper for tailored polarization states using a birefringent prism

    Page(s): 053110 - 053110-8
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    A new polarization pulse shaping method utilizing a birefringent prism as both the spectrally dispersing and polarization separating element is presented and analyzed. The method of appropriate prism design is first examined, followed by calibration technique and experimental demonstration of the pulse shaper. Using phase-only modulation by means of a spatial light modulator, we obtain near-transform limited pulses. Furthermore, a sinusoidal spectral phase imparted on the pulse is retrieved and qualitatively compares well with the theoretical target field. View full abstract»

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  • Depolarization ratio measurement using single photomultiplier tube in micropulse lidar

    Page(s): 053111 - 053111-5
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    The conventional dual polarization micropulse lidar uses two separate photomultiplier tubes (PMT) to detect both the copolarized and cross-polarized beam. The prominent sources of error in the depolarization ratio measurement are mismatch in PMT, improper selection of discriminator threshold and unequal PMT high voltage. In the present work a technique for the measurement of lidar depolarization ratio using only one PMT sensor has been developed. The same PMT detects both copolarized and cross-polarized lidar backscatter. A stepper motor is used along with the mirrors to bring both the received polarization signals over the PMT window. Application of the same PMT minimizes the error caused in the depolarization ratio measurement due to error in photon counting of an individual channel. The design description of this technique along with the preliminary results depicting its functionality has been mentioned in this article. View full abstract»

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  • Study on single-transverse mode output of high-power flat He–Ne laser

    Page(s): 053112 - 053112-3
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    The multimode output power of He–Ne lasers with a flat discharge tube can be enhanced by increasing the transverse size of the discharge tube. By using an N-type fold optical resonator, the high-power flat He–Ne laser tube can give the output in the lower-order mode. Inserting a limiting-mode circular-hole diaphragm into the N-type fold optical resonator, the lower-order modes are suppressed gradually with the reduction in its aperture. The high-power flat He–Ne laser tube of 1.4 m discharge length can achieve above 80 mW of the single-transverse mode output power using an N-type fold optical resonator with a limiting-mode circular-hole diaphragm of 4 mm aperture. Its output characteristics and laser mode patterns are investigated experimentally. The experimental method is introduced and its results are discussed briefly in this paper. View full abstract»

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  • Polarization mode dispersion emulation using polarization maintaining fibers: Fixed root-mean-square differential group delay but varying second-order polarization mode dispersion

    Page(s): 053113 - 053113-5
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    We report on a polarization mode dispersion (PMD) emulator with a fixed root-mean-square differential group delay (RMS-DGD) but varying second-order PMD (SO-PMD) using only a combination of polarization maintaining fibers and a polarization controller. The SO-PMD control mechanism is not completely in real time. Besides controlling the mean PMD values of the emulator, simultaneous adjustments in the maximum and minimum values of PMD statistics can be performed. We therefore illustrate irregular fluctuations that occur around the RMS-DGD due to SO-PMD. This novel design can be used to further show the impact of a high first-order PMD segment on the DGD and SO-PMD statistical distributions that might occur in an optical network system. View full abstract»

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  • Separation algorithm for a 2D refractive index distribution and thickness profile of a phase object by laser diode-based multiwavelength interferometry

    Page(s): 053114 - 053114-5
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    A separation algorithm that uses three wavelengths for the simultaneous measurement of the two-dimensional refractive index distribution and thickness profile of transparent samples is proposed. The optical system is based on a Mach–Zehnder interferometer with laser diode-based multiwavelength sources. A liquid crystal retarder is used to obtain interference images at four states with phases, and the optical phase of the object is then calculated with a four-bucket algorithm. A glass rod and several samples, including a slide glass, a glass wafer, and a cover glass are used to obtain experimental results at wavelengths of 635, 660, and 675 nm. The refractive indices of the sample are distributed with an accuracy of less than 0.0003 and the thickness profile is calculated on the basis of the measured refractive index. This result demonstrates that the proposed algorithm can be used to separate the refractive index distribution and thickness profile of samples in two dimensions. View full abstract»

