Science.gov

Sample records for 4d ultrafast electron

  1. 4D Electron Tomography

    NASA Astrophysics Data System (ADS)

    Kwon, Oh-Hoon; Zewail, Ahmed H.

    2010-06-01

    Electron tomography provides three-dimensional (3D) imaging of noncrystalline and crystalline equilibrium structures, as well as elemental volume composition, of materials and biological specimens, including those of viruses and cells. We report the development of 4D electron tomography by integrating the fourth dimension (time resolution) with the 3D spatial resolution obtained from a complete tilt series of 2D projections of an object. The different time frames of tomograms constitute a movie of the object in motion, thus enabling studies of nonequilibrium structures and transient processes. The method was demonstrated using carbon nanotubes of a bracelet-like ring structure for which 4D tomograms display different modes of motion, such as breathing and wiggling, with resonance frequencies up to 30 megahertz. Applications can now make use of the full space-time range with the nanometer-femtosecond resolution of ultrafast electron tomography.

  2. 4-D ultrafast shear-wave imaging.

    PubMed

    Gennisson, Jean-Luc; Provost, Jean; Deffieux, Thomas; Papadacci, Clément; Imbault, Marion; Pernot, Mathieu; Tanter, Mickael

    2015-06-01

    Over the last ten years, shear wave elastography (SWE) has seen considerable development and is now routinely used in clinics to provide mechanical characterization of tissues to improve diagnosis. The most advanced technique relies on the use of an ultrafast scanner to generate and image shear waves in real time in a 2-D plane at several thousands of frames per second. We have recently introduced 3-D ultrafast ultrasound imaging to acquire with matrix probes the 3-D propagation of shear waves generated by a dedicated radiation pressure transducer in a single acquisition. In this study, we demonstrate 3-D SWE based on ultrafast volumetric imaging in a clinically applicable configuration. A 32 × 32 matrix phased array driven by a customized, programmable, 1024-channel ultrasound system was designed to perform 4-D shear-wave imaging. A matrix phased array was used to generate and control in 3-D the shear waves inside the medium using the acoustic radiation force. The same matrix array was used with 3-D coherent plane wave compounding to perform high-quality ultrafast imaging of the shear wave propagation. Volumetric ultrafast acquisitions were then beamformed in 3-D using a delay-and-sum algorithm. 3-D volumetric maps of the shear modulus were reconstructed using a time-of-flight algorithm based on local multiscale cross-correlation of shear wave profiles in the three main directions using directional filters. Results are first presented in an isotropic homogeneous and elastic breast phantom. Then, a full 3-D stiffness reconstruction of the breast was performed in vivo on healthy volunteers. This new full 3-D ultrafast ultrasound system paves the way toward real-time 3-D SWE. PMID:26067040

  3. On the dynamical nature of the active center in a single-site photocatalyst visualized by 4D ultrafast electron microscopy

    PubMed Central

    Yoo, Byung-Kuk; Su, Zixue; Thomas, John Meurig; Zewail, Ahmed H.

    2016-01-01

    Understanding the dynamical nature of the catalytic active site embedded in complex systems at the atomic level is critical to developing efficient photocatalytic materials. Here, we report, using 4D ultrafast electron microscopy, the spatiotemporal behaviors of titanium and oxygen in a titanosilicate catalytic material. The observed changes in Bragg diffraction intensity with time at the specific lattice planes, and with a tilted geometry, provide the relaxation pathway: the Ti4+=O2− double bond transformation to a Ti3+−O1− single bond via the individual atomic displacements of the titanium and the apical oxygen. The dilation of the double bond is up to 0.8 Å and occurs on the femtosecond time scale. These findings suggest the direct catalytic involvement of the Ti3+−O1− local structure, the significance of nonthermal processes at the reactive site, and the efficient photo-induced electron transfer that plays a pivotal role in many photocatalytic reactions. PMID:26729878

  4. Scanning ultrafast electron microscopy

    PubMed Central

    Yang, Ding-Shyue; Mohammed, Omar F.; Zewail, Ahmed H.

    2010-01-01

    Progress has been made in the development of four-dimensional ultrafast electron microscopy, which enables space-time imaging of structural dynamics in the condensed phase. In ultrafast electron microscopy, the electrons are accelerated, typically to 200 keV, and the microscope operates in the transmission mode. Here, we report the development of scanning ultrafast electron microscopy using a field-emission-source configuration. Scanning of pulses is made in the single-electron mode, for which the pulse contains at most one or a few electrons, thus achieving imaging without the space-charge effect between electrons, and still in ten(s) of seconds. For imaging, the secondary electrons from surface structures are detected, as demonstrated here for material surfaces and biological specimens. By recording backscattered electrons, diffraction patterns from single crystals were also obtained. Scanning pulsed-electron microscopy with the acquired spatiotemporal resolutions, and its efficient heat-dissipation feature, is now poised to provide in situ 4D imaging and with environmental capability. PMID:20696933

  5. 4D electron microscopy: principles and applications.

    PubMed

    Flannigan, David J; Zewail, Ahmed H

    2012-10-16

    achievable with short intense pulses containing a large number of electrons, however, are limited to tens of nanometers and nanoseconds, respectively. This is because Coulomb repulsion is significant in such a pulse, and the electrons spread in space and time, thus limiting the beam coherence. It is therefore not possible to image the ultrafast elementary dynamics of complex transformations. The challenge was to retain the high spatial resolution of a conventional TEM while simultaneously enabling the temporal resolution required to visualize atomic-scale motions. In this Account, we discuss the development of four-dimensional ultrafast electron microscopy (4D UEM) and summarize techniques and applications that illustrate the power of the approach. In UEM, images are obtained either stroboscopically with coherent single-electron packets or with a single electron bunch. Coulomb repulsion is absent under the single-electron condition, thus permitting imaging, diffraction, and spectroscopy, all with high spatiotemporal resolution, the atomic scale (sub-nanometer and femtosecond). The time resolution is limited only by the laser pulse duration and energy carried by the electron packets; the CCD camera has no bearing on the temporal resolution. In the regime of single pulses of electrons, the temporal resolution of picoseconds can be attained when hundreds of electrons are in the bunch. The applications given here are selected to highlight phenomena of different length and time scales, from atomic motions during structural dynamics to phase transitions and nanomechanical oscillations. We conclude with a brief discussion of emerging methods, which include scanning ultrafast electron microscopy (S-UEM), scanning transmission ultrafast electron microscopy (ST-UEM) with convergent beams, and time-resolved imaging of biological structures at ambient conditions with environmental cells.

  6. Ultrafast free electron quantum optics

    NASA Astrophysics Data System (ADS)

    Becker, Maria Gabriel

    Free electron quantum optics is an emerging sub-field of physics that uses laser light, often in combination with nano-structures, to manipulate electrons in free space. Integration of femtosecond lasers into this technology is facilitating the move of free electron quantum optics into the ultrafast regime. A vision for this technology is ultrahigh temporal resolution in free electron time-of-flight experiments. Such a system would make fundamental physics studies involving small forces accessible that are not feasible with current technology. Realization of this vision will require an ultrafast source and an ultrafast detection scheme. Tungsten nano-tip sources capable of generating sub-100 fs electron pulses are already in use in our lab. Elsewhere, this type of source has been reported to emit on a sub-cycle timescale. Following up on a proposed scheme for observing sub-cycle emission, a two-color interferometer has been built and pump-probe electron emission measurements have been performed. Other efforts to develop ultrafast sources have involved implementing additional control parameters. GaAs has been investigated as a possible ultrafast source of spin-polarized electrons, and tungsten nano-tips have been modified with an ion beam to create a double tip source. Spin control and transverse separation control are expected to make studies of Pauli degeneracy pressure possible. The temporal resolution of current electronic particle detectors is ~1 ns. Schemes involving the interaction of laser pulses with nanostructures could improve this resolution by several orders of magnitude. As a first step towards a femtosecond electron switch, the temporal resolution of a nano-fabricated plasmonic antenna has been measured in a femtosecond pump-probe experiment. The possibility of an ultrafast diffraction switch has also been analyzed for nonrelativistic and relativistic electrons. In an application of a free electron time-of-flight system, the prediction of

  7. Ultrafast magnetization dynamics: Microscopic electronic configurations and ultrafast spectroscopy

    NASA Astrophysics Data System (ADS)

    Locht, I. L. M.; Di Marco, I.; Garnerone, S.; Delin, A.; Battiato, M.

    2015-08-01

    We provide an approach for the identification of the electronic and magnetic configurations of ferromagnetic Fe after an ultrafast decrease or increase of the magnetization. The model is based on the well-grounded assumption that, after an ultrafast variation of the magnetization, the system achieves a partial thermal equilibrium. With statistical arguments we show that the magnetic configurations are qualitatively different in the case of reduced or increased magnetization. The predicted magnetic configurations are then used to compute the dielectric response at the 3 p (M ) absorption edge, which is directly related to the changes observed in the experimental T-MOKE data. The good qualitative agreement between theory and experiment offers a substantial support for the validity of the model, and to the very existence of an ultrafast increase of the magnetization.

  8. Ultrafast Electron Diffraction: How It Works

    SciTech Connect

    2015-08-05

    A new technology at SLAC uses high-energy electrons to unravel motions in materials that are faster than a tenth of a trillionth of a second, opening up new research opportunities in ultrafast science.

  9. Four-dimensional ultrafast electron microscopy of phase transitions.

    PubMed

    Grinolds, Michael S; Lobastov, Vladimir A; Weissenrieder, Jonas; Zewail, Ahmed H

    2006-12-01

    Reported here is direct imaging (and diffraction) by using 4D ultrafast electron microscopy (UEM) with combined spatial and temporal resolutions. In the first phase of UEM, it was possible to obtain snapshot images by using timed, single-electron packets; each packet is free of space-charge effects. Here, we demonstrate the ability to obtain sequences of snapshots ("movies") with atomic-scale spatial resolution and ultrashort temporal resolution. Specifically, it is shown that ultrafast metal-insulator phase transitions can be studied with these achieved spatial and temporal resolutions. The diffraction (atomic scale) and images (nanometer scale) we obtained manifest the structural phase transition with its characteristic hysteresis, and the time scale involved (100 fs) is now studied by directly monitoring coordinates of the atoms themselves. PMID:17130445

  10. Biomechanics of DNA structures visualized by 4D electron microscopy

    PubMed Central

    Lorenz, Ulrich J.; Zewail, Ahmed H.

    2013-01-01

    We present a technique for in situ visualization of the biomechanics of DNA structural networks using 4D electron microscopy. Vibrational oscillations of the DNA structure are excited mechanically through a short burst of substrate vibrations triggered by a laser pulse. Subsequently, the motion is probed with electron pulses to observe the impulse response of the specimen in space and time. From the frequency and amplitude of the observed oscillations, we determine the normal modes and eigenfrequencies of the structures involved. Moreover, by selective “nano-cutting” at a given point in the network, it was possible to obtain Young’s modulus, and hence the stiffness, of the DNA filament at that position. This experimental approach enables nanoscale mechanics studies of macromolecules and should find applications in other domains of biological networks such as origamis. PMID:23382239

  11. Ultrafast electronic relaxation in superheated bismuth

    NASA Astrophysics Data System (ADS)

    Gamaly, E. G.; Rode, A. V.

    2013-01-01

    Interaction of moving electrons with vibrating ions in the lattice forms the basis for many physical properties from electrical resistivity and electronic heat capacity to superconductivity. In ultrafast laser interaction with matter the electrons are heated much faster than the electron-ion energy equilibration, leading to a two-temperature state with electron temperature far above that of the lattice. The rate of temperature equilibration is governed by the strength of electron-phonon energy coupling, which is conventionally described by a coupling constant, neglecting the dependence on the electron and lattice temperature. The application of this constant to the observations of fast relaxation rate led to a controversial notion of ‘ultra-fast non-thermal melting’ under extreme electronic excitation. Here we provide theoretical grounds for a strong dependence of the electron-phonon relaxation time on the lattice temperature. We show, by taking proper account of temperature dependence, that the heating and restructuring of the lattice occurs much faster than were predicted on the assumption of a constant, temperature independent energy coupling. We applied the temperature-dependent momentum and energy transfer time to experiments on fs-laser excited bismuth to demonstrate that all the observed ultra-fast transformations of the transient state of bismuth are purely thermal in nature. The developed theory, when applied to ultrafast experiments on bismuth, provides interpretation of the whole variety of transient phase relaxation without the non-thermal melting conjecture.

  12. Real-Space Mapping of Surface Trap States in CIGSe Nanocrystals Using 4D Electron Microscopy.

    PubMed

    Bose, Riya; Bera, Ashok; Parida, Manas R; Adhikari, Aniruddha; Shaheen, Basamat S; Alarousu, Erkki; Sun, Jingya; Wu, Tom; Bakr, Osman M; Mohammed, Omar F

    2016-07-13

    Surface trap states in copper indium gallium selenide semiconductor nanocrystals (NCs), which serve as undesirable channels for nonradiative carrier recombination, remain a great challenge impeding the development of solar and optoelectronics devices based on these NCs. In order to design efficient passivation techniques to minimize these trap states, a precise knowledge about the charge carrier dynamics on the NCs surface is essential. However, selective mapping of surface traps requires capabilities beyond the reach of conventional laser spectroscopy and static electron microscopy; it can only be accessed by using a one-of-a-kind, second-generation four-dimensional scanning ultrafast electron microscope (4D S-UEM) with subpicosecond temporal and nanometer spatial resolutions. Here, we precisely map the collective surface charge carrier dynamics of copper indium gallium selenide NCs as a function of the surface trap states before and after surface passivation in real space and time using S-UEM. The time-resolved snapshots clearly demonstrate that the density of the trap states is significantly reduced after zinc sulfide (ZnS) shelling. Furthermore, the removal of trap states and elongation of carrier lifetime are confirmed by the increased photocurrent of the self-biased photodetector fabricated using the shelled NCs. PMID:27228321

  13. Imaging population transfer in atoms with ultrafast electron pulses

    NASA Astrophysics Data System (ADS)

    Shao, Hua-Chieh; Starace, Anthony F.

    2016-09-01

    We propose the use of ultrafast electron diffraction (UED) to image a controllable, laser-driven coherent electron population transfer in lithium atoms with currently available femtosecond electron pulses. Our simulations demonstrate the ability of ultrafast electrons to image such an electronic population transfer, thus validating UED as a direct means of investigating electron dynamics. Provided the incident electron pulses have sufficient temporal resolution, the diffraction images are shown to resolve also the relative phases of the target electronic wave functions.

  14. Ultrafast Time-Resolved Electron Diffraction with Megavolt Electron Beams

    SciTech Connect

    Hastings, J.B.; Rudakov, F.M.; Dowell, D.H.; Schmerge, J.F.; Cardoza, J.D.; Castro, J.M.; Gierman, S.M.; Loos, H.; Weber, P.M.; /Brown U.

    2006-10-24

    An rf photocathode electron gun is used as an electron source for ultrafast time-resolved pump-probe electron diffraction. We observed single-shot diffraction patterns from a 160 nm Al foil using the 5.4 MeV electron beam from the Gun Test Facility at the Stanford Linear Accelerator. Excellent agreement with simulations suggests that single-shot diffraction experiments with a time resolution approaching 100 fs are possible.

  15. Ultrafast electronic dynamics driven by nuclear motion

    NASA Astrophysics Data System (ADS)

    Vendrell, Oriol

    2016-05-01

    The transfer of electrical charge on a microscopic scale plays a fundamental role in chemistry, in biology, and in technological applications. In this contribution, we will discuss situations in which nuclear motion plays a central role in driving the electronic dynamics of photo-excited or photo-ionized molecular systems. In particular, we will explore theoretically the ultrafast transfer of a double electron hole between the functional groups of glycine after K-shell ionization and subsequent Auger decay. Although a large energy gap of about 15 eV initially exists between the two electronic states involved and coherent electronic dynamics play no role in the hole transfer, we will illustrate how the double hole can be transferred within 3 to 4 fs between both functional ends of the glycine molecule driven solely by specific nuclear displacements and non-Born-Oppenheimer effects. This finding challenges the common wisdom that nuclear dynamics of the molecular skeleton are unimportant for charge transfer processes at the few-femtosecond time scale and shows that they can even play a prominent role. We thank the Hamburg Centre for Ultrafast Imaging and the Volkswagen Foundation for financial support.

  16. Imaging Coherent Electronic Motion in Atoms by Ultrafast Electron Diffraction

    NASA Astrophysics Data System (ADS)

    Shao, Hua-Chieh; Starace, Anthony F.

    2014-05-01

    Ultrafast electron diffraction from time-varying coherent electronic states of the H atom is investigated. Electron diffraction from coherent electronic states exhibiting breathing and wiggling modes of electronic motion are simulated in order to demonstrate the capability of attosecond electron pulses to image electron dynamics. A theoretical analysis identifies the conditions necessary to obtain time-resolved measurements. The scattering patterns and their temporal behaviors are shown to differentiate the two kinds of target electronic motion. Moreover, our simulations show that inelastic processes contribute significantly to the diffraction patterns. Thus although the diffraction patterns clearly distinguish different modes of target electronic motion, they cannot be easily related to the time-dependent target charge density. Finally, we note that detection of the scattered electron energy can provide more information on time-dependent target electronic motion. This work is supported in part by AFOSR Award No. FA9550-12-1-0149.

  17. Neutral wind estimation from 4-D ionospheric electron density images

    NASA Astrophysics Data System (ADS)

    Datta-Barua, S.; Bust, G. S.; Crowley, G.; Curtis, N.

    2009-06-01

    We develop a new inversion algorithm for Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE). The EMPIRE method uses four-dimensional images of global electron density to estimate the field-aligned neutral wind ionospheric driver when direct measurement is not available. We begin with a model of the electron continuity equation that includes production and loss rate estimates, as well as E × B drift, gravity, and diffusion effects. We use ion, electron, and neutral species temperatures and neutral densities from the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM-ASPEN) for estimating the magnitude of these effects. We then model the neutral wind as a power series at a given longitude for a range of latitudes and altitudes. As a test of our algorithm, we have input TIMEGCM electron densities to our algorithm. The model of the neutral wind is computed at hourly intervals and validated by comparing to the “true” TIMEGCM neutral wind fields. We show results for a storm day: 10 November 2004. The agreement between the winds derived from EMPIRE versus the TIMEGCM “true” winds appears to be time-dependent for the day under consideration. This may indicate that the diurnal variation in certain driving processes impacts the accuracy of our neutral wind model. Despite the potential temporal and spatial limits on accuracy, estimating neutral wind speed from measured electron density fields via our algorithm shows great promise as a complement to the more sparse radar and satellite measurements.

  18. Imaging ultrafast electronic motion by x-ray scattering

    NASA Astrophysics Data System (ADS)

    Dixit, Gopal; Santra, Robin

    2014-04-01

    Time-resolved ultrafast x-ray scattering is an emerging approach to probe the temporally evolving electronic charge distribution in real-space and in real-time. In this contribution, time-resolved ultrafast x-ray scattering from an electronic wave packet is presented. It is shown that the spatial and temporal correlations are imprinted in the scattering patterns, obtained by ultrafast x-ray scattering from an electronic wave packet, which deviate drastically from the notion that the instantaneous electronic density is the key quantity being probed. Furthermore, a detailed analysis of ultrafast x-ray scattering from a sample containing a mixture of non-stationary and stationary electrons along with the role of scattering interference between a non-stationary and several stationary electrons to the total scattering signal is discussed.

  19. Imaging coherent electronic motion in atoms by ultrafast electron diffraction

    NASA Astrophysics Data System (ADS)

    Shao, Hua-Chieh; Starace, Anthony F.

    2013-12-01

    Ultrafast electron diffraction from time-varying coherent electronic states of the H atom is analyzed theoretically. This theoretical analysis identifies the conditions necessary to obtain time-resolved measurements. Electron diffraction from coherent electronic states exhibiting breathing and wiggling modes of electronic motion are simulated numerically in order to demonstrate the capability of attosecond electron pulses to image electron dynamics. The scattering patterns and their temporal behaviors are shown to differentiate the two kinds of target electronic motion. Moreover, our simulations show that inelastic processes contribute significantly to the diffraction patterns. Thus, although the diffraction patterns clearly distinguish different modes of target electronic motion, they cannot be easily related to the time-dependent target charge density.

  20. Probing Structural and Electronic Dynamics with Ultrafast Electron Microscopy

    SciTech Connect

    Plemmons, DA; Suri, PK; Flannigan, DJ

    2015-05-12

    In this Perspective, we provide an overview,of the field of ultrafast electron microscopy (UEM). We begin by briefly discussing the emergence of methods for probing ultrafast structural dynamics and the information that can be obtained. Distinctions are drawn between the two main types a probes for femtosecond (fs) dynamics fast electrons and X-ray photons and emphasis is placed on hour the nature of charged particles is exploited in ultrafast electron-based' experiments:. Following this, we describe the versatility enabled by the ease with which electron trajectories and velocities can be manipulated with transmission electron microscopy (TEM): hardware configurations, and we emphasize how this is translated to the ability to measure scattering intensities in real, reciprocal, and energy space from presurveyed and selected rianoscale volumes. Owing to decades of ongoing research and development into TEM instrumentation combined with advances in specimen holder technology, comprehensive experiments can be conducted on a wide range of materials in various phases via in situ methods. Next, we describe the basic operating concepts, of UEM, and we emphasize that its development has led to extension of several of the formidable capabilities of TEM into the fs domain, dins increasing the accessible temporal parameter spade by several orders of magnitude. We then divide UEM studies into those conducted in real (imaging), reciprocal (diffraction), and energy (spectroscopy) spate. We begin each of these sections by providing a brief description of the basic operating principles and the types of information that can be gathered followed by descriptions of how these approaches are applied in UM, the type of specimen parameter space that can be probed, and an example of the types of dynamics that can be resolved. We conclude with an Outlook section, wherein we share our perspective on some future directions of the field pertaining to continued instrument development and

  1. Imaging population transfer in atoms with ultrafast electron pulses

    NASA Astrophysics Data System (ADS)

    Shao, Hua-Chieh; Starace, Anthony F.

    2016-05-01

    Ultrafast electron diffraction and microscopy have made significant progress recently in investigating atomic-scale structural dynamics in gas-phase and condensed materials. With these advances, direct imaging of electronic motions in atoms and molecules by ultrafast electron diffraction is anticipated. We propose imaging a laser-driven coherent population transfer in lithium atoms by femtosecond ultrafast electron pulses. Valuable information and insight can be obtained from studying such a system in order to refine ultrafast electron techniques and to interpret experimental results. Adiabatic passage by level crossing is used to transfer the electron population from the 2 s to the 2 p state. Our simulations demonstrate the ability of ultrafast electron diffraction to image this population transfer, as the time-dependent diffraction images reflect the electronic motion in the scattering intensity and angular distribution. Furthermore, asymmetric diffraction patterns indicate that even the relative phases of the electronic wave function can be resolved, provided there is sufficient temporal resolution. This work has been supported in part by DOE Award No. DE-SC0012193 [H.-C.S.] and by NSF Grant No. PHYS-1505492 [A.F.S.].

  2. Ultrafast electron transport in graphene and magnetic nanostructures

    NASA Astrophysics Data System (ADS)

    Turchinovich, Dmitry

    2016-03-01

    Ultrafast terahertz spectroscopy is an ideal tool for observation of dynamics of charge, lattice and spin in solids on the most elementary timescale: in the regime ωτ ~ 1, where ω is the electromagnetic wave oscillation frequency, and τ is the characteristic timescale at which the fundamental phenomena in the three subsystems comprising the solid occur. In this paper two case studies will be discussed. (i) Ultrafast electron transport in graphene. We will show, that the free-carrier conductivity of graphene in arbitrary ultrafast, (sub-)picosecond electric fields is defined by the thermodynamic balance maintained within the electronic structure of graphene acting as thermalized electron gas. Within this simple thermodynamic picture, the electron gas quasi-instantaneously increases its temperature by absorbing the energy of driving ultrafast electric field, and at the same time cools down via a time-retarded, few picosecond-long process of phonon emission. The asymmetry in electron heating and cooling dynamics leads to heat accumulation in the electron population of graphene, concomitantly lowering the chemical potential for hotter electrons, and thereby reducing the intraband conductivity of graphene - an effect crucially important for understanding of ultrafast graphene transistors and photodetectors. (ii) We will also discuss the fundamental observation of spin-controlled electron conduction of Fermilevel electrons in ferromagnetic metals, and will directly quantify the Mott picture of conduction in ferromagnets - the effect directly employed in modern magnetic sensor technologies such as giant magnetoresistance.

  3. Space charge effects in ultrafast electron diffraction and imaging

    SciTech Connect

    Tao Zhensheng; Zhang He; Duxbury, P. M.; Berz, Martin; Ruan, Chong-Yu

    2012-02-15

    Understanding space charge effects is central for the development of high-brightness ultrafast electron diffraction and microscopy techniques for imaging material transformation with atomic scale detail at the fs to ps timescales. We present methods and results for direct ultrafast photoelectron beam characterization employing a shadow projection imaging technique to investigate the generation of ultrafast, non-uniform, intense photoelectron pulses in a dc photo-gun geometry. Combined with N-particle simulations and an analytical Gaussian model, we elucidate three essential space-charge-led features: the pulse lengthening following a power-law scaling, the broadening of the initial energy distribution, and the virtual cathode threshold. The impacts of these space charge effects on the performance of the next generation high-brightness ultrafast electron diffraction and imaging systems are evaluated.

  4. Ultrafast electronic transport in low dimensional semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Choi, Hyunyong; Norris, Theodore B.; Faist, Jérôme; Capasso, Federico

    2009-02-01

    Ultrafast time-resolved pump-probe measurements are used to study low energy excitations and dynamics of electronic transport in various semiconductor nanostructures. In quantum cascade lasers, we observe ultrafast gain recovery dynamics due to electronic transport in the structures. In particular, the nature of electronic transport had been addressed by using ultrafast optical techniques. Sub-picosecond resonant tunneling injection from the quantum cascade laser injector ground state into the upper lasing state was found to be incoherent due to strong dephasing in the active subband. We also observed the strong coupling of the electronic transport to the intra-cavity photon density, which we term "photon-driven transport". Note that this invited paper reviews the details of our recent observations (H. Choi et al., Phys. Rev. Lett., 100, 167401, 2008 and H. Choi, et al., Appl. Phys. Lett. 92, 122114 (2008)).

  5. Ultrafast electron dynamics in phenylalanine initiated by attosecond pulses

    NASA Astrophysics Data System (ADS)

    Calegari, F.; Ayuso, D.; Trabattoni, A.; Belshaw, L.; De Camillis, S.; Anumula, S.; Frassetto, F.; Poletto, L.; Palacios, A.; Decleva, P.; Greenwood, J. B.; Martín, F.; Nisoli, M.

    2014-10-01

    In the past decade, attosecond technology has opened up the investigation of ultrafast electronic processes in atoms, simple molecules, and solids. Here, we report the application of isolated attosecond pulses to prompt ionization of the amino acid phenylalanine and the subsequent detection of ultrafast dynamics on a sub-4.5-femtosecond temporal scale, which is shorter than the vibrational response of the molecule. The ability to initiate and observe such electronic dynamics in polyatomic molecules represents a crucial step forward in attosecond science, which is progressively moving toward the investigation of more and more complex systems.

  6. Enhanced Optoelectronic Performance of a Passivated Nanowire-Based Device: Key Information from Real-Space Imaging Using 4D Electron Microscopy.

    PubMed

    Khan, Jafar I; Adhikari, Aniruddha; Sun, Jingya; Priante, Davide; Bose, Riya; Shaheen, Basamat S; Ng, Tien Khee; Zhao, Chao; Bakr, Osman M; Ooi, Boon S; Mohammed, Omar F

    2016-05-01

    Managing trap states and understanding their role in ultrafast charge-carrier dynamics, particularly at surface and interfaces, remains a major bottleneck preventing further advancements and commercial exploitation of nanowire (NW)-based devices. A key challenge is to selectively map such ultrafast dynamical processes on the surfaces of NWs, a capability so far out of reach of time-resolved laser techniques. Selective mapping of surface dynamics in real space and time can only be achieved by applying four-dimensional scanning ultrafast electron microscopy (4D S-UEM). Charge carrier dynamics are spatially and temporally visualized on the surface of InGaN NW arrays before and after surface passivation with octadecylthiol (ODT). The time-resolved secondary electron images clearly demonstrate that carrier recombination on the NW surface is significantly slowed down after ODT treatment. This observation is fully supported by enhancement of the performance of the light emitting device. Direct observation of surface dynamics provides a profound understanding of the photophysical mechanisms on materials' surfaces and enables the formulation of effective surface trap state management strategies for the next generation of high-performance NW-based optoelectronic devices. PMID:26938476

  7. Investigations of ultrafast dynamics in electronically excited alkylbenzenes

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Gerber, T.; Radi, P.; Sych, Y.; Maksyutenko, P.; Knopp, G.

    2013-03-01

    We investigate ultrafast dynamics in electronically excited states of some typical alkylbenzenes by time-resolved two-colour four wave mixing and velocity map imaging as complementary methods. In this context an upgraded double-sided time-resolved velocity map imaging setup is also proposed.

  8. Photon gating in four-dimensional ultrafast electron microscopy

    PubMed Central

    Hassan, Mohammed T.; Liu, Haihua; Baskin, John Spencer; Zewail, Ahmed H.

    2015-01-01

    Ultrafast electron microscopy (UEM) is a pivotal tool for imaging of nanoscale structural dynamics with subparticle resolution on the time scale of atomic motion. Photon-induced near-field electron microscopy (PINEM), a key UEM technique, involves the detection of electrons that have gained energy from a femtosecond optical pulse via photon–electron coupling on nanostructures. PINEM has been applied in various fields of study, from materials science to biological imaging, exploiting the unique spatial, energy, and temporal characteristics of the PINEM electrons gained by interaction with a “single” light pulse. The further potential of photon-gated PINEM electrons in probing ultrafast dynamics of matter and the optical gating of electrons by invoking a “second” optical pulse has previously been proposed and examined theoretically in our group. Here, we experimentally demonstrate this photon-gating technique, and, through diffraction, visualize the phase transition dynamics in vanadium dioxide nanoparticles. With optical gating of PINEM electrons, imaging temporal resolution was improved by a factor of 3 or better, being limited only by the optical pulse widths. This work enables the combination of the high spatial resolution of electron microscopy and the ultrafast temporal response of the optical pulses, which provides a promising approach to attain the resolution of few femtoseconds and attoseconds in UEM. PMID:26438835

  9. Ultrafast Optical Spin Echo for Electron Spins in Semiconductors

    SciTech Connect

    Clark, Susan M.; Fu, Kai-Mei C.; Zhang Qiang; Ladd, Thaddeus D.; Yamamoto, Yoshihisa; Stanley, Colin

    2009-06-19

    Spin-based quantum computing and magnetic resonance techniques rely on the ability to measure the coherence time T{sub 2} of a spin system. We report on the experimental implementation of all-optical spin echo to determine the T{sub 2} time of a semiconductor electron-spin system. We use three ultrafast optical pulses to rotate spins an arbitrary angle and measure an echo signal as the time between pulses is lengthened. Unlike previous spin-echo techniques using microwaves, ultrafast optical pulses allow clean T{sub 2} measurements of systems with dephasing times (T{sub 2}*) fast in comparison to the time scale for microwave control. This demonstration provides a step toward ultrafast optical dynamic decoupling of spin-based qubits.

  10. Mega-electron-volt ultrafast electron diffraction at SLAC National Accelerator Laboratory

    SciTech Connect

    Weathersby, S. P.; Brown, G.; Centurion, M.; Chase, T. F.; Coffee, R.; Corbett, J.; Eichner, J. P.; Frisch, J. C.; Fry, A. R.; Gühr, M.; Hartmann, N.; Hast, C.; Hettel, R.; Jobe, R. K.; Jongewaard, E. N.; Lewandowski, J. R.; Li, R. K.; Lindenberg, A. M.; Makasyuk, I.; May, J. E.; McCormick, D.; Nguyen, M. N.; Reid, A. H.; Shen, X.; Sokolowski-Tinten, K.; Vecchione, T.; Vetter, S. L.; Wu, J.; Yang, J.; Dürr, H. A.; Wang, X. J.

    2015-07-01

    Ultrafast electron probes are powerful tools, complementary to x-ray free-electron lasers, used to study structural dynamics in material, chemical, and biological sciences. High brightness, relativistic electron beams with femtosecond pulse duration can resolve details of the dynamic processes on atomic time and length scales. SLAC National Accelerator Laboratory recently launched the Ultrafast Electron Diffraction (UED) and microscopy Initiative aiming at developing the next generation ultrafast electron scattering instruments. As the first stage of the Initiative, a mega-electron-volt (MeV) UED system has been constructed and commissioned to serve ultrafast science experiments and instrumentation development. The system operates at 120-Hz repetition rate with outstanding performance. In this paper, we report on the SLAC MeV UED system and its performance, including the reciprocal space resolution, temporal resolution, and machine stability.

  11. Mega-electron-volt ultrafast electron diffraction at SLAC National Accelerator Laboratory

    SciTech Connect

    Weathersby, S. P.; Brown, G.; Chase, T. F.; Coffee, R.; Corbett, J.; Eichner, J. P.; Frisch, J. C.; Fry, A. R.; Gühr, M.; Hartmann, N.; Hast, C.; Hettel, R.; Jobe, R. K.; Jongewaard, E. N.; Lewandowski, J. R.; Li, R. K. Lindenberg, A. M.; Makasyuk, I.; May, J. E.; McCormick, D.; and others

    2015-07-15

    Ultrafast electron probes are powerful tools, complementary to x-ray free-electron lasers, used to study structural dynamics in material, chemical, and biological sciences. High brightness, relativistic electron beams with femtosecond pulse duration can resolve details of the dynamic processes on atomic time and length scales. SLAC National Accelerator Laboratory recently launched the Ultrafast Electron Diffraction (UED) and microscopy Initiative aiming at developing the next generation ultrafast electron scattering instruments. As the first stage of the Initiative, a mega-electron-volt (MeV) UED system has been constructed and commissioned to serve ultrafast science experiments and instrumentation development. The system operates at 120-Hz repetition rate with outstanding performance. In this paper, we report on the SLAC MeV UED system and its performance, including the reciprocal space resolution, temporal resolution, and machine stability.

  12. Ultrafast electron transport across nano gaps in nanowire circuits

    SciTech Connect

    Potma, Eric O.

    2015-07-31

    In this Program we aim for a closer look at electron transfer through single molecules. To achieve this, we use ultrafast laser pulses to time stamp an electron tunneling event in a molecule that is connected between two metallic electrodes, while reading out the electron current. A key aspect of this project is the use of metallic substrates with plasmonic activity to efficiently manipulate the tunneling probability. The first Phase of this program is concerned with developing highly sensitive tools for the ultrafast optical manipulation of tethered molecules through the evanescent surface field of plasmonic substrates. The second Phase of the program aims to use these tools for exercising control over the electron tunneling probability.

  13. Dynamics of chemical bonding mapped by energy-resolved 4D electron microscopy.

    PubMed

    Carbone, Fabrizio; Kwon, Oh-Hoon; Zewail, Ahmed H

    2009-07-10

    Chemical bonding dynamics are fundamental to the understanding of properties and behavior of materials and molecules. Here, we demonstrate the potential of time-resolved, femtosecond electron energy loss spectroscopy (EELS) for mapping electronic structural changes in the course of nuclear motions. For graphite, it is found that changes of milli-electron volts in the energy range of up to 50 electron volts reveal the compression and expansion of layers on the subpicometer scale (for surface and bulk atoms). These nonequilibrium structural features are correlated with the direction of change from sp2 [two-dimensional (2D) graphene] to sp3 (3D-diamond) electronic hybridization, and the results are compared with theoretical charge-density calculations. The reported femtosecond time resolution of four-dimensional (4D) electron microscopy represents an advance of 10 orders of magnitude over that of conventional EELS methods. PMID:19589997

  14. High-brightness electron beams for ultrafast electron microdiffraction and imaging

    NASA Astrophysics Data System (ADS)

    Sun, Tianyin; Zhou, Faran; Chang, Kiseok; Tao, Zhensheng; Williams, Joe; Ruan, Chong-Yu; MSU UEM Collaboration

    Currently the ultrafast electron diffraction has achieved sub-picosecond temporal resolution and atomic resolution. However, direct ultrafast imaging of a nanometer scale specimen through coherent single-particle diffraction has not been achieved largely due to insufficient intensity when tuned to a coherence length that matches the size of the specimen under the projected phase space density. Utilizing a recently implemented high-brightness electron source with flexible optical design, we test the performance of ultrafast electron microdiffraction and coherence imaging. We demonstrate the feasibilities of single-shot microdiffraction on a single micrometer-sized domain in Highly Ordered Pyrolytic Graphite (HOPG) and coherent diffractive imaging of 10 nm scale charge-ordered domain structures in single-crystal complex materials, as validated by the measured brightness at the sample plane. These initial results show that source-limited performance even from a sub-relativistic electron beamline can drastically improve the current performance of ultrafast electron imaging and diffraction.

  15. Ultrafast demagnetization by hot electrons: Diffusion or super-diffusion?

    PubMed Central

    Salvatella, G.; Gort, R.; Bühlmann, K.; Däster, S.; Vaterlaus, A.; Acremann, Y.

    2016-01-01

    Ultrafast demagnetization of ferromagnetic metals can be achieved by a heat pulse propagating in the electron gas of a non-magnetic metal layer, which absorbs a pump laser pulse. Demagnetization by electronic heating is investigated on samples with different thicknesses of the absorber layer on nickel. This allows us to separate the contribution of thermalized hot electrons compared to non-thermal electrons. An analytical model describes the demagnetization amplitude as a function of the absorber thickness. The observed change of demagnetization time can be reproduced by diffusive heat transport through the absorber layer.

  16. Imaging electronic motions in atoms by energy-resolved ultrafast electron diffraction

    NASA Astrophysics Data System (ADS)

    Shao, Hua-Chieh; Starace, Anthony F.

    2014-09-01

    We propose energy-resolved ultrafast electron diffraction as a means of directly imaging target electronic motions whose space, time, and energy information can be simultaneously retrieved from time-resolved diffraction measurements. The energy-resolved diffraction images are simulated for breathing, wiggling, and hybrid modes of electronic motion in the H atom. The simulations demonstrate the capabilities of ultrafast electron diffraction to image and distinguish different kinds of electronic motion. The theoretical analysis of the scattering process identifies the requirements for time- and state-resolved imaging of electronic motion and provides interpretations of the results.

  17. Ultrafast Charge Transfer Visualized by Two-Dimensional Electronic Spectroscopy

    NASA Astrophysics Data System (ADS)

    Bixner, O.; Christensson, N.; Hauer, J.; Milota, F.; Mančal, T.; Lukeš, V.; Kauffmann, H. F.

    2013-03-01

    Two-dimensional electronic spectroscopy (2D-ES) is used to investigate ultrafast excited-state dynamics in a lutetium bisphthalocyanine dimer. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra. The combination of density matrix propagation and quantum chemical calculations results in a molecular view of the charge transfer dynamics and highlights the role of the counter-ion in providing an energetic perturbation which promotes charge transfer across the complex.

  18. Ultrafast electron diffraction with megahertz MeV electron pulses from a superconducting radio-frequency photoinjector

    SciTech Connect

    Feng, L. W.; Lin, L.; Huang, S. L.; Quan, S. W.; Hao, J. K.; Zhu, F.; Wang, F.; Liu, K. X.; Jiang, T.; Zhu, P. F.; Fu, F.; Wang, R.; Zhao, L.; Xiang, D.

    2015-11-30

    We report ultrafast relativistic electron diffraction operating at the megahertz repetition rate where the electron beam is produced in a superconducting radio-frequency (rf) photoinjector. We show that the beam quality is sufficiently high to provide clear diffraction patterns from gold and aluminium samples. With the number of electrons, several orders of magnitude higher than that from a normal conducting photocathode rf gun, such high repetition rate ultrafast MeV electron diffraction may open up many new opportunities in ultrafast science.

  19. Ultrafast electron diffraction from aligned molecules

    SciTech Connect

    Centurion, Martin

    2015-08-17

    The aim of this project was to record time-resolved electron diffraction patterns of aligned molecules and to reconstruct the 3D molecular structure. The molecules are aligned non-adiabatically using a femtosecond laser pulse. A femtosecond electron pulse then records a diffraction pattern while the molecules are aligned. The diffraction patterns are then be processed to obtain the molecular structure.

  20. Ultrafast terahertz electrodynamics of photonic and electronic nanostructures

    NASA Astrophysics Data System (ADS)

    Luo, Liang

    This thesis summarizes my work on using ultrafast laser pulses to study Terahertz (THz) electrodynamics of photonic and electronic nanostructures and microstructures. Ultrafast time-resolved (optical, NIR, MIR, THz) pump-probe spectroscopy setup has been successfully built, which enables me to perform a series of relevant experiments. Firstly, a novel high efficiency and compact THz wave emitter based on split-ring-resonators has been developed and characterized. The emitter can be pumped at any wavelength by tailoring the magnetic resonance and could generate gapless THz waves covering the entire THz band. Secondly, two kinds of new photonic structures for THz wave manipulation have been successfully designed and characterized. One is based on the 1D and 2D photo-imprinted diffractive elements. The other is based on the photoexcited double-split-ring-resonator metamaterials. Both structures are flexible and can modulate THz waves with large tunability. Thirdly, the dark excitons in semiconducting single-walled carbon nanotubes are studied by optical pump and THz probe spectroscopy, which provides the first insights into the THz responses of nonequilibrium excitonic correlations and dynamics from the dark ground states in carbon nanotubes. Next, several on-going projects are briefly presented such as the study of ultrafast THz dynamics of Dirac fermions in topological insulator Bi_{2}Se_{3} with Mid-infrared excitation. Finally, the thesis ends with a summary of the completed experiments and an outlook of the future plan.

  1. Ultrafast studies of coexisting electronic order in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Hinton, James; Thewalt, Eric; Alpichshev, Zhanybek; Sternbach, Aaron; McLeod, Alex; Ji, L.; Veit, Mike; Dorrow, Chelsey; Koralek, Jake; Xhao, Xudong; Barisic, Neven; Kemper, Alexander; Gedik, Nuh; Greven, Martin; Basov, Dimitri; Orenstein, Joe

    The cuprate family of high temperature superconductors displays a variety of electronic phases which emerge when charge carriers are added to the antiferromagnetic parent compound. These electronic phases are characterized by subtle differences in the low energy electronic excitations. Ultrafast time-resolved reflectivity (TRR) provides an ideal tool for investigating the cuprate phase diagram, as small changes in the electronic structure can produce significant contrast in the non-equilibrium reflectivity. Here we present TRR measurements of cuprate superconductors, focusing on the model single-layer cuprate HgBa2CuO4+δ. We observe a cusp-like feature in the quasiparticle lifetime near the superconducting transition temperature Tc. This feature can be understood using a model of coherently-mixed charge-density wave and superconducting pairing. We propose extending this technique to the nanoscale using ultrafast scattering scanning near-field microscopy (u-SNOM). This will allow us to explore how these electronic phases coexist and compete in real-space.

  2. Mapping Carrier Dynamics on Material Surfaces in Space and Time using Scanning Ultrafast Electron Microscopy.

    PubMed

    Sun, Jingya; Adhikari, Aniruddha; Shaheen, Basamat S; Yang, Haoze; Mohammed, Omar F

    2016-03-17

    Selectively capturing the ultrafast dynamics of charge carriers on materials surfaces and at interfaces is crucial to the design of solar cells and optoelectronic devices. Despite extensive research efforts over the past few decades, information and understanding about surface-dynamical processes, including carrier trapping and recombination remains extremely limited. A key challenge is to selectively map such dynamic processes, a capability that is hitherto impractical by time-resolved laser techniques, which are limited by the laser's relatively large penetration depth and consequently these techniques record mainly bulk information. Such surface dynamics can only be mapped in real space and time by applying four-dimensional (4D) scanning ultrafast electron microscopy (S-UEM), which records snapshots of materials surfaces with nanometer spatial and subpicosecond temporal resolutions. In this method, the secondary electron (SE) signal emitted from the sample's surface is extremely sensitive to the surface dynamics and is detected in real time. In several unique applications, we spatially and temporally visualize the SE energy gain and loss, the charge carrier dynamics on the surface of InGaN nanowires and CdSe single crystal and its powder film. We also discuss the mechanisms for the observed dynamics, which will be the foundation for future potential applications of S-UEM to a wide range of studies on material surfaces and device interfaces.

  3. Ultrafast dynamics of electrons at interfaces

    SciTech Connect

    McNeill, Jason D.

    1999-05-03

    Electronic states of a thin layer of material on a surface possess unique physical and chemical properties. Some of these properties arise from the reduced dimensionality of the thin layer with respect to the bulk or the properties of the electric field where two materials of differing dielectric constants meet at an interface. Other properties are related to the nature of the surface chemical bond. Here, the properties of excess electrons in thin layers of Xenon, Krypton, and alkali metals are investigated, and the bound state energies and effective masses of the excess electrons are determined using two-photon photoemission. For Xenon, the dependence of bound state energy, effective mass, and lifetime on layer thickness from one to nine layers is examined. Not all quantities were measured at each coverage. The two photon photoemission spectra of thin layers of Xenon on a Ag(111) substrate exhibit a number of sharp, well-defined peaks. The binding energy of the excess electronic states of Xenon layers exhibited a pronounced dependence on coverage. A discrete energy shift was observed for each additional atomic layer. At low coverage, a series of states resembling a Rydberg series is observed. This series is similar to the image state series observed on clean metal surfaces. Deviations from image state energies can be described in terms of the dielectric constant of the overlayer material and its effect on the image potential. For thicker layers of Xe (beyond the first few atomic layers), the coverage dependence of the features begins to resemble that of quantum well states. Quantum well states are related to bulk band states. However, the finite thickness of the layer restricts the perpendicular wavevector to a discrete set of values. Therefore, the spectrum of quantum well states contains a series of peaks which correspond to the various allowed values of the perpendicular wavevector. Analysis of the quantum well spectrum yields electronic band structure

  4. Cardiac function and perfusion dynamics measured on a beat-by-beat basis in the live mouse using ultra-fast 4D optoacoustic imaging

    NASA Astrophysics Data System (ADS)

    Ford, Steven J.; Deán-Ben, Xosé L.; Razansky, Daniel

    2015-03-01

    The fast heart rate (~7 Hz) of the mouse makes cardiac imaging and functional analysis difficult when studying mouse models of cardiovascular disease, and cannot be done truly in real-time and 3D using established imaging modalities. Optoacoustic imaging, on the other hand, provides ultra-fast imaging at up to 50 volumetric frames per second, allowing for acquisition of several frames per mouse cardiac cycle. In this study, we combined a recently-developed 3D optoacoustic imaging array with novel analytical techniques to assess cardiac function and perfusion dynamics of the mouse heart at high, 4D spatiotemporal resolution. In brief, the heart of an anesthetized mouse was imaged over a series of multiple volumetric frames. In another experiment, an intravenous bolus of indocyanine green (ICG) was injected and its distribution was subsequently imaged in the heart. Unique temporal features of the cardiac cycle and ICG distribution profiles were used to segment the heart from background and to assess cardiac function. The 3D nature of the experimental data allowed for determination of cardiac volumes at ~7-8 frames per mouse cardiac cycle, providing important cardiac function parameters (e.g., stroke volume, ejection fraction) on a beat-by-beat basis, which has been previously unachieved by any other cardiac imaging modality. Furthermore, ICG distribution dynamics allowed for the determination of pulmonary transit time and thus additional quantitative measures of cardiovascular function. This work demonstrates the potential for optoacoustic cardiac imaging and is expected to have a major contribution toward future preclinical studies of animal models of cardiovascular health and disease.

  5. Electronic/photonic interfaces for ultrafast data processing.

    SciTech Connect

    Overberg, Mark E.; Geib, Kent Martin; Serkland, Darwin Keith; Hsu, Alan Yuan-Chun; Keeler, Gordon Arthur; Finnegan, Patrick Sean

    2008-09-01

    This report summarizes a 3-month program that explored the potential areas of impact for electronic/photonic integration technologies, as applied to next-generation data processing systems operating within 100+ Gb/s optical networks. The study included a technology review that targeted three key functions of data processing systems, namely receive/demultiplexing/clock recovery, data processing, and transmit/multiplexing. Various technical approaches were described and evaluated. In addition, we initiated the development of high-speed photodetectors and hybrid integration processes, two key elements of an ultrafast data processor. Relevant experimental results are described herein.

  6. Structural Preablation Dynamics of Graphite Observed by Ultrafast Electron Crystallography

    SciTech Connect

    Carbone, Fabrizio; Baum, Peter; Zewail, Ahmed H.; Rudolf, Petra

    2008-01-25

    By means of time-resolved electron crystallography, we report direct observation of the structural dynamics of graphite, providing new insights into the processes involving coherent lattice motions and ultrafast graphene ablation. When graphite is excited by an ultrashort laser pulse, the excited carriers reach their equilibrium in less then one picosecond by transferring heat to a subset of strongly coupled optical phonons. The time-resolved diffraction data show that on such a time scale the crystal undergoes a contraction whose velocity depends on the excitation fluence. The contraction is followed by a large expansion which, at sufficiently high fluence, leads to the ablation of entire graphene layers, as recently predicted theoretically.

  7. Nanofriction visualized in space and time by 4D electron microscopy.

    PubMed

    Flannigan, David J; Park, Sang Tae; Zewail, Ahmed H

    2010-11-10

    In this letter, we report a novel method of visualizing nanoscale friction in space and time using ultrafast electron microscopy (UEM). The methodology is demonstrated for a nanoscale movement of a single crystal beam on a thin amorphous membrane of silicon nitride. The movement results from the elongation of the crystal beam, which is initiated by a laser (clocking) pulse, and we examined two types of beams: those that are free of friction and the others which are fixed on the substrate. From observations of image change with time we are able to decipher the nature of microscopic friction at the solid-solid interface: smooth-sliding and periodic slip-stick friction. At the molecular and nanoscale level, and when a force parallel to the surface (expansion of the beam) is applied, the force of gravity as a (perpendicular) load cannot explain the observed friction. An additional effective load being 6 orders of magnitude larger than that due to gravity is attributed to Coulombic/van der Waals adhesion at the interface. For the case under study, metal-organic crystals, the gravitational force is on the order of piconewtons whereas the static friction force is 0.5 μN and dynamic friction is 0.4 μN; typical beam expansions are 50 nm/nJ for the free beam and 10 nm/nJ for the fixed beam. The method reported here should have applications for other materials, and for elucidating the origin of periodic and chaotic friction and their relevance to the efficacy of nano(micro)-scale devices.

  8. Ultrafast electronic processes in highly excited solids: subpicosecond optical studies

    NASA Astrophysics Data System (ADS)

    Petite, Guillaume

    1998-09-01

    Modern short pulse lasers are efficient tools for production of high levels of electronic excitation in solids under irradiation, a state which mimics that of the same materials after the passage of any particle which deposits its energy under the form of electronic excitation. Because they can also be used in a number of optical experiments of charge carriers and defect detection, they offer the unique opportunity of unraveling the ultrafast kinetic aspects of atomic processes induced by the electronic excitation, whose final state is the only aspect accessible in the case of other irradiations. After mentioning a few orders of magnitudes concerning the energy deposition, we will show some examples of recent experiments concerning the mechanisms of irradiation defect creation in insulators. The perspectives opened by recent developments of light sources in a wide range of wavelengths will be finally presented.

  9. Electron theory of fast and ultrafast dissipative magnetization dynamics.

    PubMed

    Fähnle, M; Illg, C

    2011-12-14

    For metallic magnets we review the experimental and electron-theoretical investigations of fast magnetization dynamics (on a timescale of ns to 100 ps) and of laser-pulse-induced ultrafast dynamics (few hundred fs). It is argued that for both situations the dominant contributions to the dissipative part of the dynamics arise from the excitation of electron-hole pairs and from the subsequent relaxation of these pairs by spin-dependent scattering processes, which transfer angular momentum to the lattice. By effective field theories (generalized breathing and bubbling Fermi-surface models) it is shown that the Gilbert equation of motion, which is often used to describe the fast dissipative magnetization dynamics, must be extended in several aspects. The basic assumptions of the Elliott-Yafet theory, which is often used to describe the ultrafast spin relaxation after laser-pulse irradiation, are discussed very critically. However, it is shown that for Ni this theory probably yields a value for the spin-relaxation time T(1) in good agreement with the experimental value. A relation between the quantity α characterizing the damping of the fast dynamics in simple situations and the time T(1) is derived. PMID:22089491

  10. Investigations on interfacial dynamics with ultrafast electron diffraction

    NASA Astrophysics Data System (ADS)

    Murdick, Ryan A.

    An ultrafast electron diffractive voltammetry (UEDV) technique is introduced, extended from ultrafast electron diffraction, to investigate the ultrafast charge transport dynamics at interfaces and in nanostructures. Rooted in Coulomb-induced refraction, formalisms are presented to quantitatively deduce the transient surface voltages (TSVs), caused by photoinduced charge redistributions at interfaces, and are applied to examine a prototypical Si/SiO2 interface, known to be susceptible to photoinduced interfacial charging The ultrafast time resolution and high sensitivity to surface charges of this electron diffractive approach allows direct elucidation of the transient effects of photoinduced hot electron transport at nanometer (˜2 nm) interfaces. Two distinctive regimes are uncovered, characterized by the time scales associated with charge separation. At the low fluence regime, the charge transfer is described by a thermally-mediated process with linear dependence on the excitation fluence. Theoretical analysis of the transient thermal properties of the carriers show that it is well-described by a direct tunneling of the laser heated electrons through the dielectric oxide layer to surface states. At higher fluences, a coherent multiphoton absorption process is invoked to directly inject electrons into the conduction band of SiO2, leading to a more efficient surface charge accumulation. A quadratic fluence dependence on this coherent, 3-photon lead electron injection is characterized by the rapid dephasing of the intermediately generated hot electrons from 2-photon absorption, limiting the yield of the consecutive 1-photon absorption by free carriers. The TSV formalism is extended beyond the simple slab geometry associated with planar surfaces (Si/SiO2), to interfaces with arbitrary geometrical features, by imposing a corrective scheme to the slab model. The validity of this treatment is demonstrated in an investigation of the charge transfer dynamics at a metal

  11. Probing Transient Electron Dynamics Using Ultrafast X Rays

    NASA Astrophysics Data System (ADS)

    Bucksbaum, Philip

    2016-05-01

    Linear x-ray absorption in atoms or molecules creates highly excited multi-electron quantum systems, which relax rapidly by fluorescence or Auger emission. These relaxation rates are usually less than a few femtoseconds in duration, and so they can reveal transient elecronic states in molecules as they undergo photo-induced transformations. I will show recent results from femtosecond x-ray experiments that display this phenomenon. There are efforts underway to push the temporal resolving power of ultrafast x-ray pulses into the attosecond regime, using stronger fields to initiate nonlinear absorption processes such as transient stimulated electronic Raman scattering. I will discuss current progress and future prospects for research in this area. This research is supported through Stanford PULSE Institute, SLAC National Accelerator Lab by the U.S. Department of Energy, Office of Basic Energy Sciences, Atomic, Molecular, and Optical Science Program.

  12. Ultrafast Electron-Ion Dynamics Near Aluminum Surfaces

    NASA Astrophysics Data System (ADS)

    Schleife, Andre; Wells, Kai; Knewstub, Sam

    Computational physics and materials research have greatly benefited from high-performance computing; modern first-principles simulations allow insight with unprecedented accuracy and detail. Here we use a recent highly parallel implementation of Ehrenfest molecular dynamics based on real-time time-dependent density functional theory to describe non-adiabatic ultrafast electron-ion dynamics using accurate first-principles calculations. We investigate aluminum subject to highly energetic particle radiation (hydrogen projectile) and study energy deposition due to the fast projectiles. Their high velocity makes it necessary to overcome the Born-Oppenheimer approximation. Using our first-principles calculations we study the behavior of fast ions near the surface of aluminum slabs and investigate, for instance, the influence of velocity and impact angle of the projectile ion. From the emerging non-adiabatic electron-ion dynamics we gain insight into the material on an atto-second time scale.

  13. Using attosecond pulses to probe ultrafast electronic motions inside atoms

    NASA Astrophysics Data System (ADS)

    Collins, L. A.; Hu, S. X.

    2006-05-01

    With using an efficient and accurate parallel solver for the time-dependent Schr"odinger equation, we have performed full-dimensional numerical simulations of the proposed attosecond pump-probe for exploring the extremely fast motion of an electronic wave packet inside atoms. Pumped by a broadband femtosecond UV pulse, one electron of ground-state Helium can be launched into a superposition of low-lying excited states, thus forming a bound wavepacket oscillating relative to the atomic core. A time-delayed attosecond EUV (probe) pulse then ionizes the atom causing three-body breakup. Measuring either the energy sharing of the ionized electrons or the total ionization probability as a function of the time delay traces out the internal motion of the excited electron. Our simulations have shown that an ultrashort oscillating period of 2 fs can be followed for several cylces. This opens the prospect of a wealth of similar pump-probe experiments to examine ultrafast electronic motions.

  14. Nonequilibrium phase transitions in cuprates observed by ultrafast electron crystallography.

    PubMed

    Gedik, Nuh; Yang, Ding-Shyue; Logvenov, Gennady; Bozovic, Ivan; Zewail, Ahmed H

    2007-04-20

    Nonequilibrium phase transitions, which are defined by the formation of macroscopic transient domains, are optically dark and cannot be observed through conventional temperature- or pressure-change studies. We have directly determined the structural dynamics of such a nonequilibrium phase transition in a cuprate superconductor. Ultrafast electron crystallography with the use of a tilted optical geometry technique afforded the necessary atomic-scale spatial and temporal resolutions. The observed transient behavior displays a notable "structural isosbestic" point and a threshold effect for the dependence of c-axis expansion (Deltac) on fluence (F), with Deltac/F = 0.02 angstrom/(millijoule per square centimeter). This threshold for photon doping occurs at approximately 0.12 photons per copper site, which is unexpectedly close to the density (per site) of chemically doped carriers needed to induce superconductivity. PMID:17446397

  15. Theoretical and experimental investigations of the electronic structure configuration during ultrafast demagnetization of Co

    NASA Astrophysics Data System (ADS)

    Turgut, Emrah; Grychtol, Patrik; Zusin, Dmitry; Kapteyn, Henry C.; Murnane, Margaret M.; Legut, Dominik; Carva, Karel; Oppeneer, Peter M.; Mathias, Stefan; Aeschlimann, Martin; Schneider, Claus M.; Shaw, Justin; Knut, Ronny; Nembach, Hans; Silva, Thomas J.

    2014-03-01

    We report on theoretical and experimental studies of the electronic structure configuration during the ultrafast demagnetization in Co thin films. After an ultrafast optical laser excitation of a ferromagnetic material, the magnetization of the material decreases rapidly in less than a picosecond. This ultrafast behavior has attracted a significant amount of attention for more than two decades; however, the underlying driving mechanism is still unclear. In this work, we use an extreme ultraviolet, broad-bandwidth, tabletop, ultrafast, and element-selective magnetization probe that employs the transverse magneto-optical Kerr effect to extract the energy- and time-resolved dynamics of the off-diagonal dielectric tensor element that is proportional to the magnetization. We compare our data with theoretical optical predictions based upon ab-initio calculations of the electronic structure, with the ultimate goal of determining how the occupation of majority and minority states vs. energy evolves after ultrafast optical pumping.

  16. Ultrafast electronic relaxation in colloidal gold (I) sulfide nanoparticles

    NASA Astrophysics Data System (ADS)

    Grant, Christian D.; Norman, Thaddeus J., Jr.; Morris, Todd; Szulczewski, Greg; Zhang, Jin Z.

    2002-11-01

    Ultrafast electronic relaxation dynamics in Au2S colloidal nanoparticles have been studied using fs transient absorption spectroscopy. The electronic absorption spectrum of the nanoparticles exhibits a broad featureless absorption with increasing intensity from the near-IR into the visible and UV, indicating that Au2S is an indirect bandgap semiconductor. The electronic relaxation dynamics have been measured with 390 nm excitation and probing at 790 and 850 nm. The transient absorption decay profiles can be fit to a double exponential with time constants of 600 fs and 23 ps. The fast decay can be assigned to trapping of electrons from the conduction band to shallow trap states or from shallow traps to deep traps, while the long decay is assigned to recombination from shallow or deep trap states. The overall fast relaxation can be attributed to a high density of intrinsic or surface trap states. This fast decay is non-radiative and consistent with no observable luminescence at room temperature. EXAFS data show a 20% decrease in the first coordination shell for nanoparticles relative to bulk, which suggests a large number of surface dangling bounds that can contribute to a high density of surface trap states.

  17. Kikuchi ultrafast nanodiffraction in four-dimensional electron microscopy.

    PubMed

    Yurtsever, Aycan; Zewail, Ahmed H

    2011-02-22

    Coherent atomic motions in materials can be revealed using time-resolved X-ray and electron Bragg diffraction. Because of the size of the beam used, typically on the micron scale, the detection of nanoscale propagating waves in extended structures hitherto has not been reported. For elastic waves of complex motions, Bragg intensities contain all polarizations and they are not straightforward to disentangle. Here, we introduce Kikuchi diffraction dynamics, using convergent-beam geometry in an ultrafast electron microscope, to selectively probe propagating transverse elastic waves with nanoscale resolution. It is shown that Kikuchi band shifts, which are sensitive only to the tilting of atomic planes, reveal the resonance oscillations, unit cell angular amplitudes, and the polarization directions. For silicon, the observed wave packet temporal envelope (resonance frequency of 33 GHz), the out-of-phase temporal behavior of Kikuchi's edges, and the magnitude of angular amplitude (0.3 mrad) and polarization elucidate the nature of the motion: one that preserves the mass density (i.e., no compression or expansion) but leads to sliding of planes in the antisymmetric shear eigenmode of the elastic waveguide. As such, the method of Kikuchi diffraction dynamics, which is unique to electron imaging, can be used to characterize the atomic motions of propagating waves and their interactions with interfaces, defects, and grain boundaries at the nanoscale. PMID:21245348

  18. Imaging electronic motions in atoms by energy-resolved ultrafast electron diffraction

    NASA Astrophysics Data System (ADS)

    Shao, Hua-Chieh; Starace, Anthony F.

    2015-05-01

    We present a general analysis of energy-resolved ultrafast electron diffraction for imaging target electronic motion and numerical simulations of time-resolved spectra of ultrafast electrons scattered from the breathing, wiggling, and hybrid modes of electronic motion in the H atom. We consider pump-probe processes in which a laser pulse creates a coherent superposition of target states that are probed by the electron pulses. Varying the pump-probe delay time, the delay-dependent scattering intensities record the ensuing electronic motions. The kinematics of the scattered electrons is fully resolved; both the scattering angles and the kinetic energies are measured. Therefore, besides the spatial and temporal information, the energy content of the electronic motions can be retrieved from the energy-resolved diffraction patterns, which provide unequivocal interpretations of the electronic motions. Because of this, we are able to explain the counterintuitive temporal behavior of the diffraction images, which show a quite different temporal behavior and little connection to the electron densities. This work has been supported in part by AFOSR Award No. FA9550-12-1-0149.

  19. Ultrafast electron injection into photo-excited organic molecules.

    PubMed

    Cvetko, Dean; Fratesi, Guido; Kladnik, Gregor; Cossaro, Albano; Brivio, Gian Paolo; Venkataraman, Latha; Morgante, Alberto

    2016-08-10

    Charge transfer rates at metal/organic interfaces affect the efficiencies of devices for organic based electronics and photovoltaics. A quantitative study of electron transfer rates, which take place on the femtosecond timescale, is often difficult, especially since in most systems the molecular adsorption geometry is unknown. Here, we use X-ray resonant photoemission spectroscopy to measure ultrafast charge transfer rates across pyridine/Au(111) interfaces while also controlling the molecular orientation on the metal. We demonstrate that a bi-directional charge transfer across the molecule/metal interface is enabled upon creation of a core-exciton on the molecule with a rate that has a strong dependence on the molecular adsorption angle. Through density functional theory calculations, we show that the alignment of molecular levels relative to the metal Fermi level is dramatically altered when a core-hole is created on the molecule, allowing the lowest unoccupied molecular orbital to fall partially below the metal Fermi level. We also calculate charge transfer rates as a function of molecular adsorption geometry and find a trend that agrees with the experiment. These findings thus give insight into the charge transfer dynamics of a photo-excited molecule on a metal surface. PMID:27444572

  20. Attosecond electron emission probes of ultrafast nanolocalized fields

    NASA Astrophysics Data System (ADS)

    Kling, Matthias

    2011-05-01

    Ongoing experimental and theoretical work on the temporal and spatial characterization of nanolocalized plasmonic fields will be presented. Because of their broad spectral bandwidth, plasmons in metal nanoparticles undergo ultrafast dynamics with timescales as short as a few hundred attoseconds. So far, the spatiotemporal dynamics of optical fields localized on the nanoscale has been hidden from direct access in the real space and time domain. Our ultimate goal is to characterize the nanoplasmonic fields not only on a nanometer spatial scale but also on ~100 attosecond temporal scale. Information about the nanoplasmonic fields, which are excited by few-cycle laser pulses with stable electric field waveform, can be obtained by the measurement of photoemitted electrons. We will present recent results on the large acceleration of recollision electrons in nanolocalized fields near dielectric nanoparticles following the excitation by 5-fs near-infrared laser pulses with controlled electric field waveforms. This work has been carried out in collaboration with Th. Fennel (University of Rostock), E. Ruehl (FU Berlin), and M.I. Stockman (GSU Atlanta). We acknowledge support by the DFG via Emmy-Noether program and SPP1391.

  1. Design of a high-flux instrument for ultrafast electron diffraction and microscopy

    NASA Astrophysics Data System (ADS)

    Filippetto, D.; Qian, H.

    2016-05-01

    We present the design and optimization of a new instrument for ultrafast electron diffraction and imaging. The proposed instrument merges the high peak current and relativistic electron energies of radio-frequency guns, with the high average electron flux of static electron microscopes, extending the beam parameter space achievable with relativistic electrons by many orders of magnitude. An immediate consequence of this work is a broader range of accessible science by using electron probes, enabling techniques as femtosecond nano-diffraction and coherent diffraction imaging, and paving the way to direct observation of ultrafast dynamics in complex and isolated samples, from nanocrystals, to nano/micro droplets and organic molecules.

  2. Role of electron-electron interference in ultrafast time-resolved imaging of electronic wavepackets

    NASA Astrophysics Data System (ADS)

    Dixit, Gopal; Santra, Robin

    2013-04-01

    Ultrafast time-resolved x-ray scattering is an emerging approach to image the dynamical evolution of the electronic charge distribution during complex chemical and biological processes in real-space and real-time. Recently, the differences between semiclassical and quantum-electrodynamical (QED) theory of light-matter interaction for scattering of ultrashort x-ray pulses from the electronic wavepacket were formally demonstrated and visually illustrated by scattering patterns calculated for an electronic wavepacket in atomic hydrogen [G. Dixit, O. Vendrell, and R. Santra, Proc. Natl. Acad. Sci. U.S.A. 109, 11636 (2012)], 10.1073/pnas.1202226109. In this work, we present a detailed analysis of time-resolved x-ray scattering from a sample containing a mixture of non-stationary and stationary electrons within both the theories. In a many-electron system, the role of scattering interference between a non-stationary and several stationary electrons to the total scattering signal is investigated. In general, QED and semiclassical theory provide different results for the contribution from the scattering interference, which depends on the energy resolution of the detector and the x-ray pulse duration. The present findings are demonstrated by means of a numerical example of x-ray time-resolved imaging for an electronic wavepacket in helium. It is shown that the time-dependent scattering interference vanishes within semiclassical theory and the corresponding patterns are dominated by the scattering contribution from the time-independent interference, whereas the time-dependent scattering interference contribution do not vanish in the QED theory and the patterns are dominated by the scattering contribution from the non-stationary electron scattering.

  3. Free electron laser-driven ultrafast rearrangement of the electronic structure in Ti

    PubMed Central

    Principi, E.; Giangrisostomi, E.; Cucini, R.; Bencivenga, F.; Battistoni, A.; Gessini, A.; Mincigrucci, R.; Saito, M.; Di Fonzo, S.; D'Amico, F.; Di Cicco, A.; Gunnella, R.; Filipponi, A.; Giglia, A.; Nannarone, S.; Masciovecchio, C.

    2015-01-01

    High-energy density extreme ultraviolet radiation delivered by the FERMI seeded free-electron laser has been used to create an exotic nonequilibrium state of matter in a titanium sample characterized by a highly excited electron subsystem at temperatures in excess of 10 eV and a cold solid-density ion lattice. The obtained transient state has been investigated through ultrafast absorption spectroscopy across the Ti M2,3-edge revealing a drastic rearrangement of the sample electronic structure around the Fermi level occurring on a time scale of about 100 fs. PMID:26798835

  4. Ultrafast Molecular Three-Electron Collective Auger Decay

    NASA Astrophysics Data System (ADS)

    Feifel, Raimund

    2016-06-01

    A new class of many-electron Auger transitions in atoms was initially proposed over 40 years ago, but the first tentative evidence for its real existence was only adduced by Lee et al. in 1993, on the basis of the resonant Auger spectrum of Kr. Using a multi-electron coincidence technique with synchrotron radiation, we unambiguously showed very recently that the transition suggested by Lee et al. in Kr really does take place, but with a rather small branching ratio. Related inter-atomic three-electron transitions in rare gas clusters were recently predicted by Averbukh and Kolorenc and demonstrated by Ouchi et al.. From consideration of the energy levels involved it seems that the basic three-electron process could occur in molecules too, wherever a double inner-valence shell vacancy lies at a higher energy than the molecular triple ionisation onset. Experiments on CH_3F reveal for the first time the existence of this new decay pathway there, and calculations show that despite its three-electron nature, its effective oscillator strength is orders of magnitudes higher than in atoms, allowing an efficient competition with both molecular dissociation and two-electron decay channels on the ultrafast time scale. The dramatic enhancement of the molecular three-electron Auger transition can be explained in terms of a partial breakdown of the molecular orbital picture of ionisation. We predict that the collective decay pathway will be significant in a wide variety of heteroatomic molecules ionised by extreme UV and soft X-rays, particularly at Free-Electron-Lasers where double inner-shell vacancies can be created efficiently by two-photon transitions. G.N. Ogurtsov et al., Sov. Phys. Tech. Phys. 15, 1656 (1971) and V.V. Afrosimov et al., JETP Lett. 21, 249 (1975). I. Lee, R. Wehlitz, U. Becker and M. Ya. Amusia, J. Phys. B: At. Mol. Opt. Phys. 26, L41 (1993). J.H.D. Eland, R.J. Squibb, M. Mucke, S. Zagorodskikh, P. Linusson, and R. Feifel, New J. Phys. 17, 122001 (2015). V

  5. Quantum effects in ultrafast electron transfers within cryptochromes.

    PubMed

    Firmino, Thiago; Mangaud, Etienne; Cailliez, Fabien; Devolder, Adrien; Mendive-Tapia, David; Gatti, Fabien; Meier, Christoph; Desouter-Lecomte, Michèle; de la Lande, Aurélien

    2016-08-21

    Cryptochromes and photolyases are flavoproteins that may undergo ultrafast charge separation upon electronic excitation of their flavin cofactors. Charge separation involves chains of three or four tryptophan residues depending on the protein of interest. The molecular mechanisms of these processes are not completely clear. In the present work we investigate the relevance of quantum effects like the occurrence of nuclear tunneling and of coherences upon charge transfer in Arabidopsis thaliana cryptochromes. The possible breakdown of the Condon approximation is also investigated. We have devised a simulation protocol based on the realization of molecular dynamics simulations on diabatic potential energy surfaces defined at the hybrid constrained density functional theory/molecular mechanics level. The outcomes of the simulations are analyzed through various dedicated kinetics schemes related to the Marcus theory that account for the aforementioned quantum effects. MD simulations also provide a basic material to define realistic model Hamiltonians for subsequent quantum dissipative dynamics. To carry out quantum simulations, we have implemented an algorithm based on the Hierarchical Equations of Motion. With this new tool in hand we have been able to model the electron transfer chain considering either two- or three-state models. Kinetic models and quantum simulations converge to the conclusion that quantum effects have a significant impact on the rate of charge separation. Nuclear tunneling involving atoms of the tryptophan redox cofactors as well as of the environment (protein atoms and water molecules) is significant. On the other hand non-Condon effects are negligible in most simulations. Taken together, the results of the present work provide new insights into the molecular mechanisms controlling charge separation in this family of flavoproteins. PMID:27427185

  6. Probing the ultrafast electron transfer at the CuPc/Au(111) interface

    SciTech Connect

    Chen Wei; Wang Li; Qi Dongchen; Chen Shi; Gao Xingyu; Wee, Andrew Thye Shen

    2006-05-01

    Core-hole clock spectroscopy and near-edge x-ray-absorption fine structure measurements have been used to investigate the ultrafast electron transfer dynamics at the Copper(II) phthalocyanine (CuPc)/Au(111) interface. It was found that the strong electronic coupling between the first layer of CuPc molecules and Au(111) substrate favors ultrafast electron transfer from the lowest unoccupied molecular orbital of the CuPc molecules to the conduction band of Au(111) in the time scale of {approx}6 fs. In contrast, the intermolecular electron transfer within multilayers of CuPc molecules via the weak van der Waals interaction was much slower.

