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Jan 2007

Volume 78, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 78, 011302 (2007); http://dx.doi.org/10.1063/1.2431313 (39 pages)

R. D. Gehrz, T. L. Roellig, M. W. Werner, G. G. Fazio, J. R. Houck, F. J. Low, G. H. Rieke, B. T. Soifer, D. A. Levine, and E. A. Romana
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Photonic Doppler velocimetry of laser-ablated ultrathin metals

A. R. Valenzuela, G. Rodriguez, S. A. Clarke, and K. A. Thomas

Rev. Sci. Instrum. 78, 013101 (2007); http://dx.doi.org/10.1063/1.2424434 (7 pages) | Cited 12 times

Online Publication Date: 4 January 2007

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Obtaining velocity information from the interaction of a laser pulse on a metal layer provides insight into the rapid dynamics of material removal and plasma plume physics during ablation. A traditional approach involves using a velocity interferometer system for any reflector (VISAR) on a reflective metal surface. However, when the target is a thin metal layer, the cohesion of the surface is quickly lost resulting in a large spread of particle velocities that cannot be easily resolved by VISAR. This is due to material ejection“confusing” the VISAR measurement surface, effectively washing out the spatial fringe visibility in the VISAR interferometer. A new heterodyne-based optical velocimeter method is the photonic Doppler velocimeter (PDV). Because PDV tracks motion in a frequency encoded temporal electro-optical signal, velocity information is preserved and allows for multiple velocity components to be recorded simultaneously. The challenge lies in extracting PDV velocity information at short (nanosecond) laser ablation time scales with rapidly varying heterodyne beats by using electronic, optical, and analytical techniques to recover the velocity information from a fleeting signal. Here we show how we have been able to obtain velocity information on the nanosecond time scale and are able to compare it to hydrodynamic simulations. Also, we examine refinements to our PDV system by increasing the bandwidth, utilizing different probes, and sampling different analysis techniques.
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06.30.Gv Velocity, acceleration, and rotation
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Large atom number Bose-Einstein condensate of sodium

K. M. R. van der Stam, E. D. van Ooijen, R. Meppelink, J. M. Vogels, and P. van der Straten

Rev. Sci. Instrum. 78, 013102 (2007); http://dx.doi.org/10.1063/1.2424439 (10 pages) | Cited 15 times

Online Publication Date: 4 January 2007

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We describe the setup to create a large Bose-Einstein condensate containing more than 120×106 atoms. In the experiment a thermal beam is slowed by a Zeeman slower and captured in a dark-spot magneto-optical trap (MOT). A typical dark-spot MOT in our experiments contains 2.0×1010 atoms with a temperature of 320 μK and a density of about 1.0×1011 atoms/cm3. The sample is spin polarized in a high magnetic field before the atoms are loaded in the magnetic trap. Spin polarizing in a high magnetic field results in an increase in the transfer efficiency by a factor of 2 compared to experiments without spin polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50 s by evaporative cooling. To suppress the three-body losses at the end of the evaporation, the magnetic trap is decompressed in the axial direction.
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37.10.De Atom cooling methods
37.10.Gh Atom traps and guides
32.60.+i Zeeman and Stark effects
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

High throughput spectrometer for fast localized Doppler measurements

D. Craig, D. J. Den Hartog, D. A. Ennis, S. Gangadhara, and D. Holly

Rev. Sci. Instrum. 78, 013103 (2007); http://dx.doi.org/10.1063/1.2424450 (6 pages) | Cited 12 times

Online Publication Date: 4 January 2007

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A new custom-built duo spectrometer has been commissioned for fast localized Doppler measurements of plasma ions in the Madison Symmetric Torus. The instrument combines very high optical throughput (transmission efficiency of 6% and etendue of 0.80 mm2 sr divided into two simultaneous measurements) with good resolution (λ/Δλ = 5600). The design is a double grating variant of the Czerny-Turner layout and has been carefully optimized for fast (100 kHz) measurements of the C VI line at 343.4 nm. The instrument is currently being applied for high speed charge exchange recombination spectroscopy measurements.
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07.60.Rd Visible and ultraviolet spectrometers
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
42.79.Dj Gratings

Reflection of attosecond x-ray free electron laser pulses

Stefan P. Hau-Riege and Henry N. Chapman

Rev. Sci. Instrum. 78, 013104 (2007); http://dx.doi.org/10.1063/1.2428271 (3 pages) | Cited 2 times

