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Review of Scientific Instruments

Issue 11 • Date Nov 2007

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Displaying Results 1 - 25 of 61
  • Issue Cover

    Page(s): c1
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  • Issue Table of Contents

    Page(s): toc1
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  • Invited Article: An improved double-toroidal spectrometer for gas phase (e,2e) studies

    Page(s): 111301 - 111301-20
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    A new spectrometer is described for measuring the momentum distributions of scattered electrons arising from electron-atom and electron-molecule ionization experiments. It incorporates and builds on elements from a number of previous designs, namely, a source of polarized electrons and two high-efficiency electrostatic electron energy analyzers. The analyzers each comprise a seven-element retarding-electrostatic lens system, four toroidal-sector electrodes, and a fast position-and-time-sensitive two-dimensional delay-line detector. Results are presented for the electron-impact-induced ionization of helium and the elastic scattering of electrons from argon and helium which demonstrate that high levels of momentum resolution and data-collection efficiency are achieved. Problematic aspects regarding variations in collection efficiency over the accepted momentum phase space are addressed and a methodology for their correction presented. Principles behind the present design and previous designs for electrostatic analyzers based around electrodes of toroidal-sector geometry are discussed and a framework is provided for optimizing future devices. View full abstract»

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  • An atomic jet in a heat pipe for multiphoton spectroscopy

    Page(s): 113101 - 113101-3
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    A conventional heat pipe is modified to operate as a novel atomic jet setup with unprecedented advantages for multiphoton spectroscopy of alkaline-earth atoms especially to study the effect of external electric field, controlled excitation of forbidden transitions and for the study of collisional broadening and shift of excited states, and time evolution of Rydberg atoms. View full abstract»

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  • Common-path optical coherence tomography with side-viewing bare fiber probe for endoscopic optical coherence tomography

    Page(s): 113102 - 113102-4
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    All-fiber-optic common-path optical coherence tomography (OCT) using a side-viewing bare fiber probe has been demonstrated and analyzed. A bare single mode fiber tip is angle cleaved at ∼49° to enable side illumination due to total internal reflection. The bare fiber probe was inserted in an arterial tissue and a circumferential OCT scan was obtained. The research is aimed at realizing highly miniaturized monolithic probes for possible applications in miniature endoscopic OCT or intravascular OCT. The effects of the angle of the cleaved fiber on reference reflection and the sensitivity of the common-path OCT system have been studied theoretically. The angle cleaved fiber probe is also used in series with a microlens to analyze and optimize its performance in a common-path OCT system. Our research aims to explore the combined advantages of common-path OCT and extremely simplified miniature probe design and to discuss how it may greatly simplify the endoscopic OCT instrumentation eventually. View full abstract»

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  • A diffraction-compensating 0–25 ns free space terahertz delay line for coherent quantum control

    Page(s): 113103 - 113103-5
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    Free space delay lines provide pulses of variable time spacing for optical experiments such as pump-probe spectroscopy and coherent quantum control, including spin and photon echo techniques. However, in the terahertz region of the spectrum, beam divergence due to diffraction limits the useful length of traditional free space delay lines. We present a novel double-folded variable delay line for light in the frequency range 0.24–1.2 THz, which incorporates a symmetric arrangement of lenses whose spacing can be adjusted to compensate for diffraction at each delay. Scalable for use in other wavelength regimes, the design relays an input Gaussian beam waist to the output with up to 25 ns (∼8 m) total delay and is enclosed in a desiccated volume of ≪0.5 m3. The delay line can deliver two or three pulses with relative amplitudes controlled via variable spacing silicon étalon beam splitters. Profiles of a 0.24 THz beam show good agreement with calculations at long delays, with insertion loss per delay stage of ∼3 dB. View full abstract»

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  • High repetition rate laser produced soft x-ray source for ultrafast x-ray absorption near edge structure measurements

    Page(s): 113104 - 113104-7
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    Recent progress in high intensity ultrafast laser systems provides the opportunity to produce laser plasma x-ray sources exhibiting broad spectrum and high average x-ray flux that are well adapted to x-ray absorption measurements. In this paper, the development of a laser based x-ray absorption near edge structure (XANES) beamline exhibiting high repetition rate by using the Advanced Laser Light Source (ALLS) facility 100 Hz laser system (100 mJ, 35 fs at 800 nm) is presented. This system is based on a broadband tantalum solid target soft x-ray source and a grazing incidence grating spectrometer in the 1–5 nm wavelength range. To demonstrate the high potential of this laser based XANES technique in condensed matter physics, material science, or biology, measurements realized with several samples are presented: VO2 vanadium L edge, Si3N4 nitrogen K edge, and BPDA/PPD polyimide carbon K edge. The characteristics of this laser based beamline are discussed in terms of brightness, signal to noise ratio, and compared to conventional synchrotron broadband x-ray sources which allow achieving similar measurements. Apart from the very compact size and the relative low cost, the main advantages of such a laser based soft x-ray source are the picosecond pulse duration and the perfect synchronization between this x-ray probe and a laser pulse excitation which open the way to the realization of time resolved x-ray absorption measurements with picosecond range time resolution to study the dynamics of ultrafast processes and phase transition. View full abstract»

