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Nanosecond pulsed discharges were applied to an experimental study for exploring the temporal response of a premixed methane/air Bunsen flame with two optical diagnostic methods. The microstructure and dynamic response of flame to the discharges was observed by a schlieren system, and the radial velocity of the shock wave was also measured. Time-resolved optical emission spectroscopy offered intermediate species, their evolutionary timescales and temperature in the plasma region. While the ultrafast heating mechanism of NPD was confirmed, the experimental results also provided lots of critical data for understanding the dynamics of non-equilibrium plasma produced by NPD and performing further numerical simulation. In addition, it also indicates that NPD can stir reactant gases and interact with flame by the generated shock wave and vortices while it produces more reactive plasma than LIBS. It makes the technique may be more suited for applications in combustion enhancement and instability control. [ABSTRACT FROM AUTHOR]

We present X-ray scattering data obtained with the new high temperature setup based on aerodynamic levitation and laser heating. This sample environment has been designed for X-ray scattering experiments up to 3000 °C in static and dynamic regimes. X-ray scattering data with good statistics have been recorded during the glass transition of a molten oxide close to an enstatite chondrite composition (Si24AlFe5Mg22Ca16046) with a 30 ms time resolution. Static measurements on both liquid and glass phases have been also performed with high resolution in both direct and reciprocal spaces. [ABSTRACT FROM AUTHOR]

A novel fiber-optic taper (FOT) coupled with a charge-coupled device (CCD) X-ray detector was developed as a basic module of the simultaneous small- and wide-angle X-ray scattering measurement apparatus at SPring-8 BL45XU. The detector consists of two identical units, each comprising a phosphor (CsI:Tl, 80 μm thickness), a 2:1 demagnifying FOT, and an interline transfer-type CCD as an image sensor. The CCD has a 4000 × 2624 pixel format with a 9 μm pitch, resulting in an effective pixel size of 18 μm at the large end of the FOT. The active area size is 72.0 mm × 47.2 mm in each unit. The image stored in the CCD can be readout through the dual readout channels with 12 bits ADC within 220 ms without binning and 65 ms with 8 × 8 binning, respectively. Moreover, this detector is not necessary to stop the incoming X-rays during the CCD readout and can simultaneously execute both exposure and readout on the CCD with a small dead time of ∼1 μs so that a duty-cycle ratio of almost 100% is achieved. Therefore, it allows the continuous rotation method, where data is collected without stopping the rotation of a sample crystal in macromolecular crystallography. The continuous rotation method was performed with a total data collection time of 12 s for a range of 180° with 1.5° per frame (120 frames). In this paper, the design, performance characteristics, and verification experiment of the detector will be described. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The FEMTO source under construction at the μXAS beamline is designed to enable tunable time-resolved laser/x-ray absorption and diffraction experiments in photochemistry and condensed matter with ps- and sub-ps resolution. The design takes advantage of (1) the highly stable operation of the SLS storage ring, (2) the reliable high harmonic operation of small gap, short period undulators to generate hard x-rays with energy 3–18 keV at 2.4 GeV beam energy, and (3) the progress in high power, high repetition rate fs solid-state laser technology to employ laser/e-beam ‘slicing’ to reach a time resolution of ultimately 100 fs. The source will profit from the inherently synchronized pump (laser I: 100 fs, 2 mJ, 1 kHz) and probe (sliced X-rays, laser II: 50 fs, 5 mJ, 1 kHz) pulses, and from the excellent stability of the SLS storage ring which is operated in top-up mode and controlled by a fast orbit feedback (FOFB). Coherent radiation emitted at THz frequencies by the sliced 100 fs electron bunches will be monitored as on-line cross-correlation signal to keep the laser-electron beam interaction at optimum. The source is designed to provide at 8 keV (100 fs) a monochromized flux of 104 ph/s/0.01% bw (Si crystal monochromator) and 106 ph/s/1.5% bw (multilayer monochromator) at the sample. It is operated in parasitic mode using a hybrid bunch filling pattern. Because of the low intensity measurements are carried out repetitively over many shots using refreshing samples and gated detectors. ‘Diffraction gating’ experiments will be used to characterize the sub-ps X-ray pulses. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

