bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of surface-emitting laser diodes by modulating the distributed Bragg mirror reflectivity: Small-signal analysis
Authors: Avrutin E. A. , Gorfinkel V. B. , Luryi S. , Shore K. A.
Published: July 2002

Cavity-loss control of surface emitting distributed Bragg reflector lasers by electro-optic modulation of the Bragg mirror reflectivity is shown to be more efficient at high frequencies than the conventional control by current modulation. Combining both means of control offers additional possibilities, such as the elimination of relaxation oscillations and the achievement of a pure frequency-modulation regime.
Carrier lifetime versus anneal in low temperature growth GaAs
Authors: Harmon E. S. , Melloch M. R. , Woodall J. M. , Nolte D. D. , Otsuka N. , Chang C. L.
Published: July 2002

The photoexcited carrier lifetimes in ex situ-annealed low temperature growth GaAs are measured with a femtosecond transient absorption experiment. The study encompassed two low temperature growth GaAs films with approximately 0.3% and 0.9% excess arsenic incorporated during growth. The observed lifetimes are found to be a function of the spacing of arsenic precipitates formed during the 30 s anneals to temperatures between 650 and 1000 °C. The carrier lifetime for unannealed films was found to be less than ∼200 fs. The carrier lifetimes increased from ∼2 to ∼10 ps as the average precipitate spacing was increased from ∼400 to ∼900 Å. These results are in sharp contrast to recent reports of subpicosecond lifetimes in similar GaAs annealed at 600 °C.
Fiber optic sensor for chlorinated hydrocarbons in water based on infrared fibers and tunable diode lasers
Authors: Krska R. , Kellner R. , Schiessl U. , Tacke M. , Katzir A.
Published: July 2002

A novel fiber optic evanescent wave spectroscopy (FEWS) system is based on a tunable diode laser (TDL) source, on a polymer-coated AgClBr infrared transmitting fiber, and on a mercury cadmium telluride detector. This system was used for sensing low levels of chlorinated hydrocarbons in water. The detection limit was 100 μg/ℓ (100 ppb), which is an improvement by a factor of 50 in comparison to a similar system that is based on a Fourier transform infrared spectrometer, and the measurement time was reduced by a factor of 3. The TDL-FEWS system shows significant potential for in situ monitoring of ground water.
Preferential donor–acceptor pairing results for ZnSe:Na
Authors: Radomsky L. , Yi G.-J. , Neumark G. F.
Published: July 2002

Preferential pairing between donors and acceptors, which results from the Coulomb attraction between ionized donors and acceptors, has frequently been suggested, but has been very difficult to establish conclusively. We here report definitive identification of such preferential pairing, from donor-acceptor pair luminescence. We observed identical close pair lines (both in location and in relative intensity) in two samples of Na-doped ZnSe, but the associated distant pair peak was observed at different energies in the two samples. We explain this by assuming that there is strong preferential pairing in one sample and weak or random pairing in the other.
Photoluminescence decay measurements of n- and p-type doped ZnSe grown by molecular beam epitaxy
Authors: Massa J. S. , Buller G. S. , Walker A. C. , Simpson J. , Prior K. A. , Cavenett B. C.
Published: July 2002

Time-resolved photoluminescence has been used to study carrier recombination in n- and p-type doped ZnSe at room temperature. A band-edge photoluminescence decay time of ∼240 ps has been measured for heavily doped n-type material together with a relaxation time of a few microseconds for the associated deep-level emission. The band-edge photoluminescence decay time for p-type doped material was ≤11 ps and is indicative of a high level of nonradiative Shockley–Read recombination.
(Dy0.5Er0.5)Al2: A large magnetocaloric effect material for low-temperature magnetic refrigeration
Authors: Gschneidner K. A. , Takeya H. , Moorman J. O. , Pecharsky V. K.
Published: July 2002

The low-temprature heat capacity and ac and dc magnetic properties of (Dy0.5Er0.5)Al2 have been studied as a function of magnetic fields up to ∼10 T. The magnetocaloric effect in (Dy0.5Er0.5)Al2 is 30% larger than that of the prototype material, GdPd. Magnetic measurements show that there is no measurable magnetic hysteresis above ∼17 K. These results suggest that (Dy0.5Er0.5)Al2 would be a significantly better magnetic refrigerant than GdPd.
Spectroscopy of the transient oscillations in a Nd3+-doped fiber laser for the four-level 4F3/2-4I11/2 (1060 nm) and three-level 4F3/2-4I9/2 (900-nm) transitions
Authors: Okhotnikov O. G. , Salcedo J. R.
Published: July 2002

We performed spectroscopic measurements of the relaxation oscillations in a tunable Nd3+-doped fiber laser for the four-level (4F3/2-4I11/2) and for the three-level (4F3/2-4I9/2) transitions. We observed that the relaxation oscillation frequency for the three-level transition exhibited a strong wavelength dependence; in contrast, the relaxation oscillation frequency for the four-level transition did not exhibit any wavelength dependence. A simple theory to explain this remarkable feature was developed, confirming that the wavelength dependence is related to the thermal laser level population, which is significant in three-level systems but negligible in four-level systems. This should be taken into account for a careful description of laser systems, and is also instrumental for predicting oscillator or amplifier performance.
New technique for measuring two-dimensional oxidation-enhanced diffusion in silicon at low temperatures
Authors: van Dort M. J. , Lifka H. , Zalm P. C. , de Boer W. B. , Woerlee P. H. , Slotboom J. W. , Cowern N. E. B.
Published: July 2002

