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Review of Scientific Instruments

Issue 4 • Date Apr 1986

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Displaying Results 1 - 25 of 30
  • Heterodyne and nonheterodyne laser transceivers

    Page(s): 519 - 528
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    The fundamental characteristics of heterodyne and nonheterodyne imaging laser radars are presented in terms of information content, structual complexity, and sensitivity limits. The sensitivity characteristics of heterodyne and nonheterodyne laser receivers are quantitatively compared. When feedback amplification or low‐noise multiplication gain is available in the receivers, the direct detection of laser signals can approach or even surpass the sensitivity or coherent detection. The concept of ‘‘self‐homodyne’’ is introduced and its potential application to laser radar measurements is addressed. View full abstract»

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  • Heterodyne technique for measuring photodetector frequency response without rf interference

    Page(s): 529 - 533
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    For heterodyning two optical beams it is necessary to obtain two almost coherent waves. Rather than using an extremely stable laser source, it is possible to split the beam from a single source and use a modulator to shift the frequency of one of the waves. The heterodyne signal generated is at the frequency of modulation, thus, it is susceptible to rf interference by the high modulation voltage. Using two electro‐optical modulators, one can utilize the signal at the sum or difference frequency at which no high voltage is present. It is shown that using a single source and two modulators one obtains a signal without any interference leakage. Thus it is possible to measure easily the frequency response of photodetectors up to high frequencies. This configuration also doubles the frequency range obtainable from a single modulator. The theoretical expressions for the intensities at the various frequencies are presented. Noise equivalent power (NEP) measurements of heterodyne signals performed using this setup are very close to the theoretical limit. View full abstract»

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  • Compact and reliable discharge‐pumped XeCl laser with automatic preionization

    Page(s): 534 - 538
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    A compact discharge‐pumped XeCl laser is described with high efficiency and reliability at low operating pressures below 2 atm. Using 65.8% Ne, 30.0% Ar, 4.0% Xe, and 0.2% HCl mixture, the maximum total efficiency of 0.9% was obtained at the total gas pressure of 1.8 atm and the charging voltage of 18 kV. That efficiency was fairly high for the low operating pressure and the compact size of the laser chamber. The shot‐to‐shot reproducibility of the laser pulse was excellent, and the laser energy stability was within ±4%. View full abstract»

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  • Fast λ/4 and λ/2 voltage Pockels cell driver for an internally seeded and cavity dumped regenerative laser amplifier

    Page(s): 539 - 543
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    A krytron‐based electrical circuit of a λ/4 and λ/2 voltage pulse generator for a Pockels cell incorporated in a self‐injected and cavity dumped short‐pulse laser source is described. The circuit supplies three independent high‐tension pulses having amplitudes between 1 and 2.5 kV, fall and rise times ≪2 ns, and jitter ≪2 ns. Pulse durations and interpulse distances are adjustable. View full abstract»

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  • Design of a rocket‐borne radiometer for stratospheric ozone measurements

    Page(s): 544 - 551
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    A four‐filter ultraviolet radiometer for measuring stratospheric ozone is described. The payload is launched aboard a Super‐Loki rocket to an apogee of 70 km. The instrument measures the solar ultraviolet irradiance over its filter wavelengths as it descends on a parachute. The amount of ozone in the path between the radiometer and the sun is calculated from the attenuation of solar flux using the Beer–Lambert law. Radar at the launch site measures the height of the instrument throughout its flight. The fundamental ozone value measured by the ROCOZ‐A radiometer is the vertical ozone overburden as a function of geometric altitude. Ozone measurements are obtained for altitudes from 55 to 20 km, extending well above the altitude range of balloon‐borne ozone‐measuring instruments. The optics and electronics in the radiometer have been designed within relatively severe size and weight limitations imposed by the launch vehicle. The electronics in the improved rocket ozonesonde (ROCOZ‐A) provide essentially drift‐free outputs throughout 40‐min ozone soundings at stratospheric temperatures. The modest cost of the payload precludes recovery and makes the instrument a versatile tool compared to larger ozonesondes. View full abstract»

