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Apr 2012

Volume 83, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 83, 041101 (2012); http://dx.doi.org/10.1063/1.3697599 (19 pages)

Michael A. Duncan

The laser vaporization cluster source in the "cutaway" configuration. The sample rod is mounted from above with a flexible nylon screw in a holding block. The pulsed gas valve is mounted in the stainless steel can (left) and the skimmer is mounted on the opposite wall.

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back to top Optics; Atoms and Molecules; Spectroscopy; Photon Detectors

High passive-stability diode-laser design for use in atomic-physics experiments

Eryn C. Cook, Paul J. Martin, Tobias L. Brown-Heft, Jeffrey C. Garman, and Daniel A. Steck

Rev. Sci. Instrum. 83, 043101 (2012); http://dx.doi.org/10.1063/1.3698003 (9 pages) | Cited 1 time

Online Publication Date: 4 April 2012

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We present the design and performance characterization of an external-cavity diode-laser system optimized for high stability, low passive spectral linewidth, low cost, and ease of in-house assembly. The main cavity body is machined from a single aluminum block for robustness to temperature changes and mechanical vibrations, and features a stiff and light diffraction-grating arm to suppress low-frequency mechanical resonances. The cavity is vacuum sealed, and a custom-molded silicone external housing further isolates the system from acoustic noise and temperature fluctuations. Beam shaping, optical isolation, and fiber coupling are integrated, and the design is easily adapted to many commonly used wavelengths. Resonance data, passive-linewidth data, and passive stability characterization of the new design demonstrate that its performance exceeds published specifications for commercial precision diode-laser systems. The design is fully documented and freely available.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Experimental analysis and computer simulation of a methodology for laser focusing in the solar cell characterization by laser beam induced current

J. Navas, R. Alcántara, C. Fernández-Lorenzo, and J. Martín-Calleja

Rev. Sci. Instrum. 83, 043102 (2012); http://dx.doi.org/10.1063/1.3700214 (10 pages) | Cited 1 time

Online Publication Date: 4 April 2012

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This paper presents a quick methodology for focusing a laser beam on a photoactive surface based on performing a single line scan while simultaneously modifying the laser's position over the surface and the distance between the focusing lens and the active surface. The methodology was tested using the computer simulation technique. Several configurations were computer simulated by programming different experimental situations to discover the situations in which this focusing methodology would provide optimum results. The conclusions obtained from computer simulation methodology were checked by means of experimental tests using several solar cells, such as a thin-film amorphous silicon solar cell, a monocrystalline silicon solar cell, and a polycrystalline silicon solar cell. From the tests performed, we concluded that optimum focusing is achieved in systems in which the laser beam induced current signal generated by the photoactive surface has no large heterogeneities (e.g., fingers or grain boundaries), artefacts, or defects. Thus, the best results are achieved in systems where the surface of the photovoltaic device has a certain degree of homogeneity.
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88.40.jj Silicon solar cells

An integrated ion trap and time-of-flight mass spectrometer for chemical and photo- reaction dynamics studies

Steven J. Schowalter, Kuang Chen, Wade G. Rellergert, Scott T. Sullivan, and Eric R. Hudson

Rev. Sci. Instrum. 83, 043103 (2012); http://dx.doi.org/10.1063/1.3700216 (6 pages) | Cited 2 times

Online Publication Date: 5 April 2012

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We demonstrate the integration of a linear quadrupole trap with a simple time-of-flight mass spectrometer with medium-mass resolution (m/Δm ∼ 50) geared towards the demands of atomic, molecular, and chemical physics experiments. By utilizing a novel radial ion extraction scheme from the linear quadrupole trap into the mass analyzer, a device with large trap capacity and high optical access is realized without sacrificing mass resolution. This provides the ability to address trapped ions with laser light and facilitates interactions with neutral background gases prior to analyzing the trapped ions. Here, we describe the construction and implementation of the device as well as present representative ToF spectra. We conclude by demonstrating the flexibility of the device with proof-of-principle experiments that include the observation of molecular-ion photodissociation and the measurement of trapped-ion chemical reaction rates.
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82.80.Rt Time of flight mass spectrometry
33.15.Ta Mass spectra
37.10.Ty Ion trapping
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
07.75.+h Mass spectrometers