In this letter, a new high-resolution technique is presented for determining the lateral extent of oxidation-enhanced diffusion (OED). A periodic grid of lines and spacings is used as an oxidation mask. It will be shown that a simple secondary ion mass spectroscopy measurement permits the extraction of parameters in the lateral direction with a resolution which can be as good as 10 nm. The lateral extent of OED is depth dependent, consistent with a physical model of point-defect recombination at the Si/SiO2 interface.
Ultralow dark current p-type strained-layer InGaAs/InAlAs quantum well infrared photodetector with background limited performance for T≤100 K
Authors: Wang Y. H. , Li Sheng S. , Chu J. , Ho Pin
Published: July 2002

An ultralow dark current normal incidence p-type strained-layer In0.3Ga0.7Al/In0.52Al0.48As quantum well infrared photodetector (PSL-QWIP) grown on (100) semi-insulating InP substrate by molecular beam epitaxy technique for 8–12 μm infrared detection was demonstrated for the first time. This PSL-QWIP shows background limited performance (BLIP) for T≤100 K, which is the highest BLIP temperature ever reported for a QWIP. Due to a 1.5% lattice mismatch between the substrate and quantum well, a biaxial tensile strain was created in the In0.3Ga0.7As well layers. As a result, the light-hole state becomes the ground state for the free hole with small effective mass. The dramatic increase of optical absorption can be attributed to the large in-plane density of states and the small light-hole effective mass as a result of heavy- and light-hole state inversion. The dark current density and BLIP detectivity for this PSL-QWIP were found to be 7×10−8 A/cm2 and 5.9×1010 cm−√Hz/W, respectively, at λp=8.1 μm, Vb=2 V, and T=77 K.
Adhesion force imaging in air and liquid by adhesion mode atomic force microscopy
Authors: van der Werf Kees O. , Putman Constant A. J. , de Grooth Bart G. , Greve Jan
Published: July 2002

A new imaging mode for the atomic force microscope (AFM), yielding images mapping the adhesion force between tip and sample, is introduced. The adhesion mode AFM takes a force curve at each pixel by ramping a piezoactuator, moving the silicon-nitride tip up and down towards the sample. During the retrace the tip leaves the sample with an adhesion dip showing up in the force curve. Adhesion force images mapping parameters describing this adhesion dip, such as peak value, width, and area, are acquired on-line together with the sample topography. Imaging in air gives information on the differences in hydrophobicity of sample features. While imaging a mercaptopentadecane-gold layer on glass in demineralized water, the adhesion force could be modulated by adding phosphate buffered saline.
New catalysts for diamond growth under high pressure and high temperature
Authors: Kanda Hisao , Akaishi Minoru , Yamaoka Shinobu
Published: July 2002

Diamond has been found to grow from copper, zinc, and germanium when temperatures and pressures in excess of those usually used for growth via conventional catalysts are used. Around their melting temperatures these metals are inert with respect to graphite. However, under the conditions used in this study, namely temperatures of 1600 °C and pressures of 6 GPa, they exhibit catalytic action. The conventional catalysts, which were first discovered by General Electric, act as catalysts immediately after melting in the presence of graphite, and this distinguishes them from the catalysts used in this study which should therefore be placed in a different category. A new model of diamond growth is proposed in order to explain the behavior of these new catalysts.
Strain in pseudomorphic films grown on arbitrarily oriented substrates
Authors: Yang Kai , Anan Takayoshi , Schowalter Leo J.
Published: July 2002

The constraint equations for the unit translation vectors of a pseudomorphic film grown on an arbitrarily oriented substrate are correctly given for the first time. The strain in a pseudomorphic film grown on an arbitrarily oriented substrate is calculated via energy minimization under the pseudomorphic constraint. The strain tensor and the rotation tensor are concisely expressed in terms of lattice mismatch, elastic constants, and the substrate orientation vector. An expression is given for the piezoelectrically generated electric field in a pseudomorphic zinc blende film.
Sharp excitonic photoluminescence from epitaxial InAs
Authors: Lacroix Y. , Watkins S. P. , Tran C. A. , Thewalt M. L. W.
Published: July 2002

The optically excited luminescence of epitaxial InAs has been studied at 1.4 K, revealing well-resolved emission lines identified as the exciton–polariton, neutral–acceptor–bound exciton principal and two-hole transitions, donor–acceptor pair band, and phonon assisted transitions. These features are seen in samples of high purity InAs grown by metalorganic chemical vapor deposition on InAs substrates using tertiarybutylarsine and trimethylindium. Only one acceptor species is observed, having a 1 S3/2–2 S3/2 transition energy of 13.39±0.01 meV, and an acceptor–bound exciton binding energy of 2.11±0.03 meV.
Flat-plate radiometer
Authors: Hager N. E.
Published: July 2002