  7. Ultrafast electronic dynamics in the metal-insulator transition compound NdNiO3

    NASA Astrophysics Data System (ADS)

    Ruello, P.; Zhang, S.; Laffez, P.; Perrin, B.; Gusev, V.

    2007-10-01

    Visible ultrafast optical property studies have been performed in the metal-insulator transition compound NdNiO3 from room temperature down to 16K . A clear slowing down of the electronic relaxation is reported when the system becomes insulating. Two characteristic times of electronic relaxation have been found in the insulating phase while a single one is observed in the metallic state. Moreover, the magnitude of the ultrafast electronic transient reflectivity exhibits a drastic increase in the insulating state. Finally, a hysteresis of the electronic response is evidenced in accordance with electrical resistivity measurements.

  8. An ultrafast electron microscope gun driven by two-photon photoemission from a nanotip cathode

    SciTech Connect

    Bormann, Reiner; Strauch, Stefanie; Schäfer, Sascha Ropers, Claus

    2015-11-07

    We experimentally and numerically investigate the performance of an advanced ultrafast electron source, based on two-photon photoemission from a tungsten needle cathode incorporated in an electron microscope gun geometry. Emission properties are characterized as a function of the electrostatic gun settings, and operating conditions leading to laser-triggered electron beams of very low emittance (below 20 nm mrad) are identified. The results highlight the excellent suitability of optically driven nano-cathodes for the further development of ultrafast transmission electron microscopy.

  9. Ultrafast electron microscopy and diffraction with laser-driven field emitters

    NASA Astrophysics Data System (ADS)

    Ropers, Claus

    2015-03-01

    Ultrafast structural dynamics in solids and nanostructures can be investigated by an increasing number of sophisticated electron and x-ray diffraction techniques. Electrons are particularly suited for this purpose, exhibiting high scattering cross-sections and allowing for beam control by versatile electrostatic or magnetic lens systems. The capabilities of time-resolved electron imaging techniques critically depend on the employed source of laser-driven ultrashort electron pulses. Nanoscopic sources offer exceptional possibilities for the generation of electron probe pulses with very short durations and high spatial beam coherence. In this talk, I will discuss recent progress in the development of ultrafast electron microscopy and diffraction based on nanoscopic photocathodes. In particular, we implemented ultrafast low-energy electron diffraction (ULEED) and ultrafast transmission electron microscopy (UTEM) driven by nonlinear photoemission from field emission tips. ULEED enables the study of structural changes with high temporal resolution and ultimate surface sensitivity, at sub-keV electron energies. As a first application of this technique, we studied the structural phase transition in a stripe-like polymer superstructure on freestanding monolayer graphene. An advanced UTEM instrument was realized by custom modifications of a standard transmission electron microscope, leading to electron focal spot sizes in the microscope's sample plane of about 10 nm and electron pulse durations of less than 700 fs. Utilizing these features, we investigate the quantum-coherent interaction between the ultrashort electron pulse and the optical near-field of an illuminated nanostructure. Finally, further applications and prospects of ultrafast electron imaging, diffraction and spectroscopy using nanoscale field emitters will be discussed.

  10. Exceptional rigidity and biomechanics of amyloid revealed by 4D electron microscopy.

    PubMed

    Fitzpatrick, Anthony W P; Park, Sang Tae; Zewail, Ahmed H

    2013-07-01

    Amyloid is an important class of proteinaceous material because of its close association with protein misfolding disorders such as Alzheimer's disease and type II diabetes. Although the degree of stiffness of amyloid is critical to the understanding of its pathological and biological functions, current estimates of the rigidity of these β-sheet-rich protein aggregates range from soft (10(8) Pa) to hard (10(10) Pa) depending on the method used. Here, we use time-resolved 4D EM to directly and noninvasively measure the oscillatory dynamics of freestanding, self-supporting amyloid beams and their rigidity. The dynamics of a single structure, not an ensemble, were visualized in space and time by imaging in the microscope an amyloid-dye cocrystal that, upon excitation, converts light into mechanical work. From the oscillatory motion, together with tomographic reconstructions of three studied amyloid beams, we determined the Young modulus of these highly ordered, hydrogen-bonded β-sheet structures. We find that amyloid materials are very stiff (10(9) Pa). The potential biological relevance of the deposition of such a highly rigid biomaterial in vivo are discussed.

  11. 4d electron Ruthenate systems: their unique and new magnetic properties

    NASA Astrophysics Data System (ADS)

    Lee, Seungran; Shin, Yeongjae; Anwar, M. S.; Sugimoto, Yusuke; Lee, Mincheol; Kang, Sungjin; Yonezawa, Shingo; Maeno, Yoshiteru; Noh, Taewon

    The Ruddlesden-Popper series (PR) of Srn+1RunO3n+1 has attract much interest of their unique physical properties. Among them, SrRuO3 (n = ∞) (SRO) is the only ferromagnetic metallic oxide especially in Ru 4d transition metal oxides. Bulk SRO has orthorhombic structure showing the Curie temperature (TC) ~ 160 K. It is well known that RuO6 octahedral distortion plays critical roles in its mangetic properties. In film systems, such RuO6 octahedra can be easily controlled by strain-engineering. In this talk, with high quality SRO films fully strained (-1.7%-1%) using various substrates, we systematically studied their structural changes and associated magnetic properties. Compared to theoretical predictions, the structural changes can be explained, while the magnetic property changes cannot be understood. Surprisingly, when SRO113 is grown on its PR series of Sr2RuO4 (n=1) (SRO214) single crystal, the exact substrate of SRO214 magnetization results in strongly enhanced magnetization (M > 3 μB/Ru, TC ~ 160 K), which has never found SRO113 (001) since the low-spin configuration of SRO113 prevent M never exceed 2 μB/Ru. The mystery of M in SRO113 (especially SRO113/SRO214) will be further discussed.

  12. Proposed Imaging of the Ultrafast Electronic Motion in Samples using X-Ray Phase Contrast

    NASA Astrophysics Data System (ADS)

    Dixit, Gopal; Slowik, Jan Malte; Santra, Robin

    2013-03-01

    Tracing the motion of electrons has enormous relevance to understanding ubiquitous phenomena in ultrafast science, such as the dynamical evolution of the electron density during complex chemical and biological processes. Scattering of ultrashort x-ray pulses from an electronic wave packet would appear to be the most obvious approach to image the electronic motion in real time and real space with the notion that such scattering patterns, in the far-field regime, encode the instantaneous electron density of the wave packet. However, recent results by Dixit et al. [Proc. Natl. Acad. Sci. U.S.A. 109, 11 636 (2012)] have put this notion into question and have shown that the scattering in the far-field regime probes spatiotemporal density-density correlations. Here, we propose a possible way to image the instantaneous electron density of the wave packet via ultrafast x-ray phase contrast imaging. Moreover, we show that inelastic scattering processes, which plague ultrafast scattering in the far-field regime, do not contribute in ultrafast x-ray phase contrast imaging as a consequence of an interference effect. We illustrate our general findings by means of a wave packet that lies in the time and energy range of the dynamics of valence electrons in complex molecular and biological systems. This present work offers a potential to image not only instantaneous snapshots of nonstationary electron dynamics, but also the Laplacian of these snapshots which provide information about the complex bonding and topology of the charge distributions in the systems.

  13. Graphene-layered steps and their fields visualized by 4D electron microscopy

    PubMed Central

    Park, Sang Tae; Yurtsever, Aycan; Baskin, John Spencer; Zewail, Ahmed H.

    2013-01-01

    Enhanced image contrast has been seen at graphene-layered steps a few nanometers in height by means of photon-induced near-field electron microscopy (PINEM) using synchronous femtosecond pulses of light and electrons. The observed steps are formed by the edges of graphene strips lying on the surface of a graphene substrate, where the strips are hundreds of nanometers in width and many micrometers in length. PINEM measurements reflect the interaction of imaging electrons and induced (near) electric fields at the steps, and this leads to a much higher contrast than that achieved in bright-field transmission electron microscopy imaging of the same strips. Theory and numerical simulations support the experimental PINEM findings and elucidate the nature of the electric field at the steps formed by the graphene layers. These results extend the range of applications of the experimental PINEM methodology, which has previously been demonstrated for spherical, cylindrical, and triangular nanostructures, to shapes of high aspect ratio (rectangular strips), as well as into the regime of atomic layer thicknesses. PMID:23690572

  14. Transverse and longitudinal space-charge-induced broadenings of ultrafast electron packets

    SciTech Connect

    Collin, S.; Merano, M.; Gatri, M.; Sonderegger, S.; Renucci, P.; Ganiere, J.-D.; Deveaud, B.

    2005-11-01

    High brightness ultrafast electron sources are limited by space-charge effects. In the high-electron-density regime, Coulomb repulsion induces both transverse and longitudinal broadenings of electron packets. We describe a three-dimensional mean-field model, which takes into account Coulomb repulsion in all directions. Measurements of spatial electron pulse widths are carried out after extraction from a photoemission electron gun. Experiments and simulation results are in very good agreement. Coulomb repulsion effects are found to occur close to the photocathode in the extraction region. The correlation between transverse and temporal broadenings of electron packets is discussed and gives the limits for the generation of high-electron-density ultrafast electron pulses. Pulses of temporal length of about 2 ps and a diameter of about 30 {mu}m should be obtained.

  15. Exciton dispersion in silicon nanostructures formed by intense, ultra-fast electronic excitation

    NASA Astrophysics Data System (ADS)

    Hamza, A. V.; Newman, M. W.; Thielen, P. A.; Lee, H. W. H.; Schenkel, T.; McDonald, J. W.; Schneider, D. H.

    The intense, ultra-fast electronic excitation of clean silicon (100)-(2×1) surfaces leads to the formation of silicon nanostructures embedded in silicon, which photoluminesce in the yellow-green ( 2-eV band gap). The silicon surfaces were irradiated with slow, highly charged ions (e.g. Xe44+ and Au53+) to produce the ultra-fast electronic excitation. The observation of excitonic features in the luminescence from these nanostructures has recently been reported. In this paper we report the dispersion of the excitonic features with laser excitation energy. A phonon-scattering process is proposed to explain the observed dispersion.

  16. An ultrafast nanotip electron gun triggered by grating-coupled surface plasmons

    NASA Astrophysics Data System (ADS)

    Schröder, Benjamin; Sivis, Murat; Bormann, Reiner; Schäfer, Sascha; Ropers, Claus

    2015-12-01

    We demonstrate multiphoton photoelectron emission from gold nanotips induced by nanofocusing surface plasmons, resonantly excited on the tip shaft by a grating coupler. The tip is integrated into an electron gun assembly, which facilitates control over the spatial emission sites and allows us to disentangle direct grating emission from plasmon-triggered apex emission. The nanoscale source size of this electron gun concept enables highly coherent electron pulses with applications in ultrafast electron imaging and diffraction.

  17. An ultrafast nanotip electron gun triggered by grating-coupled surface plasmons

    SciTech Connect

    Schröder, Benjamin; Sivis, Murat; Bormann, Reiner; Schäfer, Sascha; Ropers, Claus

    2015-12-07

    We demonstrate multiphoton photoelectron emission from gold nanotips induced by nanofocusing surface plasmons, resonantly excited on the tip shaft by a grating coupler. The tip is integrated into an electron gun assembly, which facilitates control over the spatial emission sites and allows us to disentangle direct grating emission from plasmon-triggered apex emission. The nanoscale source size of this electron gun concept enables highly coherent electron pulses with applications in ultrafast electron imaging and diffraction.

  18. Analysis of ultrafast electronic and magnetic response of ferromagnetic transition metals

    NASA Astrophysics Data System (ADS)

    Knorren, R.; Bennemann, K. H.

    We study the ultrafast dynamics of the electronic and magnetic properties of ferromagnetic transition metals after optical excitation. The time scales are given by the fast electronic response leading to thermalization of the electronic distribution and consequently also of the magnetization. We propose a theoretical model describing thermalization of nonequilibrium electrons and calculate the time evolution of the temperature and the magnetization-dependent second-harmonic generation. We compare our theoretical analysis with experimental results on Ni.

  19. Chemical bonding and electronic structure of 4d-metal monocarbides

    NASA Astrophysics Data System (ADS)

    Wang, Jinping; Sun, Xiaobo; Wu, Zhijian

    2006-07-01

    Bond distances, vibrational frequencies, dissociation energies, electron affinities, ionization potentials and dipole moments of the title molecules in neutral and charged ions were studied by use of density functional method. Ground states for each molecule were assigned. For neutral and cationic molecules, the bond distance decreases from YC (YC +) to RhC (RhC +), then increases, while for anionic molecules, the bond distance decreases from YC - to RuC -, then increases. Opposite trend was observed for vibrational frequency. The bond ionic character decreases from ZrC to PdC for neutral molecules. The bonding patterns are discussed and compared with the available studies.

  20. Ultrafast electronic dynamics in polyatomic molecules studied using femtosecond vacuum ultraviolet and x-ray pulses

    NASA Astrophysics Data System (ADS)

    Suzuki, Toshinori

    2014-06-01

    Time-resolved velocity map photoelectron imaging is performed using sub-20 fs deep ultraviolet and vacuum ultraviolet pulses to study electronic dynamics of isolated polyatomic molecules. The non-adiabatic dynamics of pyrazine, furan and carbon disulfide (CS2) are described as examples. Also described is sub-picosecond time-resolved x-ray direct absorption spectroscopy using a hard x-ray free electron laser (SACLA) and a synchronous near ultraviolet laser to study ultrafast electronic dynamics in solutions.

  1. Ultrafast electronic relaxation of excited state vitamin B 12 in the gas phase

    NASA Astrophysics Data System (ADS)

    Shafizadeh, Niloufar; Poisson, Lionel; Soep, Benoıˆt

    2008-06-01

    The time evolution of electronically excited vitamin B 12 (cyanocobalamin) has been observed for the first time in the gas phase. It reveals an ultrafast decay to a state corresponding to metal excitation. This decay is interpreted as resulting from a ring to metal electron transfer. This opens the observation of the excited state of other complex biomimetic systems in the gas phase, the key to the characterisation of their complex evolution through excited electronic states.

  2. Ultrafast quenching of electron-boson interaction and superconducting gap in a cuprate superconductor.

    PubMed

    Zhang, Wentao; Hwang, Choongyu; Smallwood, Christopher L; Miller, Tristan L; Affeldt, Gregory; Kurashima, Koshi; Jozwiak, Chris; Eisaki, Hiroshi; Adachi, Tadashi; Koike, Yoji; Lee, Dung-Hai; Lanzara, Alessandra

    2014-01-01

    Ultrafast spectroscopy is an emerging technique with great promise in the study of quantum materials, as it makes it possible to track similarities and correlations that are not evident near equilibrium. Thus far, however, the way in which these processes modify the electron self-energy--a fundamental quantity describing many-body interactions in a material--has been little discussed. Here we use time- and angle-resolved photoemission to directly measure the ultrafast response of self-energy to near-infrared photoexcitation in high-temperature cuprate superconductor. Below the critical temperature of the superconductor, ultrafast excitations trigger a synchronous decrease of electron self-energy and superconducting gap, culminating in a saturation in the weakening of electron-boson coupling when the superconducting gap is fully quenched. In contrast, electron-boson coupling is unresponsive to ultrafast excitations above the critical temperature of the superconductor and in the metallic state of a related material. These findings open a new pathway for studying transient self-energy and correlation effects in solids.

  3. Ultrafast Spin Density Wave Transition in Chromium Governed by Thermalized Electron Gas

    NASA Astrophysics Data System (ADS)

    Nicholson, C. W.; Monney, C.; Carley, R.; Frietsch, B.; Bowlan, J.; Weinelt, M.; Wolf, M.

    2016-09-01

    The energy and momentum selectivity of time- and angle-resolved photoemission spectroscopy is exploited to address the ultrafast dynamics of the antiferromagnetic spin density wave (SDW) transition photoexcited in epitaxial thin films of chromium. We are able to quantitatively extract the evolution of the SDW order parameter Δ through the ultrafast phase transition and show that Δ is governed by the transient temperature of the thermalized electron gas, in a mean field description. The complete destruction of SDW order on a sub-100 fs time scale is observed, much faster than for conventional charge density wave materials. Our results reveal that equilibrium concepts for phase transitions such as the order parameter may be utilized even in the strongly nonadiabatic regime of ultrafast photoexcitation.

  4. Ultrafast time dynamics studies of periodic lattices with free electron laser radiation

    SciTech Connect

    Quevedo, W.; Busse, G.; Hallmann, J.; More, R.; Petri, M.; Rajkovic, I.; Krasniqi, F.; Rudenko, A.; Tschentscher, T.; Stojanovic, N.; Duesterer, S.; Treusch, R.; Tolkiehn, M.; Techert, S.

    2012-11-01

    It has been proposed that radiation from free electron laser (FEL) at Hamburg (FLASH) can be used for ultrafast time-resolved x-ray diffraction experiments based on the near-infrared (NIR) pump/FEL probe scheme. Here, investigation probing the ultrafast structural dynamics of periodic nano-crystalline organic matter (silver behenate) with such a scheme is reported. Excitation with a femtosecond NIR laser leads to an ultrafast lattice modification which time evolution has been studied through the scattering of vacuum ultraviolet FEL pulses. The found effect last for 6 ps and underpins the possibility for studying nanoperiodic dynamics down to the FEL source time resolution. Furthermore, the possibility of extending the use of silver behenate (AgBh) as a wavelength and temporal calibration tool for experiments with soft x-ray/FEL sources is suggested.

  5. Anomalous ultrafast dynamics of hot plasmonic electrons in nanostructures with hot spots.

    PubMed

    Harutyunyan, Hayk; Martinson, Alex B F; Rosenmann, Daniel; Khorashad, Larousse Khosravi; Besteiro, Lucas V; Govorov, Alexander O; Wiederrecht, Gary P

    2015-09-01

    The interaction of light and matter in metallic nanosystems is mediated by the collective oscillation of surface electrons, called plasmons. After excitation, plasmons are absorbed by the metal electrons through inter- and intraband transitions, creating a highly non-thermal distribution of electrons. The electron population then decays through electron-electron interactions, creating a hot electron distribution within a few hundred femtoseconds, followed by a further relaxation via electron-phonon scattering on the timescale of a few picoseconds. In the spectral domain, hot plasmonic electrons induce changes to the plasmonic resonance of the nanostructure by modifying the dielectric constant of the metal. Here, we report on the observation of anomalously strong changes to the ultrafast temporal and spectral responses of these excited hot plasmonic electrons in hybrid metal/oxide nanostructures as a result of varying the geometry and composition of the nanostructure and the excitation wavelength. In particular, we show a large ultrafast, pulsewidth-limited contribution to the excited electron decay signal in hybrid nanostructures containing hot spots. The intensity of this contribution correlates with the efficiency of the generation of highly excited surface electrons. Using theoretical models, we attribute this effect to the generation of hot plasmonic electrons from hot spots. We then develop general principles to enhance the generation of energetic electrons through specifically designed plasmonic nanostructures that could be used in applications where hot electron generation is beneficial, such as in solar photocatalysis, photodetectors and nonlinear devices.

  6. Ultrafast Electronic And Nuclear Dynamics In Dissociative Photoionization Of Molecular Hydrogen and Deuterium

    NASA Astrophysics Data System (ADS)

    Billaud, P.; Picard, Y. J.; Géléoc, M.; Hergott, J.-F.; Carré, B.; Breger, P.; Ruchon, T.; Veyrinas, K.; Roulliay, M.; Delmotte, F.; Böttcher, M.; Huetz, A.; Dowek, D.

    2012-11-01

    Single-photon dissociative photoionization of H2/D2 in the Q1, Q2 doubly excited states resonance regions, where ultrafast electronic and nuclear dynamics are coupled, is studied using the vector-correlation method with single selected femtosecond high-order harmonic and synchrotron radiation in the VUV. Results are compared at the level of electron-ion kinetic energy correlation diagrams, asymmetry parameters, and the molecular frame photoelectron angular distributions.

  7. Discrete Chromatic Aberrations Arising from Photoinduced Electron-Photon Interactions in Ultrafast Electron Microscopy.

    PubMed

    Plemmons, Dayne A; Flannigan, David J

    2016-05-26

    In femtosecond ultrafast electron microscopy (UEM) experiments, the initial excitation period is composed of spatiotemporal overlap of the temporally commensurate pump photon pulse and probe photoelectron packet. Generation of evanescent near-fields at the nanostructure specimens produces a dispersion relation that enables coupling of the photons (ℏω = 2.4 eV, for example) and freely propagating electrons (200 keV, for example) in the near-field. Typically, this manifests as discrete peaks occurring at integer multiples (n) of the photon energy in the low-loss/gain region of electron-energy spectra (i.e., at 200 keV ± nℏω eV). Here, we examine the UEM imaging resolution implications of the strong inelastic near-field interactions between the photons employed in optical excitation and the probe photoelectrons. We find that the additional photoinduced energy dispersion occurring when swift electrons pass through intense evanescent near-fields results in a discrete chromatic aberration that limits the spatial resolving power to several angstroms during the excitation period. PMID:27111530

  8. Atomic-scale imaging in real and energy space developed in ultrafast electron microscopy.

    PubMed

    Park, Hyun Soon; Baskin, J Spencer; Kwon, Oh-Hoon; Zewail, Ahmed H

    2007-09-01

    In this contribution, we report the development of ultrafast electron microscopy (UEM) with atomic-scale real-, energy-, and Fourier-space resolutions. This second-generation UEM provides images, diffraction patterns, and electron energy spectra, and here we demonstrate its potential with applications for nanostructured materials and organometallic crystals. We clearly resolve the separation between atoms in the direct images and the Bragg spots/Debye-Scherrer rings in diffraction and obtain the electronic structure and elemental energies in the electron energy loss spectra (EELS) and energy filtered transmission electron microscopy (EFTEM).

  9. Quantum coherent optical phase modulation in an ultrafast transmission electron microscope.

    PubMed

    Feist, Armin; Echternkamp, Katharina E; Schauss, Jakob; Yalunin, Sergey V; Schäfer, Sascha; Ropers, Claus

    2015-05-14

    Coherent manipulation of quantum systems with light is expected to be a cornerstone of future information and communication technology, including quantum computation and cryptography. The transfer of an optical phase onto a quantum wavefunction is a defining aspect of coherent interactions and forms the basis of quantum state preparation, synchronization and metrology. Light-phase-modulated electron states near atoms and molecules are essential for the techniques of attosecond science, including the generation of extreme-ultraviolet pulses and orbital tomography. In contrast, the quantum-coherent phase-modulation of energetic free-electron beams has not been demonstrated, although it promises direct access to ultrafast imaging and spectroscopy with tailored electron pulses on the attosecond scale. Here we demonstrate the coherent quantum state manipulation of free-electron populations in an electron microscope beam. We employ the interaction of ultrashort electron pulses with optical near-fields to induce Rabi oscillations in the populations of electron momentum states, observed as a function of the optical driving field. Excellent agreement with the scaling of an equal-Rabi multilevel quantum ladder is obtained, representing the observation of a light-driven 'quantum walk' coherently reshaping electron density in momentum space. We note that, after the interaction, the optically generated superposition of momentum states evolves into a train of attosecond electron pulses. Our results reveal the potential of quantum control for the precision structuring of electron densities, with possible applications ranging from ultrafast electron spectroscopy and microscopy to accelerator science and free-electron lasers.

  10. Quantum coherent optical phase modulation in an ultrafast transmission electron microscope

    NASA Astrophysics Data System (ADS)

    Feist, Armin; Echternkamp, Katharina E.; Schauss, Jakob; Yalunin, Sergey V.; Schäfer, Sascha; Ropers, Claus

    2015-05-01

    Coherent manipulation of quantum systems with light is expected to be a cornerstone of future information and communication technology, including quantum computation and cryptography. The transfer of an optical phase onto a quantum wavefunction is a defining aspect of coherent interactions and forms the basis of quantum state preparation, synchronization and metrology. Light-phase-modulated electron states near atoms and molecules are essential for the techniques of attosecond science, including the generation of extreme-ultraviolet pulses and orbital tomography. In contrast, the quantum-coherent phase-modulation of energetic free-electron beams has not been demonstrated, although it promises direct access to ultrafast imaging and spectroscopy with tailored electron pulses on the attosecond scale. Here we demonstrate the coherent quantum state manipulation of free-electron populations in an electron microscope beam. We employ the interaction of ultrashort electron pulses with optical near-fields to induce Rabi oscillations in the populations of electron momentum states, observed as a function of the optical driving field. Excellent agreement with the scaling of an equal-Rabi multilevel quantum ladder is obtained, representing the observation of a light-driven `quantum walk' coherently reshaping electron density in momentum space. We note that, after the interaction, the optically generated superposition of momentum states evolves into a train of attosecond electron pulses. Our results reveal the potential of quantum control for the precision structuring of electron densities, with possible applications ranging from ultrafast electron spectroscopy and microscopy to accelerator science and free-electron lasers.

  11. Communication: Effects of thermionic-gun parameters on operating modes in ultrafast electron microscopy.

    PubMed

    Kieft, Erik; Schliep, Karl B; Suri, Pranav K; Flannigan, David J

    2015-09-01

    Ultrafast electron microscopes with thermionic guns and LaB6 sources can be operated in both the nanosecond, single-shot and femtosecond, single-electron modes. This has been demonstrated with conventional Wehnelt electrodes and absent any applied bias. Here, by conducting simulations using the General Particle Tracer code, we define the electron-gun parameter space within which various modes may be optimized. The properties of interest include electron collection efficiency, temporal and energy spreads, and effects of laser-pulse duration incident on the LaB6 source. We find that collection efficiencies can reach 100% for all modes, despite there being no bias applied to the electrode.

  12. Excitation of the 4d shell in Sb, Te, and BaF2 with inelastic electron scattering: Collective or single particle?

    NASA Astrophysics Data System (ADS)

    Franck, Carl; Schnatterly, S. E.

    1982-06-01

    Simple models suggest that the momentum-transfer (q) dependence of inelastic electron scattering is sensitive to the difference between collective and single-particle behavior in atomic dynamics. We measured the energy centroid of the 4d continuum peak for 04d shells: Sb, Te, and BaF2, and find that a single-particle description is favored.

  13. Ultrafast electronic dynamics in laser-excited crystalline bismuth

    NASA Astrophysics Data System (ADS)

    Melnikov, A.; Misochko, O.; Chekalin, S.

    2013-03-01

    Femtosecond spectroscopy was applied to capture complex dynamics of non equilibrium electrons in bismuth. Data analysis reveals significant wavevector dependence of electron-hole and electron-phonon coupling strength along the Γ-T direction of the Brillouin zone

  14. Ultrafast excited state relaxation dynamics of electron deficient porphyrins: Conformational and electronic factors

    NASA Astrophysics Data System (ADS)

    Okhrimenko, Albert N.

    Metallo-tetrapyrroles (MTP) are highly stable macrocyclic pi-systems that display interesting properties that make them potential candidates for various applications. Among these applications are optoelectronics, magnetic materials, photoconductive materials, non-linear optical materials and photo tumor therapeutic drugs. These applications are generally related to their high stability and efficient light absorption ability in the visible and near-infrared region of the optical spectrum. Metallo porphyrins are well known and widely studied representatives of metallotetrapyrroles. Electron deficient substituents in the meso positions are well known to greatly influence the interaction between the metal d-orbitals and the nitrogen orbitals of the tetrapyrrole macrocycle. In this work, a series of electron deficient porphyrins has been studied to gain some knowledge about the change in the excited state dynamics with structural and electronic modifications. Among these porphyrins is nickel and iron modified species bearing perfluoro-, perprotio-, p-nitrophenyl- and perfluorophenyl-meso substituents. Ultrafast transient absorption spectrometry has been used as the main research instrument along with other spectroscopic and electrochemical methods. A new technique has been employed to study the photophysical properties of zinc (II) tetraphenylporphine cation radical. It employs a combination of controlled potential coulometry and femtosecond absorption spectrometry. The fast transient lifetime of 17 ps of the pi-cation species originates in very efficient mixing of the a2u HOMO cation orbital that places electronic density mainly on pyrrolic nitrogens and metal d-orbitals. That explains the lack of any emission of the cationic species. This non-radiative decay process might elucidate the processes taking place in photosynthetic systems when electron is removed from porphyrinic moiety and the hole is produced. In this work zinc(II) meso-tetraphenylporphine radial cation

  15. Tuning ultrafast electron thermalization pathways in a van der Waals heterostructure

    NASA Astrophysics Data System (ADS)

    Ma, Qiong; Andersen, Trond I.; Nair, Nityan L.; Gabor, Nathaniel M.; Massicotte, Mathieu; Lui, Chun Hung; Young, Andrea F.; Fang, Wenjing; Watanabe, Kenji; Taniguchi, Takashi; Kong, Jing; Gedik, Nuh; Koppens, Frank H. L.; Jarillo-Herrero, Pablo

    2016-05-01

    Ultrafast electron thermalization--the process leading to carrier multiplication via impact ionization, and hot-carrier luminescence--occurs when optically excited electrons in a material undergo rapid electron-electron scattering to redistribute excess energy and reach electronic thermal equilibrium. Owing to extremely short time and length scales, the measurement and manipulation of electron thermalization in nanoscale devices remains challenging even with the most advanced ultrafast laser techniques. Here, we overcome this challenge by leveraging the atomic thinness of two-dimensional van der Waals (vdW) materials to introduce a highly tunable electron transfer pathway that directly competes with electron thermalization. We realize this scheme in a graphene-boron nitride-graphene (G-BN-G) vdW heterostructure, through which optically excited carriers are transported from one graphene layer to the other. By applying an interlayer bias voltage or varying the excitation photon energy, interlayer carrier transport can be controlled to occur faster or slower than the intralayer scattering events, thus effectively tuning the electron thermalization pathways in graphene. Our findings, which demonstrate a means to probe and directly modulate electron energy transport in nanoscale materials, represent a step towards designing and implementing optoelectronic and energy-harvesting devices with tailored microscopic properties.

  16. Ultrafast imaging of electronic relaxation in n-propylbenzene: Direct observation of intermediate state

    NASA Astrophysics Data System (ADS)

    Liu, Yuzhu; Gerber, Thomas; Radi, Peter; Knopp, Gregor

    2015-10-01

    The ultrafast dynamics of the second singlet electronically excited state (S2) in n-propylbenzene has been investigated by femtosecond time-resolved photoelectron imaging coupled with photofragmentation spectroscopy. The intermediate state for the deactivation of the S2 state is observed by transient photoelectron kinetic energy distributions and photoelectron angular distributions. An ultrafast electronic relaxation process on timescale of the fitted ∼50 fs was observed in the S2 state by time-resolved photoelectron imaging and it is attributed to the S1 ← S2 internal conversion (IC). The time constant of 1.23 (±0.2) ps is determined for the further deactivation of the intermediate S1 state.

  17. New aspects of the ultrafast electronic decay of Malachite Green in solution

    NASA Astrophysics Data System (ADS)

    Gottfried, N. H.; Roither, B.; Scherer, P. O. J.

    1997-02-01

    The triphenyl methane dye Malachite Green was studied in solution by a ultrafast fluorescence upconversion technique. A non-exponential decay was found following electronic excitation of the S(1) state. A novel contribution to the fast component was postulated in the form of a loss of transition intensity following a rotation of the phenyl rings. This notion was verified by a quantum chemical calculation. Also, no evidence for a level crossing of the S(0) and S(1) states was found.

  18. Absolute measurement of the ultrafast nonlinear electronic and rovibrational response in H2 and D2

    NASA Astrophysics Data System (ADS)

    Wahlstrand, J. K.; Zahedpour, S.; Cheng, Y.-H.; Palastro, J. P.; Milchberg, H. M.

    2015-12-01

    The electronic, rotational, and vibrational components of the ultrafast optical nonlinearity in H2 and D2 are measured directly and absolutely at intensities up to the ionization threshold of ˜1014W/cm 2 . As the most basic nonlinear interactions of the simplest molecules exposed to high fields, these results constitute a benchmark for high-field laser-matter theory and simulation.

  19. Ultrafast phase transition via catastrophic phonon collapse driven by plasmonic hot-electron injection.

    PubMed

    Appavoo, Kannatassen; Wang, Bin; Brady, Nathaniel F; Seo, Minah; Nag, Joyeeta; Prasankumar, Rohit P; Hilton, David J; Pantelides, Sokrates T; Haglund, Richard F

    2014-03-12

    Ultrafast photoinduced phase transitions could revolutionize data-storage and telecommunications technologies by modulating signals in integrated nanocircuits at terahertz speeds. In quantum phase-changing materials (PCMs), microscopic charge, lattice, and orbital degrees of freedom interact cooperatively to modify macroscopic electrical and optical properties. Although these interactions are well documented for bulk single crystals and thin films, little is known about the ultrafast dynamics of nanostructured PCMs when interfaced to another class of materials as in this case to active plasmonic elements. Here, we demonstrate how a mesh of gold nanoparticles, acting as a plasmonic photocathode, induces an ultrafast phase transition in nanostructured vanadium dioxide (VO2) when illuminated by a spectrally resonant femtosecond laser pulse. Hot electrons created by optical excitation of the surface-plasmon resonance in the gold nanomesh are injected ballistically across the Au/VO2 interface to induce a subpicosecond phase transformation in VO2. Density functional calculations show that a critical density of injected electrons leads to a catastrophic collapse of the 6 THz phonon mode, which has been linked in different experiments to VO2 phase transition. The demonstration of subpicosecond phase transformations that are triggered by optically induced electron injection opens the possibility of designing hybrid nanostructures with unique nonequilibrium properties as a critical step for all-optical nanophotonic devices with optimizable switching thresholds.

  20. Ultrafast electronic motion in hydrogen molecular ions induced by a high power intense laser

    NASA Astrophysics Data System (ADS)

    Mineo, H.; Teranishi, Y.; Chao, S. D.; Lin, S. H.

    2010-10-01

    In this Letter we report a method for controlling electronic localization in a molecular ion, on an attosecond time scale, using a high-intensity laser, based on two different excitation mechanisms. One takes place during ionization, and the other takes place sequentially, following ionization. The electronic excited states of the hydrogen molecular ion are created during ionization by taking the configuration interaction mixing of neutral molecules into account. We detect the ultrafast oscillatory electronic motion between two atoms in a hydrogen molecular ion occurring due to the creation of excited states during the course of ionization.

  1. Nanowires: Enhanced Optoelectronic Performance of a Passivated Nanowire-Based Device: Key Information from Real-Space Imaging Using 4D Electron Microscopy (Small 17/2016).

    PubMed

    Khan, Jafar I; Adhikari, Aniruddha; Sun, Jingya; Priante, Davide; Bose, Riya; Shaheen, Basamat S; Ng, Tien Khee; Zhao, Chao; Bakr, Osman M; Ooi, Boon S; Mohammed, Omar F

    2016-05-01

    Selective mapping of surface charge carrier dynamics of InGaN nanowires before and after surface passivation with octadecylthiol (ODT) is reported by O. F. Mohammed and co-workers on page 2313, using scanning ultrafast electron microscopy. In a typical experiment, the 343 nm output of the laser beam is used to excite the microscope tip to generate pulsed electrons for probing, and the 515 nm output is used as a clocking excitation pulse to initiate dynamics. Time-resolved images demonstrate clearly that carrier recombination is significantly slowed after ODT treatment, which supports the efficient removal of surface trap states. PMID:27124006

  2. Ultrafast proton-coupled electron transfer in heterogenous photocatalysis

    NASA Astrophysics Data System (ADS)

    Zhao, Jin; Onda, Ken; Li, Bin; Petek, Hrvoje

    2006-08-01

    At metal-oxide/protic-solvent interfaces, partially hydrated or "wet electron" states represent the lowest energy pathway for electron transfer. Here we study the photoinduced charge transfer at the H IIO/TiO II(110) interface by means of timeresolved two-photon photoemission spectroscopy and electronic structure theory. At ~1 monolayer coverage of H IIO on partially hydroxylated TiO II surfaces we find an unoccupied electronic state 2.4+/-0.1 eV above the Fermi level. Density functional theory shows this to be a two-dimensional "wet electron" state, which is distinct from hydrated electrons observed on water-covered metal surfaces. The decay of electrons from the wet electron state by the resonant charge transfer to the conduction band of TiO II occurs in <=15 femtoseconds. Similar unoccupied electronic structure is observed for CH 3OH covered TiO II(110) surfaces; however, the electron dynamics are considerably more complex. The wet electron state dynamics of CH 3OH/TiO II exhibit both energy and population decay. The excited state lifetime is strongly coverage dependent increasing to >100 fs range above 1 ML CH 3OH coverage. Significantly, a pronounced deuterium isotope effect (CH 3OD) indicates a strong correlation between the interfacial electron transfer and the motion of protons in the molecular overlayer.

  3. Identification of ultra-fast electronic and thermal processes during femtosecond laser ablation of Si

    NASA Astrophysics Data System (ADS)

    Bashir, Shazia; Shahid Rafique, M.; Husinsky, Wolfgang

    2012-11-01

    Ultra-fast electronic and thermal processes for the energy deposition mechanism during femtosecond laser ablation of Si have been identified by means of atomic force microscopy and Raman scattering techniques. For this purpose, Si targets were exposed with 800-nm, 25-fs Ti:sapphire laser pulses for different laser fluencies in air and under UHV (ultra high vacuum) conditions. Various nano- and microstructures on the surface of the irradiated samples are revealed by a detailed surface topography analysis. Ultra-fast electronic processes are dominant in the lower-fluence regime. Therefore, by starting from the ablation threshold three different fluence regimes have been chosen: a lower-fluence regime (0.06-0.5 J cm-2 single-shot irradiation under UHV condition and 0.25-2.5 J cm-2 single-shot irradiation in ambient condition), a moderate-fluence regime (0.25-1.5 J cm-2 multiple-shot irradiation), and a higher-fluence regime (2.5-3.5 J cm-2 multiple-shot irradiation). Around the ablation threshold fluence, most significant features identified at the Si surface are nanohillock-like structures. The appearance of these nanohillocks is regarded as typical features for fast electronic processes (correlated with existence of hot electrons) and is explained on the basis of Coulomb explosion. The growth of these typical features (nanohillocks) by femtosecond laser irradiation is an element of novelty. At moderate irradiation fluence, a ring-shaped ablation with larger bumps and periodic surface structures is observed and is considered as a footprint of ultra-fast melting. Further increase in the laser fluence, i.e. a higher-fluence regime, resulted in strong enhancement of the thermal process with the appearance of larger islands. The change in surface topography provides an innovative clue to differentiate between ultra-fast electronic processes, i.e. Coulomb explosion (sub-100 fs) at a lower-fluence regime and ultra-fast melting (hundreds of fs) at a moderate-fluence regime

  4. Ultrafast dynamics in photo-induced correlated electronic states in ladder cuprates

    NASA Astrophysics Data System (ADS)

    Ishihara, Sumio; Hashimoto, Hiroshi

    2014-03-01

    Ultrafast photo-induced dynamics in correlated electron systems, in particular, photon irradiation effects in half filled Mott insulators have been studied intensively from theoretical and experimental sides, and photo-induced Mott insulator to metal transition has been observed. On the other side, in recent ultrafast pump-probe experiments in ladder cuprates away from half filling, photo-irradiation weakens initial metallic state. We study ultrafast dynamics in photo-induced states in a ladder system. Real time dynamics in a ladder-type Hubbard model are analyzed by the numerical exact diagonalization method. Optical conductivity spectra and density of states show that the initial metallic state is changed into a bad metallic state by photo irradiation, in contrast to the photo-doped effect in half-filled Mott insulators. Through the calculation of the carrier pair correlation functions, we find that coherent motion of carrier pairs in initial states are reduced by pump photon irradiation. We further simulate a double pulse irradiation. Our simulations as well as the experimental results suggest an optical control of pair coherence in correlated electron system.

  5. Ultrafast Electronic Dynamics in Solid and Liquid Gallium Nanoparticles

    NASA Astrophysics Data System (ADS)

    Nisoli, M.; Stagira, S.; de Silvestri, S.; Stella, A.; Tognini, P.; Cheyssac, P.; Kofman, R.

    1997-05-01

    The electron thermalization process both in solid and liquid metallic gallium nanoparticles with radii in the range 50-90 Å is investigated by femtosecond pump-probe measurements. The results show that the temporal behavior of the electron energy relaxation is similar in both phases, with a time constant varying from ~0.6 to ~1.6 ps by increasing the nanoparticle size. We interpret the experimental data in terms of a size-dependent electron-surface interaction model and show the importance of the energy exchange with surface phonons in the electronic thermalization.

  6. Ultrafast electronic dynamics in laser-excited crystalline bismuth

    NASA Astrophysics Data System (ADS)

    Melnikov, Alexey A.; Misochko, Oleg V.; Chekalin, Sergey V.

    2013-07-01

    Femtosecond spectroscopy is applied to study transient electronic processes in bismuth. The components with relaxation times of 1 ps, 7 ps, and ˜1 ns are detected in the photoinduced reflectivity response of the crystal. To facilitate assignment of the observed relaxation to the decay of particular excited electronic states, we use pump pulses with central wavelengths ranging from 400 to 2300 nm. Additionally, we examine the variation of parameters of coherent A1g phonons upon the change of excitation and probing conditions. Data analysis reveals significant wavevector dependence of electron-hole and electron-phonon coupling strength along Γ-T direction of the Brillouin zone.

  7. Ultrafast studies of electron dynamics at metal-dielectric interfaces

    SciTech Connect

    Ge, Nien-Hui

    1998-10-01

    Femtosecond time- and angle-resolved two-photon photoemission spectroscopy has been used to study fundamental aspects of excited electron dynamics at metal-dielectric interfaces, including layer-by-layer evolution of electronic structure and two-dimensional electron localization. On bare Ag(111), the lifetimes of image states are dominated by their position with respect to the projected bulk band structure. The n = 2 state has a shorter lifetime than the n = 1 state due to degeneracy with the bulk conduction band. As the parallel momentum of the n = 1 image electron increases, the lifetime decreases. With decreasing temperatures, the n = 1 image electrons, with zero or nonzero parallel momentum, all become longer lived. Adsorption of one to three layers of n-heptane results in an approximately exponential increase in lifetime as a function of layer thickness. This results from the formation of a tunneling barrier through which the interfacial electrons must decay, consistent with the repulsive bulk electron affinity of n-alkanes. The lifetimes of the higher quantum states indicate that the presence of the monolayer significantly reduces coupling of the image states to the bulk band structure. These results are compared with predictions of a dielectric continuum model. The study of electron lateral motion shows that optical excitation creates interfacial electrons in quasifree states for motion parallel to the n-heptane/Ag(111) interface. These initially delocalized electrons decay into a localized state within a few hundred femtoseconds. The localized electrons then decay back to the metal by tunneling through the adlayer potential barrier. The localization time depends strongly on the electron's initial parallel momentum and exhibits a non-Arrhenius temperature dependence. The experimental findings are consistent with a 2-D self-trapping process in which electrons become localized by interacting with the topmost plane of the alkane layer. The energy dependence of

  8. Coherently driven, ultrafast electron-phonon dynamics in transport junctions

    SciTech Connect

    Szekely, Joshua E.; Seideman, Tamar

    2014-07-28

    Although the vast majority of studies of transport via molecular-scale heterojunctions have been conducted in the (static) energy domain, experiments are currently beginning to apply time domain approaches to the nanoscale transport problem, combining spatial with temporal resolution. It is thus an opportune time for theory to develop models to explore both new phenomena in, and new potential applications of, time-domain, coherently driven molecular electronics. In this work, we study the interaction of a molecular phonon with an electronic wavepacket transmitted via a conductance junction within a time-domain model that treats the electron and phonon on equal footing and spans the weak to strong electron-phonon coupling strengths. We explore interference between two coherent energy pathways in the electronic subspace, thus complementing previous studies of coherent phenomena in conduction junctions, where the stationary framework was used to study interference between spatial pathways. Our model provides new insights into phase decoherence and population relaxation within the electronic subspace, which have been conventionally treated by density matrix approaches that often rely on phenomenological parameters. Although the specific case of a transport junction is explored, our results are general, applying also to other instances of coupled electron-phonon systems.

  9. Theory of the Control of Ultrafast Interfacial Electron Transfer

    NASA Astrophysics Data System (ADS)

    Rasmussen, Andrew Musso

    This dissertation describes the theoretial exploration of electron transfer (ET) processes at the interface between bulk and molecular or nanoscale materials. Analysis of simple model Hamiltonians, those for the two- and three-level electronic systems as well as for a single electronic level coupled to a continuum, inform an understanding of electron transfer in nontrivial systems. A new treatment of the three-level system at an undergraduate level encapsulates the hopping and superexchange mechanisms of electron transfer. The elegance of the behavior of ET from a single-level/continuum system precedes a treatment of the reverse process---quasicontinuum-to-discrete level ET. This reverse process, relevant to ET from a bulk material to a semiconductor quantum dot (QD) offers a handle for the coherent control of ET at an interface: the shape of an electronic wavepacket within the quasicontinuum. An extension of the single-level-to-continuum ET process is the injection of an electron from a QD to a wide-bandgap semiconductor nanoparticle (NP). We construct a minimal model to explain trends in ET rates at the QD/NP interface as a function of QD size. Finally, we propose a scheme to gate ET through a molecular junction via the coherent control of the torsional mode(s) of a linking molecule within the junction.

  10. Light-emitting nanostructures formed by intense, ultrafast electronic excitation in silicon (100)

    NASA Astrophysics Data System (ADS)

    Hamza, Alex V.; Newman, Micheal W.; Thielen, Peter A.; Lee, Howard W. H.; Schenkel, Thomas; McDonald, Joseph W.; Schneider, Dieter H.

    2001-10-01

    The intense, ultrafast electronic excitation of clean silicon (100)-(2×1) surfaces leads to the formation of silicon nanostructures embedded in silicon, which photoluminescence at ˜560 nm wavelength (˜2 eV band gap). The silicon surfaces were irradiated with slow, highly charged ions (e.g., Xe44+ and Au53+) to produce the electronic excitation. The observation of excitonic features in the luminescence is particularly unusual for silicon nanostructures. The temperature dependence and the measurement of the triplet-singlet splitting of the emission strongly support the excitonic assignment.

  11. Imaging Ultra-fast Molecular Dynamics in Free Electron Laser Field

    NASA Astrophysics Data System (ADS)

    Zhang, Y. Z.; Jiang, Y. H.

    The free electron laser (FEL) provides the coherent, brilliant and ultrashort light pulse in short wavelength (extreme ultraviolet and X-ray) regimes, opening up possibilities to study ultra-fast molecular dynamics in photo-induced chemical reactions with new methodologies. In this chapter, we introduce the time-resolved pump-probe experiments on gas-phase targets with FEL facilities to image the nuclear and electronic motions in molecular reactions, which serve as a benchmark for further FEL applications like coherent diffraction imaging and coherent control of functional dynamics in complex molecular reactions.

  12. Ultrafast electron diffraction optimized for studying structural dynamics in thin films and monolayers

    PubMed Central

    Badali, D. S.; Gengler, R. Y. N.; Miller, R. J. D.

    2016-01-01

    A compact electron source specifically designed for time-resolved diffraction studies of free-standing thin films and monolayers is presented here. The sensitivity to thin samples is achieved by extending the established technique of ultrafast electron diffraction to the “medium” energy regime (1–10 kV). An extremely compact design, in combination with low bunch charges, allows for high quality diffraction in a lensless geometry. The measured and simulated characteristics of the experimental system reveal sub-picosecond temporal resolution, while demonstrating the ability to produce high quality diffraction patterns from atomically thin samples. PMID:27226978

  13. Multiobjective optimizations of a novel cryocooled dc gun based ultrafast electron diffraction beam line

    NASA Astrophysics Data System (ADS)

    Gulliford, Colwyn; Bartnik, Adam; Bazarov, Ivan

    2016-09-01

    We present the results of multiobjective genetic algorithm optimizations of a single-shot ultrafast electron diffraction beam line utilizing a 225 kV dc gun with a novel cryocooled photocathode system and buncher cavity. Optimizations of the transverse projected emittance as a function of bunch charge are presented and discussed in terms of the scaling laws derived in the charge saturation limit. Additionally, optimization of the transverse coherence length as a function of final rms bunch length at the sample location have been performed for three different sample radii: 50, 100, and 200 μ m , for two final bunch charges: 1 05 electrons (16 fC) and 1 06 electrons (160 fC). Example optimal solutions are analyzed, and the effects of disordered induced heating estimated. In particular, a relative coherence length of Lc ,x/σx=0.27 nm /μ m was obtained for a final bunch charge of 1 05 electrons and final bunch length of σt≈100 fs . For a final charge of 1 06 electrons the cryogun produces Lc ,x/σx≈0.1 nm /μ m for σt≈100 - 200 fs and σx≥50 μ m . These results demonstrate the viability of using genetic algorithms in the design and operation of ultrafast electron diffraction beam lines.

  14. Ultrafast electronic readout of diamond nitrogen-vacancy centres coupled to graphene

    NASA Astrophysics Data System (ADS)

    Brenneis, Andreas; Gaudreau, Louis; Seifert, Max; Karl, Helmut; Brandt, Martin S.; Huebl, Hans; Garrido, Jose A.; Koppens, Frank H. L.; Holleitner, Alexander W.

    2015-02-01

    Non-radiative transfer processes are often regarded as loss channels for an optical emitter because they are inherently difficult to access experimentally. Recently, it has been shown that emitters, such as fluorophores and nitrogen-vacancy centres in diamond, can exhibit a strong non-radiative energy transfer to graphene. So far, the energy of the transferred electronic excitations has been considered to be lost within the electron bath of the graphene. Here we demonstrate that the transferred excitations can be read out by detecting corresponding currents with a picosecond time resolution. We detect electronically the spin of nitrogen-vacancy centres in diamond and control the non-radiative transfer to graphene by electron spin resonance. Our results open the avenue for incorporating nitrogen-vacancy centres into ultrafast electronic circuits and for harvesting non-radiative transfer processes electronically.

  15. Detecting ultrafast interatomic electronic processes in media by fluorescence

    NASA Astrophysics Data System (ADS)

    Knie, André; Hans, Andreas; Förstel, Marko; Hergenhahn, Uwe; Schmidt, Philipp; Reiß, Philipp; Ozga, Christian; Kambs, Benjamin; Trinter, Florian; Voigtsberger, Jörg; Metz, Daniel; Jahnke, Till; Dörner, Reinhard; Kuleff, Alexander I.; Cederbaum, Lorenz S.; Demekhin, Philipp V.; Ehresmann, Arno

    2014-10-01

    Interatomic coulombic decay (ICD), a radiationless transition in weakly bonded systems, such as solutes or van der Waals bound aggregates, is an effective source for electrons of low kinetic energy. So far, the ICD processes could only be probed in ultra-high vacuum by using electron and/or ion spectroscopy. Here we show that resonant ICD processes can also be detected by measuring the subsequently emitted characteristic fluorescence radiation, which makes their study in dense media possible.

  16. The development of femtosecond electron diffraction for direct measurements of ultrafast atomic motions

    NASA Astrophysics Data System (ADS)

    Park, Hyuk

    The evolution of material structures is governed by the making and breaking of chemical bonds and the rearrangement of atoms, which occurs on the time scale of an atomic vibrational period, hundreds of femtoseconds. Atomic motion on this time scale ultimately determines the course of phase transitions in solids, the kinetic pathways of chemical reactions, and even the function of biological processes. Direct observation and understanding these ultrafast structural dynamics at the time and length scales of atomic motions represent an important frontier in scientific research and applications. We have developed a femtosecond electron diffraction system (FED) capable of directly measuring the atomic motions in sub-picosecond temporal resolution and sub-milli-angstrom spatial resolution. In the path of the development of FED various technical challenges have been overcome and an unprecedented capability has been achieved. These advancements allow us to study a range of ultrafast structural dynamics directly on the fundamental level of atomic motions for the first time. With FED we measured laser-induced ultrafast structural dynamics in a 20-nm Al film by taking real-time snapshots of transmission electron patterns. The damped single-mode breathing motion of the Al film along the surface normal was recorded as coherent and in-phase oscillations of all the Bragg peak positions. The concurrent lattice heating was measured by tracking the associated Bragg peak intensity attenuation. This acoustic phonon can be well fitted with a classical harmonic oscillator model using a driving force which includes both electronic and lattice contribution. The pressure of the free electrons contributes significantly in driving the coherent acoustic phonons under nonequilibrium conditions when electrons and phonons are not thermalized. In addition, by using a pair of optical excitation pulses and varying their time delay and relative pulse intensities, we demonstrated successful control

  17. Quantum coherent optical phase modulation in an ultrafast transmission electron microscope.

    PubMed

    Feist, Armin; Echternkamp, Katharina E; Schauss, Jakob; Yalunin, Sergey V; Schäfer, Sascha; Ropers, Claus

    2015-05-14

    Coherent manipulation of quantum systems with light is expected to be a cornerstone of future information and communication technology, including quantum computation and cryptography. The transfer of an optical phase onto a quantum wavefunction is a defining aspect of coherent interactions and forms the basis of quantum state preparation, synchronization and metrology. Light-phase-modulated electron states near atoms and molecules are essential for the techniques of attosecond science, including the generation of extreme-ultraviolet pulses and orbital tomography. In contrast, the quantum-coherent phase-modulation of energetic free-electron beams has not been demonstrated, although it promises direct access to ultrafast imaging and spectroscopy with tailored electron pulses on the attosecond scale. Here we demonstrate the coherent quantum state manipulation of free-electron populations in an electron microscope beam. We employ the interaction of ultrashort electron pulses with optical near-fields to induce Rabi oscillations in the populations of electron momentum states, observed as a function of the optical driving field. Excellent agreement with the scaling of an equal-Rabi multilevel quantum ladder is obtained, representing the observation of a light-driven 'quantum walk' coherently reshaping electron density in momentum space. We note that, after the interaction, the optically generated superposition of momentum states evolves into a train of attosecond electron pulses. Our results reveal the potential of quantum control for the precision structuring of electron densities, with possible applications ranging from ultrafast electron spectroscopy and microscopy to accelerator science and free-electron lasers. PMID:25971512

  18. Ultrafast photo-induced charge transfer unveiled by two-dimensional electronic spectroscopy

    NASA Astrophysics Data System (ADS)

    Bixner, Oliver; Lukeš, Vladimír; Mančal, Tomáš; Hauer, Jürgen; Milota, Franz; Fischer, Michael; Pugliesi, Igor; Bradler, Maximilian; Schmid, Walther; Riedle, Eberhard; Kauffmann, Harald F.; Christensson, Niklas

    2012-05-01

    The interaction of exciton and charge transfer (CT) states plays a central role in photo-induced CT processes in chemistry, biology, and physics. In this work, we use a combination of two-dimensional electronic spectroscopy (2D-ES), pump-probe measurements, and quantum chemistry to investigate the ultrafast CT dynamics in a lutetium bisphthalocyanine dimer in different oxidation states. It is found that in the anionic form, the combination of strong CT-exciton interaction and electronic asymmetry induced by a counter-ion enables CT between the two macrocycles of the complex on a 30 fs timescale. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra, and we monitor how the excited state charge density ultimately localizes on the macrocycle closest to the counter-ion within 100 fs. A comparison with the dynamics in the radical species further elucidates how CT states modulate the electronic structure and tune fs-reaction dynamics. Our experiments demonstrate the unique capability of 2D-ES in combination with other methods to decipher ultrafast CT dynamics.

  19. Ultrafast Diagnostics for Electron Beams from Laser Plasma Accelerators

    SciTech Connect

    Matlis, N. H.; Bakeman, M.; Geddes, C. G. R.; Gonsalves, T.; Lin, C.; Nakamura, K.; Osterhoff, J.; Plateau, G. R.; Schroeder, C. B.; Shiraishi, S.; Sokollik, T.; Tilborg, J. van; Toth, Cs.; Leemans, W. P.

    2010-11-04

    We present an overview of diagnostic techniques for measuring key parameters of electron bunches from Laser Plasma Accelerators (LPAs). The diagnostics presented here were chosen because they highlight the unique advantages (e.g. diverse forms of electromagnetic emission) and difficulties (e.g. shot-to-shot variability) associated with LPAs. Non destructiveness and high resolution (in space and time and energy) are key attributes that enable the formation of a comprehensive suite of simultaneous diagnostics which are necessary for the full characterization of the ultrashort, but highly-variable electron bunches from LPAs.

  20. Ultrafast Diagnostics for Electron Beams from Laser Plasma Accelerators

    SciTech Connect

    Matlis, N. H.; Bakeman, M.; Geddes, C. G. R.; Gonsalves, T.; Lin, C.; Nakamura, K.; Osterhoff, J.; Plateau, G. R.; Schroeder, C. B.; Shiraishi, S.; Sokollik, T.; van Tilborg, J.; Toth, Cs.; Leemans, W. P.

    2010-06-01

    We present an overview of diagnostic techniques for measuring key parameters of electron bunches from Laser Plasma Accelerators (LPAs). The diagnostics presented here were chosen because they highlight the unique advantages (e.g., diverse forms of electromagnetic emission) and difficulties (e.g., shot-to-shot variability) associated with LPAs. Non destructiveness and high resolution (in space and time and energy) are key attributes that enable the formation of a comprehensive suite of simultaneous diagnostics which are necessary for the full characterization of the ultrashort, but highly-variable electron bunches from LPAs.

  1. Ultrafast electron diffraction from laser-aligned molecules in the gas phase

    NASA Astrophysics Data System (ADS)

    Yang, Jie

    Ultrafast electron diffraction has emerged since the end of last century, and has become an increasingly important tool for revealing great details of molecular dynamics. In comparison to spectroscopic techniques, ultrafast electron diffraction directly probes time-resolved structure of target molecules, and therefore can potentially provide "molecular movies" of the reactions being studied. These molecular movies are critical for understanding and ultimately controlling the energy conversion pathways and efficiencies of photochemical processes. In this dissertation, I have focused on ultrafast electron diffraction from gas-phase molecules, and have investigated several long-standing challenges that have been preventing researchers from being able to achieve 3-D molecular movies of photochemical reactions. The first challenge is to resolve the full 3-D structure for molecules in the gas phase. The random orientation of molecules in the gas phase smears out the diffraction signal, which results in only 1-D structural information being accessible. The second challenge lies in temporal resolution. In order to resolve coherent nuclear motions on their natural time scale, a temporal resolution of ˜200 femtosecond or better is required. However, due to experimental limitations the shortest temporal resolution that had been achieved was only a few picoseconds in early 2000, by Zewail group from Caltech. The first challenge is tackled by laser-alignment. In the first half of the dissertation, I approach this method both theoretically and experimentally, and demonstrate that by using a short laser pulse to transiently align target molecules in space, 3-D molecular structure can be reconstructed ab-initio from diffraction patterns. The second half of the dissertation presents two experiments, both of which are important steps toward imaging coherent nuclear motions in real time during photochemical reactions. The first experiment simultaneously resolves molecular alignment

  2. Ultrafast Electronic Excitation in CaF2 Crystals

    NASA Astrophysics Data System (ADS)

    Xu, Shizhen; Jia, Tianqing; Li, Xiaoxi; Feng, Donghai; Sun, Haiyi; Li, Chengbin; Wang, Xiaofeng; Kuroda, Hirao; Li, Ruxin; Xu, Zhizhan

    2005-11-01

    A new pump and probe experimental system was developed, the pump pulse duration of which is stretched and is much longer than that of the probe pulse. Using this system, time-resolved electronic excitation processes and damage mechanisms in CaF2 crystals were studied. The measured reflectivity of the probe pulse begins to increase at the peak of the pump pulse and increases rapidly in the latter half of the pump pulse, when the pump pulse duration is stretched to 580 fs. Our experimental results indicate that both multiphoton ionization and impact ionization play important roles in the generation of conduction band electrons, at least they do so when the pump pulse durations are equal to or longer than 580 fs.

  3. Ultrafast electronic energy redistribution in hollow gold nanoparticles.

    NASA Astrophysics Data System (ADS)

    Knappenberger, Kenneth; Schwartzberg, Adam

    2009-03-01

    Nanostructured materials offer great potential for novel ways to generate, utilize, store and transport energy. These unique opportunities arise because nanoclusters often portray strikingly different chemical and physical properties than their bulk counterparts, and, perhaps more intriguingly, these vary widely with cluster size and shape. Here we report on the redistribution of electronic energy to thermal phonons in a series of hollow gold nanoparticles using femtosecond transient absorption. Qualitatively, the relaxation processes are similar to those of solid nanoparticles, however distinct differences are observed, likely owing to the unique properties of the hollow structures. In particular, a larger excitation power density is required to observe coherent vibrational oscillations in hollow gold nanoparticles than is needed for solid particles following electronic excitation. This effect is systematically studied over a range of hollow and solid particles, including multiple diameters and wall thicknesses. Models will be presented to account for the different relaxation mechanism observed for hollow and solid gold nanoparticles.

  4. Ultrafast electronic relaxation and vibrational dynamics in a polyacetylene derivative

    NASA Astrophysics Data System (ADS)

    Kobayashi, Takayoshi; Iiyama, Tsugumasa; Okamura, Kotaro; Du, Juan; Masuda, Toshio

    2013-04-01

    Real-time vibrational spectra in a polyacetylene derivative, poly[o-TFMPA([o-(trifluoromethyl) phenyl]acetylene)] in a broad electronic spectral region were observed using a sub-7-fs laser. Using the frequencies and initial phases of vibrational modes obtained by the spectroscopy, the assignment of the wavepackets was made. From the first moment, Huang-Rhys parameters were determined for six most prominent modes, which characterize the potential hypersurface composed of multi-dimensional vibrational mode spaces.

  5. Electron-phonon scattering dynamics in ferromagnetic metals and their influence on ultrafast demagnetization processes

    NASA Astrophysics Data System (ADS)

    Essert, Sven; Schneider, Hans Christian

    2011-12-01

    We theoretically investigate spin-dependent carrier dynamics due to the electron-phonon interaction after ultrafast optical excitation in ferromagnetic metals. We calculate the electron-phonon matrix elements including the spin-orbit interaction in the electronic wave functions and the interaction potential. Using the matrix elements in Boltzmann scattering integrals, the momentum-resolved carrier distributions are obtained by solving their equation of motion numerically. We find that the optical excitation with realistic laser intensities alone leads to a negligible magnetization change, and that the demagnetization due to electron-phonon interaction is mostly due to hole scattering. Importantly, the calculated demagnetization quenching due to this Elliot-Yafet-type depolarization mechanism is not large enough to explain the experimentally observed result. We argue that the ultrafast demagnetization of ferromagnets does not occur exclusively via an Elliott-Yafet type process, i.e., scattering in the presence of the spin-orbit interaction, but is influenced to a large degree by a dynamical change of the band structure, i.e., the exchange splitting.

  6. Ultrafast Control of the electronic phase of a manganite viamode-selective vibrational excitation

    SciTech Connect

    Rini, Matteo; Tobey, Ra'anan I.; Dean, Nicky; Tokura, Yoshinori; Schoenlein, Robert W.; Cavalleri, Andrea

    2007-05-01

    Controlling a phase of matter by coherently manipulatingspecific vibrational modes has long been an attractive (yet elusive) goalfor ultrafast science. Solids with strongly correlated electrons, inwhich even subtle crystallographic distortions can result in colossalchanges of the electronic and magnetic properties, could be directedbetween competing phases by such selective vibrational excitation. Inthis way, the dynamics of the electronic ground state of the systembecome accessible, and new insight into the underlying physics might begained. Here we report the ultrafast switching of the electronic phase ofa magnetoresistive manganite via direct excitation of a phonon mode at 71meV (17 THz). A prompt, five-order-of-magnitude drop in resistivity isobserved, associated with a non-equilibrium transition from the stableinsulating phase to a metastable metallic phase. In contrast withlight-induced, and current-driven phase transitions, the vibrationallydriven bandgap collapse observed here is not related to hot-carrierinjection and is uniquely attributed to a large-amplitude Mn-Odistortion. This corresponds to a perturbation of theperovskite-structure tolerance factor, which in turn controls theelectronic bandwidth via inter-site orbital overlap. Phase control bycoherent manipulation of selected metal--oxygen phonons should findextensive application in other complex solids--notably in copper oxidesuperconductors, in which the role of Cu-O vibrations on the electronicproperties is currently controversial.

  7. Ultrafast XUV spectroscopy: Unveiling the nature of electronic couplings in molecular dynamics

    NASA Astrophysics Data System (ADS)

    Timmers, Henry Robert

    Molecules are traditionally treated quantum mechanically using the Born-Oppenheimer formalism. In this formalism, different electronic states of the molecule are treated independently. However, most photo-initiated phenomena occurring in nature are driven by the couplings between different electronic states in both isolated molecules and molecular aggregates, and therefore occur beyond the Born-Oppenheimer formalism. These couplings are relevant in reactions relating to the perception of vision in the human eye, the oxidative damage and repair of DNA, the harvesting of light in photosynthesis, and the transfer of charge across large chains of molecules. While these reaction dynamics have traditionally been studied with visible and ultraviolet spectroscopy, attosecond XUV pulses formed through the process of high harmonic generation form a perfect tool for probing coupled electronic dynamics in molecules. In this thesis, I will present our work in using ultrafast, XUV spectroscopy to study these dynamics in molecules of increasing complexity. We begin by probing the relaxation dynamics of superexcited states in diatomic O 2. These states can relax via two types of electronic couplings, either through autoionization or neutral dissociation. We find that our pump-probe scheme can disentangle the two relaxation mechanisms and independently measure their contributing lifetimes. Next, we present our work in observing a coherent electron hole wavepacket initiated by the ionization of polyatomic CO 2 near a conical intersection. The electron-nuclear couplings near the conical intersection drive the electron hole between different orbital configurations. We find that we can not only measure the lifetime of quantum coherence in the electron hole wavepacket, but also control its evolution with a strong, infrared probing field. Finally, we propose an experiment to observe the migration of an electron hole across iodobenzene on the few-femtosecond timescale. We present

  8. Impact of ultrafast electronic damage in single-particle x-ray imaging experiments

    NASA Astrophysics Data System (ADS)

    Lorenz, U.; Kabachnik, N. M.; Weckert, E.; Vartanyants, I. A.

    2012-11-01

    In single-particle coherent x-ray diffraction imaging experiments, performed at x-ray free-electron lasers (XFELs), samples are exposed to intense x-ray pulses to obtain single-shot diffraction patterns. The high intensity induces electronic dynamics on the femtosecond time scale in the system, which can reduce the contrast of the obtained diffraction patterns and adds an isotropic background. We quantify the degradation of the diffraction pattern from ultrafast electronic damage by performing simulations on a biological sample exposed to x-ray pulses with different parameters. We find that the contrast is substantially reduced and the background is considerably strong only if almost all electrons are removed from their parent atoms. This happens at fluences of at least one order of magnitude larger than provided at currently available XFEL sources.

  9. Communication: Effects of thermionic-gun parameters on operating modes in ultrafast electron microscopy

    PubMed Central

    Kieft, Erik; Schliep, Karl B.; Suri, Pranav K.; Flannigan, David J.

    2015-01-01

    Ultrafast electron microscopes with thermionic guns and LaB6 sources can be operated in both the nanosecond, single-shot and femtosecond, single-electron modes. This has been demonstrated with conventional Wehnelt electrodes and absent any applied bias. Here, by conducting simulations using the General Particle Tracer code, we define the electron-gun parameter space within which various modes may be optimized. The properties of interest include electron collection efficiency, temporal and energy spreads, and effects of laser-pulse duration incident on the LaB6 source. We find that collection efficiencies can reach 100% for all modes, despite there being no bias applied to the electrode. PMID:26798820

  10. Ultrafast Electron Trapping in Ligand-Exchanged Quantum Dot Assemblies

    NASA Astrophysics Data System (ADS)

    Kikkawa, J. M.; Turk, M. E.; Vora, P. M.; Fafarman, A. T.; Diroll, B. T.; Murray, C. B.; Kagan, C. R.

    2015-03-01

    We use time-integrated and time-resolved photoluminescence and absorption to characterize the low-temperature (10 K) optical properties of CdSe quantum dot (QD) solids with different ligand and annealing preparation. Close-packed CdSe quantum dot solids are prepared with native aliphatic ligands and with thiocyanate with and without thermal annealing. Using sub-picosecond, broadband time-resolved photoluminescence and absorption, we find that ligand exchange increases the rate of carrier surface trapping. We further determine that holes within the QD core, rather than electrons, can bleach the band-edge transition in these samples at low temperature, a finding that comes as a surprise given what is known about the surface treatment in these QDs. We find that our ligand treatments lead to faster electron trapping to the quantum dot surface, a greater proportion of surface photoluminescence, and an increased rate of nonradiative decay due to enhanced interparticle coupling upon exchange and annealing. All aspects of this work supported by the U.S. Department of Energy Office of Basic Energy Sciences, Division of Materials Science and Engineering, under Award No. DE-SC0002158.

  11. Towards disentangling coupled electronic-vibrational dynamics in ultrafast non-adiabatic processes

    PubMed

    Blanchet; Lochbrunner; Schmitt; Shaffer; Larsen; Zgierski; Seideman; Stolow

    2000-01-01

    Femtosecond time-resolved photoelectron spectroscopy is emerging as a new technique for investigating polyatomic excited state dynamics. Due to the sensitivity of photoelectron spectroscopy to both electronic configurations and vibrational dynamics, it is well suited to the study of non-adiabatic processes such as internal conversion, which often occur on sub-picosecond time scales. We discuss the technical requirements for such experiments, including lasers systems, energy- and angle-resolved photoelectron spectrometers and new detectors for coincidence experiments. We present a few examples of these methods applied to problems in diatomic wavepacket dynamics and ultrafast non-adiabatic processes in polyatomic molecules.

  12. Ablation of GaAs by Intense, Ultrafast Electronic Excitation from Highly Charged Ions

    NASA Astrophysics Data System (ADS)

    Schenkel, T.; Hamza, A. V.; Barnes, A. V.; Schneider, D. H.; Banks, J. C.; Doyle, B. L.

    1998-09-01

    We have measured total ablation rates and secondary ion yields from undoped GaAs(100) interacting with slow \\(v = 6.6×105 m/s\\), very highly charged ions. Ablation rates increase strongly as a function of projectile charge. Some 1400 target atoms are removed when a single Th70+ ion deposits a potential energy of 152.6 keV within a few femtoseconds into a nanometer-sized target volume. We discuss models for ablation of semiconductors by intense, ultrafast electronic excitation.

  13. Using Ultrafast Pulse Shaping to Probe Electronic Interference in Strong Field Ionization

    NASA Astrophysics Data System (ADS)

    Zhao, Arthur; Sándor, Péter; Rozgonyi, Tamás; Weinacht, Thomas

    2014-05-01

    We make use of shaped ultrafast laser pulses, velocity map imaging and coincidence detection to study electron dynamics in Strong Field Ionization (SFI) of small molecules. In particular, we consider the role of interference between different pathways during ionization. In one experiment, the molecule is ionized with a phase locked pulse pair. We study the ionization yield as a function of the delay and the relative phase between pulses, and interpret its variation in terms of strong field laser molecule phase matching. The authors gratefully acknowledge support from the National Science Foundation under award number 1205397 and the Hungarian National Development Agency under grant number KTIA AIK 12-1-2012-0014.