Application of a transmission crystal x-ray spectrometer to moderate-intensity laser driven sources

J. Y. Mao, L. M. Chen, L. T. Hudson, J. F. Seely, L. Zhang, Y. Q. Sun, X. X. Lin, and J. Zhang

Rev. Sci. Instrum. 83, 043104 (2012); http://dx.doi.org/10.1063/1.3700212 (6 pages)

Online Publication Date: 6 April 2012

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In the pursuit of novel, laser-produced x-ray sources for medical imaging applications, appropriate instrumental diagnostics need to be developed concurrently. A type of transmission crystal spectroscopy has previously been demonstrated as a survey tool for sources produced by high-power and high-energy lasers. The present work demonstrates the extension of this method into the study of medium-intensity laser driven hard x-ray sources with a design that preserves resolving power while maintaining high sensitivity. Specifically, spectroscopic measurements of characteristic Kα and Kβ emissions were studied from Mo targets irradiated by a 100 fs, 200 mJ, Ti: sapphire laser with intensity of 1017 W/cm2 to 1018 W/cm2 per shot. Using a transmission curved crystal spectrometer and off-Rowland circle imaging, resolving powers (E/ΔE) of around 300 for Mo Kα2 at 17.37 keV were obtained with an end-to-end spectrometer efficiency of (1.13 ± 0.10) × 10−5. This sensitivity is sufficient for registering x-ray lines with high signal to background from targets following irradiation by a single laser pulse, demonstrating the utility of this method in the study of the development of medium-intensity laser driven x-ray sources.
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07.85.Nc X-ray and γ-ray spectrometers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

The INE-Beamline for actinide science at ANKA

J. Rothe, S. Butorin, K. Dardenne, M. A. Denecke, B. Kienzler, M. Löble, V. Metz, A. Seibert, M. Steppert, T. Vitova, C. Walther, and H. Geckeis

Rev. Sci. Instrum. 83, 043105 (2012); http://dx.doi.org/10.1063/1.3700813 (13 pages) | Cited 4 times

Online Publication Date: 9 April 2012

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Since its inauguration in 2005, the INE-Beamline for actinide research at the synchrotron source ANKA (KIT North Campus) provides dedicated instrumentation for x-ray spectroscopic characterization of actinide samples and other radioactive materials. R&D work at the beamline focuses on various aspects of nuclear waste disposal within INE's mission to provide the scientific basis for assessing long-term safety of a final nuclear waste repository. The INE-Beamline is accessible for the actinide and radiochemistry community through the ANKA proposal system and the European Union Integrated Infrastructure Initiative ACTINET-I3. Experiments with activities up to 1 × 10+6 times the European exemption limit are feasible within a safe but flexible containment concept. Measurements with monochromatic radiation are performed at photon energies varying between ∼2.1 keV (P K-edge) and ∼25 keV (Pd K-edge), including the lanthanide L-edges and the actinide M- and L3-edges up to Cf. The close proximity of the INE-Beamline to INE controlled area labs offers infrastructure unique in Europe for the spectroscopic and microscopic characterization of actinide samples. The modular beamline design enables sufficient flexibility to adapt sample environments and detection systems to many scientific questions. The well-established bulk techniques x-ray absorption fine structure (XAFS) spectroscopy in transmission and fluorescence mode have been augmented by advanced methods using a microfocused beam, including (confocal) XAFS/x-ray fluorescence detection and a combination of (micro-)XAFS and (micro-)x-ray diffraction. Additional instrumentation for high energy-resolution x-ray emission spectroscopy has been successfully developed and tested.
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07.85.Nc X-ray and γ-ray spectrometers

Sensitivity test of a blue-detuned dipole trap designed for parity non-conservation measurements in Fr

