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Aug 2009

Volume 80, Issue 8, Articles (08xxxx)

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Invited Review Article: Imaging techniques for harmonic and multiphoton absorption fluorescence microscopy

Ramón Carriles, Dawn N. Schafer, Kraig E. Sheetz, Jeffrey J. Field, Richard Cisek, Virginijus Barzda, Anne W. Sylvester, and Jeffrey A. Squier

Rev. Sci. Instrum. 80, 081101 (2009); http://dx.doi.org/10.1063/1.3184828 (23 pages) | Cited 18 times

Online Publication Date: 5 August 2009

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We review the current state of multiphoton microscopy. In particular, the requirements and limitations associated with high-speed multiphoton imaging are considered. A description of the different scanning technologies such as line scan, multifoci approaches, multidepth microscopy, and novel detection techniques is given. The main nonlinear optical contrast mechanisms employed in microscopy are reviewed, namely, multiphoton excitation fluorescence, second harmonic generation, and third harmonic generation. Techniques for optimizing these nonlinear mechanisms through a careful measurement of the spatial and temporal characteristics of the focal volume are discussed, and a brief summary of photobleaching effects is provided. Finally, we consider three new applications of multiphoton microscopy: nonlinear imaging in microfluidics as applied to chemical analysis and the use of two-photon absorption and self-phase modulation as contrast mechanisms applied to imaging problems in the medical sciences.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.62.Fi Laser spectroscopy
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
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Collinear interferometer with variable delay for carrier-envelope offset frequency measurement

Monika Pawłowska, Filip Ozimek, Piotr Fita, and Czesław Radzewicz

Rev. Sci. Instrum. 80, 083101 (2009); http://dx.doi.org/10.1063/1.3197404 (5 pages)

Online Publication Date: 18 August 2009

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We demonstrate a novel scheme for measuring the carrier-envelope offset frequency in a femtosecond optical frequency comb. Our method is based on a common-path interferometer with a calcite Babinet–Soleil compensator employed to control the delay between the two interfering beams of pulses. The large delay range (up to 8 ps) of our device is sufficient for systems that rely on spectral broadening in microstructured fibers. We show an experimental proof that the stability of a common-path arrangement is superior to that of the standard interferometers.
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07.60.Ly Interferometers
06.30.Ft Time and frequency
06.60.Jn High-speed techniques (microsecond to femtosecond)

Toward ultrafast time-resolved Debye–Scherrer x-ray diffraction using a laser-plasma source

U. Shymanovich, M. Nicoul, W. Lu, S. Kähle, A. Tarasevitch, K. Sokolowski-Tinten, and D. von der Linde

Rev. Sci. Instrum. 80, 083102 (2009); http://dx.doi.org/10.1063/1.3196180 (3 pages)

Online Publication Date: 21 August 2009

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An elliptical glass capillary has been used to focus ultrashort Cu Kα x-ray pulses emitted from a femtosecond laser-produced plasma. Due to its high magnification (7×), the optic transforms the divergent x-ray emission of the plasma into a quasicollimated x-ray beam with a divergence of only 0.18°. As an application we demonstrate the possibility to perform Debye–Scherrer diffraction experiments with the simultaneous detection of several diffraction orders. This will allow one to extend time-resolved x-ray diffraction with femtosecond laser-plasma x-ray sources to a much wider range of materials, which are not easily available as single crystals.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
61.05.cp X-ray diffraction

Production of a single spin-rotational state [(J,M) = (2,2)] selected molecular oxygen (3Σg−) beam by a hexapole magnet

Mitsunori Kurahashi and Yasushi Yamauchi

Rev. Sci. Instrum. 80, 083103 (2009); http://dx.doi.org/10.1063/1.3206299 (4 pages) | Cited 1 time

