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Apr 2009

Volume 80, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 80, 041301 (2009); http://dx.doi.org/10.1063/1.3116085 (11 pages)

Aroh Barjatya, Charles M. Swenson, Donald C. Thompson, and Kenneth H. Wright, Jr.

FPMU: Floating Potential Measurement Unit is a suite of Langmuir and Plasma Impedance Probes deployed on the International Space Station (ISS) to study the surface charging of ISS. They also perform multi-instrument common volume measurement of plasma parameters such as plasma density and temperature. NASA image S124E010013 and S126E011385.

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Invited Article: Data analysis of the Floating Potential Measurement Unit aboard the International Space Station

Aroh Barjatya, Charles M. Swenson, Donald C. Thompson, and Kenneth H. Wright, Jr.

Rev. Sci. Instrum. 80, 041301 (2009); http://dx.doi.org/10.1063/1.3116085 (11 pages) | Cited 3 times

Online Publication Date: 17 April 2009

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We present data from the Floating Potential Measurement Unit (FPMU) that is deployed on the starboard truss of the International Space Station. The FPMU is a suite of instruments capable of redundant measurements of various plasma parameters. The instrument suite consists of a floating potential probe, a wide-sweeping spherical Langmuir probe, a narrow-sweeping cylindrical Langmuir probe, and a plasma impedance probe. This paper gives a brief overview of the instrumentation and the received data quality, and then presents the algorithm used to reduce I-V curves to plasma parameters. Several hours of data are presented from August 5, 2006 and March 3, 2007. The FPMU derived plasma density and temperatures are compared with the International Reference Ionosphere (IRI) and Utah State University-Global Assimilation of Ionospheric Measurement (USU-GAIM) models. Our results show that the derived in situ density matches the USU-GAIM model better than the IRI, and the derived in situ temperatures are comparable to the average temperatures given by the IRI.
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52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
94.80.+g Instrumentation for space plasma physics, ionosphere, and magnetosphere
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A Fourier transform spectrometer without a beam splitter for the vacuum ultraviolet range: From the optical design to the first UV spectrum

N. de Oliveira, D. Joyeux, D. Phalippou, J. C. Rodier, F. Polack, M. Vervloet, and L. Nahon

Rev. Sci. Instrum. 80, 043101 (2009); http://dx.doi.org/10.1063/1.3111452 (13 pages) | Cited 13 times

Online Publication Date: 13 April 2009

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We describe a Fourier transform (FT) spectrometer designed to operate down to 60 nm (20 eV) on a synchrotron radiation beamline for high resolution absorption spectrometry. As far as we know, such an instrument is not available below 140 nm mainly because manufacturing accurate and efficient beam splitters remains a major problem at these wavelengths, especially if a wide bandwidth operation is desired. In order to overcome this difficulty, we developed an interferometer based on wave front division instead of amplitude division. It relies on a modified Fresnel bimirror configuration that requires only flat mirrors. The instrument provides path difference scanning through the translation of one reflector. During the scanning, the moving reflector is controlled by an optical system that keeps its direction constant within a tolerable value and provides an accurate interferometric measurement of the path difference variation. Therefore, a regular interferogram sampling is obtained, producing a nominal spectral impulse response and an accurate spectral calibration. The first results presented in this paper show a measured spectral resolution of δσ = 0.33 cm−1 (interval between spectral samples). This was obtained with a sampling interval of 29 nm (path difference) and 512 K samples from a one-sided interferogram using a cosine FT. Such a sampling interval should allow the recording of large bandwidth spectra down to math = 58 nm with an ultimate resolving power of 500 000 at this wavelength. In order to check the instrument performances, we first recorded an interferogram from a He–Ne stabilized laser. This provided the actual spectral impulse function, which was found to be fully satisfactory. The determination of the impulse response distortion and of the noise on the vacuum ultraviolet (VUV) spectral range provided accurate information in the sampling error profile over a typical scan. Finally, the instrument has been moved to the SU5 undulator-based synchrotron radiation beamline (Super-ACO facility, LURE, Orsay, France). A high resolution spectrum of O2 (the Schumann–Runge absorption bands, 185–200 nm) was computed from recorded interferograms using the beamline monochromator at the zeroth order to feed the instrument with an 11% relative bandwidth “white” beam (2003). These UV measurements are very close to those found in the literature, showing nominal performances of the FT spectrometer that should translate into an unprecedented resolving power at shortest VUV wavelengths. A recent upgrade (2007) and future developments will be discussed in light of the current installation of the upgraded FT spectrometer as a permanent endstation for ultrahigh resolution absorption spectrometry on the VUV beamline DESIRS at SOLEIL, the new French third generation synchrotron facility.
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07.60.Rd Visible and ultraviolet spectrometers
42.15.Eq Optical system design
42.79.Bh Lenses, prisms and mirrors
07.85.Qe Synchrotron radiation instrumentation
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
07.60.Ly Interferometers

