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Sample records for 4d ultrafast electron

  1. 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

  2. Scanning ultrafast electron microscopy.

    PubMed

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

    2010-08-24

    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.

  3. 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.

  4. Ultra-Fast Silicon Detectors for 4D tracking

    NASA Astrophysics Data System (ADS)

    Sola, V.; Arcidiacono, R.; Bellora, A.; Cartiglia, N.; Cenna, F.; Cirio, R.; Durando, S.; Ferrero, M.; Galloway, Z.; Gruey, B.; Freeman, P.; Mashayekhi, M.; Mandurrino, M.; Monaco, V.; Mulargia, R.; Obertino, M. M.; Ravera, F.; Sacchi, R.; Sadrozinski, H. F.-W.; Seiden, A.; Spencer, N.; Staiano, A.; Wilder, M.; Woods, N.; Zatserklyaniy, A.

    2017-02-01

    We review the progress toward the development of a novel type of silicon detectors suited for tracking with a picosecond timing resolution, the so called Ultra-Fast Silicon Detectors. The goal is to create a new family of particle detectors merging excellent position and timing resolution with GHz counting capabilities, very low material budget, radiation resistance, fine granularity, low power, insensitivity to magnetic field, and affordability. We aim to achieve concurrent precisions of ~ 10 ps and ~ 10 μm with a 50 μm thick sensor. Ultra-Fast Silicon Detectors are based on the concept of Low-Gain Avalanche Detectors, which are silicon detectors with an internal multiplication mechanism so that they generate a signal which is factor ~ 10 larger than standard silicon detectors.

  5. 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

  6. Ultrafast Science Opportunities with Electron Microscopy

    SciTech Connect

    Durr, Hermann

    2016-04-28

    X-rays and electrons are two of the most fundamental probes of matter. When the Linac Coherent Light Source (LCLS), the world’s first x-ray free electron laser, began operation in 2009, it transformed ultrafast science with the ability to generate laser-like x-ray pulses from the manipulation of relativistic electron beams. This document describes a similar future transformation. In Transmission Electron Microscopy, ultrafast relativistic (MeV energy) electron pulses can achieve unsurpassed spatial and temporal resolution. Ultrafast temporal resolution will be the next frontier in electron microscopy and can ideally complement ultrafast x-ray science done with free electron lasers. This document describes the Grand Challenge science opportunities in chemistry, material science, physics and biology that arise from an MeV ultrafast electron diffraction & microscopy facility, especially when coupled with linac-based intense THz and X-ray pump capabilities.

  7. Ultrafast Electron Microscopes: Design Criteria, Electron Sources, and Column Modeling

    NASA Astrophysics Data System (ADS)

    Berger, Joel A.

    Dynamic Transmission Electron Microscopy, and its picosecond/femtosecond subclass Ultrafast Electron Microscopy, is an emerging field in instrumentation science. It attempts to combine the nanoscale spatial resolution of transmission electron microscopes with the temporal resolution of modern ultrafast lasers. In this thesis, I present my contributions to this young field. These include a novel model for simulating the dynamics of ultrafast electron pulses in electron microscope systems, design criteria for constructing such a system, and theoretical and experimental groundwork geared towards selecting a useful photocathode for electron pulse generation. I also present the prototype ultrafast electron microscope system being built at UIC.

  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. Ultrafast Electron Diffraction: How It Works

    ScienceCinema

    None

    2016-07-12

    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.

  10. Local control approach to ultrafast electron transfer

    NASA Astrophysics Data System (ADS)

    Vindel-Zandbergen, Patricia; Meier, Christoph; Sola, Ignacio R.

    2016-10-01

    We study ultrafast electron transfer between separated nuclei using local control theory. By imposing electron ionization and electron transport through the continuum, different local control formulations are used to increase the yield of retrapping the electron at the desired nuclei. The control mechanism is based on impulsive de-excitation. Both symmetric and asymmetric nuclear arrangements are analyzed, as well as the role of the nuclear motion.

  11. 4D ultrafast ultrasound flow imaging: in vivo quantification of arterial volumetric flow rate in a single heartbeat

    NASA Astrophysics Data System (ADS)

    Correia, Mafalda; Provost, Jean; Tanter, Mickael; Pernot, Mathieu

    2016-12-01

    We present herein 4D ultrafast ultrasound flow imaging, a novel ultrasound-based volumetric imaging technique for the quantitative mapping of blood flow. Complete volumetric blood flow distribution imaging was achieved through 2D tilted plane-wave insonification, 2D multi-angle cross-beam beamforming, and 3D vector Doppler velocity components estimation by least-squares fitting. 4D ultrafast ultrasound flow imaging was performed in large volumetric fields of view at very high volume rate (>4000 volumes s-1) using a 1024-channel 4D ultrafast ultrasound scanner and a 2D matrix-array transducer. The precision of the technique was evaluated in vitro by using 3D velocity vector maps to estimate volumetric flow rates in a vessel phantom. Volumetric Flow rate errors of less than 5% were found when volumetric flow rates and peak velocities were respectively less than 360 ml min-1 and 100 cm s-1. The average volumetric flow rate error increased to 18.3% when volumetric flow rates and peak velocities were up to 490 ml min-1 and 1.3 m s-1, respectively. The in vivo feasibility of the technique was shown in the carotid arteries of two healthy volunteers. The 3D blood flow velocity distribution was assessed during one cardiac cycle in a full volume and it was used to quantify volumetric flow rates (375  ±  57 ml min-1 and 275  ±  43 ml min-1). Finally, the formation of 3D vortices at the carotid artery bifurcation was imaged at high volume rates.

  12. 4D ultrafast ultrasound flow imaging: in vivo quantification of arterial volumetric flow rate in a single heartbeat.

    PubMed

    Correia, Mafalda; Provost, Jean; Tanter, Mickael; Pernot, Mathieu

    2016-12-07

    We present herein 4D ultrafast ultrasound flow imaging, a novel ultrasound-based volumetric imaging technique for the quantitative mapping of blood flow. Complete volumetric blood flow distribution imaging was achieved through 2D tilted plane-wave insonification, 2D multi-angle cross-beam beamforming, and 3D vector Doppler velocity components estimation by least-squares fitting. 4D ultrafast ultrasound flow imaging was performed in large volumetric fields of view at very high volume rate (>4000 volumes s(-1)) using a 1024-channel 4D ultrafast ultrasound scanner and a 2D matrix-array transducer. The precision of the technique was evaluated in vitro by using 3D velocity vector maps to estimate volumetric flow rates in a vessel phantom. Volumetric Flow rate errors of less than 5% were found when volumetric flow rates and peak velocities were respectively less than 360 ml min(-1) and 100 cm s(-1). The average volumetric flow rate error increased to 18.3% when volumetric flow rates and peak velocities were up to 490 ml min(-1) and 1.3 m s(-1), respectively. The in vivo feasibility of the technique was shown in the carotid arteries of two healthy volunteers. The 3D blood flow velocity distribution was assessed during one cardiac cycle in a full volume and it was used to quantify volumetric flow rates (375  ±  57 ml min(-1) and 275  ±  43 ml min(-1)). Finally, the formation of 3D vortices at the carotid artery bifurcation was imaged at high volume rates.

  13. Ultrafast Dynamics of Electrons in Ammonia

    NASA Astrophysics Data System (ADS)

    Vöhringer, Peter

    2015-04-01

    Solvated electrons were first discovered in solutions of metals in liquid ammonia. The physical and chemical properties of these species have been studied extensively for many decades using an arsenal of electrochemical, spectroscopic, and theoretical techniques. Yet, in contrast to their hydrated counterpart, the ultrafast dynamics of ammoniated electrons remained completely unexplored until quite recently. Femtosecond pump-probe spectroscopy on metal-ammonia solutions and femtosecond multiphoton ionization spectroscopy on the neat ammonia solvent have provided new insights into the optical properties and the reactivities of this fascinating species. This article reviews the nature of the optical transition, which gives the metal-ammonia solutions their characteristic blue appearance, in terms of ultrafast relaxation processes involving bound and continuum excited states. The recombination processes following the injection of an electron via photoionization of the solvent are discussed in the context of the electronic structure of the liquid and the anionic defect associated with the solvated electron.

  14. Development of Scanning Ultrafast Electron Microscope Capability.

    SciTech Connect

    Collins, Kimberlee Chiyoko; Talin, Albert Alec; Chandler, David W.; Michael, Joseph R.

    2016-11-01

    Modern semiconductor devices rely on the transport of minority charge carriers. Direct examination of minority carrier lifetimes in real devices with nanometer-scale features requires a measurement method with simultaneously high spatial and temporal resolutions. Achieving nanometer spatial resolutions at sub-nanosecond temporal resolution is possible with pump-probe methods that utilize electrons as probes. Recently, a stroboscopic scanning electron microscope was developed at Caltech, and used to study carrier transport across a Si p-n junction [ 1 , 2 , 3 ] . In this report, we detail our development of a prototype scanning ultrafast electron microscope system at Sandia National Laboratories based on the original Caltech design. This effort represents Sandia's first exploration into ultrafast electron microscopy.

  15. 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

  16. 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.

  17. 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.

  18. Ultrafast Electron Pulse (e,2e) Processes

    NASA Astrophysics Data System (ADS)

    Shao, Hua-Chieh; Starace, Anthony; Madsen, Lars

    2012-06-01

    Techniques for producing ultrafast electron pulses have been proposedootnotetextP. Baum and A.H. Zewail, Proc. Natl. Acad. Sci. U.S.A. 104, 18409 (2007); S.A. Hilbert, C. Ulterwaal, B. Barwick, H. Betalaan, and A.H. Zewail, ibid. 106, 10558 (2009). and prospects for using such pulses to image electron dynamics in the H atom and the hydrogen molecular ion have been theoretically demonstrated.ootnotetextH.-C. Shao and A.F. Starace, Phys. Rev. Lett. 105, 263201 (2010). The (e,2e) process provides a means to directly image the momentum distribution of the target.ootnotetextM.A. Coplan, J.H. Moore, and J.P. Doering, Rev. Mod. Phys. 66, 985 (1994). We explore here the possibility of observing the time dependence of a coherent superposition of target orbitals by means of the (e,2e) process with ultrafast incident electron pulses. Using scattering theory for a longitudinally coherent beam,ootnotetextF. Robicheaux, Phys. Rev. A 62, 062706 (2000). we find that the momentum distribution of a coherent state of the H atom can be retrieved.

  19. 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.

  20. Ultrafast electron dynamics in gold nanoshells

    NASA Astrophysics Data System (ADS)

    Westcott, Sarah Linda

    2001-10-01

    In metallic nanostructures, the interaction of excited electrons with the nanostructure surface may result in electron relaxation dynamics that are significantly different than those predicted by electron-lattice coupling. These ultrafast electron dynamics were monitored by pump-probe measurements of the time-resolved change in transmission. Using femtosecond pulses from a cavity-dumped titanium-doped sapphire laser, two types of nanoparticles with a core-shell geometry were studied. Nanoshells are nanoparticles with a dielectric core surrounded by a continuous thin metal shell. For nanoshells, the plasmon resonance wavelength is tunable by changing the core and shell dimensions. For nanoshells with a gold sulfide core and a gold shell, two conditions were observed under which electron relaxation was different than predicted by electron-phonon coupling. First, electron relaxation occurred more rapidly for gold-gold sulfide nanoshells embedded in polymer films than for nanoshells dispersed in water, with lifetimes of 1.6 ps and 3 to 5 ps, respectively. Second, for nanoshells dispersed in water, the electron relaxation lifetime decreased with adsorption of p-aminobenzoic acid (to 1.7 ps) or aniline (to 1.9 ps) on the nanoshells. With adsorbed n-propylamine or p-mercaptobenzoic acid, electron relaxation transpired in 2.8 ps or 2.4 ps, respectively. Density functional theory calculations indicated that the molecules leading to the fastest electron relaxation possessed the largest induced dipole moments near a metal surface. Semicontinuous gold films grown around a silica nanoparticle core exhibited spectral and dynamical optical signatures of the percolation threshold. Compared to continuous shells, the electron dynamics in the semicontinuous shell layer were dramatically different as additional induced bleaching was observed in the first 500 fs. The observed dynamics are consistent with a rate equation model in which the electrons are initially excited in localized

  1. 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

  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

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

    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 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.

  5. Ultrafast electron dynamics in phenylalanine initiated by attosecond pulses.

    PubMed

    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

    2014-10-17

    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. 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

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

    PubMed

    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.

  8. 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.

  9. 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.

  10. 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.

  11. 4D in-vivo ultrafast ultrasound imaging using a row-column addressed matrix and coherently-compounded orthogonal plane waves.

    PubMed

    Flesch, Martin; Pernot, Mathieu; Provost, Jean; Ferin, Guillaume; Nguyen-Dinh, An; Tanter, Mickael; Deffieux, Thomas

    2017-03-01

    4D ultrafast ultrasound imaging was recently shown using a 2D matrix (i.e., fully populated) connected to a 1024-channel ultrafast ultrasound scanner. In this study, we investigate the Row-Column Addressing (RCA) matrix approach, which allows a reduction of independent channels from N x N to N + N, with a dedicated beamforming strategy for ultrafast ultrasound imaging based on the coherent compounding of Orthogonal Plane Wave (OPW). OPW is based on coherent compounding of plane wave transmissions in one direction with receive beamforming along the orthogonal direction and its orthogonal companion sequence. Such coherent recombination of complementary orthogonal sequences leads to virtual transmit focusing in both directions which results into a final isotropic Point Spread Function (PSF). In this study, a 32 x 32 2D matrix array probe (1024 channels), centered at 5 MHz was considered. An RCA array, of same footprint with 32 + 32 elements (64 channels), was emulated by summing the elements either along a line or a column in software prior to beamforming. This approach allowed for the direct comparison of the 32 + 32 RCA scheme to the optimal fully sampled 32 x 32 2D matrix configuration, which served as the gold standard. This approach was first studied through PSF simulations and then validated experimentally on a phantom consisting of anechoic cysts and echogenic wires. The Contrast-to-Noise Ratio (CNR) and the lateral resolution of the RCA approach were found to be approximately equal to half (in decibel) and twice the values, respectively, obtained when using the 2D matrix approach. Results in a Doppler phantom and the human humeral artery in vivo confirmed that OPW compound imaging using emulated RCA matrix can achieve a power Doppler with sufficient contrast to recover the vein shape and provides an accurate Doppler spectrum.

  12. 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. PMID:27795975

  13. Ultrafast Imaging of Electronic Motion in Atoms and Molecules

    DTIC Science & Technology

    2016-01-12

    AFRL-AFOSR-VA-TR-2016-0045 Ultrafast Imaging of Electronic Motion in Atoms and Molecules Martin Centurion UNIVERSITY OF NEBRSKA Final Report 01/12...2016 DISTRIBUTION A: Distribution approved for public release. AF Office Of Scientific Research (AFOSR)/ RTB1 Arlington, Virginia 22203 Air Force ...Research Laboratory Air Force Materiel Command REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188 The public reporting burden for this collection

  14. Ultrafast electron microscopy in materials science, biology, and chemistry

    SciTech Connect

    King, Wayne E.; Campbell, Geoffrey H.; Frank, Alan; Reed, Bryan; Schmerge, John F.; Siwick, Bradley J.; Stuart, Brent C.; Weber, Peter M.

    2005-06-01

    The use of pump-probe experiments to study complex transient events has been an area of significant interest in materials science, biology, and chemistry. While the emphasis has been on laser pump with laser probe and laser pump with x-ray probe experiments, there is a significant and growing interest in using electrons as probes. Early experiments used electrons for gas-phase diffraction of photostimulated chemical reactions. More recently, scientists are beginning to explore phenomena in the solid state such as phase transformations, twinning, solid-state chemical reactions, radiation damage, and shock propagation. This review focuses on the emerging area of ultrafast electron microscopy (UEM), which comprises ultrafast electron diffraction (UED) and dynamic transmission electron microscopy (DTEM). The topics that are treated include the following: (1) The physics of electrons as an ultrafast probe. This encompasses the propagation dynamics of the electrons (space-charge effect, Child's law, Boersch effect) and extends to relativistic effects. (2) The anatomy of UED and DTEM instruments. This includes discussions of the photoactivated electron gun (also known as photogun or photoelectron gun) at conventional energies (60-200 keV) and extends to MeV beams generated by rf guns. Another critical aspect of the systems is the electron detector. Charge-coupled device cameras and microchannel-plate-based cameras are compared and contrasted. The effect of various physical phenomena on detective quantum efficiency is discussed. (3) Practical aspects of operation. This includes determination of time zero, measurement of pulse-length, and strategies for pulse compression. (4) Current and potential applications in materials science, biology, and chemistry. UEM has the potential to make a significant impact in future science and technology. Understanding of reaction pathways of complex transient phenomena in materials science, biology, and chemistry will provide fundamental

  15. Ultrafast voltage sampling using single-electron wavepackets

    NASA Astrophysics Data System (ADS)

    Johnson, N.; Fletcher, J. D.; Humphreys, D. A.; See, P.; Griffiths, J. P.; Jones, G. A. C.; Farrer, I.; Ritchie, D. A.; Pepper, M.; Janssen, T. J. B. M.; Kataoka, M.

    2017-03-01

    We demonstrate an ultrafast voltage sampling technique using a stream of electron wavepackets. Electrons are emitted from a single-electron pump and travel through electron waveguides towards a detector potential barrier. Our electrons sample an instantaneous voltage on the gate upon arrival at the detector barrier. Fast sampling is achieved by minimising the duration that the electrons interact with the barrier, which can be made as small as a few picoseconds. The value of the instantaneous voltage can be determined by varying the gate voltage to match the barrier height to the electron energy, which is used as a stable reference. The test waveform can be reconstructed by shifting the electron arrival time against it. Although we find that the our current system is limited by the experimental line bandwidth to 12-18 GHz, we argue that this method has scope to increase the bandwidth of voltage sampling to 100 GHz and beyond.

  16. 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.

  17. 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.

  18. 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.

  19. Ultrafast Photoinduced Electron Transfer from Peroxide Dianion.

    PubMed

    Anderson, Bryce L; Maher, Andrew G; Nava, Matthew; Lopez, Nazario; Cummins, Christopher C; Nocera, Daniel G

    2015-06-18

    The encapsulation of peroxide dianion by hexacarboxamide cryptand provides a platform for the study of electron transfer of isolated peroxide anion. Photoinitiated electron transfer (ET) between freely diffusing Ru(bpy)3(2+) and the peroxide dianion occurs with a rate constant of 2.0 × 10(10) M(-1) s(-1). A competing electron transfer quenching pathway is observed within an ion pair. Picosecond transient spectroscopy furnishes a rate constant of 1.1 × 10(10) s(-1) for this first-order process. A driving force dependence for the ET rate within the ion pair using a series of Ru(bpy)3(2+) derivatives allows for the electronic coupling and reorganization energies to be assessed. The ET reaction is nonadiabatic and dominated by a large inner-sphere reorganization energy, in accordance with that expected for the change in bond distance accompanying the conversion of peroxide dianion to superoxide anion.

  20. The evolution of ultrafast electron microscope instrumentation.

    PubMed

    Reed, B W; Armstrong, M R; Browning, N D; Campbell, G H; Evans, J E; LaGrange, T; Masiel, D J

    2009-08-01

    Extrapolating from a brief survey of the literature, we outline a vision for the future development of time-resolved electron probe instruments that could offer levels of performance and flexibility that push the limits of physical possibility. This includes a discussion of the electron beam parameters (brightness and emittance) that limit performance, the identification of a dimensionless invariant figure of merit for pulsed electron guns (the number of electrons per lateral coherence area, per pulse), and calculations of how this figure of merit determines the trade-off of spatial against temporal resolution for different imaging modes. Modern photonics' ability to control its fundamental particles at the quantum level, while enjoying extreme flexibility and a very large variety of operating modes, is held up as an example and a goal. We argue that this goal may be approached by combining ideas already in the literature, suggesting the need for large-scale collaborative development of next-generation time-resolved instruments.

  1. Unusual molecular material formed through irreversible transformation and revealed by 4D electron microscopy.

    PubMed

    van der Veen, Renske M; Tissot, Antoine; Hauser, Andreas; Zewail, Ahmed H

    2013-05-28

    Four-dimensional (4D) electron microscopy (EM) uniquely combines the high spatial resolution to pinpoint individual nano-objects, with the high temporal resolution necessary to address the dynamics of their laser-induced transformation. Here, using 4D-EM, we demonstrate the in situ irreversible transformation of individual nanoparticles of the molecular framework Fe(pyrazine)Pt(CN)4. The newly formed material exhibits an unusually large negative thermal expansion (i.e. contraction), which is revealed by time-resolved imaging and diffraction. Negative thermal expansion is a unique property exhibited by only few materials. Here we show that the increased flexibility of the metal-cyanide framework after the removal of the bridging pyrazine ligands is responsible for the negative thermal expansion behavior of the new material. This in situ visualization of single nanostructures during reactions should be extendable to other classes of reactive systems.

  2. Imaging rotational dynamics of nanoparticles in liquid by 4D electron microscopy

    NASA Astrophysics Data System (ADS)

    Fu, Xuewen; Chen, Bin; Tang, Jau; Hassan, Mohammed Th.; Zewail, Ahmed H.

    2017-02-01

    In real time and space, four-dimensional electron microscopy (4D EM) has enabled observation of transient structures and morphologies of inorganic and organic materials. We have extended 4D EM to include liquid cells without the time resolution being limited by the response of the detector. Our approach permits the imaging of the motion and morphological dynamics of a single, same particle on nanometer and ultrashort time scales. As a first application, we studied the rotational dynamics of gold nanoparticles in aqueous solution. A full transition from the conventional diffusive rotation to superdiffusive rotation and further to a ballistic rotation was observed with increasing asymmetry of the nanoparticle morphology. We explored the underlying physics both experimentally and theoretically according to the morphological asymmetry of the nanoparticles.

  3. Ultrafast terahertz electrodynamics of photonic and electronic nanostructures

    SciTech Connect

    Luo, Liang

    2015-01-01

    This thesis summarizes my work on using ultrafast laser pulses to study Terahertz (THz) electrodynamics of photonic and electronic nanostructures and microstructures. Ultrafast timeresolved (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 e ciency 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 di ractive elements. The other is based on the photoexcited double-split-ring-resonator metamaterials. Both structures are exible and can modulate THz waves with large tunability. Thirdly, the dark excitons in semiconducting singlewalled carbon nanotubes are studied by optical pump and THz probe spectroscopy, which provides the rst 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 brie y presented such as the study of ultrafast THz dynamics of Dirac fermions in topological insulator Bi2Se3 with Mid-infrared excitation. Finally, the thesis ends with a summary of the completed experiments and an outlook of the future plan.

  4. 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.

  5. Ultrafast Manipulation of Electron Spin Coherence

    NASA Astrophysics Data System (ADS)

    Gupta, J. A.; Awschalom, D. D.; Knobel, R.; Samarth, N.

    2002-03-01

    A technique is developed with the potential for coherent all-optical control over electron spins in semiconductors on femtosecond time scales.footnote J.A. Gupta et al., Science 292, 2458 (2001) The experiments show that optical “tipping” pulses can enact significant rotations of electron spins through an effective magnetic field generated when the tipping pulse energy is tuned below the semiconductor bandgap (the optical Stark effect). Measurements of Stark shifts in ZnCdSe quantum wells suggest that field strengths of order 20T are achieved. Rotations due to this effective field approaching 90 degrees were measured as changes in the amplitude of spin precession following optical excitation in a transverse magnetic field. A prototype sequence of two tipping pulses indicates that the rotation is reversible, a result that establishes the coherent nature of the tipping process.

  6. Ultrafast dynamics of electrons at interfaces

    SciTech Connect

    McNeill, Jason Douglas

    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

  7. 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.

  8. Adapting High Brightness Relativistic Electron Beams for Ultrafast Science

    NASA Astrophysics Data System (ADS)

    Scoby, Cheyne Matthew

    This thesis explores the use of ultrashort bunches generated by a radiofrequency electron photoinjector driven by a femtosecond laser. Rf photoinjector technology has been developed to generate ultra high brightness beams for advanced accelerators and to drive advanced light source applications. The extremely good quality of the beams generated by this source has played a key role in the development of 4th generation light sources such as the Linac Coherent Light Source, thus opening the way to studies of materials science and biological systems with high temporal and spatial resolution. At the Pegasus Photoinjector Lab, we have developed the application of a BNL/SLAC/UCLA 1.6-cell rf photoinjector as a tool for ultrafast science in its own right. It is the aim of this work to explore the generation of ultrashort electron bunches, give descriptions of the novel ultrafast diagnostics developed to be able to characterize the electron bunch and synchronize it with a pump laser, and share some of the scientific results that were obtained with this technology at the UCLA Pegasus laboratory. This dissertation explains the requirements of the drive laser source and describes the principles of rf photoinjector design and operation necessary to produce electron bunches with an rms longitudinal length < 100 femtoseconds containing 107 - 108 electrons per bunch. In this condition, when the laser intensity is sufficiently high, multiphoton photoemission is demonstrated to be more efficient in terms of charge yield than single photon photoemission. When a short laser pulse hits the cathode the resulting beam dynamics are dominated by a strong space charge driven longitudinal expansion which leads to the creation of a nearly ideal uniformly filled ellipsoidal distribution. These beam distributions are characterized by linear space charge forces and hence by high peak brightness and small transverse emittances. This regime of operation of the RF photoinjector is also termed the

  9. Ultrafast electron dynamics following outer-valence ionization: The impact of low-lying relaxation satellite states

    NASA Astrophysics Data System (ADS)

    Lünnemann, Siegfried; Kuleff, Alexander I.; Cederbaum, Lorenz S.

    2009-04-01

    Low-lying relaxation satellites give rise to ultrafast electron dynamics following outer-valence ionization of a molecular system. To demonstrate the impact of such satellites, the evolution of the electronic cloud after sudden removal of an electron from the highest occupied molecular orbital (HOMO) of the organic unsaturated nitroso compound 2-nitroso[1,3]oxazolo[5,4-d][1,3]oxazole is traced in real time and space using ab initio methods only. Our results show that the initially created hole charge remains stationary but on top of it the system reacts by an ultrafast π-π ∗ excitation followed by a cyclic excitation-de-excitation process which leads to a redistribution of the charge. The π-π ∗ excitation following the removal of the HOMO electron takes place on a subfemtosecond time scale and the period of the excitation-de-excitation alternations is about 1.4 fs. In real space the processes of excitation and de-excitation represent ultrafast delocalization and localization of the charge. The results are analyzed by simple two- and three-state models.

  10. Special issue on ultrafast electron and molecular dynamics

    NASA Astrophysics Data System (ADS)

    Hishikawa, Akiyoshi; Martin, Fernando; Vrakking, Marc

    2013-07-01

    Your invitation to submit. Journal of Physics. B: Atomic Molecular and Optical Physics (JPhysB) is delighted to announce a forthcoming special issue on ultrafast electron and molecular dynamics to appear in 2014, and invites you to submit a paper. Within the last decade, a number of novel approaches have emerged, both experimental and theoretical, that allow the investigation of (time-resolved) molecular dynamics in novel ways not anticipated before. Experimentally, the introduction of novel light sources such as high-harmonic generation and XUV/x-ray free electron lasers, and the emergence of novel detection strategies, such as time-resolved electron/x-ray diffraction and the fully coincident detection of electrons and fragment ions in reaction microscopes, has significantly expanded the arsenal of available techniques, and has taken studies of molecular dynamics into new domains of spectroscopic, spatial and temporal resolution, the latter including first explorations into the attosecond domain. Along the way, particular types of molecular dynamics, such as dynamics around conical intersections, have gained an increased prominence, sparked by an emerging realization about the essential role that this dynamics plays in relaxation pathways in important bio-molecular systems. The progress on the theoretical side has been no less impressive. Novel generations of supercomputers and a series of novel computational strategies have allowed nearly exact calculations in small molecules, as well as highly successful approximate calculations in large, polyatomic molecules. Frequent and intensive collaborations involving both theory and experiment have been essential for the progress that has been accomplished. The special issue 'Ultrafast electron and molecular dynamics' seeks to provide an overview of some of the most important developments in the field, while at the same time indicating how studies of (time-resolved) molecular dynamics are likely to evolve in the coming

  11. 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.

  12. 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.

  13. Ultrafast structural and electronic dynamics of the metallic phase in a layered manganite.

    PubMed

    Piazza, L; Ma, C; Yang, H X; Mann, A; Zhu, Y; Li, J Q; Carbone, F

    2014-01-01

    The transition between different states in manganites can be driven by various external stimuli. Controlling these transitions with light opens the possibility to investigate the microscopic path through which they evolve. We performed femtosecond (fs) transmission electron microscopy on a bi-layered manganite to study its response to ultrafast photoexcitation. We show that a photoinduced temperature jump launches a pressure wave that provokes coherent oscillations of the lattice parameters, detected via ultrafast electron diffraction. Their impact on the electronic structure are monitored via ultrafast electron energy loss spectroscopy, revealing the dynamics of the different orbitals in response to specific structural distortions.

  14. Special issue on ultrafast electron and molecular dynamics

    NASA Astrophysics Data System (ADS)

    Martin, Fernando; Hishikawa, Akiyoshi; Vrakking, Marc

    2014-06-01

    In the last few years, the advent of novel experimental and theoretical approaches has made possible the investigation of (time-resolved) molecular dynamics in ways not anticipated before. Experimentally, the introduction of novel light sources such as high-harmonic generation (HHG) and XUV/x-ray free electron lasers, and the emergence of novel detection strategies, such as time-resolved electron/x-ray diffraction and the fully coincident detection of electrons and fragment ions in reaction microscopes, has significantly expanded the arsenal of available techniques, and has taken studies of molecular dynamics into new domains of spectroscopic, spatial and temporal resolution, the latter including first explorations into the attosecond domain, thus opening completely new avenues for imaging electronic and nuclear dynamics in molecules. Along the way, particular types of molecular dynamics, e.g., dynamics around conical intersections, have gained an increased prominence, sparked by the realization of the essential role that this dynamics plays in relaxation pathways in important bio-molecular systems. In the short term, this will allow one to uncover and control the dynamics of elementary chemical processes such as, e.g., ultrafast charge migration, proton transfer, isomerization or multiple ionization, and to address new key questions about the role of attosecond coherent electron dynamics in chemical reactivity. The progress on the theoretical side has been no less impressive. Novel generations of supercomputers and a series of novel computational strategies have allowed nearly exact calculations in small molecules, as well as highly successful approximate calculations in large, polyatomic molecules, including biomolecules. Frequent and intensive collaborations involving both theory and experiment have been essential for the progress that has been accomplished. The special issue 'Ultrafast electron and molecular dynamics' seeks to provide an overview of the current

  15. Ultrafast Spectroscopy of Delocalized Excited States of the Hydrated Electron

    SciTech Connect

    Paul F. Barbara

    2005-09-28

    Research under support of this grant has been focused on the understanding of highly delocalized ''conduction-band-like'' excited states of solvated electrons in bulk water, in water trapped in the core of reverse micelles, and in alkane solvents. We have strived in this work to probe conduction-band-like states by a variety of ultrafast spectroscopy techniques. (Most of which were developed under DOE support in a previous funding cycle.) We have recorded the optical spectrum of the hydrated electron for the first time. This was accomplished by applying a photo-detrapping technique that we had developed in a previous funding cycle, but had not yet been applied to characterize the actual spectrum. In the cases of reverse micelles, we have been investigating the potential role of conduction bands in the electron attachment process and the photoinduced detrapping, and have published two papers on this topic. Finally, we have been exploring solvated electrons in isooctane from various perspectives. All of these results strongly support the conclusion that optically accessible, highly delocalized electronic states exist in these various media.

  16. 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.

  17. Ultrafast modulation of electronic structure by coherent phonon excitations

    NASA Astrophysics Data System (ADS)

    Weisshaupt, J.; Rouzée, A.; Woerner, M.; Vrakking, M. J. J.; Elsaesser, T.; Shirley, E. L.; Borgschulte, A.

    2017-02-01

    Femtosecond x-ray absorption spectroscopy with a laser-driven high-harmonic source is used to map ultrafast changes of x-ray absorption by femtometer-scale coherent phonon displacements. In LiBH4, displacements along an Ag phonon mode at 10 THz are induced by impulsive Raman excitation and give rise to oscillatory changes of x-ray absorption at the Li K edge. Electron density maps from femtosecond x-ray diffraction data show that the electric field of the pump pulse induces a charge transfer from the BH4- to neighboring Li+ ions, resulting in a differential Coulomb force that drives lattice vibrations in this virtual transition state.

  18. 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.

  19. 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.