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  • Multichannel spectrometer for plasma diagnostics

    Page(s): 552 - 559
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    A multichannel vacuum ultraviolet spectrometer has been constructed to provide time‐resolved measurements of line radiation from a plasma. The spectrometer may simultaneously view up to 40 preselected narrow spectral bands or lines from a common viewing chord in a wide spectral region (∼60–450 nm) with the maximum frequency response limited to 80 MHz by the photomultipliers and 350 kHz by the data‐acquisition system. Rapid reselection of impurity lines is facilitated by the use of multiple slits cut in a metal foil placed at the Rowland circle of the instrument. Due to the limitation imposed by the present fiber‐optic coupling to the plasma the results to date are from impurity wavelength in excess of about 220 nm. View full abstract»

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  • Dual homodyne detection system for measuring asymmetric spectra in the far‐infrared regime

    Page(s): 560 - 565
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    A dual homodyne detection system for measuring scattered radiation from plasmas has been fabricated. The system is operative in the far‐infrared regime, and with it the power spectral distribution of the scattered radiation in the upper and lower sidebands with respect to the frequency of the incident wave can be obtained. Theory of operation and experimental results for simulated radiation fields are given. View full abstract»

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  • New method of observing nonlinear waves in a plasma

    Page(s): 566 - 571
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    A new method for observing a nonlinear wave is proposed and illustrated with sample measurements. Observations are performed by using the time‐of‐flight method by counting the temporal upper hybrid wave packets which pass through the gap between two antennae. Two types of nonlinear waves were found in the experiment. One is outlined in the Korteweg de Vries equation by its behavior through the dispersion relation and the other behaves as a shock wave which represents the relaxing oscillation. The method of observation and the characteristics of the nonlinear waves are discussed circumstantially. View full abstract»

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  • Integrated development facility for the calibration of low‐energy charged particle flight instrumentation

    Page(s): 572 - 582
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    A system has been developed specifically for the calibration and development of thermal ion instrumentation. The system is optimized to provide an extended, approximately 80‐cm2 beam, with usable current rates ∼1 pA/cm2 at beam energies as low as 1 eV, with much higher values available with increasing energy. The beam energy spread is typically less than 2 eV/charge and the average angular divergence is approximately 2.5°. A tandem electrostatic and variable geometry magnetic mirror configuration within the ion source optimizes the use of the ionizing electrons, thus decreasing the gas and nonthermal electron throughput to the instrument chamber while improving the current density uniformity. The system is integrated under microcomputer control to allow automatic control and monitoring of the beam energy and composition and the mass‐ and angle‐dependent response of the instrument under test. The data can be transmitted in nearly real time to the interested investigators for comparison with expected results over existing computer networks. The system is pumped by a combination of carbon vane and cryogenic sorption roughing pumps and ion and liquid‐helium operating pumps. This allows testing and final calibration of flight instrumentation in an ultraclean environment. View full abstract»

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  • New time‐of‐flight mass spectrometer for improved mass resolution, versatility, and mass spectrometry/mass spectrometry studies

    Page(s): 583 - 592
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    Reported here is the design and experimental investigation of the performance characteristics of a new time‐of‐flight (TOF) mass spectrometer. The instrument combines the advantages of beam deflection for ion pulse formation with an electrostatic analyzer which reduces the energy spread of the ions admitted to the TOF region. The instrument is able to use ion sources which cannot be pulsed on a time scale suitable for conventional TOF analysis (e. g., chemical ionization sources). Improved mass resolution is demonstrated over a wide mass range such that all of the ions are in focus simultaneously. A resolution of 982 (full width at half‐maximum) is achieved for the molecular ion peak of perfluorotributylamine at m/z 614. A preliminary investigation of a proposed technique for collecting information typically obtained by tandem mass spectrometry (MS/MS) has also been conducted using this instrument. This new method, named time‐resolved ion kinetic energy spectrometry (TRIKES), combines time‐of‐flight (velocity) and kinetic energy analysis of undissociated parent ions and daughter ions which are products of decompositions occurring between the ion source and electrostatic analyzer. Unit resolution of the daughter ions produced upon metastable decomposition of the molecular ion of n‐decane has been achieved in constant parent scans. The realization of rapid time‐of‐flight data collection rates in TRIKES may yield improved data collection rates in MS/MS. View full abstract»

