bluuebunny/crossref_metadata_2025 huggingface dataset:
Miniature fiber-optic refractometer for measurement of salinity in double-diffusive thermohaline systems
Authors: Bergman T. L. , Incropera F. P. , Stevenson W. H.
Published: July 2002

Information on salinity and temperature distributions is important in the study of thermohaline systems. In order to overcome difficulties associated with existing measurement methods, a miniature fiber-optic probe has been developed. The probe, which is capable of local quasisteady and fluctuating salinity and temperature measurements, is easily constructed, calibrated, and utilized. Probe measurements compare favorably with results obtained using a slant-wire shadowgraph technique and clearly show local phenomena in double-diffusive thermohaline systems.
Systematic errors in conductimetric instrumentation due to bubble adhesions on the electrodes: An experimental assessment
Authors: Neelakantaswamy P. S. , Rajaratnam A. , Kisdnasamy S. , Das N. P.
Published: July 2002

Systematic errors in conductimetric measurements are often encountered due to partial screening of interelectrode current paths resulting from adhesion of bubbles on the electrode surfaces of the cell. A method of assessing this error quantitatively by a simulated electrolytic tank technique is proposed here. The experimental setup simulates the bubble-curtain effect in the electrolytic tank by means of a pair of electrodes partially covered by a monolayer of small polystyrene-foam spheres representing the bubble adhesions. By varying the number of spheres stuck on the electrode surface, the fractional area covered by the bubbles is controlled; and by measuring the interelectrode impedance, the systematic error is determined as a function of the fractional area covered by the simulated bubbles. A theoretical model which depicts the interelectrode resistance and, hence, the systematic error caused by bubble adhesions is calculated by considering the random dispersal of bubbles on the electrodes. Relevant computed results are compared with the measured impedance data obtained from the electrolytic tank experiment. Results due to other models are also presented and discussed. A time-domain measurement on the simulated cell to study the capacitive effects of the bubble curtain is also explained.
High-voltage ac power supply with variable frequency output from 0.5 to 10 Hz
Authors: Tochitani Yoshiro
Published: July 2002

A special high-voltage ac power supply has been designed and constructed to supply a voltage with a peculiar waveform to a pair of electrodes sandwiching a dielectric liquid in which some rate process is to be electrically augmented. It consisted of two combined dc-to-dc inverters to which the primary voltage was controlled to a prescribed waveform. The output voltage is from 1.5 to 12.5 kV and the maximum current is 0.1 mA. The frequency range is from 0.5 to 10 Hz. The output bears a ripple which is as large as ±15% at a voltage of 12.5 kV. The distinctive features, besides the waveform, lie in that it simultaneously serves the two electrodes with voltages of the same magnitude and of different polarities so that the electric potential at the center of the electrodes is always maintained at the ground level, and that the modification of the output waveform is possible by making a change in the waveform to the dc-to-dc inverters.
Interface circuit between a capacitance meter (PAR 410) and a microcomputer (Apple II)
Authors: Bohlin K.
Published: July 2002

An interface circuit between a capacitance meter (PAR 410) and a microcomputer (Apple II) is presented. The interface circuit is constituted by a 12-bit D/A converter and a 10-bit A/D converter. A program has been written which utilizes the capacitance measurement for determination of physical parameters on both MOS devices and Schottky barrier diodes. The circuit is of general usefulness and can be adapted for other applications where capacitance measurements are of interest.
Mass spectrometer utilizing permanent magnets
Authors: Trow John R.
Published: July 2002

A fairly compact mass spectrometer suitable for vacuum use, and requiring no cooling, was built utilizing permanent magnets. A uniform, variable magnetic field, with a maximum of 2800 G, was produced in a 0.6-cm-wide gap by using a rotating block of samarium–cobalt permanent magnets, and an iron yoke assembly.
Computer-assisted high-voltage waveform measurement
Authors: Walter C. W. , McMillian G. B. , Smith K. A. , Dunning F. B.
Published: July 2002

A simple apparatus for computer-assisted measurement of a repetitive, high-voltage pulse waveform is described. The apparatus has been applied in studies of electric field ionization of atoms in high Rydberg states, but is generally applicable in other areas.
Pockels readout optical modulator: An x-ray imaging detector that maintains good efficiency over a broad energy range
Authors: Stokes Grant H. , Stupin David M. , Elliott Norman E. , Graser Michael
Published: July 2002

We present measurements of the performance of a Pockels readout optical modulator (PROM) x-ray imaging detector using a 30-kV constant potential bremsstrahlung source. A nickel step wedge was used to measure the spatial resolution and noise of the PROM image. PROMs are unique high-efficiency x-ray detectors that image with good spatial resolution over a wide range of x-ray energy. The PROM is constructed from an optically transparent, active crystal that is sensitive to x-ray dose. This unique construction allows the use of a thick crystal to increase efficiency for x-ray detection while avoiding the spatial resolution degradation that usually accompanies thick detectors.
Total automation of static and dynamic light scattering experiments with the aid of a special purpose robot
Authors: Ganz A. M. , Boeger B. E.
Published: July 2002

