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Dec 2008

Volume 79, Issue 12, Articles (12xxxx)

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A frequency-stabilized difference frequency generation laser spectrometer for precise line profile studies in the midinfrared

Wen-Ping Deng, Bo Gao, Cun-Feng Cheng, Guo-Sheng Cheng, Shui-Ming Hu, and Qing-Shi Zhu

Rev. Sci. Instrum. 79, 123101 (2008); http://dx.doi.org/10.1063/1.3033164 (5 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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A midinfrared laser spectrometer is built up based on the difference frequency generation (DFG) of a Nd:YAG (yttrium aluminum garnet) laser and a tunable Ti:sapphire (Ti:Sa) laser. Tuning the Ti:Sa laser and operating properly with the periodically poled lithium niobate crystal, the DFG emission is tunable in the spectral range of 2.3–5.0 μm. The 1064 nm Nd:YAG laser frequency is stabilized to the 10−6 cm−1 level on a Doppler-broadened I2 absorption line at 532 nm. As a result, the DFG emission frequency is stabilized within 1×10−4 cm−1. The measurement of an absorption line of CH4 near 3 μm demonstrates that the DFG spectrometer is very suitable for the molecular absorption line profile studies in the midinfrared region.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Fc Modulation, tuning, and mode locking
33.20.Ea Infrared spectra
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Cavity-dumped 2.70 μm erbium laser using optomechanical shutter

Young Ho Park, Dong Won Lee, Hong Jin Kong, and Yeong Sik Kim

Rev. Sci. Instrum. 79, 123102 (2008); http://dx.doi.org/10.1063/1.3036976 (3 pages)

Online Publication Date: 1 December 2008

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A cavity-dumped 2.70 μm erbium laser with a frustrated total internal reflection (FTIR) shutter was investigated and compared with a Q-switched erbium laser using the FTIR shutter. The Q-switched and the cavity-dumped 2.70 μm laser outputs were obtained with a dichroic coated mirror with high reflectance at 2.70 μm and high transmittance at 2.79 μm. For the Q-switched operation, a maximum peak power of 33.5 kW was achieved, and its pulse width was 1.3 μs. For the cavity-dumped operation, the laser pulse energy was optimized by changing the switching time of the FTIR shutter. When the pulse width is reduced to 210 ns, the peak power increases to 154 kW.
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42.60.-v Laser optical systems: design and operation
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New versatile and linear optical sensor based on electro-optical modulation and compensation

Rémy Claverie, Jean Paul Salvestrini, Marc D. Fontana, and Pascal Ney

Rev. Sci. Instrum. 79, 123103 (2008); http://dx.doi.org/10.1063/1.3036979 (8 pages)

Online Publication Date: 1 December 2008

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This paper is devoted to the description and characterization of a new electro-optic sensor based on a polarimetric device operating in reflection mode, and on a closed-loop controller. The main features of the proposed sensor are versatility, insensitivity to the laser beam optical power fluctuation, and fully linear working mode. The resolution of the sensor, in terms of phase shift, is shown to be better than ±20 mrad and its accuracy to ±50 mrad.
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07.60.Fs Polarimeters and ellipsometers
42.79.Hp Optical processors, correlators, and modulators
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
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High-density, high-temperature alkali vapor cell

V. O. Lorenz, X. Dai, H. Green, T. R. Asnicar, and S. T. Cundiff

Rev. Sci. Instrum. 79, 123104 (2008); http://dx.doi.org/10.1063/1.3036982 (4 pages)

Online Publication Date: 2 December 2008

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We present a vapor cell design that enables resonant optical spectroscopy in high-density, high-temperature alkali metal vapors. Optical access is provided via reflection from the interface between the vapor and a sapphire window. The cell resists corrosion from the highly reactive alkali vapors, in our case, potassium, up to 800 °C (number densities up to 1019 cm−3). The cells maintain their integrity for an average of 100 h above 500 °C with about 10 heating/cooling cycles.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.20.Ka High-temperature instrumentation; pyrometers
07.60.Rd Visible and ultraviolet spectrometers
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Imaging piezospectroscopy

