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May 2007

Volume 78, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 78, 051301 (2007); http://dx.doi.org/10.1063/1.2735447 (12 pages)

K. H. Michaelian
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Perspective: Photoacoustic spectroscopy: “Linearization and signal recovery in photoacoustic infrared spectroscopy” [ Rev. Sci. Instrum. 78, 051301 (2007) ]

John F. McClelland

Rev. Sci. Instrum. 78, 050901 (2007); http://dx.doi.org/10.1063/1.2736265 (2 pages)

Online Publication Date: 15 May 2007

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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
43.58.Kr
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Invited Article: Linearization and signal recovery in photoacoustic infrared spectroscopy

K. H. Michaelian

Rev. Sci. Instrum. 78, 051301 (2007); http://dx.doi.org/10.1063/1.2735447 (12 pages) | Cited 2 times

Online Publication Date: 15 May 2007

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Photoacoustic (PA) infrared spectroscopy enables the characterization of a wide variety of materials, affording the spectroscopist several advantages over more traditional infrared methods. While PA spectra are readily acquired using commercial instrumentation, the quality of the data can be improved substantially through the use of specialized numerical and experimental procedures. Two of these methods are the subject of this review. Specifically, this article describes (a) linearization of PA infrared spectra, a calculation that incorporates phase and amplitude information to extend the range of linearity for strongly absorbing samples, and (b) lock-in and digital signal-recovery procedures in step-scan phase-modulation PA infrared spectroscopy. Linearization yields significant improvement in band definition, especially in the low-wavenumber region. This numerical method succeeds in situations where the PA phase of the sample is less than that of the reference (carbon black). When this criterion is not met initially, the sample or reference interferograms can be manipulated prior to the calculation. The steps involved in linearization are illustrated in detail and approximations are discussed. Lock-in demodulation of the step-scan phase-modulation signal is compared to digital (software) demodulation in this study; the lock-in technique is found to be superior in several cases. The imaginary interferograms in these experiments sometimes lack a strong central feature, a situation that necessitates the application of less commonly used methods for phase correction and spectrum calculation. These methods, which are available in commercial software, include two-quadrant and stored-phase corrections. The PA phase spectrum resembles amplitude and absorption spectra when real and imaginary PA spectra are correctly calculated.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
43.58.-e Acoustical measurements and instrumentation
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Design and performance of a curved-crystal x-ray emission spectrometer

A. C. Hudson, W. C. Stolte, D. W. Lindle, and R. Guillemin

Rev. Sci. Instrum. 78, 053101 (2007); http://dx.doi.org/10.1063/1.2735933 (5 pages) | Cited 11 times

Online Publication Date: 8 May 2007

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A curved-crystal x-ray emission spectrometer has been designed and built to measure 2–5 keV x-ray fluorescence resulting from a core-level excitation of gas phase species. The spectrometer can rotate 180°, allowing detection of emitted x rays with variable polarization angles, and is capable of collecting spectra over a wide energy range (20 eV wide with 0.5 eV resolution at the Cl K edge) simultaneously. In addition, the entire experimental chamber can be rotated about the incident-radiation axis by nearly 360° while maintaining vacuum, permitting measurements of angular distributions of emitted x rays.
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07.85.Nc X-ray and γ-ray spectrometers
41.50.+h X-ray beams and x-ray optics
29.30.Kv X- and γ-ray spectroscopy
42.15.Eq Optical system design

Low-noise rotating sample holder for ultrafast transient spectroscopy at cryogenic temperatures

R. Fanciulli, I. Cerjak, and J. L. Herek

Rev. Sci. Instrum. 78, 053102 (2007); http://dx.doi.org/10.1063/1.2735557 (5 pages) | Cited 1 time

Online Publication Date: 9 May 2007

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We present the design and testing of a rotating device that fits within a commercial helium cryostat and is capable of providing at 4 K a fresh sample surface for subsequent shots of a 1–10 kHz amplified pulsed laser. We benchmark this rotator in a transient-absorption experiment on molecular switches. After showing that the device introduces only a small amount of additional noise, we demonstrate how the effect of signal degradation due to high fluence is completely resolved.
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
06.60.Ei Sample preparation (including design of sample holders)
42.15.Eq Optical system design

Fully automated time domain spectrometer for the absorption and scattering characterization of diffusive media

Antonio Pifferi, Alessandro Torricelli, Paola Taroni, Daniela Comelli, Andrea Bassi, and Rinaldo Cubeddu

