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Photon Energy (photon + energy)
Terms modified by Photon Energy Selected AbstractsPhotoionization of C2F4 in the VUV regionINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2006A. S. Dos Santos Abstract We report calculated cross sections and asymmetry parameters for photoionization out of the outermost valence orbital 2b2u of C2F4 for photon energies ranging from near-threshold to 19 eV. We also report asymmetry parameters for photoionization out of the eight outermost orbitals of C2F4 at the He I radiation energy (21.23 eV). The iterative Schwinger variational method at the exact static-exchange level is used to obtain the continuum photoelectron orbitals. Our calculated results are compared with experimental results available in the literature. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] A new technique for angle-dispersive powder diffraction using an energy-dispersive setup and synchrotron radiationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2004Yanbin Wang A new diffraction technique for combined angle- and energy-dispersive structural analysis and refinement (CAESAR), by collecting angle-dispersive data using a solid-state detector (SSD) and white synchrotron radiation, is introduced. By step scanning a well calibrated SSD over a limited 2, range, a series of one-dimensional energy-dispersive data (intensity versus energy) are obtained as a function of 2,. The entire intensity (Int) data set consists of several thousand channels covering a range of photon energies, E (up to ,150,keV), at each of the ,1000 2, steps, forming a 2,4 mega-element two-dimensional array, Int(E, 2,). These intensity data are then regrouped according to photon energies, which are defined in the multichannel SSD as individual channels, yielding a large number of intensity versus 2, (angle-dispersive) data sets, Int(E = const., 2,), each of which corresponds to a given photon energy or wavelength. The entire data set, selected subsets or composite scans can be used for multiple data set Rietveld refinement. Data collected both on ,-Al2O3 (a NIST diffraction standard) at ambient conditions and on a mixture of MgO and Au at high pressure were analyzed using the Rietveld technique, with varying schemes of data treatment. Furthermore, it is demonstrated that data within certain energy bands (,E/E = ±10%) may be binned together to improve counting statistics in a composite angle-dispersive scan, even when collected with much coarser scan steps of 0.1 or 0.2°. This technique is useful for high-pressure as well as general purpose powder diffraction studies that have limited X-ray access to the sample using synchrotron radiation. Several advantages are discussed. [source] Photoionization cross sections with optimized orbital exponents within the complex basis function methodJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2008Masato Morita Abstract We show a new direction to expand the applicability of the complex basis function method for calculating photoionization cross sections through the imaginary part of the frequency-dependent polarizability. Based on the variational stability of the frequency-dependent polarizability, we made nonlinear optimizations of complex orbital exponents in basis functions representing continuum wave functions, and obtained fairly accurate results for H atom with only one or two complex basis functions particularly with dipole velocity gauge. Results were almost independent of whether Slater-type or Gaussian-type orbitals are used, implying the applicability to general many electron problems. The method was also applied to the 1S (1s)2 , 1P (1s)1(kp)1 cross section of He atom and the optimized complex orbital exponents were related to those of H atom through the scaling property. The nonlinear optimizations have converged smoothly and the cross sections were in excellent agreement with experiment throughout wide photon energies, which suggest the effectiveness of the approach for many-electron systems. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Photoionization studies on various quinones by an infrared laser desorption/tunable VUV photoionization TOF mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2008Yang Pan Abstract Photoionization and dissociative photoionization characters of six quinones, including 1,2-naphthoquinone (1,2-NQ), 1,4-naphthoquinone (1,4-NQ), 9,10-phenanthroquinone (PQ), 9,10-anthraquinone (AQ), benz[a]- anthracene-7,12-dione (BAD) and 1,2-acenaphthylenedione (AND) have been studied with an infrared laser desorption/tunable synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (IR LD/VUV PIMS) technique. Mass spectra of these compounds are obtained at different VUV photon energies. Consecutive losses of two carbon monoxide (CO) groups are found to be the main fragmentation pathways for all the quinones. Detailed dissociation processes are discussed with the help of ab initio B3LYP calculations. Ionization energies (IEs) of these quinones and appearance energies (AEs) of major fragments are obtained by measuring the photoionization efficiency (PIE) spectra. The experimental results are in good agreement with the theoretical