Showing papers in "Review of Scientific Instruments in 1983"
TL;DR: A comprehensive review of low-temperature specific heat (LTSH) measurements can be found in this article, where the most reliable measurements of the LTSH of 84 of the elements are presented.
Abstract: The measurement of low‐temperature specific heat (LTSH) (0.1 K
304 citations
TL;DR: In this article, the optimal dimensions of thin coils for producing uniform magnetic fields were calculated for three and four square coils, and the sensitivity of the uniformity to the precision of construction was discussed.
Abstract: The optimal dimensions of thin coil systems of three and four square coils for producing uniform magnetic fields are calculated We find that for three square coils, of side d and separation s between the outer coils, the most uniform field distribution occurs with s/d=0821 116 and with I′/I=0512 797 I′/I is the ratio of the currents in the center coil to that of the outer coils With four square coils, the best uniformity is obtained when a/d=0128 106 and b/d=0505 492, where a is the distance from the center to the inner coils and b is the distance from the center to the outer coils The ratio of the current in the inner pair of coils to that in the outer pair must be I′/I=0423 514 We compare the uniformity of the field produced by these coil systems with each other and with Rubens’ five‐coil system, both on and off axis It is shown that the optimal four‐coil design is superior to the three‐ and five‐coil systems The sensitivity of the uniformity to the precision of construction is discussed Di
275 citations
TL;DR: An alternative method, the binomial smoothing filter, is shown to be preferable to LSP smoothing in many cases, and it is faster, better behaved in both the data and the frequency domains for many applications, and simpler to use and to program or to implement in hardware.
Abstract: Some pitfalls of least‐squares polynomial (LSP) smoothing (better known to analytical chemists as Savitzky–Golay smoothing) are demonstrated and discussed, as well as some remedies. For instance, smoothing by long LSP sequences leads to transmission zeros, phase reversals, and overshoots that may be objectionable in some applications. An alternative method, the binomial smoothing filter, is described and some of its properties are presented. It is shown to be preferable to LSP smoothing in many cases. It is faster, better behaved in both the data and the frequency domains for many applications, and simpler to use and to program or to implement in hardware. Finally, the action of a filter of a given order is easy to predict.
237 citations
TL;DR: In this paper, a dual-beam UV-absorption instrument for balloon-borne measurements of atmospheric ozone is described, which has two identical absorption chambers, each alternating between reference mode (ozone free) and sample mode by means of a four-port valve and ozone scrubber.
Abstract: Various types of ozone detectors are currently in use, each with different advantages and compromises in response time, portability, sensitivity, accuracy, need for repeated calibration, and expense. We describe here a new dual‐beam UV‐absorption instrument for balloon‐borne measurements of atmospheric ozone. It has two identical absorption chambers, each alternating between reference mode (ozone free) and sample mode by means of a four‐port valve and ozone scrubber. The ratio of the absorption signals, along with the known lengths and ozone absorption cross section, yield the ozone concentration. The dual‐beam feature cancels the effects of lamp intensity fluctuations, while the mode alternation compensates for mechanical changes and also provides continuous measurements. The absorption measurement requires no calibration and, hence, is independent of gas flow rate. The response time is 1 s and, for this measurement duration, the minimum ozone concentration detectable by this instrument (one standard dev...
196 citations
TL;DR: In this paper, a permanent magnet filter together with a small positive bias voltage on the plasma grid can produce a very significant reduction in electron drain as well as a sizable increase in H− ions available for extraction.
Abstract: H− ions formed by volume processes are extracted from a multicusp ion source. It is shown that a permanent magnet filter together with a small positive bias voltage on the plasma grid can produce a very significant reduction in electron drain as well as a sizable increase in H− ions available for extraction. A further reduction in electron current is achieved by installing a pair of ceramic magnets at the extraction aperture. The combined arrangement improves the ratio of extracted H− ion current to electron current to about unity.
195 citations
TL;DR: In this article, a single frequency dye laser is used as a plasma diagnostic for measuring ion velocity distributions with a resolution limited only by the natural linewidth of the laser excited resonance transition.