A thermocouple-type radiometer is constructed by mounting a blackened thin-foil heat-flux sensor on a reflective heat-sink block. Either the sensor alone or the completed assembly is calibrated in a thermal conductivity apparatus. The device measures total hemispheric radiation and is estimated to be accurate to within 2%. Simplicity and ruggedness make the radiometer well suited for measuring output of radiant heaters in hostile factory environments.
Compact, movable Faraday cup for intense electron beam pulses
Authors: Matsuzawa Hidenori , Akitsu Tetsuya
Published: July 2002

A compact, axially movable Faraday cup of low noise level was devised for measuring an intense electron beam of a duration time of 10 ns or less, with a replaceable aperture to limit incident electron beams in diameter.
Accurate measurement of the temperature of a junction
Authors: Stievenard D. , Bourgoin J. C.
Published: July 2002

Knowledge of the temperature of a junction is very useful for experimenters or technologists. We propose here an easy but accurate method to measure it for any type of junction, isolated or in a device. The method is based on a numerical analysis of a transient signal, provided by the change of capacitance of the space-charge region of the junction due to the emission of majority carriers from a trap. This method has been tested on different junctions made on n-GaAs with traps introduced by electron irradiation or originating from the technology. Here we provide, for illustration, results showing the variation of a junction temperature as a function of the injected current density.
On the concentration, focusing, and collimation of x-rays and neutrons using microchannel plates and configurations of holes
Authors: Wilkins Stephen W. , Stevenson Andrew W. , Nugent Keith A. , Chapman Henry , Steenstrup Stig
Published: July 2002

A new class of focusing, condensing, and collimating devices for x rays, γ rays, and neutrons is described which is based on the use of microchannel plates (MCPs) or configurations of holes. As well as providing a simple collimating action due to the absorption of severely divergent rays in the channel walls, the microchannel-plate-type structures are capable of providing a focusing and collimating action arising from the reflection of near-grazing-incidence rays at the channel walls. The focusing action is in principle controllable by mechanical bending or slump forming of the channel plates or by appropriate shaping of the channel walls and is remarkably insensitive to source location, device alignment, and wavelength. Theoretical predictions for the performance of such devices are presented via both simple model calculations and Monte Carlo simulations. These suggest that some simple scaling relations hold between key parameters, and provide a guide to the optimum performance levels achievable with such devices for a wide range of geometries. Some experimental observations of the focusing action of MCPs for 0.071-nm x rays are presented. A wide variety of x-ray and neutron optical applications is possible.
First experimental experience with a VUV polarimeter at BESSY
Authors: Gaupp A. , Mast M.
Published: July 2002

A polarimeter has been designed and built to completely analyze the state of polarization of  VUV radiation. It is based on the changes in amplitude and phase occurring upon reflection from a metal surface. The first experimental experience indicates the usefulness of this device provided the alignment problem can be solved satisfactorily.
Apparent displacement of the synchrotron radiation beam observed on beamline 4 of the Photon Factory storage ring
Authors: Katsura T. , Kamiya Y. , Mitsuhashi T. , Nakamura N. , Haga K. , Iida A.
Published: July 2002

The photon beam radiating from the position-stabilized storage ring tended to show large vertical drift at some beamlines. It had earlier been pointed that the beam drift might be due to the local floor displacement which was caused by the thermal distortion of the storage ring building. An estimate of the floor displacement was made by using a simulation model which takes into account the thermal stress due to the sunbeam heating of the buildings, and it seemed to give an explanation for the amount of photon-beam displacement. This raised a question whether the local floor movement is fully responsible for the apparent displacement of the photon beam. Detailed study was primarily carried out for beamline 4. First, the level of the beamline was surveyed and found to be small compared with the amount of beam displacement actually observed. Second, when beam displacement was measured with respect to two independent frames of reference located at the upstream and downstream ends of the beamline, no difference was found between the two. Both the level survey and the displacement measurement led us to conclude that the large photon-beam drift was produced not by the local floor movement, but by the beam itself.
High-current surface-plasma negative-ion sources with geometrical focusing
Authors: Belchenko Yu. I. , Kupriyanov A. S.
Published: July 2002

Long-pulsed surface plasma multiaperture models with hydrogen negative-ions output of up to 1 A and with an average current density of 60 mA/cm2 are described. The experimental and simulated negative-ion production efficiencies of pure hydrogen and cesiated surface-plasma sources with geometrical focusing are compared.
A cylindrical furnace with homogeneous temperature distribution for use in a cubic high-pressure press
Authors: Kawashima Yasushi , Tsuchida Yoshihiko , Utsumi Wataru , Yagi Takehiko
Published: July 2002

A cylindrical furnace with a homogeneous temperature distribution was designed for use in a cubic press by using the difference method. This method consists of three tubes and is applicable to the very small sample chamber of high-pressure apparatus. The temperature distribution in the furnace thus designed was measured at high pressure and temperature using two methods: (1) by measuring the thermal expansion of NaCl contained in the sample chamber; and (2) by observing the area of molten Pb which was mixed with the NaCl. Both of these measurements were performed by high-pressure and temperature in situ x-ray techniques. It was confirmed from these experiments that the furnace has a homogeneous temperature distribution and the difference in temperature is less than 5 °C when the center is about 600 °C. The homogeneity in temperature is nearly constant, even when the thermal conductivity of the sample is decreased by two orders of magnitude.
New high-resolution electrostatic ion mass analyzer using time of flight
Authors: Hamilton D. C. , Gloeckler G. , Ipavich F. M. , Lundgren R. A. , Sheldon R. B. , Hovestadt D.
Published: July 2002

