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  • Articles  (102,840)
  • 2000-2004  (102,840)
  • 1980-1984
  • 2000  (102,840)
  • Biology  (81,110)
  • Energy, Environment Protection, Nuclear Power Engineering  (14,407)
  • Electrical Engineering, Measurement and Control Technology  (8,638)
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  • 2000-2004  (102,840)
  • 1980-1984
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  • 1
    Electronic Resource
    Electronic Resource
    Apparatus for in situ x-ray absorption fine structure studies on catalytic systems in the energy range 1000 eV〈E〈3500 eV (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3260-3266 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new apparatus for in situ x-ray absoprtion fine structure measurements in the medium energy range of 1000–3500 eV has been developed. Measurements can be performed in a gaseous environment (max. pressure 1 bar) at temperatures ranging from 80 to 750 K. Pre-treatments can be performed at 5 bar and 750 K in the same cell, after which XAFS measurements can be done without exposing the sample to ambient air. In a modular set-up several detector systems can be used: fluorescence detection using a gas proportional counter, a photodiode or a microstrip detector. All detectors are highly integrated into the cell, gaining solid angle for detection. Electron yield detection can be used simultaneously using conversion electron yield or total electron yield. The performance of the new apparatus is demonstrated by a study of the K edge of Al in Zeolite Beta. The Al content is as low as 2 wt%. It will be shown that octahedral framework Al is formed while adding gaseous water at room temperature after ammonia removal (at 450 °C) of an NH4-Beta. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287634
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  • 2
    Electronic Resource
    Electronic Resource
    Log spiral of revolution highly oriented pyrolytic graphite monochromator for fluorescence x-ray absorption edge fine structure (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3267-3273 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have constructed an x-ray monochromator based on a log spiral of revolution covered with highly oriented pyrolytic graphite. Such a monochromator is used for obtaining x-ray absorption edge fine structure by the fluorescence method, and is particularly useful for measuring the fine structure of dilute element A in a concentrated matrix of element B, where B is to the left of A in the Periodic Table. Using the log spiral monochromator, we measure good Cr x-ray fine structure in an alloy of 1% Cr in a V matrix, whereas the corresponding spectrum is severely distorted by the V background if nonmonochromatized fluorescence is used. We also obtain excellent rejection of Mn fluorescence relative to Cr fluorescence in a Cr80Mn20 alloy, and can tune the monochromator such that the entire Mn step height is significantly smaller than the Cr x-ray absorption edge fine structure oscillations for this system. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287753
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  • 3
    Electronic Resource
    Electronic Resource
    Active length control of two phase locked CO2 lasers with a digital signal processor (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3298-3305 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two CO2 lasers are phase locked together by injection locking, where radiation between the two lasers is exchanged using a copper prism as a beam folding device in the resonators. Extraction of the output radiation is achieved by a common output coupler. As this method is only utilizing reflective optics (except for the output coupler), it is also practical as a technique for phase-locking lasers with powers in the multikilowatt range. Single frequency oscillation is only achieved if the lengths of both resonators are within a so-called locking range. This can only be fulfilled if the length of one resonator is actively controlled. The method of detection of the phase difference between the lasers and actively controlling the length of one resonator is presented as well as its implementation into a digital signal processor. Stable phase locked operation is achieved and proved through detection of twice the intensity in the far field in the phase-locked regime. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288263
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  • 4
    Electronic Resource
    Electronic Resource
    Novel device for the generation of controlled prepulses in a Ti:sapphire laser amplifier chain (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3313-3316 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For the generation of a well defined prepulse in high intensity laser plasma interactions, we implemented a newly developed prepulse device into a multiterawatt titanium:sapphire amplifier system. The temporal delay between the prepulse and main pulse is variable between −350 ps and + 100 ps. If the laser pulse is focused on a target, the spatial overlap of the two pulses in the focal point is corrected automatically over the entire range. It is possible to attenuate the main pulse as well as the prepulse independently of each other by more than one order of magnitude. We investigated the dependence of the Kα emission of the laser produced plasma of a silicon target on the delay between the prepulse and main pulse. An increase of the yield of the Kα emission by a factor of 2 for a temporal delay of several tens of picoseconds between the prepulse and main pulse was measured. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287049
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  • 5
    Electronic Resource
    Electronic Resource
    A technique for accurate measurements of ion beam current density using a Faraday cup (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3326-3330 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have performed measurements of the spatial distribution of current in various alkali and reactive ion beams over the energy range 5–600 eV using a Faraday cup. Ion beam current densities have been extracted from these measurements using a simple deconvolution procedure. Our results reveal that the beams are Gaussian in shape with a constant width, σ, for energies greater than approximately 75 eV and for all ion species investigated. This width is consistent with that determined from the distribution of oxygen on a Cu(001) crystal after an O+ ion beam deposition, measured using Auger electron spectroscopy. Using the measurement technique outlined in this article, together with the linear relationship between current density and Faraday cup current, it is possible to determine the beam current density using a single current measurement. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287635
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  • 6
    Electronic Resource
    Electronic Resource
    Plasma generation and confinement in a toroidal magnetic cusp (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3351-3361 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The first measurements of plasma parameters in a discharge created by electron cyclotron resonance heating in a toroidal cusp configuration are discussed along with the predictions of particle orbits and confinement from a guiding center model. The configuration appears to be suitable for basic investigations of the physics of plasma flows and instabilities around a magnetic null, hence of magnetic reconnection. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287340
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  • 7
    Electronic Resource
    Electronic Resource
    Simple and inexpensive current-driven magnetic multipole plasma homogenizer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3373-3376 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Magnetic multipole plasma confinement geometries employing permanent magnets are commonly used to confine laboratory plasmas and improve uniformity. Here we describe the design and operation of a particularly simple and low-cost kind of current-driven multipole system that makes use of a similar magnetic field structure but does not require permanent magnets. The magnetic field is generated by current carrying wires attached to the inside wall of a cylindrical supporting structure to provide a magnetic field resembling that of permanent multipole magnetic homogenizers. We demonstrate the use of the current-driven homogenizer to improve the uniformity of the radial density profile of a vacuum arc generated metal plasma. Our configuration of metal plasma gun, macroparticle filter, and current-driven homogenizer was used for thin film deposition, and was able to produce a relatively homogeneous film thickness profile while maintaining a deposition rate comparable to that at the peak point of the freely expanded beam at the same location. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287751
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  • 8
    Electronic Resource
    Electronic Resource
    Simultaneous soft x-ray emissivity profile measurements in poloidally separate locations of the Alcator C-Mod edge plasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3385-3390 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two high resolution edge x-ray imaging diagnostics have been installed in the Alcator C-Mod tokamak. One array measures the radial soft x-ray emissivity profiles at the top of the plasma with 1.2 mm radial resolution, mapped along flux surfaces to the midplane, whereas the other measures the radial soft x-ray emissivity profiles at the outboard edge with 1.5 mm radial resolution mapped to the midplane. The two diagnostics measure the chord brightness profiles, which are then inverted to get soft x-ray emissivity simultaneously with a 12 μs sampling time. This allows us to determine if the soft x-ray emissivity, and therefore the fluorine density, is constant on a flux surface during steady state high confinement mode conditions, as well as during fast transient edge events, such as edge localized modes or transitions from the high confinement mode to the low confinement mode. Measurements are presented showing that the soft x-ray emissivity is not constant on a flux surface, but instead shows a large poloidal variation, contrary to what is assumed in the inversion routine. The effects of the poloidal variation on the inversion accuracy are estimated numerically. It is found that the emissivity is systematically overestimated at the top, and underestimated at the outboard edge, by less than 15%. The width of the x-ray emissivity pedestal is accurate to within 15%, and the location of the pedestal is accurate to within 1 mm. Measurements showing a poloidal propagation delay for the onset of the transition from high confinement mode (H mode) to low confinement mode (L mode) are also presented. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287048
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  • 9
    Electronic Resource
    Electronic Resource
    A new method for searching for free fractional charge particles in bulk matter (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3409-3414 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a new experimental method for searching for free fractional charge in bulk matter; this new method derives from the traditional Millikan liquid drop method but allows the use of much larger drops, 20–100 μm in diameter, compared to the traditional method that uses drops less than 15 μm in diameter. These larger drops provide the substantial advantage that it is then much easier to consistently generate drops containing liquid suspensions of powdered meteorites and other special minerals. These materials are of great importance in bulk searches for fractional charge particles that may have been produced in the early universe. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1308268
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  • 10
    Electronic Resource
    Electronic Resource
    Triode electron bombardment evaporation source for ultrahigh vacuum thin film deposition (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3444-3450 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new electron bombardment evaporation source for ultrahigh vacuum (UHV) thin film deposition is presented. It is based on an original electrodes configuration (modeled on that of a vacuum triode) featuring, besides anode and filament, a biased grid acting as a power modulator. The presence of a polarized grid helps to minimize space charge problems, to improve electron focusing and to fine control the dissipation on the evaporating material, governing the sublimation rate. The electrodes geometry was optimized by studying electron trajectories and electrical field distribution in the electrodes zone with ray-tracing analysis. Mechanical solutions and electrodes geometry were designed to ensure low outgassing and UHV compatibility, as well as to facilitate maintenance and source cleaning. The evaporator is water cooled and a mechanically operated shutter is present. The working principles and the technical details are presented together with operating data and evaporation performances. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287624
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  • 11
    Electronic Resource
    Electronic Resource
    Multichannel ellipsometer for real time spectroscopy of thin film deposition from 1.5 to 6.5 eV (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3451-3460 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A rotating polarizer multichannel ellipsometer has been optimized for operation well into the ultraviolet (UV) spectral range. With this instrument, 132 spectral points in the ellipsometric parameters (ψ, Δ) over the photon energy range from 1.5 eV (827 nm) to 6.5 eV (191 nm) can be collected in a minimum acquisition time of 24.5 ms, corresponding to one optical cycle of the rotating polarizer. Averages over two and 80 optical cycles (obtained in 49 ms and 1.96 s, respectively) give standard deviations in (ψ, Δ) of less than (0.04°, 0.08°) and (0.007°, 0.015°), respectively, for the energy range from 3.5 to 6.0 eV, as determined from successive measurements of a stable thermally oxidized silicon wafer. Key modifications to previous instrument designs include: (i) a tandem in-line Xe/D2 source configuration for usable spectral output from 1.5 to 6.5 eV; (ii) MgF2 Rochon polarizers for high transmission in the UV without the need for optical activity corrections; (iii) a spectrograph with a grating blazed at 250 nm and two stages of internally mounted order-sorting filters; and (iv) nonuniform grouping of the pixels of the photodiode array detector for a more uniform spectral resolution versus photon energy, with energy spreads per pixel group ranging from 0.02 eV at 1.6 eV to 0.05 eV at 5.1 eV. As an example of the application of this instrument, results of real time spectroscopic ellipsometry studies are reported for the deposition of an amorphous silicon nitride thin film by radio-frequency magnetron sputtering onto a silicon wafer substrate. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288260
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  • 12
    Electronic Resource
    Electronic Resource