  20. Clocking the anisotropic lattice dynamics of multi-walled carbon nanotubes by four-dimensional ultrafast transmission electron microscopy.

    PubMed

    Cao, Gaolong; Sun, Shuaishuai; Li, Zhongwen; Tian, Huanfang; Yang, Huaixin; Li, Jianqi

    2015-02-12

    Recent advances in the four-dimensional ultrafast transmission electron microscope (4D-UTEM) with combined spatial and temporal resolutions have made it possible to directly visualize structural dynamics of materials at the atomic level. Herein, we report on our development on a 4D-UTEM which can be operated properly on either the photo-emission or the thermionic mode. We demonstrate its ability to obtain sequences of snapshots with high spatial and temporal resolutions in the study of lattice dynamics of the multi-walled carbon nanotubes (MWCNTs). This investigation provides an atomic level description of remarkable anisotropic lattice dynamics at the picosecond timescales. Moreover, our UTEM measurements clearly reveal that distinguishable lattice relaxations appear in intra-tubular sheets on an ultrafast timescale of a few picoseconds and after then an evident lattice expansion along the radial direction. These anisotropic behaviors in the MWCNTs are considered arising from the variety of chemical bonding, i.e. the weak van der Waals bonding between the tubular planes and the strong covalent sp(2)-hybridized bonds in the tubular sheets.

  1. Clocking the anisotropic lattice dynamics of multi-walled carbon nanotubes by four-dimensional ultrafast transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Cao, Gaolong; Sun, Shuaishuai; Li, Zhongwen; Tian, Huanfang; Yang, Huaixin; Li, Jianqi

    2015-02-01

    Recent advances in the four-dimensional ultrafast transmission electron microscope (4D-UTEM) with combined spatial and temporal resolutions have made it possible to directly visualize structural dynamics of materials at the atomic level. Herein, we report on our development on a 4D-UTEM which can be operated properly on either the photo-emission or the thermionic mode. We demonstrate its ability to obtain sequences of snapshots with high spatial and temporal resolutions in the study of lattice dynamics of the multi-walled carbon nanotubes (MWCNTs). This investigation provides an atomic level description of remarkable anisotropic lattice dynamics at the picosecond timescales. Moreover, our UTEM measurements clearly reveal that distinguishable lattice relaxations appear in intra-tubular sheets on an ultrafast timescale of a few picoseconds and after then an evident lattice expansion along the radial direction. These anisotropic behaviors in the MWCNTs are considered arising from the variety of chemical bonding, i.e. the weak van der Waals bonding between the tubular planes and the strong covalent sp2-hybridized bonds in the tubular sheets.

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

    SciTech Connect

    Dixit, Gopal; Santra, Robin

    2013-04-07

    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)]. 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. Ultrafast science: A multiscale modeling approach to femtosecond electron diffraction and its applications

    NASA Astrophysics Data System (ADS)

    Portman, Jenni Minttu Eleonora

    The focus of this work is the study of processes at the edge of the current space and time resolutions. This includes both efforts in the development of an ultrafast electron microscope (UEM) and in the study of correlated electron systems that reflect measurements taken with this instrument. The development of a reliable ultrafast electron diffraction and imaging system requires a low emittance source of photoemitted electrons and an understanding of how the properties of the generated bunch depend on the photocathode properties. In order to gain more understanding of this process, we combine the so-called three-step photoemission model with N-particle electron simulations. By using the Fast Multipole Method to treat space charge effects, we are able to follow the time evolution of pulses containing over 106 electrons and investigate the role of laser fluence and extraction field on the total number of electrons that escape the surface as well as virtual cathode physics and the limits to spatio-temporal and spectroscopic resolution originating from the image charge on the surface and from the profile of the exciting laser pulse. The results of these simulations are compared to experimental images of the photoemission process collected using the shadow imaging technique. By contrasting the effect of varying surface properties (leading to expanding or pinned image charge) and laser profiles (Gaussian, uniform and elliptical) under different extraction field strengths and numbers of generated electrons, we quantify the effect of these experimental parameters on macroscopic pulse properties such as emittance, brightness (4D and 6D), coherence length and energy spread. Based on our results, we outline optimal conditions of pulse generation for UEM systems. With our knowledge of the photoemitted pulse properties, we also present our development of a design for the whole UEM column using the Analytic Gaussian model. We summarize the derivation of the equations governing

  6. 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.

  7. Probing phase transitions at surfaces with ultrafast electron diffraction

    NASA Astrophysics Data System (ADS)

    Horn von Hoegen, Michael

    2013-03-01

    The multitude of possible processes that can occur at surfaces cover many orders of magnitude in the time domain. While large scale growth and structure formation happens on a timescale of minutes and seconds, diffusion is already much faster, but can still be observed by electron microscopy. Many other processes as chemical reactions, phonon dynamics, or phase transitions, however, take place on the femto- and picosecond timescale and are yet way to fast for imaging techniques. In order to study such ultrafast processes at surfaces we have combined modern surface science techniques with fs laser pulses in a pump probe scheme. We use a RHEED setup with grazing incident electrons of 7 - 30 keV to ensure surface sensitivity. In order to overcome the velocity mismatch between light and electrons a tilted pulse front scheme is used to achieve a time resolution of less than 2 ps. The sample is excited with 800 nm photons with a pulse energy of 0.5 mJ at 5 kHz repetition rate. The huge potential of this technique for the study of transient surface phenomena is demonstrated with the non-equilibrium dynamics of the In induced c(8x2) reconstruction on Si(111). This surface exhibits a Peierls-like phase transition at 100 K from a c(8x2) groundstate, which is accompanied by the formation of a charge density wave (CDW), to (4x1) excited state. Upon excitation by the fs-laser pulse this structural phase transition is driven into the excited (4x1) state at a sample temperature of 20 K. The surface is only excited electronically, the CDW is lifted by photo doping and the surface remains up to 500 ps in a super cooled excited (4x1) state. Relaxation into the c(8x2) groundstate happens delayed through the nucleation of the c(8x2) at defects which triggers a 1-dim. recrystallisation front which propagates with the velocity of sound. Utilizing the Debye Waller effect, the excitation, conversion and relaxation of vibrational excitations in monolayer adsorbate systems like the Pb

  8. 4-d magnetism: Electronic structure and magnetism of some Mo-based alloys

    NASA Astrophysics Data System (ADS)

    Liu, Yong; Bose, S. K.; Kudrnovský, J.

    2017-02-01

    We report results of a first-principles density-functional study of alloys of the 4 d -element Mo with group IV elements Si, Ge and Sn in zinc blende (ZB) and rock salt (RS) structures. The study was motivated by a similar study of ours based on the 4 d -element Tc, which showed the presence of half-metallic states with integer magnetic moment (1μB) per formula unit in TcX (X=C, Si, Ge) alloys. The calculated Curie temperatures for the ferromagnetic (FM) phases were low, around or less than 300 K. Searching for the possibility of 4 d -based alloys with higher Curie temperatures we have carried out the study involving the elements Mo, Ru and Rh. Among these the most promising case appears to be that involving the element Mo. Among the MoX (X=Si, Ge, Sn) alloys in ZB and RS structures, both MoGe and MoSn in ZB structures are found to possess an integer magnetic moment of 2μB per formula unit. ZB MoSn can be classified as a marginal/weak half-metal or a spin gapless semiconductor, while ZB MoGe would be best described as a gapless magnetic semiconductor. The calculated Curie temperatures are in the range 300-700 K. Considering the theoretical uncertainty in the band gaps due not only to the treatment of exchange and correlation effects, but density functional theory itself, these classifications may change somewhat, but both merit investigation from the viewpoint of potential spintronic application. Based on their higher Curie temperatures, Mo-based alloys would serve such purpose better than the previously reported Tc-based ones.

  9. 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.

  10. 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.

  11. Theory of time-resolved nonresonant x-ray scattering for imaging ultrafast coherent electron motion

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    Future ultrafast x-ray light sources might image ultrafast coherent electron motion in real space and in real time. For a rigorous understanding of such an imaging experiment, we extend the theory of nonresonant x-ray scattering to the time domain. The role of energy resolution of the scattering detector is investigated in detail. We show that time-resolved nonresonant x-ray scattering with no energy resolution offers an opportunity to study time-dependent electronic correlations in nonequilibrium quantum systems. Furthermore, our theory presents a unified description of ultrafast x-ray scattering from electronic wave packets and the dynamical imaging of ultrafast dynamics using inelastic x-ray scattering by Abbamonte and co-workers. We examine closely the relation of the scattering signal and the linear density response of electronic wave packets. Finally, we demonstrate that time-resolved x-ray scattering from a crystal consisting of identical electronic wave packets recovers the instantaneous electron density.

  12. 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.

  13. Electron and lattice dynamics of transition metal thin films observed by ultrafast electron diffraction and transient optical measurements

    PubMed Central

    Nakamura, A.; Shimojima, T.; Nakano, M.; Iwasa, Y.; Ishizaka, K.

    2016-01-01

    We report the ultrafast dynamics of electrons and lattice in transition metal thin films (Au, Cu, and Mo) investigated by a combination of ultrafast electron diffraction (UED) and pump-probe optical methods. For a single-crystalline Au thin film, we observe the suppression of the diffraction intensity occuring in 10 ps, which direcly reflects the lattice thermalization via the electron-phonon interaction. By using the two-temperature model, the electron-phonon coupling constant (g) and the electron and lattice temperatures (Te, Tl) are evaluated from UED, with which we simulate the transient optical transmittance. The simulation well agrees with the experimentally obtained transmittance data, except for the slight deviations at the initial photoexcitation and the relaxed quasi-equilibrium state. We also present the results similarly obtained for polycrystalline Au, Cu, and Mo thin films and demonstrate the electron and lattice dynamics occurring in metals with different electron-phonon coupling strengths. PMID:28004010

  14. 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

  15. 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.

  16. Ultrafast Plasmon-Enhanced Hot Electron Generation at Ag Nanocluster/Graphite Heterojunctions.

    PubMed

    Tan, Shijing; Liu, Liming; Dai, Yanan; Ren, Jindong; Zhao, Jin; Petek, Hrvoje

    2017-04-12

    Hot electron processes at metallic heterojunctions are central to optical-to-chemical or electrical energy transduction. Ultrafast nonlinear photoexcitation of graphite has been shown to create hot thermalized electrons at temperatures corresponding to the solar photosphere in less than 25 fs. Plasmonic resonances in metallic nanoparticles are also known to efficiently generate hot electrons. Here we combine Ag nanoparticles with graphite (Gr) to study the ultrafast hot electron generation and dynamics in their plasmonic heterojunctions by means of time-resolved two-photon photoemission (2PP) spectroscopy. Tuning the wavelength of p-polarized femtosecond excitation pulses we find enhancement of 2PP yields by two orders-of-magnitude, which we attribute to excitation of a surface normal Mie plasmon mode of Ag/Gr heterojunctions at 3.6 eV. The 2PP spectra include contributions from: i) coherent two-photon absorption of an occupied interface state 0.2 eV below Fermi level, which electronic structure calculations assign to chemisorption-induced charge transfer; and ii) hot electrons in the π*-band of graphite, which are excited through the coherent screening response of the substrate. Ultrafast pump-probe measurements show that the interface state photoemission occurs via virtual intermediate states, whereas the characteristic lifetimes attribute the hot electrons to the population of the π*-band of Gr via the plasmon dephasing. Our study directly probes the mechanisms for enhanced hot electron generation and decay in a model plasmonic heterojunction.

  17. Design and commissioning of an aberration-corrected ultrafast spin-polarized low energy electron microscope with multiple electron sources.

    PubMed

    Wan, Weishi; Yu, Lei; Zhu, Lin; Yang, Xiaodong; Wei, Zheng; Liu, Jefferson Zhe; Feng, Jun; Kunze, Kai; Schaff, Oliver; Tromp, Ruud; Tang, Wen-Xin

    2016-12-27

    We describe the design and commissioning of a novel aberration-corrected low energy electron microscope (AC-LEEM). A third magnetic prism array (MPA) is added to the standard AC-LEEM with two prism arrays, allowing the incorporation of an ultrafast spin-polarized electron source alongside the standard cold field emission electron source, without degrading spatial resolution. The high degree of symmetries of the AC-LEEM are utilized while we design the electron optics of the ultrafast spin-polarized electron source, so as to minimize the deleterious effect of time broadening, while maintaining full control of electron spin. A spatial resolution of 2nm and temporal resolution of 10ps (ps) are expected in the future time resolved aberration-corrected spin-polarized LEEM (TR-AC-SPLEEM). The commissioning of the three-prism AC-LEEM has been successfully finished with the cold field emission source, with a spatial resolution below 2nm.

  18. Direct monitoring of ultrafast electron and hole dynamics in perovskite solar cells.

    PubMed

    Piatkowski, Piotr; Cohen, Boiko; Javier Ramos, Francisco; Di Nunzio, Maria; Nazeeruddin, Mohammad Khaja; Grätzel, Michael; Ahmad, Shahzada; Douhal, Abderrazzak

    2015-06-14

    Organic-inorganic hybrid perovskite solar cells have emerged as cost effective efficient light-to-electricity conversion devices. Unravelling the time scale and the mechanisms that govern the charge carrier dynamics is of paramount importance for a clear understanding and further optimization of the perovskite based devices. For the classical FTO/bulk titania blocking layer/mesoporous titania/perovskite/Spiro-OMeTAD (FTO/TPS) cell, further detailed and systematic studies of the ultrafast events related to exciton generation, electron and hole transfer, ultrafast relaxation are still needed. We characterize the initial ultrafast processes attributed to the exciton-perovskite lattice interactions influenced by charge transfer to the electron and hole transporters that precede the exciton diffusion into free charge carriers occurring in the sensitizer. Time-resolved transient absorption studies of the FTO/perovskite and FTO/TPS samples under excitation at different wavelengths and at low fluence 2 (μJ cm(-2)) indicate the sub-picosecond electron and hole injection into titania and Spiro-OMeTAD, respectively. Furthermore, the power-dependent femtosecond transient absorption measurements support the ultrafast charge transfer and show strong Auger-type multiparticle interactions at early times. We reveal that the decays of the internal trap states are the same for both films, while those at surfaces differ. The contribution of the former in the recombination is small, thus increasing the survival probability of the charges in the excited perovskite.

  19. 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.

  20. Ultrafast Studies on Electron Transfer in the Betaines: Evidence for Local Heating

    DTIC Science & Technology

    1992-05-18

    should limit the rate. 12-14 In inverted regime reactions, intrarnolecular vibrational modes can a&elerate the reaction by reducing the effective...is the reverse ET or ground state recovery. This electron transfer occurs in the inverted regime. Therefore, we expect that intramolecular vibrational ... modes will be important in ET dynamics. We have used ultrafast pump probe spectroscopy to investigate the ET kinetics of the lowest electronic

  1. Direct observation of ultrafast many-body electron dynamics in an ultracold Rydberg gas

    PubMed Central

    Takei, Nobuyuki; Sommer, Christian; Genes, Claudiu; Pupillo, Guido; Goto, Haruka; Koyasu, Kuniaki; Chiba, Hisashi; Weidemüller, Matthias; Ohmori, Kenji

    2016-01-01

    Many-body correlations govern a variety of important quantum phenomena such as the emergence of superconductivity and magnetism. Understanding quantum many-body systems is thus one of the central goals of modern sciences. Here we demonstrate an experimental approach towards this goal by utilizing an ultracold Rydberg gas generated with a broadband picosecond laser pulse. We follow the ultrafast evolution of its electronic coherence by time-domain Ramsey interferometry with attosecond precision. The observed electronic coherence shows an ultrafast oscillation with a period of 1 femtosecond, whose phase shift on the attosecond timescale is consistent with many-body correlations among Rydberg atoms beyond mean-field approximations. This coherent and ultrafast many-body dynamics is actively controlled by tuning the orbital size and population of the Rydberg state, as well as the mean atomic distance. Our approach will offer a versatile platform to observe and manipulate non-equilibrium dynamics of quantum many-body systems on the ultrafast timescale. PMID:27849054

  2. Direct observation of ultrafast many-body electron dynamics in an ultracold Rydberg gas

    NASA Astrophysics Data System (ADS)

    Takei, Nobuyuki; Sommer, Christian; Genes, Claudiu; Pupillo, Guido; Goto, Haruka; Koyasu, Kuniaki; Chiba, Hisashi; Weidemüller, Matthias; Ohmori, Kenji

    2016-11-01

    Many-body correlations govern a variety of important quantum phenomena such as the emergence of superconductivity and magnetism. Understanding quantum many-body systems is thus one of the central goals of modern sciences. Here we demonstrate an experimental approach towards this goal by utilizing an ultracold Rydberg gas generated with a broadband picosecond laser pulse. We follow the ultrafast evolution of its electronic coherence by time-domain Ramsey interferometry with attosecond precision. The observed electronic coherence shows an ultrafast oscillation with a period of 1 femtosecond, whose phase shift on the attosecond timescale is consistent with many-body correlations among Rydberg atoms beyond mean-field approximations. This coherent and ultrafast many-body dynamics is actively controlled by tuning the orbital size and population of the Rydberg state, as well as the mean atomic distance. Our approach will offer a versatile platform to observe and manipulate non-equilibrium dynamics of quantum many-body systems on the ultrafast timescale.

  3. Coulomb interaction-induced jitter amplification in RF-compressed high-brightness electron source ultrafast electron diffraction

    NASA Astrophysics Data System (ADS)

    Qi, Yingpeng; Pei, Minjie; Qi, Dalong; Li, Jing; Yang, Yan; Jia, Tianqing; Zhang, Shian; Sun, Zhenrong

    2017-02-01

    We have theoretically and experimentally demonstrated an RF compression-based jitter-amplification effect in high-brightness electron source ultrafast electron diffraction (UED), which degrades the temporal resolution significantly. A detailed analysis and simulations reveal the crucial role of the longitudinal and transverse Coulomb interaction for this jitter-amplification effect, which accord very well with experimental results. An optimized compact UED structure for full compression has been proposed, which can suppress the jitter by half and improve the temporal resolution to sub-100 fs. This Coulomb interaction-induced jitter amplification exists in nearly the whole ultrafast physics field where laser-electron synchronization is required. Moreover, it cannot be suppressed completely. The quantified explanation for the mechanism and optimization provides important guidance for photocathode accelerators and other compression-based ultrashort electron pulse generation and precise control.

  4. 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.

  5. 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.

  6. Ultrafast Electrons and X-rays as Probe of Biomolecular Dynamics

    NASA Astrophysics Data System (ADS)

    Subramanian, Ganesh

    The structure-function relation in Biology suggests that every biological molecule has evolved its structure to carry out a specific function. However, for many of these processes (such as those with catalytic activity) the structure of the biomolecule changes during the course of a reaction. Understanding the structure-function relation thus becomes a question of understanding biomolecular dynamics that span a variety of timescales (from electronic rearrangements in the femtoseconds to side-chain alteration in the microseconds and more). This dissertation deals with the study of biomolecular dynamics in the ultrafast timescales (fs-ns) using electron and X-ray probes in both time and frequency domains. It starts with establishing the limitations of traditional electron diffraction coupled with molecular replacement to study biomolecular structure and proceeds to suggest a pulsed electron source Hollow-Cone Transmission Electron Microscope as an alternative scheme to pursue ultrafast biomolecular imaging. In frequency domain, the use of Electron Energy Loss Spectroscopy as a tool to access ultrafast nuclear dynamics in the steady state, is detailed with the new monochromated NiON UltraSTEM and examples demonstrating this instrument's capability are provided. Ultrafast X-ray spectroscopy as a tool to elucidate biomolecular dynamics is presented in studying X-ray as a probe, with the study of the photolysis of Methylcobalamin using time-resolved laser pump--X-ray probe absorption spectroscopy. The analysis in comparison to prior literature as well as DFT based XAS simulations offer good agreement and understanding to the steady state spectra but are so far inadequate in explaining the time-resolved data. However, the trends in the absorption simulations for the transient intermediates show a strong anisotropic dependence on the axial ligation, which would define the direction for future studies on this material to achieve a solution.

  7. 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

  8. Electron dynamics at GaAs-AlGaAs heterojunction studied by ultrafast spectroscopy

    NASA Astrophysics Data System (ADS)

    Leontyev, A. V.; Ivanin, K. V.; Mitrofanova, T. G.; Lobkov, V. S.; Samartsev, V. V.

    2013-12-01

    In this letter the electron and spin dynamics at GaAs/AlGaAs heterojunction was studied by ultrafast spectroscopy techniques (photon echo and transient grating studies). Relaxation times and diffusion coefficients of photoexcited electrons and spins were obtained using pure optical setup. The estimated spin diffusion coefficient value of 160 cm2/s is relatively high and comparable to the electron diffusion coefficient of 200 cm2/s. This feature makes GaAs/AlGaAs heterosructure a promising material for practical application in semiconductor spintronics.

  9. Electron diffraction using ultrafast electron bunches from a laser-wakefield accelerator at kHz repetition rate

    NASA Astrophysics Data System (ADS)

    He, Z.-H.; Thomas, A. G. R.; Beaurepaire, B.; Nees, J. A.; Hou, B.; Malka, V.; Krushelnick, K.; Faure, J.

    2013-02-01

    We show that electron bunches in the 50-100 keV range can be produced from a laser wakefield accelerator using 10 mJ, 35 fs laser pulses operating at 0.5 kHz. It is shown that using a solenoid magnetic lens, the electron bunch distribution can be shaped. The resulting transverse and longitudinal coherence is suitable for producing diffraction images from a polycrystalline 10 nm aluminum foil. The high repetition rate, the stability of the electron source, and the fact that its uncorrelated bunch duration is below 100 fs make this approach promising for the development of sub-100 fs ultrafast electron diffraction experiments.

  10. Non-thermal hot electrons ultrafastly generating hot optical phonons in graphite

    NASA Astrophysics Data System (ADS)

    Ishida, Y.; Togashi, T.; Yamamoto, K.; Tanaka, M.; Taniuchi, T.; Kiss, T.; Nakajima, M.; Suemoto, T.; Shin, S.

    2011-08-01

    Investigation of the non-equilibrium dynamics after an impulsive impact provides insights into couplings among various excitations. A two-temperature model (TTM) is often a starting point to understand the coupled dynamics of electrons and lattice vibrations: the optical pulse primarily raises the electronic temperature Tel while leaving the lattice temperature Tl low; subsequently the hot electrons heat up the lattice until Tel = Tl is reached. This temporal hierarchy owes to the assumption that the electron-electron scattering rate is much larger than the electron-phonon scattering rate. We report herein that the TTM scheme is seriously invalidated in semimetal graphite. Time-resolved photoemission spectroscopy (TrPES) of graphite reveals that fingerprints of coupled optical phonons (COPs) occur from the initial moments where Tel is still not definable. Our study shows that ultrafast-and-efficient phonon generations occur beyond the TTM scheme, presumably associated to the long duration of the non-thermal electrons in graphite.

  11. Electron-Ion Equilibration in Ultrafast Heated Graphite

    NASA Astrophysics Data System (ADS)

    White, T. G.; Hartley, N. J.; Borm, B.; Crowley, B. J. B.; Harris, J. W. O.; Hochhaus, D. C.; Kaempfer, T.; Li, K.; Neumayer, P.; Pattison, L. K.; Pfeifer, F.; Richardson, S.; Robinson, A. P. L.; Uschmann, I.; Gregori, G.

    2014-04-01

    We have employed fast electrons produced by intense laser illumination to isochorically heat thermal electrons in solid density carbon to temperatures of ˜10 000 K. Using time-resolved x-ray diffraction, the temperature evolution of the lattice ions is obtained through the Debye-Waller effect, and this directly relates to the electron-ion equilibration rate. This is shown to be considerably lower than predicted from ideal plasma models. We attribute this to strong ion coupling screening the electron-ion interaction.

  12. Characterization of fast photoelectron packets in weak and strong laser fields in ultrafast electron microscopy.

    PubMed

    Plemmons, Dayne A; Tae Park, Sang; Zewail, Ahmed H; Flannigan, David J

    2014-11-01

    The development of ultrafast electron microscopy (UEM) and variants thereof (e.g., photon-induced near-field electron microscopy, PINEM) has made it possible to image atomic-scale dynamics on the femtosecond timescale. Accessing the femtosecond regime with UEM currently relies on the generation of photoelectrons with an ultrafast laser pulse and operation in a stroboscopic pump-probe fashion. With this approach, temporal resolution is limited mainly by the durations of the pump laser pulse and probe electron packet. The ability to accurately determine the duration of the electron packets, and thus the instrument response function, is critically important for interpretation of dynamics occurring near the temporal resolution limit, in addition to quantifying the effects of the imaging mode. Here, we describe a technique for in situ characterization of ultrashort electron packets that makes use of coupling with photons in the evanescent near-field of the specimen. We show that within the weakly-interacting (i.e., low laser fluence) regime, the zero-loss peak temporal cross-section is precisely the convolution of electron packet and photon pulse profiles. Beyond this regime, we outline the effects of non-linear processes and show that temporal cross-sections of high-order peaks explicitly reveal the electron packet profile, while use of the zero-loss peak becomes increasingly unreliable.

  13. Bunch evolution study in optimization of MeV ultrafast electron diffraction

    NASA Astrophysics Data System (ADS)

    Lu, Xian-Hai; Du, Ying-Chao; Huang, Wen-Hui; Tang, Chuan-Xiang

    2014-12-01

    Megaelectronvolt ultrafast electron diffraction (UED) is a promising detection tool for ultrafast processes. The quality of diffraction image is determined by the transverse evolution of the probe bunch. In this paper, we study the contributing terms of the emittance and space charge effects to the bunch evolution in the MeV UED scheme, employing a mean-field model with an ellipsoidal distribution as well as particle tracking simulation. The small transverse dimension of the drive laser is found to be critical to improve the reciprocal resolution, exploiting both smaller emittance and larger transverse bunch size before the solenoid. The degradation of the reciprocal spatial resolution caused by the space charge effects should be carefully controlled.

  14. 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

  15. 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.

  16. Ultrafast electron diffraction from non-equilibrium phonons in femtosecond laser heated Au films

    SciTech Connect

    Chase, T.; Trigo, M.; Reid, A. H.; Li, R.; Vecchione, T.; Shen, X.; Weathersby, S.; Coffee, R.; Hartmann, N.; Reis, D. A.; Wang, X. J.; Dürr, H. A.

    2016-01-25

    We use ultrafast electron diffraction to detect the temporal evolution of non-equilibrium phonons in femtosecond laser-excited ultrathin single-crystalline gold films. From the time-dependence of the Debye-Waller factor, we extract a 4.7 ps time-constant for the increase in mean-square atomic displacements. The observed increase in the diffuse scattering intensity demonstrates that the energy transfer from laser-heated electrons to phonon modes near the X and K points in the Au fcc Brillouin zone proceeds with timescales of 2.3 and 2.9 ps, respectively, faster than the Debye-Waller average mean-square displacement.

  17. 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

  18. Ultrafast spatiotemporal relaxation dynamics of excited electrons in a metal nanostructure detected by femtosecond-SNOM.

    PubMed

    Li, Zhi; Yue, Song; Chen, Jianjun; Gong, Qihuang

    2010-06-21

    Ultrahigh spatiotemporal resolved pump-probe signal near a gold nano-slit is detected by femtosecond-SNOM. By employing two-color pump-probe configuration and probing at the interband transition wavelength of the gold, signal contributed by surface plasmon polariton is avoided and spatiotemporal evolvement of excited electrons is successfully observed. From the contrast decaying of the periodical distribution of the pump-probe signal, ultrafast diffusion of excited electrons with a time scale of a few hundred femtoseconds is clearly identified. For comparison, such phenomenon cannot be observed by the one-color pump-probe configuration.

  19. Ultrafast dynamics in solids probed by femtosecond time-resolved broadband electronic sum frequency generation

    NASA Astrophysics Data System (ADS)

    Foglia, Laura; Wolf, Martin; Stähler, Julia

    2016-11-01

    Time-resolved sum frequency generation is an established tool to investigate the ultrafast vibrational dynamics with surface and interface specificity, which can be extended to the regime of electronic transitions using a white light continuum as demonstrated previously by studies of liquid interfaces. We expand this technique to the investigation of solid single crystal samples. In particular, we demonstrate the potential of electronic sum frequency generation by probing the non-equilibrium dynamics at excitonic resonances in ZnO with a sensitivity as small as 0.6% and with a time resolution of 160 fs.

  20. 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.

  1. Electronic structure of warm dense copper studied by ultrafast x-ray absorption spectroscopy.

    PubMed

    Cho, B I; Engelhorn, K; Correa, A A; Ogitsu, T; Weber, C P; Lee, H J; Feng, J; Ni, P A; Ping, Y; Nelson, A J; Prendergast, D; Lee, R W; Falcone, R W; Heimann, P A

    2011-04-22

    We use time-resolved x-ray absorption spectroscopy to investigate the unoccupied electronic density of states of warm dense copper that is produced isochorically through the absorption of an ultrafast optical pulse. The temperature of the superheated electron-hole plasma, which ranges from 4000 to 10 000 K, was determined by comparing the measured x-ray absorption spectrum with a simulation. The electronic structure of warm dense copper is adequately described with the high temperature electronic density of state calculated by the density functional theory. The dynamics of the electron temperature is consistent with a two-temperature model, while a temperature-dependent electron-phonon coupling parameter is necessary.

  2. Direct observation of martensitic phase-transformation dynamics in iron by 4D single-pulse electron microscopy.

    PubMed

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

    2009-11-01

    The in situ martensitic phase transformation of iron, a complex solid-state transition involving collective atomic displacement and interface movement, is studied in real time by means of four-dimensional (4D) electron microscopy. The iron nanofilm specimen is heated at a maximum rate of approximately 10(11) K/s by a single heating pulse, and the evolution of the phase transformation from body-centered cubic to face-centered cubic crystal structure is followed by means of single-pulse, selected-area diffraction and real-space imaging. Two distinct components are revealed in the evolution of the crystal structure. The first, on the nanosecond time scale, is a direct martensitic transformation, which proceeds in regions heated into the temperature range of stability of the fcc phase, 1185-1667 K. The second, on the microsecond time scale, represents an indirect process for the hottest central zone of laser heating, where the temperature is initially above 1667 K and cooling is the rate-determining step. The mechanism of the direct transformation involves two steps, that of (barrier-crossing) nucleation on the reported nanosecond time scale, followed by a rapid grain growth typically in approximately 100 ps for 10 nm crystallites.

  3. 10-fs-level synchronization of photocathode laser with RF-oscillator for ultrafast electron and X-ray sources

    PubMed Central

    Yang, Heewon; Han, Byungheon; Shin, Junho; Hou, Dong; Chung, Hayun; Baek, In Hyung; Jeong, Young Uk; Kim, Jungwon

    2017-01-01

    Ultrafast electron-based coherent radiation sources, such as free-electron lasers (FELs), ultrafast electron diffraction (UED) and Thomson-scattering sources, are becoming more important sources in today’s ultrafast science. Photocathode laser is an indispensable common subsystem in these sources that generates ultrafast electron pulses. To fully exploit the potentials of these sources, especially for pump-probe experiments, it is important to achieve high-precision synchronization between the photocathode laser and radio-frequency (RF) sources that manipulate electron pulses. So far, most of precision laser-RF synchronization has been achieved by using specially designed low-noise Er-fibre lasers at telecommunication wavelength. Here we show a modular method that achieves long-term (>1 day) stable 10-fs-level synchronization between a commercial 79.33-MHz Ti:sapphire laser oscillator and an S-band (2.856-GHz) RF oscillator. This is an important first step toward a photocathode laser-based femtosecond RF timing and synchronization system that is suitable for various small- to mid-scale ultrafast X-ray and electron sources. PMID:28067288

  4. 10-fs-level synchronization of photocathode laser with RF-oscillator for ultrafast electron and X-ray sources

    NASA Astrophysics Data System (ADS)

    Yang, Heewon; Han, Byungheon; Shin, Junho; Hou, Dong; Chung, Hayun; Baek, In Hyung; Jeong, Young Uk; Kim, Jungwon

    2017-01-01

    Ultrafast electron-based coherent radiation sources, such as free-electron lasers (FELs), ultrafast electron diffraction (UED) and Thomson-scattering sources, are becoming more important sources in today’s ultrafast science. Photocathode laser is an indispensable common subsystem in these sources that generates ultrafast electron pulses. To fully exploit the potentials of these sources, especially for pump-probe experiments, it is important to achieve high-precision synchronization between the photocathode laser and radio-frequency (RF) sources that manipulate electron pulses. So far, most of precision laser-RF synchronization has been achieved by using specially designed low-noise Er-fibre lasers at telecommunication wavelength. Here we show a modular method that achieves long-term (>1 day) stable 10-fs-level synchronization between a commercial 79.33-MHz Ti:sapphire laser oscillator and an S-band (2.856-GHz) RF oscillator. This is an important first step toward a photocathode laser-based femtosecond RF timing and synchronization system that is suitable for various small- to mid-scale ultrafast X-ray and electron sources.