D. Sheng, J. Zhang, and L. A. Orozco

Rev. Sci. Instrum. 83, 043106 (2012); http://dx.doi.org/10.1063/1.3701714 (5 pages) | Cited 4 times

Online Publication Date: 11 April 2012

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A dynamic blue-detuned optical dipole trap with stable 87Rb atoms produces a differential ac Stark shift of 18 Hz in the ground state hyperfine transition, and it preserves the ground state hyperfine superpositions for a long coherence time of 180 ms. The trapped atoms undergoing microwave Rabi oscillations are sensitive to a small signal, artificially generated with a second microwave source, phase locked to the first allowing a simple and effective method for determining signal-to-noise ratio limits through interference techniques. This provides an excellent means of calibrating sensitivity in experiments such as our ongoing Fr parity non-conservation measurement.
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37.10.Gh Atom traps and guides
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
31.30.Gs Hyperfine interactions and isotope effects
32.60.+i Zeeman and Stark effects

The soft x-ray instrument for materials studies at the linac coherent light source x-ray free-electron laser

W. F. Schlotter, J. J. Turner, M. Rowen, P. Heimann, M. Holmes, O. Krupin, M. Messerschmidt, S. Moeller, J. Krzywinski, R. Soufli, M. Fernández-Perea, N. Kelez, S. Lee, R. Coffee, G. Hays, et al.

Rev. Sci. Instrum. 83, 043107 (2012); http://dx.doi.org/10.1063/1.3698294 (10 pages) | Cited 10 times

Online Publication Date: 12 April 2012

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The soft x-ray materials science instrument is the second operational beamline at the linac coherent light source x-ray free electron laser. The instrument operates with a photon energy range of 480–2000 eV and features a grating monochromator as well as bendable refocusing mirrors. A broad range of experimental stations may be installed to study diverse scientific topics such as: ultrafast chemistry, surface science, highly correlated electron systems, matter under extreme conditions, and laboratory astrophysics. Preliminary commissioning results are presented including the first soft x-ray single-shot energy spectrum from a free electron laser.
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07.85.-m X- and γ-ray instruments

A photodiode amplifier system for pulse-by-pulse intensity measurement of an x-ray free electron laser

Togo Kudo, Kensuke Tono, Makina Yabashi, Tadashi Togashi, Takahiro Sato, Yuichi Inubushi, Motohiko Omodani, Yoichi Kirihara, Tomohiro Matsushita, Kazuo Kobayashi, Mitsuhiro Yamaga, Sadayuki Uchiyama, and Takaki Hatsui

Rev. Sci. Instrum. 83, 043108 (2012); http://dx.doi.org/10.1063/1.3701713 (6 pages) | Cited 1 time

Online Publication Date: 12 April 2012

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We have developed a single-shot intensity-measurement system using a silicon positive-intrinsic-negative (PIN) photodiode for x-ray pulses from an x-ray free electron laser. A wide dynamic range (103–1011 photons/pulse) and long distance signal transmission (>100 m) were required for this measurement system. For this purpose, we developed charge-sensitive and shaping amplifiers, which can process charge pulses with a wide dynamic range and variable durations (ns-μs) and charge levels (pC-μC). Output signals from the amplifiers were transmitted to a data acquisition system through a long cable in the form of a differential signal. The x-ray pulse intensities were calculated from the peak values of the signals by a waveform fitting procedure. This system can measure 103–109 photons/pulse of ∼10 keV x-rays by direct irradiation of a silicon PIN photodiode, and from 107–1011 photons/pulse by detecting the x-rays scattered by a diamond film using the silicon PIN photodiode. This system gives a relative accuracy of ∼10−3 with a proper gain setting of the amplifiers for each measurement. Using this system, we succeeded in detecting weak light at the developmental phase of the light source, as well as intense light during lasing of the x-ray free electron laser.
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07.60.-j Optical instruments and equipment
78.70.Ck X-ray scattering
85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Full characterization and optimization of a femtosecond ultraviolet laser source for time and angle-resolved photoemission on solid surfaces

