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Review of Scientific Instruments

Issue 7 • Date Jul 2002

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Displaying Results 1 - 25 of 45
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • High-frequency near-field microscopy

    Page(s): 2505 - 2525
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    Conventional optics in the radio frequency (rf) through far-infrared (FIR) regime cannot resolve microscopic features since resolution in the far field is limited by wavelength. With the advent of near-field microscopy, rf and FIR microscopy have gained more attention because of their many applications including material characterization and integrated circuit testing. We provide a brief historical review of how near-field microscopy has developed, including a review of visible and infrared near-field microscopy in the context of our main theme, the principles and applications of near-field microscopy using millimeter to micrometer electromagnetic waves. We discuss and compare aspects of the remarkably wide range of different near-field techniques, which range from scattering type to aperture to waveguide structures. © 2002 American Institute of Physics. View full abstract»

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  • Optimization of a rotary Q-switched Er:YAG laser

    Page(s): 2526 - 2532
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    An erbium:yttrium–aluminum–garnet Er:YAG (λ=2.94 μm) rotary Q-switched laser was optimized for long-term stability and reliability, maximum output energy, and TEMoo mode quality. This optimization was achieved employing a close-coupled BaSO4 diffuse reflector pump chamber and a dehumidifying assembly and an ultra-dry-air purge system. The performance and efficiency of the Er:YAG laser were further enhanced by appropriate variations in the coolant temperature, rotational frequency of the Q-switch mirror, and pulse repetition rate. These improvements should facilitate the implementation of rotating mirror Q-switched Er:YAG lasers in various laser photoablation and depth-profiling applications. © 2002 American Institute of Physics. View full abstract»

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  • Cryogenic InSb detector for radiation measurements

    Page(s): 2533 - 2536
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    The energy spectra of 241Am alpha particles were measured by a detector employing the compound semiconductor InSb at an operating temperature below 4.2 K. The fabrication method and current–voltage curves are shown. Though the energy resolution of the detector is not discussed in this article, this is the first report on an InSb radiation detector. © 2002 American Institute of Physics. View full abstract»

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  • Absolute small angle light scattering measurements from weakly scattering systems in a shear flow apparatus

    Page(s): 2537 - 2543
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    We describe an optical detection layout that allows absolute small angle light scattering measurements on samples sheared in a concentric cylinders geometry. The two main features are the use of a focused incident beam and of a spatial filter that minimize the problem of stray light arising from digs and scratches in the optical path. The scattering intensity is imaged directly onto a cooled 12 bits charge-coupled device sensor. We are thus able to measure scattering intensities as low as about 4×10-4cm-1 (about ten times the intensity scattered from a toluene standard) for scattering wave vector values between 5×10-5 and 3.5×10-4 Å-1. Some preliminary results of experiments on dilute surfactant solutions are given to demonstrate the performance of the instrument. © 2002 American Institute of Physics. View full abstract»

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  • Long-term drift laser frequency stabilization using purely optical reference

    Page(s): 2544 - 2548
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    We describe an apparatus for the stabilization of laser frequencies that prevents long-term frequency drifts. A Fabry–Perot interferometer is thermostated by referencing it to a stabilized He–Ne laser (master), and its length is scanned over more than one free spectral range allowing the analysis of one or more lines generated by other (slave) lasers. A digital acquisition system makes the detection of the position of all the laser peaks possible, thus producing both feedback for the thermostat and the error signal used for stabilizing the slave lasers. This technique also allows for easy, referenced scanning of the slave laser frequencies over range of several hundred MHz, with a precision of the order of a few MHz. This kind of stabilization system is particularly useful when no atomic or molecular reference lines are available, as in the case of rare or short lived radioactive species. © 2002 American Institute of Physics. View full abstract»

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  • A moving-mirror frequency modulator for cold atom spectroscopy