  5. First-principles calculations of heat capacities of ultrafast laser-excited electrons in metals

    NASA Astrophysics Data System (ADS)

    Bévillon, E.; Colombier, J. P.; Recoules, V.; Stoian, R.

    2015-05-01

    Ultrafast laser excitation can induce fast increases of the electronic subsystem temperature. The subsequent electronic evolutions in terms of band structure and energy distribution can determine the change of several thermodynamic properties, including one essential for energy deposition; the electronic heat capacity. Using density functional calculations performed at finite electronic temperatures, the electronic heat capacities dependent on electronic temperatures are obtained for a series of metals, including free electron like, transition and noble metals. The effect of exchange and correlation functionals and the presence of semicore electrons on electronic heat capacities are first evaluated and found to be negligible in most cases. Then, we tested the validity of the free electron approaches, varying the number of free electrons per atom. This shows that only simple metals can be correctly fitted with these approaches. For transition metals, the presence of localized d electrons produces a strong deviation toward high energies of the electronic heat capacities, implying that more energy is needed to thermally excite them, compared to free sp electrons. This is attributed to collective excitation effects strengthened by a change of the electronic screening at high temperature.

  6. Probing ultrafast dynamics of 5f electrons in crystalline UO2

    SciTech Connect

    An, Yong Q; Taylor, Antoinette J; Durakiewicz, Tomasz; Rodriguez, George

    2010-01-01

    The electronic structure and ultrafast dynamics of photoexcited carriers of Mott insulators attracts considerable attention in modern condensed matter physics. Cubic structured UO{sub 2} is a model system for understanding the physics of strongly correlated electrons in Mott insulators. Its 5f electrons may produce special electronic states and dynamics because of their complex nature. It shows an anti ferromagnetic transition at T{sub N} = 30.8 K. Several recent theoretical works have predicted the ground states and Mott characteristics of crystalline UO{sub 2}. It is believed that the band gap of UO{sub 2} is on the order of {approx} 2 eV and excitations across the gap are of the f-f character. We have performed ultrafast optical studies of carrier dynamics related to the Mott gap and its Hubbard bands with femtosecond pump-probe transient reflection measurements. From pump-probe reflectance measurements, we find the lifetimes of photoexcited 5f electrons in crystalline UO{sub 2}, {approx} 1.2 ns for midgap states and {approx} 2 {mu}s for upper Hubbard band states at low temperatures, and identify magnetic transitions.

  7. Photoinduced phase transitions in vanadium dioxide revealed by ultrafast electron diffraction and mid-infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Tiwari, Kunal; Morrison, Vance; Chatelain, Robert; Hendaoui, Ali; Bruhacs, Andrew; Chaker, Mohamed; Siwick, Bradley

    2015-03-01

    The complex interplay between strong electron-electron correlations and structural distortions is thought to determine the electronic properties of many oxides, but the respective role of these two contributions is often difficult to determine. We report combined radio-frequency compressed ultrafast electron diffraction (RF-UED) and infrared transmissivity experiments in which we directly monitor and separate the lattice and charge density reorganizations associated with the optically induced semiconductor-to-metal phase transition in vanadium dioxide. These studies have uncovered a previously unreported photoinduced transition to a metastable phase retaining the periodic lattice distortion characteristic of the insulating phase, but differing by a reorganization of charge density along the vanadium dimer chains and a transition to metal-like mid IR optical properties. These results demonstrate that UED is able to follow details of both lattice and electronic structural dynamics on the ultrafast timescale. Supported by Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, the Canada Research Chairs program, NSERC PGS-D and CGS-D fellowships, and Fonds de Récherche du Québec-Nature et Technologies.

  8. Ultrafast static and diffusion-controlled electron transfer at Ag29 nanocluster/molecular acceptor interfaces

    NASA Astrophysics Data System (ADS)

    Aly, Shawkat M.; Abdulhalim, Lina G.; Besong, Tabot M. D.; Soldan, Giada; Bakr, Osman M.; Mohammed, Omar F.

    2016-03-01

    Efficient absorption of visible light and a long-lived excited state lifetime of silver nanoclusters (Ag29 NCs) are integral properties for these new clusters to serve as light-harvesting materials. Upon optical excitation, electron injection at Ag29 NC/methyl viologen (MV2+) interfaces is very efficient and ultrafast. Interestingly, our femto- and nanosecond time-resolved results demonstrate clearly that both dynamic and static electron transfer mechanisms are involved in photoluminescence quenching of Ag29 NCs.Efficient absorption of visible light and a long-lived excited state lifetime of silver nanoclusters (Ag29 NCs) are integral properties for these new clusters to serve as light-harvesting materials. Upon optical excitation, electron injection at Ag29 NC/methyl viologen (MV2+) interfaces is very efficient and ultrafast. Interestingly, our femto- and nanosecond time-resolved results demonstrate clearly that both dynamic and static electron transfer mechanisms are involved in photoluminescence quenching of Ag29 NCs. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05328e

  9. 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.

  10. Ultrafast electron dynamics in epitaxial graphene investigated with time- and angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Ulstrup, Søren; Johannsen, Jens Christian; Crepaldi, Alberto; Cilento, Federico; Zacchigna, Michele; Cacho, Cephise; Chapman, Richard T.; Springate, Emma; Fromm, Felix; Raidel, Christian; Seyller, Thomas; Parmigiani, Fulvio; Grioni, Marco; Hofmann, Philip

    2015-04-01

    In order to exploit the intriguing optical properties of graphene it is essential to gain a better understanding of the light-matter interaction in the material on ultrashort timescales. Exciting the Dirac fermions with intense ultrafast laser pulses triggers a series of processes involving interactions between electrons, phonons and impurities. Here we study these interactions in epitaxial graphene supported on silicon carbide (semiconducting) and iridium (metallic) substrates using ultrafast time- and angle-resolved photoemission spectroscopy (TR-ARPES) based on high harmonic generation. For the semiconducting substrate we reveal a complex hot carrier dynamics that manifests itself in an elevated electronic temperature and an increase in linewidth of the π band. By analyzing these effects we are able to disentangle electron relaxation channels in graphene. On the metal substrate this hot carrier dynamics is found to be severely perturbed by the presence of the metal, and we find that the electronic system is much harder to heat up than on the semiconductor due to screening of the laser field by the metal.

  11. 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

  12. Ultrafast molecular imaging by laser-induced electron diffraction

    SciTech Connect

    Peters, M.; Nguyen-Dang, T. T.; Cornaggia, C.; Saugout, S.; Charron, E.; Keller, A.; Atabek, O.

    2011-05-15

    We address the feasibility of imaging geometric and orbital structures of a polyatomic molecule on an attosecond time scale using the laser-induced electron diffraction (LIED) technique. We present numerical results for the highest molecular orbitals of the CO{sub 2} molecule excited by a near-infrared few-cycle laser pulse. The molecular geometry (bond lengths) is determined within 3% of accuracy from a diffraction pattern which also reflects the nodal properties of the initial molecular orbital. Robustness of the structure determination is discussed with respect to vibrational and rotational motions with a complete interpretation of the laser-induced mechanisms.

  13. Ultrafast electron trapping in ligand-exchanged quantum dot assemblies.

    PubMed

    Turk, Michael E; Vora, Patrick M; Fafarman, Aaron T; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R; Kikkawa, James M

    2015-02-24

    We use time-integrated and time-resolved photoluminescence and absorption to characterize the low-temperature optical properties of CdSe quantum dot solids after exchanging native aliphatic ligands for thiocyanate and subsequent thermal annealing. In contrast to trends established at room temperature, our data show that at low temperature the band-edge absorptive bleach is dominated by 1S3/2h hole occupation in the quantum dot interior. We find that our ligand treatments, which bring enhanced interparticle coupling, lead to faster surface state electron trapping, a greater proportion of surface-related photoluminescence, and decreased band-edge photoluminescence lifetimes.

  14. Electron work function and surface energy of body-centered and face-centered cubic modifications of 4 d- and 5 d-metals

    NASA Astrophysics Data System (ADS)

    Aref'eva, L. P.; Shebzukhova, I. G.

    2016-07-01

    A technique for the evaluation of the electron work function of metallic single crystals and the electron work function anisotropy has been developed in the framework of the electron-statistical method. The surface energy and the electron work function have been calculated for crystal faces of allotropic modifications of 4 d- and 5 d-metals. A change in the electron work function due to the allotropic transformations has been estimated, and the periodic dependence of the electron work function has been determined. It has been shown that the results obtained using the proposed technique correlate with the available experimental data for polycrystals.

  15. 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.

  16. Ultrafast Electron Diffraction Tomography for Structure Determination of the New Zeolite ITQ-58

    PubMed Central

    2016-01-01

    In this work a new ultrafast data collection strategy for electron diffraction tomography is presented that allows reducing data acquisition time by one order of magnitude. This methodology minimizes the radiation damage of beam-sensitive materials, such as microporous materials. This method, combined with the precession of the electron beam, provides high quality data enabling the determination of very complex structures. Most importantly, the implementation of this new electron diffraction methodology is easily affordable in any modern electron microscope. As a proof of concept, we have solved a new highly complex zeolitic structure named ITQ-58, with a very low symmetry (triclinic) and a large unit cell volume (1874.6 Å3), containing 16 silicon and 32 oxygen atoms in its asymmetric unit, which would be very difficult to solve with the state of the art techniques. PMID:27478889

  17. 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.

  18. Ultrafast photo-induced electron-transfer from coumarin dyes adsorbed on semiconductor nanoclusters surfaces

    SciTech Connect

    Castner, E.W. Jr.; Murakoshi, Kei; Yanagida, Shozo

    1997-12-31

    Photosensitizers adsorbed directly on semiconductor surfaces provide the basis for solar photoelectrochemical devices. Semiconductor nanoclusters in solution allow for simple preparation of the photosensitized surface, with very large surface area. To optimize the efficiency of the photoelectrochemical cycle, one must know the rates of forward and reverse electron-transfer from the excited state dye to the semiconductor conduction band. We present measurements of the ultrafast forward electron-transfer rates for three coumarin dyes (Coumarins 343, D-1421, and D-126) bound by the carboxylic acid group to the metal cationic sites of TiO{sub 2} and ZnO semiconductor nanocluster surfaces. These rates are obtained directly from the ultrafast fluorescence dynamics, measured using the femotosecond upconversion technique. Coumarins 343 and D-1421 on TiO{sub 2} nanoclusters in aqueous solution display very rapid forward electron-transfer with rate constants exceeding 10{sup 13} s{sup -1}. Substantially slower rates are observed for the same coumarin TiO{sub 2} systems in methanol solution.

  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 Intramolecular Electron and Proton Transfer in Bis(imino)isoindole Derivatives.

    PubMed

    Driscoll, Eric; Sorenson, Shayne; Dawlaty, Jahan M

    2015-06-04

    Concerted motion of electrons and protons in the excited state is pertinent to a wide range of chemical phenomena, including those relevant for solar-to-fuel light harvesting. The excited state dynamics of small proton-bearing molecules are expected to serve as models for better understanding such phenomena. In particular, for designing the next generation of multielectron and multiproton redox catalysts, understanding the dynamics of more than one proton in the excited state is important. Toward this goal, we have measured the ultrafast dynamics of intramolecular excited state proton transfer in a recently synthesized dye with two equivalent transferable protons. We have used a visible ultrafast pump to initiate the proton transfer in the excited state, and have probed the transient absorption of the molecule over a wide bandwidth in the visible range. The measurement shows that the signal which is characteristic of proton transfer emerges within ∼710 fs. To identify whether both protons were transferred in the excited state, we have measured the ultrafast dynamics of a related derivative, where only a single proton was available for transfer. The measured proton transfer time in that molecule was ∼427 fs. The observed dynamics in both cases were reasonably fit with single exponentials. Supported by the ultrafast observations, steady-state fluorescence, and preliminary computations of the relaxed excited states, we argue that the doubly protonated derivative most likely transfers only one of its two protons in the excited state. We have performed calculations of the frontier molecular orbitals in the Franck-Condon region. The calculations show that in both derivatives, the excitation is primarily from the HOMO to LUMO causing a large rearrangement of the electronic charge density immediately after photoexcitation. In particular, charge density is shifted away from the phenolic protons and toward the proton acceptor nitrogens. The proton transfer is

  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. Effect of donor orientation on ultrafast intermolecular electron transfer in coumarin-amine systems

    SciTech Connect

    Singh, P. K.; Nath, S.; Bhasikuttan, A. C.; Kumbhakar, M.; Mohanty, J.; Sarkar, S. K.; Mukherjee, T.; Pal, H.

    2008-09-21

    Effect of donor amine orientation on nondiffusive ultrafast intermolecular electron transfer (ET) reactions in coumarin-amine systems has been investigated using femtosecond fluorescence upconversion measurements. Intermolecular ET from different aromatic and aliphatic amines used as donor solvents to the excited coumarin-151 (C151) acceptor occurs with ultrafast rates such that the shortest fluorescence lifetime component ({tau}{sub 1}) is the measure of the fastest ET rate ({tau}{sub 1}={tau}{sub ET}{sup fast}=(k{sub ET}{sup fast}){sup -1}), assigned to the C151-amine contact pairs in which amine donors are properly oriented with respect to C151 to maximize the acceptor-donor electronic coupling (V{sub el}). It is interestingly observed that as the amine solvents are diluted by suitable diluents (either keeping solvent dielectric constant similar or with increasing dielectric constant), the {tau}{sub 1} remains almost in the similar range as long as the amine dilution does not cross a certain critical limit, which in terms of the amine mole fraction (x{sub A}) is found to be {approx}0.4 for aromatic amines and {approx}0.8 for aliphatic amines. Beyond these dilutions in the two respective cases of the amine systems, the {tau}{sub 1} values are seen to increase very sharply. The large difference in the critical x{sub A} values involving aromatic and aliphatic amine donors has been rationalized in terms of the largely different orientational restrictions for the ET reactions as imposed by the aliphatic (n-type) and aromatic ({pi}-type) nature of the amine donors [A. K. Satpati et al., J. Mol. Struct. 878, 84 (2008)]. Since the highest occupied molecular orbital (HOMO) of the n-type aliphatic amines is mostly centralized at the amino nitrogen, only some specific orientations of these amines with respect to the close-contact acceptor dye [also of {pi}-character; A. K. Satpati et al., J. Mol. Struct. 878, 84 (2008) and E. W. Castner et al., J. Phys. Chem. A 104, 2869

  3. 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.

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

    PubMed

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

    2014-02-11

    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.

  5. Microbunching instability in relativistic electron bunches: direct observations of the microstructures using ultrafast YBCO detectors.

    PubMed

    Roussel, E; Evain, C; Szwaj, C; Bielawski, S; Raasch, J; Thoma, P; Scheuring, A; Hofherr, M; Ilin, K; Wünsch, S; Siegel, M; Hosaka, M; Yamamoto, N; Takashima, Y; Zen, H; Konomi, T; Adachi, M; Kimura, S; Katoh, M

    2014-08-29

    Relativistic electron bunches circulating in accelerators are subjected to a dynamical instability leading to microstructures at millimeter to centimeter scale. Although this is a well-known fact, direct experimental observations of the structures, or the field that they emit, remained up to now an open problem. Here, we report the direct, shot-by-shot, time-resolved recording of the shapes (including envelope and carrier) of the pulses of coherent synchrotron radiation that are emitted, and that are a "signature" of the electron bunch microstructure. The experiments are performed on the UVSOR-III storage ring, using electrical field sensitive YBa2Cu3O(7-x) thin-film ultrafast detectors. The observed patterns are subjected to permanent drifts, that can be explained from a reasoning in phase space, using macroparticle simulations.

  6. Ultrafast control of electron spin in a quantum dot using geometric phase

    NASA Astrophysics Data System (ADS)

    Malinovsky, V. S.; Rudin, S.

    2012-12-01

    We propose a scheme to perform arbitrary unitary operations on a single electron-spin qubit in a quantum dot. The design is solely based on the geometrical phase that the qubit state acquires after a cyclic evolution in the parameter space. The scheme is utilizing ultrafast linearly-chirped pulses providing adiabatic excitation of the qubit states and the geometric phase is fully controlled by the relative phase between pulses. The analytic expression of the evolution operator for the electron spin in a quantum dot, which provides a clear geometrical interpretation of the qubit dynamics is obtained. Using parameters of InGaN/GaN, GaN/AlN quantum dots we provide an estimate for the time scale of the qubit rotations and parameters of the external fields.

  7. Interplay of electron heating and saturable absorption in ultrafast extreme ultraviolet transmission of condensed matter

    NASA Astrophysics Data System (ADS)

    Di Cicco, Andrea; Hatada, Keisuke; Giangrisostomi, Erika; Gunnella, Roberto; Bencivenga, Filippo; Principi, Emiliano; Masciovecchio, Claudio; Filipponi, Adriano

    2014-12-01

    High intensity pulses obtained by modern extreme ultraviolet (EUV) and x-ray photon sources allows the observation of peculiar phenomena in condensed matter. Experiments performed at the Fermi@Elettra FEL-1 free-electron-laser source at 23.7, 33.5, and 37.5 eV on Al thin films, for an intermediate-fluence range up to about 20 J /cm2, show evidence for a nonmonotonic EUV transmission trend. A decreasing transmission up to about 5 -10 J /cm2 is followed by an increase at higher fluence, associated with saturable absorption effects. The present findings are interpreted within a simplified three-channel model, showing that an account of the interplay between ultrafast electron heating and saturation effects is required to explain the observed transmission trend.

  8. Theory of ultrafast optical manipulation of electron spins in quantum wells

    NASA Astrophysics Data System (ADS)

    Jin, Jinshuang; Li, Xin-Qi

    2005-12-01

    Based on a multiparticle-state stimulated Raman adiabatic passage approach, a comprehensive theoretical study of the ultrafast optical manipulation of electron spins in quantum wells is presented. In addition to corroborating experimental findings [Gupta et al., Science 292, 2458 (2001)], we improve the expression for the optical-pulse-induced effective magnetic field, in comparison with the one obtained via the conventional single-particle ac Stark shift. Further study of the effect of hole-spin relaxation reveals that, while the coherent optical manipulation of electron spin in undoped quantum wells would deteriorate in the presence of relatively fast hole-spin relaxation, the coherent control in doped systems can be quite robust against decoherence. The implications of the present results on quantum dots will also be discussed.

  9. 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.

  10. Ultrafast electron-phonon coupling at the metal-dielectric interface

    NASA Astrophysics Data System (ADS)

    Yao, Qiaomu

    The pump-probe technique is an ultrafast spectroscopy method of detecting the dynamics of energy carriers such as electrons, phonons, and holes with transient thermal reflectance measurement. A laser beam is divided into a pump beam and probe beam with different wavelength or polarization and time delay. According to the transient reflectance result, this method could be applied to investigate the interaction between electron-phonon and electron-electron coupling with a high temporal resolution on the order of 10 femtoseconds. Energy transfer of photo-excited electrons in a metal film to the dielectric substrate at the metal-dielectric interface is important for understanding the ultrafast heat transfer process across the two materials. Many researches have been conducted in finding this energy transfer process in different materials. In this thesis, by measuring the transient reflectance variation, the two-temperature model (TTM) is used to analyze the interface metal electron and dielectric substrate coupling. In order to relate temperature to the reflectance change, a temperature and wavelength dependent Drude-Lorentz model was developed which represents the temperature dependent dielectric constant and can be used to calculate reflectance variation. Ultrafast pump-and-probe interband transition measurements on Au-Si samples were carried out, where the probe photon energy was chosen to be close to the interband transition threshold (ITT) of gold to minimize the influence of non-equilibrium or non-thermalized electrons on the optical response, and to increase the signal to noise ratio for reflectance change. In the experiment, different pump fluences have been used to test the transient reflectance variation on Au-Si samples of different thicknesses. The pump wavelength is taken as 800 nm while the probe wavelength is taken as 490 nm. A thick gold of 1000 nm thickness has been used to determine the electron-phonon coupling strength represented by a constant G 0

  11. Ultrafast Photoinduced Symmetry-Breaking Charge Separation and Electron Sharing in Perylenediimide Molecular Triangles.

    PubMed

    Wu, Yilei; Young, Ryan M; Frasconi, Marco; Schneebeli, Severin T; Spenst, Peter; Gardner, Daniel M; Brown, Kristen E; Würthner, Frank; Stoddart, J Fraser; Wasielewski, Michael R

    2015-10-21

    We report on a visible-light-absorbing chiral molecular triangle composed of three covalently linked 1,6,7,12-tetra(phenoxy)perylene-3,4:9,10-bis(dicarboximide) (PDI) units. The rigid triangular architecture reduces the electronic coupling between the PDIs, so ultrafast symmetry-breaking charge separation is kinetically favored over intramolecular excimer formation, as revealed by femtosecond transient absorption spectroscopy. Photoexcitation of the PDI triangle dissolved in CH2Cl2 gives PDI(+•)-PDI(-•) in τCS = 12.0 ± 0.2 ps. Fast subsequent intramolecular electron/hole hopping can equilibrate the six possible energetically degenerate ion-pair states, as suggested by electron paramagnetic resonance/electron-nuclear double resonance spectroscopy, which shows that one-electron reduction of the PDI triangle results in complete electron sharing among the three PDIs. Charge recombination of PDI(+•)-PDI(-•) to the ground state occurs in τCR = 1.12 ± 0.01 ns with no evidence of triplet excited state formation.

  12. 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

    2013-08-02

    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.

  13. 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

  14. Relativistic ultrafast electron diffraction from molecules in the gas phase (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Yang, Jie; Guehr, Markus; Vecchione, Theodore; Robinson, Matthew S.; Li, Renkai; Hartmann, Nick; Shen, Xiaozhe; Centurion, Martin; Wang, Xijie

    2016-10-01

    Ultrafast electron diffraction (UED) is a powerful technique that can be used to resolve structural changes of gas molecules during a photochemical reaction. However, the temporal resolution in pump-probe experiments has been limited to the few-ps level by the space-charge effect that broadens the electron pulse duration and by velocity mismatch between the pump laser pulses and the probe electron pulses, making only long-lived intermediate states accessible. Taking advantage of relativistic effects, Mega-electron-volt (MeV) electrons can be used to suppress both the space-charge effect and the velocity mismatch, and hence to achieve a temporal resolution that is fast enough to follow coherent nuclear motion in the target molecules. In this presentation, we show the first MeV UED experiments on gas phase targets. These experiments not only demonstrate that femtosecond temporal resolution is achieved, but also show that the spatial resolution is not compromised. This unprecedented combination of spatiotemporal resolution is sufficient to image coherent nuclear motions, and opens the door to a new class of experiments where the structural changes can be followed simultaneously in both space and time.

  15. Ultrafast electronic response of graphene to a strong and localized electric field

    NASA Astrophysics Data System (ADS)

    Gruber, Elisabeth; Wilhelm, Richard A.; Pétuya, Rémi; Smejkal, Valerie; Kozubek, Roland; Hierzenberger, Anke; Bayer, Bernhard C.; Aldazabal, Iñigo; Kazansky, Andrey K.; Libisch, Florian; Krasheninnikov, Arkady V.; Schleberger, Marika; Facsko, Stefan; Borisov, Andrei G.; Arnau, Andrés; Aumayr, Friedrich

    2016-12-01

    The way conduction electrons respond to ultrafast external perturbations in low dimensional materials is at the core of the design of future devices for (opto)electronics, photodetection and spintronics. Highly charged ions provide a tool for probing the electronic response of solids to extremely strong electric fields localized down to nanometre-sized areas. With ion transmission times in the order of femtoseconds, we can directly probe the local electronic dynamics of an ultrathin foil on this timescale. Here we report on the ability of freestanding single layer graphene to provide tens of electrons for charge neutralization of a slow highly charged ion within a few femtoseconds. With values higher than 1012 A cm-2, the resulting local current density in graphene exceeds previously measured breakdown currents by three orders of magnitude. Surprisingly, the passing ion does not tear nanometre-sized holes into the single layer graphene. We use time-dependent density functional theory to gain insight into the multielectron dynamics.

  16. Ultrafast electronic response of graphene to a strong and localized electric field

    PubMed Central

    Gruber, Elisabeth; Wilhelm, Richard A.; Pétuya, Rémi; Smejkal, Valerie; Kozubek, Roland; Hierzenberger, Anke; Bayer, Bernhard C.; Aldazabal, Iñigo; Kazansky, Andrey K.; Libisch, Florian; Krasheninnikov, Arkady V.; Schleberger, Marika; Facsko, Stefan; Borisov, Andrei G.; Arnau, Andrés; Aumayr, Friedrich

    2016-01-01

    The way conduction electrons respond to ultrafast external perturbations in low dimensional materials is at the core of the design of future devices for (opto)electronics, photodetection and spintronics. Highly charged ions provide a tool for probing the electronic response of solids to extremely strong electric fields localized down to nanometre-sized areas. With ion transmission times in the order of femtoseconds, we can directly probe the local electronic dynamics of an ultrathin foil on this timescale. Here we report on the ability of freestanding single layer graphene to provide tens of electrons for charge neutralization of a slow highly charged ion within a few femtoseconds. With values higher than 1012 A cm−2, the resulting local current density in graphene exceeds previously measured breakdown currents by three orders of magnitude. Surprisingly, the passing ion does not tear nanometre-sized holes into the single layer graphene. We use time-dependent density functional theory to gain insight into the multielectron dynamics. PMID:28000666

  17. 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

  18. 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.

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

    SciTech Connect

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

    2016-08-02

    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. Until now, 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 2 potential.

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

    DOE PAGES

    Levantino, Matteo; Schirò, Giorgio; Lemke, Henrik Till; ...

    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

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

    PubMed Central

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

    2015-01-01

    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. PMID:25832715

  2. Alignment dependent ultrafast electron-nuclear dynamics in molecular high-order harmonic generation

    NASA Astrophysics Data System (ADS)

    Li, Mu-Zi; Jia, Guang-Rui; Bian, Xue-Bin

    2017-02-01

    We investigated the high-order harmonic generation (HHG) process of diatomic molecular ion H2+ in non-Born-Oppenheimer approximations (NBOA). The corresponding three-dimensional time-dependent Schrödinger equation is solved with arbitrary alignment angles. It is found that the nuclear motion can lead to spectral modulation of HHG in both the tunneling and multiphoton ionization regimes. The universal redshifts of the whole spectrum are unique in molecular HHG. The spectral width of HHG increases in NBOA. We calculated possible influences on redshifts of HHG in real experimental conditions and found that redshifts decrease with the increase of alignment angles of the molecules and are sensitive to the initial vibrational states. It can be used to extract the ultrafast electron-nuclear dynamics and image molecular structure. It will be instructive to related experiments.

  3. Imaging polyatomic molecules with ultrafast laser-induced electron diffraction (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Le, Anh-Thu; Lin, Chii-Dong

    2016-10-01

    Molecular structure determination of chemical reactions or processes has been one of the grand challenges in physics, chemistry, and biology. To image these processes, it typically requires sub-Angstrom spatial and femtosecond temporal resolutions. One of the standard imaging techniques, X-ray diffraction, however, currently suffers from temporal jitters and is available only at large facilities. Furthermore, it also suffers from very low elastic scattering cross sections, which make it difficult to apply to gas phase molecules. Another technique, ultrafast electron diffraction (UED), overcomes this low cross section problem, but the temporal resolution is still limited to hundreds of femtoseconds, mainly due to Coulomb repulsion in electron beam and velocity mismatch between laser-pump pulse and electron probe pulse in a typical pump-probe scheme. The recently proposed laser-induced electron diffraction (LIED) is based on two basic ideas. First, an electron wave packet can be generated from a target itself by an intense laser pulse and driven back within the subsequent half-cycle of the laser to rescatter from the parent ion, thus realizing a self-imaging process. Laser-free elastic differential cross sections (DCS) can then be extracted from high-energy electron spectra, as demonstrated by the Quantitative Rescattering theory (QRS). Second, the target structure information can be retrieved from the DCS. This retrieval is further simplified by using back-scattered electrons with collision energy of about 100 eV, for which the independent-atom model (IAM) can be employed to quite accurately simulate the DCS. Demonstration of ultrafast imaging with the LIED has been reported so far on simple diatomic molecules. Here we discuss recent progress in LIED with polyatomic molecules in two examples. The first one is aligned acetylene (C2H2) and the second one is benzene (C6H6). In both cases, two bond lengths, C-C and C-H have been successfully retrieved. For even more

  4. Static and Dynamic Electron Microscopy Investigations at the Atomic and Ultrafast Scales

    NASA Astrophysics Data System (ADS)

    Suri, Pranav Kumar

    Advancements in the electron microscopy capabilities - aberration-corrected imaging, monochromatic spectroscopy, direct-electron detectors - have enabled routine visualization of atomic-scale processes with millisecond temporal resolutions in this decade. This, combined with progress in the transmission electron microscopy (TEM) specimen holder technology and nanofabrication techniques, allows comprehensive experiments on a wide range of materials in various phases via in situ methods. The development of ultrafast (sub-nanosecond) time-resolved TEM with ultrafast electron microscopy (UEM) has further pushed the envelope of in situ TEM to sub-nanosecond temporal resolution while maintaining sub-nanometer spatial resolution. A plethora of materials phenomena - including electron-phonon coupling, phonon transport, first-order phase transitions, bond rotation, plasmon dynamics, melting, and dopant atoms arrangement - are not yet clearly understood and could be benefitted with the current in situ TEM capabilities having atomic-level and ultrafast precision. Better understanding of these phenomena and intrinsic material dynamics (e.g. how phonons propagate in a material, what time-scales are involved in a first-order phase transition, how fast a material melts, where dopant atoms sit in a crystal) in new-generation and technologically important materials (e.g. two-dimensional layered materials, semiconductor and magnetic devices, rare-earth-element-free permanent magnets, unconventional superconductors) could bring a paradigm shift in their electronic, structural, magnetic, thermal and optical applications. Present research efforts, employing cutting-edge static and dynamic in situ electron microscopy resources at the University of Minnesota, are directed towards understanding the atomic-scale crystallographic structural transition and phonon transport in an iron-pnictide parent compound LaFeAsO, studying the mechanical stability of fast moving hard-drive heads in heat

  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. Ultrafast electron and hole transfer in bulk heterojunctions of low-bandgap polymers

    NASA Astrophysics Data System (ADS)

    Kozlov, Oleg V.; Pavelyev, Vlad G.; de Gier, Hilde D.; Havenith, Remco W. A.; van Loosdrecht, Paul H. M.; Hummelen, Jan C.; Pshenichnikov, Maxim S.

    2016-12-01

    In modern bulk heterojunction (BHJ) organic solar cells, blends of low-bandgap polymer and [70]PCBM acceptor are used in the active layer. In this combination, the polymer absorbs photons from the red and near-IR parts of the solar spectrum, while the blue and near-UV photons are harvested by [70]PCBM. As a result, both electron transfer from polymer to [70]PCBM and hole transfer from [70]PCBM to polymer are of utmost importance in free charge generation and have to be optimized simultaneously. Here we study electron and hole transfer processes in BHJ blends of two low-bandgap polymers, BTT-DPP and PCPDTBT, by ultrafast photoinduced spectroscopy (PIA). By tracking the PIA dynamics, we observed substantially different charge separation pathways in BHJs of the two polymers with [70]PCBM. From the photoinduced anisotropy dynamics, we demonstrated that in the PCPDTBT:[70]PCBM system both electron and hole transfer processes are highly efficient, while in the BTTBPP:[ 70]PCBM electron transfer is blocked due to the unfortunate energy level alignment leaving hole transfer the only pathway to free charge generation. Calculations at the density functional theory level are used to gain more insight into our findings. The presented results highlight the importance of the energy level alignment on the charge separation process.

  7. 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.

  8. 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.

  9. Infrared PINEM developed by diffraction in 4D UEM.

    PubMed

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

    2016-02-23

    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.

