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Aug 2008

Volume 79, Issue 8, Articles (08xxxx)

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Performance of a Ge-microstrip imaging detector and polarimeter

U. Spillmann, H. Bräuning, S. Hess, H. Beyer, Th. Stöhlker, J.-Cl. Dousse, D. Protic, and T. Krings

Rev. Sci. Instrum. 79, 083101 (2008); http://dx.doi.org/10.1063/1.2963046 (8 pages) | Cited 7 times

Online Publication Date: 1 August 2008

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Using 98% linearly polarized radiation at the European Synchrotron Radiation Facility in Grenoble, the performance of a prototype two-dimensional microstrip Ge(i) detector for x-ray imaging and as a Compton polarimeter has been evaluated. Using the energy and position sensitivity of the detector, the ability to obtain a complete reconstruction of the Compton event has been demonstrated. The modulation coefficient of the polarimeter is in good agreement with the theoretical limit of a perfect detector.
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29.40.Wk Solid-state detectors
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
29.40.Gx Tracking and position-sensitive detectors

Accurate and quick calibration method for polarization-modulation spectroscopy using an ac-modulated polarizing undulator

Masahito Tanaka, Kazutoshi Yagi-Watanabe, Fusae Kaneko, and Kazumichi Nakagawa

Rev. Sci. Instrum. 79, 083102 (2008); http://dx.doi.org/10.1063/1.2964112 (9 pages) | Cited 3 times

Online Publication Date: 1 August 2008

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An accurate calibration method in which an ac-modulated polarizing undulator is used for polarization modulation spectroscopy such as circular dichroism (CD) and linear dichroism (LD) has been proposed and successfully applied to vacuum ultraviolet (vuv) CD and LD spectra measured at beamline BL-5B in the electron storage ring, TERAS, at AIST. This calibration method employs an undulator-modulation spectroscopic method with a multireflection polarimeter, and it uses electronic and optical elements identical to those used for the CD and LD measurements. This method regards the polarimeter as a standard sample for the CD and LD measurements in the vuv region in which a standard sample has not yet been established. The calibration factors for the CD and LD spectra are obtained over a wide range of wavelengths, from 120 to 230 nm, at TERAS BL-5B. The calibrated CD and LD spectra measured at TERAS exhibit good agreement with the standard spectra for wavelengths greater than 170 nm; the mean differences between the standard and calibrated CD and LD spectra are approximately 7% and 4%, respectively. This method enables a remarkable reduction in the experimental time, from approximately 1 h to less than 10 min that is sufficient to observe the storage-ring current dependence of the calibration factors. This method can be applied to the calibration of vuv-CD spectra measured using a conventional photoelastic modulator and for performing an accurate analysis of protein secondary structures.
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87.80.Dj Spectroscopies
07.60.Fs Polarimeters and ellipsometers
06.20.F- Units and standards
29.20.db Storage rings and colliders

Interference and crosstalk in double optical tweezers using a single laser source

Pierre Mangeol and Ulrich Bockelmann

Rev. Sci. Instrum. 79, 083103 (2008); http://dx.doi.org/10.1063/1.2957652 (8 pages) | Cited 1 time

Online Publication Date: 4 August 2008

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Experimental studies of single molecule mechanics require high force sensitivity and low drift, which can be achieved with optical tweezers. We built an optical tweezer setup for force measurements in a two bead assay. A cw infrared laser beam is split by polarization and focused by a high numerical aperture objective to create two traps. The same laser is used to form both traps and to measure the force by back focal plane interferometry. We show that although the two beams entering the microscope are designed to exhibit orthogonal polarization, interference and a significant parasitic force signal occur. Comparing the experimental results with a ray optics model, we show that the interference patterns are caused by the rotation of polarization on microscope lens surfaces and slides. The model qualitatively describes the pattern and the dependence of the parasitic force signal on the experimental parameters. We present two different approaches to experimentally reduce the crosstalk, namely, polarization rectification and frequency shifting.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
07.60.Ly Interferometers