John B. Abbiss and Bauke Heeg

Rev. Sci. Instrum. 79, 123105 (2008); http://dx.doi.org/10.1063/1.3030776 (9 pages) | Cited 1 time

Online Publication Date: 4 December 2008

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A novel instrument is described for obtaining accurate high-resolution residual stress images of aluminum oxide materials, based on the piezospectroscopy of Cr3+ dopant ions. The instrument employs a charge coupled device camera, a narrow bandpass tunable filter and the use of Tikhonov regularization for reconstruction of the raw spectral data. The experimental accuracy and spectral shift resolution of this method were analyzed with two calibration light sources and with independently measured spectra, and were found to be approximately ±0.01 nm across the pixel array. This is close to the theoretically obtainable accuracy for the particular filter used, a solid etalon Fabry–Pérot filter with a passband of 0.25 nm, based on an analysis with simulated data. The spectral resolution corresponds to a stress resolution, under biaxial stress conditions, of ±40 MPa.
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07.60.-j Optical instruments and equipment
07.10.-h Mechanical instruments and equipment
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High-resolution Rydberg tagging time-of-flight measurements of atomic photofragments by single-photon vacuum ultraviolet laser excitation

Brant Jones, Jingang Zhou, Lei Yang, and C. Y. Ng

Rev. Sci. Instrum. 79, 123106 (2008); http://dx.doi.org/10.1063/1.3043427 (10 pages) | Cited 4 times

Online Publication Date: 12 December 2008

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By coupling a comprehensive tunable vacuum ultraviolet (VUV) laser system to a velocity-mapped ion imaging apparatus, we show that high-resolution high-n Rydberg tagging time-of-flight (TOF) measurements of nascent atomic photofragments formed by laser photodissociation can be made using single-photon VUV laser photoexcitation. To illustrate this single-photon Rydberg tagging TOF method, we present here the results of the VUV laser high-n Rydberg tagging TOF measurements of O(3P2) and S(3P2) formed in the photodissociation of SO2 and CS2 at 193.3 and 202.3 nm, respectively. These results are compared to those obtained by employing the VUV laser photoionization time-sliced velocity-mapped ion imaging technique. The fact that the kinetic energy resolutions achieved in the VUV laser high-n Rydberg tagging TOF measurements of O and S atoms are found to be higher than those observed in the VUV laser photoionization, time-sliced velocity-mapped ion imaging studies show that the single-photon VUV laser high-n Rydberg tagging TOF method is useful and complementary to state-of-the-art time-sliced velocity-mapped ion imaging measurements of heavier atomic photofragments, such as O and S atoms. Furthermore, the general agreement observed between the VUV laser high-n Rydberg tagging TOF and velocity-mapped ion imaging experiments supports the conclusion that the lifetimes of the tagged Rydberg states of O and S atoms are sufficiently long to allow the reliable determination of state-resolved UV photodissociation cross sections of SO2 and CS2 by using the VUV laser high-n Rydberg tagging TOF method.
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82.50.Hp Processes caused by visible and UV light
32.80.Ee Rydberg states
82.80.-d Chemical analysis and related physical methods of analysis
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A time-resolved single-pass technique for measuring optical absorption coefficients of window materials under 100 GPa shock pressures

Jun Li, Xianming Zhou, and Jiabo Li

Rev. Sci. Instrum. 79, 123107 (2008); http://dx.doi.org/10.1063/1.3046279 (6 pages) | Cited 4 times

Online Publication Date: 12 December 2008

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An experimental method was developed to perform time-resolved, single-pass optical absorption measurements and to determine absorption coefficients of window materials under strong shock compression up to ∼ 200 GPa. Experimental details are described of (i) a configuration to generate an in situ dynamic, bright, optical source and (ii) a sample assembly with a lithium fluoride plate to essentially eliminate heat transfer from the hot radiator into the specimen and to maintain a constant optical source within the duration of the experiment. Examples of measurements of optical absorption coefficients of several initially transparent single crystal materials at high shock pressures are presented.
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07.60.-j Optical instruments and equipment
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.-a Optical materials
62.50.Ef Shock wave effects in solids and liquids
42.72.-g Optical sources and standards
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Near UV-near IR Fourier transform spectrometer using the beam-folding position-tracking method based on retroreflectors