data. Copyright © 2008 John Wiley & Sons, Ltd. [source] Concept of a spectrometer for resonant inelastic X-ray scattering with parallel detection in incoming and outgoing photon energiesJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2010V. N. Strocov A spectrometer for resonant inelastic X-ray scattering (RIXS) is proposed where imaging and dispersion actions in two orthogonal planes are combined to deliver a full two-dimensional map of RIXS intensity in one shot with parallel detection at incoming hvin and outgoing hvout photon energies. Preliminary ray-tracing simulations with a typical undulator beamline demonstrate a resolving power well above 11000 with both hvin and hvout near 930,eV, with a vast potential for improvement. Combining this instrument , nicknamed hv2 spectrometer , with an X-ray free-electron laser source simplifies its technical implementation and enables efficient time-resolved RIXS experiments. [source] Bond cutting in K-doped tris(8-hydroxyquinoline) aluminiumJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2008Hsin-Han Lee A series of Al 2p, K 2p, O 1s and N 1s core-level spectra have been used to characterize the interaction between potassium (K) and tris(8-hydroxyquinoline) aluminium (Alq3) molecules in the K-doped Alq3 layer. All core-level spectra were tuned to be very surface sensitive in selecting various photon energies provided by the wide-range beamline at the National Synchrotron Radiation Research Center, Taiwan. A critical K concentration (x = 2.4) exists in the K-doped Alq3 layer, below which the K-doped atoms generate a strained environment near the O and N atoms within 8-quinolinoline ligands. This creates new O 1s and N 1s components on the lower binding-energy side. Above the critical K coverage, the K-doped atoms attach the O atoms in the Al,O,C bonds next to the phenoxide ring and replace Al,O,C bonds by forming K,O,C bonds. An Alq3 molecule is disassembled into Alq2 and Kq by bond cutting and bond formation. The Alq2 molecule can be further dissociated into Alq, or even Al, through subsequent formations of Kq. [source] Compton scattering of Fe K, lines in magnetic cataclysmic variablesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008A. L. McNamara ABSTRACT Compton scattering of X-rays in the bulk flow of the accretion column in magnetic cataclysmic variables (mCVs) can significantly shift photon energies. We present Monte Carlo simulations based on a non-linear algorithm demonstrating the effects of Compton scattering on the H-, He-like and neutral Fe K, lines produced in the post-shock region of the accretion column. The peak line emissivities of the photons in the post-shock flow are taken into consideration and frequency shifts due to Doppler effects are also included. We find that line profiles are most distorted by Compton scattering effects in strongly magnetized mCVs with a low white dwarf mass and high mass accretion rate and which are viewed at an oblique angle with respect to the accretion column. The resulting line profiles are most sensitive to the inclination angle. We have also explored the effects of modifying the accretion column width and using a realistic emissivity profile. We find that these do not have a significant overall effect on the resulting line profiles. A comparison of our simulated line spectra with high-resolution Chandra/HETGS observations of the mCV GK Per indicates that a wing feature redward of the 6.4-keV line may result from Compton recoil near the base of the accretion column. [source] A detailed study of the 5-Hz quasi-periodic oscillations in the bright X-ray transient and black hole candidate GRS 1739,278MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001Rudy Wijnands We present a detailed study of the 5-Hz quasi-periodic oscillation (QPO) recently discovered in the bright X-ray transient and black hole candidate (BHC) GRS (Borozdin & Trudolyubov) during a Rossi X-ray Timing Explorer observation taken on 1996 March 31. In total 6.6 ksec of on-source data were obtained, divided in two data sets of 3.4 and 3.2 ksec which were separated by ,2.6 ksec. The 5-Hz QPO was only present during the second data set. The QPO increased in strength from below 2 per cent rms amplitude for photon energies below 4 keV to ,5 per cent rms amplitude for energies above 10 keV. The soft QPO photons (below 5 keV) lagged the hard ones (above 10 keV) by almost 1.5 rad. Besides the QPO fundamental, its first overtone was detected. The strength of the overtone increased with photon energy (from < 2 per cent rms below 5 keV to ,8 per cent rms above 10 keV). Although limited statistics did not allow for an accurate determination of the lags of the first overtone, indications are that also for this QPO the soft photons lagged the hard ones. When the 5-Hz QPO was not detected (i.e., during the first part of the observation), a broad noise component was found for photon energies below 10 keV but it became almost a true QPO (with a Q value of ,1.9) above that energy, with a frequency of ,3 Hz. Its hard photons preceded the soft ones in a way reminiscent of the 5-Hz QPO, strongly suggesting that both features are physically related. We discuss our finding in the framework