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Oct 2008

Volume 79, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 79, 101301 (2008); http://dx.doi.org/10.1063/1.2982492 (7 pages)

Jordan D. Olliges, Taylor C. Lilly, Thomas B. Joslyn, and Andrew D. Ketsdever

False color photograph of an acrylic (PMMA) hybrid motor fuel grain (black and blue correspond to regions of high spectral intensity). The region of high intensity inside the fuel grain is from the ignition system. Hybrid rocket firings were used to demonstrate time accurate mass flow measurements in solid-fueled systems.

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Invited Article: Time accurate mass flow measurements of solid-fueled systems

Jordan D. Olliges, Taylor C. Lilly, Thomas B. Joslyn, and Andrew D. Ketsdever

Rev. Sci. Instrum. 79, 101301 (2008); http://dx.doi.org/10.1063/1.2982492 (7 pages)

Online Publication Date: 7 October 2008

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A novel diagnostic method is described that utilizes a thrust stand mass balance (TSMB) to directly measure time-accurate mass flow from a solid-fuel thruster. The accuracy of the TSMB mass flow measurement technique was demonstrated in three ways including the use of an idealized numerical simulation, verifying a fluid mass calibration with high-speed digital photography, and by measuring mass loss in more than 30 hybrid rocket motor firings. Dynamic response of the mass balance was assessed through weight calibration and used to derive spring, damping, and mass moment of inertia coefficients for the TSMB. These dynamic coefficients were used to determine the mass flow rate and total mass loss within an acrylic and gaseous oxygen hybrid rocket motor firing. Intentional variations in the oxygen flow rate resulted in corresponding variations in the total propellant mass flow as expected. The TSMB was optimized to determine mass losses of up to 2.5 g and measured total mass loss to within 2.5% of that calculated by a NIST-calibrated digital scale. Using this method, a mass flow resolution of 0.0011 g/s or 2% of the average mass flow in this study has been achieved.
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89.20.Kk Engineering
89.40.Dd Air transporation
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Development of high resolution Michelson interferometer for stable phase-locked ultrashort pulse pair generation

Takumi Okada, Kazuhiro Komori, Keishiro Goshima, Shohgo Yamauchi, Isao Morohashi, Takeyoshi Sugaya, Mutsuo Ogura, and Noriaki Tsurumachi

Rev. Sci. Instrum. 79, 103101 (2008); http://dx.doi.org/10.1063/1.2993980 (7 pages) | Cited 1 time

Online Publication Date: 8 October 2008

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We developed a high resolution Michelson interferometer with a two-frequency He–Ne laser positioning system in order to stabilize the relative phase of a pulse pair. The control resolution corresponded to a 12 as time resolution or a phase of 1.5° at 900 nm. This high resolution Michelson interferometer can generate a phase-locked pulse pair either with a specific relative phase such as 0 or π radians or with an arbitrary phase. Coherent control of an InAs self-assembled quantum dot was demonstrated using the high resolution Michelson interferometer with a microspectroscopy system.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
42.62.Fi Laser spectroscopy
07.60.Ly Interferometers
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots

A new magneto-optical trap-target recoil ion momentum spectroscopy apparatus for ion-atom collisions and trapped atom studies

J. Blieck, X. Fléchard, A. Cassimi, H. Gilles, S. Girard, and D. Hennecart

Rev. Sci. Instrum. 79, 103102 (2008); http://dx.doi.org/10.1063/1.2994151 (11 pages) | Cited 1 time

Online Publication Date: 9 October 2008

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A new magneto-optical trap-target recoil ion momentum spectroscopy apparatus has been built and tested at the LPC-CAEN. Dedicated to ion-atom collisions studies and excited fraction measurements, the setup combines a projectile ion beam line, a target of cold rubidium atoms provided by a magneto-optical trap (MOT), and a recoil ion momentum spectrometer. In a test experiment using a beam of Na+ projectiles, we demonstrate its capability to measure, with a very high signal over background ratio, fully differential cross sections in scattering angle, initial state, and final state of the system. We detail, in this work, features that had not been described previously in the literature: an extraction of the recoil ions transverse to the ion beam axis, and a fast switch for the MOT magnetic field. Advantages of transverse versus longitudinal extraction are discussed, and future possibilities for the setup are presented.
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33.57.+c Magneto-optical and electro-optical spectra and effects
34.50.-s Scattering of atoms and molecules