We have developed a high-resolution mass analyzer that utilizes a measurement of an ion’s time of flight (TOF) in an electrostatic field that is configured to produce a harmonic potential. The TOF corresponds to one-half period of a harmonic oscillator and is independent of ion energy, in analogy to the amplitude independence of a harmonic oscillator’s period, and is proportional to the square root of the ion’s mass per charge ratio. The TOF is determined from a start pulse from secondary electrons produced when the ion passes through a thin carbon foil (1–3 μg/cm2) at the entrance of the TOF region and a stop pulse from the ion striking a microchannel plate (MCP) upon exiting the region. The energy independence of the TOF implies there is no degradation of resolution from energy straggling in the foil. We have achieved a mass resolution M/ΔM (FWHM) of greater than 100 with a laboratory prototype. Three versions of this analyzer for solar wind measurements are included on upcoming space missions and will be flown on the GGS/WIND spacecraft, the SOHO spacecraft, and the ACE spacecraft.
Spatial Fourier calibration method for multichannel SQUID magnetometers
Authors: Bruno A. C. , Ribeiro P. Costa
Published: July 2002

When using multichannel SQUID magnetometers for biomagnetic applications, the correct measurement of the Tesla/volt calibration factor of each channel is of extreme importance, in order to avoid gross errors when analyzing the results. We propose a general calibration method valid for all kinds of gradiometer arrays. One of the main properties of this method is that the gradiometer position inside the cryogenic Dewar does not need to be known precisely. When tested, calibration factors with accuracies ranging from 0.3% to 0.8% were obtained. It is based on a spatial Fourier technique and on the fact that the gradiometer acts as a discrete spatial filter.
A simple miniature magnetic probe with inherent electrostatic rejection
Authors: Loewenhardt P. K. , Blackwell B. D. , Zhang Beichao
Published: July 2002

A modification of a basic center-tapped magnetic probe design has been developed wherein subtraction of capacitive signals is carried out by the probe itself. The electrostatic rejection of this probe is compared with other typical designs.
Experimental tests of a mass-angle spectrograph with poloidal ion optics
Authors: Bratschi O. , Ghielmetti A. G. , Shelley E. G. , Balsiger H.
Published: July 2002

A new mass spectrograph for making simultaneous measurements of the mass-angle distributions of charged particles in the energy range up to 30 keV has been tested. The analyzer serially combines two rotationally symmetric poloidal analyzers to achieve a nearly double-focusing image in the radial plane and a 360° field-of-view in the azimuthal direction. Experimental tests have provided information on first- and second-order imaging properties, and have furthermore led to the development of highly effective antiscattering baffles for reducing particle background. The experimental results obtained with this laboratory prototype agree well with the predictions of the semiempirical theory for poloidal analyzers.
A cryogenic test insert with a high vacuum sample space
Authors: Engelhardt R. , Rando N. , Peacock A.
Published: July 2002

An insert based on a top-loading, fully welded stainless-steel design, with a special steel-copper weld is described. It has been developed explicitly for pumped helium cryostats, down to a temperature of about 1.2 K. The principal characteristics of this insert are a large high vacuum sample space, the absence of any cold seal, and the reliability and flexibility of use. Typical applications are optical/UV/x-ray photon counting experiments based on cryogenic detectors and the development of advanced heterodyne receivers using Superconductor–Insulator–Superconductor junctions as mixers in the millimeter and submillimeter regimes.
Cryogenic apparatus for scattering and phase equilibrium studies
Authors: Londono J. D. , Cochran H. D. , Bienkowski P. R. , Shah V. M.
Published: July 2002

A cryogenic apparatus has been developed for neutron scattering and phase equilibrium studies on supercritical inert gas mixtures. Scattering and phase equilibrium studies can be performed in the same apparatus; the whole apparatus is transportable to any scattering facility. It centers on a stirred, batch, view cell of unique design. By changing only three parts of simple design (two windows, one sample cylinder) to an appropriate material, this apparatus can be used for studies involving wide or small angle scattering of neutrons or x rays. Its use can also be extended to pure fluids, liquids, and states away from the critical point. It operates within pressure and temperature ranges of 0–13.8 MPa and 20–300 K. To our knowledge this is the first neutron scattering cell with axial fluid mixing and with a temperature gradient of 10 mK or less over a large sample volume (1-cm diameter, 5-cm long). The accuracy and performance of the apparatus was tested on pure neon by reproducing its saturation curve and by performing small angle neutron scattering on some supercritical states.
Deformation apparatus for use in high-resolution, high-temperature studies of mantle rheology
Authors: Hanson David R. , Spetzler Hartmut A. , Getting Ivan C.
Published: July 2002

A uniaxial dead weight creep apparatus has been designed to investigate the low stress, low strain-rate rheologic behavior of refractory minerals. Displacement and displacement rate resolutions of 0.5 μm and 0.1 nm/s, respectively, on samples of 1.5-mm cross section and 3.0-mm length at temperatures up to 1900 K have been achieved. Oxygen fugacity is controlled to 0.1 log unit, load to 0.1 N, and temperature to 5 K. Maximum stresses applied were between 25 and 30 MPa. Use of this apparatus has allowed the investigation of the transient creep regime in olivine, an important mineral in the Earth’s mantle.
H− and D− scaling laws for Penning surface-plasma sources
Authors: Smith H. Vernon , Allison Paul , Sherman Joseph D.
Published: July 2002

