Rev. Sci. Instrum. - Review of Scientific Instruments

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Fiber-optic Fourier transform infrared spectroscopy for remote label-free sensing of medical device surface contamination

Moinuddin Hassan, Xin Tan, Elissa Welle, and Ilko Ilev

Rev. Sci. Instrum. 84, 053101 (2013); http://dx.doi.org/10.1063/1.4803182 (4 pages)

Online Publication Date: 7 May 2013

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As a potential major source of biochemical contamination, medical device surfaces are of critical safety concerns in the clinical practice and public health. The development of innovative sensing methods for accurate and real-time detection of medical device surface contamination is essential to protect patients from high risk infection. In this paper, we demonstrate an alternative fiber-optic Fourier Transform Infrared (FTIR) spectroscopy based sensing approach for remote, non-contact, and label-free detection of biochemical contaminants in the mid-infrared (mid-IR) region. The sensing probe is designed using mid-IR hollow fibers and FTIR measurements are carried out in reflection mode. Bovine Serum Albumin (BSA) and bacterial endotoxin of different concentrations under thoroughly dry condition are used to evaluate the detection sensitivity. The devised system can identify ≤0.0025% (≤4 × 10¹¹ molecules) BSA and 0.5% (0.5 EU/ml) endotoxin concentration. The developed sensing approach may be applied to detect various pathogens that pose public health threats.

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87.85.Ox	Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.81.Pa	Sensors, gyros
87.14.E-	Proteins
87.15.R-	Reactions and kinetics
87.64.km	Infrared

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A seven-crystal Johann-type hard x-ray spectrometer at the Stanford Synchrotron Radiation Lightsource

D. Sokaras, T.-C. Weng, D. Nordlund, R. Alonso-Mori, P. Velikov, D. Wenger, A. Garachtchenko, M. George, V. Borzenets, B. Johnson, T. Rabedeau, and U. Bergmann

Rev. Sci. Instrum. 84, 053102 (2013); http://dx.doi.org/10.1063/1.4803669 (8 pages)

Online Publication Date: 7 May 2013

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We present a multicrystal Johann-type hard x-ray spectrometer (∼5–18 keV) recently developed, installed, and operated at the Stanford Synchrotron Radiation Lightsource. The instrument is set at the wiggler beamline 6-2 equipped with two liquid nitrogen cooled monochromators – Si(111) and Si(311) – as well as collimating and focusing optics. The spectrometer consists of seven spherically bent crystal analyzers placed on intersecting vertical Rowland circles of 1 m of diameter. The spectrometer is scanned vertically capturing an extended backscattering Bragg angular range (88°–74°) while maintaining all crystals on the Rowland circle trace. The instrument operates in atmospheric pressure by means of a helium bag and when all the seven crystals are used (100 mm of projected diameter each), has a solid angle of about 0.45% of 4π sr. The typical resolving power is in the order of math

∼ 10 000. The spectrometer's high detection efficiency combined with the beamline 6-2 characteristics permits routine studies of x-ray emission, high energy resolution fluorescence detected x-ray absorption and resonant inelastic x-ray scattering of very diluted samples as well as implementation of demanding in situ environments.

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07.85.Nc

X-ray and γ-ray spectrometers

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Optical design of the short pulse x-ray imaging and microscopy time-angle correlated diffraction beamline at the Advanced Photon Source

R. Reininger, E. M. Dufresne, M. Borland, M. A. Beno, L. Young, K.-J. Kim, and P. G. Evans

Rev. Sci. Instrum. 84, 053103 (2013); http://dx.doi.org/10.1063/1.4804197 (7 pages)

Online Publication Date: 10 May 2013

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The short pulse x-ray imaging and microscopy beamline is one of the two x-ray beamlines that will take full advantage of the short pulse x-ray source in the Advanced Photon Source (APS) upgrade. A horizontally diffracting double crystal monochromator which includes a sagittally focusing second crystal will collect most of the photons generated when the chirped electron beam traverses the undulator. A Kirkpatrick-Baez mirror system after the monochromator will deliver to the sample a beam which has an approximately linear correlation between time and vertical beam angle. The correlation at the sample position has a slope of 0.052 ps/μrad extending over an angular range of 800 μrad for a cavity deflection voltage of 2 MV. The expected time resolution of the whole system is 2.6 ps. The total flux expected at the sample position at 10 keV with a 0.9 eV energy resolution is 5.7 × 10¹² photons/s at a spot having horizontal and vertical full width at half maximum of 33 μm horizontal by 14 μm vertical. This new beamline will enable novel time-dispersed diffraction experiments on small samples using the full repetition rate of the APS.

