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Review of Scientific Instruments

Issue 6 • Date Jun 2004

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Displaying Results 1 - 25 of 48
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Development of very large helicon plasma source

    Page(s): 1941 - 1946
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    We have developed a very large volume, high-density helicon plasma source, 75 cm in diameter and 486 cm in axial length; full width at half maximum of the plasma density is up to ∼42 cm with good plasma uniformity along the z axis. By the use of a spiral antenna located just outside the end of the vacuum chamber through a quartz-glass window, plasma can be initiated with a very low value of radio frequency (rf) power (≪1 W), and an electron density of more than 1012cm-3 is successfully produced with less than several hundred Watt; achieving excellent discharge efficiency. It is possible to control the radial density profile in this device by changing the magnetic field configurations near the antenna and/or the antenna radiation-field patterns. © 2004 American Institute of Physics. View full abstract»

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  • Biaxial stress ring applications to magneto-optical studies of semiconductor films

    Page(s): 1947 - 1951
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    We present a magneto-optical system to study semiconductor heterostructures in the presence of an external biaxial tensile strain. The pressure cell is based on the deflection of a plate (the sample) placed between a sphere and a ring. This externally applied stress is easily controlled and can achieve a deformation of up to ∼0.25% for GaAs films. This device is very useful for band structure study and optical resonance experiments in heterostructures. We also present the application of the device to study the behavior of the magneto-excitons in InP epitaxial layer as a function of the biaxial strain. We observed that the diamagnetic and Zeeman effects in InP films are affected by the biaxial tensile strain. © 2004 American Institute of Physics. View full abstract»

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  • A novel fiber optic sensor for multiple and simultaneous measurement of vibration velocity

    Page(s): 1952 - 1958
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    Simultaneous and multipoint assessment of vibration velocities is an important issue for the development of advanced noncontact vibrometers. In this article a novel fiber optic vibrometer is presented. The architecture of the sensor is based on a simple optical layout and it is characterized by multiple fiber optic interferometric sensors which are operated in the homodyne mode. Optical configuration and operation of the single-point version of the sensor, as well as the two-points measurement version, are described and typical measured signals with the operating range are shown. The sensor can easily be configured in order to perform a higher number of point measurements. Some details regarding signal acquisition and processing are also given and the ways in which Doppler demodulation is performed are discussed. Finally tests with sinusoidal target excitation in the range 0–1.8 kHz have been conducted. © 2004 American Institute of Physics. View full abstract»

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  • TiC–diamond composite disk-heater cell assembly to generate temperature of 2000 °C in a large-volume belt-type high-pressure apparatus at 10 GPa

    Page(s): 1959 - 1962
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    A TiC–diamond composite was prepared for the heater of a large-volume belt type high-pressure apparatus. Graphite has conventionally been used for the heater in high-pressure studies, but it cannot be used at pressure higher than 10 GPa and above 1500 °C because of the problem associated with the graphite-to-diamond phase transformation. New TiC–diamond heater overcomes this problem and achieves stable temperature generation by using a belt-type high-pressure apparatus. The composite was fabricated by heat-treatment of a mixture of diamond and TiC0.8 with nonstoichiometric composition at ambient pressure. By optimizing the preparation conditions, we obtained TiC–diamond composites that exhibited mechanical and electrical properties suitable for a heater material without any volatile component such as resin. Since reported conventional TiC–diamond composite heaters include epoxy resin as binder, volatile components arise from decomposition of the resin at high temperature preventing stable high-pressure/high-temperature experiment above 2000 °C. Attainment of reproducible temperature-generation efficiency in the present heater makes it possible to perform stable experiments at high temperature and pressure, i.e., in the region of 2000 °C and 10 GPa. © 2004 American Institute of Physics. View full abstract»

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  • Low aberration permanent hexapole magnet for atom and molecular beam research