Focusing mirror for x-ray free-electron lasers

Hidekazu Mimura, Shinya Morita, Takashi Kimura, Daisuke Yamakawa, Weimin Lin, Yoshihiro Uehara, Satoshi Matsuyama, Hirokatsu Yumoto, Haruhiko Ohashi, Kenji Tamasaku, Yoshinori Nishino, Makina Yabashi, Tetsuya Ishikawa, Hitoshi Ohmori, and Kazuto Yamauchi

Rev. Sci. Instrum. 79, 083104 (2008); http://dx.doi.org/10.1063/1.2964928 (4 pages) | Cited 12 times

Online Publication Date: 6 August 2008

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We present the design, fabrication, and evaluation of a large total-reflection mirror for focusing x-ray free-electron laser beams to nanometer dimensions. We used an elliptical focusing mirror made of silicon that was 400 mm long and had a focal length of 550 mm. Electrolytic in-process dressing grinding was used for initial-step figuring and elastic emission machining was employed for final figuring and surface smoothing. A figure accuracy with a peak-to-valley height of 2 nm was achieved across the entire area. Characterization of the focused beam was performed at BL29XUL of SPring-8. The focused beam size was 75 nm at 15 keV, which is almost equal to the theoretical size.
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42.79.Bh Lenses, prisms and mirrors
42.60.By Design of specific laser systems
41.60.Cr Free-electron lasers

X-ray spectropolarimeter

E. O. Baronova, M. M. Stepanenko, and A. M. Stepanenko

Rev. Sci. Instrum. 79, 083105 (2008); http://dx.doi.org/10.1063/1.2964121 (4 pages)

Online Publication Date: 7 August 2008

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We have constructed a novel single-crystal x-ray spectropolarimeter that separates spatially the two perpendicularly polarized components of an x-ray beam. We have tested this device by using an x-ray tube, and confirmed its performance to be satisfactory as expected from its design.
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07.85.Nc X-ray and γ-ray spectrometers
42.15.Eq Optical system design
42.79.Ci Filters, zone plates, and polarizers
07.60.Fs Polarimeters and ellipsometers

Research on the magneto-optic current sensor for high-current pulses

Xiangyang Deng, Zeren Li, Qixian Peng, Jun Liu, and Jianhua Tian

Rev. Sci. Instrum. 79, 083106 (2008); http://dx.doi.org/10.1063/1.2968200 (4 pages) | Cited 1 time

Online Publication Date: 12 August 2008

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A new magneto-optic current sensor with a dual-orthogonal configuration is proposed and demonstrated, which can resolve the problem which value of high-current pulses is ambiguous from the Faraday rotation in the conventional magneto-optic current sensor. In this dual-orthogonal configuration, the transmission axis of the polarizer makes two given angles, which are 0° and 45°, with the orientation of the s-polarized lights of two polarizing cube beam splitters. If the intrinsic linear birefringence of the sensing element is one-fourth less than the Faraday rotation generated from the high-current pulse, the measurement current influenced by it can be ignored and four outputs of the magneto-optic current sensor are in quadrature. The value of the current pulse can be calculated by an arctangent data reduction method, which can avoid the insensitive zone of the sine function, where the measurement current has a reduced accuracy. A measurement of the high-current pulse (up to 720 kA) of an electric gun, with good theoretical accuracy ( ∼ 3%) and in agreement well with that of the calibrated Rogowski coil, is launched.
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07.60.-j Optical instruments and equipment
42.79.Fm Reflectors, beam splitters, and deflectors
42.79.Ci Filters, zone plates, and polarizers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.70.Sq Magnetooptical devices
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Novel angular encoder for a quick-extended x-ray absorption fine structure monochromator

