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Review of Scientific Instruments

Issue 5 • Date May 1994

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Displaying Results 1 - 25 of 61
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • First use of the UV Super‐ACO free‐electron laser: Fluorescence decays and rotational dynamics of the NADH coenzyme

    Page(s): 1485 - 1495
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    Significant improvements in the performances of the Super‐ACO storage ring free‐electron laser (FEL) at 800 MeV have been obtained recently: enhancement of the output power in the ultraviolet, laser duration of 10 h for the same injection of positrons, long‐term stability with a micropulse of 60 ps FWHM. A first series of experiments using this FEL has then been successfully performed. Taking advantage of the time structure, the polarization and the high power of the source at 350 nm, the polarized fluorescence decays of the reduced nicotinamide adenine dinucleotide coenzyme (NADH) were studied in aqueous solution, using the single‐photon counting (SPC) technique. The experimental setup is described, including the Super‐ACO FEL characteristics and diagnostics. The FEL working point has been first optimized by monitoring the SPC apparatus function. A complete fluorescence experiment required about 30 min of data acquisition, during which the best integrated instrumental response had a FWHM of 110 ps. Measurements performed in such a way lead to the unambiguous separation of two close lifetime components of 0.28 and 0.62 ns in the fluorescence decays of NADH at 20 °C, in good agreement with previous works. The thermodynamic parameters obtained from temperature studies show that the NADH fluorescence heterogeneity is consistent with the ground‐state folding equilibrium of the coenzyme, as characterized by many other spectroscopic techniques. From the fluorescence anisotropy decays, an apparent hydrodynamic radius of about 6 Å is determined, while on the other hand, a large initial depolarization of the fluorescence indicates a fast independent motion of the nicotinamide ring. The quality of the collected data fully meets the requirements for the study of more complex systems such as fluorescent compounds bound to proteins or membranes. Thus, the feasibility of use of a storage ring UV FEL for this type- of time‐resolved experiments on the subnanosecond time scale has been demonstrated. View full abstract»

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  • Broadband Pockels cell and driver for a Mark III‐type free electron laser

    Page(s): 1496 - 1501
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    A Pockels cell with an operating range of 2 to 10 μm has been designed, constructed, and tested for use with the Vanderbilt free electron laser. The Pockels cell can be continuously adjusted to switch out from 80 ns to the full 6 μs duration of the FEL macropulse. The extinction ratio is better than 180:1 and the optical pulse is square with rise and fall times under 10 ns. The high voltage drivers are based on semiconductor switches that are compact and mounted directly to the Pockels cell; this design avoids problems associated with fast, high voltage pulses traveling in cables. In addition, designs for two alternative drivers to generate optical pulses with durations ranging from a few nanoseconds down to the subnanosecond regime are presented here. Prototypes using single high voltage transitions have been constructed and tested electrically.   View full abstract»

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  • A laser diode system stabilized on the Caesium D2 line

    Page(s): 1502 - 1505
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    We describe a complete diode laser system stabilized at 852 nm on the D2 line of Cs with a linewidth narrower than 100 kHz. This system is intended to be employed for optical pumping, cooling, and detection of Cs atoms in atomic frequency standards. The square root of the Allan variance, evaluated by measuring the beat‐note of two similar systems, is better than 1×10-12 for τ up to 1000 s. A month of continuous locked operation has been observed. View full abstract»

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  • Optical monitoring of protein crystals in time‐resolved x‐ray experiments: Microspectrophotometer design and performance

    Page(s): 1506 - 1511
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    We describe a single crystal microspectrophotometer for optical monitoring of protein crystals during time‐resolved x‐ray diffraction experiments. It is a single beam device with a diode array detector for simultaneous multiwavelength measurement of optical spectra. The time resolution of the microspectrophotometer is 2.5 ms, which matches the ms time resolution of the x‐ray experiments obtained at existing synchrotron sources. Optical densities of single crystals can be reliably measured up to 2.5 OD, with the linear range extending to 2 OD. The tight focusing of the light beam allows monitoring of crystals as small as 30–50 μm, an important feature since successful reaction initiation and optical monitoring of crystals in time‐resolved x‐ray diffraction experiments often require very small crystals. The compact design of the microspectrophotometer and the long objective‐to‐crystal distance make it compatible with the crowded environment of time‐resolved x‐ray diffraction experiments. View full abstract»