  10. 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

  11. Current Theoretical Challenges in Proton-Coupled Electron Transfer: Electron-Proton Nonadiabaticity, Proton Relays, and Ultrafast Dynamics

    SciTech Connect

    Hammes-Schiffer, Sharon

    2011-06-16

    Proton-coupled electron transfer (PCET) reactions play an important role in a wide range of biological and chemical processes. The motions of the electrons, transferring protons, solute nuclei, and solvent nuclei occur on a wide range of timescales and are often strongly coupled. As a result, the theoretical description of these processes requires a combination of quantum and classical methods. This perspective discusses three of the current theoretical challenges in the field of PCET. The first challenge is the calculation of electron-proton nonadiabatic effects, which are significant for these reactions because the hydrogen tunneling is often faster than the electronic transition. The second challenge is the modeling of electron transfer coupled to proton transport along hydrogen-bonded networks. The third challenge is the simulation of the ultrafast dynamics of nonequilibrium photoinduced PCET reactions in solution. Insights provided by theoretical studies may assist in the design of more effective catalysts for energy conversion processes. The proton relay portion of this review is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

  12. Current Theoretical Challenges in Proton-Coupled Electron Transfer: Electron Proton Nonadiabaticity, Proton Relays, and Ultrafast Dynamics

    SciTech Connect

    Hammes-Schiffer, Sharon

    2011-06-16

    Proton-coupled electron transfer (PCET) reactions play an important role in a wide range of biological and chemical processes. The motions of the electrons, transferring protons, solute nuclei, and solvent nuclei occur on a wide range of time scales and are often strongly coupled. As a result, the theoretical description of these processes requires a combination of quantum and classical methods. This Perspective discusses three of the current theoretical challenges in the field of PCET. The first challenge is the calculation of electron proton nonadiabatic effects, which are significant for these reactions because the hydrogen tunneling is often faster than the electronic transition. The second challenge is the modeling of electron transfer coupled to proton transport along hydrogen-bonded networks. The third challenge is the simulation of the ultrafast dynamics of nonequilibrium photoinduced PCET reactions in solution. Insights provided by theoretical studies may assist in the design of more effective catalysts for energy conversion processes. The proton relay portion of this review is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

  13. Ultrafast scattering processes of hot electrons in InSb studied by time- and angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Tanimura, H.; Kanasaki, J.; Tanimura, K.

    2015-01-01

    Ultrafast scattering processes of hot electrons photoinjected into the conduction band of InSb have been studied using time- and angle-resolved photoemission spectroscopy. The nascent distributions of hot-electron packets are captured directly in energy and momentum spaces, and their ultrafast scattering processes are traced at femtosecond temporal resolution on a state-resolved basis. Hot electrons injected in the Γ valley with excess energies above the minimum of the L valley show ultrafast intervalley scattering, with transition times of the order of 40 fs. The relaxation processes in the L valley are resolved in energy and momentum spaces, including their backscattering into the Γ valley during relaxation. In contrast, relaxation of hot electrons with excess energy below the minimum of the L valley is governed by the direct impact ionization (IMP). We reveal state-selective features of the IMP process, and we have determined the direct IMP rate to be 7 ×1012s-1 for hot electrons with excess energy in the range of 0.35 to 0.6 eV. The direct IMP process results in a rapid increase, within 300 fs after excitation, of the electron density at the conduction band minimum (CBM), and phonon-assisted IMP by hot electrons scattered in the L valley and those backscattered into the Γ valley persistently enhances the electron density up to 8 ps after excitation. By analyzing correlations between the IMP rates of hot electrons and the electron densities near the CBM, an important role of a transient Auger recombination is proposed to quantify the yield of low-energy electrons generated in the IMP process.

  14. 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.

  15. Ultrafast-electron-diffraction studies of predamaged tungsten excited by femtosecond optical pulses

    NASA Astrophysics Data System (ADS)

    Mo, M.; Chen, Z.; Li, R.; Wang, Y.; Shen, X.; Dunning, M.; Weathersby, S.; Makasyuk, I.; Coffee, R.; Zhen, Q.; Kim, J.; Reid, A.; Jobe, K.; Hast, C.; Tsui, Y.; Wang, X.; Glenzer, S.

    2016-10-01

    Tungsten is considered as the main candidate material for use in the divertor of magnetic confinement fusion reactors. However, radiation damage is expected to occur because of its direct exposure to the high flux of hot plasma and energetic neutrons in fusion environment. Hence, understanding the material behaviors of W under these adverse conditions is central to the design of magnetic fusion reactors. To do that, we have recently developed an MeV ultrafast electron diffraction probe to resolve the structural evolution of optically excited tungsten. To simulate the radiation damage effect, the tungsten samples were bombarded with 500 keV Cu ions. The pre-damaged and pristine W's were excited by 130fs, 400nm laser pulses, and the subsequent heated system was probed with 3.2MeV electrons. The pump probe measurement shows that the ion bombardment to the W leads to larger decay in Bragg peak intensities as compared to pristine W, which may be due to a phonon softening effect. The measurement also shows that pre-damaged W transitions into complete liquid phase for conditions where pristine W stays solid. Our new capability is able to test the theories of structural dynamics of W under conditions relevant to fusion reactor environment. The research was funded by DOE Fusion Energy Science under FWP #100182.

  16. Monitoring one-electron photo-oxidation of guanine in DNA crystals using ultrafast infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Hall, James P.; Poynton, Fergus E.; Keane, Páraic M.; Gurung, Sarah P.; Brazier, John A.; Cardin, David J.; Winter, Graeme; Gunnlaugsson, Thorfinnur; Sazanovich, Igor V.; Towrie, Michael; Cardin, Christine J.; Kelly, John M.; Quinn, Susan J.

    2015-12-01

    To understand the molecular origins of diseases caused by ultraviolet and visible light, and also to develop photodynamic therapy, it is important to resolve the mechanism of photoinduced DNA damage. Damage to DNA bound to a photosensitizer molecule frequently proceeds by one-electron photo-oxidation of guanine, but the precise dynamics of this process are sensitive to the location and the orientation of the photosensitizer, which are very difficult to define in solution. To overcome this, ultrafast time-resolved infrared (TRIR) spectroscopy was performed on photoexcited ruthenium polypyridyl-DNA crystals, the atomic structure of which was determined by X-ray crystallography. By combining the X-ray and TRIR data we are able to define both the geometry of the reaction site and the rates of individual steps in a reversible photoinduced electron-transfer process. This allows us to propose an individual guanine as the reaction site and, intriguingly, reveals that the dynamics in the crystal state are quite similar to those observed in the solvent medium.

  17. OSA Proceedings on Ultrafast Electronics and Optoelectronics Held in San Francisco, California on January 25 -27, 1993. Volume 14,

    DTIC Science & Technology

    1993-01-27

    Venkatesan, Zhi- Yuan Shen, Philip Pang, Dennis J. Kountz, and William L Holstein Response of a Nb/A1203/Nb Tunnel Junction to Picosecond Electrical Pulses...Mwhra (edo) 0 1993 Optical Sockty ofAnierica 152 Ultrafast Electronics and Optoelectronics core cladding COW MAD 75. 4UHN 1058nm 50Ps A A optical...Maryland. College Park; Maryland 20742 7hi-Yuan Shen, Philip Pang, Dennis J. Kountz, and William L. Holstein Central Research and Development, Du Pont, PO

  18. Free-Energy-Gap Law for Ultrafast Charge Recombination of Ion Pairs Formed by Intramolecular Photoinduced Electron Transfer.

    PubMed

    Nazarov, Alexey E; Malykhin, Roman; Ivanov, Anatoly I

    2017-01-26

    In this article, regularities of ultrafast charge recombination (CR) kinetics in photoinduced intramolecular electron transfer in polar solvents are studied. The kinetics of charge separation and ensuing ultrafast CR are simulated within the framework of the multichannel stochastic model. This model accounts for the reorganization of both the solvent and a number of intramolecular high-frequency vibrational modes. The solvent relaxation is described in terms of two relaxation modes. For ultrafast CR, the free-energy-gap law strongly depends on the parameters: the electronic coupling, reorganization energy of intramolecular high-frequency vibrational modes, and the vibrational and solvent relaxation times. The semilog dependence of the CR rate constant on the free-energy gap varies from a parabolic shape to a nearly linear one with increasing the electronic coupling and decreasing the vibrational relaxation time. The dynamic solvent effect in CR is predicted to be large in the area of strong exergonicity and small in the area of weak exergonicity. This regularity is opposite to that observed for the thermal reactions.

  19. The first picoseconds in bacterial photosynthesis--ultrafast electron transfer for the efficient conversion of light energy.

    PubMed

    Zinth, Wolfgang; Wachtveitl, Josef

    2005-05-01

    In this Minireview, we describe the function of the bacterial reaction centre (RC) as the central photosynthetic energy-conversion unit by ultrafast spectroscopy combined with structural analysis, site-directed mutagenesis, pigment exchange and theoretical modelling. We show that primary energy conversion is a stepwise process in which an electron is transferred via neighbouring chromophores of the RC. A well-defined chromophore arrangement in a rigid protein matrix, combined with optimised energetics of the different electron carriers, allows a highly efficient charge-separation process. The individual molecular reactions at room temperature are well described by conventional electron-transfer theory.

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

    DOE PAGES

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

    2016-08-02

    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.more » Until now, 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 2 potential.« less

  1. Ultrafast relaxation dynamics of electronically excited piperidine: ionization signatures of Rydberg/valence evolution.

    PubMed

    Klein, Liv B; Thompson, James O F; Crane, Stuart W; Saalbach, Lisa; Sølling, Theis I; Paterson, Martin J; Townsend, Dave

    2016-09-14

    We have investigated the electronic relaxation dynamics of gas-phase piperidine (a secondary aliphatic amine) using time-resolved photoelectron imaging. Following 200 nm excitation, spectrally sharp and highly anisotropic photoelectron data reveal ultrafast (60 fs) internal conversion between the initially excited 3px Rydberg state and the lower-lying 3s Rydberg state, mediated by the evolution of nσ* valence character along the 3px N-C bond. This behaviour is in good agreement with previously reported findings for several tertiary aliphatic amines. In contrast to the these systems, however, much broader photoelectron signals exhibiting only very small angular anisotropy and two distinct decay timescales (180 fs and 1.7 ps) were also observed. As confirmed by our supporting calculations, this is attributable to nσ* valence character now evolving along the N-H stretching coordinate within the 3s Rydberg state as the molecule starts dissociating to yield H atom photoproducts in conjunction with ground state piperidinyl radicals. By analogy with systems such as ammonia and morpholine, we conclude this event may occur either promptly or, alternatively, via a "frustrated" process where the system repeatedly traverses the upper cone of a conical intersection with the ground state until the required region of phase space is sampled to facilitate non-adiabatic population transfer. Our findings reveal the role of several different nuclear coordinate motions in driving stepwise internal conversion across multiple potential energy surfaces and the distinct photoionization signatures that are associated with these processes.

  2. 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

  3. 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.

  4. Verifying 4D gated radiotherapy using time-integrated electronic portal imaging: a phantom and clinical study

    PubMed Central

    van Sörnsen de Koste, John R; Cuijpers, Johan P; de Geest, Frank GM; Lagerwaard, Frank J; Slotman, Ben J; Senan, Suresh

    2007-01-01

    Background Respiration-gated radiotherapy (RGRT) can decrease treatment toxicity by allowing for smaller treatment volumes for mobile tumors. RGRT is commonly performed using external surrogates of tumor motion. We describe the use of time-integrated electronic portal imaging (TI-EPI) to verify the position of internal structures during RGRT delivery Methods TI-EPI portals were generated by continuously collecting exit dose data (aSi500 EPID, Portal vision, Varian Medical Systems) when a respiratory motion phantom was irradiated during expiration, inspiration and free breathing phases. RGRT was delivered using the Varian RPM system, and grey value profile plots over a fixed trajectory were used to study object positions. Time-related positional information was derived by subtracting grey values from TI-EPI portals sharing the pixel matrix. TI-EPI portals were also collected in 2 patients undergoing RPM-triggered RGRT for a lung and hepatic tumor (with fiducial markers), and corresponding planning 4-dimensional CT (4DCT) scans were analyzed for motion amplitude. Results Integral grey values of phantom TI-EPI portals correlated well with mean object position in all respiratory phases. Cranio-caudal motion of internal structures ranged from 17.5–20.0 mm on planning 4DCT scans. TI-EPI of bronchial images reproduced with a mean value of 5.3 mm (1 SD 3.0 mm) located cranial to planned position. Mean hepatic fiducial markers reproduced with 3.2 mm (SD 2.2 mm) caudal to planned position. After bony alignment to exclude set-up errors, mean displacement in the two structures was 2.8 mm and 1.4 mm, respectively, and corresponding reproducibility in anatomy improved to 1.6 mm (1 SD). Conclusion TI-EPI appears to be a promising method for verifying delivery of RGRT. The RPM system was a good indirect surrogate of internal anatomy, but use of TI-EPI allowed for a direct link between anatomy and breathing patterns. PMID:17760960

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Ultrafast electron diffraction and electron microscopy: present status and future prospects

    NASA Astrophysics Data System (ADS)

    Ishchenko, A. A.; Aseyev, S. A.; Bagratashvili, V. N.; Panchenko, V. Ya; Ryabov, E. A.

    2014-07-01

    Acting as complementary research tools, high time-resolved spectroscopy and diffractometry techniques proceeding from various physical principles open up new possibilities for studying matter with necessary integration of the 'structure-dynamics-function' triad in physics, chemistry, biology and materials science. Since the 1980s, a new field of research has started at the leading research laboratories, aimed at developing means of filming the coherent dynamics of nuclei in molecules and fast processes in biological objects ('atomic and molecular movies'). The utilization of ultrashort laser pulse sources has significantly modified traditional electron beam approaches to and provided high space-time resolution for the study of materials. Diffraction methods using frame-by-frame filming and the development of the main principles of the study of coherent dynamics of atoms have paved the way to observing wave packet dynamics, the intermediate states of reaction centers, and the dynamics of electrons in molecules, thus allowing a transition from the kinetics to the dynamics of the phase trajectories of molecules in the investigation of chemical reactions.

  10. 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.

  11. Unexpectedly broad photoelectron spectrum as a signature of ultrafast electronic relaxation of Rydberg states of carbon dioxide

    NASA Astrophysics Data System (ADS)

    Adachi, Shunsuke; Sato, Motoki; Suzuki, Toshinori; Grebenshchikov, Sergy Yu.

    2017-03-01

    The dynamics of CO2 excited into Rydberg states lying 0.2 eV below the ionization threshold is studied by means of time resolved photoelectron imaging. Over 3 eV broad photoelectron spectra are measured for all pump-probe delay times. Quantum mechanical calculations demonstrate that the spectral broadening is due to ultrafast electronic relaxation of Rydberg states and identify the likely relaxation pathways. Experiment and theory bracket the relaxation time between 15 and 65 fs. A weak time independent ionization signal is attributed to CO2 trapped in near-threshold triplet states.

  12. Single-shot, ultrafast diagnostics of light-speed plasma structures and accelerating GeV electrons

    NASA Astrophysics Data System (ADS)

    Chang, Yen-Yu; Shaw, Joseph M.; Welch, James; Weichman, Kathleen; Hannasch, Andrea; LaBerge, Maxwell; Henderson, Watson; Zgadzaj, Rafal; Bernstein, Aaron; Downer, Mike

    2017-03-01

    We have experimentally demonstrated ultrafast diagnostics to visualize the laser wakefield acceleration process in a single-shot mode. We measured the Faraday rotation of a probe pulse due to the magnetic field induced by GeV electrons in low-density plasmas. In addition, we improved the temporal resolution of Frequency Domain Streak Camera (FDSC) to ˜10 fs by broadening the bandwidth of the probe beam, enabling visualization of the bubble dynamics. A prototype experiment using the broad bandwidth FDSC was performed.

  13. 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

  14. Basic nanosystems of early 4d and 5d transition metals: Electronic properties and the effect of spin-orbit interaction

    NASA Astrophysics Data System (ADS)

    Bala, Anu; Nautiyal, Tashi; Auluck, Sushil

    2008-07-01

    There are various possibilities for the structure as well as for the growth of nanosystems, particularly of nanowires. The ultimate one-dimensional material—linear chains—are difficult to exploit for applications due to their transient nature. Nonetheless these are a good prototype for studying one-dimensional materials and project the kind of behavior one may expect from ultrathin nanowires. Likewise monolayers are the ultimate two-dimensional materials and their study is helpful in understanding the behavior of two-dimensional materials. We present a theoretical study on basic nanosystems—linear chains and monolayers—of the 4d (Y, Zr, Nb, Mo, and Tc) and 5d (Hf, Ta, W, and Re) transition metals of groups 3-7 by means of an all-electron density functional approach. We have explored all kinds of magnetic configurations: nonmagnetic, ferromagnetic, and antiferromagnetic, by (i) inclusion and (ii) omission of spin-orbit interaction. We find that though this interaction has a marginal effect on nanosystems of 4d transition metals, its impact becomes stronger with lowering of dimensionality. Further it has a significant effect on properties of nanosystems of 5d transition metals as well as those of bulk. It is interesting to note that the monolayers of 5d transition metals seem reluctant to order magnetically despite the general tendency of nanosystems of 4d transition metals and linear chains of 5d transition metals to woo magnetic ordering. The nanosystems with preference for antiferromagnetic ordering are found to be stable at larger nearest-neighbor distances compared to the ferromagnetic and nonmagnetic phases. Specially, antiferromagnetic monolayers of Nb and Mo are predicted to exhibit larger separations with respect to bulk, a feature observed only for some low-dimensional systems. All the monolayers, except Y, are predicted to have a nonmagnetic state almost degenerate with ferromagnetic or antiferromagnetic state. Therefore suitable substrate

  15. 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.

  16. 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.; ...

    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

  17. 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.

  18. Ultrafast electron transfer from low band gap conjugated polymer to quantum dots in hybrid photovoltaic materials

    NASA Astrophysics Data System (ADS)

    Couderc, Elsa; Greaney, Matthew J.; Thornbury, William; Brutchey, Richard L.; Bradforth, Stephen E.

    2014-09-01

    Ultrafast transient absorption spectroscopy is used in conjunction with chemical doping experiments to study the photo-generation of charges in hybrid thin films composed of PCPDTBT and CdSe quantum dots. We show how we use chemical doping experiments to de-convolute the spectral signatures of the transient states in the near infrared.

  19. 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.

  20. Ultrafast photoinduced electron transfer in the micelle and the gel phase of a PEO-PPO-PEO triblock copolymer

    SciTech Connect

    Mandal, Ujjwal; Ghosh, Subhadip; Dey, Shantanu; Adhikari, Aniruddha; Bhattacharyya, Kankan

    2008-04-28

    Ultrafast photoinduced electron transfer (PET) from N,N-dimethylaniline (DMA) to coumarin dyes is studied in the micelle and the gel phase of a triblock copolymer, (PEO){sub 20}-(PPO){sub 70}-(PEO){sub 20} (Pluronic P123) by picosecond and femtosecond emission spectroscopies. The rate of PET in a P123 micelle and gel is found to be nonexponential and faster than the slow components of solvation dynamics. In a P123 micelle and gel, PET occurs on multiple time scales ranging from a subpicosecond time scale to a few nanoseconds. In the gel phase, the highest rate constant (9.3x10{sup 9} M{sup -1} s{sup -1}) of ET for C152 is about two times higher than that (3.8x10{sup 9} M{sup -1} s{sup -1}) observed in micelle phase. The ultrafast components of electron transfer (ET) exhibits a bell shaped dependence with the free energy change which is similar to the Marcus inversion. Possible reasons for slower PET in P123 micelle compared to other micelles and relative to P123 gel are discussed.

  1. 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.

  2. 4-D photoacoustic tomography.

    PubMed

    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.

  3. 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.

  4. Room Temperature Deposition Processes Mediated By Ultrafast Photo-Excited Hot Electrons

    DTIC Science & Technology

    2014-01-30

    CVD Diamond Growth, Low Temperature, Ultra-fast lasers , Non-equilibrium processes REPORT DOCUMENTATION PAGE 11. SPONSOR/MONITOR’S REPORT NUMBER(S...technological problem, we have identified a novel approach. In this approach, wavelength specific, femtosecond laser pulses are used to control material...progress 6 3.2 Procedure for the determination of surface modification thresholds: optimal power and substrate temperature 7 3.3 Laser

  5. 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

  6. 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

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

    DOE PAGES

    Mo, M. Z.; Shen, X.; Chen, Z.; ...

    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

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

    SciTech Connect

    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.

    2016-08-04

    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. This experimental capability opens up an exciting opportunity to unravel the atomic dynamics of structural phase transitions in warm dense matter regime

  9. Ultrafast and nanoscale diodes

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Lau, Y. Y.

    2016-10-01

    Charge carrier transport across interfaces of dissimilar materials (including vacuum) is the essence of all electronic devices. Ultrafast charge transport across a nanometre length scale is of fundamental importance in the miniaturization of vacuum and plasma electronics. With the combination of recent advances in electronics, photonics and nanotechnology, these miniature devices may integrate with solid-state platforms, achieving superior performance. This paper reviews recent modelling efforts on quantum tunnelling, ultrafast electron emission and transport, and electrical contact resistance. Unsolved problems and challenges in these areas are addressed.

  10. 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.; ...

    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

  11. Ultrafast internal conversion of excited cytosine via the lowest pipi electronic singlet state.

    PubMed

    Merchán, Manuela; Serrano-Andrés, Luis

    2003-07-09

    Computational evidence at the CASPT2 level supports that the lowest excited state pipi* contributes to the S1/S0 crossing responsible for the ultrafast decay of singlet excited cytosine. The computed radiative lifetime, 33 ns, is consistent with the experimentally derived value, 40 ns. The nOpi* state does not play a direct role in the rapid repopulation of the ground state; it is involved in a S2/S1 crossing. Alternative mechanisms through excited states pisigma* or nNpi* are not competitive in cytosine.

  12. 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

  13. 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.

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

    PubMed

    Lal, Shankar; Pant, K K

    2014-12-01

    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.

  15. Picosecond infared study of ultrafast electron transfer and vibrational energy relaxation in a mixed-valent ruthenium dimer

    SciTech Connect

    Doorn, S.K.; Stoutland, P.O.; Dyer, R.B.; Woodruff, W.H.

    1992-04-08

    Mixed-valent transition-metal dimers have become key systems for understanding many fundamental aspects of electron-transfer dynamics. The mixed-valent dimer [(NC){sub 5}Ru{sup II}CNRu{sup III}-(NH{sub 3}){sub 5}]{sup 1-} is an interesting member of this class. In this complex, the ruthenium centers are strongly coupled through a short cyanide bridge, but because the [(NC){sub 5}Ru{sub III}CNRu{sub II}(NH{sub 3}){sub 5}]{sub -1} state of this systems lies approximately 8000cm{sup -1} higher in energy, the odd electron is localized on the ruthenium cyanide center. Optical excitation onto the metal-metal charge transfer (MMCT) band leads to reduction of the ruthenium ammine site. This state is highly unstable with respect to back electron transfer. The MMCT excitation is followed by back electron transfer, which may occur on very short time scales, allowing one to observe effects due to ultrafast reorganization processes, to discern excited state/ground state coupling phenomena, and to test modern electron-transfer theories. In this communication, the authors report a picosecond infrared study of the dynamics of [(NC){sub 5}Ru{sup II}CNRu{sup III} (NH{sub 3}){sub 5}]{sup 1-} following MMCT optical excitation. 18 refs., 1 fig., 1 tab.

  16. Ultrafast Terahertz Probe of Transient Evolution of Charged and Neutral Phase of Photoexcited Electron-hole Gas in Monolayer Semiconductor

    NASA Astrophysics Data System (ADS)

    Liu, Xuefeng; Ji, Qingqing; Gao, Zhihan; Ge, Shaofeng; Qiu, Jun; Liu, Zhongfan; Zhang, Yanfeng; Sun, Dong

    2015-03-01

    We investigate the dynamical formation of excitons from photoexcited electron-hole plasma and its subsequent decay dynamics in monolayer MoS2 grown by chemical vapor deposition using ultrafast pump and terahertz probe spectroscopy under temperature down to 78 K. The observed transient THz transmission can be fit with two decay components: a fast component with decay lifetime of 20 ps, which is attributed to exciton life time including the exciton formation and subsequent intraexciton relaxation; a slow component with extremely long decay lifetime of several ns which is attributed to long live dark exciton or localized exciton state. Further temperature and pump fluence dependent studies of the two decay components verify the above relaxation dynamics. The measured time resolved evolution of photoexcited carriers provides new opportunities in developing novel optoelectronic and excitonic devices based on monolayer transition-metal dichalcogenides.

  17. Optimal control of ultrafast laser driven many-electron dynamics in a polyatomic molecule: N-methyl-6-quinolone

    NASA Astrophysics Data System (ADS)

    Klamroth, Tillmann

    2006-04-01

    We report time-dependent configuration interaction singles calculations for the ultrafast laser driven many-electron dynamics in a polyatomic molecule, N-methyl-6-quinolone. We employ optimal control theory to achieve a nearly state-selective excitation from the S0 to the S1 state, on a time scale of a few (≈6) femtoseconds. The optimal control scheme is shown to correct for effects opposing a state-selective transition, such as multiphoton transitions and other, nonlinear phenomena, which are induced by the ultrashort and intense laser fields. In contrast, simple two-level π pulses are not effective in state-selective excitations when very short pulses are used. Also, the dependence of multiphoton and nonlinear effects on the number of states included in the dynamical simulations is investigated.

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

    PubMed

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

    2013-05-15

    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.

  19. Ultrafast hydrogen-bonding dynamics in the electronic excited state of photoactive yellow protein revealed by femtosecond stimulated Raman spectroscopy.

    PubMed

    Nakamura, Ryosuke; Hamada, Norio; Abe, Kenta; Yoshizawa, Masayuki

    2012-12-27

    The ultrafast structural dynamics in the electronic excited state of photoactive yellow protein (PYP) is studied by femtosecond stimulated Raman spectroscopy. Stimulated Raman spectra in the electronic excited state, S(1), can be obtained by using a Raman pump pulse in resonance with the S(1)-S(0) transition. This is confirmed by comparing the experimental results with numerical calculations based on the density matrix treatment. We also investigate the hydrogen-bonding network surrounding the wild-type (WT)-PYP chromophore in the ground and excited states by comparing its stimulated Raman spectra with those of the E46Q-PYP mutant. We focus on the relative intensity of the Raman band at 1555 cm(-1), which includes both vinyl bond C═C stretching and ring vibrations and is sensitive to the hydrogen-bonding network around the phenolic oxygen of the chromophore. The relative intensity for the WT-PYP decreases after actinic excitation within the 150 fs time resolution and reaches a similar intensity to that for E46Q-PYP. These observations indicate that the WT-PYP hydrogen-bonding network is immediately rearranged in the electronic excited state to form a structure similar to that of E46Q-PYP.

  20. 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.

  1. Role of thermal excitation in ultrafast energy transfer in chlorosomes revealed by two-dimensional electronic spectroscopy.

    PubMed

    Jun, Sunhong; Yang, Cheolhee; Kim, Tae Wu; Isaji, Megumi; Tamiaki, Hitoshi; Ihee, Hyotcherl; Kim, Jeongho

    2015-07-21

    Chlorosomes are the largest light harvesting complexes in nature and consist of many bacteriochlorophyll pigments forming self-assembled J-aggregates. In this work, we use two-dimensional electronic spectroscopy (2D-ES) to investigate ultrafast dynamics of excitation energy transfer (EET) in chlorosomes and their temperature dependence. From time evolution of the measured 2D electronic spectra of chlorosomes, we directly map out the distribution of the EET rate among the manifold of exciton states in a 2D energy space. In particular, it is found that the EET rate varies gradually depending on the energies of energy-donor and energy-acceptor states. In addition, from comparative 2D-ES measurements at 77 K and room temperature, we show that the EET rate exhibits subtle dependence on both the exciton energy and temperature, demonstrating the effect of thermal excitation on the EET rate. This observation suggests that active thermal excitation at room temperature prevents the excitation trapping at low-energy states and thus promotes efficient exciton diffusion in chlorosomes at ambient temperature.

  2. Coherent phonon excitation and linear thermal expansion in structural dynamics and ultrafast electron diffraction of laser-heated metals

    NASA Astrophysics Data System (ADS)

    Tang, Jau

    2008-04-01

    In this study, we examine the ultrafast structural dynamics of metals induced by a femtosecond laser-heating pulse as probed by time-resolved electron diffraction. Using the two-temperature model and the Grüneisen relationship we calculate the electron temperature, phonon temperature, and impulsive force at each atomic site in the slab. Together with the Fermi-Pasta-Ulam anharmonic chain model we calculate changes of bond distance and the peak shift of Bragg spots or Laue rings. A laser-heated thin slab is shown to exhibit "breathing" standing-wave behavior, with a period equal to the round-trip time for sound wave and a wavelength twice the slab thickness. The peak delay time first increases linearly with the thickness (<70nm for aluminum and <200nm for gold), but becomes less dependent if further thickness increases. Coherent phonon excitation and propagation from the stressed bulk atoms due to impulsive forces as well as the linear thermal expansion due to lattice temperature jump are shown to contribute to the overall structural changes. Differences between these two mechanisms and their dependence on film thickness and other factors are discussed.

  3. 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.

  4. Direct spectroscopic evidence of ultrafast electron transfer from a low band gap polymer to CdSe quantum dots in hybrid photovoltaic thin films.

    PubMed

    Couderc, Elsa; Greaney, Matthew J; Brutchey, Richard L; Bradforth, Stephen E

    2013-12-11

    Ultrafast transient absorption spectroscopy is used to study charge transfer dynamics in hybrid films composed of the low band gap polymer PCPDTBT and CdSe quantum dots capped with tert-butylthiol ligands. By selectively exciting the polymer, a spectral signature for electrons on the quantum dots appears on ultrafast time scales (≲ 65 fs), which indicates ultrafast electron transfer. From this time scale, the coupling between the polymer chains and the quantum dots is estimated to be J ≳ 17 meV. The reduced quantum dot acceptors exhibit an unambiguous spectral bleach signature, whose amplitude allows for the first direct calculation of the absolute electron transfer yield in a hybrid solar cell (82 ± 5%). We also show that a limitation of the hybrid system is rapid and measurable geminate recombination due to the small separation of the initial charge pair. The fast recombination is consistent with the internal quantum efficiency of the corresponding solar cell. We therefore have identified and quantified a main loss mechanism in this type of third generation solar cell.

  5. Ultrafast Charge Recombination Dynamics in Ternary Electron Donor-Acceptor Complexes: (Benzene)2-Tetracyanoethylene Complexes.

    PubMed

    Chiu, Chih-Chung; Hung, Chih-Chang; Cheng, Po-Yuan

    2016-12-08

    The charge-transfer (CT) state relaxation dynamics of the binary (1:1) and ternary (2:1) benzene/tetracyanoethylene (BZ/TCNE) complexes are reported. Steady-state and ultrafast time-resolved broadband fluorescence (TRFL) spectra of TCNE dissolved in a series of BZ/CCl4 mixed solvents are measured to elucidate the spectroscopic properties of the BZ/TCNE complexes and their CT-state relaxation dynamics. Both steady-state and TRFL spectra exhibit marked BZ concentration dependences, which can be attributed to the formation of two types of 2:1 complexes in the ground and excited states. By combining with the density functional theory (DFT) calculations, it was concluded that the BZ concentration dependence of the absorption spectra is mainly due to the formation and excitation of the sandwich-type 2:1 ternary complexes, whereas the changes in fluorescence spectra at high BZ concentrations are due to the formation of the asymmetric-type 2:1 ternary complex CT1 state. A unified mechanism involving both direct excitation and secondary formation of the 2:1 complexes CT states are proposed to account for the observations. The equilibrium charge recombination (CR) time constant of the 1:1 CT1 state is determined to be ∼150 ps in CCl4, whereas that of the 2:1 DDA-type CT1 state becomes ∼70 ps in 10% BZ/CCl4 and ∼34 ps in pure BZ. The CR rates and the CT1-S0 energy gap of these complexes in different solvents exhibit a correlation conforming to the Marcus inverted region. It is concluded that partial charge resonance occurring between the two adjacent BZs in the asymmetric-type 2:1 CT1-state reduces the CR reaction exothermicity and increases the CR rate.

  6. 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.

  7. Nanoscale heat transport from Ge hut, dome, and relaxed clusters on Si(001) measured by ultrafast electron diffraction

    SciTech Connect

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

    2015-02-02

    The thermal transport properties of crystalline nanostructures on Si were studied by ultra-fast surface sensitive time-resolved electron diffraction. Self-organized growth of epitaxial Ge hut, dome, and relaxed clusters was achieved by in-situ deposition of 8 monolayers of Ge on Si(001) at 550 °C under UHV conditions. The thermal response of the three different cluster types subsequent to impulsive heating by fs laser pulses was determined through the Debye-Waller effect. Time resolved spot profile analysis and life-time mapping was employed to distinguish between the thermal response of the different cluster types. While dome clusters are cooling with a time constant of τ = 150 ps, which agrees well with numerical simulations, the smaller hut clusters with a height of 2.3 nm exhibit a cooling time constant of τ = 50 ps, which is a factor of 1.4 slower than expected.