J. Stötzel, D. Lützenkirchen-Hecht, E. Fonda, N. De Oliveira, V. Briois, and R. Frahm

Rev. Sci. Instrum. 79, 083107 (2008); http://dx.doi.org/10.1063/1.2966393 (4 pages) | Cited 11 times

Online Publication Date: 15 August 2008

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New concepts for time-resolved x-ray absorption spectroscopy using the quick-extended x-ray absorption fine structure (QEXAFS) method are presented. QEXAFS is a powerful tool to gain structural information about, e.g., fast chemical reactions or phase transitions on a subsecond scale. This can be achieved with a monochromator design that employs a channel-cut crystal on a cam driven tilt table for rapid angular oscillations of the Bragg angle. A new angular encoder system and a new data acquisition were described and characterized that were applied to a QEXAFS monochromator to get spectra with a directly measured accurate energy scale. New electronics were designed to allow a fast acquisition of the Bragg angle values and the absorption data during the measurements simultaneously.
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07.85.-m X- and γ-ray instruments
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Optical delay line for high time resolution measurement: W-type delay line

Kyohei Hashimoto, Satoru S. Kano, and Akihide Wada

Rev. Sci. Instrum. 79, 083108 (2008); http://dx.doi.org/10.1063/1.2968116 (3 pages)

Online Publication Date: 15 August 2008

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We propose and demonstrate a newly designed optical delay line (W-type delay line) that improves the resolution of optical path length, namely, time resolution, by an order of more than 3 in comparison to the spatial resolution of a conventionally used translational stage. Using a conventional mechanical translational stage having a spatial resolution of 1 μm, the performance of the W-type delay line was evaluated by interferometric measurements with a diode laser, and the time resolution of 16 as was confirmed.
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42.55.Px Semiconductor lasers; laser diodes
42.79.-e Optical elements, devices, and systems

An advanced magnetic reflectometer

Sebastian Brück, Steffen Bauknecht, Bernd Ludescher, Eberhard Goering, and Gisela Schütz

Rev. Sci. Instrum. 79, 083109 (2008); http://dx.doi.org/10.1063/1.2970941 (6 pages) | Cited 8 times

Online Publication Date: 19 August 2008

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A new experimental setup dedicated to the measurement of soft-x-ray magnetic absorption spectroscopy and soft-x-ray resonant magnetic reflectometry (soft-XRMR) is presented. XRMR is the combination of standard x-ray reflectometry with x-ray magnetic circular dichroism which provides chemical and magnetic depth profiles of layered thin-film samples. This new diffractometer is optimized for a broad variety of sample systems. Therefore a balanced design focusing on high magnetic fields, low temperatures, and full freedom of rotation has been realized in UHV. First experimental results obtained on a NiCoO/Co bilayer sample are presented showing the potential of the setup.
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78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

A bent electrostatic ion beam trap for simultaneous measurements of fragmentation and ionization of cluster ions

O. Aviv, Y. Toker, M. Errit, K. G. Bhushan, H. B. Pedersen, M. L. Rappaport, O. Heber, D. Schwalm, and D. Zajfman

Rev. Sci. Instrum. 79, 083110 (2008); http://dx.doi.org/10.1063/1.2972151 (8 pages) | Cited 7 times

Online Publication Date: 25 August 2008

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We describe a bent electrostatic ion beam trap in which cluster ions of several keV kinetic energy can be stored on a V-shaped trajectory by means of an electrostatic deflector placed between two electrostatic mirrors. While maintaining all the advantages of its linear counterpart [ Zajfman et al., Phys. Rev. A 55, R1577 (1997) ; Dahan et al., Rev. Sci. Instrum. 69, 76 (1998) ], such as long storage times, straight segments, and a field-free region for merged or crossed beam experiments, the bent trap allows for simultaneous measurement of charged and neutral fragments and determination of the average kinetic energy released in the fragmentation. These unique properties of the bent trap are illustrated by first results concerning the competition between delayed fragmentation and ionization of Aln− clusters after irradiation by a short laser pulse.
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36.40.Qv Stability and fragmentation of clusters
36.40.Wa Charged clusters
32.80.Fb Photoionization of atoms and ions
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Absolute calibration of an electron spectrometer using high energy electrons produced by the laser-plasma interaction

