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Aug 1994

Volume 65, Issue 8, pp. 2433-2740

Page 1 of 3 Pages Next Page | Jump to Page

Applications of resonance ionization mass spectrometry

M. G. Payne, Lu Deng, and N. Thonnard

Rev. Sci. Instrum. 65, 2433 (1994); http://dx.doi.org/10.1063/1.1144702 (27 pages) | Cited 31 times

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We describe here several types of mass spectrometry in which the mass selectivity is combined with a highly selective laser ionization method to achieve both high sensitivity and very high selectivity. These methods combine the most sensitive and highly selective laser ionization methods with mass selectivity in order to improve on both the sensitivity and the Z and A selectivity previously achievable in detecting atomic species. Applications of these methods include the dating of geophysical specimens, the on line analysis of rare short‐lived isotopes produced in high‐energy collisions, the detection of low levels of heavy metals or radioactive isotopes in biological samples, the detection of impurities in ultrapure materials, and a host of other applications. Because some versions of this method offer sensitivity to a hundred atoms of a particular isotope of an element in a macroscopic sample, there are new possibilities for fundamental studies of rare events. Several types of facilities for elemental and isotopic analysis will be described.
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07.75.+h Mass spectrometers
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

300 ps ruby laser using stimulated Brillouin scattering pulse compression

Yu. Nizienko, A. Mamin, P. Nielsen, and B. Brown

Rev. Sci. Instrum. 65, 2460 (1994); http://dx.doi.org/10.1063/1.1144703 (4 pages) | Cited 6 times

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Using the stimulated Brillouin scattering phase conjugation and pulse compression technique, a conventional long pulse ruby laser was successfully converted to give 300 ps pulses at 1 J energy level. The technique allows the use of smaller amplifiers than required in a conventional short pulse laser which in turn leads to operation at increased repetition rate. The completed laser when operated at 1.5 Hz produces stable output parameters. Each laser pulse is characterized by a sharp rise and a measured pre‐pulse level of less than 10−6 of the main pulse, making it suitable for LIDAR Thomson scattering measurements.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.55.Px Semiconductor lasers; laser diodes
42.65.Es Stimulated Brillouin and Rayleigh scattering

A simple and efficient external gas filtration and trapping system for excimer lasers

R. E. Stevens, C. Y. Kung, C. Kittrell, and J. L. Kinsey

Rev. Sci. Instrum. 65, 2464 (1994); http://dx.doi.org/10.1063/1.1145227 (6 pages)

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Excimer lasers are excellent sources of coherent light in the ultraviolet range of the spectrum. However, they have the drawback of requiring significant maintenance due to the corrosive gases, generation of dust, and contamination of the laser chamber optics which occur during normal operation. Improvements which are generally applicable to any excimer laser system are specifically described in terms of the two Questek (Lambda Physik, Acton, MA) model 2860 lasers in our lab. The same basic procedures are currently being implemented in two Lambda lasers in other research groups at our university. A novel gas triple filtration system, a simple cold trap with a counter‐flow heat exchanger, and a careful selection of valves have been added to minimize dust contamination of the optics, to decrease contamination and leakage of the gas fill, to provide safe and easy dust removal, and to reduce maintenance downtime.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

A wavemeter for measuring changes in wavelength of pulsed dye lasers

S. S. Thattey, A. S. Dongare, K. Dasgupta, S. R. More, and L. G. Nair

Rev. Sci. Instrum. 65, 2470 (1994); http://dx.doi.org/10.1063/1.1144704 (5 pages)

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The performance of a simple wavemeter for measuring changes in wavelength of a pulsed dye laser is described. Details of optics and electronic circuitary used, along with the algorithm for wavelength measurement, are given. Using this instrument wavelength changes of a dye laser could be measured, as well as introduced through a user interface, with an accuracy of 1 ppm.  
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42.55.Mv Dye lasers
42.60.Fc Modulation, tuning, and mode locking
07.60.Ly Interferometers