  8. Photoinduced bimolecular electron transfer from aromatic amines to pentafluorophenyl porphyrin combined with ultrafast charge recombination persistence with Marcus inverted region.

    PubMed

    Venkatesh, Yeduru; Munisamy, Venkatesan; Ramakrishna, Bheerappagari; Kumar, Pippara Hemant; Mandal, Haraprasad; Bangal, Prakriti Ranjan

    2017-02-15

    The dynamics of photoinduced bimolecular reductive electron transfer between meso-tetrakis(pentafluorophenyl)porphyrin (H2F20TPP), an acceptor (A), and five aromatic amines (donor (D)) with varying oxidation potentials (aniline (AN), N-methylaniline (MAN), N-ethylaniline (EAN), N,N-dimethylaniline (DMAN) and N,N-diethylaniline (DEAN)) in dichloromethane (DCM) as a solvent as well as in neat donor solvents were investigated by employing nanosecond to femtosecond time-resolved fluorescence spectroscopy and femtosecond time-resolved transient absorption spectroscopy upon S2 excitation of H2F20TPP. Systematic studies of time-resolved fluorescence quenching dependent on the donor concentration in the concentration range of 0.01-2 M and finally in neat donor solvents broadly enabled us to determine the electron transfer dynamics in three regimes of electron transfer: stationary or diffusion-controlled electron transfer, non-stationary electron transfer and intrinsic or ultrafast electron transfer. Depending upon the electron-donating ability of the studied donors, intrinsic electron transfer was found to occur in the time domain of ∼1-9 ps and diffusion-controlled ET dynamics was observed in the time domain of 200-500 ps, whereas the maximum limit of non-stationary electron transfer could be observed in the time domain of 15-50 ps. Femtosecond transient absorption studies together with global and target analysis helped to identify the spectral signature of the (H2F20TPP˙(-)) radical anion as the product of ET. To the best of our knowledge, this is the first ever evidence that shows the spectra of an anion as the product of ET for any porphyrin-based electron transfer dynamics. However, transient absorption measurements confirm that intrinsic ET occurs in the Qy state, whereas diffusion-controlled ET occurs in the hot Qx as well as in the thermal equilibrium Qx state. The most remarkable fact derived from the measurements of transient absorption was that the rate of

  9. Numerical simulation of THz-wave-assisted electron diffraction for ultrafast molecular imaging

    NASA Astrophysics Data System (ADS)

    Kanya, Reika; Yamanouchi, Kaoru

    2017-03-01

    A scheme for achieving high temporal resolution in gas electron diffraction is proposed, in which time-dependent electron diffraction patterns can be obtained from energy-resolved angular distributions of electrons scattered by molecules in dynamical processes under the presence of a single-cycle THz-wave pulse. Derived formulae of the differential cross section and numerical simulations of electron signals scattered by Ar atoms and C l2 molecules show that the temporal resolution of the proposed method can be <10 fs in the pump-probe measurement without scanning the time delay.

  10. Electronic dynamics by ultrafast pump photoelectron detachment probed by ionization: a dynamical simulation of negative-neutral-positive in LiH(-).

    PubMed

    Mignolet, B; Levine, R D; Remacle, F

    2014-08-21

    The control of electronic dynamics in the neutral electronic states of LiH before the onset of significant nuclei motion is investigated using a negative-neutral-positive (NeNePo) ultrafast IR pump-attoescond pulse train (APT) probe scheme. Starting from the ground state of the anion (LiH(-)), multiphoton ultrafast electron detachment and subsequent excitation of the neutral by a few femtosecond intense IR pulse produces a non-equilibrium electronic density in neutral LiH. The coherent electronic wave packet is then probed by angularly resolved photoionization to the cation by an APT generated from a replica of the pump IR pulse at several time delays. Realistic parameters for the pump and the APT are used. Several NeNePo schemes are simulated using different IR carrier frequencies, showing that the delay between the successive attosecond pulses in the train can be used as a filter to probe the different pairs of states present in the coherent electronic wave packet produced by the pump pulse. The dynamical simulations include the pump and the probe pulses to all orders by solving the time-dependent Schrödinger equation using a coupled equation scheme for the manifolds of the anion, neutral, and cation subspaces. We show that an incomplete molecular orientation of the molecule in the laboratory frame does not prevent probing the electronic density localization by angularly resolved photoelectron maps.

  11. Quantum computers based on electron spins controlled by ultrafast off-resonant single optical pulses.

    PubMed

    Clark, Susan M; Fu, Kai-Mei C; Ladd, Thaddeus D; Yamamoto, Yoshihisa

    2007-07-27

    We describe a fast quantum computer based on optically controlled electron spins in charged quantum dots that are coupled to microcavities. This scheme uses broadband optical pulses to rotate electron spins and provide the clock signal to the system. Nonlocal two-qubit gates are performed by phase shifts induced by electron spins on laser pulses propagating along a shared waveguide. Numerical simulations of this scheme demonstrate high-fidelity single-qubit and two-qubit gates with operation times comparable to the inverse Zeeman frequency.

  12. Ultrafast events in the electron photodetachment from the hexacyanoferrate(II) complex in solution

    NASA Astrophysics Data System (ADS)

    Pommeret, Stanislas; Naskrecki, Ryszard; van der Meulen, Peter; Ménard, Marjorie; Vigneron, Georges; Gustavsson, Thomas

    1998-05-01

    Following excitation of the hexacyanoferrate(II) complex in water with a 40 fs laser pulse at 267 nm, the absorption of the hydrated electron rises with a global time constant of 510 fs, whereas the characteristic absorption of the hexacyanoferrate(III) appears almost instantaneously. A transient absorption band around 490 nm is tentatively assigned to the charge-transfer-to-solvent (CTTS) state of the hexacyanoferrate(II). Its ultra-rapid decay (≪60 fs) is due to the electronic repulsion between the electron and its parent core.

  13. 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.

  14. Ultrafast Electron Dynamics in Gold in the Presence of Laser Excited Surface Plasma Waves

    SciTech Connect

    Raynaud, M.

    2010-02-02

    Surface plasmon excitation with ultrashort intense laser pulses enhances efficiently laser absorption in metals and creates local high fields and non-equilibrium hot electrons population that have attractivity for numerous applications such as the development of intense sources of high-energy particles or photons and in the fast ignitor scheme in the framework of inertial fusion. In this context, the knowledge of the dynamics of relaxation of the collective electrons behavior is of importance. Using gold grating, we have investigated electrons relaxation in the presence of laser excited surface plasmon waves using a multiple-wavelengh femtosecond pump-probe technique. The results yield evidence of longer relaxation time in the presence of the collective excitation than that of individual electronic states.

  15. Accelerating calculations of ultrafast time-resolved electronic spectra with efficient quantum dynamics methods.

    PubMed

    Wehrle, Marius; Sulc, Miroslav; Vanícek, Jirí

    2011-01-01

    We explore three specific approaches for speeding up the calculation of quantum time correlation functions needed for time-resolved electronic spectra. The first relies on finding a minimum set of sufficiently accurate electronic surfaces. The second increases the time step required for convergence of exact quantum simulations by using different split-step algorithms to solve the time-dependent Schrödinger equation. The third approach lowers the number of trajectories needed for convergence of approximate semiclassical dynamics methods.

  16. 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.

  17. Ultrafast Interfacial Electron and Hole Transfer from CsPbBr3 Perovskite Quantum Dots.

    PubMed

    Wu, Kaifeng; Liang, Guijie; Shang, Qiongyi; Ren, Yueping; Kong, Degui; Lian, Tianquan

    2015-10-14

    Recently reported colloidal lead halide perovskite quantum dots (QDs) with tunable photoluminescence (PL) wavelengths covering the whole visible spectrum and exceptionally high PL quantum yields (QYs, 50-90%) constitute a new family of functional materials with potential applications in light-harvesting and -emitting devices. By transient absorption spectroscopy, we show that the high PL QYs (∼79%) can be attributed to negligible electron or hole trapping pathways in CsPbBr3 QDs: ∼94% of lowest excitonic states decayed with a single-exponential time constant of 4.5 ± 0.2 ns. Furthermore, excitons in CsPbBr3 QDs can be efficiently dissociated in the presence of electron or hole acceptors. The half-lives of electron transfer (ET) to benzoquinone and subsequent charge recombination are 65 ± 5 ps and 2.6 ± 0.4 ns, respectively. The half-lives for hole transfer (HT) to phenothiazine and the subsequent charge recombination are 49 ± 6 ps and 1.0 ± 0.2 ns, respectively. The lack of electron and hole traps and fast interfacial ET and HT rates are key properties that may enable the development of efficient lead halide perovskite QDs-based light-harvesting and -emitting devices.

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

    DOE PAGES

    Ayzner, Alexander L.; Nordlund, Dennis; Kim, Do -Hwan; ...

    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

  19. 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.

  20. 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 .

  1. 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}.

  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. 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.

  4. Ultrafast optical coherent control of individual electron and hole spins in a semiconductor quantum dot

    NASA Astrophysics Data System (ADS)

    de Greve, Kristiaan

    2012-02-01

    We report on the complete optical coherent control of individual electron and hole spin qubits in InAs quantum dots. With a magnetic field in Voigt geometry, broadband, detuned optical pulses couple the spin-split ground states, resulting in Rabi flopping. In combination with the Larmor precession around the external magnetic field, this allows an arbitrary single-qubit operation to be realized in less than 20 picoseconds [1,2]. Slow fluctuations in the spin's environment lead to shot-to-shot variations in the Larmor precession frequency. In a time-ensemble measurement, these would prevent a measurement of the true decoherence of the qubit, and instead give rise to ensemble dephasing. This effect was overcome by implementing a spin echo measurement scheme for both electron and hole spins, where an optical π-pulse refocuses the spin coherence and filters out the slow variations in Larmor precession frequency. We measured coherence times up to 3 microseconds [2,3]. Finally, our optical pulse manipulation scheme allows us to probe the hyperfine interaction between the single spin and the nuclei in the quantum dot. Interesting non-Markovian dynamics could be observed in the free-induction decay of a single electron spin, whereas the complete absence of such effects illustrates the reduction of the hyperfine interaction for hole spin qubits. We measured and modeled these effects, and explain the non-Markovian electron spin dynamics as involving a feedback effect resulting from both the strong Overhauser shift of the electron spin and spin dependent nuclear relaxation [2,4]. [4pt] [1] D. Press, T. D. Ladd, B. Zhang and Y. Yamamoto, Nature 456, 218 (2008)[0pt] [2] K. De Greve, P. McMahon, D. Press et al., Nat. Phys. 7, 872 (2011)[0pt] [3] D. Press, K. De Greve, P. McMahon et al., Nat. Phot. 4, 367 (2010)[0pt] [4] T. D. Ladd, D. Press, K. De Greve et al., Phys. Rev. Lett. 105, 107401 (2010)

  5. Comparison of influence of incorporated 3d-, 4d- and 4f-metal chlorides on electronic properties of single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Kharlamova, M. V.

    2013-06-01

    In the present work, the channels of single-walled carbon nanotubes were filled with melts of ZnCl2, CdCl2, and TbCl3 by a capillary method with subsequent slow cooling. The detailed study of electronic structure of filled nanotubes was performed using Raman, optical absorption, and X-ray photoelectron spectroscopy. The obtained data are in mutual agreement and it proves that the filling of carbon nanotube channels with all these salts leads to the charge transfer from nanotube walls to the incorporated compounds, thus acceptor doping of nanotubes takes place. It was found out that encapsulated terbium chloride has the largest influence on the electronic properties of carbon nanotubes.

  6. Ultrafast nonradiative dynamics in electronically excited hexafluorobenzene by femtosecond time-resolved mass spectrometry

    NASA Astrophysics Data System (ADS)

    Studzinski, Harald; Zhang, Song; Wang, Yanmei; Temps, Friedrich

    2008-04-01

    The fast nonradiative decay dynamics of the lowest two excited ππ * electronic states (S2 and S3) of hexafluorobenzene have been investigated by using femtosecond time-resolved time-of-flight mass spectrometry. The molecules were excited at wavelengths between 265nm⩾λpump⩾217nm and probed by four- and three-photon ionization at λprobe=775nm. The observed temporal profiles exhibit two exponential decay times (τ1=0.54-0.1ps and τ2=493-4.67ps, depending on the excitation wavelength) and a superimposed coherent oscillation with vibrational frequency νosc=97cm-1 and damping time τD that is two to three times longer than the respective τ1. The first decay component (τ1) is assigned to rapid radiationless transfer from the excited optically bright ππ * electronic state (S2 or S3, respectively) through a conical intersection (CI) to the lower-lying optically dark πσ * state (S1) of the molecule; the second component (τ2) is attributed to the subsequent slower relaxation from the S1 state back to the electronic ground state (S0). τ2 dramatically decreases with increasing vibronic excitation energy up to the CI connecting the πσ * with the S0 state. The coherent oscillation is identified as nuclear motion along the out-of-plane vibration ν16a (notation as for benzene), which has e2u symmetry and acts as coupling mode between the ππ * and πσ * states.

  7. Ultrafast laser-driven microlens to focus and energy-select mega-electron volt protons.

    PubMed

    Toncian, Toma; Borghesi, Marco; Fuchs, Julien; d'Humières, Emmanuel; Antici, Patrizio; Audebert, Patrick; Brambrink, Erik; Cecchetti, Carlo Alberto; Pipahl, Ariane; Romagnani, Lorenzo; Willi, Oswald

    2006-04-21

    We present a technique for simultaneous focusing and energy selection of high-current, mega-electron volt proton beams with the use of radial, transient electric fields (10(7) to 10(10) volts per meter) triggered on the inner walls of a hollow microcylinder by an intense subpicosecond laser pulse. Because of the transient nature of the focusing fields, the proposed method allows selection of a desired range out of the spectrum of the polyenergetic proton beam. This technique addresses current drawbacks of laser-accelerated proton beams, such as their broad spectrum and divergence at the source.

  8. Ultrafast electron radiography of magnetic fields in high-intensity laser-solid interactions.

    PubMed

    Schumaker, W; Nakanii, N; McGuffey, C; Zulick, C; Chyvkov, V; Dollar, F; Habara, H; Kalintchenko, G; Maksimchuk, A; Tanaka, K A; Thomas, A G R; Yanovsky, V; Krushelnick, K

    2013-01-04

    Using electron bunches generated by laser wakefield acceleration as a probe, the temporal evolution of magnetic fields generated by a 4 × 10(19) W/cm(2) ultrashort (30 fs) laser pulse focused on solid density targets is studied experimentally. Magnetic field strengths of order B(0) ~ 10(4) T are observed expanding at close to the speed of light from the interaction point of a high-contrast laser pulse with a 10-μm-thick aluminum foil to a maximum diameter of ~1 mm. The field dynamics are shown to agree with particle-in-cell simulations.

  9. 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

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

    NASA Astrophysics Data System (ADS)

    Müller, L.; Gutt, C.; Streit-Nierobisch, S.; Walther, M.; Schaffert, S.; Pfau, B.; Geilhufe, J.; Büttner, F.; Flewett, S.; Günther, C. M.; Eisebitt, S.; Kobs, A.; Hille, M.; Stickler, D.; Frömter, R.; Oepen, H. P.; Lüning, J.; Grübel, G.

    2013-01-01

    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_3N_4 membranes and pump-laser-induced grid structures in multilayer samples.

  11. 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.

  12. Ultrafast Self-Healing Nanocomposites via Infrared Laser and Their Application in Flexible Electronics.

    PubMed

    Wu, Shuwen; Li, Jinhui; Zhang, Guoping; Yao, Yimin; Li, Gang; Sun, Rong; Wong, Chingping

    2017-01-25

    The continuous evolution toward flexible electronics with mechanical robust property and restoring structure simultaneously places high demand on a set of polymeric material substrate. Herein, we describe a composite material composed of a polyurethane based on Diels-Alder chemistry (PU-DA) covalently linked with functionalized graphene nanosheets (FGNS), which shows mechanical robust and infrared (IR) laser self-healing properties at ambient conditions and is therefore suitable for flexible substrate applications. The mechanical strength can be tuned by varying the amount of FGNS and breaking strength can reach as high as 36 MPa with only 0.5 wt % FGNS loading. On rupture, the initial mechanical properties are restored with more than 96% healing efficiency after 1 min irradiation time by 980 nm IR laser. Especially, this is the highest value of healing efficiency reported in the self-healable materials based on DA chemistry systems until now, and the composite exhibits a high volume resistivity up to 5.6 × 10(11) Ω·cm even the loading of FGNS increased to 1.0 wt %. Moreover, the conductivity of the broken electric circuit which was fabricated by silver paste drop-cast on the healable composite substrate was completely recovered via IR laser irradiating bottom substrate mimicking human skin. These results demonstrate that the FGNS-PU-DA nanocomposite can be used as self-healing flexible substrate for the next generation of intelligent flexible electronics.

  13. Ultrafast energy and electron transfers in structurally well addressable BODIPY-porphyrin-fullerene polyads.

    PubMed

    Gao, Di; Aly, Shawkat M; Karsenti, Paul-Ludovic; Brisard, Gessie; Harvey, Pierre D

    2017-01-25

    Two electron transfer polyads built upon [C60]-[ZnP]-[BODIPY] (1) and [ZnP]-[ZnP](-[BODIPY])(-[C60]) (2), where [C60] = N-methyl-2-phenyl-3,4-fulleropyrrolidine, [BODIPY] = boron dipyrromethane, and [ZnP] = zinc(ii) porphyrin, were synthesized along with their corresponding energy transfer polyads [ZnP]-[BODIPY] (1a) and [ZnP]-[ZnP]-[BODIPY] (2a) as well as relevant models. These polyads were studied using cyclic voltammetry, DFT computations, steady state and time-resolved fluorescence spectroscopy, and fs transient absorption spectroscopy. The rates for energy transfer, kET, [BODIPY]* → [ZnP] are ∼2.8 × 10(10) s(-1) for both 1a and 2a, with an efficiency of 99%. Concurrently, the fast appearance of the [C60](-)˙ anion for 1 and 2 indicates that the charge separation occurs on the 20-30 ps timescale with the rates of electron transfer, ket, [ZnP]*/[C60] → [ZnP](+)˙/[C60](-)˙ of ∼0.9 × 10(10) to ∼3.8 × 10(10) s(-1). The latter value is among the fastest for these types of polyads. Conversely, the charge recombination operates on the ns timescale. These rates are comparable to or faster than those reported for other more flexible [C60]-[ZnP]-[BODIPY] polyads, which can be rationalized by the donor-acceptor separations.

  14. 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

  15. 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

  16. Ultrafast electron dynamics at the Dirac node of the topological insulator Sb2Te3.

    PubMed

    Zhu, Siyuan; Ishida, Yukiaki; Kuroda, Kenta; Sumida, Kazuki; Ye, Mao; Wang, Jiajia; Pan, Hong; Taniguchi, Masaki; Qiao, Shan; Shin, Shik; Kimura, Akio

    2015-08-21

    Topological insulators (TIs) are a new quantum state of matter. Their surfaces and interfaces act as a topological boundary to generate massless Dirac fermions with spin-helical textures. Investigation of fermion dynamics near the Dirac point (DP) is crucial for the future development of spintronic devices incorporating topological insulators. However, research so far has been unsatisfactory because of a substantial overlap with the bulk valence band and a lack of a completely unoccupied DP. Here, we explore the surface Dirac fermion dynamics in the TI Sb2Te3 by time- and angle-resolved photoemission spectroscopy (TrARPES). Sb2Te3 has an in-gap DP located completely above the Fermi energy (EF). The excited electrons in the upper Dirac cone stay longer than those below the DP to form an inverted population. This was attributed to a reduced density of states (DOS) near the DP.

  17. Ultrafast Relaxation Dynamics of a High Density Electron-Hole Plasma in High Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Lee, Jinho; Reitze, Dave H.; Kono, Junichiro; Belyanin, Alexey; Solomon, Glenn; McGill, Steve

    2009-03-01

    We study the inter-Landau level relaxation dynamics of a dense electron-hole plasma in high magnetic fields (up to 31 T). Intense 150 fs pump pulses create carrier densities approaching 10^13/cm^2 in In0.2Ga0.8As/GaAs multiple quantum wells. Relaxation dynamics are probed as a function of Landau level (LL) and magnetic field using time-resolved transient absorption (TRTA) and time-resolved photoluminescence (TRPL), which provide complementary information about the relaxation processes. Manifestly non-exponential decays of the TRTA signals are observed at high fields (above 15 T). TRPL emissions measured in the plane of the wells reveal the presence of multiple emission bursts from the LLs at high magnetic fields, suggesting a complicated relaxation process mediated by the field whereby carriers get trapped in a specific LL, emit PL though recombination, and then `reload' as the carriers relax down to the previously occupied LLs.

  18. Ultrafast electron dynamics at the Dirac node of the topological insulator Sb2Te3

    PubMed Central

    Zhu, Siyuan; Ishida, Yukiaki; Kuroda, Kenta; Sumida, Kazuki; Ye, Mao; Wang, Jiajia; Pan, Hong; Taniguchi, Masaki; Qiao, Shan; Shin, Shik; Kimura, Akio

    2015-01-01

    Topological insulators (TIs) are a new quantum state of matter. Their surfaces and interfaces act as a topological boundary to generate massless Dirac fermions with spin-helical textures. Investigation of fermion dynamics near the Dirac point (DP) is crucial for the future development of spintronic devices incorporating topological insulators. However, research so far has been unsatisfactory because of a substantial overlap with the bulk valence band and a lack of a completely unoccupied DP. Here, we explore the surface Dirac fermion dynamics in the TI Sb2Te3 by time- and angle-resolved photoemission spectroscopy (TrARPES). Sb2Te3 has an in-gap DP located completely above the Fermi energy (EF). The excited electrons in the upper Dirac cone stay longer than those below the DP to form an inverted population. This was attributed to a reduced density of states (DOS) near the DP. PMID:26294343

  19. 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.

  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

    2012-12-07

    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 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.

  2. 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.

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

    DOE PAGES

    Zastrau, U.; Sperling, P.; Fortmann-Grote, C.; ...

    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

  4. 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

  5. Ultrafast Optical Electronics Center

    DTIC Science & Technology

    1990-08-28

    probe beam, while the longitudinal crystal, fabricated of deuterated potassium dihydrogen phosphate (KD*P), is used to measure field components that are...clad between 0.1 4am p+ cap layer and a I .m n buffer layer grown on top of the semi- insulating (SI) substrate. Tunneling is only possible through the...Twenty-five periods of the double-QW structure were grown on an n -type GaAs substrate and n -type GaAs buffer layer. A semitransparent Al Schottky 11 CF

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

    SciTech Connect

    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 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. 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.

  7. Exploring the time-scale of photo-initiated interfacial electron transfer through first-principles interpretation of ultrafast X-ray spectroscopy (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Prendergast, David; Pemmaraju, Sri Chaitanya Das

    2015-09-01

    With the advent of X-ray free electron lasers and table-top high-harmonic-generation X-ray sources, we can now explore changes in electronic structure on ultrafast time scales -- at or less than 1ps. Transient X-ray spectroscopy of this kind provides a direct probe of relevant electronic levels related to photoinitiated processes and associated interfacial electron transfer as the initial step in solar energy conversion. However, the interpretation of such spectra is typically fraught with difficulty, especially since we rarely have access to spectral standards for nonequilibrium states. To this end, direct first-principles simulations of X-ray absorption spectra can provide the necessary connection between measurements and reliable models of the atomic and electronic structure. We present examples of modeling excited states of materials interfaces relevant to solar harvesting and their corresponding X-ray spectra in either photoemission or absorption modalities. In this way, we can establish particular electron transfer mechanisms to reveal detailed working principles of materials systems in solar applications and provide insight for improved efficiency.

  8. Semiclassical study of quantum coherence and isotope effects in ultrafast electron transfer reactions coupled to a proton and a phonon bath.

    PubMed

    Venkataraman, Charulatha

    2011-11-28

    The linearized semiclassical initial value representation is employed to describe ultrafast electron transfer processes coupled to a phonon bath and weakly coupled to a proton mode. The goal of our theoretical investigation is to understand the influence of the proton on the electronic dynamics in various bath relaxation regimes. More specifically, we study the impact of the proton on coherences and analyze if the coupling to the proton is revealed in the form of an isotope effect. This will be important in distinguishing reactions in which the proton does not undergo significant rearrangement from those in which the electron transfer is accompanied by proton transfer. Unlike other methodologies widely employed to describe nonadiabatic electron transfer, this approach treats the electronic and nuclear degrees of freedom consistently. However, due to the linearized approximation, quantum interference effects are not captured accurately. Our study shows that at small phonon bath reorganization energies, coherent oscillations and isotope effect are observed in both slow and fast bath regimes. The coherences are more substantially damped by deuterium in comparison to the proton. Further, in contrast to the dynamics of the spin-boson model, the coherences are not long-lived. At large bath reorganization energies, the decay is incoherent in the slow and fast bath regimes. In this case, the extent of the isotope effect depends on the relative relaxation timescales of the proton mode and the phonon bath. The isotope effect is magnified for baths that relax on picosecond timescales in contrast to baths that relax in femtoseconds.

  9. 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.

  10. A general method for baseline-removal in ultrafast electron powder diffraction data using the dual-tree complex wavelet transform

    PubMed Central

    René de Cotret, Laurent P.; Siwick, Bradley J.

    2016-01-01

    The general problem of background subtraction in ultrafast electron powder diffraction (UEPD) is presented with a focus on the diffraction patterns obtained from materials of moderately complex structure which contain many overlapping peaks and effectively no scattering vector regions that can be considered exclusively background. We compare the performance of background subtraction algorithms based on discrete and dual-tree complex (DTCWT) wavelet transforms when applied to simulated UEPD data on the M1–R phase transition in VO2 with a time-varying background. We find that the DTCWT approach is capable of extracting intensities that are accurate to better than 2% across the whole range of scattering vector simulated, effectively independent of delay time. A Python package is available. PMID:28083543

  11. Ultrafast forward and backward electron transfer dynamics of coumarin 337 in hydrogen-bonded anilines as studied with femtosecond UV-pump/IR-probe spectroscopy.

    PubMed

    Ghosh, Hirendra N; Verma, Sandeep; Nibbering, Erik T J

    2011-02-10

    Femtosecond infrared spectroscopy is used to study both forward and backward electron transfer (ET) dynamics between coumarin 337 (C337) and the aromatic amine solvents aniline (AN), N-methylaniline (MAN), and N,N-dimethylaniline (DMAN), where all the aniline solvents can donate an electron but only AN and MAN can form hydrogen bonds with C337. The formation of a hydrogen bond with AN and MAN is confirmed with steady state FT-IR spectroscopy, where the C═O stretching vibration is a direct marker mode for hydrogen bond formation. Transient IR absorption measurements in all solvents show an absorption band at 2166 cm(-1), which has been attributed to the C≡N stretching vibration of the C337 radical anion formed after ET. Forward electron transfer dynamics is found to be biexponential with time constants τ(ET)(1) = 500 fs, τ(ET)(2) = 7 ps in all solvents. Despite the presence of hydrogen bonds of C337 with the solvents AN and MAN, no effect has been found on the forward electron transfer step. Because of the absence of an H/D isotope effect on the forward electron transfer reaction of C337 in AN, hydrogen bonds are understood to play a minor role in mediating electron transfer. In contrast, direct π-orbital overlap between C337 and the aromatic amine solvents causes ultrafast forward electron transfer dynamics. Backward electron transfer dynamics, in contrast, is dependent on the solvent used. Standard Marcus theory explains the observed backward electron transfer rates.

  12. Sub-nanometer-scale measurements of the interaction of ultrafast soft x-ray free-electron-laser pulses with matter

    SciTech Connect

    Hau-Riege, S; Chapman, H; Krzywinski, J; Sobierajski, R; London, R; Bionta, R; Bergh, M; Caleman, C; Nietubyc, R; Juha, L; Kuba, J; Bajt, S; Spiller, E; Baker, S; Kjornrattanawanich, B; Gullikson, E; Tschentscher, T; Plonjes, E; Toleikis, S

    2006-08-02

    Femtosecond pulses from soft-x-ray free-electron lasers (FELs) [1] are ideal for directly probing matter at atomic length scales and timescales of atomic motion. An important component of understanding ultrafast phenomena of light-matter interactions is concerned with the onset of atomic motion which is impeded by the atoms inertia. This delay of structural changes will enable atomic-resolution flash-imaging [2-3] to be performed at upcoming x-ray FELs [4-5] with pulses intense enough to record the x-ray scattering from single molecules [6]. We explored this ultrafast high-intensity regime with the FLASH soft-x-ray FEL [7-8] by measuring the reflectance of nanostructured multilayer mirrors using pulses with fluences far in excess of the mirrors damage threshold. Even though the nanostructures were ultimately completely destroyed, we found that they maintained their integrity and reflectance characteristics during the 25-fs-long pulse, with no evidence for any structural changes during that time over lengths greater than 3 {angstrom}. In the recently built FLASH FEL [7], x-rays are produced from short electron pulses oscillating in a periodic magnet array, called an undulator, by the principle of self-amplification of spontaneous emission [9-10]. The laser quality of the x-ray pulses can be quantified by the peak spectral brilliance of the source, which is 10{sup 28} photons/(s mm2 mrad2 0.1% bandwidth) [8]; this is up to seven orders of magnitude higher than modern third-generation synchrotron sources. For our studies, the machine operated with pulses of 25 fs duration at a wavelength of 32.5 nm and energies up to 21 {micro}J. We focused these pulses to 3 x 10{sup 14} W/cm{sup 2} onto our nanostructured samples, resulting in an the unprecedented heating rate of 5 x 10{sup 18} K/s, while probing the irradiated structures at the nanometer length scale. The x-ray reflectivity of periodic nanometer-scale multilayers [11] is very sensitive to changes in the atomic

  13. 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.

  14. Imaging ultrafast excited state pathways in transition metal complexes by X-ray transient absorption and scattering using X-ray free electron laser source.

    PubMed

    Chen, Lin X; Shelby, Megan L; Lestrange, Patrick J; Jackson, Nicholas E; Haldrup, Kristoffer; Mara, Michael W; Stickrath, Andrew B; Zhu, Diling; Lemke, Henrik; Chollet, Matthieu; Hoffman, Brian M; Li, Xiaosong

    2016-12-16

    This report will describe our recent studies of transition metal complex structural dynamics on the fs and ps time scales using an X-ray free electron laser source, Linac Coherent Light Source (LCLS). Ultrafast XANES spectra at the Ni K-edge of nickel(ii) tetramesitylporphyrin (NiTMP) were measured for optically excited states at a timescale from 100 fs to 50 ps, providing insight into its sub-ps electronic and structural relaxation processes. Importantly, a transient reduced state Ni(i) (π, 3dx(2)-y(2)) electronic state is captured through the interpretation of a short-lived excited state absorption on the low-energy shoulder of the edge, which is aided by the computation of X-ray transitions for postulated excited electronic states. The observed and computed inner shell to valence orbital transition energies demonstrate and quantify the influence of the electronic configuration on specific metal orbital energies. A strong influence of the valence orbital occupation on the inner shell orbital energies indicates that one should not use the transition energy from 1s to other orbitals to draw conclusions about the d-orbital energies. For photocatalysis, a transient electronic configuration could influence d-orbital energies up to a few eV and any attempt to steer the reaction pathway should account for this to ensure that external energies can be used optimally in driving desirable processes. NiTMP structural evolution and the influence of the porphyrin macrocycle conformation on relaxation kinetics can be likewise inferred from this study.

  15. Imaging ultrafast excited state pathways in transition metal complexes by X-ray transient absorption and scattering using X-ray free electron laser source

    SciTech Connect

    Chen, Lin X.; Shelby, Megan L.; Lestrange, Patrick J.; Jackson, Nicholas E.; Haldrup, Kristoffer; Mara, Michael W.; Stickrath, Andrew B.; Zhu, Diling; Lemke, Henrik; Chollet, Matthieu; Hoffman, Brian M.; Li, Xiaosong

    2016-01-01

    This report will describe our recent studies of transition metal complex structural dynamics on the fs and ps time scales using an X-ray free electron laser source, Linac Coherent Light Source (LCLS). Ultrafast XANES spectra at the Ni K-edge of nickel(II) tetramesitylporphyrin (NiTMP) were successfully measured for optically excited state at a timescale from 100 fs to 50 ps, providing insight into its sub-ps electronic and structural relaxation processes. Importantly, a transient reduced state Ni(I) (π, 3dx2-y2) electronic state is captured through the interpretation of a short-lived excited state absorption on the low-energy shoulder of the edge, which is aided by the computation of X-ray transitions for postulated excited electronic states. The observed and computed inner shell to valence orbital transition energies demonstrate and quantify the influence of electronic configuration on specific metal orbital energies. A strong influence of the valence orbital occupation on the inner shell orbital energies indicates that one should not use the transition energy from 1s to other orbitals to draw conclusions about the d-orbital energies. For photocatalysis, a transient electronic configuration could influence d-orbital energies up to a few eV and any attempt to steer the reaction pathway should account for this to ensure that external energies can be used optimally in driving desirable processes. NiTMP structural evolution and the influence of the porphyrin macrocycle conformation on relaxation kinetics can be likewise inferred from this study.