    Langmuir–Taylor surface ionization of alkali (Li, Na, K) and alkaline earth (Ca, Sr, Ba) atoms attached to helium droplets (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3480-3484 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A beam of superfluid helium droplets (HeN, N(approximate)104) doped with alkali and alkaline earth atoms is detected by Langmuir–Taylor surface ionization. We measured detection efficiencies and time constants as a function of the temperature of a hot rhenium surface. Compared to results on free K, Na, and Ba atoms we find practically no differences in the detection properties; apparently the helium host environment does not significantly influence the mechanism of surface ionization. In addition, data for Li, Ca, and Sr on detection probabilities and residence times of the ions on the hot rhenium surface will be presented for the first time. Time constants and desorption energies are extracted; for alkaline earth atoms the latter are found to be significantly higher compared to the desorption of the alkalis. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287750
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  • 13
    Electronic Resource
    Electronic Resource
    Laser induced fluorescence measurements of dissolved oxygen concentration fields near air bubble surfaces (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3494-3501 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article describes a laser-induced fluorescence (LIF) technique for measuring dissolved oxygen concentration gradients in water near the surface of an air bubble. Air bubbles are created at the tip of a needle in a rectangular bubble column filled with water that contains pyrenebutyric acid (PBA). The fluorescence of the PBA is induced by a planar pulse of nitrogen laser light. Oxygen transferring from the air bubble to the deoxygenated water quenches the fluorescence of the PBA. Images of the instantaneous and two-dimensional fluorescence field are obtained by a UV-intensified charge-coupled device (CCD) camera. Quenching of fluorescence intensity is determined at each pixel in the CCD image to measure dissolved oxygen concentration. Two-dimensional concentration fields are presented for a series of measurements of oxygen transfer from 1.6 mm bubbles suspended on the tip of a needle in a quiescent fluid. The images show the spatially varying concentration profiles, gradients, and boundary layer thicknesses at positions around the bubble surfaces. These direct and local measurements of concentration behavior within the mass transfer boundary layer show the potential of this LIF technique for the development of general and mechanistic models for oxygen transport across the air–water interface. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287341
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  • 14
    Electronic Resource
    Electronic Resource
    An equipment for three-dimensional spatially resolved gas analysis (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3513-3521 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The apparatus described is able to measure three-dimensional temperature and partial pressure distributions in gas mixtures with a spatial resolution better than 0.5 mm. The measurements are performed in a well defined laminar gas flow in a duct of rectangular cross section. The gas mixture is sampled locally with a quartz tube orifice leak movable in three dimensions. Mass spectrometry is used for partial pressure measurements. The total pressure in the duct can be regulated in the range 50–760 Torr and the gas temperature can be varied between room temperature and 500 °C. The apparatus is primarily designed for studies of the distribution of reactants and products over catalytic surfaces. Because of the well defined gas flow in the duct the partial pressure distributions of reactants and products over the catalytic surface can be calculated with good accuracy. By comparing calculated pressure distributions to measured ones the local reaction rate on the catalytic surface as well as the pressures of reactants and products at the surface can be obtained. As an example it is shown how the hydrogen distribution over a platinum surface exposed to a mixture of hydrogen, oxygen, and argon can be used to calculate the local water formation rate on the platinum surface. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287342
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  • 15
    Electronic Resource
    Electronic Resource
    A newly developed low drift fast response salinity meter (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3539-3542 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Here a new conductivity probe, which is basically a stainless steel tube with a plastic plug with a hole, plugged in one end, is described. The tube is externally insulated and the other electrode is (usually earthed) a metallic slab fixed in the fluid. The electronic used is of a conventional type and uses a 1 kHz signal whose amplitude is modulated by the conductance across the probes terminals. The signal is amplified, rectified, and filtered. The probe is different from the conventional probes, in that the fluid is sucked through the small hole in the probe tip, and only through the fluid in the tip can an electric current flow. Hence, the output and the dynamic response depend, respectively, on the conductivity of the small volume of the fluid in the tip, and how fast it can be replaced. Tests on this and other types of probes, show that this probe has almost no drift and has a satisfactory dynamic response. Probes with different tip geometries have also been tested and show that the frequency response of the probe (typically 200 Hz) does not change significantly. Possible adaptation of such a probe for oceanographic measurements will be discussed. The author has successfully used such a system for laboratory study of turbulence in stratified fluids. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287620
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  • 16
    Electronic Resource
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    A high-bandwidth electrical waveform generator based on an aperture-coupled stripline (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3559-3566 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An electrical waveform generator based on an aperture-coupled stripline is described. The device is a four-port electrical directional coupler consisting of two striplines coupled through an aperture in their common ground plane. Replacing the aperture layer of the device can produce arbitrarily shaped electrical waveforms with 100 ps structure over a pulse envelope of several nanoseconds. A numerical solution of the telegraph equations using the method of characteristics is used to model and design devices. Excellent agreement is obtained between the model and device performance. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288254
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  • 17
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    Highly accurate smoothing filter (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3570-3578 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An iterative filter for the smoothing of degraded line shapes with Gaussian noise, and a signal to noise ratio defined in a wide interval 20–∞ is presented. The smoothed line shape shows errors below 2% in its height and width parameters with regard to the true values used in the simulation. The filter reduces the Gaussian noise to less than a half. In the tests carried out with a PC computer, the new filter proved that the original line shape for a linewidth of 5–30 is better recovered than the Savitsky–Golay filter. The application of the procedure only involves the use of the linewidth parameter of the degraded peak which simplifies the smoothing process. The filter follows two basic operations: first, an oversmoothing is applied to the degraded line and second, an iterative enhancement on the oversmoothing spectrum is made. The resulting spectrum of these two operations is compared with the degraded line by a least squares fitting method. When the filter is used in a simplified version, it is useful not only to determine very overlapped lines in a degraded spectrum, but also to calculate the background in an experimental spectrum. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287040
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  • 18
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    Ultrasonic imaging, particle detection, and V(z) measurements in molten zinc using focused clad buffer rods (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3579-3586 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Ultrasonic imaging, particle detection, and V(z) measurements have been performed using focused clad buffer rods in molten zinc at temperature more than 600 °C. The focused ultrasonic waves are generated by a spherical or cylindrical acoustic lens which is fabricated at the end of the clad buffer rod. In order to evaluate its focusing ability, several experiments are carried out at 10 MHz in a pulse-echo mode. The lateral resolution at the focus of the spherical acoustic lens in molten zinc is quantitatively examined and compared with that in water using a thin stainless wire with a diameter of 380 μm. High resolution ultrasonic imaging is carried out by the common C-scan technique. The signal-to-noise ratio of the reflected signals from the flat sample surface at the focus is better than 35 dB. Ultrasonic images are obtained from the amplitude and time delay variations of the reflected signals. An attempt has also been made to detect particles suspended in molten zinc. Backscattered signals from particles are clearly visible at the focal region of the lens. For quantitative materials evaluation, V(z) curve measurements are performed using both spherical and cylindrical surface lenses and the leaky surface acoustic wave velocity of a ceramic (SiC) plate immersed in molten zinc is successfully determined. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287041
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  • 19
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    The use of pressure controlled Fabry-Pérot interferometer with linear scanning of data for Brillouin-type experiments (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2988-2991 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The article presents results from work with Fabry-Pérot interferometers in Brillouin laser light scattering experiments, where optical signals of very low level intensity are observed. The information presented here can be useful in other types of optical experiments where scanning in the Fabry-Pérot interferometer spectral range has to be used. In such situations the shape of spectral lines as well as their relative distances can be detected. The key to the solution presented here is the use of a silicon-membrane pressure sensor coupled to a pressure chamber. It makes it possible to view spectral lines equally spaced after nonlinear flow of air from a chamber where the Fabry-Pérot interferometer is placed. Linear scanning in the spectral range equal to a frequency of about 150 GHz is possible. The method can be applied to Fabry-Pérot's etalons, very frequently produced some years ago. Now it should find new fields of application, in a simple and cost effective way, in student laboratories as well as in other research institutions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1304872
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  • 20
    Electronic Resource
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    dc and ac optical nulling bridges for sensitive transmittance measurements (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2995-3003 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a formal comparison between dc and ac nulling optical bridges. We consider their performance in monitoring over long periods of time (several minutes), small and slow (in a time scale of seconds) changes in transmittance of an optical component. We consider two fundamentally different ac optical bridges (OB), an amplitude modulated optical bridge (AM-OB), and a switching optical bridge (Sw-OB). For each OB, we derive a general expression for the minimum detectable change in transmittance (|ΔT|min), taking into account all the important noises. It is found that under optimum conditions the dc- and AM-OB have similar detection limits imposed by the 1/f noise of the photodetectors. It is shown that the Sw-OB can in principle overcome the 1/f noise of the detector and approach the shot-noise limit; however, it is sensitive to switching device imperfections (to first order in smallness), which could easily prevent achieving a detection limit below the 1/f noise. It is also shown that the Sw-OB has intrinsic advantages over the dc- and AM-OB for its use in remote sensors. It can eliminate more efficiently noise induced along the propagation of light from the sensing point to the photodetector. We conclude that when using low power optics (P≤1 mW) and considering a bench instrument, the dc- and AM-OB can be used for a target resolution down to |ΔT|min(approximate)10−5–10−6. The Sw-OB optical bridges should be chosen if |ΔT|min(approximate)10−6–10−8 is to be attempted. In any case, strict conditions are to be met before considering approaching the detection limits imposed by electronic noises. These conditions are discussed in detail. In particular, atmospheric isolation will be needed in general below |ΔT|min(approximate)10−4. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1305509
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    Design of a scanning atom probe with improved mass resolution (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3016-3023 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A design for a high mass resolution scanning atom probe is described, which utilizes a two-conductor microelectrode held at 10–100 μm from the specimen. Field evaporation pulses are applied to the part of the counter-electrode closest to the specimen, while the output is maintained at ground. If the gap between the two conductors is small, field evaporated ions pass through the microelectrode while the pulse voltage is essentially constant, and thus the resultant spread in ion energies is small and the mass resolution in time-of-flight mass spectrometry is correspondingly improved. Initial results indicate improvements of 4–5 times over the mass resolution obtained with a simple counter electrode. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1304877
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    Direct imaging of highly charged ions in an electron beam ion trap (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3050-3058 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have directly observed the ion cloud distribution in an electron beam ion trap using visible and ultraviolet fluorescence from lines in the ground term of Ar13+, Xe31+ and Xe32+ ions. Using a gated intensified charge coupled device camera, we have the capability to measure both static and dynamic ion cloud distributions. The images provide information about the trapped highly charged ions which is difficult to obtain by other methods. To demonstrate the usefulness of the technique, we took images of static ion clouds under different conditions and compared the distributions to a simple model. We also recorded time resolved images which show that we can monitor the relaxation of the ion cloud toward equilibrium when the trapping conditions are suddenly changed. The information provided by such measurements can be used to improve models of ion cloud dynamics and, combined with modeling, these techniques can help improve measurements of atomic data using electron beam ion traps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1305521