Online Publication Date: 24 August 2009

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A state-selected O2(3Σg−) molecular beam, in which nearly 100% of the molecules are in the spin-rotational state of (J,M) = (2,2), has been produced by combining a supersonic seeded O2 beam with a hexapole magnet. The (2,−2) beam has also been obtained by the state inversion of the (2,2) beam through the nonadiabatic passage in a reversing longitudinal magnetic field along the beam axis. The intensities of the other (2,M) states, which appear when applying additional transverse magnetic fields to the reversing field region, were well reproduced by the Majorana’s formula for J = 2. The (2,±2) beam, for which we can determine the spin and rotational angular momenta of O2 almost independently, is the most promising probe for studying the spin effects as well as the steric effects in O2 molecular scattering.
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37.20.+j Atomic and molecular beam sources and techniques

Error-reduced channeled spectroscopic ellipsometer with palm-size sensing head

Hiroshi Okabe, Masayuki Hayakawa, Junichi Matoba, Hitoshi Naito, and Kazuhiko Oka

Rev. Sci. Instrum. 80, 083104 (2009); http://dx.doi.org/10.1063/1.3206346 (10 pages) | Cited 1 time

Online Publication Date: 25 August 2009

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This paper describes a newly developed prototype system of the channeled spectroscopic ellipsometer (CSE). The new system has a feature that the major systematic and random error sources of the previous CSEs are effectively reduced or compensated for. In addition, the prototype preserves the advantageous features of the CSE in that it has a palm-size sensing head and that its acquisition time is as fast as 20 ms. Its performance is experimentally examined by use of 12 films whose thicknesses are ranging approximately from 3 to 4000 nm. The film thicknesses measured by the new CSE show good agreements with the ones by the rotating-compensator spectroscopic ellipsometer. The stability of the film-thickness measurement of the new CSE against the temperature change from 5 to 45 °C is less than 0.11 nm. The CSE can open up new applications of the spectroscopic ellipsometers in which the compactness, the simplicity, and the rapid response are important.
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07.60.Fs Polarimeters and ellipsometers
77.55.-g Dielectric thin films

A compact molecular beam machine

Paul Jansen, David W. Chandler, and Kevin E. Strecker

Rev. Sci. Instrum. 80, 083105 (2009); http://dx.doi.org/10.1063/1.3206367 (5 pages) | Cited 2 times

Online Publication Date: 31 August 2009

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We have developed a compact, low cost, modular, crossed molecular beam machine. The new apparatus utilizes several technological advancements in molecular beams valves, ion detection, and vacuum pumping to reduce the size, cost, and complexity of a molecular beam apparatus. We apply these simplifications to construct a linear molecular beam machine as well as a crossed-atomic and molecular beam machine. The new apparatus measures almost 50 cm in length, with a total laboratory footprint less than 0.25 m2 for the crossed-atomic and molecular beam machine. We demonstrate the performance of the apparatus by measuring the rotational temperature of nitric oxide from three common molecular beam valves and by observing collisional energy transfer in nitric oxide from a collision with argon.
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07.75.+h Mass spectrometers
07.30.Cy Vacuum pumps
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Three-dimensional velocity map imaging: Setup and resolution improvement compared to three-dimensional ion imaging

S. Kauczok, N. Gödecke, A. I. Chichinin, M. Veckenstedt, C. Maul, and K.-H. Gericke

Rev. Sci. Instrum. 80, 083301 (2009); http://dx.doi.org/10.1063/1.3186734 (10 pages) | Cited 4 times

Online Publication Date: 3 August 2009

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For many years the three-dimensional (3D) ion imaging technique has not benefited from the introduction of ion optics into the field of imaging in molecular dynamics. Thus, a lower resolution of kinetic energy as in comparable techniques making use of inhomogeneous electric fields was inevitable. This was basically due to the fact that a homogeneous electric field was needed in order to obtain the velocity component in the direction of the time of flight spectrometer axis. In our approach we superimpose an Einzel lens field with the homogeneous field. We use a simulation based technique to account for the distortion of the ion cloud caused by the inhomogeneous field. In order to demonstrate the gain in kinetic energy resolution compared to conventional 3D Ion Imaging, we use the spatial distribution of H+ ions emerging from the photodissociation of HCl following the two photon excitation to the V 1∑+ state. So far a figure of merit of approximately four has been achieved, which means in absolute numbers Δv/v = 0.022 compared to 0.086 at v ≈ 17 000 m/s. However, this is not a theoretical limit of the technique, but due to our rather short TOF spectrometer (15 cm). The photodissociation of HBr near 243 nm has been used to recognize and eliminate systematic deviations between the simulation and the experimentally observed distribution. The technique has also proven to be essential for the precise measurement of translationally cold distributions.
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82.50.-m Photochemistry
82.20.Hf Product distribution
82.80.Dx Analytical methods involving electronic spectroscopy