300 mm reference wafer fabrication by using direct laser lithography

Hyug-Gyo Rhee, Dongik Kim, Seung-Ki Hong, and Yun-Woo Lee

Rev. Sci. Instrum. 79, 103103 (2008); http://dx.doi.org/10.1063/1.2999827 (5 pages) | Cited 1 time

Online Publication Date: 17 October 2008

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We propose a new method based on direct laser lithography to fabricate reference chromium patterns on a silicon wafer. Our method is able to fabricate a maximum 360-mm-diameter pattern with 651-nm-position uncertainty. The minimum pattern size is about 0.8 μm (linewidth value) and the maximum available height of the pattern is slightly over 400 nm.
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85.40.Hp Lithography, masks and pattern transfer

A widely tunable laser frequency offset lock with digital counting

Joshua Hughes and Chad Fertig

Rev. Sci. Instrum. 79, 103104 (2008); http://dx.doi.org/10.1063/1.2999544 (7 pages) | Cited 1 time

Online Publication Date: 21 October 2008

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We demonstrate a hybrid analog+digital electronic lock to stabilize a dynamically tunable rf offset between two lasers. Our method features an 80 MHz capture range, ±7 GHz tuning range, frequency agility of 1 MHz/μs, and low (<30 ppm) drift in the absolute optical frequency difference after ∼ 1000 s. With this scheme, multiple slave lasers can easily be referenced to one stable master laser, while each remains rapidly and accurately tunable over the wide frequency ranges encountered in typical laser cooling and trapping experiments.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.50.Wk Mechanical effects of light on material media, microstructures and particles

Portable light-emitting diode-based photometer with one-shot optochemical sensors for measurement in the field

A. J. Palma, J. M. Ortigosa, A. Lapresta-Fernández, M. D. Fernández-Ramos, M. A. Carvajal, and L. F. Capitán-Vallvey

Rev. Sci. Instrum. 79, 103105 (2008); http://dx.doi.org/10.1063/1.3000682 (8 pages) | Cited 2 times

Online Publication Date: 21 October 2008

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This report describes the electronics of a portable, low-cost, light-emitting diode (LED)-based photometer dedicated to one-shot optochemical sensors. Optical detection is made through a monolithic photodiode with an on-chip single-supply transimpedance amplifier that reduces some drawbacks such as leakage currents, interferences, and parasitic capacitances. The main instrument characteristics are its high light source stability and thermal correction. The former is obtained by means of the optical feedback from the LED polarization circuit, implementing a pseudo-two light beam scheme from a unique light source with a built-in beam splitter. The feedback loop has also been used to adjust the LED power in several ranges. Moreover, the low-thermal coefficient achieved (−90 ppm/°C) is compensated by thermal monitoring and calibration function compensation in the digital processing. The hand-held instrument directly gives the absorbance ratio used as the analytical parameter and the analyte concentration after programming the calibration function in the microcontroller. The application of this photometer for the determination of potassium and nitrate, using one-shot sensors with ionophore-based chemistries is also demonstrated, with a simple analytical methodology that shortens the analysis time, eliminating some calibrating solutions (HCl, NaOH, and buffer). Therefore, this compact instrument is suitable for real-time analyte determination and operation in the field.
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07.60.Dq Photometers, radiometers, and colorimeters
85.60.Jb Light-emitting devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis

Rapid photoreflectance spectroscopy for strained silicon metrology

H. Chouaib, M. E. Murtagh, V. Guènebaut, S. Ward, P. V. Kelly, M. Kennard, Y. M. Le Vaillant, M. G. Somekh, M. C. Pitter, and S. D. Sharples

Rev. Sci. Instrum. 79, 103106 (2008); http://dx.doi.org/10.1063/1.2999919 (3 pages) | Cited 5 times

Online Publication Date: 22 October 2008

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We present an improved photoreflectance (PR) spectroscopy technique upon the prior art in providing a rapid acquisition method of the PR spectrum in a simultaneous and multiplexed manner. Rapid PR (RPR) application is the on-line monitoring of strained silicon. Shrinkage in the silicon bandgap is measured and converted to strain, using theoretical models. Experimental RPR results are in good correlation with Raman spectroscopy.
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78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.30.Am Elemental semiconductors and insulators
71.20.Mq Elemental semiconductors
77.65.-j Piezoelectricity and electromechanical effects

