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Review of Scientific Instruments

Issue 12 • Date Dec 1985

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Displaying Results 1 - 25 of 34
  • Use of an optical multichannel analyzer for recording absorption spectra of short‐lived transients

    Page(s): 2199 - 2204
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    Characteristics of an adapted commercial optical multichannel analyzer system for recording of transient absorption spectra in single‐shot pulse radiolysis and flash photolysis are described. The features discussed include temporal (2 μs) and spectral (1 nm) resolution, signal‐to‐noise ratio and its improvement, linearity of response, and wavelength coverage (300–650 nm). The system is intermediate in both cost and capabilities compared to two other methods: (1) recording transient spectra by repetitive pulsing and (2) using an image converter streak camera. This system is convenient for discrimination of small differences in fine structured absorption of spectra short‐lived species. View full abstract»

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  • High‐resolution picosecond transient absorption spectrometer utilizing dye emission and a streak camera

    Page(s): 2205 - 2208
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    A high‐resolution picosecond transient absorption spectrometer utilizing dye emission and a streak camera is presented and compared with other methods of picosecond transient absorption measurements. Typical transient absorption and ground‐state bleach recovery kinetics measured with this spectrometer are shown. Single wavelength transient absorption or ground‐state bleach recovery kinetics are determined on the basis of a single laser shot with this spectrometer, so that the samples are relatively free from decomposition by irradiation. Excellent kinetics may be obtained from the near UV to the near IR and are not subject to interference from luminescence of samples. The sensitivity of this spectrometer is very high and it is reasonably easy and convenient to set up and use. View full abstract»

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  • Spatially resolved matrix isolation spectroscopy I: Visible spectra

    Page(s): 2209 - 2212
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    An apparatus is described for measuring visible absorption spectra across the lateral dimension of a cryogenic matrix isolation sample. By exploiting the rigidity of the matrix, the spatially resolved spectra can be parametrically labeled by another experimental variable, such as photolysis wavelength from dispersed radiation, resulting in a multiplex advantage in data collection rates. Alternatively, the apparatus can be used to measure the visible absorption spectrum of a spatially uniform sample in ≤1 second, a speed which is important for photochemically active samples. View full abstract»

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  • Measurements of density, surface recombination coefficient, and diffusion coefficient of hydrogen atoms by Lα laser fluorescence spectroscopy

    Page(s): 2213 - 2216
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    The technique of laser fluorescence spectroscopy at the Lyman‐alpha (Lα) wavelength in hydrogen was used to measure the temporally and spatially resolved atomic density, the surface recombination coefficient γ, and the diffusion coefficient DH,H2 of the atomic hydrogen in molecular hydrogen. At the same time, it revealed a temporal change of γ, probably due to the change of surface number density of trapped hydrogen atoms. The present technique provides a new and powerful means for determinations of values associated with hydrogen atoms by absolute and local measurements of the atoms at the detection limit of extremely low concentrations. View full abstract»

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  • Rotating mirror device for nonresonant laser Raman difference spectroscopy

    Page(s): 2217 - 2221
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    A novel sample switching device for laser Raman difference spectroscopy (LRDS) has been designed for use with nonresonant samples. The device utilizes a single motor driven rotating mirror, fabricated by diamond turning techniques, which switches both exciting and scattered light 60 times per second. Electronic timing signals are obtained to gate photon counting pulses into separate scalers. The use of fixed capillary sample cells allows for the first time in LRDS the examination of fibers, single crystals, and liquid samples of 10‐μl volume and improved access to samples for thermostating, etc. Alignment of the optics is described. Proper operation of the system is illustrated by examination of pyridine and pyridine‐d5. Comparing spectra of the neat liquids and a mixture of them gives examples of a frequency shift of ≪1 cm-1, a width change, and other bands with no changes. Advantages, limitations, and future extensions of the instrument are described. View full abstract»

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  • Polarization modulation ellipsometry: A compact and easy handling instrument

    Page(s): 2222 - 2227
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    A polarization modulation ellipsometer for measurements of the complex dielectric function of opaque and reflecting materials in the wavelength range 230–920 nm is presented. The instrument can be built at relatively moderate cost but offers reasonable accuracy. It is suitable for routine measurements in a general solid‐state laboratory because of its easy handling and maintenance. View full abstract»

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  • Imaging differential polarization microscope with electronic readout

    Page(s): 2228 - 2236
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    A differential polarization microscope forms two images: one of the transmitted intensity and the other due to the change in intensity between images formed when different polarizations of light are used. The interpretation of these images for linear dichroism and circular dichroism are described. The design constraints on the data acquisition systems and the polarization modulation are described. The advantage of imaging several biological systems which contain optically anisotropic structures are described. View full abstract»