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41.85.Si	Particle beam collimators, monochromators
07.85.-m	X- and γ-ray instruments

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Improving the accuracy of optical rotation measurement based on optical null methods by curve-fitting

Zhenhao Yang and Hongzhi Jia

Rev. Sci. Instrum. 84, 053104 (2013); http://dx.doi.org/10.1063/1.4804596 (4 pages)

Online Publication Date: 13 May 2013

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An optical rotation measuring system using optical null methods is set up. The system is based on a step-motor rotating stage structure and a modulated laser, which both are controlled by digital signal processor. By introducing a curve-fitting method, the optical rotation angle is obtained from the step difference between the crossed positions in light signal curves with or without sample. The principle of this method is studied, and the system performance is investigated experimentally. We achieved an accuracy of the order of 10⁻³ degree in at least ±45° range, which is an improvement compared with the resolution of 0.01° for step-motor rotation stage.

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07.60.-j	Optical instruments and equipment
06.30.Bp	Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
02.60.Ed	Interpolation; curve fitting
42.60.Fc	Modulation, tuning, and mode locking
42.62.Eh	Metrological applications; optical frequency synthesizers for precision spectroscopy
07.68.+m	Photography, photographic instruments; xerography

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Modified Fabry-Perot interferometer for displacement measurement in ultra large measuring range

Chung-Ping Chang, Pi-Cheng Tung, Lih-Horng Shyu, Yung-Cheng Wang, and Eberhard Manske

Rev. Sci. Instrum. 84, 053105 (2013); http://dx.doi.org/10.1063/1.4803672 (8 pages)

Online Publication Date: 14 May 2013

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Laser interferometers have demonstrated outstanding measuring performances for high precision positioning or dimensional measurements in the precision industry, especially in the length measurement. Due to the non-common-optical-path structure, appreciable measurement errors can be easily induced under ordinary measurement conditions. That will lead to the limitation and inconvenience for in situ industrial applications. To minimize the environmental and mechanical effects, a new interferometric displacement measuring system with the common-optical-path structure and the resistance to tilt-angle is proposed. With the integration of optomechatronic modules in the novel interferometric system, the resolution up to picometer order, high precision, and ultra large measuring range have been realized. For the signal stabilization of displacement measurement, an automatic gain control module has been proposed. A self-developed interpolation model has been employed for enhancing the resolution. The novel interferometer can hold the advantage of high resolution and large measuring range simultaneously. By the experimental verifications, it has been proven that the actual resolution of 2.5 nm can be achieved in the measuring range of 500 mm. According to the comparison experiments, the maximal standard deviation of the difference between the self-developed Fabry-Perot interferometer and the reference commercial Michelson interferometer is 0.146 μm in the traveling range of 500 mm. With the prominent measuring characteristics, this should be the largest dynamic measurement range of a Fabry-Perot interferometer up till now.

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06.30.Bp	Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.60.Ly	Interferometers

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Absolute photo-destruction and photo-fragmentation cross section measurements using an electrostatic ion beam trap

O. Aviv, B. Kafle, V. Chandrasekaran, O. Heber, M. L. Rappaport, H. Rubinstein, D. Schwalm, D. Strasser, Y. Toker, and D. Zajfman

Rev. Sci. Instrum. 84, 053106 (2013); http://dx.doi.org/10.1063/1.4804646 (10 pages)

Online Publication Date: 15 May 2013

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We describe a technique to measure absolute photo-induced cross sections for cluster anions stored in an electrostatic ion beam trap (EIBT) with a central deflector. The setup allows determination of total photo-destruction cross sections as well as partial cross sections for fragmentation and electron detachment. The unique properties of this special EIBT setup are investigated and illustrated using small Al n− clusters.

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33.80.Eh	Autoionization, photoionization, and photodetachment
37.10.Ty	Ion trapping
36.40.Wa	Charged clusters
36.40.Qv	Stability and fragmentation of clusters

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A testbed for wide-field, high-resolution, gigapixel-class cameras

David S. Kittle, Daniel L. Marks, Hui S. Son, Jungsang Kim, and David J. Brady

Rev. Sci. Instrum. 84, 053107 (2013); http://dx.doi.org/10.1063/1.4804199 (11 pages)