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  • Variable magnetic bottle for precision geonium experiments

    Page(s): 593 - 597
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    A novel technique has been developed which allows a quadratic magnetic field to be continuously varied (via a superconducting flux transformer) from the outside of an ultrahigh‐vacuum container placed within a superconducting solenoid. Enclosed within each of these vacuum vessels is a high‐precision (compensated) Penning trap which is used in a variety of geonium experiments at the University of Washington. By varying the dc current in an outer (normal) primary solenoid, the secondary current flowing within a shorted superconducting loop is varied accordingly. The superconducting loop need only be placed in a cylindrically symmetric position within the Penning trap in order to generate the B2 term, and with a clever choice of geometry, the zeroth‐order term can be totally eliminated. As an additional highlight, the uniform field from the main solenoid is drift stabilized to the same degree as the basic cancellation and further, an auxiliary trim coil can be used to fine trim the zeroth‐order null. View full abstract»

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  • Prospects of centrifugation of cells, liquids, and gases at multimillion g‐forces in magnetically suspended microrotors

    Page(s): 598 - 601
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    Prototypes of magnetically suspended rotors for centrifugation of cells, organic and inorganic solutions, and gases are Fe‐containing glass and metallic hollow microspheres 0.1–2 mm in diameter, composite steel‐glass disks up to 1 cm, and microspheres of porous steel and Fe‐impregnated porous glass. Fe‐coated microcapsules with cells can be used for lower centrifugal forces. Predictable applications include cell hybridization and homogenization, spinning of samples at the ‘‘magic angle’’ in nuclear‐magnetic resonance (NMR), intensification of nuclear fusion by high‐speed rotation of microspheres with deuterium and tritium, and other examples. Rotor contents can be examined under the microscope during centrifugation, or the spinning rotor can be frozen and its contents freeze dried for further examination. View full abstract»

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  • Flash x‐ray computed tomography facility for microsecond events

    Page(s): 602 - 611
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    A new computed tomography imaging device that allows four orders of magnitude improvement in temporal resolution over currently available systems is described. Using 21 simultaneously triggered flash x‐ray sources and 21 detector arrays, density resolution of several percent for a 1‐cm region, lateral spatial projection resolution of 2 mm on a 200‐mm object, and a temporal resolution of 10-6 s are predicted. To achieve this time resolution with only 21 views, both the spatial and contrast resolution are degraded when compared with medical CT systems. The system has multislice capability when used with film/screen detectors. The design, construction, and projected capabilities of the facility are detailed. View full abstract»

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  • High‐speed digital image processing system, MFIP, with bus‐oriented architecture

    Page(s): 612 - 616
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    A general purpose high‐speed digital image processing system with bus‐oriented architecture has been developed using a time‐shared multiframe data bus with the data transferring rate of 80 Mbytes/s. This system is equipped with special purpose hardware for executing frame‐to‐frame operation, 2‐D convolution, and 2‐D recursive filtering, allowing image processing of dynamic scenes can be performed in real time. The architecture and hardware of the developed system are presented, and the manufacture of special purpose hardware is described. Experimental results have demonstrated the ability to accomplish image processing of moving objects in real time, and 2‐D convolution and 2‐D recursive filtering at high speed. View full abstract»

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  • Frequency modulated (FM) time delay photoacoustic and photothermal wave spectroscopies. Technique, instrumentation, and detection. Part I: Theoretical