Probing thermal waves on the free surface of various media: Surface fluctuation specular reflection spectroscopy

A. Tay, C. Thibierge, D. Fournier, C. Fretigny, F. Lequeux, C. Monteux, J. P. Roger, and L. Talini

Rev. Sci. Instrum. 79, 103107 (2008); http://dx.doi.org/10.1063/1.3002424 (7 pages) | Cited 2 times

Online Publication Date: 23 October 2008

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Thermal motion gives rise to fluctuations in free surfaces; measurement of the thermally excited waves on such surfaces provides information on the mechanical properties of the medium. We have developed an optical tool to probe the thermally excited waves on free surfaces: surface fluctuation specular reflection (SFSR) spectroscopy. It consists in measuring the fluctuations in the position of a laser beam that is specularly reflected onto the free surface of a medium. The position of the reflected beam is sensitive to the roughness of the probed surface; the thermal waves are detected by subtracting the light intensities collected on the two quadrants of a photodiode, on which the beam is centered. We show how the measured signal is related to the medium properties. We also present measurements performed on Newtonian liquids as well as on a viscoelastic solid; we show that in all cases, there is a very good agreement between experimental and computed spectra. SFSR thus applies to a broad range of materials. It moreover offers a very good temporal resolution and should provide a useful tool for dynamical measurements on complex fluids.
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68.35.Gy Mechanical properties; surface strains
66.20.-d Viscosity of liquids; diffusive momentum transport
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Extreme-ultraviolet polarimeter utilizing laser-generated high-order harmonics

Nicole Brimhall, Matthew Turner, Nicholas Herrick, David D. Allred, R. Steven Turley, Michael Ware, and Justin Peatross

Rev. Sci. Instrum. 79, 103108 (2008); http://dx.doi.org/10.1063/1.2999543 (7 pages) | Cited 4 times

Online Publication Date: 27 October 2008

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We describe an extreme-ultraviolet (EUV) polarimeter that employs laser-generated high-order harmonics as the light source. The polarimeter is designed to characterize materials and thin films for use with EUV light. Laser high harmonics are highly directional with easily rotatable linear polarization, not typically available with other EUV sources. The harmonics have good wavelength coverage, potentially spanning the entire EUV from a few to a hundred nanometers. Our instrument is configured to measure reflectances from 14 to 30 nm and has ∼ 180 spectral resolution (λ/Δλ). The reflection from a sample surface can be measured over a continuous range of incident angles (5°–75°). A secondary 14 cm gas cell attenuates the harmonics in a controlled way to keep signals within the linear dynamic range of the detector, comprised of a microchannel plate coupled to a phosphorous screen and charge coupled device camera. The harmonics are produced using ∼ 10 mJ, ∼ 35 fs, and ∼ 800 nm laser pulses with a repetition rate of 10 Hz. Per-shot energy monitoring of the laser discriminates against fluctuations. The polarimeter reflectance data agree well with data obtained at the Advanced Light Source Synchrotron (Beamline 6.3.2).
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81.70.Fy Nondestructive testing: optical methods
07.60.Fs Polarimeters and ellipsometers
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.72.Bj Visible and ultraviolet sources
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Pw Imaging detectors and sensors

High-resolution imaging spectrometer for recording absolutely calibrated far ultraviolet spectra from laser-produced plasmas

Charles M. Brown, John F. Seely, Uri Feldman, Glenn E. Holland, James L. Weaver, Steven P. Obenschain, Benjawan Kjornrattanawanich, and Drew Fielding

Rev. Sci. Instrum. 79, 103109 (2008); http://dx.doi.org/10.1063/1.3000685 (11 pages)