Xuzhu Wang, Robert K. Y. Chan, and Amelia S. K. Cheng

Rev. Sci. Instrum. 79, 123108 (2008); http://dx.doi.org/10.1063/1.3046281 (6 pages) | Cited 3 times

Online Publication Date: 16 December 2008

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A near UV-near IR Fourier transform spectrometer based on a beam-folding position-tracking method realized by using retroreflectors is reported. The use of retroreflectors maintains all beams in the beam-fold arrangement in parallel with the incident beams. The beam-folding interferometer used for position tracking is arranged to have optical path symmetry with the measurement interferometer in the zero path difference position of the measurement interferometer, and the vertex of the movable retroreflector in the measurement interferometer is arranged very close to the midpoint of the vertices of two movable retroreflectors in the position-tracking interferometer. These measures keep the equivalent optical axis of the position-tracking interferometer well in line with that of the measurement interferometer even with translational misalignments. Therefore, the change in the optical path difference of the position-tracking interferometer is always synchronous to that of the measurement interferometer during the scanning process. That is, the position-tracking error can be suppressed to very small values during a scan. We have demonstrated a UV-near IR Fourier transform spectrometer with a standard quality ball-bearing translation stage achieving a resolution close to the theoretical resolution of ∼ 0.28 cm−1 at the He–Ne laser wavelength when the scan distance reaches the travel distance of over 2 cm. This was achieved without the need for elaborate optics, sophisticated detecting electronics, and high-precision servomotion control.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Rd Visible and ultraviolet spectrometers
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A new titration system of a novel split-type superconducting magnet NMR spectrometer

Isao Kitagawa, Hideki Tanaka, Michiya Okada, Hitoshi Kitaguchi, and Takamitsu Kohzuma

Rev. Sci. Instrum. 79, 123109 (2008); http://dx.doi.org/10.1063/1.3048542 (4 pages)

Online Publication Date: 16 December 2008

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A new titration system for studying protein-ligand interactions has been developed. In this system, the sample solution is circulated in the route formed by an access path in a split superconducting magnet to maintain a constant protein concentration during the titration experiments. A concentration-control procedure for the ligand/protein ratio is devised, and the ligand/protein ratio is well controlled by this apparatus.
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87.15.kp Protein-ligand interactions
82.56.Pp NMR of biomolecules
82.56.Dj High resolution NMR
82.39.-k Chemical kinetics in biological systems
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A broadband absorption spectrometer using light emitting diodes for ultrasensitive, in situ trace gas detection

Justin M. Langridge, Stephen M. Ball, Alexander J. L. Shillings, and Roderic L. Jones

Rev. Sci. Instrum. 79, 123110 (2008); http://dx.doi.org/10.1063/1.3046282 (14 pages) | Cited 12 times