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  • IMPACT: A facility to study the interaction of low-energy intense particle beams with dynamic heterogeneous surfaces

    Page(s): 113105 - 113105-14
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    The Interaction of Materials with Particles and Components Testing (IMPACT) experimental facility is furnished with multiple ion sources and in situ diagnostics to study the modification of surfaces undergoing physical, chemical, and electronic changes during exposure to energetic particle beams. Ion beams with energies in the range between 20 and 5000 eV can bombard samples at flux levels in the range of 1010–1015 cm-2 s-1; parameters such as ion angle of incidence and exposed area are also controllable during the experiment. IMPACT has diagnostics that allow full characterization of the beam, including a Faraday cup, a beam imaging system, and a retarding field energy analyzer. IMPACT is equipped with multiple diagnostics, such as electron (Auger, photoelectron) and ion scattering spectroscopies that allow different probing depths of the sample to monitor compositional changes in multicomponent and/or layered targets. A unique real-time erosion diagnostic based on a dual quartz crystal microbalance measures deposition from an eroding surface with rates smaller than 0.01 nm/s, which can be converted to a sputter yield measurement. The monitoring crystal can be rotated and placed in the target position so that the deposited material on the quartz crystal oscillator surface can be characterized without transfer outside of the vacuum chamber. View full abstract»

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  • Four-point bisensitivity velocity interferometer with a multireflection etalon

    Page(s): 113106 - 113106-4
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    A four-point bisensitivity velocity interferometer system for any reflector (VISAR) with a renovative delay etalon is proposed and demonstrated. In this interferometer, we introduce a new film-coating strategy to accurately measure small velocity with relatively short and cheap etalon. Laser pointing to the etalon is split into two beams with different incident angles with each beam going through the etalon in different path. The beam with the smaller incident angle is reflected three times before it leaves the etalon, while the other beam with larger incident angle goes through the etalon to and forth only once. The delay time of the laser beam with smaller incident angle is almost three times longer than that of the beam with larger incident angle. In the example of the laser with a smaller incident angle, the velocity per fringe of this interferometer can be reduced by approximately three times. The etalon is optimized so that four laser beams can be penetrated in the vertical direction at the meantime. With an etalon of 200 mm in diameter and 150 mm in length, a four-point bisensitivity velocity interferometer can achieve the velocity per fringe of 100 and 350 m/s fringe. A measurement has been successfully undertaken for the steel flyer driven by the explosive where the developed interferometer applies. View full abstract»

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  • Flexible lock-in detection system based on synchronized computer plug-in boards applied in sensitive gas spectroscopy

    Page(s): 113107 - 113107-7
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    We present a flexible and compact, digital, lock-in detection system and its use in high-resolution tunable diode laser spectroscopy. The system involves coherent sampling, and is based on the synchronization of two data acquisition cards running on a single standard computer. A software-controlled arbitrary waveform generator is used for laser modulation, and a four-channel analog/digital board records detector signals. Gas spectroscopy is performed in the wavelength modulation regime. The coherently detected signal is averaged a selected number of times before it is stored or analyzed by software-based, lock-in techniques. Multiple harmonics of the modulation signal (1f, 2f, 3f, 4f, etc.) are available in each single data set. The sensitivity is of the order of 10-5, being limited by interference fringes in the measurement setup. The capabilities of the system are demonstrated by measurements of molecular oxygen in ambient air, as well as dispersed gas in scattering materials, such as plants and human tissue. View full abstract»

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  • Manufacturing a thin wire electrostatic trap for ultracold polar molecules

    Page(s): 113108 - 113108-4
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    We present a detailed description on how to build a thin wire electrostatic trap (TWIST) for ultracold polar molecules. It is the first design of an electrostatic trap that can be superimposed directly onto a magneto-optical trap (MOT). We can thus continuously produce ultracold polar molecules via photoassociation from a two species MOT and instantaneously trap them in the TWIST without the need for complex transfer schemes. Despite the spatial overlap of the TWIST and the MOT, the two traps can be operated and optimized completely independently due to the complementary nature of the utilized trapping mechanisms. View full abstract»

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  • Operating a triple stack microchannel plate-phosphor assembly for single particle counting in the 12–300 K temperature range