  14. Ablation of GaAs by Intense, Ultrafast Electronic Excitation from Highly Charged Ions

    SciTech Connect

    Schenkel, T.; Hamza, A.V.; Barnes, A.V.; Schneider, D.H.; Banks, J.C.; Doyle, B.L.

    1998-09-01

    We have measured total ablation rates and secondary ion yields from undoped GaAs(100) interacting with slow (v=6.6{times}10{sup 5} m /s) , very highly charged ions. Ablation rates increase strongly as a function of projectile charge. Some 1400thinspthinsptarget atoms are removed when a single Th{sup 70+} ion deposits a potential energy of 152.6thinspthinspkeV within a few femtoseconds into a nanometer-sized target volume. We discuss models for ablation of semiconductors by intense, ultrafast electronic excitation. {copyright} {ital 1998} {ital The American Physical Society}

  15. Ultrafast Coherent Diffraction Imaging with X-ray Free-Electron Lasers

    SciTech Connect

    Chapman, H N; Bajt, S; Barty, A; Benner, W; Bogan, M; Frank, M; Hau-Riege, S; London, R; Marchesini, S; Spiller, E; Szoke, A; Woods, B; Boutet, S; Hodgson, K; Hajdu, J; Bergh, M; Burmeister, F; Caleman, C; Huldt, G; Maia, F; Seibert, M M; der Spoel, D v

    2006-08-22

    The ultrafast pulses from X-ray free-electron lasers will enable imaging of non-periodic objects at near-atomic resolution [1, Neutze]. These objects could include single molecules, protein complexes, or virus particles. The specimen would be completely destroyed by the pulse in a Coulomb explosion, but that destruction will only happen after the pulse. The scattering from the sample will give structural information about the undamaged object. There are many technical challenges that must be addressed before carrying out such experiments at an XFEL, which we are doing so with experiments at FLASH, the soft-X-ray FEL at DESY.

  16. Ultrafast electronic deactivation dynamics of the rare natural nucleobase hypoxanthine

    NASA Astrophysics Data System (ADS)

    Röttger, Katharina; Siewertsen, Ron; Temps, Friedrich

    2012-05-01

    The electronic deactivation of the 6-oxopurine derivative hypoxanthine, its nucleoside inosine and the nucleotide inosine monophosphate have been studied by femtosecond time-resolved spectroscopy after ππ∗ photoexcitation at λ = 260 nm. The development of a highly sensitive parallel broadband (near-UV/VIS) and single-color (deep-UV) transient absorption setup enabled us to monitor the excited-state decay and the ground-state recovery dynamics in one and the same experiment. The measurements revealed similar relaxation behavior, with time constants of τ1 ≲ 0.1 ps, τ2 ≈ 0.21 ± 0.08 ps and τ3 ≈ 1.8 ± 0.4 ps, for all three investigated molecules. The observed dynamics are assumed to take place through a conical intersection involving an out-of-plane puckering mode of the six-membered ring similar to guanine.

  17. Ultrafast Electronic Processes At Semiconductor Polymer Heterojunctions: A Molecular-Level, Quantum-Dynamical Analysis

    SciTech Connect

    Burghardt, I.; Tamura, H.; Bittner, E. R.

    2009-03-09

    This contribution gives an overview of our recent study of phonon-driven exciton dissociation at semiconductor polymer heterojunctions, using a quantum dynamical analysis based on a linear vibronic coupling model parametrized for three electronic states and 20-30 phonon modes. The decay of the photogenerated exciton towards an interfacial charge transfer state is an ultrafast (femtosecond to picosecond scale) process which initiates the photocurrent generation. We consider several representative interface configurations, which are shown to exhibit an efficient exciton dissociation. The process depends critically on the presence of intermediate states, and on the dynamical interplay between high-frequency (C=C stretch) and low-frequency (ring-torsional) modes. The dynamical mechanism is interpreted in terms of a hierarchical electron-phonon model which allows one to identify generalized reaction coordinates for the nonadiabatic process. This analysis highlights that the electron-phonon coupling is dominated by the high-frequency modes, but the low-frequency modes are crucial in mediating the transition to a charge-separated state. The ultra-fast, highly nonequilibrium dynamics is in accordance with spectroscopic observations.

  18. Ultrafast Electronic Processes At Semiconductor Polymer Heterojunctions: A Molecular-Level, Quantum-Dynamical Analysis

    NASA Astrophysics Data System (ADS)

    Burghardt, I.; Bittner, E. R.; Tamura, H.

    2009-03-01

    This contribution gives an overview of our recent study of phonon-driven exciton dissociation at semiconductor polymer heterojunctions, using a quantum dynamical analysis based on a linear vibronic coupling model parametrized for three electronic states and 20-30 phonon modes. The decay of the photogenerated exciton towards an interfacial charge transfer state is an ultrafast (femtosecond to picosecond scale) process which initiates the photocurrent generation. We consider several representative interface configurations, which are shown to exhibit an efficient exciton dissociation. The process depends critically on the presence of intermediate states, and on the dynamical interplay between high-frequency (C=C stretch) and low-frequency (ring-torsional) modes. The dynamical mechanism is interpreted in terms of a hierarchical electron-phonon model which allows one to identify generalized reaction coordinates for the nonadiabatic process. This analysis highlights that the electron-phonon coupling is dominated by the high-frequency modes, but the low-frequency modes are crucial in mediating the transition to a charge-separated state. The ultra-fast, highly nonequilibrium dynamics is in accordance with spectroscopic observations.

  19. Ultrafast spectroscopic investigations of cadmium chalcogenides: Nanoscale electronic relaxation and transfer

    NASA Astrophysics Data System (ADS)

    Spann, Bryan Thomas

    Harnessing solar energy more effectively remains one of the most important scientific challenges in recent history. Various strategies have been developed to capture the sun's energy to generate usable electricity. Recently, advances in chemistry have allowed researchers to synthesize semiconducting nanocrystals which show great promise in capturing and converting solar energy in a cheap and efficient way. In this dissertation, aspects of energy conversion processes in semiconducting nanocrystals are explored to elucidate their potential for photovoltaic applications. Various forms of linear and non-linear optical spectroscopy techniques were employed to explore electronic relaxation and transfer phenomena in nanoscale cadmium chalcogenide materials and heterojunctions. Ultrafast transient absorption studies were performed on various sizes of CdSe quantum dots (QDs) and quantum rods (QRs) with similar bandedge energies. These studies reviled that QRs have increased intraband relaxation times when compared with QDs as a result of an ultrafast formation of a 1D exciton along the elongated axis of the QR. The formation of the 1D exciton reduces the electron-to-hole scattering potential, consequently reducing the Auger thermalization mechanism. Furthermore, QD samples made in film form showed increased intraband relaxation times as a result of a hydrazine treatment which removed (in part) the organic ligands attached to the surface. As a result of removing the ligands, the ligand based relaxation pathway for the holes was also reduced, causing longer intraband relaxation. In addition to the studies on CdSe nanocrystals (NCs), ultrafast spectroscopy was used to study aspects of charge transfer in CdS -- TiO2 NC heterojunctions. This study revealed a means of increasing photo-induced ultrafast charge transfer in successive ionic layer adsorption and reaction (SILAR) CdS--TiO2 NC heterojunctions using pulsed laser sintering of TiO2 nanocrystals. The enhanced charge

  20. Ultrafast tryptophan-to-heme electron transfer in myoglobins revealed by UV 2D spectroscopy.

    PubMed

    Consani, Cristina; Auböck, Gerald; van Mourik, Frank; Chergui, Majed

    2013-03-29

    Tryptophan is commonly used to study protein structure and dynamics, such as protein folding, as a donor in fluorescence resonant energy transfer (FRET) studies. By using ultra-broadband ultrafast two-dimensional (2D) spectroscopy in the ultraviolet (UV) and transient absorption in the visible range, we have disentangled the excited state decay pathways of the tryptophan amino acid residues in ferric myoglobins (MbCN and metMb). Whereas the more distant tryptophan (Trp(7)) relaxes by energy transfer to the heme, Trp(14) excitation predominantly decays by electron transfer to the heme. The excited Trp(14)→heme electron transfer occurs in <40 picoseconds with a quantum yield of more than 60%, over an edge-to-edge distance below ~10 angstroms, outcompeting the FRET process. Our results raise the question of whether such electron transfer pathways occur in a larger class of proteins.

  1. Advances in Ultrafast Control and Probing of Correlated-Electron Materials

    SciTech Connect

    Wall, Simon; Rini, Matteo; Dhesi, Sarnjeet S.; Schoenlein, Robert W.; Cavalleri, Andrea

    2011-02-24

    Here in this paper, we present recent results on ultrafast control and probing of strongly correlated-electron materials. We focus on magnetoresistive manganites, applying excitation and probing wavelengths that cover the mid-IR to the soft X-rays. In analogy with near-equilibrium filling and bandwidth control of phase transitions, our approach uses both visible and mid-IR pulses to stimulate the dynamics by exciting either charges across electronic bandgaps or specific vibrational resonances. Lastly, x-rays are used to unambiguously measure the microscopic electronic, orbital, and structural dynamics. Our experiments dissect and separate the nonequilibrium physics of these compounds, revealing the complex interplay and evolution of spin, lattice, charge, and orbital degrees of freedoms in the time domain.

  2. Optical Probing of Ultrafast Electronic Decay in Bi and Sb with Slow Phonons

    NASA Astrophysics Data System (ADS)

    Li, J. J.; Chen, J.; Reis, D. A.; Fahy, S.; Merlin, R.

    2013-01-01

    Illumination with laser sources leads to the creation of excited electronic states of particular symmetries, which can drive isosymmetric vibrations. Here, we use a combination of ultrafast stimulated and cw spontaneous Raman scattering to determine the lifetime of A1g and Eg electronic coherences in Bi and Sb. Our results both shed new light on the mechanisms of coherent phonon generation and represent a novel way to probe extremely fast electron decoherence rates. The Eg state, resulting from an unequal distribution of carriers in three equivalent band regions, is extremely short lived. Consistent with theory, the lifetime of its associated driving force reaches values as small as 2 (6) fs for Bi (Sb) at 300 K.

  3. Ultrafast Surface-Enhanced Raman Probing of the Role of Hot Electrons in Plasmon-Driven Chemistry.

    PubMed

    Brandt, Nathaniel C; Keller, Emily L; Frontiera, Renee R

    2016-08-18

    Hot electrons generated through plasmonic excitations in metal nanostructures show great promise for efficiently driving chemical reactions with light. However, the lifetime, yield, and mechanism of action of plasmon-generated hot electrons involved in a given photocatalytic process are not well understood. Here, we develop ultrafast surface-enhanced Raman scattering (SERS) as a direct probe of plasmon-molecule interactions in the plasmon-catalyzed dimerization of 4-nitrobenzenethiol to p,p'-dimercaptoazobenzene. Ultrafast SERS probing of these molecular reporters in plasmonic hot spots reveals transient Fano resonances, which we attribute to near-field coupling of Stokes-shifted photons to hot electron-driven metal photoluminescence. Surprisingly, we find that hot spots that yield more photoluminescence are much more likely to drive the reaction, which indirectly proves that plasmon-generated hot electrons induce the photochemistry. These ultrafast SERS results provide insight into the relative reactivity of different plasmonic hot spot environments and quantify the ultrafast lifetime of hot electrons involved in plasmon-driven chemistry. PMID:27488515

  4. Ultrafast Surface-Enhanced Raman Probing of the Role of Hot Electrons in Plasmon-Driven Chemistry.

    PubMed

    Brandt, Nathaniel C; Keller, Emily L; Frontiera, Renee R

    2016-08-18

    Hot electrons generated through plasmonic excitations in metal nanostructures show great promise for efficiently driving chemical reactions with light. However, the lifetime, yield, and mechanism of action of plasmon-generated hot electrons involved in a given photocatalytic process are not well understood. Here, we develop ultrafast surface-enhanced Raman scattering (SERS) as a direct probe of plasmon-molecule interactions in the plasmon-catalyzed dimerization of 4-nitrobenzenethiol to p,p'-dimercaptoazobenzene. Ultrafast SERS probing of these molecular reporters in plasmonic hot spots reveals transient Fano resonances, which we attribute to near-field coupling of Stokes-shifted photons to hot electron-driven metal photoluminescence. Surprisingly, we find that hot spots that yield more photoluminescence are much more likely to drive the reaction, which indirectly proves that plasmon-generated hot electrons induce the photochemistry. These ultrafast SERS results provide insight into the relative reactivity of different plasmonic hot spot environments and quantify the ultrafast lifetime of hot electrons involved in plasmon-driven chemistry.

  5. Understanding the Electronic Structure of 4d Metal Complexes: From Molecular Spinors to L-Edge Spectra of a di-Ru Catalyst

    SciTech Connect

    Alperovich, Igor; Smolentsev, Grigory; Moonshiram, Dooshaye; Jurss, Jonah W.; Concepcion, Javier J.; Meyer, Thomas J.; Soldatov, Alexander; Pushkar, Yulia

    2015-09-17

    L{sub 2,3}-edge X-ray absorption spectroscopy (XAS) has demonstrated unique capabilities for the analysis of the electronic structure of di-Ru complexes such as the blue dimer cis,cis-[Ru{sub 2}{sup III}O(H{sub 2}O){sub 2}(bpy){sub 4}]{sup 4+} water oxidation catalyst. Spectra of the blue dimer and the monomeric [Ru(NH{sub 3}){sub 6}]{sup 3+} model complex show considerably different splitting of the Ru L{sub 2,3} absorption edge, which reflects changes in the relative energies of the Ru 4d orbitals caused by hybridization with a bridging ligand and spin-orbit coupling effects. To aid the interpretation of spectroscopic data, we developed a new approach, which computes L{sub 2,3}-edges XAS spectra as dipole transitions between molecular spinors of 4d transition metal complexes. This allows for careful inclusion of the spin-orbit coupling effects and the hybridization of the Ru 4d and ligand orbitals. The obtained theoretical Ru L{sub 2,3}-edge spectra are in close agreement with experiment. Critically, existing single-electron methods (FEFF, FDMNES) broadly used to simulate XAS could not reproduce the experimental Ru L-edge spectra for the [Ru(NH{sub 3}){sub 6}]{sup 3+} model complex nor for the blue dimer, while charge transfer multiplet (CTM) calculations were not applicable due to the complexity and low symmetry of the blue dimer water oxidation catalyst. We demonstrated that L-edge spectroscopy is informative for analysis of bridging metal complexes. The developed computational approach enhances L-edge spectroscopy as a tool for analysis of the electronic structures of complexes, materials, catalysts, and reactive intermediates with 4d transition metals.

  6. Effects of electron-phonon coupling and electron diffusion on ripples growth on ultrafast-laser-irradiated metals

    SciTech Connect

    Colombier, J. P.; Garrelie, F.; Faure, N.; Reynaud, S.; Bounhalli, M.; Audouard, E.; Stoian, R.; Pigeon, F.

    2012-01-15

    Metals exposed to ultrafast laser irradiation close to ablative regimes show often a submicron-scale (near 0.5 {mu}m) periodic organization of the surface as ripples. Using two classes of metallic materials (transition and noble), we have determined that the ripples amplitude is strongly correlated to the material transport properties, namely electron-phonon relaxation strength, electronic diffusion, and to the energy band characteristics of the electronic laser excitation. This particularly depends on the topology of the electronic structure, including d-band effects on electronic excitation. Comparing the effects of electron-phonon nonequilibrium lifetimes for the different metals under similar irradiation conditions, we indicate how the electron-phonon coupling strength affects the electronic thermal diffusion, the speed of phase transformation and impacts on the ripples contrast. The highest contrast is observed for ruthenium, where the electron-phonon coupling is the strongest, followed by tungsten, nickel, and copper, the latter with the least visible contrast. The dependence of surface patterns contrast with fluence is linked to the dependence of the relaxation characteristics with the electronic temperature.

  7. Visualization of carrier dynamics in p(n)-type GaAs by scanning ultrafast electron microscopy

    PubMed Central

    Cho, Jongweon; Hwang, Taek Yong; Zewail, Ahmed H.

    2014-01-01

    Four-dimensional scanning ultrafast electron microscopy is used to investigate doping- and carrier-concentration-dependent ultrafast carrier dynamics of the in situ cleaved single-crystalline GaAs(110) substrates. We observed marked changes in the measured time-resolved secondary electrons depending on the induced alterations in the electronic structure. The enhancement of secondary electrons at positive times, when the electron pulse follows the optical pulse, is primarily due to an energy gain involving the photoexcited charge carriers that are transiently populated in the conduction band and further promoted by the electron pulse, consistent with a band structure that is dependent on chemical doping and carrier concentration. When electrons undergo sufficient energy loss on their journey to the surface, dark contrast becomes dominant in the image. At negative times, however, when the electron pulse precedes the optical pulse (electron impact), the dynamical behavior of carriers manifests itself in a dark contrast which indicates the suppression of secondary electrons upon the arrival of the optical pulse. In this case, the loss of energy of material’s electrons is by collisions with the excited carriers. These results for carrier dynamics in GaAs(110) suggest strong carrier–carrier scatterings which are mirrored in the energy of material’s secondary electrons during their migration to the surface. The approach presented here provides a fundamental understanding of materials probed by four-dimensional scanning ultrafast electron microscopy, and offers possibilities for use of this imaging technique in the study of ultrafast charge carrier dynamics in heterogeneously patterned micro- and nanostructured material surfaces and interfaces. PMID:24469803

  8. Ultrafast photoinduced electron transfer between an incarcerated donor and a free acceptor in aqueous solution.

    PubMed

    Porel, Mintu; Chuang, Chi-Hung; Burda, Clemens; Ramamurthy, Vaidhyanathan

    2012-09-12

    Supramolecular photoinduced electron transfer dynamics between coumarin 153 (C153) and 4,4'-dimethyl viologen dichloride (MV(2+)) across the molecular barrier of a host molecule, octa acid (OA), has been investigated with femtosecond time resolution. The ultrafast electron transfer from C153 to MV(2+) followed excitation with 150 fs laser pulses at a wavelength of 390 nm despite the fact that C153 was incarcerated within an OA(2) capsule. As a result, the photoexcited coumarin did not show any of the typical relaxation dynamics that is usually observed in free solution. Instead, the excited electron was transferred across the molecular wall of the capsuleplex within 20 ps. Likewise, the lifetime of the charge transfer state was short (724 ps), and electron back-transfer reestablished the ground state of the system within 1 ns, showing strong electronic coupling among the excited electron donor, host, and acceptor. When the donor was encapsulated into the host molecule, the electron transfer process showed significantly accelerated dynamics and essentially no solvent relaxation compared with that in free solution. The study was also extended to N-methylpyridinium iodide as the acceptor with similar results. PMID:22931120

  9. Ultrafast electronic state conversion at room temperature utilizing hidden state in cuprate ladder system

    PubMed Central

    Fukaya, R.; Okimoto, Y.; Kunitomo, M.; Onda, K.; Ishikawa, T.; Koshihara, S.; Hashimoto, H.; Ishihara, S.; Isayama, A.; Yui, H.; Sasagawa, T.

    2015-01-01

    Photo-control of material properties on femto- (10−15) and pico- (10−12) second timescales at room temperature has been a long-sought goal of materials science. Here we demonstrate a unique ultrafast conversion between the metallic and insulating state and the emergence of a hidden insulating state by tuning the carrier coherence in a wide temperature range in the two-leg ladder superconductor Sr14-xCaxCu24O41 through femtosecond time-resolved reflection spectroscopy. We also propose a theoretical scenario that can explain the experimental results. The calculations indicate that the holes injected by the ultrashort light reduce the coherence among the inherent hole pairs and result in suppression of conductivity, which is opposite to the conventional photocarrier-doping mechanism. By using trains of ultrashort laser pulses, we successively tune the carrier coherence to within 1 picosecond. Control of hole-pair coherence is shown to be a realistic strategy for tuning the electronic state on ultrafast timescales at room temperature. PMID:26481604

  10. Using Betatron Emissions from Laser Wakefield Accelerated Electrons to Probe Ultra-fast Warm Dense Matter

    NASA Astrophysics Data System (ADS)

    Kotick, Jordan; Schumaker, Will; Condamine, Florian; Albert, Felicie; Barbrel, Benjamin; Galtier, Eric; Granados, Eduardo; Ravasio, Alessandra; Glenzer, Siegfried

    2015-11-01

    Laser wakefield acceleration (LWFA) has been shown to produce short X-ray pulses from betatron oscillations of electrons within the plasma wake. These betatron X-rays pulses have a broad, synchrotron-like energy spectrum and a duration on the order of the driving laser pulse, thereby enabling probing of ultrafast interactions. Using the 1 J, 40fs short-pulse laser at the Matter in Extreme Conditions experimental station at LCLS, we have implemented LWFA to generate and subsequently characterized betatron X-rays. Notch filtering and single photon counting techniques were used to measure the betatron X-ray spectrum while the spatial profile was measured using X-ray CCDs and image plates. We used an ellipsoidal mirror to focus the soft betatron X-rays for pump-probe studies on various targets in conjunction with LCLS X-ray and optical laser pulses. This experimental platform provides the conditions necessary to do a detailed study of warm-dense matter dynamics on the ultrafast time-scale.

  11. Ultrafast electronic state conversion at room temperature utilizing hidden state in cuprate ladder system

    NASA Astrophysics Data System (ADS)

    Fukaya, R.; Okimoto, Y.; Kunitomo, M.; Onda, K.; Ishikawa, T.; Koshihara, S.; Hashimoto, H.; Ishihara, S.; Isayama, A.; Yui, H.; Sasagawa, T.

    2015-10-01

    Photo-control of material properties on femto- (10-15) and pico- (10-12) second timescales at room temperature has been a long-sought goal of materials science. Here we demonstrate a unique ultrafast conversion between the metallic and insulating state and the emergence of a hidden insulating state by tuning the carrier coherence in a wide temperature range in the two-leg ladder superconductor Sr14-xCaxCu24O41 through femtosecond time-resolved reflection spectroscopy. We also propose a theoretical scenario that can explain the experimental results. The calculations indicate that the holes injected by the ultrashort light reduce the coherence among the inherent hole pairs and result in suppression of conductivity, which is opposite to the conventional photocarrier-doping mechanism. By using trains of ultrashort laser pulses, we successively tune the carrier coherence to within 1 picosecond. Control of hole-pair coherence is shown to be a realistic strategy for tuning the electronic state on ultrafast timescales at room temperature.

  12. Infrared PINEM developed by diffraction in 4D UEM

    PubMed Central

    Liu, Haihua; Baskin, John Spencer; Zewail, Ahmed H.

    2016-01-01

    The development of four-dimensional ultrafast electron microscopy (4D UEM) has enabled not only observations of the ultrafast dynamics of photon–matter interactions at the atomic scale with ultrafast resolution in image, diffraction, and energy space, but photon–electron interactions in the field of nanoplasmonics and nanophotonics also have been captured by the related technique of photon-induced near-field electron microscopy (PINEM) in image and energy space. Here we report a further extension in the ongoing development of PINEM using a focused, nanometer-scale, electron beam in diffraction space for measurements of infrared-light-induced PINEM. The energy resolution in diffraction mode is unprecedented, reaching 0.63 eV under the 200-keV electron beam illumination, and separated peaks of the PINEM electron-energy spectrum induced by infrared light of wavelength 1,038 nm (photon energy 1.2 eV) have been well resolved for the first time, to our knowledge. In a comparison with excitation by green (519-nm) pulses, similar first-order PINEM peak amplitudes were obtained for optical fluence differing by a factor of more than 60 at the interface of copper metal and vacuum. Under high fluence, the nonlinear regime of IR PINEM was observed, and its spatial dependence was studied. In combination with PINEM temporal gating and low-fluence infrared excitation, the PINEM diffraction method paves the way for studies of structural dynamics in reciprocal space and energy space with high temporal resolution. PMID:26848135

  13. Measurement of Two Low-Temperature Energy Gaps in the Electronic Structure of Antiferromagnetic USb2 Using Ultrafast Optical Spectroscopy

    NASA Astrophysics Data System (ADS)

    Qi, J.; Durakiewicz, T.; Trugman, S. A.; Zhu, J.-X.; Riseborough, P. S.; Baumbach, R.; Bauer, E. D.; Gofryk, K.; Meng, J.-Q.; Joyce, J. J.; Taylor, A. J.; Prasankumar, R. P.

    2013-08-01

    Ultrafast optical spectroscopy is used to study the antiferromagnetic f-electron system USb2. We observe the opening of two charge gaps at low temperatures (≲45K), arising from renormalization of the electronic structure. Analysis of our data indicates that one gap is due to hybridization between localized f-electron and conduction electron bands, while band renormalization involving magnons leads to the emergence of the second gap. These experiments thus enable us to shed light on the complex electronic structure emerging at the Fermi surface in f-electron systems.

  14. Measurement of two low-temperature energy gaps in the electronic structure of antiferromagnetic USb2 using ultrafast optical spectroscopy.

    PubMed

    Qi, J; Durakiewicz, T; Trugman, S A; Zhu, J-X; Riseborough, P S; Baumbach, R; Bauer, E D; Gofryk, K; Meng, J-Q; Joyce, J J; Taylor, A J; Prasankumar, R P

    2013-08-01

    Ultrafast optical spectroscopy is used to study the antiferromagnetic f-electron system USb(2). We observe the opening of two charge gaps at low temperatures (electronic structure. Analysis of our data indicates that one gap is due to hybridization between localized f-electron and conduction electron bands, while band renormalization involving magnons leads to the emergence of the second gap. These experiments thus enable us to shed light on the complex electronic structure emerging at the Fermi surface in f-electron systems.

  15. Resolving the role of femtosecond heated electrons in ultrafast spin dynamics

    PubMed Central

    Mendil, J.; Nieves, P.; Chubykalo-Fesenko, O.; Walowski, J.; Santos, T.; Pisana, S.; Münzenberg, M.

    2014-01-01

    Magnetization manipulation is essential for basic research and applications. A fundamental question is, how fast can the magnetization be reversed in nanoscale magnetic storage media. When subject to an ultrafast laser pulse, the speed of the magnetization dynamics depends on the nature of the energy transfer pathway. The order of the spin system can be effectively influenced through spin-flip processes mediated by hot electrons. It has been predicted that as electrons drive spins into the regime close to almost total demagnetization, characterized by a loss of ferromagnetic correlations near criticality, a second slower demagnetization process takes place after the initial fast drop of magnetization. By studying FePt, we unravel the fundamental role of the electronic structure. As the ferromagnet Fe becomes more noble in the FePt compound, the electronic structure is changed and the density of states around the Fermi level is reduced, thereby driving the spin correlations into the limit of critical fluctuations. We demonstrate the impact of the electrons and the ferromagnetic interactions, which allows a general insight into the mechanisms of spin dynamics when the ferromagnetic state is highly excited, and identifies possible recording speed limits in heat-assisted magnetization reversal. PMID:24496221

  16. Effects of intense femtosecond pumping on ultrafast electronic-vibrational dynamics in molecular systems with relaxation

    NASA Astrophysics Data System (ADS)

    Egorova, Dassia; Gelin, Maxim F.; Thoss, Michael; Wang, Haobin; Domcke, Wolfgang

    2008-12-01

    We investigate the influence of strong femtosecond optical pulses on the ultrafast dynamics of molecular systems. The study is based on a series of generic molecular models of increasing complexity, which incorporate multiple and mutually coupled electronic states, electronic-vibrational interaction, and vibrational relaxation. The influence of vibrational relaxation is treated using multilevel Redfield theory. Comparisons to benchmark results of the multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) method demonstrate the validity of the field-free implementation of Redfield theory employed in this work for weak system-bath interaction. The calculated electronic population and vibrational wave-packet dynamics demonstrate the intricate interplay of strong-field excitation, laser-induced Rabi oscillations, electronic interaction, vibronic coupling, and dissipation. In particular, we show that the interaction with a strong laser pulse may result in pronounced coherent vibrational motion in a dissipative system, even for laser pulses that are longer than the vibrational period. Furthermore, vibrational relaxation in combination with strong laser pulse excitation can lead to revivals of the electronic population after the excitation pulse is over.

  17. Ultrafast myoglobin structural dynamics observed with an X-ray free-electron laser

    DOE PAGES

    Levantino, Matteo; Schirò, Giorgio; Lemke, Henrik Till; Cottone, Grazia; Glownia, James Michael; Zhu, Diling; Chollet, Mathieu; Ihee, Hyotcherl; KAIST, Daejeon; Cupane, Antonio; et al

    2015-04-02

    Light absorption can trigger biologically relevant protein conformational changes. The light induced structural rearrangement at the level of a photoexcited chromophore is known to occur in the femtosecond timescale and is expected to propagate through the protein as a quake-like intramolecular motion. Here we report direct experimental evidence of such ‘proteinquake’ observed in myoglobin through femtosecond X-ray solution scattering measurements performed at the Linac Coherent Light Source X-ray free-electron laser. An ultrafast increase of myoglobin radius of gyration occurs within 1 picosecond and is followed by a delayed protein expansion. As the system approaches equilibrium it undergoes damped oscillations withmore » a ~3.6-picosecond time period. Our results unambiguously show how initially localized chemical changes can propagate at the level of the global protein conformation in the picosecond timescale.« less

  18. Mapping multidimensional electronic structure and ultrafast dynamics with single-element detection and compressive sensing

    PubMed Central

    Spencer, Austin P.; Spokoyny, Boris; Ray, Supratim; Sarvari, Fahad; Harel, Elad

    2016-01-01

    Compressive sensing allows signals to be efficiently captured by exploiting their inherent sparsity. Here we implement sparse sampling to capture the electronic structure and ultrafast dynamics of molecular systems using phase-resolved 2D coherent spectroscopy. Until now, 2D spectroscopy has been hampered by its reliance on array detectors that operate in limited spectral regions. Combining spatial encoding of the nonlinear optical response and rapid signal modulation allows retrieval of state-resolved correlation maps in a photosynthetic protein and carbocyanine dye. We report complete Hadamard reconstruction of the signals and compression factors as high as 10, in good agreement with array-detected spectra. Single-point array reconstruction by spatial encoding (SPARSE) Spectroscopy reduces acquisition times by about an order of magnitude, with further speed improvements enabled by fast scanning of a digital micromirror device. We envision unprecedented applications for coherent spectroscopy using frequency combs and super-continua in diverse spectral regions. PMID:26804546

  19. Ultrafast Relaxation Dynamics of Photoexcited Zinc-Porphyrin: Electronic-Vibrational Coupling.

    PubMed

    Abraham, Baxter; Nieto-Pescador, Jesus; Gundlach, Lars

    2016-08-18

    Cyclic tetrapyrroles are the active core of compounds with crucial roles in living systems, such as hemoglobin and chlorophyll, and in technology as photocatalysts and light absorbers for solar energy conversion. Zinc-tetraphenylporphyrin (Zn-TPP) is a prototypical cyclic tetrapyrrole that has been intensely studied in past decades. Because of its importance for photochemical processes the optical properties are of particular interest, and, accordingly, numerous studies have focused on light absorption and excited-state dynamics of Zn-TPP. Relaxation after photoexcitation in the Soret band involves internal conversion that is preceded by an ultrafast process. This relaxation process has been observed by several groups. Hitherto, it has not been established if it involves a higher lying "dark" state or vibrational relaxation in the excited S2 state. Here we combine high time resolution electronic and vibrational spectroscopy to show that this process constitutes vibrational relaxation in the anharmonic S2 potential. PMID:27482847

  20. Mapping multidimensional electronic structure and ultrafast dynamics with single-element detection and compressive sensing

    NASA Astrophysics Data System (ADS)

    Spencer, Austin P.; Spokoyny, Boris; Ray, Supratim; Sarvari, Fahad; Harel, Elad

    2016-01-01

    Compressive sensing allows signals to be efficiently captured by exploiting their inherent sparsity. Here we implement sparse sampling to capture the electronic structure and ultrafast dynamics of molecular systems using phase-resolved 2D coherent spectroscopy. Until now, 2D spectroscopy has been hampered by its reliance on array detectors that operate in limited spectral regions. Combining spatial encoding of the nonlinear optical response and rapid signal modulation allows retrieval of state-resolved correlation maps in a photosynthetic protein and carbocyanine dye. We report complete Hadamard reconstruction of the signals and compression factors as high as 10, in good agreement with array-detected spectra. Single-point array reconstruction by spatial encoding (SPARSE) Spectroscopy reduces acquisition times by about an order of magnitude, with further speed improvements enabled by fast scanning of a digital micromirror device. We envision unprecedented applications for coherent spectroscopy using frequency combs and super-continua in diverse spectral regions.

  1. Ultrafast Imaging of Electronic Relaxation in Ortho-xylene: New Features from Fragmentation-Ion Spectroscopy

    NASA Astrophysics Data System (ADS)

    Liu, Yu-Zhu; Knopp, Gregor; Xiao, Shao-Rong; Gerber, Thomas

    2014-12-01

    As a continuous work of tracking electronic relaxation of the S2 state in o-xylene by photoelectron imaging [Y. Liu et al., Phys. Chem. Chem. Phys. 15 (2013) 18101], we report another contribution from the view of fragment-ion spectroscopy. Three components with time constants of τ1 cong60 fs, τ2 = 55(±20) fs and τ3 = 6.99(±0.25) ps are observed for the only fragment-ion C6H4CH3+. The velocity map image of the fragment-ion against the delay time are also measured. Transient information about the kinetic energy of the fragment-ion and angular distribution are analyzed and discussed. New features for competing ultrafast internal conversion and intersystem crossing are obtained.

  2. Ultrafast myoglobin structural dynamics observed with an X-ray free-electron laser

    SciTech Connect

    Levantino, Matteo; Schirò, Giorgio; Lemke, Henrik Till; Cottone, Grazia; Glownia, James Michael; Zhu, Diling; Chollet, Mathieu; Ihee, Hyotcherl; KAIST, Daejeon; Cupane, Antonio; Cammarata, Marco

    2015-04-02

    Light absorption can trigger biologically relevant protein conformational changes. The light induced structural rearrangement at the level of a photoexcited chromophore is known to occur in the femtosecond timescale and is expected to propagate through the protein as a quake-like intramolecular motion. Here we report direct experimental evidence of such ‘proteinquake’ observed in myoglobin through femtosecond X-ray solution scattering measurements performed at the Linac Coherent Light Source X-ray free-electron laser. An ultrafast increase of myoglobin radius of gyration occurs within 1 picosecond and is followed by a delayed protein expansion. As the system approaches equilibrium it undergoes damped oscillations with a ~3.6-picosecond time period. Our results unambiguously show how initially localized chemical changes can propagate at the level of the global protein conformation in the picosecond timescale.

  3. Mapping multidimensional electronic structure and ultrafast dynamics with single-element detection and compressive sensing.

    PubMed

    Spencer, Austin P; Spokoyny, Boris; Ray, Supratim; Sarvari, Fahad; Harel, Elad

    2016-01-25

    Compressive sensing allows signals to be efficiently captured by exploiting their inherent sparsity. Here we implement sparse sampling to capture the electronic structure and ultrafast dynamics of molecular systems using phase-resolved 2D coherent spectroscopy. Until now, 2D spectroscopy has been hampered by its reliance on array detectors that operate in limited spectral regions. Combining spatial encoding of the nonlinear optical response and rapid signal modulation allows retrieval of state-resolved correlation maps in a photosynthetic protein and carbocyanine dye. We report complete Hadamard reconstruction of the signals and compression factors as high as 10, in good agreement with array-detected spectra. Single-point array reconstruction by spatial encoding (SPARSE) Spectroscopy reduces acquisition times by about an order of magnitude, with further speed improvements enabled by fast scanning of a digital micromirror device. We envision unprecedented applications for coherent spectroscopy using frequency combs and super-continua in diverse spectral regions.

  4. Ultrafast demagnetization after femtosecond laser pulses: Transfer of angular momentum from the electronic system to magnetoelastic spin-phonon modes

    NASA Astrophysics Data System (ADS)

    Tsatsoulis, T.; Illg, C.; Haag, M.; Mueller, B. Y.; Zhang, L.; Fähnle, M.

    2016-04-01

    During ultrafast demagnetization after the excitation of ferromagnetic films with femtosecond laser pulses, the angular momentum of the electronic system is transferred to the lattice via electron-phonon scatterings. The actual amount of transfer is calculated for Ni and Fe by considering spin-phonon eigenmodes, which have a sharp angular momentum. Because the considered Hamiltonian is not isotropic, the total angular momentum is not conserved.

  5. Tilted femtosecond pulses for velocity matching in gas-phase ultrafast electron diffraction

    NASA Astrophysics Data System (ADS)

    Zhang, Ping; Yang, Jie; Centurion, Martin

    2014-08-01

    Recent advances in pulsed electron gun technology have resulted in femtosecond electron pulses becoming available for ultrafast electron diffraction experiments. For experiments investigating chemical dynamics in the gas phase, the resolution is still limited to picosecond time scales due to the velocity mismatch between laser and electron pulses. Tilted laser pulses can be used for velocity matching, but thus far this has not been demonstrated over an extended target in a diffraction setting. We demonstrate an optical configuration to deliver high-intensity laser pulses with a tilted pulse front for velocity matching over the typical length of a gas jet. A laser pulse is diffracted from a grating to introduce angular dispersion, and the grating surface is imaged on the target using large demagnification. The laser pulse duration and tilt angle were measured at and near the image plane using two different techniques: second harmonic cross correlation and an interferometric method. We found that a temporal resolution on the order of 100 fs can be achieved over a range of approximately 1 mm around the image plane.

  6. Ultrafast Electron Transfer Between Dye and Catalyst on a Mesoporous NiO Surface.

    PubMed

    Brown, Allison M; Antila, Liisa J; Mirmohades, Mohammad; Pullen, Sonja; Ott, Sascha; Hammarström, Leif

    2016-07-01

    The combination of molecular dyes and catalysts with semiconductors into dye-sensitized solar fuel devices (DSSFDs) requires control of efficient interfacial and surface charge transfer between the components. The present study reports on the light-induced electron transfer processes of p-type NiO films cosensitized with coumarin C343 and a bioinspired proton reduction catalyst, [FeFe](mcbdt)(CO)6 (mcbdt = 3-carboxybenzene-1,2-dithiolate). By transient optical spectroscopy we find that ultrafast interfacial electron transfer (τ ≈ 200 fs) from NiO to the excited C343 ("hole injection") is followed by rapid (t1/2 ≈ 10 ps) and efficient surface electron transfer from C343(-) to the coadsorbed [FeFe](mcbdt)(CO)6. The reduced catalyst has a clear spectroscopic signature that persists for several tens of microseconds, before charge recombination with NiO holes occurs. The demonstration of rapid surface electron transfer from dye to catalyst on NiO, and the relatively long lifetime of the resulting charge separated state, suggests the possibility to use these systems for photocathodes on DSSFDs. PMID:27314570

  7. Electro-optic sampling for time resolving relativistic ultrafast electron diffraction

    SciTech Connect

    Scoby, C. M.; Musumeci, P.; Moody, J.; Gutierrez, M.; Tran, T.

    2009-01-22

    The Pegasus laboratory at UCLA features a state-of-the-art electron photoinjector capable of producing ultrashort (<100 fs) high-brightness electron bunches at energies of 3.75 MeV. These beams recently have been used to produce static diffraction patterns from scattering off thin metal foils, and it is foreseen to take advantage of the ultrashort nature of these bunches in future pump-probe time-resolved diffraction studies. In this paper, single shot 2-d electro-optic sampling is presented as a potential technique for time of arrival stamping of electron bunches used for diffraction. Effects of relatively low bunch charge (a few 10's of pC) and modestly relativistic beams are discussed and background compensation techniques to obtain high signal-to-noise ratio are explored. From these preliminary tests, electro-optic sampling is suitable to be a reliable nondestructive time stamping method for relativistic ultrafast electron diffraction at the Pegasus lab.

  8. Ultrafast terahertz probes of transient conducting and insulating phases in an electron-hole gas.

    PubMed

    Kaindl, R A; Carnahan, M A; Hägele, D; Lövenich, R; Chemla, D S

    2003-06-12

    Many-body systems in nature exhibit complexity and self-organization arising from seemingly simple laws. For example, the long-range Coulomb interaction between electrical charges has a simple form, yet is responsible for a plethora of bound states in matter, ranging from the hydrogen atom to complex biochemical structures. Semiconductors form an ideal laboratory for studying many-body interactions of electronic quasiparticles among themselves and with lattice vibrations and light. Oppositely charged electron and hole quasiparticles can coexist in an ionized but correlated plasma, or form bound hydrogen-like pairs called excitons. The pathways between such states, however, remain elusive in near-visible optical experiments that detect a subset of excitons with vanishing centre-of-mass momenta. In contrast, transitions between internal exciton levels, which occur in the far-infrared at terahertz (1012 s(-1)) frequencies, are independent of this restriction, suggesting their use as a probe of electron-hole pair dynamics. Here we employ an ultrafast terahertz probe to investigate directly the dynamical interplay of optically-generated excitons and unbound electron-hole pairs in GaAs quantum wells. Our observations reveal an unexpected quasi-instantaneous excitonic enhancement, the formation of insulating excitons on a 100-ps timescale, and the conditions under which excitonic populations prevail.

  9. Ultrafast Electron Transfer Between Dye and Catalyst on a Mesoporous NiO Surface.

    PubMed

    Brown, Allison M; Antila, Liisa J; Mirmohades, Mohammad; Pullen, Sonja; Ott, Sascha; Hammarström, Leif

    2016-07-01

    The combination of molecular dyes and catalysts with semiconductors into dye-sensitized solar fuel devices (DSSFDs) requires control of efficient interfacial and surface charge transfer between the components. The present study reports on the light-induced electron transfer processes of p-type NiO films cosensitized with coumarin C343 and a bioinspired proton reduction catalyst, [FeFe](mcbdt)(CO)6 (mcbdt = 3-carboxybenzene-1,2-dithiolate). By transient optical spectroscopy we find that ultrafast interfacial electron transfer (τ ≈ 200 fs) from NiO to the excited C343 ("hole injection") is followed by rapid (t1/2 ≈ 10 ps) and efficient surface electron transfer from C343(-) to the coadsorbed [FeFe](mcbdt)(CO)6. The reduced catalyst has a clear spectroscopic signature that persists for several tens of microseconds, before charge recombination with NiO holes occurs. The demonstration of rapid surface electron transfer from dye to catalyst on NiO, and the relatively long lifetime of the resulting charge separated state, suggests the possibility to use these systems for photocathodes on DSSFDs.

  10. Electronic and quantum dynamical insight into the ultrafast proton transfer of 1-hydroxy-2-acetonaphthone

    SciTech Connect

    Ortiz-Sanchez, Juan Manuel; Gelabert, Ricard; Moreno, Miquel; Lluch, Jose M.

    2007-08-28

    The ultrafast proton-transfer dynamics of 1-hydroxy-2-acetonaphthone has been theoretically analyzed in the ground and first singlet excited electronic states by density functional theory calculations and quantum dynamics. The potential energies obtained in the ground electronic state reveal that the proton-transfer process does not lead to a stable keto tautomer unless the transfer of the hydrogen from the enol form is accompanied by an internal rotation of the newly formed O-H bond. Calculations in the first singlet excited electronic state point to a very low barrier for the formation of the keto tautomer. The analysis of the calculated frequencies of the two tautomers in the excited state unveils a coupling of the skeletal motions (low frequency modes) with the proton-transfer process, as it has been stated from time-resolved experiments. The electronic energies obtained by the time-dependent density functional theory formalism have been fitted to a monodimensional potential energy surface in order to perform an exact quantum dynamics study of the process. Our results show that the proton-transfer process is completed within 25.5 fs, in remarkable good agreement with experiments.

  11. Design and implementation of electronics and data acquisition system for Ultra-Fast Flash Observatory

    NASA Astrophysics Data System (ADS)

    Jung, A.; Ahmad, S.; Barrillon, P.; Brandt, S.; Budtz-Jørgensen, C.; Castro-Tirado, A. J.; Chang, S.-H.; Chang, Y.-Y.; Chen, C. R.; Chen, P.; Choi, H. S.; Choi, Y. J.; Connell, P.; Dagoret-Campagne, S.; Eyles, C.; Grossan, B.; Huang, J. J.; Huang, M.-H. A.; Jeong, S.; Kim, J. E.; Kim, M.; Kim, S.-W.; Kim, Y. W.; Krasnov, A. S.; Lee, J.; Lim, H.; Lin, C.-Y.; Linder, E. V.; Liu, T.-C.; Lund, N.; Nam, J. W.; Min, K. W.; Na, G. W.; Panasyuk, M. I.; Park, I. H.; Reglero, V.; Ripa, J.; Rodrigo, J. M.; Smoot, G. F.; Suh, J. E.; Svertilov, S.; Vedenkin, N.; Wang, M.-Z.; Yashin, I.

    2013-07-01

    The Ultra-Fast Flash Observatory (UFFO) Pathfinder for Gamma-Ray Bursts (GRBs) consists of two telescopes. The UFFO Burst Alert & Trigger Telescope (UBAT) handles the detection and localization of GRBs, and the Slewing Mirror Telescope (SMT) conducts the measurement of the UV/optical afterglow. UBAT is equipped with an X-ray detector, analog and digital signal readout electronics that detects X-rays from GRBs and determines the location. SMT is equipped with a stepping motor and the associated electronics to rotate the slewing mirror targeting the GRBs identified by UBAT. First the slewing mirror points to a GRB, then SMT obtains the optical image of the GRB using the intensified CCD and its readout electronics. The UFFO Data Acquisition system (UDAQ) is responsible for the overall function and operation of the observatory and the communication with the satellite main processor. In this paper we present the design and implementation of the electronics of UBAT and SMT as well as the architecture and implementation of UDAQ.

  12. Materials Properties and Solvated Electron Dynamics of Isolated Nanoparticles and Nanodroplets Probed with Ultrafast Extreme Ultraviolet Beams.

    PubMed

    Ellis, Jennifer L; Hickstein, Daniel D; Xiong, Wei; Dollar, Franklin; Palm, Brett B; Keister, K Ellen; Dorney, Kevin M; Ding, Chengyuan; Fan, Tingting; Wilker, Molly B; Schnitzenbaumer, Kyle J; Dukovic, Gordana; Jimenez, Jose L; Kapteyn, Henry C; Murnane, Margaret M

    2016-02-18

    We present ultrafast photoemission measurements of isolated nanoparticles in vacuum using extreme ultraviolet (EUV) light produced through high harmonic generation. Surface-selective static EUV photoemission measurements were performed on nanoparticles with a wide array of compositions, ranging from ionic crystals to nanodroplets of organic material. We find that the total photoelectron yield varies greatly with nanoparticle composition and provides insight into material properties such as the electron mean free path and effective mass. Additionally, we conduct time-resolved photoelectron yield measurements of isolated oleylamine nanodroplets, observing that EUV photons can create solvated electrons in liquid nanodroplets. Using photoemission from a time-delayed 790 nm pulse, we observe that a solvated electron is produced in an excited state and subsequently relaxes to its ground state with a lifetime of 151 ± 31 fs. This work demonstrates that femotosecond EUV photoemission is a versatile surface-sensitive probe of the properties and ultrafast dynamics of isolated nanoparticles. PMID:26807653

  13. Ultrafast Electron and Ion Dynamics in Strong-Field-Ionized Liquid Water

    NASA Astrophysics Data System (ADS)

    Loh, Zhi-Heng; Li, Jialin; Nie, Zhaogang; Zheng, Yi Ying; Dong, Shuo; Low, Pei Jiang

    2016-05-01

    The ionization of liquid water functions as the principal trigger for a myriad of phenomena that are relevant to radiation chemistry and biology. The earliest events that follow the ionization of water, however, remain relatively unknown. Here, femtosecond coherence spectroscopy is combined with polarization anisotropy measurements to elucidate the ultrafast electron and ion dynamics in ionized water. The results show that strong-field ionization of liquid water produces an aligned p electron distribution. Furthermore oscillations observed in the polarization anisotropy are suggestive of valence electron motion in the highly reactive H2 O+ radical cation, whose lifetime with respect to proton transfer is found to be 196 +/- 5 fs. Coherent intermolecular motions that signal initial solvent reorganization and subsequent long-lived ballistic proton transport that involves the H3 O+ end-product are also detected in the time domain. These results offer new insight into the elementary dynamics of ionized liquid water. This work is supported by the Ministry of Education (MOE2014-T2-2-052), A*Star (122-PSF-0011), and the Nanyang Assistant Professorship.

  14. Ultrafast spectroscopy of prototypes of electronically nonadiabatic dynamics in solution chemistry

    NASA Astrophysics Data System (ADS)

    Silva, Carlos

    Femtosecond pump-probe spectroscopy of the equilibrated hydrated electron has been recorded with 35-femtosecond time resolution, revealing unprecedented transient features on the 30-80 fs time scales, which exhibit a solvent deuterium isotope effect (τ(D2O)/τ(H2O)~1.4). These previously unresolved dynamics have been assigned to inertial solvation dynamics of the photoexcited excess electron. The results support the importance of librational water motion in the relaxation dynamics of the hydrated electron. High excitation-pulse-intensity measurements reveal evidence of a two-photon channel involving ejection of the hydrated electron from its initial site to a different site in the solvent. Further pump-probe spectroscopy of the equilibrated solvated electron in alcohols has been studied with ~300 fs time resolution. At low pump power the observed dynamics are assigned to s→p excitation and subsequent relaxation of a localized solvated electron. In contrast, at high pump power, two-photon absorption apparently produces mobile 'conduction band' electrons, which are subsequently trapped and relax at a remote site from the initial equilibrated electron as observed for the hydrated electron. The two-photon excitation channel is also observed to induce an ultrafast proton-transfer reaction from the solvent to the excess electron. The metal-metal, charge-transfer (MMCT) absorption bands of the mixed-valence compounds (NH3)5RuIIINCRuII(CN)5/sp- (RuRu) and (NH3)5RuIIINCFeII(CN)5/sp- (RuFe) are studied with sufficient time resolution to measure the back-electron transfer (b-ET) time. In RuRu, the b-ET occurs in 85 ± 10 fs in H2O and increases to 122 ± 20 fs in D2O. Similar b-ET rates in these solvents are also observed for RuFe. The deuterium isotope effect is shown to originate from the solvent demonstrating that hydrogenic solvent motions are directly coupled to the electron transfer event. The pump-probe spectroscopy on the MMCT band also provides information on the

  15. A systematic study of thermodynamic and transport properties of layered 4d and 5d correlated electron systemsph.d

    NASA Astrophysics Data System (ADS)

    Chikara, Shalinee

    Correlated electron materials have been at the forefront of condensed matter research in the past couple of decades. Correlation in materials, especially, with open d and f electronic shells often lead to very exciting and intriguing phenomenon like high temperature superconductivity, Mott metal-insulator transition, colossal magnetoresistance (CMR). This thesis focuses on triple-layered Sr4Ru3O10, Sr substituted double layered (Ca1 - xAx) 3Ru2O7 (A = Ba, Sr) and 5d system Sr2IrO4 and Sr3Ir2O7. Triple-layered Sr4Ru3O10 displays interesting phenomena ranging from quantum oscillations, tunneling magnetoresistance, unusual low temperature specific heat, strong spin-lattice coupling to switching behavior. The central feature, however, is the unique borderline magnetism: along the c-axis. Sr4Ru3O10 shows spontaneous ferromagnetism, indicating a strong Coulomb exchange interaction, U and a large density of states at the Fermi surface, g( EF), hence Ug(EF) ≥ 1 (Stoner criterion). But within the ab-plane it features a pronounced peak in magnetization and a first-order metamagnetic transition. The coexistence of the interlayer ferromagnetism and the intralayer metamagnetism makes Sr4Ru3O10 a really unique system. Also, in this thesis the spin-valve behavior exhibited by impurity doping at the Ca site by Ba and Sr in the double layered Ca3Ru2O 7 is reported. Spin valve effect is a phenomenon only realized in multilayer thin films. Here, spin valve is observed in bulk single crystals of impurity doped Ca3Ru2O7, Ca3(Ru 1-xCrx) 2O7 and (Ca1 - xAx) 3Ru2O7 (A = Ba, Sr). 5d Iridates are expected to be more metallic and less magnetic than their 3d and 4f counterparts because of the extended 5d orbitals. In marked contrast, many iridates are magnetic insulators with exotic properties. The focus in this thesis is on Sr2IrO4 which diplays a novel Jeff = 1=2 Mott state. Magnetic, electrical, and thermal measurements on single-crystals of Sr2IrO4, reveal a novel giant magneto

  16. Relationships between the surface electronic and chemical properties of doped 4d and 5d late transition metal dioxides.

    PubMed

    Xu, Zhongnan; Kitchin, John R

    2015-03-14

    Density functional theory calculations were performed to elucidate the underlying physics describing the adsorption energies on doped late transition metal dioxide rutiles. Adsorption energies of atomic oxygen on doped rutiles M(D)-M(H)O2, where transition metal M(D) is doped into M(H)O2, were expressed in terms of a contribution from adsorption on the pure oxide of the dopant M(D) and perturbations to this adsorption energy caused by changing its neighboring metal cations and lattice parameters to that of the host oxide M(H)O2, which we call the ligand and strain effects, respectively. Our analysis of atom projected density of states revealed that the t2g-band center had the strongest correlation with adsorption energies. We show that charge transfer mediated shifts to the t2g-band center describe the ligand effect, and the radii of the atomic orbitals of metal cations can predict the magnitude and direction of this charge transfer. Strain produces systematic shifts to all features of the atom projected density of states, but correlations between the strain effect and the electronic structure were dependent on the chemical identity of the metal cation. The slope of these correlations can be related to the idealized d-band filling. This work elucidates the underlying physics describing adsorption on doped late transition metal oxides and establishes a foundation for models that use known chemical properties for the prediction of reactivity.

  17. Relationships between the surface electronic and chemical properties of doped 4d and 5d late transition metal dioxides

    SciTech Connect

    Xu, Zhongnan; Kitchin, John R.

    2015-03-14

    Density functional theory calculations were performed to elucidate the underlying physics describing the adsorption energies on doped late transition metal dioxide rutiles. Adsorption energies of atomic oxygen on doped rutiles M{sup D}-M{sup H}O{sub 2}, where transition metal M{sup D} is doped into M{sup H}O{sub 2}, were expressed in terms of a contribution from adsorption on the pure oxide of the dopant M{sup D} and perturbations to this adsorption energy caused by changing its neighboring metal cations and lattice parameters to that of the host oxide M{sup H}O{sub 2}, which we call the ligand and strain effects, respectively. Our analysis of atom projected density of states revealed that the t{sub 2g}-band center had the strongest correlation with adsorption energies. We show that charge transfer mediated shifts to the t{sub 2g}-band center describe the ligand effect, and the radii of the atomic orbitals of metal cations can predict the magnitude and direction of this charge transfer. Strain produces systematic shifts to all features of the atom projected density of states, but correlations between the strain effect and the electronic structure were dependent on the chemical identity of the metal cation. The slope of these correlations can be related to the idealized d-band filling. This work elucidates the underlying physics describing adsorption on doped late transition metal oxides and establishes a foundation for models that use known chemical properties for the prediction of reactivity.

  18. Study of classical thermo-mechanical equations in ultrafast thermo-elastic domain: electronic sputtering from metal-dielectric nanocomposites

    NASA Astrophysics Data System (ADS)

    Singh, Fouran; Stoquert, J. P.; Pivin, J. C.

    2013-08-01

    The utility of thermo-mechanical equations in the ultrafast thermo-elastic domain is tested by studying the electronic sputtering from metal-dielectric nanocomposites (NCs) induced by swift heavy ion irradiation. It is observed that the sputtering yield of metal atoms from such NC films strongly depends on the size of the metal nanoparticles (NPs) and the properties of host dielectric matrices. The decrease of the melting temperature of small NPs, superheating at the surface of NPs due to additional electron-surface scattering and transient melting of the dielectric matrices induce complex thermal effects. The dependence of the sputtering yield on the size of the NPs has been obtained by evaluating the transient stress and strain induced by thermal effects in the framework of the ultrafast thermo-elastic model.

  19. Ultrafast studies of excess electrons in liquid acetonitrile: revisiting the solvated electron/solvent dimer anion equilibrium.

    PubMed

    Doan, Stephanie C; Schwartz, Benjamin J

    2013-04-25

    We examine the ultrafast relaxation dynamics of excess electrons injected into liquid acetonitrile using air- and water-free techniques and compare our results to previous work on this system [Xia, C. et al. J. Chem. Phys. 2002, 117, 8855]. Excess electrons in liquid acetonitrile take on two forms: a "traditional" solvated electron that absorbs in the near-IR, and a solvated molecular dimer anion that absorbs weakly in the visible. We find that excess electrons initially produced via charge-transfer-to-solvent excitation of iodide prefer to localize as solvated electrons, but that there is a subsequent equilibration to form the dimer anion on an ~80 ps time scale. The spectral signature of this interconversion between the two forms of the excess electron is a clear isosbestic point. The presence of the isosbestic point makes it possible to fully deconvolute the spectra of the two species. We find that solvated molecular anion absorbs quite weakly, with a maximum extinction coefficient of ~2000 M(-1)cm(-1). With the extinction coefficient of the dimer anion in hand, we are also able to determine the equilibrium constant for the two forms of excess electron, and find that the molecular anion is favored by a factor of ~4. We also find that relatively little geminate recombination takes place, and that the geminate recombination that does take place is essentially complete within the first 20 ps. Finally, we show that the presence of small amounts of water in the acetonitrile can have a fairly large effect on the observed spectral dynamics, explaining the differences between our results and those in previously published work.

  20. Diffraction contrast as a sensitive indicator of femtosecond sub-nanoscale motion in ultrafast transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Cremons, Daniel R.; Schliep, Karl B.; Flannigan, David J.

    2013-09-01

    With ultrafast transmission electron microscopy (UTEM), access can be gained to the spatiotemporal scales required to directly visualize rapid, non-equilibrium structural dynamics of materials. This is achieved by operating a transmission electron microscope (TEM) in a stroboscopic pump-probe fashion by photoelectrically generating coherent, well-timed electron packets in the gun region of the TEM. These probe photoelectrons are accelerated down the TEM column where they travel through the specimen before reaching a standard, commercially-available CCD detector. A second laser pulse is used to excite (pump) the specimen in situ. Structural changes are visualized by varying the arrival time of the pump laser pulse relative to the probe electron packet at the specimen. Here, we discuss how ultrafast nanoscale motions of crystalline materials can be visualized and precisely quantified using diffraction contrast in UTEM. Because diffraction contrast sensitively depends upon both crystal lattice orientation as well as incoming electron wavevector, minor spatial/directional variations in either will produce dynamic and often complex patterns in real-space images. This is because sections of the crystalline material that satisfy the Laue conditions may be heterogeneously distributed such that electron scattering vectors vary over nanoscale regions. Thus, minor changes in either crystal grain orientation, as occurs during specimen tilting, warping, or anisotropic expansion, or in the electron wavevector result in dramatic changes in the observed diffraction contrast. In this way, dynamic contrast patterns observed in UTEM images can be used as sensitive indicators of ultrafast specimen motion. Further, these motions can be spatiotemporally mapped such that direction and amplitude can be determined.

  1. Ultrafast coherent X-ray diffractive imaging with the FLASH Free-Electron Laser

    NASA Astrophysics Data System (ADS)

    Chapman, H. N.; Bajt, S.; Barty, A.; Benner, W. H.; Bogan, M. J.; Boutet, S.; Cavalleri, A.; Düsterer, S.; Frank, M.; Hajdu, J.; Hau-Riege, S. P.; Iwan, B.; Marchesini, S.; Sokolowski-Tinten, K.; Siebert, M. M.; Treusch, R.; Woods, B. W.

    High-resolution ultrafast coherent diffractive imaging has been carried out at the FLASH FEL. Reconstructed images show no effect of sample destruction. Time resolved imaging was achieved by time-delay holography and with a synchronized optical laser.

  2. 4D-QSAR investigation and pharmacophore identification of pyrrolo[2,1-c][1,4]benzodiazepines using electron conformational-genetic algorithm method.

    PubMed

    Özalp, A; Yavuz, S Ç; Sabancı, N; Çopur, F; Kökbudak, Z; Sarıpınar, E

    2016-04-01

    In this paper, we present the results of pharmacophore identification and bioactivity prediction for pyrrolo[2,1-c][1,4]benzodiazepine derivatives using the electron conformational-genetic algorithm (EC-GA) method as 4D-QSAR analysis. Using the data obtained from quantum chemical calculations at PM3/HF level, the electron conformational matrices of congruity (ECMC) were constructed by EMRE software. The ECMC of the lowest energy conformer of the compound with the highest activity was chosen as the template and compared with the ECMCs of the lowest energy conformer of the other compounds within given tolerances to reveal the electron conformational submatrix of activity (ECSA, i.e. pharmacophore) by ECSP software. A descriptor pool was generated taking into account the obtained pharmacophore. To predict the theoretical activity and select the best subset of variables affecting bioactivities, the nonlinear least square regression method and genetic algorithm were performed. For four types of activity including the GI50, TGI, LC50 and IC50 of the pyrrolo[2,1-c][1,4] benzodiazepine series, the r(2)train, r(2)test and q(2) values were 0.858, 0.810, 0.771; 0.853, 0.848, 0.787; 0.703, 0.787, 0.600; and 0.776, 0.722, 0.687, respectively. PMID:27121415

  3. Photoelectron diffraction from single oriented molecules: Towards ultrafast structure determination of molecules using x-ray free-electron lasers

    NASA Astrophysics Data System (ADS)

    Kazama, Misato; Fujikawa, Takashi; Kishimoto, Naoki; Mizuno, Tomoya; Adachi, Jun-ichi; Yagishita, Akira

    2013-06-01

    We provide a molecular structure determination method, based on multiple-scattering x-ray photoelectron diffraction (XPD) calculations. This method is applied to our XPD data on several molecules having different equilibrium geometries. Then it is confirmed that, by our method, bond lengths and bond angles can be determined with a resolution of less than 0.1 Å and 10∘, respectively. Differently from any other scenario of ultrafast structure determination, we measure the two- or three-dimensional XPD of aligned or oriented molecules in the energy range from 100 to 200 eV with a 4π detection velocity map imaging spectrometer. Thanks to the intense and ultrashort pulse properties of x-ray free-electron lasers, our approach exhibits the most probable method for obtaining ultrafast real-time structural information on small to medium-sized molecules consisting of light elements, i.e., a “molecular movie.”

  4. Short electron bunch generation using single-cycle ultrafast electron guns

    NASA Astrophysics Data System (ADS)

    Fallahi, Arya; Fakhari, Moein; Yahaghi, Alireza; Arrieta, Miguel; Kärtner, Franz X.

    2016-08-01

    We introduce a solution for producing ultrashort (˜fs ) high charge (˜pC ) from ultracompact guns utilizing single-cycle THz pulses. We show that the readily available THz pulses with energies as low as 20 μ J are sufficient to generate multi-10 keV electron bunches. Moreover, it is demonstrated that THz energies of 2 mJ are sufficient to generate relativistic electron bunches with higher than 2 MeV energy. The high acceleration gradients possible in the structures provide 30 fs electron bunches at 30 keV energy and 45 fs bunches at 2 MeV energy. These structures will underpin future devices for strong field THz physics in general and miniaturized electron guns, in which the high fields combined with the short pulse duration enable electron beams with ultrahigh brightness.

  5. Electronic structure of low-dimensional 4d(5) oxides: interplay of ligand distortions, overall lattice anisotropy, and spin-orbit interactions.

    PubMed

    Katukuri, Vamshi M; Roszeitis, Karla; Yushankhai, Viktor; Mitrushchenkov, Alexander; Stoll, Hermann; van Veenendaal, Michel; Fulde, Peter; van den Brink, Jeroen; Hozoi, Liviu

    2014-05-19

    The electronic structure of the low-dimensional 4d(5) oxides Sr2RhO4 and Ca3CoRhO6 is herein investigated by embedded-cluster quantum chemistry calculations. A negative tetragonal-like t2g splitting is computed in Sr2RhO4 and a negative trigonal-like splitting is predicted for Ca3CoRhO6, in spite of having positive tetragonal distortions in the former material and cubic oxygen octahedra in the latter. Our findings bring to the foreground the role of longer-range crystalline anisotropy in generating noncubic potentials that compete with local distortions of the ligand cage, an issue not addressed in standard textbooks on crystal-field theory. We also show that sizable t2g(5)-t2g(4)eg(1) couplings via spin-orbit interactions produce in Sr2RhO4 ⟨Z⟩ = ⟨Σ(i)l(i)·s(i)⟩ ground-state expectation values significantly larger than 1, quite similar to theoretical and experimental data for 5d(5) spin-orbit-driven oxides such as Sr2IrO4. On the other hand, in Ca3CoRhO6, the ⟨Z⟩ values are lower because of larger t2g-eg splittings. Future X-ray magnetic circular dichroism experiments on these 4d oxides will constitute a direct test for the ⟨Z⟩ values that we predict here, the importance of many-body t2g-eg couplings mediated by spin-orbit interactions, and the role of low-symmetry fields associated with the extended surroundings. PMID:24779549

  6. Electronic Coupling Dependence of Ultrafast Interfacial Electron Transfer on Nanocrystalline Thin Films and Single Crystal

    SciTech Connect

    Lian, Tianquan

    2014-04-22

    The long-term goal of the proposed research is to understand electron transfer dynamics in nanoparticle/liquid interface. This knowledge is essential to many semiconductor nanoparticle based devices, including photocatalytic waste degradation and dye sensitized solar cells.

  7. Non-Markovian response of ultrafast coherent electronic ring currents in chiral aromatic molecules in a condensed phase

    SciTech Connect

    Mineo, H.; Lin, S. H.; Fujimura, Y.; Xu, J.; Xu, R. X.; Yan, Y. J.

    2013-12-07

    Results of a theoretical study on non-Markov response for femtosecond laser-driven coherent ring currents in chiral aromatic molecules embedded in a condensed phase are presented. Coherent ring currents are generated by coherent excitation of a pair of quasi-degenerated π-electronic excited states. The coherent electronic dynamical behaviors are strongly influenced by interactions between the electronic system and phonon bath in a condensed phase. Here, the bath correlation time is not instantaneous but should be taken to be a finite time in ultrashort time-resolved experiments. In such a case, Markov approximation breaks down. A hierarchical master equation approach for an improved semiclassical Drude dissipation model was adopted to examine the non-Markov effects on ultrafast coherent electronic ring currents of (P)-2,2{sup ′}-biphenol in a condensed phase. Time evolution of the coherent ring current derived in the hierarchical master equation approach was calculated and compared with those in the Drude model in the Markov approximation and in the static limit. The results show how non-Markovian behaviors in quantum beat signals of ring currents depend on the Drude bath damping constant. Effects of temperatures on ultrafast coherent electronic ring currents are also clarified.

  8. Ultrafast terahertz dynamics of hot Dirac-electron surface scattering in the topological insulator Bi2Se3

    NASA Astrophysics Data System (ADS)

    Sim, Sangwan; Brahlek, Matthew; Koirala, Nikesh; Cha, Soonyoung; Oh, Seongshik; Choi, Hyunyong

    2014-04-01

    Two-dimensional surface-scattering dynamics are central in the physics of topological insulators. Numerous electrical and optical measurements have evidenced that the origins of novel optoelectronic response can be traced back to Dirac surface-electron dynamics. Intrinsic surface dynamics, however, remain elusive because these experiments cannot access the frequencies of the surface-scattering rate. Time-resolved terahertz spectroscopy is the only apparatus for directly probing the collective response of low-energy electronic transitions. Here, by utilizing ultrafast optical-pump terahertz-probe spectroscopy, we discovered anomalous characteristics of the surface-scattering dynamics. Upon photoexcitation, the surface-scattering rate is increased and results in negative dynamic conductance at low temperature. Surprisingly, the differential changes of the surface-scattering rate are strongly reduced by photoexcited electrons at elevated temperature. We find that this nontrivial surface-electron dynamics is due to opening a carrier-relaxation channel from bulk to the surface state—one distinct characteristic of topological insulators. Our observations reveal unexpected surface dynamics of hot Dirac electrons, providing experimental a priori knowledge toward ultrafast optoelectronic operations.

  9. Non-Markovian response of ultrafast coherent electronic ring currents in chiral aromatic molecules in a condensed phase

    NASA Astrophysics Data System (ADS)

    Mineo, H.; Lin, S. H.; Fujimura, Y.; Xu, J.; Xu, R. X.; Yan, Y. J.

    2013-12-01

    Results of a theoretical study on non-Markov response for femtosecond laser-driven coherent ring currents in chiral aromatic molecules embedded in a condensed phase are presented. Coherent ring currents are generated by coherent excitation of a pair of quasi-degenerated π-electronic excited states. The coherent electronic dynamical behaviors are strongly influenced by interactions between the electronic system and phonon bath in a condensed phase. Here, the bath correlation time is not instantaneous but should be taken to be a finite time in ultrashort time-resolved experiments. In such a case, Markov approximation breaks down. A hierarchical master equation approach for an improved semiclassical Drude dissipation model was adopted to examine the non-Markov effects on ultrafast coherent electronic ring currents of (P)-2,2'-biphenol in a condensed phase. Time evolution of the coherent ring current derived in the hierarchical master equation approach was calculated and compared with those in the Drude model in the Markov approximation and in the static limit. The results show how non-Markovian behaviors in quantum beat signals of ring currents depend on the Drude bath damping constant. Effects of temperatures on ultrafast coherent electronic ring currents are also clarified.

  10. Ultrafast Excitation of an Inner-Shell Electron by Laser-Induced Electron Recollision.

    PubMed

    Deng, Yunpei; Zeng, Zhinan; Jia, Zhengmao; Komm, Pavel; Zheng, Yinhui; Ge, Xiaochun; Li, Ruxin; Marcus, Gilad

    2016-02-19

    Extreme ultraviolet attosecond pulses, generated by a process known as laser-induced electron recollision, are a key ingredient for attosecond metrology, providing a tool to precisely initiate and probe subfemtosecond dynamics in atoms, molecules, and solids. However, extending attosecond metrology to scrutinize the dynamics of the inner-shell electrons is a challenge, that is because of the lower efficiency in generating the required soft x-ray (ℏω>300  eV) attosecond bursts. A way around this problem is to use the recolliding electron to directly initiate the desired inner-shell process, instead of using the currently low flux x-ray attosecond sources. Such an excitation process occurs in a subfemtosecond time scale, and may provide the necessary "pump" step in a pump-probe experiment. Here we used a few cycle infrared (λ_{0}≈1800  nm) source and observed direct evidence for inner-shell excitations through the laser-induced electron recollision process. It is the first step toward time-resolved core-hole studies in the keV energy range with subfemtosecond time resolution. PMID:26943536

  11. Ultrafast Excitation of an Inner-Shell Electron by Laser-Induced Electron Recollision

    NASA Astrophysics Data System (ADS)

    Deng, Yunpei; Zeng, Zhinan; Jia, Zhengmao; Komm, Pavel; Zheng, Yinhui; Ge, Xiaochun; Li, Ruxin; Marcus, Gilad

    2016-02-01

    Extreme ultraviolet attosecond pulses, generated by a process known as laser-induced electron recollision, are a key ingredient for attosecond metrology, providing a tool to precisely initiate and probe subfemtosecond dynamics in atoms, molecules, and solids. However, extending attosecond metrology to scrutinize the dynamics of the inner-shell electrons is a challenge, that is because of the lower efficiency in generating the required soft x-ray (ℏω >300 eV ) attosecond bursts. A way around this problem is to use the recolliding electron to directly initiate the desired inner-shell process, instead of using the currently low flux x-ray attosecond sources. Such an excitation process occurs in a subfemtosecond time scale, and may provide the necessary "pump" step in a pump-probe experiment. Here we used a few cycle infrared (λ0≈1800 nm ) source and observed direct evidence for inner-shell excitations through the laser-induced electron recollision process. It is the first step toward time-resolved core-hole studies in the keV energy range with subfemtosecond time resolution.