Online Publication Date: 18 December 2008

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A broadband absorption spectrometer has been developed for highly sensitive and target-selective in situ trace gas measurements. The instrument employs two distinct modes of operation: (i) broadband cavity enhanced absorption spectroscopy (BBCEAS) is used to quantify the concentration of gases in sample mixtures from their characteristic absorption features, and (ii) periodic measurements of the cavity mirrors’ reflectivity are made using step-scan phase shift cavity ringdown spectroscopy (PSCRDS). The latter PSCRDS method provides a stand-alone alternative to the more usual method of determining mirror reflectivities by measuring BBCEAS absorption spectra for calibration samples of known composition. Moreover, the instrument’s two modes of operation use light from the same light emitting diode transmitted through the cavity in the same optical alignment, hence minimizing the potential for systematic errors between mirror reflectivity determinations and concentration measurements. The ability of the instrument to quantify absorber concentrations is tested in instrument intercomparison exercises for NO2 (versus a laser broadband cavity ringdown spectrometer) and for H2O (versus a commercial hygrometer). A method is also proposed for calculating effective absorption cross sections for fitting the differential structure in BBCEAS spectra due to strong, narrow absorption lines that are under-resolved and hence exhibit non-Beer–Lambert law behavior at the resolution of the BBCEAS measurements. This approach is tested on BBCEAS spectra of water vapor’s 4v+δ absorption bands around 650 nm. The most immediate analytical application of the present instrument is in quantifying the concentration of reactive trace gases in the ambient atmosphere. The instrument’s detection limits for NO3 as a function of integration time are considered in detail using an Allan variance analysis. Experiments under laboratory conditions produce a 1σ detection limit of 0.25 pptv for a 10 s acquisition time, which improves with further signal averaging to 0.09 pptv in 400 s. Finally, an example of the instrument’s performance under field work conditions is presented, in this case of measurements of the sum of NO3+N2O5 concentrations in the marine boundary layer acquired during the Reactive Halogens in the Marine Boundary Layer field campaign.
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07.60.Rd Visible and ultraviolet spectrometers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
06.20.fb Standards and calibration
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.-q Absorption and reflection spectra: visible and ultraviolet
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A newly designed single etalon double edge Doppler wind lidar receiving optical system

Dukhyeon Kim, Seongok Kwon, Hyungki Cha, Younggi Kim, and Jeonghaei Sunwoo

Rev. Sci. Instrum. 79, 123111 (2008); http://dx.doi.org/10.1063/1.3053338 (4 pages)

Online Publication Date: 23 December 2008

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A new optical Doppler lidar receiving system which can measure Doppler-shifted incoherent scattering light has been proposed and tested. This system functions in a manner similar to two edge filters and consists of a single etalon, a polarization beam splitter, and mirrors that can guide scattered light into a single etalon with two different angles. These two incident angles are precisely adjusted by the polarization beam splitter and mirrors. Using this optical receiving system we can measure a moving target with a high sensitivity. Theoretical calculations show that this system will have a better optical sensitivity than a single edge system and will allow the use of incoherent Doppler lidar for wind velocity measurements.
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42.79.Qx Range finders, remote sensing devices; laser Doppler velocimeters, SAR, and LIDAR
42.79.Fm Reflectors, beam splitters, and deflectors
07.60.Ly Interferometers
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A short working distance multiple crystal x-ray spectrometer

B. Dickinson, G. T. Seidler, Z. W. Webb, J. A. Bradley, K. P. Nagle, S. M. Heald, R. A. Gordon, and I. M. Chou

Rev. Sci. Instrum. 79, 123112 (2008); http://dx.doi.org/10.1063/1.3048544 (8 pages) | Cited 7 times

Online Publication Date: 23 December 2008

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For x-ray spot sizes of a few tens of microns or smaller, a millimeter-sized flat analyzer crystal placed ∼ 1 cm from the sample will exhibit high energy resolution while subtending a collection solid angle comparable to that of a typical spherically bent crystal analyzer (SBCA) at much larger working distances. Based on this observation and a nonfocusing geometry for the analyzer optic, we have constructed and tested a short working distance (SWD) multicrystal x-ray spectrometer. This prototype instrument has a maximum effective collection solid angle of 0.14 sr, comparable to that of 17 SBCA at 1 m working distance. We find good agreement with prior work for measurements of the Mn Kβ x-ray emission and resonant inelastic x-ray scattering for MnO, and also for measurements of the x-ray absorption near-edge structure for Dy metal using Lα2 partial-fluorescence yield detection. We discuss future applications at third- and fourth-generation light sources. For concentrated samples, the extremely large collection angle of SWD spectrometers will permit collection of high-resolution x-ray emission spectra with a single pulse of the Linac Coherent Light Source. The range of applications of SWD spectrometers and traditional multi-SBCA instruments has some overlap, but also is significantly complementary.
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07.85.Nc X-ray and γ-ray spectrometers
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
78.70.Dm X-ray absorption spectra
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
78.70.En X-ray emission spectra and fluorescence
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Scalable time-correlated photon counting system with multiple independent input channels