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  • On the use of the open photoacoustic cell technique for studying photosynthetic O2 evolution of undetached leaves: Comparison with Clark‐type O2 electrode

    Page(s): 1512 - 1516
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    The leaf photosynthetic O2 evolution detected by the open photoacoustic cell (OPC) technique is compared to the measurements using a Clark‐type O2 electrode detector. In vivo and in situ measurements were carried out with undetached maize leaves. From the correlation between these two methods the possibility of a calibration is proposed for the oxygen evolution OPC signal.   View full abstract»

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  • A millimeter/submillimeter spectrometer for high resolution studies of transient molecules

    Page(s): 1517 - 1522
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    A design is presented for a millimeter/submillimeter direct absorption spectrometer for studies of the pure rotational spectra of metal‐bearing free radicals. The spectrometer operates in the frequency range of 65–550 GHz with an instrumental resolution of 200–1000 kHz and an absorption sensitivity of a few ppm. The instrument utilizes phase‐locked Gunn oscillators as the tunable, coherent source of radiation from 65–140 GHz. Higher source frequencies are obtained with Schottky diode multipliers. The gas cell and optics path are designed utilizing Gaussian beam optics to achieve maximum interaction between molecules and the mm‐wave radiation in the reaction region. Scalar feedhorns and a series of PTFE lenses are used to propagate the source signal. The gas cell is a cylindrical tube 0.5 m in length with a detachable Broida‐type oven. The detector for the spectrometer is a helium‐cooled InSb hot electron bolometer. Phase‐sensitive detection is achieved by FM modulation of the Gunn oscillators and use of a lock‐in amplifier. Spectra are recorded by electrical tuning of the Gunn oscillator, which is done under computer control. The millimeter and sub‐mm rotational spectra of several free radicals have been observed for the first time using this instrument, including CaOH, MgOH, CaH, MgF, and BaOH. View full abstract»

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  • A static gas phase cell for optical spectroscopy in the 300–700 K range

    Page(s): 1523 - 1526
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    A static cell has been developed for routine gas phase spectroscopy under high vacuum conditions. Its design provides both reusability and convenience using parts readily available from commercial vendors at an economical price. The cell features a warm‐up cycle that keeps the windows free of condensation and an operating range of 300–700 K that offers good uniformity of temperature throughout the cell for extended periods of time. The operation of the cell is illustrated with absorption spectra of a zinc metalloporphyrin in the gas phase. View full abstract»

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  • A new technique for visualization of acoustic particle agglomeration

    Page(s): 1527 - 1536
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    A new visualization technique is presented for microscopic particle trajectories displaying interaction and agglomeration phenomena in a high intensity acoustic field. The experiments are carried out in a small‐scale observation chamber using a CCD camera in conjunction with a high resolution video system. A homogeneous acoustic velocity field is generated by two square, flat‐membrane loudspeakers which comprise two opposing walls in the observation chamber. Glass microspheres (diameters 8.1 and 22.1 μm) and arbitrarily shaped quartz particles (diameter≪50 μm) are used for the observation of interaction and agglomeration trajectories under the influence of an intense acoustic velocity field (1.2–0.53 m/s 400–900 Hz). The new technique allows the observation of the particles’ general motion as well as acoustically induced oscillations. The direction of propagation of a particle can be extracted by following its trajectory in a 2D laser lightsheet. Image processing of the digitized data allows the reconstruction of particle trajectories for time spans up to 0.5 s. From the images, the particle size can be estimated based on measurements of the acoustic entrainment factor. Most importantly, with the new experimental technique it is possible to resolve particle interaction and agglomeration processes caused by the acoustic field. The recorded digitized images show a number of different interaction phenomena as well as one distinct pattern that resembles the shape of a tuning fork (thus called the tuning fork agglomeration). The latter appears to be the predominant agglomeration mechanism leading to rapid particle approach and multiple, subsequent particle interactions at high frequencies and large acoustic velocities. View full abstract»