Magnetic pulse compressor for prepulse discharge in spiker‐sustainer excitation technique for XeCl lasers

G. Giordano, T. Letardi, F. Muzzi, and C. E. Zheng

Rev. Sci. Instrum. 65, 2475 (1994); http://dx.doi.org/10.1063/1.1144705 (7 pages) | Cited 3 times

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A high‐voltage pulse output modulator using a step‐up transformer with two stages of magnetic pulse compression circuits has been developed as a spiker for the purpose of obtaining the breakdown of the gas mixture when using the spiker‐sustainer excitation technique for pumping XeCl discharge lasers. When the transformer input is fed by a current pulse with a peak value and a full width of 1.16 kA and 1.6 μs, respectively, formed by a discharge of an initially charged 19‐kV, 57‐nF capacitance in series in the transformer primary loop, the 2.7‐nF output capacitor bank (Cp) of the spiker can be charged up to 67 kV with a (10%–90%) rise time of 59 ns. The modulator has been tested at a repetition rate of up to 600 Hz in burst mode using a resistor in parallel with Cp as the load.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers

Resonance‐tracking servo for an acousto‐optic modulator

E. Krüger and T. Kersebom

Rev. Sci. Instrum. 65, 2482 (1994); http://dx.doi.org/10.1063/1.1144706 (7 pages) | Cited 3 times

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A new scheme for locking an acoustic resonance of an acousto‐optic modulator to the exciting rf field applied for laser mode locking is presented. The resonance of the mode‐locking quartz prism is temperature‐tuned to match the synthesizer frequency. Deviation from perfect matching is sensed by observing the relative phase of the rf wave reflected at the device, and the error signal is fed back by a servo loop adjusting the heat delivered by a heating transistor to maintain the temperature required for exact resonance. The performance of the resonance‐tracking loop was checked on several different resonances of the modulator (used in an argon‐ion laser), because switching to another resonance is a simple and attractive way for changing the laser pulse repetition rate (or mode spacing) without replacing the mode‐locker unit. Excellent loop response was found in all cases. The new tracking principle provides a widely extended tracking range, improved tracking accuracy and laser stability, and simplifies the laser adjustment.
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42.79.Jq Acousto-optical devices
42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.Fc Modulation, tuning, and mode locking

Optical interference method to obtain thickness and refractive indices of a uniaxial medium

F. Carreño, J. C. Martínez‐Antón, and E. Bernabeu

Rev. Sci. Instrum. 65, 2489 (1994); http://dx.doi.org/10.1063/1.1144707 (5 pages) | Cited 6 times

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Optical interference fringe measurements of the thickness of weakly absorbing media can be rapid, accurate, and nondestructive. When the refractive index n of the sample is known, it will give us the layer thickness d. If, however, n is unknown, at least two independent spectrophotometric measurements are needed to obtain both n and d. A statistically based scheme is proposed to analyze the interference pattern in order to determine the refractive index and the thickness of the sample. The absolute interference order is also determined with the proposed technique. The major approximation inherent in the method is that the layer must be weakly absorbing and nondispersive over the wavelength region of interest. The method is applied to determine the optical constants of a uniaxial medium with the optical axis parallel to the faces.
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07.60.Ly Interferometers

An ultrahigh vacuum chamber for simultaneous Fourier transform infrared spectroscopy and microgravimetric measurements

Guorong Zhuang, Gary Chottiner, In Tae Bae, Euijin Hwang, and Daniel A. Scherson

Rev. Sci. Instrum. 65, 2494 (1994); http://dx.doi.org/10.1063/1.1144640 (6 pages) | Cited 2 times