    Page(s): 1963 - 1970
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    We present details of an 800-mm-long, 4.80 mm bore, 1.32 T pole-tip field permanent hexapole (sextupole) magnet system with exceptionally low field aberrations. The assembly was developed as an atom optical element for use in the Cambridge 3He Spin-Echo Spectrometer. Our 12 segment magnet is an improved version of the well-known Halbach design, in which we refine the pole piece shape to improve the field characteristics. Semi-analytic simulations and finite element modeling were performed to optimize the pole piece shape, in order to maximize field strength while minimizing higher order multipole aberrations. High precision machining and assembly techniques were used to construct the device and the resultant field was measured. The measured pole-tip field of 1.25 T is in good agreement with the simulations (5% error) and the measured aberrations that are at least 5 times smaller than those theoretically possible with an ideal 12 segment system using the conventional design. Finally, the application of the hexapole magnet was demonstrated in our spectrometer, as a composite magnetic lens, used to analyze the nuclear spin of surface-scattered 3He atoms from a polarized incident beam. © 2004 American Institute of Physics. View full abstract»

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  • Correlation method in period measurement of a torsion pendulum

    Page(s): 1971 - 1974
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    The correlation method is used to determine the period of a torsion pendulum. Calculation shows that this method cannot only suppress the disturbance of white noise, but it is also insensitive to drift and damping of the torsion pendulum. An estimate of the frequency based on this method is an approximative minimum variance unbiased estimator. © 2004 American Institute of Physics. View full abstract»

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  • Alpha: A large-area plasma helicon array

    Page(s): 1975 - 1981
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    Helicon sources are extremely efficient in creating high density, current free plasma discharges. However, these sources typically have a small cross-sectional area and are unsuitable for studies that require a large diameter plasma. We report the construction of a plasma facility that overcomes this limitation by using multiple helicon sources in a close-packed array. A large-area plasma helicon array (Alpha) is a 4 m long, 50 cm diam device that uses seven helicon sources to generate a large diameter rf plasma. The facility is designed to study basic plasma wave phenomena in a high-density, current-free plasma. The helicon array can operate in one of two modes, creating either seven distinct plasma columns or an integrated uniform large diameter plasma column. Details of the facility specifications, construction, and initial plasma parameters of the multihelicon source are reported. © 2004 American Institute of Physics. View full abstract»

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  • Using 15 fs, LINAC-generated electron bunches for naturally synchronized infrared pump x-ray probe experiments with coherent synchrotron radiation

    Page(s): 1982 - 1987
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    It is proposed to use highly compressed 15 fs bunches from a linear accelerator, such as the Stanford Linear Accelerator, for the production of both ultrashort x rays and mid-infrared coherent synchrotron radiation (CSR). The two types of radiation are synchronized with each other on the femtosecond time scale and can be used for pump–probe experiments in the study of ultrafast phenomena. A possible extension to 3 fs bunches is discussed, where the CSR serves both, as a source of pump radiation and as an indicator for those bunches that are perfectly compressed. © 2004 American Institute of Physics. View full abstract»

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  • Normal and torsional spring constants of atomic force microscope cantilevers

    Page(s): 1988 - 1996
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    Two methods commonly used to measure the normal spring constants of atomic force microscope cantilevers are the added mass method of Cleveland etal [J. P. Cleveland etal, Rev. Sci. Instrum. 64, 403 (1993)], and the unloaded resonance technique of Sader etal [J. E. Sader, J. W. M. Chon, and P. Mulvaney, Rev. Sci. Instrum. 70, 3967 (1999)]. The added mass method involves measuring the change in resonant frequency of the fundamental mode of vibration upon the addition of known masses to the free end of the cantilever. In contrast, the unloaded resonance technique requires measurement of the unloaded resonant frequency and quality factor of the fundamental mode of vibration, as well as knowledge of the plan view dimensions of the cantilever and properties of the fluid. In many applications, such as frictional force microscopy, the torsional spring constant is often required. Consequently, in this article, we extend both of these techniques to allow simultaneous calibration of both the normal and torsional spring constants. We also investigate the validity and applicability of the unloaded resonance method when a mass is attached to the free end of the cantilever due to its importance in practice. © 2004 American Institute of Physics. View full abstract»