A fully automated laser light scattering apparatus has been built and is now operational. A specially designed robot moves samples from a thermostatted holding rack to the spectrometer water bath. Use of a smoothly operating robot enables the study of multiphase fluids without disturbing sensitive interfaces. A computer controls virtually all the supporting hardware. Laser input intensity is adjusted by a rotating polarizer and the scattering angle is varied by a stepper motor built into the goniometer. Fiber optics and a silicon photodetector are employed to determine incident and transmitted intensity. Variables such as time base and prescaling on the autocorrelator are optimized by the software according to the characteristics of the sample. Safety and verification procedures are described. The trade off in signal-to-noise requirements of both dynamic and classical light scattering are considered in order to enable simultaneous dynamic and classical intensity measurements. An example of the utility of the instrument for studying critical phenomena is given.
Application of a microwave preamplifier to an ESR spectrometer
Authors: Grampp Günter
Published: July 2002

The aim of this investigation was to measure the sensitivity improvement reached on a commercial homodyne X-band ESR spectrometer by installing a microwave GaAs–FET type preamplifier (8.5–9.6 GHz). Up to a power level of 1 mW a factor of 3 was obtained in signal improvement. Saturation occurred near 30 mW. Both theoretical and experimental results were described and discussed. In addition, a circuit diagram for easy installation of the microwave preamplifier was given.
Versatile X-UV spectrogoniometer with multilayer interference mirrors
Authors: Arbaoui M. , André J. M. , Couillaux P. , Barchewitz R.
Published: July 2002

A versatile X-UV spectrogoniometer based on a modular system is described. The heart of the apparatus is a computer-controlled θ-2θ goniometer with 1.8 arcs θ angular resolution. This main unit can be connected to with a (+1, −1) double-crystal premonochromator and a double-mirror high-frequency rejector. The dispersive performance of a multilayer interference mirror (MIM) and a lead stearate pseudocrystal are compared at three wavelengths: 13.3 Å (Cu-Lα), 44.8 Å (C-Kα), and 67.7 Å (B-Kα). The MIM appears as a useful dispersing device for a low resolution flat ‘‘one-crystal’’ spectrometer in this spectral region.
An improved optical system for photofield emission
Authors: Donders P. J. , Hadley K. W. , Lee M. J. G.
Published: July 2002

An improved optical system has been designed for use in experimental studies of photofield emission. By increasing the angle of convergence of the focused laser beam onto the field emitter a smaller focal spot is obtained. For a given beam intensity, this results in a substantial increase in the irradiance at the emitting surface. In addition, the smaller focal spot reduces the laser-induced temperature rise of the field emitter for a given irradiance. The design of the improved optical system is discussed and its performance is evaluated.
State-of-the-art time-resolved emission Mössbauer spectrometer
Authors: Purcell Keith F. , Edwards Michael P. , Curnutte Basil , Eck John S.
Published: July 2002

We report on the design, construction, and operation of a time-resolved emission Mössbauer spectrometer which has as its central component a microcomputer for data recording and manipulation. The philosophy of data acquisition affords previously unrealized flexibility in data handling and spectral analysis in both the time and frequency domains.
Accurate (0.25 mrad) perpendicular alignment of a continuous-wave single-mode dye laser beam and an atomic beam
Authors: Verheijen M. J. , Beijerinck H. C. W. , Verster N. F.
Published: July 2002

Two simple methods are described for an accurate perpendicular alignment of a laser beam and an atomic beam, which is required for a velocity independent, i.e., Doppler-free interaction, of the laser beam with the atomic beam. With the first method a free running single-mode cw dye laser beam and an atomic beam are aligned perpendicular with an accuracy of 0.25 mrad. This alignment takes typically 2 h. The second method needs a laser beam that is absolutely stabilized to the investigated atomic transition. With this method a 0.2-mrad accurate perpendicular alignment is obtained within only 5 min.
Laser frequency offset synthesizer
Authors: Lewis D. A. , Evans R. M. , Finn M. A.
Published: July 2002

A method for servolocking the beat frequency between two lasers is described in which the lasers in effect replace the voltage-controlled oscillator in an indirect frequency synthesizer. The system is simple, relatively free from systematic frequency errors, and has good stability as characterized by Allan variance measurements.
Passive radon/thoron personal dosimeter using an electrostatic collector and a diffused-junction detector
Authors: Bigu J. , Raz R.
Published: July 2002

A solid-state alpha dosimeter has been designed and tested suitable for personal and environmental radon/thoron monitoring. The dosimeter basically consists of an electrostatic collector and an alpha-particle counting system with spectroscopy capabilities. The sensitive volume (∼20 cm3) of the electrostatic collector consists of a cylindrically shaped metal wire screen and a diffused-junction silicon alpha-detector covered with a thin aluminized Mylar sheet. A dc voltage (∼500 V) is applied between the wire screen and the Mylar sheet, with the latter held at negative potential relative to the former. Data can be retrieved during or after sampling by means of a microcomputer (Epson HX20) via a RS–232 communication interface unit. The dosimeter has been calibrated in a large (26 m3) radon/thoron test facility. A linear relationship was found between the dosimeter’s alpha-count and both radon gas concentration and radon daughter working level. The dosimeter is mounted on top of an ordinary miner’s cap lamp battery and is ideally suited for personal monitoring in underground uranium mines and other working areas. The dosimeter presented here is a considerably improved version of an earlier prototype.
Simple, inexpensive autocorrelator for use with cw mode-locked lasers
Authors: Demmer D. R. M. , Leyland A. , Szymanski M. , Steer R. P.
Published: July 2002