Use of ruthenium dyes for subnanosecond detector fidelity testing in real time transient absorption

Martin Byrdin, Viruthachalam Thiagarajan, Sandrine Villette, Agathe Espagne, and Klaus Brettel

Rev. Sci. Instrum. 80, 043102 (2009); http://dx.doi.org/10.1063/1.3117208 (5 pages) | Cited 4 times

Online Publication Date: 13 April 2009

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Transient absorption spectroscopy is a powerful tool for the study of photoreactions on time scales from femtoseconds to seconds. Typically, reactions slower than ∼ 1 ns are recorded by the “classical” technique; the reaction is triggered by an excitation flash, and absorption changes accompanying the reaction are recorded in real time using a continuous monitoring light beam and a detection system with sufficiently fast response. The pico- and femtosecond region can be accessed by the more recent “pump-probe” technique, which circumvents the difficulties of real time detection on a subnanosecond time scale. This is paid for by accumulation of an excessively large number of shots to sample the reaction kinetics. Hence, it is of interest to extend the classical real time technique as far as possible to the subnanosecond range. In order to identify and minimize detection artifacts common on a subnanosecond scale, like overshoot, ringing, and signal reflections, rigorous testing is required of how the detection system responds to fast changes of the monitoring light intensity. Here, we introduce a novel method to create standard signals for detector fidelity testing on a time scale from a few picoseconds to tens of nanoseconds. The signals result from polarized measurements of absorption changes upon excitation of ruthenium complexes {[Ru(bpy)3]2+ and a less symmetric derivative} by a short laser flash. Two types of signals can be created depending on the polarization of the monitoring light with respect to that of the excitation flash: a fast steplike bleaching at magic angle and a monoexponentially decaying bleaching for parallel polarizations. The lifetime of the decay can be easily varied via temperature and viscosity of the solvent. The method is applied to test the performance of a newly developed real time transient absorption setup with 300 ps time resolution and high sensitivity.
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82.50.-m Photochemistry
78.47.jj Transient grating spectroscopy
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A multimodal spectroscopy system for real-time disease diagnosis

Obrad R. Šćepanović, Zoya Volynskaya, Chae-Ryon Kong, Luis H. Galindo, Ramachandra R. Dasari, and Michael S. Feld

Rev. Sci. Instrum. 80, 043103 (2009); http://dx.doi.org/10.1063/1.3117832 (9 pages) | Cited 13 times

Online Publication Date: 17 April 2009

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The combination of reflectance, fluorescence, and Raman spectroscopy—termed multimodal spectroscopy (MMS)—provides complementary and depth-sensitive information about tissue composition. As such, MMS is a promising tool for disease diagnosis, particularly in atherosclerosis and breast cancer. We have developed an integrated MMS instrument and optical fiber spectral probe for simultaneous collection of all three modalities in a clinical setting. The MMS instrument multiplexes three excitation sources, a xenon flash lamp (370–740 nm), a nitrogen laser (337 nm), and a diode laser (830 nm), through the MMS probe to excite tissue and collect the spectra. The spectra are recorded on two spectrograph/charge-coupled device modules, one optimized for visible wavelengths (reflectance and fluorescence) and the other for the near-infrared (Raman), and processed to provide diagnostic parameters. We also describe the design and calibration of a unitary MMS optical fiber probe 2 mm in outer diameter, containing a single appropriately filtered excitation fiber and a ring of 15 collection fibers, with separate groups of appropriately filtered fibers for efficiently collecting reflectance, fluorescence, and Raman spectra from the same tissue location. A probe with this excitation/collection geometry has not been used previously to collect reflectance and fluorescence spectra, and thus physical tissue models (“phantoms”) are used to characterize the probe’s spectroscopic response. This calibration provides probe-specific modeling parameters that enable accurate extraction of spectral parameters. This clinical MMS system has been used recently to analyze artery and breast tissue in vivo and ex vivo.
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87.64.kp Raman
42.62.Fi Laser spectroscopy
87.64.kv Fluorescence
87.64.km Infrared
87.19.xj Cancer
07.60.Vg Fiber-optic instruments
42.62.Be Biological and medical applications

Three-dimensional fluence rate measurement and data acquisition system for minimally invasive light therapies