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    Spectral resolution for a five-element, filtered, x-ray detector array using the method of Backus and Gilbert (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3072-3079 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The generalized method of Backus and Gilbert (BG) is described and applied to the inverse problem of obtaining the spectrum from a five-channel, filtered array of x-ray detectors. This diagnostic is routinely fielded on the Z facility at Sandia National Laboratories to study soft x-ray photons (∼100–2300 eV), emitted by high density Z-pinch plasmas. The BG method defines spectral resolution limits on the system of response functions that are in good agreement with a classical unfold method, based on a histogram representation of the source spectrum. The resolution so defined is independent of the source spectrum. For noise-free, simulated data the BG approximating function is also in reasonable agreement with the source spectrum (150 eV blackbody) and the unfolded spectrum. This function may be used as an initial trial function for iterative methods or a regularization model.© 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1304869
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    Correlation-based phase noise measurements (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3085-3091 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In the characterization of the phase noise of a component, it is common practice to measure the cross-spectrum density at the output of two phase detectors that simultaneously compare the component output signal to a common reference. This technique, which is based on correlation and averaging, allows the rejection of the phase detector noise. On the other hand, it is known that the interferometer exhibits lower noise floor and higher conversion gain than other phase detectors suitable to radio-frequency and microwave bands. Thus, we experimented on an improved instrument in which the phase noise of a component is measured by correlating and averaging the output of two interferometers. The measurement sensitivity, given in terms of noise floor, turns out to be limited by the temperature uniformity of the instrument, instead of the absolute temperature T. This feature makes the instrument suitable to investigate the spectrum Scursive-phi(f) of phase fluctuations below kBT/Po, i.e., the thermal energy kBT referred to the carrier power Po. The described method is suitable to the implementation of instruments in a wide frequency range, from some 100 kHz to 40 GHz and beyond. In principle, this method can also be exploited for the measurement of amplitude noise. Theory and experimental proof are given. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1304871
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    Microscope system for use in high magnetic fields (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3108-3110 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a microscope system, with video output, that operates within the confines and the high magnetic field of the 195 mm wide bore, 20 T resistive magnet at the National High Magnetic Field Laboratory. The accessibility of this system allows the user to vary the field of view and focus in situ and to produce images with up to 10 micron resolution. It allows for temperature regulation of samples to within 1 °C and in situ sample manipulation. Images of a biological specimen, Xenopus laevis embryos, in high magnetic field are presented. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1304880
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    Reflection surface x-ray diffraction patterns: k-space images (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3132-3137 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For the past two decades, x-ray diffraction has been utilized for surface structural determination. Unlike reflection high-energy electron diffraction (RHEED) which is a complicated dynamical scattering process, x-ray surface analysis is simple and straightforward due to the kinematic nature of x rays. Using high brilliance x rays from an undulator beamline and a highly sensitive charge coupled device detector, we successfully observed RHEED-like x-ray diffraction patterns. The patterns were recorded during the preparation of Si(111)-(7×7), transformation to Ge/Si(111)-(5×5) and Ge growth. Also, simultaneous measurements of x-ray reflectivity and crystal truncation rods are shown feasible with this technique. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1305512
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    Miniature rotatable vacuum cell for low-temperature thermal measurements in high magnetic field (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3148-3150 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a miniature vacuum cell allowing thermal measurements in liquid He medium. The small size of the cell allows rotation in the limited space of high field magnets. A useful accessory for cell evacuation is also described. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1305507
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    Characterization of coatings on magnetic metal using the swept-frequency eddy current method (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3161-3167 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A measurement technique using the swept-frequency eddy current (SFEC) method for determining the thickness, conductivity, and permeability of metallic coatings on metal substrates for the case when either coating, substrate, or both are magnetic was developed. This technique involved using the empirically determined permeability of the metals as input to the model calculation. This technique is demonstrated for nickel layers (25–200 μm) over copper substrates, copper layers (25–200 μm) over nickel substrates, and zinc layers (50–400 μm) over steel substrates. The electrical impedance was measured for air-core coils in the presence and absence of the layer using a 4194A Hewlett–Packard impedance analyzer. An analytic closed-form solution for calculating the impedance of a cylindrical air-core probe over a layered metallic half-space is presented. The determination of coating thickness and conductivity and permeability of the metals is based on the comparison of the data taken with air-core coils and theoretical calculation that using the closed-form solution developed. Most of the cases studied show experiment and theory agreeing fairly well, within 10%, with no adjustable parameters. The physical phenomena of eddy currents interaction with the coated magnetic metals are also discussed. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1304862
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    Precision microwave dielectric and magnetic susceptibility measurements of correlated electronic materials using superconducting cavities (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3151-3160 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We analyze microwave cavity perturbation methods, and show that the technique is an excellent, precision method to study the dynamic magnetic and dielectric response in the GHz frequency range. Using superconducting cavities, we obtain exceptionally high precision and sensitivity for measurements of relative changes. A dynamic electromagnetic susceptibility ζ˜(T)=ζ′+iζ″ is introduced, which is obtained from the measured parameters: the shift of cavity resonant frequency δf and quality factor Q. We focus on the case of a spherical sample placed at the center of a cylindrical cavity resonant in the TE011 mode. Depending on the sample characteristics, the magnetic permeability μ˜, the dielectric permittivity ε˜=ε′+iε″, and the complex conductivity σ˜=σ′+iσ″ can be extracted from ζ˜H. A full spherical wave analysis of the cavity perturbation indicates that: (i) In highly insulating samples with dielectric constant ε′∼1, the measured ζ˜H∼χ˜M, enabling direct measurement of the magnetic susceptibility. The sensitivity of the method equals or surpasses that of dc superconducting quantum interference device measurements for the relative changes in magnetic susceptibility. (ii) For moderate ε˜ and conductivity σ˜, ζ˜H∝ε˜+iωσ˜/ε0−1, thus enabling direct measurement of the sample dielectric constant ε˜, even though the sample is placed in a microwave magnetic field. (iii) For large σ we recover the surface impedance limit. (iv) Expressions are provided for the general case of a lossy dielectric represented by ε˜+iωσ˜/ε0. We show that an inversion procedure can be used to obtain ε˜+iωσ˜/ε0 in a wide range of parameter values. This analysis has led to the observation of new phenomena in novel low-dimensional materials. We discuss results on magneto dynamics of the three-dimensional (3D) antiferromagnetic state of the spin chain compound Sr2CuO3. In dielectric susceptibility measurements in Sr14Cu24O41, we directly observe a dielectric loss peak. Dimensional resonances in the paraelectric material SrTiO3 are shown to occur due to the rapid increase of dielectric constant with decreasing temperature. The cavity perturbation methods are thus an extremely sensitive probe of charge and spin dynamics in electronic materials. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1305519
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    The construction of a gas aggregation source for the preparation of size-selected nanoscale transition metal clusters (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3178-3183 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The design and operation of a gas aggregation source is described. The source combines the attributes of high-temperature operation (enabling preparation of transition metal clusters), mass selection, ultrahigh vacuum compatibility, and transportability. This makes it ideally suited to in situ studies such as scanning tunneling microscope or synchrotron radiation experiments. Data are presented to illustrate the performance of the source; recent results obtained in synchrotron radiation studies are highlighted. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1304868
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    A scanning dual-capillary-tube viscometer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3188-3192 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The present study introduces the concept of a new scanning dual-capillary-tube viscometer (SDCV) for viscosity measurements of both Newtonian and non-Newtonian fluids, including whole blood, over a wide range of shear rates. The flow rate and pressure drop measurements that are usually required for the operation of a capillary-tube viscometer are replaced with two measurements of liquid-height variation with time. Using a charge-coupled device sensor array, one could measure the variation of fluid levels at each riser tube, h1(t) and h2(t), from which the test fluid viscosity was calculated. The feasibility and accuracy of the SDCV technique has been demonstrated for a standard-viscosity oil and for bovine blood by comparing results against established viscosity measurement techniques. A power-law viscosity model was used to correlate the data for the latter. The dual-capillary-tube viscometer extends the shear rate range as low as 0.1 s−1 for both the viscosity of mineral oil (9.9 cP at 25 °C) and bovine blood with 3% ethylenediaminetetraacetic acid at room temperature. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1305513
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    A medium-frequency interferometer for studying auroral radio emissions (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3200-3206 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An interferometer for use between 2.5 and 3.0 MHz has recently been developed for the purpose of studying auroral radio emissions. The instrument consists of an array of 17 antennas, associated electronics for amplitude and phase measurements, and computer hardware for instrument control and data recording. In its standard operational mode, the instrument sweeps from 2.5 to 3.0 MHz in 1 kHz steps every 1.5 s. The intensity of the received signal and the phase at each antenna is measured for each 1-kHz-wide bin. These data can be used to produce spectrograms showing the intensity of the received signal versus frequency and time and for determining the direction of arrival for any signal in the instrument bandwidth. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1305518
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    Adjustable resonant cavity for measuring the complex permittivity of dielectric materials (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3207-3209 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An adjustable resonance cavity was developed to measure the complex permittivity of dielectric materials. The cavity has an inner diameter of 16.400 cm and an inner height of 2.54 cm. The aluminum stationary wall holder was positioned about 10.8 cm above the top of the cavity. It was fixed into place by three 1.27-cm-diam linear shafts. By suspending from the wall holder, the movable wall moved vertically by sliding on 1.27 cm bore-closed ball bushings. By turning a 1 in.-12 nut, the movable wall could be positioned so that the cavity height equaled the height of the sample. Therefore, this enables the measurement of the permittivity of samples with heights between 0.88 and 1.91 cm and radius between 1.27 and 3.18 cm. The complex permittivity of the sample was calculated based upon the sample dimensions, central frequency of TMono modes, and Q factor of the resonance curve using an exact solution. The complex permittivity was measured at the three lowest modes, where the frequency span is 1–4 GHz. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1304865
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    Six-degree-of-freedom displacement measurement system using a diffraction grating (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3214-3219 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Six-degree-of-freedom displacement measurement systems are applicable in many fields: precision machine control, precision assembly, vibration analysis, and so on. This article presents a new six-degree-of-freedom displacement measurement system utilizing typical features of a diffraction grating. It is composed of a laser source, three position sensitive detectors, a diffraction grating target, and several optical components. Six-degree-of-freedom displacement is calculated from the coordinates of diffracted rays on the detectors. A forward and an inverse problem were solved to compute the full pose of an object through kinematic analysis. The experimental results show that the measurement system had a maximum error of ±10 μm for translation and ±0.012° for rotation. The repeatability is about 10 μm for translation and 0.01° for rotation. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1305816
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    Femtoampere current reference stable over atmospheric temperatures (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3231-3232 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Calibration of ultralow current ammeters deployed in atmospheric ion counters requires stable current references operating at high source impedance. Using standard precision components, this current reference generates equal bipolar currents of nominally ±500 fA, cyclically for 32 s each. The currents were found to be stable to 2 fA over the temperature range −20 to 20 °C, typical of atmospheric conditions. The output current is delivered via a capacitor, and by arranging for the capacitor to be guarded at ground potential when the system is not generating a current, the reference can be permanently connected to an electrometer with minimal leakage. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1304859