Michael Wahl, Hans-Jürgen Rahn, Tino Röhlicke, Gerald Kell, Daniel Nettels, Frank Hillger, Ben Schuler, and Rainer Erdmann

Rev. Sci. Instrum. 79, 123113 (2008); http://dx.doi.org/10.1063/1.3055912 (8 pages) | Cited 4 times

Online Publication Date: 29 December 2008

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Time-correlated single photon counting continues to gain importance in a wide range of applications. Most prominently, it is used for time-resolved fluorescence measurements with sensitivity down to the single molecule level. While the primary goal of the method used to be the determination of fluorescence lifetimes upon optical excitation by short light pulses, recent modifications and refinements of instrumentation and methodology allow for the recovery of much more information from the detected photons, and enable entirely new applications. This is achieved most successfully by continuously recording individually detected photons with their arrival time and detection channel information (time tagging), thus avoiding premature data reduction and concomitant loss of information. An important property of the instrumentation used is the number of detection channels and the way they interrelate. Here we present a new instrument architecture that allows scalability in terms of the number of input channels while all channels are synchronized to picoseconds of relative timing and yet operate independent of each other. This is achieved by means of a modular design with independent crystal-locked time digitizers and a central processing unit for sorting and processing of the timing data. The modules communicate through high speed serial links supporting the full throughput rate of the time digitizers. Event processing is implemented in programmable logic, permitting classical histogramming, as well as time tagging of individual photons and their temporally ordered streaming to the host computer. Based on the time-ordered event data, any algorithms and methods for the analysis of fluorescence dynamics can be implemented not only in postprocessing but also in real time. Results from recently emerging single molecule applications are presented to demonstrate the capabilities of the instrument.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
33.50.Dq Fluorescence and phosphorescence spectra
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.80.-b Photon interactions with molecules
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Simple two-dimensional-imaging spectrograph with wedged narrow band filters

Martin Divoký and Petr Straka

Rev. Sci. Instrum. 79, 123114 (2008); http://dx.doi.org/10.1063/1.3058603 (4 pages)

Online Publication Date: 29 December 2008

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A minute, yet practical, modification of a well-known spectrograph based on a set of wedged narrow band filters is presented. It makes possible two-dimensional-imaging spectral measurements with a potential subpixel precision of a few micrometers. The simple spectroscopic device can evaluate dispersion of quantities which can be transformed into an image, e.g., into a spatial beam distribution. The spectrograph was used to measure angular dispersion of both a laser oscillator producing femtosecond pulses and a simple dispersive optical system, an optical wedge.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Rd Visible and ultraviolet spectrometers
42.79.Ci Filters, zone plates, and polarizers
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Pw Imaging detectors and sensors
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Velocity map imaging in time of flight mass spectrometry

M. Brouard, E. K. Campbell, A. J. Johnsen, C. Vallance, W. H. Yuen, and A. Nomerotski

Rev. Sci. Instrum. 79, 123115 (2008); http://dx.doi.org/10.1063/1.3036978 (8 pages) | Cited 3 times

Online Publication Date: 31 December 2008

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A new variation on time of flight mass spectrometry is presented, which uses a fast framing charge coupled device camera to velocity map image multiple product masses in a single acquisition. The technique is demonstrated on two photofragmentation processes, those of CS2 and CH3S2CH3 (dimethyldisulfide) at a photolysis wavelength of 193 nm. In both cases, several mass fragments are imaged simultaneously, and speed distributions and anisotropy parameters are extracted that are comparable to those obtained by imaging each fragment separately in conventional velocity map imaging studies.
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82.50.Hp Processes caused by visible and UV light
42.79.Pw Imaging detectors and sensors
82.80.Rt Time of flight mass spectrometry
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Transferring cold atoms in double magneto-optical trap by a continuous-wave transfer laser beam with large red detuning

