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Jun 1999

Volume 70, Issue 6, pp. 2567-2883

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Introduction to time and frequency metrology

Judah Levine

Rev. Sci. Instrum. 70, 2567 (1999); http://dx.doi.org/10.1063/1.1149844 (30 pages) | Cited 19 times

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In this article, I will review the definition of time and time interval, and I will describe some of the devices that are used to realize these definitions. I will then introduce the principles of time and frequency metrology, including a discussion of some of the types of measurement hardware in common use and the statistical machinery that is used to analyze these data. I will also introduce various techniques of distributing time and frequency information, with special emphasis on the global positioning system satellites. I will then discuss the advantages of clock ensembles and a prototype time-scale algorithm. I will conclude with a discussion of how clocks are synchronized to remote servers using noisy and poorly characterized transmission channels.
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06.30.Ft Time and frequency
06.20.F- Units and standards
05.45.Xt Synchronization; coupled oscillators
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
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back to top OPTICS; ATOMS and MOLECULES; SPECTROSCOPY

Transmission grating spectroscopy in the 10 keV range

E. Fill, K.-H. Stephan, P. Predehl, G. Pretzler, K. Eidmann, and A. Saemann

Rev. Sci. Instrum. 70, 2597 (1999); http://dx.doi.org/10.1063/1.1149815 (4 pages) | Cited 4 times

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We demonstrate the feasibility of transmission grating spectroscopy in the 10 keV range. The diffraction efficiency of a 5000 l/mm free-standing gold transmission grating was measured at the three photon energies of 1.49, 5.4, and 8.04 keV (Kα of Al, Cr, and Cu). At 1.49 keV, the measured efficiencies agree well with efficiencies calculated by standard grating theory. At 5.4 and 8.04 keV, the measured efficiencies significantly exceed the theoretical ones. For Cu Kα, the absolute efficiency into first order is still as high as 3.3%. We present spectra of fs laser plasmas generated by irradiating Al, Cr, and Cu targets. © 1999 American Institute of Physics.
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07.85.Nc X-ray and γ-ray spectrometers
29.30.Kv X- and γ-ray spectroscopy
52.70.La X-ray and γ-ray measurements
42.79.Dj Gratings

Construction of the multilayered-mirror monochromator beam line for the study of synchrotron radiation stimulated process

Harutaka Mekaru, Yoshiyuki Tsusaka, Takayuki Miyamae, Toyohiko Kinoshita, Tsuneo Urisu, Shin Masui, Eijiro Toyota, and Hisataka Takenaka

Rev. Sci. Instrum. 70, 2601 (1999); http://dx.doi.org/10.1063/1.1149816 (5 pages)

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A multilayered-mirror (MLM) monochromator beam line designed specially for synchrotron radiation (SR) stimulated process experiments has been constructed for the first time. The beam line was designed by the criteria; a beam spot size on the sample surface ≥ 3×3 mm2, a density of total irradiated photons ≥ 1018 photons/cm2 (for an irradiation time of a few tens of minutes to a few hours), and low-energy background ⩽1% of the output. The performance of the beam line was evaluated by measuring the transmitted photon flux of an Al filter around the Al L2,3 absorption edge and by measuring the photoemission spectra of Ta using the output beam as an excitation light source. The Al thin film deposition was successfully demonstrated by using the monochromatized output beam. We conclude that this MLM monochromator performs sufficiently well to study the excitation energy dependence in SR-stimulated processes. © 1999 American Institute of Physics.
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07.85.Qe Synchrotron radiation instrumentation
41.85.Si Particle beam collimators, monochromators
41.60.Ap Synchrotron radiation

Rotatable source crossed molecular beams apparatus with pulsed ultraviolet/vacuum ultraviolet photoionization detection

P. A. Willis, H. U. Stauffer, R. Z. Hinrichs, and H. F. Davis

Rev. Sci. Instrum. 70, 2606 (1999); http://dx.doi.org/10.1063/1.1149817 (9 pages) | Cited 24 times