  12. High quality single shot ultrafast MeV electron diffraction from a photocathode radio-frequency gun.

    PubMed

    Fu, Feichao; Liu, Shengguang; Zhu, Pengfei; Xiang, Dao; Zhang, Jie; Cao, Jianming

    2014-08-01

    A compact ultrafast electron diffractometer, consisting of an s-band 1.6 cell photocathode radio-frequency gun, a multi-function changeable sample chamber, and a sensitive relativistic electron detector, was built at Shanghai Jiao Tong University. High-quality single-shot transmission electron diffraction patterns have been recorded by scattering 2.5 MeV electrons off single crystalline gold and polycrystalline aluminum samples. The high quality diffraction pattern indicates an excellent spatial resolution, with the ratio of the diffraction ring radius over the ring rms width beyond 10. The electron pulse width is estimated to be about 300 fs. The high temporal and spatial resolution may open new opportunities in various areas of sciences.

  13. High quality single shot ultrafast MeV electron diffraction from a photocathode radio-frequency gun

    SciTech Connect

    Fu, Feichao; Liu, Shengguang; Zhu, Pengfei; Xiang, Dao Zhang, Jie; Cao, Jianming

    2014-08-15

    A compact ultrafast electron diffractometer, consisting of an s-band 1.6 cell photocathode radio-frequency gun, a multi-function changeable sample chamber, and a sensitive relativistic electron detector, was built at Shanghai Jiao Tong University. High-quality single-shot transmission electron diffraction patterns have been recorded by scattering 2.5 MeV electrons off single crystalline gold and polycrystalline aluminum samples. The high quality diffraction pattern indicates an excellent spatial resolution, with the ratio of the diffraction ring radius over the ring rms width beyond 10. The electron pulse width is estimated to be about 300 fs. The high temporal and spatial resolution may open new opportunities in various areas of sciences.

  14. 4-D Photoacoustic Tomography

    NASA Astrophysics Data System (ADS)

    Xiang, Liangzhong; Wang, Bo; Ji, Lijun; Jiang, Huabei

    2013-01-01

    Photoacoustic tomography (PAT) offers three-dimensional (3D) structural and functional imaging of living biological tissue with label-free, optical absorption contrast. These attributes lend PAT imaging to a wide variety of applications in clinical medicine and preclinical research. Despite advances in live animal imaging with PAT, there is still a need for 3D imaging at centimeter depths in real-time. We report the development of four dimensional (4D) PAT, which integrates time resolutions with 3D spatial resolution, obtained using spherical arrays of ultrasonic detectors. The 4D PAT technique generates motion pictures of imaged tissue, enabling real time tracking of dynamic physiological and pathological processes at hundred micrometer-millisecond resolutions. The 4D PAT technique is used here to image needle-based drug delivery and pharmacokinetics. We also use this technique to monitor 1) fast hemodynamic changes during inter-ictal epileptic seizures and 2) temperature variations during tumor thermal therapy.

  15. Probing ultrafast electronic and molecular dynamics with free-electron lasers

    NASA Astrophysics Data System (ADS)

    Fang, L.; Osipov, T.; Murphy, B. F.; Rudenko, A.; Rolles, D.; Petrovic, V. S.; Bostedt, C.; Bozek, J. D.; Bucksbaum, P. H.; Berrah, N.

    2014-06-01

    Molecular dynamics is an active area of research, focusing on revealing fundamental information on molecular structures and photon-molecule interaction and with broad impacts in chemical and biological sciences. Experimental investigation of molecular dynamics has been advanced by the development of new light sources and techniques, deepening our understanding of natural processes and enabling possible control and modification of chemical and biomolecular processes. Free-electron lasers (FELs) deliver unprecedented intense and short photon pulses in the vacuum ultraviolet and x-ray spectral ranges, opening a new era for the study of electronic and nuclear dynamics in molecules. This review focuses on recent molecular dynamics investigations using FELs. We present recent work concerning dynamics of molecular interaction with FELs using an intrinsic clock within a single x-ray pulse as well as using an external clock in a pump-probe scheme. We review the latest developments on correlated and coincident spectroscopy in FEL-based research and recent results revealing photo-induced interaction dynamics using these techniques. We also describe new instrumentations to conduct x-ray pump-x-ray probe experiments with spectroscopy and imaging detectors.

  16. Pump-probe reflectivity study of ultrafast dynamics of strongly correlated 5f electrons inUO2

    SciTech Connect

    Au, Yongqiang Q; Taylor, Antoinette J; Durakiewicz, Tomasz; Rodriguez, George

    2010-01-01

    5f electrons in the Mott insulator UO{sub 2} produce intriguing electronic states and dynamics, such as strong correlation and f-f excitations. We have performed femtosecond pump-probe reflectivity measurements on a single crystal UO{sub 2} at temperatures 5-300 K to study the ultrafast dynamics of photoexcited 5f electrons. The laser pulses at 400 nm pump 5 f electrons across the Mott gap, while those at 800 nm probe the pump-induced change of reflectivity. We find temperature-dependent excitation and relaxation processes and long-lived acoustic phonons, and extract picosecond risetimes and microsecond relaxation times at low temperatures. The observed slow relaxation is ascribed to the decay of Hubbard excitons formed by U{sup 3+}-U{sup 5+} pairs.

  17. Ultrafast gating of a mid-infrared laser pulse by a sub-pC relativistic electron beam

    SciTech Connect

    Cesar, D. B.; Musumeci, P.; Alesini, D.

    2015-12-21

    In this paper we discuss a relative time-of-arrival measurement scheme between an electron beam and a mid-infrared laser pulse based on the electron-beam controlled transmission in semiconductor materials. This technique can be used as a time-stamping diagnostic in ultrafast electron diffraction or microscopy. In particular, our characterization of Germanium demonstrates that sub-ps time-of-arrival sensitivity could be achieved in a single shot and with very low charge beams (<1 pC). Detailed measurements as a function of the beam charge and the laser wavelength offer insights on the free carrier dynamics in the semiconductor upon excitation by the electron beam.

  18. Evidence of apoptotic effects of 2,4-D and butachlor on walking catfish, Clarias batrachus, by transmission electron microscopy and DNA degradation studies.

    PubMed

    Ateeq, Bushra; Farah, M Abul; Ahmad, Waseem

    2006-01-25

    Apoptosis or programmed cell death is characterized morphologically by chromatin condensation, cell shrinkage, fragmentation of the nucleus and cytoplasm, and consequently formation of apoptotic bodies. It has also been best characterized by the cleavage of DNA into nucleosomal size fragments of 180-200 bp or multiples of the same. Contrary to this, under extreme conditions, the cells were found to show adaptive response to apoptosis and unable to regulate their own death; necrosis is therefore predominantly observed. In the present study, we showed induction of apoptosis in Clarias batrachus due to sublethal concentration of 2,4-D and butachlor at multiple exposure time. The first phase of the study involved light microscopy (LM) and transmission electron microscopy (TEM) for ultrastructural abnormalities of the germinal tissues. While, in the second phase of the study, DNA degradation of blood and hepatic tissue was resolved on agarose gel electrophoresis. In histopathological studies, large numbers of stage II oocytes were noted for nuclear blebbing irrespective of the test chemical. Some of the butachlor-exposed oocytes showed vacuolation and electron dense cytoplasm along with thickened nuclear envelope, having close association with the lysosomes on the cytoplasmic side. Some oocytes undergo nuclear blebbing having inner dense core and translucent cytoplasm. Leydig cells were slightly hypertrophied and few appeared pycnotic, a process involving necrotic changes in which the cell nuclei were characterized by rounding up and condensation resulting in hyperchromatic staining or pycnosis. In testicular tissue, spermatogonial nuclei had irregular large clumps of heterochromatin adjoining the nuclear membrane indicating initial stage of apoptotic cell death. Electrophoretic separation resulted in a ladder pattern of blood DNA and smear like pattern of hepatic DNA. These results indicate that the above herbicides are able to induce apoptosis both at molecular as

  19. Towards simultaneous measurements of electronic and structural properties in ultra-fast x-ray free electron laser absorption spectroscopy experiments

    SciTech Connect

    Gaudin, J.; Fourment, C.; Cho, B. I.; Engelhorn, K.; Galtier, E.; Harmand, M.; Leguay, P. M.; Lee, H. J.; Nagler, B.; Nakatsutsumi, M.; Ozkan, C.; Störmer, M.; Toleikis, S.; Tschentscher, Th.; Heimann, P. A.; Dorchies, F.

    2014-04-17

    The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called “molecular movie” within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level of the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.

  20. Towards simultaneous measurements of electronic and structural properties in ultra-fast x-ray free electron laser absorption spectroscopy experiments

    DOE PAGES

    Gaudin, J.; Fourment, C.; Cho, B. I.; Engelhorn, K.; Galtier, E.; Harmand, M.; Leguay, P. M.; Lee, H. J.; Nagler, B.; Nakatsutsumi, M.; et al

    2014-04-17

    The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called “molecular movie” within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level ofmore » the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.« less

  1. Towards simultaneous measurements of electronic and structural properties in ultra-fast x-ray free electron laser absorption spectroscopy experiments

    NASA Astrophysics Data System (ADS)

    Gaudin, J.; Fourment, C.; Cho, B. I.; Engelhorn, K.; Galtier, E.; Harmand, M.; Leguay, P. M.; Lee, H. J.; Nagler, B.; Nakatsutsumi, M.; Ozkan, C.; Störmer, M.; Toleikis, S.; Tschentscher, Th; Heimann, P. A.; Dorchies, F.

    2014-04-01

    The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called ``molecular movie'' within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level of the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.

  2. Towards simultaneous measurements of electronic and structural properties in ultra-fast x-ray free electron laser absorption spectroscopy experiments.

    PubMed

    Gaudin, J; Fourment, C; Cho, B I; Engelhorn, K; Galtier, E; Harmand, M; Leguay, P M; Lee, H J; Nagler, B; Nakatsutsumi, M; Ozkan, C; Störmer, M; Toleikis, S; Tschentscher, Th; Heimann, P A; Dorchies, F

    2014-04-17

    The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called "molecular movie" within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level of the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.

  3. Dynamic Processes in Biology, Chemistry, and Materials Science: Opportunities for UltraFast Transmission Electron Microscopy - Workshop Summary Report

    SciTech Connect

    Kabius, Bernd C.; Browning, Nigel D.; Thevuthasan, Suntharampillai; Diehl, Barbara L.; Stach, Eric A.

    2012-07-25

    This report summarizes a 2011 workshop that addressed the potential role of rapid, time-resolved electron microscopy measurements in accelerating the solution of important scientific and technical problems. A series of U.S. Department of Energy (DOE) and National Academy of Science workshops have highlighted the critical role advanced research tools play in addressing scientific challenges relevant to biology, sustainable energy, and technologies that will fuel economic development without degrading our environment. Among the specific capability needs for advancing science and technology are tools that extract more detailed information in realistic environments (in situ or operando) at extreme conditions (pressure and temperature) and as a function of time (dynamic and time-dependent). One of the DOE workshops, Future Science Needs and Opportunities for Electron Scattering: Next Generation Instrumentation and Beyond, specifically addressed the importance of electron-based characterization methods for a wide range of energy-relevant Grand Scientific Challenges. Boosted by the electron optical advancement in the last decade, a diversity of in situ capabilities already is available in many laboratories. The obvious remaining major capability gap in electron microscopy is in the ability to make these direct in situ observations over a broad spectrum of fast (µs) to ultrafast (picosecond [ps] and faster) temporal regimes. In an effort to address current capability gaps, EMSL, the Environmental Molecular Sciences Laboratory, organized an Ultrafast Electron Microscopy Workshop, held June 14-15, 2011, with the primary goal to identify the scientific needs that could be met by creating a facility capable of a strongly improved time resolution with integrated in situ capabilities. The workshop brought together more than 40 leading scientists involved in applying and/or advancing electron microscopy to address important scientific problems of relevance to DOE’s research

  4. Probing in Space and Time the Nuclear Motion Driven by Nonequilibrium Electronic Dynamics in Ultrafast Pumped N2.

    PubMed

    Ajay, J; Šmydke, J; Remacle, F; Levine, R D

    2016-05-19

    An ultrafast electronic excitation of N2 in the vacuum ultraviolet creates a nonstationary coherent linear superposition of interacting valence and Rydberg states resulting in a net oscillating dipole moment. There is therefore a linear response to an electrical field that can be queried by varying the time delay between the pump and a second optical probe pulse. Both the pump and probe pulses are included in our computation as part of the Hamiltonian, and the time-dependent wave function for both electronic and nuclear dynamics is computed using a grid representation for the internuclear coordinate. Even on an ultrafast time scale there are several processes that can be discerned beyond the expected coherence oscillations. In particular, the coupling between the excited valence and Rydberg states of the same symmetry is very evident and can be directly probed by varying the delay between pulse and probe. For quite a number of vibrations the nuclear motion does not dephase the electronic disequilibrium. However, the nuclear motion does modulate the dipolar response by taking the wave packet in and out of the Franck-Condon region and by its strong influence on the coupling of the Rydberg and valence states. A distinct isotope effect arises from the dependence of the interstate coupling on the nuclear mass.

  5. Real-time observation of multiexcitonic states in ultrafast singlet fission using coherent 2D electronic spectroscopy.

    PubMed

    Bakulin, Artem A; Morgan, Sarah E; Kehoe, Tom B; Wilson, Mark W B; Chin, Alex W; Zigmantas, Donatas; Egorova, Dassia; Rao, Akshay

    2016-01-01

    Singlet fission is the spin-allowed conversion of a spin-singlet exciton into a pair of spin-triplet excitons residing on neighbouring molecules. To rationalize this phenomenon, a multiexcitonic spin-zero triplet-pair state has been hypothesized as an intermediate in singlet fission. However, the nature of the intermediate states and the underlying mechanism of ultrafast fission have not been elucidated experimentally. Here, we study a series of pentacene derivatives using ultrafast two-dimensional electronic spectroscopy and unravel the origin of the states involved in fission. Our data reveal the crucial role of vibrational degrees of freedom coupled to electronic excitations that facilitate the mixing of multiexcitonic states with singlet excitons. The resulting manifold of vibronic states drives sub-100 fs fission with unity efficiency. Our results provide a framework for understanding singlet fission and show how the formation of vibronic manifolds with a high density of states facilitates fast and efficient electronic processes in molecular systems.

  6. Real-time observation of multiexcitonic states in ultrafast singlet fission using coherent 2D electronic spectroscopy

    NASA Astrophysics Data System (ADS)

    Bakulin, Artem A.; Morgan, Sarah E.; Kehoe, Tom B.; Wilson, Mark W. B.; Chin, Alex W.; Zigmantas, Donatas; Egorova, Dassia; Rao, Akshay

    2016-01-01

    Singlet fission is the spin-allowed conversion of a spin-singlet exciton into a pair of spin-triplet excitons residing on neighbouring molecules. To rationalize this phenomenon, a multiexcitonic spin-zero triplet-pair state has been hypothesized as an intermediate in singlet fission. However, the nature of the intermediate states and the underlying mechanism of ultrafast fission have not been elucidated experimentally. Here, we study a series of pentacene derivatives using ultrafast two-dimensional electronic spectroscopy and unravel the origin of the states involved in fission. Our data reveal the crucial role of vibrational degrees of freedom coupled to electronic excitations that facilitate the mixing of multiexcitonic states with singlet excitons. The resulting manifold of vibronic states drives sub-100 fs fission with unity efficiency. Our results provide a framework for understanding singlet fission and show how the formation of vibronic manifolds with a high density of states facilitates fast and efficient electronic processes in molecular systems.

  7. Femtosecond time-resolved photoelectron imaging on ultrafast electronic dephasing in an isolated molecule

    NASA Astrophysics Data System (ADS)

    Suzuki, Toshinori; Wang, Li; Kohguchi, Hiroshi

    1999-09-01

    Ultrafast dephasing in an intermediate case of molecular radiationless transition has been visualized for the first time by femtosecond time-resolved photoelectron imaging. The decay of photoexcited S1(n,π*) state of pyrazine in 100 ps and the corresponding build-up of triplet states were clearly observed.

  8. Comment on ``Ultrafast Demagnetization Measurements Using Extreme Ultraviolet Light: Comparison of Electronic and Magnetic Contributions''

    NASA Astrophysics Data System (ADS)

    Vodungbo, Boris; Gautier, Julien; Lambert, Guillaume; Zeitoun, Philippe; Lüning, Jan

    2013-07-01

    The time-resolved transverse magneto-optical Kerr effect using high-order harmonics is a very promising technique to study ultrafast magnetization dynamics. Recently, it was claimed that this technique was free of any nonmagnetic artifact. Here, we show that this report was not fully supported. We propose simple additional measurements that can unambiguously demonstrate this affirmation.

  9. Ultrafast single-electron transfer in coupled quantum dots driven by a few-cycle chirped pulse

    SciTech Connect

    Yang, Wen-Xing; Chen, Ai-Xi; Bai, Yanfeng; Lee, Ray-Kuang

    2014-04-14

    We theoretically study the ultrafast transfer of a single electron between the ground states of a coupled double quantum dot (QD) structure driven by a nonlinear chirped few-cycle laser pulse. A time-dependent Schrödinger equation without the rotating wave approximation is solved numerically. We demonstrate numerically the possibility to have a complete transfer of a single electron by choosing appropriate values of chirped rate parameters and the intensity of the pulse. Even in the presence of the spontaneous emission and dephasing processes of the QD system, high-efficiency coherent transfer of a single electron can be obtained in a wide range of the pulse parameters. Our results illustrate the potential to utilize few-cycle pulses for the excitation in coupled quantum dot systems through the nonlinear chirp parameter control, as well as a guidance in the design of experimental implementation.

  10. Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters

    NASA Astrophysics Data System (ADS)

    Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y.; Nobusada, Katsuyuki; Jin, Rongchao

    2016-03-01

    Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared

  11. Ultrafast Dynamics of a Nucleobase Analogue Illuminated by a Short Intense X-ray Free Electron Laser Pulse

    NASA Astrophysics Data System (ADS)

    Nagaya, K.; Motomura, K.; Kukk, E.; Fukuzawa, H.; Wada, S.; Tachibana, T.; Ito, Y.; Mondal, S.; Sakai, T.; Matsunami, K.; Koga, R.; Ohmura, S.; Takahashi, Y.; Kanno, M.; Rudenko, A.; Nicolas, C.; Liu, X.-J.; Zhang, Y.; Chen, J.; Anand, M.; Jiang, Y. H.; Kim, D.-E.; Tono, K.; Yabashi, M.; Kono, H.; Miron, C.; Yao, M.; Ueda, K.

    2016-04-01

    Understanding x-ray radiation damage is a crucial issue for both medical applications of x rays and x-ray free-electron-laser (XFEL) science aimed at molecular imaging. Decrypting the charge and fragmentation dynamics of nucleobases, the smallest units of a macro-biomolecule, contributes to a bottom-up understanding of the damage via cascades of phenomena following x-ray exposure. We investigate experimentally and by numerical simulations the ultrafast radiation damage induced on a nucleobase analogue (5-iodouracil) by an ultrashort (10 fs) high-intensity radiation pulse generated by XFEL at SPring-8 Angstrom Compact free electron Laser (SACLA). The present study elucidates a plausible underlying radiosensitizing mechanism of 5-iodouracil. This mechanism is independent of the exact composition of 5-iodouracil and thus relevant to other such radiosensitizers. Furthermore, we found that despite a rapid increase of the net molecular charge in the presence of iodine, and of the ultrafast release of hydrogen, the other atoms are almost frozen within the 10-fs duration of the exposure. This validates single-shot molecular imaging as a consistent approach, provided the radiation pulse used is brief enough.

  12. Ultrafast electronic and spin dynamics in thin iron films: electron-magnon and electron-phonon interactions

    NASA Astrophysics Data System (ADS)

    Carpene, E.; Mancini, E.; Dallera, C.; Brenna, M.; Puppin, E.; De Silvestri, S.

    The electronic and spin dynamics in thin iron films have been investigated by means of time-resolved reflectivity and magneto-optical Kerr effect. The electron-magnon and the electron-phonon coupling times are extrapolated and their influence is discussed.

  13. Excited states of the high-frequency vibrational modes and kinetics of ultrafast photoinduced electron transfer

    NASA Astrophysics Data System (ADS)

    Barykov, V. Yu.; Ivanov, A. I.

    2016-02-01

    The effect of the carrier frequency of the exciting laser pulse on the kinetics of intramolecular photoinduced charge transfer in the multi-channel stochastic model is studied. It is shown that the population of different states of high-frequency intramolecular modes upon varying the frequency of the excitation pulse can considerably alter the rate constant of ultrafast charge transfer. It is found that a negative vibrational spectral effect is expected in the vicinity of a barrier-free area (the rate constant of photoinduced charge transfer decreases along with the carrier frequency of the excitation pulse), while a positive effect is predicted in areas of high and low exergonicity (an inverse dependence). It is concluded that the value of the spectral effect falls along with the time of vibrational relaxation. For ultrafast photo-induced charge transfer, however, it remains considerable up to relaxation times of 100 fs.

  14. Single-shot mega-electronvolt ultrafast electron diffraction for structure dynamic studies of warm dense matter

    NASA Astrophysics Data System (ADS)

    Mo, M. Z.; Shen, X.; Chen, Z.; Li, R. K.; Dunning, M.; Sokolowski-Tinten, K.; Zheng, Q.; Weathersby, S. P.; Reid, A. H.; Coffee, R.; Makasyuk, I.; Edstrom, S.; McCormick, D.; Jobe, K.; Hast, C.; Glenzer, S. H.; Wang, X.

    2016-11-01

    We have developed a single-shot mega-electronvolt ultrafast-electron-diffraction system to measure the structural dynamics of warm dense matter. The electron probe in this system is featured by a kinetic energy of 3.2 MeV and a total charge of 20 fC, with the FWHM pulse duration and spot size at sample of 350 fs and 120 μm respectively. We demonstrate its unique capability by visualizing the atomic structural changes of warm dense gold formed from a laser-excited 35-nm freestanding single-crystal gold foil. The temporal evolution of the Bragg peak intensity and of the liquid signal during solid-liquid phase transition are quantitatively determined. This experimental capability opens up an exciting opportunity to unravel the atomic dynamics of structural phase transitions in warm dense matter regime.

  15. Water-Stable, Hydroxamate Anchors for Functionalization of TiO2 Surfaces with Ultrafast Interfacial Electron Transfer

    SciTech Connect

    McNamara, W.R.; Milot, R.L.; Song, H.; Snoeberger III, R.C.; Batista, Victor S.; Schmuttenmaer, C.A.; Brudvig, Gary W; Crabtree, Robert H

    2010-01-01

    A novel class of derivatized hydroxamic acid linkages for robust sensitization of TiO{sub 2} nanoparticles (NPs) under various aqueous conditions is described. The stability of linkages bound to metal oxides under various conditions is important in developing photocatalytic cells which incorporate transition metal complexes for solar energy conversion. In order to compare the standard carboxylate anchor to hydroxamates, two organic dyes differing only in anchoring groups were synthesized and attached to TiO{sub 2} NPs. At acidic, basic, and close to neutral pH, hydroxamic acid linkages resist detachment compared to the labile carboxylic acids. THz spectroscopy was used to compare ultrafast interfacial electron transfer (IET) into the conduction band of TiO{sub 2} for both linkages and found similar IET characteristics. Observable electron injection and stronger binding suggest that hydroxamates are a suitable class of anchors for designing water stable molecules for functionalizing TiO{sub 2}.

  16. Single-shot mega-electronvolt ultrafast electron diffraction for structure dynamic studies of warm dense matter

    DOE PAGES

    Mo, M. Z.; Shen, X.; Chen, Z.; Li, R. K.; Dunning, M.; Sokolowski-Tinten, K.; Zheng, Q.; Weathersby, S. P.; Reid, A. H.; Coffee, R.; et al

    2016-08-04

    We have developed a single-shot mega-electronvolt ultrafast-electron-diffraction system to measure the structural dynamics of warm dense matter. The electron probe in this system is featured by a kinetic energy of 3.2 MeV and a total charge of 20 fC, with the FWHM pulse duration and spot size at sample of 350 fs and 120 µm respectively. We demonstrate its unique capability by visualizing the atomic structural changes of warm dense gold formed from a laser-excited 35-nm freestanding single-crystal gold foil. The temporal evolution of the Bragg peak intensity and of the liquid signal during solid-liquid phase transition are quantitatively determined.more » This experimental capability opens up an exciting opportunity to unravel the atomic dynamics of structural phase transitions in warm dense matter regime« less

  17. Tracking the evolution of electronic and structural properties of VO2 during the ultrafast photoinduced insulator-metal transition

    NASA Astrophysics Data System (ADS)

    Wall, S.; Foglia, L.; Wegkamp, D.; Appavoo, K.; Nag, J.; Haglund, R. F., Jr.; Stähler, J.; Wolf, M.

    2013-03-01

    We present a detailed study of the photoinduced insulator-metal transition in VO2 with broadband time-resolved reflection spectroscopy. This allows us to separate the response of the lattice vibrations from the electronic dynamics and observe their individual evolution. When we excite VO2 above the photoinduced phase transition threshold, we find that the restoring forces that describe the ground-state monoclinic structure are lost during the excitation process, suggesting that an ultrafast change in the lattice potential drives the structural transition. However, by performing a series of pump-probe measurements during the nonequilibrium transition, we observe that the electronic properties of the material evolve on a different, slower time scale. This separation of time scales suggests that the early state of VO2, immediately after photoexcitation, is a nonequilibrium state that is not well defined by either the insulating or the metallic phase.

  18. Vibrational and electronic dynamics of nitrogen-vacancy centres in diamond revealed by two-dimensional ultrafast spectroscopy

    NASA Astrophysics Data System (ADS)

    Huxter, V. M.; Oliver, T. A. A.; Budker, D.; Fleming, G. R.

    2013-11-01

    The optical and material properties of negatively charged nitrogen-vacancy (NV) centres in diamond make them attractive for applications ranging from quantum information to electromagnetic sensing. These properties are strongly dependent on the vibrational manifold associated with the centre, which determines phenomena associated with decoherence, relaxation and spin-orbit coupling. Despite its paramount importance in tuning these properties, the role of the vibrational bath and its effect on the electronic-state dynamics of NV centres in diamond is not fully understood. To elucidate the role of the bath, we present two-dimensional electronic spectroscopic studies of ensembles of negatively charged NV defect centres in diamond (NVD). We observe picosecond non-radiative relaxation within the phonon sideband and find that strongly coupled local modes dominate the vibrational bath. These findings provide a starting point for new insights into dephasing, spin addressing and relaxation in NVD with broad implications for magnetometry, quantum information, nanophotonics, sensing and ultrafast spectroscopy.

  19. Development of high-brightness ultrafast electron microscope for studying nanoscale dynamics associated with strongly correlated materials

    NASA Astrophysics Data System (ADS)

    Tao, Zhensheng

    Strongly correlated-electron materials are a class of materials that exhibit numerous intriguing emergent phenomena, including metal-to-insulator transition, colossal magnetoresistance, high-temperature superconductivity, etc. These phenomena are beyond the reach of the conventional solid state physics, which is based on the band theory. Instead, strong electron-electron correlations are found to play important roles, which leads to complicated interplay between different degrees of freedoms (charge, lattice, spins...). In this thesis, ultrafast electron diffraction (UED) is used to investigate the photo-induced ultrafast structural dynamics of strongly correlated materials, among which VO2 is taken as an exemplar system, one that reveals the fundamental physics behind photo-induced phase transitions, electron-electron correlation on nanometer scales, and the electron-phonon coupling in this exotic class of materials. The phenomena presented here are expected to have more general significance as they may reflect the physics to which other strongly correlated materials also conform. In polycrystalline VO2 thin films, the structural changes resulting from photoexcitation with femtosecond laser pulses with different wavelengths are observed to lead to non-thermal phase transitions, which require less energy compared to the phase transitions induced by thermal excitation. The details of the structural change are extracted from the UED results revealing stepwise atomic movements after photoexcitation, which suggests the phase transition starts with a dilation of the correlated d electrons. On the other hand, the structural phase transition is found to be decoupled from the metal-to-insulator transition when the sample dimension is reduced to the sub-micrometer scale, which is attributed to the interface charge doping effects from different substrates. A new phase (M3, monoclinic metallic phase) is distinguished, which has not been discussed by the existing theoretical

  20. Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters.

    PubMed

    Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y; Nobusada, Katsuyuki; Jin, Rongchao

    2016-04-01

    Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.

  1. Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters

    DOE PAGES

    Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y.; Nobusada, Katsuyuki; Jin, Rongchao

    2016-02-29

    Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state inmore » more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. As a result, the detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.« less

  2. Ultrafast coherent dynamics of Rydberg electrons bound in the image potential near a single metallic nano-object (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Robin, Jörg; Vogelsang, Jan; Nagy, Benedek J.; Gross, Petra; Lienau, Christoph

    2015-09-01

    Image potential states are well established surface states of metallic films [1]. For a single metallic nanostructure these surface states can be localized in the near-field arising from illumination by a strong laser field. Thus single metallic nanostructures offer the unique possibility to study quantum systems with both high spatial and ultrafast temporal resolution. Here, we investigate the dynamics of Rydberg states localized to a sharp metallic nanotaper. For this purpose we realized a laser system delivering few-cycle pulses tunable over a wide wavelength range [2]. Pulses from a regenerative titanium:sapphire amplifier generate a white light continuum, from which both a proportion in the visible and in the infrared are amplified in two non-collinear optical parametric amplification (NOPA) stages. Difference frequency generation (DFG) of both stages provides pulses in the near-infrared. With a precisely delayed sequence of few-cycle pulses centered around 600 nm (NOPA#1 output) and 1600 nm (DFG output) we illuminate the apex of a sharply etched gold tip. Varying the delay we observe an exponential decay of photoemitted electrons with a distinctly asymmetric decay length on both sides, indicating the population of different states. Superimposed on the decay is a clearly discernible quantum beat pattern with a period of <50 fs, which arises from the motion of Rydberg photoelectrons bound within their own image potential. These results therefore constitute a step towards controlling single electron wavepackets released from a gold tip opening up fascinating perspectives for applications in ultrafast electron microscopy [3]. [1] Hofer, U. et al. Science 277, 1480 (1997) [2] Vogelsang, J., Robin J. et al. Opt. Express 22, 25295 (2014) [3] Petek, H. et al. ACS Nano 8, 5 (2014)

  3. Monitoring Ultrafast Chemical Dynamics by Time-Domain X-ray Photo- and Auger-Electron Spectroscopy.

    PubMed

    Gessner, Oliver; Gühr, Markus

    2016-01-19

    The directed flow of charge and energy is at the heart of all chemical processes. Extraordinary efforts are underway to monitor and understand the concerted motion of electrons and nuclei with ever increasing spatial and temporal sensitivity. The element specificity, chemical sensitivity, and temporal resolution of ultrafast X-ray spectroscopy techniques hold great promise to provide new insight into the fundamental interactions underlying chemical dynamics in systems ranging from isolated molecules to application-like devices. Here, we focus on the potential of ultrafast X-ray spectroscopy techniques based on the detection of photo- and Auger electrons to provide new fundamental insight into photochemical processes of systems with various degrees of complexity. Isolated nucleobases provide an excellent testing ground for our most fundamental understanding of intramolecular coupling between electrons and nuclei beyond the traditionally applied Born-Oppenheimer approximation. Ultrafast electronic relaxation dynamics enabled by the breakdown of this approximation is the major component of the nucleobase photoprotection mechanisms. Transient X-ray induced Auger electron spectroscopy on photoexcited thymine molecules provides atomic-site specific details of the extremely efficient coupling that converts potentially bond changing ultraviolet photon energy into benign heat. In particular, the time-dependent spectral shift of a specific Auger band is sensitive to the length of a single bond within the molecule. The X-ray induced Auger transients show evidence for an electronic transition out of the initially excited state within only ∼200 fs in contrast to theoretically predicted picosecond population trapping behind a reaction barrier. Photoinduced charge transfer dynamics between transition metal complexes and semiconductor nanostructures are of central importance for many emerging energy and climate relevant technologies. Numerous demonstrations of photovoltaic and

  4. Study of beam loading and its compensation in the Compact Ultrafast Terahertz Free-Electron Laser injector linac

    SciTech Connect

    Lal, Shankar Pant, K. K.

    2014-12-15

    The RF properties of an accelerating structure, and the pulse structure and charge per bunch in the electron beam propagating through it are important parameters that determine the impact of beam loading in the structure. The injector linac of the Compact Ultrafast Terahertz Free-Electron Laser (CUTE-FEL) has been operated with two different pulse structures during initial commissioning experiments and the effect of beam loading on the accelerated electron beam parameters has been studied analytically for these two pulse structures. This paper discusses the analytical study of beam loading in a Standing Wave, Plane Wave Transformer linac employed in the CUTE-FEL setup, and a possible technique for its compensation for the electron beam parameters of the CUTE-FEL. A parametric study has been performed to study beam loading for different beam currents and to optimize injection time of the electron beam to compensate beam loading. Results from the parametric study have also been used to explain previously observed results from acceleration experiments in the CUTE-FEL setup.

  5. Ultrafast Electronic Phase Transition in La1/2Sr3/2MnO4 by Coherent Vibrational Excitation: Evidence for Nonthermal Melting of Orbital Order

    NASA Astrophysics Data System (ADS)

    Tobey, R. I.; Prabhakaran, D.; Boothroyd, A. T.; Cavalleri, A.

    2008-11-01

    An ultrafast electronic phase transition, associated with melting of orbital order, is driven in La1/2Sr3/2MnO4 by selectively exciting the Mn-O stretching mode with femtosecond pulses at 16μm wavelength. The energy coupled into this vibration is less than 1% of that necessary to induce the transition thermally. Nonthermal melting of this electronic phase originates from coherent lattice displacements comparable to the static Jahn-Teller distortion.

  6. Soft Route to 4D Tomography.

    PubMed

    Taillandier-Thomas, Thibault; Roux, Stéphane; Hild, François

    2016-07-01

    Based on the assumption that the time evolution of a sample observed by computed tomography requires many less parameters than the definition of the microstructure itself, it is proposed to reconstruct these changes based on the initial state (using computed tomography) and very few radiographs acquired at fixed intervals of time. This Letter presents a proof of concept that for a fatigue cracked sample its kinematics can be tracked from no more than two radiographs in situations where a complete 3D view would require several hundreds of radiographs. This 2 order of magnitude gain opens the way to a "computed" 4D tomography, which complements the recent progress achieved in fast or ultrafast computed tomography, which is based on beam brightness, detector sensitivity, and signal acquisition technologies.

  7. Soft Route to 4D Tomography

    NASA Astrophysics Data System (ADS)

    Taillandier-Thomas, Thibault; Roux, Stéphane; Hild, François

    2016-07-01

    Based on the assumption that the time evolution of a sample observed by computed tomography requires many less parameters than the definition of the microstructure itself, it is proposed to reconstruct these changes based on the initial state (using computed tomography) and very few radiographs acquired at fixed intervals of time. This Letter presents a proof of concept that for a fatigue cracked sample its kinematics can be tracked from no more than two radiographs in situations where a complete 3D view would require several hundreds of radiographs. This 2 order of magnitude gain opens the way to a "computed" 4D tomography, which complements the recent progress achieved in fast or ultrafast computed tomography, which is based on beam brightness, detector sensitivity, and signal acquisition technologies.

  8. Ultrafast electronic and vibrational dynamics of a ruthenium porphyrin complex in intersystem crossing

    NASA Astrophysics Data System (ADS)

    Kobayashi, Takayoshi; Iwakura, Izumi; Yabushita, Atsushi

    Using sub-5fs visible laser pulses, ultrafast time-resolved absorption change was observed for RuII (TPP)(CO) (TPP=5,10, 15, 20 tetraphenylporphirine) solved in chloroform. Exponential fitting of the time traces estimated decay life times of intermediates as 230±70 fs, 1150±260 fs, 2150±360 fs, and ≫4.8 ps for 1Q x(1 , 0) /(π ,π∗) ,1Q x(0 , 0)(π ,π∗) , 3(d ,π∗) , and 3(π ,π∗) , respectively. Real-time 4.8 change of instantaneous molecular vibration frequency was studied by spectrogram analysis, which reflects gradual vibration mode change in the intersystem crossing from singlet state to triplet state.

  9. Ultrafast optical nonlinearity, electronic absorption, vibrational spectra and solvent effect studies of ninhydrin

    NASA Astrophysics Data System (ADS)

    Sajan, D.; Devi, T. Uma; Safakath, K.; Philip, Reji; Němec, Ivan; Karabacak, M.

    2013-05-01

    FT-IR, FT-Raman and UV-Vis spectra of the nonlinear optical molecule ninhydrin have been recorded and analyzed. The equilibrium geometry, bonding features, and harmonic vibrational wavenumbers have been investigated with the help of B3LYP density functional theory method. A detailed interpretation of the vibrational spectra is carried out with the aid of normal coordinate analysis following the scaled quantum mechanical force field methodology. Solvent effects have been calculated using time-dependent density functional theory in combination with the polarized continuum model. Natural bond orbital analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule. Employing the open-aperture z-scan technique, nonlinear optical absorption of the sample has been studied in the ultrafast and short-pulse excitation regimes, using 100 fs and 5 ns laser pulses respectively. It is found that ninhydrin exhibits optical limiting for both excitations, indicating potential photonic applications.

  10. Ultrafast electronic dynamics in unipolar n-doped indium gallium arsenide/gallium arsenide self-assembled quantum dots

    NASA Astrophysics Data System (ADS)

    Wu, Zong-Kwei J.

    2006-12-01

    Photodetectors based on intraband infrared absorption in the quantum dots have demonstrated improved performance over its quantum well counterpart by lower dark current, relative temperature insensitivity, and its ability for normal incidence operation. Various scattering processes, including phonon emission/absorption and carrier-carrier scattering, are critical in understanding device operation on the fundamental level. In previous studies, our group has investigated carrier dynamics in both low- and high-density regime. Ultrafast electron-hole scattering and the predicted phonon bottleneck effect in intrinsic quantum dots have been observed. Further examination on electron dynamics in unipolar structures is presented in this thesis. We used n-doped quantum dot in mid-infrared photodetector device structure to study the electron dynamics in unipolar structure. Differential transmission spectroscopy with mid-infrared intraband pump and optical interband probe was implemented to measure the electron dynamics directly without creating extra electron-hole pair, Electron relaxation after excitation was measured under various density and temperature conditions. Rapid capture into quantum dot within ˜ 10 ps was observed due to Auger-type electron-electron scattering. Intradot relaxation from the quantum dot excited state to the ground state was also observed on the time scale of 100 ps. With highly doped electron density in the structure, the inter-sublevel relaxation is dominated by Auger-type electron-electron scattering and the phonon bottleneck effect is circumvented. Nanosecond-scale recovery in larger-sized quantum dots was observed, not intrinsic to electron dynamics but due to band-bending and built-in voltage drift. An ensemble Monte Carlo simulation was also established to model the dynamics in quantum dots and in goad agreement with the experimental results. We presented a comprehensive picture of electron dynamics in the unipolar quantum dot structure

  11. Ultrafast saturation of electronic-resonance-enhanced coherent anti-Stokes Raman scattering and comparison for pulse durations in the nanosecond to femtosecond regime

    NASA Astrophysics Data System (ADS)

    Patnaik, Anil K.; Roy, Sukesh; Gord, James R.

    2016-02-01

    The saturation threshold of a probe pulse in an ultrafast electronic-resonance-enhanced (ERE) coherent anti-Stokes Raman spectroscopy (CARS) configuration is calculated. We demonstrate that while the underdamping condition is a sufficient condition for saturation of ERE-CARS with the long-pulse excitations, a transient gain must be achieved to saturate the ERE-CARS signal for the ultrafast probe regime. We identify that the area under the probe pulse can be used as a definitive parameter to determine the criterion for a saturation threshold for ultrafast ERE-CARS. From a simplified analytical solution and a detailed numerical calculation based on density-matrix equations, the saturation threshold of ERE-CARS is compared for a wide range of probe-pulse durations from the 10-ns to the 10-fs regime. The theory explains both qualitatively and quantitatively the saturation thresholds of resonant transitions and also gives a predictive capability for other pulse duration regimes. The presented criterion for the saturation threshold will be useful in establishing the design parameters for ultrafast ERE-CARS.

  12. Ultrafast laser and swift heavy ion irradiation: Response of Gd2O3 and ZrO2 to intense electronic excitation

    NASA Astrophysics Data System (ADS)

    Rittman, Dylan R.; Tracy, Cameron L.; Cusick, Alex B.; Abere, Michael J.; Torralva, Ben; Ewing, Rodney C.; Yalisove, Steven M.

    2015-04-01

    In order to investigate the response of materials to extreme conditions, there are several approaches to depositing extremely high concentrations of energy into very small volumes of material, including ultrafast laser and swift heavy ion (SHI) irradiation. In this study, crystalline-to-crystalline phase transformations in cubic Gd2O3 and monoclinic ZrO2 have been investigated using ultrafast laser irradiation. The phases produced by the extreme conditions of irradiation were characterized by grazing incidence x-ray diffraction (GIXRD) and Raman spectroscopy. Gd2O3 exhibited a cubic-to-monoclinic phase transformation, as evidenced by the appearance of the monoclinic (40 2 ¯ ), (003), (310), and (11 2 ¯ ) peaks in the GIXRD pattern and of four Ag and three Bg Raman modes. ZrO2 underwent a monoclinic-to-tetragonal phase transformation, as evidenced by the emergence of the tetragonal (101) peak in the GIXRD pattern and of Eg and A1g Raman modes. The new phases formed by ultrafast laser irradiation are high temperature polymorphs of the two materials. No evidence of amorphization was seen in the GIXRD data, though Raman spectroscopy indicated point defect accumulation. These results are identical to those produced by irradiation with SHIs, which also deposit energy in materials primarily through electronic excitation. The similarity in damage process and material response between ultrafast laser and SHI irradiation suggests a fundamental relationship between these two techniques.

  13. Imaging Acoustic Phonon Dynamics on the Nanometer-Femtosecond Spatiotemporal Length-Scale with Ultrafast Electron Microscopy

    NASA Astrophysics Data System (ADS)

    Plemmons, Dayne; Flannigan, David

    Coherent collective lattice oscillations known as phonons dictate a broad range of physical observables in condensed matter and act as primary energy carriers across a wide range of material systems. Despite this omnipresence, analysis of phonon dynamics on their ultrashort native spatiotemporal length scale - that is, the combined nanometer (nm), spatial and femtosecond (fs), temporal length-scales - has largely remained experimentally inaccessible. Here, we employ ultrafast electron microscopy (UEM) to directly image discrete acoustic phonons in real-space with combined nm-fs resolution. By directly probing electron scattering in the image plane (as opposed to the diffraction plane), we retain phase information critical for following the evolution, propagation, scattering, and decay of phonons in relation to morphological features of the specimen (i.e. interfaces, grain boundaries, voids, ripples, etc.). We extract a variety of morphologically-specific quantitative information from the UEM videos including phonon frequencies, phase velocities, and decays times. We expect these direct manifestations of local elastic properties in the vicinity of material defects and interfaces will aide in the understanding and application of phonon-mediated phenomena in nanostructures. Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN, 55455, USA.

  14. Ultrafast spectroscopic measurement of the optical and electronic properties of narrow-band-gap semiconductor laser materials

    NASA Astrophysics Data System (ADS)

    Anson, Scott Allen

    1999-12-01

    Semiconductor lasers operating in the mid-infrared region of the spectrum (2-5 μm) are of interest for a variety of potential applications and therefore are currently the focus of intense research and development. One of the main impediments to the development of these lasers is a non-radiative loss process know as Auger recombination. It is this loss mechanism that leads to the relatively low temperature operation of these lasers. In addition to Auger recombination, there is an interest in suppressing laser which can lead to the degradation and catastrophic failure of devices at high output powers. The tendency for filament formation is suppressed in materials with small linewidth enhancement factors. To improve the performance of these semiconductor lasers, band structure engineering techniques have been employed to the design of narrow band-gap III-V semiconductor active regions based on GaInSb/InAs superlattices. These superlattice structures are designed to have favorable material properties that allow for the suppression of Auger recombination and a reduction of the linewidth enhancement factor. In addition to Auger recombination and the linewidth enhancement factor, a number of other optical and electronic properties in these superlattice structures are also of interest, including the differential gain, differential index, Shockley-Read-Hall recombination, and in-plane carrier diffusion. In this dissertation measurements of the optical and electronic properties in these structures conducted using two ultrafast spectroscopic techniques, time-resolved differential transmission and photogenerated transient grating is discussed. These ultrafast spectroscopic measurements are performed using 140 fs pump pulses from a mode-locked Ti:sapphire laser operating at 840 nm and 170 fs probe pulses from a synchronously-pumped optical parametric oscillator which is tunable between 2.65 to 4.4 μm. The measurements show that these superlattices have favorable material

  15. Ultrafast Photoinduced Interfacial Proton Coupled Electron Transfer from CdSe Quantum Dots to 4,4'-Bipyridine.

    PubMed

    Chen, Jinquan; Wu, Kaifeng; Rudshteyn, Benjamin; Jia, Yanyan; Ding, Wendu; Xie, Zhao-Xiong; Batista, Victor S; Lian, Tianquan

    2016-01-27

    Pyridine and derivatives have been reported as efficient and selective catalysts for the electrochemical and photoelectrochemical reduction of CO2 to methanol. Although the catalytic mechanism remains a subject of considerable recent debate, most proposed models involve interfacial proton coupled electron transfer (PCET) to electrode-bound catalysts. We report a combined experimental and theoretical study of the photoreduction of 4,4'-bipyridium (bPYD) using CdSe quantum dots (QDs) as a model system for interfacial PCET. We observed ultrafast photoinduced PCET from CdSe QDs to form doubly protonated [bPYDH2](+•) radical cations at low pH (4-6). Through studies of the dependence of PCET rate on isotopic substitution, pH and bPYD concentration, the radical formation mechanism was identified to be a sequential interfacial electron and proton transfer (ET/PT) process with a rate-limiting pH independent electron transfer rate constant, kint, of 1.05 ± 0.13 × 10(10) s(-1) between a QD and an adsorbed singly protonated [bPYDH](+). Theoretical studies of the adsorption of [bPYDH](+) and methylviologen on QD surfaces revealed important effects of hydrogen bonding with the capping ligand (3-mercaptopropionic acid) on binding geometry and interfacial PCET. In the presence of sacrificial electron donors, this system was shown to be capable of generating [bPYDH2](+•) radical cations under continuous illumination at 405 nm with a steady-state photoreduction quantum yield of 1.1 ± 0.1% at pH 4. The mechanism of bPYD photoreduction reported in this work may provide useful insights into the catalytic roles of pyridine and pyridine derivatives in the electrochemical and photoelectrochemical reduction of CO2. PMID:26713752

  16. Ultrafast electronic processes in an insulator: The Be and O sites in BeO

    NASA Astrophysics Data System (ADS)

    Schiwietz, G.; Beye, M.; Czerski, K.; Föhlisch, A.; Könnecke, R.; Roth, M.; Schlappa, J.; Staufenbiel, F.; Suljoti, E.; Kuusik, I.; Grande, P. L.

    2013-12-01

    The short-time dynamics of amorphous beryllium oxide (a-BeO) has been investigated for electronic excitation/ionization by fast incident electrons, as well as by Ar7+, Ar15+, Xe15+, and Xe31+ ions at velocities of 6-10% the speed of light. Site specific Auger-electron spectra induced by fast heavy ions are the central point of this investigation. Electron induced Auger spectra serve as a reference and electron-energy loss (EELS) spectroscopy as well as resonant inelastic X-ray scattering (RIXS) are invoked for quantitative understanding. For the heavy-ion case, we observe strong variations in the corresponding spectral distributions of Be-K and O-K Auger lines. These are related to local changes of the electron density, of the electron temperature and even of the electronic band structure of BeO on a femtosecond time scale after the passage of highly charged heavy ions.

  17. Ultrafast harmonic rf kicker design and beam dynamics analysis for an energy recovery linac based electron circulator cooler ring

    NASA Astrophysics Data System (ADS)

    Huang, Yulu; Wang, Haipeng; Rimmer, Robert A.; Wang, Shaoheng; Guo, Jiquan

    2016-08-01

    An ultrafast kicker system is being developed for the energy recovery linac (ERL) based electron circulator cooler ring (CCR) in the proposed Jefferson Lab Electron Ion Collider (JLEIC, previously named MEIC). In the CCR, the injected electron bunches can be recirculated while performing ion cooling for 10-30 turns before the extraction, thus reducing the recirculation beam current in the ERL to 1 /10 -1 /30 (150 mA -50 mA ) of the cooling beam current (up to 1.5 A). Assuming a bunch repetition rate of 476.3 MHz and a recirculating factor of 10 in the CCR, the kicker is required to operate at a pulse repetition rate of 47.63 MHz with pulse width of around 2 ns, so that only every 10th bunch in the CCR will experience a transverse kick while the rest of the bunches will not be disturbed. Such a kicker pulse can be synthesized by ten harmonic modes of the 47.63 MHz kicker pulse repetition frequency, using up to four quarter wavelength resonator (QWR) based deflecting cavities. In this paper, several methods to synthesize such a kicker waveform will be discussed and a comparison of their beam dynamics performance is made using ELEGANT. Four QWR cavities are envisaged with high transverse shunt impedance requiring less than 100 W of total rf power for a Flat-Top kick pulse. Multipole fields due to the asymmetry of this type of cavity are analyzed. The transverse emittance growth due to the sextupole component is simulated in ELEGANT. Off-axis injection and extraction issues and beam optics using a multicavity kick-drift scheme will also be discussed.

  18. Ultrafast harmonic rf kicker design and beam dynamics analysis for an energy recovery linac based electron circulator cooler ring

    DOE PAGES

    Huang, Yulu; Wang, Haipeng; Rimmer, Robert A.; Wang, Shaoheng; Guo, Jiquan

    2016-08-01

    An ultrafast kicker system is being developed for the energy recovery linac (ERL) based electron circulator cooler ring (CCR) in the proposed Jefferson Lab Electron Ion Collider (JLEIC, previously named MEIC). In the CCR, the injected electron bunches can be recirculated while performing ion cooling for 10–30 turns before the extraction, thus reducing the recirculation beam current in the ERL to 1/10–1/30 (150mA–50 mA) of the cooling beam current (up to 1.5 A). Assuming a bunch repetition rate of 476.3 MHz and a recirculating factor of 10 in the CCR, the kicker is required to operate at a pulse repetitionmore » rate of 47.63 MHz with pulse width of around 2 ns, so that only every 10th bunch in the CCR will experience a transverse kick while the rest of the bunches will not be disturbed. Such a kicker pulse can be synthesized by ten harmonic modes of the 47.63 MHz kicker pulse repetition frequency, using up to four quarter wavelength resonator (QWR) based deflecting cavities. In this paper, several methods to synthesize such a kicker waveform will be discussed and a comparison of their beam dynamics performance is made using ELEGANT. Four QWR cavities are envisaged with high transverse shunt impedance requiring less than 100 W of total rf power for a Flat-Top kick pulse. Multipole fields due to the asymmetry of this type of cavity are analyzed. The transverse emittance growth due to the sextupole component is simulated in ELEGANT. In conclusion, off-axis injection and extraction issues and beam optics using a multicavity kick-drift scheme will also be discussed.« less

  19. A simple electron time-of-flight spectrometer for ultrafast vacuum ultraviolet photoelectron spectroscopy of liquid solutions.

    PubMed

    Arrell, C A; Ojeda, J; Sabbar, M; Okell, W A; Witting, T; Siegel, T; Diveki, Z; Hutchinson, S; Gallmann, L; Keller, U; van Mourik, F; Chapman, R T; Cacho, C; Rodrigues, N; Turcu, I C E; Tisch, J W G; Springate, E; Marangos, J P; Chergui, M

    2014-10-01

    We present a simple electron time of flight spectrometer for time resolved photoelectron spectroscopy of liquid samples using a vacuum ultraviolet (VUV) source produced by high-harmonic generation. The field free spectrometer coupled with the time-preserving monochromator for the VUV at the Artemis facility of the Rutherford Appleton Laboratory achieves an energy resolution of 0.65 eV at 40 eV with a sub 100 fs temporal resolution. A key feature of the design is a differentially pumped drift tube allowing a microliquid jet to be aligned and started at ambient atmosphere while preserving a pressure of 10(-1) mbar at the micro channel plate detector. The pumping requirements for photoelectron (PE) spectroscopy in vacuum are presented, while the instrument performance is demonstrated with PE spectra of salt solutions in water. The capability of the instrument for time resolved measurements is demonstrated by observing the ultrafast (50 fs) vibrational excitation of water leading to temporary proton transfer.

  20. A simple electron time-of-flight spectrometer for ultrafast vacuum ultraviolet photoelectron spectroscopy of liquid solutions

    SciTech Connect

    Arrell, C. A. Ojeda, J.; Mourik, F. van; Chergui, M.; Sabbar, M.; Gallmann, L.; Keller, U.; Okell, W. A.; Witting, T.; Siegel, T.; Diveki, Z.; Hutchinson, S.; Tisch, J. W.G.; Marangos, J. P.; Chapman, R. T.; Cacho, C.; Rodrigues, N.; Turcu, I. C.E.; Springate, E.

    2014-10-01

    We present a simple electron time of flight spectrometer for time resolved photoelectron spectroscopy of liquid samples using a vacuum ultraviolet (VUV) source produced by high-harmonic generation. The field free spectrometer coupled with the time-preserving monochromator for the VUV at the Artemis facility of the Rutherford Appleton Laboratory achieves an energy resolution of 0.65 eV at 40 eV with a sub 100 fs temporal resolution. A key feature of the design is a differentially pumped drift tube allowing a microliquid jet to be aligned and started at ambient atmosphere while preserving a pressure of 10⁻¹ mbar at the micro channel plate detector. The pumping requirements for photoelectron (PE) spectroscopy in vacuum are presented, while the instrument performance is demonstrated with PE spectra of salt solutions in water. The capability of the instrument for time resolved measurements is demonstrated by observing the ultrafast (50 fs) vibrational excitation of water leading to temporary proton transfer.

  1. Reply to ``Comment on `Ultrafast Demagnetization Measurements Using Extreme Ultraviolet Light: Comparison of Electronic and Magnetic Contributions' ''

    NASA Astrophysics Data System (ADS)

    Turgut, Emrah; Grychtol, Patrik; La-O-Vorakiat, Chan; Adams, Daniel E.; Kapteyn, Henry C.; Murnane, Margaret M.; Mathias, Stefan; Aeschlimann, Martin; Schneider, Claus M.; Shaw, Justin M.; Nembach, Hans T.; Silva, Thomas J.

    2013-07-01

    The Comment of Vodungbo et al. recognizes that a unique determination of the refractive-index variation over time is not possible using the data set in our paper, “Ultrafast Demagnetization Measurements Using Extreme Ultraviolet Light: Comparison of Electronic and Magnetic Contributions.” Furthermore, it was suggested that the lack of uniqueness allows for the possibility of a very specific time-dependent trajectory of the refractive index in the complex plane that could give rise to a large nonmagnetic modulation of the measured asymmetry, in spite of a negligible change in the s-polarized reflectivity. In this Reply, we conclusively show that any nonmagnetic contribution to the measured asymmetry is indeed negligible (<2%), below the noise level of the magnetic-asymmetry measurements. First, we use a few additional measurements to unambiguously rule out the presence of any nonmagnetic contributions to the signal. Second, we show that the scenario proposed by Vodungbo et al. would require both exotic time and energy dependences of the refractive index near the M edge that are extremely unlikely (virtually impossible) in real materials. Thus, the conclusions of our original article are preserved.

  2. Role of Macromolecular Structure in the Ultrafast Energy and Electron Transfer Dynamics of a Light-Harvesting Polymer.

    PubMed

    Morseth, Zachary A; Pho, Toan V; Gilligan, Alexander T; Dillon, Robert J; Schanze, Kirk S; Reynolds, John R; Papanikolas, John M

    2016-08-18

    Ultrafast energy and electron transfer (EnT and ET, respectively) are characterized in a light-harvesting assembly based on a π-conjugated polymer (poly(fluorene)) functionalized with broadly absorbing pendant organic isoindigo (iI) chromophores using a combination of femtosecond transient absorption spectroscopy and large-scale computer simulation. Photoexcitation of the π-conjugated polymer leads to near-unity quenching of the excitation through a combination of EnT and ET to the iI pendants. The excited pendants formed by EnT rapidly relax within 30 ps, whereas recombination of the charge-separated state formed following ET occurs within 1200 ps. A computer model of the excited-state processes is developed by combining all-atom molecular dynamics simulations, which provides a molecular-level view of the assembly structure, with a kinetic model that accounts for the multiple excited-state quenching pathways. Direct comparison of the simulations with experimental data reveals that the underlying structure has a dramatic effect on the partitioning between EnT and ET in the polymer assembly, where the distance and orientation of the pendants in relation to the backbone serve to direct the dominant quenching pathway. PMID:27433946

  3. Ultrafast charge-transfer-to-solvent dynamics of iodide in tetrahydrofuran. 2. Photoinduced electron transfer to counterions in solution.

    PubMed

    Bragg, Arthur E; Schwartz, Benjamin J

    2008-04-24

    The excited states of atomic anions in liquids are bound only by the polarization of the surrounding solvent. Thus, the electron-detachment process following excitation to one of these solvent-bound states, known as charge-transfer-to-solvent (CTTS) states, provides a useful probe of solvent structure and dynamics. These transitions and subsequent relaxation dynamics also are influenced by other factors that alter the solution environment local to the CTTS anion, including the presence of cosolutes, cosolvents, and other ions. In this paper, we examine the ultrafast CTTS dynamics of iodide in liquid tetrahydrofuran (THF) with a particular focus on how the solvent dynamics and the CTTS electron-ejection process are altered in the presence of various counterions. In weakly polar solvents such as THF, iodide salts can be strongly ion-paired in solution; the steady-state UV-visible absorption spectroscopy of various iodide salts in liquid THF indicates that the degree of ion-pairing changes from strong to weak to none as the counterion is switched from Na+ to tetrabutylammonium (t-BA+) to crown-ether-complexed Na+, respectively. In our ultrafast experiments, we have excited the I- CTTS transition of these various iodide salts at 263 nm and probed the dynamics of the CTTS-detached electrons throughout the visible and near-IR. In the previous paper of this series (Bragg, A. E.; Schwartz, B. J. J. Phys. Chem. B 2008, 112, 483-494), we found that for "counterion-free" I- (obtained by complexing Na+ with a crown ether) the CTTS electrons were ejected approximately 6 nm from their partner iodine atoms, the result of significant nonadiabatic coupling between the CTTS excited state and extended electronic states supported by the naturally existing solvent cavities in liquid THF, which also serve as pre-existing electron traps. In contrast, for the highly ion-paired NaI/THF system, we find that approximately 90% of the CTTS electrons are "captured" by a nearby Na+ to form (Na

  4. Size effects in the ultrafast electronic dynamics of metallic tin nanoparticles

    NASA Astrophysics Data System (ADS)

    Stella, A.; Nisoli, M.; de Silvestri, S.; Svelto, O.; Lanzani, G.; Cheyssac, P.; Kofman, R.

    1996-06-01

    We report on femtosecond transient reflectivity measurements performed on metallic tin nanoparticles, embedded in an Al2O3 matrix, with average radii in the range 20-60 Å. It was observed that the time behavior of the transient reflectivity decays depends upon particle size. The results can be interpreted in terms of a size-dependent electron-surface interaction in the thermalization process and of a substantially size-independent electron-electron thermalization.

  5. Nonequilibrium Dynamics in a Quasi-Two-Dimensional Electron Plasma after Ultrafast Intersubband Excitation

    SciTech Connect

    Lutgen, S.; Kaindl, R.A.; Woerner, M.; Elsaesser, T.; Hase, A.; Kuenzel, H.; Gulia, M.; Meglio, D.; Lugli, P.

    1996-10-01

    The dynamics of electrons in GaInAs/AlInAs quantum wells is studied after excitation from the {ital n}=1 to the {ital n}=2 conduction subband. Femtosecond pump-probe experiments demonstrate for the first time athermal distributions of {ital n}=1 electrons on a surprisingly long time scale of 2ps. Thermalization involves intersubband scattering of excited electrons via optical phonon emission with a time constant of 1ps and intrasubband Coulomb and phonon scattering. Ensemble Monte Carlo simulations show that the slow electron equilibration results from Pauli blocking and screening of carrier-carrier scattering. {copyright} {ital 1996 The American Physical Society.}

  6. Experimental and computational studies of a multi-electron donor-acceptor ligand containing the thiazolo[5,4-d]thiazole core and its incorporation into a metal-organic framework.

    PubMed

    Rizzuto, Felix J; Faust, Thomas B; Chan, Bun; Hua, Carol; D'Alessandro, Deanna M; Kepert, Cameron J

    2014-12-22

    A ligand containing the thiazolo[5,4-d]thiazole (TzTz) core (acceptor) with terminal triarylamine moieties (donors), N,N'-(thiazolo[5,4-d]thiazole-2,5-diylbis(4,1-phenylene))bis(N-(pyridine-4-yl)pyridin-4-amine (1), was designed as a donor-acceptor system for incorporation into electronically active metal-organic frameworks (MOFs). The capacity for the ligand to undergo multiple sequential oxidation and reduction processes was examined using UV/Vis-near-infrared spectroelectrochemistry (UV/Vis-NIR SEC) in combination with DFT calculations. The delocalized nature of the highest occupied molecular orbital (HOMO) was found to inhibit charge-transfer interactions between the terminal triarylamine moieties upon oxidation, whereas radical species localized on the TzTz core were formed upon reduction. Conversion of 1 to diamagnetic 2+ and 4+ species resulted in marked changes in the emission spectra. Incorporation of this highly delocalized multi-electron donor-acceptor ligand into a new two-dimensional MOF, [Zn(NO3 )2 (1)] (2), resulted in an inhibition of the oxidation processes, but retention of the reduction capability of 1. Changes in the electrochemistry of 1 upon integration into 2 are broadly consistent with the geometric and electronic constraints enforced by ligation. PMID:25346539

  7. Modeling time-coincident ultrafast electron transfer and solvation processes at molecule-semiconductor interfaces

    SciTech Connect

    Li, Lesheng; Giokas, Paul G.; Moran, Andrew M. E-mail: ammoran@email.unc.edu; Kanai, Yosuke E-mail: ammoran@email.unc.edu

    2014-06-21

    Kinetic models based on Fermi's Golden Rule are commonly employed to understand photoinduced electron transfer dynamics at molecule-semiconductor interfaces. Implicit in such second-order perturbative descriptions is the assumption that nuclear relaxation of the photoexcited electron donor is fast compared to electron injection into the semiconductor. This approximation breaks down in systems where electron transfer transitions occur on 100-fs time scale. Here, we present a fourth-order perturbative model that captures the interplay between time-coincident electron transfer and nuclear relaxation processes initiated by light absorption. The model consists of a fairly small number of parameters, which can be derived from standard spectroscopic measurements (e.g., linear absorbance, fluorescence) and/or first-principles electronic structure calculations. Insights provided by the model are illustrated for a two-level donor molecule coupled to both (i) a single acceptor level and (ii) a density of states (DOS) calculated for TiO{sub 2} using a first-principles electronic structure theory. These numerical calculations show that second-order kinetic theories fail to capture basic physical effects when the DOS exhibits narrow maxima near the energy of the molecular excited state. Overall, we conclude that the present fourth-order rate formula constitutes a rigorous and intuitive framework for understanding photoinduced electron transfer dynamics that occur on the 100-fs time scale.

  8. Contribution of electronic excitation to the structural evolution of ultrafast laser-irradiated tungsten nanofilms

    NASA Astrophysics Data System (ADS)

    Murphy, Samuel T.; Giret, Yvelin; Daraszewicz, Szymon L.; Lim, Anthony C.; Shluger, Alexander L.; Tanimura, Katsumi; Duffy, Dorothy M.

    2016-03-01

    The redistribution of the electron density in a material during laser irradiation can have a significant impact on its structural dynamics. This electronic excitation can be incorporated into two temperature molecular dynamics (2T-MD) simulations through the use of electronic temperature dependent potentials. Here, we study the structural dynamics of laser irradiated tungsten nanofilms using 2T-MD simulations with an electronic temperature dependent potential and compare the results to equivalent simulations that employ a ground-state interatomic potential. Electronic excitation leads to an expansion of the crystal and a decrease in the melting point of tungsten. During laser irradiation these factors ensure that the threshold fluences to the different melting regimes are reduced. Furthermore, both heterogenous and homogeneous melting are predicted to occur more rapidly due to excitation and oscillations in the film thickness will be accentuated.

  9. Ultrafast electron transfer in the recognition of different DNA sequences by a DNA-binding protein with different dynamical conformations.

    PubMed

    Mondol, Tanumoy; Batabyal, Subrata; Pal, Samir Kumar

    2012-01-01

    Ultrafast electron transfer (ET) phenomenon in protein and protein-DNA complex is very much crucial and often leads to the regulation of various kinds of redox reactions in biological system. Although, the conformation of the protein in protein-DNA complex is concluded to play the key role in the ET process, till date very little evidences exist in the literature. λ-repressor-operator DNA interaction, particularly O(R)1 and O(R)2, is a key component of the λ-genetic switch and is a model system for understanding the chemical principles of the conformation-dependent ET reaction, governed by differential protein dynamics upon binding with different DNA target sequences. Here, we have explored the photoinduced electron transfer from the tryptophan moieties of the protein λ-repressor to two operators DNA of different sequences (O(R)1 and O(R)2) using picosecond-resolved fluorescence spectroscopy. The enhanced flexibility and different conformation of the C-terminal domain of the repressor upon complexation with O(R)1 DNA compared to O(R)2 DNA are found to have pronounced effect on the rate of ET. We have also observed the ET phenomenon from a dansyl chromophore, bound to the lysine residue, distal from the DNA-binding domain of the protein to the operator DNA with a specific excitation at 299 nm wavelength. The altered ET dynamics as a consequence of differential protein conformation upon specific DNA sequence recognition may have tremendous biological implications. PMID:22686485

  10. Ultrafast relaxation of electronically-excited states of a styryl dye in the cavity of cucurbit[n]urils (n = 6, 7)

    NASA Astrophysics Data System (ADS)

    Petrov, N. Kh.; Ivanov, D. A.; Shandarov, Yu. A.; Kryukov, I. V.; Ivanov, A. A.; Alfimov, M. V.; Lobova, N. A.; Gromov, S. P.

    2016-03-01

    The ultrafast relaxation of an electronically-excited styryl dye and its complexes with cucurbit[n]urils was studied by the fluorescence up-conversion technique at various fluorescence wavelengths. The relaxation is faster at a blue side of the fluorescence band than at a red one where a fluorescence rise was observed. Addition of either cucurbiturils significantly increases the longest decay time from about 50 ps to that in the range of 100-200 ps. Such features are attributed to displacements of the electronically-excited styryl dye deep into the cavity, increasing the potential barrier between the intramolecular charge transfer state and the conical intersection region.

  11. Electronic structure near the Fermi level in the ferromagnetic semiconductor GaMnAs studied by ultrafast time-resolved light-induced reflectivity measurements

    NASA Astrophysics Data System (ADS)

    Ishii, Tomoaki; Kawazoe, Tadashi; Hashimoto, Yusuke; Terada, Hiroshi; Muneta, Iriya; Ohtsu, Motoichi; Tanaka, Masaaki; Ohya, Shinobu

    2016-06-01

    Clarification of the electronic structure near the Fermi level is important in understanding the origin of ferromagnetism in the prototypical ferromagnetic semiconductor GaMnAs. Here, we perform ultrafast transient reflectivity spectra measurement, which is a powerful tool for selective detection of absorption edges in GaMnAs. The results show that the Fermi level of GaMnAs exists in the band gap. By using the Kramers-Kronig relation, we find the Mn-induced electronic states around the Fermi level, confirming that the ferromagnetism is stabilized by spin-polarized impurity-band holes.

  12. Optical manipulation of ultrafast electron and nuclear motion on metal surfaces

    SciTech Connect

    Petek, Hrvoje

    2009-12-02

    We study the unoccupied electronic structure and dynamics of chemisorbed atoms and molecules on metal surfaces by time resolved two-photon photoemission (TR-2PP). spectroscopy, low temperature scanning tunneling microscopy (LT-STM), and theory. Our research concerns simple atomic adsorbates such as alkali and alkaline earth atoms, which provide fundamentally important models for adsorbate-surface interactions, and more complex adsorbates such as fullerenes on noble metals, which illustrate emergent interfacial properties that derive from intrinsic molecular attributes, and moleculemolecule and molecule-surface interactions. Our goal is to understand how these interactions contribute to formation of the interfacial electronic structure, and how thus formed electronic properties affect interfacial phenomena of importance to energy transduction and storage. Moreover, we explore how the interfacial electronic excitation drives dynamical phenomena such as charge transfer and surface femtochemistry.

  13. Vibrational and electronic ultrafast relaxation of the nitrogen-vacancy centers in diamond

    NASA Astrophysics Data System (ADS)

    Huxter, M.; Oliver, T. A. A.; Budker, D.; Fleming, G. R.

    2013-03-01

    Two dimensional electronic spectroscopy and transient grating measurements were performed, for the first time, on nitrogen-vacancy centers in diamond. These measurements reveal energy transfer and vibrational pathways with consequences for spin coherence.

  14. Nonlinear Ultrafast Spectroscopy of Electron and Energy Transfer in Molecule Complexes

    SciTech Connect

    Mukamel, Shaul

    2006-02-09

    The proposed research program will focus on the development of a unified dynamical theoretical framework for calculating the optical response of molecular assemblies and applying it towards studying the interplay of energy and charge transfer in artificial chromophore-aggregate complexes. Applications will be made to poly (p phenylene vinylene), (PPV) oligomers, several families of stilbenoid aggregates with stacking through a cyclophane group, coupled porphyrin arrays, and energy funneling in phenylacetylene dendrimers. The approach is based on formulating the problem using the density- matrix and developing Liouville-space techniques which provide physical insight and are particularly suitable for computing both coherent and incoherent transport. A physical picture based on collective electronic normal modes which represent the dynamics of the optically-driven reduced single electron density matrix will be established. Femtosecond signals and optical properties will be directly related to the motions of electron-hole pairs in real space, completely avoiding the calculation of many-electron excited-state wavefunctions, thus, considerably reducing computational effort. Vibrational and solvent effects will be incorporated. Guidelines for the synthesis of new donor/bridge/acceptor molecules with desired properties such as carrier transport, optical response time scales and fluorescence quantum yields will be developed. The analogy with Thz emission spectroscopy which probes charge carrier dynamic is in semiconductor superlattices will be explored. A systematic procedure for identifying the electronic coherence sizes which control the transport and optical properties will be developed. Localization of electronic transition density matrices of large molecules will be used to break the description of their optical response into coupled chromophores. The proposal is divided into four parts: (i) Collective-Oscillator Representation of Electronic Excitations in Molecular

  15. Modeling ultrafast electronic processes in solids excited by femtosecond VUV-XUV laser Pulse

    NASA Astrophysics Data System (ADS)

    Medvedev, Nikita

    2012-07-01

    A detailed description of the method of calculation of electron inelastic scattering cross-section and mean free path in solid SiO2 is presented. The method is based upon the complex dielectric function formalism. It allows obtaining the inelastic mean free path of a charged particle in solids with high accuracy. The calculated inelastic mean free path of electrons in silicon dioxide presented in this contribution shows a very good agreement with the experimental data and with other theoretical calculations.

  16. Ultrafast spectroscopy of electron transfer dynamics in liquids; excitation transfer studies of phase transitions

    NASA Astrophysics Data System (ADS)

    Goun, Alexei A.