Abstract: In this paper we report the development of the single frequency dye laser as a plasma diagnostic for measuring ion velocity distributions with a resolution limited only by the natural linewidth of the laser excited resonance transition. For the 6S1/2–6P1/2 transition in Ba+ this corresponds to a velocity uncertainty of 103 cm/s. Velocity selection is performed by the laser as it scans the Doppler broadened plasma absorption line, in contrast with the usual method of scanning an emission line with a high‐resolution spectrometer. Both sensitivity and resolution are improved by 2 orders of magnitude, allowing nonperturbing measurements to be made at densities below 107 cm−3. In addition to a description of the technique, sample measurements of time‐resolved wave induced modifications of ion velocity distributions are shown.
125 citations
TL;DR: In this paper, the design and construction of a new UV resonance Raman spectrometer continuously tunable between 217-750 nm is described, where the excitation source is based on a YAG laser which is frequency doubled or tripled to pump a dye laser.
Abstract: The design and construction of a new UV resonance Raman spectrometer continuously tunable between 217–750 nm are described. The excitation source is based on a YAG laser which is frequency doubled or tripled to pump a dye laser. UV light is generated by nonlinear frequency doubling and mixing of the dye laser output or doubled output with the 1.06‐μm YAG fundamental. The detection system utilizes an intensified Reticon multichannel array. Commercially available monochromators are modified to make them useful for UV resonance Raman spectroscopy. Some sampling methodologies important for UV resonance Raman measurements are described. Examples of the sensitivity of UV resonance Raman spectroscopy are illustrated.
114 citations
TL;DR: In this article, the authors used a very short-lived fluorophore to mimic the excitation pulse shape at the wavelength of sample emission, λem, yielding the convoluted mimic decay function Cm(λem,t).
Abstract: The determination of accurate subnanosecond fluorescence lifetimes by the time‐correlated single‐photon counting technique is often limited by difficulties in obtaining the correct instrumental response function f(λ,t) to the excitation pulse. These difficulties are increased when a grating monochromator is used to disperse the emission due to the introduction of an additional temporal broadening of f(λ,t). A technique for determining the correct f(λ,t) at the wavelength of sample emission, λem, is described. The technique consists of using a very short‐lived fluorophore to ‘‘mimic’’ the excitation pulse shape at λem, yielding the convoluted mimic decay function Cm(λem,t), and then to computationally extract f (λem,t) from Cm(λem,t). The technique is experimentally and computationally simple and yields the desired instrumental response function at λem which eliminates problems due to the sensitivity of f(λ,t) to λ (color shift artifact). The photomultiplier tube receives spatially equal illumination when ...
113 citations
TL;DR: The unique advantages of the elliptical analyzer for precise and absolute spectral measurements are noted and detailed descriptions of its geometrical and physical optics are presented in this paper, where the authors compared the plane, convex, and concave fixed crystal analyzers which may be applied to the spectrometry of concentrated, intense plasma sources of x radiation involved in fusion energy and x-ray laser research.
Abstract: The general characteristics are compared for the plane, convex, and concave fixed crystal analyzers which may be applied to the spectrometry of concentrated, intense plasma sources of x radiation involved, for example, in fusion energy and x‐ray laser research. The unique advantages of the elliptical analyzer for precise and absolute spectral measurements are noted and detailed descriptions of its geometrical and physical optics are presented. With a source point at one of the foci of the elliptical analyzer profile, the spectrum is Bragg reflected (45°<2θ<135°) at normal incidence upon a detection circle with its center at the second focal point, at which an effective scatter aperture and filter window is located. A primary monochromator consisting of a cylindrical, grazing‐incidence mirror is placed between the source and the analyzer to provide an efficient cutoff for high‐order diffracted background radiation and to focus the divergent rays so as to obtain an adjustable spectral line length at the detection circle. Photographic film may be transported along the detection circle. Linear position‐sensitive electronic detection arrays or a streak camera slit window may be placed along a chord of the detection circle. Calibration procedures for absolute line and continuum intensity measurement are described and examples of calibrating spectra are presented as measured with elliptical analyzers of LiF, PET, KAP, and molecular multilayers for the 80–8000‐eV photon energy region. The instrumental effects that contribute to the spectral line shape as measured by the elliptical analyzer spectrograph are defined and a simple line‐shape analysis procedure is presented for the determination of the line‐broadening contributions of the source. The effects of an off‐axis positioning of a source point and of an extended source are analyzed and the application of the elliptical analyzer spectrograph for one‐ and two‐dimensional imaging or an extended source at a given photon energy is discussed. Finally, methods and materials for the construction of the elliptical analyzers are described.