Benjamin Lai, Maxim Loshchenov, Alexander Douplik, Rob Rusnov, Marcos Jimenez-Davila, George Netchev, and Lothar Lilge

Rev. Sci. Instrum. 80, 043104 (2009); http://dx.doi.org/10.1063/1.3125062 (5 pages) | Cited 1 time

Online Publication Date: 30 April 2009

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Light based therapies such as photodynamic therapy are in need of advanced tools for light fluence rate dosimetry and monitoring within the context of therapy planning and light delivery to ensure maximum treatment efficacy. The use of a single, multisensor fiber-based fluorescent probe capable of performing spatially resolved fluence rate measurements along an axis was demonstrated. This work extends the previous technique and describes a fluence rate quantification system able to employ up to 12 multisensor probes to simultaneously measure fluence rate distribution throughout a 3D treatment volume. The system optoelectronics provides for sensor calibration, data acquisition, and weighted least-squares processing to extract localized fluence rate information in real-time. Core components include an integrating cylinder for source sensor calibration, a 2D back thin CCD detector for sensor signal detection from multiple probes, high-speed data acquisition card, and custom software for real-time extraction of fluence rate information from all sensors.
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87.50.wp Therapeutic applications
87.50.wj Dosimetry/exposure assessment
87.57.N- Image analysis
42.79.Pw Imaging detectors and sensors

Advanced photoelectric effect experiment beamline at Elettra: A surface science laboratory coupled with Synchrotron Radiation

G. Panaccione, I. Vobornik, J. Fujii, D. Krizmancic, E. Annese, L. Giovanelli, F. Maccherozzi, F. Salvador, A. De Luisa, D. Benedetti, A. Gruden, P. Bertoch, F. Polack, D. Cocco, G. Sostero, et al.

Rev. Sci. Instrum. 80, 043105 (2009); http://dx.doi.org/10.1063/1.3119364 (12 pages) | Cited 15 times

Online Publication Date: 30 April 2009

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We report the main characteristics of the advanced photoelectric effect experiments beamline, operational at Elettra storage ring, featuring a fully independent double branch scheme obtained by the use of chicane undulators and able to keep polarization control in both linear and circular mode. The paper describes the novel technical solutions adopted, namely, (a) the design of a quasiperiodic undulator resulting in optimized suppression of higher harmonics over a large photon energy range (10–100 eV), (b) the thermal stability of optics under high heat load via cryocoolers, and (c) the end station interconnected setup allowing full access to off-beam and on-beam facilities and, at the same time, the integration of users’ specialized sample growth chambers or modules.
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29.27.-a Beams in particle accelerators
29.20.db Storage rings and colliders
41.60.Ap Synchrotron radiation
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Fluorescence decay-time constants in organic liquid scintillators

T. Marrodán Undagoitia, F. von Feilitzsch, L. Oberauer, W. Potzel, A. Ulrich, J. Winter, and M. Wurm

Rev. Sci. Instrum. 80, 043301 (2009); http://dx.doi.org/10.1063/1.3112609 (8 pages) | Cited 12 times

Online Publication Date: 21 April 2009

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The fluorescence decay-time constants have been measured for several scintillator mixtures based on phenyl-o-xylylethane (PXE) and linear alkylbenzene (LAB) solvents. The resulting values are of relevance for the physics performance of the proposed large-volume liquid scintillator detector Low Energy Neutrino Astronomy (LENA). In particular, the impact of the measured values to the search for proton decay via p→K+math is evaluated in this work.
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29.40.Mc Scintillation detectors
13.30.Ce Leptonic, semileptonic, and radiative decays
14.20.Dh Protons and neutrons
78.55.Bq Liquids

Rapidly pulsed helium droplet source

Dominik Pentlehner, Ricarda Riechers, Bernhard Dick, Alkwin Slenczka, Uzi Even, Nachum Lavie, Raviv Brown, and Kfir Luria

Rev. Sci. Instrum. 80, 043302 (2009); http://dx.doi.org/10.1063/1.3117196 (9 pages) | Cited 14 times

Online Publication Date: 22 April 2009

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A pulsed valve connected to a closed-cycle cryostat was optimized for producing helium droplets. The pulsed droplet beam appeared with a bimodal size distribution. The leading part of the pulse consists of droplets suitable for doping with molecules. The average size of this part can be varied between 104 and 106 helium atoms, and the width of the distribution is smaller as compared to a continuous-flow droplet source. The system has been tested in a single pulse mode and at repetition rates of up to 500 Hz with almost constant intensity. The droplet density was found to be increased by more than an order of magnitude as compared to a continuous-flow droplet source.
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03.75.Kk Dynamic properties of condensates; collective and hydrodynamic excitations, superfluid flow
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Development of a compact electron ion coincidence analyzer using a coaxially symmetric mirror electron energy analyzer and a miniature polar-angle-resolved time-of-flight ion mass spectrometer with four concentric anodes