Online Publication Date: 28 October 2008

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An imaging spectrometer was designed and fabricated for recording far ultraviolet spectra from laser-produced plasmas with wavelengths as short as 155 nm. The spectrometer implements a Cassegrain telescope and two gratings in a tandem Wadsworth optical configuration that provides diffraction limited resolution. Spectral images were recorded from plasmas produced by the irradiation of various target materials by intense KrF laser radiation with 248 nm wavelength. Two pairs of high-resolution gratings can be selected for the coverage of two wavebands, one grating pair with 1800 grooves/mm and covering approximately 155–175 nm and another grating pair with 1200 grooves/mm covering 230–260 nm. The latter waveband includes the 248 nm KrF laser wavelength, and the former waveband includes the wavelength of the two-plasmon decay instability at ⅔ the KrF laser wavelength (165 nm). The detection media consist of a complementary metal oxide semiconductor imager, photostimulable phosphor image plates, and a linear array of 1 mm2 square silicon photodiodes with 0.4 ns rise time. The telescope mirrors, spectrometer gratings, and 1 mm2 photodiode were calibrated using synchrotron radiation, and this enables the measurement of the absolute emission from the laser-produced plasmas with temporal, spatial, and spectral resolutions. The spectrometer is capable of measuring absolute spectral emissions at 165 nm wavelength as small as 5×10−7 J/nm from a plasma source area of 0.37 mm2 and with 0.4 ns time resolution.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
07.60.Rd Visible and ultraviolet spectrometers
06.20.fb Standards and calibration
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

A frequency stabilization technique for diode lasers based on frequency-shifted beams from an acousto-optic modulator

Mevan Gunawardena, Paul W. Hess, Jared Strait, and P. K. Majumder

Rev. Sci. Instrum. 79, 103110 (2008); http://dx.doi.org/10.1063/1.3006386 (6 pages) | Cited 2 times

Online Publication Date: 30 October 2008

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We present a simple method for diode laser frequency stabilization that makes use of a Doppler-broadened vapor cell absorption signals of two frequency-shifted laser beams. Using second-order-diffracted, double-passed beams from an acousto-optic modulator, we achieve a frequency separation roughly equal to the Doppler half width. The differential transmission signals of the two beams provide an error signal with a very large linear feature, allowing frequency stabilization over a range of greater than 1 GHz by means of standard proportional-integral-derivative servo feedback to the piezoelectric control of the grating in our external cavity diode laser. We have applied this technique to two different diode laser systems, one used to lock to the 410 nm E1 transition in indium and another for locking to the M1/E2 transition in thallium at 1283 nm. In both cases the technique reduces frequency fluctuation to roughly 1 MHz over time scales from 10−3 to 102 s.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems
42.79.Jq Acousto-optical devices
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Generation and dose distribution measurement of flash x-ray in KALI-5000 system

Rakhee Menon, Amitava Roy, S. Mitra, A. Sharma, J. Mondal, K. C. Mittal, K. V. Nagesh, and D. P. Chakravarthy

Rev. Sci. Instrum. 79, 103301 (2008); http://dx.doi.org/10.1063/1.3005485 (5 pages) | Cited 2 times

Online Publication Date: 27 October 2008

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Flash x-ray generation studies have been carried out in KALI-5000 Pulse power system. The intense relativistic electron beam has been bombarded on a tantalum target at anode to produce flash x-ray via bremsstrahlung conversion. The typical electron beam parameter was 360 kV, 18 kA, and 100 ns, with a few hundreds of A/cm2 current density. The x-ray dose has been measured with calcium sulfate:dysposium (CaSO4:Dy) thermoluminescent dosimeter and the axial dose distribution has been characterized. It has been observed that the on axis dose falls of with distance ∼ 1/xn, where n varies from 1.8 to 1.85. A maximum on axis dose of 46 mrad has been measured at 1 m distance from the source. A plastic scintillator with optical fiber coupled to a photomultiplier tube has been developed to measure the x-ray pulse width. The typical x-ray pulse width varied from 50 to 80 ns.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
41.75.Ht Relativistic electron and positron beams

The use and characterization of a backilluminated charge-coupled device in investigations of pulsed x-ray and radiation sources

Wilfred Fullagar, Jens Uhlig, Monika Walczak, Sophie Canton, and Villy Sundström

Rev. Sci. Instrum. 79, 103302 (2008); http://dx.doi.org/10.1063/1.3000003 (8 pages) | Cited 2 times