A fast, direct x-ray detection charge-coupled device

P. Denes, D. Doering, H. A. Padmore, J.-P. Walder, and J. Weizeorick

Rev. Sci. Instrum. 80, 083302 (2009); http://dx.doi.org/10.1063/1.3187222 (5 pages) | Cited 8 times

Online Publication Date: 6 August 2009

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A charge-coupled device (CCD) capable of 200 Mpixels/s readout has been designed and fabricated on thick, high-resistivity silicon. The CCDs, up to 600 μm thick, are fully depleted, ensuring good infrared to x-ray detection efficiency, together with a small point spread function. High readout speed, with good analog performance, is obtained by the use of a large number of parallel output ports. A set of companion 16-channel custom readout integrated circuits, capable of 15 bits of dynamic range, is used to read out the CCD. A gate array-controlled back end data acquisition system frames and transfers images, as well as provides the CCD clocks.
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85.30.Tv Field effect devices
29.40.-n Radiation detectors

Experimental demonstration of high quality MeV ultrafast electron diffraction

Renkai Li, Chuanxiang Tang, Yingchao Du, Wenhui Huang, Qiang Du, Jiaru Shi, Lixin Yan, and Xijie Wang

Rev. Sci. Instrum. 80, 083303 (2009); http://dx.doi.org/10.1063/1.3194047 (4 pages) | Cited 8 times

Online Publication Date: 18 August 2009

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The simulation optimization and an experimental demonstration of improved performances of mega-electron-volt ultrafast electron diffraction (MeV UED) are reported in this paper. Using ultrashort high quality electron pulses from an S-band photocathode rf gun and a polycrystalline aluminum foil as the sample, we experimentally demonstrated an improved spatial resolution of MeV UED, in which the Debye–Scherrer rings of the (111) and (200) planes were clearly resolved. This result showed that MeV UED is capable to achieve an atomic level spatial resolution and a ∼ 100 fs temporal resolution simultaneously, and will be a unique tool for ultrafast structural dynamics studies.
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61.05.J- Electron diffraction and scattering
02.60.Pn Numerical optimization
85.60.Ha Photomultipliers; phototubes and photocathodes

Emittance characterization of a hot-cavity laser ion source at Holifield Radioactive Ion Beam Facility

Y. Liu, C. Baktash, J. R. Beene, Ch. Geppert, T. Gottwald, C. C. Havener, T. Kessler, H. F. Krause, D. R. Schultz, D. W. Stracener, C. R. Vane, K. Wies, and K. Wendt

Rev. Sci. Instrum. 80, 083304 (2009); http://dx.doi.org/10.1063/1.3184343 (10 pages) | Cited 4 times

Online Publication Date: 18 August 2009

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The first investigation of the transverse emittance of a hot-cavity laser ion source based on all-solid-state Ti:sapphire lasers is presented. The emittances of 63Cu ion beams generated by three-photon resonant ionization are measured and compared with that of the 69Ga and 39K ion beams resulting from surface ionization in the same ion source. A self-consistent unbiased elliptical exclusion method is adapted for noise reduction and emittance analysis. Typical values of the rms and 90% fractional emittances of the Cu ion beams at 20 keV energy are found to be about 2 and 8 π mm mrad, respectively, for the ion currents of 2–40 nA investigated. The emittances of the laser-produced Cu ion beams are smaller than those of the surface-ionized Ga and K ion beams.
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29.25.Lg Ion sources: polarized
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
42.55.Rz Doped-insulator lasers and other solid state lasers
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A dual-channel, curved-crystal spectrograph for petawatt laser, x-ray backlighter source studies

W. Theobald, C. Stoeckl, P. A. Jaanimagi, P. M. Nilson, M. Storm, D. D. Meyerhofer, T. C. Sangster, D. Hey, A. J. MacKinnon, H.-S. Park, P. K. Patel, R. Shepherd, R. A. Snavely, M. H. Key, J. A. King, et al.