    The transfer of an electron from a donor to an acceptor is the fundamental step in a wide range of chemical and biological processes. As a result, electron-transfer reactions have been the focus of numerous theoretical and experimental efforts aimed at understanding the kinetics and mechanism of the transfer event. Liquid solvents are an important medium for electron-transfer processes. The influences of the distance dependence, diffusion, the radial distribution function, and the hydrodynamic effect have been incorporated into the theory of electron transfer in solution, as well as into the theory of electron transfer between donors and acceptors in the head group regions of micelles. The development of new laser system with a pulse duration of tens of femtoseconds, with tunable wavelength allowed us to study these processes on a considerably shorter time scale than previous studies. This allowed us to observe not only the diffusion controlled but also the kinetics of electron transfer for donor/acceptor pairs that are in close proximity. In one set of experiments we have studied the kinetics of electron transfer in electron accepting molecule (rhodamine 3B) dissolved in electron donating solvent (N,N-dimethylaniline). The data for the forward electron transfer and geminate recombination are approximated by the statistical theory of the electron transfer. Optical anisotropy observed in the experiment demonstrates the orientation dependence of the electron transfer rate. In further experiments we investigated the electron transfer in non-hydrogen bonding liquids of increasing viscosity. The effective value of the donor/acceptor electronic coupling was found to decrease with viscosity. Electron transfer experiments were also carried out on the surface of micelles. The systems studied are the hole donor octadecyl-rhodamine B (ODRB) and the hole acceptor N,N-dimethyl-aniline (DMA) in micelles made of dodecyltrimethylammonium bromide (DTAB) and

  17. Ultrafast Electron Transfer Kinetics in the LM Dimer of Bacterial Photosynthetic Reaction Center from Rhodobacter sphaeroides.

    PubMed

    Sun, Chang; Carey, Anne-Marie; Gao, Bing-Rong; Wraight, Colin A; Woodbury, Neal W; Lin, Su

    2016-06-23

    It has become increasingly clear that dynamics plays a major role in the function of many protein systems. One system that has proven particularly facile for studying the effects of dynamics on protein-mediated chemistry is the bacterial photosynthetic reaction center from Rhodobacter sphaeroides. Previous experimental and computational analysis have suggested that the dynamics of the protein matrix surrounding the primary quinone acceptor, QA, may be particularly important in electron transfer involving this cofactor. One can substantially increase the flexibility of this region by removing one of the reaction center subunits, the H-subunit. Even with this large change in structure, photoinduced electron transfer to the quinone still takes place. To evaluate the effect of H-subunit removal on electron transfer to QA, we have compared the kinetics of electron transfer and associated spectral evolution for the LM dimer with that of the intact reaction center complex on picosecond to millisecond time scales. The transient absorption spectra associated with all measured electron transfer reactions are similar, with the exception of a broadening in the QX transition and a blue-shift in the QY transition bands of the special pair of bacteriochlorophylls (P) in the LM dimer. The kinetics of the electron transfer reactions not involving quinones are unaffected. There is, however, a 4-fold decrease in the electron transfer rate from the reduced bacteriopheophytin to QA in the LM dimer compared to the intact reaction center and a similar decrease in the recombination rate of the resulting charge-separated state (P(+)QA(-)). These results are consistent with the concept that the removal of the H-subunit results in increased flexibility in the region around the quinone and an associated shift in the reorganization energy associated with charge separation and recombination. PMID:27243380

  18. Roadmap on ultrafast optics

    NASA Astrophysics Data System (ADS)

    Reid, Derryck T.; Heyl, Christoph M.; Thomson, Robert R.; Trebino, Rick; Steinmeyer, Günter; Fielding, Helen H.; Holzwarth, Ronald; Zhang, Zhigang; Del'Haye, Pascal; Südmeyer, Thomas; Mourou, Gérard; Tajima, Toshiki; Faccio, Daniele; Harren, Frans J. M.; Cerullo, Giulio

    2016-09-01

    The year 2015 marked the 25th anniversary of modern ultrafast optics, since the demonstration of the first Kerr lens modelocked Ti:sapphire laser in 1990 (Spence et al 1990 Conf. on Lasers and Electro-Optics, CLEO, pp 619-20) heralded an explosion of scientific and engineering innovation. The impact of this disruptive technology extended well beyond the previous discipline boundaries of lasers, reaching into biology labs, manufacturing facilities, and even consumer healthcare and electronics. In recognition of such a milestone, this roadmap on Ultrafast Optics draws together articles from some of the key opinion leaders in the field to provide a freeze-frame of the state-of-the-art, while also attempting to forecast the technical and scientific paradigms which will define the field over the next 25 years. While no roadmap can be fully comprehensive, the thirteen articles here reflect the most exciting technical opportunities presented at the current time in Ultrafast Optics. Several articles examine the future landscape for ultrafast light sources, from practical solid-state/fiber lasers and Raman microresonators to exotic attosecond extreme ultraviolet and possibly even zeptosecond x-ray pulses. Others address the control and measurement challenges, requiring radical approaches to harness nonlinear effects such as filamentation and parametric generation, coupled with the question of how to most accurately characterise the field of ultrafast pulses simultaneously in space and time. Applications of ultrafast sources in materials processing, spectroscopy and time-resolved chemistry are also discussed, highlighting the improvements in performance possible by using lasers of higher peak power and repetition rate, or by exploiting the phase stability of emerging new frequency comb sources.

  19. Roadmap on ultrafast optics

    NASA Astrophysics Data System (ADS)

    Reid, Derryck T.; Heyl, Christoph M.; Thomson, Robert R.; Trebino, Rick; Steinmeyer, Günter; Fielding, Helen H.; Holzwarth, Ronald; Zhang, Zhigang; Del’Haye, Pascal; Südmeyer, Thomas; Mourou, Gérard; Tajima, Toshiki; Faccio, Daniele; Harren, Frans J. M.; Cerullo, Giulio

    2016-09-01

    The year 2015 marked the 25th anniversary of modern ultrafast optics, since the demonstration of the first Kerr lens modelocked Ti:sapphire laser in 1990 (Spence et al 1990 Conf. on Lasers and Electro-Optics, CLEO, pp 619–20) heralded an explosion of scientific and engineering innovation. The impact of this disruptive technology extended well beyond the previous discipline boundaries of lasers, reaching into biology labs, manufacturing facilities, and even consumer healthcare and electronics. In recognition of such a milestone, this roadmap on Ultrafast Optics draws together articles from some of the key opinion leaders in the field to provide a freeze-frame of the state-of-the-art, while also attempting to forecast the technical and scientific paradigms which will define the field over the next 25 years. While no roadmap can be fully comprehensive, the thirteen articles here reflect the most exciting technical opportunities presented at the current time in Ultrafast Optics. Several articles examine the future landscape for ultrafast light sources, from practical solid-state/fiber lasers and Raman microresonators to exotic attosecond extreme ultraviolet and possibly even zeptosecond x-ray pulses. Others address the control and measurement challenges, requiring radical approaches to harness nonlinear effects such as filamentation and parametric generation, coupled with the question of how to most accurately characterise the field of ultrafast pulses simultaneously in space and time. Applications of ultrafast sources in materials processing, spectroscopy and time-resolved chemistry are also discussed, highlighting the improvements in performance possible by using lasers of higher peak power and repetition rate, or by exploiting the phase stability of emerging new frequency comb sources.

  20. Theory of ultrafast photoinduced electron transfer from a bulk semiconductor to a quantum dot

    SciTech Connect

    Rasmussen, Andrew M. Ramakrishna, S.; Weiss, Emily A.; Seideman, Tamar

    2014-04-14

    This paper describes analytical and numerical results from a model Hamiltonian method applied to electron transfer (ET) from a quasicontinuum (QC) of states to a set of discrete states, with and without a mediating bridge. Analysis of the factors that determine ET dynamics yields guidelines for achieving high-yield electron transfer in these systems, desired for instance for applications in heterogeneous catalysis. These include the choice of parameters of the laser pulse that excites the initial state into a continuum electronic wavepacket and the design of the coupling between the bridge molecule and the donor and acceptor. The vibrational mode on a bridging molecule between donor and acceptor has an influence on the yield of electron transfer via Franck-Condon factors, even in cases where excited vibrational states are only transiently populated. Laser-induced coherence of the initial state as well as energetic overlap is crucial in determining the ET yield from a QC to a discrete state, whereas the ET time is influenced by competing factors from the coupling strength and the coherence properties of the electronic wavepacket.

  1. Probing ultrafast electronic motions in atoms with the attosecond pump-probe

    NASA Astrophysics Data System (ADS)

    Collins, Lee; Hu, Suxing; Schneider, Barry

    2006-03-01

    Through full-dimensional numerical simulations with using our recently-developed efficient and accurate parallel solver for the time-dependent Schrödinger equation, we have demonstrated that an attosecond pulse can effectively probe the extremely fast motion of an electronic wave packet in atoms. Pumped by a broadband femtosecond UV pulse, one electron of ground-state Helium can be launched into a superposition of low-lying excited states, thus forming a wavepacket that begins to orbit the atomic core. A time-delayed attosecond EUV pulse (probe) then ionizes the atom causing three-body breakup. Measuring either the energy sharing of the ionized electrons or the total ionization probability as a function of the time delay displays the internal motion of the excited electron. Our simulation has shown that an ultrashort Kepler period of 2 fs can be followed for several cylces. This opens the prospect of a wealth of similar pump-probe experiments to examine electronic motion.

  2. Synthesis, optical properties and ultrafast electronic relaxation of metal (silver, gold, platinum) and manganese(2+)-doped zinc sulfide nanoparticles

    NASA Astrophysics Data System (ADS)

    Smith, Brian Ampere

    Ultrafast transient absorption and time-dependent luminescence spectroscopy have been performed on metal (Ag, Au, Pt) and semiconductor (Mn2+ doped ZnS) nanoparticles respectively. In metal nanoparticles it was found that the decay dynamics exhibit a complex size and surface dependence. Specifically, the photoinduced dynamics show an exponential time constant that is longer than the same in bulk for particle sizes of 4-40 nm. When particle size is reduced further the plasmon band is drastically broadened and the relaxation time constant is similar to bulk. Upon reducing the size still further to only 13 atoms per cluster a much longer electronic relaxation is observed. These results are attributed to an intrinsic size dependent reduction in the electron-phonon coupling when particle size is reduced. This slows down the electronic relaxation compared to bulk. The increase in the number of surface collisions for very small particles increases the rate of electronic relaxation relative to larger particles. For particles on the order of 13 atoms the excitation is more singular in nature and the long relaxation is attributed to the fact that the excited species is a molecular as opposed to a fermi system. Also, the synthesis and luminescence decay kinetics of 1.2 nm Mn 2+ doped ZnS nanoclusters grown in reverse micelles are reported. The preparation method produces small particles with narrow size distribution and fluorescence bands near 400-450 nm and 585 nm. Time-dependent fluorescence decay measurements using picosecond, nanosecond and millisecond techniques reveal relaxation processes on all three time scales. In the doped sample, the red emission detected at 600 nm exhibits an 1-2 ms decay in addition to faster decays with time constants on the order of hundreds of ps, a few ns and tens of μs. While the slow decay is the same as that of bulk Mn 2+ doped ZnS, the fast decays are present for both doped and undoped samples and are unique to nanocluster ZnS, which are

  3. Probing Ultrafast Nuclear Dynamics in Halomethanes by Time-Resolved Electron and Ion Imaging

    NASA Astrophysics Data System (ADS)

    Ziaee, F.; Rudenko, A.; Rolles, D.; Savelyev, E.; Bomme, C.; Boll, R.; Manschwetus, B.; Erk, B.; Trippel, S.; Wiese, J.; Kuepper, J.; Amini, K.; Lee, J.; Brouard, M.; Brausse, F.; Rouzee, A.; Olshin, P.; Mereshchenko, A.; Lahl, J.; Johnsson, P.; Simon, M.; Marchenko, T.; Holland, D.; Underwood, J.

    2016-05-01

    Femtosecond pump-probe experiments provide opportunities to investigate photochemical reaction dynamics and the resulting changes in molecular structure in detail. Here, we present a study of the UV-induced photodissociation of gas-phase halomethane molecules (CH3 I, CH2 IBr, ...) in a pump-probe arrangement using two complementary probe schemes, either using a femtosecond near-infrared laser or the FLASH free-electron laser. We measured electrons and ions produced during the interaction using a double-sided velocity map imaging spectrometer equipped with a CCD camera for electron detection and with the Pixel Imaging Mass Spectrometry (PImMS) camera for ions, which can record the arrival time for up to four ions per pixel. This project is supported by the DOE, Office of Science, BES, Division of Chemical, Geological, and Biological Sciences.

  4. Ultrafast electronic disorder in heat-induced structural deformations and phase transitions in metals

    NASA Astrophysics Data System (ADS)

    Guo, Chunlei; Taylor, Antoinette J.

    2000-09-01

    Heat-induced structural deformations and phase transitions of gold and silver are studied using 1.55-eV, 120-fs ultrashort laser pulses. The dynamics of the heating process is monitored by measuring the time evolution of the dielectric constants following optical excitation. Intensity-dependent dielectric constants in silver and gold show similarities with the photon-energy-dependent dielectric constants, which is shown to indirectly map out the degree of heat-induced electronic disorder in these noble metals. This observation strongly suggests that the heat-induced structural deformations and phase transitions in metals are tied to the electronic disorder and band-structure collapse.

  5. Ultrafast laser and swift heavy ion irradiation: Response of Gd{sub 2}O{sub 3} and ZrO{sub 2} to intense electronic excitation

    SciTech Connect

    Rittman, Dylan R.; Tracy, Cameron L.; Cusick, Alex B.; Abere, Michael J.; Yalisove, Steven M.; Torralva, Ben; Ewing, Rodney C.

    2015-04-27

    In order to investigate the response of materials to extreme conditions, there are several approaches to depositing extremely high concentrations of energy into very small volumes of material, including ultrafast laser and swift heavy ion (SHI) irradiation. In this study, crystalline-to-crystalline phase transformations in cubic Gd{sub 2}O{sub 3} and monoclinic ZrO{sub 2} have been investigated using ultrafast laser irradiation. The phases produced by the extreme conditions of irradiation were characterized by grazing incidence x-ray diffraction (GIXRD) and Raman spectroscopy. Gd{sub 2}O{sub 3} exhibited a cubic-to-monoclinic phase transformation, as evidenced by the appearance of the monoclinic (402{sup ¯}), (003), (310), and (112{sup ¯}) peaks in the GIXRD pattern and of four A{sub g} and three B{sub g} Raman modes. ZrO{sub 2} underwent a monoclinic-to-tetragonal phase transformation, as evidenced by the emergence of the tetragonal (101) peak in the GIXRD pattern and of E{sub g} and A{sub 1g} Raman modes. The new phases formed by ultrafast laser irradiation are high temperature polymorphs of the two materials. No evidence of amorphization was seen in the GIXRD data, though Raman spectroscopy indicated point defect accumulation. These results are identical to those produced by irradiation with SHIs, which also deposit energy in materials primarily through electronic excitation. The similarity in damage process and material response between ultrafast laser and SHI irradiation suggests a fundamental relationship between these two techniques.

  6. Ultrafast photoinduced electron transfer reactions in supramolecular arrays: From charge separation and storage to molecular switches

    SciTech Connect

    Wasielewski, M.R.

    1992-01-01

    Photoinduced charge separation reactions form the basis for energy storage processes in both natural and artificial photosynthesis. Moreover, rapid reversible photoinduced electron transfer reactions are a class of photophysical phenomena that can be exploited to develop schemes for optical switching. Examples from each of these fields are discussed.

  7. Ultrafast photoinduced electron transfer reactions in supramolecular arrays: From charge separation and storage to molecular switches

    SciTech Connect

    Wasielewski, M.R.

    1992-08-01

    Photoinduced charge separation reactions form the basis for energy storage processes in both natural and artificial photosynthesis. Moreover, rapid reversible photoinduced electron transfer reactions are a class of photophysical phenomena that can be exploited to develop schemes for optical switching. Examples from each of these fields are discussed.

  8. Ultrafast laser and amplifier sources

    NASA Astrophysics Data System (ADS)

    Rundquist, A.; Durfee, C.; Chang, Z.; Taft, G.; Zeek, E.; Backus, S.; Murnane, M. M.; Kapteyn, H. C.; Christov, I.; Stoev, V.

    1997-08-01

    There has been remarkable progress in the development of high peak-power ultrafast lasers in recent years. Lasers capable of generating terawatt peak powers with unprecedented short pulse durations can now be built on a single optical table in a small laboratory. The rapid technological progress has made possible a host of new scientific advances in high-field science, such as the generation of coherent femtosecond X-ray pulses, and the generation of MeV-energy electron beams and high-energy ions. In this paper, we review progress in the development and design of ultrafast high-power lasers based on Ti:sapphire, including the ultrafast laser oscillators that are a very important enabling technology for high-power ultrafast systems, and ultrafast amplified laser systems that generate 20 fs duration pulses with several watts average power at kilohertz repetition-rates. Ultrafast waveform measurements of these pulses demonstrate that such short pulses can be generated with high fidelity. Finally, we discuss applications of ultrafast high-power pulses, including the generation of femtosecond to attosecond X-ray pulses.

  9. Ultrafast Electron Transfer at Organic Semiconductor Interfaces: Importance of Molecular Orientation.

    PubMed

    Ayzner, Alexander L; Nordlund, Dennis; Kim, Do-Hwan; Bao, Zhenan; Toney, Michael F

    2015-01-01

    Much is known about the rate of photoexcited charge generation in at organic donor/acceptor (D/A) heterojunctions overaged over all relative arrangements. However, there has been very little experimental work investigating how the photoexcited electron transfer (ET) rate depends on the precise relative molecular orientation between D and A in thin solid films. This is the question that we address in this work. We find that the ET rate depends strongly on the relative molecular arrangement: The interface where the model donor compound copper phthalocyanine is oriented face-on with respect to the fullerene C60 acceptor yields a rate that is approximately 4 times faster than that of the edge-on oriented interface. Our results suggest that the D/A electronic coupling is significantly enhanced in the face-on case, which agrees well with theoretical predictions, underscoring the importance of controlling the relative interfacial molecular orientation. PMID:26263084

  10. Theory of ultrafast heterogeneous electron transfer: Contributions of direct charge transfer excitations to the absorbance

    NASA Astrophysics Data System (ADS)

    Wang, Luxia; Willig, Frank; May, Volkhard

    2007-04-01

    Absorption spectra related to heterogeneous electron transfer are analyzed with the focus on direct charge transfer transition from the surface attached molecule into the semiconductor band states. The computations are based on a model of reduced dimensionality with a single intramolecular vibrational coordinate but a complete account for the continuum of conduction band states. The applicability of this model to perylene on TiO2 has been demonstrated in a series of earlier papers. Here, based on a time-dependent formulation, the absorbance is calculated with the inclusion of charge transfer excitations. A broad parameter set inspired by the perylene TiO2 systems is considered. In particular, the description generalizes the Fano effect to heterogeneous electron transfer reactions. Preliminary simulations of measured spectra are presented for perylene-catechol attached to TiO2.

  11. Theory of ultrafast heterogeneous electron transfer: Contributions of direct charge transfer excitations to the absorbance

    SciTech Connect

    Wang, Luxia; Willig, Frank; May, Volkhard

    2007-04-07

    Absorption spectra related to heterogeneous electron transfer are analyzed with the focus on direct charge transfer transition from the surface attached molecule into the semiconductor band states. The computations are based on a model of reduced dimensionality with a single intramolecular vibrational coordinate but a complete account for the continuum of conduction band states. The applicability of this model to perylene on TiO{sub 2} has been demonstrated in a series of earlier papers. Here, based on a time-dependent formulation, the absorbance is calculated with the inclusion of charge transfer excitations. A broad parameter set inspired by the perylene TiO{sub 2} systems is considered. In particular, the description generalizes the Fano effect to heterogeneous electron transfer reactions. Preliminary simulations of measured spectra are presented for perylene-catechol attached to TiO{sub 2}.

  12. Ultrafast electron transfer at organic semiconductor interfaces: Importance of molecular orientation

    DOE PAGES

    Ayzner, Alexander L.; Nordlund, Dennis; Kim, Do -Hwan; Bao, Zhenan; Toney, Michael F.

    2014-12-04

    Much is known about the rate of photoexcited charge generation in at organic donor/acceptor (D/A) heterojunctions overaged over all relative arrangements. However, there has been very little experimental work investigating how the photoexcited electron transfer (ET) rate depends on the precise relative molecular orientation between D and A in thin solid films. This is the question that we address in this work. We find that the ET rate depends strongly on the relative molecular arrangement: The interface where the model donor compound copper phthalocyanine is oriented face-on with respect to the fullerene C60 acceptor yields a rate that is approximatelymore » 4 times faster than that of the edge-on oriented interface. Our results suggest that the D/A electronic coupling is significantly enhanced in the face-on case, which agrees well with theoretical predictions, underscoring the importance of controlling the relative interfacial molecular orientation.« less

  13. Ultrafast electron transfer at organic semiconductor interfaces: Importance of molecular orientation

    SciTech Connect

    Ayzner, Alexander L.; Nordlund, Dennis; Kim, Do -Hwan; Bao, Zhenan; Toney, Michael F.

    2014-12-04

    Much is known about the rate of photoexcited charge generation in at organic donor/acceptor (D/A) heterojunctions overaged over all relative arrangements. However, there has been very little experimental work investigating how the photoexcited electron transfer (ET) rate depends on the precise relative molecular orientation between D and A in thin solid films. This is the question that we address in this work. We find that the ET rate depends strongly on the relative molecular arrangement: The interface where the model donor compound copper phthalocyanine is oriented face-on with respect to the fullerene C60 acceptor yields a rate that is approximately 4 times faster than that of the edge-on oriented interface. Our results suggest that the D/A electronic coupling is significantly enhanced in the face-on case, which agrees well with theoretical predictions, underscoring the importance of controlling the relative interfacial molecular orientation.

  14. Ultrafast Electronic Disorder in Heat-induced Structural Phase Transitions in Metal

    NASA Astrophysics Data System (ADS)

    Taylor, Antoinette; Guo, Chunlei

    2000-03-01

    Heat-induced structural phase transitions of noble metals silver and gold are studied using 1.5 eV, 120 fs ultrashort laser pulses. The dynamics of heating process is monitored by measuring the time evolution of the dielectric constants following optical excitation, which shows behavior consistent with that reported previously. Fluence-dependent dielectric constants in silver and gold show similarities with the photon-energy-dependent dielectric constants, which in fact indirectly map out the degree of the heat-induced electronic disorder in noble metals. The results demonstrate, for the first time, that the heat-induced structural phase transition in metal is in fact tied to the electronic disorder and band structure collapse.

  15. Ultrafast Optical Control of the Electronic Properties of Zr Te5

    NASA Astrophysics Data System (ADS)

    Manzoni, G.; Sterzi, A.; Crepaldi, A.; Diego, M.; Cilento, F.; Zacchigna, M.; Bugnon, Ph.; Berger, H.; Magrez, A.; Grioni, M.; Parmigiani, F.

    2015-11-01

    We report on the temperature dependence of the Zr Te5 electronic properties, studied at equilibrium and out of equilibrium, by means of time and angle resolved photoelectron spectroscopy. Our results unveil the dependence of the electronic band structure across the Fermi energy on the sample temperature. This finding is regarded as the dominant mechanism responsible for the anomalous resistivity observed at T*˜160 K along with the change of the charge carrier character from holelike to electronlike. Having addressed these long-lasting questions, we prove the possibility to control, at the ultrashort time scale, both the binding energy and the quasiparticle lifetime of the valence band. These experimental evidences pave the way for optically controlling the thermoelectric and magnetoelectric transport properties of Zr Te5 .

  16. Ultrafast Coherent Photoelectron Spectroscopy of Electronic States on a Cu (111) Surface

    NASA Astrophysics Data System (ADS)

    Carr, Adra; Chen, Cong; Tao, Zhensheng; Murnane, Margaret; Kapteyn, Henry; Matyba, Piotr; Emmerich, Sebastian; Aeschlimann, Martin; Hoefer, Ulrich

    2015-03-01

    We use laser-assisted high-harmonic time- and angle-resolved photoemission to directly observe coherent photoemission from a Cu(111) metal surface and the interferences between the emitted photoelectron wavepackets. A comb of high harmonics in combination with interferometrically timed infrared pulses enable a powerful combination of attosecond time resolution and high energy resolution, making it possible to extract phase information about the emitted photoelectron wavepackets and the distinct electronic states from which they emerge. By comparing photoemission from the well-known Shockley surface state to the sp and d bulk bands of Cu(111), we can observe non-negligible phase shifts in the emitted wavepackets, which cannot be attributed to time delays resulting from classical electron transport to the surface. Rather, we interpret these phase shifts as due to an intrinsic photoemission phase that is different for the sp and d band wavefunctions, thus providing a physical interpretation of temporal delays observed in photoemission from surfaces.

  17. Subwavelength ripples adjustment based on electron dynamics control by using shaped ultrafast laser pulse trains.

    PubMed

    Jiang, Lan; Shi, Xuesong; Li, Xin; Yuan, Yanping; Wang, Cong; Lu, Yongfeng

    2012-09-10

    This study reveals that the periods, ablation areas and orientations of periodic surface structures (ripples) in fused silica can be adjusted by using designed femtosecond (fs) laser pulse trains to control transient localized electron dynamics and corresponding material properties. By increasing the pulse delays from 0 to 100 fs, the ripple periods are changed from ~550 nm to ~255 nm and the orientation is rotated by 90°. The nearwavelength/subwavelength ripple periods are close to the fundamental/second-harmonic wavelengths in fused silica respectively. The subsequent subpulse of the train significantly impacts free electron distributions generated by the previous subpulse(s), which might influence the formation mechanism of ripples and the surface morphology.

  18. Ultrafast conformational dynamics of electron transfer in ExBox4+⊂perylene.

    PubMed

    Young, Ryan M; Dyar, Scott M; Barnes, Jonathan C; Juríček, Michal; Stoddart, J Fraser; Co, Dick T; Wasielewski, Michael R

    2013-11-27

    Multielectron acceptors are essential components for artificial photosynthetic systems that must deliver multiple electrons to catalysts for solar fuels applications. The recently developed boxlike cyclophane incorporating two extended viologen units joined end-to-end by two p-phenylene linkers-namely, ExBox(4+)-has a potential to be integrated into light-driven systems on account of its ability to complex with π-electron-rich guests such as perylene, which has been utilized to great extent in many light-harvesting applications. Photodriven electron transfer to ExBox(4+) has not previously been investigated, however, and so its properties, following photoreduction, are largely unknown. Here, we investigate the structure and energetics of the various accessible oxidation states of ExBox(4+) using a combination of spectroscopy and computation. In particular, we examine photoinitiated electron transfer from perylene bound within ExBox(4+) (ExBox(4+)⊂perylene) using visible and near-infrared femtosecond transient absorption (fsTA) spectroscopy. The structure and conformational relaxation dynamics of ExBox(3+)⊂perylene(+) are observed with femtosecond stimulated Raman spectroscopy (FSRS). From the fsTA and FSRS spectra, we observe that the central p-phenylene spacer in one of the extended viologen units on one side of the cyclophane becomes more coplanar with its neighboring pyridinium units over the first ∼5 ps after photoreduction. When the steady-state structure of chemically generated ExBox(2+) is investigated using Raman spectroscopy, it is found to have the central p-phenylene rings in both of its extended viologen units rotated to be more coplanar with their neighboring pyridinium units, further underscoring the importance of this subunit in the stabilization of the reduced states of ExBox(4+). PMID:24148089

  19. Ultrafast Heme Dynamics of Ferric Cytochrome c in Different Environments: Electronic, Vibrational, and Conformational Relaxation.

    PubMed

    Karunakaran, Venugopal

    2015-12-21

    The excited-state dynamics of ferric cytochrome c (Cyt c), an important electron-transfer heme protein, in acidic to alkaline medium and in its unfolded form are investigated by using femtosecond pump-probe spectroscopy, exciting the heme and Tryptophan (Trp) to understand the electronic, vibrational, and conformational relaxation of the heme. At 390 nm excitation, the electronic relaxation of heme is found to be ≈150 fs at different pH values, increasing to 480 fs in the unfolded form. Multistep vibrational relaxation dynamics of the heme, including fast and slow processes, are observed at pH 7. However, in the unfolded form and at pH 2 and 11, fast phases of vibrational relaxation dominate, revealing the energy dissipation occurring through the covalent bond interaction between the heme and the nearest amino acids. A significant shortening of the excited-state lifetime of Trp is observed at various pH values at 280 nm excitation due to resonance energy transfer to the heme. The longer time constant (25 ps) observed in the unfolded form is attributed to a complete global conformational relaxation of Cyt c.

  20. Breaking the Attosecond, Angstrom and TV/m Field Barriers with Ultrafast Electron Beams

    SciTech Connect

    Rosenzweig, J. B.; Andonian, G.; Fukasawa, A.; Hemsing, E.; Marcus, G.; Marinelli, A.; Musumeci, P.; O'Shea, B.; O'Shea, F.; Pellegrini, C.; Schiller, D.; Travish, G.; Bucksbaum, P.; Hogan, M.; Krejcik, Patrick; Ferrario, M.; Muggli, Patric

    2010-11-04

    Recent initiatives at UCLA concerning ultra-short, GeV electron beam generation have been aimed at achieving sub-fs pulses capable of driving X-ray free-electron lasers (FELs) in single-spike mode. This scheme uses very low charge beams, which may allow existing FEL injectors to produce few-100 attosecond pulses, with very high brightness. Towards this end, recent experiments at the Stanford X-ray FEL (LCLS, first of its kind, built with essential UCLA leadership) have produced {approx}2 fs, 20 pC electron pulses. We discuss here extensions of this work, in which we seek to exploit the beam brightness in FELs, in tandem with new developments at UCLA in cryogenic undulator technology, to create compact accelerator/undulator systems that can lase below 0.15 Angst , or be used to permit 1.5 Angst operation at 4.5 GeV. In addition, we are now developing experiments which use the present LCLS fs pulses to excite plasma wakefields exceeding 1 TV/m, permitting a table-top TeV accelerator for frontier high energy physics applications. We discuss the experimental issues associated with this initiative.

  1. Ultrafast electronic and vibrational dynamics in brominated aluminum corroles: Energy relaxation and triplet formation.

    PubMed

    Stensitzki, T; Yang, Y; Berg, A; Mahammed, A; Gross, Z; Heyne, K

    2016-07-01

    We combined femtosecond (fs) VIS pump-IR probe spectroscopy with fs VIS pump-supercontinuum probe spectroscopy to characterize the photoreaction of the hexacoordinated Al(tpfc-Br8)(py)2 in a comprehensive way. Upon fs excitation at ∼400 nm in the Soret band, the excitation energy relaxes with a time constant of (250 ± 80) fs to the S2 and S1 electronic excited states. This is evident from the rise time of the stimulated emission signal in the visible spectral range. On the same time scale, narrowing of broad infrared signals in the C=C stretching region around 1500 cm(-1) is observed. Energy redistribution processes are visible in the vibrational and electronic dynamics with time constants between ∼2 ps and ∼20 ps. Triplet formation is detected with a time constant of (95 ± 3) ps. This is tracked by the complete loss of stimulated emission. Electronic transition of the emerging triplet absorption band overlaps considerably with the singlet excited state absorption. In contrast, two well separated vibrational marker bands for triplet formation were identified at 1477 cm(-1) and at 1508 cm(-1). These marker bands allow a precise identification of triplet dynamics in corrole systems. PMID:27226980

  2. Ultrafast electronic and vibrational dynamics in brominated aluminum corroles: Energy relaxation and triplet formation

    PubMed Central

    Stensitzki, T.; Yang, Y.; Berg, A.; Mahammed, A.; Gross, Z.; Heyne, K.

    2016-01-01

    We combined femtosecond (fs) VIS pump–IR probe spectroscopy with fs VIS pump–supercontinuum probe spectroscopy to characterize the photoreaction of the hexacoordinated Al(tpfc-Br8)(py)2 in a comprehensive way. Upon fs excitation at ∼400 nm in the Soret band, the excitation energy relaxes with a time constant of (250 ± 80) fs to the S2 and S1 electronic excited states. This is evident from the rise time of the stimulated emission signal in the visible spectral range. On the same time scale, narrowing of broad infrared signals in the C=C stretching region around 1500 cm−1 is observed. Energy redistribution processes are visible in the vibrational and electronic dynamics with time constants between ∼2 ps and ∼20 ps. Triplet formation is detected with a time constant of (95 ± 3) ps. This is tracked by the complete loss of stimulated emission. Electronic transition of the emerging triplet absorption band overlaps considerably with the singlet excited state absorption. In contrast, two well separated vibrational marker bands for triplet formation were identified at 1477 cm−1 and at 1508 cm−1. These marker bands allow a precise identification of triplet dynamics in corrole systems. PMID:27226980

  3. Ultrafast electronic dynamics in Helium nanodroplets studied by femtosecond time-resolved EUV photoelectron imaging

    NASA Astrophysics Data System (ADS)

    Gessner, Oliver; Kornilov, Oleg; Wang, Chia; Leonard, Mathew; Healy, Andrew; Leone, Stephen; Neumark, Daniel

    2009-05-01

    Helium nanodroplets constitute a unique cryogenic matrix for the creation, isolation and spectroscopy of regular and exotic species, such as free radicals and molecules in high-spin states. The droplets readily pick up atoms and molecules but interact only very weakly with the respective dopants due to their superfluid nature. Despite the remarkable number of experimental and theoretical studies that have been performed on this new type of matter, neither the electronic structure nor the electron dynamics after EUV excitation are even remotely understood. We have performed the first femtosecond EUV-pump, IR-probe experiment to study the photoionization dynamics of pure Helium nanodroplets below the atomic Helium IP (24.6 eV) in real-time. Using Velocity-Map Imaging (VMI) photoelectron spectroscopy we were able to discern processes with associated timescales ranging from tens of femtoseconds to tens of picoseconds. The results will be discussed in the light of complementary energy-domain studies and theoretical models of the droplet's electronic and nuclear dynamics.

  4. Breaking the Attosecond, Angstrom and TV/M Field Barriers with Ultra-Fast Electron Beams

    SciTech Connect

    Rosenzweig, James; Andonian, Gerard; Fukasawa, Atsushi; Hemsing, Erik; Marcus, Gabriel; Marinelli, Agostino; Musumeci, Pietro; O'Shea, Brendan; O'Shea, Finn; Pellegrini, Claudio; Schiller, David; Travish, Gil; Bucksbaum, Philip; Hogan, Mark; Krejcik, Patrick; Ferrario, Massimo; Full, Steven; Muggli, Patric; /Southern California U.

    2012-06-22

    Recent initiatives at UCLA concerning ultra-short, GeV electron beam generation have been aimed at achieving sub-fs pulses capable of driving X-ray free-electron lasers (FELs) in single-spike mode. This use of very low Q beams may allow existing FEL injectors to produce few-100 attosecond pulses, with very high brightness. Towards this end, recent experiments at the LCLS have produced {approx}2 fs, 20 pC electron pulses. We discuss here extensions of this work, in which we seek to exploit the beam brightness in FELs, in tandem with new developments in cryogenic undulator technology, to create compact accelerator-undulator systems that can lase below 0.15 {angstrom}, or be used to permit 1.5 {angstrom} operation at 4.5 GeV. In addition, we are now developing experiments which use the present LCLS fs pulses to excite plasma wakefields exceeding 1 TV/m, permitting a table-top TeV accelerator for frontier high energy physics applications.

  5. Ultrafast electron transfer reactions initiated by excited CT states of push pull perylenes

    NASA Astrophysics Data System (ADS)

    Miller, Scott E.; Zhao, Yongyu; Schaller, Richard; Mulloni, Viviana; Just, Eric M.; Johnson, Robert C.; Wasielewski, Michael R.

    2002-01-01

    Two new chromophores that absorb in the visible spectrum, the 9-( N-pyrrolidinyl)- and 9-( N-piperidinyl)perylene-3,4-dicarboximides, 5PMI and 6PMI, respectively, were synthesized and shown to possess lowest excited singlet states with about 70% charge transfer (CT) character. Changing the ring size of the cyclic amine from 5 to 6 significantly changes the energies of the CT states, as well as the redox potentials of the chromophores. These chromophores were linked to pyromellitimide (PI) and 1,8:4,5-naphthalenediimide (NI) electron acceptors using a single N-N bond between their respective imides to yield the corresponding donor-acceptor dyads 5PMI-PI, 5PMI-NI, 6PMI-PI, and 6PMI-NI. The donors and acceptors in these molecules are positioned relative to one another in a rod-like arrangement at fixed distances and restricted orientations. The rates of charge separation and recombination were measured using transient absorption spectroscopy. These chromophores were also used to prepare rigid donor-acceptor triads 5PMI-PI-NI and 6PMI-PI-NI, which display one- or two-step electron transfer mechanisms that depend on solvent polarity. These compounds exhibit a broad range of structure and media driven changes in electron transfer mechanism.

  6. Ultrafast electron crystallography of the cooperative reaction path in vanadium dioxide

    PubMed Central

    Yang, Ding-Shyue; Baum, Peter; Zewail, Ahmed H.

    2016-01-01

    Time-resolved electron diffraction with atomic-scale spatial and temporal resolution was used to unravel the transformation pathway in the photoinduced structural phase transition of vanadium dioxide. Results from bulk crystals and single-crystalline thin-films reveal a common, stepwise mechanism: First, there is a femtosecond V−V bond dilation within 300 fs, second, an intracell adjustment in picoseconds and, third, a nanoscale shear motion within tens of picoseconds. Experiments at different ambient temperatures and pump laser fluences reveal a temperature-dependent excitation threshold required to trigger the transitional reaction path of the atomic motions. PMID:27376103

  7. Ultrafast electronic and structural dynamics in solids using femtosecond laser techniques

    NASA Astrophysics Data System (ADS)

    Wang, Jincheng

    This dissertation investigates the electronic and structural dynamics in solid materials driven by femtosecond laser pulses. Two series of experiments are presented. Firstly, the femtosecond laser induced periodic surface structures (LIPSSs) generated on different noble metal surfaces are systematically studied. For the first time, it is found that LIPSSs show distinctly different morphological appearance on different noble metals. The experimental observations suggest that the electron-phonon coupling strength plays the dominant role, which is supported by numerical analysis we performed subsequently on heat transfer in metals using the finite difference in time domain (FDTD) technique. Some special LIPSSs generated on metal surfaces using femtosecond lasers are also observed, and their generation mechanisms are investigated. Extraordinary uniform type-c LIPSSs that are parallel orientated to the incident light polarization can be formed on metal surfaces with p-polarized incident laser pulses at relatively large incident angles. A study of the angular dependence of the structures' periods supports the conjecture that surface plasmons play an important role during the formation of the type-c LIPSSs. Formation of mirror symmetrically orientated periodic structures by using circularly polarized light are also observed for the first time, which may be the only phenomena that can permanently record light helicity with an optically inactive material. In the second set of experiments, coherent acoustic phonons in solids generated by femtosecond laser excitation are studied. A sensitive surface plasmon probing technique is applied to measure coherent acoustic phonon dynamics in metal thin films. The effect of hot electrons excited by femtosecond laser pulses is studied. It is shown that hot electron pressure contributes to the generation of coherent acoustic phonons in metal thin films. Using a metal thin film as a transducer, long-lived propagating acoustic phonons are

  8. Ultrafast electronic spectroscopy for chemical analysis near liquid water interfaces: concepts and applications

    NASA Astrophysics Data System (ADS)

    Link, O.; Lugovoy, E.; Siefermann, K.; Liu, Y.; Faubel, M.; Abel, B.

    2009-07-01

    Electron spectroscopy for chemical analysis (ESCA) being conceptually a photoelectron spectroscopy is established as a chemically specific probe mostly for surface analysis. Liquid phase ESCA for volatile liquids has become possible through the development of the liquid microjet technique in vacuum enabling the measurement of liquid interface photoelectron emission at the high vapor pressure of volatile liquids. Recently we have been able to add the dimension of time to the liquid interface ESCA technique employing high-harmonics soft X-ray and UV/near IR femtosecond pulses in combination with liquid water micro beams in vacuum. The concepts as well as technical details are outlined and several characteristic applications are highlighted.

  9. Endstation for ultrafast magnetic scattering experiments at the free-electron laser in Hamburg

    SciTech Connect

    Mueller, L.; Gutt, C.; Streit-Nierobisch, S.; Walther, M.; Gruebel, G.; Schaffert, S.; Pfau, B.; Flewett, S.; Geilhufe, J.; Eisebitt, S.; Buettner, F.; Guenther, C. M.; Kobs, A.; Hille, M.; Stickler, D.; Froemter, R.; Oepen, H. P.; Luening, J.

    2013-01-15

    An endstation for pump-probe small-angle X-ray scattering (SAXS) experiments at the free-electron laser in Hamburg (FLASH) is presented. The endstation houses a solid-state absorber, optical incoupling for pump-probe experiments, time zero measurement, sample chamber, and detection unit. It can be used at all FLASH beamlines in the whole photon energy range offered by FLASH. The capabilities of the setup are demonstrated by showing the results of resonant magnetic SAXS measurements on cobalt-platinum multilayer samples grown on freestanding Si{sub 3}N{sub 4} membranes and pump-laser-induced grid structures in multilayer samples.

  10. Ultrafast electron crystallography of the cooperative reaction path in vanadium dioxide.

    PubMed

    Yang, Ding-Shyue; Baum, Peter; Zewail, Ahmed H

    2016-05-01

    Time-resolved electron diffraction with atomic-scale spatial and temporal resolution was used to unravel the transformation pathway in the photoinduced structural phase transition of vanadium dioxide. Results from bulk crystals and single-crystalline thin-films reveal a common, stepwise mechanism: First, there is a femtosecond V-V bond dilation within 300 fs, second, an intracell adjustment in picoseconds and, third, a nanoscale shear motion within tens of picoseconds. Experiments at different ambient temperatures and pump laser fluences reveal a temperature-dependent excitation threshold required to trigger the transitional reaction path of the atomic motions. PMID:27376103

  11. Ultrafast probing of the x-ray-induced lattice and electron dynamics in graphite at atomic-resolution

    SciTech Connect

    Hau-Riege, S

    2010-10-07

    We used LCLS pulses to excite thin-film and bulk graphite with various different microstructures, and probed the ultrafast ion and electron dynamics through Bragg and x-ray Thomson scattering (XRTS). We pioneered XRTS at LCLS, making this technique viable for other users. We demonstrated for the first time that the LCLS can be used to characterize warm-dense-matter through Bragg and x-ray Thomson scattering. The warm-dense-matter conditions were created using the LCLS beam. Representative examples of the results are shown in the Figure above. In our experiment, we utilized simultaneously both Bragg and two Thomson spectrometers. The Bragg measurements as a function of x-ray fluence and pulse length allows us to characterize the onset of atomic motion at 2 keV with the highest resolution to date. The Bragg detector was positioned in back-reflection, providing us access to scattering data with large scattering vectors (nearly 4{pi}/{lambda}). We found a clear difference between the atomic dynamics for 70 and 300 fs pulses, and we are currently in the process of comparing these results to our models. The outcome of this comparison will have important consequences for ultrafast diffractive imaging, for which it is still not clear if atomic resolution can truly be achieved. The backward x-ray Thomson scattering data suggests that the average graphite temperature and ionization was 10 eV and 1.0, respectively, which agrees with our models. In the forward scattering data, we observed an inelastic feature in the Thomson spectrum that our models currently do not reproduce, so there is food for thought. We are in the process of writing these results up. Depending on if we can combine the Bragg and Thomson data or not, we plan to publish them in a single paper (e.g. Nature or Science) or as two separate papers (e.g. two Phys. Rev. Lett.). We will present the first analysis of the results at the APS Plasma Meeting in November 2010. We had a fantastic experience performing our

  12. Spot profile analysis and lifetime mapping in ultrafast electron diffraction: Lattice excitation of self-organized Ge nanostructures on Si(001)

    PubMed Central

    Frigge, T.; Hafke, B.; Tinnemann, V.; Witte, T.; Horn-von Hoegen, M.

    2015-01-01

    Ultrafast high energy electron diffraction in reflection geometry is employed to study the structural dynamics of self-organized Germanium hut-, dome-, and relaxed clusters on Si(001) upon femtosecond laser excitation. Utilizing the difference in size and strain state the response of hut- and dome clusters can be distinguished by a transient spot profile analysis. Surface diffraction from {105}-type facets provide exclusive information on hut clusters. A pixel-by-pixel analysis of the dynamics of the entire diffraction pattern gives time constants of 40, 160, and 390 ps, which are assigned to the cooling time constants for hut-, dome-, and relaxed clusters. PMID:26798797

  13. Ultrafast triggered transient energy storage by atomic layer deposition into porous silicon for integrated transient electronics

    NASA Astrophysics Data System (ADS)

    Douglas, Anna; Muralidharan, Nitin; Carter, Rachel; Share, Keith; Pint, Cary L.

    2016-03-01

    Here we demonstrate the first on-chip silicon-integrated rechargeable transient power source based on atomic layer deposition (ALD) coating of vanadium oxide (VOx) into porous silicon. A stable specific capacitance above 20 F g-1 is achieved until the device is triggered with alkaline solutions. Due to the rational design of the active VOx coating enabled by ALD, transience occurs through a rapid disabling step that occurs within seconds, followed by full dissolution of all active materials within 30 minutes of the initial trigger. This work demonstrates how engineered materials for energy storage can provide a basis for next-generation transient systems and highlights porous silicon as a versatile scaffold to integrate transient energy storage into transient electronics.Here we demonstrate the first on-chip silicon-integrated rechargeable transient power source based on atomic layer deposition (ALD) coating of vanadium oxide (VOx) into porous silicon. A stable specific capacitance above 20 F g-1 is achieved until the device is triggered with alkaline solutions. Due to the rational design of the active VOx coating enabled by ALD, transience occurs through a rapid disabling step that occurs within seconds, followed by full dissolution of all active materials within 30 minutes of the initial trigger. This work demonstrates how engineered materials for energy storage can provide a basis for next-generation transient systems and highlights porous silicon as a versatile scaffold to integrate transient energy storage into transient electronics. Electronic supplementary information (ESI) available: (i) Experimental details for ALD and material fabrication, ellipsometry film thickness, preparation of gel electrolyte and separator, details for electrochemical measurements, HRTEM image of VOx coated porous silicon, Raman spectroscopy for VOx as-deposited as well as annealed in air for 1 hour at 450 °C, SEM and transient behavior dissolution tests of uniformly coated VOx on

  14. Ultrafast triggered transient energy storage by atomic layer deposition into porous silicon for integrated transient electronics.

    PubMed

    Douglas, Anna; Muralidharan, Nitin; Carter, Rachel; Share, Keith; Pint, Cary L

    2016-04-14

    Here we demonstrate the first on-chip silicon-integrated rechargeable transient power source based on atomic layer deposition (ALD) coating of vanadium oxide (VOx) into porous silicon. A stable specific capacitance above 20 F g(-1) is achieved until the device is triggered with alkaline solutions. Due to the rational design of the active VOx coating enabled by ALD, transience occurs through a rapid disabling step that occurs within seconds, followed by full dissolution of all active materials within 30 minutes of the initial trigger. This work demonstrates how engineered materials for energy storage can provide a basis for next-generation transient systems and highlights porous silicon as a versatile scaffold to integrate transient energy storage into transient electronics. PMID:26984120

  15. Direct observation of ultrafast surface transport of laser-driven fast electrons in a solid target

    SciTech Connect

    Singh, Prashant Kumar; Chatterjee, Gourab; Adak, Amitava; Ahmed, Saima; Lad, Amit D.; Ravindra Kumar, G.; Cui, Y. Q.; Wang, W. M.; Sheng, Z. M.

    2013-11-15

    We demonstrate rapid spread of surface ionization on a glass target excited by an intense, ultrashort laser pulse at an intensity of 3 × 10{sup 17} W cm{sup −2}. Time- and space-resolved reflectivity of the target surface indicates that the initial plasma region created by the pump pulse expands at c/7. The measured quasi-static megagauss magnetic field is found to expand in a manner very similar to that of surface ionization. Two-dimensional particle-in-cell simulations reproduce measurements of surface ionization and magnetic fields. Both the experiment and simulation convincingly demonstrate the role of self-induced electric and magnetic fields in confining fast electrons along the target-vacuum interface.

  16. Ultrafast Electronic Energy Transfer Beyond the Weak Coupling Limit in a Proximal but Orthogonal Molecular Dyad.

    PubMed

    Hedley, Gordon J; Ruseckas, Arvydas; Benniston, Andrew C; Harriman, Anthony; Samuel, Ifor D W

    2015-12-24

    Electronic energy transfer (EET) from a donor to an acceptor is an important mechanism that controls the light harvesting efficiency in a wide variety of systems, including artificial and natural photosynthesis and contemporary photovoltaic technologies. The detailed mechanism of EET at short distances or large angles between the donor and acceptor is poorly understood. Here the influence of the orientation between the donor and acceptor on EET is explored using a molecule with two nearly perpendicular chromophores. Very fast EET with a time constant of 120 fs is observed, which is at least 40 times faster than the time predicted by Coulombic coupling calculations. Depolarization of the emission signal indicates that the transition dipole rotates through ca. 64°, indicating the near orthogonal nature of the EET event. The rate of EET is found to be similar to structural relaxation rates in the photoexcited oligothiophene donor alone, which suggests that this initial relaxation brings the dyad to a conical intersection where the excitation jumps to the acceptor.

  17. Ultrafast Electronic Energy Transfer Beyond the Weak Coupling Limit in a Proximal but Orthogonal Molecular Dyad.

    PubMed

    Hedley, Gordon J; Ruseckas, Arvydas; Benniston, Andrew C; Harriman, Anthony; Samuel, Ifor D W

    2015-12-24

    Electronic energy transfer (EET) from a donor to an acceptor is an important mechanism that controls the light harvesting efficiency in a wide variety of systems, including artificial and natural photosynthesis and contemporary photovoltaic technologies. The detailed mechanism of EET at short distances or large angles between the donor and acceptor is poorly understood. Here the influence of the orientation between the donor and acceptor on EET is explored using a molecule with two nearly perpendicular chromophores. Very fast EET with a time constant of 120 fs is observed, which is at least 40 times faster than the time predicted by Coulombic coupling calculations. Depolarization of the emission signal indicates that the transition dipole rotates through ca. 64°, indicating the near orthogonal nature of the EET event. The rate of EET is found to be similar to structural relaxation rates in the photoexcited oligothiophene donor alone, which suggests that this initial relaxation brings the dyad to a conical intersection where the excitation jumps to the acceptor. PMID:26617059

  18. Ultrafast electron kinetics in short pulse laser-driven dense hydrogen

    SciTech Connect

    Zastrau, U.; Sperling, P.; Fortmann-Grote, C.; Bornath, T.; Bredow, R.; Doppner, T.; Fennel, T.; Fletcher, L. B.; Forster, E.; Gode, S.; Gregori, G.; Harmand, M.; Hilbert, V.; Laarmann, T.; Lee, H. J.; Ma, T.; Meiwes-Broer, K. H.; Mithen, J. P.; Murphy, C. D.; Nakatsutsumi, M.; Neumayer, P.; Przystawik, A.; Skruszewicz, S.; Tiggesbaumker, J.; Toleikis, S.; White, T. G.; Glenzer, S. H.; Redmer, R.; Tschentscher, T.

    2015-09-25

    Dense cryogenic hydrogen is heated by intense femtosecond infrared laser pulses at intensities of ${10}^{15}-{10}^{16}\\;$ W cm–2. Three-dimensional particle-in-cell (PIC) simulations predict that this heating is limited to the skin depth, causing an inhomogeneously heated outer shell with a cold core and two prominent temperatures of about $25$ and $40\\;\\mathrm{eV}$ for simulated delay times up to $+70\\;\\mathrm{fs}$ after the laser pulse maximum. Experimentally, the time-integrated emitted bremsstrahlung in the spectral range of 8–18 nm was corrected for the wavelength-dependent instrument efficiency. The resulting spectrum cannot be fit with a single temperature bremsstrahlung model, and the best fit is obtained using two temperatures of about 13 and $30\\;$eV. The lower temperatures in the experiment can be explained by missing energy-loss channels in the simulations, as well as the inclusion of hot, non-Maxwellian electrons in the temperature calculation. In conclusion, we resolved the time-scale for laser-heating of hydrogen, and PIC results for laser–matter interaction were successfully tested against the experiment data.

  19. Ultrafast electron kinetics in short pulse laser-driven dense hydrogen

    NASA Astrophysics Data System (ADS)

    Zastrau, U.; Sperling, P.; Fortmann-Grote, C.; Becker, A.; Bornath, T.; Bredow, R.; Döppner, T.; Fennel, T.; Fletcher, L. B.; Förster, E.; Göde, S.; Gregori, G.; Harmand, M.; Hilbert, V.; Laarmann, T.; Lee, H. J.; Ma, T.; Meiwes-Broer, K. H.; Mithen, J. P.; Murphy, C. D.; Nakatsutsumi, M.; Neumayer, P.; Przystawik, A.; Skruszewicz, S.; Tiggesbäumker, J.; Toleikis, S.; White, T. G.; Glenzer, S. H.; Redmer, R.; Tschentscher, T.

    2015-11-01

    Dense cryogenic hydrogen is heated by intense femtosecond infrared laser pulses at intensities of {10}15-{10}16 W cm-2. Three-dimensional particle-in-cell (PIC) simulations predict that this heating is limited to the skin depth, causing an inhomogeneously heated outer shell with a cold core and two prominent temperatures of about 25 and 40 {eV} for simulated delay times up to +70 {fs} after the laser pulse maximum. Experimentally, the time-integrated emitted bremsstrahlung in the spectral range of 8-18 nm was corrected for the wavelength-dependent instrument efficiency. The resulting spectrum cannot be fit with a single temperature bremsstrahlung model, and the best fit is obtained using two temperatures of about 13 and 30 eV. The lower temperatures in the experiment can be explained by missing energy-loss channels in the simulations, as well as the inclusion of hot, non-Maxwellian electrons in the temperature calculation. We resolved the time-scale for laser-heating of hydrogen, and PIC results for laser-matter interaction were successfully tested against the experiment data.

  20. Ultrafast probing of ejection dynamics of Rydberg atoms and molecular fragments from electronically excited helium nanodroplets.

    PubMed

    Bünermann, Oliver; Kornilov, Oleg; Haxton, Daniel J; Leone, Stephen R; Neumark, Daniel M; Gessner, Oliver

    2012-12-01

    The ejection dynamics of Rydberg atoms and molecular fragments from electronically excited helium nanodroplets are studied with time-resolved extreme ultraviolet ion imaging spectroscopy. At excitation energies of 23.6 ± 0.2 eV, Rydberg atoms in n = 3 and n = 4 states are ejected on different time scales and with significantly different kinetic energy distributions. Specifically, n = 3 Rydberg atoms are ejected with kinetic energies as high as 0.85 eV, but their appearance is delayed by approximately 200 fs. In contrast, n = 4 Rydberg atoms appear within the time resolution of the experiment with considerably lower kinetic energies. Major features in the Rydberg atom kinetic energy distributions for both principal quantum numbers can be described within a simple elastic scattering model of localized perturbed atomic Rydberg atoms that are expelled from the droplet due to their repulsive interaction with the surrounding helium bath. Time-dependent kinetic energy distributions of He(2) (+) and He(3) (+) ions are presented that support the formation of molecular ions in an indirect droplet ionization process and the ejection of neutral Rydberg dimers on a similar time scale as the n = 3 Rydberg atoms.

  1. Ultrafast modulation of polarization amplitude by terahertz fields in electronic-type organic ferroelectrics

    NASA Astrophysics Data System (ADS)

    Miyamoto, Tatsuya; Yada, Hiroyuki; Yamakawa, Hiromichi; Okamoto, Hiroshi

    2013-10-01

    Ferroelectrics sometimes show large electro-optical and non-linear optical effects, available for polarization rotation and frequency conversion of light, respectively. If the amplitude of ferroelectric polarization is modulated in the picosecond time domain, terahertz repetition of optical switching via electro-optical and non-linear optical effects would be achieved. Here we show that polarization amplitude can be rapidly modulated by a terahertz electric field in an organic ferroelectric, tetrathiafulvalene-p-chloranil (TTF-CA). In this compound, alternately stacked donor (TTF) and acceptor (CA) molecules are dimerized via the spin-Peierls mechanism, and charge transfer within each dimer results in a new type of ferroelectricity called electronic-type ferroelectricity. Using a terahertz field, the intradimer charge transfer is strongly modulated, producing a subpicosecond change in the macroscopic polarization, which is demonstrated by transient reflectivity and second-harmonic generation measurements. Subsequently, coherent oscillation of the dimeric molecular displacements occur, which is explained by the modulation of the spin moment of each molecule.

  2. Ultrafast electron kinetics in short pulse laser-driven dense hydrogen

    DOE PAGES

    Zastrau, U.; Sperling, P.; Fortmann-Grote, C.; Becker, A.; Bornath, T.; Bredow, R.; Doppner, T.; Fennel, T.; Fletcher, L. B.; Forster, E.; et al

    2015-09-25

    Dense cryogenic hydrogen is heated by intense femtosecond infrared laser pulses at intensities ofmore » $${10}^{15}-{10}^{16}\\;$$ W cm–2. Three-dimensional particle-in-cell (PIC) simulations predict that this heating is limited to the skin depth, causing an inhomogeneously heated outer shell with a cold core and two prominent temperatures of about $25$ and $$40\\;\\mathrm{eV}$$ for simulated delay times up to $$+70\\;\\mathrm{fs}$$ after the laser pulse maximum. Experimentally, the time-integrated emitted bremsstrahlung in the spectral range of 8–18 nm was corrected for the wavelength-dependent instrument efficiency. The resulting spectrum cannot be fit with a single temperature bremsstrahlung model, and the best fit is obtained using two temperatures of about 13 and $$30\\;$$eV. The lower temperatures in the experiment can be explained by missing energy-loss channels in the simulations, as well as the inclusion of hot, non-Maxwellian electrons in the temperature calculation. In conclusion, we resolved the time-scale for laser-heating of hydrogen, and PIC results for laser–matter interaction were successfully tested against the experiment data.« less

  3. Ultrafast laser induced electronic and structural modifications in bulk fused silica

    NASA Astrophysics Data System (ADS)

    Mishchik, K.; D'Amico, C.; Velpula, P. K.; Mauclair, C.; Boukenter, A.; Ouerdane, Y.; Stoian, R.

    2013-10-01

    Ultrashort laser pulses can modify the inner structure of fused silica, generating refractive index changes varying from soft positive (type I) light guiding forms to negative (type II) values with void presence and anisotropic sub-wavelength modulation. We investigate electronic and structural material changes in the type I to type II transition via coherent and incoherent secondary light emission reflecting free carrier behavior and post-irradiation material relaxation in the index change patterns. Using phase contrast microscopy, photoluminescence, and Raman spectroscopy, we determine in a space-resolved manner defect formation, redistribution and spatial segregation, and glass network reorganization paths in conditions marking the changeover between type I and type II photoinscription regimes. We first show characteristic patterns of second harmonic generation in type I and type II traces, indicating the collective involvement of free carriers and polarization memory. Second, incoherent photoemission from resonantly and non-resonantly excited defect states reveals accumulation of non-bridging oxygen hole centers (NBOHCs) in positive index domains and oxygen deficiency centers (ODCs) with O2- ions segregation in void-like regions and in the nanostructured domains, reflecting the interaction strength. Complementary Raman investigations put into evidence signatures of the different environments where photo-chemical densification (bond rearrangements) and mechanical effects can be indicated. NBOHCs setting in before visible index changes serve as precursors for subsequent compaction build-up, indicating a scenario of cold, defect-assisted densification for the soft type I irradiation regime. Additionally, we observe hydrodynamic effects and severe bond-breaking in type II zones with indications of phase transition. These observations illuminate densification paths in fused silica in low power irradiation regimes, and equally in energetic ranges, characterized by

  4. Nondipole Effects in Xe 4d Photoemission

    SciTech Connect

    Hemmers, O; Guillemin, R; Wolska, A; Lindle, D W; Rolles, D; Cheng, K T; Johnson, W R; Zhou, H L; Manson, S T

    2004-07-14

    We measured the nondipole parameters for the spin-orbit doublets Xe 4d{sub 5/2} and Xe 4d{sub 3/2} over a photon-energy range from 100 eV to 250 eV at beamline 8.0.1.3 of the Advanced Light Source at the Lawrence Berkeley National Laboratory. Significant nondipole effects are found at relatively low energies as a result of Cooper minima in dipole channels and interchannel coupling in quadrupole channels. Most importantly, sharp disagreement between experiment and theory, when otherwise excellent agreement was expected, has provided the first evidence of satellite two-electron quadrupole photoionization transitions, along with their crucial importance for a quantitatively accurate theory.

  5. Ultrafast photoinduced charge transport in Pt(II) donor-acceptor assembly bearing naphthalimide electron acceptor and phenothiazine electron donor.

    PubMed

    Sazanovich, Igor V; Best, Jonathan; Scattergood, Paul A; Towrie, Michael; Tikhomirov, Sergei A; Bouganov, Oleg V; Meijer, Anthony J H M; Weinstein, Julia A

    2014-12-21

    Visible light-induced charge transfer dynamics were investigated in a novel transition metal triad acceptor-chromophore-donor, (NDI-phen)Pt(II)(-C≡C-Ph-CH2-PTZ)2 (1), designed for photoinduced charge separation using a combination of time-resolved infrared (TRIR) and femtosecond electronic transient absorption (TA) spectroscopy. In 1, the electron acceptor is 1,4,5,8-naphthalene diimide (NDI), and the electron donor is phenothiazine (PTZ), and [(phen)Pt(-C≡C-Ph-)], where phen is 1,10-phenanthroline, represents the chromophoric core. The first excited state observed in 1 is a (3)MLCT/LL'CT, with {Pt(II)-acetylide}-to-phen character. Following that, charge transfer from the phen-anion onto the NDI subunit to form NDI(-)-phen-[Pt-(C≡C)2](+)-PTZ2 occurs with a time constant of 2.3 ps. This transition is characterised by appearance of the prominent NDI-anion features in both TRIR and TA spectra. The final step of the charge separation in 1 proceeds with a time constant of ∼15 ps during which the hole migrates from the [Pt-(C≡C)2] subunit to one of the PTZ groups. Charge recombination in 1 then occurs with two distinct time constants of 36 ns and 107 ns, corresponding to the back electron transfer to each of the two donor groups; a rather rare occurrence which manifests that the hole in the final charge-separated state is localised on one of the two donor PTZ groups. The assignment of the nature of the excited states and dynamics in 1 was assisted by TRIR investigations of the analogous previously reported ((COOEt)2bpy)Pt(C≡C-Ph-CH2-PTZ)2 (2), (J. E. McGarrah and R. Eisenberg, Inorg. Chem., 2003, 42, 4355; J. E. McGarrah, J. T. Hupp and S. N. Smirnov, J. Phys. Chem. A, 2009, 113, 6430) as well as (bpy)Pt(C≡C-Ph-C7H15)2, which represent the acceptor-free dyad, and the chromophoric core, respectively. Thus, the step-wise formation of the full charge-separated state on the picosecond time scale and charge recombination via tunnelling have been established; and

  6. Strong electronic coupling and ultrafast electron transfer between PbS quantum dots and TiO2 nanocrystalline films.

    PubMed

    Yang, Ye; Rodríguez-Córdoba, William; Xiang, Xu; Lian, Tianquan

    2012-01-11

    Hot carrier and multiple exciton extractions from lead salt quantum dots (QDs) to TiO(2) single crystals have been reported. Implementing these ideas on practical solar cells likely requires the use of nanocrystalline TiO(2) thin films to enhance the light harvesting efficiency. Here, we report 6.4 ± 0.4 fs electron transfer time from PbS QDs to TiO(2) nanocrystalline thin films, suggesting the possibility of extracting hot carriers and multiple excitons in solar cells based on these materials.

  7. Plasmonic enhanced ultrafast switch.

    SciTech Connect

    Subramania,Ganapathi Subramanian; Reno, John Louis; Passmore, Brandon Scott; Harris, Tom.; Shaner, Eric Arthur; Barrick, Todd A.

    2009-09-01

    Ultrafast electronic switches fabricated from defective material have been used for several decades in order to produce picosecond electrical transients and TeraHertz radiation. Due to the ultrashort recombination time in the photoconductor materials used, these switches are inefficient and are ultimately limited by the amount of optical power that can be applied to the switch before self-destruction. The goal of this work is to create ultrafast (sub-picosecond response) photoconductive switches on GaAs that are enhanced through plasmonic coupling structures. Here, the plasmonic coupler primarily plays the role of being a radiation condenser which will cause carriers to be generated adjacent to metallic electrodes where they can more efficiently be collected.

  8. Electron Excitation Cross Sections for the C II Transitions 2s(exp 2)2p P-2(exp 0) yields 2s2p(exp 2) P-4, D-2, and S-2

    NASA Technical Reports Server (NTRS)

    Smith, Steven J.; Zuo, M.; Chutjian, A.; Tayal, S. S.; Williams, I. D.

    1996-01-01

    Experimental and theoretical excitation cross sections are reported for the transitions 2s(exp 2) 2p-2(exp 0) yield 2s2p(exp 2)P-4, D-2, and S-2 in C II. The transition wavelengths (energies) are 2324 A (5.34 eV), 1335 x (9.29 eV), and 1036 A (11.97 eV), respectively. Use is made of electron energy-loss and merged beams methods. The energy range covered is from below each threshold (4 - 11 eV) to 15-24 eV. As in previous work with O II, care was taken to assess and minimize the metastable fraction in the C II beam, to account for contributions from nearby energy-loss features, and to collect the full angular range of inelastically scattered electrons. A comparison is made for each transition between experiment and new 8-state R-matrix calculations. Subject headings: atomic data ultraviolet: general

  9. Photoionization and electron radical recombination dynamics in photoactive yellow protein investigated by ultrafast spectroscopy in the visible and near-infrared spectral region.

    PubMed

    Zhu, Jingyi; Paparelli, Laura; Hospes, Marijke; Arents, Jos; Kennis, John T M; van Stokkum, Ivo H M; Hellingwerf, Klaas J; Groot, Marie Louise

    2013-09-26

    Photoinduced ionization of the chromophore inside photoactive yellow protein (PYP) was investigated by ultrafast spectroscopy in the visible and near-infrared spectral regions. An absorption band that extended from around 550 to 850 nm was observed and ascribed to solvated electrons, ejected from the p-hydroxycinnamic acid anion chromophore upon the absorption of two 400 nm photons. Global kinetic analysis showed that the solvated electron absorption decayed in two stages: a shorter phase of around 10 ps and a longer phase of more than 3 ns. From a simulation based on a diffusion model we conclude that the diffusion rate of the electron is about 0.8 Å(2)/ps in wild type PYP, and that the electron is ejected to a short distance of only several angstroms away from the chromophore. The chromophore-protein pocket appears to provide a water-similar local environment for the electron. Because mutations at different places around the chromophore have different effect on the electron recombination dynamics, we suggest that solvated electrons could provide a new method to investigate the local dielectric environment inside PYP and thus help to understand the role of the protein in the photoisomerization process.

  10. MRCI study of spectroscopic and molecular properties of X2Πg, a 4Πu, A2Πu, b 4 ? , D2Δg and B2 ? electronic states of ? ion

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoniu; Shi, Deheng; Sun, Jinfeng; Zhu, Zunlue

    2011-06-01

    The potential energy curves (PECs) of six low-lying electronic states (X2Πg, a 4Πu, A2Πu, b 4 ? , D2Δg and B2 ? ) of ? ion were studied by the ab initio quantum chemical method. The calculations were carried out with the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in combination with large correlation-consistent basis sets. Effects on the PECs of the core-valence correlation and relativistic corrections are taken into account. The way to consider the relativistic correction is to use the second-order Douglas-Kroll Hamiltonian (DKH2) approximation. The core-valence correlation correction is carried out with the cc-pCVQZ basis set, and the relativistic correction is performed at the level of cc-pVQZ basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size-extensivity errors by means of the Davidson modification (MRCI + Q). These PECs are extrapolated to the complete basis set (CBS) limit by the two-point total-energy extrapolation scheme. With these PECs, the spectroscopic parameters (Te , De , D 0, Re , ωe , ωexe , αe and Be ) are determined and compared with those reported in the literature. The conclusion can be reached that the effect on the spectroscopic parameters of the core-valence correlation correction is larger than that of the relativistic correction. With the PECs obtained by the MRCI + Q/CV+DK+56 calculations, the vibrational levels and inertial rotation constants of the first 26 vibrational states are determined for these electronic states of non-rotating ? ion. Comparison with the experimental data shows that the present spectroscopic parameters and molecular constants are accurate.

  11. Ultrafast electron transfer in all-carbon-based SWCNT-C60 donor-acceptor nanoensembles connected by poly(phenylene-ethynylene) spacers.

    PubMed

    Barrejón, Myriam; Gobeze, Habtom B; Gómez-Escalonilla, María J; Fierro, José Luis G; Zhang, Minfang; Yudasaka, Masako; Iijima, Sumio; D'Souza, Francis; Langa, Fernando

    2016-08-21

    Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an electron donating or accepting photosensitizer while the second part should fulfil the role of an electron acceptor or donor. In the present work, we have successfully addressed this issue by synthesizing covalently linked all-carbon-based donor-acceptor nanoensembles using single-walled carbon nanotubes (SWCNTs) as the donor and C60 as the acceptor. The donor-acceptor entities in the nanoensembles were connected by phenylene-ethynylene spacer units to achieve better electronic communication and to vary the distance between the components. These novel SWCNT-C60 nanoensembles have been characterized by a number of techniques, including TGA, FT-IR, Raman, AFM, absorbance and electrochemical methods. The moderate number of fullerene addends present on the side-walls of the nanotubes largely preserved the electronic structure of the nanotubes. The thermodynamic feasibility of charge separation in these nanoensembles was established using spectral and electrochemical data. Finally, occurrence of ultrafast electron transfer from the excited nanotubes in these donor-acceptor nanohybrids has been established by femtosecond transient absorption studies, signifying their utility in building light energy harvesting devices.

  12. Ultrafast electron transfer in all-carbon-based SWCNT-C60 donor-acceptor nanoensembles connected by poly(phenylene-ethynylene) spacers.

    PubMed

    Barrejón, Myriam; Gobeze, Habtom B; Gómez-Escalonilla, María J; Fierro, José Luis G; Zhang, Minfang; Yudasaka, Masako; Iijima, Sumio; D'Souza, Francis; Langa, Fernando

    2016-08-21

    Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an electron donating or accepting photosensitizer while the second part should fulfil the role of an electron acceptor or donor. In the present work, we have successfully addressed this issue by synthesizing covalently linked all-carbon-based donor-acceptor nanoensembles using single-walled carbon nanotubes (SWCNTs) as the donor and C60 as the acceptor. The donor-acceptor entities in the nanoensembles were connected by phenylene-ethynylene spacer units to achieve better electronic communication and to vary the distance between the components. These novel SWCNT-C60 nanoensembles have been characterized by a number of techniques, including TGA, FT-IR, Raman, AFM, absorbance and electrochemical methods. The moderate number of fullerene addends present on the side-walls of the nanotubes largely preserved the electronic structure of the nanotubes. The thermodynamic feasibility of charge separation in these nanoensembles was established using spectral and electrochemical data. Finally, occurrence of ultrafast electron transfer from the excited nanotubes in these donor-acceptor nanohybrids has been established by femtosecond transient absorption studies, signifying their utility in building light energy harvesting devices. PMID:27305145

  13. Electron-phonon interactions in MoS{sub 2} probed with ultrafast two-dimensional visible/far-infrared spectroscopy

    SciTech Connect

    Guo, Xunmin; Chen, Hailong; Wen, Xiewen; Zheng, Junrong

    2015-06-07

    An ultrafast two-dimensional visible/far-IR spectroscopy based on the IR/THz air biased coherent detection method and scanning the excitation frequencies is developed. The method allows the responses in the far-IR region caused by various electronic excitations in molecular or material systems to be observed in real time. Using the technique, the relaxation dynamics of the photo-excited carriers and electron/phonon coupling in bulk MoS{sub 2} are investigated. It is found that the photo-generation of excited carriers occurs within two hundred fs and the relaxation of the carriers is tens of ps. The electron-phonon coupling between the excitations of electrons and the phonon mode E{sub 1u} of MoS{sub 2} is also directly observed. The electron excitation shifts the frequency of the phonon mode 9 cm{sup −1} higher, resulting in an absorption peak at 391 cm{sup −1} and a bleaching peak at 382 cm{sup −1}. The frequency shift diminishes with the relaxation of the carriers.