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A newly constructed universal crossed molecular beams apparatus for studies of bimolecular chemical reaction dynamics is described. The apparatus employs two rotatable molecular beam sources and a fixed ultrahigh vacuum (UHV) quadrupole mass spectrometer with electron impact or pulsed photoionization of reaction products. Electronically cold neutral supersonic transition metal atomic beams are produced in one of the rotatable sources using laser vaporization. The beams are characterized by laser induced fluorescence spectroscopy, photodepletion spectroscopy, and time-of-flight analysis. Photoionization of the ZrC2H2 products from the crossed beam reaction Zr+C2H4→ZrC2H2+H2 is carried out using the pulsed 157 nm radiation from a F2 excimer laser in the UHV region of the mass spectrometer. Compared to conventional electron impact ionization, 157 nm photoionization improves signal-to-noise ratios by more than two orders of magnitude for experiments using pulsed beam sources where cross correlation methods cannot be used. We also demonstrate the use of 1+1 resonance enhanced multiphoton ionization for state selective detection of nonreactively scattered transition metal atoms from decay of long-lived collision complexes. Due to the small reaction cross sections for Y+C2H6→YC2H4+H2 and Y+CD3CDO→DYCD3+CO, these reactions could not be studied using electron impact ionization. However, photoionization detection permitted direct studies of the reactions with excellent signal-to-noise ratios. The greatly improved sensitivity of the photoionization technique facilitates studies of transition metal systems not previously amenable to the crossed beams method. © 1999 American Institute of Physics.
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37.20.+j Atomic and molecular beam sources and techniques
34.50.Lf Chemical reactions
07.75.+h Mass spectrometers
07.77.Gx Atomic and molecular beam sources and detectors
33.80.Eh Autoionization, photoionization, and photodetachment
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

High resolution pulsed field ionization photoelectron spectroscopy using multibunch synchrotron radiation: Time-of-flight selection scheme

G. K. Jarvis, Y. Song, and C. Y. Ng

Rev. Sci. Instrum. 70, 2615 (1999); http://dx.doi.org/10.1063/1.1149818 (7 pages) | Cited 42 times

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We have developed an efficient electron time-of-flight (TOF) selection scheme for high resolution pulsed field ionization (PFI) photoelectron (PFI-PE) measurements using monochromatized multibunch undulator synchrotron radiation at the Advanced Light Source. By employing a simple electron TOF spectrometer, we show that PFI-PEs produced by the PFI in the dark gap of a synchrotron ring period can be cleanly separated from prompt background photoelectrons. A near complete suppression of prompt electrons was achieved in PFI-PE measurements by gating the PFI-PE TOF peak, as indicated by monitoring background electron counts at the Ar(11s′) autoionizing Rydberg peak, which is adjacent to the Ar+(2P3/2) PFI-PE band. The rotational-resolved PFI-PE band for H2+ (X 2Σg+,v+ = 0) measured using this electron TOF selection scheme is nearly free from residues of nearby autoionizing features, which were observed in the previous measurement by employing an electron spectrometer equipped with a hemispherical energy analyzer. This comparison indicates that the TOF PFI-PE scheme is significantly more effective in suppressing the hot-electron background. In addition to attaining a high PFI-PE transmission, a major advantage of the electron TOF scheme is that it allows the use of a smaller pulsed electric field and thus results in a higher instrumental PFI-PE resolution. We have demonstrated instrumental resolutions of 1.0 cm−1 full width at half maximum (FWHM) and 1.9 cm−1 FWHM in the PFI-PE bands for Xe+(2P3/2) and Ar+(2P3/2) at 12.123 and 15.760 eV, respectively. These resolutions are more than a factor 2 better than those achieved in previous synchrotron based PFI-PE studies. © 1999 American Institute of Physics.
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07.81.+a Electron and ion spectrometers
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
29.30.Aj Charged-particle spectrometers: electric and magnetic
29.30.Ep Charged-particle spectroscopy
32.80.Fb Photoionization of atoms and ions

Setting up and time-resolution measurement of a radio-frequency-based streak camera