Rev. Sci. Instrum. 80, 083501 (2009); http://dx.doi.org/10.1063/1.3193716 (9 pages)

Online Publication Date: 10 August 2009

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A dual-channel, curved-crystal spectrograph was designed to measure time-integrated x-ray spectra in the ∼ 1.5 to 2 keV range (6.2–8.2 Å wavelength) from small-mass, thin-foil targets irradiated by the VULCAN petawatt laser focused up to 4×1020 W/cm2. The spectrograph consists of two cylindrically curved potassium-acid-phthalate crystals bent in the meridional plane to increase the spectral range by a factor of ∼ 10 compared to a flat crystal. The device acquires single-shot x-ray spectra with good signal-to-background ratios in the hard x-ray background environment of petawatt laser-plasma interactions. The peak spectral energies of the aluminum Heα and Lyα resonance lines were ∼ 1.8 and ∼ 1.0 mJ/eV sr ( ∼ 0.4 and 0.25 J/Å sr), respectively, for 220 J, 10 ps laser irradiation.
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07.85.Nc X-ray and γ-ray spectrometers
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)

Deconvolution-based correction of alkali beam emission spectroscopy density profile measurements

I. Pusztai, G. Pokol, D. Dunai, D. Réfy, G. Pór, G. Anda, S. Zoletnik, and J. Schweinzer

Rev. Sci. Instrum. 80, 083502 (2009); http://dx.doi.org/10.1063/1.3205930 (8 pages) | Cited 1 time

Online Publication Date: 20 August 2009

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A deconvolution-based correction method of the beam emission spectroscopy (BES) density profile measurement is demonstrated by its application to simulated measurements of the COMPASS and TEXTOR tokamaks. If the line of sight is far from tangential to the flux surfaces, and the beam width is comparable to the scale length on which the light profile varies, the observation may cause an undesired smoothing of the light profile, resulting in a non-negligible underestimation of the calculated density profile. This effect can be reduced significantly by the emission reconstruction method, which gives an estimate of the emissivity along the beam axis from the measured light profile, taking the finite beam width and the properties of the measurement into account in terms of the transfer function of the observation. Characteristics and magnitude of the mentioned systematic error and its reduction by the introduced method are studied by means of the comprehensive alkali BES simulation code RENATE.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.55.Fa Tokamaks, spherical tokamaks
52.65.-y Plasma simulation

Operating a radio-frequency plasma source on water vapor

Sonca V. T. Nguyen, John E. Foster, and Alec D. Gallimore

Rev. Sci. Instrum. 80, 083503 (2009); http://dx.doi.org/10.1063/1.3202250 (8 pages) | Cited 1 time

Online Publication Date: 24 August 2009

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A magnetically enhanced radio-frequency (rf) plasma source operating on water vapor has an extensive list of potential applications. In this work, the use of a rf plasma source to dissociate water vapor for hydrogen production is investigated. This paper describes a rf plasma source operated on water vapor and characterizes its plasma properties using a Langmuir probe, a residual gas analyzer, and a spectrometer. The plasma source operated first on argon and then on water vapor at operating pressures just over 300 mtorr. Argon and water vapor plasma number densities differ significantly. In the electropositive argon plasma, quasineutrality requires ni ≃ ne, where ni is the positive ion density. But in the electronegative water plasma, quasineutrality requires ni+ = ni−+ne. The positive ion density and electron density of the water vapor plasma are approximately one and two orders of magnitude lower, respectively, than those of argon plasma. These results suggest that attachment and dissociative attachment are present in electronegative water vapor plasma. The electron temperature for this water vapor plasma source is between 1.5 and 4 eV. Without an applied axial magnetic field, hydrogen production increases linearly with rf power. With an axial magnetic field, hydrogen production jumps to a maximum value at 500 W and then saturates with rf power. The presence of the applied axial magnetic field is therefore shown to enhance hydrogen production.
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52.50.Dg Plasma sources
52.70.Ds Electric and magnetic measurements