  14. Doping dependence of the ultrafast electronic dynamics of Y1-xPrxBa2Cu3O7-δ thin-film superconductors from femtosecond optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Luo, C. W.; Lo, H. P.; Su, C. H.; Wu, I. H.; Chen, Y.-J.; Wu, K. H.; Lin, J.-Y.; Uen, T. M.; Juang, J. Y.; Kobayashi, T.

    2010-09-01

    Time-domain spectroscopy, which probes the dynamics of the electronic states near Fermi surface that are associated with superconductivity, has proven to be a powerful method for providing insights into the fundamental nature of both pseudogap and superconducting gap. This study shows that the unique T-x phase diagram with the time-evolving ultrafast dynamics of Y1-xPrxBa2Cu3O7-δ can be used to identify clearly the Nernst, pseudogap, and superconducting regions. All of the orders appear together at a specific delay time, such as 1.2-3 ps, after pumping by an ultrashort pulse. These discoveries suggest that the Nernst effect, the pseudogap and even superconductivity may have the same physical origin.

  15. Effect of high-optical excitation on the ultrafast electron dynamics in stacked-monolayer graphene samples

    NASA Astrophysics Data System (ADS)

    Castañeda, Juan A.; Guimarães Rosa, Henrique; Gomes, José C. V.; Thoroh de Souza, Eunezio A.; de Brito-Cruz, Carlos H.; Fragnito, Hugo L.; Padilha, Lázaro A.

    2016-05-01

    We report on transient absorption experiments performed at high optical excitation fluences and used to study the ultrafast dynamics in graphene. We employed a degenerated scheme of pump and probe at 800 nm (1.55 eV). The time resolution of our measurements was limited by the pulse duration ~ 100 fs. The samples were prepared by chemical vapor deposition (CVD) as single-layers on silica and, then staked layer-by-layer in order to make a stack of up to 5 graphene monolayers. We observed saturable absorption (SA) and fluence-dependent relaxation times. We see that the ultrafast carrier dynamics is composed by two decay mechanisms, one with response time of about 200 fs and a slower process of about 1 ps. The fast decay, due to both carrier-carrier and carrier-optical phonon scattering, becomes slower when the density of excited carrier was increased. We implemented a theoretical model and found that both the optical phonon rate emission and the optical phonon lifetime are affect by the pump fluence.

  16. PREFACE: Ultrafast biophotonics Ultrafast biophotonics

    NASA Astrophysics Data System (ADS)

    Gu, Min; Reid, Derryck; Ben-Yakar, Adela

    2010-08-01

    The use of light to explore biology can be traced to the first observations of tissue made with early microscopes in the mid-seventeenth century, and has today evolved into the discipline which we now know as biophotonics. This field encompasses a diverse range of activities, each of which shares the common theme of exploiting the interaction of light with biological material. With the rapid advancement of ultrafast optical technologies over the last few decades, ultrafast lasers have increasingly found applications in biophotonics, to the extent that the distinctive new field of ultrafast biophotonics has now emerged, where robust turnkey ultrafast laser systems are facilitating cutting-edge studies in the life sciences to take place in everyday laboratories. The broad spectral bandwidths, precision timing resolution, low coherence and high peak powers of ultrafast optical pulses provide unique opportunities for imaging and manipulating biological systems. Time-resolved studies of bio-molecular dynamics exploit the short pulse durations from such lasers, while other applications such as optical coherence tomography benefit from the broad optical bandwidths possible by using super-continuum generation and additionally allowing for high speed imaging with speeds as high as 47 000 scans per second. Continuing progress in laser-system technology is accelerating the adoption of ultrafast techniques across the life sciences, both in research laboratories and in clinical applications, such as laser-assisted in situ keratomileusis (LASIK) eye surgery. Revolutionizing the field of optical microscopy, two-photon excitation fluorescence (TPEF) microscopy has enabled higher spatial resolution with improved depth penetration into biological specimens. Advantages of this nonlinear optical process include: reduced photo-interactions, allowing for extensive imaging time periods; simultaneously exciting multiple fluorescent molecules with only one excitation wavelength; and

  17. Effect of Molecular Coupling on Ultrafast Electron-Transfer and Charge-Recombination Dynamics in a Wide-Gap ZnS Nanoaggregate Sensitized by Triphenyl Methane Dyes.

    PubMed

    Debnath, Tushar; Maity, Partha; Dana, Jayanta; Ghosh, Hirendra N

    2016-03-01

    Wide-band-gap ZnS nanocrystals (NCs) were synthesized, and after sensitizing the NCs with series of triphenyl methane (TPM) dyes, ultrafast charge-transfer dynamics was demonstrated. HRTEM images of ZnS NCs show the formation of aggregate crystals with a flower-like structure. Exciton absorption and lumimescence, due to quantum confinement of the ZnS NCs, appear at approximately 310 and 340 nm, respectively. Interestingly, all the TPM dyes (pyrogallol red, bromopyrogallol red, and aurin tricarboxylic acid) form charge-transfer complexes with the ZnS NCs, with the appearance of a red-shifted band. Electron injection from the photoexcited TPM dyes into the conduction band of the ZnS NCs is shown to be a thermodynamically viable process, as confirmed by steady-state and time-resolved emission studies. To unravel charge-transfer (both electron injection and charge recombination) dynamics and the effect of molecular coupling, femtosecond transient absorption studies were carried out in TPM-sensitized ZnS NCs. The electron-injection dynamics is pulse-width-limited in all the ZnS/TPM dye systems, however, the back electron transfer differs, depending on the molecular coupling of the sensitizers (TPM dyes). The detailed mechanisms for the above-mentioned processes are discussed. PMID:26548569

  18. Ultrafast Extreme Ultraviolet Absorption Spectroscopy of Methylammonium Lead Iodide Perovskite

    NASA Astrophysics Data System (ADS)

    Verkamp, Max A.; Lin, Ming-Fu; Ryland, Elizabeth S.; Vura-Weis, Josh

    2016-06-01

    Methylammonium lead iodide (perovskite) is a leading candidate for use in next-generation solar cell devices. However, the photophysics responsible for its strong photovoltaic qualities are not fully understood. Ultrafast extreme ultraviolet (XUV) absorption was used to investigate electron and hole dynamics in perovskite by observing transitions from a common inner-shell level (I 4d) to the valence and conduction bands. Ultrashort (30 fs) pulses of XUV radiation with a broad spectrum (40-70 eV) were generated via high-harmonic generation using a tabletop instrument. Transient absorption measurements with visible pump and XUV probe directly observed the relaxation of charge carriers in perovskite after above-band excitation in the femtosecond and picosecond time ranges.

  19. Ultrafast Electronic and Vibrational Dynamics of Stabilized A State Mutants of the Green Fluorescent Protein (GFP): Snipping the Proton Wire

    PubMed Central

    Stoner-Ma, Deborah; Jaye, Andrew A.; Ronayne, Kate L.; Nappa, Jerome; Tonge, Peter J.; Meech, Stephen R.

    2008-01-01

    Two blue absorbing and emitting mutants (S65G/T203V/E222Q and S65T at pH 5.5) of the green fluorescent protein (GFP) have been investigated through ultrafast time resolved infra-red (TRIR) and fluorescence spectroscopy. In these mutants, in which the excited state proton transfer reaction observed in wild type GFP has been blocked, the photophysics are dominated by the neutral A state. It was found that the A* excited state lifetime is short, indicating that it is relatively less stabilised in the protein matrix than the anionic form. However, the lifetime of the A* state can be increased through modifications to the protein structure. The TRIR spectra show that a large shifts in protein vibrational modes on excitation of the A* state occurs in both these GFP mutants. This is ascribed to a change in H-bonding interactions between the protein matrix and the excited state. PMID:19554079

  20. Ultrafast electronic and vibrational dynamics of stabilized A state mutants of the green fluorescent protein (GFP): Snipping the proton wire

    NASA Astrophysics Data System (ADS)

    Stoner-Ma, Deborah; Jaye, Andrew A.; Ronayne, Kate L.; Nappa, Jérôme; Tonge, Peter J.; Meech, Stephen R.

    2008-06-01

    Two blue absorbing and emitting mutants (S65G/T203V/E222Q and S65T at pH 5.5) of the green fluorescent protein (GFP) have been investigated through ultrafast time resolved infra-red (TRIR) and fluorescence spectroscopy. In these mutants, in which the excited state proton transfer reaction observed in wild-type GFP has been blocked, the photophysics are dominated by the neutral A state. It was found that the A∗ excited state lifetime is short, indicating that it is relatively less stabilised in the protein matrix than the anionic form. However, the lifetime of the A state can be increased through modifications to the protein structure. The TRIR spectra show that a large shifts in protein vibrational modes on excitation of the A state occurs in both these GFP mutants. This is ascribed to a change in H-bonding interactions between the protein matrix and the excited state.

  1. Discontinuity of the ultrafast electronic response of underdoped superconducting Bi2Sr2CaCu2O8+δ strongly excited by ultrashort light pulses

    NASA Astrophysics Data System (ADS)

    Giannetti, Claudio; Coslovich, Giacomo; Cilento, Federico; Ferrini, Gabriele; Eisaki, Hiroshi; Kaneko, Nobuhisa; Greven, Martin; Parmigiani, Fulvio

    2009-06-01

    We report the experimental evidence of an abrupt transition of the ultrafast electronic response of underdoped superconducting Bi2Sr2CaCu2O8+δ , under the impulsive photoinjection of a high density of excitations, using ultrashort laser pulses and avoiding significant laser heating. The direct proof of this process is the discontinuity of the transient optical electronic response, observed at a critical fluence of Φth≃70μJ/cm2 . Below this threshold, the recovery dynamics is described by the Rothwarf-Taylor equations, whereas, above the critical intensity, a fast electronic response is superimposed to a slower dynamics related to the superconductivity recovery. We discuss our experimental findings within the frame of the available models for nonequilibrium superconductivity, i.e., the Teff and μeff models. The measured critical fluence is compatible with a first-order photoinduced phase transition triggered by the impulsive shift of the chemical potential. The measured value, significantly in excess of the condensation energy, indicates that, close to the threshold, the largest amount of energy is delivered to phonons or to other gap-energy excitations strongly coupled to Cooper pairs.

  2. Excited-state intramolecular hydrogen transfer (ESIHT) of 1,8-dihydroxy-9,10-anthraquinone (DHAQ) characterized by ultrafast electronic and vibrational spectroscopy and computational modeling.

    PubMed

    Mohammed, Omar F; Xiao, Dequan; Batista, Victor S; Nibbering, Erik T J

    2014-05-01

    We combine ultrafast electronic and vibrational spectroscopy and computational modeling to investigate the photoinduced excited-state intramolecular hydrogen-transfer dynamics in 1,8-dihydroxy-9,10-anthraquinone (DHAQ) in tetrachloroethene, acetonitrile, dimethyl sulfoxide, and methanol. We analyze the electronic excited states of DHAQ with various possible hydrogen-bonding schemes and provide a general description of the electronic excited-state dynamics based on a systematic analysis of femtosecond UV/vis and UV/IR pump-probe spectroscopic data. Upon photoabsorption at 400 nm, the S2 electronic excited state is initially populated, followed by a rapid equilibration within 150 fs through population transfer to the S1 state where DHAQ exhibits ESIHT dynamics. In this equilibration process, the excited-state population is distributed between the 9,10-quinone (S2) and 1,10-quinone (S1) states while undergoing vibrational energy redistribution, vibrational cooling, and solvation dynamics on the 0.1-50 ps time scale. Transient UV/vis pump-probe data in methanol also suggest additional relaxation dynamics on the subnanosecond time scale, which we tentatively ascribe to hydrogen bond dynamics of DHAQ with the protic solvent, affecting the equilibrium population dynamics within the S2 and S1 electronic excited states. Ultimately, the two excited singlet states decay with a solvent-dependent time constant ranging from 139 to 210 ps. The concomitant electronic ground-state recovery is, however, only partial because a large fraction of the population relaxes to the first triplet state. From the similarity of the time scales involved, we conjecture that the solvent plays a crucial role in breaking the intramolecular hydrogen bond of DHAQ during the S2/S1 relaxation to either the ground or triplet state. PMID:24684387

  3. Ultrafast electron transfer in all-carbon-based SWCNT-C60 donor-acceptor nanoensembles connected by poly(phenylene-ethynylene) spacers

    NASA Astrophysics Data System (ADS)

    Barrejón, Myriam; Gobeze, Habtom B.; Gómez-Escalonilla, María J.; Fierro, José Luis G.; Zhang, Minfang; Yudasaka, Masako; Iijima, Sumio; D'Souza, Francis; Langa, Fernando

    2016-08-01

    Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an electron donating or accepting photosensitizer while the second part should fulfil the role of an electron acceptor or donor. In the present work, we have successfully addressed this issue by synthesizing covalently linked all-carbon-based donor-acceptor nanoensembles using single-walled carbon nanotubes (SWCNTs) as the donor and C60 as the acceptor. The donor-acceptor entities in the nanoensembles were connected by phenylene-ethynylene spacer units to achieve better electronic communication and to vary the distance between the components. These novel SWCNT-C60 nanoensembles have been characterized by a number of techniques, including TGA, FT-IR, Raman, AFM, absorbance and electrochemical methods. The moderate number of fullerene addends present on the side-walls of the nanotubes largely preserved the electronic structure of the nanotubes. The thermodynamic feasibility of charge separation in these nanoensembles was established using spectral and electrochemical data. Finally, occurrence of ultrafast electron transfer from the excited nanotubes in these donor-acceptor nanohybrids has been established by femtosecond transient absorption studies, signifying their utility in building light energy harvesting devices.Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an

  4. Impact of metal ions in porphyrin-based applied materials for visible-light photocatalysis: key information from ultrafast electronic spectroscopy.

    PubMed

    Kar, Prasenjit; Sardar, Samim; Alarousu, Erkki; Sun, Jingya; Seddigi, Zaki S; Ahmed, Saleh A; Danish, Ekram Y; Mohammed, Omar F; Pal, Samir Kumar

    2014-08-11

    Protoporphyrin IX-zinc oxide (PP-ZnO) nanohybrids have been synthesized for applications in photocatalytic devices. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and steady-state infrared, absorption, and emission spectroscopies have been used to analyze the structural details and optical properties of these nanohybrids. Time-resolved fluorescence and transient absorption techniques have been applied to study the ultrafast dynamic events that are key to photocatalytic activities. The photocatalytic efficiency under visible-light irradiation in the presence of naturally abundant iron(III) and copper(II) ions has been found to be significantly retarded in the former case, but enhanced in the latter case. More importantly, femtosecond (fs) transient absorption data have clearly demonstrated that the residence of photoexcited electrons from the sensitizer PP in the centrally located iron moiety hinders ground-state bleach recovery of the sensitizer, affecting the overall photocatalytic rate of the nanohybrid. The presence of copper(II) ions, on the other hand, offers additional stability against photobleaching and eventually enhances the efficiency of photocatalysis. In addition, we have also explored the role of UV light in the efficiency of photocatalysis and have rationalized our observations from femtosecond- to picosecond-resolved studies.

  5. An ultrafast terahertz probe of the transient evolution of the charged and neutral phase of photo-excited electron-hole gas in a monolayer semiconductor

    NASA Astrophysics Data System (ADS)

    Liu, Xuefeng; Yu, Hongyi; Ji, Qingqing; Gao, Zhihan; Ge, Shaofeng; Qiu, Jun; Liu, Zhongfan; Zhang, Yanfeng; Sun, Dong

    2016-03-01

    We investigate the dynamical formation of an exciton from photo-excited electron-hole plasma and its subsequent decay dynamics in monolayer MoS2 grown by chemical vapor deposition (CVD) using ultrafast pump and terahertz probe spectroscopy. Different photo-excited electron-hole states are resolved based on their distinct responses to THz photon and decay lifetimes. The observed transient THz transmission can be fitted with two decay components: a fast component with a decay lifetime of 20 ps, which is attributed to the exciton lifetime, including its formation and subsequent intra-exciton relaxation; a slow component with an extremely long decay lifetime of several ns, possibly due to a long-lived dark exciton state. The relaxation dynamics are further supported by temperature and pump-fluence-dependent studies of the decay time constants. The sign of the transient THz observed in this experiment is the opposite of that measured in a recent parallel transient THz work on MoS2 [1]. The observed decay dynamics are also different, and the possible reasons for these discrepancies are discussed.

  6. Impact of metal ions in porphyrin-based applied materials for visible-light photocatalysis: key information from ultrafast electronic spectroscopy.

    PubMed

    Kar, Prasenjit; Sardar, Samim; Alarousu, Erkki; Sun, Jingya; Seddigi, Zaki S; Ahmed, Saleh A; Danish, Ekram Y; Mohammed, Omar F; Pal, Samir Kumar

    2014-08-11

    Protoporphyrin IX-zinc oxide (PP-ZnO) nanohybrids have been synthesized for applications in photocatalytic devices. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and steady-state infrared, absorption, and emission spectroscopies have been used to analyze the structural details and optical properties of these nanohybrids. Time-resolved fluorescence and transient absorption techniques have been applied to study the ultrafast dynamic events that are key to photocatalytic activities. The photocatalytic efficiency under visible-light irradiation in the presence of naturally abundant iron(III) and copper(II) ions has been found to be significantly retarded in the former case, but enhanced in the latter case. More importantly, femtosecond (fs) transient absorption data have clearly demonstrated that the residence of photoexcited electrons from the sensitizer PP in the centrally located iron moiety hinders ground-state bleach recovery of the sensitizer, affecting the overall photocatalytic rate of the nanohybrid. The presence of copper(II) ions, on the other hand, offers additional stability against photobleaching and eventually enhances the efficiency of photocatalysis. In addition, we have also explored the role of UV light in the efficiency of photocatalysis and have rationalized our observations from femtosecond- to picosecond-resolved studies. PMID:25044047

  7. Ultrafast and steady-state laser heating effects on electron relaxation and phonon coupling mechanisms in thin gold films

    SciTech Connect

    Hopkins, Patrick E.; Duda, John C.; Kaehr, Bryan; Wang Zhou, Xiao; Peter Yang, C.-Y.; Jones, Reese E.

    2013-11-18

    We study the scattering mechanisms driving electron-phonon relaxation in thin gold films via pump-probe time-domain thermoreflectance. Electron-electron scattering can enhance the effective rate of electron-phonon relaxation when the electrons are out of equilibrium with the phonons. In order to correctly and consistently infer electron-phonon coupling factors in films on different substrates, we must account for the increase in steady-state lattice temperature due to laser heating. Our data provide evidence that a thermalized electron population will not directly exchange energy with the substrate during electron-phonon relaxation, whereas this pathway can exist between a non-equilibrium distribution of electrons and a non-metallic substrate.

  8. Modulation of ultrafast photoinduced electron transfer in H-bonding environment: PET from aniline to coumarin 153 in the presence of an inert co-solvent cyclohexane.

    PubMed

    Barman, Nabajeet; Hossen, Tousif; Mondal, Koushik; Sahu, Kalyanasis

    2015-12-28

    Despite intensive research, the role of the H-bonding environment on ultrafast PET remains illusive. For example, coumarin 153 (C153) undergoes ultrafast photoinduced electron transfer (PET) in electron-donating solvents, in both aniline (AN) and N,N-dimethylaniline (DMA), despite their very different H-bonding abilities. Thus, donor-acceptor (AN-C153) H-bonding may have only a minor role in PET (Yoshihara and co-workers, J. Phys. Chem. A, 1998, 102, 3089). However, donor-acceptor H-bonding may be somehow less effective in the neat H-bonding environment but could become dominant in the presence of an inert solvent (Phys. Chem. Chem. Phys., 2014, 16, 6159). We successfully applied and tested the proposal here. The nature of PET modulation of C153 in the presence of a passive component cyclohexane is found to be very different for aniline and DMA. Upon addition of cyclohexane to DMA, the PET process gradually becomes retarded but in the case of AN, the PET rate was indeed found to be accelerated at some intermediate composition (mole fraction of aniline, XAN∼ 0.74) compared to that of neat aniline. It is intuitive that cyclohexane may replace some of the donors (AN or DMA) from the vicinity of the acceptor and, thus, should disfavour PET. However, in the hydrogen bonding environment using molecular dynamics simulation, for the first time, we show that the average number of aniline molecules orienting their N-H group in the proximity of the C=O group of C153 is actually higher at the intermediate mole fraction (0.74) of aniline in a mixture rather than in neat aniline. This small but finite excess of C153-AN H-bonding already present in the ground state may possibly account for the anomalous effect. The TD-DFT calculations presented here showed that the intermolecular H-bonding between C153 and AN strengthens from 21.1 kJ mol(-1) in the ground state to 33.0 kJ mol(-1) in the excited state and, consequently, H-bonding may assist PET according to the Zhao and Han

  9. 4-D OCT in Developmental Cardiology

    NASA Astrophysics Data System (ADS)

    Jenkins, Michael W.; Rollins, Andrew M.

    Although strong evidence exists to suggest that altered cardiac function can lead to CHDs, few studies have investigated the influential role of cardiac function and biophysical forces on the development of the cardiovascular system due to a lack of proper in vivo imaging tools. 4-D imaging is needed to decipher the complex spatial and temporal patterns of biomechanical forces acting upon the heart. Numerous solutions over the past several years have demonstrated 4-D OCT imaging of the developing cardiovascular system. This chapter will focus on these solutions and explain their context in the evolution of 4-D OCT imaging. The first sections describe the relevant techniques (prospective gating, direct 4-D imaging, retrospective gating), while later sections focus on 4-D Doppler imaging and measurements of force implementing 4-D OCT Doppler. Finally, the techniques are summarized, and some possible future directions are discussed.

  10. Methods for studying the coherent 4D structural dynamics of free molecules and condensed state of matter

    NASA Astrophysics Data System (ADS)

    Ishchenko, A. A.; Bagratashvili, V. N.; Avilov, A. S.

    2011-09-01

    Studies in the coupled 4D spatial and temporal continuum are necessary for understanding the dynamic features of molecular systems with a complex profile of the potential energy surface. The introduction of time sweep into diffraction methods and the development of principles for studying coherent processes have revealed new approaches to the analysis of the dynamics of wave packets, the intermediate products and the transition state of the reaction center, and short-lived compounds in gaseous and condensed media. The use of picosecond and femtosecond electron probe pulses, synchronized with excitation laser pulses, determined the development of ultrafast electron crystallography, time-resolved X-ray diffraction, and dynamic transmission electron microscopy (DTEM). One of the most promising applications of the developed diffraction methods is the characterization and visualization of the processes occurring upon the photoexcitation of free molecules and biological objects and the analysis of surface and thin films. The whole set of spectral and diffraction methods based on different physical principles, which are complementary and make it possible to perform the photoexcitation of nuclei and electrons and carry out diagnostics of their dynamics at ultrashort time sequences, reveal new possibilities for studies with the necessary integration of the "structure-dynamics-function" triad in chemistry, biology, and materials science.

  11. Substitutional 4d and 5d impurities in graphene.

    PubMed

    Alonso-Lanza, Tomás; Ayuela, Andrés; Aguilera-Granja, Faustino

    2016-08-21

    We describe the structural and electronic properties of graphene doped with substitutional impurities of 4d and 5d transition metals. The adsorption energies and distances for 4d and 5d metals in graphene show similar trends for the later groups in the periodic table, which are also well-known characteristics of 3d elements. However, along earlier groups the 4d impurities in graphene show very similar adsorption energies, distances and magnetic moments to the 5d ones, which can be related to the influence of the 4d and 5d lanthanide contraction. Surprisingly, within the manganese group, the total magnetic moment of 3 μB for manganese is reduced to 1 μB for technetium and rhenium. We find that compared with 3d elements, the larger size of the 4d and 5d elements causes a high degree of hybridization with the neighbouring carbon atoms, reducing spin splitting in the d levels. It seems that the magnetic adjustment of graphene could be significantly different if 4d or 5d impurities are used instead of 3d impurities.

  12. Substitutional 4d and 5d impurities in graphene.

    PubMed

    Alonso-Lanza, Tomás; Ayuela, Andrés; Aguilera-Granja, Faustino

    2016-08-21

    We describe the structural and electronic properties of graphene doped with substitutional impurities of 4d and 5d transition metals. The adsorption energies and distances for 4d and 5d metals in graphene show similar trends for the later groups in the periodic table, which are also well-known characteristics of 3d elements. However, along earlier groups the 4d impurities in graphene show very similar adsorption energies, distances and magnetic moments to the 5d ones, which can be related to the influence of the 4d and 5d lanthanide contraction. Surprisingly, within the manganese group, the total magnetic moment of 3 μB for manganese is reduced to 1 μB for technetium and rhenium. We find that compared with 3d elements, the larger size of the 4d and 5d elements causes a high degree of hybridization with the neighbouring carbon atoms, reducing spin splitting in the d levels. It seems that the magnetic adjustment of graphene could be significantly different if 4d or 5d impurities are used instead of 3d impurities. PMID:27439363

  13. Ultrafast structural dynamics in metals

    NASA Astrophysics Data System (ADS)

    Nie, Shouhua

    Direct observation and understanding of atomic-level structural dynamics are important frontiers in scientific research and applications. Femtosecond electron diffraction (FED), a technique that combines time-resolved pump-probe and electron diffraction concepts, holds a great promise to reveal the dynamical processes of ultrafast phenomena in biology, chemistry and solid-state physics at the atomic time and length scales. This thesis presents the development of a tabletop femtosecond electron diffractometer and its applications to study the ultrafast structural dynamics of thin metal films. Using a delicate instrument design and careful experimental configuration, sub-picosecond temporal and sub-milli-angstrom spatial resolutions are maintained simultaneously in the diffractometer. Using this diffractometer, we have studied the dynamics of coherent and random thermal lattice motions initiated by femtosecond laser pulses in ultrathin metal films, and particularly, the mechanism of coherent acoustic phonon generation. We also introduce a new approach to measure the electronic Gruneisen parameter in metals using FED at and above room temperature. Finally, we study the ultrafast demagnetization process in ferromagnetic transition metal Ni by monitoring the transient lattice dynamics with FED.

  14. The Verification of the Usefulness of Electronic Nose Based on Ultra-Fast Gas Chromatography and Four Different Chemometric Methods for Rapid Analysis of Spirit Beverages

    PubMed Central

    Śliwińska, Magdalena; Namieśnik, Jacek; Wardencki, Waldemar; Dymerski, Tomasz

    2016-01-01

    Spirit beverages are a diverse group of foodstuffs. They are very often counterfeited which cause the appearance of low quality products or wrongly labelled products on the market. It is important to find a proper quality control and botanical origin method enabling the same time preliminary check of the composition of investigated samples, which was the main goal of this work. For this purpose, the usefulness of electronic nose based on ultra-fast gas chromatography (fast GC e-nose) was verified. A set of 24 samples of raw spirits, 33 samples of vodkas, and 8 samples of whisky were analysed by fast GC e-nose. Four data analysis methods were used. The PCA was applied for the visualization of dataset, observation of the variation inside groups of samples, and selection of variables for the other three statistical methods. The SQC method was utilized to compare the quality of the samples. Both the DFA and SIMCA data analysis methods were used for discrimination of vodka, whisky, and spirits samples. The fast GC e-nose combined with four statistical methods can be used for rapid discrimination of raw spirits, vodkas, and whisky and in the same for preliminary determination of the composition of investigated samples. PMID:27446633

  15. Ultrafast time-resolved electron diffraction revealing the nonthermal dynamics of near-UV photoexcitation-induced amorphization in Ge2Sb2Te5

    PubMed Central

    Hada, Masaki; Oba, Wataru; Kuwahara, Masashi; Katayama, Ikufumi; Saiki, Toshiharu; Takeda, Jun; Nakamura, Kazutaka G.

    2015-01-01

    Because of their robust switching capability, chalcogenide glass materials have been used for a wide range of applications, including optical storages devices. These phase transitions are achieved by laser irradiation via thermal processes. Recent studies have suggested the potential of nonthermal phase transitions in the chalcogenide glass material Ge2Sb2Te5 triggered by ultrashort optical pulses; however, a detailed understanding of the amorphization and damage mechanisms governed by nonthermal processes is still lacking. Here we performed ultrafast time-resolved electron diffraction and single-shot optical pump-probe measurements followed by femtosecond near-ultraviolet pulse irradiation to study the structural dynamics of polycrystalline Ge2Sb2Te5. The experimental results present a nonthermal crystal-to-amorphous phase transition of Ge2Sb2Te5 initiated by the displacements of Ge atoms. Above the fluence threshold, we found that the permanent amorphization caused by multi-displacement effects is accompanied by a partial hexagonal crystallization. PMID:26314613

  16. Ultrafast time-resolved electron diffraction revealing the nonthermal dynamics of near-UV photoexcitation-induced amorphization in Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Hada, Masaki; Oba, Wataru; Kuwahara, Masashi; Katayama, Ikufumi; Saiki, Toshiharu; Takeda, Jun; Nakamura, Kazutaka G.

    2015-08-01

    Because of their robust switching capability, chalcogenide glass materials have been used for a wide range of applications, including optical storages devices. These phase transitions are achieved by laser irradiation via thermal processes. Recent studies have suggested the potential of nonthermal phase transitions in the chalcogenide glass material Ge2Sb2Te5 triggered by ultrashort optical pulses; however, a detailed understanding of the amorphization and damage mechanisms governed by nonthermal processes is still lacking. Here we performed ultrafast time-resolved electron diffraction and single-shot optical pump-probe measurements followed by femtosecond near-ultraviolet pulse irradiation to study the structural dynamics of polycrystalline Ge2Sb2Te5. The experimental results present a nonthermal crystal-to-amorphous phase transition of Ge2Sb2Te5 initiated by the displacements of Ge atoms. Above the fluence threshold, we found that the permanent amorphization caused by multi-displacement effects is accompanied by a partial hexagonal crystallization.

  17. The Verification of the Usefulness of Electronic Nose Based on Ultra-Fast Gas Chromatography and Four Different Chemometric Methods for Rapid Analysis of Spirit Beverages.

    PubMed

    Wiśniewska, Paulina; Śliwińska, Magdalena; Namieśnik, Jacek; Wardencki, Waldemar; Dymerski, Tomasz

    2016-01-01

    Spirit beverages are a diverse group of foodstuffs. They are very often counterfeited which cause the appearance of low quality products or wrongly labelled products on the market. It is important to find a proper quality control and botanical origin method enabling the same time preliminary check of the composition of investigated samples, which was the main goal of this work. For this purpose, the usefulness of electronic nose based on ultra-fast gas chromatography (fast GC e-nose) was verified. A set of 24 samples of raw spirits, 33 samples of vodkas, and 8 samples of whisky were analysed by fast GC e-nose. Four data analysis methods were used. The PCA was applied for the visualization of dataset, observation of the variation inside groups of samples, and selection of variables for the other three statistical methods. The SQC method was utilized to compare the quality of the samples. Both the DFA and SIMCA data analysis methods were used for discrimination of vodka, whisky, and spirits samples. The fast GC e-nose combined with four statistical methods can be used for rapid discrimination of raw spirits, vodkas, and whisky and in the same for preliminary determination of the composition of investigated samples. PMID:27446633

  18. Infrared and electronic absorption spectra as well as ultrafast spin dynamics in isolated Co3+(EtOH) and Co3+(EtOH,H2O) clusters

    NASA Astrophysics Data System (ADS)

    Jin, Wei; Becherer, Markus; Bellaire, Daniel; Lefkidis, Georgios; Gerhards, Markus; Hübner, Wolfgang

    2014-04-01

    We present a combined theoretical and experimental study of the infrared (IR) and electronic absorption spectra in a molecular beam experiment as well as an analysis of spin dynamics in the clusters Co3+(EtOH) and Co3+(EtOH,H2O). The calculated IR and ground-state absorption spectra show very good agreement with experiment. By using high-level quantum chemistry methods, laser-induced ultrafast spin-flip scenarios in these structures are predicted. For the spin flip in Co3+(EtOH), our investigation indicates a 5 meV tolerance with respect to the laser detuning and a 6.5 meV tolerance with respect to the pulse spectral broadening, which are quite acceptable for the experimental implementation. In addition, we find that with the increase of the laser detuning the fitness of the processes gradually decays to zero on both sides but with different origins. This joint study of the homotrinuclear clusters provides insight into the experimentally observed spectra and optical properties, and steps towards the optical control of molecular magnetism for future spintronics application.

  19. The Verification of the Usefulness of Electronic Nose Based on Ultra-Fast Gas Chromatography and Four Different Chemometric Methods for Rapid Analysis of Spirit Beverages.

    PubMed

    Wiśniewska, Paulina; Śliwińska, Magdalena; Namieśnik, Jacek; Wardencki, Waldemar; Dymerski, Tomasz

    2016-01-01

    Spirit beverages are a diverse group of foodstuffs. They are very often counterfeited which cause the appearance of low quality products or wrongly labelled products on the market. It is important to find a proper quality control and botanical origin method enabling the same time preliminary check of the composition of investigated samples, which was the main goal of this work. For this purpose, the usefulness of electronic nose based on ultra-fast gas chromatography (fast GC e-nose) was verified. A set of 24 samples of raw spirits, 33 samples of vodkas, and 8 samples of whisky were analysed by fast GC e-nose. Four data analysis methods were used. The PCA was applied for the visualization of dataset, observation of the variation inside groups of samples, and selection of variables for the other three statistical methods. The SQC method was utilized to compare the quality of the samples. Both the DFA and SIMCA data analysis methods were used for discrimination of vodka, whisky, and spirits samples. The fast GC e-nose combined with four statistical methods can be used for rapid discrimination of raw spirits, vodkas, and whisky and in the same for preliminary determination of the composition of investigated samples.

  20. Advances in 4D radiation therapy for managing respiration: part I - 4D imaging.

    PubMed

    Hugo, Geoffrey D; Rosu, Mihaela

    2012-12-01

    Techniques for managing respiration during imaging and planning of radiation therapy are reviewed, concentrating on free-breathing (4D) approaches. First, we focus on detailing the historical development and basic operational principles of currently-available "first generation" 4D imaging modalities: 4D computed tomography, 4D cone beam computed tomography, 4D magnetic resonance imaging, and 4D positron emission tomography. Features and limitations of these first generation systems are described, including necessity of breathing surrogates for 4D image reconstruction, assumptions made in acquisition and reconstruction about the breathing pattern, and commonly-observed artifacts. Both established and developmental methods to deal with these limitations are detailed. Finally, strategies to construct 4D targets and images and, alternatively, to compress 4D information into static targets and images for radiation therapy planning are described.

  1. Advances in 4D Radiation Therapy for Managing Respiration: Part I – 4D Imaging

    PubMed Central

    Hugo, Geoffrey D.; Rosu, Mihaela

    2014-01-01

    Techniques for managing respiration during imaging and planning of radiation therapy are reviewed, concentrating on free-breathing (4D) approaches. First, we focus on detailing the historical development and basic operational principles of currently-available “first generation” 4D imaging modalities: 4D computed tomography, 4D cone beam computed tomography, 4D magnetic resonance imaging, and 4D positron emission tomography. Features and limitations of these first generation systems are described, including necessity of breathing surrogates for 4D image reconstruction, assumptions made in acquisition and reconstruction about the breathing pattern, and commonly-observed artifacts. Both established and developmental methods to deal with these limitations are detailed. Finally, strategies to construct 4D targets and images and, alternatively, to compress 4D information into static targets and images for radiation therapy planning are described. PMID:22784929

  2. ULTRAFAST ELECTRON SPIN DYNAMICS OF AS-GROWN Ga1-xMnxAs WITH APPROPRIATE Mn DOPING

    NASA Astrophysics Data System (ADS)

    Yue, Han

    2013-06-01

    The electron spin dynamics in the as-grown Ga1-xMnxAs films with appropriate Mn doping of x 2-5% is studied using time-resolved magneto-optical Kerr effect measurements. Due to the existence of Mn interstitials, the s-d exchange scattering is found to play an important role for the as-grown Ga1-xMnxAs, and compete with p-d exchange coupling to dominate the electron spin relaxation process. The contribution of electron-electron Coulomb scattering to the electron spin dynamics for the as-grown Ga1-x MnxAs appears to be as important as that of the annealed ones. Our findings are fundamentally important for better understanding the electron spin dynamics in Ga1-xMnxAs for its future spintronic applications.

  3. Partially coherent ultrafast spectrography

    PubMed Central

    Bourassin-Bouchet, C.; Couprie, M.-E.

    2015-01-01

    Modern ultrafast metrology relies on the postulate that the pulse to be measured is fully coherent, that is, that it can be completely described by its spectrum and spectral phase. However, synthesizing fully coherent pulses is not always possible in practice, especially in the domain of emerging ultrashort X-ray sources where temporal metrology is strongly needed. Here we demonstrate how frequency-resolved optical gating (FROG), the first and one of the most widespread techniques for pulse characterization, can be adapted to measure partially coherent pulses even down to the attosecond timescale. No modification of experimental apparatuses is required; only the processing of the measurement changes. To do so, we take our inspiration from other branches of physics where partial coherence is routinely dealt with, such as quantum optics and coherent diffractive imaging. This will have important and immediate applications, such as enabling the measurement of X-ray free-electron laser pulses despite timing jitter. PMID:25744080

  4. Partially coherent ultrafast spectrography

    NASA Astrophysics Data System (ADS)

    Bourassin-Bouchet, C.; Couprie, M.-E.

    2015-03-01

    Modern ultrafast metrology relies on the postulate that the pulse to be measured is fully coherent, that is, that it can be completely described by its spectrum and spectral phase. However, synthesizing fully coherent pulses is not always possible in practice, especially in the domain of emerging ultrashort X-ray sources where temporal metrology is strongly needed. Here we demonstrate how frequency-resolved optical gating (FROG), the first and one of the most widespread techniques for pulse characterization, can be adapted to measure partially coherent pulses even down to the attosecond timescale. No modification of experimental apparatuses is required; only the processing of the measurement changes. To do so, we take our inspiration from other branches of physics where partial coherence is routinely dealt with, such as quantum optics and coherent diffractive imaging. This will have important and immediate applications, such as enabling the measurement of X-ray free-electron laser pulses despite timing jitter.

  5. Ultrafast electronic response of Ag(111) and Cu(111) surfaces: From early excitonic transients to saturated image potential

    NASA Astrophysics Data System (ADS)

    Silkin, V. M.; Lazić, P.; Došlić, N.; Petek, H.; Gumhalter, B.

    2015-10-01

    We investigate the evolution of attosecond to femtosecond screening and emergent potentials that govern the dynamics and energetics of electrons and holes excited in the various stages of multiphoton photoemission processes and control the photoelectron yield in recently reported experiments [X. Cui, C. Wang, A. Argondizzo, S. Garrett-Roe, B. Gumhalter, and H. Petek, Nat. Phys. 10, 505 (2014), 10.1038/nphys2981]. The study is focused on the dynamical screening of holes created in preexistent quasi-two-dimensional Shockley state bands on Ag(111) and Cu(111) surfaces and of electrons excited to the intermediate and emerging screened states. Using the formalism of self-consistent electronic response, we analyze first the effects of screening on the dynamics of photoexcited electrons and holes and then of the Coulomb correlated photoexcited pair. Special attention is paid to the correlated primary electron-hole states, which commence as transient surface excitons and develop in the course of screening into uncorrelated electrons and holes propagating in the image potential and surface state bands, respectively. The obtained results enable to establish a consistent picture of transient electron dynamics at Ag(111) and Cu(111) surfaces that are becoming accessible by the time-, energy-, and momentum-resolved pump-probe multiphoton photoelectron spectroscopies.

  6. Semiconductors Under Ion Radiation: Ultrafast Electron-Ion Dynamics in Perfect Crystals and the Effect of Defects

    NASA Astrophysics Data System (ADS)

    Lee, Cheng-Wei; Schleife, André

    Stability and safety issues have been challenging difficulties for materials and devices under radiation such as solar panels in outer space. On the other hand, radiation can be utilized to modify materials and increase their performance via focused-ion beam patterning at nano-scale. In order to grasp the underlying processes, further understanding of the radiation-material and radiation-defect interactions is required and inevitably involves the electron-ion dynamics that was traditionally hard to capture. By applying Ehrenfest dynamics based on time-dependent density functional theory, we have been able to perform real-time simulation of electron-ion dynamics in MgO and InP/GaP. By simulating a high-energy proton penetrating the material, the energy gain of electronic system can be interpreted as electronic stopping power and the result is compared to existing data. We also study electronic stopping in the vicinity of defects: for both oxygen vacancy in MgO and interface of InP/GaP superlattice, electronic stopping shows strong dependence on the velocity of the proton. To study the energy transfer from electronic system to lattice, simulations of about 100 femto-seconds are performed and we analyze the difference between Ehrenfest and Born-Oppenheimer molecular dynamics.

  7. Ultrafast and Efficient Transport of Hot Plasmonic Electrons by Graphene for Pt Free, Highly Efficient Visible-Light Responsive Photocatalyst.

    PubMed

    Kumar, Dinesh; Lee, Ahreum; Lee, Taegon; Lim, Manho; Lim, Dong-Kwon

    2016-03-01

    We report that reduced graphene-coated gold nanoparticles (r-GO-AuNPs) are excellent visible-light-responsive photocatalysts for the photoconversion of CO2 into formic acid (HCOOH). The wavelength-dependent quantum and chemical yields of HCOOH shows a significant contribution of plasmon-induced hot electrons for CO2 photoconversion. Furthermore, the presence and reduced state of the graphene layers are critical parameters for the efficient CO2 photoconversion because of the electron mobility of graphene. With an excellent selectivity toward HCOOH (>90%), the quantum yield of HCOOH using r-GO-AuNPs is 1.52%, superior to that of Pt-coated AuNPs (quantum yield: 1.14%). This indicates that r-GO is a viable alternative to platinum metal. The excellent colloidal stability and photocatalytic stability of r-GO-AuNPs enables CO2 photoconversion under more desirable reaction conditions. These results highlight the role of reduced graphene layers as highly efficient electron acceptors and transporters to facilitate the use of hot electrons for plasmonic photocatalysts. The femtosecond transient spectroscopic analysis also shows 8.7 times higher transport efficiency of hot plasmonic electrons in r-GO-AuNPs compared with AuNPs. PMID:26854830

  8. Los Alamos National Laboratory 4D Database

    SciTech Connect

    Atencio, Julian J.

    2014-05-02

    4D is an integrated development platform - a single product comprised of the components you need to create and distribute professional applications. You get a graphical design environment, SQL database, a programming language, integrated PHP execution, HTTP server, application server, executable generator, and much more. 4D offers multi-platform development and deployment, meaning whatever you create on a Mac can be used on Windows, and vice-versa. Beyond productive development, 4D is renowned for its great flexibility in maintenance and modification of existing applications, and its extreme ease of implementation in its numerous deployment options. Your professional application can be put into production more quickly, at a lower cost, and will always be instantly scalable. 4D makes it easy, whether you're looking to create a classic desktop application, a client-server system, a distributed solution for Web or mobile clients - or all of the above!

  9. Indirect excitation of ultrafast demagnetization

    PubMed Central

    Vodungbo, Boris; Tudu, Bahrati; Perron, Jonathan; Delaunay, Renaud; Müller, Leonard; Berntsen, Magnus H.; Grübel, Gerhard; Malinowski, Grégory; Weier, Christian; Gautier, Julien; Lambert, Guillaume; Zeitoun, Philippe; Gutt, Christian; Jal, Emmanuelle; Reid, Alexander H.; Granitzka, Patrick W.; Jaouen, Nicolas; Dakovski, Georgi L.; Moeller, Stefan; Minitti, Michael P.; Mitra, Ankush; Carron, Sebastian; Pfau, Bastian; von Korff Schmising, Clemens; Schneider, Michael; Eisebitt, Stefan; Lüning, Jan

    2016-01-01

    Does the excitation of ultrafast magnetization require direct interaction between the photons of the optical pump pulse and the magnetic layer? Here, we demonstrate unambiguously that this is not the case. For this we have studied the magnetization dynamics of a ferromagnetic cobalt/palladium multilayer capped by an IR-opaque aluminum layer. Upon excitation with an intense femtosecond-short IR laser pulse, the film exhibits the classical ultrafast demagnetization phenomenon although only a negligible number of IR photons penetrate the aluminum layer. In comparison with an uncapped cobalt/palladium reference film, the initial demagnetization of the capped film occurs with a delayed onset and at a slower rate. Both observations are qualitatively in line with energy transport from the aluminum layer into the underlying magnetic film by the excited, hot electrons of the aluminum film. Our data thus confirm recent theoretical predictions. PMID:26733106

  10. Indirect excitation of ultrafast demagnetization.

    PubMed

    Vodungbo, Boris; Tudu, Bharati; Tudu, Bahrati; Perron, Jonathan; Delaunay, Renaud; Müller, Leonard; Berntsen, Magnus H; Grübel, Gerhard; Malinowski, Grégory; Weier, Christian; Gautier, Julien; Lambert, Guillaume; Zeitoun, Philippe; Gutt, Christian; Jal, Emmanuelle; Reid, Alexander H; Granitzka, Patrick W; Jaouen, Nicolas; Dakovski, Georgi L; Moeller, Stefan; Minitti, Michael P; Mitra, Ankush; Carron, Sebastian; Pfau, Bastian; von Korff Schmising, Clemens; Schneider, Michael; Eisebitt, Stefan; Lüning, Jan

    2016-01-01

    Does the excitation of ultrafast magnetization require direct interaction between the photons of the optical pump pulse and the magnetic layer? Here, we demonstrate unambiguously that this is not the case. For this we have studied the magnetization dynamics of a ferromagnetic cobalt/palladium multilayer capped by an IR-opaque aluminum layer. Upon excitation with an intense femtosecond-short IR laser pulse, the film exhibits the classical ultrafast demagnetization phenomenon although only a negligible number of IR photons penetrate the aluminum layer. In comparison with an uncapped cobalt/palladium reference film, the initial demagnetization of the capped film occurs with a delayed onset and at a slower rate. Both observations are qualitatively in line with energy transport from the aluminum layer into the underlying magnetic film by the excited, hot electrons of the aluminum film. Our data thus confirm recent theoretical predictions. PMID:26733106

  11. Indirect excitation of ultrafast demagnetization

    DOE PAGES

    Vodungbo, Boris; Tudu, Bahrati; Perron, Jonathan; Delaunay, Renaud; Müller, Leonard; Berntsen, Magnus H.; Grübel, Gerhard; Malinowski, Grégory; Weier, Christian; Gautier, Julien; et al

    2016-01-06

    Does the excitation of ultrafast magnetization require direct interaction between the photons of the optical pump pulse and the magnetic layer? Here, we demonstrate unambiguously that this is not the case. For this we have studied the magnetization dynamics of a ferromagnetic cobalt/palladium multilayer capped by an IR-opaque aluminum layer. Upon excitation with an intense femtosecond-short IR laser pulse, the film exhibits the classical ultrafast demagnetization phenomenon although only a negligible number of IR photons penetrate the aluminum layer. In comparison with an uncapped cobalt/palladium reference film, the initial demagnetization of the capped film occurs with a delayed onset andmore » at a slower rate. Both observations are qualitatively in line with energy transport from the aluminum layer into the underlying magnetic film by the excited, hot electrons of the aluminum film. As a result, our data thus confirm recent theoretical predictions.« less

  12. Time-Dependent Multiconfiguration Theory and Its Application to Ultrafast Electronic Dynamics of Molecules in an Intense Laser Field

    NASA Astrophysics Data System (ADS)

    Kato, T.; Oyamada, T.; Kono, H.; Koseki, S.

    We outlined a time-dependent multiconfiguration theory todescribe electronic dynamics of molecules, where the many-electron wave function at time t, Φ(t), is expanded in terms of different electron configurations Φ_I(t) composed of time-dependent one-electron orbitals (spin-orbitals) as Φ(t) = sum_I C_I(t) Φ_I(t). The equations of motion (EOMs) for spin-orbitals in coordinate representation are derived together with the EOMs for configuration interaction coefficients C_I(t). As an example of application to molecules, we presented the results of investigation of the ionization dynamics of H_2 interacting with a near-infrared intense laser filed. By extending the concept of Hartree-Fock orbital energy to multiconfiguration theory, we newly introduced the ``molecular orbital energies" of natural spin-orbitals (NSOs) { j } of a many-electron system and defined the orbital potentials bar{ɛ}_j (t) and correlation energies V^c_j(t) of NSOs. The total energy E(t) is decomposed into individual components as E(t) = sum_j ω_j(t) bar{ɛ}_j (t) as in thermodynamics, where ω_j(t) are the occupation numbers of { j }. We proved that this type of partition of the total energy is interpreted as the time-dependent chemical potential for the two-electron system. The newly defined correlation energy V^c_j(t) associated with the {j}th NSO, involved in bar{ɛ}_j (t), reflects dynamical electron correlations on the attosecond timescale. We also compared the energy ζ_j(t) directly supplied by the applied field with the net energy gain Δbar{{ɛ}}_j(t) for respective natural orbitals. The responses of natural orbitals can be classified into three: Δbar{{ɛ}}_j(t) = ζ_j(t) (spectator orbital); Δbar{{ɛ}}_j(t) < ζ_j(t) (energy donor orbital); and Δbar{{ɛ}}_j(t) > ζ_j(t) (energy acceptor orbital). We found that ionization of H_2 most efficiently occurs from a time-developing energy acceptor NSO 2σ_g for the case of the present applied field. We concluded that energy acceptor

  13. Ultrafast Strong-Field Photoemission from Plasmonic Nanoparticles

    PubMed Central

    2013-01-01

    We demonstrate the ultrafast generation of electrons from tailored metallic nanoparticles and unravel the role of plasmonic field enhancement in this process by comparing resonant and off-resonant particles, as well as different particle geometries. We find that electrons become strongly accelerated within the evanescent fields of the plasmonic nanoparticles and escape along straight trajectories with orientations governed by the particle geometry. These results establish plasmonic nanoparticles as versatile ultrafast, nanoscopic sources of electrons. PMID:23339740

  14. Helical 4D CT and Comparison with Cine 4D CT

    NASA Astrophysics Data System (ADS)

    Pan, Tinsu

    4D CT was one of the most important developments in radiation oncology in the last decade. Its early development in single slice CT and commercialization in multi-slice CT has radically changed our practice in radiation treatment of lung cancer, and has enabled the stereotactic radiosurgery of early stage lung cancer. In this chapter, we will document the history of 4D CT development, detail the data sufficiency condition governing the 4D CT data collection; present the design of the commercial helical 4D CTs from Philips and Siemens; compare the differences between the helical 4D CT and the GE cine 4D CT in data acquisition, slice thickness, acquisition time and work flow; review the respiratory monitoring devices; and understand the causes of image artifacts in 4D CT.

  15. Excitation laser energy dependence of surface-enhanced fluorescence showing plasmon-induced ultrafast electronic dynamics in dye molecules

    NASA Astrophysics Data System (ADS)

    Itoh, Tamitake; Yamamoto, Yuko S.; Tamaru, Hiroharu; Biju, Vasudevanpillai; Murase, Norio; Ozaki, Yukihiro

    2013-06-01

    We find unique properties accompanying surface-enhanced fluorescence (SEF) from dye molecules adsorbed on Ag nanoparticle aggregates, which generate surface-enhanced Raman scattering. The properties are observed in excitation laser energy dependence of SEF after excluding plasmonic spectral modulation in SEF. The unique properties are large blue shifts of fluorescence spectra, deviation of ratios between anti-Stokes SEF intensity and Stokes from those of normal fluorescence, super-broadening of Stokes spectra, and returning to original fluorescence by lower energy excitation. We elucidate that these properties are induced by electromagnetic enhancement of radiative decay rates exceeding the vibrational relaxation rates within an electronic excited state, which suggests that molecular electronic dynamics in strong plasmonic fields can be largely deviated from that in free space.

  16. Cooperative catalysis: electron-rich Fe-H complexes and DMAP, a successful "joint venture" for ultrafast hydrogen production.

    PubMed

    Rommel, Susanne; Hettmanczyk, Lara; Klein, Johannes E M N; Plietker, Bernd

    2014-08-01

    A series of defined iron-hydrogen complexes was prepared in a straightforward one-pot approach. The structure and electronic properties of such complexes were investigated by means of quantum-chemical analysis. These new complexes were then applied in the dehydrogenative silylation of methanol. The complex (dppp)(CO)(NO)FeH showed a remarkable activity with a TOF of more than 600 000 h(-1) of pure hydrogen gas within seconds.

  17. Synthesis, optical properties and ultrafast electronic relaxation of layered semiconductor nanoparticles: Lead iodide, bismuth iodide, bismuth sulfide

    NASA Astrophysics Data System (ADS)

    Sengupta, Archita

    The first direct observation of the electronic relaxation dynamics in PbI2, BiI3 and Bi2S3 nanoparticles using femtosecond transient spectroscopy has been reported. The nanoparticles were synthesized in polar and nonpolar solvents, polymer matrices and inverse micelles using colloidal chemistry methods and in thin films. The particle sizes were determined using TEM which provided direct evidence of photodegradation of nanoparticles. The ground state electronic absorption spectra of PbI 2 and BiI3 colloidal nanoparticles show well-resolved peaks in the near UV and visible region. Using a particle in an anisotropic box model the blue shift and increase in absorption of these peaks with simultaneous decrease in particle size have been explained. The UV-visible absorption spectra of Bi2S3 colloidal nanoparticles have very different features compared to those of PbI2 and BiI3 nanoparticles. Similarities and differences found among these nanoparticle systems, PbI 2, BiI3 and Bi2S3, in terms of optical properties and femtosecond electronic relaxation dynamics have been discussed. For PbI2, BiI3 and Bi2S3 with excitation at 390 nm and probing in the near infrared, the electronic relaxation dynamics were directly monitored and found to be sensitive to solvent and insensitive to particle size. For both PbI2 and BiI3 there appeared to be an oscillatory feature at early times with a period changing with solvent but not with particle size. However, for BiI3, the oscillation periods were slightly shorter and overall relaxation was somewhat faster than that in PbI2. The possibilities of the origin of this feature have been addressed. For Bi2S3 system, the early time dynamics did not show any resolvable oscillation. It could be due to the fact that the origin of oscillations in PbI2 and BiI3 nanoparticle system is connected to layered iodide structure and thus is not found in layered sulfide structure or the feature was not observed due to overall fast relaxation in Bi2S3

  18. 4D flow imaging with MRI

    PubMed Central

    Stankovic, Zoran; Allen, Bradley D.; Garcia, Julio; Jarvis, Kelly B.

    2014-01-01

    Magnetic resonance imaging (MRI) has become an important tool for the clinical evaluation of patients with cardiovascular disease. Since its introduction in the late 1980s, 2-dimensional phase contrast MRI (2D PC-MRI) has become a routine part of standard-of-care cardiac MRI for the assessment of regional blood flow in the heart and great vessels. More recently, time-resolved PC-MRI with velocity encoding along all three flow directions and three-dimensional (3D) anatomic coverage (also termed ‘4D flow MRI’) has been developed and applied for the evaluation of cardiovascular hemodynamics in multiple regions of the human body. 4D flow MRI allows for the comprehensive evaluation of complex blood flow patterns by 3D blood flow visualization and flexible retrospective quantification of flow parameters. Recent technical developments, including the utilization of advanced parallel imaging techniques such as k-t GRAPPA, have resulted in reasonable overall scan times, e.g., 8-12 minutes for 4D flow MRI of the aorta and 10-20 minutes for whole heart coverage. As a result, the application of 4D flow MRI in a clinical setting has become more feasible, as documented by an increased number of recent reports on the utility of the technique for the assessment of cardiac and vascular hemodynamics in patient studies. A number of studies have demonstrated the potential of 4D flow MRI to provide an improved assessment of hemodynamics which might aid in the diagnosis and therapeutic management of cardiovascular diseases. The purpose of this review is to describe the methods used for 4D flow MRI acquisition, post-processing and data analysis. In addition, the article provides an overview of the clinical applications of 4D flow MRI and includes a review of applications in the heart, thoracic aorta and hepatic system. PMID:24834414

  19. Ultra-fast framing camera tube

    DOEpatents

    Kalibjian, Ralph

    1981-01-01

    An electronic framing camera tube features focal plane image dissection and synchronized restoration of the dissected electron line images to form two-dimensional framed images. Ultra-fast framing is performed by first streaking a two-dimensional electron image across a narrow slit, thereby dissecting the two-dimensional electron image into sequential electron line images. The dissected electron line images are then restored into a framed image by a restorer deflector operated synchronously with the dissector deflector. The number of framed images on the tube's viewing screen is equal to the number of dissecting slits in the tube. The distinguishing features of this ultra-fast framing camera tube are the focal plane dissecting slits, and the synchronously-operated restorer deflector which restores the dissected electron line images into a two-dimensional framed image. The framing camera tube can produce image frames having high spatial resolution of optical events in the sub-100 picosecond range.

  20. Phosphodiesterase4D (PDE4D)--A risk factor for atrial fibrillation and stroke?

    PubMed

    Jørgensen, Carina; Yasmeen, Saiqa; Iversen, Helle K; Kruuse, Christina

    2015-12-15

    Mutations in the gene encoding phosphodiesterase 4D (PDE4D) enzyme are associated with ischemic stroke; however the functional implications of such mutations are not well understood. PDE4D is part of a complex protein family modulating intracellular signalling by cyclic nucleotides. The PDE4 family includes subtypes A-D, all of which show unique intracellular, cellular and tissue distribution. PDE4D is the major subtype expressed in human atrial myocytes and involved in the pathophysiology of arrhythmias, such as atrial fibrillation. The PDE4D enzyme hydrolyses cyclic adenosine monophosphate (cAMP). Though diverging results are reported, several population based studies describe association of various PDE4D single nucleotide polymorphisms (SNP) with cardio-embolic stroke in particular. Functionally, a down regulation of PDE4D variants has been reported in stroke patients. The anti-inflammatory and vasodilator properties of PDE4 inhibitors make them suitable for treatment of stroke and cardiovascular disease. PDE4D has recently been suggested as factor in atrial fibrillation. This review summarizes the possible function of PDE4D in the brain, heart, and vasculature. Further, association of the described SNPs, in particular, with cardioembolic stroke, is reviewed. Current findings on the PDE4D mutations suggest functionality involves an increased cardiac risk factor as well as augmented risk of atrial fibrillation. PMID:26671126

  1. Attosecond Light and Science at the Time-scale of the Electron - Coherent X-Rays from Tabletop Ultrafast Lasers

    SciTech Connect

    Margaret, Murnane

    2010-03-31

    Ever since the invention of the laser 50 years ago and its application in nonlinear optics, scientists have been striving to extend coherent laser beams into the x-ray region of the spectrum. Very recently however, the prospects for tabletop coherent sources at very short wavelengths, even in the hard x-ray region of the spectrum at wavelengths < 1nm, have brightened considerably. This advance is possible by taking nonlinear optics techniques to an extreme - physics that is the direct result of a new ability to manipulate electrons on the fastest, attosecond, time-scales of our natural world. Several applications have already been demonstrated, including making a movie of how electrons rearrange in a chemical bond changes shape as a molecule breaks apart, following how fast a magnetic material can flip orientation, understanding how fast heat flows in a nanocircuit, or building a microscope without lenses. Nature 460, 1088 (2009); Science 317, 775 (2007); Physical Review Letters 103, 257402 (2009); Nature Materials 9, 26 (2010); Nature 463, 214 (2010); Science 322, 1207 (2008).

  2. Imaging molecules from within: Ultrafast angstroem-scale structure determination of molecules via photoelectron holography using free-electron lasers

    SciTech Connect

    Krasniqi, F.; Rolles, D.; Najjari, B.; Voitkiv, A.; Strueder, L.; Ullrich, J.

    2010-03-15

    A scheme based on (i) upcoming brilliant x-ray free-electron laser (FEL) sources, (ii) innovative energy and angular-dispersive large-area electron imagers, and (iii) the well-known photoelectron holography is elaborated that provides time-dependent three-dimensional structure determination of small to medium-sized molecules with Angstroem spatial and femtosecond time resolution. Inducing molecular dynamics, wave-packet motion, dissociation, passage through conical intersections, or isomerization by a pump pulse this motion is visualized by the x-ray FEL probe pulse launching keV photoelectrons within a few femtoseconds from specific and well-defined sites, deep core levels of individual atoms, inside the molecule. On their way out, the photoelectrons are diffracted generating a hologram on the detector that encodes the molecular structure at the instant of photoionization, thus providing 'femtosecond snapshot images of the molecule from within'. Detailed calculations in various approximations of increasing sophistication are presented and three-dimensional retrieval of the spatial structure of the molecule with Angstroem spatial resolution is demonstrated. Due to the large photoabsorption cross sections the method extends x-ray-diffraction-based time-dependent structure investigations envisioned at FEL's to new classes of samples that are not accessible by any other method. Among them are dilute samples in the gas phase such as aligned, oriented, or conformer-selected molecules, ultracold ensembles and/or molecular or cluster objects containing mainly light atoms that do not scatter x rays efficiently.

  3. Attosecond Light and Science at the Time-scale of the Electron - Coherent X-Rays from Tabletop Ultrafast Lasers

    ScienceCinema

    Margaret, Murnane [University of Colorado, Boulder and NIST

    2016-07-12

    Ever since the invention of the laser 50 years ago and its application in nonlinear optics, scientists have been striving to extend coherent laser beams into the x-ray region of the spectrum. Very recently however, the prospects for tabletop coherent sources at very short wavelengths, even in the hard x-ray region of the spectrum at wavelengths < 1nm, have brightened considerably. This advance is possible by taking nonlinear optics techniques to an extreme - physics that is the direct result of a new ability to manipulate electrons on the fastest, attosecond, time-scales of our natural world. Several applications have already been demonstrated, including making a movie of how electrons rearrange in a chemical bond changes shape as a molecule breaks apart, following how fast a magnetic material can flip orientation, understanding how fast heat flows in a nanocircuit, or building a microscope without lenses. Nature 460, 1088 (2009); Science 317, 775 (2007); Physical Review Letters 103, 257402 (2009); Nature Materials 9, 26 (2010); Nature 463, 214 (2010); Science 322, 1207 (2008).

  4. First Results on Ultrafast and Ultraintense X-Ray Studies of Molecular Photoabsorption using the LCLS Free Electron Laser

    NASA Astrophysics Data System (ADS)

    Berrah, Nora

    2010-03-01

    The study of atomic and molecular inner-shell photoionization with conventional x-ray sources is dominated by processes involving the production of single core holes. However, the unprecedented short pulses and peak power at x-ray wavelengths of the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory provides new research opportunities and opens the door to study ultra fast, nonlinear x-ray physics. We have used the LCLS to investigate fundamental questions concerning laser pulse duration dependent ionization as well as examine the creation and decay of multiple core-holes. In particular, we focused on double core-holes ionization in N2. We measured the photoelectron, Auger and secondary electron relaxation pathways subsequent to multiple core vacancies in molecules as well as the fragmentation patterns and the charge-state distributions of the resulting ions as a function of wavelength, pulse duration and intensity. The new light source allows the characterization of the molecular ionization and dissociation dynamics and provides new insight into the interaction of matter with intense short pulses. In addition we expect our results to contribute to the foundation for future imaging experiments on molecules. The LCLS photon beam was focused to about 2μm^2 area producing an intense x-ray laser beam of up to 10^18 W/cm^2. We have used x-ray pulses with duration from about 7fs to 280 fs and a photon energy of 1.1 keV to investigate the production of multiple core holes. We have observed the multiple ionization of N2 resulting in fragment ions of up to bare N^7+ [1]. Furthermore, evidence for double core hole has been observed. The experiment was performed at the LCLS AMO beamline which is equipped with an ion time-of-flight spectrometer to determine the ion charge state distribution as well five angle and energy resolving electron time-of-flight spectrometers to detect the emitted photoelectrons and Auger electrons. [4pt] [1] Work done in

  5. Shadow-driven 4D haptic visualization.

    PubMed

    Zhang, Hui; Hanson, Andrew

    2007-01-01

    Just as we can work with two-dimensional floor plans to communicate 3D architectural design, we can exploit reduced-dimension shadows to manipulate the higher-dimensional objects generating the shadows. In particular, by taking advantage of physically reactive 3D shadow-space controllers, we can transform the task of interacting with 4D objects to a new level of physical reality. We begin with a teaching tool that uses 2D knot diagrams to manipulate the geometry of 3D mathematical knots via their projections; our unique 2D haptic interface allows the user to become familiar with sketching, editing, exploration, and manipulation of 3D knots rendered as projected imageson a 2D shadow space. By combining graphics and collision-sensing haptics, we can enhance the 2D shadow-driven editing protocol to successfully leverage 2D pen-and-paper or blackboard skills. Building on the reduced-dimension 2D editing tool for manipulating 3D shapes, we develop the natural analogy to produce a reduced-dimension 3D tool for manipulating 4D shapes. By physically modeling the correct properties of 4D surfaces, their bending forces, and their collisions in the 3D haptic controller interface, we can support full-featured physical exploration of 4D mathematical objects in a manner that is otherwise far beyond the experience accessible to human beings. As far as we are aware, this paper reports the first interactive system with force-feedback that provides "4D haptic visualization" permitting the user to model and interact with 4D cloth-like objects.

  6. 4D Confocal Imaging of Yeast Organelles.

    PubMed

    Day, Kasey J; Papanikou, Effrosyni; Glick, Benjamin S

    2016-01-01

    Yeast cells are well suited to visualizing organelles by 4D confocal microscopy. Typically, one or more cellular compartments are labeled with a fluorescent protein or dye, and a stack of confocal sections spanning the entire cell volume is captured every few seconds. Under appropriate conditions, organelle dynamics can be observed for many minutes with only limited photobleaching. Images are captured at a relatively low signal-to-noise ratio and are subsequently processed to generate movies that can be analyzed and quantified. Here, we describe methods for acquiring and processing 4D data using conventional scanning confocal microscopy. PMID:27631997

  7. The scientific value of 4D visualizations

    NASA Astrophysics Data System (ADS)

    Minster, J.; Olsen, K.; Day, S.; Moore, R.; Jordan, T. H.; Maechling, P.; Chourasia, A.

    2006-12-01

    Significant scientific insights derive from viewing measured, or calculated three-dimensional, time-dependent -- that is four-dimensional-- fields. This issue cuts across all disciplines of Earth Sciences. Addressing it calls for close collaborations between "domain" scientists and "IT" visualization specialists. Techniques to display such 4D fields in a intuitive way are a major challenge, especially when the relevant variables to be displayed are not scalars but tensors. This talk will illustrate some attempts to deal with this challenge, using seismic wave fields as specific objects to display. We will highlight how 4D displays can help address very difficult issues of significant scientific import.

  8. Ultrafast electronic processes in CVD diamonds and GaAs: picosecond photoconductivity and high-voltage switching

    NASA Astrophysics Data System (ADS)

    Garnov, Serge V.; Klimentov, Sergei M.; Pimenov, Sergej M.; Konov, Vitali I.; Kononenko, V. V.; Tsarkova, Olga G.; Gloor, S.; Luethy, Willy A.; Weber, Heinz P.

    1998-04-01

    An 'electrode-free' transient photoconductivity technique was applied to investigate excitation, drift and recombination of non-equilibrium free charge carriers in high quality synthetic polycrystalline diamond films, natural diamond crystals and low-conductive GaAs with a time resolution better than 200 ps. Picosecond laser pulses of UV, visible and Ir spectral range were applied for single- photon excitation of free charge carriers with initial concentrations of (1012-1019) cm-3. Dependences of amplitude and duration of photocurrent on laser intensity/carrier density were measured. Lifetimes, drift mobilities and carrier photoexcitation cross sections as a function of electron concentration were estimated. Computer calculations of conduction and displacement currents, induced space charge and electric field spatial distribution have been performed for the real experimental conditions. Based on the obtained results, high voltage diamond-based switches triggered by ultra-short laser pulses have been designed. Special attention was paid to metal- dielectric interface investigation and ohmic contacts formation. The developed diamond-base module permitted to switch electric fields as high as 100 kV/cm within a time interval less than 200 ps. The amplitude of photocurrent reached 100 A and the electrical resistance reduce by a factor of 1010.

  9. New Insights into the Composition and Texture of Lunar Regolith Using Ultrafast Automated Electron-Beam Analysis

    NASA Technical Reports Server (NTRS)

    Rickman, Doug; Wentworth, Susan J.; Schrader, Christian M.; Stoeser, Doug; Botha, Pieter WSK; Butcher, Alan R.; Horsch, Hanna E.; Benedictus, Aukje; Gottlieb, Paul; McKay, David

    2008-01-01

    Sieved grain mounts of Apollo 16 drive tube samples have been examined using QEMSCAN - an innovative electron beam technology. By combining multiple energy-dispersive X-ray detectors, fully automated control, and off-line image processing, to produce digital mineral maps of particles exposed on polished surfaces, the result is an unprecedented quantity of mineralogical and petrographic data, on a particle-by-particle basis. Experimental analysis of four size fractions (500-250 microns, 150-90 microns, 75-45 microns and < 20 microns), prepared from two samples (64002,374 and 64002,262), has produced a robust and uniform dataset which allows for the quantification of mineralogy; texture; particle shape, size and density; and the digital classification of distinct particle types in each measured sample. These preliminary data show that there is a decrease in plagioclase modal content and an opposing increase in glass modal content, with decreasing particle size. These findings, together with data on trace phases (metals, sulphides, phosphates, and oxides), provide not only new insights into the make-up of lunar regolith at the Apollo 16 landing site, but also key physical parameters which can be used to design lunar simulants, and compute Figures of Merit for each material produced.

  10. Ultrafast Photodriven Intramolecular Electron Transfer from a Zinc Porphyrin to a Readily Reduced Diiron Hydrogenase Model Complex

    SciTech Connect

    Samuel, Amanda P.S.; Co, Dick T.; Stern, C. L.; Wasielewski, Michael R.

    2010-06-10

    Diiron complexes modeled on the active site of the [FeFe] hydrogenases having the general formula [Fe2(μ-R)(CO)6-n(L)n], where commonly R = alkyl or aryl dithiolate and L = CO, CN-, or PR3, are a promising class of catalysts for use in photodriven H2 production. However, many of these catalysts are difficult to photoreduce using chromophores that absorb visible light. Here we report the synthesis and spectroscopic characterization of a naphthalene-4,5-dicarboximide-1,8-dithiolate diiron complex [NMI-Fe2S2(CO)6, 1] and a covalently linked, fixed-distance zinc 5,10,15-tri-n-pentyl-20-phenylporphyrin-NMI-Fe2S2(CO)6 donor-acceptor dyad (2). The electron-withdrawing nature of the NMI group makes the diiron complex among the most easily reduced hydrogenase mimics reported to date (-0.74 V vs SCE). In the presence of triflic acid, the cyclic voltammogram of 1 showed an increase in current at the first reduction wave at -0.78 V and a new reduction wave at -1.4 V. As the acid concentration was increased, the current at -0.78 V remained constant while the current at -1.4 V increased significantly, which is consistent with a catalytic proton reduction process. Selective photoexcitation of the Zn porphyrin in 2 with 553 nm, 110 fs laser pulses in both toluene and CH2Cl2 yielded transient absorption spectra showing a distinct peak at 616 nm, which has been assigned to [NMI-Fe2S2(CO)6]-• on the basis of spectroelectrochemical measurements on 1. The 616 nm peak was used to monitor the charge separation (CS) and charge recombination (CR) dynamics of 2, which yielded τCS = 12 ± 1 ps and τCR = 3.0 ± 0.2 ns in toluene and τCS = 24 ± 1 ps and τCR = 57 ± 1 ps in CH2Cl2. Photoexcitation of the disulfide precursor to

  11. Constrained reconstructions for 4D intervention guidance.

    PubMed

    Kuntz, J; Flach, B; Kueres, R; Semmler, W; Kachelriess, M; Bartling, S

    2013-05-21

    Image-guided interventions are an increasingly important part of clinical minimally invasive procedures. However, up to now they cannot be performed under 4D (3D + time) guidance due to the exceedingly high x-ray dose. In this work we investigate the applicability of compressed sensing reconstructions for highly undersampled CT datasets combined with the incorporation of prior images in order to yield low dose 4D intervention guidance. We present a new reconstruction scheme prior image dynamic interventional CT (PrIDICT) that accounts for specific image features in intervention guidance and compare it to PICCS and ASD-POCS. The optimal parameters for the dose per projection and the numbers of projections per reconstruction are determined in phantom simulations and measurements. In vivo experiments in six pigs are performed in a cone-beam CT; measured doses are compared to current gold-standard intervention guidance represented by a clinical fluoroscopy system. Phantom studies show maximum image quality for identical overall doses in the range of 14 to 21 projections per reconstruction. In vivo studies reveal that interventional materials can be followed in 4D visualization and that PrIDICT, compared to PICCS and ASD-POCS, shows superior reconstruction results and fewer artifacts in the periphery with dose in the order of biplane fluoroscopy. These results suggest that 4D intervention guidance can be realized with today's flat detector and gantry systems using the herein presented reconstruction scheme.