J. Faure, J. Mauchain, E. Papalazarou, W. Yan, J. Pinon, M. Marsi, and L. Perfetti

Rev. Sci. Instrum. 83, 043109 (2012); http://dx.doi.org/10.1063/1.3700190 (7 pages) | Cited 7 times

Online Publication Date: 13 April 2012

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A novel experimental apparatus for time and angle-resolved photoemission on solid surfaces is presented. A 6.28 eV laser source operating at 250 kHz repetition rate is obtained by frequency mixing in nonlinear beta barium borate crystals. This UV light source has a high photon flux of 1013 photons/s with relatively low number of photons/pulse so that Fermi surface mapping over a wide region of the Brillouin zone is possible while mitigating space charge effects. The UV source has been fully characterized spatially, spectrally, and temporally. Its potential for time and angle-resolved photoemission is demonstrated through Fermi surface mapping and photoexcited electron dynamics in Bismuth. True femtosecond time resolution <65 fs is obtained while the energy resolution of 70 meV appears to be mainly limited by the laser bandwidth.
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78.47.D- Time resolved spectroscopy (>1 psec)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
77.22.Jp Dielectric breakdown and space-charge effects

Microcontroller based resonance tracking unit for time resolved continuous wave cavity-ringdown spectroscopy measurements

Ondrej Votava, Milan Mašát, Alexander E. Parker, Chaithania Jain, and Christa Fittschen

Rev. Sci. Instrum. 83, 043110 (2012); http://dx.doi.org/10.1063/1.3698061 (7 pages) | Cited 2 times

Online Publication Date: 18 April 2012

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We present in this work a new tracking servoloop electronics for continuous wave cavity-ringdown absorption spectroscopy (cw-CRDS) and its application to time resolved cw-CRDS measurements by coupling the system with a pulsed laser photolysis set-up. The tracking unit significantly increases the repetition rate of the CRDS events and thus improves effective time resolution (and/or the signal-to-noise ratio) in kinetics studies with cw-CRDS in given data acquisition time. The tracking servoloop uses novel strategy to track the cavity resonances that result in a fast relocking (few ms) after the loss of tracking due to an external disturbance. The microcontroller based design is highly flexible and thus advanced tracking strategies are easy to implement by the firmware modification without the need to modify the hardware. We believe that the performance of many existing cw-CRDS experiments, not only time-resolved, can be improved with such tracking unit without any additional modification to the experiment.
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07.60.Rd Visible and ultraviolet spectrometers
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
82.80.Dx Analytical methods involving electronic spectroscopy
07.07.Tw Servo and control equipment; robots
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques

Measurement and control of residual amplitude modulation in optical phase modulation

Liufeng Li, Fang Liu, Chun Wang, and Lisheng Chen

Rev. Sci. Instrum. 83, 043111 (2012); http://dx.doi.org/10.1063/1.4704084 (10 pages) | Cited 4 times

Online Publication Date: 19 April 2012

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Residual amplitude modulation is one of the major sources of instability in ultra-sensitive optical detections based on frequency modulation. Using a MgO·LiNbO3 electro-optic crystal, we systematically measure the temperature and polarization dependence of residual amplitude modulation and our experimental results are in good agreement with a previous theoretical analysis. After optical phase modulation, two independent arms including optical detection and frequency demodulation are employed to closely examine the instability of the residual amplitude modulation. Residual amplitude modulation below 25 ppm is obtained with an active cancellation scheme in which the crystal temperature is varied so as to zero the baseline drifts with different origins. Possible improvements for better suppression and stability are discussed.
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07.60.-j Optical instruments and equipment

A high resolution and large solid angle x-ray Raman spectroscopy end-station at the Stanford Synchrotron Radiation Lightsource

D. Sokaras, D. Nordlund, T.-C. Weng, R. Alonso Mori, P. Velikov, D. Wenger, A. Garachtchenko, M. George, V. Borzenets, B. Johnson, Q. Qian, T. Rabedeau, and U. Bergmann

Rev. Sci. Instrum. 83, 043112 (2012); http://dx.doi.org/10.1063/1.4704458 (9 pages) | Cited 8 times