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  • New polarization‐modulation spectrometer for simultaneous circular dichroism and optical rotary dispersion measurements (I): Instrument design, analysis, and evaluation

    Page(s): 2237 - 2242
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    The Mueller matrix approach is used for designing, analyzing, and evaluating a new polarization‐modulation spectrometer for simultaneous measurements of circular dichroism (CD) and optical rotatory dispersion (ORD). The same approach is applied to commercial CD spectropolarimeters for the evaluation of their performance in order to clarify our new spectrometer. On the basis of the results obtained, our JASCO J‐500 CD spectropolarimeter was converted into the new spectrometer. Preliminary experiments indicate that CD and ORD can be measured simultaneously above 400 nm. It is also shown that this new spectrometer can be used for measuring linear dichroism and linear birefringence simultaneously. View full abstract»

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  • Application of diode array spectrometers in microscope photometry

    Page(s): 2243 - 2247
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    Multichannel fast scanning diode array spectrometers represent a new class of spectroscopic instruments. They feature a unique combination of novel technologies, speed, comfort in handling, and ease of operation. In a research study the potentials of this powerful instrument in the field of microscope photometry are evaluated. As examples for possible applications the results of typical spectral measurements in absorption and reflection, including film‐thickness determination of microstructured semiconductor layers, are presented. View full abstract»

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  • Simple and compact neutral metal vapor laser assembly operating in a low‐temperature region

    Page(s): 2248 - 2250
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    A compact and inexpensive technique is reported for a discharge‐excited pulsed metal vapor laser (MVL) at a low operating temperature utilizing an air‐blown‐type spark‐gap switch. A laser is excited in an aperiodic pulse train by successive pulsed discharges of a storage capacitor through a spark‐gap switch. A variety of neutral metal vapor laser (MVL) using metal compound as a lasant is briefly reported with the compact device. View full abstract»

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  • TEA CO2 laser with a SiC anode

    Page(s): 2251 - 2252
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    It is demonstrated that the use of a SiC plane anode and a Dumanchin–Farcy type cathode in the TEA CO2 laser system yields very uniform glow discharges producing high specific peak power. View full abstract»

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  • Large aperture, high‐speed calorimeter for high‐energy optical pulses

    Page(s): 2253 - 2258
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    A radiometric calorimeter is described in which the energy absorber works at the same time as a temperature sensor so that thermal equilibrium for the entire volume of absorber is not required before measuring an incident energy. The achievable frequency response is therefore quite high, and this is not offset by the size and/or damage threshold of energy receiver. The device, formerly called Rat’s Nest Calorimeter (RNC), has been found quite useful for measuring the total energy of modern pulsed lasers with a large beam cross section. The aperture (presently 6 cm) can be increased arbitrarily without degrading the rise time. Excellent stability and high damage threshold (≫439 MW/cm2) result when a thick wire bolometer and amplifier combination is used. Response time (∼9 μs) and spectral flatness are much better than previously reported. Potentials of the RNC for measuring any energy which it absorbs up to 2 kJ at the rise time 60 ns (∼10 MHz) are discussed. The maximum sensitivity of the model 3.5 mJ/cm2 is sufficient to detect the radiative energy emitting from today’s fusion test plasmas. View full abstract»

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  • Microcomputer‐based spectrum‐resolved second‐harmonic generation correlator for fast measurement of ultrashort pulses

    Page(s): 2259 - 2262
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    A new spectrum‐resolved second‐harmonic generation correlator using a single‐line image sensor array and a microcomputer has been developed. It allows us acquisition of many spectrum‐resolved second‐harmonic generation correlation traces in a single scan of the optical delay. Using this correlator, the pulse properties of a colliding pulse mode‐locked ring dye laser have been investigated. It was found that the measuring time can be reduced by an order of magnitude compared with the conventional repeat‐scan method. View full abstract»

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  • Fast heterodyne interferometer with electronically stabilized initial phase

    Page(s): 2263 - 2266
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    A heterodyne interferometer setup with initial‐phase stabilization is described, which allows the full range of ‘‘half a fringe’’ to be used without ambiguity, using only one phase comparator. This phase stabilization is achieved by the insertion of a voltage‐controlled delay line in the reference path of the phase comparator. The system is used to measure the electron line density of pulsed plasmas (with pulse lengths of 1 ms) in the range 5×1019–2×1021 m-2 with a time resolution of 200 ns. The resolution of the electronic system is approximately (half a fringe)/200. View full abstract»