77 citations
TL;DR: In this paper, a directional velocity analyzer was developed for measuring electron distribution functions in plasmas, which contains a collimating aperture which selects particles from a narrow cone in velocity space and a retarding potential analyzer.
Abstract: A directional velocity analyzer has been developed for measuring electron distribution functions in plasmas. It contains a collimating aperture which selects particles from a narrow cone in velocity space and a retarding potential analyzer. The distribution function f(v, theta, phi) is obtained from a large number of analyzer traces taken at different angles theta, phi. In addition, the small analyzer can be moved in space and the measurements are time resolved so as to obtain the complete phase space information f(v,r,t). The large data flow of this seven-variable function is processed with a high-speed digital data-acquisition system. The new electron velocity analyzer is applicable over a wide parameter range in electron energies and densities. Various cases of anisotropic distributions such as beams, shells, tails, and drifts have been successfully investigated.
73 citations
TL;DR: In this article, the Hamamatsu R928 side-window photomultiplier tube has been evaluated in the picosecond time domain and twice the resolution has been obtained.
Abstract: The performance characteristics of the Hamamatsu R928 side‐window photomultiplier tube have been evaluated in the picosecond time domain. This phototube is proposed as an attractive solution to the problem of high time resolution when a sync‐pumped dye laser is combined with the single‐photon time correlation method for determining fluorescence lifetimes and measuring time‐resolved emission spectra and polarization anisotropy. It combines excellent timing characteristics in the single‐photon mode and a small‐to‐negligible wavelength effect with high gain, low noise, and low cost. Twice the resolution previously reported has been obtained.
TL;DR: In this paper, the infrared spectra of the antisymmetric stretching bands of dilute solutions of nitrite and nitrate ions in sodium bromide were used as pressure gauges for use with anvils and other apparatuses.
Abstract: The infrared spectra of the antisymmetric stretching bands of dilute solutions of nitrite and nitrate ions in sodium bromide are proposed as pressure gauges for use with anvils and other apparatuses Their frequencies, which are at 12790 and 14013 cm−1 respectively at zero pressure, were measured up to 186 kbar relative to the R1 fluorescence line of ruby The pressure is related to the shift Δν of the frequency of the nitrite ion at 22 °C from the zero‐pressure value by the equation p/kbar=2356(Δν/cm−1)−1334(Δν/cm−1)exp(−Δν/92 cm−1), and to the shift Δν of the frequency of the nitrate ion by the equation p/kbar=1775(Δν/cm−1)−07495(Δν/cm−1) ×exp(−Δν/78 cm−1) Both equations were fitted by least squares, assuming that the error is in the pressure only, and the standard deviation of the pressure is 11 and 14 kbar, respectively
TL;DR: In this paper, a Seya-Namioka monochromator combined with a position-sensitive channel plate device for parallel detection of a wavelength range of 165 A is used as a photon detector and covers an energy regime from 10 to 40 eV with a resolution of 5 A.
Abstract: A spectrometer for momentum‐resolved and polarization‐dependent bremsstrahlung spectroscopy (inverse photoemission) in the vacuum UV range is described and the performance of the apparatus is discussed. A Seya–Namioka monochromator combined with a position‐sensitive channel plate device for parallel detection of a wavelength range of 165 A is used as a photon detector and covers an energy regime from 10 to 40 eV with a resolution of 5 A. Due to the polarization‐dependent reflectivity of the gold‐coated gratings, the monchromator is also inherently an analyzer for the polarization of the detected light. A space‐charge‐limited Pierce‐type electron gun comprising a BaO dispenser cathode is used as an electron source with 0.1‐A−1 momentum resolution. The overall energy resolution of the apparatus is 0.3 eV at 20 eV photon energy. The sensitivity is 1.8×104 counts per Coulomb and eV for the unoccupied s, p bands of a polycrystalline gold sample.