Online Publication Date: 29 October 2008

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Examinations of bremsstrahlung and energetic electron beams from a novel laser plasma source motivate and assist characterization of a backthinned, backilluminated direct detection x-ray charge-coupled device (CCD), a topology that is uncommon in hard x-ray work. Behavior toward pseudomonochromatic (55Fe) and multichromatic (241Am) sources is briefly reviewed under optimized noise conditions. Results collectively establish the previously unknown functional depth structure. Several modes of usage are illustrated in ∼ 4–20 keV x-ray laser plasma source investigations, where the significance of the characterization is briefly discussed. The spectral redistribution associated with this CCD topology is unfavorable, yet appropriate analysis ensures that sufficient spectral information remains for quantitative determination of broadband x-ray flux and spectra in essentially single laser shot measurements. The energy dependence of nascent electron cloud radii in silicon is determined using broadband x-rays from the laser plasma source, turning the narrow depletion depth to advantage. Finally, the characterization is used to quantify recent x-ray spectral explorations of the water jet laser plasma source operating under aspirator vacuum. These results will have key value for establishment of laboratory based ultrafast extended x-ray absorption fine structure experiments using microbolometric detectors.
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52.59.Px Hard X-ray sources
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
42.55.Vc X- and γ-ray lasers
41.75.Fr Electron and positron beams
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Four free parameter empirical parametrization of glow discharge Langmuir probe data

A. A. Azooz

Rev. Sci. Instrum. 79, 103501 (2008); http://dx.doi.org/10.1063/1.2976755 (6 pages)

Online Publication Date: 3 October 2008

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For the purpose of developing a simple empirical model capable of producing the electron energy distribution function (EEDF) from Langmuir probe I-V characteristics, a four parameter empirical equation that fits most Langmuir probe experimental data is suggested. The four free fitting parameters are related to the main plasma properties. These properties include the ion and electron saturation currents and the plasma electron temperature. This equation can be readily differentiated twice to give the EEDF according to the Druyvesteyn formula. Furthermore, a MATLAB platform based computer code based on this model yielding results for the plasma potential and all plasma parameters mentioned above is presented. The information given below can be used to write other computer codes for the same purpose in any other programming language.
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52.70.Ds Electric and magnetic measurements
52.80.Hc Glow; corona
52.25.Fi Transport properties

Diagnosis of high-intensity pulsed heavy ion beam generated by a novel magnetically insulated diode with gas puff plasma gun

H. Ito, H. Miyake, and K. Masugata

Rev. Sci. Instrum. 79, 103502 (2008); http://dx.doi.org/10.1063/1.2999904 (5 pages) | Cited 3 times

Online Publication Date: 15 October 2008

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Intense pulsed heavy ion beam is expected to be applied to materials processing including surface modification and ion implantation. For those applications, it is very important to generate high-purity ion beams with various ion species. For this purpose, we have developed a new type of a magnetically insulated ion diode with an active ion source of a gas puff plasma gun. When the ion diode was operated at a diode voltage of about 190 kV, a diode current of about 15 kA, and a pulse duration of about 100 ns, the ion beam with an ion current density of 54 A/cm2 was obtained at 50 mm downstream from the anode. By evaluating the ion species and the energy spectrum of the ion beam via a Thomson parabola spectrometer, it was confirmed that the ion beam consists of nitrogen ions (N+ and N2+) of energy of 100–400 keV and the proton impurities of energy of 90–200 keV. The purity of the beam was evaluated to be 94%. The high-purity pulsed nitrogen ion beam was successfully obtained by the developed ion diode system.
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52.77.Dq Plasma-based ion implantation and deposition
52.70.-m Plasma diagnostic techniques and instrumentation
52.50.-b Plasma production and heating

High precision (14 bit), high density (octal) analog to digital converter for spectroscopy applications

E. T. Subramaniam, Mamta Jain, R. K. Bhowmik, and Michel Tripon

Rev. Sci. Instrum. 79, 103503 (2008); http://dx.doi.org/10.1063/1.2999546 (7 pages) | Cited 3 times