Junmin Wang, Jing Wang, Shubin Yan, Tao Geng, and Tiancai Zhang

Rev. Sci. Instrum. 79, 123116 (2008); http://dx.doi.org/10.1063/1.3058607 (5 pages) | Cited 5 times

Online Publication Date: 31 December 2008

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A novel scheme of transferring cold atoms in a double magneto-optical trap (MOT) system has been experimentally demonstrated. Cold cesium atoms trapped in a vapor-cell MOT are efficiently transferred to an ultrahigh-vacuum (UHV) MOT by a continuous-wave divergent Gaussian transfer laser beam. When large red detuning and moderate intensity are adopted for the transfer laser beam, enhancement of the recapturing of atoms in the UHV MOT is clearly observed. Using the divergent transfer laser beam (diameter of ~1.60 mm in the vapor-cell MOT region) with typical power of ~20.2 mW, up to ~85% of transfer efficiency is obtained when the frequency detuning is set to around −1.2 GHz, and it is not sensitive to small detuning variation. This transfer is much efficient compared with that in the case of continuous-wave near-resonance weak transfer laser beam (typical power of order of ∼ 100 μW and typical frequency detuning of ~−10 MHz) which is normally used in double-MOT experiment. The enhancement is ascribed to the guiding effect on cold atomic flux by transverse dipole potential of the large red-detuned transfer laser beam.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
37.10.Gh Atom traps and guides
37.10.De Atom cooling methods
42.50.Wk Mechanical effects of light on material media, microstructures and particles
85.70.Sq Magnetooptical devices
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A new spin-polarized photoemission spectrometer with very high efficiency and energy resolution

Taichi Okuda, Yasuo Takeichi, Yuuki Maeda, Ayumi Harasawa, Iwao Matsuda, Toyohiko Kinoshita, and Akito Kakizaki

Rev. Sci. Instrum. 79, 123117 (2008); http://dx.doi.org/10.1063/1.3058757 (5 pages) | Cited 18 times

Online Publication Date: 31 December 2008

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A new spin- and angle-resolved photoemission spectrometer was developed adopting the very-low-energy-electron-diffraction (VLEED)-type spin polarimeter. The Fe(001)p(1×1)–O film grown on MgO(001) crystal for the VLEED target yields significantly high spin-resolving power, the effective Sherman function of 0.40±0.02, with long lifetime and stability compared to the conventional Fe(001) target. Under the favor of high resolving power, approximately 100 times higher efficiency than that of conventional Mott-type spin polarimeter, the figure of merit of 1.9±0.2×10−2 was achieved. Owing to this high efficiency, high-energy resolution can be realized with this new spin-polarized photoemission spectrometer. The simplified ways of target preparation and revitalization make the VLEED spin polarimeter much more convenient and feasible for the spin-polarized photoemission spectroscopy.
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79.60.Dp Adsorbed layers and thin films
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
68.55.-a Thin film structure and morphology
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Simulation and analysis of solenoidal ion sources

A. R. Alderwick, A. P. Jardine, H. Hedgeland, D. A. MacLaren, W. Allison, and J. Ellis

Rev. Sci. Instrum. 79, 123301 (2008); http://dx.doi.org/10.1063/1.3030858 (9 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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We present a detailed analysis and simulation of solenoidal, magnetically confined electron bombardment ion sources, aimed at molecular beam detection. The aim is to achieve high efficiency for singly ionized species while minimizing multiple ionization. Electron space charge plays a major role and we apply combined ray tracing and finite element simulations to determine the properties of a realistic geometry. The factors controlling electron injection and ion extraction are discussed. The results from simulations are benchmarked against experimental measurements on a prototype source.
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52.50.Dg Plasma sources
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Design and characterization of combined function multipole magnet for accelerators

Gautam Sinha and Gurnam Singh

Rev. Sci. Instrum. 79, 123302 (2008); http://dx.doi.org/10.1063/1.3039976 (9 pages) | Cited 1 time