TL;DR: In this article, a model and a computer simulation were used to quantitatively reproduce the experimental results of Panitz and Foesch's experiments. But the authors focused on the enhancement of quantum efficiencies in the case of extreme UV wavelengths.
Abstract: High quantum efficiency and two-dimensional imaging capabilities make the microchannel plate (MCP) a suitable detector for a sky survey instrument. The Extreme Ultraviolet Explorer satellite, to be launched in 1987, will use MCP detectors. A feature which limits MCP efficiency is related to the walls of individual channels. The walls are of finite thickness and thus form an interchannel web. Under normal circumstances, this web does not contribute to the detector's quantum efficiency. Panitz and Foesch (1976) have found that in the case of a bombardment with ions, electrons were ejected from the electrode material coating the web. By applying a small electric field, the electrons were returned to the MCP surface where they were detected. The present investigation is concerned with the enhancement of quantum efficiencies in the case of extreme UV wavelengths. Attention is given to a model and a computer simulation which quantitatively reproduce the experimental results.
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TL;DR: In this article, a high-density magnetized plasma is seen to heat small diameter tungsten wire probes to electron emission, and the use of these self-emissive probes to determine the plasma potential in a tandem mirror plasma is investigated.
Abstract: A high‐density magnetized plasma is seen to heat small diameter tungsten wire probes to electron emission. The use of these self‐emissive probes to determine the plasma potential in a tandem mirror plasma is investigated. A simplified model is presented and comparison is made with conventional emissive probe behavior.
TL;DR: An accurate light scattering photometer capable of measuring both the angular distribution of intensity and the intensity fluctuation spectrum of laser light scattered from a wide variety of samples including solutions of polymers and other macromolecules is described in this article.
Abstract: An accurate light scattering photometer capable of measuring both the angular distribution of intensity and the intensity fluctuation spectrum of laser light scattered from a wide variety of samples including solutions of polymers and other macromolecules is described. The photometer employs 18 fixed scattering angles ranging from 2.6° to 163° and is sufficiently accurate to measure a molecular radius of gyration as small as 60 A reliably. Stray elastically scattered light normally comprises less than 1% of the light scattered from pure toluene at the smallest scattering angle and is unmeasurable at other angles. The apparatus employs optical fibers to transmit the scattered light to a single photomultiplier tube and functions automatically under microprocessor control, with sample temperature controlled to ±0.1 mK.
TL;DR: An angle-resolving electron energy analyzer capable of operating at an energy resolution of ≲20 meV and an angular resoltuion of ≳ 1/4° has been designed, constructed, and tested as discussed by the authors.
Abstract: An angle‐resolving electron energy analyzer capable of operating at an energy resolution of ≲20 meV and an angular resoltuion of ≲1/4° has been designed, constructed, and tested. A novel input lens allows independent control over both the energy and angular resolution. A series of tests has been performed which indicates that the analyzer operates at the theoretical resolution limit for the lowest values used.
TL;DR: In this paper, a 3mm-diam, dual hot-wire aspiring probe is described which can simultaneously measure total temperature and total pressure in an unsteady high-speed gas flow.
Abstract: A 3‐mm‐diam, dual hot‐wire aspiring probe is described which can simultaneously measure total temperature and total pressure in an unsteady high‐speed gas flow. The probe consists of two coplanar constant temperature hot wires at different overheat ratios operated in a 1.5‐mm‐diam channel with a choked exit. Thus, the constant Mach number flow by the wires is influenced only by free‐stream total temperature and pressure. The probe design is a compromise between the conflicting requirements of spatial resolution, frequency response, and angular sensitivity. The dc temperature accuracy of the probe is about 1% while the resolution is 0.3%. Frequency response of the present design is dc to 20 kHz.