    Page(s): 2549 - 2551
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    We have investigated the use of a moving or “Doppler” mirror to probe laser cooled atoms. The device uses the Doppler shift induced on reflection at a moving surface to modulate the frequency of a probing laser beam, with a modulation bandwidth and frequency resolution sufficient for the narrow spectral features typically encountered. We anticipate that the device could be a simple and cost-effective alternative to acousto-optic modulators for cold atom spectroscopy, and demonstrate its usefulness by performing stimulated optical Compton scattering on an optical molasses. © 2002 American Institute of Physics. View full abstract»

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  • Studies of electron beams propagation in space-charge regime

    Page(s): 2552 - 2556
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    We report the experimental characteristics of electron beam propagation under space-charge regime. The electron beams were generated by a Nb polycrystalline photocathode illuminated by two different excimer lasers, a XeCl (308 nm) and a KrCl (222 nm). The laser photon energies were very close to the Nd work function. The cathode surface was mechanically worked in order to study the photoemission from a smooth and a rough surface. At low accelerating voltage the electron beam was dominated by the space-charge effect and its resulting pulse never clipped as predicted by the Child–Langmuir law. Instead, it presented as fast a rise time as the laser one, an intermediate zone, and a tail longer than the laser pulse one. On the other hand, under saturation regime the output current wave form was similar to the laser one. The quantum efficiency was higher for the rough cathode. It corresponded to 3.2×10-5 and 6.7×10-7 for the KrCl and XeCl irradiation, respectively. The maximum current value was an electron bunch containing 980 mA (8.9 nC), by means of 1.7 mJ KrCl laser energy and 10 kV of accelerating voltage. © 2002 American Institute of Physics. View full abstract»

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  • Improved alternating gradient transport and focusing of neutral molecules

    Page(s): 2557 - 2565
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    Polar molecules, in strong-field seeking states, can be transported and focused by an alternating sequence of electric field gradients that focus in one transverse direction while defocusing in the other. We show, by calculation and numerical simulation, how one may greatly improve the alternating gradient transport and focusing of molecules. We use a new optimized multipole lens design, a FODO-lattice beam transport line, and lenses to match the beam transport line to the beam source and to the final focus. We derive analytic expressions for the potentials, fields, and gradients that may be used to design these lenses. We describe a simple lens optimization procedure and derive the equations of motion for tracking molecules through a beam transport line. As an example, we model a straight beamline that transports a 560 m/s jet-source beam of methyl fluoride 15 m from its source and focuses it to 2 mm diameter. We calculate the beam transport line acceptance and beam survival, for a beam with a velocity spread, and estimate the transmitted intensity for specified source conditions. Possible applications are discussed. © 2002 American Institute of Physics. View full abstract»

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  • Modified neural networks for rapid recovery of tokamak plasma parameters for real time control

    Page(s): 2566 - 2577
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    Two modified neural network techniques are used for the identification of the equilibrium plasma parameters of the Superconducting Steady State Tokamak I from external magnetic measurements. This is expected to ultimately assist in a real time plasma control. As different from the conventional network structure where a single network with the optimum number of processing elements calculates the outputs, a multinetwork system connected in parallel does the calculations here in one of the methods. This network is called the double neural network. The accuracy of the recovered parameters is clearly more than the conventional network. The other type of neural network used here is based on the statistical function parametrization combined with a neural network. The principal component transformation removes linear dependences from the measurements and a dimensional reduction process reduces the dimensionality of the input space. This reduced and transformed input set, rather than the entire set, is fed into the neural network input. This is known as the principal component transformation-based neural network. The accuracy of the recovered parameters in the latter type of modified network is found to be a further improvement over the accuracy of the double neural network. This result differs from that obtained in an earlier work where the double neural network showed better performance. The conventional network and the function parametrization methods have also been used for comparison. The conventional network has been used for an optimization of the set of magnetic diagnostics. The effective set of sensors, as assessed by this network, are compared with the principal component based network. Fault tolerance of the neural networks has been tested. The double neural network showed the maximum resistance to faults in the diagnostics, while the principal component based network performed poorly. Finally the processing times of the methods have been compared. The double netw- ork and the principal component network involve the minimum computation time, although the conventional network also performs well enough to be used in real time. © 2002 American Institute of Physics. View full abstract»