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  • A frequency‐agile hybrid spectral correlator for mm‐wave radio interferometry

    Page(s): 1537 - 1540
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    A correlation spectrometer for the IRAM Plateau de Bure radio astronomy observatory is presented. It can process up to 960 MHz wide IF signals coming from the 4‐antenna connected array. An IF processor selects the frequency window of interest, both in width and central frequency. A digital correlator produces channelized amplitude and phase information for the six pairs of antennas, which is later used for aperture synthesis mapping. Some original technical features are detailed. Some improvements suggested by observing results are discussed. View full abstract»

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  • Investigations of polarization profiles in multilayer systems by using the laser intensity modulation method

    Page(s): 1541 - 1550
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    The laser intensity modulation method (LIMM), developed by Lang in the early eighties, is a useful technique for determining the spatial polarization and/or space charge distributions in pyroelectric and/or piezoelectric materials, for instance in thin polymer electret films. The advantage of the LIMM is the high spatial resolution near the irradiated side. Therefore, we introduced the logarithmic spatial grid distribution into the deconvolution process. For the first time the self‐consistency method developed by Honerkamp and Weese is applied to the deconvolution program with respect to LIMM. Using multilayer systems with known spatial distributions our new equipment is tested with regard to providing reasonable results as well as the deconvolution program to represent the known spatial distributions. View full abstract»

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  • Scanning tunneling microscope calibration and reconstruction of real image: Drift and slope elimination

    Page(s): 1551 - 1557
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    Drift, slope of sample, and indeterminate sensitivity of piezoceramics are considered as the origin of the linear scanning tunneling microscope (STM) image distortions. A special algorithm of STM scanning and reconstruction of image of unknown atomic structures is suggested and tested. This algorithm allows us to measure three components of the drift velocity and two angles, characterizing the average slope of scanning surface. On the one hand, using this algorithm, one can perform the STM calibration by a known surface structure (for example, the highly oriented pyrolytic graphite surface) even in the presence of a drift. This enables us to determine all the three piezoceramics constants of STM piezoscanner and the deviation of the real scanner axes X and Y from orthogonality. On the other hand, using such a calibrated STM and the described algorithm, it is possible to obtain the real STM image and make measurements for unknown surfaces with atomic resolution without the distortions mentioned above. As it has been proved, the error of interatomic distance measurements does not exceed 5% (∼0.1 Å) for any direction along the surface, even in the presence of a drift up to 0.4 Å/s and the sample slope angle up to 10°. View full abstract»

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  • Preparation and characterization of tungsten tips for scanning tunneling microscopy

    Page(s): 1558 - 1560
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    Tungsten tips obtained through electrochemical etching have been characterized by scanning electron microscopy, scanning Auger microscopy, and scanning tunneling microscopy. While such tips resulted to be very sharp, a thick oxide layer (∼10 nm) is present at the apex. High‐vacuum annealing at 1800 K removes most of such oxide. View full abstract»

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  • Effect of PZT and PMN actuator hysteresis and creep on nanoindentation measurements using force microscopy

    Page(s): 1561 - 1565
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    Nanoindentation measurements performed using the atomic force microscope (AFM) are significantly affected, both with regard to indentation curve shape and quantitative values of the measurements (70% variation in measured modulus), by the well‐known effects of hysteresis and creep in the lead zirconate titanate (PZT) piezoceramic actuators used to control the positioning and motion of the mechanical components of the AFM. A capacitance‐based displacement calibrator has been built and it was discovered that the response of PZT ceramics may vary (up to 66%) depending upon the conditions under which the piezoceramic is calibrated. By replacing the PZT actuators with lead magnesium niobate (PMN) electrostrictive actuators, nanoindentation measurements have been obtained using the AFM that are both reproducible and quantitative. View full abstract»

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  • A dynamic model for analyzing piezoelectric stepmotors