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    Current mode Schmitt trigger for a phototransistor/resistor detector (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3233-3233 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A current mode Schmitt trigger for a phototransistor/resistor detector is presented. It can be successfully operated with a 1.5 V power supply. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1304860
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    Elliptical x-ray microprobe mirrors by differential deposition (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2635-2639 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A differential coating method is described for fabricating high-performance x-ray microfocusing mirrors. With this method, the figure of ultrasmooth spherical mirrors can be modified to produce elliptical surfaces with low roughness and low figure errors. Submicron focusing is demonstrated with prototype mirrors. The differential deposition method creates stiff monolithic mirrors which are compact, robust, and easy to cool and align. Prototype mirrors have demonstrated gains of more than 104 in beam intensity while maintaining submilliradian divergence on the sample. This method of producing elliptical mirrors is well matched to the requirements of an x-ray microdiffraction Kirkpatrick–Baez focusing system. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150668
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    A simple microbeam profiling technique for x-ray optics (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2640-2643 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Enhancement of the quality of images or maps obtained using micro x-ray fluorescence spectrometry requires knowledge of the flux distribution profile of the primary x-ray beam. A simple procedure based on a wire scan was developed for the determination of an x-ray microbeam profile. This technique is simple and can be used for a given excitation/detection geometry without any change in spectrometer configuration. However, the result of such a scan is a convolution of the beam profile with the shape of the wire. To restore the actual distribution of photon flux density, a nonlinear least-squares procedure was adapted to model the profile using a parametric function to describe the flux distribution. Among the algorithms tested, a sigmoid function was found to be the best for describing the beam profile. The results of calculations were verified by measurements using a charge coupled device camera. Reasonably good agreement was obtained between the two different techniques. The results of this work confirmed that a wire scan combined with a mathematical restoration procedure is useful for describing the actual profile of an x-ray microbeam created using a pinhole collimator. An advantage is that the microbeam profile is calculated at the location of the measured samples. The results indicated that the χ2 value could be used to select the optimum function to describe the microbeam profile. The procedure can also be used to evaluate the quality of a pinhole collimator. We plan to use measured microbeam profiles in combination with mathematical procedures to improve the spatial resolution of linear scans of patterned samples. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150669
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    Doppler-free modulation transfer spectroscopy of rubidium 52S1/2–62P1/2 transitions using a frequency-doubled diode laser blue-light source (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2655-2662 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A frequency-doubled diode laser spectrometer in the blue-wavelength region with a continuous-frequency tuning range of up to ∼7 GHz has been developed, comprising a powerful fundamental light source based on a master/slave laser combination coupled with a KNbO3 crystal for second-harmonic generation in a power-enhancement cavity. It has been employed for the observation of saturated absorption spectra in 52S1/2–62P1/2 hyperfine transitions of atomic rubidium with the aid of a modulation transfer spectroscopic technique, and also the frequency stabilization to one of them has been demonstrated, suggesting the possibility of the establishment of a precision optical frequency marker in the blue range. A relative stability of better than 2.8×10−10 is estimated based on the locked error signal in the preliminary stabilization. With a further study of the frequency instability and uncertainty, in addition to supplementary improvements of apparatus, one may expect a realization of a stabilized laser in the blue-spectral domain. Details of the developed blue-light source are described and the demonstrated results of the rubidium spectroscopy are also described and discussed. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150672
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    Michelson interferometry with 10 pm accuracy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2669-2676 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We demonstrate a new heterodyne Michelson interferometer design for displacement measurements capable of fringe interpolation accuracy of one part in 36 000. Key to this level of accuracy are the use of two acousto-optic modulators for heterodyne frequency generation and digital signal processing demodulation electronics. We make a direct comparison of our interferometer to a commercial interferometer based on a Zeeman-stabilized laser, and show that the residual periodic errors in ours are two orders of magnitude lower than those in the commercial unit. We discuss electronically induced optical cross talk and optical feedback as sources of periodic error. Our new interferometer is simple, robust, and readily implemented.
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    URL: http://dx.doi.org/10.1063/1.1150715
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    Ultrasmall volume refractive index detection using microinterferometry (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2684-2692 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A microinterferometric backscatter detector (MIBD) has been developed to perform subnanoliter volume refractive index measurements using a simple, folded optical train based on the interaction of a laser beam and a fused silica capillary tube. Positional changes of the interference pattern extrema (fringes) allow for the determination of Δn at the 10−7 level, corresponding to 5.3 pmole or 0.48 ng of solute, when thermal noise is controlled at 8×10−3 °C. MIBD is relatively path-length insensitive for capillaries ranging in inner diameter from 75 to 775 μm, allowing a large range of detection volumes, from 350 pL to 40 nL, to be produced. A theoretical model of the microinterferometric backscatter detector has also been developed and evaluated and has been found to be in agreement with experimental data. This model indicates increased sensitivity of the instrument as the wavelength of the probe beam and the wall thickness of the capillary tube are reduced. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150675
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    High-energy neutral particle measurement system in the large helical device (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2698-2703 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The development of a high-energy neutral particle measurement system for ion temperature measurements and high-energy particle confinement analysis during neutral beam injection and ion cyclotron resonance frequency heating experiments in the large helical device (LHD) is described here. We have been improving the time-of-flight neutral particle analyzer for the LHD which had been developed in ENEA Frascati. The control and data acquisition systems were designed to be suitable for long discharges in the LHD. The horizontal and vertical movable stage is prepared to investigate pitch-angle distribution and loss cone. We have resolved many difficulties at installation, for example, the strong leakage magnetic field from the LHD and the limitations of magnetized materials near the LHD, the quench of the superconducting magnetic field, the narrow viewing port, and the fully remote control system. The preliminary results in plasma experiments are also described here. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150677
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    Detection efficiency of a channel electron multiplier for low energy incident noble gas ions (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2704-2709 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The absolute detection efficiency of a continuous channel electron multiplier (DeTech 407-EIC) has been measured for the noble gas ions He+, Ar+, and Xe+, with energies up to 4.9 keV. For all ions, the detection efficiency initially rises linearly as a function of velocity. Our results and a reanalysis of literature data show that the threshold velocity below which a multiplier does not respond to impinging ions cannot be regarded as independent of the ion's atomic number, Z, as previously reported. Instead, the threshold velocity is proportional to Z−c. The experimentally obtained efficiency-versus-velocity curves for our detector have been analyzed in the region of linear increase. The resulting expression for the detector efficiency, cursive-epsilon, is a function of the ion's atomic number and velocity, v, and can be written as cursive-epsilon(v,Z)=a(v−b/Zc)Zn, with a, b, c, and n being constants. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150678
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    A sensitive dispersion interferometer with high temporal resolution for electron density measurements (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2710-2715 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A dispersion interferometer with a sensitivity of up to 10−4 fringe shifts and a time resolution of about 1 ns was developed. This time resolution exceeds previous systems by three orders. The operation of the dispersion interferometer and its characteristic properties are discussed and the experimental setup of the installation is explained in detail. The stability of the interferometer was tested and it was shown that its operation point drifts less than 0.25 rad/h. The interferometer was used to investigate the high power ion diodes at the pulse generator KALIF, where focused proton beams with power densities of up to 1 TW/cm2 are generated. For the very first time the electron line density inside the diode gap, where the protons are accelerated, could be directly measured. The line density was on the order of several 1013 cm−2. A straightforward estimation of the line density using a simplified diode model proved to be in excellent agreement with the results. The dispersion interferometer can be used for sensitive electron density measurements on nanosecond time scales. Further developments to improve the sensitivity are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150679
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    Simple microwave preionization source for ohmic plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2728-2732 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A simple economical 2.45 GHz microwave system has been developed and utilized for preionization on the Korea Advanced Institute of Science and Technology (KAIST)-TOKAMAK. The magnetron microwave source was obtained from a widely used, household microwave oven. Since ac operation of the magnetron is not suitable for tokamak application, the magnetron cathode bias circuit was modified to obtain continuous and stable operation of the magnetron for several hundred milliseconds. Application of the developed microwave system to KAIST-TOKAMAK resulted in a reduction of ohmic flux consumption. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150682
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    Ion dynamics in the sheath in multicomponent plasma with negative ions (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2733-2736 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Observations on steady state ion-rich sheath around a negatively biased grid in a double plasma device have been made in multicomponent plasma with negative ions. A hump in the potential profile is found to occur at the sheath edge. The characteristics of the hump depend on the grid voltage, source biasing voltage, density difference in the two chambers, and the negative to positive ion concentration ratio. It is argued that resonance which is coupled with the beam ions and background ions is associated in the excitation mechanism to create the nonsymmetrical structures in the plasma potential profile. Below the critical concentration ratio, the hump grows in height and above the critical ratio, the width of the hump increases but the height decreases and ultimately it vanishes. The variation in the hump potential profile due to the injection of negative ions can be explained by the ion momentum exchange and by their dynamics. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150683
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    Subresolution axial distance measurements in far-field fluorescence microscopy with precision of 1 nanometer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2742-2745 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Fluorescent objects closer than the diffraction resolution limit can be distinguished in far-field microscopy provided they feature different emission spectra. Utilizing the superior axial resolution of 4Pi-confocal microscopy of 100–150 nm, we investigate the precision with which fluorescence objects with subdiffraction axial distance can be measured in the far field. At a wavelength of 820 nm distances on the order of 60 nm between beads and a monomolecular Langmuir–Blodgett layer were determined with a precision of 1.2 nm within 3.2 s. The reduced spatial extent of the 4Pi-confocal point-spread-function improves the precision of colocalization measurements in double stained specimens and opens up the prospect on far-field fluorescence profilometry with (sub) nanometer height resolution. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150685
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    Quantitative imaging of dielectric permittivity and tunability with a near-field scanning microwave microscope (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2751-2758 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the use of a near-field scanning microwave microscope to image the permittivity and tunability of bulk and thin film dielectric samples on a length scale of about 1 μm. The microscope is sensitive to the linear permittivity, as well as to nonlinear dielectric terms, which can be measured as a function of an applied electric field. We introduce a versatile finite element model for the system, which allows quantitative results to be obtained. We demonstrate use of the microscope at 7.2 GHz with a 370 nm thick Ba0.6Sr0.4TiO3 thin film on a LaAlO3 substrate. This technique is nondestructive and has broadband (0.1–50 GHz) capability. The sensitivity of the microscope to changes in permittivity is Δεr=2 at εr=500, while the nonlinear dielectric tunability sensitivity is Δε113=10−3 (kV/cm)−1. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150687