Online Publication Date: 20 May 2013

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The high resolution and wide field of view (FOV) of the AWARE (Advanced Wide FOV Architectures for Image Reconstruction and Exploitation) gigapixel class cameras present new challenges in calibration, mechanical testing, and optical performance evaluation. The AWARE system integrates an array of micro-cameras in a multiscale design to achieve gigapixel sampling at video rates. Alignment and optical testing of the micro-cameras is vital in compositing engines, which require pixel-level accurate mappings over the entire array of cameras. A testbed has been developed to automatically calibrate and measure the optical performance of the entire camera array. This testbed utilizes translation and rotation stages to project a ray into any micro-camera of the AWARE system. A spatial light modulator is projected through a telescope to form an arbitrary object space pattern at infinity. This collimated source is then reflected by an elevation stage mirror for pointing through the aperture of the objective into the micro-optics and eventually the detector of the micro-camera. Different targets can be projected with the spatial light modulator for measuring the modulation transfer function (MTF) of the system, fiducials in the overlap regions for registration and compositing, distortion mapping, illumination profiles, thermal stability, and focus calibration. The mathematics of the testbed mechanics are derived for finding the positions of the stages to achieve a particular incident angle into the camera, along with calibration steps for alignment of the camera and testbed coordinate axes. Measurement results for the AWARE-2 gigapixel camera are presented for MTF, focus calibration, illumination profile, fiducial mapping across the micro-camera for registration and distortion correction, thermal stability, and alignment of the camera on the testbed.

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81.70.Bt	Mechanical testing, impact tests, static and dynamic loads
06.20.fb	Standards and calibration

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Capacitive readout and gating of superconducting single photon detectors

Hatim Azzouz, Reinier W. Heeres, Sander N. Dorenbos, Raymond N. Schouten, and Valery Zwiller

Rev. Sci. Instrum. 84, 053108 (2013); http://dx.doi.org/10.1063/1.4805055 (4 pages)

Online Publication Date: 22 May 2013

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We propose and develop a readout scheme for superconducting single-photon detectors based on an integrated circuit, relaxing the need for large bandwidth amplification and resulting in voltage steps proportional to the number of detected photons. We also demonstrate time gating, to filter scattered light in time and reduce dark counts. This could lead to a higher signal-to-noise ratio. The gate pulse is generated on the detection of a photon created by a spontaneous parametric down-conversion source, heralding the presence of a second photon. These two schemes could find applications within advanced multi-array imaging detection systems.

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85.60.Gz	Photodetectors (including infrared and CCD detectors)
85.25.Oj	Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)

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Generation of first hard X-ray pulse at Tsinghua Thomson Scattering X-ray Source

Yingchao Du (杜应超), Lixin Yan (颜立新), Jianfei Hua (华剑飞), Qiang Du (杜强), Zhen Zhang (张振), Renkai Li (李任恺), Houjun Qian (钱厚俊), Wenhui Huang (黄文会), Huaibi Chen (陈怀璧), and Chuanxiang Tang (唐传祥)

Rev. Sci. Instrum. 84, 053301 (2013); http://dx.doi.org/10.1063/1.4803671 (7 pages)

Online Publication Date: 8 May 2013

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Tsinghua Thomson Scattering X-ray Source (TTX) is the first-of-its-kind dedicated hard X-ray source in China based on the Thomson scattering between a terawatt ultrashort laser and relativistic electron beams. In this paper, we report the experimental generation and characterization of the first hard X-ray pulses (51.7 keV) via head-on collision of an 800 nm laser and 46.7 MeV electron beams. The measured yield is 1.0 × 10⁶ per pulse with an electron bunch charge of 200 pC and laser pulse energy of 300 mJ. The angular intensity distribution and energy spectra of the X-ray pulse are measured with an electron-multiplying charge-coupled device using a CsI scintillator and silicon attenuators. These measurements agree well with theoretical and simulation predictions. An imaging test using the X-ray pulse at the TTX is also presented.

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07.85.-m	X- and γ-ray instruments
84.37.+q	Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
41.75.Ht	Relativistic electron and positron beams
42.55.Vc	X- and γ-ray lasers
85.30.Tv	Field effect devices

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Thomson spectrometer–microchannel plate assembly calibration for MeV-range positive and negative ions, and neutral atoms

R. Prasad, F. Abicht, M. Borghesi, J. Braenzel, P. V. Nickles, G. Priebe, M. Schnürer, and S. Ter-Avetisyan

Rev. Sci. Instrum. 84, 053302 (2013); http://dx.doi.org/10.1063/1.4803670 (6 pages)

Online Publication Date: 9 May 2013

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We report on the absolute calibration of a microchannel plate (MCP) detector, used in conjunction with a Thomson parabola spectrometer. The calibration delivers the relation between a registered count numbers in the CCD camera (on which the MCP phosphor screen is imaged) and the number of ions incident on MCP. The particle response of the MCP is evaluated for positive, negative, and neutral particles at energies below 1 MeV. As the response of MCP depends on the energy and the species of the ions, the calibration is fundamental for the correct interpretation of the experimental results. The calibration method and arrangement exploits the unique emission symmetry of a specific source of fast ions and atoms driven by a high power laser.