An improved method of obtaining variable pulse spacing for use in a cw SHG autocorrelation interferometer is described.
Improved flow visualization technique for quantitative velocity measurement in small test volumes
Authors: Johnson G. R. , Marschall E. , Esdorn J. H.
Published: July 2002

A flow visualization technique which utilized a photochromic dye in solution was introduced by Popovich and Hummel in 1967. The dye was activated along narrow trace lines by passing sharply focused beams from an ultraviolet light source through the solution. The movement of the dye traces were recorded by high-speed cinematography and velocities were found from analysis of the resulting pictures. Two variations to this basic method are described. These permit more accurate velocity measurements to be made in certain liquid systems where test volumes are small or near physical barriers, and where the flow is two dimensional or is time dependent. Manufacture of a suitable dye and construction of an inexpensive pulse laser which may be used as an ultraviolet light source are discussed.
Measurements on a dc volume H− multicusp ion source for TRIUMF
Authors: Kendall K. R. , McDonald M. , Mosscrop D. R. , Schmor P. W. , Yuan D. , Dammertz G. , Piosczyk B. , Olivo M.
Published: July 2002

We describe a dc volume H− source, employing multicusp plasma confinement, which has been constructed for use with the TRIUMF cyclotron. An extracted H− current density of 12 mA/cm2 has been obtained. Beam emittance and brightness have been measured as a function of current density and beam fraction. Beam brightness values for normalized beam emittances of the order of 0.2 πmm mrad at 81% beam fraction are typically 10 mA/(mm mrad)2 [equivalent rms B=223 mA/(mm mrad)2].
Time response of various types of photomultipliers and its wavelength dependence in time-correlated single-photon counting with an ultimate resolution of 47 ps FWHM
Authors: Bebelaar Dick
Published: July 2002

The time response of the classical photomultipliers 56DUVP and XP2020 in time-correlated single-photon counting has been measured at several wavelengths between 257 and 630 nm with a best result of 235 ps FWHM. Also, the time response has been measured of the microchannel-plate photomultiplier R1564U-01 and the crossed-field photomultiplier VPM-154M at the two wavelengths 273 and 546 nm. The best result was 47 ps at λ=273 nm. The use of a fast constant-fraction discriminator was crucial. The origin of after pulses in the time response curve of photomultipliers is discussed.
Sealed-off CO2 laser with In–Au alloy sealing
Authors: Iehisa N. , Fukaya K. , Karube N.
Published: July 2002

The In–Au alloy sealing was found to satisfy all the requirements imposed on the sealed-off CO2 lasers. The sealing between different materials such as quartz, SUS 303, Si, and ZnSe was shown to withstand the thermal shock test, and gave the He leak rate lower than 1×10−9 atm cc/s both before and after the tests. It was also proved that the transmittance characteristics of dielectric coated output couplers did not change after the sealing. The sealed-off CO2 lasers with La1−xSrxCoO3 perovskite oxide cathodes sealed with this technique produced the operational life of 3000 h at the laser power level of 50 W/m.
UHV sample mount for the temperature range 10–1300 K
Authors: Palmer R. E. , Head P. V. , Willis R. F.
Published: July 2002

We describe a sample mounting facility capable of cooling a graphite crystal to temperatures of around 10 K (to enable investigation of low-temperature physisorbed phases) and which at the same time permits the crystal to be heated to 1300 K for surface cleaning. A demountable resistive heating mechanism avoids the conductive loading of the sample which normally inhibits the attainment of very low temperatures.
Inert gas excimer radiation from a free jet expansion
Authors: Baldwin K. G. H. , Swift R. Paul , Watts R. O.
Published: July 2002

A molecular beam source incorporating a dc discharge is used to study the emission spectrum of helium excimers near 600 Å and of argon excimers near 1070 Å. It is shown that under certain conditions the strength of the excimer radiation approaches that due to the helium resonance lines. The new source is expected to be useful for studying other excimers in the vacuum ultraviolet region of the spectrum.
Inexpensive transistor curve tracer
Authors: Seyhoonzadeh Amir , Chang Hong-Young , Lonngren Karl E.
Published: July 2002

This paper describes an inexpensive versatile electronic circuit which will allow a conventional oscilloscope or an XY recorder to be used as a transistor curve tracer. It can also be used to obtain Langmuir probe characteristics in plasma physics experiments.
Hybrid clock oscillator modules as deposition monitors
Authors: Huner B. , Klinkhachorn P. , Overton E. B.
Published: July 2002

The construction of an inexpensive vacuum deposition monitor made from commercially available hybrid quartz-crystal oscillator modules is described. The monitor is intended for use in odd-job vapor-plating applications. The design, however, has distinct advantages over conventional deposition monitors which suggests that it might have broader applications. Both the sensor crystal and its oscillator and the reference oscillator are placed together in the vacuum system. Thermal gradients and capacitance variations which potentially limit the sensitivity of the system are eliminated. Even without water cooling at deposition rates approaching 45 Å/s and deposition times exceeding 100 s a linear response for the monitor is observed.
Ru(bipy)3Cl2 luminescence as optical step signal for detector testing
Authors: Brettel K. , Schlodder E.
Published: July 2002