of low-frequency QPOs and their properties in BHCs. [source] Optical, structural, and electrical properties of Cu2O thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2010Ferid Chaffar Akkari Abstract Glancing-angle deposition (GLAD) was used in this work to grow transparent oxide Cu2O thin films by annealing in air at 185,°C of copper films deposited firstly by this method onto glass substrates. The annealing temperature of 185,°C corresponds to the optimal temperature that corresponds to the formation of Cu2O phase. The copper was sculptured into a zigzag shape, which present case (i) one column with inclined angle ,, case (ii) two columns with inclined angles , and ,,, and case (iii) three copper inclined columns with inclined angles ,, ,,, and , where , is the deposition angle between the incident flux and the substrate surface normal. The films after annealing have thicknesses of 165, 185, and 265,nm for cases (i), (ii), and (iii), respectively. The air-annealed copper films were characterized for their structural, surface morphological; electrical and optical properties by using X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical resistivity, and optical (transmittance and reflectance) measurement techniques. Optical studies show a direct allowed transition around 2.5,eV for the three cases. High absorptions coefficients in the range 2,×,105,3.7,×,106,cm,1 were found for photon energies higher than 2.7,eV. The Cu2O films exhibit in cases (i) and (ii) p-type conductivity but in case (iii) the Cu2O films exhibit n-type conductivity. [source] Investigation of phase contrast hard X-ray microscopy using planar sets of refractive crossed linear parabolic lenses made from SU-8 polymerPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2007E. Reznikova Abstract Planar X-ray refractive lenses with parabolic surface profile, and in crossed geometry to provide 2D focusing, are fabricated from SU-8 polymer using the LIGA process and deep X-ray lithography technology. A transmission X-ray microscope (TXM) using a condenser and an objective lens based on this type of X-ray optics was set up at the ESRF beamline BM 5, for photon energies of 17.1 and 18 keV. Test structures made of gold and SU-8, with different thicknesses, were imaged with this TXM using in-line phase-contrast, with X-ray magnification factors of 13,20, spatial resolution between 0.2 and 0.3 µm and exposure times around 1 s. The advantages of a TXM based on refractive SU-8 planar crossed condenser and objective and the optimisation of the optical scheme and of the condenser focusing profile are discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pressure dependence of photoluminescence of InAs/InP self-assembled quantum wiresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007M. Ruiz-Castillo Abstract This paper investigates the electronic structure of self-assembled InAs quantum wires (QWrs), grown under different conditions by molecular beam epitaxy on InP, by means of photoluminescence measurements under pressure. In samples with regularly distributed QWrs, room pressure photoluminescence spectra consist of a broad band centred at about 0.85 eV, which can be easily de-convoluted in a few Gaussian peaks. In samples with isolated QWrs, photoluminescence spectra exhibit up to four clearly resolved bands. Applying hydrostatic pressure, the whole emission band monotonously shifts towards higher photon energies with pressure coefficients ranging from 72 to 98 meV/GPa. In contrast to InAs quantum dots on GaAs, quantum wires photoluminescence is observed up to 10 GPa, indicating that InAs QWrs are metastable well above pressure at which bulk InAs undergoes a phase transition to the rock-salt phase (7 GPa). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Empirical model including band-to-band Coulomb interaction for refractive indices of GaAs and InP-based materials at photon energies near and above the band-gapPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2006E. Y. Lin Abstract New improved formulas of refractive indices of III-V materials to energies somewhat above the band gap have been developed from an absorption model with Coulomb interaction and a double-Lorentzian model for broadening. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigation of AlGaN/GaN HEMTs on Si Substrate Using BackgatingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003M. Marso Abstract The influence of a substrate voltage on the dc characteristics of an AlGaN/GaN HEMT on silicon (111) substrate is investigated. This effect, known as backgating, is used to study traps that are located between substrate and 2DEG channel. The transient of the drain current after applying a negative substrate voltage is evaluated for measurements with and without illumination. Several trap contributions are resolved by measurements at different photon energies. A photocurrent is observed up to 600 nm wavelength. Up to this wavelength the backgating effect can be compensated and the drain current restored by a short light pulse. The experiments are performed on completed HEMTs, allowing investigation of the influence of device fabrication technology. [source] Optical investigations on the