    Page(s): 617 - 621
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    A conceptual basis for the technique of time delay photothermal wave spectroscopy is presented. The signal generation and appropriate system functions in the time delay and frequency domains are introduced and discussed from the point of view of correlation and spectral analysis and processing. View full abstract»

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  • Frequency modulated (FM) time delay photoacoustic and photothermal wave spectroscopies. Technique, instrumentation, and detection. Part II: Mirage effect spectrometer design and performance

    Page(s): 622 - 629
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    FM time delay laser excitation has been implemented in a photothermal deflection spectrometric apparatus with fast rise‐time optics. The performance of the system was studied in both frequency and time delay domains. The spectrometer was further used in the study of thin quartz layers on an opaque substrate. In this work we have demonstrated the operation of the first frequency modulated (FM) time delay photothermal deflection (mirage effect) spectrometer with a ns rise time spectrally flat beam position detector unit. It was established by use of a blackbody reference that the spectrometer is responsive to impulsive heat sources in the sample with no measureable instrumental distortion of the frequency or time delay domain responses. The sensitivity of the device was tested successfully in the measurement of thermal parameters of thin quartz layers on absorbing backings. It was further shown that our spectrometer is sensitive to thin SiO2 layers on Si wafers. The data were largely consistent with Green’s function models of heat conduction in the liquid interface and bulk. The ability of the spectrometer to perform high‐quality frequency response measurements via fast Fourier transformations of the input data in very short time compared to the conventional lock‐in detection is an extremely useful feature for thermal‐wave applications. View full abstract»

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  • Frequency modulated (FM) time delay photoacoustic and photothermal wave spectroscopies. Technique, instrumentation, and detection. Part III: Mirage effect spectrometer, dynamic range, and comparison to pseudo‐random‐binary‐sequence (PRBS) method

    Page(s): 630 - 635
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    A detailed comparison is presented between the time delay and the pseudo‐random‐binary‐sequence (PRBS) methods of excitation and mirage effect response. Both time delay domain dynamic system response and frequency domain spectral functions were calculated via FFT methods. The results show that the FM time delay spectrometer exhibits superior performance to the PRBS device and is optimally suitable for nondestructive and depth‐profiling studies. The detailed examination of, and comparison between, the time delay and spectral dynamic functions of our FM time delay photothermal wave spectrometer and those of a PRBS‐driven device has proven that the former apparatus is capable of producing superior quality time delay and spectral function information when tested on a fast, flat frequency response mirage effect system. The FM time delay photoacoustic/photothermal wave technique and instrumentation of this work holds excellent promise for nondestructive evaluation and depth‐profiling applications in scientific research as well as industrial development laboratories. View full abstract»

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  • Acoustic microscopy applied to physical acoustics

    Page(s): 636 - 638
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    An acoustic microscope setup has been applied to determine Rayleigh wave velocities in crystals from acoustic materials signatures. The Rayleigh wave velocity close to and above the phase transition in SrTiO3 has been measured as a function of temperature. It has been shown that propane can be used as a coupling liquid between the acoustic lens and the sample enabling acoustic microscopy in the temperature region 85–220 K. View full abstract»

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  • High‐frequency response heat‐flux gauge

    Page(s): 639 - 649
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    A double‐sided, high‐frequency response heat‐flux gauge has been developed which allows measurement of heat flux from dc to 100 kHz. The instrument is designed for heat‐flux magnitudes ranging from one to several hundred kW/m2 at temperatures up to 400 °C and is independent of the test article material. The gauges consist of a metal film (1500 Å) resistance thermometers sputtered on both sides of a thin (25 μm) polyimide sheet. The sheet, which can contain many gauges, is then adhesively bonded to a test article. The temperature difference across the polyimide is a direct measure of the heat flux at low frequencies, while a quasi‐1D analysis is used to infer the high‐frequency heat flux from the upper surface temperature history. The design criteria, construction and application techniques, and a novel, ratiometric calibration procedure are discussed in detail. View full abstract»

