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Nov 1994

Volume 65, Issue 11, pp. 3309-3594

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Signal‐to‐noise ratio in lock‐in amplifier synchronous detection: A generalized communications systems approach with applications to frequency, time, and hybrid (rate window) photothermal measurements

Andreas Mandelis

Rev. Sci. Instrum. 65, 3309 (1994); http://dx.doi.org/10.1063/1.1144568 (15 pages) | Cited 21 times

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Detailed analytical models of signal‐to‐noise ratios (SNR) of the conventional frequency domain (FD) and time domain (TD) photothermal measurement methodologies are developed and compared to the rate‐window photothermal method, both theoretically and experimentally. The conclusions of this study demonstrate that the lock‐in amplifier (LIA) rate‐window measurement mode in general, and the digital LIA mode, in particular, exhibits superior SNR to both the conventional frequency‐scanned LIA FD method and to the transient, time‐averaged TD method. Between the pulse‐duration‐scanned and pulse‐repetition‐period scanned rate‐window methodologies, the former clearly exhibits superior SNR. The theoretical conclusions are in agreement with experimental SNRs using the implementation of the foregoing measurement methodologies with simple infrared photothermal radiometric setups.  
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

A powerful eyesafe infrared aerosol lidar: Application of stimulated Raman backscattering of 1.06 μm radiation

W. Carnuth and T. Trickl

Rev. Sci. Instrum. 65, 3324 (1994); http://dx.doi.org/10.1063/1.1144569 (8 pages) | Cited 4 times

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A powerful infrared aerosol lidar operating at the eyesafe wavelength of 1.56 μm has been developed. More than 140 mJ per pulse are obtained from stimulated Raman backscattering narrow‐band Nd:YAG laser radiation in deuterium. The mobile lidar system was successfully applied during the VAST and MAPTIP international aerosol field campaigns in 1992 and 1993. A range between 0.3 and more than 10 km is demonstrated for slant‐path measurements in the presence of aerosols or cirrus clouds.
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42.68.Kh Effects of air pollution
42.68.Jg Effects of aerosols
42.68.Ge Effects of clouds and water; ice crystal phenomena
92.60.Mt Particles and aerosols

Construction of a time‐frequency two‐dimensional multiplex coherent anti‐Stokes Raman scattering spectrometer having 15 ps time resolution

Tahei Tahara and Hiro‐o Hamaguchi

Rev. Sci. Instrum. 65, 3332 (1994); http://dx.doi.org/10.1063/1.1145204 (7 pages) | Cited 6 times

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A picosecond time‐resolved multiplex coherent anti‐Stokes Raman scattering (CARS) spectrometer based on a new principle has been constructed using a femtosecond laser, nanosecond lasers, and a streak camera. The second harmonic of the output from the femtosecond Ti:sapphire oscillator/regenerative‐amplifier system is used for the photoexcitation. The second harmonic of a nanosecond Nd:YLF laser is used as CARS probing ω1 radiation, and the output of a nanosecond broadband dye laser is used as ω2 radiation. CARS signals, which are generated from the sample during the nanosecond probing pulses, are analyzed in the frequency domain by a spectrograph and are resolved in the time domain by a streak camera. This enables us multiplex CARS measurements not only in the frequency domain but also in the time domain (termed two‐dimensional multiplex CARS). Consequently, CARS spectra at various delay times are obtainable with a single measurement. Owing to the short duration and high stability of the femtosecond pumping pulses, time resolution as high as 15 ps has been achieved. Picosecond time‐resolved CARS spectra of all‐trans retinal and β‐carotene are presented to demonstrate the high capability of the constructed system. The factors which determine the time resolution of this CARS spectrometer are discussed.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
37.20.+j Atomic and molecular beam sources and techniques
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Rd Visible and ultraviolet spectrometers

A new continuum‐source atomic absorption spectrometer

David T. Williams and Alex E. S. Green

Rev. Sci. Instrum. 65, 3339 (1994); http://dx.doi.org/10.1063/1.1144570 (5 pages) | Cited 1 time