S. Masuda, E. Miura, K. Koyama, and S. Kato

Rev. Sci. Instrum. 79, 083301 (2008); http://dx.doi.org/10.1063/1.2969655 (4 pages) | Cited 5 times

Online Publication Date: 19 August 2008

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An in situ observation system has been developed to observe the absolute electron energy spectra of electron beams generated by laser-plasma interaction. A phosphor screen (DRZ) coupled with a charge coupled device camera is used to detect the electrons. A new method is proposed to calibrate the absolute sensitivity of the detection system for a wide energy range with a single shot by using an electron beam generated by laser-plasma interaction. The sensitivity of the system is found to be high, which is comparable to that of an imaging plate.
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07.81.+a Electron and ion spectrometers
41.75.Fr Electron and positron beams
06.20.F- Units and standards
42.79.Pw Imaging detectors and sensors

Properties of the electron beam in a room-temperature electron beam ion source investigated by position sensitive x-ray detection

A. Silze, G. Zschornack, V. P. Ovsyannikov, and F. Ullmann

Rev. Sci. Instrum. 79, 083302 (2008); http://dx.doi.org/10.1063/1.2960568 (5 pages) | Cited 4 times

Online Publication Date: 21 August 2008

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The evolution of the charge state distribution inside an electron beam ion source or trap (EBIS/T) is determined by interactions of the electron beam with the ions in the trap region. Hence, detailed information about the electron beam is required for evaluations of spectroscopic and ion extraction measurements performed at EBIS/T facilities. This article presents the results of investigations on the electron beam properties of an ion source of the Dresden EBIS type. For the first time theoretical predictions of the shape of the beam were tested for a noncryogenic EBIS working with low magnetic flux densities provided by permanent magnets. Position and width of the electron beam were measured at different electron energies showing an oscillation in the beam structure. At an energy of Ee = 16 keV and an emission current of Ie = 30 mA the beam is compressed to a radius of re = 57 μm (80% current). This refers to an average current density of 〈je〉 = 232 A/cm2.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
29.40.Gx Tracking and position-sensitive detectors
41.75.Fr Electron and positron beams
07.77.Ka Charged-particle beam sources and detectors

High efficiency electron spin polarization analyzer based on exchange scattering at Fe/W(001)

A. Winkelmann, D. Hartung, H. Engelhard, C.-T. Chiang, and J. Kirschner

Rev. Sci. Instrum. 79, 083303 (2008); http://dx.doi.org/10.1063/1.2949877 (6 pages) | Cited 17 times

Online Publication Date: 22 August 2008

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We report on a compact electron spin analyzer based on exchange scattering from a magnetic surface. The heart of the detector is an Fe(001) thin film grown on W(001) with chemisorbed oxygen in the p(1×1) structure. The device is mounted at the exit of an energy dispersive analyzer and works at a scattering energy of about 13.5 eV. Its figure of merit is 2×10−3, combined with an excellent stability of more than 2 weeks in UHV.
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85.75.Ss Magnetic field sensors using spin polarized transport
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
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Use of the absolute phase in frequency modulated continuous wave plasma reflectometry

G. Cunningham

Rev. Sci. Instrum. 79, 083501 (2008); http://dx.doi.org/10.1063/1.2964233 (5 pages)