The luminescence of tris(2, 2′-bipyridyl)ruthenium(II)chloride [Ru(bipy)3Cl2] excited by picosecond-laser pulses is introduced as an optical step signal for testing of the time response of optical detection systems in the time range of a few nanoseconds.
Pulsed 500-MHz arbitrary waveform generator
Authors: Adler R. J. , Busby K. O.
Published: July 2002

Unipolar and bipolar arbitrary waveform generators (AWGs) are described. Starting from a single 2-ns-wide pulse, a train of 2-ns-wide, variable amplitude pulses are formed by splitting the initial pulse into multiple, equal amplitude pulses and then delaying and attenuating each of these pulses separately. By choosing the proper attenuation (pulse amplitudes) and adding the train of pulses together, an arbitrary unipolar waveform can be constructed. With the addition of a second pulse generator of opposite polarity, an arbitrary bipolar waveform can be generated.
Small multicusp H− source
Authors: Leung K. N. , Ehlers K. W. , Hauck C. A. , Kunkel W. B. , Lietzke A. F.
Published: July 2002

High-quality H− beams have been generated from a multicusp source equipped with a permanent magnet filter. It is shown that a large improvement in H− yield can be achieved by employing a small multicusp source, fabricated with the proper wall material and extraction chamber length. From this small source, H− current densities higher than 250 mA/cm2 have been extracted from a 1-mm-diam aperture for a discharge voltage of 150 V and a discharge current of 450 A. When the source is operated with deuterium, the extractable negative ion current density is reduced by approximately 30%.
Molecular electron diffraction from a space-charge limited beam
Authors: Faust W. L. , Ewbank J. D. , Monts D. L. , Schafer L.
Published: July 2002

We are developing an apparatus to employ gas electron diffraction (GED) for the study of transient molecular species generated by a pulsed excimer/dye-laser system, in a new type of excite-and-probe experiment. This paper treats problems which arise in design of a suitable pulsed electron-beam source, to provide relatively high instantaneous current. Standard electron-beam theory is extended to define focal conditions under which sharp patterns may be recorded. We have characterized several components of blur and distortion, particularly those due to electrostatic repulsion between the main beam and the diffracted electrons. The analysis may find use in other work, e.g., with microscopic beams.
Enhanced state-machine pulse programmer for very-high-precision pulse programming
Authors: Wachter E. A. , Sidky E. Y. , Farrar T. C.
Published: July 2002

An enhanced state-machine pulse programmer has been developed for use in microcomputer-controlled instrumentation; the device uses TTL logic, and is capable of operation with a 100-MHz clock. A hybrid counter is utilized which restricts the high-frequency clock to a small portion of the whole device, thereby limiting overall demands on circuit performance. For the device, timing resolution is determined by the speed of the delay counter circuitry utilized, while minimum event duration is limited by access times of the static RAM used for program storage. The device reported here, which utilizes a 32-bit delay counter, and which has 32 kwords of 150-ns program memory, is capable of generating events with a duration between 150 ns and 42.9 s at a constant resolution of 10 ns; the maximum duration can be extended indefinitely if looping is utilized. The hardware cost of the device, which has 16 output lines, is under $400.
Calibration of a surface barrier detector for 14-MeV neutron flux measurements on TFTR
Authors: Bosch H.-S. , Strachan J. D. , Barnes Cris W. , Nieschmidt E. B.
Published: July 2002

Nuclear reactions in silicon semiconductor detectors with an energy threshold above 2.5 MeV can be used to measure dt neutrons in a high background of low-energy dd neutrons. This allows the measurement of 14-MeV neutrons from the d(t, n)α reaction in deuterium plasmas, where the tritons from the d(d, t)p reaction create 14-MeV neutrons due to burnup. Measurements with a surface barrier detector are presented together with the calibration of such a detector to measure the absolute 14-MeV neutron source strength.
Franck–Condon energy spread in diagnostic neutral-particle-beam probes
Authors: Foote James H.
Published: July 2002

Plasma potentials can be measured in open-ended magnetic-fusion experiments with neutral beams injected at angles within the loss cone. Beam atoms that are ionized by the plasma follow magnetic-field lines and leave the machine with energy equal to their original beam energy plus the potential through which they have dropped. These diagnostic neutral beams often are composed of hydrogen or deuterium, and they can have components with energy less than the full beam energy because of the breakup of diatomic and triatomic molecules. The Franck–Condon energy released in this breakup can create a considerable energy spread in these lower-energy components. Here experimental results for this spread are summarized, obtained while using neutral beams for plasma-potential measurements in the Tandem Mirror Experiment-Upgrade (TMX-U). These energy-spread results agree with theoretical estimates. This inherent energy spread is emphasized because it can be important in interpreting plasma-potential data obtained with neutral-particle-beam probes and because its existence is not always anticipated.
Improved cavity alignment system for Spectra Physics 380 D single-mode ring dye lasers
Authors: van der Spek A. M. , Magendans P. , Kemper A. H.
Published: July 2002

A description and working experience of an improved mechanical alignment system of a Spectra Physics 380 D ring dye laser is given.
Light collection and wavelength calibration for an extreme ultraviolet diode array spectrograph
Authors: Marconi M. C. , Schmerge J. F. , Rocca J. J.
Published: July 2002

