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Nov 2008

Volume 79, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 79, 111301 (2008); http://dx.doi.org/10.1063/1.3005784 (14 pages)

Anita Sengupta, James Kulleck, Norm Hill, and Wayne Ohlinger

Post life test (30,472 hour) condition of the interior of an impregnated-cathode showing a cascade of crystallites emanating from the cathode orifice plate, a result of tungsten transport and redeposition processes. This cathode was the electron source of the Deep Space 1 flight spare ion thruster.

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Invited Article: Physical and chemical analyses of impregnated cathodes operated in a plasma environment

Anita Sengupta, James Kulleck, Norm Hill, and Wayne Ohlinger

Rev. Sci. Instrum. 79, 111301 (2008); http://dx.doi.org/10.1063/1.3005784 (14 pages) | Cited 2 times

Online Publication Date: 20 November 2008

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Destructive analyses of impregnated-cathode assemblies from an ion thruster life test were performed to characterize erosion and degradation after 30 472 h of operation. Post-test inspection of each cathode included examination of the emitter (insert), orifice plate, cathode tube, heater, anode assembly, insulator, and propellant isolator. The discharge-cathode assembly experienced significant erosion due to ion sputtering from the discharge plasma. The keeper electrode plate was removed and the heater and orifice plate were heavily eroded at the conclusion of the test. Had the test continued, these processes would likely have led to cathode failure. The discharge cathode insert experienced significant tungsten transport and temperature dependent barium oxide depletion within the matrix. Using barium depletion semiempirical relations developed by Palluel and Shroff, it is estimated that 25 000 h of operation remained in the discharge insert at the conclusion of the test. In contrast, the neutralizer insert exhibited significantly less tungsten transport and barium oxide depletion consistent with its lower current operation. The neutralizer was estimated to have 140 000 h of insert life remaining at the conclusion of the test. Neither insert had evidence of tungstate or oxide layer formation, previously known to have impeded cathode ignition and operation in similar long duration hollow-cathode tests. The neutralizer cathode was in excellent condition at the conclusion of the test with the exception of keeper tube erosion from direct plume-ion impingement, a previously underappreciated life-limiting mechanism. The most critical finding from the test was a power dependent deposition process within the neutralizer-cathode orifice. The process manifested at low-power operation and led to the production of energetic ions in the neutralizer plume, a potential life-limiting process for the neutralizer. Subsequent return of the engine and neutralizer operation to full-power removed the deposits and energetic ion production ceased.
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82.45.Fk Electrodes
52.80.-s Electric discharges
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A compact all-fiber displacement interferometer for measuring the foil velocity driven by laser

Jidong Weng, Xiang Wang, Yun Ma, Hua Tan, Lingcang Cai, Jianfeng Li, and Cangli Liu

Rev. Sci. Instrum. 79, 113101 (2008); http://dx.doi.org/10.1063/1.3020700 (3 pages) | Cited 3 times

Online Publication Date: 7 November 2008

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A compact all-fiber displacement interferometer (AFDI) system, working at 1550 nm, has been developed and tested, and its working fundamentals will be introduced in this letter. In contrast with other models of fiber-optic velocity interferometer system, AFDI adopts a single-mode optic fiber pigtail as the detect head, diameter of which is only 1 mm, to collect directly the reflect laser beam from the moving surface, which makes this instrument have some unique advantages in observing the point movements of a small flyer. Preliminary experiments using this instrument to measure the velocity history of a small aluminum thin foil driven by a nanosecond pulse laser were conducted successfully, the precise velocity history profile deduced from the sharp interference fringes and the nanometer resolution in displacement gives an eloquent proof of its eminent abilities. The field depth ( ∼ 2 mm) of our AFDI is a little smaller than the DISAR [ Weng et al., Appl. Phys. Lett. 89, 111101 (2006) ] system, but its compact structure makes it much convenient to operate. Further applications for multipoints velocity history measurements of small targets are under consideration.
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07.60.Ly Interferometers

Evaluation of the sensitivity and fading characteristics of an image plate system for x-ray diagnostics

A. L. Meadowcroft, C. D. Bentley, and E. N. Stott

Rev. Sci. Instrum. 79, 113102 (2008); http://dx.doi.org/10.1063/1.3013123 (4 pages) | Cited 14 times