A. V. Aleksandrov, N. S. Dikansky, V. Guidi, G. V. Lamanna, P. V. Logatchov, S. V. Shiyankov, and L. Tecchio

Rev. Sci. Instrum. 70, 2622 (1999); http://dx.doi.org/10.1063/1.1149819 (5 pages)

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We have experimented with a radio-frequency-based streak camera. The basic idea behind the method consists of magnetic deflection of the electron beam imparted by a radio-frequency cavity. All the components of the camera were tested and the time resolution was measured to lie within the sub-ps domain. Further advantages of the method are simplification of triggering, weaker dependence on space-charge effect within the electron beam, high modularity, and ease of implementation. © 1999 American Institute of Physics.
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85.60.Ha Photomultipliers; phototubes and photocathodes
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Ls Scanners, image intensifiers, and image converters
07.68.+m Photography, photographic instruments; xerography
42.79.Pw Imaging detectors and sensors
06.60.Jn High-speed techniques (microsecond to femtosecond)

Three-dimensional optical trapping and evanescent wave light scattering for direct measurement of long range forces between a colloidal particle and a surface

A. R. Clapp, A. G. Ruta, and R. B. Dickinson

Rev. Sci. Instrum. 70, 2627 (1999); http://dx.doi.org/10.1063/1.1149820 (10 pages) | Cited 12 times

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A novel technique is described to measure weaker long range forces between a single colloidal particle and a flat surface as a function of separation distance. The technique uses a three-dimensional optical trap as a force transducer and evanescent wave light scattering to measure the particle-surface separation distance. The three-dimensional optical trap allows direct manipulation of the particle near the surface, and the measured displacement of the particle from the center of the optical trap determines the force of interaction between the particle and the surface. The particle position is determined by measuring the scattered light from the particle in an evanescent wave created by total internal reflection of a laser beam on the surface. This combination of optical techniques allows forces to be directly measured for smaller particles (∼0.25–5.0 μm) and over a range of forces ( ∼ 10−14–10−11 N) than has been previously reported for similar force measurement techniques such as atomic force microscopy and total internal reflection microscopy. The experimental results have been compared with DLVO theory predictions for 1.5 μm silica microspheres interacting with glass in NaCl solutions of known ionic strength. © 1999 American Institute of Physics.
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42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
82.70.Dd Colloids
07.10.Pz Instruments for strain, force, and torque
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.25.Fx Diffraction and scattering
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
back to top CHARGED PARTICLE SOURCES, OPTICS and ACCELERATION

Experimental studies on a compact electron cyclotron resonance plasma x-ray source

R. Baskaran and T. S. Selvakumaran

Rev. Sci. Instrum. 70, 2637 (1999); http://dx.doi.org/10.1063/1.1149821 (9 pages) | Cited 11 times

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A compact electron cyclotron resonance plasma x-ray source, which has a potential use for medical imaging is presented in this article. In this article, the experimental system and the characterization studies on plasma and x ray are presented. Using a Langmuir probe, the plasma parameters are measured for different magnetic field profiles and gas pressures. The x-ray spectrum is obtained for various gas pressures and magnetic field profiles. In the x-ray spectrum, the Bremstrahlung radiation, peaking at 20–60 keV is observed and the final energy of the x ray is extended up to ∼200 keV. Thermo luminescence dosimeter (CaSO4 sample) is used for estimating the dose at the port and these results are presented for typical x-ray spectra. Using a teletector, the dose at the port for various coil current is measured and these are compared with the estimated dose obtained from the x-ray spectrum. © 1999 American Institute of Physics.
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52.50.Dg Plasma sources
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.70.La X-ray and γ-ray measurements
52.50.Gj Plasma heating by particle beams
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium

First investigations of a warm electron beam ion trap for the production of highly charged ions

V. P. Ovsyannikov and G. Zschornack

Rev. Sci. Instrum. 70, 2646 (1999); http://dx.doi.org/10.1063/1.1149822 (6 pages) | Cited 25 times