Online Publication Date: 4 August 2008

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In frequency modulated continuous wave reflectometry, used for density profile measurement in fusion plasmas, it is usual to measure the beat frequency between the launched wave and the reflected wave, and from this to calculate the position of the reflecting layer in the plasma. The absolute phase of the beat signal is usually neglected. The reason is that the phase shift between sweeps is usually comparable with or more than 2π, leading to an ambiguity that is impossible to resolve. However, recent observations on the MAST tokamak have shown that, under quiet plasma conditions (this term has to be defined), the phase shift between sweeps is small compared with 2π and the phase ambiguity can be readily resolved. The reflectometer signal is then being analyzed as an interferometer signal would normally be, and there is a substantial improvement in spatial resolution. The method is illustrated by application to small edge localized mode precursor and allows what is believed to be the first quantitative measurement of the displacement of the plasma boundary by such a precursor mode. The errors in both the absolute phase measurement and the more conventional frequency measurement are also estimated.
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52.70.-m Plasma diagnostic techniques and instrumentation
52.55.Fa Tokamaks, spherical tokamaks
52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

A new diagnostic of the plasma density profile near the edge transport barrier from measurements of the radial profile of the Hα line intensity

G. S. Voronov

Rev. Sci. Instrum. 79, 083502 (2008); http://dx.doi.org/10.1063/1.2964925 (5 pages)

Online Publication Date: 6 August 2008

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An edge transport barrier is now one of the most important subjects of controlled fusion research. The edge transport barrier is located in the plasma region where hydrogen atoms readily penetrate, so the intensity of the Hα (Dα) line is high enough. A new diagnostic method uses the well-known property of hydrogen atoms that the ratio of the ionization rate Si to the excitation rate Sv for the Hα line is nearly constant over a wide range of plasma temperatures and densities. An expression has been derived that relates the radial profiles of the plasma density and Hα intensity. The use of charge coupled device detectors makes it possible to measure the radial profile of Hα line intensity with a resolution ∼ 0.1 cm; a high intensity of the Hα line ensures a high time resolution ∼ 1 ms. A high resolution is thus achieved for the density profile calculated from the Hα intensity profile. The method was tested when studying the plasma density profile in the region of edge transport barrier in the L-2M stellarator. It has been shown that the density gradient varies during the barrier formation and that a fine structure of the density profile correlates with a character of the plasma transport near resonance magnetic flux surfaces.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Fi Transport properties

Development and research of a coaxial microwave plasma thruster

Juan Yang, Yingqiao Xu, Jinlan Tang, Genwang Mao, Tielian Yang, and Xiaoquen Tan

Rev. Sci. Instrum. 79, 083503 (2008); http://dx.doi.org/10.1063/1.2967340 (6 pages)

Online Publication Date: 7 August 2008

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An overview of the research on a coaxial microwave plasma thruster at Northwestern Polytechnic University is presented. Emphasis is put on the development and research on key components of the thruster system, a microthrust balance, plasma plume diagnostics, and a numerical simulation of the plasma flow field inside the thruster cavity. The developed thruster cavity is chosen from a coaxial resonant cavity with concentrated capacitance, which can operate well in atmosphere and vacuum conditions. The development of a microwave source shows that a magnetron powered by a switch power supply has advantages in the power level and efficiency, but a solid state microwave source synthesized from the arsenide field effect transistor is superior in weight and volume. Through elimination of the effect of large gravity and resistance force induced by a gas pipe line and a microwave transmitting line on the microthrust, 15 mN and 340 s in the performance of the microwave plasma thruster at 70 W and with helium gas are measured. Diagnosing experiment shows that the plasma plume density is in the range of (1–7.2)×1016/m3. Numerical simulation of the plasma flow field inside the coaxial thruster cavity shows that there is a good match between the microwave power and gas flow rate.
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52.75.Di Ion and plasma propulsion
52.50.Sw Plasma heating by microwaves; ECR, LH, collisional heating
52.30.-q Plasma dynamics and flow
52.65.-y Plasma simulation
52.70.-m Plasma diagnostic techniques and instrumentation
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