Online Publication Date: 20 October 2008

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Nuclear and particle physics experiments with large number of detectors require signal processing and data collection strategies that call for the ability to collect large amount of data while not sacrificing the precision and accuracy of the data being collected. This paper deals with the development of a high precision pulse peak detection, analog to digital converter (ADC) module with eight independent channels in plug-in daughter card motherboard model, best suited for spectroscopy experiments. This module provides multiple channels without cross-talk and of 14 bit resolution, while maintaining high density (each daughter card has an area of just 4.2″×0.51″) and exhibiting excellent integral nonlinearity ( ≤ ±2 mV or ±0.02% full scale reading) and differential nonlinearity ( ≤ ±1%). It was designed, developed and tested, in house, and gives added advantages of cost effectiveness and ease of maintenance.
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84.30.-r Electronic circuits

Low temperature plasma diagnostics with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry

Jing Wang, Yuyang Li, Zhenyu Tian, Taichang Zhang, Fei Qi, and Xiaoping Tao

Rev. Sci. Instrum. 79, 103504 (2008); http://dx.doi.org/10.1063/1.2999906 (5 pages) | Cited 4 times

Online Publication Date: 21 October 2008

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Plasma-based technology is of great importance for a range of industrial applications. However, due to the complexity of gas-phase and surface chemical reactions, the underlying plasma chemistry is still poorly understood, leading to a growing demand for experimental setups on plasma diagnostics. In this paper, we report an apparatus that combines tunable synchrotron vacuum ultraviolet (VUV) photoionization with molecular-beam mass spectrometry for detecting ionic and neutral species formed in the processes of plasma discharge. The products including reactive intermediates such as enols can be identified unambiguously with the measurements of photoionization mass spectrometry (PIMS) and photoionization efficiency spectra. The tunable VUV PIMS has been proven as an ideal and sensitive tool for a comprehensive understanding of plasma chemistry.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.-s Electric discharges
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
07.75.+h Mass spectrometers

A correlation electron cyclotron emission diagnostic and the importance of multifield fluctuation measurements for testing nonlinear gyrokinetic turbulence simulations

A. E. White, L. Schmitz, W. A. Peebles, T. A. Carter, T. L. Rhodes, E. J. Doyle, P. A. Gourdain, J. C. Hillesheim, G. Wang, C. Holland, G. R. Tynan, M. E. Austin, G. R. McKee, M. W. Shafer, K. H. Burrell, et al.

Rev. Sci. Instrum. 79, 103505 (2008); http://dx.doi.org/10.1063/1.2981186 (8 pages) | Cited 10 times

Online Publication Date: 28 October 2008

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A correlation electron cyclotron emission (CECE) diagnostic has been used to measure local, turbulent fluctuations of the electron temperature in the core of DIII-D plasmas. This paper describes the hardware and testing of the CECE diagnostic and highlights the importance of measurements of multifield fluctuation profiles for the testing and validation of nonlinear gyrokinetic codes. The process of testing and validating such codes is critical for extrapolation to next-step fusion devices. For the first time, the radial profiles of electron temperature and density fluctuations are compared to nonlinear gyrokinetic simulations. The CECE diagnostic at DIII-D uses correlation radiometry to measure the rms amplitude and spectrum of the electron temperature fluctuations. Gaussian optics are used to produce a poloidal spot size with wo ∼ 1.75 cm in the plasma. The intermediate frequency filters and the natural linewidth of the EC emission determine the radial resolution of the CECE diagnostic, which can be less than 1 cm. Wavenumbers resolved by the CECE diagnostic are kθ ≤ 1.8 cm−1 and kr ≤ 4 cm−1, relevant for studies of long-wavelength turbulence associated with the trapped electron mode and the ion temperature gradient mode. In neutral beam heated L-mode plasmas, core electron temperature fluctuations in the region 0.5<r/a<0.9, increase with radius from ∼ 0.5% to ∼ 2%, similar to density fluctuations that are measured simultaneously with beam emission spectroscopy. After incorporating “synthetic diagnostics” to effectively filter the code output, the simulations reproduce the characteristics of the turbulence and transport at one radial location r/a = 0.5, but not at a second location, r/a = 0.75. These results illustrate that measurements of the profiles of multiple fluctuating fields can provide a significant constraint on the turbulence models employed by the code.
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52.70.Nc Particle measurements
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.35.Ra Plasma turbulence
52.25.Gj Fluctuation and chaos phenomena
52.25.Fi Transport properties
52.25.Tx Emission, absorption, and scattering of particles
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A flexible, highly stable electrochemical scanning probe microscope for nanoscale studies at the solid-liquid interface