Eiichi Kobayashi, Akira Nambu, Kazuhiko Mase, Kouji Isari, Kenichiro Tanaka, Masanobu Mori, Koji K. Okudaira, and Nobuo Ueno

Rev. Sci. Instrum. 80, 043303 (2009); http://dx.doi.org/10.1063/1.3116442 (6 pages)

Online Publication Date: 23 April 2009

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A compact electron ion coincidence (EICO) analyzer that uses a coaxially symmetric mirror electron energy analyzer and a miniature polar-angle-resolved time-of-flight ion mass spectrometer with four concentric anodes was developed for surface science and surface analysis. The apparatus is especially useful in the study of ion desorption stimulated by an Auger process because information on the mass, yield, desorption polar angle, and kinetic energy of ions can be obtained for the selected core-ionization-final-states or the selected Auger-final-states. The analyzer can be used also for analysis of the configuration of specific surface molecules because the desorption polar angles reflect the direction of surface bonds. The EICO analyzer was evaluated by measuring polar-angle-resolved-ion yield spectra and coincidence spectra of Auger-electron and polar-angle-resolved H+ from condensed water.
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07.81.+a Electron and ion spectrometers
07.75.+h Mass spectrometers
79.20.Fv Electron impact: Auger emission

Arc discharge ion source for europium and other refractory metals implantation

M. Turek, S. Prucnal, A. Droździel, and K. Pyszniak

Rev. Sci. Instrum. 80, 043304 (2009); http://dx.doi.org/10.1063/1.3117357 (5 pages) | Cited 8 times

Online Publication Date: 24 April 2009

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The best method for the impurity doping to the host material is the ion implantation. Due to high melting point of the rare earth standard metal ion sources are useless. One of the solution is to use chemical compounds of rare earths characterized by low melting point. In this paper we describe the novel design of the ion source suitable for refractory metal (e.g., rare earths) ion implantation. The dependencies of Eu+ current on cathode and arc currents as well as on hydrogen flow are presented. Europium (III) chloride as the source of the europium atoms was used. Europium ions were produced during collisions of evaporated and decomposed EuCl3 molecules with fast electrons. The typical current of the europium ion beam extracted from the ion source was 25 μA for the extraction voltage of 25 kV. The ion source works without maintenance breaks for approximately 50 h, which enables high dose implantation. The presented ion source needs neither advanced high power supplies nor high vacuum regime.
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61.72.up Other materials
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
64.70.dj Melting of specific substances
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Porous plug gas injection systems for studies of hydrocarbon dissociation and transport in the DIII-D tokamak

A. G. McLean, J. W. Davis, P. C. Stangeby, N. H. Brooks, R. M. Ellis, A. A. Haasz, D. L. Rudakov, W. P. West, D. G. Whyte, and C. P. C. Wong

Rev. Sci. Instrum. 80, 043501 (2009); http://dx.doi.org/10.1063/1.3100180 (8 pages) | Cited 2 times

Online Publication Date: 3 April 2009

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A probe has been designed, constructed, and successfully used to inject methane into the DIII-D lower divertor in a manner imitating natural release by chemical erosion. This porous plug injector (PPI) probe consists of a self-contained gas reservoir with an integrated pressure gauge and a 3 cm diameter porous surface through which gas is injected into the lower divertor of the tokamak. The probe is positioned flush with the divertor target surface by means of the divertor materials evaluation system. Two gas delivery systems were developed: in the first, gas flow is regulated by a remotely controlled microvalve and in the second by a fixed micro-orifice flow restrictor. Because of the large area of the porous surface through which gas is admitted, the injected hydrocarbon molecules see a local carbon surface (>90% carbon) similar to that seen by hydrocarbons being emitted by chemical sputtering from surrounding carbon tiles. The distributed gas source also reduces the disturbance to the local plasma while providing sufficient signal for spectroscopic detection. In situ spectroscopic measurements with the PPI in DIII-D allow the direct calibration of response for measured plasma conditions from a known influx of gas.
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52.70.Ds Electric and magnetic measurements
52.55.Rk Power exhaust; divertors
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Multichannel microwave interferometer for the levitated dipole experiment

Alexander C. Boxer, Darren T. Garnier, and Michael E. Mauel

Rev. Sci. Instrum. 80, 043502 (2009); http://dx.doi.org/10.1063/1.3095684 (4 pages) | Cited 2 times