We describe the use of a simple spherical aluminum-coated mirror to image the radiation of a distant XUV-emitting plasma in the slit of a vacuum spectrograph. Calculations to determine the optimum position and curvature radius of the mirror as a function of the divergence of the emitted plasma radiation are described. Efficient light collection by the grazing incidence mirror allows calibration of an intensified diode array used as a detector with a low-pressure (10−4 Torr) dc capillary discharge that does not require a complex differential pumping system.
Measurement of picosecond-pulse durations in the ultraviolet
Authors: Noordam L. D. , ten Wolde A. , van Linden van den Heuvell H. B.
Published: July 2002

A cross correlator for measurements of ultrashort UV pulses is described. The optical system is based on down-conversion of the UV pulses. The system can also be used to measure the second- and third-order autocorrelation function of pulses in the visible. The system is experimentally tested with UV pulses of 23-ps duration, that appear to be symmetric.
Interactive data-acquisition and evaluation system for quasielastic light scattering
Authors: Fuchs Heribert F. , Jorde Christian , Glatter Otto
Published: July 2002

A photoelectron-counting system has been constructed for all kinds of quasielastic light-scattering studies. The system consists of two parts, a data-acquisition unit, based upon a 16-bit microprocessor with additional hardware and software, and an evaluation unit, which can be any minicomputer, provided it has a parallel input port. The sample time resolution of the data-acquisition system is 500 ns at a data width of 4 bits, 1 μs at 8 bits, and 50 μs at 16 bits. The storage size is 2 Mbyte or more. The system also controls and remotes the measurement, as it is necessary for electrophoretic experiments or for time-resolved investigations. It is possible to store the raw data on a file. The evaluation either leads to a power spectrum or performs an autocorrelation function, with the time-critical parts written in assembly language.
Development and characterization of a charge-coupled device detection system for ion microscopy
Authors: Turner Lisa K. , Mantus David S. , Ling Yong-Chien , Bernius Mark T. , Morrison George H.
Published: July 2002

The construction of a prototype system capable of directly detecting and digitizing secondary-ion images using a charge-coupled device (CCD) is described. The CCD, alone, replaces the microchannel plate, fluorescent screen, and optical recording medium currently in use as the detection system on a CAMECA IMS-3f ion microanalyzer. Using the CCD as the image detector ensures that the secondary-ion signal is digitized in the most direct manner possible. A description of the hardware and image-acquisition process is given. Some of the first secondary-ion images to be detected using a CCD are presented, and the performance of the CCD as a detector of keV ions is evaluated. While preliminary trials appear promising, results indicate that the optimum efficiency is limited by the design of CCDs commercially available.
Simple top-loading cryostat insert for a SQUID magnetometer
Authors: Lamarche Gilles
Published: July 2002

A simple arrangement to introduce samples into a low-temperature cryostat from above and to regulate their temperature is described. This approach has been developed in designing a low-field SQUID magnetometer to operate from 4.2 K to room temperature. Some details on the assembly of the system and the procedures used in carrying out the measurements are given, together with an illustrative example of the performance of the magnetometer.
Pressure contact probe for resistivity measurements in the temperature range 77 K<T<200 K
Authors: Tritt T. M. , Ehrlich A. C. , Davis H. S.
Published: July 2002

We have designed and built a sample probe that is particularly well suited for measuring the resistivity and superconducting transition temperature Tc of bulk high-Tc materials of nonuniform shape, in the temperature range 77 K<T<200 K. The probe uses spring-loaded indium pressure contacts and allows electrical contact to be made without altering or contaminating the sample. The probe is relatively efficient because of its short turn-around time in mounting of samples and cylcing of temperature. The resistivity and Tc of a bulk Y1Ba2Cu3−xAgxO7 sample was measured and the results compared with those from a more elaborate sample probe and Dewar system.
Driven pendulum for studying chaos
Authors: Blackburn James A. , Vik S. , Wu Binruo , Smith H. J. T.
Published: July 2002

An instrument suitable for experimental studies of chaotic motion is described. It consists of a mechanical pendulum driven by both steady and alternating torques, together with interface electronics for data logging. An optical shaft encoder serves as the transducer for measuring the instantaneous pendulum coordinate. The entire system is controlled from a personal computer. Sample phase-plane and Poincaré plots are presented.
An easy modification of epoxy adhesive agents for low-temperature use
Authors: Mizuno Kiyoshi , Kume Kiyoshi
Published: July 2002

Various epoxy adhesive agents mixed with fine alumina powder have been used at low temperatures as an alternative to Stycast 2850GT.
A Macintosh based transistor curve tracer and analyzer
Authors: Lim Wee Beng , Tai Kim , Seyhoonzadeh Amir , Tao Jin , Cooney Jamie , Forsling Peter , Ghaemi Mohammad S. , Bailey Mark , Malik Norbert R. , Lonngren Karl E.
Published: July 2002

A technique to easily and quickly obtain, display, and analyze the transistor characteristics of pnp and npn bipolar junction transistors with a Macintosh personal computer is reported. Both the necessary hardware and software are described.
Integrating multichannel scaler for photon counting in laser radar application
Authors: Viterbini Maurizio , Adriani Alberto
Published: July 2002