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A compact warm electron beam ion trap (WEBIT) is described and investigated experimentally. The trap design is based on permanent magnets, an electron gun with a cathode emissivity of 25 A/cm2 and a gun perveance of 0.1 μA/V3/2 as well as a vacuum vessel allowing trap operation at pressures of 10−10 Torr. The electron beam diameter measured with a pinhole camera was 160 μm corresponding to an electron beam density of 248 A cm−2. X-ray spectra measured with a Si(Li) semiconductor detector indicate the production of Xe44+ and Ir59+. © 1999 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
29.25.Ni Ion sources: positive and negative
37.20.+j Atomic and molecular beam sources and techniques
41.75.Ak Positive-ion beams
41.85.-p Beam optics

Improvement of beam emittance of the CEA high intensity proton source SILHI

R. Gobin, P.-Y. Beauvais, R. Ferdinand, P.-A. Leroy, L. Celona, G. Ciavola, and S. Gammino

Rev. Sci. Instrum. 70, 2652 (1999); http://dx.doi.org/10.1063/1.1149823 (3 pages) | Cited 9 times

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The emittance of the intense proton beam extracted by the source SILHI at Commisariat à l’Energie Atomique (CEA)-Saclay is a key parameter for the design of the IPHI Project RFQ. This parameter has a relevant role even for the design of an intense proton source for the TRASCO project of Istituto Nazionale di Fisica Nucleare (INFN). The tests performed in the framework of CEA-INFN collaboration have been mainly devoted to a 75 mA beam emittance investigation injecting different gases in the beam line. The results show that the rms normalized emittance decreases up to a factor 3 while the beam losses induced by recombination are contained within 5%. Normalized emittance in r-r′ plane of about 0.1 π min mrad have been obtained using Ar and Kr. © 1999 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
29.27.Fh Beam characteristics

New method of designing pole profile in combined function magnets of high field quality

P. R. Sarma, S. K. Pattanayak, and R. K. Bhandari

Rev. Sci. Instrum. 70, 2655 (1999); http://dx.doi.org/10.1063/1.1149824 (6 pages) | Cited 2 times

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Combined function magnets are often used in synchrotrons and beam lines. The field quality of such magnets depends mainly on the pole profile. A new method is described for determining the finite pole shapes of such magnets for obtaining field qualities of 1×10−4 or better. Profiles of the typical quadrupole-sextupole and dipole-quadrupole magnets are presented. © 1999 American Institute of Physics.
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41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
29.27.Eg Beam handling; beam transport
07.55.Db Generation of magnetic fields; magnets
84.71.Ba Superconducting magnets; magnetic levitation devices
29.20.db Storage rings and colliders
29.20.dk Synchrotrons
02.30.Sa Functional analysis
back to top NUCLEAR PHYSICS, FUSION and PLASMAS

Characteristics of 63.6° cylindrical energy analyzer used as charge exchange neutral particle analyzer

T. Goto, K. Ishii, A. Nagao, Y. Goi, Y. Katsuki, N. Kikuno, N. Ishibashi, Y. Ono, M. Yamanashi, Y. Nakashima, T. Tamano, and K. Yatsu

Rev. Sci. Instrum. 70, 2661 (1999); http://dx.doi.org/10.1063/1.1149825 (4 pages) | Cited 1 time

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A charge exchange neutral particle analyzer including a newly designed multichannel 63.6° cylindrical electrostatic energy analyzer was constructed. Since the energy analyzer can simultaneously adopt a small radius of cylindrical electrodes and a large width of an entrance slit, high incident current can be analyzed while the size of the analyzer remain compact. Characteristics of the analyzer were investigated using hydrogen beam with energies from about 0.5 to 5 keV. The experimental results are compared well with the numerical analysis. © 1999 American Institute of Physics.
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52.70.Nc Particle measurements
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
07.77.-n Atomic, molecular, and charged-particle sources and detectors
41.85.Qg Particle beam analyzers, beam monitors, and Faraday cups

Liquid stub tuner for ion cyclotron heating

R. Kumazawa, T. Mutoh, T. Seki, F. Sinpo, G. Nomura, T. Ido, T. Watari, Jean-Marie Noterdaeme, and Yangping Zhao

Rev. Sci. Instrum. 70, 2665 (1999); http://dx.doi.org/10.1063/1.1149826 (9 pages) | Cited 22 times