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A small UHV chamber that fits in the sample compartment of a commercial Fourier transform infrared spectrometer (IBM‐98, Brucker) has been designed and constructed to acquire reflection/absorption spectra of species adsorbed and/or condensed on metal films vapor deposited in situ on the surface of a quartz‐crystal microbalance (QCM). The QCM is mounted on a variable‐temperature Au‐plated Cu block, which houses a second (reference) QCM, attached in turn to a liquid‐He cold finger. The unique capabilities of this apparatus make it possible to correlate quantitatively various spectral characteristics, including peak widths and intensities, with the absolute mass of adsorbed and/or condensed material per unit area m, or coverage, over a wide range of m and temperatures. Results obtained using tetrahydrofuran (THF) condensed on freshly vapor deposited gold films have shown that the sensitivity of the instrument is sufficient to detect mTHF on the order of a single monolayer. Plots of the intensity of the most prominent THF peak at 1064 cm−1 as a function of mTHF were found to deviate significantly from linearity in the range 0.1<mTHF<2.8 μg/cm2. In addition, the relative intensities of the most prominent THF peaks for even the largest mTHF examined differed markedly from those of bulk‐like THF, an effect that can be attributed to a preferential orientation of THF microcrystals with respect to the underlying substrate. In the case of coverages on the order of one monolayer, such spectral behavior may arise from specific adsorbate/substrate interactions, which can cause a lowering in the molecular symmetry and/or distortions in the structure of the adsorbate. Evidence in support of a Au‐induced THF activation was obtained from independent temperature programmed desorption (TPD) measurements involving perdeuterated THF (TDF) performed in a separate UHV system. In particular, for exposures of about 1.5 L, the TPD spectra for the largest m/e features, i.e., 80, 48, and 30, revealed the presence of a peak centered at a higher temperature (∼180 K) than that found for much larger exposures (120 K).  
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.30.-t Vacuum apparatus
78.66.Qn Polymers; organic compounds
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

High‐speed digitizer/averager data‐acquisition system for Fourier transform electron paramagnetic resonance spectroscopy

Thomas J. Pohida, Hal A. Fredrickson, Rolf G. Tschudin, Joseph F. Fessler, Murali C. Krishna, John Bourg, Frank Harrington, and Sankaran Subramanian

Rev. Sci. Instrum. 65, 2500 (1994); http://dx.doi.org/10.1063/1.1145223 (5 pages) | Cited 16 times

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A high‐speed digitizer/averager data‐acquisition system designed and built as part of a 300‐MHz Fourier transform electron paramagnetic resonance spectrometer is described. There are two key features of the system: (1) the maximum digitizing rate is 300 Msamples/s and (2) a 256‐point free‐induction‐decay signal running summation can be updated in less than 3 μs. At the maximum digitizing rate, the system can sum 65 536 FIDs in 220 ms. The system consists of an analog‐to‐digital converter/adder unit (ADCA) and an IBM compatible personal computer. The ADCA is comprised of a digitizer, high‐speed sample buffers, high‐speed adders/memory, and control hardware. Design techniques, such as parallel processing, utilized to meet the high‐speed performance requirements are described. Trigger and timing signals for the system are derived from the spectrometer. System efficiency, synchronization, and time base stability are demonstrated in the spectrometer at a sampling frequency of 200 MHz. Signal‐to‐noise ratio enhancements are shown using a lithium phthalocyanine test sample.
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87.64.K- Spectroscopy
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
07.05.-t Computers in experimental physics

A simple, quantitative method for measuring pulsed soft x rays

Yoshio Takahama, Jian Du, Takeshi Yanagidaira, and Katsumi Hirano

Rev. Sci. Instrum. 65, 2505 (1994); http://dx.doi.org/10.1063/1.1144641 (5 pages) | Cited 6 times

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A simple quantitative image processing system for pulsed soft x rays with time and spatial resolution is described. The system consists of easily obtained commercial components including a microchannel plate–phosphor screen combination, a charge coupled device camera, an image memory board, and a personal computer. To make a quantitative measurement possible, the image processing is used in conjunction with measurement of the ‘‘phosphor screen current.’’ Performance of the system is examined using a soft x‐ray source generated with a plasma focus device. The order of intensity, ∼1012 photons/s mm2 mrad2 0.01% BW of Ar K lines is observed for about 20 ns from the pinched plasma in which 3% of Ar is added to the 6 Torr H2.
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07.85.-m X- and γ-ray instruments
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