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  • Induced thermal stress fields for three-dimensional distortion control of Si wafer topography

    Page(s): 1997 - 2002
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    Localized, controlled heating can induce a thermal stress field in silicon wafers and displace the surface topography in three dimensions, which is useful for nanoscale regulation of overlay in microcontact printing systems. Simulation and experimental results are presented to demonstrate the use of a thermal array consisting of a dense distribution of independent heating elements to locally displace silicon wafer alignment microstructures. An experimental apparatus comprised of a 7×7 array of thermal cycling sources is used to control the absolute three-dimensional position of surface microstructures. The system is used to demonstrate out-of-plane sensitivity of 1.4 μm/°C by thermomechanical displacement contributions from thermal expansion of the heating element. Rolloff in out-of-plane displacement of 200 nm/mm/°C in silicon at the boundary between heated and nonheated regions in this apparatus is exhibited. Dynamic real-time control of the substrate flatness is thus feasible and is demonstrated with the apparatus using feedback from three alignment microscopes, to sub-100 nm levels of regulation. Control of the in-plane microstructure position is achieved by stabilizing the vertical displacement with a mechanical nanopositioning stage, while establishing a thermal stress field to produce displacement sensitivity of 70 nm/°C. Real-time feedback control of the in-plane microstructure position is demonstrated, also within sub-100 nm of the target regulation level. © 2004 American Institute of Physics. View full abstract»

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  • A spin rotator for spin-polarized scanning electron microscopy

    Page(s): 2003 - 2007
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    A Wien filter, which is a common energy analyzer, was modified as a spin rotator for use in a spin-polarized scanning electron microscope. By switching the spin rotator on and off, magnetic domain images of all three magnetization vectors can be produced in one scan. The electrodes and the magnetic pole pieces were specially designed by using a three-dimensional computer simulation for electric and magnetic fields, electron trajectories, and spin rotation; the broad beam of the secondary electrons passes through to the spin detector with a 90° rotation. The structure is simple with only two electrodes that have hyperbolically curved surfaces to create a stigmatic focusing effect, while the surfaces of the magnetic pole pieces are flat to enable a uniform rotation of all electron spins. The performance was tested and confirmed to be effective by observing the magnetic domain structures of Fe(001) with in-surface-plane magnetization and a TbFeCo magneto-optical medium with surface normal magnetization. © 2004 American Institute of Physics. View full abstract»

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  • 32-channel arbitrary waveform generator for bistable nematic devices

    Page(s): 2008 - 2012
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    All commercially available liquid crystal nematic displays use cells with strong surface anchoring conditions and under field bulk monostable texture distortions. About ten years ago, a technological research line started to study liquid crystal nematic displays with intrinsic bistable textures. It implies pixels with two distinct stable states in the absence of field, but electrically switchable. Bistability allows infinite multiplexing for passive matrix displays: It suppresses the need of refreshing permanent informations. At present, commercial active matrix displays behave like bistable displays by means of electronic elements (TFT or diodes), one for each pixel. This is not an intrinsic bistability, because it is due to external active devices placed on the screen surface. The aim of the present research is to design a suitable and flexible experimental setup to create addressing waveforms for passive electro-optical intrinsically bistable devices. © 2004 American Institute of Physics. View full abstract»

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  • Push–pull fiber optic inclinometer based on a Mach–Zehnder optical low-coherence reflectometor

    Page(s): 2013 - 2015
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    A push–pull inclinometer based on the gravity-referenced rotation fiber optic sensing system is demonstrated by using a specially designed parallelogram pendulum. It measures the angle variations between a nominally vertical reference line in the civil structure and the direction of gravity. By using a low-coherence fiber optic Mach–Zehnder interferometric technique, rotation sensitivity in the two perpendicular vertical planes of 0.2 can be achieved. The total measurement range is ±5° and the temperature cross-sensitivity is expected to be very low. These values compare favorably to the high-end of electronic inclinometers and are well suited for the monitoring of civil structures such as bridges, towers, and anchored walls. The small size of the sensors and the mechanical design make them suitable for open-air use, while the low temperature sensitivity makes them ideal for eliminating temperature-induced rotations. The proposed inclinometer has a resolution of 0.2 and a precision of 1 full scale. © 2004 American Institute of Physics. View full abstract»