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42.79.Pw	Imaging detectors and sensors
06.20.fb	Standards and calibration
29.40.Gx	Tracking and position-sensitive detectors
29.30.-h	Spectrometers and spectroscopic techniques

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Development of a fast scintillator based beam phase measurement system for compact superconducting cyclotrons

Tanushyam Bhattacharjee, Malay Kanti Dey, Partha Dhara, Suvodeep Roy, Jayanta Debnath, Rajendra Balakrishna Bhole, Atanu Dutta, Jedidiah Pradhan, Sarbajit Pal, Gautam Pal, Amitava Roy, and Alok Chakrabarti

Rev. Sci. Instrum. 84, 053303 (2013); http://dx.doi.org/10.1063/1.4807076 (5 pages)

Online Publication Date: 21 May 2013

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In an isochronous cyclotron, measurements of central phase of the ion beam with respect to rf and the phase width provide a way to tune the cyclotron for maximum energy gain per turn and efficient extraction. We report here the development of a phase measurement system and the measurements carried out at the Variable Energy Cyclotron Centre's (VECC’s) K = 500 superconducting cyclotron. The technique comprises detecting prompt γ-rays resulting from the interaction of cyclotron ion beam with an aluminium target mounted on a radial probe in coincidence with cyclotron rf. An assembly comprising a fast scintillator and a liquid light-guide inserted inside the cyclotron was used to detect the γ-rays and to transfer the light signal outside the cyclotron where a matching photo-multiplier tube was used for light to electrical signal conversion. The typical beam intensity for this measurement was a few times 10¹¹ pps.

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29.40.Mc	Scintillation detectors
29.27.-a	Beams in particle accelerators
85.60.Ha	Photomultipliers; phototubes and photocathodes
85.25.Oj	Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
29.20.dg	Cyclotrons
84.37.+q	Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

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Development of the gas-puff imaging diagnostic in the TEXTOR tokamak

I. Shesterikov, Y. Xu, M. Berte, P. Dumortier, M. Van Schoor, M. Vergote, B. Schweer, and G. Van Oost

Rev. Sci. Instrum. 84, 053501 (2013); http://dx.doi.org/10.1063/1.4803934 (11 pages)

Online Publication Date: 9 May 2013

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Gas puff imaging (GPI) [S. J. Zweben, D. P. Stotler et al., Phys. Plasmas 9, 1981 (2002)10.1063/1.1445179; R. J. Maqueda, G. A. Wurden et al., Rev. Sci. Instrum. 74, 2020 (2003)10.1063/1.1535249] is a powerful diagnostic that permits a two-dimensional measurement of turbulence in the edge region of a fusion plasma and is based on the observation of the local emission of a neutral gas, actively puffed into the periphery of the plasma. The developed in-vessel GPI telescope observes the emission from the puffed gas along local (at the puff) magnetic field lines. The GPI telescope is specially designed to operate in severe TEXTOR conditions and can be treated as a prototype for the GPI systems on next generation machines. Also, the gas puff nozzle is designed to have a lower divergence of the gas flow than previous GPI diagnostics. The resulting images show poloidally and radially propagating structures, which are associated with plasma blobs. We demonstrate that the local gas puff does not disturb plasma properties. Our results indicate also that the neutral gas emission intensity is more sensitive to the electron density than the electron temperature. Here, we present implementation details of the GPI system on TEXTOR and discuss some design and diagnostic issues related to the development of GPI systems in general.

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52.70.Kz	Optical (ultraviolet, visible, infrared) measurements
52.55.Fa	Tokamaks, spherical tokamaks
52.35.Ra	Plasma turbulence

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Data processing and analysis of the imaging Thomson scattering diagnostic system on HT-7 tokamak

Xiaofeng Han, Chunqiang Shao, Xiaoqi Xi, Junyu Zhao, Zang Qing, Jianhua Yang, Xingxing Dai, and Kado Shinichiro

Rev. Sci. Instrum. 84, 053502 (2013); http://dx.doi.org/10.1063/1.4804161 (5 pages)

Online Publication Date: 15 May 2013

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A high spatial resolution imaging Thomson scattering diagnostic system was developed in ASIPP (Institute of Plasma Physics, Chinese Academy of Sciences). After about one month trial running on the superconducting HT-7 (Hefei Tokamak-7) tokamak, the system was proved to be capable of measuring plasma electron temperature. The system setup and data calibration are described in this paper and then the instrument function is studied in detail, as well as the measurement capability, an electron temperature of 50 eV to 2 keV and density beyond 1 × 10¹⁹ m⁻³. Finally, the data processing method and experimental results are presented.