Online Publication Date: 10 January 2007

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In order to utilize hard x-ray free electron lasers (XFEL’s) when they are extended to attosecond pulse lengths, it is necessary to choose optical elements with minimal response time. Specular grazing-incidence optics made of low-Z materials are popular candidates for reflectors since they are likely to withstand x-ray damage and provide sufficiently large reflectivities. Using linear-optics reflection theory, we calculated the transient reflectivity of a delta-function electric pulse from a homogenous semi-infinite medium as a function of angle of incidence for s- and p-polarized light. We specifically considered the pulse response of beryllium, diamond, silicon carbide, and silicon, all of which are of relevance to the XFEL’s that are currently being built. We found that the media emit energy in a damped oscillatory way, and that the impulse-response times are shorter than 0.3 fs for normal incidence. For grazing incidence, the impulse-response time is substantially shorter, making grazing-incidence mirrors a good choice for deep subfemtosecond reflective optics.
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41.60.Cr Free-electron lasers
42.55.Vc X- and γ-ray lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
07.85.-m X- and γ-ray instruments
41.50.+h X-ray beams and x-ray optics
42.79.Bh Lenses, prisms and mirrors

Mode-locking optimization with a real-time feedback system in a Nd:yttrium lithium fluoride laser cavity

C. Marengoni, F. Canova, D. Batani, R. Benocci, M. Librizzi, V. Narayanan, M. Gomareschi, G. Lucchini, A. Kilpio, E. Shashkov, I. Stuchebrukhov, V. Vovchenko, V. Chernomyrdin, I. Krasuyk, T. Hall, et al.

Rev. Sci. Instrum. 78, 013105 (2007); http://dx.doi.org/10.1063/1.2356853 (8 pages)

Online Publication Date: 17 January 2007

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We present a control system, which allows an automatic optimization of the pulse train stability in a mode-locked laser cavity. In order to obtain real-time corrections, we chose a closed loop approach. The control variable is the cavity length, mechanically adjusted by gear system acting on the rear cavity mirror, and the controlled variable is the envelope modulation of the mode-locked pulse train. Such automatic control system maintains the amplitude of the mode-locking pulse train stable within a few percent rms during the working time of the laser. Full implementation of the system on an Nd:yttrium lithium fluoride actively mode-locked laser is presented.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.79.Bh Lenses, prisms and mirrors
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Discrete retardance second harmonic generation ellipsometry

Christopher J. Dehen, R. Michael Everly, Ryan M. Plocinik, Hartmut G. Hedderich, and Garth J. Simpson

Rev. Sci. Instrum. 78, 013106 (2007); http://dx.doi.org/10.1063/1.2400011 (7 pages) | Cited 2 times

Online Publication Date: 17 January 2007

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A new instrument was constructed to perform discrete retardance nonlinear optical ellipsometry (DR-NOE). The focus of the design was to perform second harmonic generation NOE while maximizing sample and application flexibility and minimizing data acquisition time. The discrete retardance configuration results in relatively simple computational algorithms for performing nonlinear optical ellipsometric analysis. NOE analysis of a disperse red 19 monolayer yielded results that were consistent with previously reported values for the same surface system, but with significantly reduced acquisition times.
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07.60.Fs Polarimeters and ellipsometers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.15.Eq Optical system design

Stable, mode-matched, medium-finesse optical cavity incorporating a microcantilever mirror: Optical characterization and laser cooling

J. G. E. Harris, B. M. Zwickl, and A. M. Jayich

Rev. Sci. Instrum. 78, 013107 (2007); http://dx.doi.org/10.1063/1.2405373 (4 pages) | Cited 13 times

Online Publication Date: 22 January 2007

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A stable optical resonator has been built using a 30-μm-wide, metal-coated microcantilever as one mirror. The second mirror was a 12.7-mm-diameter concave dielectric mirror. By positioning the two mirrors 75 mm apart in a near-hemispherical configuration, a Fabry-Pérot cavity with a finesse equal to 55 was achieved. The finesse was limited by the optical loss in the cantilever’s metal coating; diffraction losses from the small mirror were negligible. The cavity achieved passive laser cooling of the cantilever’s Brownian motion.
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42.79.Bh Lenses, prisms and mirrors
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

New developments for an electron impact (e,2e)/(e,3e) spectrometer with multiangle collection and multicoincidence detection

F. Catoire, E. M. Staicu-Casagrande, A. Lahmam-Bennani, A. Duguet, A. Naja, X. G. Ren, B. Lohmann, and L. Avaldi

Rev. Sci. Instrum. 78, 013108 (2007); http://dx.doi.org/10.1063/1.2428275 (8 pages) | Cited 19 times

Online Publication Date: 22 January 2007

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We describe new developments aimed to extend the capabilities and the sensitivity of the (e,2e)∕(e,3e) multicoincidence spectrometer at Orsay University [ Duguet et al., Rev. Sci. Instrum. 69, 3524 (1998) ]. The spectrometer has been improved by the addition of a third multiangle detection channel for the fast “scattered” electron. The present system is unique in that it is the only system which combines three toroidal analyzers all equipped with position sensitive detectors, thus allowing the triple coincidence detection of the three electrons present in the final state of an electron impact double ionization process. The setup allows measurement of the angular and energy distributions of the ejected electrons over almost the totality of the collision plane as well as that of the scattered electron over a large range of scattering angles in the forward direction. The resulting gain in sensitivity ( ∼ 25) has rendered feasible a whole class of experiments which could not be otherwise envisaged. The setup is described with a special emphasis on the new toroidal analyzer, data acquisition hardware, and data analysis procedures. The performances are illustrated by selected results of (e,2e) and (e,3e) experiments on the rare gases.
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07.81.+a Electron and ion spectrometers
34.80.Dp Atomic excitation and ionization
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)