Online Publication Date: 11 November 2008

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Image plates (IPs) are a reusable recording media capable of detecting ionizing radiation, used to diagnose x-ray emission from laser-plasma experiments. Due to their superior performance characteristics in x-ray applications [ C. C. Bradford, W. W. Peppler, and J. T. Dobbins III, Med. Phys. 26, 27 (1999) and J. Digit. Imaging. 12, 54 (1999) ], the Fuji Biological Analysis System (BAS) IPs are fielded on x-ray diagnostics for the HELEN laser by the Plasma Physics Department at AWE. The sensitivities of the Fuji BAS IPs have been absolutely calibrated for absolute measurements of x-ray intensity in the energy range of 0–100 keV. In addition, the Fuji BAS IP fading as a function of time was investigated. We report on the characterization of three Fuji BAS IP responses to x-rays using a radioactive source, and discrete x-ray line energies generated by the Excalibur soft x-ray facility and the Defense Radiological Standards Centre filter-fluorescer hard x-ray system at AWE.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.70.La X-ray and γ-ray measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Ph X-ray, γ-ray, and particle generation

Assessing the validity of modulation transfer function evaluation techniques with application to small area and scanned digital detectors

B. D. Price, C. J. Esbrand, A. Olivo, A. P. Gibson, J. C. Hebden, R. D. Speller, and G. J. Royle

Rev. Sci. Instrum. 79, 113103 (2008); http://dx.doi.org/10.1063/1.3020696 (6 pages) | Cited 1 time

Online Publication Date: 12 November 2008

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A novel prototype step and shoot x-ray system, the intelligent imaging system (I-Imas), has been developed in the UCL Radiation Physics laboratories. The system uses collimators to split the beam into two: the first, “scout” beam, strongly attenuated, identifies regions of interest in the image. This information is then fed back to the system so that the intensity of the second beam is modulated to optimize the dose distribution—i.e., “interesting” regions of the sample receive a higher dose, whereas other regions receive a lower one. Such systems may be capable of improved diagnostic capability at the same overall patient dose levels as typical when using large area digital plates. This acquisition mode means that large overall images are obtained by aligning many smaller images. This paper investigates the effects that this acquisition modality has on the overall spatial resolution of the system. We review different modulation transfer function (MTF) evaluation techniques and those shown to be optimal are used in the investigation of two considerations key to such a system: (i) whether there is a minimum size sensor whose MTF can accurately be determined using these techniques and (ii) whether the MTF of the large overall image differs significantly from those of the many constituent images. As the use of step and shoot systems is becoming more and more widespread, both are important considerations. We found that, for a fixed pixel pitch, the MTF is determined marginally less accurately the smaller the sensor area, with the perceived resolution varying by up to 0.1 lp/mm. It was also found that use of such a step and shoot technique does cause a very small overall degradation in resolution. The resolution of overall images was calculated to be 0.1 lp/mm lower than that of the individual images acquired.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
29.40.-n Radiation detectors
87.53.Bn Dosimetry/exposure assessment
87.59.bf Digital radiography

Diagnosis of x-ray heated Mg/Fe opacity research plasmas

J. E. Bailey, G. A. Rochau, R. C. Mancini, C. A. Iglesias, J. J. MacFarlane, I. E. Golovkin, J. C. Pain, F. Gilleron, C. Blancard, Ph. Cosse, G. Faussurier, G. A. Chandler, T. J. Nash, D. S. Nielsen, and P. W. Lake

Rev. Sci. Instrum. 79, 113104 (2008); http://dx.doi.org/10.1063/1.3020710 (11 pages) | Cited 6 times