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52.70.Kz	Optical (ultraviolet, visible, infrared) measurements
52.55.Fa	Tokamaks, spherical tokamaks
52.25.Os	Emission, absorption, and scattering of electromagnetic radiation
52.55.Jd	Magnetic mirrors, gas dynamic traps
52.25.-b	Plasma properties

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Hard x-ray tomographic studies of the destruction of an energetic electron ring

Y. Wang, W. Gekelman, and P. Pribyl

Rev. Sci. Instrum. 84, 053503 (2013); http://dx.doi.org/10.1063/1.4804354 (10 pages)

Online Publication Date: 15 May 2013

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A tomography system was designed and built at the Large Plasma Device to measure the spatial distribution of hard x-ray (100 KeV-3 MeV) emissivity. The x-rays were generated when a hot electron ring was significantly disrupted by a shear Alfvén wave. The plasma is pulsed at 1 Hz (1 shot/s). A lead shielded scintillator detector with an acceptance angle defined by a lead pinhole is mounted on a rotary gimbal and used to detect the x-rays. The system measures one chord per plasma shot using only one detector. A data plane usually consists of several hundred chords. A novel Dot by Dot Reconstruction (DDR) method is introduced to calculate the emissivity profile from the line integrated data. In the experiments, there are often physical obstructions, which make measurements at certain angles impossible. The DDR method works well even in this situation. The method was tested with simulated data, and was found to be more effective than previously published methods for the specific geometry of this experiment. The reconstructed x-ray emissivity from experimental data by this method is shown.

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07.85.Tt	X-ray microscopes
06.30.Bp	Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

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Modification of tokamak edge plasma turbulence and transport by biasing and resonant helical magnetic field

Mansoureh Lafouti, Mahmood Ghoranneviss, Sakineh Meshkani, and Ahmad Salar Elahi

Rev. Sci. Instrum. 84, 053504 (2013); http://dx.doi.org/10.1063/1.4805066 (6 pages)

Online Publication Date: 21 May 2013

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In this paper, both Resonant Helical magnetic Field (RHF) and limiter biasing have been applied to the tokamak. We have investigated their effects on the turbulence and transport of the particles at the edge of the plasma. The biased limiter voltage has been fixed at 200 V and RHF has L = 2 and L = 3. Also, the effects of the time order of the application of RHF and biasing to the tokamak have been explored. The experiment has been performed under three conditions. At first, the biasing and RHF were applied at t = 15 ms and at t = 20 ms. In the next step, RHF and biasing were applied at t = 15 ms and t = 20 ms, respectively. Finally, both of them were turned on at t = 15 ms until the end of the shot. For this purpose, the ion saturation current (I_sat) and the floating potential (V_f) have been measured by the Langmuir probe at r/a = 0.9. Moreover, the power spectra of I_sat and floating potential gradient (∇V_f), the coherency, the phase between them, and the particle diffusion coefficient have been calculated. The density fluctuations of the particles have been measured by the Rake probe and they have been analyzed with the Probability Distribution Function (PDF) technique. Also the particle diffusion coefficient has been determined by the Fick's law. The results show that, when RHF and biasing were applied at the same time to the plasma (during flatness region of plasma current), the radial particle density gradient, the radial particle flux, and the particle diffusion coefficient decrease about 50%, 60%, and 55%, respectively, compared to the other conditions. For more precision, the average values of the particle flux and the particle density gradient were calculated in the work. When the time is less than 15 ms, the average values of the particle flux and the particle density gradient are identical under all conditions, but in the other time interval they change. They reduce with the simultaneous application of biasing and RHF. The same results obtain from the histogram of the particle flux and the gradient of the particle density and the particle diffusion coefficient. Consequently, the simultaneous application of biasing and RHF is more effective for the plasma confinement.