Rev. Sci. Instrum. 78, 053103 (2007); http://dx.doi.org/10.1063/1.2735567 (10 pages) | Cited 19 times

Online Publication Date: 15 May 2007

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We describe a system for absorption and scattering spectroscopy of diffusive media based on time-resolved reflectance and transmittance measurements. The system is operated with mode-locked lasers tunable in the 550–1050 nm spectral range and on a detection chain based on time-correlated single-photon counting. All measurement procedures such as laser tuning and optimization, signal conditioning, data acquisition, and analysis are completely automated, permitting spectral measurements over the whole range in a few minutes. The criticalities of the system are discussed together with the strategies to compensate them. The Medphot protocol devised for the characterization of photon migration instruments was applied to assess the system performances in terms of accuracy, linearity, noise, stability, and reproducibility. Finally, an example of application of the instrument to the spectroscopy of powders is presented.
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07.60.Rd Visible and ultraviolet spectrometers
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
42.72.-g Optical sources and standards
42.60.Fc Modulation, tuning, and mode locking

Closed-loop wavelength stabilization of an optical parametric oscillator as a front end of a high-power iodine laser chain

L. Kral

Rev. Sci. Instrum. 78, 053104 (2007); http://dx.doi.org/10.1063/1.2740473 (5 pages) | Cited 1 time

Online Publication Date: 21 May 2007

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We present a complex stabilization and control system for a commercially available optical parametric oscillator. The system is able to stabilize the oscillator’s output wavelength at a narrow spectral line of atomic iodine with subpicometer precision, allowing utilization of this solid-state parametric oscillator as a front end of a high-power photodissociation laser chain formed by iodine gas amplifiers. In such setup, a precise wavelength matching between the front end and the amplifier chain is necessary due to extremely narrow spectral lines of the gaseous iodine ( ∼ 20 pm). The system is based on a personal computer, a heated iodine cell, and a few other low-cost components. It automatically identifies the proper peak within the iodine absorption spectrum, and then keeps the oscillator tuned to this peak with high precision and reliability. The use of the solid-state oscillator as the front end allows us to use the whole iodine laser system as a pump laser for the optical parametric chirped pulse amplification, as it enables precise time synchronization with a signal Ti:sapphire laser.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
42.65.Yj Optical parametric oscillators and amplifiers

Experimental technique using FTIR to estimate IR optical properties at variable temperatures: Application to PMDA-ODA polyimide thin films from 100 to 380 °C

Ramesh Chandrasekharan, Richard I. Masel, and Mark A. Shannon

Rev. Sci. Instrum. 78, 053105 (2007); http://dx.doi.org/10.1063/1.2736337 (8 pages)

Online Publication Date: 21 May 2007

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An experimental technique is presented to measure reflectance at high sample temperature with respect to room temperature in the infrared using Fourier transform infrared fitted with a reflectometer. Sample temperature artifacts are accounted for by sequential measurements taken with the lamp source on and with the lamp source off. The sequential measurements are shown mathematically to correct for the modulation of sample and detector thermal emissions. Further, the technique is applied to a polyimide (PMDA-ODA) film on a layer of gold deposited on a thermally oxidized Si wafer. It is shown that the optical properties (index of refraction and extinction coefficient) remain relatively constant with temperature (from room temperature to 380 °C) in the 4000–6000 cm−1 spectral region. The significant changes that occur with temperature are the change in thickness of the film and also the spectral properties in the 2000–4000 cm−1 region. Also, by using a Lorentz oscillator model, it is shown that this method is able to discern that spectral features corresponding to the OH stretching bands at 3630 and 3470 cm−1 show significant variation with increasing temperature.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Hv Refractometers and reflectometers
78.66.Qn Polymers; organic compounds
78.30.Jw Organic compounds, polymers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

All fiber based multispeckle modality endoscopic system for imaging medical cavities

V. M. Murukeshan and N. Sujatha

Rev. Sci. Instrum. 78, 053106 (2007); http://dx.doi.org/10.1063/1.2737772 (8 pages) | Cited 2 times