Online Publication Date: 19 April 2012

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We present a new x-ray Raman spectroscopy end-station recently developed, installed, and operated at the Stanford Synchrotron Radiation Lightsource. The end-station is located at wiggler beamline 6-2 equipped with two monochromators-Si(111) and Si(311) as well as collimating and focusing optics. It consists of two multi-crystal Johann type spectrometers arranged on intersecting Rowland circles of 1 m diameter. The first one, positioned at the forward scattering angles (low-q), consists of 40 spherically bent and diced Si(110) crystals with 100 mm diameters providing about 1.9% of 4π sr solid angle of detection. When operated in the (440) order in combination with the Si (311) monochromator, an overall energy resolution of 270 meV is obtained at 6462.20 eV. The second spectrometer, consisting of 14 spherically bent Si(110) crystal analyzers (not diced), is positioned at the backward scattering angles (high-q) enabling the study of non-dipole transitions. The solid angle of this spectrometer is about 0.9% of 4π sr, with a combined energy resolution of 600 meV using the Si (311) monochromator. These features exceed the specifications of currently existing relevant instrumentation, opening new opportunities for the routine application of this photon-in/photon-out hard x-ray technique to emerging research in multidisciplinary scientific fields, such as energy-related sciences, material sciences, physical chemistry, etc.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.85.Nc X-ray and γ-ray spectrometers
41.85.Si Particle beam collimators, monochromators

An improved microfluidics approach for monitoring real-time interaction profiles of ultrafast molecular recognition

Subrata Batabyal, Surajit Rakshit, Shantimoy Kar, and Samir Kumar Pal

Rev. Sci. Instrum. 83, 043113 (2012); http://dx.doi.org/10.1063/1.4704839 (6 pages) | Cited 2 times

Online Publication Date: 23 April 2012

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Our study illustrates the development of a microfluidics (MF) platform combining fluorescence microscopy and femtosecond/picosecond-resolved spectroscopy to investigate ultrafast chemical processes in liquid-phase diffusion-controlled reactions. By controlling the flow rates of two reactants in a specially designed MF chip, sub-100 ns time resolution for the exploration of chemical intermediates of the reaction in the MF channel has been achieved. Our system clearly rules out the possibility of formation of any intermediate reaction product in a so-called fast ionic reaction between sodium hydroxide and phenolphthalein, and reveals a microsecond time scale associated with the formation of the reaction product. We have also used the developed system for the investigation of intermediate states in the molecular recognition of various macromolecular self-assemblies (micelles) and genomic DNA by small organic ligands (Hoechst 33258 and ethidium bromide). We propose our MF-based system to be an alternative to the existing millisecond-resolved “stopped-flow” technique for a broad range of time-resolved (sub-100 ns to minutes) experiments on complex chemical/biological systems.
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07.10.Cm Micromechanical devices and systems
47.60.Dx Flows in ducts and channels
47.70.Fw Chemically reactive flows
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.80.Ek Mechanical and micromechanical techniques
87.80.St Genomic techniques

Tunable optical tweezers for wavelength-dependent measurements

Brooke Hester, Gretchen K. Campbell, Carlos López-Mariscal, Carly Levin Filgueira, Ryan Huschka, Naomi J. Halas, and Kristian Helmerson

Rev. Sci. Instrum. 83, 043114 (2012); http://dx.doi.org/10.1063/1.4704373 (8 pages)

Online Publication Date: 23 April 2012

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Optical trapping forces depend on the difference between the trap wavelength and the extinction resonances of trapped particles. This leads to a wavelength-dependent trapping force, which should allow for the optimization of optical tweezers systems, simply by choosing the best trapping wavelength for a given application. Here we present an optical tweezer system with wavelength tunability, for the study of resonance effects. With this system, the optical trap stiffness is measured for single trapped particles that exhibit either single or multiple extinction resonances. We include discussions of wavelength-dependent effects, such as changes in temperature, and how to measure them.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
07.60.-j Optical instruments and equipment