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    Imaging of liquid crystals using a new scanning near-field optical microscope with microfabricated tips and shear force detection (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2759-2764 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report results obtained with a scanning near-field optical microscope which was developed, recently. The scanning head of the device is mounted on an inverted polarizing microscope. The sample is illuminated through a microfabricated tip which is mounted on a single-mode optical wave-guiding fiber. The light transmitted through the sample is collected in the far field by a microscope lens. The distance between the tip and the sample is controlled by shear force detection, using a nonconventional setup. We applied this new equipment successfully in order to investigate birefringent and dichroic liquid crystal films, using polarization modulation or fluorescence detection, respectively. An optical resolution down to (approximate)200 nm was obtained on the sample of a cholesteric liquid crystal for a wavelength of 488 nm. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150688
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    Fundamental limits to force detection using quartz tuning forks (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2776-2780 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This paper explores the fundamental limits of the use of quartz tuning forks as force detectors in scanned probe microscopy. It is demonstrated that at room temperature, pressure, and atmosphere these force sensors have a noise floor of 0.62 pN/Hz and exhibit a root mean square Brownian motion of only 0.32 pm. When operated as a shear force sensor both dissipative and reactive forces are detected on approach to the sample. These forces are sufficient to reduce the amplitude of motion of the probe nearly to zero without physically contacting the surface. It is also demonstrated that conventional proportional-integral feedback control yields closed loop responses at least 40 times faster than their open loop response. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150691
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    Ultrahigh pressure cell for materials synthesis (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2784-2790 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe here an apparatus for generating ultrahigh pressures and temperatures for materials synthesis. The system uses a spherically shaped explosive charge to radially compress various materials contained within the sample cavity. The results show the system is completely reproducible and, because of the geometry of the loading system, the workpiece that holds the precursor material is in excellent postshock condition. Samples are subjected to a pressure pulse of approximately 230 GPa for a period of 4 μs. Using this system, C60 has been compressed using a variety of quenching materials to attempt to generate diamond. Two organic precursors have also been tested to determine if the high stress conditions are suitable to synthesize β-carbon nitride. In this article, the design of the system, the numerical modeling using Dyna East Finite Element Lagrangian and CTH hydrocodes, and the results of the synthesis experiments will be presented. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150693
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    An automated apparatus for measuring the tensile strength and compressibility of fine cohesive powders (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2791-2795 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes an apparatus based on a novel use of a powder bed, whereby the relationship between consolidation stress, tensile strength, and free volume of fine powder is measured. The powder to be tested is first initialized to a reproducible state. The initialized powder is next consolidated either beyond its own weight or below its own weight by means of a controlled flow of gas. An ultrasonic device measures the height of the bed, thus providing an average value of the powder free volume. Next the consolidated bed of powder is subjected to a slowly increasing gas flow, so directed as to put the powder under tension. The overpressure causing the powder to break provides a measure of the tensile strength of the powder, which in turn is a function of the consolidation and free volume. The relationship between consolidation stress, tensile strength, and free volume is related to powder flowability. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150694
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    Alignment visualization using electroconvection of planar nematics (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2800-2806 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In electroconvection experiments with planarly aligned nematic liquid crystals the director orientation is, conventionally, fixed through a mechanical treatment (rubbing) of the polymer-coated electrodes. Without rubbing, on the other hand, the flow direction during sample filling imposes the director orientation. We report atomic force microscopy and x-ray measurements that show an anisotropy in the polymer surface structure on several scales as a result of the rubbing. In particular we observe a fish-bone structure on a 10 nm scale. We visualize the orientation of the director both during and after filling the system using the electroconvection pattern. This is a convenient tool for exploring new director configurations. We confirm for the observed surface structure that when flow and surface designate different orientations, the mechanical surface treatment dominates. We have been able to obtain regions with radial director orientation of millimeter size. Such an alignment renders possible new types of electroconvection experiments. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150696
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    Deposition of mass-selected clusters studied by thermal energy atom scattering and low-temperature scanning tunneling microscopy: An experimental setup (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2818-2828 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present an experimental setup for the investigation of the processes occurring during the deposition of mass-selected clusters on a well-defined surface. The sample is analyzed in situ by two complementary methods: thermal energy atom scattering (TEAS) and scanning tunneling microscopy (STM). TEAS is used to study the dynamical processes during the deposition and to gather statistical information about the resulting structures on the surface. Subsequent STM measurements allow us to investigate the collision outcome on an atomic scale. The setup is highly versatile and guarantees ultra-high-vacuum conditions and cryogenic temperatures ((approximate)30 K) of the sample at all times even during sample transfer. Clusters are produced in a CORDIS-type cluster source. A new compact multichannel effusive He source in combination with a new Wien-filter-based He detector are used for TEAS measurements. The new low-temperature STM allows measurements in a temperature range between 8 and 450 K. Atomic resolution on the Pt(111) surface is regularly observed at Tsample=8 K. The performances of the setup are illustrated by STM images obtained after the deposition of Ag7+ clusters with Ekin=95 and 1000 eV on bare Pt(111) and by measurements made of the deposition of Ag7+ clusters with Ekin=20 eV in a Xe–rare-gas matrix adsorbed on Pt(111). © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150717
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    Direct temperature monitoring for semiconductors in plasma immersion ion implantation (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2839-2842 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In situ temperature monitoring is extremely important in plasma immersion ion implantation (PIII) of semiconductors. For instance, the silicon wafer must be heated to 600 °C or higher in separation by plasma implantation of oxygen, and in the PIII/ion-cut process, the wafer temperature must remain below 300 °C throughout the experiment. In this article, we present a thermocouple-based direct temperature measurement system for planar samples such as silicon wafers. In order to ensure reliable high-voltage operation and overall electrical isolation, the thermocouple assembly and wires are integrated into the sample chuck and feedthrough. Hydrogen plasma immersion ion implantation is performed in silicon to demonstrate the effectiveness and reliability of the device. Our experimental results indicate that instrumental parameters such as implantation voltage, pulse duration, and pulsing frequency affect the sample temperature to a different extent. The measured temperature rise is higher than that predicted by a theoretical model based on the Child–Langmuir law. The discrepancy is attributed to the finite-sample size and the nonplanar, conformal plasma sheath. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150700
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    Resonant ultrasound spectroscopy for measurement of mechanical damping: Comparison with broadband viscoelastic spectroscopy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2855-2861 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article compares resonant ultrasound spectroscopy (RUS) and other resonant methods for the determination of viscoelastic properties such as damping. RUS scans from 50 to 500 kHz were conducted on cubical specimens of several materials including brass, aluminum alloys, and polymethyl (methacrylate) (PMMA), a glassy polymer. Comparison of damping over the frequency ranges for broadband viscoelastic spectroscopy (BVS) and RUS for indium tin alloy in shear modes of deformation discloses a continuation of the tan δ power-law trend for ultrasonic frequencies up to 300 kHz. For PMMA, resonant peaks were sufficiently broad that higher modes in RUS began to overlap. Tan δ via RUS and BVS for PMMA agreed well in the frequency range where the methods overlap. RUS is capable of measuring tan δ as high as several percent at the fundamental frequency. Since higher modes are closely spaced, it is impractical to determine tan δ above 0.01–0.02 at frequencies other than the fundamental. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150703
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    New impedance spectrometer for scientific and clinical studies of the respiratory system (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2867-2872 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The simple techniques generally used to investigate the biomechanical properties associated with the respiratory process are able to identify only basic characteristics, just supplying an initial representation of the complex behavior of the respiratory system. A much more detailed description can be obtained by the forced oscillation technique (FOT). Requiring very little cooperation of the subject, this technique allows a noninvasive evaluation of the mechanical impedance of the respiratory system. Although the FOT has a great scientific and clinical potential, this is attended by technical difficulties and has yet to be put to widespread use. In this context, this work describes a new flexible, open architecture, virtual-instrument-based impedance spectrometer for the FOT. After the design details are described, the system accuracy is evaluated investigating mechanical models simulating normal and individuals with restrictive disease. This analysis revealed errors smaller than 4% in modulus and 7° in phase. Experimental results obtained in a normal and an asthmatic subject, presented as examples, revealed mean resistance in asthmatic (5.72 cm H2O/l/s) higher than in normal (2.47 cm H2O/l/s). The mean-reactance curve revealed higher resonance frequency in the asthmatic subject (∼29 Hz) than in the normal one (∼9 Hz). A higher influence of the upper airways impedance of the asthmatic individual was also observed. These results are in close agreement with physiological fundamentals, supplying substantial evidence that this instrument can contribute to the production of more detailed biophysical respiratory descriptions and composes an improved basis for the fast and easy implementation of complex medical research projects. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150705
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    High Tc superconducting asymmetric gradiometer for biomagnetic applications (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2873-2881 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a high transition temperature superconducting, first-order gradiometer intended for biomagnetic measurements in an unshielded environment. The gradiometer involves a single-layer, planar flux transformer with two loops of unequal size, the smaller of which is inductively coupled to the pickup loop of a directly coupled magnetometer. In this configuration, the presence of the flux transformer reduces the sensitivity of the magnetometer by only about 5%. The flux transformer is patterned in a thin film of YBa2Cu3O7−δ deposited on a 100 mm diam wafer, and has a baseline of 48 mm. The flux transformer and magnetometer substrates are permanently bonded together in a flipchip arrangement. The common mode rejection of uniform magnetic field fluctuations in any direction is better than 1 part per 100. The outputs of two such gradiometers are subtracted to form a second-order gradiometer, which rejects first-order gradient fluctuations to about 1 part in 100. With the aid of three orthogonally mounted magnetometers, one can reduce the response of the gradiometers to uniform field fluctuations to below 100 ppm. This system is used to detect magnetic signals from the human heart in an unshielded environment. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150706
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    Control of the double pendulum optics suspension system of a 30 m triangular Fabry–Pérot cavity (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2890-2894 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a technique for the control of a double pendulum suspension system used to carry the optical elements of a 30 m long Fabry–Pérot cavity, a prototype for the mode cleaner of the VIRGO experiment. The movement of the payload is sensed with a charge coupled device camera, and the feedback forces are applied to the intermediate stage of the suspension via coil–magnet systems. The control strategy is explained and the application of the system for the longitudinal locking of the cavity is demonstrated. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150708
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    Toroidal cross capacitor for measuring the dielectric constant of gases (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2914-2921 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe toroidal cross capacitors built to accurately measure the dielectric constant of gases. We tested the capacitors by measuring the dielectric polarizability of helium and argon at 7 and 50 °C at pressures up to 3 MPa. For helium, the results are consistent with the ab initio calculation of the molar polarizability and are limited by the uncertainties of the capacitance measurements. For argon, the results are consistent with the best previously published measurements of the polarizability and are limited by the uncertainties of the pressure measurements. Lessons learned are provided.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150716