A compact submicrosecond, high current generator

B. M. Kovalchuk, A. V. Kharlov, V. B. Zorin, and A. A. Zherlitsyn

Rev. Sci. Instrum. 80, 083504 (2009); http://dx.doi.org/10.1063/1.3193714 (6 pages) | Cited 3 times

Online Publication Date: 26 August 2009

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Pulsed current generator was developed for experiments with current carrying pulsed plasma. Main parts of the generator are capacitor bank, low inductive current driving lines, and central load part. Generator consists of four identical sections, connected in parallel to one load. Capacitor bank is assembled from 24 capacitor blocks (100 kV, 80 nF), connected in parallel. It stores 9.6 kJ at 100 kV charging voltage. Each capacitor block incorporates a multigap spark switch, which is able to commute by six parallel channels. Switches operate in dry air at atmospheric pressure. The generator was tested with an inductive load and a liner load. At 17.5 nH inductive load and 100 kV of charging voltage it provides 650 kA of current amplitude with 390 ns rise time with 0.6 Ω damping resistors in discharge circuit of each capacitor block. The net generator inductance without a load was optimized to be as low as 15 nH, which results in extremely low impedance of the generator ( ∼ 0.08 Ω). It ensures effective energy coupling with a low impedance load such as Z pinch. The generator operates reliably without any adjustments in 70–100 kV range of charging voltage. Jitter in delay between output pulse and triggering pulse is less than 5 ns at 70–100 kV charging voltage. Operation and handling are very simple, because no oil or purified gases are required for the generator. The generator has dimensions 5.24×1.2×0.18 m3 and total weight about 1400 kg, thus manifesting itself as simple, robust, and cost effective apparatus.
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84.30.Ng Oscillators, pulse generators, and function generators
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
84.32.Tt Capacitors

Broadband, high dynamics and high resolution charge coupled device-based spectrometer in dynamic mode for multi-keV repetitive x-ray sources

C. Fourment, N. Arazam, C. Bonte, T. Caillaud, D. Descamps, F. Dorchies, M. Harmand, S. Hulin, S. Petit, and J. J. Santos

Rev. Sci. Instrum. 80, 083505 (2009); http://dx.doi.org/10.1063/1.3189004 (10 pages) | Cited 8 times

Online Publication Date: 27 August 2009

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We present a new operating mode, using a charged coupled device as dispersionless spectrometer dedicated to repetitive x-ray sources in the multi-keV domain. This enables to get spectra with high statistics in a short acquisition time and a way compatible with the operation of other diagnostics requiring accumulation. Several reconstruction algorithms for the spreading events are discussed, and a near Fano-limited resolution is demonstrated by using single pixel events. In this case, a method to take into account partial canceling of the events is presented. Experimental characterization and detailed modeling of the detector are performed, which allow to determine absolute number of photon with ±35% accuracy. Characterization of the 5–25 keV x rays emitted by a short pulse laser-produced plasma is reported, as well as their dependency with the atomic number, the laser duration, and energy.
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52.59.Px Hard X-ray sources
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

A contoured gap coaxial plasma gun with injected plasma armature

F. Douglas Witherspoon, Andrew Case, Sarah J. Messer, Richard Bomgardner, II, Michael W. Phillips, Samuel Brockington, and Raymond Elton

Rev. Sci. Instrum. 80, 083506 (2009); http://dx.doi.org/10.1063/1.3202136 (15 pages) | Cited 3 times

Online Publication Date: 27 August 2009

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A new coaxial plasma gun is described. The long term objective is to accelerate 100–200 μg of plasma with density above 1017 cm−3 to greater than 200 km/s with a Mach number above 10. Such high velocity dense plasma jets have a number of potential fusion applications, including plasma refueling, magnetized target fusion, injection of angular momentum into centrifugally confined mirrors, high energy density plasmas, and others. The approach uses symmetric injection of high density plasma into a coaxial electromagnetic accelerator having an annular gap geometry tailored to prevent formation of the blow-by instability. The injected plasma is generated by numerous (currently 32) radially oriented capillary discharges arranged uniformly around the circumference of the angled annular injection region of the accelerator. Magnetohydrodynamic modeling identified electrode profiles that can achieve the desired plasma jet parameters. The experimental hardware is described along with initial experimental results in which approximately 200 μg has been accelerated to 100 km/s in a half-scale prototype gun. Initial observations of 64 merging injector jets in a planar cylindrical testing array are presented. Density and velocity are presently limited by available peak current and injection sources. Steps to increase both the drive current and the injected plasma mass are described for next generation experiments.
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52.50.-b Plasma production and heating
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.80.-s Electric discharges
52.75.-d Plasma devices