Online Publication Date: 6 April 2009

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A four-channel microwave interferometer (center frequency: 60 GHz) has been constructed to measure plasma density profiles in the levitated dipole experiment (LDX). The LDX interferometer has a unique design owing to the unique geometry of LDX. The main design features of the interferometer are: (1) the transmitted beam traverses the plasma entirely in O-mode; (2) the interferometer is a heterodyne system employing two free-running oscillators; (3) four signals of data are received from just on transmitted beam; (4) phase shifts are detected in quadrature. Calibration tests demonstrate that the interferometer measures phase shifts with an uncertainty of approximately 5°. Plasma densities in LDX corresponding to phase shifts of up to 5π are routinely and successfully measured.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
06.20.fb Standards and calibration
52.70.Gw Radio-frequency and microwave measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

A digital control system for external magnetohydrodynamic modes in tokamak plasmas

J. M. Hanson, A. J. Klein, M. E. Mauel, D. A. Maurer, G. A. Navratil, and T. Sunn Pedersen

Rev. Sci. Instrum. 80, 043503 (2009); http://dx.doi.org/10.1063/1.3112607 (7 pages) | Cited 3 times

Online Publication Date: 10 April 2009

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A feedback system for controlling external, long-wavelength magnetohydrodynamic activity is described. The system is comprised of a network of localized magnetic pickup and control coils driven by four independent, low-latency field-programable gate array controllers. The control algorithm incorporates digital spatial filtering to resolve low mode number activity, temporal filtering to correct for frequency-dependent amplitude and phase transfer effects in the control hardware, and a Kalman filter to distinguish the unstable plasma mode from noise.
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52.55.Fa Tokamaks, spherical tokamaks
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Seeding magnetic fields for laser-driven flux compression in high-energy-density plasmas

O. V. Gotchev, J. P. Knauer, P. Y. Chang, N. W. Jang, M. J. Shoup, III, D. D. Meyerhofer, and R. Betti

Rev. Sci. Instrum. 80, 043504 (2009); http://dx.doi.org/10.1063/1.3115983 (9 pages) | Cited 4 times

Online Publication Date: 14 April 2009

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A compact, self-contained magnetic-seed-field generator (5 to 16 T) is the enabling technology for a novel laser-driven flux-compression scheme in laser-driven targets. A magnetized target is directly irradiated by a kilojoule or megajoule laser to compress the preseeded magnetic field to thousands of teslas. A fast (300 ns), 80 kA current pulse delivered by a portable pulsed-power system is discharged into a low-mass coil that surrounds the laser target. A >15 T target field has been demonstrated using a <100 J capacitor bank, a laser-triggered switch, and a low-impedance (<1 Ω) strip line. The device has been integrated into a series of magnetic-flux-compression experiments on the 60 beam, 30 kJ OMEGA laser [ T. R. Boehly et al., Opt. Commun. 133, 495 (1997) ]. The initial application is a novel magneto-inertial fusion approach [ O. V. Gotchev et al., J. Fusion Energy 27, 25 (2008) ] to inertial confinement fusion (ICF), where the amplified magnetic field can inhibit thermal conduction losses from the hot spot of a compressed target. This can lead to the ignition of massive shells imploded with low velocity—a way of reaching higher gains than is possible with conventional ICF.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.-z Laser inertial confinement
52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects

Diagnostic development in precise opacity measurement of radiatively heated Al plasma on Shenguang II laser facility

Yang Zhao, Jiamin Yang, Jiyan Zhang, Jinsong Liu, Xiao Yuan, and Fengtao Jin

Rev. Sci. Instrum. 80, 043505 (2009); http://dx.doi.org/10.1063/1.3116483 (5 pages) | Cited 5 times

Online Publication Date: 15 April 2009

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Simultaneous measurements of the self-emission spectrum, the backlighting source spectrum, and the transmission spectrum in one shot, which reduce the experimental uncertainties from shot-to-shot fluctuation, are essential for precise opacity experiments. In order to achieve precise absorption spectrum of Al plasmas, a special half sample sandwich target was designed and short backlighter was used to provide time- and space-resolving diagnostics on the Shenguang II high power laser facility. In the measurement, a cylindrical cavity with CH foam baffles was used to provide a clean x-ray radiation environment for sample heating. The x-ray source spectrum, the transmission spectrum, and the self-emission spectrum of the soft x-ray heated Al sample were recorded in one shot with a penta-erythritol tetrakis (hydroxymethy) methane C(CH2OH)4 (PET) crystal spectrometer by using the point-projection method. Experimental results have been compared with the calculation results of a detailed level accounting opacity code.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.-z Laser inertial confinement