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  • Single-board computer based control system for a portable Raman device with integrated chemical identification

    Page(s): 2016 - 2023
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    We report the development of a battery-powered portable chemical identification device for field use consisting of an acousto-optic tunable filter (AOTF)-based Raman spectrometer with integrated data processing and analysis software. The various components and custom circuitry are integrated into a self-contained instrument by control software that runs on an embedded single-board computer (SBC), which communicates with the various instrument modules through a 48-line bidirectional TTL bus. The user interacts with the instrument via a touch-sensitive liquid crystal display unit (LCD) that provides soft buttons for user control as well as visual feedback (e.g., spectral plots, stored data, instrument settings, etc.) from the instrument. The control software manages all operational aspects of the instrument with the exception of the power management module that is run by embedded firmware. The SBC-based software includes both automated and manual library searching capabilities, permitting rapid identification of samples in the field. The use of the SBC in tandem with the LCD touchscreen for interfacing and control provides the instrument with a great deal of flexibility as its function can be customized to specific users or tasks via software modifications alone. The instrument, as currently configured, can be operated as a research-grade Raman spectrometer for scientific applications and as a “black-box” chemical identification system for field use. The instrument can acquire 198-point spectra over a spectral range of 238–1620 cm-1, perform a library search, and display the results in less than 14 s. The operating modes of the instrument are demonstrated illustrating the utility and flexibility afforded the system by the SBC–LCD control module. © 2004 American Institute of Physics. View full abstract»

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  • Conical crystal spectrograph for high brightness x-ray spectroscopy in subpicosecond laser–solid interaction

    Page(s): 2024 - 2028
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    A high brightness crystal spectrograph was designed and successfully used to study the x-ray spectrum of aluminum as a diagnostic for target heating due to suprathermal electrons in subpicosecond laser–solid interaction experiments. Conical geometry was chosen in order to enhance spatial focusing, since an extremely low signal-to-noise ratio was expected for the photon flux, and to have a reasonable spectral range while occupying only a small solid angle within the target chamber. Very high image brightness is obtained through strong spatial focusing, as well as good spectral resolution. A simple analytical model and three-dimensional numerical simulation are presented to describe the crystal characteristics. The performance of the spectrograph was tested both on an optical bench and with a ray-tracing code. The experimental spectra allowed us to estimate the target temperature and characterize the fast electron transport. The spectrograph is considered to be particularly useful, in the configuration described here, for high power laser experiments where the solid angle accessible to the spectrograph is small and blast and debris damage from the laser produced plasma is significant. © 2004 American Institute of Physics. View full abstract»

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  • Millikelvin scanned probe for measurement of nanostructures

    Page(s): 2029 - 2032
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    We demonstrate a scanning force microscope, based upon a quartz tuning fork, that operates below 100 mK and in magnetic fields up to 6 T. The microscope has a conducting tip for electrical probing of nanostructures of interest, and it incorporates a low noise cryogenic amplifier to measure both the vibrations of the tuning fork and the electrical signals from the nanostructures. At millikelvin temperatures, the imaging resolution is below 1 μm in a 22 μm×22 μm range, and a coarse motion provides translations of a few mm. This scanned probe is useful for high bandwidth measurement of many high impedance nanostructures on a single sample. We show data locating a single electron transistor within an array and measure its Coulomb blockade with a sensitivity of

    2.6×10-5 e/ Hz .
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  • Image-based autonomous micromanipulation system for arrangement of spheres in a scanning electron microscope