A rigid, monolithic but still scannable cavity ring-down spectroscopy cell

Yongxin Tang, Shaoyue L. Yang, and Kevin K. Lehmann

Rev. Sci. Instrum. 83, 043115 (2012); http://dx.doi.org/10.1063/1.3700978 (7 pages) | Cited 1 time

Online Publication Date: 25 April 2012

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A novel cell for continuous wave cavity ring-down spectroscopy (cw-CRDS) is described and tested. The cell is monolithic and maintains a rigid alignment of the two cavity mirrors. Two high-resolution and high-force piezoelectric transducers are used to sweep the length of the cell by elastic deformation of the 2.86 cm outer diameter stainless steel tube that makes up the body of the cell. The cavity length is scanned more than 1/2 wavelength of the near-IR light used, which ensures that at least one TEM00 mode of the cavity will pass through resonance with the laser. This allows the use of a frequency-locked-laser cw-CRDS technique, which increases the precision of the measurements compared to the alternative of sweeping the laser more than one free spectral range of the cavity. The performance of the cell is demonstrated by using it to detect the absorption spectrum of methane (CH4) at the wavenumber regions of around 6051.8–6057.7 cm−1.
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43.38.Fx Piezoelectric and ferroelectric transducers
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Two-dimensional imaging velocity interferometry: Data analysis techniques

David J. Erskine, R. F. Smith, C. A. Bolme, P. M. Celliers, and G. W. Collins

Rev. Sci. Instrum. 83, 043116 (2012); http://dx.doi.org/10.1063/1.4704840 (10 pages)

Online Publication Date: 27 April 2012

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We describe data analysis procedures for an emerging interferometric technique for measuring target motion across a two-dimensional image at a moment in time, i.e., a snapshot 2D-VISAR. Conventional VISARs (velocity interferometer system for any reflector) are commonly used in shock physics to measure velocity history at a single point or many points across a line on target. These however are not recorded in two-dimensions and cannot be used with ultrashort pulsed illumination because the coherence length is smaller than the interferometer delay, preventing fringe formation. In our scheme, dual matched interferometers allow use of low- or incoherent illumination such as ultrashort laser pulses to freeze motion of target, allowing use of slow CCD imaging detectors. Quadrature phase recording and push-pull data analysis simultaneously produces an ordinary nonfringing reflectivity image and a fringing image. The latter is converted into a 2D-phase map which is proportional to target velocity. Example data on shocked crystalline [111] Si shows incipient features of ∼50 μm scale.
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07.60.Ly Interferometers
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
06.30.Gv Velocity, acceleration, and rotation
42.79.Pw Imaging detectors and sensors

Design of a beam emission spectroscopy diagnostic for negative ions radio frequency source SPIDER

B. Zaniol, R. Pasqualotto, and M. Barbisan

Rev. Sci. Instrum. 83, 043117 (2012); http://dx.doi.org/10.1063/1.4705739 (8 pages) | Cited 3 times

Online Publication Date: 30 April 2012

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A facility will be built in Padova (Italy) to develop, commission, and optimize the neutral beam injection system for ITER. The full scale prototype negative ion radio frequency source SPIDER, featuring up to 100 kV acceleration voltage, includes a full set of diagnostics, required for safe operation and to measure and optimize the beam performance. Among them, beam emission spectroscopy (BES) will be used to measure the line integrated beam uniformity, divergence, and neutralization losses inside the accelerator (stripping losses). In the absence of the neutralization stage, SPIDER beam is mainly composed by H− or D− particles, according to the source filling gas. The capability of a spectroscopic diagnostic of an H− (D−) beam relies on the interaction of the beam particles with the background gas particles. The BES diagnostic will be able to acquire the Hα (Dα) spectrum from up to 40 lines of sight. The system is capable to resolve stripping losses down to 2 keV and to measure beam divergence with an accuracy of about 10%. The design of this diagnostic is reported, with discussion of the layout and its components, together with simulations of the expected performance.
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29.27.Fh Beam characteristics
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
29.25.Ni Ion sources: positive and negative
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