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    Simultaneous, noninvasive measurements of convective heat transfer and solid volume fraction at the wall of an entrained gas–solid suspension (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2922-2927 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe an instrument for local, instantaneous, noninvasive, simultaneous measurements of solid volume fraction and convective heat transfer at the wall of a vertical tube containing a relatively dense, entrained suspension of gas and fine solids. The instrument combines a small platinum coil and a guarded capacitance sensor. The capacitance sensor records instantaneous solid volume fraction in the near vicinity of the wall. The coil is maintained at constant temperature by a rapid anemometer bridge circuit. The vessel is wrapped in electric heaters to avoid artificially high rates associated with developing heat transfer and to minimize conduction losses from the coil. Using a model capturing these losses, convective heat transfer rates are inferred from the power input to the coil. The instrument is tested in a cold circulating fluidized bed riser. The temporal response of the thermal sensor is faster than 30 ms. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150711
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    Thermal-wave resonator cavity design and measurements of the thermal diffusivity of liquids (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2933-2937 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A liquid-ambient-compatible thermal wave resonant cavity (TWRC) has been constructed for the measurement of the thermal diffusivity of liquids. The thermal diffusivities of distilled water, glycerol, ethylene glycol, and olive oil were determined at room temperature (25 °C), with four-significant-figure precision as follows: (0.1445±0.0002)×10−2 cm2/s (distilled water); (0.0922±0.0002)×10−2 cm2/s (glycerol); (0.0918±0.0002)×10−2 cm2/s (ethylene glycol); and (0.0881±0.0004)×10−2 cm2/s (olive oil). The liquid-state TWRC sensor was found to be highly sensitive to various mixtures of methanol and salt in distilled water with sensitivity limits 0.5% (v/v) and 0.03% (w/v), respectively. The use of the TWRC to measure gas evolution from liquids and its potential for environmental applications has also been demonstrated. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150713
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    Investigation of integrated diffractive/refractive microlens microfabricated by focused ion beam (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2263-2266 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Integrated diffractive/refractive microlens with dual focus point is introduced in detail in the view of design, microfabrication, and testing. Two manufacturing methods—milling and deposition directly by focused ion beam technology is discussed and compared. It was shown by testing results that the deposition method is more suitable to form the refractive spherical/aspherical lens and milling is suitable for microfabrication of diffractive optical elements. Focusing spot size (full width at half maximum) are 0.55 and 0.87 μm (λ=638 nm) for refractive and diffractive lens, respectively, with NA 0.35 and 0.5. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150661
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    Reflectance and transmittance measurements of anisotropically scattering samples in focusing Coblentz spheres (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2270-2278 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A procedure for obtaining the correct hemispherical reflectance and transmittance of anisotropically scattering samples in focusing Coblentz spheres are presented. Consideration is taken not only to the angle-dependent detector efficiency and to multiple reflections between sample and detector, but a separation of the scattered light into a low and a high angle fraction is also introduced. To validate the formalism, the correction procedure is applied to six samples with different scattering characteristics in the visible and near-infrared region. The agreement with results from a double beam spectrophotometer, equipped with an integrating sphere, was found to be good. Without making the separation into high and low angle scattering, it was not possible to reach agreement between the results from the Coblentz and integrating spheres, and errors of the order of 10% could be obtained. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150440
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    Efficient discharge pumping of a copper vapor laser using a cylindrical grid electrode (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2288-2291 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Experimental investigation of laser output characteristics of an elemental copper vapor laser using a cylindrical grid electrode has been carried out. The grid electrode, which is placed at the inside of a cathode and separated 2 cm away from a cathode, is used for increasing the output power by improving the discharge characteristics. When the grid electrode is coupled with a peaking capacitor, it is observed that the peak voltage (voltage hold-off) in the pulsed discharge wave forms increases by about 20%. Also, the initial part of the discharge current pulse is reduced. The laser average output power increased from 16 to 21 W. Additionally, when applying dc voltage (0–100 V) to the grid electrode, the output power increased by around 6%. The effect of employing the grid electrode and the mechanisms responsible for the improved characteristics are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150443
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    Novel method to measure bulk absorption in optically transparent materials (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2279-2282 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel method to measure low absorption of pulsed laser radiation by materials with high optical transparency is demonstrated. The absorbed energy generates a temperature gradient and thus a refractive index profile. A probe laser beam is deflected by the refractive index profile and its deflection is a measure of pure volume absorption without interference from surface effects. Numerical calculations were carried out to estimate the sensitivity of the discussed laser induced deflection (LID) arrangement and to optimize the path of the probe beam in relation to the irradiated field within the sample. The experimental results agree sufficiently with numerical calculations by finite element method combined with raytracing procedures. Because the transparency is not measured directly a calibration is necessary. To provide this, a sample with known bulk absorption coefficient and thermal properties was used. In order to compensate probe beam fluctuations in air outside the sample, a double beam arrangement was designed. The LID method is applied to investigate fused silica with high ultraviolet (UV) transparency under KrF excimer laser irradiation (λ=248 nm). A He/Ne laser serves as probe beam source. Using sample dimensions of 20×20×10 mm3 and UV beam cross sections of 5×5 mm2 absorbed power down to 1 mW is detected. At typical irradiation conditions (50 s−1, 300 mJ/cm2), this value corresponds with an absorption coefficient of around 2.5×10−4 cm−1. The limitation of the absorption measurement depends on the input power of the pump laser. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150441
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    Reducing tilt errors in moiré linear encoders using phase-modulated grating (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2296-2300 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new hardware compensation method reducing displacement measurement errors, caused by tilt of the index scale in a moiré linear encoder, has been developed. In conventional moiré linear encoders, the detectors are aligned perpendicular to the line of the moiré fringes and this structure is very sensitive to an unwanted tilt of the gratings. In this article, a newly designed grating, called a phase-modulated grating, is developed to compensate for nonorthogonal errors. By using the phase-modulated grating instead of a conventional index, it is possible to reduce nonorthogonal errors of the moiré linear encoder. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150445
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    Fast impedance spectroscopy: General aspects and performance study for single ion channel measurements (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2309-2320 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In the present work, we propose a novel technical approach in time domain impedance spectroscopy enabling both enhanced time and current resolution by an improved data analysis and hardware setup. We introduce nonstationary time-to-frequency conversion methods such as short-time Fourier transform and wavelet transform resulting in an improved time resolution. The combination of a time domain impedance spectrometer with a patch-clamp amplifier enables the resolution of gigaohm impedance at low perturbation signal amplitudes. A fast impedance spectroscopy (FIS) setup is presented which is optimized for biophysical application of single ion channel measurements in supported biomembranes. The applicability and performance of the technique is first evaluated by simulations. It is then verified by measurements on model circuits which exhibit the characteristic key properties of single ion channel measurements. Here, FIS improves the time resolution by about three orders of magnitude down to milliseconds. The general aspects derived in this work are also valid in other fields, where the spectral information of a perturbation applied on a system and its response is analyzed, e.g., mechanical impedance spectroscopy and microrheology. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150447
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    Design and optimization of a corona discharge ionization source for ion mobility spectrometry (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2321-2328 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this work the possibility of using corona discharge as an ionization source in ion mobility spectrometry has been investigated. The results for both positive and negative polarity in air are consistent with the Townsend formula which states that I/V is a linear function of V. The distribution profile of the corona ions has also been investigated and compared with that of the 63Ni ionization source. Generally, the total ion current obtained from the corona ionization source was greater than that of the 63Ni source by about an order of magnitude, which results in a better sensitivity and a higher signal-to-noise ratio. The positive and negative spectra of air were recorded and the positive spectra of acetone and dimethylmethyl-phosphonate were compared with that of 63Ni. In the negative mode, a number of new peaks, apart from those of reactant ions, were observed which are mainly due to nitrogen oxides, formed by corona discharge. This problem was minimized by increasing the interdistance of the electrodes. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150618
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    Development of a novel fast frequency modulation scheme for the Joint European Torus multichannel reflectometer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2353-2359 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel frequency modulation scheme has been developed for the multichannel reflectometer used to measure density profiles and density fluctuations on the Joint European Torus (JET) tokamak. This reflectometer normally uses slow frequency sweeping (6 ms), combined with fixed-frequency operation, to measure the group delay, as well as plasma fluctuations, at ten different microwave frequencies. The novel scheme uses continuous frequency modulation on a time scale much shorter (1/65 μs) than that of plasma fluctuations, the main aim being to make the group delay measurement more robust against plasma fluctuations. This article discusses the theoretical background of the scheme, gives a detailed description of the system, and presents results from plasma measurements. Although the implementation used suffered from an excessive power-dependent group delay distortion (resulting in a positional error of 10 cm), the main objectives have been achieved. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150660
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    Doppler-free two-photon excitation of Lyman-α fluorescence for the diagnostics of magnetically confined fusion plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2334-2352 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Doppler-free two-photon excitation of hydrogen Lyman-α fluorescence is investigated as a possible laser-induced fluorescence (LIF) technique for the diagnosis of magnetically confined fusion (MCF) plasmas. A formal analysis is presented of the underlying atomic and plasma physics as well as of various practical aspects, such as parameter optimization and experimental precision. The latter is analyzed with regard to the photon noise and to the sensitivity of the fluorescence signals to the plasma and laser parameters. The diagnostic potential of the LIF technique described relies on its high spectral resolution. Thus, the absorption lines of the hydrogen isotopes H, D, and T are clearly separated from each other and can serve for isotope-selective density measurements. In addition, using a tunable laser system with small bandwidth, various plasma parameters can be inferred from the spectral line shapes, such as the neutrals' temperatures or the effective charge number Zeff. The polarization of the fluorescence can, under favorable circumstances, be exploited for magnetic field measurements. The photon statistics impose neutral densities above 1014 m−3 and thus make the diagnostic suitable primarily for the plasma edge. However, previous work has shown that it is applicable even in the plasma bulk of large machines if a neutral beam is used that generates sufficient neutral densities by charge exchange with the plasma ions. Variations or insufficient knowledge of the neutrals' temperatures are found to seriously affect the precision of absolute isotope density measurements. They are rather uncritical, however, for the determination of the H/D/T density ratios, which are of prime importance for the burn control of large MCF devices. A notable sensitivity is also found to variations of the laser frequency detuning, which should be known and stable to better than 100 MHz. The perspectives demonstrated in the present study and the success of a first experiment on the plasma generator PSI 1 at IPP Berlin are considered to be sufficient motivation for testing the diagnostic on a tokamak or other MCF device. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150620