A multichannel scaler for photon counting is described. Single photon pulses can be collected up to rates of 100 MHz during a programmed dwell time and an integration versus time can be done for each of the 999 channels on a user-programmable number of successive measurements. A live, dynamic display is provided. Data can be easily sent to any computer for recording or to a telemetry system for remote transmission.
Novel circuit for phase locking two mode-locked lasers
Authors: Kauffman J. F. , Côté M. J. , Smith P. G. , McDonald J. D.
Published: July 2002

We describe a phase-locking circuit which we have used to phase lock a cw mode-locked Nd:YAG which synchronously pumps a tunable dye laser with a mode-locked, Q-switched, cavity dumped Nd:YAG laser which is used to amplify the dye laser output. Though both lasers are free running, the phase locker maintains the timing jitter at less than 20 ps.
Evaluation of a galvanometric scanner for rapid tuning of CO2 lasers
Authors: Gautier Cynthia R. , Fox Jay A. , Ahl Jeffrey L.
Published: July 2002

Remote sensing of gaseous constituents in the atmosphere is possible with a single laser system operating at high (more than 100 Hz) pulse tuning rates so as to minimize the effects of atmospheric turbulence. This article investigates the possibility of using a galvanometric scanner as a rapid tuning device for both pulsed and continuous-wave CO2 lasers. Preliminary cw experiments, performed in anticipation of future heterodyne lidar development, indicated that lines could be switched at rates up to 77 Hz over the entire spectrum, while much greater rates were achieved by restricting the angular displacement of the galvanometer. When used with a transversely excited atmospheric (TEA) laser, the galvanometer was able to switch lines as fast as 140 Hz. However, amplitude-dependent position adjustments were necessary to compensate for settling time and/or thermal drift effects in order to obtain maximum energy output. A calibration curve was constructed and tested, but predictions of peak energy positions were accurate only for high gain lines. Using a 16-bit D to A converter with computer control, there was more than adequate resolution available to extract the maximum energy from each line, even at low gain line positions. Only a small amount (250 μrad maximum) of far-field beam wander was measured during tuning between any two lines at maximum tuning rates. Thus, it appears that tuning a CO2 laser at line switching rates greater than 70 Hz is possible, but requires a feedback mechanism and/or additional sensor for accurate positioning. Although the galvanometer itself is a relatively simple and compact device, practical utilization may require additional equipment or algorithms.
Low-frequency noise reduction in SQUID measurements using a laser-driven superconducting switch. Part A: Direct input circuit switching
Authors: Anderson J. T. , Cabrera B. , Taber M. A. , Felch S. B. , Tate J.
Published: July 2002

We describe a technique for substantially decreasing the noise in SQUID measurement applications which are intrinsically low frequency or dc and thus fall below the 1/f knee in the SQUID noise energy spectrum. The technique involves reversing the SQUID input leads at a chopping frequency of ∼100 Hz using laser-driven switches which form a double-pole–double-throw network. For sufficiently low noise switching, the demodulate output no longer contains the SQUID low-frequency noise but rather noise at the SQUID white-noise floor. We present data demonstrating the low noise performance of a single laser switch, and include the electronics design required for the full implementation of the scheme.
A pressure modulator radiometer for measuring stratospheric trace gases
Authors: Drummond J. R. , Turner D. , Ashton A.
Published: July 2002

This article describes a pressure-modulator instrument which is designed to measure trace constituents of the stratosphere from a balloon platform at an altitude of about 40 km. Double-sided limb-scanning allows profiling below the instrument and a direct determination of the instrument attitude from the radiance data. The instrument is described in detail and the methods of radiance measurement and calibration are discussed. Some of the supporting laboratory measurements are described. A concentration profile of carbon monoxide from 20 to 45 km is presented as an example of the results of the first series of flights.
PC-based interface for the Cameca IMS-3f ion microscope
Authors: Corcoran S. F. , Woodward W. S. , Linton R. W. , Griffis D. P.
Published: July 2002

The IBM PC and its various clones have found extensive use in the analytical laboratory. Hardware advances have been paralleled by the development of high and low level languages which allow the programmer to better access the capabilities of the PC for instrument control and data acquisition. This paper reports on the design and implementation of a PC based digital interface for the Cameca IMS-3f, a commercial secondary ion mass spectrometer. The IMS-3f was originally interfaced to a Hewlett-Packard 9845B computer. The new interface is completely compatible with the PC architecture and the existing IMS-3f circuitry. Implementation of the PC interface has enabled the incorporation of other commercially available PC hardware to enhance the analytical capabilities of the IMS-3f.
A novel approach to image processing in spin-polarized electron microscopy
Authors: VanZandt T. , Browning R. , Helms C. R. , Poppa H. , Landolt M.
Published: July 2002

The value of spin-polarized electron micrographs may be enhanced dramatically by the use of statistical image analysis techniques. These techniques can be used to display the vectorial nature of spin polarization data and give images of the highest magnetic contrast. The resulting images are free of the difficulties of interpretation inherent in the conventional dual grey-scale imaging technique and allow for quantification of the spatially resolved spin-polarized signal. The techniques are illustrated using the results from a Fe-4% Si crystal surface.
Accurate method for the determination of the refractive index of liquids using a laser
Authors: Zaidi A. A. , Makdisi Y. , Bhatia K. S. , Abutahun I.
Published: July 2002