    Page(s): 2033 - 2042
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    The micromanipulation technique in a scanning electron microscope (SEM) has been attracting interest as a technique to produce microstructures such as three-dimensional photonic crystals or advanced high-density electronic circuits. However, it is difficult to fabricate a large-scale structure or to conduct a systematic experiment using numbers of structures, as long as we rely on manually operated micromanipulation. In this study, we constructed an automatic system which arranges 10-μm-sized microspheres into a given two-dimensional pattern in a SEM. The spheres are picked up by touching with the center of the planar tip of a probe (needle), and placed on the substrate by moving the contact point to the edge of the tip and inclining the probe. The positions of the probe and the spheres are visually recognized from the SEM image from above and the optical microscope image from the side. The generalized Hough transform, which can robustly detect arbitrary shape from the edge fragments, is employed for the image recognition. Contact force information obtained by a force sensor with a resolution of 14 μN is also utilized for the control. Completely automatic rearrangement of randomly sprinkled metal spheres with a diameter of 30 μm into arbitrary patterns was successfully demonstrated. Autonomous micromanipulation technique under the observation of a SEM would contribute not merely to laboratories but also to the opto-electronics industry. © 2004 American Institute of Physics. View full abstract»

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  • System to monitor data analyses and results of physics data validation between pulses at DIII–D

    Page(s): 2043 - 2047
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    A data analysis monitoring (DAM) system has been developed to monitor between pulse physics analysis at the DIII–D National Fusion Facility (http://nssrv1.gat.com:8000/dam). The system allows for rapid detection of discrepancies in diagnostic measurements or the results from physics analysis codes. This enables problems to be detected and possibly fixed between pulses as opposed to after the experimental run has concluded, thus increasing the efficiency of experimental time. An example of a consistency check is comparing the experimentally measured neutron rate and the expected neutron emission, RDD0D. A significant difference between these two values could indicate a problem with one or more diagnostics, or the presence of unanticipated phenomena in the plasma. This system also tracks the progress of MDSplus dispatched data analysis software and the loading of analyzed data into MDSplus. DAM uses a Java Servlet to receive messages, C Language Integrated Production System to implement expert system logic, and displays its results to multiple web clients via Hypertext Markup Language. If an error is detected by DAM, users can view more detailed information so that steps can be taken to eliminate the error for the next pulse. © 2004 American Institute of Physics. View full abstract»

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  • Performance evaluation of pulsed photothermal profiling of port wine stain in human skin

    Page(s): 2048 - 2055
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    Treatment of port wine stain (PWS) birthmarks in human skin by pulsed laser irradiation requires the knowledge of the maximum epidermal temperature rise and PWS depth for an attending physician to select the optimal light dosage, irradiation wavelength, and cryogen spray cooling spurt duration on an individual patient basis. Pulsed photothermal radiometry (PPTR) is a promising technique to provide such information. In this article, computer simulations are performed to evaluate the performance of PPTR depth profiling of the laser-induced temperature rise in PWS. An iterative, non-negatively constrained conjugate gradient algorithm is used to reconstruct the laser-induced temperature profile from simulated PPTR signals. Human skin is assumed to contain an epidermal melanin layer and a single homogeneous PWS layer in the dermis. The influence of structural, experimental, and algorithm parameters on the temperature profile reconstruction are discussed. Accuracy of the maximum epidermal temperature rise and PWS depth determined from the reconstructed profiles is statistically analyzed. The simulations show that when the melanin and PWS layers are physically discrete, a good reconstruction can be obtained and the maximum epidermal temperature rise and PWS depth can be determined with accuracy sufficient for the intended clinical application. Measurements and reconstructions from PWS patients are performed and the results are in agreement with the simulations. © 2004 American Institute of Physics. View full abstract»

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  • Liquid helium cryostat with internal fluorescence detection for x-ray absorption studies in the 2–6 keV energy region