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Ion cyclotron range of frequency (ICRF) heating on the large helical device (LHD) is characterized by high power (up to 12 MW) and steady state operation (30 min). The LHD is a helical device (with a major radius of 3.9 m and a minor radius of 0.6 m) with superconducting coil windings (l = 2, m = 10). The main purpose of physical research is to investigate currentless and disruption-free plasma. Research and development for steady state ICRF heating has been carried out in recent years: A high rf power transmission system consisting of stub tuners, a ceramic feedthrough, and an ion cyclotron heating loop antenna has been developed. In addition, steady state operation of a rf oscillator has been achieved at a power higher than 1 MW. A liquid stub tuner has been proposed as an innovation. The liquid stub tuner makes use of the difference between the rf wavelengths in liquid and in gas due to the different relative dielectric constants. The liquid stub tuner has been experimentally proved to be a reliable rf component for high power transmission systems. Test results have quantitatively demonstrated that it can be used at high rf voltage: 61 kV for 10 s and 50 kV for 30 min. Furthermore, the liquid surface can be shifted under high rf voltage without breakdown, which suggests that it can be employed as a feedback control impedance matching tool to keep reflected rf power at a low level with regard to a temporal variation of plasma loading resistance. © 1999 American Institute of Physics.
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52.50.Gj Plasma heating by particle beams
52.55.Jd Magnetic mirrors, gas dynamic traps
28.52.Av Theory, design, and computerized simulation

Spatially resolved spectra of resonantly pumped laser produced plasmas of lithium

Tom McCormack and Gerry O’Sullivan

Rev. Sci. Instrum. 70, 2674 (1999); http://dx.doi.org/10.1063/1.1149827 (7 pages) | Cited 8 times

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Spatially resolved visible spectra emitted from a plasma formed by focusing the output of a flashlamp pumped dye laser onto solid targets of lithium have been recorded. The effects of laser wavelength on plasma formation have been analyzed by tuning the laser to the first resonance transition in lithium at 6708 Å and comparing the results with those obtained at an off resonance wavelength of 6728 Å. Laser energies varied from 430 to 645 mJ and were focused to a spot diameter of 300 μm with a pulse length of 850 ns. Light from the plasma was focused onto the slit of a Hilger spectrograph, which incorporated a Pellin–Broca prism whose output was focused onto a charge-coupled device camera. Electron densities of 1016–1018 cm−3 were deduced from Stark width and shift measurements of the Li II 2s–2p line at 5485 Å and from the Li I 2p–4d line at 4603 Å. In this way the electron density could be mapped as a function of distance from the target. By observing emission at 5485 Å the electron density was observed to increase when the laser was tuned on resonance compared to off. This was not the case when the neutral Li I 2p–4d line was used as a diagnostic. The anomaly is accounted for by referring to both the ionization rates involved and the temporal profile of the emission. © 1999 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
31.50.Df Potential energy surfaces for excited electronic states
32.30.Jc Visible and ultraviolet spectra
32.60.+i Zeeman and Stark effects

A 400 kHz, fast-sweep Langmuir probe for measuring plasma fluctuations

G. Chiodini, C. Riccardi, and M. Fontanesi

Rev. Sci. Instrum. 70, 2681 (1999); http://dx.doi.org/10.1063/1.1149828 (8 pages) | Cited 16 times

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A novel, fast-sweep Langmuir probe has been constructed and successfully operated on “Thorello.” It is based on a novel, dual channel circuit that compensates for stray capacitance and permits sweep speeds up to 400 kHz. The circuit response has been tested by measuring the known current–voltage characteristics of resistors and diodes. In addition, the probe has been used to measure the electron temperature and density as well as the plasma potential of plasmas generated in Thorello. A method of three-parameter curve fitting is used to analyze the time-dependent data. The measurements compare favorably with those derived from other standard probe techniques. © 1999 American Institute of Physics.
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52.70.Ds Electric and magnetic measurements
52.25.Gj Fluctuation and chaos phenomena
52.35.Ra Plasma turbulence