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Metallic toxics such as mercury, lead, cadmium, manganese, and other species are now of particular importance in relationship to coal‐based utilities, waste‐to‐energy plants, medical waste incinerators, and other industrial sources of atmospheric emissions or residues deposited in landfills. These metals are strong emitters or absorbers of middle ultraviolet light in the same general spectral region where important molecular pollutants are active. The furnace system of a commercial atomic absorption spectrometer, a continuum ultraviolet light source (a deuterium arc), and an oscillating entrance slit (adapted from second derivative spectroscopy) are applied to the measurement of toxic metals. The second‐harmonic ripple in the output of the photomultiplier tube is amplified by use of a tuned amplifier. A large signal‐to‐noise improvement is achieved when this system is calibrated and optimized with the metallic species of interest. This approximately compensates for the selectivity loss in using a continuum source in place of special lamps. Employment of this system is described in detail for the detection of mercury and the results are given for eight metals (Hg, Cd, Mn, Zn, Pb, Ni, Cu, and Cr). Data scatter when using this second‐harmonic spectrometer system is roughly 1/10 that of standard procedures.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
89.60.-k Environmental studies

A new‐regime Wiley–McLaren time‐of‐flight mass spectrometer

F. Chandezon, B. Huber, and C. Ristori

Rev. Sci. Instrum. 65, 3344 (1994); http://dx.doi.org/10.1063/1.1144571 (10 pages) | Cited 19 times

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A modified version of the classic Wiley–McLaren time‐of‐flight mass spectrometer (TOFMS) is presented here. Owing to a second‐order compensation of the initial position effect, a mass resolution m/δm higher than 2000 is obtained with large ion volumes, of the order of 0.2 cm3 for Na+55 (1265 a.m.u.). Sodium clusters Na+n with n up to 530 (≂12200 a.m.u.) are separated. The spectrometer can be used for the analysis of ionized clusters in a mass range from 1 to about 20000 a.m.u. as well as for the measurement of the kinetic energy of molecular fragments after a Coulomb explosion of a molecule. The performance of this spectrometer is demonstrated with sodium clusters and molecules.
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07.75.+h Mass spectrometers
36.40.-c Atomic and molecular clusters
33.15.Ta Mass spectra

A personal computer‐based nuclear magnetic resonance spectrometer

Constantin Job, Robert M. Pearson, and Michael F. Brown

Rev. Sci. Instrum. 65, 3354 (1994); http://dx.doi.org/10.1063/1.1144572 (9 pages) | Cited 12 times

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Nuclear magnetic resonance (NMR) spectroscopy using personal computer‐based hardware has the potential of enabling the application of NMR methods to fields where conventional state of the art equipment is either impractical or too costly. With such a strategy for data acquisition and processing, disciplines including civil engineering, agriculture, geology, archaeology, and others have the possibility of utilizing magnetic resonance techniques within the laboratory or conducting applications directly in the field. Another aspect is the possibility of utilizing existing NMR magnets which may be in good condition but unused because of outdated or nonrepairable electronics. Moreover, NMR applications based on personal computer technology may open up teaching possibilities at the college or even secondary school level. The goal of developing such a personal computer (PC)‐based NMR standard is facilitated by existing technologies including logic cell arrays, direct digital frequency synthesis, use of PC‐based electrical engineering software tools to fabricate electronic circuits, and the use of permanent magnets based on neodymium‐iron‐boron alloy. Utilizing such an approach, we have been able to place essentially an entire NMR spectrometer console on two printed circuit boards, with the exception of the receiver and radio frequency power amplifier. Future upgrades to include the deuterium lock and the decoupler unit are readily envisioned. The continued development of such PC‐based NMR spectrometers is expected to benefit from the fast growing, practical, and low cost personal computer market.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
07.05.Bx Computer systems: hardware, operating systems, computer languages, and utilities

Multigap parallel‐plate bracelet resonator frequency determination and applications

Patrick Gonord, Siew Kan, Anne Leroy‐Willig, and Claire Wary

Rev. Sci. Instrum. 65, 3363 (1994); http://dx.doi.org/10.1063/1.1144573 (4 pages) | Cited 7 times