Online Publication Date: 31 May 2007

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Disease detection in body cavities, such as the detection of abnormal growths in the colon path, has been illustrated here using an image fiber guided catheter based multispeckle modality endoscopic system. An all fiber-optic approach for the illumination and imaging of the inner cavity walls is adopted here. An endoscope probe to carry the illumination fibers as well as the imaging lens–image fiber unit is designed and custom fabricated in order to operate the probe in its various direction sensitive configurations. This is facilitated by the selection of suitable optical elements such as beam combiner and biprism at the probe proximal end. Experimental investigations were carried out using the endoscope system employing phantom model of colon as the test specimen that has normal and abnormal (representing growth) regions and the obtained results indicated the system effectiveness in identifying the abnormal growths at an early stage.
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87.63.L- Visual imaging
87.19.X- Diseases
42.81.Pa Sensors, gyros
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Characterization of plasma parameters, first beam results, and status of electron cyclotron resonance source

S. K. Jain, Akhilesh Jain, P. R. Hannurkar, and S. Kotaiah

Rev. Sci. Instrum. 78, 053301 (2007); http://dx.doi.org/10.1063/1.2735629 (6 pages) | Cited 2 times

Online Publication Date: 2 May 2007

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Electron cyclotron resonance (ECR) plasma source at 50 keV, 30 mA proton current has been designed, fabricated, and assembled. Its plasma study has been done. Plasma chamber was excited with 350 W of microwave power at 2450 MHz, along with nitrogen and hydrogen gases. Microwave power was fed to the plasma chamber through waveguide. Plasma density and electron temperature were studied under various operating conditions, such as magnetic field, gas pressure, and transversal distance. Langmuir probe was used for plasma characterization using current-voltage variation. The nitrogen plasma density calculated was approximately 4.5×1011 cm−3, and electron temperatures of 3–10 eV (cold) and 45–85 eV (hot) were obtained. The total ion beam current of 2.5 mA was extracted, with two-electrode extraction geometry, at 15 keV beam energy. The optimization of the source is under progress to extract 30 mA proton beam current at 50 keV beam energy, using three-electrode extraction geometry. This source will be used as an injector to continuous wave radio frequency quadrupole, a part of 100 MeV proton linac. The required root-mean-square normalized beam emittance is less than 0.2π mm mrad. This article presents the study of plasma parameters, first beam results, and status of ECR proton source.
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52.50.Dg Plasma sources
52.25.Fi Transport properties
52.70.Ds Electric and magnetic measurements
29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors
29.27.Ac Beam injection and extraction

36-segmented high magnetic field hexapole magnets for electron cyclotron resonance ion source

L. T. Sun, H. W. Zhao, Z. M. Zhang, H. Wang, B. H. Ma, X. Z. Zhang, X. X. Li, Y. C. Feng, J. Y. Li, X. H. Guo, Y. Shang, and H. Y. Zhao

Rev. Sci. Instrum. 78, 053302 (2007); http://dx.doi.org/10.1063/1.2740147 (8 pages)

Online Publication Date: 18 May 2007

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Two high magnetic field hexapoles for electron cyclotron resonance ion source (ECRIS) have successfully fabricated to provide sufficient radial magnetic confinement to the ECR plasma. The highest magnetic field at the inner pole tip of one of the magnets exceeds 1.5 T, with the inner diameter (i.d.) = 74 mm. The other hexapole magnet provides more than 1.35 T magnetic field at the inner pole tip, and the i.d. is 84 mm. In this article, we discuss the necessity to have a good radial magnetic field confinement and the importance of a Halbach hexapole to a high performance ECRIS. The way to design a high magnetic field Halbach structure hexapole and one possible solution to the self-demagnetization problem are both discussed. Based on the above discussions, two high magnetic field hexapoles have been fabricated to be utilized on two high performance ECRISs in Lanzhou. The preliminary results obtained from the two ECR ion sources are given.
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52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.50.Dg Plasma sources
07.55.Db Generation of magnetic fields; magnets
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Characterization of a heat flux sensor using short pulse laser calibration

Stefan Löhle, Jean-Luc Battaglia, Jean-Christophe Batsale, Olivier Enouf, Jimmy Dubard, and Jean-Remy Filtz

Rev. Sci. Instrum. 78, 053501 (2007); http://dx.doi.org/10.1063/1.2736388 (6 pages) | Cited 2 times