  16. 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

  17. Ultrafast technologies for photonic networks

    NASA Astrophysics Data System (ADS)

    Prucnal, Paul R.; Baby, Varghese; Xu, Lei; Glesk, Ivan

    2004-10-01

    Considerable progress has been in the last decade in the fields of photonic networks and ultra-fast optics. The past few years has seen the widespread use of wavelength division multiplexing (WDM) to provide enormous point-to-point capacity in the backbone and metro area networks. Remarkable progress in electronics, in terms of both costs and performance speeds, has to some extent alleviated the 'electronic bottleneck'. Developments in fiber-optics such as novel fiber types and Raman amplification have opened up additional wavelength regions of operation resulting in great expansion of usable fiber bandwidth. There exist unique opportunities for ultrafast technologies - a subject of much interest in the last decade and reaching a point of maturity - to complement these advances and spark the next generation networks. In our talk, we will mention two networking environments very different from WDM - (1) optical time division multiplexing (OTDM) and (2) optical code division multiple access (OCDMA). We will look at the potential of both these scenarios for different applications, focusing in particular on the latter as an approach that provides maximum flexibility to utilize the immense bandwidth of the optical fiber. We will also describe various ultra-fast technologies that have been developed e.g. .high repetition rate pulsed lasers, ultra-fast optical switches, time delay elements etc. which have a direct relevance to both these types of networks.

  18. 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.

  19. Ultrafast charge separation and recombination dynamics in lead sulfide quantum dot-methylene blue complexes probed by electron and hole intraband transitions.

    PubMed

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

    2011-06-22

    Lead salt quantum dots (QDs) have emerged as attractive materials for solar energy conversion because of their broad spectral response, long exciton lifetime, and efficient multiexciton generation. However, charge separation dynamics from these QDs remain poorly understood. In this study we investigate charge separation and recombination dynamics in PbS-methylene blue (MB(+)) complexes by femtosecond transient absorption spectroscopy. We show that while the 1S electrons and holes in excited PbS QDs lead to overlapping transient absorption features in the visible and near-IR regions, their intraband absorptions in the mid-IR can be monitored independently to directly follow the charge separation and recombination processes. The charge separation and recombination rates in PbS-MB(+) complexes were found to be (2.7 ± 0.2) × 10(12) and (1.1 ± 0.2) × 10(11) s(-1), respectively. The ultrafast charge separation rate suggests the possibility of hot electron injection and multiexciton dissociation from these strongly quantum confined QDs, consistent with recent reports of these phenomena at lead salt QD/TiO(2) interfaces.

  20. 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

  1. EDITORIAL: Ultrafast magnetization processes

    NASA Astrophysics Data System (ADS)

    Hillebrands, Burkard

    2008-09-01

    This Cluster Issue of Journal of Physics D: Applied Physics is devoted to ultrafast magnetization processes. It reports on the scientific yield of the Priority Programme 1133 'Ultrafast Magnetization Processes' which was funded by the Deutsche Forschungsgemeinschaft in the period 2002-2008 in three successive two-year funding periods, supporting research of 17-18 groups in Germany. Now, at the end of this Priority Programme, the members feel that the achievements made in the course of the programme merit communication to the international scientific community in a concerted way. Therefore, each of the projects of the last funding period presents a key result in a published contribution to this Cluster Issue. The purpose of the funding by a Priority Programme is to advance knowledge in an emerging field of research through collaborative networked support over several locations. Priority Programmes are characterized by their enhanced quality of research through the use of new methods and forms of collaboration in emerging fields, by added value through interdisciplinary cooperation, and by networking. The aim of the Priority Programme 1133 'Ultrafast Magnetization Processes' may be well characterized by the call for projects in June 2001 after the programme was approved by the Deutsche Forschungsgemeinschaft: 'The aim of the priority programme is the achievement of a basic understanding of the temporal evolution of fast magnetization processes in magnetically ordered films, multilayers and micro-structured systems. The challenge lies in the advancement of the field of ultrafast magnetization processes into the regime of a few femtoseconds to nanoseconds, a topic not yet well explored. A general aim is to understand the fundamental mechanisms needed for applications in ultrafast magneto-electronic devices. The fundamental topic to be addressed is the response of the magnetization of small structures upon the application of pulsed magnetic fields, laser pulses or

  2. Dynamics of the 3MLCT in Ru(II) terpyridyl complexes probed by ultrafast spectroscopy: evidence of excited-state equilibration and interligand electron transfer.

    PubMed

    Hewitt, Joshua T; Vallett, Paul J; Damrauer, Niels H

    2012-11-29

    Ground- and excited-state properties of [Ru(tpy)(2)](2+), [Ru(tpy)(ttpy)](2+), and [Ru(ttpy)(2)](2+) (where tpy = 2,2':6',2″-terpyridine and ttpy = 4'-(4-methylphenyl)-2,2':6',2″-terpyridine) in room temperature acetonitrile have been investigated using linear absorption, electrochemical, and ultrafast transient pump-probe techniques. Spectroelectrochemistry was used to assign features observed in the transient spectra while single wavelength kinetics collected at a variety of probe wavelengths were used to monitor temporal evolution of the MLCT excited state. From these data, the excited-state lifetime of each complex was recovered and the rate limiting decay step was identified. In the bis-heteroleptic complex [Ru(tpy)(ttpy)](2+), photoexcitation to the (1)MLCT manifold generates both tpy-localized and ttpy-localized excited states. Accordingly, interligand electron transfer (ILET) from tpy-localized to the ttpy-localized (3)MLCT excited states is observable and the time scale has been measured to be 3 ps. For the homoleptic complex [Ru(tpy)(2)](2+), evidence for equilibration of the (3)MLCT excited-state population with the (3)MC has been observed and the time scale is reported at 2 ps.

  3. 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

  4. 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

  5. Combined convective and diffusive simulations: VERB-4D comparison with 17 March 2013 Van Allen Probes observations: VERB-4D

    SciTech Connect

    Shprits, Yuri Y.; Kellerman, Adam C.; Drozdov, Alexander Y.; Spence, Harlan E.; Reeves, Geoffrey D.; Baker, Daniel N.

    2015-11-19

    Our study 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. This 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. Our 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.

  6. Combined convective and diffusive simulations: VERB-4D comparison with 17 March 2013 Van Allen Probes observations: VERB-4D

    DOE PAGES

    Shprits, Yuri Y.; Kellerman, Adam C.; Drozdov, Alexander Y.; ...

    2015-11-19

    Our study 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. This 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,more » 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. Our 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.« less

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. Natural dyes adsorbed on TiO2 nanowire for photovoltaic applications: enhanced light absorption and ultrafast electron injection.

    PubMed

    Meng, Sheng; Ren, Jun; Kaxiras, Efthimios

    2008-10-01

    We investigate the electronic coupling between a TiO2 nanowire and a natural dye sensitizer, using state-of-the-art time-dependent first-principles calculations. The model dye molecule, cyanidin, is deprotonated into the quinonoidal form upon adsorption on the wire surface. This results in its highest occupied molecular orbital (HOMO) being located in the middle of the TiO2 bandgap and its lowest unoccupied molecular orbital (LUMO) being close to the TiO2 conduction band minimum (CBM), leading to greatly enhanced visible light absorption with two prominent peaks at 480 and 650 nm. We find that excited electrons are injected into the TiO2 conduction band within a time scale of 50 fs with negligible electron-hole recombination and energy dissipation, even though the dye LUMO is located 0.1-0.3 eV lower than the CBM of the TiO2 nanowire.

  13. 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

  14. 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

    2016-01-06

    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 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.

  15. Indirect excitation of ultrafast demagnetization

    DOE PAGES

    Vodungbo, Boris; Tudu, Bahrati; Perron, Jonathan; ...

    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

  16. Indirect excitation of ultrafast demagnetization

    SciTech Connect

    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

    2016-01-06

    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 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. As a result, our data thus confirm recent theoretical predictions.

  17. Ultrafast fluorescence quenching dynamics of Atto655 in the presence of N-acetyltyrosine and N-acetyltryptophan in aqueous solution: proton-coupled electron transfer versus electron transfer.

    PubMed

    Zhang, Ying; Yuan, Shuwei; Lu, Rong; Yu, Anchi

    2013-06-20

    We studied the ultrafast fluorescence quenching dynamics of Atto655 in the presence of N-acetyltyrosine (AcTyr) and N-acetyltryptophan (AcTrp) in aqueous solution with femtosecond transient absorption spectroscopy. We found that the charge-transfer rate between Atto655 and AcTyr is about 240 times smaller than that between Atto655 and AcTrp. The pH value and D2O dependences of the excited-state decay kinetics of Atto655 in the presence of AcTyr and AcTrp reveal that the quenching of Atto655 fluorescence by AcTyr in aqueous solution is via a proton-coupled electron-transfer (PCET) process and that the quenching of Atto655 fluorescence by AcTrp in aqueous solution is via an electron-transfer process. With the version of the semiclassical Marcus ET theory, we derived that the electronic coupling constant for the PCET reaction between Atto655 and AcTyr in aqueous solution is 8.3 cm(-1), indicating that the PCET reaction between Atto655 and AcTyr in aqueous solution is nonadiabatic.

  18. 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.

  19. Production and synchronization of electron beams from RF photoinjector/compressor systems for ultra-fast applications

    NASA Astrophysics Data System (ADS)

    Thompson, M. C.; Rosenzweig, J. B.

    2001-05-01

    The RF photoinjector, when coupled with a magnetic pulse compression system, is now a ubiquitous tool for production of sub-picosecond electron beam pulses which are to be used in advanced accelerator and light source experiments. As the time-scale for both pulse lengths and synchronization to external systems approaches the femtosecond level, a clear understanding of the longitudinal dynamics of the electron injector is required. This paper presents an analysis of the longitudinal beam dynamics of electron bunches in the photoinjector/compressor system from birth at the photocathode, through their initial violent acceleration in the RF gun, and subsequent phase space manipulation in the post-acceleration linac and magnetic chicane. The phenomena of phase focusing due to RF forces, and defocusing due to longitudinal space-charge, are discussed, as is the process of magnetic pulse compression. The issues relevant to synchronization of electron pulses with external lasers are examined, using the examples of beat-wave acceleration and Compton light sources, and solutions involving appropriate compressor configurations are proposed. Diagnosis of the relevant physical effects in such schemes is discussed.

  20. Ultrafast photoinduced charge transfer in pi-conjugated electron systems: Effects of structure, delocalization, and energetics (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Schanze, Kirk S.; Jones, Austin; Gish, Melissa; Zeman, Charles J.; Alsam, Amani A.; Aly, Shawkat M.; Papanikolas, John M.; Mohammed, Omar F.

    2016-09-01

    Photoinduced charge transfer is a key step in the mechanism of charge generation in organic solar cells. Charge transfer typically occurs from a photoexcited conjugated polymer donor to an electron acceptor. In an effort to better understand the primary events in solar cells, we have investigated photoinduced charge transfer in model donor-acceptor systems consisting of pi-conjugated oligomer donors that are covalently linked to diimide electron acceptors. These studies utilized oligo(thiophene), oligo(phenylene ethynylene) and oligo(fluorene) pi-conjugated systems with lengths varying from 4 to 12 repeat units linked to naphthalene diimide electron acceptors. Excitation with 100 femtosecond pulses at wavelengths correspoinding to the conjugated oligomer absorption band(s) leads to rapid photoinduced charge transfer to produce a charge separated state, (oligomer+)-(NDI-), which subsequently decays on timescales ranging from 100 ps to 5 ns. The dynamics of the forward and reverse electron transfer reactions depend strongly on the structure and length of the pi-conjugated oligomers, with the fastest rates occurring for oligo(thiophene)s, and considerably slower rates for oligo(phenylene ethynylene)s. The talk will discuss the structure-property relationships and energetic correlations that control the dynamics of charge separation and recombination.

  1. Ultrafast pseudospin dynamics in graphene

    NASA Astrophysics Data System (ADS)

    Trushin, M.; Grupp, A.; Soavi, G.; Budweg, A.; De Fazio, D.; Sassi, U.; Lombardo, A.; Ferrari, A. C.; Belzig, W.; Leitenstorfer, A.; Brida, D.

    2015-10-01

    Interband optical transitions in graphene are subject to pseudospin selection rules. Impulsive excitation with linearly polarized light generates an anisotropic photocarrier occupation in momentum space that evolves at time scales shorter than 100 fs. Here, we investigate the evolution of nonequilibrium charges towards an isotropic distribution by means of fluence-dependent ultrafast spectroscopy and develop an analytical model able to quantify the isotropization process. In contrast to conventional semiconductors, the isotropization is governed by optical phonon emission, rather than electron-electron scattering, which nevertheless contributes in shaping the anisotropic photocarrier occupation within the first few femtoseconds.

  2. On the participation of photoinduced N-H bond fission in aqueous adenine at 266 and 220 nm: a combined ultrafast transient electronic and vibrational absorption spectroscopy study.

    PubMed

    Roberts, Gareth M; Marroux, Hugo J B; Grubb, Michael P; Ashfold, Michael N R; Orr-Ewing, Andrew J

    2014-11-26

    A combination of ultrafast transient electronic absorption spectroscopy (TEAS) and transient vibrational absorption spectroscopy (TVAS) is used to investigate whether photoinduced N–H bond fission, mediated by a dissociative 1πσ(*) state, is active in aqueous adenine (Ade) at 266 and 220 nm. In order to isolate UV/visible and IR spectral signatures of the adeninyl radical (Ade[-H]), formed as a result of N–H bond fission, TEAS and TVAS are performed on Ade in D2O under basic conditions (pD = 12.5), which forms Ade[-H](-) anions via deprotonation at the N7 or N9 sites of Ade's 7H and 9H tautomers. At 220 nm we observe one-photon detachment of an electron from Ade[-H](-), which generates solvated electrons (eaq(-)) together with Ade[-H] radicals, with clear signatures in both TEAS and TVAS. Additional wavelength dependent TEAS measurements between 240–260 nm identify a threshold of 4.9 ± 0.1 eV (∼250 nm) for this photodetachment process in D2O. Analogous TEAS experiments on aqueous Ade at pD = 7.4 generate a similar photoproduct signal together with eaq(-) after excitation at 266 and 220 nm. These eaq(-) are born from ionization of Ade, together with Ade(+) cations, which are indistinguishable from Ade[-H] radicals in TEAS. Ade(+) and Ade[-H] are found to have different signatures in TVAS and we verify that the pD = 7.4 photoproduct signal observed in TEAS following 220 nm excitation is solely due to Ade(+) cations. Based on these observations, we conclude that: (i) N–H bond fission in aqueous Ade is inactive at wavelengths ≥220 nm; and (ii) if such a channel exists in aqueous solution, its threshold is strongly blue-shifted relative to the onset of the same process in gas phase 9H-Ade (≤233 nm). In addition, we extract excited state lifetimes and vibrational cooling dynamics for 9H-Ade and Ade[-H](-). In both cases, excited state lifetimes of <500 fs are identified, while vibrational cooling occurs within a time frame of 4–5 ps. In contrast, 7H

  3. Ultrafast Relaxation Dynamics of Photoexcited Heme Model Compounds: Observation of Multiple Electronic Spin States and Vibrational Cooling.

    PubMed

    Govind, Chinju; Karunakaran, Venugopal

    2017-04-04

    Hemin is a unique model compound of heme proteins carrying out variable biological functions. Here, the excited state relaxation dynamics of heme model compounds in the ferric form are systematically investigated by changing the axial ligand (Cl/Br), the peripheral substituent (vinyl/ethyl-meso), and the solvent (methanol/DMSO) using femtosecond pump-probe spectroscopy upon excitation at 380 nm. The relaxation time constants of these model compounds are obtained by global analysis. Excited state deactivation pathway of the model compounds comprising the decay of the porphyrin excited state (S*) to ligand to metal charge transfer state (LMCT, τ1), back electron transfer from metal to ligand (MLCT, τ2), and relaxation to the ground state through different electronic spin states of iron (τ3 and τ4) are proposed along with the vibrational cooling processes. This is based on the excited state absorption spectral evolution, similarities between the transient absorption spectra of the ferric form and steady state absorption spectra of the low-spin ferrous form, and the data analysis. The observation of an increase of all the relaxation time constants in DMSO compared to the methanol reflects the stabilization of intermediate states involved in the electronic relaxation. The transient absorption spectra of met-myoglobin are also measured for comparison. Thus, the transient absorption spectra of these model compounds reveal the involvement of multiple iron spin states in the electronic relaxation dynamics, which could be an alternative pathway to the ground state beside the vibrational cooling processes and associated with the inherent features of the heme b type.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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).

  9. Ultrafast photodriven intramolecular electron transfer from an iridium-based water-oxidation catalyst to perylene diimide derivatives

    PubMed Central

    Vagnini, Michael T.; Smeigh, Amanda L.; Blakemore, James D.; Eaton, Samuel W.; Schley, Nathan D.; D’Souza, Francis; Crabtree, Robert H.; Brudvig, Gary W.; Co, Dick T.; Wasielewski, Michael R.

    2012-01-01

    Photodriving the activity of water-oxidation catalysts is a critical step toward generating fuel from sunlight. The design of a system with optimal energetics and kinetics requires a mechanistic understanding of the single-electron transfer events in catalyst activation. To this end, we report here the synthesis and photophysical characterization of two covalently bound chromophore-catalyst electron transfer dyads, in which the dyes are derivatives of the strong photooxidant perylene-3,4:9,10-bis(dicarboximide) (PDI) and the molecular catalyst is the Cp∗Ir(ppy)Cl metal complex, where ppy = 2-phenylpyridine. Photoexcitation of the PDI in each dyad results in reduction of the chromophore to PDI•- in less than 10 ps, a process that outcompetes any generation of 3∗PDI by spin-orbit-induced intersystem crossing. Biexponential charge recombination largely to the PDI-Ir(III) ground state is suggestive of multiple populations of the PDI•--Ir(IV) ion-pair, whose relative abundance varies with solvent polarity. Electrochemical studies of the dyads show strong irreversible oxidation current similar to that seen for model catalysts, indicating that the catalytic integrity of the metal complex is maintained upon attachment to the high molecular weight photosensitizer. PMID:22586073

  10. 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).

  11. Ultrafast vibrational spectroscopy of water and aqueous N-methylacetamide: Comparison of different electronic structure/molecular dynamics approaches.

    PubMed

    Schmidt, J R; Corcelli, S A; Skinner, J L

    2004-11-08

    Kwac and Cho [J. Chem. Phys. 119, 2247 (2003)] have recently developed a combined electronic structure/molecular dynamics approach to vibrational spectroscopy in liquids. The method involves fitting ab initio vibrational frequencies for a solute in a cluster of solvent molecules to a linear combination of the electrostatic potentials on the solute atoms due to the charges on the solvent molecules. These authors applied their method to the N-methylacetamide-D/D(2)O system. We (S. A. Corcelli, C. P. Lawrence, and J. L. Skinner, [J. Chem. Phys. 120, 8107 (2004)]) have recently explored a closely related method, where instead of the electrostatic potential, the solute vibrational frequencies are fit to the components of the electric fields on the solute atoms due to the solvent molecules. We applied our method to the HOD/D(2)O and HOD/H(2)O systems. In order to make a direct comparison of these two approaches, in this paper we apply their method to the water system, and our method to the N-methylacetamide system. For the water system we find that the electric field method is superior to the potential approach, as judged by comparison with experiments for the absorption line shape. For the N-methylacetamide system the two methods are comparable.

  12. 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.

  13. Optimized PET imaging for 4D treatment planning in radiotherapy: the virtual 4D PET strategy.

    PubMed

    Gianoli, Chiara; Riboldi, Marco; Fontana, Giulia; Giri, Maria G; Grigolato, Daniela; Ferdeghini, Marco; Cavedon, Carlo; Baroni, Guido

    2015-02-01

    The purpose of the study is to evaluate the performance of a novel strategy, referred to as "virtual 4D PET", aiming at the optimization of hybrid 4D CT-PET scan for radiotherapy treatment planning. The virtual 4D PET strategy applies 4D CT motion modeling to avoid time-resolved PET image acquisition. This leads to a reduction of radioactive tracer administered to the patient and to a total acquisition time comparable to free-breathing PET studies. The proposed method exploits a motion model derived from 4D CT, which is applied to the free-breathing PET to recover respiratory motion and motion blur. The free-breathing PET is warped according to the motion model, in order to generate the virtual 4D PET. The virtual 4D PET strategy was tested on images obtained from a 4D computational anthropomorphic phantom. The performance was compared to conventional motion compensated 4D PET. Tests were also carried out on clinical 4D CT-PET scans coming from seven lung and liver cancer patients. The virtual 4D PET strategy was able to recover lesion motion, with comparable performance with respect to the motion compensated 4D PET. The compensation of the activity blurring due to motion was successfully achieved in terms of spill out removal. Specific limitations were highlighted in terms of partial volume compensation. Results on clinical 4D CT-PET scans confirmed the efficacy in 4D PET count statistics optimization, as equal to the free-breathing PET, and recovery of lesion motion. Compared to conventional motion compensation strategies that explicitly require 4D PET imaging, the virtual 4D PET strategy reduces clinical workload and computational costs, resulting in significant advantages for radiotherapy treatment planning.

  14. 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!

  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. Proton-Coupled Electron-Transfer Processes in Ultrafast Time Domain: Evidence for Effects of Hydrogen-Bond Stabilization on Photoinduced Electron Transfer.

    PubMed

    Dey, Ananta; Dana, Jayanta; Aute, Sunil; Maity, Partha; Das, Amitava; Ghosh, Hirendra N

    2017-03-08

    The proton-coupled electron-transfer (PCET) reaction is investigated for a newly synthesized imidazole-anthraquinone biomimetic model with a photoactive Ru(II) -polypyridyl moiety that is covalently coupled to the imidazole fragment. Intramolecular H-bonding interactions between imidazole and anthraquinone moieties favor the PCET process; this can be correlated to an appreciable positive shift in the one-electron reduction potential of the coordinated anthraquinone moiety functionalized with the imidazole fragment. This can also be attributed to the low luminescence quantum yield of the Ru(II) -polypyridyl complex used. The dynamics of the intramolecular electron-transfer (ET) and PCET processes are studied by using femtosecond transient absorption spectroscopy. The steady-state spectroscopic studies and the results of the time-resolved absorption studies confirm that H-bonded water molecules play a major role in both ET and PCET dynamics as a proton relay in the excited state. The electron-transfer process is followed by a change in the H-bonding equilibrium between AQ and imidazole in acetonitrile solvent, and protonation of AQ(.-) by water leads to PCET in the presence of water. A slower forward and backward electron-transfer rate is observed in the presence of D2 O compared with that in H2 O. These results provide further experimental support for a detailed understanding of the PCET process.

  17. 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

  18. Ultrafast laser IR countermeasures

    NASA Astrophysics Data System (ADS)

    Rafailov, Michael K.

    2009-05-01

    Directional Infrared Countermeasures (DIRCM) is an effective technique to defeat heat-seeking missiles. The major problem of existing DIRCM is that it may work like a beacon for threats that are not susceptible to the jamming code implemented: attracting a missile instead of re-directing it away from the aircraft. Ultra-fast laser pulse technology is discussed as an alternative to a conventional laser DIRCM. An ultra-fast laser is capable of providing a different type of countermeasure which is compatible with existing laser based DIRCM pointing systems as it requires much less peak power than damage inducing systems. A foundation of ultra-fast technology is its unique ability to alter the intrinsic characteristics of the semiconductor. In this paper, we will only consider the effects of a mild lattice disturbance caused by relatively low energy ultra-fast (femto-second) and, to some extent, fast (pico-second) laser pulses.

  19. GL4D: a GPU-based architecture for interactive 4D visualization.

    PubMed

    Chu, Alan; Fu, Chi-Wing; Hanson, Andrew J; Heng, Pheng-Ann

    2009-01-01

    This paper describes GL4D, an interactive system for visualizing 2-manifolds and 3-manifolds embedded in four Euclidean dimensions and illuminated by 4D light sources. It is a tetrahedron-based rendering pipeline that projects geometry into volume images, an exact parallel to the conventional triangle-based rendering pipeline for 3D graphics. Novel features include GPU-based algorithms for real-time 4D occlusion handling and transparency compositing; we thus enable a previously impossible level of quality and interactivity for exploring lit 4D objects. The 4D tetrahedrons are stored in GPU memory as vertex buffer objects, and the vertex shader is used to perform per-vertex 4D modelview transformations and 4D-to-3D projection. The geometry shader extension is utilized to slice the projected tetrahedrons and rasterize the slices into individual 2D layers of voxel fragments. Finally, the fragment shader performs per-voxel operations such as lighting and alpha blending with previously computed layers. We account for 4D voxel occlusion along the 4D-to-3D projection ray by supporting a multi-pass back-to-front fragment composition along the projection ray; to accomplish this, we exploit a new adaptation of the dual depth peeling technique to produce correct volume image data and to simultaneously render the resulting volume data using 3D transfer functions into the final 2D image. Previous CPU implementations of the rendering of 4D-embedded 3-manifolds could not perform either the 4D depth-buffered projection or manipulation of the volume-rendered image in real-time; in particular, the dual depth peeling algorithm is a novel GPU-based solution to the real-time 4D depth-buffering problem. GL4D is implemented as an integrated OpenGL-style API library, so that the underlying shader operations are as transparent as possible to the user.

  20. 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.

  1. Ultrafast science using Laser Wakefield Accelerators

    NASA Astrophysics Data System (ADS)

    Thomas, Alec G. R.

    2016-10-01

    Recent progress in laser wakefield acceleration has led to the emergence of a new generation of electron and X-ray sources that may have considerable benefits for ultrafast science. Laser wakefield acceleration provides radiation pulses that have femtosecond duration and intrinsic synchronisation with the laser source, allowing for pump-probe measurements with unprecedented temporal resolution. These pulses can be used to study ultrafast dynamical phenomena in plasma and dense material, such as transient magnetic fields, rapidly evolving plasma dynamics and crystal lattice oscillations. In this talk, I will review recent experiments in laser wakefield acceleration and energetic photon generation using the laser systems HERCULES and Lambda-Cubed at the University of Michigan and their use for capturing the dynamics of laser-pumped samples. Studies of the electron beam hosing instability and the generation of annular phase space distributions increase X-ray flux while maintaining its femtosecond duration. Single-shot, spectrally resolved absorption measurements in laser pumped foils can be made on ultrafast timescales using this broadband photon source. Ultrafast electron radiography is able to temporally resolve relativistically expanding magnetic fields in high-intensity laser-solid interactions and the evolution of electric fields in low density plasma. Time-resolved electron diffraction captures structural dynamics in crystalline silicon. I will also discuss the technological needs for and potential impact of such revolutionary compact radiation sources for ultrafast science in the future. US Air Force Office of Scientific Research under Award Number FA9550-12-1-0310, the US National Science Foundation Grants No. 1054164, 0935197, 1535628 and 0810979, US Department of Energy Grant No. DE-NA0002372 and Army Research Office Grant No. W911NF1.

  2. 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.

  3. 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.

  4. Ultra-fast intensified frame images from an electron cyclotron resonance hydrogen plasma at 2.45 GHz: some space distributions of visible and monochromatic emissions.

    PubMed

    Cortázar, O D; Megía-Macías, A; Vizcaíno-de-Julián, A; Tarvainen, O; Komppula, J; Koivisto, H

    2014-02-01

    First results from an ultra-fast frame image acquisition diagnostic coupled to a 2.45 GHz microwave hydrogen discharge are presented. The plasma reactor has been modified to include a transparent doubled shielded quartz window allowing to viewing the full plasma volume. Pictures describing the breakdown process at 1 μs exposure time have been obtained for integrated visible light signal, Balmer-alpha, Balmer-beta lines, and Fulcher-band. Several different plasma emission distributions are reported. The distribution depends on the magnetic field configuration, incident microwave power, and neutral gas pressure.

  5. 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.

  6. 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.

  7. 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.

  8. Respiratory gating and 4-D tomotherapy

    SciTech Connect

    Zhang Tiezhi

    2004-12-01

    Helical tomotherapy is a new intensity-modulated radiotherapy (IMRT) delivery process developed at the University of Wisconsin and TomoTherapy Inc. Tomotherapy may be of advantage in lung cancer treatment due to its rotational delivery mode. As with conventional IMRT delivery, however, intrafraction respiratory motion during a tomotherapy treatment causes unnecessary radiation to the healthy tissue. Possible solutions to these problems associated with intrafraction motion have been studied in this thesis. A spirometer is useful for monitoring breathing because of its direct correlation with lung volume changes. However, its inherent drift prevents its application in long-term breathing monitoring. With calibration and stabilization algorithms, a spirometer is able to provide accurate, long-term lung volume change measurements. Such a spirometer system is most suited for deep inspiration breath-hold (DIBH) treatments. An improved laser-spirometer combined system has also been developed for target tracking in 4-D treatment. Spirometer signals are used to calibrate the displacement measurements into lung volume changes, thereby eliminating scaling errors from daily setup variations. The laser displacement signals may also be used to correct spirometer drifts during operation. A new 4-D treatment technique has been developed to account for intrafraction motion in treatment planning. The patient's breathing and the beam delivery are synchronized, and the target motion/deformation is incorporated into treatment plan optimization. Results show that this new 4D treatment technique significantly reduces motion effects and provides improved patient tolerance.

  9. 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

  10. 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.

  11. 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.

  12. 4d Spectra from BPS Quiver Dualities

    NASA Astrophysics Data System (ADS)

    Espahbodi, Sam

    We attack the question of BPS occupancy in a wide class of 4d N = 2 quantum field theories. We first review the Seiberg-Witten approach to finding the low energy Wilsonian effective action actions of such theories. In particular, we analyze the case of Gaiotto theories, which provide a large number of non-trivial examples in a unified framework. We then turn to understanding the massive BPS spectrum of such theories, and in particular their relation to BPS quivers. We present a purely 4d characterization of BPS quivers, and explain how a quiver's representation theory encodes the solution to the BPS occupancy problem. Next, we derive a so called mutation method, based on exploiting quiver dualities, to solve the quiver's representation theory. This method makes previously intractable calculations nearly trivial in many examples. As a particular highlight, we apply our methods to understand strongly coupled chambers in ADE SYM gauge theories with matter. Following this, we turn to the general story of quivers for theories of the Gaiotto class. We present a geometric approach to attaining quivers for the rank 2 theories, leading to a very elegant solution which includes a specification of quiver superpotentials. Finally, we solve these theories by an unrelated method based on gauging flavor symmetries in their various dual weakly coupled Lagrangian descriptions. After seeing that this method agrees in the rank 2 case, we will apply our new approach to the case of rank n.

  13. Imaging the Temporal Evolution of Molecular Orbitals during Ultrafast Dissociation

    NASA Astrophysics Data System (ADS)

    Sann, H.; Havermeier, T.; Müller, C.; Kim, H.-K.; Trinter, F.; Waitz, M.; Voigtsberger, J.; Sturm, F.; Bauer, T.; Wallauer, R.; Schneider, D.; Weller, M.; Goihl, C.; Tross, J.; Cole, K.; Wu, J.; Schöffler, M. S.; Schmidt-Böcking, H.; Jahnke, T.; Simon, M.; Dörner, R.

    2016-12-01

    We investigate the temporal evolution of molecular frame angular distributions of Auger electrons emitted during ultrafast dissociation of HCl following a resonant single-photon excitation. The electron emission pattern changes its shape from that of a molecular σ orbital to that of an atomic p state as the system evolves from a molecule into two separated atoms.

  14. 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.

  15. Controlled Source 4D Seismic Imaging

    NASA Astrophysics Data System (ADS)

    Luo, Y.; Morency, C.; Tromp, J.