Online Publication Date: 9 December 2008

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This paper presents the design and analysis of a multipurpose combined function magnet for use in accelerators. This magnet consists of three corrector magnets: (i) skew quadrupole, (ii) horizontal dipole, and (iii) vertical dipole magnets, along with the main sextupole magnet. The strength of the corrector magnets is smaller than that of the main sextupole magnet. The strength of all the four magnets can be varied independently. The excitation strength required to produce skew quadrupole gradient and the presence of various multipole components in the magnet are estimated using first order perturbation theory. The experimental data for the variation of the sextupole strength and its higher order multipoles in the presence of skew quadrupole excitations are presented and compared to the theoretical predictions. Simulation using two-dimensional fine element code, Poisson, is also done. Results obtained from all the above three methods are found to be in good agreement with each other. The variations of skew quadrupole gradient for different sextupole excitations are also measured. The validity of this theory is also checked for various combinations of excitations including the case where magnet gets saturated. The excitation strengths required for producing the horizontal and vertical dipole fields are estimated analytically along with the presence of various multipoles. Theoretical predictions of permissible multipoles are compared to the results obtained from simulation.
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29.27.-a Beams in particle accelerators
07.55.Db Generation of magnetic fields; magnets
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Correction of spherical aberration for an electrostatic gridded lens

Alexander Pikin and Ahovi Kponou

Rev. Sci. Instrum. 79, 123303 (2008); http://dx.doi.org/10.1063/1.3030857 (4 pages) | Cited 1 time

Online Publication Date: 10 December 2008

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Two methods to correct spherical aberration in electrostatic gridded lenses have been studied using ray-tracing simulations. Both methods are based on modifying the electrostatic field on the radial periphery of the lens. In the simplest case, the modification is done by extending the grid support axially. In the second method, the electric field on a radial periphery of the lens is modified by applying optimum voltage on an isolated correcting electrode. It is demonstrated that, for a given focal length, the voltage on this lens can be optimized for minimum aberration, and also that these lenses reduce the emittance growth of the ion beam.
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42.15.Fr Aberrations
41.85.Gy Chromatic and geometrical aberrations
41.85.Ne Electrostatic lenses, septa
42.15.Dp Wave fronts and ray tracing
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High precision high voltage divider and its application to electron beam ion traps

W. D. Chen, J. Xiao, Y. Shen, Y. Q. Fu, F. C. Meng, C. Y. Chen, Y. Zou, and R. Hutton

Rev. Sci. Instrum. 79, 123304 (2008); http://dx.doi.org/10.1063/1.3053449 (7 pages) | Cited 4 times

Online Publication Date: 24 December 2008

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A high precision high voltage divider has been developed for the electron beam ion trap in Shanghai. The uncertainty caused by the temperature coefficient of resistance (TCR) and the voltage coefficient of resistance has been studied in detail and was minimized to the level of ppm (10−6) range. Once the TCR was matched between the resistors, the precision of the dividing ratio finally reached the ppm range also. We measured the delay of the divider caused by the capacitor introduced to minimize voltage ripple to be 2.35 ms. Finally we applied the divider to an experiment to measure resonant energies for some dielectronic recombination processes for highly charged xenon ions. The final energies include corrections for both space charge and fringe field effects are mostly under 0.03%.
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
29.20.-c Accelerators
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Development of compact size penning ion source for compact neutron generator

Basanta Kumar Das and Anurag Shyam

Rev. Sci. Instrum. 79, 123305 (2008); http://dx.doi.org/10.1063/1.3054268 (4 pages) | Cited 3 times