Online Publication Date: 20 November 2008

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Understanding stellar interiors, inertial confinement fusion, and Z pinches depends on opacity models for mid-Z plasmas in the 100–300 eV temperature range. These models are complex and experimental validation is crucial. In this paper we describe the diagnosis of the first experiments to measure iron plasma opacity at a temperature high enough to produce the charge states and electron configurations that exist in the solar interior. The dynamic Hohlraum x-ray source at Sandia National Laboratories’ Z facility was used to both heat and backlight Mg/Fe CH tamped foils. The backlighter equivalent brightness temperature was estimated to be Tr ∼ 314 eV±8% using time-resolved x-ray power and imaging diagnostics. This high brightness is significant because it overwhelms the sample self-emission. The sample transmission in the 7–15.5 Å range was measured using two convex potassium acid phthalate crystal spectrometers that view the backlighter through the sample. The average spectral resolution over this range was estimated to be λ/δλ ∼ 700 by comparing theoretical crystal resolution calculations with measurements at 7.126, 8.340, and 12.254 Å. The electron density was determined to be ne = 6.9±1.7×1021 cm−3 using the Stark-broadened Mg Heβ, Heγ, and Heδ lines. The temperature inferred from the H-like to He-like Mg line ratios was Te = 156±6 eV. Comparisons with three different spectral synthesis models all have normalized χ2 that is close to unity, indicating quantitative consistency in the inferred plasma conditions. This supports the reliability of the results and implies the experiments are suitable for testing iron opacity models.
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52.70.La X-ray and γ-ray measurements
52.80.-s Electric discharges

A positron trap and beam apparatus for atomic and molecular scattering experiments

J. P. Sullivan, A. Jones, P. Caradonna, C. Makochekanwa, and S. J. Buckman

Rev. Sci. Instrum. 79, 113105 (2008); http://dx.doi.org/10.1063/1.3030774 (5 pages) | Cited 24 times

Online Publication Date: 21 November 2008

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An instrument has been designed and constructed to provide new insights into fundamental, low energy positron scattering processes. The design is based on the Surko trap system and produces a pulsed positron beam with an energy resolution of as good as 54 meV. The design and operation of the apparatus is explained, while the first experimental results from this apparatus have been demonstrated in recent publications.
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07.77.Ka Charged-particle beam sources and detectors
37.20.+j Atomic and molecular beam sources and techniques
37.10.-x Atom, molecule, and ion cooling methods
34.80.Uv Positron scattering
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An active drop counting device using condenser microphone for superheated emulsion detector

Mala Das, A S. Arya, C. Marick, D. Kanjilal, and S. Saha

Rev. Sci. Instrum. 79, 113301 (2008); http://dx.doi.org/10.1063/1.3020698 (6 pages) | Cited 1 time

Online Publication Date: 7 November 2008

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An active device for superheated emulsion detector is described. A capacitive diaphragm sensor or condenser microphone is used to convert the acoustic pulse of drop nucleation to electrical signal. An active peak detector is included in the circuit to avoid multiple triggering of the counter. The counts are finally recorded by a microprocessor based data acquisition system. Genuine triggers, missed by the sensor, were studied using a simulated clock pulse. The neutron energy spectrum of 252Cf fission neutron source was measured using the device with R114 as the sensitive liquid and compared with the calculated fission neutron energy spectrum of 252Cf. Frequency analysis of the detected signals was also carried out.
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29.40.Rg Nuclear emulsions
84.32.Tt Capacitors
29.50.+v Computer interfaces
29.85.Ca Data acquisition and sorting
29.25.Dz Neutron sources
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Design and application of a mechanical load frame for in situ investigation of ferromagnetic shape memory alloys by magnetic force microscopy

D. Niklasch, H. J. Maier, and I. Karaman

Rev. Sci. Instrum. 79, 113701 (2008); http://dx.doi.org/10.1063/1.3010383 (4 pages) | Cited 2 times

Online Publication Date: 4 November 2008

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An in situ mechanical load frame has been developed for a commercially available atomic force microscope. This frame allows examining changes in topography and magnetic domain configuration under a given constant load or strain. First results obtained on Ni–Mn–Ga ferromagnetic shape memory alloy single crystals are presented. The magnetic force microscopy (MFM) measurements under different strain levels confirm the one-to-one correspondence, i.e., the magnetomicrostructural coupling between the martensite twins and the magnetic domains. Additionally, the growth of the twin variant with favorable orientation to the compression axis during martensite detwinning was observed. It will be shown that this load frame can be used for the investigation of the relationship between the microstructure and the magnetic domain structure in ferromagnetic shape memory alloys by MFM.
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81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity

Implementation on a desktop computer of the real time feedback control loop of a scanning probe microscope

G. Aloisi, F. Bacci, M. Carlà, D. Dolci, and L. Lanzi

Rev. Sci. Instrum. 79, 113702 (2008); http://dx.doi.org/10.1063/1.2992483 (7 pages) | Cited 4 times