existence of phase transition in ZnO:Li thin films prepared by DC sputtering methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2008A. Abu EL-Fadl Abstract We investigated the effect of temperature on the absorption spectra of Zn0.8Li0.2O thin films (ZnO:Li), deposited at 573 K, in the wavelength range 190-800 nm. The films were deposited on sapphire, MgO or quartz substrates by DC sputtering method. The results show a shift of the optical energy gap (Eg), with direct allowed transition type near the fundamental edge, to lower wavelengths as the temperature increases. The temperature rate of Eg changes considerably showing an anomaly around 320 K depending on type of substrate. The founded results indicated that replacement of Zn ions with Li ions induces a ferroelectric phase in the ZnO wurtzite-type semiconductor. The exponential dependence of the absorption coefficient on the incident photon energy suggests the validity of the Urbach rule. (© 2007 WILEY -VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Energy of Charge-Transfer States in Electron Donor,Acceptor Blends: Insight into the Energy Losses in Organic Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Dirk Veldman Abstract Here, a general experimental method to determine the energy ECT of intermolecular charge-transfer (CT) states in electron donor,acceptor (D,A) blends from ground state absorption and electrochemical measurements is proposed. This CT energy is calibrated against the photon energy of maximum CT luminescence from selected D,A blends to correct for a constant Coulombic term. It is shown that ECT correlates linearly with the open-circuit voltage (Voc) of photovoltaic devices in D,A blends via eVoc,=,ECT,,,0.5,eV. Using the CT energy, it is found that photoinduced electron transfer (PET) from the lowest singlet excited state (S1 with energy Eg) in the blend to the CT state (S1,,,CT) occurs when Eg,,,ECT,>,0.1,eV. Additionally, it is shown that subsequent charge recombination from the CT state to the lowest triplet excited state (ET) of D or A (CT,,,T1) can occur when ECT,,,ET,>,0.1,eV. From these relations, it is concluded that in D,A blends optimized for photovoltaic action: i) the maximum attainable Voc is ultimately set by the optical band gap (eVoc,=,Eg,,,0.6,eV) and ii) the singlet,triplet energy gap should be ,EST,<,0.2,eV to prevent recombination to the triplet state. These favorable conditions have not yet been met in conjugated materials and set the stage for further developments in this area. [source] A new technique for angle-dispersive powder diffraction using an energy-dispersive setup and synchrotron radiationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2004Yanbin Wang A new diffraction technique for combined angle- and energy-dispersive structural analysis and refinement (CAESAR), by collecting angle-dispersive data using a solid-state detector (SSD) and white synchrotron radiation, is introduced. By step scanning a well calibrated SSD over a limited 2, range, a series of one-dimensional energy-dispersive data (intensity versus energy) are obtained as a function of 2,. The entire intensity (Int) data set consists of several thousand channels covering a range of photon energies, E (up to ,150,keV), at each of the ,1000 2, steps, forming a 2,4 mega-element two-dimensional array, Int(E, 2,). These intensity data are then regrouped according to photon energies, which are defined in the multichannel SSD as individual channels, yielding a large number of intensity versus 2, (angle-dispersive) data sets, Int(E = const., 2,), each of which corresponds to a given photon energy or wavelength. The entire data set, selected subsets or composite scans can be used for multiple data set Rietveld refinement. Data collected both on ,-Al2O3 (a NIST diffraction standard) at ambient conditions and on a mixture of MgO and Au at high pressure were analyzed using the Rietveld technique, with varying schemes of data treatment. Furthermore, it is demonstrated that data within certain energy bands (,E/E = ±10%) may be binned together to improve counting statistics in a composite angle-dispersive scan, even when collected with much coarser scan steps of 0.1 or 0.2°. This technique is useful for high-pressure as well as general purpose powder diffraction studies that have limited X-ray access to the sample using synchrotron radiation. Several advantages are discussed. [source] Maximum pixel spectrum: a new tool for detecting and recovering rare, unanticipated features from spectrum image data cubesJOURNAL OF MICROSCOPY, Issue 2 2004D. S. BRIGHT Summary A new software tool, the maximum pixel spectrum, detects rare events within a spectrum image data cube, such as that generated with electron-excited energy-dispersive X-ray spectrometry in a scanning electron microscope. The maximum pixel spectrum is a member of a class of ,derived spectra' that are constructed from the spectrum image data cube. Similar to a conventional spectrum, a derived spectrum is a linear array of intensity vs. channel index that corresponds to photon energy. A derived spectrum has the principal characteristics of a real spectrum so that X-ray peaks can be recognized. A common example of a derived