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    Calibration of a multiple microchannel plate detectors system by α-induced secondary electrons (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2367-2370 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: α particles emitted from an 241Am radioactive source at energies of 5.4 MeV generate bursts of about ten electrons when passing through an aluminized Mylar foil. Besides the typical surface barrier electrons, the energy spectra of the secondary electrons clearly reveal two additional peaks. One at 66 eV is ascribed to aluminum LVV Auger electrons and another at 10.5 eV is attributed to the decay of aluminum volume plasmons. The well-resolved angular and energy distributions of these secondary electrons are used to calibrate the relative detection efficiencies of a large set of individual detectors of a complex multicoincidence system. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150622
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    A proposed new microstructure for gas radiation detectors: The microhole and strip plate (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2371-2376 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new type of microstructure device for a gas radiation detector is proposed. This microstructure, the microhole and strip plate structure, merges the structures of a gas electron multiplier and a microstrip plate in one single plate. This design allows two-multiplication stages and a separation of the sensitive and the detection regions, with full optical positive feedback suppression. Simulations for gas gain and electron transparency of the microstructure are presented. Different applications are discussed. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150623
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    Nitrogen-filled tube as a sensor of ionizing radiation (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2377-2379 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The influence of secondary electrons released by gamma radiation from the cathode of a nitrogen-filled tube, on probability of electrical breakdown and memory curve, has been investigated. The results show that the nitrogen-filled tube is sensitive to gamma radiation only at longer afterglow periods in the case of overvoltage values grater than 50%. For shorter afterglow periods, the lower values of overvoltages can be used to separate the contribution of gamma rays. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150662
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    Characterization of a microfocused circularly polarized x-ray probe (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2386-2390 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report on the development of a circularly polarized x-ray microprobe in the intermediate energy range from 5 to 10 keV. In this experiment linearly polarized synchrotron radiation was circularly polarized by means of a Bragg-diffracting diamond phase retarder and subsequently focused down to a spot size of about 4×2 μm2 by a Fresnel zone plate. The properties of the microprobe were characterized, and the technique was applied to the two-dimensional mapping of magnetic domains in HoFe2. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150625
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    Miniature photoconducting capacitor array as a source for tunable THz radiation (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2380-2385 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The prospects of a miniature photoconducting capacitor array as a source for THz radiation are discussed. The device consists of an alternately biased capacitor array built on a semiconductor substrate and illuminated by a short laser pulse. The laser pulse creates a propagating plasma front inside the crystal volume by side illumination, and triggers the discharging of the capacitor by shorting out the photoconducting material between each capacitor plate. The sequential discharge of the capacitor array inside the expending plasma region can be considered as an interaction between a static wave and a superluminous ionizing front. In the present article we have demonstrated production of two cycle pulses with a center frequency of up to 1.5 THz. The device combines elements from the well-known "frozen-wave" generator and from the photoconducting switches array. The underlying physics of this radiation mechanism is very similar to the dc-to-ac conversion mechanism inside a gas-filled capacitor array which generates coherent microwave radiation. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150624
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    Tip–sample distance feedback control in a scanning evanescent microwave probe for nonlinear dielectric imaging (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2414-2417 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We implemented tip–sample distance control in a scanning evanescent microwave probe for nonlinear dielectric microscopy. With the analytic expression of the tip–sample capacitance as a function of tip–sample distance, we can quantitatively regulate the tip–sample separation and independently measure the dielectric nonlinearity by application of an ac bias voltage. Simultaneous imaging of topography and ferroelectric domains has been demonstrated on periodically poled LiNbO3 single crystals. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150629
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    Nanoscale elasticity measurement with in situ tip shape estimation in atomic force microscopy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2403-2408 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For a quantitative evaluation of nanoscale elasticity, atomic force microscopy, and related methods measure the contact stiffness (or force gradient) between the tip and sample surface. In these methods the key parameter is the contact radius, since the contact stiffness is changed not only by the elasticity of the sample but also by the contact radius. However, the contact radius is very uncertain and it makes the precision of measurements questionable. In this work, we propose a novel in situ method to estimate the tip shape and the contact radius at the nanoscale contact of the tip and sample. Because the measured resonance frequency sometimes does not depend so sensitively on the contact force as expected from the parabolic tip model, we introduced a more general model of an axial symmetric body and derived an equation for the contact stiffness. Then, the parameters in the model are unambiguously determined from a contact force dependence of the cantilever resonance frequency. We verified that this method is able to provide an accurate prediction of the cantilever thickness, the tip shape, and the effective elasticity of soft and rigid samples. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150627
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    Quantitative measurement of sliding friction dynamics at mesoscopic scales: The lateral force apparatus (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2391-2402 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe an apparatus designed to quantitatively measure friction dynamics at the mesoscopic scale. This lateral force apparatus, LFA, uses double parallel leaf springs in leaf-spring units as force transducers and two focus error detection optical heads, optical heads, to measure deflections. The design of the leaf-spring units is new. Normal spring constants are in the range of 20–4000 N/m, and lateral spring constants are 7–1000 N/m. The optical heads combine a 10 nm sensitivity with a useful range of about 100 μm. The proven range of normal forces is 400 nN–150 mN. The leaf-spring units transduce friction and normal forces independently. Absolute values of normal and friction forces are calibrated. Typical errors are less than 10%. The calibration is partly in situ, for the sensitivity of the optical heads, and partly ex situ for the normal and lateral spring constants of the leaf-spring units. There is minimal coupling between the deflection measurements in the lateral and normal directions. This coupling is also calibrated in situ. It is typically 1% and can be as low as 0.25%. This means that the displacements of the tip can be measured accurately in the sliding direction and normal to the surface. Together, these characteristics make the LFA, well suited for quantitative study of friction dynamics at mesoscopic scales. Furthermore the design of the leaf-spring unit allows exchange of tips which may be fabricated (e.g., etched) from wire material (d(approximate)0.4 mm) and can have customized shapes, e.g., polished flat squares. The ability of the LFA to study friction dynamics is briefly illustrated by results of stick-slip measurements on soft polymer surfaces. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150626
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    Automatization of a multipurpose astronomical spectrograph (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2598-2602 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article deals with the study and fabrication of a system for the automation of a multipurpose spectrograph used in Astronomy. This system allows the 19 movements of the instrument to run by using high-level software, a "master" board, and 19 "slave" boards. The Astrophysique Lineal et BIdimensional par RÉseaux Optiques (ALBIREO) spectrograph has three working modes and is installed in the Observatorio de Sierra Nevada, Granada, Spain. We describe a low-cost system realized for the automatization of a multifunction spectrograph. It allows the control of a large number of motors: 19 for Albireo; the theoretical limit is 32 768! Another advantage of this architecture based on "slave" boards is to supply each motor with exactly the current it needs to reach the required torque (reliability and repetitivity of motions are obtained when the motor torque is at least twice the resistant torque). Thus, we can avoid unnecessary overheating which would be detrimental to the material as well as to the local image quality (seeing). The reliability of the system is obtained by software filtering the commands and also by using optocoupled electronics to avoid interference. For a complex instrument, the high-level software must be user friendly. The efficiency of the present software in this respect has been appreciated since first being used on the telescope. This system may be of interest to laboratories and observatories with similar needs for automation of motions. The adoption of this system will be supported by the IAA Laboratory, Granada, Spain. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150655
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    Capacitive position sensor with simultaneous, linear X–Y readout (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2603-2607 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A design is presented for a compact capacitive position sensor suitable for operation at cryogenic temperatures and high magnetic fields. The four quadrants of a base electrode are excited with phases differing by 90°; from its in- and out-of-phase components, the current injected into the movable electrode yields simultaneous information about the x and y sensor positions. This current is also linear in the position of the sensor. The effects of possible sensor imperfections are analyzed in detail. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150656
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    Microsphere plate detectors used with a compact Mott polarimeter for time-of-flight studies (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2608-2609 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A compact retarding-potential Mott polarimeter combined with microsphere plates (MSP) as electron detectors was built to perform spin-resolved time-of-flight electron spectroscopy. The comparison of the performance of MSP and channeltron detectors shows that the MSP detector has a better time resolution but a lower efficiency. The overall time resolution of the system was determined to be 350 ps using synchrotron radiation pulses. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150657
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    Femtosecond pulse shaping using spatial light modulators (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1929-1960 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We review the field of femtosecond pulse shaping, in which Fourier synthesis methods are used to generate nearly arbitrarily shaped ultrafast optical wave forms according to user specification. An emphasis is placed on programmable pulse shaping methods based on the use of spatial light modulators. After outlining the fundamental principles of pulse shaping, we then present a detailed discussion of pulse shaping using several different types of spatial light modulators. Finally, new research directions in pulse shaping, and applications of pulse shaping to optical communications, biomedical optical imaging, high power laser amplifiers, quantum control, and laser-electron beam interactions are reviewed. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150614
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    PC control and data processing in relation with a standalone laser beam analyzer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2610-2611 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this note we present a PC-based remote control and data processing setup and the associated software, developed in LabVIEW, working in conjunction with a laser beam analyzer. The setup expands the imaging processing techniques for the laser beam profile, especially in relation to the three-dimensional data representation and manipulation, by using the strong graphical processing and presentation libraries of the HIQ and IMAQ Vision software packages. One novelty of the proposed program consists in its multi-image processing ability with regard to images acquired under different conditions, and which have to be processed aligned to their centroids and their major axes. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150658
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    A selection method to improve temperature compensation of current regulator (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2582-2584 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A selection method to improve temperature compensation is proposed, which is effective in forming current regulator device with low temperature coefficient. The experimental results show that the temperature coefficients are of the order of 10−5/°C. The method is simple and the device stable and reliable. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150652
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  • 86
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    A highly sensitive photoacoustic spectrometer for near infrared overtone (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1975-1980 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: By optimizing the size of a photoacoustic cell for decreasing acoustic loss and noise, and using a proper multipass arrangement for increasing light power in the cell and optical coupling to the acoustic wave, a high-resolution external laser photoacoustic spectrometer with a detection sensitivity of 6.35×10−9 cm−1 (1:1 signal to noise level) has been developed. Using this apparatus, the high quality Doppler-limited overtone spectra of AsH3 (600) and H2Se (60) have been observed at room temperature in the wave number regions 11 500–11 650 and 12 600–12 925 cm−1, respectively. Results are presented which highlight the applicability of this apparatus to the spectroscopy of weak optical transitions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150564