Online Publication Date: 5 November 2008

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A software package has been developed to implement the real time feedback control loop needed in scanning probe microscopy on a general purpose desktop computer of the current high-speed/multicore generation. The main features of the implementation of both the feedback loop and the control of the experiment on the same computer are discussed. The package can work with several general purpose data acquisition boards and can be extended in a modular way to further board models; timing performance has been tested with several hardware configurations and some applications common in scanning probe microscopy. The package is available under an Open Source license.
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87.64.Dz Scanning tunneling and atomic force microscopy
29.85.Ca Data acquisition and sorting

Instrumental development attachable to high magnification microscopes for obtaining totally focalized images

Francisco Javier Navas, Moritz Kulawik, and Joaquín Martín

Rev. Sci. Instrum. 79, 113703 (2008); http://dx.doi.org/10.1063/1.3020703 (7 pages)

Online Publication Date: 7 November 2008

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A complete system (instrumentation and software) for acquiring micrograph images with an extended depth of focus and with no alteration to the original chromaticity has been developed. The buildup system includes (a) the electromechanical components to be coupled to a commercial microscope in order to improve it, (b) a computer program with which the focusing distance can be micrometrically modified at the same time that a set of digital images can be acquired, and (c) software that permits the in-focus pixels of each image to be extracted and incorporated into a global image with an extended depth of focus greater than that supplied by the optical characteristics of the objective used to visualize the sample. The algorithm used does not have any influence on the sample chromaticity and the generated image can be obtained with full chromaticity.
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07.60.Pb Conventional optical microscopes
42.79.-e Optical elements, devices, and systems

PolLux: A new facility for soft x-ray spectromicroscopy at the Swiss Light Source

J. Raabe, G. Tzvetkov, U. Flechsig, M. Böge, A. Jaggi, B. Sarafimov, M. G. C. Vernooij, T. Huthwelker, H. Ade, D. Kilcoyne, T. Tyliszczak, R. H. Fink, and C. Quitmann

Rev. Sci. Instrum. 79, 113704 (2008); http://dx.doi.org/10.1063/1.3021472 (10 pages) | Cited 30 times

Online Publication Date: 13 November 2008

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We report on the successful installation and operation of a scanning transmission x-ray microspectroscope (STXM) at the PolLux facility at the Swiss Light Source. This integration of an advanced STXM with improved sample handling capabilities and a novel beamline provides unique capabilities. PolLux uses linearly or circularly polarized x-rays from a bending magnet with an extended photon energy range (200–1400 eV). It is therefore well suited to determine a sample’s quantitative chemical composition, molecular orientation, or thickness of organic as well as condensed matter materials. The local magnetic state of magnetic thin films is accessible through fast helicity switching by steering the electron beam off axis through the bending magnet. Ex vacuo girder movers allow fast and highly reproducible (<1 μm) alignment of the instrument with respect to the photon beam. The present spatial resolution is ∼ 20 nm, limited by the zone plates utilized. The instrument has the stability and positional resolution to operate with much higher resolution optics as it becomes available. In addition to characterization experiments, we present several typical examples from materials research and environmental science to exemplify the capabilities.
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07.85.Nc X-ray and γ-ray spectrometers
42.79.Ci Filters, zone plates, and polarizers
42.72.-g Optical sources and standards
07.85.Tt X-ray microscopes

A new physical model for resonance shear measurement of confined liquids between solid surfaces

Masashi Mizukami and Kazue Kurihara

Rev. Sci. Instrum. 79, 113705 (2008); http://dx.doi.org/10.1063/1.3012811 (6 pages) | Cited 3 times

Online Publication Date: 18 November 2008

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This paper describes a new physical model for resonance shear measurement. The resonance shear method developed by us provides a tool for investigating the rheological and tribological properties of liquids confined between two surfaces as a function of the surface distance from micrometer to zero (contact) with nanometer level resolution with high sensitivity and stability. The properties of the confined liquid can be quantitatively studied by analyzing the resonance curve using a physical model. However, the quantitative analysis using the previously developed model was applicable only for the condition of the relatively low liquid viscosity (below ∼ 100 Pa s). A new physical model described in this paper enabled us to continuously analyze the properties of confined liquids at all distances, which was not possible by the previous model. It became possible to calculate the movement of a lower surface and the shear rate applied on the confined sample using the parameters obtained from the resonance curves.
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61.30.-v Liquid crystals
61.25.Em Molecular liquids
61.20.Gy Theory and models of liquid structure
62.10.+s Mechanical properties of liquids
61.20.Ja Computer simulation of liquid structure