A multichannel, frequency-modulated, tunable Doppler backscattering and reflectometry system

J. C. Hillesheim, W. A. Peebles, T. L. Rhodes, L. Schmitz, T. A. Carter, P.-A. Gourdain, and G. Wang

Rev. Sci. Instrum. 80, 083507 (2009); http://dx.doi.org/10.1063/1.3205449 (8 pages) | Cited 11 times

Online Publication Date: 31 August 2009

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A novel multichannel Doppler backscattering system has been designed and tested for application on the DIII-D [ J. L. Luxon, Fusion Sci. Technol. 48, 828 (2005) ] and National Spherical Torus Experiment (NSTX) [ M. Ono et al., Nucl. Fusion 40, 557 (2000) ] fusion plasma devices. Doppler backscattering measures localized intermediate wavenumber (k⊥ρi ∼ 1–4,k⊥ ∼ 2–15 cm−1) density fluctuations and the propagation velocity of turbulent structures. Microwave radiation is launched at a frequency that approaches a cutoff layer in the plasma and at an angle that is oblique to the cutoff layer. Bragg backscattering occurs near the cutoff layer for fluctuations with k⊥ ≈ −2ki, where ki is the incident probe wave vector at the scattering location. The turbulence propagation velocity can be determined from the Doppler shift in the return signal together with knowledge of the scattering wavenumber. Ray tracing simulations are used to determine k⊥ and the scattering location. Frequency modulation of a voltage-controlled solid state microwave source followed by frequency multiplication is used to create an array of finely spaced (Δf = 350 MHz) frequencies spanning 1.4 GHz. The center of the array bandwidth is tunable within the range of ∼ 53–78 GHz. This article details the system design, laboratory tests, and presents initial data from DIII-D plasmas.
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52.58.-c Other confinement methods
52.75.-d Plasma devices
52.35.Ra Plasma turbulence
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Nanoscale phase transformation in Ge2Sb2Te5 using encapsulated scanning probes and retraction force microscopy

Harish Bhaskaran, Abu Sebastian, Andrew Pauza, Haralampos Pozidis, and Michel Despont

Rev. Sci. Instrum. 80, 083701 (2009); http://dx.doi.org/10.1063/1.3204449 (6 pages) | Cited 6 times

Online Publication Date: 20 August 2009

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Encapsulated conducting probes that can sustain high currents are used to study the nanoscale properties of thin-film stacks comprising of a phase-change chalcogenide, Ge2Sb2Te5. Scaling studies on this promising candidate for random-access memory devices had thus far required extensive lithography and nanoscale growth. This seriously hampers rapid materials characterization. This article describes the use of two key techniques, an encapsulated conductive probe and its use in retraction mode, whereby the attractive force between tip and sample is used to maintain electrical contact. The effective transformation of nanoscale dots of amorphous Ge2Sb2Te5 into the crystalline state is achieved and the electrical conductivity of the transformed structures is probed. The use of retraction force microscopy in a robust manner is demonstrated by reading the conductivity of the crystalline dots. Both these techniques could enable rapid electrical characterization of nanoscale materials, without extensive nanopatterning, thus reducing material development cycles.
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64.70.K- Solid-solid transitions
73.21.La Quantum dots
81.16.Nd Micro- and nanolithography
73.61.Jc Amorphous semiconductors; glasses
61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.ag Semiconductors

A versatile dual spot laser scanning confocal microscopy system for advanced fluorescence correlation spectroscopy analysis in living cell

Patrick Ferrand, Martina Pianta, Alla Kress, Alexandre Aillaud, Hervé Rigneault, and Didier Marguet