Online Publication Date: 4 May 2007

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A method to calibrate classical heat flux sensors is presented. The classical approach to measure the temperature inside a known material by using a thermocouple fails when the measurement time is very short. In this work the surface heat flux is determined by solving the inverse heat conduction problem using a noninteger identified system as a direct model for the estimation process. Using short pulse laser calibration measurements the crucial design aspects of the sensor that play a significant role when assuming one-dimensional, semi-infinite heat transfer have been accounted for. The theoretical approach as well as the calibration results are presented and comparisons to the classical approach and results from finite element modeling are shown. It is concluded that the new method ameliorate the heat flux sensor significantly and extend its application to very short measurement times.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.20.Dt Thermometers
06.20.fb Standards and calibration
44.10.+i Heat conduction
44.05.+e Analytical and numerical techniques
02.70.Dh Finite-element and Galerkin methods

Magnetically driven filament probe

A. Schmid, A. Herrmann, V. Rohde, M. Maraschek, H. W. Müller, and the ASDEX Upgrade Team

Rev. Sci. Instrum. 78, 053502 (2007); http://dx.doi.org/10.1063/1.2735942 (6 pages) | Cited 5 times

Online Publication Date: 10 May 2007

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A radially movable probe has been developed for studies of filamentary transport in ASDEX Upgrade during edge localized modes (ELMs) by means of Langmuir tips and magnetic pickup coils. The probe is permanently installed at the low field side in the ASDEX Upgrade vacuum vessel and is not subject to limitations in probe size, as, for example, probes on a shared manipulator are. The probe is moved by a magnetic drive, which allows for easy installation in the vessel, and has moderate machine requirements, as it will only require an electric feedthrough and an external power supply. The drive gives a linear motion with a radial range of 5 cm within 50 ms, where range and velocity can be largely scaled according to experimental requirements. The probe has been installed in the outer midplane of the ASDEX Upgrade vessel, where ELM filaments are expected to have their maximum amplitude. Filaments are coherent substructures within an ELM, carrying a fraction of the ELM released energy towards the wall. The new probe allows to measure the structure of these filaments, in particular, parameters such as filament rotation (by time delay measurements) and size (by peak width analysis). Activating the drive moves the probe from a safe position behind the limiter to a position in front of the limiters, i.e., exposes the Langmuir pins to the scrape-off layer plasma.
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52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks
52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Characterization of the diffraction properties of quantum-dot-array diffraction grating

Chuanke Wang, Longyu Kuang, Zhebin Wang, Shenye Liu, Yongkun Ding, Leifeng Cao, Eckhart Foerster, Deqiang Wang, Changqing Xie, and Tianchun Ye

Rev. Sci. Instrum. 78, 053503 (2007); http://dx.doi.org/10.1063/1.2737775 (4 pages) | Cited 6 times

Online Publication Date: 16 May 2007

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A new dispersive element named as quantum-dot-array diffraction grating [ L. F. Cao, China patent No. 200410081499 (August 10, 2004) ] for visible light has been developed and characterized experimentally. A large number of quantum dots distributed on a substrate as sinusoidal function can be used to diffract x rays without higher-order diffraction. The experimental patterns show that the higher-order diffractions which inevitably exist in the spectrum recorded using traditional diffraction gratings can be eliminated effectively by this newly designed element. It indicates that quantum-dot-array diffraction grating could be an attractive alternative of presently used diffraction grating in soft x-ray spectroscopy application to get rid of the higher-order diffraction distortions.
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42.79.Dj Gratings
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.15.Eq Optical system design
41.50.+h X-ray beams and x-ray optics

Neutral particle analyzer measurements on the SSPX spheromak

E. D. Mezonlin, S. Roberson, C. Raynor, R. Appartaim, J. A. Johnson, III, V. I. Afanasyev, S. S. Kozlovsky, J. M. Moller, D. N. Hill, E. B. Hooper, H. S. McLean, and R. D. Wood

Rev. Sci. Instrum. 78, 053504 (2007); http://dx.doi.org/10.1063/1.2737756 (7 pages) | Cited 7 times

Online Publication Date: 18 May 2007

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A neutral particle analyzer is used to measure the time-resolved energy spectrum of neutral hydrogen leaving a spheromak plasma. A gas cell filled with 10–50 mTorr of helium is used to strip electrons from incoming neutral hydrogen, lowering the minimum detectable energy well below that obtained with thin foils. Effective neutral particle temperature is calculated by fitting a Maxwellian energy distribution to the measured energy spectrum above and below ∼ 300 eV. A computational model with approximated profiles of plasma density and neutral density is used with the measured neutral hydrogen flux to estimate the ion temperature. Measurement of the power flux due to neutral hydrogen emitted at the measurement location is extended to the whole plasma surface to estimate the total charge exchange power loss from the plasma. The initial results indicate that the charge exchange power loss represents only 2% of the total input gun power during the sustainment phase of the discharge.
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52.70.Nc Particle measurements
52.55.Ip Spheromaks
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.20.Fs Electron collisions
52.25.Ya Neutrals in plasmas