The small-angle source (SAS), 4X source, and 8X source are Penning surface-plasma sources that produce high-current, high-brightness H− ion beams for accelerator applications. The scaling from the SAS (1X source) to the 4X source, and from the 4X source to the 8X source is at least as good as predicted by the scaling laws. In many instances, the scaling is better than predicted, particularly in the critical area of the efficiency with which H− ions are produced per unit of discharge power. Using ζ=jH−/FC, where FC is the cathode power density load, ζ4X≊2ζSAS and ζ8X≊1.5ζ4X. The jH− scaling is at least as good as predicted by the scaling laws—we have been able to produce the predicted H− current in both the 4X and the 8X sources. The SAS was scaled up in size to the 4X source, and the 4X source was scaled up in size to the 8X source, on the assumption that the effective kTH−=5 eV. We also assume that the effective kTH−=the effective kTD−. These temperature scalings appear to be obeyed. The D− current scaling appears to be even better than assumed, namely, jD−≊jH−.
Surface-plasma sources with an intense cathode and anode productions of negative ions
Authors: Belchenko Yu. I. , Kupriyanov A. S.
Published: July 2002

Two types of the surface-plasma sources of negative hydrogen ions developed at Budker Institute of Nuclear Physics are discussed. The source characteristics and the mechanism of negative ion production are presented. It is shown that several channels of plasma particle surface conversion and desorption are responsible for an intense negative ion production in these sources. The results of a detailed study of the quasistationary honeycomb and its comparison with the data for hollow-cathode Penning sources are presented.
High flux and high resolution beamline for elliptically polarized radiation in the vacuum ultraviolet and soft x-ray regions
Authors: Derossi A. , Lama F. , Piacentini M. , Prosperi T. , Zema N.
Published: July 2002

A dedicated beamline with a broad energy range of photons and with high flux and a high degree of circular polarization has been designed for the ELETTRA storage ring. The beamline exploits the circularly polarized radiation produced by an electromagnetic elliptical wiggler and cover the (5–1200) eV photon energy range using a double-incidence spherical grating monochromator.
Phase contrast studies of biological specimens with the x-ray microscope at BESSY (invited)
Authors: Schmahl Günter , Rudolph Dietbert , Guttmann Peter , Schneider Gerd , Thieme Jürgen , Niemann Bastian
Published: July 2002

The transmission x-ray microscope at the BESSY storage ring is being used for investigations in the fields of biology, biophysics, medicine, colloid chemistry, and soil sciences. The system has been instrumented for phase contrast studies with the possibility of quick change between imaging in amplitude and phase contrast mode. Phase contrast has the advantage of considerable higher image contrast and reduced radiation dosage compared to amplitude contrast. A cryogenic object chamber has been implemented on the x-ray microscope. First experiments have shown that at cryogenic temperatures the structural stability of biological specimens is increased by three orders of magnitude in comparison with unfixed wet specimens at room temperature.
Applications of a CCD detector in scanning transmission x-ray microscope
Authors: Chapman Henry N. , Jacobsen Chris , Williams Shawn
Published: July 2002

New operational modes have been added to the Stony Brook scanning transmission x-ray microscope at the NSLS by the incorporation of a CCD detector. A zone plate focuses x rays to a microprobe, through which a specimen can be scanned. The x rays transmitted by the specimen are detected in the far field, at high angular resolution, by the CCD. The microdiffraction patterns so obtained may be used in several ways to obtain information about the sample: by obtaining structural information about the specimen from the patterns on a point-by-point basis, by building up scanned images from signals derived from the CCD frames, or by deconvolving the four-dimensional dataset. These modes increase the resolution that can be achieved in the microscope, offer new imaging methods, and ways of obtaining phase and amplitude maps of a specimen.
Thomson scattering system on FTU tokamak: Calibration, operation, resultsa)
Authors: Orsitto F. , Brusadin A. , Giovannozzi E. , Santi D. , Bartiromo R. , Pizzolati P.
Published: July 2002

The Frascati tokamak upgrade (FTU) Thomson scattering system is employed for the measurement of the electron temperature and density spatial profiles along the vertical torus diameter in 19 spatial points up to ten times in a single plasma discharge with a spatial resolution ranging from 2 cm in the central region to 4 cm in the plasma edge. The radiation source is a Nd:YLF laser at 1053 nm. The scattered radiation is collected by two objectives: the first looks at the plasma center, the second at the plasma edge. Bundles of optical fibers in the focal plane of the objectives carry the scattered light from the tokamak hall to a set of 19 interference filter polychromators, whose transmission is 70% and the rejection of the stray light at the laser wavelength is 1/107. The detectors are avalanche photodiodes with a NEP of the order of 10−13 W/(Hz)1/2 at 1053 nm. The absolute calibration for the electron density measurement has been carried out by Raman scattering on hydrogen and deuterium. Examples of temporal evolution of Te and ne spatial profiles are presented for ohmic plasma heating, lower hybrid current drive, and pellet injection experiment. A comparison between scattering data with interferometer for the density measurement, and ECE for the electron temperature shows agreement between the diagnostics. The system is controlled by two computers: a real-time computer for the laser settings, while the detection system parameters and data acquisition are managed using CAMAC by the data acquisition system (DAS) of FTU.
An inexpensive hybrid video imaging system
Authors: Walkenstein J. A. , Pardo W. B. , Robertson H. S. , Monti M.
Published: July 2002