Measurements of plasma potential in high-pressure microwave plasmas

A. V. Tarasova, N. K. Podder, and E. J. Clothiaux

Rev. Sci. Instrum. 80, 043506 (2009); http://dx.doi.org/10.1063/1.3125624 (5 pages)

Online Publication Date: 29 April 2009

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Plasma potential of a high-pressure ( ∼ 1 Torr) microwave-generated argon plasma is measured using a Langmuir probe and a cold emissive probe. The operation of a hot emissive probe in a high-pressure plasma has been very difficult due to frequent burn-outs and significantly reduced lifetime of the probe filament, which, in turn, limits the possibility of collecting a wide range of data. The I-V characteristics from both Langmuir and emissive probes are interpreted using the collisionless probe theory since the collision correction factor is not very significant. The plasma potential determined from both Langmuir and cold emissive probe characteristics agrees well with one another and is observed to be dependent on the operating gas pressure but relatively unchanged as a function of the microwave power. An average plasma potential determined over the operating range of microwave powers varies nonlinearly with the gas pressure.
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52.70.Ds Electric and magnetic measurements
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A microcomputed tomography guided fluorescence tomography system for small animal molecular imaging

Dax Kepshire, Niculae Mincu, Michael Hutchins, Josiah Gruber, Hamid Dehghani, Justin Hypnarowski, Frederic Leblond, Mario Khayat, and Brian W. Pogue

Rev. Sci. Instrum. 80, 043701 (2009); http://dx.doi.org/10.1063/1.3109903 (10 pages) | Cited 37 times

Online Publication Date: 1 April 2009

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A prototype small animal imaging system was created for coupling fluorescence tomography (FT) with x-ray microcomputed tomography (microCT). The FT system has the potential to provide synergistic information content resultant from using microCT images as prior spatial information and then allows overlay of the FT image onto the original microCT image. The FT system was designed to use single photon counting to provide maximal sensitivity measurements in a noncontact geometry. Five parallel detector locations are used, each allowing simultaneous sampling of the fluorescence and transmitted excitation signals through the tissue. The calibration and linearity range performance of the system are outlined in a series of basic performance tests and phantom studies. The ability to image protoporphyrin IX in mouse phantoms was assessed and the system is ready for in vivo use to study biological production of this endogenous marker of tumors. This multimodality imaging system will have a wide range of applications in preclinical cancer research ranging from studies of the tumor microenvironment and treatment efficacy for emerging cancer therapeutics.
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87.63.L- Visual imaging
87.57.Q- Computed tomography
07.60.Dq Photometers, radiometers, and colorimeters
06.20.F- Units and standards

A metrological large range atomic force microscope with improved performance

Gaoliang Dai, Helmut Wolff, Frank Pohlenz, and Hans-Ulrich Danzebrink

Rev. Sci. Instrum. 80, 043702 (2009); http://dx.doi.org/10.1063/1.3109901 (10 pages) | Cited 5 times

Online Publication Date: 2 April 2009

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A metrological large range atomic force microscope (Met. LR-AFM) has been set up and improved over the past years at Physikalisch-Technische Bundesanstalt (PTB). Being designed as a scanning sample type instrument, the sample is moved in three dimensions by a mechanical ball bearing stage in combination with a compact z-piezostage. Its topography is detected by a position-stationary AFM head. The sample displacement is measured by three embedded miniature homodyne interferometers in the x, y, and z directions. The AFM head is aligned in such a way that its cantilever tip is positioned on the sample surface at the intersection point of the three interferometer measurement beams for satisfying the Abbe measurement principle. In this paper, further improvements of the Met. LR-AFM are reported. A new AFM head using the beam deflection principle has been developed to reduce the influence of parasitic optical interference phenomena. Furthermore, an off-line Heydemann correction method has been applied to reduce the inherent interferometer nonlinearities to less than 0.3 nm (p-v). Versatile scanning functions, for example, radial scanning or local AFM measurement functions, have been implemented to optimize the measurement process. The measurement software is also improved and allows comfortable operations of the instrument via graphical user interface or script-based command sets. The improved Met. LR-AFM is capable of measuring, for instance, the step height, lateral pitch, line width, nanoroughness, and other geometrical parameters of nanostructures. Calibration results of a one-dimensional grating and a set of film thickness standards are demonstrated, showing the excellent metrological performance of the instrument.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
06.20.F- Units and standards
68.55.jd Thickness
61.46.-w Structure of nanoscale materials

Reconstruction of atomic force microscopy image by using nanofabricated tip characterizer toward the actual sample surface topography