TL;DR: In this paper, a detailed discussion is presented on the major components of a LEED diffractometer and compared briefly to some other techniques that are sensitive to surface structure, and the properties of LEED instruments that are important in performing these measurements are described.
Abstract: Recent developments in instrumentation for low‐energy electron diffraction (LEED) are reviewed After a summary of the major types of measurements in LEED, the properties of LEED instruments that are important in performing these measurements are described A detailed discussion is presented on the major components of a LEED diffractometer LEED is compared briefly to some other techniques that are sensitive to surface structure
TL;DR: In this paper, a four-probe technique is described for measuring the electrical resistance of metals in a diamond anvil cell at pressures up to 40 GPa, and the most reliable gaskets were composites of sheet mica and MgO powder.
Abstract: A four‐probe technique is described for measuring the electrical resistance of metals in a diamond‐anvil cell at pressures up to 40 GPa. The pressure range for electrical resistance measurements was extended by developing insulating gaskets that provide the necessary support for the diamonds and the electrical leads at the diamond edges. The various gasket materials and construction methods that were tested fall into two categories: (1) gaskets made entirely of insulating materials, and (2) gaskets made of metal coated with insulating materials. Gaskets developed in each category were used successfully in making resistance measurements up to 40 GPa. The most reliable gaskets were composites of sheet mica and MgO powder. This report describes the testing and development of the gaskets and presents electrical resistance data obtained for iron and beryllium to 40 GPa.
TL;DR: Diamagnetic measurements of a field‐reversed theta‐pinch plasma are performed with a simplified diagnostic consisting of either a single‐flux loop and several magnetic probes or magnetic probes only and numerical and experimental evidence of the validity of these techniques is presented.
Abstract: Diamagnetic measurements of a field‐reversed theta‐pinch plasma are performed with a simplified diagnostic consisting of either a single‐flux loop and several magnetic probes or magnetic probes only Numerical and experimental evidence of the validity of these techniques is presented
TL;DR: In this article, a beam splitter is described, which is capable of producing a division of light in a polarization independent manner, where the reflection/refraction ratio at the two boundaries are then complementary and the combined effect is insensitive to the polarization of the incident beam.
Abstract: A new type of beam splitter is described, which is capable of producing a division of light in a polarization independent manner. Typical beam splitters (used off-axis) have a pronounced polarization dependence. The device is a thin plate of suitably oriented, birefringent material having a thickness chosen to interchange the characteristic polarizations of the beam between the faces of the plate. The reflection/refraction ratio at the two boundaries are then complementary and the combined effect is insensitive to the polarization of the incident beam.
TL;DR: In this paper, the transient hot-strip (THS) method has been developed for experimental situations with two different materials kept against the sides of the strip and good contact is established between the probe and the sample.
Abstract: The transient hot‐strip (THS) method has been developed for experimental situations with two different materials kept against the sides of the strip. Based on this development THS probes, with known or separately measured thermal properties, have been designed and used successfully in a series of reported experiments. If the thermal diffusivity of the probe is less than that of the material under study and good contact is established between the probe and the sample, the accuracy of the measurements turns out to be as good as with the ordinary transient hot‐strip method.
TL;DR: In this article, a system that uses a helium-neon laser and lateral effect photodiodes to monitor the θ and φ angles of a test mirror is described.
Abstract: A system is described that uses a helium–neon laser and lateral effect photodiodes to monitor the θ and φ angles of a test mirror. Accuracies of 0.01 arcsec are achieved short term in a laboratory environment. A bandwidth of 900 Hz allows simultaneous real‐time angle monitoring on both coarse (10 000 arcsec) and fine (300 arcsec) angular ranges.
TL;DR: In this article, a modified hot-wall epitaxy (HWE) system for the growth of multiple heterolayers is described, which consists of two identical HWE furnaces.
Abstract: A modified hot‐wall epitaxy (HWE) system for the growth of multiple heterolayers is described which consists of two identical HWE furnaces. The substrate furnaces are mounted on a rotatable plate which allows the growth of heterolayers under nearly identical conditions for each individual layer. Single layers and multilayer heterostructures of the PbTe/Pb1−xSnxTe system were grown with this apparatus and typical results are presented.