Rev. Sci. Instrum. 80, 083702 (2009); http://dx.doi.org/10.1063/1.3205447 (8 pages) | Cited 5 times

Online Publication Date: 20 August 2009

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A fluorescence correlation spectroscopy system based on two independent measurement volumes is presented. The optical setup and data acquisition hardware are detailed, as well as a complete protocol to control the location, size, and shape of the measurement volumes. A method that allows to monitor independently the excitation and collection efficiency distribution is proposed. Finally, a few examples of measurements that exploit the two spots in static and/or scanning schemes are reported.
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87.64.kv Fluorescence
87.64.M- Optical microscopy
87.18.-h Biological complexity

Combined holographic-mechanical optical tweezers: Construction, optimization, and calibration

Richard D. L. Hanes, Matthew C. Jenkins, and Stefan U. Egelhaaf

Rev. Sci. Instrum. 80, 083703 (2009); http://dx.doi.org/10.1063/1.3196181 (7 pages) | Cited 4 times

Online Publication Date: 26 August 2009

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A spatial light modulator (SLM) and a pair of galvanometer-mounted mirrors (GMM) were combined into an optical tweezers setup. This provides great flexibility as the SLM creates an array of traps, which can be moved smoothly and quickly with the GMM. To optimize performance, the effect of the incidence angle on the SLM with respect to phase and intensity response was investigated. Although it is common to use the SLM at an incidence angle of 45°, smaller angles give a full 2π phase shift and an output intensity which is less dependent on the magnitude of the phase shift. The traps were calibrated using an active oscillatory technique and a passive probability distribution method.
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42.40.Eq Holographic optical elements; holographic gratings
42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.79.Hp Optical processors, correlators, and modulators
06.20.F- Units and standards
02.50.Ng Distribution theory and Monte Carlo studies
42.79.Bh Lenses, prisms and mirrors

Design of a variable temperature scanning force microscope

E. Nazaretski, K. S. Graham, J. D. Thompson, J. A. Wright, D. V. Pelekhov, P. C. Hammel, and R. Movshovich

Rev. Sci. Instrum. 80, 083704 (2009); http://dx.doi.org/10.1063/1.3212561 (6 pages) | Cited 4 times

Online Publication Date: 31 August 2009

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We have developed the variable temperature scanning force microscope capable of performing both magnetic resonance force microscopy (MRFM) and magnetic force microscopy (MFM) measurements in the temperature range between 5 and 300 K. Modular design, large scanning area, and interferometric detection of the cantilever deflection make it a sensitive, easy to operate, and reliable instrument suitable for studies of the dynamic and static magnetization in various systems. We have verified the performance of the microscope by imaging vortices in a Nb thin film in the MFM mode of operation. MRFM spectra in a diphenyl-picryl-hydrazyl film were recorded to evaluate the MRFM mode of operation.
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07.79.Lh Atomic force microscopes
07.79.Pk Magnetic force microscopes
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Wideband digital frequency detector with subtraction-based phase comparator for frequency modulation atomic force microscopy

Yuji Mitani, Mamoru Kubo, Ken-ichiro Muramoto, and Takeshi Fukuma

Rev. Sci. Instrum. 80, 083705 (2009); http://dx.doi.org/10.1063/1.3212670 (3 pages) | Cited 3 times

Online Publication Date: 31 August 2009

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We have developed a wideband digital frequency detector for high-speed frequency modulation atomic force microscopy (FM-AFM). We used a subtraction-based phase comparator (PC) in a phase-locked loop circuit instead of a commonly used multiplication-based PC, which has enhanced the detection bandwidth to 100 kHz. The quantitative analysis of the noise performance revealed that the internal noise from the developed detector is small enough to provide the theoretically limited noise performance in FM-AFM experiments in liquid. FM-AFM imaging of mica in liquid was performed with the developed detector, showing its stability and applicability to true atomic-resolution imaging in liquid.
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07.79.Lh Atomic force microscopes
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
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Characterization of hydrogen storage materials by means of pressure concentration isotherms based on the mass flow method

Michael Bielmann, Shunsuke Kato, Philippe Mauron, Andreas Borgschulte, and Andreas Züttel