In-vessel visible inspection system on KSTAR

Jinil Chung and D. C. Seo

Rev. Sci. Instrum. 79, 083504 (2008); http://dx.doi.org/10.1063/1.2969654 (4 pages) | Cited 5 times

Online Publication Date: 18 August 2008

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To monitor the global formation of the initial plasma and damage to the internal structures of the vacuum vessel, an in-vessel visible inspection system has been installed and operated on the Korean superconducting tokamak advanced research (KSTAR) device. It consists of four inspection illuminators and two visible/H-alpha TV cameras. Each illuminator uses four 150 W metal-halide lamps with separate lamp controllers, and programmable progressive scan charge-coupled device cameras with 1004×1004 resolution at 48 frames/s and a resolution of 640×480 at 210 frames/s are used to capture images. In order to provide vessel inspection capability under any operation condition, the lamps and cameras are fully controlled from the main control room and protected by shutters from deposits during plasma operation. In this paper, we describe the design and operation results of the visible inspection system with the images of the KSTAR Ohmic discharges during the first plasma campaign.
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52.55.Fa Tokamaks, spherical tokamaks
28.52.Av Theory, design, and computerized simulation
84.71.Ba Superconducting magnets; magnetic levitation devices
52.80.-s Electric discharges
28.52.Fa Materials

Two-dimensional micron-step probe drive for laboratory plasma measurement

A. Collette and W. Gekelman

Rev. Sci. Instrum. 79, 083505 (2008); http://dx.doi.org/10.1063/1.2972150 (4 pages) | Cited 1 time

Online Publication Date: 25 August 2008

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Laboratory measurement of small-scale ( ∼ 1 mm) magnetic phenomena over an extended area is a challenge requiring precise diagnostics. We present a novel two dimensional magnetic probe platform capable of directly measuring the magnetic field over a 36 cm2 region at spatial resolutions better than 1 mm. The platform is discussed in the context of an experiment at the Large Plasma Device facility at UCLA, designed to measure the magnetic interaction between two counterpropagating laser-produced plasmas. The use of a precise, repeatable positioning platform enables the recovery of information about the interaction using cross-correlation techniques.
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52.70.Ds Electric and magnetic measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Controlled reproducible alignment of cone targets and mitigation of preplasma in high intensity laser interactions

Nathalie Renard-Le Galloudec, Byoung-Ick Cho, Jens Osterholz, and Todd Ditmire

Rev. Sci. Instrum. 79, 083506 (2008); http://dx.doi.org/10.1063/1.2972152 (4 pages) | Cited 3 times

Online Publication Date: 25 August 2008

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The use of cone targets in high intensity laser-plasma experiments has been of recent interest because of their potential use in integrated fast ignition experiments. Simpler experiments provide a good avenue for understanding the underlying physics, however precise control of the alignment along with good pointing accuracy is of crucial importance. While on big laser facilities target alignment is done precisely with several microscopes, it is not always the case on smaller facilities. This can have a detrimental effect on the quality of the results. We have developed and characterized a method for accurate alignment of intense laser pulses into a cone target. This, along with optimal positioning of the focus compared to the tip, efficiently uses the shape of the target to microfocus the laser light and concentrates the hot electrons in the tip, and can mitigate preplasma issues.
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52.38.-r Laser-plasma interactions

Magnetically and optoelectronically isolated trigger for pulse-power applications

Yi Yu, Yi-Zhi Wen, Chang-Xuan Yu, Shu-De Wan, and Wan-Dong Liu

Rev. Sci. Instrum. 79, 083507 (2008); http://dx.doi.org/10.1063/1.2972173 (4 pages)