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A loop made from a length of transmission line with alternate electrical discontinuities (gaps) on the two conductors behaves as a resonator whose resonant frequency is a function of the transmission line parameters as well as its form and the number (n) of gaps. For a given loop diameter, one can thus design a wide range of resonant frequency by choice of n and the characteristic impedance Zc of the line. The analysis is illustrated by a parallel‐plate transmission line resonator in the form of a bracelet. Experimental resonant frequencies obtained from resonators of various dimensions are in good agreement with calculated values. Two resonators were tested on a 3 T NMR imager: A 11 cm diameter 1H surface coil, yielding results comparable to those obtained from a lumped capacitor coil and a 13 cm diameter volume coil to perform in vivo muscle 13C spectroscopy without 1H decoupling.
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84.40.Az Waveguides, transmission lines, striplines
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Confocal theta microscope with three objective lenses

Steffen Lindek, Rainer Pick, and Ernst H. K. Stelzer

Rev. Sci. Instrum. 65, 3367 (1994); http://dx.doi.org/10.1063/1.1144574 (6 pages) | Cited 9 times

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A microscope using three water immersion objective lenses which realizes confocal, 4Pi‐confocal and various confocal theta microscopies in fluorescence, transmission, scattered, and reflection mode is described. An argon‐ion laser is the primary light source. A pulsed titanium‐sapphire laser allows two‐photon absorption fluorescence microscopy. The instrument has a predicted resolution of 100 nm along the illumination axis and a three‐dimensional resolution of 5×106 nm3 for lenses each with a numerical aperture of 0.75. This is an improvement of an order of magnitude over a confocal fluorescence microscope using the same lens. Applications of the microscope range from observation of a sample at three different angles, to confocal theta fluorescence microscopy with multiphoton absorption. Since mounting and immersion media are identical, aberrations become negligible. The large working distance of 2 mm makes the instrument ideal for the observation of biological samples of up to 1.5 mm in diameter such as drosophila embryos.
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07.60.Pb Conventional optical microscopes
87.64.K- Spectroscopy

An atomic‐resolution cryogenic scanning tunneling microscope

X. Chen, E. R. Frank, and R. J. Hamers

Rev. Sci. Instrum. 65, 3373 (1994); http://dx.doi.org/10.1063/1.1144575 (5 pages) | Cited 4 times

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A design is presented for a cryogenic scanning tunneling microscope which has demonstrated atomic resolution at temperatures between 300 and 120 K in ultrahigh vacuum. The design features simple in situ exchange of samples and tips, active cooling of the sample, excellent visibility of the sample‐tip region, and the use of a thermally isolated inchworm translator for coarse approach. It has demonstrated atomic resolution on SI(111)‐(7×7) and Si(001) surfaces at 120 K.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Sampled waveform measurement in integrated circuits using heterodyne electrostatic force microscopy

G. E. Bridges, R. A. Said, M. Mittal, and D. J. Thomson

Rev. Sci. Instrum. 65, 3378 (1994); http://dx.doi.org/10.1063/1.1144576 (4 pages) | Cited 3 times

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A high‐resolution noncontact scanned probe technique has been developed for sampling the internal signals of an operating integrated circuit. The signal waveform is extracted by sensing the localized electrostatic force between a small probe and point on the circuit being measured. A heterodyne approach is used to enable the sampled measurement of high‐frequency digital or analog waveforms. In conjunction with a nulling method, the technique is capable of accurate signal measurement without complex calibration or probe positioning, and can be performed over passivated structures. Measurement of digital and analog signals is demonstrated with a voltage accuracy of less than 100 mV.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

A new image processing method for extracting integrated intensities from low‐energy electron diffraction spots

Jahansooz Toofan and Philip R. Watson

Rev. Sci. Instrum. 65, 3382 (1994); http://dx.doi.org/10.1063/1.1144577 (7 pages) | Cited 2 times

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We have devised and programmed a new scheme based on image processing techniques for extracting the intensity of fluorescent display low‐energy electron diffraction spots. The method make no assumptions about spot shape, does not use thresholding, and can deal with badly behaved backgrounds, noise spikes, and dead pixels. All decisions about whether a particular pixel belongs to a spot or to the background are made on purely logical grounds with generally binary operator masks. Once the spot edge has been defined, a local background is subtracted to generate an integrated spot intensity. Extensive tests with diffraction features ranging from very strong to indistinguishable from background by eye show this method to be stable, fast, and reproducible.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
42.30.Va Image forming and processing

New technique to enable measurement of the x‐ray absorption spectra of single crystals