TL;DR: In this article, a laboratory x-ray absorption spectrometer is described, which consists of a Johansson cut bent crystal, a rotating anode xray generator, and a fast SSD (solid-state detector).
Abstract: A laboratory x‐ray absorption spectrometer is described which consists of a Johansson‐cut bent crystal, a rotating anode x‐ray generator, and a fast SSD (solid‐state detector). Because the SSD can completely discriminate the undesired reflections, contamination of the harmonics is avoided while maintaining a high‐source voltage necessary for strong x‐ray flux. Fast electronics equipment is employed to keep up with high‐x‐ray intensity. It is also possible to utilize higher‐order reflections for high resolving power. The data of quality comparable to those obtained at synchrotron radiation facilities can be obtained in a comparable period of time. In addition, the determination of the absolute absorbance as defined is possible, which makes the problem of the background subtraction in EXAFS analysis easy.
TL;DR: A 10Hz coherent anti-Stokes Raman spectroscopy (CARS) instrument capable of simultaneous thermometry and N2-concentration measurements in a turbulent flame has been designed and constructed and described in detail.
Abstract: A 10‐Hz coherent anti‐Stokes Raman spectroscopy (CARS) instrument capable of simultaneous thermometry and N2‐concentration measurements in a turbulent flame has been designed and constructed and is described in detail. The instrument employs the doubled output of a pulsed Nd:YAG laser for pumping a broadband dye laser and also for the CARS pump beam. The broadband dye laser is used to excite, during a single pulse, the entire Q Branch of N2, the CARS signal of which is recorded by a multichannel analyzer. Special problems which were encounted with the multichannel analyzer include signal retention and limited dynamic range. The former was greatly reduced by employing cleansing scans between laser firings, and the latter was circumvented by employing a multiple beamsplitter arrangement in which the CARS signal was divided into four separate intensity regions, each of which covered a specific temperature range. The 10‐Hz operation of the instrument required the use of a mass storage device such as an 800‐bi...
TL;DR: In this paper, a new method of measuring the plasma potential using emissive probes is presented; the "droop" method is used in a steady-state experiment in which Te≫Tw, where Te and Tw are the electron and filament temperatures, respectively.
Abstract: A new method of measuring the plasma potential using emissive probes is presented; the ‘‘droop’’ method This method may be used in a steady‐state experiment in which Te≫Tw, where Te and Tw are the electron and filament temperatures, respectively The method is based on the observation that the floating potential of an emissive probe depends on Tw A filament temperature which changes in time causes the floating potential also to vary The proportionality constant between the two is extremely sensitive to whether the probe is above or below the plasma potential Thus, a floating emissive probe which is allowed to cool can be used to discriminate between voltages above and below the space potential
TL;DR: In this article, an instrument to detect the vaporization of superheated drops is described, and quantitative tests have been performed of the response of the super-heated drop neutron detector.
Abstract: An instrument to detect the vaporization of superheated drops is described. Using this instrument, quantitative tests have been performed of the response of the superheated drop neutron detector [Nucl. Instrum. Methods 162, 603 (1979)], a tool for possible use in neutron dosimetry, area monitoring, and nuclear spectroscopy.
TL;DR: An unusually rugged highly sensitive and inexpensive bubble tiltmeter has been designed, tested, and built in quantity as discussed by the authors, which is presently used on two volcanoes and an Alaskan glacier, where they continuously monitor surface tilts of geological interest.
Abstract: An unusually rugged highly sensitive and inexpensive bubble tiltmeter has been designed, tested, and built in quantity. These tiltmeters are presently used on two volcanoes and an Alaskan glacier, where they continuously monitor surface tilts of geological interest. This paper discusses the
mechanical, thermal, and electric details of the meter, and illustrates its performance characteristics in both large ( > 10^(-4) radian) and small ( < 10^(-6) radian) tilt environments. The meter's ultimate sensitivity is better than 2 X 10^(-8) radians rms for short periods (hours), and its useful dynamic range is greater than 10^4. Included is a short description of field use of the instrument for volcano monitoring.