The core components of a low-cost hybrid imaging system are an 80386-based computer, a video digitizer board (frame grabber), and a consumer video camera/recorder. With the addition of a rotating mirror (or chopper), optical filters, and software from the Internet, this system becomes a powerful and versatile diagnostic tool. Although the system is bound by the NTSC or PAL video standards, an understanding of these limitations allows the development of techniques that fully utilize its characteristic spatiotemporal resolutions. The operation of the system is demonstrated via data acquisition from an ac neon Geissler tube.
Dielectric resonator for measuring the magnetic penetration depth at low temperature in high-T
c superconducting thin films
Authors: Mourachkine A. P.
Published: July 2002

Knowledge of magnetic penetration depth λ(T) at low temperatures allows one to determine the pairing state in the superconductors. A simple method for the evaluation of λ(T) of small (∼1 cm×∼1 cm), flat, high-Tc superconductive samples at low T is discussed. The resolution of the method is a few Å. In addition to high resolution, the method has several advantages including nondestructive analysis, flexibility in sample size, and minimal requirements on the dielectric resonator. The current distribution within the sample being tested can also be accurately calculated, the experimental setup is convenient, and the procedure is comparatively rapid and can be performed in the necktube of a liquid-helium storage Dewar. The measurements for YBCO thin films have been performed at 14.4 GHz.
High resolution low dose scattered gamma-ray tomography
Authors: Thoe R. S.
Published: July 2002

This paper discusses a technique which uses Compton scattered gamma radiation to obtain high contrast, highly spatially resolved, three-dimensional images in optically opaque objects. A highly desirable property of this technology is that this method allows the acquisition of radiographs without the necessity of placing the object between the source and detector. This paper describes a prototype apparatus which is capable of obtaining images with a spatial resolution of about 1 mm at a depth of 25 mm in steel of normal density with the source and detector both on the same side of the object. Some modeling calculations, reconstruction algorithms, and data verifying the performance of this technique will be presented as well as details of how the efficiency and throughput of this system could be increased by over two orders of magnitude.
Polarization reversal of stored proton beams in the Indiana Cooler
Authors: von Przewoski B. , Dezarn W. A. , Doskow J. , Hardie J. G. , Meyer H. O. , Pollock R. E. , Rinckel T. , Sperisen F. , Haeberli W. , Lorentz B. , Rathmann F. , Wise T. , Pancella P. V.
Published: July 2002

A spin flipper of reliable and robust long-term operation was developed and has been used successfully at the Indiana University Cooler Storage Ring. To reverse the polarization of the stored beam, the frequency of a rf solenoid is swept adiabatically across a depolarizing resonance frequency. Depolarizing sidebands to the resonance are eliminated by shorting out the ring’s bunching rf cavity prior to the frequency sweep. With the spin flipper it is no longer necessary to dump the stored beam and to refill the ring with protons of opposite spin state. Rather, beam accumulation continues without reversing the spin at injection, and instead the polarization of the stored beam is flipped periodically. Thus the luminosity is significantly increased when the flipper is used.
A versatile interface bus
Authors: Labbé R.
Published: July 2002

A versatile interface bus was designed. It allows the control of up to 16 instruments using an IBM XT/AT—or compatible—personal computer. Its main features are simplicity and flexibility to connect it with instruments not necessarily designed to be controlled by a computer, greatly improving their performance.
Near-field scanning optical microscopy in reflection: A study of far-field collection geometry effects
Authors: Weston Kenneth D. , DeAro Jessie A. , Buratto Steven K.
Published: July 2002

We have designed and demonstrated two simple and versatile reflection mode near-field scanning optical microscopes (NSOMs). In one scanner far-field collection is coaxial with the NSOM tip, and in the other scanner, the far-field collection is at a 45° angle to the NSOM tip. We quantitatively compare images obtained with the two scanners. While off-axis collection offers a significantly higher signal-to-noise ratio, it also introduces tip shadowing in samples with topographic features larger than approximately 40 nm. The additional contrast from the shadowing further complicates image interpretation and must be considered when performing NSOM in reflection with off-axis collection. In addition, we discuss some general issues that should be considered when designing a reflection NSOM.
Sensor measurement and experimental control in nuclear magnetic resonance imaging
Authors: Green Derrick P. , Balcom Bruce J. , Lees Thomas J.
Published: July 2002

A dual purpose sensor acquisition and experimental control system which functions in the demanding environment of a nuclear magnetic resonance imaging (NMRI) spectrometer is described. The system ensures accurate sensor readings during imaging and protects sensitive electronic equipment from the effects of the intense radio frequency pulses and magnetic field gradient switches in NMRI. A homebuilt isolation network was constructed with isolation transformers and optoisolators. A variety of hardware and software methods are implemented to ensure accurate sensor data. The system also allows for the ready incorporation of external events into the NMRI pulse sequence. LabVIEWTM, a graphical programming environment, is the heart of our acquisition/control system. LabVIEW’s graphical interface and modular design enables flexible programs to be constructed which are easily understood and modified by the user. Applications of the system, monitoring photopolymerization and controlling ultrasonic cavitation in conjunction with NMRI, are outlined.
Historical review of electron beam ion sources (invited)
Authors: Donets Evgeni D.
Published: July 2002