J. Pant and T. M. Hayes

Rev. Sci. Instrum. 65, 3389 (1994); http://dx.doi.org/10.1063/1.1144511 (4 pages) | Cited 1 time

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X‐ray absorption spectroscopy measurements of single‐crystal samples have not been possible due to the appearance of diffraction features in the spectra. To deal with this problem a unique magnetically driven sample oscillator has been designed and built. Its effectiveness in enabling x‐ray absorption spectroscopy studies of single crystals is demonstrated. Furthermore, it is compatible with a cryogenic environment in size, mass, and principle of operation.
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61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
78.70.Dm X-ray absorption spectra

An automated test system for measuring x‐ray transmission through glass polycapillaries

B. K. Rath, R. Youngman, and C. A. MacDonald

Rev. Sci. Instrum. 65, 3393 (1994); http://dx.doi.org/10.1063/1.1144512 (6 pages) | Cited 3 times

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To support the development of the recently invented capillary‐based x‐ray optics technology, it is necessary to have quick and repeatable precision measurements of x‐ray transmission. A novel fully automated measurement system has been built for this purpose. Measurements are reproducible within half a percent.
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78.70.-g Interactions of particles and radiation with matter
61.80.Cb X-ray effects

Neutron focusing optic for submillimeter materials analysis

Q. F. Xiao, H. Chen, V. A. Sharov, D. F. R. Mildner, R. G. Downing, N. Gao, and D. M. Gibson

Rev. Sci. Instrum. 65, 3399 (1994); http://dx.doi.org/10.1063/1.1144513 (4 pages) | Cited 13 times

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A neutron lens constructed with polycapillary glass fibers is used to focus a 50×45 mm2 beam exiting a cold neutron guide onto a spot of 0.53 mm (full width at half maximum) with a current density gain of 80. The characteristics of the lens are presented. This lens is designed to enhance the detection limit and lateral resolution for prompt gamma activation analysis using cold neutron beams.
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41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
82.80.Jp Activation analysis and other radiochemical methods

Temperature distribution, deformations, and x‐ray diffraction in the inclined high heat load monochromator: Analytical solutions

Vladimir Kushnir

Rev. Sci. Instrum. 65, 3403 (1994); http://dx.doi.org/10.1063/1.1145199 (5 pages) | Cited 1 time

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Analytical solutions for the temperature distribution and displacement field gradients in the high heat load monochromator are presented. The footprint of the incident x‐ray beam on the crystal surface is approximated by an infinitely long narrow strip, which is applicable in the case of the inclined diffraction geometry. The two‐dimensional problem in the cross section of the crystal normal to the footprint is considered. The solutions for the temperature distribution and displacement field gradients are found in terms of Fourier integrals. These expressions are also valid for x‐ray mirrors. The deviation of the incident beam from exact Bragg position produced by this deformation is calculated. All numerical examples are calculated for the special undulator which is to be installed in the sector III of the Advanced Photon Source.
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41.85.Si Particle beam collimators, monochromators
41.50.+h X-ray beams and x-ray optics
41.60.Ap Synchrotron radiation
41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles

Space‐resolving flat‐field vacuum ultraviolet spectrograph for plasma diagnostics

Naohiro Yamaguchi, Jungo Katoh, Yukiko Sato, Tatsuya Aota, Atsusi Mase, and Teruo Tamano

Rev. Sci. Instrum. 65, 3408 (1994); http://dx.doi.org/10.1063/1.1144514 (7 pages) | Cited 5 times

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A spatial imaging vacuum ultraviolet (VUV) spectrograph has been constructed for simultaneous observation of spatial and spectral distributions of plasma radiation in the wavelength range 150–1050 Å. The spectrograph consists of an entrance slit of limited height which provides spatial resolution, an aberration‐corrected concave grating with varied spacing grooves which gives a flat‐field spectral output plane, and an image‐intensified two‐dimensional detector system. The basic characteristics of the spectrograph have been investigated by ray‐tracing calculations. The expected performance has been confirmed through experiments using a dc glow discharge source on the reciprocal dispersion, the spatial resolution, or the incident angle dependence of spectral images. VUV spectra with spatial and time resolution have been obtained successfully in the GAMMA10 tandem mirror experiment.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium

Tomography on tokamak fusion test reactor

Y. Nagayama

Rev. Sci. Instrum. 65, 3415 (1994); http://dx.doi.org/10.1063/1.1144515 (8 pages) | Cited 8 times

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Reconstruction techniques have been developed to obtain 2D images of plasmas from the electron cyclotron emission (ECE) and soft x‐ray emission signals by taking advantage of the large toroidal rotation rate on the tokamak fusion test reactor (TFTR). From the numerical examination using the sawtooth crash model, we found that the rotational tomography is effective if the crash time is longer than the two rotation periods.
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52.70.La X-ray and γ-ray measurements
52.55.Fa Tokamaks, spherical tokamaks
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Modified Fowler–Milne method for the spectroscopic measurement of temperature and composition of multielement thermal plasmas

A. B. Murphy

Rev. Sci. Instrum. 65, 3423 (1994); http://dx.doi.org/10.1063/1.1144516 (5 pages) | Cited 12 times

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A technique is presented by which the Fowler–Milne spectroscopic method can be applied to thermal plasmas containing two or more atomic elements. The technique requires the measurement of the emission coefficient for an atomic transition of each element. These values are normalized to the maximum emission coefficient for each transition in the respective single‐element plasmas. Neither calibration of the sensitivity of the apparatus nor knowledge of atomic transition probabilities is required. The technique allows the relative concentration of the elements to be derived significantly more precisely than other spectroscopic methods. The technique is applied to the measurement of the radial profiles of temperature and composition of free‐burning arcs in mixtures of argon and nitrogen. Significant demixing is observed, with the direction of the demixing depending on the relative concentrations of argon and nitrogen.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Multichannel submillimeter interferometer/polarimeter for TdeV

J.‐L. Lachambre and M. Gagné

Rev. Sci. Instrum. 65, 3428 (1994); http://dx.doi.org/10.1063/1.1144517 (6 pages) | Cited 7 times

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An interferometer/polarimeter has been developed and tested for operation on the TdeV tokamak. The system operates at 393.6 μm on 7 channels equally spaced over the plasma diameter. The interferometer has operated routinely for six years and is used for density feedback control on TdeV, with very little supervision and maintenance. A sensitivity of 2.5×10−16 m−2 and a response time of 5 μs enables small density perturbations (Δn≥0.005mathe) and fast transients to be resolved. With the appropriate choice of assumptions and boundary conditions, the system can supply credible electron density profiles together with their temporal evolution, using as isocontours the flux surfaces obtained from equilibrium calculations. When operated as a polarimeter, the system now routinely provides current‐density profile measurements as well. Optical cross‐talk between channels, identified as the main obstacle to the extension of the interferometer to polarimetry, was mastered using optical isolation techniques. The system can now resolve, on each chord, a Faraday rotation of 1.5 mrad, limited by vibration, cross‐talk and deflection. Using a parametric approach, poloidal field and current‐density profiles, as well as the axial safety factor and internal inductance of the discharge, are made available after each shot. The apparatus will be used for current‐transport, MHD‐equilibrium and current‐drive studies on TdeV.
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52.70.Gw Radio-frequency and microwave measurements
52.55.Fa Tokamaks, spherical tokamaks
07.60.Ly Interferometers
07.60.Fs Polarimeters and ellipsometers

Development of a real time visualization system for the shape of a tokamak plasma cross section

S. Hara, K. Takeuchi, M. Abe, and M. Otsuka

Rev. Sci. Instrum. 65, 3434 (1994); http://dx.doi.org/10.1063/1.1144518 (5 pages)

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A real time visualization system for the shape of a tokamak plasma cross section has been developed by using Versa Module Europebus (VME)‐standardized modules. Digital signal processors (DSPs) are used in parallel for magnetic analysis. A fast and high resolution graphics control processor is adopted for part of the display system. Fast shape identification methods are presented in which tabulated Green’s functions are utilized. The analysis errors are evaluated with Hitachi tokamak 2 (HT‐2) experimental data. The plasma shape is visualized in real time with the cycle time of 30 ms. When this system is applied to the International Thermonuclear Experimental Reactor (ITER), the estimated cycle time for visualizing the plasma shape is 40 ms.
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52.70.-m Plasma diagnostic techniques and instrumentation
07.05.Hd Data acquisition: hardware and software
07.05.Kf Data analysis: algorithms and implementation; data management
07.05.Rm Data presentation and visualization: algorithms and implementation