Rev. Sci. Instrum. 80, 083901 (2009); http://dx.doi.org/10.1063/1.3186731 (7 pages) | Cited 2 times

Online Publication Date: 3 August 2009

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The determination of the equilibrium thermodynamic parameters of hydrogen storage materials from quasiequilibrium pressure data using the mass flow pressure concentration isotherm (pcI) method is presented. The method bases on the acquisition of pcI curves at different flow rates using a thermal mass flow controller to determine the amount of ad/desorbed hydrogen. These measurements provide a set of corresponding quasiequilibrium pressure functions from, which the true equilibrium pressure of the hydride is calculated by extrapolation to zero flow. The governing thermodynamic parameters can then be determined to characterize the material by the construction of a van’t Hoff plot, extracting enthalpy of reaction ΔHr and entropy of reaction ΔSr from the equilibrium pressure peq as a function of temperature. Naturally, true equilibrium can never be reached and therefore can only be approximated by measurement––a drawback that all experimental techniques share. This complication is alleviated by the flow-pcI approach at different flow rates. The compilation of the peq(T) data from pcI-measurements can be performed by different methods, whereas the so called Sieverts apparatus is most commonly used. In this paper, we elaborate the differences and advantages of the mass flow-pcI over the Sieverts Apparatus and present measurements and results on LaNi5 as a benchmark. Measurements at different flow rates are presented and equilibrium pressures at zero flow are achieved by extrapolation. The obtained results of ΔHd = 32.5 kJ mol−1 H2 and ΔSd = 115 J K−1 mol−1 H2 (desorption process) perfectly match literature values, emphasizing the excellent quality of the measurements and the performance of this measurement apparatus.
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84.60.-h Direct energy conversion and storage
82.60.Cx Enthalpies of combustion, reaction, and formation
65.40.gd Entropy
68.43.Mn Adsorption kinetics
68.43.Nr Desorption kinetics

The experimental realization of a two-dimensional colloidal model system

F. Ebert, P. Dillmann, G. Maret, and P. Keim

Rev. Sci. Instrum. 80, 083902 (2009); http://dx.doi.org/10.1063/1.3188948 (12 pages) | Cited 12 times

Online Publication Date: 3 August 2009

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We present the technical details of an experimental method to realize a model system for two-dimensional (2D) phase transitions and the glass transition. The system consists of several hundred thousand colloidal superparamagnetic particles confined by gravity at a flat water-air interface of a pending water droplet where they are subjected to Brownian motion. The dipolar pair potential and, therefore, the system temperature are not only known precisely but also directly and instantaneously controllable via an external magnetic field H. In the case of a one-component system of monodisperse particles the system can crystallize upon application of H whereas in a two component system it undergoes a glass transition. Up to 10 000 particles are observed by video microscopy and image processing provides their trajectories on all relative length and time scales. The position of the interface is actively regulated thereby reducing surface fluctuations to less than 1 μm and the setup inclination is controlled to an accuracy of ±1 μrad. The sample quality being necessary to enable the experimental investigation of the 2D melting scenario, 2D crystallization, and the 2D glass transition, is discussed.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
64.70.pm Liquids
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Mm Magnetic liquids
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
64.70.dj Melting of specific substances

A compact apparatus for studies of element and phase-resolved ferromagnetic resonance

D. A. Arena, Y. Ding, E. Vescovo, S. Zohar, Y. Guan, and W. E. Bailey

Rev. Sci. Instrum. 80, 083903 (2009); http://dx.doi.org/10.1063/1.3190402 (7 pages) | Cited 4 times

Online Publication Date: 11 August 2009

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We present a compact sample holder equipped with electromagnets and high frequency transmission lines; the sample holder is intended for combined x-ray magnetic circular dichroism (XMCD) and ferromagnetic resonance measurements (FMR). Time-resolved measurements of resonant x-ray detected FMR during forced precession are enabled by use of a rf excitation that is phase-locked to the storage ring bunch clock. Several applications of the combined XMCD+FMR technique are presented, demonstrating the flexibility of the experimental design.
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07.55.-w Magnetic instruments and components
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
78.20.Ls Magneto-optical effects
07.85.-m X- and γ-ray instruments
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