Mingsheng Xu, Daisuke Fujita, and Keiko Onishi

Rev. Sci. Instrum. 80, 043703 (2009); http://dx.doi.org/10.1063/1.3115182 (6 pages) | Cited 10 times

Online Publication Date: 10 April 2009

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The atomic force microscopy (AFM) image is a dilation of the sample surface topography due to the finite-sized AFM tip. We accurately estimated the tip apex shape with a nanofabricated Si tip characterizer and applied the estimated tip shape function to a dilation-erosion algorithm for image reconstruction. The reconstructed images from the original AFM images attained with different AFM tips show consistent surface features and closely match the high-resolution field-emission scanning electron microscope image. The results demonstrate the reliability of our method and suggest the importance of AFM image reconstruction for a variety of technologies requiring new strategies of measuring, interpreting, manipulating, and positioning in the submicrometer and nanometer range.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
07.05.Pj Image processing

Development of wearable optical topography system for mapping the prefrontal cortex activation

Hirokazu Atsumori, Masashi Kiguchi, Akiko Obata, Hiroki Sato, Takusige Katura, Tsukasa Funane, and Atsushi Maki

Rev. Sci. Instrum. 80, 043704 (2009); http://dx.doi.org/10.1063/1.3115207 (6 pages) | Cited 18 times

Online Publication Date: 13 April 2009

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Optical topography (OT) based on near infrared spectroscopy is effective for measuring changes in the concentrations of oxygenated hemoglobin (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb) in the brain. It can be used to investigate brain functions of subjects of all ages because it is noninvasive and less constraining for subjects. Conventional OT systems use optical fibers to irradiate the scalp and detect light transmitted through the tissue in the human head, but optical fibers limit the subject’s head position, so some small systems have been developed without using optical fibers. These systems, however, have a small number of measurement channels. We developed a prototype of a small, light, and wearable OT system that covers the entire forehead. We measured changes in the concentrations of oxy-Hb and deoxy-Hb in the prefrontal cortex while a subject performed a word fluency task. The results show typical changes in oxy-Hb and deoxy-Hb during the task and suggest that the prototype of our system can be used to investigate functions in the prefrontal cortex.
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87.64.km Infrared
87.19.lh Optical imaging of neuronal activity
87.14.E- Proteins
87.19.lv Learning and memory
87.15.N- Properties of solutions of macromolecules
87.15.M- Spectra of biomolecules

Effects of anisotropic material property on the spring constant and the resonant frequency of atomic force microscope cantilever

Meng-Kao Yeh, Nyan-Hwa Tai, and Bo-Yi Chen

Rev. Sci. Instrum. 80, 043705 (2009); http://dx.doi.org/10.1063/1.3115212 (7 pages) | Cited 1 time

Online Publication Date: 13 April 2009

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Atomic force microscope (AFM) is a powerful tool for force measurement in nanoscale. Many methods have been developed to obtain the precise cantilever’s spring constant for improving the accuracy of force measurement. AFM cantilevers are usually made by single crystal silicon of which the anisotropic material property seriously affects the spring constant of cantilevers and has not considered before. In this paper, the density function theory was used to calculate the anisotropic stiffness matrix of crystal silicon, which was used in the finite element analysis to calculate lateral, axial, bending spring constants, and resonant frequencies of rectangular AFM cantilevers. These results were compared with those derived from other theoretical methods and with those provided by the manufacturers. The results showed that the anisotropic material property significantly affected the spring constants and the resonant frequencies of the AFM cantilever. The assumption of equivalent isotropic property of the rectangular AFM cantilever would cause an error up to 29.72%. Furthermore, two equations were proposed to obtain the spring constants and the resonant frequencies of crystal silicon AFM cantilever with the axis located at different cantilever-crystal angles.
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07.79.Lh Atomic force microscopes
07.10.Pz Instruments for strain, force, and torque
02.70.Dh Finite-element and Galerkin methods

A system for high-resolution depth-resolved optical imaging of fluorescence and absorption contrast

Baohong Yuan, Sean A. Burgess, Amir Iranmahboob, Matthew B. Bouchard, Nicole Lehrer, Clémence Bordier, and Elizabeth M. C. Hillman

Rev. Sci. Instrum. 80, 043706 (2009); http://dx.doi.org/10.1063/1.3117204 (11 pages) | Cited 9 times