Highly efficient microwave coupling devices for remote plasma applications

C. Dupret, P. Supiot, O. Dessaux, and P. Goudmand

Rev. Sci. Instrum. 65, 3439 (1994); http://dx.doi.org/10.1063/1.1144519 (5 pages) | Cited 3 times

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Microwave resonant cavities running at 2.45 GHz are now being investigated for use in the high power remote plasma processings. The present paper deals with the design of two coupling devices, e.g., one coaxial cavity and one TM012 mode cylindrical cavity, using an antenna coupling. Their main attractive feature is the ability to run at powers as high as 3 and 6 kW, respectively. A basic model used to describe the wave–plasma interaction is developed and leads to the main consequences for the cavities conception thanks to the deduced equivalent electrical circuits. Their high efficiency is experimentally demonstrated for nitrogen, oxygen, air, and argon.
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52.50.Dg Plasma sources

Beam diagnostics with localized space‐charge waves

J. G. Wang and M. Reiser

Rev. Sci. Instrum. 65, 3444 (1994); http://dx.doi.org/10.1063/1.1144520 (5 pages) | Cited 2 times

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A new method for the diagnostics of charged particle beams by employing localized space‐charge waves is presented. The propagation of space‐charge waves in the form of localized perturbations can be measured easily and accurately in experiments. The results carry valuable information about many beam parameters such as the wave speed, the geometry factor g for the longitudinal space‐charge field, the beam radius, the beam impedance under longitudinal perturbations, etc. The principle of this technique and an experimental example are given in this article.
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41.75.-i Charged-particle beams
41.85.Ja Particle beam transport
41.85.Qg Particle beam analyzers, beam monitors, and Faraday cups

Experimental investigation and analysis of the operation characteristics of a planar Cs–Ba tacitron

Bernard Wernsman, Mohamed S. El‐Genk, and Vladimir Z. Kaibyshev

Rev. Sci. Instrum. 65, 3449 (1994); http://dx.doi.org/10.1063/1.1144521 (6 pages) | Cited 3 times

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The experimentally measured modulation characteristics of a planar Cs–Ba plasma switch (tacitron) are presented and discussed. Tests are performed that focus on characterizing the operation capabilities of a planar Cs–Ba tacitron. Results show that the operation characteristics of the device are independent of geometry (cylindrical or planar). The forward voltage drop decreases as either the grid‐collector (GC) gap size and/or the Cs pressure increases. Also, stable current modulation is easier to sustain when the grid is placed closer to the collector, at the expense of increasing the forward voltage drop across the device.
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52.75.Kq Plasma switches (e.g., spark gaps)

New method for the measurement of gadolinium atomic beam velocity using Langmuir probes

Koichi Ogura and Takemasa Shibata

Rev. Sci. Instrum. 65, 3455 (1994); http://dx.doi.org/10.1063/1.1144522 (3 pages) | Cited 4 times

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The velocity of a gadolinium atomic beam produced by electron beam heating was found to range from 700 to 1000 m/s by measuring the drift velocity of the plasma, which is produced by ionizing atoms in the atomic beam with pulsed dye lasers and using Langmuir probes. The measured atomic beam velocity spread agrees with that determined by the microbalance method.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
06.30.Gv Velocity, acceleration, and rotation

High efficiency molecular‐beam ionization detector with short ionization region

K. Kuhnke, K. Kern, R. David, and G. Comsa

Rev. Sci. Instrum. 65, 3458 (1994); http://dx.doi.org/10.1063/1.1144523 (8 pages) | Cited 25 times

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A mass selective electron‐impact ionization detector for use in energy resolved thermal He scattering experiments is presented. The detector combines a short effective ionization region (approximately 3 mm FWHM) with a high detection efficiency of 10−5 at 2 mA electron emission. An efficiency of 10−4 at 10 mA emission current can be achieved if time resolution below 20 μs is dispensable. The design is discussed and measurements of detection efficiency and time resolution are presented. The ionizer can likewise be employed for an efficient detection of other types of atoms or molecules.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
37.20.+j Atomic and molecular beam sources and techniques
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