Development of a local electromagnetic shielding for an extremity magnetic resonance imaging system

Shinya Handa, Tomoyuki Haishi, and Katsumi Kose

Rev. Sci. Instrum. 79, 113706 (2008); http://dx.doi.org/10.1063/1.3030856 (3 pages) | Cited 1 time

Online Publication Date: 24 November 2008

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A local radio frequency (rf) shielding consisting of a Cu plate and an LC balun circuit has been developed for a compact magnetic resonance imaging (MRI) system with a 0.3 T permanent magnet. Performance of the local rf shielding was evaluated using an artificial external noise source irradiating a human subject whose hand was inserted into the rf coil of the MRI system. Power spectra of the rf signal detected through the rf coil demonstrated that the local rf shield achieved 30.1 dB external noise suppression. With the local rf shielding, a MRI of the subject’s hand was performed using a three-dimensional gradient-echo sequence. Anatomical structures of the subject’s hand were clearly visualized. It was concluded that the local rf shielding could be used for the compact MRI system instead of a rf shielded room.
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07.50.Hp Electrical noise and shielding equipment
85.70.-w Magnetic devices
87.61.-c Magnetic resonance imaging
87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
84.40.-x Radiowave and microwave (including millimeter wave) technology

All low voltage lateral junction scanning tunneling microscope with very high precision and stability

Yubin Hou, Jihui Wang, and Qingyou Lu

Rev. Sci. Instrum. 79, 113707 (2008); http://dx.doi.org/10.1063/1.3005484 (3 pages) | Cited 5 times

Online Publication Date: 25 November 2008

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We describe the first lateral junction and fully low voltage scanning tunneling microscope, featuring very high precision, stability, compactness, and image quality (highly oriented pyrolytic graphite atomic resolution images). In its core, the tip and sample each sit on one of two parallel-mounted piezoelectric tube scanners so that the tip-sample gap is regulated along the scanners’ pairing direction. The scanner’s large lateral deflection provides a large gap regulation range even under low voltages, allowing exclusively using only low voltage (less than ±15 V) operational amplifiers to precisely implement the coarse (inertial slider) and fine approach, feedback control, and hence the entire electronics. Because the scanners are identical and adjacent, thermal drifts are minimal.
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07.79.Cz Scanning tunneling microscopes

Quantitative model for near-field scanning microwave microscopy: Application to metrology of thin film dielectrics

Alexander N. Reznik and Vladimir V. Talanov

Rev. Sci. Instrum. 79, 113708 (2008); http://dx.doi.org/10.1063/1.3020705 (8 pages) | Cited 5 times

Online Publication Date: 26 November 2008

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We have experimentally verified a recently proposed theoretical model for near-field microwave microscopy of multilayer media. The model addresses a near-field microwave probe as an electrically small antenna with a Gaussian-like current distribution that has a single characteristic length scale on the order of the probe size. Electrodynamic response of an antenna is calculated using Green functions in the form of integral transforms for electric and magnetic fields (both quasistatic and propagating), which are generated by a pointlike dipole. Experimental data were obtained at 4 GHz using a near-field scanning microwave microscope with aperture size of ∼ 5 μm for a set of six SiO2 films with thickness ranging from 0.1 to 1.5 μm. For each sample the probe resonant frequency was both measured and simulated as a function of the tip-sample distance, and good agreement between the theory and experimental data was observed. It was found that the model is capable of determining thin film dielectric constant with accuracy of ∼ 5%–7%.
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07.79.-v Scanning probe microscopes and components
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ch Permittivity (dielectric function)
84.40.Ba Antennas: theory, components and accessories
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New techniques for high-temperature melting measurements in volatile refractory materials via laser surface heating

D. Manara, M. Sheindlin, W. Heinz, and C. Ronchi

Rev. Sci. Instrum. 79, 113901 (2008); http://dx.doi.org/10.1063/1.3005994 (7 pages) | Cited 6 times