Online Publication Date: 25 August 2008

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In this article the design of a magnetically and optically isolated trigger is discussed. Critical issues for trigger design are presented together with some experimental usages. In this trigger, an optical coupler is used to cut off the ground loop between the circuits of the preceding control system and the power supplies of the double functional device KT-5D (as a simple magnetic torus or a tokamak). A magnetic coupler is used to provide a pulse-power output for the silicon controlled rectifier. The output is a 230 μs transistor-transistor logic (TTL) with an amplitude of 3.0 V. The rising time and the trailing time are no more than 4.0 μs. The delay time between the input and the output of the trigger is 6.8±0.2 μs. A resistance-capacity branch is integrated into the trigger to provide an adjustable delay time of up to 72 ms. The zero quiescent dissipation character endows the trigger with a long lifetime of years dispensing with any charging or replacing batteries. It is observed that the trigger has a good stability even in a high electromagnetic circumstance (at the order of 1 T). Using it as a trigger for the silicon controlled rectifier, we realized the compatible operation of the steady state mode and the pulse mode in KT-5D.
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42.79.Gn Optical waveguides and couplers
84.30.Jc Power electronics; power supply circuits
42.82.Et Waveguides, couplers, and arrays
84.30.Sk Pulse and digital circuits
85.60.-q Optoelectronic devices

Laser-heated emissive plasma probe

Roman Schrittwieser, Codrina Ionita, Petru Balan, Ramona Gstrein, Olaf Grulke, Thomas Windisch, Christian Brandt, Thomas Klinger, Ramin Madani, George Amarandei, and Arun K. Sarma

Rev. Sci. Instrum. 79, 083508 (2008); http://dx.doi.org/10.1063/1.2968114 (9 pages) | Cited 13 times

Online Publication Date: 28 August 2008

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Emissive probes are standard tools in laboratory plasmas for the direct determination of the plasma potential. Usually they consist of a loop of refractory wire heated by an electric current until sufficient electron emission. Recently emissive probes were used also for measuring the radial fluctuation-induced particle flux and other essential parameters of edge turbulence in magnetized toroidal hot plasmas [ R. Schrittwieser et al., Plasma Phys. Controlled Fusion 50, 055004 (2008) ]. We have developed and investigated various types of emissive probes, which were heated by a focused infrared laser beam. Such a probe has several advantages: higher probe temperature without evaporation or melting and thus higher emissivity and longer lifetime, no deformation of the probe in a magnetic field, no potential drop along the probe wire, and faster time response. The probes are heated by an infrared diode laser with 808 nm wavelength and an output power up to 50 W. One probe was mounted together with the lens system on a radially movable probe shaft, and radial profiles of the plasma potential and of its oscillations were measured in a linear helicon discharge.
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52.70.Ds Electric and magnetic measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
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Improvement of a dynamic scanning force microscope for highest resolution imaging in ultrahigh vacuum

S. Torbrügge, J. Lübbe, L. Tröger, M. Cranney, T. Eguchi, Y. Hasegawa, and M. Reichling

Rev. Sci. Instrum. 79, 083701 (2008); http://dx.doi.org/10.1063/1.2964119 (7 pages) | Cited 9 times

Online Publication Date: 4 August 2008

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We report on a modification of a commercial scanning force microscope (Omicron UHV AFM/STM) operated in noncontact mode (NC-AFM) at room temperature in ultrahigh vacuum yielding a decrease in the spectral noise density from 2757 to 272 fm/math. The major part of the noise reduction is achieved by an exchange of the originally installed light emitting diode by a laser diode placed outside the vacuum, where the light is coupled into the ultrahigh vacuum chamber via an optical fiber. The setup is further improved by the use of preamplifiers having a bandpass characteristics tailored to the cantilever resonance frequency. The enhanced signal to noise ratio is demonstrated by a comparison of atomic resolution images on CeO2(111) obtained before and after the modification.
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07.79.Lh Atomic force microscopes
42.55.Px Semiconductor lasers; laser diodes
42.81.Qb Fiber waveguides, couplers, and arrays

Confocal laser scanning microscopy using a frequency doubled vertical external cavity surface emitting laser

Elric Esposito, Stefanie Keatings, Kyle Gardner, John Harris, Erling Riis, and Gail McConnell