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  • Data acquisition and instrument control system for ion flight time measurements in mass spectrometry

    Page(s): 2267 - 2273
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    A microcomputer system is described that provides instrument control and data acquisition for ion flight time measurements in mass spectrometry. This system is designed specifically for time‐resolved ion momentum spectrometry (TRIMS), a new mass spectrometry/mass spectrometry (MS/MS) technique that utilizes time‐of‐flight measurements in a magnetic sector instrument. The flexibility of the design, however, makes it applicable to many types of instruments that employ ion flight time measurements. The heart of the system is a digital boxcar integrator with 10‐ns timing precision. The microcomputer has control of both the magnetic field and the sampled flight time. Software, written in forth, allows all standard MS/MS scans to be obtained, even those requiring complex linked scans of the magnetic field strength and the sampled flight time. Data that demonstrate the accuracy of these scans are shown for metastable decompositions of n decane. View full abstract»

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  • Extraction of volume‐produced H- ions from a hybrid magnetic multicusp source

    Page(s): 2274 - 2278
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    The negative ion density n- is studied using the photodetachment technique in the extraction region of a 5.7‐l hybrid magnetic multicusp source, and is correlated with the extracted negative ion current I-. It is found that biasing positive the plasma electrode (PE) of the extractor affects in a similar way both n- and I-: both attain a maximum for a PE bias of +1.5 V, while the electron density ne and extracted current Ie exhibit a monotonic reduction. At optimum PE bias, n-/ne attains a value of 0.7. Ie is found to be comparable to the electron thermal flux through the extraction slit; this indicates that there is no potential barrier for the negative particles at the plasma border in front of the extraction slit. At optimum PE bias both Ie and I- vary in proportion to n0.8e. Two regimes characterize the variation of I- vs n-; at high density I- varies in proportion to n1- and appears to be larger than the thermal negative ion flux through the extraction slit, calculated under the assumption that the negative ion temperature is close to the neutral molecule temperature. The discrepancy is the largest (a factor of ten) at the lowest gas pressure. View full abstract»

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  • Time‐resolved measurement of energy and species of an intense pulsed ion beam

    Page(s): 2279 - 2282
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    A time‐resolvable Thomson‐parabola spectrometer is developed employing a microchannel‐plate image intensifier, which acts as a high‐speed shutter (∼5 ns) by gating the applied voltage. Using such a spectrometer, we have achieved the measurement of temporal behavior of beam energy for various ion species of an intense pulsed ion beam extracted from a dual‐current‐feed magnetically insulated diode. The energy of protons is found to be in a good agreement with the diode voltage. View full abstract»

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  • Fast, controlled stepping drive for D2 filament ejection

    Page(s): 2283 - 2286
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    Centrifugal pellet injectors are required to refuel plasma machines. The pellet feed into the centrifuge should, if possible, be direct to keep the exit angle divergence small. The D2 filaments used are first stored in a cryostat and then rapidly transported to the intake region of the centrifuge. An intermittent drive for fast, controlled ejection of D2 filaments is described here. Mean filament speed of up to 0.6 m/s per step (1.2 mm) are achieved for the centrifugal pellet injector which refuels the ASDEX tokamak at Garching. The timing of the (81) step shifts can be synchronized with the rotor motion. The drive allows rates of up to 50 pellets per second. The drive method also seems to be suitable for direct feeding of other known centrifugal pellet injectors. View full abstract»

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  • Output voltage waveform improvement of the coaxial Marx‐type high‐voltage generator

    Page(s): 2287 - 2289
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    A metal ring was installed to each of the main capacitor modules of the coaxial Marx‐type high‐voltage generator to increase the stray capacitance between the main capacitors and the cylinder of the outer conductor. Improvements in build‐up time of the output voltage were achieved and good agreements were obtained between the experimental and the simulated results. View full abstract»

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  • Use of electron beam position modulation in Auger depth profile analysis

    Page(s): 2290 - 2294
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    Auger analysis combined with ion etching in the scanning Auger microprobe (SAM) provides ‘‘three‐dimensional’’ composition information not readily obtainable from other analytical methods. As this technique is being applied to the analysis of microelectronic devices with increasingly smaller dimensions, two major limitations became evident: (1) features of interest in microelectronic circuits are often comparable in size to the beam diameter of commercial Auger microprobes and (2) the electron beam tends to drift about on the specimen surface because of mechanical instability and differential thermal expansion. We describe a technique that will reduce the error and uncertainty caused by beam instability. In our technique, the analyzing beam is scanned repetitively across the feature to be profiled and the Auger signal is synchronously detected at the scan frequency. This position modulation technique allows a tradeoff between depth resolution and sensitivity on the one hand and drift in spatial position of the analyzing electron beam. Position modulation is particularly suited to the analysis of microelectronic devices (e.g., microwave field effect transistors), where the dimensions of features of interest are comparable to the electron beam diameter. View full abstract»