A time-resolved energy-dispersive XAFS (DXAFS) station has been constructed at the bending magnet beamline BL28B2 at SPring-8 to study the local structural changes of materials during chemical reactions and functional processes. The bending magnet source at SPring-8 has a high photon flux above 50 keV. The purpose of this station is to measure DXAFS spectra in a wide energy range from 7 to 50 keV covering K-edges of lanthanides. Its main components are a polychromator with a bent silicon crystal, a mirror to reject higher harmonics, and a position-sensitive detector (PSD). To correspond to a wide energy range, polychromators for Bragg and Laue geometry were developed for the energy range below and above 12 keV, respectively. The PSD used is CCD coupled with a fluorescent screen and lens system. The fluorescent materials and their thickness were optimized for measurement in the x-ray range. Good quality spectra of Ce K-edge (40.5 keV) were obtained with exposures of 360 ms for the standard samples. The present status of the system and some experimental examples are presented in this report. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The configuration and performance of the time-resolved dispersive XAFS (DXAFS) instrument, which has been constructed at the NW2A beamline of PF-AR (KEK), are presented. The DXAFS instrument is mainly composed of a polychromator part, a position control part for sample, and a linear detector part. The Bragg- and Laue-type polychromator crystal (Si(111) or Si(311)) is bent using the holder with fixed bending radius, in which the thermostated water is circulated to prevent the temperature change of crystal due to the heat load. The photodiode array (PDA) with and without phosphor screen is used as the linear X-ray detector, and the minimum exposure time is 2 ms for the 1024-element PDA. The phosphor screen on the PDA detector prevents the damage of the chip especially for high energy X-rays but the existence reduces the energy resolution because of the scattering of the visible light converted on the phosphor. The DXAFS instrument was applied to the mechanistic study of the reduction processes of Cu supported on MFI zeolite, and the intermediate Cu(I) states have been successfully observed during the reduction from Cu(II) to Cu(0). © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

An energy dispersive XAFS (DXAFS) system has been constructed in the second optics hutch at BL14B1 in SPring-8. The system is composed of dispersive optics with a position sensitive detector and is distinguished by covering energy region as high as 80 keV. Below 40 keV, two plane mirrors were utilized in optics to eliminate higher order harmonics and to focus X-rays vertically by mechanically-bent devices. The X-rays diffracted by a polychromator have an energy band width of 0.5 ∼ 1.5 keV, and its spectrum is measured by a CCD camera. Time-resolved XANES spectra were detected near the La K-edge (38.934 keV) with the exposure time of 200 msec during reduction of LaCoO3 at 600°C. The energy resolution of DXAFS spectra near the La K-edge is as good as the conventional XAFS spectrum, and changing the valence state of La was observed during the decomposition process clearly. The Pt K-edge (78.395 keV) DXAFS spectra for a Pt foil, was observed by summing 100 sets of spectrum whose each exposure time is 500 msec. An EXAFS oscillation was extracted up to wavenumber k = 14 Å-1. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Quick-scan is an important technique for the time-resolved experiments to investigate structural variation in rapid chemical reactions or phase transitions under external perturbations in the material science. Our new quick-scan technique, implemented at BL3C1 of PLS, adopts PCI-bus instead of CAMAC based system which was used in the default quick-scan system. It uses a digital I/O and a counter/timer PCI board, which are connected to DCM encoder and to VFC, respectively. Since the trigger signal is originated for a fixed interval from the counter/timer board operating on 80 MHz internal clock, all channels are synchronized without dead or delay time. When the trigger interval was set as 20 ms for each data point, it took ∼100 seconds for each full scan at 7 keV in the range of -200 ∼ 1000 eV, and the energy step sizes corresponded to ∼0.7 eV. Overall performances of the Quick-XAFS technique will be demonstrated through an in situ electrochemical experiment for the Li-ion battery cathode material. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Recent observations of XEOL (X-ray Excited Optical Luminescence) from prototype Ru(II) complexes with excitation energies at various absorption edges of Ru, C and N, and corresponding optical XAFS (photoluminescence yield) are reported. Time-resolved XEOL using the synchrotron light pulse from the Advanced Photon Source in top-up mode and the Canadian Light Source operating in single bunch mode are also noted. These results are discussed in terms of the electronic structures of the complexes, spin-orbit coupling and radiative decay dynamics of the systems. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We demonstrate electromagnetic interaction between distant quantum dots (QDs), as is observed from transient pump-probe differential reflectivity measurements. The QD-exciton lifetime is measured as a function of the probe photon energy and shows a strong resonant behavior with respect to the QD density of states. The observed exciton lifetime spectrum reveals a subradiance-like coupling between the QD, with a 12 times enhancement of the lifetime at the center of the ground state transition. This effect is due to a mutual electromagnetic coupling between resonant QDs, which extends over distances considerably beyond the nearest neighbor QD-QD separation. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Time-resolved, optical pump-probe measurements on a thin Nb0.5Ti0.5N film in applied magnetic fields were performed at the National Synchrotron Light Source, Brookhaven National Laboratory. Despite the presence of normal cores from vortices in the films, we find that the relaxation time of photoexcited quasiparticles does not decrease with magnetic field as one might expect. The change in the far-infrared transmittance due to the applied magnetic field is also discussed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]