Refractive indices of water and several organic liquids have been determined by an accurate method using a He-Ne laser. The method is in principle simpler than those used normally for such measurements. The experimental arrangement presented here is capable of yielding results with an accuracy of the order of 2×10−5. Comparison between the measured values and precise published results shows that they are nearly same within experimental parameters.
A fast, stable quadrature phase generator for multiple-pulse NMR
Authors: Shykind D. N. , Chingas G. C. , Pines A. , Shaka A. J.
Published: July 2002

We present a fast quadrature phase generator for multiple pulse NMR experiments. The circuit maintains quadrature phase balance to 0.005°, and exhibits less than 0.03 dB of amplitude drift over a 24 hour period. The generator combines fine adjustability with a switching speed of 30 ns. It requires only a small number of rf components and can be made to operate over decade bandwidths.
A novel ultrahigh vacuum scanning tunneling microscope for surface science studies
Authors: Haase O. , Borbonus M. , Muralt P. , Koch R. , Rieder K. H.
Published: July 2002

A novel design of a scanning tunneling microscope (STM) for surface science studies is described. The STM is fully compatible with ultrahigh vacuum (UHV) and offers the possibility of performing individual STM scans over a large region of the sample surface (≂10 mm2). The sample coarse approach is realized by a fine pitch screw, which shifts two wedges against each other. In order to incorporate the STM in an UHV system for the standard preparation and analyzing techniques of surface science, a special sample holder and sample transfer system has been developed. For defined heating of the sample, disconnectable electrical wiring for both a resistively heated oven and a thermocouple has been integrated within the sample holder.
Meissner effect torsion suspension
Authors: Karen Peter , Gillies George , Ritter Rogers
Published: July 2002

The first tests of a Meissner effect torsion suspension consisting of a hollow superconducting sphere suspended above a circular superconducting coil have yielded torsion coefficients comparable to or softer than those of 25 μm (0.001 in.) fibers of the type commonly used in gravitation experiments. Data show anomalous behavior which can be attributed to trapped flux. This has at least two effects: it stiffens the torsional restoring torque and it causes a torque about an axis which is oblique to the desired vertical axis. External Helmholz coils modify this by providing compensation for axial asymmetry to reduce the torsion coefficient by a factor of 5 in these experiments. Methods to separate and evaluate the various effects are presented. With improved leveling and field-free cool down in future experiments it is likely that much larger torsion reduction factors will be reached.
Exact translational properties of magnetic field expansions: Application to NMR
Authors: Hennessy Michael , Zou Hung Bin
Published: July 2002

In many instances it is required to specify the magnetic field coefficients at various points away from the origin. Spherical harmonic expansions which are typically used to define the magnetic field are complex when undergoing spatial translation. A simpler approach is to use Cartesian coefficients. In this work, an exact expression for the translation matrix for the field expansion in Cartesian coordinates is derived. This has applications in NMR imaging and spectroscopy for shimming small volumes away from the center.
Transformation of spherical harmonic and Cartesian magnetic field expansion coefficients
Authors: Hennessy Michael , Zou Hung Bin
Published: July 2002

Transformation properties of magnetic field expansion coefficients from spherical to Cartesian coordinates are given. Since the expansions are equivalent because they satisfy the Laplace equation, the transformation is unique. Spherical-to-Cartesian and Cartesian-to-spherical transformations are listed to fifth order.
In situ monitoring of the recrystallization process of InSb films by using a TV camera
Authors: Isai Masaaki , Ohshita Masahide , Beerens J. , Cheeke J. D. N.
Published: July 2002

Thin InSb films for highly sensitive magnetoresistance elements were prepared with high reproducibility by using a TV camera monitoring system. The recrystallization process was observed by viewing with real-time video recording. This monitoring system can detect the dendritic growth through the melting-solidification process as well as reevaporation during growth. This system was evaluated by investigating the correlations between morphology changes and parameters of the process, and also by the properties of the resulting films.
Apparatus for the study of the IR multiple-photon resonances of polyatomic molecules via the optothermal technique. II. The superconducting bolometer
Authors: Sanna G. , Nardi M. , Martinis L.
Published: July 2002

A superconducting (sc) transition edge bolometer has been developed to detect the rovibrational energy gained in a multiple-photon absorption process. In this experiment, the polyatomic molecules previously cooled in a pulsed nozzle beam are irradiated by a pulsed IR laser (see Part I). The bolometer resistive element is a suitably patterned granular aluminium film deposited on a sapphire substrate. When the film is set at its operation point near the center of the sc transition (∼2 K), it exhibits an electrical resistance R∼290 Ω and a temperature derivative (dR/dT)∼2×104 Ω/K. A voltage responsivity R∼2×104 V/W and an effective time constant τe ≂60 ns (for excitation by radiation) are simultaneously obtained. The high values of the film resistance and of the responsivity allow a useful signal to be directly extracted, with a favorable signal-to-noise ratio, from the cryostat, thus avoiding the use of a cryoamplifier. An unconventional solution is used to compensate, without appreciable noise contamination, the dc voltage produced by the bolometer bias current (∼3×10−4 A). Although rather wide band amplification (0–8.3 MHz) is used to observe the signal produced by the laser irradiation of the molecular beam, in real time and without distortion, an input noise total power Pn ≂2.5×10−9 W is obtained for a single laser shot. A further reduction of the noise can be obtained by the acquisition and averaging system described in Part I.
Picosecond laser timing by rf phase shifting
Authors: Johnson Carey K. , Qian Jun
Published: July 2002