Optimized end station and operating protocols for reflection extended x-ray absorption fine structure (ReflEXAFS) investigations of surface structure at the European Synchrotron Radiation Facility beamline BM29

Víctor López-Flores, Stuart Ansell, Daniel T. Bowron, Sofía Díaz-Moreno, Silvia Ramos, and Adela Muñoz-Páez

Rev. Sci. Instrum. 78, 013109 (2007); http://dx.doi.org/10.1063/1.2409763 (12 pages) | Cited 6 times

Online Publication Date: 22 January 2007

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The development of the capability to engineer the surface properties of materials to match specific requirements demands high quality surface characterization techniques. The ideal tool should provide chemically specific structural characterization as well as surface sensitivity and depth profiling. Ideally the characterization method should also be applicable to systems both with and without long range order. X-ray absorption spectroscopy fine structure, when using the standard transmission detection system, provides all this information with the significant exception of surface sensitivity. In contrast, by detecting the reflected instead of the transmitted beam, it encompasses all these requirements because when the incident beam impinges onto a sample surface at glancing angles, in conditions close to the total reflection, only the outermost regions of the system under study are sampled. Such a technique provides information about the local structure as a function of depth as well as thin layer structure in the case of layered samples. Although it is potentially the ideal tool to study surface modified materials, experimental difficulties have hampered its widespread use in the fields of surface and materials sciences. As a solution to the experimental challenges, we provide a detailed description of an appropriate experimental station, the sample requirements, the measuring protocols, and software routines needed to optimize the collection of the data. To illustrate the capabilities of the technique the results obtained for a model multilayer sample are presented and analyzed under the total external reflection approximation.
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07.85.Nc X-ray and γ-ray spectrometers
78.70.Dm X-ray absorption spectra
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
78.66.Bz Metals and metallic alloys

High-temperature multipass cell for infrared spectroscopy of heated gases and vapors

R. Bartlome, M. Baer, and M. W. Sigrist

Rev. Sci. Instrum. 78, 013110 (2007); http://dx.doi.org/10.1063/1.2432249 (6 pages) | Cited 5 times

Online Publication Date: 22 January 2007

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In absorption spectroscopy, infrared spectra of heated gases or condensed samples in the vapor phase are usually recorded with a single pass heated gas cell. This device exhibits two orders of magnitude lower sensitivity than the high-temperature multipass cell presented in this article. Our device is a novel type of compact long path absorption cell that can withstand aggressive chemicals in addition to temperatures up to 723 K. The construction of the cell and its technical features are described in detail, paying special attention to the mechanisms that compensate for thermal expansion and that allow the user to vary the optical path length under any thermal or vacuum condition. The cell may be used with a laser source or implemented within a Fourier transform infrared spectrometer. Its design is compatible with optical arrangements using astigmatic mirrors or spherical mirrors in a Herriott configuration. Here we implement a homebuilt Herriott-type cell with a total optical path length of up to 35 m. In order to demonstrate the feasibility of the cell, methane and water vapor absorption lines showing dissimilar temperature effects on line intensity were recorded with the help of a mid-infrared laser source tunable between 3 and 4 μm. Emphasis is put on lines that are too weak to be recorded with a single pass cell.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
82.80.Dx Analytical methods involving electronic spectroscopy
07.20.Ka High-temperature instrumentation; pyrometers

Photoreflectance spectroscopy with a step-scan Fourier-transform infrared spectrometer: Technique and applications

Jun Shao, Wei Lu, Fangyu Yue, Xiang Lü, Wei Huang, Zhifeng Li, Shaoling Guo, and Junhao Chu

Rev. Sci. Instrum. 78, 013111 (2007); http://dx.doi.org/10.1063/1.2432269 (8 pages) | Cited 15 times

Online Publication Date: 24 January 2007

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We report on a new technique of realizing photoreflectance (PR) spectroscopy with a step-scan Fourier-transform infrared spectrometer. The experimental configuration is briefly described and a detailed theoretical analysis is conducted. The results reveal two distinct features of this PR technique that (i) the PR related signal is enhanced by a factor of at least 100 relative to those of the conventional PR techniques and (ii) the unwanted spurious signal introduced by either diffuse reflected pump beam or pump-beam induced material’s photoluminescence reaching the photodetector of the PR configuration is eliminated without any special consideration of normalization for deducing the final PR spectrum. Applications are given as examples in the study of GaNAs/GaAs single quantum wells and GaInP/AlGaInP multiple quantum wells, respectively, under different pump-beam excitation energy and/or power. The experimental results approve the theoretically predicted features and illustrate the possibility of investigating weak PR features by using high pump-beam power. A brief comparison of this technique with the conventional PR techniques is given, and the extendibility of this technique to long-wavelength spectral regions is pointed out.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
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