Online Publication Date: 17 April 2009

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Laminar optical tomography (LOT) is a new three-dimensional in vivo functional optical imaging technique. Adopting a microscopy-based setup and diffuse optical tomography (DOT) imaging principles, LOT can perform both absorption- and fluorescence-contrast imaging with higher resolution (100–200 μm) than DOT and deeper penetration (2–3 mm) than laser scanning microscopy. These features, as well as a large field of view and acquisition speeds up to 100 frames per second, make LOT suitable for depth-resolved imaging of stratified tissues such as retina, skin, endothelial tissues and the cortex of the brain. In this paper, we provide a detailed description of a new LOT system design capable of imaging both absorption and fluorescence contrast, and present characterization of its performance using phantom studies.
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87.63.L- Visual imaging
87.64.M- Optical microscopy
87.19.lt Sensory systems: visual, auditory, tactile, taste, and olfaction
87.19.L- Neuroscience

Tapping mode microwave impedance microscopy

K. Lai, W. Kundhikanjana, H. Peng, Y. Cui, M. A. Kelly, and Z. X. Shen

Rev. Sci. Instrum. 80, 043707 (2009); http://dx.doi.org/10.1063/1.3123406 (3 pages) | Cited 2 times

Online Publication Date: 27 April 2009

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We report tapping mode microwave impedance imaging based on atomic force microscope platforms. The shielded cantilever probe is critical to localize the tip-sample interaction near the tip apex. The modulated tip-sample impedance can be accurately simulated by the finite-element analysis and the result agrees quantitatively to the experimental data on a series of thin-film dielectric samples. The tapping mode microwave imaging is also superior to the contact mode in that the thermal drift in a long time scale is totally eliminated and an absolute measurement on the dielectric properties is possible. We demonstrated tapping images on working nanodevices, and the data are consistent with the transport results.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.79.Lh Atomic force microscopes
06.30.Ka Basic electromagnetic quantities
02.70.Dh Finite-element and Galerkin methods

Frequency noise in frequency modulation atomic force microscopy

Kei Kobayashi, Hirofumi Yamada, and Kazumi Matsushige

Rev. Sci. Instrum. 80, 043708 (2009); http://dx.doi.org/10.1063/1.3120913 (8 pages) | Cited 7 times

Online Publication Date: 27 April 2009

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Atomic force microscopy (AFM) using the frequency modulation (FM) detection method has been widely used for atomic/molecular-scale investigations of various materials. Recently, it has been shown that high-resolution imaging in liquids by the FM-AFM is also possible by reducing the noise-equivalent displacement in the cantilever displacement sensor and by oscillating the cantilever at a small amplitude even with the extremely reduced Q-factor due to the hydrodynamic interaction between the cantilever and the liquid. However, it has not been clarified how the noise reduction of the displacement sensor contributes to the reduction in the frequency noise in the FM-AFM in low-Q environments. In this article, the contribution of the displacement sensor noise to the frequency noise in the FM-AFM is described in detail to show how it is important to reduce the noise-equivalent displacement in the displacement sensor especially in low-Q environments.
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07.79.Lh Atomic force microscopes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

A control approach to cross-coupling compensation of piezotube scanners in tapping-mode atomic force microscope imaging

Ying Wu, Jian Shi, Chanmin Su, and Qingze Zou

Rev. Sci. Instrum. 80, 043709 (2009); http://dx.doi.org/10.1063/1.3124183 (10 pages) | Cited 5 times

Online Publication Date: 30 April 2009

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In this article, an approach based on the recently developed inversion-based iterative control (IIC) to cancel the cross-axis coupling effect of piezoelectric tube scanners (piezoscanners) in tapping-mode atomic force microscope (AFM) imaging is proposed. Cross-axis coupling effect generally exists in piezoscanners used for three-dimensional (x-y-z axes) nanopositioning in applications such as AFM, where the vertical z-axis movement can be generated by the lateral x-y axes scanning. Such x/y-to-z cross-coupling becomes pronounced when the scanning is at large range and/or at high speed. In AFM applications, the coupling-caused position errors, when large, can generate various adverse effects, including large imaging and topography distortions, and damage of the cantilever probe and/or the sample. This paper utilizes the IIC technique to obtain the control input to precisely track the coupling-caused x/y-to-z displacement (with sign-flipped). Then the obtained input is augmented as a feedforward control to the existing feedback control in tapping-mode imaging, resulting in the cancellation of the coupling effect. The proposed approach is illustrated through two exemplary applications in industry, the pole-tip recession examination, and the nanoasperity measurement on hard-disk drive. Experimental results show that the x/y-to-z coupling effect in large-range (20 and 45 μm) tapping-mode imaging at both low to high scan rates (2, 12.2 to 24.4 Hz) can be effectively removed.
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07.79.Lh Atomic force microscopes
06.60.Sx Positioning and alignment; manipulating, remote handling
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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