Spatiotemporal temperature fluctuation measurements by means of a fast swept Langmuir probe array

M. Schubert, M. Endler, H. Thomsen, and W7-AS Team

Rev. Sci. Instrum. 78, 053505 (2007); http://dx.doi.org/10.1063/1.2740785 (7 pages) | Cited 5 times

Online Publication Date: 18 May 2007

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Stationary Langmuir probe measurements of ion saturation current and floating potential in a plasma cannot give direct information on density and plasma potential fluctuations in the presence of temperature fluctuations. This problem can be avoided if the probe bias voltage is continuously swept faster than the fluctuation time scale, recording the current-voltage characteristic. This article reports the development of a spatiotemporal highly resolving Langmuir probe array with 15 fast swept tips, operating in the strongly magnetized, collisionless edge plasma of the Wendelstein 7-AS stellarator [ Plasma Phys. Controlled Fusion 31, 1579 (1989) ]. The probe tips are aligned in the poloidal direction, the tip spacing is 2 mm, and the sweeping frequency is 1.4 MHz. Current and voltage data are sampled with 50 MHz. The high bandwidth of the measurement is achieved by placing miniaturized differential amplifiers close to the probe tips in order to do an impedance transform. The surface-mounting technology and an additional inverse feedback module are utilized, allowing for an input voltage range of ±100 V, and a common mode rejection rate of 55 dB at 4 MHz, which is sufficient to resolve the nonlinear probe characteristic. For the evaluation of the data, a fit model for stationary probes is employed and found adequate. Changes of the plasma parameters during one voltage sweep are taken into account by a linear interpolation of the fit parameters. Spatio-temporal fluctuation data gained by a fast swept Langmuir probe array, which can be relevant for the turbulent radial transport of particles and energy, are presented.
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52.70.Ds Electric and magnetic measurements
52.25.Gj Fluctuation and chaos phenomena
52.25.Fi Transport properties
52.25.Xz Magnetized plasmas
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Jd Magnetic mirrors, gas dynamic traps
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Direct quantitative tomographic reconstruction for weakly absorbing homogeneous phase objects

B. D. Arhatari, F. De Carlo, and A. G. Peele

Rev. Sci. Instrum. 78, 053701 (2007); http://dx.doi.org/10.1063/1.2735583 (5 pages) | Cited 6 times

Online Publication Date: 3 May 2007

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We examine a direct filtered back projection approach that is suitable for the reconstruction of weakly absorbing homogeneous phase objects. Like recent similar approaches this method needs only one intensity image in each projection without the requirement for an intermediate step of phase retrieval. We tested the method using simulation and experimental results. Simulation results show good quantitative reconstruction which includes the correct refractive index value and distribution of the sample. However, experimental result still indicates the presence of artifacts.
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42.30.Wb Image reconstruction; tomography

Atomic force microscope nanolithography of polymethylmethacrylate polymer

F. S. Teixeira, R. D. Mansano, M. C. Salvadori, M. Cattani, and I. G. Brown

Rev. Sci. Instrum. 78, 053702 (2007); http://dx.doi.org/10.1063/1.2736311 (3 pages) | Cited 4 times

Online Publication Date: 3 May 2007

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We describe a nanolithography process for a polymethylmethacrylate (PMMA) surface using scanning contact atomic force microscopy. Parallel furrows were scribed with a pyramidal silicon tip using the same scan mechanism as used to image samples. The PMMA was first electron beam irradiated using a scanning electron microscope and developed. The topography formed is reproducible and predictable. Material from the region where the tip scribes is moved to nearby regions, and aligned, elongated PMMA fragments are seen to decorate the valleys between furrows.
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81.16.Nd Micro- and nanolithography
07.79.Lh Atomic force microscopes
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Automatization of nanotomography

C. Dietz, S. Röper, S. Scherdel, A. Bernstein, N. Rehse, and R. Magerle

Rev. Sci. Instrum. 78, 053703 (2007); http://dx.doi.org/10.1063/1.2736359 (5 pages) | Cited 5 times