Compact floating ion energy analyzer for measuring energy distributions of ions bombarding radio-frequency biased electrode surfaces

Erik A. Edelberg, Andrew Perry, Neil Benjamin, and Eray S. Aydil

Rev. Sci. Instrum. 70, 2689 (1999); http://dx.doi.org/10.1063/1.1149829 (10 pages) | Cited 22 times

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A compact floating retarding-field ion energy analyzer and the accompanying electronics have been designed and built to measure the energy distribution of ions bombarding radio-frequency (rf) biased electrodes in high-density plasma reactors. The design consists of two main components, a compact retarding field vacuum probe and an integrated stack of floating electronics for providing output voltages, measuring currents and voltages and transmitting data to a computer. The operation and capabilities of the energy analyzer are demonstrated through ion energy distribution measurements conducted on a 4 MHz rf-biased electrostatic chuck in a 13.56 MHz high-density transformer coupled plasma (TCP) reactor. The analyzer is capable of operating while floating on several hundreds of volts of rf bias and at pressures up to 30 mTorr without differential pumping. The effects of pressure (2–30 mTorr), TCP power (500–1500 W), rf-bias power (0–800 W), gas composition, and ion mass on the ion energy distributions are demonstrated through Ar, Ne, and Ar/Ne discharges. © 1999 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
29.25.-t Particle sources and targets
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
52.80.-s Electric discharges
back to top BASIC PHENOMENA

Constant current: A method for obtaining hysteresis loops in ferroelectric materials

José A. Giacometti, Célio Wisniewski, Walterley A. Moura, and Paulo António Ribeiro

Rev. Sci. Instrum. 70, 2699 (1999); http://dx.doi.org/10.1063/1.1149830 (4 pages) | Cited 7 times

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A new method is proposed to obtain hysteresis loops in ferroelectric materials in which the sample is submitted to a constant electric current. This technique was applied on poly(vinylidene fluoride), PVDF, biaxially stretched samples and the hysteresis loops of the electric displacement and electric polarization versus the electric field compared well with those obtained with the Sawyer–Tower method. The constant current method is advantageous in that no measuring amplifiers are needed and it is insensitive to prebreakdown noise. © 1999 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.84.Jd Polymers; organic compounds
07.68.+m Photography, photographic instruments; xerography

High accuracy magnetic field measurements with a Hall probe

C. Schott, R. S. Popovic, S. Alberti, and M. Q. Tran

Rev. Sci. Instrum. 70, 2703 (1999); http://dx.doi.org/10.1063/1.1149831 (5 pages) | Cited 9 times

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A silicon-based temperature stabilized axial Hall probe with an absolute accuracy of ±40 ppm in the full range between 0 and 6 T is presented. The absolute calibration of the probe is performed against a nuclear magnetic resonance (NMR) probe. The application of the probe to a magnetic field profile of a 5 T superconducting magnet system, with field gradients as high as 30 T/m, reaching an overall accuracy of better than ±100 ppm, is demonstrated. In addition to the high absolute accuracy, this Hall probe allows high spatial resolution measurements of inhomogeneous fields in configurations where present NMR probes are not usable. © 1999 American Institute of Physics.
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07.55.Ge Magnetometers for magnetic field measurements
07.07.Mp Transducers
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
84.71.Ba Superconducting magnets; magnetic levitation devices
06.20.F- Units and standards

Simulation and calibration of an open inductive sensor for pulsed field magnetization measurements

L. Weckhuysen, J. Vanacken, L. Trappeniers, M. J. Van Bael, W. Boon, K. Rosseel, F. Herlach, V. V. Moshchalkov, and Y. Bruynseraede

Rev. Sci. Instrum. 70, 2708 (1999); http://dx.doi.org/10.1063/1.1149832 (3 pages) | Cited 3 times