A compact laser interferometer with a piezodriven scanner for metrological measurements in regular SEMs

Takeshi Hatsuzawa, Yoshihisa Tanimura, Kouji Toyoda, Makoto Nara, Syuuji Toyonaga, Shin‐ya Hara, Hirotaka Iwasaki, and Kazuhiko Kondou

Rev. Sci. Instrum. 65, 2510 (1994); http://dx.doi.org/10.1063/1.1144642 (4 pages) | Cited 1 time

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A compact laser interferometer combined with a mechanical scanner has been developed for precise microlinewidth measurements in regular scanning electron microscopes (SEMs). Optical components and a piezodriven mechanical table are integrated on a small disk 130 mm in diameter. The device is so compact that it can be installed in the vacuum chamber of regular SEMs, and useful for accurate and precise measurements based on the laser wavelength—a practical length standard. An optical multipath technique and a differential arrangement of prisms in the interferometer, as well as electrical sensitized technique, realized a high resolution of 0.4 nm (λ/1600). By using the device and a SEM, an absolute linewidth measurement system has been constructed for microlinewidth measurements. To evaluate the system performance, a comparison has been made between a metrological SEM and the system by using a silicon test artifact. The result shows a good agreement between the two systems within an uncertainty of several nanometers. This device can be applied for various types of microscopes such as optical and scanning probing microscopes, and useful as an important scaling device for the calibration of measurement systems.
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07.60.Ly Interferometers
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Design and three dimensional calibration of a measuring scanning tunneling microscope for metrological applications

O. Jusko, X. Zhao, H. Wolff, and G. Wilkening

Rev. Sci. Instrum. 65, 2514 (1994); http://dx.doi.org/10.1063/1.1144643 (5 pages) | Cited 22 times

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A scanning‐tunneling microscope (STM) of the scanning‐sample type with transducers for the measurement of the position in all three axes has been developed. Motions in the X‐, Y‐, and Z‐axis are straight and rectangular to a high degree and the capacitance transducers are calibrated in situ by plane mirror laser‐interferometry. With these qualities as part of the design, the Abbe error may be minimized. X‐Y‐capacitance transducers and X‐Y‐piezo actuators are part of analog servo loops, thus providing positioning in the X‐Y‐plane to a desired coordinate. The STM is mainly built from commercially available parts.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

High‐temperature scanning tunneling microscope with a novel sample heater and interchangeable scan heads

Lowell I. McCann, Richard M. Smalley, and M. A. Dubson

Rev. Sci. Instrum. 65, 2519 (1994); http://dx.doi.org/10.1063/1.1144644 (4 pages)

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A UHV‐compatible, high‐temperature scanning tunneling microscope (STM) with a sample stage incorporating a Si wafer as a resistive heater is described. The design allows for rapid interchange of scanning tubes so that the maximum scan size can be varied. The thermal stability of the microscope is excellent, allowing real‐time studies of faceting and grain growth of metal surfaces at temperatures up to 400 °C with a long term drift of ∼0.05 Å/s.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

An ultrahigh‐vacuum system for STM studies

M. Wörtge, S. Dey, S. Grafström, T. Hagen, J. Kowalski, R. Neumann, and O. Probst

Rev. Sci. Instrum. 65, 2523 (1994); http://dx.doi.org/10.1063/1.1144645 (4 pages)

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An ultrahigh‐vacuum (UHV) system for STM studies is described where a home‐built STM is combined with a novel facility for in situ exchange of samples and tips. Technical details concerning the design of the sample and tip holders and the manipulation and storage equipment are given. For the preparation of organic films a compact evaporation source comprising two ovens with an excellent thermal insulation was constructed. First STM results of a coronene film on graphite and of tungsten diselenide are presented.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
07.30.-t Vacuum apparatus
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Lateral, normal, and longitudinal spring constants of atomic force microscopy cantilevers