A. Z. Stieg, H. I. Rasool, and J. K. Gimzewski

Rev. Sci. Instrum. 79, 103701 (2008); http://dx.doi.org/10.1063/1.2992480 (7 pages) | Cited 2 times

Online Publication Date: 3 October 2008

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This work describes the design, fabrication, and application of an ultrastable scanning probe microscope for nanoscale studies at the solid-liquid interface, specifically in electrolyte environments. Quantification of system noise limits in the tunneling mode, mechanical drift rates, and lowest mechanical resonance provided values of ≤ 10 pA/Hz1/2, 2 nm/min (XY) and 0.15 nm/min (Z), and 7.9 kHz, respectively. Measurement of the closed-loop transfer function in the tunneling condition demonstrated linear feedback responses up to 4.2 and 2.5 kHz in ambient and electrochemical conditions. Atomic and molecular resolution imagings have been achieved in ambient, in situ, and electrochemical imaging environments at scan rates up to 80 lines/s. A modular design approach has produced a highly flexible microscope capable of imaging and spectroscopy in tunneling, tapping force [amplitude modulation atomic force microscopy (AFM)], and noncontact force (frequency modulation-AFM) modes.
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07.79.Lh Atomic force microscopes
07.79.Cz Scanning tunneling microscopes
68.08.-p Liquid-solid interfaces
82.80.Fk Electrochemical methods
82.45.Gj Electrolytes

Robust Ohmic contact junctions between metallic tips and multiwalled carbon nanotubes for scanned probe microscopy

Suenne Kim, Jeehoon Kim, Morgann Berg, and Alex de Lozanne

Rev. Sci. Instrum. 79, 103702 (2008); http://dx.doi.org/10.1063/1.2987696 (4 pages) | Cited 2 times

Online Publication Date: 7 October 2008

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We demonstrate a simple method that uses a scanning electron microscope for making a reliable low resistance contact between a single multiwalled carbon nanotube and a metallic tungsten probe tip or a Si cantilever. This method consists of using electron beam induced decomposition of background gases and voltage pulses to remove contaminants. The electrical quality of the contact is monitored in situ by measuring the current flow at constant bias or by observing the decay of current fluctuations. The quality of the contacts is confirmed via current-voltage spectroscopy. This method produces very stable, low resistance, mechanically robust contacts with high success rates approaching 100%.
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73.40.Ns Metal-nonmetal contacts
07.79.-v Scanning probe microscopes and components

Real-time atomic force microscopy using mechanical resonator type scanner

Yongho Seo, C. S. Choi, S. H. Han, and Seung-Jin Han

Rev. Sci. Instrum. 79, 103703 (2008); http://dx.doi.org/10.1063/1.2999579 (3 pages) | Cited 5 times

Online Publication Date: 15 October 2008

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The real-time atomic force microscope for biological sample is a challenging research field. We have demonstrated a real-time atomic force microscope by implementing a mechanical resonator type scanner called by “microscanner” The microscanner was designed to have a resonance frequency in the range of 5–10 kHz and an amplitude of 1–3 μm. The resonant vibration of the microscanner was served as a fast-scan directional motion, and an image acquisition rate of 30 frames/s with 256×256 pixels per frame was achieved. Time-varying sequential images of a poly(ethylene-oxide) sample were taken as a demonstration of potential for excellence in real-time imaging a moving nano-object.
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07.79.Lh Atomic force microscopes
07.10.Cm Micromechanical devices and systems
68.37.Ps Atomic force microscopy (AFM)

High bandwidth control of precision motion instrumentation

Douglas A. Bristow, Jingyan Dong, Andrew G. Alleyne, Placid Ferreira, and Srinivas Salapaka

Rev. Sci. Instrum. 79, 103704 (2008); http://dx.doi.org/10.1063/1.2980377 (14 pages) | Cited 3 times