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The relation between the voltage induced in an open sensor and the magnetic moment of a sample during pulsed field magnetization measurements has been calculated. The calculation takes into account the size of a sample, its internal flux distribution, and its position with respect to the center of the sensor. It has been found that the behavior of the response signal with respect to the sample position is the same for homogeneously magnetized Ni samples and high temperature superconductors. Because of this universality, it is possible to calibrate the open sensor even in the case of an unfavorable sample geometry. The calculations have been experimentally verified by using Ni samples with different geometries. Our results can easily be extended to samples with an arbitrary local field distribution. © 1999 American Institute of Physics.
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07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
06.20.F- Units and standards

Superconducting quantum interference device based resistance bridge for shot noise measurement on low impedance samples

X. Jehl, P. Payet-Burin, C. Baraduc, R. Calemczuk, and M. Sanquer

Rev. Sci. Instrum. 70, 2711 (1999); http://dx.doi.org/10.1063/1.1149833 (4 pages) | Cited 5 times

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We present a resistance bridge which uses a superconducting quantum interference device (SQUID) to measure the shot noise in low impedance samples (<1 Ω). The experimental requirements are high direct current (dc) bias currents (≲10 mA), in order to obtain sufficiently high bias voltages, together with high alternating current (ac) sensitivity ( ≈ pA/math) to detect small changes of the noise away from the thermal noise ground level. These conditions are fulfilled by changing continuously the overall gain of the SQUID electronics and separating the dc and ac feedbacks. This system is used to investigate the shot noise in mesoscopic samples made with superconducting (S) and normal (N) metals (R4.2 K ≈ 0.25 Ω). This value of source resistance is out of the range of classical noise measurement schemes. Because of its low intrinsic noise (≲5 pA/math), our system is dominated by the thermal noise of the resistors composing the bridge ( ∼ 24 pA/math at 4.2 K); therefore, this method greatly simplifies the analysis of shot noise results. © 1999 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
73.50.Td Noise processes and phenomena
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
73.23.-b Electronic transport in mesoscopic systems

InAs/Al0.2Ga0.8Sb quantum well Hall sensors with improved temperature stability

J. Bekaert, V. V. Moshchalkov, Y. Bruynseraede, M. Behet, J. De Boeck, and G. Borghs

Rev. Sci. Instrum. 70, 2715 (1999); http://dx.doi.org/10.1063/1.1149834 (4 pages) | Cited 1 time

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Cross-shaped Hall sensors with high sensitivity and excellent temperature stability were fabricated from quantum wells based on an InAs/Al0.2Ga0.8Sb heterostructure. The layers were grown on semi-insulating GaAs substrates by molecular beam epitaxy. Maximum Hall mobilities of 215 000 cm2/V s with sheet carrier concentrations of 9×1011 cm−2 were measured at 4.2 K for an undoped quantum well structure. These transport properties result in sensitivities as high as 3 T−1 (for voltage drive) and 650 Ω/T (for current drive). Additional Si δ doping in the middle of the InAs quantum well leads to a highly improved temperature stability of the sensitivities. © 1999 American Institute of Physics.
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07.55.Ge Magnetometers for magnetic field measurements
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Measuring temperatures in the presence of external radiation by flash assisted multiwavelength pyrometry

H. R. Tschudi and M. Schubnell

Rev. Sci. Instrum. 70, 2719 (1999); http://dx.doi.org/10.1063/1.1149835 (9 pages) | Cited 13 times