    Page(s): 2056 - 2060
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    X-ray absorption spectroscopy (XAS) in the intermediate x-ray region (2–6 keV) for dilute biological samples has been limited because of detector/flux limitations and inadequate cryogenic instrumentation. We have designed and constructed a new tailpiece/sample chamber for a commercially available liquid helium cooled cryostat which overcomes difficulties related to low fluorescence signals by using thin window materials and incorporating an internal photodiode detector. With the apparatus, XAS data at the Cl, S, and Ca K edges have been collected on frozen solutions and biological samples at temperatures down to 60 K. A separate chamber has been incorporated for collecting room-temperature spectra of standard compounds (for energy calibration purposes) which prevents contamination of the cryostat chamber and allows the sample to remain undisturbed, both important concerns for studying dilute and radiation-sensitive samples. © 2004 American Institute of Physics. View full abstract»

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  • Radio frequency magneto-impedance effect in spin tunneling junctions

    Page(s): 2061 - 2064
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    The rf magneto-impedance effect of spin tunneling junctions Co/Al-oxide/Co fabricated on glass substrate by ion-beam sputtering is investigated. To measure junction impedance, a measurement method is established. Junction impedance can be determined from the voltages of two cobalt electrodes and a standard resistor at room temperature over a frequency range of 0.1–100 MHz using a lock-in amplifier by taking input impedance into account. The real part of magneto-impedance ratio exhibits a positive value at frequencies less than the roll-off frequency and a negative value at frequencies higher than the roll-off frequency. Furthermore, the imaginary part of the magneto-impedance ratio is found to be positive across the entire frequency region measured and to approach zero at high frequencies. © 2004 American Institute of Physics. View full abstract»

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  • New method to estimate the frequency stability of laser signals

    Page(s): 2065 - 2067
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    A frequent challenge in the scientific and commercial use of lasers is the need to determine the frequency stability of the output optical signal. In this article we present a new method to estimate this quantity while avoiding the complexity of the usual technique. The new technique displays the result in terms of the usual time domain measure of frequency stability: the square root Allan variance. © 2004 American Institute of Physics. View full abstract»

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  • Remote sensing instrument for solid samples based on open-path atomic emission spectrometry

    Page(s): 2068 - 2074
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    Design considerations and development steps towards the construction of an open-path laser-induced plasma spectrometer for remote elemental measurements are presented and the main variables influencing the analytical signal discussed. The instrument is based on a coaxial optical design where the interrogating laser beam and the returning plasma light share the same optical axis. This scheme allows both tight focusing of the infrared laser radiation to induce a plasma on a remote sample surface and collection of the ultraviolet-visible plasma emission through the same open air path. The selection of the optical scheme and the different components of the instrument are discussed on the basis of the measurement range, the light throughput and signal-to-noise ratio considerations. The results presented demonstrate the feasibility of the open-path laser-induced plasma spectrometry approach to remote atomic-emission spectrometry in the hundred meters range. Based on these results, additional estimations evidence the potential of the technique for measurements in the thousand meters range. © 2004 American Institute of Physics. View full abstract»

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  • Lead-resistance effects in a constant voltage anemometer

    Page(s): 2075 - 2081
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    Two effects of the lead resistances connecting the hot wire to a constant voltage anemometer (CVA) were analyzed and tested: one concerns the change in the sensitivity coefficient relating the anemometer output to velocity or temperature fluctuations, and the other the time constant of the hot wire determined by an in situ square-wave test technique. Small perturbations were assumed in both cases. The CVA output sensitivity was found to be reduced and the time constant increased with the lead resistance. Explicit formulas which involve the lead resistance, the cold wire resistance, and the wire overheat, as well as some characteristics of the CVA circuit, were established to take into account these effects. In the ranges tested, each effect can individually introduce as much as 10% error. Product of the two governs the overall response for the CVA. However, because the two effects change in opposite directions, interestingly, variation in the net response from their product is minimized. This feature may be very useful for many engineering applications of the CVA. Results of experiments conducted with the CVA in a subsonic jet are presented. They confirm the analysis and also establish that accurate measurements can be performed even with a large ratio of lead resistance to hot-wire resistance by applying the correction formulas developed with the analysis. Results from earlier experiments in a supersonic boundary layer also are presented. © 2004 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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Editor
Albert T. Macrander
Argonne National Laboratory