Thirty years have passed since the modern concept of the production of highly charged ions in dense electron beams was first proposed, and less since the first electron beam ion source (EBIS) was built and tested. Milestones from the EBIS history, and future prospects are described in view of today’s needs in the production and use of highly charged ions. Various versions of EBIS, such as the classic EBIS, the electron beam ion trap—EBIT, the cross-over EBIS (T)-XEBIS/T and others were constructed, studied, and used in different laboratories. The ion-by-ion and “evaporative” cooling techniques are used to increase the time of ion confinement in an electron beam, ion charge states and ion yield. An alternative way to increase the ion yield is an increase of the electron beam current. The different concept of an ion source based on EBIS which uses multiple reflection of primary electrons and formation of a so-called electron string state is studied as well. Stability of electron-ion systems and nonexcitation of internal EBIS structure are the main goals in the present EBIS studies. Fast extraction of ions from EBIS, which can be done during several microseconds makes efficient the single turn injection into ion synchrotrons.
Micro-machining workstation for a diode pumped Nd:YAG high-brightness laser system
Authors: Kleijhorst R. A. , Offerhaus H. L. , Bant P.
Published: July 2002

A Nd:YAG micro-machining workstation that allows cutting on a scale of a few microns has been developed and operated. The system incorporates a telescope viewing system that allows control during the work and a software interface to translate AutoCad files. Some examples of the performance are given. With this setup we demonstrate the possibility of machining within a few microns with a Nd:YAG laser.
Method of processing ion energy distributions using a Thomson parabola ion spectrograph with a microchannelplate image converter camera
Authors: Mróz W. , Norek P. , Prokopiuk A. , Parys P. , Pfeifer M. , Laska L. , Stöckli M. P. , Fry D. , Kasuya K.
Published: July 2002

A Thomson parabola ion spectrograph (TP) is a very useful tool for the investigation of pulsed laser ablation. Measurements performed with the TP give useful information about physical processes, ion species and their energy distributions, as well as charge states. For ions with the lower charge states, q<20, complete information about energy distributions of all ionization states of ions can be obtained from a single laser shot. For ions with higher ionization states, parabolas generated in the TP interfere and it is impossible to get energy distributions for all the ion species. In this situation, the registered ions are composed of a few groups with different charge states and different energies. The TP enables the charge states and energetic ranges of different ion groups to be estimated. This presentation describes a method of processing experimental results, obtained from a TP, using a microchannelplate (MCP) image converter. Ion energy distributions for C1+–C6+ and Ta1+–Ta12+ are shown, and the effects of correcting the obtained ion energy distributions for the detection efficiency of the MCP are illustrated.
High-resolution energy analyzer with a large angular acceptance for photoelectron spectromicroscopy applications
Authors: Belov V. D. , Yavor M. I.
Published: July 2002

A new design of an electrostatic electron energy analyzer is presented, that is characterized by a high energy resolution and a high efficiency of collection of photoelectrons originating from submicron areas. The analyzer uses an original low-aberration electrostatic mirror for collecting electrons, followed by a retarding hollow cylindrical lens and a hemispherical energy analyzer. Feasible modifications of the analyzer are discussed.
Digital scanning probe microscope controller for molecular manipulation applications
Authors: Humphry M. J. , Chettle R. , Moriarty P. J. , Upward M. D. , Beton P. H.
Published: July 2002

A versatile digital controller for scanning probe microscopy capable of data acquisition during molecular manipulation has been constructed. A commercially available digital signal processor (DSP) board connected to a Pentium PC and custom-built high voltage amplifiers were used to control a commercial ultrahigh vacuum scanning tunneling microscope and to perform molecular manipulations. Use of the DSP system to produce all analog outputs resulted in an extremely flexible system with complete control of the probe tip.
Ultrathin-film differential-thermal-analysis apparatus with simultaneous photoemission measurements
Authors: Yamamoto Yasushi , Enami Toshiaki , Kuroi Masakazu , Matsuie Noritaka , Ishii Hisao , Seki Kazuhiko , Ouchi Yukio
Published: July 2002

We developed an apparatus of differential thermal analysis (DTA) capable of simultaneous surface specific ultraviolet (UV) photoemission measurements to investigate thin-film phase transitions. The apparatus was installed in a vacuum chamber of 10−6 Torr range for thermal isolation and the measurements of UV photoemission. As a sample substrate, we used a thin (10 μm) copper sheet supported by two wires for optimal thermal resistivity. The performance of the apparatus was examined using a 650-Å-thick pentacontane (n-C50H102) film, which may exhibit a unique monolayer phase transition known as surface freezing. We observed two anomalies of DTA curve around the bulk melting temperature, one of which is apparently due to the bulk melting. Since the temperature dependence of the surface specific UV photoemission measurements showed corresponding changes in photoemission current, we could conclude that the other phase transition peak originates from the surface freezing effect. This demonstrates that our DTA-UV apparatus is sufficiently sensitive to examine such monolayer phase transitions.
Development of an isothermal titration microcalorimetric system with digital control and dynamic power Peltier compensation. I. Description and basic performance
Authors: Velázquez-Campoy A. , López-Mayorga O. , Cabrerizo-Vı́lchez M. A.
Published: July 2002