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A novel multiwavelength analysis of the radiation emitted by a hot Lambertian surface is presented allowing a reliable measurement of its surface temperature even in the presence of interfering external light sources. For the separation of thermally emitted and reflected external radiation, an accurate knowledge of the spectral emittance/reflectance of the sample is required. In our procedure, this quantity is determined in situ by performing a second measurement with additional light, e.g., from a strong electric flash. The strength of the flash and the relative spectrum of the interfering external radiation are probed with a cooled Lambertian reflectance reference near the sample. In a first step, the spectral reflectance of the sample is determined from spectra recorded with and without flash. The temperature and the total incoming irradiance are then obtained from a least-square fit of the input spectra with an analytical model of the emitted thermal plus the superimposed reflected external radiation. The method delivers also estimates for the statistical accuracy of the measured temperature and irradiance values. It causes no problem to measure temperatures through a window of sufficient optical quality and effects of absorbing gases or vapors may be minimized by an appropriate choice of the spectral intervals used for the analysis. In order to indicate statistical and systematic errors of the method under different operating conditions, extensive numerical simulations were performed. They reveal that a good statistical accuracy of the recorded spectra is crucial for a proper separation of the emitted from the reflected external radiation if one part dominates. In contrast, this separation is not affected by an erroneous calibration of the optical detection system. Finally, the question is discussed if one can dispense with the flash. Without external radiation, the “no-flash” method is equivalent to quotient pyrometry and subject to the same principal limitations. With external radiation, reasonably accurate temperatures can be expected only if thermal radiation clearly dominates or if emittance values are available from other sources. © 1999 American Institute of Physics.
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07.20.Ka High-temperature instrumentation; pyrometers

Specific heat (Cp) of Apiezon N grease (1 to 108 K) and calorimetry: Cp of copper below 30 K

C. A. Swenson

Rev. Sci. Instrum. 70, 2728 (1999); http://dx.doi.org/10.1063/1.1149836 (4 pages) | Cited 12 times

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Heat capacity (Cp) data for Apiezon N grease from 1 to 108 K are compared with previous results for this grease and for Apiezon T, with good agreement. Addenda results for a calorimeter in which Apiezon N grease is used for thermal contact between the tray and a sample suggest that a thin film of this grease has an appreciably larger Cp, below 4 K, than bulk grease. For high accuracy experiments using Apiezon N grease, care should be taken in the calculation of addenda Cp’s from bare tray data and the Cp for bulk grease. During these measurements, Cp data for a high purity electron beam melted copper sample were found to be in excellent agreement from 1 to 30 K (±0.2%) with previous measurements [Holste, Cetas, and Swenson, Rev. Sci. Instrum. 43, 670 (1972)] on a different sample using a quite different calorimeter. © 1999 American Institute of Physics.
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07.20.Fw Calorimeters
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

A simple, high sensitivity torquemeter

P. J. Flanders and G. Wu

Rev. Sci. Instrum. 70, 2732 (1999); http://dx.doi.org/10.1063/1.1149837 (3 pages) | Cited 4 times

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A simple torquemeter has been developed with a sensitivity exceeding 10−13 Nm when using a 13-μm-diam glass fiber and a low-mass suspension. The maximum twist angle of the fiber is constrained by the choice of its diameter to ∼1°. This angle is measured using a light, mirror, and split silicon photodetector, and is proportional to the torque on a sample in a rotating dc magnetic field. © 1999 American Institute of Physics.
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07.10.Pz Instruments for strain, force, and torque
42.81.Pa Sensors, gyros
07.60.Vg Fiber-optic instruments

Active low frequency vertical vibration isolation

Joel M. Hensley, Achim Peters, and Steven Chu

Rev. Sci. Instrum. 70, 2735 (1999); http://dx.doi.org/10.1063/1.1149838 (7 pages) | Cited 20 times

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We have constructed a system that isolates a key element of our experimental setup from vertical motions of the ground and the surrounding apparatus. This system combines the passive isolation of mechanical springs and an optical table floating on compressed air with an active system that measures the acceleration of the mass to be isolated and feeds back to a solenoid actuator to cancel this motion. Passive isolation alone reduces the acceleration error signal by a factor of 30–1000 from 10 to 100 Hz and by as much as a factor of 1000 above 100 Hz. With the feedback path closed, the system acts like a spring-mass system with a natural resonance frequency of 0.033 Hz. The acceleration error signal is reduced by an additional factor of up to 300 from 0.1 to 20 Hz. This system has enabled us to make precision atom interferometric measurements that would have been impossible without vibration isolation. © 1999 American Institute of Physics.
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07.10.Fq Vibration isolation
03.75.Dg Atom and neutron interferometry
06.30.Gv Velocity, acceleration, and rotation
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