spectrum is the summation spectrum, which is a linear array in which the summation of all pixels within each energy plane gives the intensity value for that channel. The summation spectrum is sensitive to the dominant features of the data cube. The maximum pixel spectrum is constructed by selecting the maximum pixel value within each X-ray energy plane, ignoring the remaining pixels. Peaks corresponding to highly localized trace constituents or foreign contaminants, even those that are confined to one pixel of the image, can be seen at a glance when the maximum pixel spectrum is compared with the summation spectrum. [source] Synthesis and properties of an ionic polyacetylene with aromatic heterocyclesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2007Yeong-Soon Gal Abstract A new ionic polyacetylene with two aromatic heterocycles (pyridyl and thienyl) was prepared by the activation polymerization of 2-ethynylpyridine by using 3-(6-bromohexyloxy)methylthiophene without any additional initiator or catalyst. The activated acetylenic triple bond of N -substituted-2-ethynylpyridinium bromide, formed at first quaternarization process, was susceptible to linear polymerization. The instrumental analysis data on the polymer structure revealed that the polymer have the conjugated polyene backbone structure with the designed two aromatic heterocycles. The photoluminescence peak is located at 510 nm corresponding to a photon energy of 2.43eV. The electrochemical properties of this ionic polyacetylene were also measured and discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5679,5685, 2007 [source] Comparison of calculated brightness and flux of radiation from a long-period wiggler and a short-period undulatorJOURNAL OF SYNCHROTRON RADIATION, Issue 4 2008T. Shaftan In this article the calculation of brightness and flux for two insertion devices of the 2.8,GeV X-ray storage ring at the NSLS is discussed. The radiation properties from the X25 linearly polarized wiggler and the new X25 short-period undulator are compared at a fixed photon energy (11.3,keV) corresponding to emission from the fifth harmonic of the short-period undulator. For this computation, three commonly available synchrotron radiation programs are used. The capabilities of each of these codes are briefly discussed, and their range of applicability are commented on. It is concluded that special care is needed when modeling the radiation of the classes of insertion devices considered here. [source] Dose dependence of radiation damage for protein crystals studied at various X-ray energiesJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2007Nobutaka Shimizu Radiation damage to protein crystals is the most serious problem in obtaining accurate structures from protein crystallography. In order to examine the photon energy dependence of radiation damage, 12 to 15 data sets from each of nine tetragonal lysozyme crystals were collected at nine different X-ray energies (6.5, 7.1, 8.3, 9.9, 12.4, 16.5, 20.0, 24.8 and 33.0,keV) using beamline BL41XU at SPring-8. All results were compared on the basis of absorbed dose, expressed in Gray (Gy). Crystallographic statistics, such as the values of lattice constants, Rmerge and I/,(I), for each data set degraded at all nine energies as the exposure time for each crystal increased. In all data sets, radiation damage was observed after the absorbed dose exceeded 106,Gy. However, from the point of view of crystallographic statistics normalized to the absorbed dose, no clear dependence on photon energy was observed in these results. Structural refinement showed that the average B -factor for the last data set was larger than that for the first data set at all energies tested. However, no energy dependence of radiation damage on B -factor was found. Furthermore, disruption of disulfide bonds due to radiation damage was observed in electron density maps even at the highest photon energy (33,keV) used in this study. Therefore, these results suggest that radiation damage in the energy range investigated could be evaluated based on absorbed dose without energy dependence, and that it is important to minimize the absorbed dose in a crystal sample for obtaining an accurate protein structure. [source] On the feasibility of large-aperture Fresnel lenses for the microfocusing of hard X-raysJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2006Werner Jark Like visible light, X-rays can also be focused by refraction in transmission lenses. For visible light this requires convex lenses while for X-rays one needs to use concave lenses instead. Both lens types can be lightened by the material removal strategy introduced by Fresnel, which results in a lens subdivided into zones. Until now, for the focusing of X-rays, stacks of standard lenses and of Fresnel lenses have mostly been produced. The first are dubbed compound refractive lenses, abbreviated as CRL. State-of-the-art systems of this kind now achieve almost theoretical performance for the focus size and the transmission. On the other hand, the latter Fresnel systems, which promise to provide larger apertures, are still in their infancy. This report discusses systematically the properties of two possible