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52.55.Fa	Tokamaks, spherical tokamaks
52.70.Ds	Electric and magnetic measurements
52.25.Fi	Transport properties
52.25.Gj	Fluctuation and chaos phenomena
52.35.Ra	Plasma turbulence
52.40.Hf	Plasma-material interactions; boundary layer effects

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Two-dimensional-spatial distribution measurement of electron temperature and plasma density in low temperature plasmas

Young-Cheol Kim, Sung-Ho Jang, Se-Jin Oh, Hyo-Chang Lee, and Chin-Wook Chung

Rev. Sci. Instrum. 84, 053505 (2013); http://dx.doi.org/10.1063/1.4802673 (7 pages)

Online Publication Date: 22 May 2013

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A real-time measurement method for two-dimensional (2D) spatial distribution of the electron temperature and plasma density was developed. The method is based on the floating harmonic method and the real time measurement is achieved with little plasma perturbation. 2D arrays of the sensors on a 300 mm diameter wafer-shaped printed circuit board with a high speed multiplexer circuit were used. Experiments were performed in an inductive discharge under various external conditions, such as powers, gas pressures, and different gas mixing ratios. The results are consistent with theoretical prediction. Our method can measure the 2D spatial distribution of plasma parameters on a wafer-level in real-time. This method can be applied to plasma diagnostics to improve the plasma uniformity of plasma reactors for plasma processing.

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52.25.Fi	Transport properties
52.70.Ds	Electric and magnetic measurements
52.80.-s	Electric discharges

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Application of dynamic displacement current for diagnostics of subnanosecond breakdowns in an inhomogeneous electric field

Tao Shao (邵涛), Victor F. Tarasenko, Cheng Zhang (章程), Alexandr G. Burachenko, Dmitry V. Rybka, Igor’ D. Kostyrya, Mikhail I. Lomaev, Evgeni Kh. Baksht, and Ping Yan (严萍)

Rev. Sci. Instrum. 84, 053506 (2013); http://dx.doi.org/10.1063/1.4807154 (7 pages)

Online Publication Date: 22 May 2013

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The breakdown of different air gaps at high overvoltages in an inhomogeneous electric field was investigated with a time resolution of up to 100 ps. Dynamic displacement current was used for diagnostics of ionization processes between the ionization wave front and a plane anode. It is demonstrated that during the generation of a supershort avalanche electron beam (SAEB) with amplitudes of ∼10 A and more, conductivity in the air gaps at the breakdown stage is ensured by the ionization wave, whose front propagates from the electrode of small curvature radius, and by the dynamic displacement current between the ionization wave front and the plane electrode. The amplitude of the dynamic displacement current measured by a current shunt is 100 times greater than the SAEB. It is shown that with small gaps and with a large cathode diameter, the amplitude of the dynamic displacement current during a subnanosecond rise time of applied pulse voltage can be higher than 4 kA.

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52.80.-s	Electric discharges
52.25.Fi	Transport properties
52.25.Jm	Ionization of plasmas
52.70.Kz	Optical (ultraviolet, visible, infrared) measurements

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Simultaneous immersion Mirau interferometry

Oleksandra V. Lyulko, Gerhard Randers-Pehrson, and David J. Brenner

Rev. Sci. Instrum. 84, 053701 (2013); http://dx.doi.org/10.1063/1.4803181 (6 pages)

Online Publication Date: 3 May 2013

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A novel technique for label-free imaging of live biological cells in aqueous medium that is insensitive to ambient vibrations is presented. This technique is a spin-off from previously developed immersion Mirau interferometry. Both approaches utilize a modified Mirau interferometric attachment for a microscope objective that can be used both in air and in immersion mode, when the device is submerged in cell medium and has its internal space filled with liquid. While immersion Mirau interferometry involves first capturing a series of images, the resulting images are potentially distorted by ambient vibrations. Overcoming these serial-acquisition challenges, simultaneous immersion Mirau interferometry incorporates polarizing elements into the optics to allow simultaneous acquisition of two interferograms. The system design and production are described and images produced with the developed techniques are presented.

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87.64.M-	Optical microscopy
07.60.Ly	Interferometers
42.25.Ja	Polarization

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Wide-area scanner for high-speed atomic force microscopy

Hiroki Watanabe, Takayuki Uchihashi, Toshihide Kobashi, Mikihiro Shibata, Jun Nishiyama, Ryohei Yasuda, and Toshio Ando

Rev. Sci. Instrum. 84, 053702 (2013); http://dx.doi.org/10.1063/1.4803449 (10 pages)

Online Publication Date: 3 May 2013

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multimedia

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High-speed atomic force microscopy (HS-AFM) has recently been established. The dynamic processes and structural dynamics of protein molecules in action have been successfully visualized using HS-AFM. However, its maximum scan ranges in the X- and Y-directions have been limited to ∼1 μm and ∼4 μm, respectively, making it infeasible to observe the dynamics of much larger samples, including live cells. Here, we develop a wide-area scanner with a maximum XY scan range of ∼46 × 46 μm² by magnifying the displacements of stack piezoelectric actuators using a leverage mechanism. Mechanical vibrations produced by fast displacement of the X-scanner are suppressed by a combination of feed-forward inverse compensation and the use of triangular scan signals with rounded vertices. As a result, the scan speed in the X-direction reaches 6.3 mm/s even for a scan size as large as ∼40 μm. The nonlinearity of the X- and Y-piezoelectric actuators’ displacements that arises from their hysteresis is eliminated by polynomial-approximation-based open-loop control. The interference between the X- and Y-scanners is also eliminated by the same technique. The usefulness of this wide-area scanner is demonstrated by video imaging of dynamic processes in live bacterial and eukaryotic cells.