Online Publication Date: 3 May 2007

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An approach for automated nanotomography, a layer-by-layer imaging technique based on scanning probe microscopy (SPM), is presented. Stepwise etching and imaging is done in situ in a liquid cell of an SPM. The flow of etching and rinsing solutions after each etching step is controlled with solenoid valves which allow for an automated measuring protocol. The thermal drift and the drift of the piezo scanner is corrected by applying offsets calculated from the cross correlation coefficients between successive images. As an example, we have imaged human bone with ∼ 10 nm resolution using tapping mode SPM and successive etching with hydrochloric acid.
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87.64.Dz Scanning tunneling and atomic force microscopy
87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications

Accurate particle position measurement from images

Y. Feng, J. Goree, and Bin Liu

Rev. Sci. Instrum. 78, 053704 (2007); http://dx.doi.org/10.1063/1.2735920 (10 pages) | Cited 30 times

Online Publication Date: 4 May 2007

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The moment method is an image analysis technique for subpixel estimation of particle positions. The total error in the calculated particle position includes effects of pixel locking and random noise in each pixel. Pixel locking, also known as peak locking, is an artifact where calculated particle positions are concentrated at certain locations relative to pixel edges. We report simulations to gain an understanding of the sources of error and their dependence on parameters the experimenter can control. We suggest an algorithm, and we find optimal parameters an experimenter can use to minimize total error and pixel locking. For a dusty plasma experiment, we find that a subpixel accuracy of 0.017 pixel or better can be attained. These results are also useful for improving particle position measurement and particle tracking velocimetry using video microscopy in fields including colloids, biology, and fluid mechanics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.65.Cc Particle orbit and trajectory
07.05.Pj Image processing
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
02.60.Cb Numerical simulation; solution of equations

Variable-temperature independently driven four-tip scanning tunneling microscope

Rei Hobara, Naoka Nagamura, Shuji Hasegawa, Iwao Matsuda, Yuko Yamamoto, Yutaka Miyatake, and Toshihiko Nagamura

Rev. Sci. Instrum. 78, 053705 (2007); http://dx.doi.org/10.1063/1.2735593 (5 pages) | Cited 14 times

Online Publication Date: 8 May 2007

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The authors have developed an ultrahigh vacuum (UHV) variable-temperature four-tip scanning tunneling microscope (STM), operating from room temperature down to 7 K, combined with a scanning electron microscope (SEM). Four STM tips are mechanically and electrically independent and capable of positioning in arbitrary configurations in nanometer precision. An integrated controller system for both of the multitip STM and SEM with a single computer has also been developed, which enables the four tips to operate either for STM imaging independently and for four-point probe (4PP) conductivity measurements cooperatively. Atomic-resolution STM images of graphite were obtained simultaneously by the four tips. Conductivity measurements by 4PP method were also performed at various temperatures with the four tips in square arrangement with direct contact to the sample surface.
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07.79.Cz Scanning tunneling microscopes
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
06.30.Ka Basic electromagnetic quantities

Feedforward correction of nonlinearities in piezoelectric scanner constructions and its experimental verification

B. Graffel, F. Müller, A.-D. Müller, and M. Hietschold

Rev. Sci. Instrum. 78, 053706 (2007); http://dx.doi.org/10.1063/1.2736786 (6 pages)

Online Publication Date: 8 May 2007

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Piezoelectrical actuators widely used in scanning devices for highly resolved displacement generation exhibit a number of known nonlinear effects as hysteresis and creep. This article describes an attempt to minimize those nonlinearities by recognizing the relation between scan range and voltage magnitude in a scanner specific function. In addition, by utilizing a strain gauge sensor system, a forward displacement correction is realized. The mathematical procedure behind the hysteresis correction is described in detail. The dependence of the higher order correction factors on parameters such as scan speed, scan range, or center position is studied carefully to extract their influence on the result. Finally, integral nonlinearities of about 1% are proven in experiments with an atomic force microscope.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Fiber optic light collection system for scanning-tunneling-microscope-induced light emission

Neil J. Watkins, James P. Long, Zakya H. Kafafi, and Antti J. Mäkinen

Rev. Sci. Instrum. 78, 053707 (2007); http://dx.doi.org/10.1063/1.2740479 (4 pages) | Cited 2 times