schemes for their realisation. It then compares the optimized apertures of these two schemes with those for CRLs. The best Fresnel lenses in this study are found to provide experimentally more than 50% of the expected refraction efficiency at 8.5,keV photon energy. The photon flux in their focus is then almost identical to that of perfect Be CRLs with the same focal length. This report will also interpret experimental data reported previously for other Fresnel lenses. [source] A new bend-magnet beamline for scanning transmission X-ray microscopy at the Advanced Light SourceJOURNAL OF SYNCHROTRON RADIATION, Issue 4 2002Harald Ade The high brightness of the bend magnets at the Advanced Light Source has been exploited to illuminate a scanning transmission X-ray microscope (STXM). This is the first diffraction-limited scanning X-ray microscope to operate with a useful count rate on a synchrotron bend-magnet source. A simple dedicated beamline has been built covering the range of photon energy from 250,eV to 600,eV. The beamline is always available and needs little adjustment. Use of this facility is much easier than that of installations that share undulator beams. This facility provides radiation for C 1s, N 1s and O 1s near-edge X-ray absorption spectromicroscopy with STXM count rates in excess of 1,MHz and with spectral resolution typically 1:2000, limited to about 1:5000. [source] Backscattering X-ray standing waves in the XUV regionJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2001T. M. Grehk It is demonstrated that Bragg reflection of XUV radiation can be used to study structural properties of crystalline materials with large unit cells. A standing-wave field is formed in a layered TiSe2 single crystal for a near-backscattering geometry (, = 88.5°). The partial electron yield is measured as a function of photon energy across the (001) Bragg reflection condition (h,, 1033,eV) and its characteristic modulation is compared with the results derived from dynamical diffraction theory in the two-wave approximation. The data reveal a large amount of disorder along the c -axis. [source] X-ray magnetic circular dichroism imaging with hard X-raysJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2001K. Sato X-ray polarization-contrast images resulting from X-ray magnetic circular dichroism (XMCD) in the hard X-ray region have been successfully recorded for the first time. The apparatus used consisted of an X-ray polarizer, double X-ray phase retarders, and a high-spatial-resolution X-ray charge-coupled-device detector. The sample used was a hexagonal-close-packed cobalt polycrystal foil having a thickness of about 4,µm. The X-ray polarization-contrast image resulting from XMCD was observed at a photon energy of 10,eV above the cobalt K -absorption edge (7709,eV). The observed contrast in the image was reversed by inversion of the magnetic field. Furthermore, the contrast was reversed again at a photon energy of 32,eV above the cobalt K -absorption edge. [source] First results from the Canadian SGM beamline at SRCJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2000B. W. Yates The first experimental results obtained from the Canadian SGM beamline at SRC (Synchrotron Radiation Centre, University of Wisconsin-Madison, USA) are reported. The beamline is based on the Dragon-type design, with a constant deviation angle, using photons from a second-generation bending-magnet light source. The medium-energy grating on this beamline covers a photon energy range from 240 to 700,eV, with a ruling density of 600,lines,mm,1. A maximum resolving power of ,10000 is achieved at a photon energy of ,400,eV. Gas-phase absorption spectra collected at the N, O and C K -edges are presented to demonstrate the excellent performance of this beamline. High-resolution absorption spectra of some C- and Ti-containing solid-state samples are also reported. [source] Two-photon Raman-type self-induced transparency forfew-cycle laser pulsesLASER PHYSICS LETTERS, Issue 3 2005I. P. Prokopovich Abstract We show the both amplitude and spectrum dynamics of few-cycle laser pulses in two-photon Raman-type self-induced transparency in Ar+ ions, that permit to generate half-cycle laser pulses (FWHM) with more high amplitudes and photon energy as well as spectral widths. (© 2005 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Accreting millisecond pulsar SAX J1808.4,3658 during its 2002 outburst: evidence for a receding discMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2009Askar Ibragimov ABSTRACT An outburst of the accreting X-ray millisecond pulsar SAX J1808.4,3658 in 2002 October,November was followed by the Rossi X-ray Timing Explorer for more than a month. A detailed analysis of this unprecedented data set is presented. For the first time, we demonstrate how the area covered by the hotspot at the neutron star surface is decreasing in the course of the outburst together with the reflection amplitude. These trends are in agreement with the natural scenario, where the disc inner edge is receding from the neutron star as the mass accretion rate drops. These findings are further supported by the variations of the pulse profiles, which clearly show the presence of the