Online Publication Date: 6 November 2008

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An original technique for the measurement of high-temperature phase transitions was implemented based on a laser-heating method, enabling chemically unstable, refractory materials to be melted under controlled conditions. This technique includes two independent but correlated methods: In the first, fast multichannel pyrometry is employed to measure thermograms and spectral emissivity; in the second, a low-power probe laser beam is used for the detection of reflectivity changes induced by phase transitions on the sample surface. The experiments are carried out under medium ( ≈ 102 kPa) or high ( ≈ 102 MPa) inert-gas pressures in order to kinetically suppress evaporation in volatile or chemically instable samples. Two models for the simulation of the laser-heating pulses are as well introduced. Some results are presented about the successful application of this technique to the study of the melting behavior of oxides such as UO2+x, ZrO2, and their mixed oxides. The method can be extended to a broad class of refractory materials.
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64.70.dj Melting of specific substances
42.62.-b Laser applications

Oscillating streaming potential measurement system for macroscopic surfaces

Martin Reischl, Stefan Köstler, Gerhard Kellner, Karin Stana-Kleinschek, and Volker Ribitsch

Rev. Sci. Instrum. 79, 113902 (2008); http://dx.doi.org/10.1063/1.3020699 (6 pages) | Cited 2 times

Online Publication Date: 14 November 2008

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A method and instrumentation is described capable of streaming potential measurements of various macroscopic surfaces. It differs from other approaches due to the creation of an oscillatory flow of electrolyte solutions through or alongside the sample. This technique offers a wide range of applied flow frequency and amplitude resulting in a fast and highly accurate measurement. This enables the streaming potential detection at rather high ionic strength and in a short time regime, which allows the monitoring of adsorption processes. Streaming potential and applied pressure are measured simultaneously, together with the specific conductivity of the bulk solution, pH value, and temperature. Combining these data, the zeta potential (ζ) for many different material types (fibers, films, foils, granules, and particles) can be calculated. The apparatus comprises reliable and robust measurements, simple handling, a high degree of automation, and advanced software control. With this setup, automated pH and concentration dependent ζ-potential measurements are possible for a variety of analytes and adsorbing species (e.g., ionic strength, surfactants, polyelectrolytes, and proteins); time-resolved measurements are facilitated down to the seconds time scale. The device allows the necessary sample preparation and equilibration outside the instrument using exchangeable sample holders. This offers the opportunity of high sample throughput.
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82.45.Jn Surface structure, reactivity and catalysis

High precision differential measurement of surface photovoltage transients on ultrathin CdS layers

Th. Dittrich, S. Bönisch, P. Zabel, and S. Dube

Rev. Sci. Instrum. 79, 113903 (2008); http://dx.doi.org/10.1063/1.3020757 (6 pages) | Cited 5 times

Online Publication Date: 14 November 2008

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Time-resolved surface photovoltage (SPV) is an important method for studying charge separation, for example, in nanostructured semiconductors. High precision differential measurement of SPV transients was realized with two identical measurement capacitors and high-impedance buffers. In addition, logarithmic readout and averaging procedures were implemented for single transients over eight magnitudes in time. As a model system ultrathin CdS layers were investigated. The thickness dependencies of the SPV amplitudes and that of the dominating relaxation mechanisms are demonstrated and discussed.
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72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
73.50.Pz Photoconduction and photovoltaic effects
68.55.ag Semiconductors

Real-time x-ray diffraction measurements of shocked polycrystalline tin and aluminum

Dane V. Morgan, Don Macy, and Gerald Stevens

Rev. Sci. Instrum. 79, 113904 (2008); http://dx.doi.org/10.1063/1.3030855 (6 pages) | Cited 1 time