Generation of picosecond and nanosecond time-scale time delays in a pump-probe laser system has been implemented without the use of an optical delay line, by rf-phase shifting of the mode-locking rf-signal. The system consists of dual picosecond dye lasers pumped by synchronized mode-locked, Q-switched, cw Nd:YAG lasers. The phase shifter operates with better than 10-ps precision and generates time delays from 0 to 26 ns.
Effect of pulse parameters on the deposition rate of hydrogenated amorphous silicon in a modified pulsed plasma discharge
Authors: Anandan C. , Mukherjee C. , Seth Tanay , Dixit P. N. , Bhattacharyya R.
Published: July 2002

Hydrogenated amorphous silicon films were deposited from 100% silane and disilane gases by a pulsed radio-frequency plasma chemical vapor deposition method in which a nonzero low power level was maintained. The pulse parameters were varied to study their effect on the deposition rate. It was found that the deposition rate depends both on the high power level and the dwell time. For a given high power level, the deposition rate is less than that of a continuous wave discharge up to a certain dwell time and increases beyond this value in both silane and disilane discharges. Onset of powder formation was observed beyond this crossover point.
LINDA: The experiment description language of the MDS-Plus data acquisition system
Authors: Manduchi G. , Flor G.
Published: July 2002

MDS-Plus is a general-purpose, data acquisition software package for pulsed physics experiments. It is based on the concept of an experiment model. The experiment model can be defined by means of the experiment description. The experiment description is a text description of the logical structure of the experiment, which defines the hardware structure together with the data acquisition actions, their sequence, and their interdependencies. The experiment description is then compiled into optimized internal data structures. A language-sensitive editor provides a user-friendly tool for producing syntactically correct experiment descriptions. The major design choices of syntax and implementation are presented and its integration with the preparation of the experiment is discussed.
Electron populations in the hot-electron ring region of mirrors and cusps, measured by a hyperbolic energy analyzer
Authors: Leal-Quiros Edbertho , Prelas Mark A. , Garcia-Otero Eduardo
Published: July 2002

A hyperbolic energy analyzer (HEA) was used to directly measure electron populations in the mirror mode and cusp mode of 14 keV average temperature electron rings in the Missouri magnetic mirror experiment (M4X). Two distinct populations of electrons were found in the mirror mode: a 17 eV group and a 147 eV group. Two distinct populations of electrons were also found in the cusp mode: a 22 eV group and a 167 eV group.
SPAM: A precision alignment device for spectrometer sightlines
Authors: Ramsey A. T. , Bartolick J. M.
Published: July 2002

As fusion devices become larger and their environments become harsher for instruments, diagnostics find themselves farther and farther away from the plasma. On TFTR, the UV survey spectrometer SPRED is over 9 m from the plasma. In these conditions, the alignment of the optical axis of the spectrometer to the desired portion of the plasma becomes both more critical and more difficult. We have developed a device which allows visual alignment along an optical axis both back into the spectrometer and toward the plasma. This SPRED alignment mechanism (SPAM) generates forward and backward laser alignment beams which are exactly coaxial, and gives coincident visual sightlines, also coaxial, in both directions. It is compact, hardy, precise, and cheap. SPAM also has been used to align visible and UV spectrometers with equal success.
Large magnetoresistance in polycrystalline La–Y–Ca–Mn–O
Authors: Jin S. , O’Bryan H. M. , Tiefel T. H. , McCormack M. , Rhodes W. W.
Published: July 2002

A large magnetoresistance ratio in excess of 10 000% (at 140 K, H=6 T) has been obtained in a sintered perovskitelike material with a composition of La0.60Y0.07Ca0.33MnOx. The doping of La–Ca–Mn–O with Y resulted in a decrease in the lattice parameter by ∼0.2%, and improved the magnetoresistance by an order of magnitude. The fact that such a large magnetoresistance can be obtained in a polycrystalline material implies that an epitaxial film growth may not be necessary for device applications, with fewer restrictions in substrate selection and processing parameters. Low field measurements at 77 K gave a magnetoresistance ratio of ∼6.5% at H=500 Oe in the La–Y–Ca–Mn–O sample.
Simple technique for loading hydrogen and other condensable gases in a diamond anvil cell
Authors: Lorenzana Hector E. , Goeb Laurent , Jeanloz Raymond
Published: July 2002

We describe a procedure for loading gases in a diamond anvil cell that requires a minimal investment of time and equipment. No specialized apparatus is needed since we precompress gases to only 35 bar prior to capture. We exploit the gasket hole deformation during loading to accomplish most of the sample compression.
Silicon nanostructures produced by laser direct etching
Authors: Müllenborn M. , Dirac H. , Petersen J. W.
Published: July 2002

A laser direct-write process has been applied to structure silicon on a nanometer scale. In this process, a silicon substrate, placed in a chlorine ambience, is locally heated above its melting point by a continuous-wave laser and translated by high-resolution direct-current motor stages. Only the molten silicon reacts spontaneously with the molecular chlorine, resulting in trenches with the width of the laser-generated melt. Trenches have been etched with a width of less than 70 nm. To explain the functional dependence of the melt size on absorbed power, the calculations based on a two-phase steady state heat model are presented, taking the temperature-dependent thermal conductivities and optical parameters into account.