Rev. Sci. Instrum. 79, 083702 (2008); http://dx.doi.org/10.1063/1.2966395 (6 pages) | Cited 1 time

Online Publication Date: 5 August 2008

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We report on a frequency doubled 980 nm vertical external cavity surface emitting laser for applications in confocal laser scanning microscopy. The beam quality, wavelength flexibility, and low noise characteristics of this compact source make this prolific imaging technique an exemplary tool. Single pass frequency doubling via KNbO3 was demonstrated, yielding 1.8 mW at 490 nm with a near diffraction limited beam quality. Detailed analysis and comparison of the laser performance with the current standard argon ion laser revealed clear advantages of the solid-state source for confocal imaging. Imaging of fluorescein and eGFP labeled biological samples using the attenuated solid-state source provided high-resolution images at lower cost and with improved reliability.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
07.60.Pb Conventional optical microscopes

A silicon metal-oxide-semiconductor field-effect transistor Hall bar for scanning Hall probe microscopy

Akinobu Yamaguchi, Hiromasa Saito, Masayoshi Shimizu, Hideki Miyajima, Satoru Matsumoto, Yoshiharu Nakamura, and Atsufumi Hirohata

Rev. Sci. Instrum. 79, 083703 (2008); http://dx.doi.org/10.1063/1.2968713 (6 pages)

Online Publication Date: 15 August 2008

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We demonstrate successful operation of a scanning Hall probe microscope with a few micron-size resolution by using a silicon metal-oxide semiconductor field-effect transistor (Si-MOSFET) Hall bar, which is designed to improve not only the mechanical strength but also the temperature stability. The Si-MOSFET micro-Hall probe is cheaper than the current micro-Hall probes and is found to be as sensitive as a micro-Hall probe with GaAs/AlGaAs heterostructure or an epitaxial InSb two-dimensional electron gas. This was used to magnetically image the surface of a Sm2Co17 permanent magnet during the magnetization reversal process as a function of an external magnetic field below 1.5 T. This revealed firm evidence of the presence of the inverse magnetic seed as theoretically predicted earlier. Magnetically pinned centers, with a typical size 80 μm, are observed to persist even under a high magnetic field, clearly indicating the robustness of the Si Hall probe against the field application as well as the repetition of the measurement.
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68.37.-d Microscopy of surfaces, interfaces, and thin films
85.30.Tv Field effect devices
81.05.Ea III-V semiconductors
85.75.Nn Hybrid Hall devices
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)

Local potentiometry using a multiprobe scanning tunneling microscope

A. Bannani, C. A. Bobisch, and R. Möller

Rev. Sci. Instrum. 79, 083704 (2008); http://dx.doi.org/10.1063/1.2968111 (6 pages) | Cited 6 times

Online Publication Date: 20 August 2008

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Scanning tunneling potentiometry (STP) is a powerful tool to analyze the conductance through thin conducting layers with lateral resolution in the nanometer range. In this work, we show how a commercial ultrahigh vacuum multiprobe system, equipped with four independent tips, can be used to perform STP experiments. Two tips are gently pushed into the surface applying a lateral current through the layer of interest. Simultaneously, the topography and the potential distribution across the metal film are measured with a third tip. The signal-to-noise ratio of the potentiometry signal may be enhanced by using a fourth tip, providing a reference potential in close vicinity of the studied area. Two different examples are presented. For epitaxial (111) oriented Bi films, grown on a Si(100)-(2×1) surface, an almost constant gradient of the potential as well as potential drops at individual Bi-domain boundaries were observed. On the surface of the Si(111)(math×math)–Ag superstructure the potential variation at individual monoatomic steps could be precisely resolved.
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07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.61.At Metal and metallic alloys
73.61.Cw Elemental semiconductors
73.25.+i Surface conductivity and carrier phenomena
68.55.-a Thin film structure and morphology
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