Online Publication Date: 22 November 2008

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A new, fast, single-pulse x-ray diffraction (XRD) diagnostic for determining phase transitions in shocked polycrystalline materials has been developed. The diagnostic consists of a 37-stage Marx bank high-voltage pulse generator coupled to a needle-and-washer electron beam diode via coaxial cable, producing line and bremsstrahlung x-ray emission in a 35 ns pulse. The characteristic Kα lines from the selected anodes of silver and molybdenum are used to produce the diffraction patterns, with thin foil filters employed to remove the characteristic Kβ line emission. The x-ray beam passes through a pinhole collimator and is incident on the sample with an approximately 3×6 mm2 spot and 1° full width half maximum angular divergence in a Bragg-reflecting geometry. For the experiments described in this report, the angle between the incident beam and the sample surface was 8.5°. A Debye–Scherrer diffraction image was produced on a phosphor located 76 mm from the polycrystalline sample surface. The phosphor image was coupled to a charge-coupled device camera through a coherent fiber-optic bundle. Dynamic single-pulse XRD experiments were conducted with thin foil samples of tin, shock loaded with a 1 mm vitreous carbon back window. Detasheet high explosive with a 2-mm-thick aluminum buffer was used to shock the sample. Analysis of the dynamic shock-loaded tin XRD images revealed a phase transformation of the tin beta phase into an amorphous or liquid state. Identical experiments with shock-loaded aluminum indicated compression of the face-centered-cubic aluminum lattice with no phase transformation.
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61.66.Bi Elemental solids
78.70.Ck X-ray scattering
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kd Metals and alloys
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A cryogenic supersonic nozzle apparatus to study homogeneous nucleation of Ar and other simple molecules

Somnath Sinha, Hartawan Laksmono, and Barbara E. Wyslouzil

Rev. Sci. Instrum. 79, 114101 (2008); http://dx.doi.org/10.1063/1.3006002 (8 pages) | Cited 4 times

Online Publication Date: 11 November 2008

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We present a supersonic nozzle apparatus to study homogeneous nucleation of argon and other simple molecules. Experiments can be conducted with pure condensable vapor or with condensable vapor-carrier gas mixtures. The flow through the nozzle is continuous, and expansions typically start at temperatures T0 in the range of 100<T0/K<120, and pressures p0 in the range of 30<p0/kPa<36. The gas mixture is cooled using a tube and fin heat exchanger by evaporating liquid nitrogen on the tube side. The nozzle sidewalls are also cooled with liquid nitrogen to maintain them at a temperature ∼ 20 K higher than the stagnation temperature. Static pressure measurements detect the onset of condensation, and the other properties of the flow are derived by integrating the diabatic flow equations. We present sample experimental results for pure argon where at the onset of condensation, temperatures Ton range from 47.5<Ton/K<49.5 and pressures pon range from 4.2<pon/kPa<4.9.
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47.60.Kz Flows and jets through nozzles
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
47.40.Ki Supersonic and hypersonic flows
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Real-time processing for Fourier domain optical coherence tomography using a field programmable gate array

Teoman E. Ustun, Nicusor V. Iftimia, R. Daniel Ferguson, and Daniel X. Hammer

Rev. Sci. Instrum. 79, 114301 (2008); http://dx.doi.org/10.1063/1.3005996 (10 pages) | Cited 20 times

Online Publication Date: 3 November 2008

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Real-time display of processed Fourier domain optical coherence tomography (FDOCT) images is important for applications that require instant feedback of image information, for example, systems developed for rapid screening or image-guided surgery. However, the computational requirements for high-speed FDOCT image processing usually exceeds the capabilities of most computers and therefore display rates rarely match acquisition rates for most devices. We have designed and developed an image processing system, including hardware based upon a field programmable gated array, firmware, and software that enables real-time display of processed images at rapid line rates. The system was designed to be extremely flexible and inserted in-line between any FDOCT detector and any Camera Link frame grabber. Two versions were developed for spectrometer-based and swept source-based FDOCT systems, the latter having an additional custom high-speed digitizer on the front end but using all the capabilities and features of the former. The system was tested in humans and monkeys using an adaptive optics retinal imager, in zebrafish using a dual-beam Doppler instrument, and in human tissue using a swept source microscope. A display frame rate of 27 fps for fully processed FDOCT images (1024 axial pixels×512 lateral A-scans) was achieved in the spectrometer-based systems.
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87.63.L- Visual imaging
87.64.M- Optical microscopy
84.30.Sk Pulse and digital circuits
87.85.-d Biomedical engineering
42.66.-p Physiological optics

Development of a portable therapeutic and high intensity ultrasound system for military, medical, and research use

George K. Lewis, Jr. and William L. Olbricht

Rev. Sci. Instrum. 79, 114302 (2008); http://dx.doi.org/10.1063/1.3020704 (7 pages) | Cited 4 times