    Page(s): 1566 - 1569
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    A new dynamic model is developed for analyzing the dynamic process of piezoelectric stepmotors. In this model the voltage applied to the piezoelectric stepmotor is equivalent to the force acting on the end of the piezoelectric stepmotor. The model is simple and convenient for applications. As an example, a model of analyzing the rotatable sample stage is presented. The theoretical results are in good agreement with the experimental results. The structural damping of the piezoelectric material is also discussed.   View full abstract»

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  • Fabrication of silicon‐based optical components for an ultraclean accelerator mass spectrometry negative ion source

    Page(s): 1570 - 1574
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    An ultraclean accelerator mass spectrometry negative ion source for semiconductor material mass analysis has been built and is in operation at the University of North Texas’ Ion Beam Modification and Analysis Laboratory (IBMAL). The source is unique in that the active surfaces and apertures of the optical components in the ion source have been fabricated from high‐purity single crystal silicon. This prevents both the 133Cs+ beam incident on the semiconductor samples and the negative ions from the sample surfaces from ‘‘seeing’’ and sputtering any metal surfaces (mostly stainless steel) in the beamline. The Cs+ beam can be rastered across the sample surface and the impact energy is adjustable to control depth‐profiling rates. An ultraclean ion source of this type is necessary to prevent the injection of Fe and other beamline elements onto the sample or into the tandem accelerator, which is equivalent to putting an impurity signal into the mass analysis of the semiconductor sample. Suppression of these elements increases the sensitivity of the analysis to one part in 1012 for many masses. The fabrication and alignment of the optical components—einzel lenses, steerers, raster/scanners, and Faraday cups—in the negative ion source will be presented. Also, simulation trajectories are presented to show (1) the interaction of the incident Cs+ ion beam, the semiconductor sample, and holder (biased up to -30 kV), the extracted beam in the sample chamber, and associated potential field lines; and (2) the potential field lines of the octupole steerers. View full abstract»

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  • Adaptation of particle‐telescope technology for medium energy ion beam analysis

    Page(s): 1575 - 1579
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    Medium energy (100–300 keV) time‐of‐flight spectrometry for surface analysis uses the correlated detection of an energetic ion and the secondary electrons emitted as it passes through a carbon foil. When microchannel plates are employed in this detection scheme, a typical mean efficiency of detection of less than 30% is achieved. When instead a surface barrier detector is used to detect the ion, providing simultaneous acquisition of velocity and energy information, certain advantages are realized over the two microchannel plate configuration in the characterization of low level constituents of surfaces. Specifically, energy‐discriminated gating of the start pulse was observed to nearly eliminate count rate dependent background in a time‐of‐flight spectrum. Further reduction in background was obtained by the selective elimination of forward recoil species or backscatters from the substrate. Replacement of the stop microchannel plate by a surface barrier detector has resulted in improved detection efficiency for He, as well as provided a means for further study of the processes which affect time‐of‐flight spectrometer response, including multiple scattering and secondary electron emission in the start foil. In this publication, we describe the application of this particle telescope to the backscattering analysis of gold on silicon and the forward scattering measurement of hydrogen in a self‐supporting carbon film. View full abstract»

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  • A study of non‐ideal focus properties of 30° parallel plate energy analyzers

    Page(s): 1580 - 1584
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    A succinct model is proposed to describe non‐ideal characteristics owing to electric field penetration into the drift region in actual parallel plate energy analyzers. A good agreement has been obtained between the theoretically expected and experimentally observed focus properties of the 30° parallel plate analyzer. View full abstract»

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  • Design parameters of dual‐stage ion reflectrons

    Page(s): 1585 - 1589
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    Exact solutions of the second‐order differential equation describing the energy dependence of ion flight time in a reflectron time‐of‐flight mass spectrometer are derived, from which numerical evaluation of the construction and operation parameters of a dual‐stage reflectron can easily be performed. Considerations in choosing the design parameters are discussed. View full abstract»

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  • Production of electron cyclotron resonance plasma for uniform deposition using a TE01 mode microwave

    Page(s): 1590 - 1593
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    An electron cyclotron resonance (ECR) plasma is produced at pressures up to 10 mTorr with a circular TE01 mode microwave. The plasma density is almost radially uniform even at 10 mTorr. SiC films are formed on silicon wafers by introducing methane gas into the ECR plasma. It is shown that a circular TE01 mode microwave is useful for the ECR plasma chemical vapor deposition (CVD).   View full abstract»