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  • Retarding potential and induction charge detectors in tandem for measuring the charge and mass of nanodroplets

    Page(s): 053301 - 053301-4
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    The determination of the mass of a nanoparticle via time-of-flight typically requires a direct measurement of its charge. This can be done with a differential retarding potential analyzer and an induction charge detector operating in tandem. The spectrometer described in this article selects a particle with a specified retarding potential from a beam and directs it to an induction charge detector where both its velocity and charge are measured. The retarding potential, velocity, and charge also yield the particle’s mass. The particle is analyzed without the need to collect it, and therefore can be employed in a subsequent experiment. The high charge sensitivity of the induction charge detector and the capability for working at low retarding potentials make the characterization of electrosprayed nanodroplets possible for the first time. View full abstract»

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  • Ion spectrometer composed of time-of-flight and Thomson parabola spectrometers for simultaneous characterization of laser-driven ions

    Page(s): 053302 - 053302-10
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    An ion spectrometer, composed of a time-of-flight spectrometer (TOFS) and a Thomson parabola spectrometer (TPS), has been developed to measure energy spectra and to analyze species of laser-driven ions. Two spectrometers can be operated simultaneously, thereby facilitate to compare the independently measured data and to combine advantages of each spectrometer. Real-time and shot-to-shot characterizations have been possible with the TOFS, and species of ions can be analyzed with the TPS. The two spectrometers show very good agreement of maximum proton energy even for a single laser shot. The composite ion spectrometer can provide two complementary spectra measured by TOFS with a large solid angle and TPS with a small one for the same ion source, which are useful to estimate precise total ion number and to investigate fine structure of energy spectrum at high energy depending on the detection position and solid angle. Advantage and comparison to other online measurement system, such as the TPS equipped with microchannel plate, are discussed in terms of overlay of ion species, high-repetition rate operation, detection solid angle, and detector characteristics of imaging plate. View full abstract»

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  • A robust method for measurement of fluctuation parallel wavenumber in laboratory plasmas

    Page(s): 053501 - 053501-5
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    Measuring the parallel wavenumber is fundamental for the experimental characterization of electrostatic instabilities. It becomes particularly important in toroidal geometry, where spatial inhomogeneities and curvature can excite both drift instabilities, whose wavenumber parallel to the magnetic field is finite, and interchange instabilities, which typically have vanishing parallel wavenumber. We demonstrate that multipoint measurements can provide a robust method for the discrimination between the two cases. View full abstract»

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  • Diamagnetic measurements in the STOR-M tokamak by a flux loop system exterior to the vacuum vessel

    Page(s): 053502 - 053502-6
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    Diamagnetic measurements of poloidal beta have been performed in the STOR-M tokamak by a flux loop placed exterior to the vacuum chamber with compensation for the vacuum toroidal field using a nonenclosing coplanar coil, and vibrational compensation from auxiliary coils. It was found that in STOR-M conditions (20% toroidal magnetic field decay over discharge) there is significant influence on the diamagnetic flux measurements from strong residual signals, presumably from image currents being induced by the toroidal field coils, requiring further compensation. A blank (nonplasma) shot is used specifically to eliminate the residual component which is not proportional to the toroidal magnetic field. Data from normal Ohmic discharge operation is presented and calculations of poloidal beta from coil data θ∼0.5) is found to be in reasonable agreement with the values of poloidal beta obtained from measurements of electron density and Spitzer temperature with neoclassical corrections for trapped electrons. Contributions present in the blank shot (residual) signal and the limitations of this method are discussed. View full abstract»

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  • Scintillator based detector for fast-ion losses induced by magnetohydrodynamic instabilities in the ASDEX upgrade tokamak