Jonas M. Neumeister and William A. Ducker

Rev. Sci. Instrum. 65, 2527 (1994); http://dx.doi.org/10.1063/1.1144646 (5 pages) | Cited 120 times

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For a V‐shaped atomic force microscopy cantilever beam, the spring constants in the three principal directions are given in terms of the beam geometry and material properties. For the lateral stiffness, a closed‐formed expression is presented. Also, the normal and the longitudinal stiffness are obtained from a few simple equations. The results are compared with a finite element study and found to be very accurate. All spring constants depend strongly on the cantilever thickness, which is difficult to measure. In addition, the lateral and longitudinal stiffness are sensitive to the location and the height of the attached pyramid.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Resonance response of scanning force microscopy cantilevers

G. Y. Chen, R. J. Warmack, T. Thundat, D. P. Allison, and A. Huang

Rev. Sci. Instrum. 65, 2532 (1994); http://dx.doi.org/10.1063/1.1144647 (6 pages) | Cited 119 times

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A variational method is used to calculate the deflection and the fundamental and harmonic resonance frequencies of commercial V‐shaped and rectangular atomic force microscopy cantilevers. The effective mass of V‐shaped cantilevers is roughly half that calculated for the equivalent rectangular cantilevers. Damping by environmental gases, including air, nitrogen, argon, and helium, affects the frequency of maximum response and to a much greater degree the quality factor Q. Helium has the lowest viscosity, resulting in the highest Q, and thus provides the best sensitivity in noncontact force microscopy. Damping in liquids is dominated by an increase in effective mass of the cantilever due to an added mass of the liquid being dragged with that cantilever.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Fabrication of optical fiber probes for nanometer‐scale dimensional metrology

H. M. Marchman, J. E. Griffith, and R. W. Filas

Rev. Sci. Instrum. 65, 2538 (1994); http://dx.doi.org/10.1063/1.1144648 (4 pages) | Cited 7 times

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The fabrication of cylindrical probes having diameters as small as 50 nm is described in this article. The planar endface (advantageously oriented perpendicular to the axis of the cylindrical probe) and sharp 90° corners of the end portion of the probe enable accurate measurement of a feature being scanned, even at sudden jumps in the surface. Conical and flaired probes can also be fabricated with variations of this technique. The fabrication techniques described in this article are simple and inexpensive; only a Teflon beaker, optical fiber, etching solution, polymer solution, fiber cleaver, and optical microscope are necessary.
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42.81.Pa Sensors, gyros
42.86.+b Optical workshop techniques
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

A fast extraction instrument of a 1‐GeV electron synchrotron

Chihiro Tsukishima and Shuhei Nakata

Rev. Sci. Instrum. 65, 2542 (1994); http://dx.doi.org/10.1063/1.1144649 (6 pages)

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A kicker magnet and a modulator were developed as a fast extraction instrument of a 1‐GeV electron synchrotron. A 1‐kG pulsed magnetic field was generated by the kicker magnet with the rise time of 40 ns. The ripple of the flattop of the current wave form was less than ±1%, and the shot‐to‐shot fluctuation of the peak current was no more than 0.1%. The modulator consists of two Blumleins in series which operate at a quarter of the charging voltage as compared to a pulse forming network (PFN) type modulator. The damped oscillating wave form of the current could decrease the residual field to be less than 0.5 G. The effect of the residual field of the kicker magnet on the dynamic aperture of the low‐energy electron beam was estimated by the tracking calculation. The result shows the dynamic aperture decreases as the residual field increases. To obtain enough accelerated current, the residual field must be less than 1 G. This restriction could be satisfied by the developed kicker magnet and the modulator. Successful extraction of eight bunches out of 15 bunches in the synchrotron were measured by a wall current monitor located in the extraction transport line.
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29.27.Ac Beam injection and extraction
29.20.dk Synchrotrons