Online Publication Date: 14 May 2007

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We report a compact light collection scheme suitable for retrofitting a scanning tunneling microscope (STM) for STM-induced light emission experiments. The approach uses a pair of optical fibers with large core diameters and high numerical apertures to maximize light collection efficiency and to moderate the mechanical precision required for alignment. Bench tests indicate that efficiency reduction is almost entirely due to reflective losses at the fiber ends, while losses due to fiber misalignment have virtually been eliminated. Photon-map imaging with nanometer features is demonstrated on a stepped Au(111) surface with signal rates exceeding 104 counts/s.
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42.81.Wg Other fiber-optical devices
07.79.Cz Scanning tunneling microscopes
42.81.Dp Propagation, scattering, and losses; solitons
42.81.Cn Fiber testing and measurement of fiber parameters

Highly absorbing gadolinium test device to characterize the performance of neutron imaging detector systems

C. Grünzweig, G. Frei, E. Lehmann, G. Kühne, and C. David

Rev. Sci. Instrum. 78, 053708 (2007); http://dx.doi.org/10.1063/1.2736892 (4 pages) | Cited 15 times

Online Publication Date: 14 May 2007

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We report on the fabrication and application of a novel neutron imaging test device made of gadolinium. It is designed for a real time evaluation of the spatial resolution, resolution direction, and distortions of a neutron imaging detector system. Measurements of the spatial resolution of 6LiF doped ZnS scintillator screens with different thicknesses and of imaging plates were performed. The obtained results are in good agreement with comparison measurements using the standard knife edge detection method.
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29.40.Mc Scintillation detectors
81.70.-q Methods of materials testing and analysis

Remote in vivo imaging of human skin corneocytes by means of an optical fiber bundle

Tanguy Dromard, Valérie Ravaine, Serge Ravaine, Jean-Luc Lévêque, and Neso Sojic

Rev. Sci. Instrum. 78, 053709 (2007); http://dx.doi.org/10.1063/1.2736346 (6 pages) | Cited 1 time

Online Publication Date: 14 May 2007

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Human corneocytes forming the outermost layer of the epidermis (stratum corneum) were imaged in vivo by epifluorescence through a coherent optical fiber bundle. A very simple and rapid method to remotely visualize the cells forming this protective layer of the skin is presented. After the topical application of fluorescein, the distal face of an optical fiber bundle is gently applied perpendicularly onto the labeled skin (contact mode). Remote fluorescence images of the corneocytes are acquired in 50 ms through the bundle comprising 30 000 individually cladded 3.5 μm diameter optical fibers. The very short focal distance which is an intrinsic characteristic of such bundles, allows visualizing only the most superficial monolayer of cells in contact with the external environment. An image displays about 400–500 cells directly on the human body. The size and the arrangement of the corneocytes can thus be acquired and analyzed in a very simple and easy way. The method is flexible and can be used for any location on the human body. Using a gradient-index lens objective (magnification 2.8×) fused to the distal face of the bundle allows the shape of the corneocytes to be better resolved. In addition, the working distance is 300 μm and hence this second approach works in a noncontact imaging mode. Both approaches are complementary and allow providing instantaneously either a global view of the cells with a possible statistical determination of their area or morphological information, which are essential for dermatology and cosmetic sciences. Finally, to improve the quality and the contrast of the recorded images, we tested silica nanoparticles containing fluorescein. In brief, this diagnostic method is nontoxic, painless, easy to use, noninvasive, and nondestructive.
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87.63.L- Visual imaging
87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.17.-d Cell processes
42.81.Pa Sensors, gyros

Compact variable-temperature scanning force microscope

Tien-Ming Chuang and Alex de Lozanne

Rev. Sci. Instrum. 78, 053710 (2007); http://dx.doi.org/10.1063/1.2735568 (7 pages) | Cited 8 times

Online Publication Date: 14 May 2007

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A compact design for a cryogenic variable-temperature scanning force microscope using a fiber-optic interferometer to measure cantilever deflection is presented. The tip-sample coarse approach and the lateral tip positioning are performed by piezoelectric positioners in situ. The microscope has been operated at temperatures between 6 and 300 K. It is designed to fit into an 8 T superconducting magnet with the field applied in the out-of-plane direction. The results of scanning in various modes are demonstrated, showing contrast based on magnetic field gradients or surface potentials.
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07.79.Lh Atomic force microscopes
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
07.60.Vg Fiber-optic instruments
07.60.Ly Interferometers
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