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  • Optical path length control in plasma absorption measurements

    Page(s): 2578 - 2582
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    An inductively coupled Gaseous Electronics Conference (GEC) cell with modified viewing ports has been used to measure in situ absorption in CF4 plasmas via Fourier transform infrared spectroscopy, and the results compared to those obtained in a standard viewport configuration. The viewing ports were modified so that the window boundary is inside, rather than outside, of the GEC cell. Because the absorption obtained is a line of sight integrated absorption, measurements made represent an averaging of absorbing species inside and outside of the plasma. This modification is made to reduce this spatial averaging and thus allow a more accurate estimation of neutral species concentrations and temperatures within the plasmas. By reducing this path length, we find that the apparent CF4 consumption increases from 65% to 95% and the apparent vibrational temperature of CF4 rises by 50–75 K. The apparent fraction of etch product SiF4 decreases from 4% to 2%. The data suggest that these density changes may be due to significant temperature gradients between the plasma and chamber viewports. © 2002 American Institute of Physics. View full abstract»

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  • A plasma focus driven by a capacitor bank of tens of joules

    Page(s): 2583 - 2587
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    As a first step in the design of a repetitive pulsed neutron generator, a very small plasma-focus device has been designed and constructed. The system operates at low energy (160 nF capacitor bank, 65 nH, 20–40 kV, and ∼32–128 J). The design of the electrode was assisted by a computer model of Mather plasma focus. A single-frame image converter camera (5 ns exposure) was used to obtain plasma images in the visible range. The umbrellalike current sheath running over the end of the coaxial electrodes and the pinch after the radial collapse can be clearly observed in the photographs. The observations are similar to the results obtained with devices operating at energies several orders of magnitude higher. The calculations indicate that yields of 104–105 neutrons per shot are expected with discharges in deuterium. © 2002 American Institute of Physics. View full abstract»

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  • Penumbral imaging for measurement of the ablation density in laser-driven targets

    Page(s): 2588 - 2596
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    One-dimensional (1D) penumbral imaging technique with high spatial resolution has been developed, and applied to density profile measurements in laser-driven Rayleigh-Taylor instability experiments at a GEKKO XII-HIPER laser system. A laser-irradiated planar target was observed with side-on x-ray backlighting. A penumbral image of an x-ray radiograph was made by using a knife-edge imager. The x-ray radiograph was, then, reconstructed by differentiating the penumbral image with a proper Wiener filtering. A density profile was deduced from the reconstructed x-ray radiograph. In a proof-of-principle experiment, the density profile of a polystyrene (PS) target before laser irradiation was measured by using this method, and high spatial resolution of 3–4 μm was demonstrated. A laser-irradiated PS target in the acceleration phase was observed. The experimentally observed density profile was found to be consistent with the prediction by a 1D hydrodynamic simulation code. The x-ray penumbral imaging is a very simple and useful technique with high spatial resolution for research in hydrodynamics relevant to inertial fusion energy. © 2002 American Institute of Physics. View full abstract»

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  • Absolute measurements of neutron yields from DD and DT implosions at the OMEGA laser facility using CR-39 track detectors

    Page(s): 2597 - 2605
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    The response of CR-39 track detectors to neutrons has been characterized and used to measure neutron yields from implosions of DD- and DT-filled targets at the OMEGA laser facility [T. R. Boehly etal, Opt. Commun. 133, 495 (1997)], and the scaling of neutron fluence with R (the target-to-detector distance) has been used to characterize the fluence of backscattered neutrons in the target chamber. A Monte-Carlo code was developed to predict the CR-39 efficiency for detecting DD neutrons, and it agrees well with the measurements. Neutron detection efficiencies of (1.1±0.2)×10-4 and (6.0±0.7)×10-5 for the DD and DT cases, respectively, were determined for standard CR-39 etch conditions. In OMEGA experiments with both DD and DT targets, the neutron fluence was observed to decrease as R-2 up to about 45 cm; at larger distances, a significant backscattered neutron component was seen. The measured backscattered component appears to be spatially uniform, and agrees with predictions of a neutron-transport code. As an additional application of the calibration results, it is shown that the neutron-induced signal in CR-39 used in charged-particle spectrometers on OMEGA can be used to determine DD and DT yields ranging from about 1010 up to 1014. With further improvements in the processing and analysis of CR-39, this upper limit can be increased by at least two orders of magnitude. © 2002 American Institute of Physics. View full abstract»