Online Publication Date: 29 December 2008

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For long-life operation, easy to mount and compact in size penning type ion sources are widely used in different fields of research such as neutron generators, material research, and surface etching. One penning type ion source has been developed in our laboratory. Applying high voltage of 2 kV between two oppositely biased electrodes and using permanent magnet of 500 gauss magnetic field along the axis, we had produced the glow discharge in the plasma region. The performance of this source was investigated using nitrogen gas. Deuterium ions were produced and extracted on the basis of chosen electrodes and the angle of extraction. Using a single aperture plasma electrode, the beam was extracted along the axial direction. The geometry of plasma electrode is an important factor for the efficient extraction of the ions from the plasma ion source. The extracted ion current depends upon the shape of the plasma meniscus. A concave shaped plasma meniscus produces converged ion beam. The convergence of extracted ions is related to the extraction electrode angle. The greater the angle, the more the beam converges. We had studied experimentally this effect with a compact size penning ion source. The detailed comparison among the different extraction geometry and different electrode angle are discussed in this paper.
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29.25.Ni Ion sources: positive and negative
29.25.Dz Neutron sources
52.80.Hc Glow; corona
52.50.-b Plasma production and heating
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A collective scattering system for measuring electron gyroscale fluctuations on the National Spherical Torus Experiment

D. R. Smith, E. Mazzucato, W. Lee, H. K. Park, C. W. Domier, and N. C. Luhmann, Jr.

Rev. Sci. Instrum. 79, 123501 (2008); http://dx.doi.org/10.1063/1.3039415 (6 pages) | Cited 11 times

Online Publication Date: 5 December 2008

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A collective scattering system has been installed on the National Spherical Torus Experiment (NSTX) to measure electron gyroscale fluctuations in NSTX plasmas. The system measures fluctuations with k⊥ρe≲0.6 and k⊥≲20 cm−1. Up to five distinct wavenumbers are measured simultaneously, and the large toroidal curvature of NSTX plasmas provides enhanced spatial localization. Steerable optics can position the scattering volume throughout the plasma from the magnetic axis to the outboard edge. Initial measurements indicate rich turbulent dynamics on the electron gyroscale. The system will be a valuable tool for investigating the connection between electron temperature gradient turbulence and electron thermal transport in NSTX plasmas.
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52.35.Ra Plasma turbulence
52.25.Gj Fluctuation and chaos phenomena
52.55.Fa Tokamaks, spherical tokamaks
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Phase-type quantum-dot-array diffraction grating

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

Rev. Sci. Instrum. 79, 123502 (2008); http://dx.doi.org/10.1063/1.3053344 (4 pages) | Cited 3 times

Online Publication Date: 23 December 2008

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A novel phase-type quantum-dot-array diffraction grating (QDADG) is reported. In contrast to an earlier amplitude-type QDADG [ C. Wang et al., Rev. Sci. Instrum. 78, 053503 (2007) ], the new phase-type QDADG would remove the zeroth order diffraction at some certain wavelength, as well as suppressing the higher-order diffractions. In this paper, the basic concept, the fabrication, the calibration techniques, and the calibration results are presented. Such a grating can be applied in the research fields of beam splitting, laser probe diagnostics, and so on.
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42.79.Dj Gratings
42.86.+b Optical workshop techniques
06.20.F- Units and standards
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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Improvement of temporal resolution for three-dimensional continuous-wave electron paramagnetic resonance imaging

Hideo Sato-Akaba, Hirotada Fujii, and Hiroshi Hirata

Rev. Sci. Instrum. 79, 123701 (2008); http://dx.doi.org/10.1063/1.3033161 (7 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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This paper describes improved temporal resolution for three-dimensional (3D) continuous-wave electron paramagnetic resonance (EPR) imaging. To improve temporal resolution, the duration of magnetic filed scanning that is used to obtain an EPR spectrum for each projection was reduced to 40 ms. The Helmholtz coil pair for field scanning was driven by triangular waves. The uniform distribution of projections was also used to reduce the number of projections for 3D image reconstruction. The reduction reaction of 4-hydroxy-2,2,6,6-tetramethyl-piperidinooxy with ascorbic acid was visualized by improved 3D EPR imaging techniques with a temporal resolution of 5.8 s.
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87.61.Tg Clinical applications
87.57.cf Spatial resolution
87.57.nf Reconstruction
07.05.Pj Image processing
87.14.Pq Vitamins
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