A detailed description of a differential isothermal titration microcalorimeter with Peltier compensation is reported here. It can be considered as a heat flux or conduction microcalorimeter with dynamic power compensation. The design, based on the twin principle, is very simple and the manufacture is of low cost and complexity. The system operation is completely automatized and computer controlled, including the data acquisition tasks, the controller of the power compensation feedback loop and the reagent injection system. The purpose of the closed loop control is to improve the dynamic performance of the microcalorimeter, resulting in an enhanced sensitivity and accuracy. The instrument performance is demonstrated by calibration experiments showing that the baseline noise (root-mean-square of the temperature difference between the cells) to be 0.4 μK and the specific sensitivity about 2–8 μJ/ml. The main time constant can be reduced from 120 s (without power compensation) to 22 s or even less (with power compensation). In a subsequent article, a precise characterization of the microcalorimeter will be given.
Development of an isothermal titration microcalorimetric system with digital control and dynamic power peltier compensation. II. Characterization and operation mode. Myoglobin adsorption onto polymeric latex particles
Authors: Velázquez-Campoy A. , López-Mayorga O. , Cabrerizo-Vı́lchez M. A.
Published: July 2002

In a previous article a comprehensive description of an isothermal titration microcalorimeter with Peltier compensation was reported. This work deals with the characterization procedure and the operation mode. The transfer function parameters (time constants, calibration constants, and thermal properties of the system components) have been determined using a rigorous physical model for the microcalorimeter. To check the good performance of the instrument, titration experiments of cytidine and adenosine protonation have been carried out. Finally, as an example of the instrument applicability, differential heat measurements of myoglobin adsorption onto polymeric (polystyrene) latex particles are presented.
Estimation of lubricant thickness on a magnetic hard disk using acoustic emission
Authors: Ravikiran A. , Low T. S.
Published: July 2002

In this note we describe a simple and relatively inexpensive method to estimate lubricant thickness on a magnetic hard disk by making use of the acoustic emission generated at the head-disk interface during sliding in a contact start stop tester.
A two-point calibration of negative temperature coefficient thermistors
Authors: Fraden Jacob
Published: July 2002

Thermistors are the most commonly used temperature sensors. Depending on the required accuracy, they are either calibrated at one temperature point (low accuracy) or three points (high accuracy). In many mass produced instruments, a precision three-point calibration provides accuracy far better than practically required, while adding extra cost for the calibration. A two-point calibration method is described. It allows the reduction of the manufacturing cost while assuring calibrating errors of a thermistor less than ±0.03 °C for a temperature range from 0 to 70 °C. The method is based on the use of a simple logarithmic model where the material characteristic beta is not considered a constant but rather modeled as a linear function of temperature.
Optimization of operating conditions for a fast-axial-flow, radio frequency discharge-excited, room-temperature CO laser
Authors: Shimizu Kouki , Taniwaki Manabu , Sato Shunichi , Nagano Hiroshi , Maeno Kazuo
Published: July 2002

To optimize the operating conditions of a fast-axial-flow, rf discharge-excited, room-temperature CO laser, we have investigated the effects of the excitation rf frequency, the diameter of the discharge tube, and the contents of added gases and impurities in the laser gas. The laser output decreased with increasing concentration of H2O, and the laser oscillation ceased at concentrations above 560 ppm. An increase in the excitation rf frequency from 13.56 to 27.12 MHz resulted in an increase in the output power by 35%. The optimum concentrations of added noble gases depended on the diameter of the discharge tube. With the discharge tube at a diameter of 19 mm, the conversion efficiency increased with increasing concentration of added Kr or Xe and the addition of Xe was more effective than that of Kr. For a tube diameter of 30 mm, however, the conversion efficiency decreased with increased concentration of added Kr or Xe and Xe was less effective than Kr. A maximum output of 910 W was obtained at a conversion efficiency of 14.7% at an rf input power of 6.2 kW using a single discharge tube with a diameter of 30 mm with 5% Kr added.
A new method to study metastable fragmentation of clusters using a reflectron time-of-flight mass spectrometer
Authors: L’Hermite J.-M. , Marcou L. , Rabilloud F. , Labastie P.
Published: July 2002

We propose a new method to study metastable fragmentation of clusters in a reflectron time-of-flight mass spectrometer. This method does not require any modification of the standard apparatus. No preselection of parents is needed: all fragmentation reactions can be analyzed by recording a few numbers of spectra obtained by changing only the repelling voltage of the reflectron Vref. The evolution of a peak as a function of 1/Vref is a straight line. The extrapolation of this line at 1/Vref=0 gives the mass of the parent M and its slope gives the mass of the fragment m: the whole decay channel set for all parents can be determined unambiguously. The intensity of a peak is stable when scanning Vref: rather accurate branching ratios can be determined. Application to the fragmentation of clusters containing Ag, H2O, and SF6 is presented. Masses are measured to an accuracy of about 0.5%, allowing for example to study independently the dissociation channels involving the two natural isotopes of silver, Ag107 and Ag109.