    Page(s): 053503 - 053503-9
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    A scintillator based detector for fast-ion losses has been designed and installed on the ASDEX upgrade (AUG) tokamak [A. Herrmann and O. Gruber, Fusion Sci. Technol. 44, 569 (2003)]. The detector resolves in time the energy and pitch angle of fast-ion losses induced by magnetohydrodynamics (MHD) fluctuations. The use of a novel scintillator material with a very short decay time and high quantum efficiency allows to identify the MHD fluctuations responsible for the ion losses through Fourier analysis. A Faraday cup (secondary scintillator plate) has been embedded behind the scintillator plate for an absolute calibration of the detector. The detector is mounted on a manipulator to vary its radial position with respect to the plasma. A thermocouple on the inner side of the graphite protection enables the safety search for the most adequate radial position. To align the scintillator light pattern with the light detectors a system composed by a lens and a vacuum-compatible halogen lamp has been allocated within the detector head. In this paper, the design of the scintillator probe, as well as the new technique used to analyze the data through spectrograms will be described. A last section is devoted to discuss the diagnosis prospects of this method for ITER [M. Shimada etal, Nucl. Fusion 47, S1 (2007)]. View full abstract»

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  • Mass- and energy-analyses of ions from plasma by means of a miniature Thomson spectrometer

    Page(s): 053504 - 053504-4
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    The paper presents an improved version of a miniature mass-spectrometer of the Thomson-type, which has been adopted for ion analysis near the dense plasma region inside a vacuum chamber. Problems connected with the separation of ions from plasma streams are considered. Input diaphragms and pumping systems, needed to ensure good vacuum inside the analyzing region, are described. The application of the miniature Thomson-type analyzer is illustrated by ion parabolas recorded in plasma-focus facility and rod plasma injector experiment. A quantitative analysis of the recorded ion parabolas is presented. Factors influencing accuracy of the ion analysis are discussed and methods of the spectrometer calibration are described. View full abstract»

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  • High resolution laser induced fluorescence Doppler velocimetry utilizing saturated absorption spectroscopy

    Page(s): 053505 - 053505-4
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    A high resolution laser induced fluorescence (LIF) system has been developed to measure the flow velocity field of neutral particles in an electron-cyclotron-resonance argon plasma. The flow velocity has been determined by the Doppler shift of the LIF spectrum, which is proportional to the velocity distribution function. Very high accuracy in velocity determination has been achieved by installing a saturated absorption spectroscopy unit into the LIF system, where the absolute value and scale of laser wavelength are determined by using the Lamb dip and the fringes of a Fabry–Pérot interferometer. The minimum detectable flow velocity of a newly developed LIF system is ±2 m/s, and this performance remains unchanged in a long-time experiment. From the radial measurements of LIF spectra of argon metastable atoms, it is found that there exists an inward flow of neutral particles associated with neutral depletion. View full abstract»

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  • A new low drift integrator system for the Experiment Advanced Superconductor Tokamak

    Page(s): 053506 - 053506-6
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    A new type of the integrator system with the low drift characteristic has been developed to accommodate the long pulse plasma discharges on Experiment Advanced Superconductor Tokamak (EAST). The integrator system is composed of the Ethernet control module and the integral module which includes one integrator circuit, followed by two isolation circuits and two program-controlled amplifier circuits. It compensates automatically integration drift and is applied in real-time control. The performance test and the experimental results in plasma discharges show that the developed integrator system can meet the requirements of plasma control on the accuracy and noise level of the integrator in long pulse discharges. View full abstract»

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  • Compact microwave re-entrant cavity applicator for plasma-assisted combustion

    Page(s): 053507 - 053507-9
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    The design and experimental operation of a compact microwave/rf applicator is described. This applicator operates at atmospheric pressure and couples electromagnetic energy into a premixed CH4/O2 flame. The addition of only 2–15 W of microwave power to a premixed combustion flame with a flame power of 10–40 W serves to extend the flammability limits for fuel lean conditions, increases the flame length and intensity, and increases the number density and mixture of excited radical species in the flame vicinity. The downstream gas temperature also increases. Optical emission spectroscopy measurements show gas rotational temperatures in the range of 2500–3600 K. At the higher input power of ≥10 W microplasma discharges can be produced in the high electric field region of the applicator. 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