    Page(s): 113301 - 113301-5
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    An assembly consisting of a stack of three microchannel plates (MCPs) and a phosphor screen anode has been operated over the temperature range from 300 to 12 K. We report on measurements at 6.4 kHz (using an alpha source) and with dark counts only (15 Hz). Without any particle source, the MCP bias current decreased by a factor of 2.1×103 when the temperature was lowered from 300 to 12 K. Using the alpha source, and a photomultiplier tube (PMT) to monitor the phosphor screen anode, we first observed an increase in the decay time of the phosphor from 12 to 45 μs when the temperature was decreased from 300 to 100 K while the decay time then decreased and reached a value of 5 μs at 12 K. The pulse height distribution from the PMT was measured between 300 and 12 K and shows a spectrum typical for a MCP phosphor setup at 300 K and 12 K but is strongly degraded for intermediate temperatures. We conclude that the present MCP-phosphor detector assembly is well suited for position-sensitive particle counting operation at temperatures down to at least 12 K even for count rates beyond 6 kHz. This result is crucial and an important part of ongoing developments of new instrumentation for investigations of, e.g., interactions involving complex molecular ions with internal qu- antum state control. View full abstract»

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  • The development of Thomson scattering system on HL-2A tokamak

    Page(s): 113501 - 113501-5
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    A new Thomson scattering diagnostic system is successfully developed to measure core plasma electron temperature (Te) and density (ne) of HL-2A tokamak (major radius R=165 cm, minor radius a=40 cm). In this system, a standard lamp-monochromator combination is utilized for the calibration of spectral responses. By sweeping in the range of 750–1200 nm with a step of 2 nm, the work can be done automatically for one-point calibration and then for other. Electronic gain calibration and gain monitoring are done by pulsed light emitting diode light. By utilizing an intense Nd:YAG laser of pulse energy up to 4 J and employing good quality interference filters in the five-channel filter polychromator to surpress greatly the stray light, the TS system can be routinely used to make measurements with good quality data. After each HL-2A plasma discharge, the measured Te and ne data are transferred to HL-2A database for lookup and analyses. View full abstract»

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  • A simple technique to estimate the fully time-resolved x-ray diameter of a z pinch

    Page(s): 113502 - 113502-4
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    Occultations are routinely used to derive information about astronomical objects. Here an occultation scheme is used to derive a fully time-resolved estimate of the x-ray emitting diameter of a z pinch. By using different filtrations on the sensors, one could for example, distinguish the size of the K-line emitting region compared to the higher energy K-continuum emitting volume. Or with suitable apertures and detector arrays, the pinch diameter could be axially and temporally resolved. View full abstract»

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  • A new multichannel interferometer system on HL-2A

    Page(s): 113503 - 113503-4
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    A new multichannel HCN interferometer has been developed on HL-2A tokamak, which is characterized by two techniques: (1) the wave-guide HCN laser with cavity length of 6 m to increase the optical resource power and (2) high response room temperature waveguide Schottky diode detectors to obtain good beat signal. The space resolution is 7 cm by the use of focusing metal mirrors mounted on the vacuum chamber and a compensated optical system. In the 2006 experiment campaign, this new interferometer has been applied for plasma density profile and density sawtooth measurement. View full abstract»

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  • High accuracy plasma density measurement using hybrid Langmuir probe and microwave interferometer method

    Page(s): 113504 - 113504-7
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    High spatial resolution plasma density measurements have been taken as part of an investigation into magnetic nozzle physics at the NASA/MSFC Propulsion Research Center. These measurements utilized a Langmuir triple probe scanned across the measurement chord of either of two stationary rf interferometers. By normalizing the scanned profile to the microwave interferometer line-integrated density measurement for each electrostatic probe measurement, the effect of shot-to-shot variation of the line-integrated density can be removed. In addition, by summing the voltage readings at each radial position in a transverse scan, the line density can be reconstituted, allowing the absolute density to be determined, assuming that the shape of the profile is constant from shot to shot. The spatial and temporal resolutions of this measurement technique depend on the resolutions of the scanned electrostatic probe and the interferometer. The measurement accuracy is 9%–15%, which is on the order of the accuracy of the rf interferometer. The measurement technique was compared directly with both scanning rf interferometer and standard Langmuir probe theory. The hybrid technique compares favorably with the scanning rf interferometer, and appears more accurate than probe theory alone. Additionally, our measurement technique is generally applicable even for nonaxisymmetric plasmas. View full abstract»

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  • Computer simulation of three-dimensional heavy ion beam trajectory imaging techniques used for magnetic field estimation