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  • Curved‐tube flowmeters

    Page(s): 2295 - 2298
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    A new flowmeter design is presented which is suitable for accurately measuring flows ranging from ≂1 to ≂1000 cm3 s-1. It may be simply constructed from readily available parts and may be adapted to measure flow of any fluid for which a noncorrosive ball and transparent tube are available. Starting with standard Venturi meter theory, a formula is derived for the volume flowrate in terms of ball and tube dimensions, ball and fluid densities, and the angle at which the ball comes to rest in the tube. Actual examples of curved‐tube flowmeters are given for particular cases of nitrogen at 0 – 42.4 cm3 s-1 and water at 0–11.4 cm3 s-1, constructed using bearing balls in standard Eastman Polyflo tubing. Using the formula as a guide, extension to lower and higher flowrates is straightforward. View full abstract»

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  • Directional sensitivity of unplated normal‐wire probes

    Page(s): 2299 - 2305
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    This paper describes an experimental study of the response to yaw of normal‐wire probes oriented at various roll angles with respect to the yaw plane. The results obtained show that unplated normal wires are most sensitive to yaw when the plane formed by the wire element and the prongs is aligned with the yaw plane. When the wire‐prongs plane is normal to the yaw plane, the sensitivity of these probes is reduced by 30 to 33%. When the wire‐prongs plane is inclined at 45° to the yaw plane, the probe response is almost insensitive to yaw within a large range of flow angles. The current experimental results are compared qualitatively with the ‘‘effective cooling velocity’’ model. It is shown that this model is too oversimplified to be correct; the tangential and the binormal cooling parameters are Re number and yaw dependent and, under certain flow conditions, the tangential cooling parameter k2 may even attain negative values. It is concluded, therefore, that much better signal‐interpretation expressions should be sought. View full abstract»

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  • Static method to measure vapor pressure in the temperature range below 1100 K

    Page(s): 2306 - 2309
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    In this paper, a static method of measuring vapor pressure with an optically flat glass‐membrane pressure sensor in the temperature range below 1100 K is described. The furnace is designed so that the pressure can be measured contactlessly by the null method. A method of automatic pressure control using this sensor is described as well. The method is capable of controlling the pressure to the order of the sensitivity of the membrane. View full abstract»

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  • Computer‐compatible, self‐contained, precision ac resistance bridge suitable for thermometry

    Page(s): 2310 - 2311
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    A precision, self‐contained, four‐terminal ac resistance bridge with phase‐sensitive detection is described. The variable element in the bridge is a digital‐to‐analog converter, so that the setting of the bridge can be computer controlled. If computer control is not required, the bridge can be set using thumbwheel switches. The accuracy of the bridge is ±(0.03% of reading +0.01% of full scale). The dissipation in the unknown resistor is less than 1 μW for a full‐scale range of 99.99 Ω, and less than 1 nW for a full‐scale range of 99.99 kΩ. The low‐power dissipation, ac excitation, and four‐terminal configuration make the bridge especially suitable for resistance thermometry. View full abstract»

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  • New microcalorimeter for the measurement of differential heats of adsorption of gases on high surface area solids

    Page(s): 2312 - 2318
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    A new calorimeter of the heat‐flow type designed to measure the differential heats of adsorption of gases on high surface area solids (e.g., catalysts) is described. Heat flow is measured using conventional thermopiles; the signals from which are amplified, digitized, and then sent to a laboratory computer for ease of data handling and analysis. The instrument allows conventional isotherm and heat data to be collected concomitantly. Other useful information obtained includes qualitative data regarding the rate at which processes take place, the total amount of gas chemisorbed, and the integrated value of the heat of adsorption. The instrument is capable of operating at temperatures from 273 to 373 K. One major advance over previous designs is that the dosing gas is allowed to thermally equilibrate before entering the sample chamber. The results of a simple study of the differential heats of adsorption of oxygen on a high surface area carbon material are presented. This study demonstrates the reliability and utility of the instrument. View full abstract»

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

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Editor
Albert T. Macrander
Argonne National Laboratory