    2009-12-01

    Earth's material properties may change after significant tectonic events, e.g., volcanic eruptions, earthquake ruptures, landslides, and hydrocarbon migration. While many studies focus on how to interpret observations in terms of changes in wavespeeds and attenuation, the oil industry is more interested in how we can identify and locate such temporal changes using seismic waves generated by controlled sources. 4D seismic analysis is indeed an important tool to monitor fluid movement in hydrocarbon reservoirs during production, improving fields management. Classic 4D seismic imaging involves comparing images obtained from two subsequent seismic surveys. Differences between the two images tell us where temporal changes occurred. However, when the temporal changes are small, it may be quite hard to reliably identify and characterize the differences between the two images. We propose to back-project residual seismograms between two subsequent surveys using adjoint methods, which results in images highlighting temporal changes. We use the SEG/EAGE salt dome model to illustrate our approach. In two subsequent surveys, the wavespeeds and density within a target region are changed, mimicking possible fluid migration. Due to changes in material properties induced by fluid migration, seismograms recorded in the two surveys differ. By back propagating these residuals, the adjoint images identify the location of the affected region. An important issue involves the nature of model. For instance, are we characterizing only changes in wavespeed, or do we also consider density and attenuation? How many model parameters characterize the model, e.g., is our model isotropic or anisotropic? Is acoustic wave propagation accurate enough or do we need to consider elastic or poroelastic effects? We will investigate how imaging strategies based upon acoustic, elastic and poroelastic simulations affect our imaging capabilities.

  16. Ultrafast fibre lasers

    NASA Astrophysics Data System (ADS)

    Fermann, Martin E.; Hartl, Ingmar

    2013-11-01

    Ultrafast fibre lasers are fundamental building blocks of many photonic systems used in industrial and medical applications as well as for scientific research. Here, we review the essential components and operation regimes of ultrafast fibre lasers and discuss how they are instrumental in a variety of applications. In regards to laser technology, we discuss the present state of the art of large-mode-area fibres and their utilization in high-power, chirped-pulse amplification systems. In terms of commercial applications, we introduce industrial micromachining and medical imaging, and describe emerging applications in the mid-infrared and extreme-ultraviolet spectral regions, as facilitated by frequency shifting induced by fibre frequency combs.

  17. 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.

  18. 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.

  19. 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.

  20. Ultrafast photophysics of transition metal complexes.

    PubMed

    Chergui, Majed

    2015-03-17

    The properties of transition metal complexes are interesting not only for their potential applications in solar energy conversion, OLEDs, molecular electronics, biology, photochemistry, etc. but also for their fascinating photophysical properties that call for a rethinking of fundamental concepts. With the advent of ultrafast spectroscopy over 25 years ago and, more particularly, with improvements in the past 10-15 years, a new area of study was opened that has led to insightful observations of the intramolecular relaxation processes such as internal conversion (IC), intersystem crossing (ISC), and intramolecular vibrational redistribution (IVR). Indeed, ultrafast optical spectroscopic tools, such as fluorescence up-conversion, show that in many cases, intramolecular relaxation processes can be extremely fast and even shorter than time scales of vibrations. In addition, more and more examples are appearing showing that ultrafast ISC rates do not scale with the magnitude of the metal spin-orbit coupling constant, that is, that there is no heavy-atom effect on ultrafast time scales. It appears that the structural dynamics of the system and the density of states play a crucial role therein. While optical spectroscopy delivers an insightful picture of electronic relaxation processes involving valence orbitals, the photophysics of metal complexes involves excitations that may be centered on the metal (called metal-centered or MC) or the ligand (called ligand-centered or LC) or involve a transition from one to the other or vice versa (called MLCT or LMCT). These excitations call for an element-specific probe of the photophysics, which is achieved by X-ray absorption spectroscopy. In this case, transitions from core orbitals to valence orbitals or higher allow probing the electronic structure changes induced by the optical excitation of the valence orbitals, while also delivering information about the geometrical rearrangement of the neighbor atoms around the atom of

  1. Resolving Ultrafast Heating of Dense Cryogenic Hydrogen

    NASA Astrophysics Data System (ADS)

    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.

    2014-03-01

    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.

  2. 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…

  3. An ultrafast look at Au nanoclusters.

    PubMed

    Yau, Sung Hei; Varnavski, Oleg; Goodson, Theodore

    2013-07-16

    In the past 20 years, researchers studying nanomaterials have uncovered many new and interesting properties not found in bulk materials. Extensive research has focused on metal nanoparticles (>3 nm) because of their potential applications, such as in molecular electronics, image markers, and catalysts. In particular, the discovery of metal nanoclusters (<3 nm) has greatly expanded the horizon of nanomaterial research. These nanosystems exhibit molecular-like characteristics as their size approaches the Fermi-wavelength of an electron. The relationships between size and physical properties for nanomaterials are intriguing, because for metal nanosystems in this size regime both size and shape determine electronic properties. Remarkably, changes in the optical properties of nanomaterials have provided tremendous insight into the electronic structure of nanoclusters. The success of synthesizing monolayer protected clusters (MPCs) in the condensed phase has allowed scientists to probe the metal core directly. Au MPCs have become the "gold" standard in nanocluster science, thanks to the rigorous structural characterization already accomplished. The use of ultrafast laser spectroscopy on MPCs in solution provides the benefit of directly studying the chemical dynamics of metal nanoclusters (core), and their nonlinear optical properties. In this Account, we investigate the optical properties of MPCs in the visible region using ultrafast spectroscopy. Based on fluorescence up-conversion spectroscopy, we propose an emission mechanism for these nanoclusters. These clusters behave differently from nanoparticles in terms of emission lifetimes as well as two-photon cross sections. Through further investigation of the transient (excited state) absorption, we have found many unique phenomena of nanoclusters, such as quantum confinement effects and vibrational breathing modes. In summary, based on the differences in the optical properties, the distinction between nanoclusters and

  4. Spatiotemporal directional analysis of 4D echocardiography

    NASA Astrophysics Data System (ADS)

    Angelini-Casadevall, Elsa D.; Laine, Andrew F.; Takuma, Shin; Homma, Shunichi

    2000-12-01

    Speckle noise corrupts ultrasonic data by introducing sharp changes in an echocardiographic image intensity profile, while attenuation alters the intensity of equally significant cardiac structures. These properties introduce inhomogeneity in the spatial domain and suggests that measures based on phase information rather than intensity are more appropriate for denoising and cardiac border detection. The present analysis method relies on the expansion of temporal ultrasonic volume data on complex exponential wavelet-like basis functions called Brushlets. These basis functions decompose a signal into distinct patterns of oriented textures. Projected coefficients are associated with distinct 'brush strokes' of a particular size and orientation. 4D overcomplete brushlet analysis is applied to temporal echocardiographic values. We show that adding the time dimension in the analysis dramatically improves the quality and robustness of the method without adding complexity in the design of a segmentation tool. We have investigated mathematical and empirical methods for identifying the most 'efficient' brush stroke sizes and orientations for decomposition and reconstruction on both phantom and clinical data. In order to determine the 'best tiling' or equivalently, the 'best brushlet basis', we use an entorpy-based information cost metric function. Quantitative validation and clinical applications of this new spatio-temporal analysis tool are reported for balloon phantoms and clinical data sets.

  5. 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.

  6. LUX - A recirculating linac-based ultrafast X-ray source

    SciTech Connect

    Corlett, J.N.; Barletta, W.A.; DeSantis, S.; Doolittle, L.; Fawley, W.M.; Green, M.A.; Heimann, P.; Leone, S.R.; Lidia, S.; Li, D.; Parmigiani, F.; Ratti, A.; Robinson, K.; Schoenlein, R.; Staples, J.; Wan, W.; Wells, R.; Wilcox, R.; Wolski, A.; Zholents, A.

    2003-08-01

    We describe the design of a proposed source of ultra-fast synchrotron radiation x-ray pulses based on a recirculating superconducting linac, with an integrated array of ultrafast laser systems. The source produces x-ray pulses with duration of 10-50 fs at a 10 kHz repetition rate, with tunability from EUV to hard x-ray regimes, and optimized for the study of ultra-fast dynamics. A high-brightness rf photocathode provides electron bunches. An injector linac accelerates the beam to the 100 MeV range, and is followed by four passes through a 700 MeV recirculating linac. Ultrafast hard x-ray pulses are obtained by a combination of electron bunch manipulation, transverse temporal correlation of the electrons, and x-ray pulse compression. EUV and soft x-ray pulses as short as 10 fs are generated in a harmonic-cascade free electron laser scheme.

  7. 17 CFR 260.4d-8 - Content.

    Code of Federal Regulations, 2010 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)...

  8. 17 CFR 260.4d-8 - Content.

    Code of Federal Regulations, 2010 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)...

  9. 17 CFR 260.4d-8 - Content.

    Code of Federal Regulations, 2010 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)...

  10. 17 CFR 260.4d-8 - Content.

    Code of Federal Regulations, 2010 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)...

  11. Stoner versus Heisenberg: Ultrafast exchange reduction and magnon generation during laser-induced demagnetization

    NASA Astrophysics Data System (ADS)

    Turgut, Emrah; Zusin, Dmitriy; Legut, Dominik; Carva, Karel; Knut, Ronny; Shaw, Justin M.; Chen, Cong; Tao, Zhensheng; Nembach, Hans T.; Silva, Thomas J.; Mathias, Stefan; Aeschlimann, Martin; Oppeneer, Peter M.; Kapteyn, Henry C.; Murnane, Margaret M.; Grychtol, Patrik

    2016-12-01

    Understanding how the electronic band structure of a ferromagnetic material is modified during laser-induced demagnetization on femtosecond time scales has been a long-standing question in condensed matter physics. Here, we use ultrafast high harmonics to measure time-, energy-, and angle-resolved M -edge magnetic asymmetry spectra for Co films after optical pumping to induce ultrafast demagnetization. This provides a complete data set that we can compare with advanced ab initio magneto-optical calculations. Our analysis identifies that the dominant mechanisms contributing to ultrafast demagnetization on time scales up to several picoseconds are a transient reduction in the exchange splitting and the excitation of ultrafast magnons. Surprisingly, we find that the magnon contribution to ultrafast demagnetization is already strong on subpicosecond time scales, while the reduction in exchange splitting persists to several picoseconds.

  12. Exploring Ultrafast Structural Dynamics for Energetic Enhancement or Disruption

    DTIC Science & Technology

    2016-03-01

    indirect laser heating and on-resonant optical pumping, to excite/perturb the energetic material to observe changes in the electronic and molecular...time scales necessary to monitor early times of energetic events. 15. SUBJECT TERMS ultrafast, energetic, femtosecond, TATB, flash heating , transient...absorption spectra of RDX after flash heating (left) Raman spectra of RDX after flash heating (right) .............................................7

  13. Suppression of ultrafast supercontinuum generation in a salivary protein.

    PubMed

    Santhosh, Chidangil; Dharmadhikari, Aditya K; Alti, Kamlesh; Dharmadhikari, Jayashree A; Mathur, Deepak

    2007-01-01

    The first studies of the propagation of ultrafast (<45 fs) pulses of intense infrared light through protein media reveal that supercontinuum (white light) generation is severely suppressed in the presence of the protein alpha-amylase, a potential stress marker in human saliva. The continuum suppression capacity is attributed to the electron scavenging property of the protein.

  14. X-ray emissions in 3d, 4d, and 5d ranges for uranium ions

    SciTech Connect

    Bonnelle, C.; Jonnard, P.; Barre, C.; Giorgi, G.; Bruneau, J.

    1997-05-01

    Radiative decay of nd{sup {minus}1}5f{sup m+1} excited states in UO{sub 2} induced by electron collisions is studied theoretically and experimentally. Energies, transition probabilities, and photoexcitation cross sections for the relevant configurations of U{sup 4+} are calculated by using the multiconfiguration Dirac-Fock method. Experimental observations are made in the 4d range. Direct recombination of the excited 5f electron to the 4d hole and 4d-6p emission in the presence of the spectator excited 5f electron are observed. From the theoretical results, the spectra are simulated and compared to the observed spectra in the three nd regions. The agreement is correct and describes the evolution of the coupling scheme in the nd{sup {minus}1}5f{sup 3} excited states from n=3 to n=5. {copyright} {ital 1997} {ital The American Physical Society}

  15. Fourier information optics for the ultrafast time domain.

    PubMed

    Weiner, Andrew M

    2008-02-01

    Ultrafast photonic signal processing based on Fourier optics principles offers exciting possibilities to go beyond the processing speeds of electronics technologies for applications in high-speed fiber communications and ultrawideband wireless. I review our recent work on processing of ultrafast optical signals via conversion between time, space, and optical frequency (Fourier) domains. Specific topics include optical arbitrary waveform generation, application of optical pulse shaping technologies for wavelength-parallel compensation of fiber transmission impairments and for experimental studies of optical code-division multiple-access communications, and application of photonic methods for precompensation of dispersion effects in wireless transmission of radio-frequency signals over ultrawideband antenna links.

  16. 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.

  17. Comprehensive Studies of Ultrafast Laser Excited Warm Dense Gold

    NASA Astrophysics Data System (ADS)

    Chen, Zhijiang; Mo, Mianzhen; Russell, Brandon; Tsui, Ying; Wang, Xijie; Ng, Andrew; Glenzer, Siegfried

    2016-10-01

    Isochoric excitation of solids by ultrafast laser pulses is an important approach to generate warm dense matter in laboratory. Electrical conductivity, structural dynamics and lattice stabilities are the most important properties in ultrafast laser excited warm dense matter. To investigate these properties, we have developed multiple advanced capabilities at SLAC recently, including the measurement of semi-DC electrical conductivity with ultrafast THz radiation, the study of solid and liquid structural dynamics by ultrafast electron diffraction (UED), and the investigation of lattice stability using frequency domain interferometry (FDI) on both front and rear surfaces. Due to the non-reversible nature in exciting solid to warm dense matter, all these diagnostics are implemented with single-shot approaches, reducing the uncertainties due to shot-to-shot fluctuations. In this talk, we will introduce these novel capabilities and present some highlighted studies in warm dense gold, which was uniformly excited by ultrafast laser pulses at 400nm. We appreciate the supports from DOE FES under FWP #100182.

  18. Ultrafast Multiphoton Thermionic Photoemission from Graphite

    NASA Astrophysics Data System (ADS)

    Tan, Shijing; Argondizzo, Adam; Wang, Cong; Cui, Xuefeng; Petek, Hrvoje

    2017-01-01

    Electronic heating of cold crystal lattices in nonlinear multiphoton excitation can transiently alter their physical and chemical properties. In metals where free electron densities are high and the relative fraction of photoexcited hot electrons is low, the effects are small, but in semimetals, where the free electron densities are low and the photoexcited densities can overwhelm them, the intense femtosecond laser excitation can induce profound changes. In semimetal graphite and its derivatives, strong optical absorption, weak screening of the Coulomb potential, and high cohesive energy enable extreme hot electron generation and thermalization to be realized under femtosecond laser excitation. We investigate the nonlinear interactions within a hot electron gas in graphite through multiphoton-induced thermionic emission. Unlike the conventional photoelectric effect, within about 25 fs, the memory of the excitation process, where resonant dipole transitions absorb up to eight quanta of light, is erased to produce statistical Boltzmann electron distributions with temperatures exceeding 5000 K; this ultrafast electronic heating causes thermionic emission to occur from the interlayer band of graphite. The nearly instantaneous thermalization of the photoexcited carriers through Coulomb scattering to extreme electronic temperatures characterized by separate electron and hole chemical potentials can enhance hot electron surface femtochemistry, photovoltaic energy conversion, and incandescence, and drive graphite-to-diamond electronic phase transition.

  19. 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.

  20. Ultrafast dynamics in the presence of antiferromagnetic correlations in electron-doped cuprate La2 -xCexCuO4 ±δ

    NASA Astrophysics Data System (ADS)

    Vishik, I. M.; Mahmood, F.; Alpichshev, Z.; Gedik, N.; Higgins, J.; Greene, R. L.

    2017-03-01

    We used femtosecond optical pump-probe spectroscopy to study the photoinduced change in reflectivity of thin films of the electron-doped cuprate La2 -xCexCuO4 (LCCO) with dopings of x =0.08 (underdoped) and x =0.11 (optimally doped). Above Tc, we observe fluence-dependent relaxation rates that begin at a temperature similar to the one where transport measurements first show signatures of antiferromagnetic correlations. Upon suppressing superconductivity with a magnetic field, it is found that the fluence and temperature dependence of relaxation rates are consistent with bimolecular recombination of electrons and holes across a gap (2 ΔAF ) originating from antiferromagnetic correlations which comprise the pseudogap in electron-doped cuprates. This can be used to learn about coupling between electrons and high-energy (ω >2 ΔAF ) excitations in these compounds and set limits on the time scales on which antiferromagnetic correlations are static.

  1. Ultrafast Photophysics of Organic Semiconductor Junctions

    NASA Astrophysics Data System (ADS)

    Burghardt, Irene; Bittner, Eric R.; Tamura, Hiroyuki; Pereverzev, Andrey; Ramon, John Glenn S.

    This contribution gives an overview of our recent studies of the electronic structure and ultrafast photophysics of semiconductor polymer junctions. We focus on the phonon-assisted exciton dissociation at donor-acceptor heterojunctions, using state-of-the-art electronic structure methods in conjunction with vibronic coupling models and multiconfigurational quantum dynamical techniques. The decay of the photogenerated exciton towards an interfacial charge-separated state is an ultrafast (femtosecond to picosecond scale) process which precedes photocurrent generation. We describe this process using a linear vibronic coupling model parametrized for two to three electronic states and 20-30 phonon modes. Several representative interface configurations are considered, which are shown to differ significantly in their cross-chain interactions but exhibit an efficient exciton dissociation in all cases investigated. The exciton decay depends critically on the presence of intermediate states and on the dynamical interplay between high-frequency (C=C stretch) and lowfrequency (ring-torsional) modes. The resulting molecular-level picture of exciton dissociation could contribute to the design of efficient polymer junctions.

  2. Nonlinear Black Phosphorus for Ultrafast Optical Switching

    NASA Astrophysics Data System (ADS)

    Uddin, Siam; Debnath, Pulak C.; Park, Kichul; Song, Yong-Won

    2017-02-01

    The outstanding electronic and optical properties of black phosphorus (BP) in a two-dimensional (2D) but unique single-layer puckered structure have opened intense research interest ranging from fundamental physics to nanoscale applications covering the electronic and optical domains. The direct and controllable electronic bandgap facilitating wide range of tunable optical response coupled with high anisotropic in-plane properties made BP a promising nonlinear optical material for broadband optical applications. Here, we investigate ultrafast optical switching relying on the optical nonlinearity of BP. Wavelength conversion for modulated signals whose frequency reaches up to 20 GHz is realized by four-wave-mixing (FWM) with BP-deposited D-shaped fiber. In the successful demonstration of the FWM based wavelength conversion, performance parameter has been increased up to ~33% after employing BP in the device. It verifies that BP is able to perform efficient optical switching in the evanescent field interaction regime at very high speed. Our results might suggest that BP-based ultra-fast photonics devices could be potentially developed for broadband applications.

  3. Nonlinear Black Phosphorus for Ultrafast Optical Switching

    PubMed Central

    Uddin, Siam; Debnath, Pulak C.; Park, Kichul; Song, Yong-Won

    2017-01-01

    The outstanding electronic and optical properties of black phosphorus (BP) in a two-dimensional (2D) but unique single-layer puckered structure have opened intense research interest ranging from fundamental physics to nanoscale applications covering the electronic and optical domains. The direct and controllable electronic bandgap facilitating wide range of tunable optical response coupled with high anisotropic in-plane properties made BP a promising nonlinear optical material for broadband optical applications. Here, we investigate ultrafast optical switching relying on the optical nonlinearity of BP. Wavelength conversion for modulated signals whose frequency reaches up to 20 GHz is realized by four-wave-mixing (FWM) with BP-deposited D-shaped fiber. In the successful demonstration of the FWM based wavelength conversion, performance parameter has been increased up to ~33% after employing BP in the device. It verifies that BP is able to perform efficient optical switching in the evanescent field interaction regime at very high speed. Our results might suggest that BP-based ultra-fast photonics devices could be potentially developed for broadband applications. PMID:28240276

  4. 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

  5. Searching for solvent cavities via electron photodetachment: The ultrafast charge-transfer-to-solvent dynamics of sodide in a series of ether solvents

    SciTech Connect

    Larsen, Molly C.; Schwartz, Benjamin J.

    2009-10-21

    It was recently predicted by simulations and confirmed by neutron diffraction experiments that the structure of liquid tetrahydrofuran (THF) contains cavities. The cavities can be quite large and have a net positive electrostatic potential, so they can serve as pre-existing traps for excess electrons created via photodetachment from various solutes. In this paper, we use electron photodetachment via charge-transfer-to-solvent (CTTS) excitation of sodide (Na{sup -}) to probe for the presence of pre-existing cavities in a series of ether solvents: THF, diethyl ether, 1,2-dimethoxyethane (DME), and diglyme (DG). We find that electrons photodetached from sodide appear after a time delay with their equilibrium spectrum in all of these solvents, suggesting that the entire series of ethers contains pre-existing solvent cavities. We then use the variation in electron recombination dynamics with CTTS excitation wavelength to probe the nature of the cavities in the different ethers. We find that the cavities that form the deepest electron traps turn on at about the same energy in all four ether solvents investigated, but that the density of cavities is lower in DG and DME than in THF. We also examine the dynamics of the neutral sodium species that remains following CTTS photodetachment of an electron from sodide. We find that the reaction of the initially created gas-phase-like Na atom to form a (Na{sup +},e{sup -}) tight-contact pair occurs at essentially the same rate in all four ether solvents, indicating that only local solvent motions and not bulk solvent rearrangements are what is responsible for driving the partial ejection of the remaining Na valence electron.

  6. 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.

  7. Ultrafast silicon nanoplasmonic grid-gate transistor

    NASA Astrophysics Data System (ADS)

    Greig, S. R.; Elezzabi, A. Y.

    2015-03-01

    We present the detailed investigation of an ultrafast silicon based nanoplasmonic three terminal device. The device operates on the principle of ponderomotive acceleration of two-photon absorption generated electrons within a nanoplasmonic waveguide structure. Due to high spatial mode confinement, high spatial asymmetry, and high enhancement of the nanoplasmonic electric field, electrons are accelerated to high kinetic energies and are directed towards the copper anode generating an output current. Application of a negative grid voltage modulates an effective energy barrier that restricts the number of electrons reaching the anode, thus reducing the output current. Operating at electric field strengths up to 1×107 V/cm generates a 150 fs output current pulse of 628 mA/μm. Careful consideration of the materials used facilitates monolithic integration with current complementary-metal-oxide-semiconductor nanoelectronics devices.

  8. 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) Each application for an order under section 304(d)...

  9. 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) Each application for an order under section 304(d)...

  10. 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) Each application for an order under section 304(d)...

  11. 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…

  12. 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

  13. 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

  14. Identification of the first steps in charge separation in bacterial photosynthetic reaction centers of Rhodobacter sphaeroides by ultrafast mid-infrared spectroscopy: electron transfer and protein dynamics.

    PubMed

    Pawlowicz, Natalia P; van Grondelle, Rienk; van Stokkum, Ivo H M; Breton, Jacques; Jones, Michael R; Groot, Marie Louise

    2008-08-01

    Time-resolved visible pump/mid-infrared (mid-IR) probe spectroscopy in the region between 1600 and 1800 cm(-1) was used to investigate electron transfer, radical pair relaxation, and protein relaxation at room temperature in the Rhodobacter sphaeroides reaction center (RC). Wild-type RCs both with and without the quinone electron acceptor Q(A), were excited at 600 nm (nonselective excitation), 800 nm (direct excitation of the monomeric bacteriochlorophyll (BChl) cofactors), and 860 nm (direct excitation of the dimer of primary donor (P) BChls (P(L)/P(M))). The region between 1600 and 1800 cm(-1) encompasses absorption changes associated with carbonyl (C=O) stretch vibrational modes of the cofactors and protein. After photoexcitation of the RC the primary electron donor P excited singlet state (P*) decayed on a timescale of 3.7 ps to the state P(+)B(L)(-) (where B(L) is the accessory BChl electron acceptor). This is the first report of the mid-IR absorption spectrum of P(+)B(L)(-); the difference spectrum indicates that the 9-keto C=O stretch of B(L) is located around 1670-1680 cm(-1). After subsequent electron transfer to the bacteriopheophytin H(L) in approximately 1 ps, the state P(+)H(L)(-) was formed. A sequential analysis and simultaneous target analysis of the data showed a relaxation of the P(+)H(L)(-) radical pair on the approximately 20 ps timescale, accompanied by a change in the relative ratio of the P(L)(+) and P(M)(+) bands and by a minor change in the band amplitude at 1640 cm(-1) that may be tentatively ascribed to the response of an amide C=O to the radical pair formation. We conclude that the drop in free energy associated with the relaxation of P(+)H(L)(-) is due to an increased localization of the electron hole on the P(L) half of the dimer and a further consequence is a reduction in the electrical field causing the Stark shift of one or more amide C=O oscillators.

  15. 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.

  16. 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.

  17. An adjustable short-focal length, high-gradient PMQ electron-beam final-focus system for the PLEIADES ultra-fast x-ray Thomson source

    NASA Astrophysics Data System (ADS)

    Lim, Jae-Ku

    In the span of a 100 year since the discovery of first x-rays by Roentgen that won him the first Nobel prize in physics, several types of radiation sources have been developed. Currently, radiations at extremely short wavelengths have only been accessed at synchrotron radiation sources. However, the current 3rd generation synchrotron sources can only produce x-rays of energy up to 60 keV and pulse lengths of several picoseconds long. But needs for shorter wavelength and shorter pulse duration radiations demanded by scientists to understand the nature of matter at atomic/molecular scale initiated the new scientific research for the production of sub-picosecond, hard x-rays. At the Lawrence Livermore National Laboratory, a Thomson x-ray source in the backscattering mode---a head-on collision between a high intensity Ti:Sapphire Chirped Pulse Amplification laser and a relativistic electron beam---called the PLEIADES (Picosecond Laser-Electron Inter-Action for the Dynamical Evaluation of Structures) laboratory has been developed. Early works demonstrated the production of quasi-monochromatic, femto-second long, hard x-rays. Initially reported x-ray flux was in the low range of 105--10 6 photons per shot. During the early stage of PLEIADES experiments, 15 T/m electromagnet final focusing quadrupoles (in a triplet lattice configuration) were employed to focus the beam to a 40-50 mum spot-size. A larger focal spot-size beam has a low-density of electron particles available at the interaction with incident photons, which leads to a low scattering probability. The current dissertation shows that by employing a 560 T/m PMQ (Permanent-Magnet Quadrupole) final focus system, an electron beam as small as 10-20 mum can be achieved. The implementation of this final focus system demonstrated the improvement of the total x-ray flux by two orders of magnitude. The PMQ final focus system also produced small electron beams consistently over 30-100 MeV electron beam energy, which

  18. Resolution limits of ultrafast ultrasound localization microscopy

    NASA Astrophysics Data System (ADS)

    Desailly, Yann; Pierre, Juliette; Couture, Olivier; Tanter, Mickael

    2015-11-01

    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

  19. 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...

  20. 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...

  1. 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.

  2. 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).

  3. Enhanced rate performance of flexible and stretchable linear supercapacitors based on polyaniline@Au@carbon nanotube with ultrafast axial electron transport

    NASA Astrophysics Data System (ADS)

    Xu, Jiang; Ding, Jianning; Zhou, Xiaoshuang; Zhang, Yang; Zhu, Wenjun; Liu, Zunfen; Ge, Shanhai; Yuan, Ningyi; Fang, Shaoli; Baughman, Ray H.

    2017-02-01

    Linear supercapacitors suffer a severe loss of capacity at high rates due to the trade-off of radial ion diffusion and axial electron transport. Optimizing axial conductivity of electrodes is a key to circumvent this trade-off. We report here the synthesis of Au nanograin decorated aligned multiwall carbon nanotube (CNT) sheets, followed by the incorporation of polyaniline (PANI). The embedded Au nanograins results in fast radial ion diffusion and enhance axial electron transport in the linear electrodes. The flexible linear solid supercapacitor fabricated by twisting two PANI@Au@CNT yarns exhibits an outstanding electrochemical performance with a total volumetric capacitance of ∼6 F cm-3 at scan rate up to 10 V s-1. Diameter of the electrode has little effect on volumetric capacitance even at high scan rates because of its high electrical conductivity. Highly stretchable supercapacitors with high rate performance and excellent cycling and stretching stability have been also fabricated using buckled linear electrodes made by wrapping PANI@Au@CNT sheet on elastic rubber fibers. The stretchable linear supercapacitor possesses a stable total volumetric capacitance of up to ∼0.2 F cm-3 at scan rate of 1 V s-1 and at 400% strain, and remarkable capacitance retention of about 95% over 1000 stretch/release cycles.

  4. 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.

  5. 4D Cellular Automaton Track Finder in the CBM Experiment

    NASA Astrophysics Data System (ADS)

    Akishina, Valentina; Kisel, Ivan

    2016-11-01

    The CBM experiment (FAIR/GSI, Darmstadt, Germany) will focus on the measurement of rare probes at interaction rates up to 10MHz with data flow of up to 1 TB/s. It requires a novel read-out and data-acquisition concept with self-triggered electronics and free-streaming data. In this case resolving different collisions is a non-trivial task and event building must be performed in software online. That requires full online event reconstruction and selection not only in space, but also in time, so-called 4D event building and selection. This is a task of the First-Level Event Selection (FLES). The FLES reconstruction and selection package consists of several modules: track finding, track fitting, short-lived particles finding, event building and event selection. The Cellular Automaton (CA) track finder algorithm was adapted towards time-based reconstruction. In this article, we describe in detail the modification done to the algorithm, as well as the performance of the developed time-based CA approach.

  6. 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.

  7. 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

  8. Ultrafast Imaging using Spectral Resonance Modulation.

    PubMed

    Huang, Eric; Ma, Qian; Liu, Zhaowei

    2016-04-28

    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.

  9. 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.

  10. 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.

  11. 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.

  12. Ultrafast gas switching experiments

    NASA Astrophysics Data System (ADS)

    Frost, C. A.; Martin, T. H.; Patterson, P. E.; Rinehart, L. F.; Rohwein, G. J.; Roose, L. D.; Aurand, J. F.; Buttram, M. T.

    1993-06-01

    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 are described. The highly overvolted peaking gaps produce powerful electromagnetic pulses with risetimes less than 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. Pulses with 50 to 100 ps risetimes to peak levels of 75 to 160 kV at pulse repetition frequencies (PRF) to 1 kHz were produced and accurately measured. 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 pressure. This technology was applied to practical systems driving ultrawideband radiating antennas and bounded wave simulators. A thyristor/pulse transformer based system using a highly overvolted cable switch was developed. This pulser driving a Sandia-designed TEM cell, provides an ultra wideband impulse with less than 200 ps risetime to the test object at a PRF greater than 1 kHz at grater tha n 100 kV/m E field.

  13. 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.

  14. Ultrafast fiber lasers: practical applications

    NASA Astrophysics Data System (ADS)

    Pastirk, Igor; Sell, Alexander; Herda, Robert; Brodschelm, Andreas; Zach, Armin

    2015-05-01

    Over past three decades ultrafast lasers have come a long way from the bulky, demanding and very sensitive scientific research projects to widely available commercial products. For the majority of this period the titanium-sapphire-based ultrafast systems were the workhorse for scientific and emerging industrial and biomedical applications. However the complexity and intrinsic bulkiness of solid state lasers have prevented even larger penetration into wider array of practical applications. With emergence of femtosecond fiber lasers, based primarily on Er-doped and Yb-doped fibers that provide compact, inexpensive and dependable fs and ps pulses, new practical applications have become a reality. The overview of current state of the art ultrafast fiber sources, their basic principles and most prominent applications will be presented, including micromachining and biomedical implementations (ophthalmology) on one end of the pulse energy spectrum and 3D lithography and THz applications on the other.

  15. Magnetic dipole transitions in 4d{sup N} configurations of tungsten ions

    SciTech Connect

    Jonauskas, V.; Kisielius, R.; Kyniene, A.; Kucas, S.; Norrington, P. H.

    2010-01-15

    Magnetic dipole transitions between the levels of ground 4d{sup N} configurations of tungsten ions were analyzed by employing a large basis of interacting configurations. Previously introduced configuration interaction strength between two configurations was used to determine the configurations with the largest contribution to wave functions of atomic states for the considered configurations. Collisional-radiative modeling was performed for the levels of the ground configuration coupled through electric dipole transitions with 4p{sup 5}4d{sup N+1} and 4d{sup N-1}4f configurations. New identification of some lines observed in the electron-beam ion trap plasma was proposed based on calculations in which wavelength convergence was reached.

  16. 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.

  17. Experimental validation of a 4D elastic registration algorithm.

    PubMed

    Leung, Corina; Hashtrudi-Zaad, Keyvan; Foroughi, Pezhman; Abolmaesumi, Purang

    2008-01-01

    This paper presents an extensive validation study of an elastic registration algorithm for dynamic 3D ultrasound images (also known as a 4D image). The registration algorithm uses attribute vectors from both a fixed and previous moving images to perform feature-based alignment of a series of images. The 4D method reduces computational requirements and increases the effective search space for the location of corresponding features, resulting in enhanced registration speed when compared to a static 3D registration technique. Experimental analysis revealed up to 32% improvement in speed when using the 4D method, which makes the algorithm attractive for real-time applications.