Online Publication Date: 15 October 2008

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This article presents a high-bandwidth control design suitable for precision motion instrumentation. Iterative learning control (ILC), a feedforward technique that uses previous iterations of the desired trajectory, is used to leverage the repetition that occurs in many tasks, such as raster scanning in microscopy. Two ILC designs are presented. The first design uses the motion system dynamic model to maximize bandwidth. The second design uses a time-varying bandwidth that is particularly useful for nonsmooth trajectories such as raster scanning. Both designs are applied to a multiaxis piezoelectric-actuated flexure system and evaluated on a nonsmooth trajectory. The ILC designs demonstrate significant bandwidth and precision improvements over the feedback controller, and the ability to achieve precision motion control at frequencies higher than multiple system resonances.
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07.05.Dz Control systems
07.05.Mh Neural networks, fuzzy logic, artificial intelligence
07.07.Tw Servo and control equipment; robots

Optical trapping and surgery of living yeast cells using a single laser

Jun Ando, Godofredo Bautista, Nicholas Smith, Katsumasa Fujita, and Vincent Ricardo Daria

Rev. Sci. Instrum. 79, 103705 (2008); http://dx.doi.org/10.1063/1.2999542 (5 pages) | Cited 10 times

Online Publication Date: 20 October 2008

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We present optical trapping and surgery of living yeast cells using two operational modes of a single laser. We used a focused laser beam operating in continuous-wave mode for noninvasive optical trapping and manipulation of single yeast cell. We verified that such operational mode of the laser does not cause any destructive effect on yeast cell wall. By changing the operation of the laser to femtosecond-pulsed mode, we show that a tightly focused beam dissects the yeast cell walls via nonlinear absorption. Lastly, using the combined technique of optical microsurgery and trapping, we demonstrate intracellular organelle extraction and manipulation from a yeast cell. The technique established here will be useful as an efficient method for both surgery and manipulation of living cells using a single laser beam.
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87.50.wp Therapeutic applications
87.85.-d Biomedical engineering
42.62.Be Biological and medical applications
87.18.-h Biological complexity

Cross-talk compensation in atomic force microscopy

Cagdas D. Onal, Bilsay Sümer, and Metin Sitti

Rev. Sci. Instrum. 79, 103706 (2008); http://dx.doi.org/10.1063/1.3002483 (7 pages) | Cited 5 times

Online Publication Date: 23 October 2008

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In this work, calibration and correction of cross-talk in atomic force microscopy (AFM) is demonstrated. Several reasons and effects of this inherent problem on experimental results are discussed. We propose a general procedure that can be used on most AFM systems to compensate for cross-talk on the cantilever bending and twisting signals. The method utilizes two initial experiments on a flat surface to achieve an affine transformation between the measured signals and the actual signals. Using this transformation directly on the voltage signals allows us to remove the detrimental effects of cross-talk on AFM-based force measurement experiments. The achieved transformation matrix can be turned into a simple circuit and applied online, by users who have access to the raw signals in the AFM head. As a case study, a lateral deflection based mechanical characterization test for a poly(methyl methacrylate) microfiber that is suspended on a trench is investigated in terms of the effectiveness of the cross-talk compensation.
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07.79.Lh Atomic force microscopes
06.20.fb Standards and calibration

Fabrication of optical tips from photonic crystal fibers

Christine A. Carlson and Jörg C. Woehl

Rev. Sci. Instrum. 79, 103707 (2008); http://dx.doi.org/10.1063/1.3002427 (5 pages)

Online Publication Date: 27 October 2008

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We present a procedure for fabricating optical tips from photonic crystal fibers which feature a solid core surrounded by a cladding with a hexagonal, multilayer arrangement of air channels running along the length of the fiber. Such optical tips may have unique advantages for the production of near-field optical aperture probes (i.e., metal-coated optical tips with a subwavelength aperture at the tip apex). With both cladding and core made of pure silica, these fibers are fluorescence-free; they support only a single mode over a broad wavelength range (covering the visible and near-infrared spectrum), which makes them useful for multicolor experiments; and they exhibit zero group velocity dispersion at visible wavelengths, which opens up the possibility of femtosecond applications in the near field. Our tip fabrication procedure leads to a sharp, protruding, central tip formed exclusively from the fiber core amidst a regular arrangement of smaller tips from the inner, microstructured region of the cladding. A mechanism for tip formation is proposed based on optical observations at various stages, which explains the self-centering nature of the process.
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42.81.Bm Fabrication, cladding, and splicing
42.70.Qs Photonic bandgap materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
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