secondary maximum at the late stages of the outburst after October 29. This fact can be interpreted as the disc receding sufficiently far from the neutron star to open the view of the lower magnetic pole. In that case, the disc inner radius can be estimated. Assuming that disc is truncated at the Alfvén radius, we constrain the stellar magnetic moment to ,= (9 ± 5) × 1025 G cm3, which corresponds to the surface field of about 108 G. On the other hand, using the magnetic moment recently obtained from the observed pulsar spin-down rate we show that the disc edge has to be within factor of 2 of the Alfvén radius, putting interesting constraints on the models of the disc,magnetosphere interaction. We also demonstrate that the sharp changes in the phase of the fundamental are intimately related to the variations of the pulse profile, which we associate with the varying obscuration of the antipodal spot. Using the phase-resolved spectra, we further argue that the strong dependence of the pulse profiles on photon energy and the observed soft time lags result from the different phase dependence of the normalizations of the two spectral components, the blackbody and the Comptonized tail, being consistent with the model, where these components have significantly different angular emission patterns. The pulse profile amplitude allows us to estimate the colatitude of the hotspot centroid to be ,4°,10°. [source] A detailed study of the 5-Hz quasi-periodic oscillations in the bright X-ray transient and black hole candidate GRS 1739,278MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001Rudy Wijnands We present a detailed study of the 5-Hz quasi-periodic oscillation (QPO) recently discovered in the bright X-ray transient and black hole candidate (BHC) GRS (Borozdin & Trudolyubov) during a Rossi X-ray Timing Explorer observation taken on 1996 March 31. In total 6.6 ksec of on-source data were obtained, divided in two data sets of 3.4 and 3.2 ksec which were separated by ,2.6 ksec. The 5-Hz QPO was only present during the second data set. The QPO increased in strength from below 2 per cent rms amplitude for photon energies below 4 keV to ,5 per cent rms amplitude for energies above 10 keV. The soft QPO photons (below 5 keV) lagged the hard ones (above 10 keV) by almost 1.5 rad. Besides the QPO fundamental, its first overtone was detected. The strength of the overtone increased with photon energy (from < 2 per cent rms below 5 keV to ,8 per cent rms above 10 keV). Although limited statistics did not allow for an accurate determination of the lags of the first overtone, indications are that also for this QPO the soft photons lagged the hard ones. When the 5-Hz QPO was not detected (i.e., during the first part of the observation), a broad noise component was found for photon energies below 10 keV but it became almost a true QPO (with a Q value of ,1.9) above that energy, with a frequency of ,3 Hz. Its hard photons preceded the soft ones in a way reminiscent of the 5-Hz QPO, strongly suggesting that both features are physically related. We discuss our finding in the framework of low-frequency QPOs and their properties in BHCs. [source] Transient Vibronic Structure in Ultrafast Fluorescence Spectra of Photoactive Yellow Protein,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2008Ryosuke Nakamura The ultrafast photo-induced dynamics of wild-type photoactive yellow protein and its site-directed mutant of E46Q in aqueous solution was studied at room temperature by femtosecond fluorescence spectroscopy using the optical Kerr-gate method. The vibronic structure appears, depending on the excitation photon energy, in the time-resolved fluorescence spectra just after photoexcitation, which winds with time and disappears on a time scale of sub-picoseconds. This result indicates that the wavepacket is localized in the electronic excited state followed by dumped oscillations and broadening, and also that the initial condition of the wavepacket prepared depending on the excitation photon energy affects much the following ultrafast dynamics in the electronic excited state. [source] Phase contrast X-ray imaging of large samples using an incoherent laboratory sourcePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2007C. Kottler Abstract An interferometric method to record quantitative X-ray phase contrast images has been developed that can be used at polychromatic and incoherent X-ray sources such as laboratory tubes. With respect to previously presented results, in this work we report on recent developments and results that have been achieved in view of potential future applications such as in medicine or biology. In particular, due to improvements in the fabrication process large area diffraction gratings with high aspect ratio were achieved. Thereby, the field of view of the interferometer has been drastically increased to 64 × 64 mm2 and the design value of the photon energy for the gratings could be increased up to 28 keV. Moreover, the use of a Medipix2 single photon-counting pixel detector shows a considerable improvement in image quality and sensitivity over the integrating detector used so far. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||||||||||||||