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07.79.Lh

Atomic force microscopes

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Differential interference contrast microscopy using light-emitting diode illumination in conjunction with dual optical traps

C. Battle, L. Lautscham, and C. F. Schmidt

Rev. Sci. Instrum. 84, 053703 (2013); http://dx.doi.org/10.1063/1.4804597 (5 pages)

Online Publication Date: 16 May 2013

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Differential interference contrast (DIC) microscopy is a common mode of biological light microscopy used to achieve maximal resolution and contrast with label-free, weakly absorbing specimens such as cells. Maintaining the polarization state of the illuminating light is essential for the technique, and this requirement can conflict with optical trapping. We describe how to optimize DIC imaging using a light-emitting diode illumination source in a microscope while integrating a dual optical trap into the set up. Every time a polarized light beam reflects off or transmits through a dichroic mirror in the beam path, its polarization state will change if it is not polarized exactly parallel (p) or perpendicular (s) to the plane of incidence. We observe wavelength-dependent optical rotation and depolarization effects in our illumination light upon reflection from/transmission through dichroic mirrors in the beam path, resulting in significant degradation of image quality. We describe a method to compensate for these effects by introducing quarter-waveplates and a laser clean-up filter into the imaging pathway. We show that this approach achieves a full recovery of image quality.

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87.80.Cc	Optical trapping
07.60.Pb	Conventional optical microscopes
87.64.M-	Optical microscopy
42.79.Ci	Filters, zone plates, and polarizers

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Theoretical and experimental study on two-stage-imaging microscopy using ellipsometric contrast for real-time visualization of molecularly thin films

Y. Kajihara, K. Fukuzawa, S. Itoh, R. Watanabe, and H. Zhang

Rev. Sci. Instrum. 84, 053704 (2013); http://dx.doi.org/10.1063/1.4804633 (9 pages)

Online Publication Date: 16 May 2013

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A two-stage-imaging ellipsometric-contrast microscope (TIEM) has been developed to measure the distribution of film thickness over a wide area of molecularly thin liquid films with a high lateral resolution, wide field of view, high thickness resolution, and high-speed. Moreover, this ellipsometric microscope enables us to achieve simultaneous measurements with other measurement apparatuses. We present the principle used to parallelize an object image to an imaging sensor and to reduce the incident angle entering the imaging sensor. In addition, we discuss the characteristic shape deformation of the object image due to oblique observation. The performance of the actual setup for TIEM was experimentally studied. A lateral resolution of about 1 μm was obtained by measuring the modulation transfer function of the TIEM. We also found that the shape deformation approximately agreed with that from theory. Furthermore, for molecularly thin films, we confirmed linearity between the film thickness and the light intensity measured with TIEM, which enables us to quantify the thickness of the films. TIEM can open up a new field of real-time imaging of thin films such as visualization of a liquid lubricant film under shear.

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07.60.Fs	Polarimeters and ellipsometers
07.60.Pb	Conventional optical microscopes
42.79.Pw	Imaging detectors and sensors
07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.30.Lr	Modulation and optical transfer functions
06.30.Bp	Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

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High-frequency annular array with coaxial illumination for dual-modality ultrasonic and photoacoustic imaging

Erwan Filoux, Ashwin Sampathkumar, Parag V. Chitnis, Orlando Aristizábal, and Jeffrey A. Ketterling

Rev. Sci. Instrum. 84, 053705 (2013); http://dx.doi.org/10.1063/1.4804636 (7 pages)