  12. 4D-Var Developement at GMAO

    NASA Technical Reports Server (NTRS)

    Pelc, Joanna S.; Todling, Ricardo; Akkraoui, Amal El

    2014-01-01

    The Global Modeling and Assimilation Offce (GMAO) is currently using an IAU-based 3D-Var data assimilation system. GMAO has been experimenting with a 3D-Var-hybrid version of its data assimilation system (DAS) for over a year now, which will soon become operational and it will rapidly progress toward a 4D-EnVar. Concurrently, the machinery to exercise traditional 4DVar is in place and it is desirable to have a comparison of the traditional 4D approach with the other available options, and evaluate their performance in the Goddard Earth Observing System (GEOS) DAS. This work will also explore the possibility for constructing a reduced order model (ROM) to make traditional 4D-Var computationally attractive for increasing model resolutions. Part of the research on ROM will be to search for a suitably acceptable space to carry on the corresponding reduction. This poster illustrates how the IAU-based 4D-Var assimilation compares with our currently used IAU-based 3D-Var.

  13. Constrained reconstructions for 4D intervention guidance

    NASA Astrophysics Data System (ADS)

    Kuntz, J.; Flach, B.; Kueres, R.; Semmler, W.; Kachelrieß, M.; Bartling, S.

    2013-05-01

    Image-guided interventions are an increasingly important part of clinical minimally invasive procedures. However, up to now they cannot be performed under 4D (3D + time) guidance due to the exceedingly high x-ray dose. In this work we investigate the applicability of compressed sensing reconstructions for highly undersampled CT datasets combined with the incorporation of prior images in order to yield low dose 4D intervention guidance. We present a new reconstruction scheme prior image dynamic interventional CT (PrIDICT) that accounts for specific image features in intervention guidance and compare it to PICCS and ASD-POCS. The optimal parameters for the dose per projection and the numbers of projections per reconstruction are determined in phantom simulations and measurements. In vivo experiments in six pigs are performed in a cone-beam CT; measured doses are compared to current gold-standard intervention guidance represented by a clinical fluoroscopy system. Phantom studies show maximum image quality for identical overall doses in the range of 14 to 21 projections per reconstruction. In vivo studies reveal that interventional materials can be followed in 4D visualization and that PrIDICT, compared to PICCS and ASD-POCS, shows superior reconstruction results and fewer artifacts in the periphery with dose in the order of biplane fluoroscopy. These results suggest that 4D intervention guidance can be realized with today’s flat detector and gantry systems using the herein presented reconstruction scheme.

  14. Ultrafast supercontinuum fiber-laser based pump-probe scanning magneto-optical Kerr effect microscope for the investigation of electron spin dynamics in semiconductors at cryogenic temperatures with picosecond time and micrometer spatial resolution.

    PubMed

    Henn, T; Kiessling, T; Ossau, W; Molenkamp, L W; Biermann, K; Santos, P V

    2013-12-01

    We describe a two-color pump-probe scanning magneto-optical Kerr effect microscope which we have developed to investigate electron spin phenomena in semiconductors at cryogenic temperatures with picosecond time and micrometer spatial resolution. The key innovation of our microscope is the usage of an ultrafast "white light" supercontinuum fiber-laser source which provides access to the whole visible and near-infrared spectral range. Our Kerr microscope allows for the independent selection of the excitation and detection energy while avoiding the necessity to synchronize the pulse trains of two separate picosecond laser systems. The ability to independently tune the pump and probe wavelength enables the investigation of the influence of excitation energy on the optically induced electron spin dynamics in semiconductors. We demonstrate picosecond real-space imaging of the diffusive expansion of optically excited electron spin packets in a (110) GaAs quantum well sample to illustrate the capabilities of the instrument.

  15. Ultrafast supercontinuum fiber-laser based pump-probe scanning magneto-optical Kerr effect microscope for the investigation of electron spin dynamics in semiconductors at cryogenic temperatures with picosecond time and micrometer spatial resolution

    SciTech Connect

    Henn, T.; Kiessling, T. Ossau, W.; Molenkamp, L. W.; Biermann, K.; Santos, P. V.

    2013-12-15

    We describe a two-color pump-probe scanning magneto-optical Kerr effect microscope which we have developed to investigate electron spin phenomena in semiconductors at cryogenic temperatures with picosecond time and micrometer spatial resolution. The key innovation of our microscope is the usage of an ultrafast “white light” supercontinuum fiber-laser source which provides access to the whole visible and near-infrared spectral range. Our Kerr microscope allows for the independent selection of the excitation and detection energy while avoiding the necessity to synchronize the pulse trains of two separate picosecond laser systems. The ability to independently tune the pump and probe wavelength enables the investigation of the influence of excitation energy on the optically induced electron spin dynamics in semiconductors. We demonstrate picosecond real-space imaging of the diffusive expansion of optically excited electron spin packets in a (110) GaAs quantum well sample to illustrate the capabilities of the instrument.

  16. Doping dependence and electron-boson coupling in the ultrafast relaxation of hot electron populations in Ba(Fe1-x Co x )2As2

    NASA Astrophysics Data System (ADS)

    Avigo, I.; Thirupathaiah, S.; Ligges, M.; Wolf, T.; Fink, J.; Bovensiepen, U.

    2016-09-01

    Using femtosecond time- and angle-resolved photoemission spectroscopy we investigate the effect of electron doping on the electron dynamics in {Ba}{({{Fe}}1-x{{Co}}x)}2{{As}}2 in a range of 0≤slant x\\lt 0.15 at temperatures slightly above the Néel temperature. By analyzing the time-dependent photoemission intensity of the pump laser excited population as a function of energy, we found that the relaxation times at 0\\lt E-{E}{{F}}\\lt 0.2 {eV} are doping dependent and about 100 fs shorter at optimal doping than for overdoped and parent compounds. Analysis of the relaxation rates also reveals the presence of a pump fluence dependent step in the relaxation time at E-{E}{{F}}=200 {meV} which we explain by coupling of the excited electronic system to a boson of this energy. We compare our results with static ARPES and transport measurements and find disagreement and agreement concerning the doping-dependence, respectively. We discuss the effect of the electron-boson coupling on the energy-dependent relaxation and assign the origin of the boson to a magnetic excitation.

  17. Interactive animation of 4D performance capture.

    PubMed

    Casas, Dan; Tejera, Margara; Guillemaut, Jean-Yves; Hilton, Adrian

    2013-05-01

    A 4D parametric motion graph representation is presented for interactive animation from actor performance capture in a multiple camera studio. The representation is based on a 4D model database of temporally aligned mesh sequence reconstructions for multiple motions. High-level movement controls such as speed and direction are achieved by blending multiple mesh sequences of related motions. A real-time mesh sequence blending approach is introduced, which combines the realistic deformation of previous nonlinear solutions with efficient online computation. Transitions between different parametric motion spaces are evaluated in real time based on surface shape and motion similarity. Four-dimensional parametric motion graphs allow real-time interactive character animation while preserving the natural dynamics of the captured performance.

  18. Interactive animation of 4D performance capture.

    PubMed

    Casas, Dan; Tejera, Margara; Guillemaut, Jean-Yves; Hilton, Adrian

    2013-05-01

    A 4D parametric motion graph representation is presented for interactive animation from actor performance capture in a multiple camera studio. The representation is based on a 4D model database of temporally aligned mesh sequence reconstructions for multiple motions. High-level movement controls such as speed and direction are achieved by blending multiple mesh sequences of related motions. A real-time mesh sequence blending approach is introduced, which combines the realistic deformation of previous nonlinear solutions with efficient online computation. Transitions between different parametric motion spaces are evaluated in real time based on surface shape and motion similarity. Four-dimensional parametric motion graphs allow real-time interactive character animation while preserving the natural dynamics of the captured performance. PMID:23492379

  19. Ultrafast electronic relaxation processes in semiconductor nanoparticles (silver iodide, silver iodide/silver sulfide, silver bromide/silver sulfide, silver sulfide, cupric sulfide, and copper sulfide) and carotenoids

    NASA Astrophysics Data System (ADS)

    Brelle, Michael Chris

    2000-11-01

    This dissertation examines primarily the ultrafast dynamics of excited state charge carriers in semiconductor nanoparticles. The dissertation also briefly examines the excited state lifetimes of a few carotenoids. Understanding the dynamic properties of charge carriers in semiconductor nanoparticles is crucial for the further development of applications utilizing these systems. The dynamic properties including shallow and deep trapping as well as recombination have been studied in a variety of semiconductor nanoparticle systems. Kinetic modeling was utilized to assist in the assignment of all observed signals and the nature of the decays. The first observation of ultrafast trapping in silver halides was observed in AgI nanoparticles including the identification that interstitial silver ions may act as deep traps. Several interesting phenomena were observed in Ag2S and CuxS nanoparticles including dark shallow trap states and shallow trap state saturation leading to increased transient absorption over transient bleach with increasing excitation intensity. These observations have provided further insight into the relaxation pathways for charge carriers in semiconductor nanoparticle systems. Lifetimes of the S2 excited states of four carotenoids have also been determined. The S2 lifetime for beta-carotene was confirmed from previous fluorescence up-conversion experiments whereas the S2 lifetimes that were previously unknown for three carotenoids, violaxanthin, neaxanthin, and lutein were discovered. These experiments together demonstrate the capabilities of femtosecond pump-probe spectroscopy to characterize and better understand the processes involved in the ultrafast relaxation events in both molecular and nanoparticle systems.

  20. Time-dependent multiconfiguration theory for ultrafast electronic dynamics of molecules in an intense laser field: Electron correlation and energy redistribution among natural orbitals

    NASA Astrophysics Data System (ADS)

    Kato, Tsuyoshi; Kono, Hirohiko

    2009-12-01

    We propose a new definition of molecular orbital energy in order to investigate the energetics of constituent molecular orbitals in the many-electron wave function calculated based on time-dependent multiconfiguration theory. It is shown that when energies are assigned to natural orbitals by a similar manner to that used in the Hartree-Fock theory, we can quantify a correction energy to the total electronic energy that represents electron correlation, and thus we can evaluate the time-dependence of the correlation energy. Our attempt is illustrated by numerical results on the time-dependence of the spatial density of the correlation energy and the orbital energies for a H 2 molecule interacting with an intense, near-infrared laser field. We compared the energy ζj( t) supplied by the applied field with the net energy gain Δɛ(t) for respective natural orbitals ϕj( t). ϕj and found that the natural orbitals with Δɛ(t)>ζj(t) play a key role in the ionization process.

  1. Crystal growth and electronic phase diagram of 4 d -doped Na1 -δFe1 -xRhxAs in comparison to 3 d -dopedNa1 -δFe1 -xCoxAs

    NASA Astrophysics Data System (ADS)

    Steckel, Frank; Roslova, Maria; Beck, Robert; Morozov, Igor; Aswartham, Saicharan; Evtushinsky, Daniil; Blum, Christian G. F.; Abdel-Hafiez, Mahmoud; Bombor, Dirk; Maletz, Janek; Borisenko, Sergey; Shevelkov, Andrei V.; Wolter, Anja U. B.; Hess, Christian; Wurmehl, Sabine; Büchner, Bernd

    2015-05-01

    Single crystals of Na1 -δFe1 -xTxAs with T = Co, Rh have been grown using a self-flux technique. The crystals were thoroughly characterized by powder x-ray diffraction, magnetic susceptibility, and electronic transport with particular focus on the Rh-doped samples. Measurements of the specific heat and ARPES were conducted exemplarily for the optimally doped compositions. The spin-density wave transition (SDW) observed for samples with low Rh concentration (0 ≤x ≤0.013 ) is fully suppressed in the optimally doped sample. The superconducting transition temperature (Tc) is enhanced from 10 K in Na1 -δFeAs to 21 K in the optimally doped sample (x =0.019 ) of the Na1 -δFe1 -xRhxAs series and decreases for the overdoped compounds, revealing a typical shape for the superconducting part of the electronic phase diagram. Remarkably, the phase diagram is almost identical to that of Co-doped Na1 -δFeAs , suggesting a generic phase diagram for both dopants.

  2. Abdominal and pancreatic motion correlation using 4D CT, 4D transponders, and a gating belt.

    PubMed

    Betancourt, Ricardo; Zou, Wei; Plastaras, John P; Metz, James M; Teo, Boon-Keng; Kassaee, Alireza

    2013-01-01

    The correlation between the pancreatic and external abdominal motion due to respiration was investigated on two patients. These studies utilized four dimensional computer tomography (4D CT), a four dimensional (4D) electromagnetic transponder system, and a gating belt system. One 4D CT study was performed during simulation to quantify the pancreatic motion using computer tomography images at eight breathing phases. The motion under free breathing and breath-hold were analyzed for the 4D electromagnetic transponder system and the gating belt system during treatment. A linear curve was fitted for all data sets and correlation factors were evaluated between the 4D electromagnetic transponder system and the gating belt system data. The 4D CT study demonstrated a modest correlation between the external marker and the pancreatic motion with R-square values larger than 0.8 for the inferior-superior (inf-sup). Then, the relative pressure from the belt gating system correlated well with the 4D electromagnetic transponder system's motion in the anterior-posterior (ant-post) and the inf-post directions. These directions have a correlation value of -0.93 and 0.76, while the lateral only had a 0.03 correlation coefficient. Based on our limited study, external surrogates can be used as predictors of the pancreatic motion in the inf-sup and the ant-post directions. Although there is a low correlation on the lateral direction, its motion is significantly shorter. In conclusion, an appropriate treatment delivery can be used for pancreatic cancer when an internal tracking system, such as the 4D electromagnetic transponder system, is unavailable. PMID:23652242

  3. Abdominal and pancreatic motion correlation using 4D CT, 4D transponders, and a gating belt.

    PubMed

    Betancourt, Ricardo; Zou, Wei; Plastaras, John P; Metz, James M; Teo, Boon-Keng; Kassaee, Alireza

    2013-05-06

    The correlation between the pancreatic and external abdominal motion due to respiration was investigated on two patients. These studies utilized four dimensional computer tomography (4D CT), a four dimensional (4D) electromagnetic transponder system, and a gating belt system. One 4D CT study was performed during simulation to quantify the pancreatic motion using computer tomography images at eight breathing phases. The motion under free breathing and breath-hold were analyzed for the 4D electromagnetic transponder system and the gating belt system during treatment. A linear curve was fitted for all data sets and correlation factors were evaluated between the 4D electromagnetic transponder system and the gating belt system data. The 4D CT study demonstrated a modest correlation between the external marker and the pancreatic motion with R-square values larger than 0.8 for the inferior-superior (inf-sup). Then, the relative pressure from the belt gating system correlated well with the 4D electromagnetic transponder system's motion in the anterior-posterior (ant-post) and the inf-post directions. These directions have a correlation value of -0.93 and 0.76, while the lateral only had a 0.03 correlation coefficient. Based on our limited study, external surrogates can be used as predictors of the pancreatic motion in the inf-sup and the ant-post directions. Although there is a low correlation on the lateral direction, its motion is significantly shorter. In conclusion, an appropriate treatment delivery can be used for pancreatic cancer when an internal tracking system, such as the 4D electromagnetic transponder system, is unavailable.

  4. SU-D-18C-01: A Novel 4D-MRI Technology Based On K-Space Retrospective Sorting

    SciTech Connect

    Liu, Y; Yin, F; Cai, J

    2014-06-01

    Purpose: Current 4D-MRI techniques lack sufficient temporal/spatial resolution and consistent tumor contrast. To overcome these limitations, this study presents the development and initial evaluation of an entirely new framework of 4D-MRI based on k-space retrospective sorting. Methods: An important challenge of the proposed technique is to determine the number of repeated scans(NR) required to obtain sufficient k-space data for 4D-MRI. To do that, simulations using 29 cancer patients' respiratory profiles were performed to derive the relationship between data acquisition completeness(Cp) and NR, also relationship between NR(Cp=95%) and the following factors: total slice(NS), respiratory phase bin length(Lb), frame rate(fr), resolution(R) and image acquisition starting-phase(P0). To evaluate our technique, a computer simulation study on a 4D digital human phantom (XCAT) were conducted with regular breathing (fr=0.5Hz; R=256×256). A 2D echo planer imaging(EPI) MRI sequence were assumed to acquire raw k-space data, with respiratory signal and acquisition time for each k-space data line recorded simultaneously. K-space data was re-sorted based on respiratory phases. To evaluate 4D-MRI image quality, tumor trajectories were measured and compared with the input signal. Mean relative amplitude difference(D) and cross-correlation coefficient(CC) are calculated. Finally, phase-sharing sliding window technique was applied to investigate the feasibility of generating ultra-fast 4D-MRI. Result: Cp increased with NR(Cp=100*[1-exp(-0.19*NR)], when NS=30, Lb=100%/6). NR(Cp=95%) was inversely-proportional to Lb (r=0.97), but independent of other factors. 4D-MRI on XCAT demonstrated highly accurate motion information (D=0.67%, CC=0.996) with much less artifacts than those on image-based sorting 4D-MRI. Ultra-fast 4D-MRI with an apparent temporal resolution of 10 frames/second was reconstructed using the phase-sharing sliding window technique. Conclusions: A novel 4D

  5. Oblique sounding using the DPS-4D stations in Europe

    NASA Astrophysics Data System (ADS)

    Mosna, Zbysek; Kouba, Daniel; Koucka Knizova, Petra; Arikan, Feza; Arikan, Orhan; Gok, Gokhan; Rejfek, Lubos

    2016-07-01

    The DPS-4D Digisondes are capable of detection of echoes from neighbouring European stations. Currently, a campaign with high-temporal resolution of 5 min is being run. Further, ionograms from regular vertical sounding with 15 min resolution provide us with oblique reflections together with vertical reflections. We analyzed profiles of electron concentration and basic ionospheric parameters derived from the ionograms. We compared results derived from reflections from the ionosphere above the stations (vertical sounding) with information derived from oblique reflections between the stations. This study is supported by the Joint TUBITAK 114E092 and AS CR 14/001 projects.

  6. Active origami by 4D printing

    NASA Astrophysics Data System (ADS)

    Ge, Qi; Dunn, Conner K.; Qi, H. Jerry; Dunn, Martin L.

    2014-09-01

    Recent advances in three dimensional (3D) printing technology that allow multiple materials to be printed within each layer enable the creation of materials and components with precisely controlled heterogeneous microstructures. In addition, active materials, such as shape memory polymers, can be printed to create an active microstructure within a solid. These active materials can subsequently be activated in a controlled manner to change the shape or configuration of the solid in response to an environmental stimulus. This has been termed 4D printing, with the 4th dimension being the time-dependent shape change after the printing. In this paper, we advance the 4D printing concept to the design and fabrication of active origami, where a flat sheet automatically folds into a complicated 3D component. Here we print active composites with shape memory polymer fibers precisely printed in an elastomeric matrix and use them as intelligent active hinges to enable origami folding patterns. We develop a theoretical model to provide guidance in selecting design parameters such as fiber dimensions, hinge length, and programming strains and temperature. Using the model, we design and fabricate several active origami components that assemble from flat polymer sheets, including a box, a pyramid, and two origami airplanes. In addition, we directly print a 3D box with active composite hinges and program it to assume a temporary flat shape that subsequently recovers to the 3D box shape on demand.

  7. Advances in 4D radiation therapy for managing respiration: part II - 4D treatment planning.

    PubMed

    Rosu, Mihaela; Hugo, Geoffrey D

    2012-12-01

    The development of 4D CT imaging technology made possible the creation of patient models that are reflective of respiration-induced anatomical changes by adding a temporal dimension to the conventional 3D, spatial-only, patient description. This had opened a new venue for treatment planning and radiation delivery, aimed at creating a comprehensive 4D radiation therapy process for moving targets. Unlike other breathing motion compensation strategies (e.g. breath-hold and gating techniques), 4D radiotherapy assumes treatment delivery over the entire respiratory cycle - an added bonus for both patient comfort and treatment time efficiency. The time-dependent positional and volumetric information holds the promise for optimal, highly conformal, radiotherapy for targets experiencing movements caused by respiration, with potentially elevated dose prescriptions and therefore higher cure rates, while avoiding the uninvolved nearby structures. In this paper, the current state of the 4D treatment planning is reviewed, from theory to the established practical routine. While the fundamental principles of 4D radiotherapy are well defined, the development of a complete, robust and clinically feasible process still remains a challenge, imposed by limitations in the available treatment planning and radiation delivery systems.

  8. Advances in 4D Radiation Therapy for Managing Respiration: Part II – 4D Treatment Planning

    PubMed Central

    Rosu, Mihaela; Hugo, Geoffrey D.

    2014-01-01

    The development of 4D CT imaging technology made possible the creation of patient models that are reflective of respiration-induced anatomical changes by adding a temporal dimension to the conventional 3D, spatial-only, patient description. This had opened a new venue for treatment planning and radiation delivery, aimed at creating a comprehensive 4D radiation therapy process for moving targets. Unlike other breathing motion compensation strategies (e.g. breath-hold and gating techniques), 4D radiotherapy assumes treatment delivery over the entire respiratory cycle – an added bonus for both patient comfort and treatment time efficiency. The time-dependent positional and volumetric information holds the promise for optimal, highly conformal, radiotherapy for targets experiencing movements caused by respiration, with potentially elevated dose prescriptions and therefore higher cure rates, while avoiding the uninvolved nearby structures. In this paper, the current state of the 4D treatment planning is reviewed, from theory to the established practical routine. While the fundamental principles of 4D radiotherapy are well defined, the development of a complete, robust and clinically feasible process still remains a challenge, imposed by limitations in the available treatment planning and radiation delivery systems. PMID:22796324

  9. Perspective: Ultrafast magnetism and THz spintronics

    NASA Astrophysics Data System (ADS)

    Walowski, Jakob; Münzenberg, Markus

    2016-10-01

    This year the discovery of femtosecond demagnetization by laser pulses is 20 years old. For the first time, this milestone work by Bigot and coworkers gave insight directly into the time scales of microscopic interactions that connect the spin and electron system. While intense discussions in the field were fueled by the complexity of the processes in the past, it now became evident that it is a puzzle of many different parts. Rather than providing an overview that has been presented in previous reviews on ultrafast processes in ferromagnets, this perspective will show that with our current depth of knowledge the first applications are developed: THz spintronics and all-optical spin manipulation are becoming more and more feasible. The aim of this perspective is to point out where we can connect the different puzzle pieces of understanding gathered over 20 years to develop novel applications. Based on many observations in a large number of experiments. Differences in the theoretical models arise from the localized and delocalized nature of ferromagnetism. Transport effects are intrinsically non-local in spintronic devices and at interfaces. We review the need for multiscale modeling to address the processes starting from electronic excitation of the spin system on the picometer length scale and sub-femtosecond time scale, to spin wave generation, and towards the modeling of ultrafast phase transitions that altogether determine the response time of the ferromagnetic system. Today, our current understanding gives rise to the first usage of ultrafast spin physics for ultrafast magnetism control: THz spintronic devices. This makes the field of ultrafast spin-dynamics an emerging topic open for many researchers right now.

  10. Ultrafast studies of solution dynamics

    SciTech Connect

    Woodruff, W.H.; Dyer, R.B.; Callender, R.H.

    1997-10-01

    This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). Fast chemical dynamics generally must be initiated photochemically. This limits the applicability of modern laser methods for following the structural changes that occur during chemical and biological reactions to those systems that have an electronic chromophore that has a significant yield of photoproduct when excited. This project has developed a new and entirely general approach to ultrafast initiation of reactions in solution: laser-induced temperature jump (T-jump). The results open entire new fields of study of ultrafast molecular dynamics in solution. The authors have demonstrated the T-jump technique on time scales of 50 ps and longer, and have applied it to study of the fast events in protein folding. They find that a general lifetime of alpha-helix formation is ca 100 ns, and that tertiary folds (in apomyoglobin) form in ca 100 {mu}s.

  11. ICT4D: A Computer Science Perspective

    NASA Astrophysics Data System (ADS)

    Sutinen, Erkki; Tedre, Matti

    The term ICT4D refers to the opportunities of Information and Communication Technology (ICT) as an agent of development. Research in that field is often focused on evaluating the feasibility of existing technologies, mostly of Western or Far East Asian origin, in the context of developing regions. A computer science perspective is complementary to that agenda. The computer science perspective focuses on exploring the resources, or inputs, of a particular context and on basing the design of a technical intervention on the available resources, so that the output makes a difference in the development context. The modus operandi of computer science, construction, interacts with evaluation and exploration practices. An analysis of a contextualized information technology curriculum of Tumaini University in southern Tanzania shows the potential of the computer science perspective for designing meaningful information and communication technology for a developing region.

  12. 4D Clinical Imaging for Dynamic CAD

    PubMed Central

    McIntyre, Frederick

    2013-01-01

    A basic 4D imaging system to capture the jaw motion has been developed that produces high resolution 3D surface data. Fluorescent microspheres are brushed onto the areas of the upper and the lower arches to be imaged, producing a high-contrast random optical pattern. A hand-held imaging device operated at about 10 cm from the mouth captures time-based perspective images of the fluorescent areas. Each set of images, containing both upper and the lower arch data, is converted to a 3d point mesh using photogrammetry, thereby providing an instantaneous relative jaw position. Eight 3d positions per second are captured. Using one of the 3d frames as a reference, incremental transforms are derived to express the free body motion of the mandible. Conventional 3d models of the dentition are directly registered to the reference frame, allowing them to be animated using the derived transforms. PMID:24082882

  13. Ultrafast hybrid plasmonics.

    SciTech Connect

    Wiederrecht, G. P.; Wurtz, G. A.; Bouhelier, A.; Univ. of North Florida; Univ. de Bourgogne

    2008-08-20

    We review our recent studies of electromagnetic coupling and associated temporal dynamics of molecular excitations with plasmonic resonances supported by either localized or extended planar geometries. We focus on coherent interactions between plasmon resonances and molecular excitations, which are experimentally challenging due to the very short ({approx}10-100 fs) coherence times of plasmons. Recent experimental results and theoretical analysis for observing and controlling coherences between molecular excitations and plasmonic polarizations are shown. Advances will explore new directions in ultrafast coherent control of molecular excited states and energy dissipation processes, as well as ultrafast addressing and switching in plasmonics-based circuit architectures.

  14. Opening the Black Box of ICT4D: Advancing Our Understanding of ICT4D Partnerships

    ERIC Educational Resources Information Center

    Park, Sung Jin

    2013-01-01

    The term, Information and Communication Technologies for Development (ICT4D), pertains to programs or projects that strategically use ICTs (e.g. mobile phones, computers, and the internet) as a means toward the socio-economic betterment for the poor in developing contexts. Gaining the political and financial support of the international community…

  15. Distributed ultrafast fibre laser

    PubMed Central

    Liu, Xueming; Cui, Yudong; Han, Dongdong; Yao, Xiankun; Sun, Zhipei

    2015-01-01

    A traditional ultrafast fibre laser has a constant cavity length that is independent of the pulse wavelength. The investigation of distributed ultrafast (DUF) lasers is conceptually and technically challenging and of great interest because the laser cavity length and fundamental cavity frequency are changeable based on the wavelength. Here, we propose and demonstrate a DUF fibre laser based on a linearly chirped fibre Bragg grating, where the total cavity length is linearly changeable as a function of the pulse wavelength. The spectral sidebands in DUF lasers are enhanced greatly, including the continuous-wave (CW) and pulse components. We observe that all sidebands of the pulse experience the same round-trip time although they have different round-trip distances and refractive indices. The pulse-shaping of the DUF laser is dominated by the dissipative processes in addition to the phase modulations, which makes our ultrafast laser simple and stable. This laser provides a simple, stable, low-cost, ultrafast-pulsed source with controllable and changeable cavity frequency. PMID:25765454

  16. Ultrafast femtosecond laser ablation of graphite

    NASA Astrophysics Data System (ADS)

    Ionin, Andrey A.; Kudryashov, Sergey I.; Makarov, Sergey V.; Mel'nik, N. N.; Saltuganov, Pavel N.; Seleznev, Leonid V.; Sinitsyn, Dmitry V.

    2015-06-01

    Fluence dependences of IR and UV reflectivity of femtosecond laser pulses on a HOPG surface demonstrate their saturation in a certain fluence range, starting from 0.2 J cm-2, where single-shot non-linear plasma emission is detected by electric probe measurements. This correlation between prompt solid-state optical/electronic dynamics and electron-ion plasma emission indicates prompt ‘freezing’ of surface electronic dynamics via its plasma-emission cooling and simultaneous ultrafast shallow laser ablation of the surface. Strong HOPG disordering is observed in Raman spectra for laser fluences, exceeding the plasma emission threshold.

  17. Time-resolved spectroscopy of CI and CII line emissions from an ultrafast laser induced solid graphite plasma

    NASA Astrophysics Data System (ADS)

    N, Smijesh; K, Chandrasekharan; Philip, Reji

    2014-10-01

    We present an experimental characterization of the evolution dynamics of CI and CII lines in an ultrafast laser produced graphite plasma under various ambient conditions. Fast and slow components are observed in the temporal evolution of CI transition at 658.7 nm (3p1P - 4d1P0) and CII transition at 426.7 nm (3d 2D - 4f 2F0). Fast peak is due to the recombination of fast ions species with electrons, found to have an increase in velocity upon increasing the ambient pressure. Whereas the slow peaks in both cases can be the results of slow ions or slow neutrals in the plume.

  18. Time-resolved spectroscopy of CI and CII line emissions from an ultrafast laser induced solid graphite plasma

    SciTech Connect

    N, Smijesh; K, Chandrasekharan; Philip, Reji

    2014-10-15

    We present an experimental characterization of the evolution dynamics of CI and CII lines in an ultrafast laser produced graphite plasma under various ambient conditions. Fast and slow components are observed in the temporal evolution of CI transition at 658.7 nm (3p{sup 1}P - 4d{sup 1}P{sup 0}) and CII transition at 426.7 nm (3d {sup 2}D - 4f {sup 2}F{sup 0}). Fast peak is due to the recombination of fast ions species with electrons, found to have an increase in velocity upon increasing the ambient pressure. Whereas the slow peaks in both cases can be the results of slow ions or slow neutrals in the plume.

  19. 17 CFR 260.4d-8 - Content.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 17 Commodity and Securities Exchanges 3 2013-04-01 2013-04-01 false Content. 260.4d-8 Section 260.4d-8 Commodity and Securities Exchanges SECURITIES AND EXCHANGE COMMISSION (CONTINUED) GENERAL RULES AND REGULATIONS, TRUST INDENTURE ACT OF 1939 Rules Under Section 304 § 260.4d-8 Content. (a)...

  20. 17 CFR 260.4d-8 - Content.

    Code of Federal Regulations, 2012 CFR

    2005-04-01

    ... 17 Commodity and Securities Exchanges 3 2005-04-01 2005-04-01 false Content. 260.4d-8 Section 260.4d-8 Commodity and Securities Exchanges SECURITIES AND EXCHANGE COMMISSION (CONTINUED) GENERAL RULES AND REGULATIONS, TRUST INDENTURE ACT OF 1939 Rules Under Section 304 § 260.4d-8 Content. (a)...

  1. 17 CFR 260.4d-8 - Content.

    Code of Federal Regulations, 2013 CFR

    2000-04-01

    ... 17 Commodity and Securities Exchanges 3 2000-04-01 2000-04-01 false Content. 260.4d-8 Section 260.4d-8 Commodity and Securities Exchanges GENERAL RULES AND REGULATIONS, TRUST INDENTURE ACT OF 1939 Rules Under Section 304 § 260.4d-8 Content. (a) Each application for an order under section 304(d)...

  2. 17 CFR 260.4d-8 - Content.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 17 Commodity and Securities Exchanges 3 2011-04-01 2011-04-01 false Content. 260.4d-8 Section 260.4d-8 Commodity and Securities Exchanges SECURITIES AND EXCHANGE COMMISSION (CONTINUED) GENERAL RULES AND REGULATIONS, TRUST INDENTURE ACT OF 1939 Rules Under Section 304 § 260.4d-8 Content. (a)...

  3. 17 CFR 260.4d-8 - Content.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 17 Commodity and Securities Exchanges 3 2012-04-01 2012-04-01 false Content. 260.4d-8 Section 260.4d-8 Commodity and Securities Exchanges SECURITIES AND EXCHANGE COMMISSION (CONTINUED) GENERAL RULES AND REGULATIONS, TRUST INDENTURE ACT OF 1939 Rules Under Section 304 § 260.4d-8 Content. (a)...

  4. 17 CFR 260.4d-8 - Content.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 17 Commodity and Securities Exchanges 3 2010-04-01 2010-04-01 false Content. 260.4d-8 Section 260.4d-8 Commodity and Securities Exchanges SECURITIES AND EXCHANGE COMMISSION (CONTINUED) GENERAL RULES AND REGULATIONS, TRUST INDENTURE ACT OF 1939 Rules Under Section 304 § 260.4d-8 Content. (a)...

  5. 76 FR 55814 - 2,4-D; Pesticide Tolerances

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-09

    ... AGENCY 40 CFR Part 180 2,4-D; Pesticide Tolerances AGENCY: Environmental Protection Agency (EPA). ACTION: Final rule. SUMMARY: This regulation establishes tolerances for residues of 2,4-D in or on teff, bran... 180.142 be amended by establishing a tolerance for residues of the herbicide 2,4-D...

  6. 17 CFR 260.4d-8 - Content.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 17 Commodity and Securities Exchanges 4 2014-04-01 2014-04-01 false Content. 260.4d-8 Section 260.4d-8 Commodity and Securities Exchanges SECURITIES AND EXCHANGE COMMISSION (CONTINUED) GENERAL RULES AND REGULATIONS, TRUST INDENTURE ACT OF 1939 Rules Under Section 304 § 260.4d-8 Content. (a)...

  7. Suppression of the molecular ultra-fast dissociation in bromomethane clusters

    SciTech Connect

    Rander, T.; Lindblad, A.; Bradeanu, I.; Svensson, S.; Björneholm, O.; Öhrwall, G.

    2014-12-14

    We address the influence of clustering on the ultra-fast dissociation of bromomethane. Valence and core photo-electron spectroscopy, partial electron yield absorption, and resonant Auger spectroscopy have been used together with ab initio calculations to investigate the properties of the ultra-fast dissociation. The ratio of ultra-fast dissociation of molecules in clusters as compared to free molecules is determined to be significantly reduced. We propose partial delocalization of the excited electronic state as being responsible for this behavior.

  8. Ultrafast limited-angle-type x-ray tomography

    SciTech Connect

    Bieberle, M.; Fischer, F.; Schleicher, E.; Hampel, U.; Koch, D.; Aktay, K. S. d. C.; Menz, H.-J.; Mayer, H.-G.

    2007-09-17

    The authors present an ultrafast electron beam x-ray computed tomography technique usable for imaging of fast processes, such as multiphase flows or moving parts in technical or biological objects. The setup consists of an electron beam unit with fast deflection capability and an ultrafast multielement x-ray detector and achieves 10 000 frames/s image rate. Since full sampling of the Radon space requires an angular overlap of source path and detector which strongly decreases axial resolution, the authors devised a limited-angle-type tomography. As a demonstration they visualized the movement of particles and gas bubbles rising in a stagnant liquid.

  9. Ultrafast exciton formation at the ZnO(1010) surface.

    PubMed

    Deinert, J-C; Wegkamp, D; Meyer, M; Richter, C; Wolf, M; Stähler, J

    2014-08-01

    We study the ultrafast quasiparticle dynamics in and below the ZnO conduction band using femtosecond time-resolved two-photon photoelectron spectroscopy. Above band gap excitation causes hot electron relaxation by electron-phonon scattering down to the Fermi level E_{F} followed by ultrafast (200 fs) formation of a surface exciton (SX). Transient screening of the Coulomb interaction reduces the SX formation probability at high excitation densities near the Mott limit. Located just below the surface, the SX are stable with regard to hydrogen-induced work function modifications and thus the ideal prerequisite for resonant energy transfer applications.

  10. Ultrafast reduction of the total magnetization in iron

    SciTech Connect

    Fognini, A. Michlmayr, T. U.; Salvatella, G.; Vaterlaus, A.; Acremann, Y.; Wetli, C.; Sorgenfrei, F.; Beye, M.; Eschenlohr, A.; Pontius, N.; Föhlisch, A.; Stamm, C.; Hieke, F.; Dell'Angela, M.; Wurth, W.; Jong, S. de; Dürr, H. A.; and others

    2014-01-20

    Surprisingly, if a ferromagnet is exposed to an ultrafast laser pulse, its apparent magnetization is reduced within less than a picosecond. Up to now, the total magnetization, i.e., the average spin polarization of the whole valence band, was not detectable on a sub-picosecond time scale. Here, we present experimental data, confirming the ultrafast reduction of the total magnetization. Soft x-ray pulses from the free electron laser in Hamburg (FLASH) extract polarized cascade photoelectrons from an iron layer excited by a femtosecond laser pulse. The spin polarization of the emitted electrons is detected by a Mott spin polarimeter.

  11. Resolving ultrafast heating of dense cryogenic hydrogen.

    PubMed

    Zastrau, U; Sperling, P; Harmand, M; Becker, A; Bornath, T; Bredow, R; Dziarzhytski, S; Fennel, T; Fletcher, L B; Förster, E; Göde, S; Gregori, G; Hilbert, V; Hochhaus, D; Holst, B; Laarmann, T; Lee, H J; Ma, T; Mithen, J P; Mitzner, R; Murphy, C D; Nakatsutsumi, M; Neumayer, P; Przystawik, A; Roling, S; Schulz, M; Siemer, B; Skruszewicz, S; Tiggesbäumker, J; Toleikis, S; Tschentscher, T; White, T; Wöstmann, M; Zacharias, H; Döppner, T; Glenzer, S H; Redmer, R

    2014-03-14

    We report on the dynamics of ultrafast heating in cryogenic hydrogen initiated by a ≲300  fs, 92 eV free electron laser x-ray burst. The rise of the x-ray scattering amplitude from a second x-ray pulse probes the transition from dense cryogenic molecular hydrogen to a nearly uncorrelated plasmalike structure, indicating an electron-ion equilibration time of ∼0.9  ps. The rise time agrees with radiation hydrodynamics simulations based on a conductivity model for partially ionized plasma that is validated by two-temperature density-functional theory.

  12. Ultrafast dynamics of single molecules.

    PubMed

    Brinks, Daan; Hildner, Richard; van Dijk, Erik M H P; Stefani, Fernando D; Nieder, Jana B; Hernando, Jordi; van Hulst, Niek F

    2014-04-21

    The detection of individual molecules has found widespread application in molecular biology, photochemistry, polymer chemistry, quantum optics and super-resolution microscopy. Tracking of an individual molecule in time has allowed identifying discrete molecular photodynamic steps, action of molecular motors, protein folding, diffusion, etc. down to the picosecond level. However, methods to study the ultrafast electronic and vibrational molecular dynamics at the level of individual molecules have emerged only recently. In this review we present several examples of femtosecond single molecule spectroscopy. Starting with basic pump-probe spectroscopy in a confocal detection scheme, we move towards deterministic coherent control approaches using pulse shapers and ultra-broad band laser systems. We present the detection of both electronic and vibrational femtosecond dynamics of individual fluorophores at room temperature, showing electronic (de)coherence, vibrational wavepacket interference and quantum control. Finally, two colour phase shaping applied to photosynthetic light-harvesting complexes is presented, which allows investigation of the persistent coherence in photosynthetic complexes under physiological conditions at the level of individual complexes. PMID:24473271

  13. Motion4D-library extended

    NASA Astrophysics Data System (ADS)

    Müller, Thomas

    2011-06-01

    The new version of the Motion4D-library now also includes the integration of a Sachs basis and the Jacobi equation to determine gravitational lensing of pointlike sources for arbitrary spacetimes.New version program summaryProgram title: Motion4D-libraryCatalogue identifier: AEEX_v3_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEEX_v3_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 219 441No. of bytes in distributed program, including test data, etc.: 6 968 223Distribution format: tar.gzProgramming language: C++Computer: All platforms with a C++ compilerOperating system: Linux, WindowsRAM: 61 MbytesClassification: 1.5External routines: Gnu Scientic Library (GSL) (http://www.gnu.org/software/gsl/)Catalogue identifier of previous version: AEEX_v2_0Journal reference of previous version: Comput. Phys. Comm. 181 (2010) 703Does the new version supersede the previous version?: YesNature of problem: Solve geodesic equation, parallel and Fermi-Walker transport in four-dimensional Lorentzian spacetimes. Determine gravitational lensing by integration of Jacobi equation and parallel transport of Sachs basis.Solution method: Integration of ordinary differential equations.Reasons for new version: The main novelty of the current version is the extension to integrate the Jacobi equation and the parallel transport of the Sachs basis along null geodesics. In combination, the change of the cross section of a light bundle and thus the gravitational lensing effect of a spacetime can be determined. Furthermore, we have implemented several new metrics.Summary of revisions: The main novelty of the current version is the integration of the Jacobi equation and the parallel transport of the Sachs basis along null geodesics. The corresponding set of equations readd2xμdλ2=-Γρ

  14. The 4D-TECS integration for NASA TSRV airplane

    NASA Technical Reports Server (NTRS)

    Kaminer, I.; Oshaughnessy, P. R.

    1989-01-01

    The integration of the Total Energy Control System (TECS) concept with 4D navigation is described. This integration was made to increase the operational capacity of modern aircraft and encourage incorporation of this increased capability with the evolving National Airspace System (NAS). Described herein is: 4D smoothing, the basic concepts of TECS, the spoiler integration concept, an algorithm for nulling out time error, speed and altitude profile modes, manual spoiler implementation, 4D logic, and the results of linear and nonlinear analysis.

  15. Killing Weeds with 2,4-D. Extension Bulletin 389.

    ERIC Educational Resources Information Center

    Lee, Oliver C.

    Discussed is the use of the herbicide 2,4-D. Though written for farmers and agricultural workers, the pamphlet considers turf weed control and use of 2,4-D near ornamental plants. Aspects of the use of this herbicide covered are: (1) the common forms of 2,4-D; (2) plant responses and tolerances to the herbicide; (3) dilution and concentration of…

  16. Pros and cons for C4d as a biomarker.

    PubMed

    Cohen, Danielle; Colvin, Robert B; Daha, Mohamed R; Drachenberg, Cinthia B; Haas, Mark; Nickeleit, Volker; Salmon, Jane E; Sis, Banu; Zhao, Ming-Hui; Bruijn, Jan A; Bajema, Ingeborg M

    2012-04-01

    The introduction of C4d in daily clinical practice in the late nineties aroused an ever-increasing interest in the role of antibody-mediated mechanisms in allograft rejection. As a marker of classical complement activation, C4d made it possible to visualize the direct link between anti-donor antibodies and tissue injury at sites of antibody binding in a graft. With the expanding use of C4d worldwide several limitations of C4d were identified. For instance, in ABO-incompatible transplantations C4d is present in the majority of grafts but this seems to point at 'graft accommodation' rather than antibody-mediated rejection. C4d is now increasingly recognized as a potential biomarker in other fields where antibodies can cause tissue damage, such as systemic autoimmune diseases and pregnancy. In all these fields, C4d holds promise to detect patients at risk for the consequences of antibody-mediated disease. Moreover, the emergence of new therapeutics that block complement activation makes C4d a marker with potential to identify patients who may possibly benefit from these drugs. This review provides an overview of the past, present, and future perspectives of C4d as a biomarker, focusing on its use in solid organ transplantation and discussing its possible new roles in autoimmunity and pregnancy. PMID:22297669

  17. Ultrafast pump-probe spectroscopy in gallium arsenide at 25 T.

    PubMed

    Curtis, Jeremy A; Tokumoto, Takahisa; Nolan, Nicholas K; McClintock, Luke M; Cherian, Judy G; McGill, Stephen A; Hilton, David J

    2014-10-01

    We have performed high-fluence, nondegenerate pump-probe spectroscopy in the Split Florida-Helix magnet at 25 T and 15 K. The electronic component of our ultrafast differential reflectivity can be described with a simplified four-level approximation to determine the scattering and recombination rates. Ultrafast oscillations are well described by a coherent acoustic phonon model. Our free-space ultrafast spectroscopic technique will permit future experimental investigations to study novel photoinduced phase transitions and complex interactions in correlated electron systems, which will require the high pulse energies of our free-space alternative.

  18. An ultrafast reciprocating probe

    NASA Astrophysics Data System (ADS)

    Liu, Wenbin; Tan, Yi; Wang, Wenhao; Gao, Zhe

    2016-11-01

    For tokamak plasma diagnostics, an ultrafast reciprocating probe system driven by magnetic field coils, achieving a maximum velocity of 21 m/s, is introduced. The probes are attached with a driving hoop made of carbon steel and accelerated by three acceleration coils in series, then decelerated by two deceleration coils and buffer springs and return slowly. The coils with a current of about 1 kA generate a magnetic field of about 1 T. This probe system has been tested on the SUNIST (Sino-UNIted Spherical Tokamak) spherical tokamak. Radial profiles of the floating potential and other plasma parameters measured by this probe system are given.

  19. Ultrafast transient absorption studies on photosystem I reaction centers from Chlamydomonas reinhardtii. 2: mutations near the P700 reaction center chlorophylls provide new insight into the nature of the primary electron donor.

    PubMed

    Holzwarth, Alfred R; Müller, Marc G; Niklas, Jens; Lubitz, Wolfgang

    2006-01-15

    The energy transfer and charge separation kinetics in several core Photosystem I particles of Chlamydomonas reinhardtii with point mutations around the PA and PB reaction center chlorophylls (Chls) have been studied using ultrafast transient absorption spectroscopy in the femtosecond to nanosecond time range to characterize the influence on the early electron transfer processes. The data have been analyzed in terms of kinetic compartment models. The adequate description of the transient absorption kinetics requires three different radical pairs in the time range up to approximately 100 ps. Also a charge recombination process from the first radical pair back to the excited state is present in all the mutants, as already shown previously for the wild-type (Müller, M. G., J. Niklas, W. Lubitz, and A. R. Holzwarth. 2003. Biophys. J. 85:3899-3922; and Holzwarth, A. R., M. G. Müller, J. Niklas, and W. Lubitz. 2005. J. Phys. Chem. B. 109:5903-59115). In all mutants, the primary charge separation occurs with the same effective rate constant within the error limits as in the wild-type (>350 ns(-1)), which implies an intrinsic rate constant of charge separation of <1 ps(-1). The rate constant of the secondary electron transfer process is slowed down by a factor of approximately 2 in the mutant B-H656C, which lacks the ligand to the central metal of Chl PB. For the mutant A-T739V, which breaks the hydrogen bond to the keto carbonyl of Chl PA, only a slight slowing down of the secondary electron transfer is observed. Finally for mutant A-W679A, which has the Trp near the PA Chl replaced, either no pronounced effect or, at best, a slight increase on the secondary electron transfer rate constants is observed. The effective charge recombination rate constant is modified in all mutants to some extent, with the strongest effect observed in mutant B-H656C. Our data strongly suggest that the Chls of the PA and PB pair, constituting what is traditionally called the "primary electron

  20. Phosphodiesterase 4D Inhibitors Limit Prostate Cancer Growth Potential

    PubMed Central

    Powers, Ginny L.; Hammer, Kimberly D.P.; Domenech, Maribella; Frantskevich, Katsiaryna; Malinowski, Rita L.; Bushman, Wade; Beebe, David J.; Marker, Paul C.

    2014-01-01

    Phosphodiesterase 4D (PDE4D) has recently been implicated as a proliferation-promoting factor in prostate cancer and is over-expressed in human prostate carcinoma. However, the effects of PDE4D inhibition using pharmacological inhibitors have not been examined in prostate cancer. These studies examined the effects of selective PDE4D inhibitors, NVP-ABE171 and cilomilast, as anti-prostate cancer therapies in both in vitro and in vivo models. The effects of PDE4D inhibitors on pathways that are critical in prostate cancer and/or downstream of cyclic AMP (cAMP) were examined. Both NVP-ABE171 and cilomilast decreased cell growth. In vitro, PDE4D inhibitors lead to decreased signaling of the sonic hedgehog (SHH), Androgen Receptor (AR), and MAPK pathways, but growth inhibition was best correlated to the sonic hedgehog pathway. PDE4D inhibition also reduced proliferation of epithelial cells induced by paracrine signaling from co-cultured stromal cells that had activated hedgehog signaling. In addition, PDE4D inhibitors decreased the weight of the prostate in wild-type mice. Prostate cancer xenografts grown in nude mice that were treated with cilomilast or NVP-ABE171 had decreased wet weight and increased apoptosis compared to vehicle treated controls. These studies suggest the pharmacological inhibition of PDE4D using small molecule inhibitors is an effective option for prostate cancer therapy. Implications PDE4D inhibitors decrease the growth of prostate cancer cells in vivo and in vitro, and PDE4D inhibition has therapeutic potential in prostate cancer. PMID:25149359

  1. Hard-X-Ray-Induced Multistep Ultrafast Dissociation

    NASA Astrophysics Data System (ADS)

    Travnikova, Oksana; Marchenko, Tatiana; Goldsztejn, Gildas; Jänkälä, Kari; Sisourat, Nicolas; Carniato, Stéphane; Guillemin, Renaud; Journel, Loïc; Céolin, Denis; Püttner, Ralph; Iwayama, Hiroshi; Shigemasa, Eiji; Piancastelli, Maria Novella; Simon, Marc

    2016-05-01

    Creation of deep core holes with very short (τ ≤1 fs ) lifetimes triggers a chain of relaxation events leading to extensive nuclear dynamics on a few-femtosecond time scale. Here we demonstrate a general multistep ultrafast dissociation on an example of HCl following Cl 1 s →σ* excitation. Intermediate states with one or multiple holes in the shallower core electron shells are generated in the course of the decay cascades. The repulsive character and large gradients of the potential energy surfaces of these intermediates enable ultrafast fragmentation after the absorption of a hard x-ray photon.

  2. 4D Printing with Mechanically Robust, Thermally Actuating Hydrogels.

    PubMed

    Bakarich, Shannon E; Gorkin, Robert; in het Panhuis, Marc; Spinks, Geoffrey M

    2015-06-01

    A smart valve is created by 4D printing of hydrogels that are both mechanically robust and thermally actuating. The printed hydrogels are made up of an interpenetrating network of alginate and poly(N-isopropylacrylamide). 4D structures are created by printing the "dynamic" hydrogel ink alongside other static materials. PMID:25864515

  3. 32 CFR 1645.4 - Exclusion from Class 4-D.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... MINISTERS OF RELIGION § 1645.4 Exclusion from Class 4-D. A registrant is excluded from Class 4-D when his... duly ordained minister of religion in accordance with the ceremonial rite or discipline of a church... principles of religion and administer the ordinances of public worship, as embodied in the creed...

  4. 4D Printing with Mechanically Robust, Thermally Actuating Hydrogels.

    PubMed

    Bakarich, Shannon E; Gorkin, Robert; in het Panhuis, Marc; Spinks, Geoffrey M

    2015-06-01

    A smart valve is created by 4D printing of hydrogels that are both mechanically robust and thermally actuating. The printed hydrogels are made up of an interpenetrating network of alginate and poly(N-isopropylacrylamide). 4D structures are created by printing the "dynamic" hydrogel ink alongside other static materials.

  5. 32 CFR 1645.4 - Exclusion from Class 4-D.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... MINISTERS OF RELIGION § 1645.4 Exclusion from Class 4-D. A registrant is excluded from Class 4-D when his... duly ordained minister of religion in accordance with the ceremonial rite or discipline of a church... principles of religion and administer the ordinances of public worship, as embodied in the creed...

  6. 32 CFR 1645.4 - Exclusion from Class 4-D.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... MINISTERS OF RELIGION § 1645.4 Exclusion from Class 4-D. A registrant is excluded from Class 4-D when his... duly ordained minister of religion in accordance with the ceremonial rite or discipline of a church... principles of religion and administer the ordinances of public worship, as embodied in the creed...

  7. 32 CFR 1645.4 - Exclusion from Class 4-D.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... MINISTERS OF RELIGION § 1645.4 Exclusion from Class 4-D. A registrant is excluded from Class 4-D when his... duly ordained minister of religion in accordance with the ceremonial rite or discipline of a church... principles of religion and administer the ordinances of public worship, as embodied in the creed...

  8. 32 CFR 1645.4 - Exclusion from Class 4-D.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... MINISTERS OF RELIGION § 1645.4 Exclusion from Class 4-D. A registrant is excluded from Class 4-D when his... duly ordained minister of religion in accordance with the ceremonial rite or discipline of a church... principles of religion and administer the ordinances of public worship, as embodied in the creed...

  9. Ultrafast scanning tunneling microscopy

    SciTech Connect

    Botkin, D.A. |

    1995-09-01

    I have developed an ultrafast scanning tunneling microscope (USTM) based on uniting stroboscopic methods of ultrafast optics and scanned probe microscopy to obtain nanometer spatial resolution and sub-picosecond temporal resolution. USTM increases the achievable time resolution of a STM by more than 6 orders of magnitude; this should enable exploration of mesoscopic and nanometer size systems on time scales corresponding to the period or decay of fundamental excitations. USTM consists of a photoconductive switch with subpicosecond response time in series with the tip of a STM. An optical pulse from a modelocked laser activates the switch to create a gate for the tunneling current, while a second laser pulse on the sample initiates a dynamic process which affects the tunneling current. By sending a large sequence of identical pulse pairs and measuring the average tunnel current as a function of the relative time delay between the pulses in each pair, one can map the time evolution of the surface process. USTM was used to measure the broadband response of the STM`s atomic size tunnel barrier in frequencies from tens to hundreds of GHz. The USTM signal amplitude decays linearly with the tunnel junction conductance, so the spatial resolution of the time-resolved signal is comparable to that of a conventional STM. Geometrical capacitance of the junction does not appear to play an important role in the measurement, but a capacitive effect intimately related to tunneling contributes to the measured signals and may limit the ultimate resolution of the USTM.

  10. Spin current generated by thermally driven ultrafast demagnetization.

    PubMed

    Choi, Gyung-Min; Min, Byoung-Chul; Lee, Kyung-Jin; Cahill, David G

    2014-01-01

    Spin current is the key element for nanoscale spintronic devices. For ultrafast operation of such nano-devices, generation of spin current in picoseconds, a timescale that is difficult to achieve using electrical circuits, is highly desired. Here we show thermally driven ultrafast demagnetization of a perpendicular ferromagnet leads to spin accumulation in a normal metal and spin transfer torque in an in-plane ferromagnet. The data are well described by models of spin generation and transport based on differences and gradients of thermodynamic parameters. The temperature difference between electrons and magnons is the driving force for spin current generation by ultrafast demagnetization. On longer timescales, a few picoseconds following laser excitation, we also observe a small contribution to spin current by a temperature gradient and the spin-dependent Seebeck effect. PMID:25007978

  11. Femtosecond laser studies of ultrafast intramolecular processes

    SciTech Connect

    Hayden, C.

    1993-12-01

    The goal of this research is to better understand the detailed mechanisms of chemical reactions by observing, directly in time, the dynamics of fundamental chemical processes. In this work femtosecond laser pulses are used to initiate chemical processes and follow the progress of these processes in time. The authors are currently studying ultrafast internal conversion and subsequent intramolecular relaxation in unsaturated hydrocarbons. In addition, the authors are developing nonlinear optical techniques to prepare and monitor the time evolution of specific vibrational motions in ground electronic state molecules.

  12. Quarterly progress report for Q2 FY06 for Complex Transient Events in Materials Studied Using Ultrafast Electron Probes and Terascale Simulation (FWP SCW0289)

    SciTech Connect

    Campbell, G H

    2006-03-29

    In this quarter (Q2 FY06), the DTEM underwent a substantial reconfiguration of its laser systems. The cathode laser system was changed to provide greater numbers of electrons per pulse by lengthening the time duration of the pulse to 30 ns. The greater number of electrons per pulse has allowed us to acquire high quality pulsed images and diffraction patterns. The spatial resolution in the single pulsed image has been measured at better than 20 nm. The diffraction patterns are now more comparable to conventional electron microscope operation. Examples are found in the body of the report. We summarize important achievements in the following list: (1) Instrument performance and design improvements--(A) The laser system was changed for the cathode photoemission system (75 ns at 1053 nm wavelength converted to 30ns at 211 nm wavelength) to give longer electron pulses at the same current to yield more electrons per pulse. (B) New specimen drive laser constructed. (C) New computer monitored and controlled alignment systems installed for both laser systems to facilitate laser alignment through a user friendly computer interface. (2) Experimental Progress--(A) The spatial resolution of pulsed images was tested by imaging a cross-section of multilayer thin foils with 30 nm and 20 nm periods. Single pulse images were observed to have spatial resolution better than 20 nm. This combination of 20 nm spatial and 30 ns temporal resolution is thought to be highest combined spatial and temporal measurement ever made. (B) The quality of single pulse electron diffraction patterns have been improved to the point where differentiating the HCP from BCC patterns in Ti is substantially easier. The spatial coherence of the electron illumination on the specimen was improved to give much smaller diffraction spots in the pattern.

  13. 4D-fingerprints, universal QSAR and QSPR descriptors.

    PubMed

    Senese, Craig L; Duca, J; Pan, D; Hopfinger, A J; Tseng, Y J

    2004-01-01

    An elusive goal in the field of chemoinformatics and molecular modeling has been the generation of a set of descriptors that, once calculated for a molecule, may be used in a wide variety of applications. Since such universal descriptors are generated free from external constraints, they are inherently independent of the data set in which they are employed. The realization of a set of universal descriptors would significantly streamline such chemoinformatics tasks as virtual high-throughout screening (VHTS) and toxicity profiling. The current study reports the derivation and validation of a potential set of universal descriptors, referred to as the 4D-fingerprints. The 4D-fingerprints are derived from the 4D-molecular similarity analysis. To evaluate the applicability of the 4D-fingerprints as universal descriptors, they are used to generate descriptive QSAR models for 5 independent training sets. Each of the training sets has been analyzed previously by several varying QSAR methods, and the results of the models generated using the 4D-fingerprints are compared to the results of the previous QSAR analyses. It was found that the models generated using the 4D-fingerprints are comparable in quality, based on statistical measures of fit and test set prediction, to the previously reported models for the other QSAR methods. This finding is particularly significant considering the 4D-fingerprints are generated independent of external constraints such as alignment, while the QSAR methods used for comparison all require an alignment analysis.

  14. 2D:4D finger ratio positively correlates with total cerebral cortex in males.

    PubMed

    Darnai, Gergely; Plózer, Enikő; Perlaki, Gábor; Orsi, Gergely; Nagy, Szilvia Anett; Horváth, Réka; Schwarcz, Attila; Kovács, Norbert; Altbäcker, Anna; Janszky, József; Clemens, Zsófia

    2016-02-26

    Although there is evidence that the ratio of 2nd-4th digit length (2D:4D) correlates with prenatal testosterone level, psychological and health traits only two studies have assessed the relationship with brain morphological features. Here we investigated the association between the 2D:4D ratio and several brain subvolumes. Seventy-five subjects between the ages of 18 and 30 were included in the study. The length of the 2nd and 4th digits were measured with an electronic vernier caliper while MRI measurements were performed on a Siemens Magnetom Trio Tim (3T) system. Freesurfer software suite was used for volumetric segmentation. Finger ratio significantly positively correlated with total cerebral cortex, total cerebellar white matter and total cerebellar cortex in males but not in females. Our results indicate that prenatal testosterone, as estimated by the 2D:4D ratio has an effect on adult brain morphology in males. PMID:26780566

  15. Interaction of 2,4-dichlorophenoxyacetic acid (2,4-D) with cell and model membranes.

    PubMed

    Suwalsky, M; Benites, M; Villena, F; Aguilar, F; Sotomayor, C P

    1996-12-01

    2,4-dichlorophenoxyacetic acid (2,4-D), a widely used herbicide, is a component of the "agent orange' whose toxicity has been extensively studied without definite conclusions. In order to evaluate its perturbing effect upon cell membranes, 2,4-D was made to interact with human erythrocytes and molecular models. These studies were performed by scanning electron microscopy on red cells, fluorescence spectroscopy on dimyristoylphosphatidylcholine (DMPC) large unilamellar vesicles and X-ray diffraction on multilayers of DMPC and dimyristoylphosphatidylethanolamine (DMPE). It was observed that 2,4-D induced a pronounced shape change to the erythrocytes. This effect is explained by the herbicide interaction with the outer monolayer of the red cell membrane. PMID:8972711

  16. Attosecond delay of xenon 4 d photoionization at the giant resonance and Cooper minimum

    NASA Astrophysics Data System (ADS)

    Magrakvelidze, Maia; Madjet, Mohamed El-Amine; Chakraborty, Himadri S.

    2016-07-01

    A Kohn-Sham time-dependent local-density-functional scheme is utilized to predict attosecond time delays of xenon 4 d photoionization that involves the 4 d giant dipole resonance and Cooper minimum. The fundamental effect of electron correlations to uniquely determine the delay at both regions is demonstrated. In particular, for the giant dipole resonance, the delay underpins strong collective effect, emulating the recent prediction at C60 giant plasmon resonance [T. Barillot et al., Phys. Rev. A 91, 033413 (2015), 10.1103/PhysRevA.91.033413]. For the Cooper minimum, a qualitative similarity with a photorecombination experiment near argon 3 p minimum [S. B. Schoun et al., Phys. Rev. Lett. 112, 153001 (2014), 10.1103/PhysRevLett.112.153001] is found. The result should encourage attosecond measurements of Xe 4 d photoemission.

  17. Real-time measurements of ultrafast electronic dynamics in the disproportionation of [TCNQ]22- using a visible sub-10 fs pulse laser

    NASA Astrophysics Data System (ADS)

    Hashimoto, Sena; Yabushita, Atsushi; Kobayashi, Takayoshi; Iwakura, Izumi

    2016-04-01

    The reduction of 7,7,8,8-tetracyanoquinodimethane (TCNQ) generates a π radical anion, TCNQrad -, that dimerizes in methanol solution. This dimer ([TCNQ]22-) exhibits a charge-transfer absorption peak at 620 nm and will disproportionate to give TCNQ and TCNQ2- in response to excitation within this charge-transfer band. The present study examined the electronic dynamics of [TCNQ]22- disproportionation. The disproportionation was found to proceed in two steps. Electron transfer, representing the first step, occurred within the 10 fs pulse window, followed by the actual dissociation, within 350 fs. The emission lifetime of the singlet excited state of TCNQ2- was estimated to be 900 fs.

  18. AttoPhotoChemistry. Probing ultrafast electron dynamics by the induced nuclear motion: The prompt and delayed predissociation of N2

    NASA Astrophysics Data System (ADS)

    Muskatel, B. H.; Remacle, F.; Levine, R. D.

    2014-05-01

    Quantum mechanical wavepacket dynamics simulation that includes the nuclear motion exhibit a prompt, few fs, dissociation of electronically attosecond excited N2 in addition to the slow dissociation evident from spectral line broadening in well resolved spectra. The simulations show that nuclear motion can probe early times electron dynamics. The separation of time scales is mimicked by a model study fashioned like chemical kinetics of unimolecular dissociation. The physical origin of the separation into prompt and delayed decay is argued to be the same in the vibrational and the present case, namely that there are more bound than dissociative channels.

  19. Training Ultrafast Laser Pulses

    NASA Astrophysics Data System (ADS)

    Averin, Ruslan; Wells, N.; Todt, M.; Smolnisky, N.; Jastram, N.; Jochim, B.; Gregerson, N.; Wells, E.; Sayler, A.; McKenna, J.; Carnes, K.; Ben-Itzhak, I.; Kling, M. F.

    2009-11-01

    Closed loop control of molecular processes utilizing shaped ultrafast laser pulses has been around for a number of years, yet this type of control has primarily utilized Time of Flight ion yield data for feedback. We present experiments using Velocity Map Imaging (VMI) as the feedback source for the closed loop control. Using VMI allows for pulse optimization not only with respect to the disassociation species but also angular information of the final state. We demonstrate the feasibility of incorporating this kind of feedback into the control loop. Using this technique, we controlled the dissociation branching ratio of CO^+ into C^+ +O or C ^+O^+ and used the VMI information to recover additional information about the control mechanism.

  20. Ultra-fast computation of electronic spectra for large systems by tight-binding based simplified Tamm-Dancoff approximation (sTDA-xTB).

    PubMed

    Grimme, Stefan; Bannwarth, Christoph

    2016-08-01

    The computational bottleneck of the extremely fast simplified Tamm-Dancoff approximated (sTDA) time-dependent density functional theory procedure [S. Grimme, J. Chem. Phys. 138, 244104 (2013)] for the computation of electronic spectra for large systems is the determination of the ground state Kohn-Sham orbitals and eigenvalues. This limits such treatments to single structures with a few hundred atoms and hence, e.g., sampling along molecular dynamics trajectories for flexible systems or the calculation of chromophore aggregates is often not possible. The aim of this work is to solve this problem by a specifically designed semi-empirical tight binding (TB) procedure similar to the well established self-consistent-charge density functional TB scheme. The new special purpose method provides orbitals and orbital energies of hybrid density functional character for a subsequent and basically unmodified sTDA procedure. Compared to many previous semi-empirical excited state methods, an advantage of the ansatz is that a general eigenvalue problem in a non-orthogonal, extended atomic orbital basis is solved and therefore correct occupied/virtual orbital energy splittings as well as Rydberg levels are obtained. A key idea for the success of the new model is that the determination of atomic charges (describing an effective electron-electron interaction) and the one-particle spectrum is decoupled and treated by two differently parametrized Hamiltonians/basis sets. The three-diagonalization-step composite procedure can routinely compute broad range electronic spectra (0-8 eV) within minutes of computation time for systems composed of 500-1000 atoms with an accuracy typical of standard time-dependent density functional theory (0.3-0.5 eV average error). An easily extendable parametrization based on coupled-cluster and density functional computed reference data for the elements H-Zn including transition metals is described. The accuracy of the method termed sTDA-xTB is first

  1. Ultra-fast computation of electronic spectra for large systems by tight-binding based simplified Tamm-Dancoff approximation (sTDA-xTB)

    NASA Astrophysics Data System (ADS)

    Grimme, Stefan; Bannwarth, Christoph

    2016-08-01

    The computational bottleneck of the extremely fast simplified Tamm-Dancoff approximated (sTDA) time-dependent density functional theory procedure [S. Grimme, J. Chem. Phys. 138, 244104 (2013)] for the computation of electronic spectra for large systems is the determination of the ground state Kohn-Sham orbitals and eigenvalues. This limits such treatments to single structures with a few hundred atoms and hence, e.g., sampling along molecular dynamics trajectories for flexible systems or the calculation of chromophore aggregates is often not possible. The aim of this work is to solve this problem by a specifically designed semi-empirical tight binding (TB) procedure similar to the well established self-consistent-charge density functional TB scheme. The new special purpose method provides orbitals and orbital energies of hybrid density functional character for a subsequent and basically unmodified sTDA procedure. Compared to many previous semi-empirical excited state methods, an advantage of the ansatz is that a general eigenvalue problem in a non-orthogonal, extended atomic orbital basis is solved and therefore correct occupied/virtual orbital energy splittings as well as Rydberg levels are obtained. A key idea for the success of the new model is that the determination of atomic charges (describing an effective electron-electron interaction) and the one-particle spectrum is decoupled and treated by two differently parametrized Hamiltonians/basis sets. The three-diagonalization-step composite procedure can routinely compute broad range electronic spectra (0-8 eV) within minutes of computation time for systems composed of 500-1000 atoms with an accuracy typical of standard time-dependent density functional theory (0.3-0.5 eV average error). An easily extendable parametrization based on coupled-cluster and density functional computed reference data for the elements H-Zn including transition metals is described. The accuracy of the method termed sTDA-xTB is first

  2. Quarterly progress report for Q1 FY06 for Complex Transient Events in Materials Studied Using Ultrafast Electron Probes and Terascale Simulation (FWP SCW0289)

    SciTech Connect

    Campbell, G

    2005-12-27

    This quarter (Q1 FY06) marked the first time that the LLNL dynamic transmission electron microscope (DTEM) configuration had advanced to the point whereby it was possible to conduct in-situ experiments on specimens. DTEM improvements continue to progress at a rapid pace. We summarize important achievements in the following list: (1) Instrument performance and design improvements - (a) Reproducibly achieving >1 x 10{sup 7} e{sup -} per pulse. Adjustments in the cathode laser system design led to an improved quantum efficiency and electron yield per pulse. The current number of electrons in the pulse is sufficient for acquiring high quality, single-shot electron diffraction patterns. (b) Implementation of computer interface and Labview{reg_sign} programs for cathode and specimen drive alignment and cathode and pump laser trigger and delay settings. These controls provide a user friendly interface and ease in the experimental setup and implementation. (c) Cathode test chamber (offline test apparatus to asses photocathode design and laser induced photoemission) construction has been completed. (2) Notable instrument features brought into service - (a) Drive laser system was enhanced to improve beam shape and uniformity and to include continuous laser energy monitoring. The drive laser spot size on the specimen was also reduced from 70 {mu}m x 110 {mu}m to 50 {mu}m x 75 {mu}m. (b) New phosphor coated face plate manufactured by TVIPS was installed. The sensitivity and signal noise ratio improved by factor 2 (sensitivity {approx}110 CCD counts/e{sup -} and signal to noise ratio {approx}5). (3) Experimental Progress - (a) First time-resolved experiment: observation of the {alpha} (hcp) to {beta} (bcc) phase transition in pure Ti films via single shot electron diffraction. Results of this experiment were published in the MRS Fall 2005 proceedings and are under review for article in the FEMMS proceedings, which will to be published in Journal of Material Science. See

  3. Ultra-fast computation of electronic spectra for large systems by tight-binding based simplified Tamm-Dancoff approximation (sTDA-xTB).

    PubMed

    Grimme, Stefan; Bannwarth, Christoph

    2016-08-01

    The computational bottleneck of the extremely fast simplified Tamm-Dancoff approximated (sTDA) time-dependent density functional theory procedure [S. Grimme, J. Chem. Phys. 138, 244104 (2013)] for the computation of electronic spectra for large systems is the determination of the ground state Kohn-Sham orbitals and eigenvalues. This limits such treatments to single structures with a few hundred atoms and hence, e.g., sampling along molecular dynamics trajectories for flexible systems or the calculation of chromophore aggregates is often not possible. The aim of this work is to solve this problem by a specifically designed semi-empirical tight binding (TB) procedure similar to the well established self-consistent-charge density functional TB scheme. The new special purpose method provides orbitals and orbital energies of hybrid density functional character for a subsequent and basically unmodified sTDA procedure. Compared to many previous semi-empirical excited state methods, an advantage of the ansatz is that a general eigenvalue problem in a non-orthogonal, extended atomic orbital basis is solved and therefore correct occupied/virtual orbital energy splittings as well as Rydberg levels are obtained. A key idea for the success of the new model is that the determination of atomic charges (describing an effective electron-electron interaction) and the one-particle spectrum is decoupled and treated by two differently parametrized Hamiltonians/basis sets. The three-diagonalization-step composite procedure can routinely compute broad range electronic spectra (0-8 eV) within minutes of computation time for systems composed of 500-1000 atoms with an accuracy typical of standard time-dependent density functional theory (0.3-0.5 eV average error). An easily extendable parametrization based on coupled-cluster and density functional computed reference data for the elements H-Zn including transition metals is described. The accuracy of the method termed sTDA-xTB is first

  4. Ultrafast X-Ray Coherent Control

    SciTech Connect

    Reis, David

    2009-05-01

    This main purpose of this grant was to develop the nascent eld of ultrafast x-ray science using accelerator-based sources, and originally developed from an idea that a laser could modulate the di racting properties of a x-ray di racting crystal on a fast enough time scale to switch out in time a shorter slice from the already short x-ray pulses from a synchrotron. The research was carried out primarily at the Advanced Photon Source (APS) sector 7 at Argonne National Laboratory and the Sub-Picosecond Pulse Source (SPPS) at SLAC; in anticipation of the Linac Coherent Light Source (LCLS) x-ray free electron laser that became operational in 2009 at SLAC (all National User Facilities operated by BES). The research centered on the generation, control and measurement of atomic-scale dynamics in atomic, molecular optical and condensed matter systems with temporal and spatial resolution . It helped develop the ultrafast physics, techniques and scienti c case for using the unprecedented characteristics of the LCLS. The project has been very successful with results have been disseminated widely and in top journals, have been well cited in the eld, and have laid the foundation for many experiments being performed on the LCLS, the world's rst hard x-ray free electron laser.