Online Publication Date: 11 November 2008

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We have developed a portable high power ultrasound system with a very low output impedance amplifier circuit (less than 0.3 Ω) that can transfer more than 90% of the energy from a battery supply to the ultrasound transducer. The system can deliver therapeutic acoustical energy waves at lower voltages than those in conventional ultrasound systems because energy losses owing to a mismatched impedance are eliminated. The system can produce acoustic power outputs over the therapeutic range (greater then 50 W) from a PZT-4, 1.54 MHz, and 0.75 in diameter piezoelectric ceramic. It is lightweight, portable, and powered by a rechargeable battery. The portable therapeutic ultrasound unit has the potential to replace “plug-in” medical systems and rf amplifiers used in research. The system is capable of field service on its internal battery, making it especially useful for military, ambulatory, and remote medical applications.
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43.38.-p Transduction; acoustical devices for the generation and reproduction of sound
43.80.Vj Acoustical medical instrumentation and measurement techniques
87.63.D- Ultrasonography
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High power microwave switching utilizing a waveguide spark gap

J. Foster, G. Edmiston, M. Thomas, and A. Neuber

Rev. Sci. Instrum. 79, 114701 (2008); http://dx.doi.org/10.1063/1.3010381 (5 pages) | Cited 5 times

Online Publication Date: 11 November 2008

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A reduction in the rise time of a 2.85 GHz high power microwave (HPM) pulse is achieved by implementing an overvoltaged spark gap inside a waveguide structure. The spark gap is oriented such that when triggered, the major electric field component of the dominant TE10 mode is shorted. The transition from a transmissive to a highly reflective microwave structure in a relatively short period of time (tens of nanoseconds) creates a means to switch multimegawatt power levels on a much faster timescale than mechanical switches. An experimental arrangement composed of the waveguide spark gap and a high power circulator is used to reduce the effective rise time of a HPM pulse from a U.S. Air Force AW/PFS-6 radar set from 600 ns down to 50 ns. The resulting HPM pulse exhibits a much more desirable excitation profile when investigating microwave induced dielectric window flashover. Since most theoretical discussions on microwave breakdown assume an ideal step excitation, achieving a “squarelike” pulse is needed if substantial comparison between experiment and theory is sought. An overview of the experimental setup is given along with relevant performance data and comparison with computer modeling of the structure.
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84.40.Az Waveguides, transmission lines, striplines
84.32.Dd Connectors, relays, and switches
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Two-tint pump-probe measurements using a femtosecond laser oscillator and sharp-edged optical filters

Kwangu Kang, Yee Kan Koh, Catalin Chiritescu, Xuan Zheng, and David G. Cahill

Rev. Sci. Instrum. 79, 114901 (2008); http://dx.doi.org/10.1063/1.3020759 (4 pages) | Cited 10 times

Online Publication Date: 7 November 2008

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We describe a simple approach for rejecting unwanted scattered light in two types of time-resolved pump-probe measurements, time-domain thermoreflectance (TDTR) and time-resolved incoherent anti-Stokes Raman scattering (TRIARS). Sharp edged optical filters are used to create spectrally distinct pump and probe beams from the broad spectral output of a femtosecond Ti:sapphire laser oscillator. For TDTR, the diffusely scattered pump light is then blocked by a third optical filter. For TRIARS, depolarized scattering created by the pump is shifted in frequency by ≈ 250 cm−1 relative to the polarized scattering created by the probe; therefore, spectral features created by the pump and probe scattering can be easily distinguished.
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78.47.D- Time resolved spectroscopy (>1 psec)
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.30.-j Infrared and Raman spectra

Pulse accumulation, radial heat conduction, and anisotropic thermal conductivity in pump-probe transient thermoreflectance

Aaron J. Schmidt, Xiaoyuan Chen, and Gang Chen

Rev. Sci. Instrum. 79, 114902 (2008); http://dx.doi.org/10.1063/1.3006335 (9 pages) | Cited 31 times

Online Publication Date: 11 November 2008

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The relationship between pulse accumulation and radial heat conduction in pump-probe transient thermoreflectance (TTR) is explored. The results illustrate how pulse accumulation allows TTR to probe two thermal length scales simultaneously. In addition, the conditions under which radial transport effects are important are described. An analytical solution for anisotropic heat flow in layered structures is given, and a method for measuring both cross-plane and in-plane thermal conductivities of thermally anisotropic thin films is described. As verification, the technique is used to extract the cross-plane and in-plane thermal conductivities of highly ordered pyrolytic graphite. Results are found to be in good agreement with literature values.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
44.10.+i Heat conduction
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