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  • A self-calibrating, multichannel streak camera for inertial confinement fusion applications

    Page(s): 2606 - 2615
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    Self-calibrating, multichannel UV streak cameras have been designed, and six units have been deployed on the OMEGA laser system. These instruments acquire 12 channels simultaneously on a low-noise, charge-coupled-device camera in single-shot operation. The instruments can discern temporal features out to a bandwidth of 11 GHz, and the peak signal-to-noise ratio in each channel is 200:1. The unique feature of this system is the self-calibration ability built into it. The geometric distortions, flat field, and sweep speed of each channel can be measured and adjusted on a routine basis. By maintaining a strick regime of weekly calibrations, accurate power-balance measurements on the OMEGA laser can be obtained. These cameras represent a cost-effective solution for power balancing the OMEGA laser system. © 2002 American Institute of Physics. View full abstract»

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  • Fiberoptic in-vessel viewing system for the International Thermonuclear Experimental Reactor

    Page(s): 2616 - 2623
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    A viewing system was designed and a prototype realized for the in-vessel inspection of the International Thermonuclear Experimental Reactor. The viewing is based on the line scanning principle, and the system consists of ten identical units installed on top of the reactor at 36° intervals. Each device contains a laser, beam steering mirrors, and viewing probe with insertion mechanics. The probe has an outside diameter of 150 mm and a length of 14 m. The illumination design applies frequency-doubled Nd: yttrium–aluminum–garnet lasers whose beams are guided through hermetically sealed windows into the vacuum vessel. The diffuser optics creates a vertically oriented light stripe onto the vessel surface that is viewed by the imaging optics, consisting of 16 modules altogether covering horizontal and vertical field-of-views of 2° and 162°. The optical images are transferred to charge coupled device cameras via coherent fiber arrays. The multifocus design uses stacked fiber rows whose ends are assembled into different axial positions. The viewing probes rotate at a constant angular speed of 1°/s and pictures are taken at 0.01° intervals. The complete picture of the vessel interior is generated in 6 min producing 5.8×109 image pixels. The image processing and analysis of possible defects in the vessel surfaces are performed off-line after the viewing procedure. A full-scale prototype of the viewing probe was constructed to demonstrate the feasibility of the design. Its illumination optics utilizes a diffractive optics element that transforms the collimated input beam into a rectangular output lobe with uniform intensity. The prototype has horizontal and vertical imaging optics field-of-views of 2° and 12°. The test results showed that the prototype can take pictures of good quality applying a continuously rotating probe having an angular speed of 0.08°/s. Under optimum condi tions, the minimum resolvable feature size at a 3 m distance is smaller than 1 mm, which satisfies the requirement specification. Further development is needed to increase the illumination power to improve the imaging speed and to develop linear fiber arrays that are compatible with the vacuum and high-flux radiation environment of the primary vacuum vessel. © 2002 American Institute of Physics. View full abstract»

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  • Determination of mesoscale crystallization by collection-mode polarization modulated near-field optical microscopy

    Page(s): 2624 - 2628
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    We present a new setup of polarization modulated near-field optical microscopy for actually measuring the mesoscale crystallization of thin films. In comparison to previous transmission mode polarization near-field optical microscopy, our new collection mode microscopy provides no axial polarization, free of fiber birefringence and flexibility for tuning wavelength. The Jones matrix calculation verifies that the crystallization of the sample can be obtained by simply subtracting the polarization vector from anisotropy of the tip. The crystallization domains for thermal annealed naphthaphenylene benzidine thin films are observed by the system, stripe domains with averaged ∼15% dichroic ratios are first measured. © 2002 American Institute of Physics. View full abstract»