High‐precision harmonic magnetic‐field measurement and analysis using a fixed angle Hall probe

C. S. Hwang, F. Y. Lin, T. H. Huang, G. J. Jan, and P. K. Tseng

Rev. Sci. Instrum. 65, 2548 (1994); http://dx.doi.org/10.1063/1.1144650 (8 pages) | Cited 1 time

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A special theoretical concept involving the harmonic magnetic‐field measurement and analysis method using a fixed angle Hall probe was developed at the Synchrotron Radiation Research Center (SRRC) for measuring as well as analyzing the triple bending achromat magnets of the storage ring. The method can be used to simulate the harmonic magnetic‐field calculation of the two‐dimensional (2D) ‘‘magnet’’ program. This method has a quite simple mechanism. The Hall plate was fixed at a 0° angle with respect to the horizontal plane of magnet to measure only the vertical field. Additionally, the 2D nonlinear least‐square fitting was used to fit the mapping data so as to find the normal and skew multipole field strength. If necessary, the angle of Hall probe could be rotated 90° precisely for measuring the horizontal field. Consequently, the skew dipole field could be obtained. A real‐time Hall‐probe automatic magnetic‐field measurement system was also developed for fulfilling the concept of the harmonic field measurement. Some special mapping trajectories for different kinds of magnets were discussed to match this special theoretical concept with the analysis methodology. This was done so as to obtain the reliable and accurate harmonic field strength. The accuracy and precision of the harmonic field strength measurement and analysis of this method being better than ±0.01% was confirmed by experimental results.
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07.55.-w Magnetic instruments and components

Analysis of the circular polarization rate delivered by an asymmetric wiggler and a two beryl crystal monochromator—Calculation and experiment

D. Lefebvre, Ph. Sainctavit, and C. Malgrange

Rev. Sci. Instrum. 65, 2556 (1994); http://dx.doi.org/10.1063/1.1145224 (6 pages) | Cited 12 times

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Synchrotrons are powerful sources of an x‐ray beam whose polarization state is well defined. The recent apparition of insertion devices able to produce high flux of circularly polarized light has impulsed new fields of solid‐state physics in spectroscopy or diffraction techniques. In this paper, the calculation of circular polarization rates taking into account the characteristics of the synchrotron source and the depolarization effect introduced by the beam monochromatization on crystals is presented here. From measurements of the circular polarization rates by x‐ray magnetic circular dichroism at nickel L2,3 edges, the experimental results are in excellent agreement with the calculations.
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41.50.+h X-ray beams and x-ray optics
78.70.Dm X-ray absorption spectra

Time‐resolved fluorescence using synchrotron radiation excitation: A powered fourth‐harmonic cavity improves pulse stability

Krzysztof Polewski, Stephen L. Kramer, Zbigniew S. Kolber, John G. Trunk, Denise C. Monteleone, and John C. Sutherland

Rev. Sci. Instrum. 65, 2562 (1994); http://dx.doi.org/10.1063/1.1144651 (6 pages) | Cited 2 times

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The pulsed nature or ‘‘time structure’’ of synchrotron radiation from electron storage rings is used to measure the kinetics of the decay of electronically excited states and is particularly useful because the wavelength of excitation can be chosen at will. However, changes in the length of the pulses of radiation from a storage ring resulting from the gradual decrease of current circulating in the ring during the course of a ‘‘fill’’ limit the duration of data collection, and hence photometric sensitivity. A fourth‐harmonic cavity that was recently added to the vacuum ultraviolet (VUV) storage ring at the National Synchrotron Light Source slows the loss of current during a fill, and thus increases the total number of photons produced. When operated in a passive (unpowered) mode, however, the fourth‐harmonic cavity increases both the average width of the photon pulses and the changes in width that occur during a fill, thus reducing the usefulness of the VUV ring in timing experiments. We demonstrate that operating the fourth‐harmonic cavity in an active (powered) mode, while further increasing pulse duration, can stabilize pulse width, thereby restoring timing capabilities.
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41.60.Ap Synchrotron radiation
29.20.db Storage rings and colliders