Online Publication Date: 21 May 2013

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This paper presents a combined ultrasound and photoacoustic (PA) imaging (PAI) system used to obtain high-quality, co-registered images of mouse-embryo anatomy and vasculature. High-frequency ultrasound (HFU, >20 MHz) is utilized to obtain high-resolution anatomical images of small animals while PAI provides high-contrast images of the vascular network. The imaging system is based on a 40 MHz, 5-element, 6 mm aperture annular-array transducer with a 800 μm diameter hole through its central element. The transducer was integrated in a cage-plate assembly allowing for a collimated laser beam to pass through the hole so that the optical and acoustic beams were collinear. The assembly was mounted on a two-axis, motorized stage to enable the simultaneous acquisition of co-registered HFU and PA volumetric data. Data were collected from all five elements in receive and a synthetic-focusing algorithm was applied in post-processing to beamform the data and increase the spatial resolution and depth-of-field (DOF) of the HFU and PA images. Phantom measurements showed that the system could achieve high-resolution images (down to 90 μm for HFU and 150 μm for PAI) and a large DOF of >8 mm. Volume renderings of a mouse embryo showed that the scanner allowed for visualizing morphologically precise anatomy of the entire embryo along with corresponding co-registered vasculature. Major head vessels, such as the superior sagittal sinus or rostral vein, were clearly identified as well as limb bud vasculature.

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87.85.-d	Biomedical engineering
87.57.-s	Medical imaging
43.60.Lq	Acoustic imaging, displays, pattern recognition, feature extraction
43.38.Hz	Transducer arrays, acoustic interaction effects in arrays
87.57.nj	Registration

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Sensorless enhancement of an atomic force microscope micro-cantilever quality factor using piezoelectric shunt control

M. Fairbairn and S. O. R. Moheimani

Rev. Sci. Instrum. 84, 053706 (2013); http://dx.doi.org/10.1063/1.4805108 (8 pages)

Online Publication Date: 23 May 2013

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The image quality and resolution of the Atomic Force Microscope (AFM) operating in tapping mode is dependent on the quality (Q) factor of the sensing micro-cantilever. Increasing the cantilever Q factor improves image resolution and reduces the risk of sample and cantilever damage. Active piezoelectric shunt control is introduced in this work as a new technique for modifying the Q factor of a piezoelectric self-actuating AFM micro-cantilever. An active impedance is placed in series with the tip oscillation voltage source to modify the mechanical dynamics of the cantilever. The benefit of using this control technique is that it removes the optical displacement sensor from the Q control feedback loop to reduce measurement noise in the loop and allows for a reduction in instrument size.

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07.79.Lh	Atomic force microscopes
85.85.+j	Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
84.37.+q	Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
42.79.Pw	Imaging detectors and sensors
85.50.-n	Dielectric, ferroelectric, and piezoelectric devices

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Relaxation calorimeter for hydrogen thermoporometry

E. Van Cleve, M. A. Worsley, and S. O. Kucheyev

Rev. Sci. Instrum. 84, 053901 (2013); http://dx.doi.org/10.1063/1.4803180 (6 pages)

Online Publication Date: 3 May 2013

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A relaxation calorimeter for measuring the heat capacity of hydrogen isotopes in nanoporous solids is described. Apparatus’ features include (i) cooling by a pulse tube refrigerator, (ii) a modular design, allowing for rapid reconfiguration and sample turn around, (iii) a thermal stability of ≲1 mK, and (iv) a bottom temperature of ∼5 K. The calorimeter is tested on effective heat capacity measurements of H₂ in Vycor (silica) nanoporous glass, yielding a very detailed pore size distribution analysis with an effectively sub-Angstrom resolution.

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07.20.Fw	Calorimeters
61.43.Gt	Powders, porous materials
61.46.-w	Structure of nanoscale materials
65.60.+a	Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

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Quantum state-resolved gas/surface reaction dynamics probed by reflection absorption infrared spectroscopy

Li Chen, Hirokazu Ueta, Régis Bisson, and Rainer D. Beck

Rev. Sci. Instrum. 84, 053902 (2013); http://dx.doi.org/10.1063/1.4803933 (9 pages)

Online Publication Date: 9 May 2013

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We report the design and characterization of a new molecular-beam/surface-science apparatus for quantum state-resolved studies of gas/surface reaction dynamics combining optical state-specific reactant preparation in a molecular beam by rapid adiabatic passage with detection of surface-bound reaction products by reflection absorption infrared spectroscopy (RAIRS). RAIRS is a non-invasive infrared spectroscopic detection technique that enables online monitoring of the buildup of reaction products on the target surface during reactant deposition by a molecular beam. The product uptake rate obtained by calibrated RAIRS detection yields the coverage dependent state-resolved reaction probability S(θ). Furthermore, the infrared absorption spectra of the adsorbed products obtained by the RAIRS technique provide structural information, which help to identify nascent reaction products, investigate reaction pathways, and determine branching ratios for different pathways of a chemisorption reaction. Measurements of the dissociative chemisorption of methane on Pt(111) with this new apparatus are presented to illustrate the utility of RAIRS detection for highly detailed studies of chemical reactions at the gas/surface interface.

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