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  • X-ray scattering microscope with a Wolter mirror

    Page(s): 2629 - 2633
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    Full-field x-ray scattering microscopic images were obtained with a Wolter mirror (×10 magnification). A synchrotron radiation white beam (4–20 keV) from a bending magnet beamline at the Photon Factory was used to obtain x-ray scattering images. The system was available for multi-kilo-electron-volt x-ray range (4–12 keV) with the Wolter mirror. The image was formed only with scattered x rays from the object, which is kind of a dark-field image. Very low absorptive materials could be imaged with this microscope. Sensitivity of the system was evaluated and also the detection limit was estimated. © 2002 American Institute of Physics. View full abstract»

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  • Reconstruction of Abel-transformable images: The Gaussian basis-set expansion Abel transform method

    Page(s): 2634 - 2642
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    In this article we present a new method for reconstructing three-dimensional (3D) images with cylindrical symmetry from their two-dimensional projections. The method is based on expanding the projection in a basis set of functions that are analytical projections of known well-behaved functions. The original 3D image can then be reconstructed as a linear combination of these well-behaved functions, which have a Gaussian-like shape, with the same expansion coefficients as the projection. In the process of finding the expansion coefficients, regularization is used to achieve a more reliable reconstruction of noisy projections. The method is efficient and computationally cheap and is particularly well suited for transforming projections obtained in photoion and photoelectron imaging experiments. It can be used for any image with cylindrical symmetry, requires minimal user’s input, and provides a reliable reconstruction in certain cases when the commonly used Fourier–Hankel Abel transform method fails. © 2002 American Institute of Physics. View full abstract»

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  • Fast driving technique for integrated thermal bimorph actuator toward high-throughput atomic-force microscopy

    Page(s): 2643 - 2646
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    A driving scheme for improving the effective response of a microfabricated cantilever with an integrated thermal bimorph actuator is proposed for applications in high-throughput atomic-force microscopy. The essential part of the proposed scheme is a tuned boost filter (BSF), which is inserted in the setup for constant force imaging and which boosts the servo signal according to its frequency. Using this setup, an imaging bandwidth of 5 kHz was obtained within an actuation range of 1.7 μm. Constant force imaging with a tip velocity of 0.62 mm/s is demonstrated and the effectiveness of the BSF is verified. The improved bandwidth is gained at the expense of the achievable deflection range. An optimized system, therefore, requires not only a BSF but also a thermal bimorph with a large power to deflection efficiency. © 2002 American Institute of Physics. View full abstract»

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  • Measurement of mechanical properties of three-dimensional nanometric objects by an atomic force microscope incorporated in a scanning electron microscope

    Page(s): 2647 - 2650
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    An atomic force microscope that mounts on a sample stage of a scanning force microscope (SEMAFM) was developed. It was implemented for measurement of static mechanical properties of three-dimensional nanometric objects. The sample stage of the AFM was equipped with piezoelectric actuators enabling raster scanning as well as three degrees of freedom positioning with sub nm resolution and mm movable range. This enabled centering the AFM tip to the field of view of the SEM. Measurement of the spring constant and rupture force of three-dimensional nanometric structures was made possible. The SEMAFM also functioned as a conventional AFM. © 2002 American Institute of Physics. View full abstract»

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  • Contactless excitation and measurement method for inspection of microstructures and thin films

    Page(s): 2651 - 2654
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    A specially designed resonator to avoid the change of the resonance characteristics by thermal influences of the laser beam was fabricated on a silicon on insulator wafer. This resonator design enables one to apply a lateral driving force to generate lateral vibration. The resonator was excited using a laser diode which was driven with sinusoidal current, and the vibration was detected by measuring intensity fluctuation of the He–Ne laser beam reflected on the resonator mass. Four evident resonance frequencies were successfully observed in the range from 100 Hz to 100 kHz. © 2002 American Institute of Physics. View full abstract»