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  • 87
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    Measurements of the velocity and temperature in a turbulent flow by the laser photothermal effect with the new compulsorily phase locked interferometer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1971-1974 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article describes measurements of the velocity and temperature in a turbulent flow by means of a photothermal effect. We developed a new differential interferometer for detecting small phase variation caused by the photothermal effect without influence of turbulent phase fluctuation. The detected fringe point of the interferometer is scanned repeatedly by moving a photomultiplier. An electric system is constructed for compulsorily operating the interferometer at the maximum inclination point of the fringe intensity curve. Using a turbulent jet of nitrogen gas mixed with ethylene gas, we confirmed that this measurement system is useful to measure the velocity and temperature in the turbulent flow. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150563
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  • 88
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    Instrumental noise and detectivity analysis of photopyroelectric destructive thermal-wave interferometry (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1961-1970 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A complete noise analysis of a two-beam photopyroelectric (thermal-wave) destructive interferometric sensor instrument is presented and compared to its single-beam, noninterferometric counterpart. The noise analysis is performed using a Green-function formalism applied to experimental observations. The instrumental background noise contribution from the detector and the amplifier is separated from the laser noise and the instrumental noise due to amplification associated with different sensitivity scales. The latter serves as the source of comparison between the two sensor configurations. It is found that the dc laser drift noise and low-frequency fluctuation noise, which are dominant in the single-beam mode, are greatly reduced to the same order of magnitude as the instrumental background noise in the two-beam mode. The system white noise resulting from the incident laser beam and from the sensitivity scale (amplification) of the demodulating lock-in amplifier are also examined in light of the experimental data. It is found that the detectivity D* (the inverse of the noise equivalent power), of the instrument is enhanced by at least 1 order of magnitude in the interferometric mode. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150562
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  • 89
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    Divergence effects in monochromatic x-ray microdiffraction using tapered capillary optics (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1991-2000 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Tapered capillaries are frequently used as beam-concentrating optics in microbeam x-ray diffraction experiments. The beams exiting such devices are usually highly divergent and may possess nonuniform intensity distributions. In addition, their alignment poses some special challenges. In this article, the effects of these factors on the precision and accuracy of diffraction data are presented. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150567
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  • 90
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    Absolute detection efficiency of a microchannel plate detector for neutral atoms (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2050-2052 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The absolute detection efficiency (ADE) of microchannel plates for neutral sodium and potassium atoms is measured in the low keV energy range. It is shown that ADE is primarily a function of the particle energy. This result is compared to measurements made by other authors for ionic particles. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150615
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  • 91
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    Low cost high resolution thermoluminescence spectrometer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2053-2057 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high-resolution thermoluminescence dosimetry (TLD) spectroscopy reader has been developed in order to perform detailed quantitative studies of the kinetics of TLD materials. The key features of this system are high wavelength resolution (1.3 nm), low cost, and compact size. In addition, the spectrometer is fiber optic coupled to the sample material isolating the system from thermal influences and electrical noise generated by the heating system. Temperature rate control can be computer set with a heat rate accuracy of better than 0.12% and a temperature readout accuracy of 1 °C or better. Analysis of all three parameters: temperature, wavelength, and intensity, is easily visualized with integrated 2D/3D analysis software. Preliminary analysis on TLD300 samples irradiated with 60Co from 5 to 60 Gy show temperature peaks and wavelength locations consistent with other published measurements. Details of the hardware system and software are discussed along with sample results. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150577
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  • 92
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    Space-time resolving vacuum ultraviolet spectrometer based on a rotating polyhedral mirror (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2068-2070 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Using a rotating polyhedral mirror and a vacuum ultraviolet (VUV) monochromater, a space-time resolving VUV diagnostic system is developed. Measurement of the O VI (103.2 nm) radiation on the HT-6M tokamak shows that the time resolution of the system is better than 4 ms and the space resolution is better than 2 cm. Compared with traditional instruments, this system has improved measurement efficiency, and error from shot-to-shot discharge variations is avoided. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150580
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  • 93
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    Simulation of the thermoelastic behavior of an LLL x-ray interferometer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1716-1722 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In order to achieve the strictest tolerances required in the manufacturing of an x-ray interferometer of the triple Laue type (LLL) to be used in the accurate determination of the silicon lattice parameter, a new shape of the analyzer crystal is considered. The simulation of its behavior proves that, if specified elastic and thermal load upper limits are satisfied, the lattice plane deformations are compatible with a measurement uncertainty of a few parts in 109. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150526
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  • 94
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    A planar x-ray waveguide with a tunable air gap for the structural investigation of confined fluids (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1723-1732 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A tunable x-ray waveguide with an air gap as the guiding medium is presented. Discrete transverse-electric modes excited in the air gap propagate almost undisturbed. Filling the air gap with a fluid allows for studies of ordering phenomena in a confined geometry. Since the guided modes are mainly confined to the guiding layer, background scattering from the plates is very low. Starting from the propagation characteristics of the modes in the empty waveguide, requirements on the x-ray source and on the positioning accuracy of the plates are derived. The construction of the waveguide is described and measurements of the far-field angular distributions of intensity exiting the waveguide are presented which illustrate the waveguide's properties. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150527
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  • 95
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    A focused magneto-optical Kerr magnetometer for Barkhausen jump observations (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1752-1755 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a modified version of a magneto-optical Kerr magnetometer which allows measuring the hysteresis loop of a specific portion of the sample surface. The diameter of the sampled area can be optically tuned from several mm down to 15 μm. High quality hysteresis loops can be measured in a few seconds. Strong fluctuations are observed when the spot diameter is reduced to a few hundred microns or less. These fluctuations are related to the well-known Barkhausen noise here investigated for the first time in a systematic way using optical techniques. Preliminary data for epitaxial Fe grown on MgO are presented. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150532
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  • 96
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    Aerodynamic laser-heated contactless furnace for neutron scattering experiments at elevated temperatures (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1745-1751 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Conventional radiative furnaces require sample containment that encourages contamination at elevated temperatures and generally need windows which restrict the entrance and exit solid angles required for diffraction and scattering measurements. We describe a contactless windowless furnace based on aerodynamic levitation and laser heating which has been designed for high temperature neutron scattering experiments. Data from initial experiments are reported for crystalline and amorphous oxides at temperatures up to 1900 °C, using the spallation neutron source ISIS together with our laser-heated aerodynamic levitator. Accurate reproduction of thermal expansion coefficients and radial distribution functions have been obtained, demonstrating the utility of aerodynamic levitation methods for neutron scattering methods. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150531
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  • 97
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    A high pressure device for measurements of the speed of sound in liquids (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1756-1765 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new measuring set for measurements of the speed of sound in liquids under high pressures (up to 300 MPa), designed and constructed in our laboratory, is described. It operates on the principle of the pulse-echo-overlap method. A single transmitting–receiving piezoelectric ceramic transducer operating at 4 MHz and an acoustic reflector were applied. Details concerning the designing and operation of all the elements of the acoustic path, assuring high accuracy of the speed measurements, are given. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150533
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  • 98
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    Comparison of two methods of measuring the rapid temperature rises in split Hopkinson bar specimens (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1766-1771 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The temperature rise produced in iron and copper specimens by high strain deformation in a compression split Hopkinson pressure bar was measured simultaneously using two independent techniques: (i) small thermocouples (0.2 mm junction size) and (ii) an infrared (IR) camera system based on mercury cadmium telluride (spectral response between 8 and 12 μm). The response time of the thermocouple system was limited by the time taken for heat to diffuse into the junction. In order to obtain useful data with the IR camera system, the emissivity of the specimen surface needed to be modified by depositing a layer of soot. Even so, the measured emissivity was low (0.4), suggesting that the soot layer was semitransparent to IR radiation. The thermocouples, however, yielded temperature measurements that were consistent with all the mechanical work performed on the specimens being converted to heat. The main positive result obtained with the IR camera system is that heating of the iron specimens was spatially nonuniform. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150534
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  • 99
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    Measurements of the double piezoelectric effect (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1772-1775 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For a piezoelectric device with multiple electrodes, it should be possible to quantitatively and conveniently measure the piezoelectric coefficient d31 by use of the double piezoelectric effect, without the need for any unusual apparatus or a calibration sample. One pair of electrodes is used to excite the piezo, and another is used to measure the response. For example, for a piezoelectric tube this should allow measurement of d31 as a function of temperature or of lateral offset voltage. An important correction to the current theory is described. Measurements on two piezo tubes are presented for excitation voltages in the range of 0.5–110 Vpp. An inductive proximity sensor was used to measure the actual piezo motion. It is shown that the current theory disagrees with this and previous experiments by a simple factor of 2 for symmetric excitations. However, for asymmetric excitations the disagreement with theory is more complex, and the current theory does not accurately predict the effects of varying tube geometry. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150535
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  • 100
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    Low-noise electrometer and its low-noise cryogenic probe with completely guarded sample chamber (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1776-1780 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a low-noise cryogenic probing system capable of measuring currents at the femtoAmpere (fA) level with integration time ≤1 s and current noise spectra at the 1 fA/(square root of)Hz level with the sample cooled to cryogenic temperatures. The system consists of a low-noise electrometer and a low-noise cryogenic probe with completely guarded sample chamber. The low-noise electrometer has amplification of 0.1 V/1 pA with f3 dB=70 Hz, 1.1 V/pA with f3 dB=20 Hz, and/or 10.1 V/pA with f3 dB=1.4 Hz, and input current noise power density of 0.4 fA/(square root of)Hz rms and input voltage noise power density of (approximate)0.3 μV/(square root of)Hz rms at 1 Hz frequency. With the cryogenic probe, the entire measurement system has input current noise of 0.8 fA/(square root of)Hz rms at 1 Hz. The completely guarded sample chamber reduces parasitic conductance to 〈10−16 S and parasitic capacitance to ≤15 fF between pairs of pins for current–voltage measurements. With this instrumentation, we are able to characterize the current and current noise of quantum well infrared photodetectors for sensitive zero-background applications. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150536
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