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  • An accelerator for alkali metal plasmas

    Page(s): 1594 - 1602
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    A washer plasma gun for alkali‐metal plasma is developed. This gun is suitable as a source for experiments on alkali‐metal plasmas, plasma diagnostics, and in various applications such as ion‐beam sputter deposition. The gun uses an injector of alkali‐metal vapor based on the principles of laser ablation. Acceleration is performed by a large electrical field provided across eight washers. The gun is compact, stable, and easy to fabricate and use. The gun produces a neutral Li0 beam current of 1 A/cm2 and a Li+ ion current of 50 A/cm2 at its exit at 10 kV of capacitor bank voltage. With this intensity, it is possible to produce beams of neutral Li0 atoms of density 6×109 cm-3 and Li+ ions of density ∼1011 cm-3 at 1 m from the gun, moving with a velocity of ∼107 cm/s.   View full abstract»

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  • Improved Ashby–Jephcott interferometer for temporal electron density measurements in plasmas

    Page(s): 1603 - 1605
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    The Ashby–Jephcott interferometer is used to measure the temporal variations in electron densities in plasmas. A double‐ended HeNe laser is used as part of an interferometer to make these measurements. In the present work, the experimental setup of the original method has been modified to prevent the drift in the temporal fringe patterns that are observed. This allows for more precise measurements of electron densities in plasmas. Further, the modification allows for commercially available HeNe lasers to be used to measure electron densities. The fringe patterns observed in a Z‐pinch discharge using the original Ashby–Jephcott method and the modified method are shown. The differences in the temporal variation of the electron density measurements using the two methods are discussed.   View full abstract»

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  • Mesh effect in a parallel‐plate analyzer

    Page(s): 1606 - 1612
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    The effect of field irregularity due to the use of conducting meshes to cover holes of a lower electrode in a parallel‐plate electrostatic analyzer, is experimentally and numerically investigated. Displacement of a focal point and degradation of analyzer characteristics are found in the experiment. Dependence of analyzer characteristics on wire spacing is obtained. Primary results are also confirmed by numerical analysis. Criteria for error estimation are theoretically derived and found to be consistent with the experiment. View full abstract»

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  • The cooling water calorimetry system at ASDEX upgrade tokamak

    Page(s): 1613 - 1615
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    At the tokamak ASDEX upgrade, an extensive cooling water calorimetry system was installed. This system has measured the toroidal and poloidal distributions of the energy deposition by monitoring the temperature rise of the cooling water in 80 separate cooling units in the divertor plates and the central heat shield. View full abstract»

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  • High‐resolution tritium calorimetry based on inertial temperature control

    Page(s): 1616 - 1620
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    A reassessment of the basic equation governing calorimetry shows the crucial importance of temperature stability in the calorimeter environment. Following the principles derived, we have developed a new temperature control method and demonstrated it in a prototype calorimeter over a wide dynamic range (5 μW–2 W). Temperature control is achieved by using a metal block of high thermal inertia, surrounded by heat flow sensing thermopile arrays, which is embedded in an isothermal environment. Any temperature fluctuations in this environment are detected by the heat flow sensors and can be corrected by conventional feedback control. The advantage of this method is its high sensitivity to temperature changes: whereas conventional thermometers typically provide signals in the order of 1×10-3 V/K-1, a correctly selected combination of inertial mass and thermopile arrays can provide signals in the order of 1 V K-1, thus permitting an improvement of temperature control by three orders of magnitude. A commercially available thermoelectric calorimeter in an isothermal environment controlled by the new method permitted measurement of sample powers with ±10 μW accuracy (long‐term, short‐term noise ∼±1 μW), whereas in a conventional thermostatic bath (temperature stability ±0.02 K h-1) its resolution was limited to ±3 mW. View full abstract»

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Review of Scientific Instruments, published by the American Institute of Physics, is devoted to scientific instruments, apparatus, and techniques.

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Editor
Albert T. Macrander
Argonne National Laboratory