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  • The modified Rankine balance: A highly efficient, low-cost method to measure low-temperature magnetic susceptibility in rock samples

    Page(s): 2655 - 2658
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    In this article, we present a method to measure the relative changes in the magnetic susceptibility of rock samples in the low-temperature range (-200 °C to +20 °C). The method differs from other experimental methods currently used in that it requires—in contrast to ac bridges, the most widely used devices—very little sophisticated laboratory equipment: A high-precision laboratory balance, a Pt-100 thermoelement and a computer with standard input/output interface and analog/digital processing capabilities, as well as a few rare earth magnets, are the only devices needed in addition to standard laboratory equipment. A Dewar container and a few plexiglass panes can either be handcrafted in the workshops of any larger research institute or are commercially available at little cost. The results of our measurements reveal that the temperature-varying magnetic properties of rock samples can be reliably observed. © 2002 American Institute of Physics. View full abstract»

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  • A microbeam collimator for high resolution x-ray diffraction investigations with conventional diffractometers

    Page(s): 2659 - 2665
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    A collimating system has been developed for condensing hard x rays, providing very thin, intense, and low divergent beams. The primary radiation is compressed down to the micrometer scale by multiple total reflections in the channel between two oblong and flexible metallic mirrors with exit aperture 4 mm×15 μm. The flexible mirrors permit variation of the channel profile and opening for the incoming radiation, adjusted for maximum transmitted x-ray intensities. The condenser, due to the high brilliance gain of the obtained beam compared to the uncompressed radiation going through a slit of the same size, can be operated even with conventional x-ray tubes, e.g., common x-ray diffractometers without the need for expensive high intensity synchrotron radiation sources, as demanded usually by the glass monocapillaries. A prototype, being mounted on a commercial theta–theta diffractometer, has been thoroughly tested for intensity gain, divergence, and spatial resolution and utilized for accurate structure determinations on very thin regions (only some tens of microns) of solid materials. This article gives an extensive description of the apparatus and presents the obtained results of some representative investigations. © 2002 American Institute of Physics. View full abstract»

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  • Novel diffractometer optimized for the study of weak superlattice reflections using crossed parabolic mirrors

    Page(s): 2666 - 2671
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    We present the development of a novel laboratory-based diffractometer optimized for high intensity and resolution matched to that of flux grown single crystal transition metal–oxide samples studied in solid state physics. This has been implemented using crossed graded d-spacing parabolic multilayer mirrors, a severely off-cut asymmetric analyzer crystal, and a microminiature cryostat. We demonstrate that the wider bandpass of the multilayer mirrors provides a significant increase in intensity compared to the use of silicon and germanium optics, but still provides the necessary resolution to obtain accurate measurements for inverse correlation lengths. The increase in flux allows the observation of features that were previously only visible with third generation synchrotron x-ray sources, shown by the observation of the very weak charge order peak without the use of a synchrotron source. Results on samples previously studied show an increase of a factor of 10 in intensity, coupled together with a factor of 7.5 increase in resolution over the previous system employed using a rotating anode source and flat pyrolytic graphite (0001) crystals. With such a diffractometer it is now possible to carry out detailed studies of charge ordering in transition metal oxides in the laboratory and the benefits of this are threefold. First, this will improve the quality of any preparation work, for subsequent experiments at synchrotron sources. This has the advantage of maximizing the efficiency of synchrotron measurements. Second, the enhanced intensity and resolution will allow experiments to be conducted in the laboratory which previously required access to synchrotron sources. Third, it will allow for synchrotron time to be used for its unique properties, i.e., wavelength tunability and polarization, which are necessary for the observation of magnetic reflections and orbital ordering by means of resonant enhancements and polarization analysis. This means that laboratory ba- sed measurements can be easily incorporated with synchrotron data, maximizing the potential of both techniques and receiving a net gain in data output. © 2002 American Institute of Physics. View full abstract»

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Aims & Scope

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

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Albert T. Macrander
Argonne National Laboratory