    Page(s): 113505 - 113505-6
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    A magnetic field mapping technique via heavy ion beam trajectory imaging is being developed on the Madison Symmetric Torus reversed field pinch. This paper describes the computational tools created to model camera images of the light emitted from a simulated ion beam, reconstruct a three-dimensional trajectory, and estimate the accuracy of the reconstruction. First, a computer model is used to create images of the torus interior from any candidate camera location. It is used to explore the visual field of the camera and thus to guide camera parameters and placement. Second, it is shown that a three-dimensional ion beam trajectory can be recovered from a pair of perspectively projected trajectory images. The reconstruction considers effects due to finite beam size, nonuniform beam current density, and image background noise. Third, it is demonstrated that the trajectory reconstructed from camera images can help compute magnetic field profiles, and might be used as an additional constraint to an equilibrium reconstruction code, such as MSTFit. View full abstract»

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  • Raman calibration of the HT-7 yttrium aluminum garnet Thomson scattering for electron density measurements

    Page(s): 113506 - 113506-4
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    A multipulse neodym doped yttrium aluminum garnet laser Thomson scattering system calibrated by the anti-Stokes rotational Raman scattering from nitrogen gas had been developed in the HT-7 superconducting Tokmak. By virtue of this system, measured electron density results of the plasma were obtained. The results showed good repeatability and its total uncertainty was estimated to be ±18%. View full abstract»

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  • Shear force control for a terahertz near field microscope

    Page(s): 113701 - 113701-6
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    We report on the advancement of apertureless terahertz microscopy by active shear force control of the scanning probe. Extreme subwavelength spatial resolution and a maximized image contrast are achieved by maintaining a tip-surface distance of about 20 nm. The constant distance between scanning tip and surface results in terahertz images that mirror the dielectric permittivity of the surface. View full abstract»

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  • Phototriggering system for an ultrahigh-speed video microscopy

    Page(s): 113702 - 113702-5
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    A phototrigger system is developed as a part of a video microscope mounting an ultrahigh-speed video camera capable of image capturing at frame rates as high as 1×106 frames/s. The extremely high frame rate is achieved by implementing in situ image storage. A distinguished feature of the camera is the on-chip overwriting mechanism that allows to keep in storage the latest image sequence of 103 frames; the old signals are continuously drained out of the storage. The trigger system is designed to synchronize recording operations with an occurrence of a target event within the limited image capturing duration. The target event is detected through a sudden change in the output of a sensor mounted to an optical port of the microscope. To reduce noise contribution, a two-sensor architecture is implemented. One sensor detects the target event while the one produces a reference signal used for noise reduction. Both sensors are connected to the same optical port by using a specially designed beam splitting unit. To provide high sensitivity, avalanche photodiodes are used as photoelements. System evaluation shows that its sensitivity is high and response time is less than 3 μs. This is sufficiently fast for high-speed video-microscopy observations at 1×106 frames/s when using a video camera with a storage of 103 frames. As an example, the system was used in a microscopic observation of a soap film collapse. View full abstract»

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  • Single-step electrochemical method for producing very sharp Au scanning tunneling microscopy tips

    Page(s): 113703 - 113703-4
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    A single-step electrochemical method for making sharp gold scanning tunneling microscopy tips is described. 3.0M NaCl in 1% perchloric acid is compared to several previously reported etchants. The addition of perchloric acid to sodium chloride solutions drastically shortens etching times and is shown by transmission electron microscopy to produce very sharp tips with a mean radius of curvature of 15 nm. View full abstract»

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  • Apparatus for real-time acoustic imaging of Rayleigh-Bénard convection

    Page(s): 113704 - 113704-8
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    We have designed and built an apparatus for real-time acoustic imaging of convective flow patterns in optically opaque fluids. This apparatus takes advantage of recent advances in two-dimensional ultrasound transducer array technology; it employs a modified version of a commercially available ultrasound camera, similar to those employed in nondestructive testing of solids. Images of convection patterns are generated by observing the lateral variation of the temperature dependent speed of sound via refraction of acoustic plane waves passing vertically through the fluid layer. The apparatus has been validated by observing convection rolls in both silicone oil and ferrofluid. View full abstract»

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  • A low temperature scanning tunneling microscope for electronic and force spectroscopy

    Page(s): 113705 - 113705-5
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    In this article, we describe and test a novel way to extend a low temperature scanning tunneling microscope with the capability to measure forces. The tuning fork that we use for this is optimized to have a high quality factor and frequency resolution. Moreover, as this technique is fully compatible with the use of bulk tips, it is possible to combine the force measurements with the use of superconductive or magnetic tips, advantageous for electronic spectroscopy. It also allows us to calibrate both the amplitude and the spring constant of the tuning fork easily, in situ and with high precision. 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