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  • Improvements in a new technique for measuring and mapping heat transfer coefficients

    Page(s): 650 - 654
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    Two important improvements in a new technique for measuring and mapping local heat transfer coefficients are described. The first improvement involves the use of a new encapsulated thermochromic liquid crystal which has better stability and a narrower bandwidth than the cholesteric crystals previously used. The second important improvement is in the packaging arrangement. In this new arrangement, useful for gas flows, the liquid crystal is applied directly on the surface of an electrically conducting gold coating used as an electric heater, and is essentially in direct contact with the fluid. The encapsulated liquid crystal used in this study was applied directly to the gold surface without affecting the electrical characteristics of the gold coating. This new packaging arrangement has two advantages. First, no correction for the temperature drop across the plastic substrate is required. Second, a significant increase in the maximum detectable frequency is predicted. View full abstract»

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  • Low‐temperature heat switch using unforced convection

    Page(s): 655 - 657
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    A new type of low‐temperature heat switch is described. The switch uses unforced convection of helium gas within a closed loop. We report measurements of the performance of a simple version of the heat switch. View full abstract»

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  • Thermal magnetic noise generated by an eddy current shielded room

    Page(s): 658 - 660
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    Using a SQUID‐based second‐order gradiometer, we have measured the thermal magnetic noise generated by a thick aluminum plate and an eddy current shielded room used for biomagnetic measurements. The measured noise agrees with the theoretical prediction for the thermal noise fields generated by infinite conducting slabs. The noise is substantial near the walls of the shielded room, but is predicted to be less than 0.02 fT/√Hz at 1 Hz at the center of the room. This is too small to influence the biomagnetic measurements usually taken at this location. View full abstract»

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  • Measurement system induced errors in diode thermometry

    Page(s): 661 - 665
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    Diode temperature sensors are capable of being used at the accuracy level of a few hundredths of a kelvin. However, in order to achieve this performance, proper measurement techniques must be used. Poorly shielded or improperly grounded measurement systems can introduce ac noise which will create an apparent shift in the dc voltage reading across a diode sensor. This results in a temperature measurement error which may approach several tenths of a kelvin. The presence of the ac noise in question is not obvious during normal usage and several quick tests are outlined to verify whether or not a noise problem exists. Experimental data and derivations from theoretical p‐n junction characteristics are given which correlate the ac noise level with possible voltage/temperature measurement errors. These results can be used in estimating the accuracy and performance of a temperature measurement system. Several of the more common problems which introduce noise into diode circuitry are described. View full abstract»

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  • An instrument for measuring turbulent pressure fluctuations

    Page(s): 666 - 673
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    An instrument is described for laboratory measurements of the fluctuating static pressure in the turbulent boundary layer above progressive water waves. It consists of a disk‐shaped sensing head properly designed to minimize the dynamic pressure variation to an acceptable level, a commercially available piezocrystal transducer housed inside a casing, and a forward‐bent connecting tube. Pressure fluctuations sampled by the disk are converted into an electrical signal by the piezocrystal transducer. Through low‐pass filtering, only the frequency range of interest is retained. The instrument was tested successfully for frequency response, dynamic and mechanical noise sensitivity, and response to spurious pressure fluctuations (produced when operating in a Eulerian wave‐following mode) inside a cylindrical chamber and in a wind–wave facility, and some sample results along with the calibration procedures and data analysis are presented. View full abstract»

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  • Mapping the quality of semiconductor wafers

    Page(s): 674 - 679
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    A new instrument has been developed to map the photovoltaic response of a semiconductor to very penetrating sub‐band‐gap radiation (for silicon, λ=1.3 μm). The minority carrier density being nearly uniform throughout the thickness of the crystal, the photovoltaic response is dominated by the carrier diffusion length and thus reflects the quality of the material. A computer‐controlled scan of the semiconductor presents a map of the gross quality of the specimen. The actual probe is a small transparent electrode (water) illuminated by an optical fiber carrying 1.3‐μm light from an LED. 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