  5. C4d staining as immunohistochemical marker in inflammatory myopathies.

    PubMed

    Pytel, Peter

    2014-10-01

    The diagnosis of an inflammatory myopathy is often established based on basic histologic studies. Additional immunohistochemical studies are sometimes required to support the diagnosis and the classification of inflammatory myopathies. Staining for major histocompatibility complex 1 (MHC1) often shows increased sarcolemmal labeling in inflammatory myopathies. Endomysial capillary staining C5b-9 (membrane attack complex) is a feature that is reported as frequently associated with dermatomyositis. Immunohistochemical staining for C4d is widely used for various applications including the assessment of antibody-mediated rejection after solid organ transplantation. In the context of dermatomyositis, C4d staining has been described in skin biopsies but not in muscle biopsies. A total of 32 muscle biopsy specimens were examined. The hematoxylin and eosin-stained slides were reviewed, and immunohistochemical studies for MHC1, C5b-9, and C4d were conducted. The staining observed for C5b-9 and C4d was compared. Overall, the staining pattern for C4d mirrored the one observed for C5b-9 in the examined muscle biopsy specimens. There was high and statistically significant (P<0.0001) correlation between the staining seen with these 2 antibodies. Both antibodies labeled the cytoplasm of degenerating necrotic myofibers. In addition, both antibodies showed distinct endomysial capillary labeling in a subset of dermatomyositis. Areas with perifascicular atrophy often exhibited the most prominent vascular labeling for C4d and C5b-9. In conclusion, C4d and C5b-9 show similar expression patterns in muscle biopsies of patients with inflammatory myopathies and both highlight the presence of vascular labeling associated with dermatomyositis. C4d antibodies are widely used and may offer an alternative for C5b-9 staining.

  6. Spin-on spintronics: ultrafast electron spin dynamics in ZnO and Zn₁-xCoxO sol-gel films.

    PubMed

    Whitaker, Kelly M; Raskin, Maxim; Kiliani, Gillian; Beha, Katja; Ochsenbein, Stefan T; Janssen, Nils; Fonin, Mikhail; Rüdiger, Ulrich; Leitenstorfer, Alfred; Gamelin, Daniel R; Bratschitsch, Rudolf

    2011-08-10

    We use time-resolved Faraday rotation spectroscopy to probe the electron spin dynamics in ZnO and magnetically doped Zn(1-x)Co(x)O sol-gel thin films. In undoped ZnO, we observe an anomalous temperature dependence of the ensemble spin dephasing time T(2), i.e., longer coherence times at higher temperatures, reaching T(2) ∼ 1.2 ns at room temperature. Time-resolved transmission measurements suggest that this effect arises from hole trapping at grain surfaces. Deliberate addition of Co(2+) to ZnO increases the effective electron Landé g factor, providing the first direct determination of the mean-field electron-Co(2+) exchange energy in Zn(1-x)Co(x)O (N(0)α = +0.25 ± 0.02 eV). In Zn(1-x)Co(x)O, T(2) also increases with increasing temperature, allowing spin precession to be observed even at room temperature.

  7. Ultrafast and nonlinear optics in carbon nanomaterials.

    PubMed

    Kono, Junichiro

    2013-02-01

    Carbon-based nanomaterials—single-wall carbon nanotubes (SWCNTs) and graphene, in particular—have emerged in the last decade as novel low-dimensional systems with extraordinary properties. Because they are direct-bandgap systems, SWCNTs are one of the leading candidates to unify electronic and optical functions in nanoscale circuitry; their diameter-dependent bandgaps can be utilized for multi-wavelength devices. Graphene's ultrahigh carrier mobilities are promising for high-frequency electronic devices, while, at the same time, it is predicted to have ideal properties for terahertz generation and detection due to its unique zero-gap, zero-mass band structure. There have been a large number of basic optical studies on these materials, but most of them were performed in the weak-excitation, quasi-equilibrium regime. In order to probe and assess their performance characteristics as optoelectronic materials under device-operating conditions, it is crucial to strongly drive them and examine their optical properties in highly non-equilibrium situations and with ultrashot time resolution. In this section, the reader will find the latest results in this rapidly growing field of research. We have assembled contributions from some of the leading experts in ultrafast and nonlinear optical spectroscopy of carbon-based nanomaterials. Specific topics featured include: thermalization, cooling, and recombination dynamics of photo-generated carriers; stimulated emission, gain, and amplification; ultrafast photoluminescence; coherent phonon dynamics; exciton–phonon and exciton–plasmon interactions; exciton–exciton annihilation and Auger processes; spontaneous and stimulated emission of terahertz radiation; four-wave mixing and harmonic generation; ultrafast photocurrents; the AC Stark and Franz–Keldysh effects; and non-perturbative light–mater coupling. We would like to express our sincere thanks to those who contributed their latest results to this special section

  8. Manipulating magnetic anisotropy and ultrafast spin dynamics of magnetic nanostructures

    NASA Astrophysics Data System (ADS)

    Cheng, Zhao-Hua; He, Wei; Zhang, Xiang-Qun; Sun, Da-Li; Du, Hai-Feng; Wu, Qiong; Ye, Jun; Fang, Ya-Peng; Liu, Hao-Liang

    2015-07-01

    We present our extensive research into magnetic anisotropy. We tuned the terrace width of Si(111) substrate by a novel method: varying the direction of heating current and consequently manipulating the magnetic anisotropy of magnetic structures on the stepped substrate by decorating its atomic steps. Laser-induced ultrafast demagnetization of a CoFeB/MgO/CoFeB magnetic tunneling junction was explored by the time-resolved magneto-optical Kerr effect (TR-MOKE) for both the parallel state (P state) and the antiparallel state (AP state) of the magnetizations between two magnetic layers. It was observed that the demagnetization time is shorter and the magnitude of demagnetization is larger in the AP state than those in the P state. These behaviors are attributed to the ultrafast spin transfer between two CoFeB layers via the tunneling of hot electrons through the MgO barrier. Our observation indicates that ultrafast demagnetization can be engineered by the hot electron tunneling current. This opens the door to manipulate the ultrafast spin current in magnetic tunneling junctions. Furthermore, an all-optical TR-MOKE technique provides the flexibility for exploring the nonlinear magnetization dynamics in ferromagnetic materials, especially with metallic materials. Project supported by the National Basic Research Program of China (Grant Nos. 2015CB921403, 2011CB921801, and 2012CB933101) and the National Natural Science Foundation of China (Grant Nos. 51427801, 11374350, 51201179, and 11274361).

  9. Ultrafast Mid-Infrared Nanoscopy of Strained Vanadium Dioxide Nanobeams.

    PubMed

    Huber, M A; Plankl, M; Eisele, M; Marvel, R E; Sandner, F; Korn, T; Schüller, C; Haglund, R F; Huber, R; Cocker, T L

    2016-02-10

    Long regarded as a model system for studying insulator-to-metal phase transitions, the correlated electron material vanadium dioxide (VO2) is now finding novel uses in device applications. Two of its most appealing aspects are its accessible transition temperature (∼341 K) and its rich phase diagram. Strain can be used to selectively stabilize different VO2 insulating phases by tuning the competition between electron and lattice degrees of freedom. It can even break the mesoscopic spatial symmetry of the transition, leading to a quasiperiodic ordering of insulating and metallic nanodomains. Nanostructuring of strained VO2 could potentially yield unique components for future devices. However, the most spectacular property of VO2--its ultrafast transition--has not yet been studied on the length scale of its phase heterogeneity. Here, we use ultrafast near-field microscopy in the mid-infrared to study individual, strained VO2 nanobeams on the 10 nm scale. We reveal a previously unseen correlation between the local steady-state switching susceptibility and the local ultrafast response to below-threshold photoexcitation. These results suggest that it may be possible to tailor the local photoresponse of VO2 using strain and thereby realize new types of ultrafast nano-optical devices.

  10. Resolution limits of ultrafast ultrasound localization microscopy.

    PubMed

    Desailly, Yann; Pierre, Juliette; Couture, Olivier; Tanter, Mickael

    2015-11-21

    As in other imaging methods based on waves, the resolution of ultrasound imaging is limited by the wavelength. However, the diffraction-limit can be overcome by super-localizing single events from isolated sources. In recent years, we developed plane-wave ultrasound allowing frame rates up to 20,000 fps. Ultrafast processes such as rapid movement or disruption of ultrasound contrast agents (UCA) can thus be monitored, providing us with distinct punctual sources that could be localized beyond the diffraction limit. We previously showed experimentally that resolutions beyond λ/10 can be reached in ultrafast ultrasound localization microscopy (uULM) using a 128 transducer matrix in reception. Higher resolutions are theoretically achievable and the aim of this study is to predict the maximum resolution in uULM with respect to acquisition parameters (frequency, transducer geometry, sampling electronics). The accuracy of uULM is the error on the localization of a bubble, considered a point-source in a homogeneous medium. The proposed model consists in two steps: determining the timing accuracy of the microbubble echo in radiofrequency data, then transferring this time accuracy into spatial accuracy. The simplified model predicts a maximum resolution of 40 μm for a 1.75 MHz transducer matrix composed of two rows of 64 elements. Experimental confirmation of the model was performed by flowing microbubbles within a 60 μm microfluidic channel and localizing their blinking under ultrafast imaging (500 Hz frame rate). The experimental resolution, determined as the standard deviation in the positioning of the microbubbles, was predicted within 6 μm (13%) of the theoretical values and followed the analytical relationship with respect to the number of elements and depth. Understanding the underlying physical principles determining the resolution of superlocalization will allow the optimization of the imaging setup for each organ. Ultimately, accuracies better than the size of

  11. Resolution limits of ultrafast ultrasound localization microscopy.

    PubMed

    Desailly, Yann; Pierre, Juliette; Couture, Olivier; Tanter, Mickael

    2015-11-21

    As in other imaging methods based on waves, the resolution of ultrasound imaging is limited by the wavelength. However, the diffraction-limit can be overcome by super-localizing single events from isolated sources. In recent years, we developed plane-wave ultrasound allowing frame rates up to 20,000 fps. Ultrafast processes such as rapid movement or disruption of ultrasound contrast agents (UCA) can thus be monitored, providing us with distinct punctual sources that could be localized beyond the diffraction limit. We previously showed experimentally that resolutions beyond λ/10 can be reached in ultrafast ultrasound localization microscopy (uULM) using a 128 transducer matrix in reception. Higher resolutions are theoretically achievable and the aim of this study is to predict the maximum resolution in uULM with respect to acquisition parameters (frequency, transducer geometry, sampling electronics). The accuracy of uULM is the error on the localization of a bubble, considered a point-source in a homogeneous medium. The proposed model consists in two steps: determining the timing accuracy of the microbubble echo in radiofrequency data, then transferring this time accuracy into spatial accuracy. The simplified model predicts a maximum resolution of 40 μm for a 1.75 MHz transducer matrix composed of two rows of 64 elements. Experimental confirmation of the model was performed by flowing microbubbles within a 60 μm microfluidic channel and localizing their blinking under ultrafast imaging (500 Hz frame rate). The experimental resolution, determined as the standard deviation in the positioning of the microbubbles, was predicted within 6 μm (13%) of the theoretical values and followed the analytical relationship with respect to the number of elements and depth. Understanding the underlying physical principles determining the resolution of superlocalization will allow the optimization of the imaging setup for each organ. Ultimately, accuracies better than the size of

  12. Attosecond Light and Science at the Time-scale of the Electron-Coherent X-Rays from Tabletop Ultrafast Lasers

    SciTech Connect

    Murnane, Margaret

    2010-03-31

    Ever since the invention of the laser 50 years ago and its application in nonlinear optics, scientists have been striving to extend coherent laser beams into the x-ray region of the spectrum. Very recently however, the prospects for tabletop coherent sources at very short wavelengths, even in the hard x-ray region of the spectrum at wavelengths < 1nm, have brightened considerably. This advance is possible by taking nonlinear optics techniques to an extreme - physics that is the direct result of a new ability to manipulate electrons on the fastest, attosecond, time-scales of our natural world. Several applications have already been demonstrated, including making a movie of how electrons rearrange in a chemical bond changes shape as a molecule breaks apart, following how fast a magnetic material can flip orientation, understanding how fast heat flows in a nanocircuit, or building a microscope without lenses. Nature 460, 1088 (2009); Science 317, 775 (2007); Physical Review Letters 103, 257402 (2009); Nature Materials 9, 26 (2010); Nature 463, 214 (2010); Science 322, 1207 (2008).

  13. UVA radiation induced ultrafast electron transfer from a food carcinogen benzo[a]pyrene to organic molecules, biological macromolecules, and inorganic nano structures.

    PubMed

    Banerjee, Soma; Sarkar, Soumik; Lakshman, Karthik; Dutta, Joydeep; Pal, Samir Kumar

    2013-04-11

    Reactions involving electron transfer (ET) and reactive oxygen species (ROS) play a pivotal role in carcinogenesis and cancer biochemistry. Our present study emphasizes UVA radiation induced ET reaction as one of the key aspects of a potential carcinogen, benzo[a]pyrene (BP), in the presence of a wide variety of molecules covering organic p-benzoquinone (BQ), biological macromolecules like calf-thymus DNA (CT-DNA), human serum albumin (HSA) protein, and inorganic zinc oxide (ZnO) nanorods (NRs). Steady-state and picosecond-resolved fluorescence spectroscopy have been used to monitor such ET reactions. Physical consequences of BP association with CT-DNA have been investigated through temperature-dependent circular dichroism (CD) spectroscopy. The temperature-dependent steady-state, picosecond-resolved fluorescence lifetime and anisotropy studies reveal the effect of temperature on the perturbation of such ET reactions from BP to biological macromolecules, highlighting their temperature-dependent association. Furthermore, the electron-donating property of BP has been corroborated by measuring wavelength-dependent photocurrent in a BP-anchored ZnO NR-based photodevice, offering new physical insights for the carcinogenic study of BP.

  14. Plasma Heating and Ultrafast Semiconductor Laser Modulation Through a Terahertz Heating Field

    NASA Technical Reports Server (NTRS)

    Li, Jian-Zhong; Ning, C. Z.

    2000-01-01

    Electron-hole plasma heating and ultrafast modulation in a semiconductor laser under a terahertz electrical field are investigated using a set of hydrodynamic equations derived from the semiconductor Bloch equations. The self-consistent treatment of lasing and heating processes leads to the prediction of a strong saturation and degradation of modulation depth even at moderate terahertz field intensity. This saturation places a severe limit to bandwidth achievable with such scheme in ultrafast modulation. Strategies for increasing modulation depth are discussed.

  15. Energy levels in Ag-like (4d{sup 10}4f, 4d{sup 10}5l (l = 0-3)), Pd-like (4d{sup 9}4f [J = 1], 4d{sup 9}5p [J = 1], 4d{sup 9}5f [J = 1]), and Rh-like (4d{sup 9} [J = 5/2, 3/2]) ions with Z {<=} 86

    SciTech Connect

    Ivanova, E.P.

    2009-11-15

    Relativistic perturbation theory with a model potential is used for the calculation of energy levels of the states 4f{sub 5/2}, 4f{sub 7/2}, 5s{sub 1/2}, 5p{sub 1/2}, 5p{sub 3/2}, 5d{sub 3/2}, 5d{sub 5/2}, 5f{sub 5/2}, and 5f{sub 7/2} above the 1s{sup 2}2s{sup 2}2p{sup 6}3s{sup 2}3p{sup 6}3d{sup 10}4s{sup 2}4p{sup 6}4d{sup 10} core, with one vacancy 4d{sub 5/2}{sup 9}, 4d{sub 7/2}{sup 9} in the same core, in the silver and rhodium isoelectronic sequences with the maximum nuclear charge Z = 86. The method of extrapolation of the model potential parameter is applied to calculate one-electron and one-vacancy wavefunctions. The wavefunctions of Ag- and Rh-like ions were used to calculate the energies of resonance transitions to the ground state {sup 1}S{sub 0} in Pd-like ions. Good agreement between the theoretical and the experimental energies of the resonance transitions in Pd-like ions indicates the reliability of the results obtained.

  16. Semaphorin 4D Promotes Skeletal Metastasis in Breast Cancer.

    PubMed

    Yang, Ying-Hua; Buhamrah, Asma; Schneider, Abraham; Lin, Yi-Ling; Zhou, Hua; Bugshan, Amr; Basile, John R

    2016-01-01

    Bone density is controlled by interactions between osteoclasts, which resorb bone, and osteoblasts, which deposit it. The semaphorins and their receptors, the plexins, originally shown to function in the immune system and to provide chemotactic cues for axon guidance, are now known to play a role in this process as well. Emerging data have identified Semaphorin 4D (Sema4D) as a product of osteoclasts acting through its receptor Plexin-B1 on osteoblasts to inhibit their function, tipping the balance of bone homeostasis in favor of resorption. Breast cancers and other epithelial malignancies overexpress Sema4D, so we theorized that tumor cells could be exploiting this pathway to establish lytic skeletal metastases. Here, we use measurements of osteoblast and osteoclast differentiation and function in vitro and a mouse model of skeletal metastasis to demonstrate that both soluble Sema4D and protein produced by the breast cancer cell line MDA-MB-231 inhibits differentiation of MC3T3 cells, an osteoblast cell line, and their ability to form mineralized tissues, while Sema4D-mediated induction of IL-8 and LIX/CXCL5, the murine homologue of IL-8, increases osteoclast numbers and activity. We also observe a decrease in the number of bone metastases in mice injected with MDA-MB-231 cells when Sema4D is silenced by RNA interference. These results are significant because treatments directed at suppression of skeletal metastases in bone-homing malignancies usually work by arresting bone remodeling, potentially leading to skeletal fragility, a significant problem in patient management. Targeting Sema4D in these cancers would not affect bone remodeling and therefore could elicit an improved therapeutic result without the debilitating side effects.

  17. Soil matrix and macropore biodegradation of 2,4-D

    SciTech Connect

    Pivetz, B.E.; Steenhuis, T.S.

    1995-07-01

    Preferential flow of pesticides in macropores can lead to decreased travel times through the vadose zone and increased groundwater contamination. Macropores, however, may present a favorable environment for biodegradation because of greater oxygen, nutrient, and substrate supply, and higher microbial populations in earthworm burrows, compared to the soil matrix. The biodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D) was measured in macropores and soil matrix of packed soil columns (7.0-cm diam., 10-cm length) and undisturbed cores contained as well-defined artificial macropore and the undisturbed cores contained earthworm-burrow macropores. A 50 {mu}g/L 2,4-D solution was continuously applied to the unsaturated soil surface and breakthrough curves (BTCs) indicating pesticide loss in the effluent were obtained from the soil matrix and macropore flow paths. Biodegradation rates were calculated separately for each flow path by comparing the BTCs to BTCs representing abiotic conditions, and dividing the 2,4-D loss by the travel time through each flow path. The biodegradation rates increased with time in both flow paths, and the final biodegradation rate in the macropore region surpassed that of the matrix, presumably because of increased microbial populations in the macropore. Complete loss of the 2,4-D in both flow paths was observed after continuous application of 2,4-D for 400 h, with maximum column-averaged 2,4-D loss rates of 0.879 {mu}g/(L h) in the matrix and 1.073 {mu}g/(L h) in the macropore. Biodegradation of 2,4-D was also observed in the macropore and matrix regions of the undisturbed soil cores. 19 refs., 7 figs., 2 tabs.

  18. Semaphorin 4D Promotes Skeletal Metastasis in Breast Cancer

    PubMed Central

    Yang, Ying-Hua; Buhamrah, Asma; Schneider, Abraham; Lin, Yi-Ling; Zhou, Hua; Bugshan, Amr; Basile, John R.

    2016-01-01

    Bone density is controlled by interactions between osteoclasts, which resorb bone, and osteoblasts, which deposit it. The semaphorins and their receptors, the plexins, originally shown to function in the immune system and to provide chemotactic cues for axon guidance, are now known to play a role in this process as well. Emerging data have identified Semaphorin 4D (Sema4D) as a product of osteoclasts acting through its receptor Plexin-B1 on osteoblasts to inhibit their function, tipping the balance of bone homeostasis in favor of resorption. Breast cancers and other epithelial malignancies overexpress Sema4D, so we theorized that tumor cells could be exploiting this pathway to establish lytic skeletal metastases. Here, we use measurements of osteoblast and osteoclast differentiation and function in vitro and a mouse model of skeletal metastasis to demonstrate that both soluble Sema4D and protein produced by the breast cancer cell line MDA-MB-231 inhibits differentiation of MC3T3 cells, an osteoblast cell line, and their ability to form mineralized tissues, while Sema4D-mediated induction of IL-8 and LIX/CXCL5, the murine homologue of IL-8, increases osteoclast numbers and activity. We also observe a decrease in the number of bone metastases in mice injected with MDA-MB-231 cells when Sema4D is silenced by RNA interference. These results are significant because treatments directed at suppression of skeletal metastases in bone-homing malignancies usually work by arresting bone remodeling, potentially leading to skeletal fragility, a significant problem in patient management. Targeting Sema4D in these cancers would not affect bone remodeling and therefore could elicit an improved therapeutic result without the debilitating side effects. PMID:26910109

  19. Ultrafast Imaging using Spectral Resonance Modulation

    NASA Astrophysics Data System (ADS)

    Huang, Eric; Ma, Qian; Liu, Zhaowei

    2016-04-01

    CCD cameras are ubiquitous in research labs, industry, and hospitals for a huge variety of applications, but there are many dynamic processes in nature that unfold too quickly to be captured. Although tradeoffs can be made between exposure time, sensitivity, and area of interest, ultimately the speed limit of a CCD camera is constrained by the electronic readout rate of the sensors. One potential way to improve the imaging speed is with compressive sensing (CS), a technique that allows for a reduction in the number of measurements needed to record an image. However, most CS imaging methods require spatial light modulators (SLMs), which are subject to mechanical speed limitations. Here, we demonstrate an etalon array based SLM without any moving elements that is unconstrained by either mechanical or electronic speed limitations. This novel spectral resonance modulator (SRM) shows great potential in an ultrafast compressive single pixel camera.

  20. Ultrafast carriers dynamics in filled-skutterudites

    NASA Astrophysics Data System (ADS)

    Guo, Liang; Xu, Xianfan; Salvador, James R.

    2015-06-01

    Carrier dynamics of filled-skutterudites, an important class of thermoelectric materials, is investigated using ultrafast optical spectroscopy. By tuning the wavelength of the probe laser, charge transfers at different electronic energy levels are interrogated. Analysis based on the Kramers-Kronig relation explains the complex spectroscopy data, which is mainly due to band filling caused by photo-excited carriers and free carrier absorption. The relaxation time of hot carriers is found to be about 0.4-0.6 ps, depending on the electronic energy level, and the characteristic time for carrier-phonon equilibrium is about 0.95 ps. These studies of carrier dynamics, which fundamentally determines the transport properties of thermoelectric material, can provide guidance for the design of materials.

  1. Ultrafast Imaging using Spectral Resonance Modulation.

    PubMed

    Huang, Eric; Ma, Qian; Liu, Zhaowei

    2016-01-01

    CCD cameras are ubiquitous in research labs, industry, and hospitals for a huge variety of applications, but there are many dynamic processes in nature that unfold too quickly to be captured. Although tradeoffs can be made between exposure time, sensitivity, and area of interest, ultimately the speed limit of a CCD camera is constrained by the electronic readout rate of the sensors. One potential way to improve the imaging speed is with compressive sensing (CS), a technique that allows for a reduction in the number of measurements needed to record an image. However, most CS imaging methods require spatial light modulators (SLMs), which are subject to mechanical speed limitations. Here, we demonstrate an etalon array based SLM without any moving elements that is unconstrained by either mechanical or electronic speed limitations. This novel spectral resonance modulator (SRM) shows great potential in an ultrafast compressive single pixel camera. PMID:27122101

  2. Ultrafast carriers dynamics in filled-skutterudites

    SciTech Connect

    Guo, Liang; Xu, Xianfan; Salvador, James R.

    2015-06-08

    Carrier dynamics of filled-skutterudites, an important class of thermoelectric materials, is investigated using ultrafast optical spectroscopy. By tuning the wavelength of the probe laser, charge transfers at different electronic energy levels are interrogated. Analysis based on the Kramers-Kronig relation explains the complex spectroscopy data, which is mainly due to band filling caused by photo-excited carriers and free carrier absorption. The relaxation time of hot carriers is found to be about 0.4–0.6 ps, depending on the electronic energy level, and the characteristic time for carrier-phonon equilibrium is about 0.95 ps. These studies of carrier dynamics, which fundamentally determines the transport properties of thermoelectric material, can provide guidance for the design of materials.

  3. Ultrafast Imaging using Spectral Resonance Modulation

    PubMed Central

    Huang, Eric; Ma, Qian; Liu, Zhaowei

    2016-01-01

    CCD cameras are ubiquitous in research labs, industry, and hospitals for a huge variety of applications, but there are many dynamic processes in nature that unfold too quickly to be captured. Although tradeoffs can be made between exposure time, sensitivity, and area of interest, ultimately the speed limit of a CCD camera is constrained by the electronic readout rate of the sensors. One potential way to improve the imaging speed is with compressive sensing (CS), a technique that allows for a reduction in the number of measurements needed to record an image. However, most CS imaging methods require spatial light modulators (SLMs), which are subject to mechanical speed limitations. Here, we demonstrate an etalon array based SLM without any moving elements that is unconstrained by either mechanical or electronic speed limitations. This novel spectral resonance modulator (SRM) shows great potential in an ultrafast compressive single pixel camera. PMID:27122101

  4. Motion artifacts occurring at the lung/diaphragm interface using 4D CT attenuation correction of 4D PET scans.

    PubMed

    Killoran, Joseph H; Gerbaudo, Victor H; Mamede, Marcelo; Ionascu, Dan; Park, Sang-June; Berbeco, Ross

    2011-11-15

    For PET/CT, fast CT acquisition time can lead to errors in attenuation correction, particularly at the lung/diaphragm interface. Gated 4D PET can reduce motion artifacts, though residual artifacts may persist depending on the CT dataset used for attenuation correction. We performed phantom studies to evaluate 4D PET images of targets near a density interface using three different methods for attenuation correction: a single 3D CT (3D CTAC), an averaged 4D CT (CINE CTAC), and a fully phase matched 4D CT (4D CTAC). A phantom was designed with two density regions corresponding to diaphragm and lung. An 8 mL sphere phantom loaded with 18F-FDG was used to represent a lung tumor and background FDG included at an 8:1 ratio. Motion patterns of sin(x) and sin4(x) were used for dynamic studies. Image data was acquired using a GE Discovery DVCT-PET/CT scanner. Attenuation correction methods were compared based on normalized recovery coefficient (NRC), as well as a novel quantity "fixed activity volume" (FAV) introduced in our report. Image metrics were compared to those determined from a 3D PET scan with no motion present (3D STATIC). Values of FAV and NRC showed significant variation over the motion cycle when corrected by 3D CTAC images. 4D CTAC- and CINE CTAC-corrected PET images reduced these motion artifacts. The amount of artifact reduction is greater when the target is surrounded by lower density material and when motion was based on sin4(x). 4D CTAC reduced artifacts more than CINE CTAC for most scenarios. For a target surrounded by water equivalent material, there was no advantage to 4D CTAC over CINE CTAC when using the sin(x) motion pattern. Attenuation correction using both 4D CTAC or CINE CTAC can reduce motion artifacts in regions that include a tissue interface such as the lung/diaphragm border. 4D CTAC is more effective than CINE CTAC at reducing artifacts in some, but not all, scenarios.

  5. 4-D reconstruction for dynamic fluorescence diffuse optical tomography.

    PubMed

    Liu, Xin; Zhang, Bin; Luo, Jianwen; Bai, Jing

    2012-11-01

    Dynamic fluorescence diffuse optical tomography (FDOT) is important for the research of drug delivery, medical diagnosis and treatment. Conventionally, dynamic tomographic images are reconstructed frame by frame, independently. This approach fails to account for the temporal correlations in measurement data. Ideally, the entire image sequence should be considered as a whole and a four-dimensional (4-D) reconstruction should be performed. However, the fully 4-D reconstruction is computationally intensive. In this paper, we propose a new 4-D reconstruction approach for dynamic FDOT, which is achieved by applying a temporal Karhunen-Loève (KL) transformation to the imaging equation. By taking advantage of the decorrelation and compression properties of the KL transformation, the complex 4-D optical reconstruction problem is greatly simplified. To evaluate the performance of the method, simulation, phantom, and in vivo experiments (N=7) are performed on a hybrid FDOT/x-ray computed tomography imaging system. The experimental results indicate that the reconstruction images obtained by the KL method provide good reconstruction quality. Additionally, by discarding high-order KL components, the computation time involved with fully 4-D reconstruction can be greatly reduced in contrast to the conventional frame-by-frame reconstruction.

  6. New C4D Sensor with a Simulated Inductor

    PubMed Central

    Lyu, Yingchao; Ji, Haifeng; Yang, Shijie; Huang, Zhiyao; Wang, Baoliang; Li, Haiqing

    2016-01-01

    A new capacitively coupled contactless conductivity detection (C4D) sensor with an improved simulated inductor is developed in this work. The improved simulated inductor is designed on the basis of the Riordan-type floating simulated inductor. With the improved simulated inductor, the negative influence of the coupling capacitances is overcome and the conductivity measurement is implemented by the series resonance principle. The conductivity measurement experiments are carried out in three pipes with different inner diameters of 3.0 mm, 4.6 mm and 6.4 mm, respectively. The experimental results show that the designs of the new C4D sensor and the improved simulated inductor are successful. The maximum relative error of the conductivity measurement is less than 5%. Compared with the C4D sensors using practical inductors, the measurement accuracy of the new C4D sensor is comparable. The research results also indicate that the adjustability of a simulated inductor can reduce the requirement for the AC source and guarantee the interchangeableness. Meanwhile, it is recommended that making the potential of one terminal of a simulated inductor stable is beneficial to the running stability. Furthermore, this work indirectly verifies the possibility and feasibility of the miniaturization of the C4D sensor by using the simulated inductor technique and lays a good foundation for future research work. PMID:26828493

  7. Ultrafast gas switching experiments

    SciTech Connect

    Frost, C.A.; Martin, T.H.; Patterson, P.E.; Rinehart, L.F.; Rohwein, G.J.; Roose, L.D.; Aurand, J.F.; Buttram, M.T.

    1993-08-01

    We describe recent experiments which studied the physics of ultrafast gas breakdown under the extreme overvoltages which occur when a high pressure gas switch is pulse charged to hundreds of kV in 1 ns or less. The highly overvolted peaking gaps produce powerful electromagnetic pulses with risetimes < 100 ps which can be used for ultrawideband radar systems, particle accelerators, laser drivers, bioelectromagnetic studies, electromagnetic effects testing, and for basic studies of gas breakdown physics. We have produced and accurately measured pulses with 50 to 100 ps risetimes to peak levels of 75 to 160 kV at pulse repetition frequencies (PRF) to 1 kHz. A unique gas switch was developed to hold off hundreds of kV with parasitic inductance less than 1 nH. An advanced diagnostic system using Fourier compensation was developed to measure single-shot risetimes below 35 ps. The complete apparatus is described and waveforms are presented. The measured data are compared with a theoretical model which predicts key features including dependence on gas species and technology to practical systems antennas and bounded wave developed a thyristor/pulse transformer based system using a highly overvolted cable switch. This pulser driving a Sandia-designed TEM cell, provides an ultra wideband impulse with < 200 ps risetime to the test object at a PRF > Khz at > 100 kV/m E field.

  8. Ultrafast gas switching experiments

    SciTech Connect

    Frost, C.A.; Martin, T.H.; Patterson, P.E.; Rinehart, L.F.; Rohwein, G.J.; Roose, L.D.; Aurand, J.F.; Buttram, M.T.

    1996-11-01

    We describe recent experiments which studied the physics of ultrafast gas breakdown under the extreme overvoltages which occur when a high pressure gas switch is pulse charged to hundreds of kV in 1 ns or less. The highly overvolted peaking gaps produce powerful electromagnetic pulses with risetimes < 100 ps which can be used for ultrawideband radar systems, particle accelerators, laser drivers, bioelectromagnetic studies, electromagnetic effects testing, and for basic studies of gas breakdown physics. We have produced and accurately measured pulses with 50 to 100 ps risetimes to peak levels of 75 to 160 kV at pulse repetition frequencies (PRF) to I kHz. A unique gas switch was developed to hold off hundreds of kV with parasitic inductance less than I nH. An advanced diagnostic system using Fourier compensation was developed to measure single-shot risetimes below 35 ps. The complete apparatus is described and wave forms are presented. The measured data are compared with a theoretical model which predicts key features including dependence on gas species and pressure. We have applied this technology to practical systems driving ultrawideband radiating antennas and bounded wave simulators. For example, we have developed a thyristor/pulse transformer based system using a highly overvolted cable switch. This pulser driving a Sandia- designed TEM cell, provides an ultra wideband impulse with < 200 ps risetime to the test object at a PRF > 1 kHz at > 100 kV/m E field.

  9. Ultrafast Thermal Nonlinearity

    PubMed Central

    Khurgin, Jacob B.; Sun, Greg; Chen, Wei Ting; Tsai, Wei-Yi; Tsai, Din Ping

    2015-01-01

    Third order nonlinear optical phenomena explored in the last half century have been predicted to find wide range of applications in many walks of life, such as all-optical switching, routing, and others, yet this promise has not been fulfilled primarily because the strength of nonlinear effects is too low when they are to occur on the picosecond scale required in today’s signal processing applications. The strongest of the third-order nonlinearities, engendered by thermal effects, is considered to be too slow for the above applications. In this work we show that when optical fields are concentrated into the volumes on the scale of few tens of nanometers, the speed of the thermo-optical effects approaches picosecond scale. Such a sub-diffraction limit concentration of field can be accomplished with the use of plasmonic effects in metal nanoparticles impregnating the thermo-optic dielectric (e.g. amorphous Si) and leads to phase shifts sufficient for all optical switching on ultrafast scale. PMID:26644322

  10. Ultrafast scanning probe microscopy

    DOEpatents

    Weiss, Shimon; Chemla, Daniel S.; Ogletree, D. Frank; Botkin, David

    1995-01-01

    An ultrafast scanning probe microscopy method for achieving subpicosecond-temporal resolution and submicron-spatial resolution of an observation sample. In one embodiment of the present claimed invention, a single short optical pulse is generated and is split into first and second pulses. One of the pulses is delayed using variable time delay means. The first pulse is then directed at an observation sample located proximate to the probe of a scanning probe microscope. The scanning probe microscope produces probe-sample signals indicative of the response of the probe to characteristics of the sample. The second pulse is used to modulate the probe of the scanning probe microscope. The time delay between the first and second pulses is then varied. The probe-sample response signal is recorded at each of the various time delays created between the first and second pulses. The probe-sample response signal is then plotted as a function of time delay to produce a cross-correlation of the probe sample response. In so doing, the present invention provides simultaneous subpicosecond-temporal resolution and submicron-spatial resolution of the sample.

  11. Ultrafast scanning probe microscopy

    DOEpatents

    Weiss, S.; Chemla, D.S.; Ogletree, D.F.; Botkin, D.

    1995-05-16

    An ultrafast scanning probe microscopy method is described for achieving subpicosecond-temporal resolution and submicron-spatial resolution of an observation sample. In one embodiment of the present claimed invention, a single short optical pulse is generated and is split into first and second pulses. One of the pulses is delayed using variable time delay means. The first pulse is then directed at an observation sample located proximate to the probe of a scanning probe microscope. The scanning probe microscope produces probe-sample signals indicative of the response of the probe to characteristics of the sample. The second pulse is used to modulate the probe of the scanning probe microscope. The time delay between the first and second pulses is then varied. The probe-sample response signal is recorded at each of the various time delays created between the first and second pulses. The probe-sample response signal is then plotted as a function of time delay to produce a cross-correlation of the probe sample response. In so doing, the present invention provides simultaneous subpicosecond-temporal resolution and submicron-spatial resolution of the sample. 6 Figs.

  12. Ultrafast electronic dynamics of monodisperse PbS and CdS nanoparticles/nanorods: Effects of size on nonlinear relaxation

    NASA Astrophysics Data System (ADS)

    Wu, Fanxin; Yu, Jung Ho; Joo, Jin; Hyeon, Taeghwan; Zhang, Jin Z.

    2007-03-01

    Effects of size on nonlinear electronic relaxation processes in highly monodisperse PbS and CdS nanoparticles (NPs)/nanorods (NRs) have been studied using femtosecond transient absorption spectroscopy. All the PbS NPs with different sizes show similar dynamic profiles and an excitation intensity dependence, which is in contrast to the excitation intensity independence observed in previous studies of PbS NPs with broader size distribution. The difference could be due to either the difference in size distribution or, more likely, difference in density and distribution of trap states. The dynamic profiles of CdS NRs and NPs with different sizes all show similar time constants for the slow linear component. However, size dependence has been observed for the fast nonlinear component attributed to exciton-exciton annihilation. This size dependence of the nonlinear component can be explained by considering the size dependence of a number of factors including quantum confinement, surface trap states, and number of excitons per particle. The number of excitons per particle appears to be the dominant factor in the nonlinear decay process.

  13. Electronic structure near the Fermi level in the ferromagnetic semiconductor GaMnAs studied by ultrafast time-resolved light-induced reflectivity measurements

    NASA Astrophysics Data System (ADS)

    Ishii, Tomoaki; Kawazoe, Tadashi; Hashimoto, Yusuke; Terada, Hiroshi; Muneta, Iriya; Ohtsu, Motoichi; Tanaka, Masaaki; Ohya, Shinobu

    The determination of the Fermi level (EF) position is important to understand the origin of the ferromagnetism in ferromagnetic semiconductor GaMnAs. The recent transient reflectivity (TR) spectroscopy measurement, which is potentially sensitive to the absorption edges, indicated that the EF exists in the valence band. However, the pump fluence in this study is rather high, and the accumulation of photo-carriers can shift the absorption edges. Thus, the definition of both the band gap and EF is obscure. Here, we have performed TR spectroscopy measurements on GaMnAs films with the pump fluence carefully controlled to suppress the accumulation of photo-carriers. The energy resolution of the TR spectrum was improved to 0.5 meV. The data shows light-induced change in the reflectivity spectra which is attributed to the band-gap renormalization and band filling. We have reproduced the observed TR spectra using the Kramers-Kronig relation and found the Mn-induced electronic states near the EF in the band gap. This work was partially supported by Grants-in-Aids for Scientific Research including Specially Promoted Research and Project for Developing Innovation Systems of MEXT.

  14. Combined convective and diffusive simulations: VERB-4D comparison with 17 March 2013 Van Allen Probes observations

    NASA Astrophysics Data System (ADS)

    Shprits, Yuri Y.; Kellerman, Adam C.; Drozdov, Alexander Y.; Spence, Harlan E.; Reeves, Geoffrey D.; Baker, Daniel N.

    2015-11-01

    This study is focused on understanding the coupling between different electron populations in the inner magnetosphere and the various physical processes that determine evolution of electron fluxes at different energies. Observations during the 17 March 2013 storm and simulations with a newly developed Versatile Electron Radiation Belt-4D (VERB-4D) are presented. Analysis of the drift trajectories of the energetic and relativistic electrons shows that electron trajectories at transitional energies with a first invariant on the scale of ~100 MeV/G may resemble ring current or relativistic electron trajectories depending on the level of geomagnetic activity. Simulations with the VERB-4D code including convection, radial diffusion, and energy diffusion are presented. Sensitivity simulations including various physical processes show how different acceleration mechanisms contribute to the energization of energetic electrons at transitional energies. In particular, the range of energies where inward transport is strongly influenced by both convection and radial diffusion are studied. The results of the 4-D simulations are compared to Van Allen Probes observations at a range of energies including source, seed, and core populations of the energetic and relativistic electrons in the inner magnetosphere.

  15. Cold atom quantum emulation of ultrafast processes

    NASA Astrophysics Data System (ADS)

    Rajagopal, Shankari; Geiger, Zachary; Fujiwara, Kurt; Singh, Kevin; Senaratne, Ruwan; Weld, David

    2016-05-01

    Pulsed lasers are an invaluable probe of fast electron dynamics in condensed matter systems. However, despite tremendous progress, physical limitations on lasers and a lack of exact theoretical models still limit the exploration of ultrafast processes in solids. We discuss a possible complementary approach, in which lattice-trapped cold neutral atoms driven far from equilibrium are used as a quantum emulator of ultrafast physics at sub-cycle timescales. The cold atom context is in many ways a natural choice for such experiments: equilibration timescales are more than ten orders of magnitude slower than those in solids, and strong driving forces are easily produced and manipulated. Our experimental approach uses ultracold strontium in optical traps. Multiple stable isotopes and a long-lived metastable state provide control over interaction strengths, while a narrow-linewidth transition expands the typical cold-atom toolbox of readout techniques. We discuss initial efforts in quantum emulation of tunnel ionization and development of a platform for more complicated endeavors, including the study of multiple-pulse sequences and recollision processes. We acknowledge support from the NSF GRFP, the AFOSR, the ARO and DURIP program, the Alfred P. Sloan Foundation, and the University of California Office of the President.

  16. A 4D Hyperspherical Interpretation of q-Space

    PubMed Central

    Hosseinbor, A. Pasha; Chung, Moo K.; Wu, Yu-Chien; Alexander, Andrew L.; Bendlin, Barbara B.

    2014-01-01

    3D q-space can be viewed as the surface of a 4D hypersphere. In this paper, we seek to develop a 4D hyperspherical interpretation of q-space by projecting it onto a hypersphere and subsequently modeling the q-space signal via 4D hyperspherical harmonics (HSH). Using this orthonormal basis, we analytically derive several quantitative indices and numerically estimate the diffusion ODF. Importantly, we derive the integral transform describing the relationship between the diffusion signal and propagator on a hypersphere. We also show that the HSH basis expends less fitting parameters than other well-established methods to achieve comparable signal and better ODF reconstructions. All in all, this work provides a new way of looking at q-space. PMID:24505799

  17. Assimilation of DMSP/SSUSI UV data into IDA4D

    NASA Astrophysics Data System (ADS)

    Gelinas, L. J.; Bust, G. S.; Brinkman, D. G.; Straus, P. R.; Swartz, R. L.

    2014-12-01

    Ionospheric Data Assimilation Four-Dimensional (IDA4D) is a continuous-time, three-dimensional imaging algorithm that can produce 4D electron density specifications for various science investigations [e.g., Bust et al., 2007]. IDA4D is based on three-dimensional variational (3DVAR) data assimilation [Daley and Barker, 2001]. The algorithm combines various data sources and their associated error covariances with a background model (in this case the IRI) and its covariances to produce an ionospheric specification with formal uncertainties. IDA4D employs a Gauss- Markov Kalman filter technique similar to that used by operational assimilation models. The model can ingest a broad spectrum of data types that are either linearly or non-linearly related to electron density, including ground-based TEC, space-based TEC as measured by GPS occultation sensors and UV emissions associated with nightside recombination of O+. IDA4D has been undergoing testing at The Aerospace Corporation to determine its performance with respect to combinations of input data sets under different conditions (solar minimum, solar maximum, geomagnetic activity). The results presented here summarize the performance of IDA4D when UV data is ingested, both with and without additional TEC measurements. The UV data used in the study summarized here are 135.6 nm emissions measured the SSUSI instruments on F16 and F18 DMSP. We discuss the process by which UV data is ingested into IDA4D, including data binning, error estimation and correction of 135.6 nm contamination from mutual neutralization of O+ and O-. Model performance is then assessed using comparisons to various ground truth data, including ISR data, Jason VTEC, CNOF/S in-situ plasma density and ionosonde-derived NmF2 values. The results of this study show that UV data improves model performance, particularly when TEC data coverage is sparse. Bust, G. S., G. Crowley, T. W. Garner, T. L. Gaussiran II, R. W. Meggs, C. N. Mitchell, P. S. J. Spencer, P

  18. Relative charge transfer cross section from Rb (4d)

    NASA Astrophysics Data System (ADS)

    Shah, M. H.; Camp, H. A.; Trachy, M. L.; Fléchard, X.; Gearba, M. A.; Nguyen, H.; Brédy, R.; Lundeen, S. R.; Depaola, B. D.

    2005-08-01

    Relative charge transfer cross section measurements for the excited state Rb(4d) with 7keV Na+ is reported. The specific channels reported are Na++Rb(4d5/2)→Na(nl)+Rb+ , where the dominant transfer cross sections channels were nl=3d and 4s . Using a combination of a magneto-optical trap and recoil ion momentum spectroscopy (MOTRIMS methodology), the cross sections were measured relative to the previously studied Na++Rb(5s,5p) systems at the same collision energy.

  19. Relative charge transfer cross section from Rb(4d)

    SciTech Connect

    Shah, M.H.; Camp, H.A.; Trachy, M.L.; De Paola, B.D.; Flechard, X.; Gearba, M.A.; Nguyen, H.; Bredy, R.; Lundeen, S.R.

    2005-08-15

    Relative charge transfer cross section measurements for the excited state Rb(4d) with 7 keV Na{sup +} is reported. The specific channels reported are Na{sup +}+Rb(4d{sub 5/2}){yields}Na(nl)+Rb{sup +}, where the dominant transfer cross sections channels were nl=3d and 4s. Using a combination of a magneto-optical trap and recoil ion momentum spectroscopy (MOTRIMS methodology), the cross sections were measured relative to the previously studied Na{sup +}+Rb(5s,5p) systems at the same collision energy.

  20. The 4-D approach to visual control of autonomous systems

    NASA Technical Reports Server (NTRS)

    Dickmanns, Ernst D.

    1994-01-01

    Development of a 4-D approach to dynamic machine vision is described. Core elements of this method are spatio-temporal models oriented towards objects and laws of perspective projection in a foward mode. Integration of multi-sensory measurement data was achieved through spatio-temporal models as invariants for object recognition. Situation assessment and long term predictions were allowed through maintenance of a symbolic 4-D image of processes involving objects. Behavioral capabilities were easily realized by state feedback and feed-foward control.

  1. Emerging Applications of Abdominal 4D Flow MRI

    PubMed Central

    Roldán-Alzate, Alejandro; Francois, Christopher J.; Wieben, Oliver; Reeder, Scott B.

    2016-01-01

    OBJECTIVE Comprehensive assessment of abdominal hemodynamics is crucial for many clinical diagnoses but is challenged by a tremendous complexity of anatomy, normal physiology, and a wide variety of pathologic abnormalities. This article introduces 4D flow MRI as a powerful technique for noninvasive assessment of the hemodynamics of abdominal vascular territories. CONCLUSION Four-dimensional flow MRI provides clinicians with a more extensive and straightforward approach to evaluate disorders that affect blood flow in the abdomen. This review presents a series of clinical cases to illustrate the utility of 4D flow MRI in the comprehensive assessment of the abdominal circulation. PMID:27187681

  2. A systematic review of the role of C4d in the diagnosis of acute antibody-mediated rejection.

    PubMed

    Sapir-Pichhadze, Ruth; Curran, Simon P; John, Rohan; Tricco, Andrea C; Uleryk, Elizabeth; Laupacis, Andreas; Tinckam, Kathryn; Sis, Banu; Beyene, Joseph; Logan, Alexander G; Kim, S Joseph

    2015-01-01

    In this study, we conducted a systematic review of the literature to re-evaluate the role of C4d in the diagnosis of acute antibody-mediated rejection of kidney allografts. Electronic databases were searched until September 2013. Eligible studies allowed derivation of diagnostic tables for the performance of C4d by immunofluorescence or immunohistochemistry with comparison to histopathological features of acute antibody-mediated rejection and/or donor-specific antibody (DSA) assays. Of 3492 unique abstracts, 29 studies encompassing 3485 indication and 868 surveillance biopsies were identified. Assessment of C4d by immunofluorescence and immunohistochemistry exhibited slight to moderate agreement with glomerulitis, peritubular capillaritis, solid-phase DSA assays, DSA with glomerulitis, and DSA with peritubular capillaritis. The sensitivity and specificity of C4d varied as a function of C4d and comparator test thresholds. Prognostically, the presence of C4d was associated with inferior allograft survival compared with DSA or histopathology alone. Thus, our findings support the presence of complement-dependent and -independent phenotypes of acute antibody-mediated rejection. Whether the presence of C4d in combination with histopathology or DSA should be considered for the diagnosis of acute antibody-mediated rejection warrants further study. PMID:24827778

  3. Ultrafast spectroscopy of novel materials

    NASA Astrophysics Data System (ADS)

    Hardison, Lindsay M.

    My research focused on steady state and time-resolved photophysical characterization of a series of semiconductor nanoparticles and water soluble conjugated polyelectrolytes. Several studies have shown that the electronic structure and relaxation dynamics in CdSe nanocrystals are not only size but are also shape and passivation dependent; however, there is no detailed comparison of the photophysical properties of ZnCdSe particles with different relative amounts of Zn. This dissertation presents data collected for colloidal CdSe, CdSe/ZnSe and ZnCdSe nanoparticles with rod-like architectures synthesized and investigated in our labs to determine how size, shape, passivation and composition affect the quantum confinement and dynamics. In addition, a series of different polymer repeat unit lengths of a linear conjugated polyelectrolyte (CPE) with a carboxylate ionic side chain have been synthesized and their photophysical properties have been explored. Spectral shifts and line broadening exhibited within the Raman spectroscopy, UV-Vis spectroscopy and photoluminescence aided in determining the extent of alloying and compositional disorder created during the alloying process. The photoluminescence quantum yield of ZnCdSe nanorods is higher than that from pristine CdSe nanorods indicating a higher binding energy of the exciton. This effect is speculated to be due to increased localization of the exciton as a result of fluctuations in the composition, ultimately resulting in increases in luminescence efficiencies. Moreover, time-resolved photoluminescence characterized lifetimes of nanoparticles with similar shape but different composition. Emission of an inhomogeneous population distribution (different sizes, shapes or composition) leads to the simultaneous probing of particles with different decaying rates. A stretched exponential function, I(t)= A*exp[-(t/tau) beta], can be used to describe these systems, where beta <1 corresponds to disperse populations. In the

  4. Graphene in Ultrafast and Ultrastrong Laser Pulses

    NASA Astrophysics Data System (ADS)

    Koochakikelardeh, Hamed; Apalkov, Vadym; Stockman, Mark

    2015-03-01

    We have shown that graphene subjected to an ultrafast (near-single-oscillation pulse) and strong (F ~ 1-3 V/Å) pulse exhibits fundamental behavior dramatically different from both insulators and metals. In such an ultrafast and ultrastrong field, the electron dynamics is coherent, in contrast to relatively long pulses (τ>100 fs) where the electron's dephasing becomes important leading to incoherent dynamics. Electron transfer from the valence band (VB) to the conduction band (CB) is deeply irreversible i.e., non-adiabatic, in which the residual CB population (after pulse ends) is close to the maximum one. The residual CB population as a function of wave vector is nonuniform with a few strongly localized spots near the Dirac points, at which the CB population is almost 100%. Furthermore, it is shown the direction of charge transfer depends on the pulse amplitude. Namely, at small pulse amplitude, <=1V/Å, the charge is transferred in the direction of the pulse maximum (positive transferred charge), while at large amplitude, >=1 V/Å, it is in opposite direction of the pulse maximum (negative transferred charge). Consequently, in terms of charge transport, graphene at small pulse intensities behaves as a dielectric while at large intensities acts as a metal. These femtosecond currents and charge transfer in graphene may provide fundamental basis for detection and calibration of ultrashort intense laser pulses and are promising for petahertz information processing. This work was supported by U.S. Office of Naval Research No. N00014-13-1-0649 and NSF Grant No. ECCS-1308473.

  5. 2,4-Dichlorophenoxyacetic acid (2,4-D)

    Integrated Risk Information System (IRIS)

    2,4 - Dichlorophenoxyacetic acid ( 2,4 - D ) ; CASRN 94 - 75 - 7 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Asses

  6. Enterococcus faecalis promotes osteoclastogenesis and semaphorin 4D expression.

    PubMed

    Wang, Shuai; Deng, Zuhui; Seneviratne, Chaminda J; Cheung, Gary S P; Jin, Lijian; Zhao, Baohong; Zhang, Chengfei

    2015-10-01

    Enterococcus faecalis is considered a major bacterial pathogen implicated in endodontic infections and contributes considerably to periapical periodontitis. This study aimed to investigate the potential mechanisms by which E. faecalis accounts for the bone destruction in periapical periodontitis in vitro. Osteoclast precursor RAW264.7 cells were treated with E. faecalis ATCC 29212 and a wild strain of E. faecalis derived clinically from an infected root canal. The results showed that, to some extent, E. faecalis induced the RAW264.7 cells to form tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclast-like cells. This pathogen markedly stimulated RAW264.7 cells to express semaphorin 4D (Sema4D), which inhibits bone formation. Once RAW264.7 cells were primed by low-dose receptor activator of nuclear factor-kappa B ligand (RANKL), E. faecalis could significantly increase the production of TRAP-positive multinucleated cells and up-regulate the expression of osteoclast-specific markers, including NFATc1, TRAP and cathepsin K. Both p38 and ERK1/2 MAPK signaling pathways were activated by E. faecalis in RANKL-primed RAW264.7 cells, and meanwhile the expression of Sema4D was highly increased. In conclusion, E. faecalis may greatly contribute to the bone resorption in periapical periodontitis by promoting RANKL-dependent osteoclastogenesis and expression of Sema4D through activation of p38 and ERK1/2 MAPK signaling pathways.

  7. Generation of attosecond electron packets via conical surface plasmon electron acceleration

    NASA Astrophysics Data System (ADS)

    Greig, S. R.; Elezzabi, A. Y.

    2016-01-01

    We present a method for the generation of high kinetic energy attosecond electron packets via magnetostatic and aperture filtering of conical surface plasmon (SP) accelerated electrons. The conical SP waves are excited by coupling an ultrafast radially polarized laser beam to a conical silica lens coated with an Ag film. Electromagnetic and particle tracking models are employed to characterize the ultrafast electron packets.

  8. 4D flow mri post-processing strategies for neuropathologies

    NASA Astrophysics Data System (ADS)

    Schrauben, Eric Mathew

    4D flow MRI allows for the measurement of a dynamic 3D velocity vector field. Blood flow velocities in large vascular territories can be qualitatively visualized with the added benefit of quantitative probing. Within cranial pathologies theorized to have vascular-based contributions or effects, 4D flow MRI provides a unique platform for comprehensive assessment of hemodynamic parameters. Targeted blood flow derived measurements, such as flow rate, pulsatility, retrograde flow, or wall shear stress may provide insight into the onset or characterization of more complex neuropathologies. Therefore, the thorough assessment of each parameter within the context of a given disease has important medical implications. Not surprisingly, the last decade has seen rapid growth in the use of 4D flow MRI. Data acquisition sequences are available to researchers on all major scanner platforms. However, the use has been limited mostly to small research trials. One major reason that has hindered the more widespread use and application in larger clinical trials is the complexity of the post-processing tasks and the lack of adequate tools for these tasks. Post-processing of 4D flow MRI must be semi-automated, fast, user-independent, robust, and reliably consistent for use in a clinical setting, within large patient studies, or across a multicenter trial. Development of proper post-processing methods coupled with systematic investigation in normal and patient populations pushes 4D flow MRI closer to clinical realization while elucidating potential underlying neuropathological origins. Within this framework, the work in this thesis assesses venous flow reproducibility and internal consistency in a healthy population. A preliminary analysis of venous flow parameters in healthy controls and multiple sclerosis patients is performed in a large study employing 4D flow MRI. These studies are performed in the context of the chronic cerebrospinal venous insufficiency hypothesis. Additionally, a

  9. 4D MR imaging using robust internal respiratory signal

    NASA Astrophysics Data System (ADS)

    Hui, CheukKai; Wen, Zhifei; Stemkens, Bjorn; Tijssen, R. H. N.; van den Berg, C. A. T.; Hwang, Ken-Pin; Beddar, Sam

    2016-05-01

    The purpose of this study is to investigate the feasibility of using internal respiratory (IR) surrogates to sort four-dimensional (4D) magnetic resonance (MR) images. The 4D MR images were constructed by acquiring fast 2D cine MR images sequentially, with each slice scanned for more than one breathing cycle. The 4D volume was then sorted retrospectively using the IR signal. In this study, we propose to use multiple low-frequency components in the Fourier space as well as the anterior body boundary as potential IR surrogates. From these potential IR surrogates, we used a clustering algorithm to identify those that best represented the respiratory pattern to derive the IR signal. A study with healthy volunteers was performed to assess the feasibility of the proposed IR signal. We compared this proposed IR signal with the respiratory signal obtained using respiratory bellows. Overall, 99% of the IR signals matched the bellows signals. The average difference between the end inspiration times in the IR signal and bellows signal was 0.18 s in this cohort of matching signals. For the acquired images corresponding to the other 1% of non-matching signal pairs, the respiratory motion shown in the images was coherent with the respiratory phases determined by the IR signal, but not the bellows signal. This suggested that the IR signal determined by the proposed method could potentially correct the faulty bellows signal. The sorted 4D images showed minimal mismatched artefacts and potential clinical applicability. The proposed IR signal therefore provides a feasible alternative to effectively sort MR images in 4D.

  10. Volumetric limiting spatial resolution analysis of four dimensional digital subtraction angiography (4D-DSA)

    NASA Astrophysics Data System (ADS)

    Davis, Brian; Oberstar, Erick; Royalty, Kevin; Schafer, Sebastian; Strother, Charles; Mistretta, Charles

    2015-03-01

    Static C-Arm CT 3D FDK baseline reconstructions (3D-DSA) are unable to provide temporal information to radiologists. 4D-DSA provides a time series of 3D volumes implementing a constrained image, thresholded 3D-DSA, reconstruction utilizing temporal dynamics in the 2D projections. Volumetric limiting spatial resolution (VLSR) of 4DDSA is quantified and compared to a 3D-DSA reconstruction using the same 3D-DSA parameters. Investigated were the effects of varying over significant ranges the 4D-DSA parameters of 2D blurring kernel size applied to the projection and threshold applied to the 3D-DSA when generating the constraining image of a scanned phantom (SPH) and an electronic phantom (EPH). The SPH consisted of a 76 micron tungsten wire encased in a 47 mm O.D. plastic radially concentric thin walled support structure. An 8-second/248-frame/198° scan protocol acquired the raw projection data. VLSR was determined from averaged MTF curves generated from each 2D transverse slice of every (248) 4D temporal frame (3D). 4D results for SPH and EPH were compared to the 3D-DSA. Analysis of the 3D-DSA resulted in a VLSR of 2.28 and 1.69 lp/mm for the EPH and SPH respectively. Kernel (2D) sizes of either 10x10 or 20x20 pixels with a threshold of 10% of the 3D-DSA as a constraining image provided 4D-DSA VLSR nearest to the 3D-DSA. 4D-DSA algorithms yielded 2.21 and 1.67 lp/mm with a percent error of 3.1% and 1.2% for the EPH and SPH respectively as compared to the 3D-DSA. This research indicates 4D-DSA is capable of retaining the resolution of the 3D-DSA.

  11. Ultrafast photoinduced charge separation in metal-semiconductor nanohybrids.

    PubMed

    Mongin, Denis; Shaviv, Ehud; Maioli, Paolo; Crut, Aurélien; Banin, Uri; Del Fatti, Natalia; Vallée, Fabrice

    2012-08-28

    Hybrid nano-objects formed by two or more disparate materials are among the most promising and versatile nanosystems. A key parameter in their properties is interaction between their components. In this context we have investigated ultrafast charge separation in semiconductor-metal nanohybrids using a model system of gold-tipped CdS nanorods in a matchstick architecture. Experiments are performed using an optical time-resolved pump-probe technique, exciting either the semiconductor or the metal component of the particles, and probing the light-induced change of their optical response. Electron-hole pairs photoexcited in the semiconductor part of the nanohybrids are shown to undergo rapid charge separation with the electron transferred to the metal part on a sub-20 fs time scale. This ultrafast gold charging leads to a transient red-shift and broadening of the metal surface plasmon resonance, in agreement with results for free clusters but in contrast to observation for static charging of gold nanoparticles in liquid environments. Quantitative comparison with a theoretical model is in excellent agreement with the experimental results, confirming photoexcitation of one electron-hole pair per nanohybrid followed by ultrafast charge separation. The results also point to the utilization of such metal-semiconductor nanohybrids in light-harvesting applications and in photocatalysis. PMID:22792998

  12. Ultrafast photo response in superconductive isotropic radiators for microwave generation

    NASA Astrophysics Data System (ADS)

    Dolasinski, Brian; Bulmer, John; Bullard, Thomas; Powers, Peter E.; Haus, Joseph W.; Haugan, Timothy

    2015-02-01

    The discovery of high temperature superconductors (HTS) and the expected applications in the field of ultrafast opto-electronics has created a unique opportunity where the technology has the potential to bridge the frequency gap from infrared to microwave. A pulsed ultrafast laser impinging on a HTS thin film grown using yttrium barium copper oxide (YBCO) excites transient electron dynamics to generate radiation that spans from the terahertz to the microwave regime. The radiation phenomena were demonstrated by making transient photo-excitation measurements using an ultrafast laser to induce non-equilibrium quasi-particle dynamics. The photo-response from a laser of an average power of 1 W and a pulse duration greater than 120 fs (808 nm wavelength) incident on charged YBa2Cu2O7-δ (YBCO) thin film at superconductive temperatures was measured using a series of microwave antennas. From the observed nanosecond response time of the transient pulse, we were able to extract frequency band structure in the GHz regime that was dependent on the incident beam diameter, pulse duration, power, and the physical structure of the YBCO thin film. The electron-phonon energy relaxation time is known to be on the order of a picosecond. However, by manipulating the resistive and kinetic inductive response of the material we demonstrate the ability to generate wideband microwave frequencies with a transient response on the order of the nanosecond time scale. Quasi-particle dynamics and the temporal response were analyzed using the Rothwarf-Taylor rate equations.

  13. Ultrafast charge localization in a stripe-phase nickelate

    SciTech Connect

    Coslovich, Giacomo; Huber, Bernhard; Lee, Wei-Sheng; Sasagawa, Takao; Hussain, Zahid; Bechtel, Hans A.; Martin, Michael C.; Shen, Zhi-Xun; W. Schoenlein, Robert; A. Kaindl, Robert

    2013-08-30

    Self-organized electronically-ordered phases are a recurring feature in correlated materials, resulting in e.g. fluctuating charge stripes whose role in high-Tc superconductivity is under debate. However, the relevant cause-effect relations between real-space charge correlations and low-energy excitations remain hidden in time-averaged studies. Here, we reveal ultrafast charge localization and lattice vibrational coupling as dynamical precursors of stripe formation in the model compound La1.75Sr0.25NiO4, using ultrafast and equilibrium mid-infrared spectroscopy. The opening of a pseudogap at a crossover temperature T* far above long-range stripe formation establishes the onset of electronic localization which is accompanied by an enhanced Fano asymmetry of Ni-O stretch vibrations. Ultrafast excitation triggers a sub-picosecond dynamics exposing the synchronous modulation of electron-phonon coupling and charge localization. These results illuminate the role of localization in forming the pseudogap in nickelates, opening a path to understanding this mysterious phase in a broad class of complex oxides.

  14. An ultrafast silicon nanoplasmonic ballistic triode

    SciTech Connect

    Greig, S. R. Elezzabi, A. Y.

    2014-12-15

    A nanoscale three terminal silicon based nanoplasmonic triode is proposed as a nanometer transistor. The device is suitable for monolithic integration with complementary-metal-oxide-semiconductor technology. Due to the highly spatially inhomogeneous, highly confined nanoplasmonic mode, electrons generated through two-photon absorption in the silicon are ponderomotively accelerated towards the copper anode producing an output current. Application of a negative grid voltage allows for control of the output current. The nanoplasmonic triode is able to achieve output current as high as 628 mA/μm on an ultrafast timescale of 150 fs in a compact footprint of 0.07 μm{sup 2}. Reduction of the plasmonic field strength allows for a CMOS compatible current of 11.7 mA/μm. The results demonstrate the potential for the compact optical control of current useful for applications in high-speed, high current switching, and amplification.

  15. Ultra-fast silicon detectors (UFSD)

    NASA Astrophysics Data System (ADS)

    Sadrozinski, H. F.-W.; Anker, A.; Chen, J.; Fadeyev, V.; Freeman, P.; Galloway, Z.; Gruey, B.; Grabas, H.; John, C.; Liang, Z.; Losakul, R.; Mak, S. N.; Ng, C. W.; Seiden, A.; Woods, N.; Zatserklyaniy, A.; Baldassarri, B.; Cartiglia, N.; Cenna, F.; Ferrero, M.; Pellegrini, G.; Hidalgo, S.; Baselga, M.; Carulla, M.; Fernandez-Martinez, P.; Flores, D.; Merlos, A.; Quirion, D.; Mikuž, M.; Kramberger, G.; Cindro, V.; Mandić, I.; Zavrtanik, M.

    2016-09-01

    We report on measurements on Ultra-Fast Silicon Detectors (UFSD) which are based on Low-Gain Avalanche Detectors (LGAD). They are n-on-p sensors with internal charge multiplication due to the presence of a thin, low-resistivity diffusion layer below the junction, obtained with a highly doped implant. We have performed several beam tests with LGAD of different gain and report the measured timing resolution, comparing it with laser injection and simulations. For the 300 μm thick LGAD, the timing resolution measured at test beams is 120 ps while it is 57 ps for IR laser, in agreement with simulations using Weightfield2. For the development of thin sensors and their readout electronics, we focused on the understanding of the pulse shapes and point out the pivotal role the sensor capacitance plays.

  16. Ultrafast charge transfer and atomic orbital polarization

    SciTech Connect

    Deppe, M.; Foehlisch, A.; Hennies, F.; Nagasono, M.; Beye, M.; Sanchez-Portal, D.; Echenique, P. M.; Wurth, W.

    2007-11-07

    The role of orbital polarization for ultrafast charge transfer between an atomic adsorbate and a substrate is explored. Core hole clock spectroscopy with linearly polarized x-ray radiation allows to selectively excite adsorbate resonance states with defined spatial orientation relative to the substrate surface. For c(4x2)S/Ru(0001) the charge transfer times between the sulfur 2s{sup -1}3p*{sup +1} antibonding resonance and the ruthenium substrate have been studied, with the 2s electron excited into the 3p{sub perpendicular}* state along the surface normal and the 3p{sub parallel}* state in the surface plane. The charge transfer times are determined as 0.18{+-}0.07 and 0.84{+-}0.23 fs, respectively. This variation is the direct consequence of the different adsorbate-substrate orbital overlap.

  17. Impact of incorporating visual biofeedback in 4D MRI.

    PubMed

    To, David T; Kim, Joshua P; Price, Ryan G; Chetty, Indrin J; Glide-Hurst, Carri K

    2016-05-08

    Precise radiation therapy (RT) for abdominal lesions is complicated by respiratory motion and suboptimal soft tissue contrast in 4D CT. 4D MRI offers improved con-trast although long scan times and irregular breathing patterns can be limiting. To address this, visual biofeedback (VBF) was introduced into 4D MRI. Ten volunteers were consented to an IRB-approved protocol. Prospective respiratory-triggered, T2-weighted, coronal 4D MRIs were acquired on an open 1.0T MR-SIM. VBF was integrated using an MR-compatible interactive breath-hold control system. Subjects visually monitored their breathing patterns to stay within predetermined tolerances. 4D MRIs were acquired with and without VBF for 2- and 8-phase acquisitions. Normalized respiratory waveforms were evaluated for scan time, duty cycle (programmed/acquisition time), breathing period, and breathing regularity (end-inhale coefficient of variation, EI-COV). Three reviewers performed image quality assessment to compare artifacts with and without VBF. Respiration-induced liver motion was calculated via centroid difference analysis of end-exhale (EE) and EI liver contours. Incorporating VBF reduced 2-phase acquisition time (4.7 ± 1.0 and 5.4 ± 1.5 min with and without VBF, respectively) while reducing EI-COV by 43.8% ± 16.6%. For 8-phase acquisitions, VBF reduced acquisition time by 1.9 ± 1.6 min and EI-COVs by 38.8% ± 25.7% despite breathing rate remaining similar (11.1 ± 3.8 breaths/min with vs. 10.5 ± 2.9 without). Using VBF yielded higher duty cycles than unguided free breathing (34.4% ± 5.8% vs. 28.1% ± 6.6%, respectively). Image grading showed that out of 40 paired evaluations, 20 cases had equivalent and 17 had improved image quality scores with VBF, particularly for mid-exhale and EI. Increased liver excursion was observed with VBF, where superior-inferior, anterior-posterior, and left-right EE-EI displacements were 14.1± 5.8, 4.9 ± 2.1, and 1.5 ± 1.0 mm, respectively, with VBF compared to 11.9

  18. Exome sequencing identifies PDE4D mutations in acrodysostosis.

    PubMed

    Lee, Hane; Graham, John M; Rimoin, David L; Lachman, Ralph S; Krejci, Pavel; Tompson, Stuart W; Nelson, Stanley F; Krakow, Deborah; Cohn, Daniel H

    2012-04-01

    Acrodysostosis is a dominantly-inherited, multisystem disorder characterized by skeletal, endocrine, and neurological abnormalities. To identify the molecular basis of acrodysostosis, we performed exome sequencing on five genetically independent cases. Three different missense mutations in PDE4D, which encodes cyclic AMP (cAMP)-specific phosphodiesterase 4D, were found to be heterozygous in three of the cases. Two of the mutations were demonstrated to have occurred de novo, providing strong genetic evidence of causation. Two additional cases were heterozygous for de novo missense mutations in PRKAR1A, which encodes the cAMP-dependent regulatory subunit of protein kinase A and which has been recently reported to be the cause of a form of acrodysostosis resistant to multiple hormones. These findings demonstrate that acrodysostosis is genetically heterogeneous and underscore the exquisite sensitivity of many tissues to alterations in cAMP homeostasis. PMID:22464252

  19. Intelligent Vehicle Systems: A 4D/RCS Approach

    SciTech Connect

    Madhavan, Raj

    2007-04-01

    This book presents new research on autonomous mobility capabilities and shows how technological advances can be anticipated in the coming two decades. An in-depth description is presented on the theoretical foundations and engineering approaches that enable these capabilities. Chapter 1 provides a brief introduction to the 4D/RCS reference model architecture and design methodology that has proven successful in guiding the development of autonomous mobility systems. Chapters 2 through 7 provide more detailed descriptions of research that has been conducted and algorithms that have been developed to implement the various aspects of the 4D/RCS reference model architecture and design methodology. Chapters 8 and 9 discuss applications, performance measures, and standards. Chapter 10 provides a history of Army and DARPA research in autonomous ground mobility. Chapter 11 provides a perspective on the potential future developments in autonomous mobility.

  20. Brain tissue segmentation in 4D CT using voxel classification

    NASA Astrophysics Data System (ADS)

    van den Boom, R.; Oei, M. T. H.; Lafebre, S.; Oostveen, L. J.; Meijer, F. J. A.; Steens, S. C. A.; Prokop, M.; van Ginneken, B.; Manniesing, R.

    2012-02-01

    A method is proposed to segment anatomical regions of the brain from 4D computer tomography (CT) patient data. The method consists of a three step voxel classification scheme, each step focusing on structures that are increasingly difficult to segment. The first step classifies air and bone, the second step classifies vessels and the third step classifies white matter, gray matter and cerebrospinal fluid. As features the time averaged intensity value and the temporal intensity change value were used. In each step, a k-Nearest-Neighbor classifier was used to classify the voxels. Training data was obtained by placing regions of interest in reconstructed 3D image data. The method has been applied to ten 4D CT cerebral patient data. A leave-one-out experiment showed consistent and accurate segmentation results.