Fabrication of Wolter‐type x‐ray focusing mirror using epoxy resin

Masaki Hasegawa, Hideki Taira, Tatsuo Harada, Sadao Aoki, and Ken Ninomiya

Rev. Sci. Instrum. 65, 2568 (1994); http://dx.doi.org/10.1063/1.1144652 (6 pages) | Cited 1 time

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We have developed a new fabrication method for Wolter‐type x‐ray focusing mirrors. In this method, a slight gap between the master mandrel and the glass replica produced by vacuum replication was filled with epoxy resin to decrease the roughness and the figure displacement of the mirror surface. The mirror was evaluated both by taking x‐ray microphotographs of No. 1000 and No. 2000 copper meshes with Al Kα and C Kα x rays, and by focusing x rays with several wavelengths using synchrotron radiation. No apparent degradation was found in the micrographs even when we changed the irradiating x rays from the C Kα to the Al Kα. The focused beam profile remained unchanged even at the wavelength of 1.24 nm. The beam size in the meridional plane also decreased to 50% of the beam size focused by a mirror fabricated only by vacuum replication. These results indicate that the present method successfully decreases the surface roughness to less than 6.2 nm (peak‐to‐valley) and improves the figure accuracy of the mirror surface.
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41.50.+h X-ray beams and x-ray optics
07.85.-m X- and γ-ray instruments
42.79.Bh Lenses, prisms and mirrors

Improved optical tomography device

M. Zintl and R. McWilliams

Rev. Sci. Instrum. 65, 2574 (1994); http://dx.doi.org/10.1063/1.1144653 (6 pages) | Cited 9 times

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We report the development of an improved optical tomography diagnostic which measures the velocity‐space distribution of a laboratory plasma in two dimensions. The new device is capable of imaging plasma distributions over a wider range of magnetic fields and plasma column diameters than the previous design, while minimizing the risk of misdiagnosis due to perturbations caused by inserting the device in the plasma. Computer‐aided control of the diagnostic allows a greater number of single‐dimensional scans to be collected in a shorter amount of time, resulting in increased resolution of the reconstructed image while freeing up more time for the user to perform the experiment. Recent data using the new device are presented to show improvement of resolution gained by doubling the number of total scans. Finally, we present a method to identify velocity‐space nonuniformities without the need to reconstruct a complete image.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements

A VUV filter spectrometer with spatial resolution and its plasma diagnostic capabilities

B. Zurro and B. García‐Castañer

Rev. Sci. Instrum. 65, 2580 (1994); http://dx.doi.org/10.1063/1.1144654 (5 pages) | Cited 3 times

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The performance of an original VUV filter spectrometer with spatial resolution is illustrated with typical applications as a plasma diagnostic. The spectrum of the total radiated power obtained in the TJ‐I tokamak, the observation of flattenings on radiation profiles associated with magnetic islands, and the determination of particle confinement times in laser blow‐off impurity injection experiments are highlighted.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.55.Fa Tokamaks, spherical tokamaks
52.25.Vy Impurities in plasmas

Gated x‐ray imager gain correction using a tapered microchannel‐plate stripline

R. G. Watt, J. Oertel, and T. Archeluta

Rev. Sci. Instrum. 65, 2585 (1994); http://dx.doi.org/10.1063/1.1144655 (2 pages) | Cited 8 times

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Gated imagers used to record x‐ray emission in the 1–5 keV range in laser‐plasma interaction experiments have suffered from resistive gain degradation between voltage drive pulse input and output ends of a microchannel‐plate stripline. The reduction in gain as the pulse travels down the strip results in a lower signal‐to‐background ratio in the last image on a strip than in the first image. Compensation for this gain nonuniformity using a tapered stripline in place of the normally straight striplines is discussed.
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52.70.La X-ray and γ-ray measurements
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