  18. Dissipative dynamics of a system passing through a conical intersection: Ultrafast pump-probe observables

    NASA Astrophysics Data System (ADS)

    Gelman, David; Katz, Gil; Kosloff, Ronnie; Ratner, Mark A.

    2005-10-01

    The dynamics of a system incorporating a conical intersection, in the presence of a dissipative environment, is studied with the purpose of identifying observable ultrafast spectroscopic signatures. A model system consisting of two vibronically coupled electronic states with two nuclear degrees of freedom is constructed. Dissipation is treated by two different methods, Lindblad semigroup formalism and the surrogate Hamiltonian approach. Pump-probe experimental expectation values such as transient emission and transient absorption are calculated and compared to the adiabatic and diabatic population transfer. The ultrafast population transfer reflecting the conical intersection is not mirrored in transient absorption measurements such as the recovery of the bleach. Emission from the excited state can be suppressed on the ultrafast time scale, but the existence of a conical intersection is only one of the possible mechanisms that can provide ultrafast damping of emission.

  19. Ultrafast optical spin echo in a single quantum dot

    NASA Astrophysics Data System (ADS)

    Press, David; de Greve, Kristiaan; McMahon, Peter L.; Ladd, Thaddeus D.; Friess, Benedikt; Schneider, Christian; Kamp, Martin; Höfling, Sven; Forchel, Alfred; Yamamoto, Yoshihisa

    2010-06-01

    Many proposed photonic quantum networks rely on matter qubits to serve as memory elements. The spin of a single electron confined in a semiconductor quantum dot forms a promising matter qubit that may be interfaced with a photonic network. Ultrafast optical spin control allows gate operations to be performed on the spin within a picosecond timescale, orders of magnitude faster than microwave or electrical control. One obstacle to storing quantum information in a single quantum dot spin is the apparent nanosecond-timescale dephasing due to slow variations in the background nuclear magnetic field. Here we use an ultrafast, all-optical spin echo technique to increase the decoherence time of a single quantum dot electron spin from nanoseconds to several microseconds. The ratio of decoherence time to gate time exceeds 105, suggesting strong promise for future photonic quantum information processors and repeater networks.

  20. Compression of Ultrafast Laser Beams

    DTIC Science & Technology

    2016-03-01

    the theory, construction, and evaluation of 2 separate algorithms, a modified genetic algorithm and the multiphoton intrapulse interference phase...pulse compression was evaluated, and it was found that the MIIPS algorithm was superior to the genetic algorithm for pulse compression. 15...SUBJECT TERMS ultrafast lasers, pulse compression, genetic algorithm, MIIPS algorithm, pulse shaping, pulse shaper construction 16. SECURITY

  1. Oscillator strengths and branching fractions of 4d75p-4d75s Rh II transitions

    NASA Astrophysics Data System (ADS)

    Bouazza, Safa

    2017-01-01

    This work reports semi-empirical determination of oscillator strengths, transition probabilities and branching fractions for Rh II 4d75p-4d75s transitions in a wide wavelength range. The angular coefficients of the transition matrix, beforehand obtained in pure SL coupling with help of Racah algebra are transformed into intermediate coupling using eigenvector amplitudes of these two configuration levels determined for this purpose; The transition integral was treated as free parameter in the least squares fit to experimental oscillator strength (gf) values found in literature. The extracted value: <4d75s|r1|4d75p> =2.7426 ± 0.0007 is slightly smaller than that computed by means of ab-initio method. Subsequently to oscillator strength evaluations, transition probabilities and branching fractions were deduced and compared to those obtained experimentally or through another approach like pseudo-relativistic Hartree-Fock model including core-polarization effects.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Microscopic model for ultrafast remagnetization dynamics.

    PubMed

    Chimata, Raghuveer; Bergman, Anders; Bergqvist, Lars; Sanyal, Biplab; Eriksson, Olle

    2012-10-12

    In this Letter, we provide a microscopic model for the ultrafast remagnetization of atomic moments already quenched above the Stoner-Curie temperature by a strong laser fluence. Combining first-principles density functional theory, atomistic spin dynamics utilizing the Landau-Lifshitz-Gilbert equation, and a three-temperature model, we analyze the temporal evolution of atomic moments as well as the macroscopic magnetization of bcc Fe and hcp Co covering a broad time scale, ranging from femtoseconds to picoseconds. Our simulations show a variety of complex temporal behavior of the magnetic properties resulting from an interplay between electron, spin, and lattice subsystems, which causes an intricate time evolution of the atomic moment, where longitudinal and transversal fluctuations result in a macrospin moment that evolves highly nonmonotonically.

  7. 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.

  8. Limits to Electron Beam Emittance from Stochastic Coulomb Interactions

    SciTech Connect

    Coleman-Smith, Christopher; Padmore, Howard A.; Wan, Weishi

    2008-08-22

    Dense electron beams can now be generated on an ultrafast timescale using laser driven photo-cathodes and these are used for a range of applications from ultrafast electron defraction to free electron lasers. Here we determine a lower bound to the emittance of an electron beam limited by fundamental stochastic Coulomb interactions.

  9. 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

  10. 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.

  11. 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.

  12. True 4D Image Denoising on the GPU.

    PubMed

    Eklund, Anders; Andersson, Mats; Knutsson, Hans

    2011-01-01

    The use of image denoising techniques is an important part of many medical imaging applications. One common application is to improve the image quality of low-dose (noisy) computed tomography (CT) data. While 3D image denoising previously has been applied to several volumes independently, there has not been much work done on true 4D image denoising, where the algorithm considers several volumes at the same time. The problem with 4D image denoising, compared to 2D and 3D denoising, is that the computational complexity increases exponentially. In this paper we describe a novel algorithm for true 4D image denoising, based on local adaptive filtering, and how to implement it on the graphics processing unit (GPU). The algorithm was applied to a 4D CT heart dataset of the resolution 512  × 512  × 445  × 20. The result is that the GPU can complete the denoising in about 25 minutes if spatial filtering is used and in about 8 minutes if FFT-based filtering is used. The CPU implementation requires several days of processing time for spatial filtering and about 50 minutes for FFT-based filtering. The short processing time increases the clinical value of true 4D image denoising significantly.

  13. Motion management with phase-adapted 4D-optimization

    NASA Astrophysics Data System (ADS)

    Nohadani, Omid; Seco, Joao; Bortfeld, Thomas

    2010-09-01

    Cancer treatment with ionizing radiation is often compromised by organ motion, in particular for lung cases. Motion uncertainties can significantly degrade an otherwise optimized treatment plan. We present a spatiotemporal optimization method, which takes into account all phases of breathing via the corresponding 4D-CTs and provides a 4D-optimal plan that can be delivered throughout all breathing phases. Monte Carlo dose calculations are employed to warrant for highest dosimetric accuracy, as pertinent to study motion effects in lung. We demonstrate the performance of this optimization method with clinical lung cancer cases and compare the outcomes to conventional gating techniques. We report significant improvements in target coverage and in healthy tissue sparing at a comparable computational expense. Furthermore, we show that the phase-adapted 4D-optimized plans are robust against irregular breathing, as opposed to gating. This technique has the potential to yield a higher delivery efficiency and a decisively shorter delivery time.

  14. 3D/4D sonography - any safety problem.

    PubMed

    Pooh, Ritsuko K; Maeda, Kazuo; Kurjak, Asim; Sen, Cihat; Ebrashy, Alaa; Adra, Abdallah; Dayyabu, Aliyu Labaran; Wataganara, Tuangsit; de Sá, Renato Augusto Moreira; Stanojevic, Milan

    2016-03-01

    Gray-scale image data are processed in 3D ultrasound by repeated scans of multiple planes within a few seconds to achieve one surface rendering image and three perpendicular plane images. The 4D image is achieved by repeating 3D images in short intervals, i.e. 3D and 4D ultrasound are based on simple B-mode images. During 3D/4D acquisition, a fetus in utero is exposed by ultrasound beam for only a few seconds, and it is as short as real-time B-mode scanning. Therefore, simple 3D imaging is as safe as a simple B-mode scan. The 4D ultrasound is also as safe as a simple B-mode scan, but the ultrasound exposure should be shorter than 30 min. The thermal index (TI) and mechanical index (MI) should both be lower than 1.0, and the ultrasound study is regulated by the Doppler ultrasound if it is combined with simple 3D or 4D ultrasound. Recently, some articles have reported the functional changes of animal fetal brain neuronal cells and liver cell apoptosis with Doppler ultrasound. We discuss cell apoptosis by ultrasound in this report. Diagnostic ultrasound safety is achieved by controlling the output pulse and continuous ultrasound waves using thermal and mechanical indices, which should be <1.0 in abdominal and transvaginal scan, pulsed Doppler, as well as 3D and 4D ultrasound. The lowest spatial peak temporal average (SPTA) intensity of the ultrasound to suppress cultured cell growth is 240 mW/cm2, below which no ultrasound effect has been reported. An ultrasound user must be trained to recognize the ultrasound bioeffects; thermal and mechanical indices, and how to reduce these when they are higher than 1.0 on the monitor display; and guide the proper use of the ultrasound under the ALARA principle, because the user is responsible for ensuring ultrasound safety.

  15. 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.

  16. 4D ultrasound imaging - ethically justifiable in India?

    PubMed

    Indiran, Venkatraman

    2017-01-01

    Four-dimensional (4D) ultrasound (real-time volume sonography), which has been used in the West since the last decade for the determination of gender as well as for bonding and entertainment of the parents, has become widely available in India in this decade. Here, I would like to discuss the ethical issues associated with 4D ultrasonography in India. These are self-referral, the use of the technology for non-medical indications, a higher possibility of the disclosure of the foetus' gender and safety concerns.

  17. 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

  18. Photonic metasurfaces for spatiotemporal and ultrafast light control

    NASA Astrophysics Data System (ADS)

    Shaltout, Amr Mohammad Emadeldin Abdelmaksoud

    The emergence of photonic metasurfaces - planar arrays of nano-antennas - has enabled a new paradigm of light control through wave-front engineering. Space-gradient metasurfaces induce spatially varying phase and/or polarization to propagating light. As a consequence, photons propagating through space-gradient metasurfaces can be engineered to undergo a change to their momentum, angular momentum and/or spin states. In our study, we implement metasurface-based devices that break the spin symmetry of light to obtain Photonic Spin Hall Effect (PSHE). We utilized PSHE to design a real-time circular dichroism spectrometer, a device vital in bio-sensing, and an optical rotator used in secure quantum communications. In addition, we developed metasurface based Fabry--Perot nano-cavities, which go beyond the diffraction limit of light, a requirement to enhance photonic spontaneous emission using the Purcell effect. In addition, we demonstrate that the field of flat photonics is further empowered by utilizing time-gradient metasurfaces with dynamic responses to propagating light. A new genus of optical devices and physical effects can be realized. Photons experience inelastic interactions with time-varying metasurfaces resulting in a Doppler-like wavelength-shift. Furthermore, Snell's relations are modified to a more universal form not limited by Lorentz reciprocity, hence meeting all the requirements to build magnetic-free optical isolators. Finally, we construct the concept of ultrafast metasurfaces. We integrate spatial interference methodology delivered by metasurfaces and temporal interference of phase-locked frequency-comb provided by ultrafast technology. This leads to generation of coherent 4D space-time optical patterns, which is implemented to achieve ultrafast laser beam steering over hundred-picosecond scale.

  19. A spectroelectrochemical cell for ultrafast two-dimensional infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    El Khoury, Youssef; Van Wilderen, Luuk J. G. W.; Vogt, Tim; Winter, Ernst; Bredenbeck, Jens

    2015-08-01

    A spectroelectrochemical cell has been designed to combine electrochemistry and ultrafast two-dimensional infrared (2D-IR) spectroscopy, which is a powerful tool to extract structure and dynamics information on the femtosecond to picosecond time scale. Our design is based on a gold mirror with the dual role of performing electrochemistry and reflecting IR light. To provide the high optical surface quality required for laser spectroscopy, the gold surface is made by electron beam evaporation on a glass substrate. Electrochemical cycling facilitates in situ collection of ultrafast dynamics of redox-active molecules by means of 2D-IR. The IR beams are operated in reflection mode so that they travel twice through the sample, i.e., the signal size is doubled. This methodology is optimal for small sample volumes and successfully tested with the ferricyanide/ferrocyanide redox system of which the corresponding electrochemically induced 2D-IR difference spectrum is reported.

  20. Atomic tungsten for ultrafast hard X-ray generation.

    PubMed

    Shan, Fang; Couch, Vernon A; Guo, Ting

    2005-05-19

    High-resolution X-ray absorption measurements (with an accuracy of +/-0.3 eV) of ZnSO(4) (aq) were performed with ultrafast selected energy X-ray absorption spectroscopy (USEXAS) using a laser-driven tungsten target X-ray source. The results were used to determine the absolute spectral positions of characteristic emission lines. By comparing these positions to those predicted for the line emission from tungsten of different oxidation states using the Dirac-Fock formula, the tungsten species responsible for ultrafast hard X-ray generation were found to be tungsten atoms. This finding provides the first direct evidence to support the mechanism of X-ray generation via high-energy electrons interacting with tungsten atoms in the solid target.

  1. A spectroelectrochemical cell for ultrafast two-dimensional infrared spectroscopy.

    PubMed

    El Khoury, Youssef; Van Wilderen, Luuk J G W; Vogt, Tim; Winter, Ernst; Bredenbeck, Jens

    2015-08-01

    A spectroelectrochemical cell has been designed to combine electrochemistry and ultrafast two-dimensional infrared (2D-IR) spectroscopy, which is a powerful tool to extract structure and dynamics information on the femtosecond to picosecond time scale. Our design is based on a gold mirror with the dual role of performing electrochemistry and reflecting IR light. To provide the high optical surface quality required for laser spectroscopy, the gold surface is made by electron beam evaporation on a glass substrate. Electrochemical cycling facilitates in situ collection of ultrafast dynamics of redox-active molecules by means of 2D-IR. The IR beams are operated in reflection mode so that they travel twice through the sample, i.e., the signal size is doubled. This methodology is optimal for small sample volumes and successfully tested with the ferricyanide/ferrocyanide redox system of which the corresponding electrochemically induced 2D-IR difference spectrum is reported.

  2. Moderately strong pump-induced ultrafast dynamics in solution

    NASA Astrophysics Data System (ADS)

    Shen, H. F.; Zhang, Yizhu; Yan, T.-M.; Wang, Z. Y.; Jiang, Y. H.

    2016-09-01

    The transient transmittance spectra of laser dye IR144 in methanol were investigated experimentally in the moderately strong pump-probe field. Observed emission spectra in the red edge of the incident-field bandwidth, created by resonant impulsive stimulated Raman scattering (RISRS), display significant nonlinear intensity dependence as the pulse intensity increases. Dynamic perspectives of RISRS spectra can be understood well in a wavepacket picture. The excitation of high vibrational levels in the ground electronic state leading to the redshift of emissions presents high dependence of the pump-pulse intensity and ultrafast dynamical features, mapping the spatial overlap and separation of ground and excited wave functions and resolving the ultrafast vibrational relaxation in the femtosecond regime.

  3. A spectroelectrochemical cell for ultrafast two-dimensional infrared spectroscopy

    SciTech Connect

    El Khoury, Youssef; Van Wilderen, Luuk J. G. W.; Vogt, Tim; Winter, Ernst; Bredenbeck, Jens E-mail: bredenbeck@biophysik.uni-frankfurt.de

    2015-08-15

    A spectroelectrochemical cell has been designed to combine electrochemistry and ultrafast two-dimensional infrared (2D-IR) spectroscopy, which is a powerful tool to extract structure and dynamics information on the femtosecond to picosecond time scale. Our design is based on a gold mirror with the dual role of performing electrochemistry and reflecting IR light. To provide the high optical surface quality required for laser spectroscopy, the gold surface is made by electron beam evaporation on a glass substrate. Electrochemical cycling facilitates in situ collection of ultrafast dynamics of redox-active molecules by means of 2D-IR. The IR beams are operated in reflection mode so that they travel twice through the sample, i.e., the signal size is doubled. This methodology is optimal for small sample volumes and successfully tested with the ferricyanide/ferrocyanide redox system of which the corresponding electrochemically induced 2D-IR difference spectrum is reported.

  4. Ultrafast Thermal Transport at Interfaces

    SciTech Connect

    Cahill, David; Murphy, Catherine; Martin, Lane

    2014-10-21

    Our research program on Ultrafast Thermal Transport at Interfaces advanced understanding of the mesoscale science of heat conduction. At the length and time scales of atoms and atomic motions, energy is transported by interactions between single-particle and collective excitations. At macroscopic scales, entropy, temperature, and heat are the governing concepts. Key gaps in fundamental knowledge appear at the transitions between these two regimes. The transport of thermal energy at interfaces plays a pivotal role in these scientific issues. Measurements of heat transport with ultrafast time resolution are needed because picoseconds are the fundamental scales where the lack of equilibrium between various thermal excitations becomes a important factor in the transport physics. A critical aspect of our work has been the development of experimental methods and model systems that enabled more precise and sensitive investigations of nanoscale thermal transport.

  5. 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.

  6. The technology and performance of 4D ultrasound.

    PubMed

    Obruchkov, Sergei

    2008-01-01

    Recent developments in 4D ultrasound imaging technology allow clinicians to obtain not only rich visual information but also quantitative data that can be used for diagnosis and treatment. Some argue that the extension of 2D ultrasound is unnecessary and does not offer any benefits to diagnosis, while others argue that it is possible to better assess an abnormality in 3D than 2D. Anatomy can be reconstructed in perspectives that were never seen with conventional 2D US imaging. Advanced rendering techniques in three dimensions can be customized to be sensitive to specific pathology, thus making diagnosis more accurate. Volume and function of certain anatomical components can be measured with greater accuracy. This article reviews physical principles behind the ultrasound technology, how they are applied to advance the field of ultrasound imaging, and maybe reach its limits. Advances in ultrasound technology make 4D ultrasound imaging faster and less dependent on the operator's expertise, thus opening up more research possibilities in the fields of data processing and visualization. Currently, 4D ultrasound is extensively used in the field of obstetrics and interven-tional radiology. The goal of 4D ultrasound is to overcome the limitations posed by its predecessor technology and to be more clinically useful as an imaging tool.

  7. 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

  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. Energy transport in ultra-fast eated solid targets

    NASA Astrophysics Data System (ADS)

    Sentoku, Yasuhiko; Johzaki, Tomoyuki; Kemp, Andreas

    2008-11-01

    We discuss hot electron generation in ultra intense laser interaction with initially non-ionized matter. Hot electron energy and the transport inside the target are strongly affected by collisional effects and ionization processes, especially in high-Z material. We have introduced an ionization model into our collisional particle-in-cell code, PICLS, to study hot electron transport in ultra-fast heated matter. Our description of collisional ionization is based on the Thomas-Fermi model, where a local average charge state is calculated from the bulk electron temperature and density. Field ionization is taken into account for ionization of low density plasmas. We have studied laser matter interaction under an irradiation of a laser with 10^20W/cm^2. A strong heat inhibition within a micron distance was observed in a gold target because of the large number of lower energy hot electrons produced at the steepened interface by the laser photon pressure. We will discuss the generation of hot electrons and their transport in ultra-fast heated solid targets of various materials.

  11. Ultrafast broadband spectroscopy of crystalline bismuth

    SciTech Connect

    Mel'nikov, A A; Misochko, Oleg V; Chekalin, Sergei V

    2013-04-30

    Femtosecond spectroscopy in the wavelength range 0.4 - 2.3 {mu}m has been used to probe ultrafast electronic and lattice processes in bismuth. The photoresponse of a bismuth crystal is shown to comprise components with relaxation times of 1 ps, 7 ps, and {approx}1 ns. The electron-hole and electron-phonon interaction strengths in bismuth are found to depend significantly on the wave vector in the {Gamma}-T direction of the Brillouin zone. Comparison of the spectral dependences of the amplitudes of coherent E{sub g} and A{sub 1g} phonons and the corresponding dependences of the Raman scattering cross sections indicates that these phonon modes differ in generation mechanism. The generation of coherent A{sub 1g} phonons is mainly due to displacement of the equilibrium position of atoms in the crystal lattice in a nonequilibrium state. This process differs fundamentally from resonance Raman scattering responsible for the coherent excitation of low-symmetry phonon modes. (extreme light fields and their applications)

  12. 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.

  13. SU-E-T-790: Validation of 4D Measurement-Guided Dose Reconstruction (MGDR) with OCTAVIUS 4D System

    SciTech Connect

    Lee, V; Leung, R; Wong, M; Law, G; Lee, K; Tung, S; Chan, M; Blanck, O

    2015-06-15

    Purpose: To validate the MGDR of OCTAVIUS 4D system (PTW, Freiburg, Germany) for quality assurance (QA) of volumetric-modulated arc radiotherapy (VMAT). Methods: 4D-MGDR measurements were divided into two parts: 1) square fields from 2×2 to 25×25 cm{sup 2} at 0°, 10° and 45° gantry, and 2) 8 VMAT plans (5 nasopharyngeal and 3 prostate) collapsed to gantry 40° in QA mode in Monaco v5.0 (Elekta, CMS, Maryland Heights, MO) were delivered on the OCTAVIUS 4D phantom with the OCTAVIUS 1500 detector plane perpendicular to either the incident beam to obtain the reconstructed dose (OCTA4D) or the 0° gantry axis to obtain the raw doses (OCTA3D) in Verisoft 6.1 (PTW, Freiburg, Germany). Raw measurements of OCTA3D were limited to < 45° gantry to avoid >0.5% variation of detector angular response with respect to 0° gantry as determined previously. Reconstructed OCTA4D and raw OCTA3D doses for all plans were compared at the same detector plane using γ criteria of 2% (local dose)/2mm and 3%/3mm criteria. Results: At gantry 0° and 10°, the γ results for all OCTA4D on detector plane coinciding with OCTA3D were over 90% at 2%/2mm except for the largest field (25×25 cm{sup 2} ) showing >88%. For square field at 45° gantry, γ passing rate is > 90% for fields smaller than 15x 15cm2 but < 80% for field size of 20 x20 cm{sup 2} upward. For VMAT, γ results showed 94% and 99% passing rate at 2%/2mm and 3%/3mm, respectively. Conclusion: OCTAVIUS 4D system has compromised accuracy in reconstructing dose away from the central beam axis, possibly due to the off-axis softening correction and errors of the percent depth dose data necessary as input for MGDR. Good results in VMAT delivery suggested that the system is relatively reliable for VMAT with small segments.

  14. Improved Respiratory Navigator Gating for Thoracic 4D flow MRI

    PubMed Central

    van Ooij, Pim; Semaan, Edouard; Schnell, Susanne; Giri, Shivraman; Stankovic, Zoran; Carr, James; Barker, Alex J.; Markl, Michael

    2016-01-01

    Background Thoracic and abdominal 4D flow MRI is typically acquired in combination with navigator respiration control which can result in highly variable scan efficiency (Seff) and thus total scan time due to inter-individual variability in breathing patterns. The aim of this study was to test the feasibility of an improved respiratory control strategy based on diaphragm navigator gating with fixed Seff, respiratory driven phase encoding, and a navigator training phase. Methods 4D flow MRI of the thoracic aorta was performed in 10 healthy subjects at 1.5T and 3T systems for the in-vivo assessment of aortic time-resolved 3D blood flow velocities. For each subject, four 4D flow scans (1: conventional navigator gating, 2–4: new implementation with fixed Seff =60%, 80% and 100%) were acquired. Data analysis included semi-quantitative evaluation of image quality of the 4D flow magnitude images (image quality grading on a four point scale), 3D segmentation of the thoracic aorta, and voxel-by-voxel comparisons of systolic 3D flow velocity vector fields between scans. Results Conventional navigator gating resulted in variable Seff = 74±13% (range = 56% – 100%) due to inter-individual variability of respiration patterns. For scans 2–4, the the new navigator implementation was able to achieve predictable total scan times with stable Seff, only depending on heart rate. Semi- and fully quantitative analysis of image quality in 4D flow magnitude images was similar for the new navigator scheme compared to conventional navigator gating. For aortic systolic 3D velocities, good agreement was found between all new navigator settings (scan 2–4) with the conventional navigator gating (scan 1) with best performance for Seff = 80% (mean difference = −0.01; limits od agreement = 0.23, Pearson’s ρ=0.89, p <0.001). No significant differences for image quality or 3D systolic velocities were found for 1.5T compared to 3T. Conclusions The findings of this study demonstrate the

  15. 4D CT sorting based on patient internal anatomy

    NASA Astrophysics Data System (ADS)

    Li, Ruijiang; Lewis, John H.; Cerviño, Laura I.; Jiang, Steve B.

    2009-08-01

    Respiratory motion during free-breathing computed tomography (CT) scan may cause significant errors in target definition for tumors in the thorax and upper abdomen. A four-dimensional (4D) CT technique has been widely used for treatment simulation of thoracic and abdominal cancer radiotherapy. The current 4D CT techniques require retrospective sorting of the reconstructed CT slices oversampled at the same couch position. Most sorting methods depend on external surrogates of respiratory motion recorded by extra instruments. However, respiratory signals obtained from these external surrogates may not always accurately represent the internal target motion, especially when irregular breathing patterns occur. We have proposed a new sorting method based on multiple internal anatomical features for multi-slice CT scan acquired in the cine mode. Four features are analyzed in this study, including the air content, lung area, lung density and body area. We use a measure called spatial coherence to select the optimal internal feature at each couch position and to generate the respiratory signals for 4D CT sorting. The proposed method has been evaluated for ten cancer patients (eight with thoracic cancer and two with abdominal cancer). For nine patients, the respiratory signals generated from the combined internal features are well correlated to those from external surrogates recorded by the real-time position management (RPM) system (average correlation: 0.95 ± 0.02), which is better than any individual internal measures at 95% confidence level. For these nine patients, the 4D CT images sorted by the combined internal features are almost identical to those sorted by the RPM signal. For one patient with an irregular breathing pattern, the respiratory signals given by the combined internal features do not correlate well with those from RPM (correlation: 0.68 ± 0.42). In this case, the 4D CT image sorted by our method presents fewer artifacts than that from the RPM signal. Our

  16. Characterization and mechanism of glass microwelding by double-pulse ultrafast laser irradiation.

    PubMed

    Wu, Sizhu; Wu, Dong; Xu, Jian; Hanada, Yasutaka; Suganuma, Ryo; Wang, Haiyu; Makimura, Testuya; Sugioka, Koji; Midorikawa, Katsumi

    2012-12-17

    We investigated the physical mechanism of high-efficiency glass microwelding by double-pulse ultrafast laser irradiation by measuring the dependences of the size of the heat-affected zone and the bonding strength on the delay time between the two pulses for delay time up to 80 ns. The size of the heat-affected zone increases rapidly when the delay time is increased from 0 to 12.5 ps. It then decreases dramatically when the delay time is further increased to 30 ps. It has a small peak around 100 ps. For delay time up to 40 ns, the size of the heat-affected zone exceeds that for a delay time of 0 ps, whereas for delay time over 60 ps, it becomes smaller than that for a delay time of 0 ps. The bonding strength exhibits the same tendency. The underlying physical mechanism is discussed in terms of initial electron excitation by the first pulse and subsequent excitation by the second pulse: specifically, the first pulse induces multiphoton ionization or tunneling ionization, while the second pulse induces electron heating or avalanche ionization or the second pulse is absorbed by the localized state. Transient absorption of glass induced by the ultrafast laser pulse was analyzed by an ultrafast pump-probe technique. We found that the optimum pulse energy ratio is unity. These results provide new insights into high-efficiency ultrafast laser microwelding of glass and suggest new possibilities for further development of other ultrafast laser processing techniques.

  17. Untangling the contributions of image charge and laser profile for optimal photoemission of high-brightness electron beams

    SciTech Connect

    Portman, J.; Zhang, H.; Makino, K.; Ruan, C. Y.; Berz, M.; Duxbury, P. M.

    2014-11-07

    Using our model for the simulation of photoemission of high brightness electron beams, we investigate the virtual cathode physics and the limits to spatio-temporal and spectroscopic resolution originating from the image charge on the surface and from the profile of the exciting laser pulse. By contrasting the effect of varying surface properties (leading to expanding or pinned image charge), laser profiles (Gaussian, uniform, and elliptical), and aspect ratios (pancake- and cigar-like) under different extraction field strengths and numbers of generated electrons, we quantify the effect of these experimental parameters on macroscopic pulse properties such as emittance, brightness (4D and 6D), coherence length, and energy spread. Based on our results, we outline optimal conditions of pulse generation for ultrafast electron microscope systems that take into account constraints on the number of generated electrons and on the required time resolution.

  18. Advanced Instrumentation for Ultrafast Science at the LCLS

    SciTech Connect

    Berrah, Nora

    2015-10-13

    This grant supported a Single Investigator and Small Group Research (SISGR) application to enable multi-user research in Ultrafast Science using the Linac Coherent Light Source (LCLS), the world’s first hard x-ray free electron laser (FEL) which lased for the first time at 1.5 Å on April 20, 2009. The goal of our proposal was to enable a New Era of Science by requesting funds to purchase and build Advanced Instrumentation for Ultrafast Science (AIUS), to utilize the intense, short x-ray pulses produced by the LCLS. The proposed instrumentation will allow peer review selected users to probe the ultrasmall and capture the ultrafast. These tools will expand on the investment already made in the construction of the light source and its instrumentation in both the LCLS and LUSI projects. The AIUS will provide researchers in the AMO, Chemical, Biological and Condensed Matter communities with greater flexibility in defining their scientific agenda at the LCLS. The proposed instrumentation will complement and significantly augment the present AMO instrument (funded through the LCLS project) through detectors and capabilities not included in the initial suite of instrumentation at the facility. We have built all of the instrumentations and they have been utilized by scientists. Please see report attached.

  19. Ultrafast Coherent Control and Characterization of Surface Reactions using FELs

    SciTech Connect

    Ogasawara, Hirohito; Nordlund, Dennis a Nilsson, Anders; /SLAC, SSRL

    2005-09-30

    The microscopic understanding of reactions at surfaces requires an in-depth knowledge of the dynamics of elementary processes on an ultrafast timescale. This can be accomplished using an ultrafast excitation to initiate a chemical reaction and then probe the progression of the reaction with an ultrashort x-ray pulse from the FEL. There is a great potential to use atom-specific spectroscopy involving core levels to probe the chemical nature, structure and bonding of species on surfaces. The ultrashort electron pulse obtained in the linear accelerator to feed the X-ray FEL can also be used for generation of coherent synchrotron radiation in the low energy THz regime to be used as a pump. This radiation has an energy close to the thermal excitations of low-energy vibrational modes of molecules on surfaces and phonons in substrates. The coherent THz radiation will be an electric field pulse with a certain direction that can collectively manipulate atoms or molecules on surfaces. In this respect a chemical reaction can be initiated by collective atomic motion along a specific reaction coordinate. If the coherent THz radiation is generated from the same source as the X-ray FEL radiation, full-time synchronization for pump-probe experiments will be possible. The combination of THz and X-ray spectroscopy could be a unique opportunity for FEL facilities to conduct ultrafast chemistry studies at surfaces.

  20. Atomic Resolution Coherent Diffractive Imaging and Ultrafast Science

    SciTech Connect

    Zuo, Jian-min

    2011-01-12

    A major scientific challenge is determining the 3-D atomic structure of small nanostructures, including single molecules. Coherent diffractive imaging (CDI) is a promising approach. Recent progress has demonstrated coherent diffraction patterns can be recorded from individual nanostructures and phased to reconstruct their structure. However, overcoming the dose limit imposed by radiation damage is a major obstacle toward the full potential of CDI. One approach is to use ultrafast x-ray or electron pulses. In electron diffraction, amplitudes recorded in a diffraction pattern are unperturbed by lens aberrations, defocus, and other microscope resolution-limiting factors. Sub-A signals are available beyond the information limit of direct imaging. Significant contrast improvement is obtained compared to high-resolution electron micrographs. progress has also been made in developing time-resolved electron diffraction and imaging for the study of ultrafast dynamic processes in materials. This talk will cover these crosscutting issues and the convergence of electron and x-ray diffraction techniques toward structure determination of single molecules.

  1. 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.

  2. A new spin foam model for 4D gravity

    NASA Astrophysics Data System (ADS)

    Freidel, Laurent; Krasnov, Kirill

    2008-06-01

    Starting from Plebanski formulation of gravity as a constrained BF theory we propose a new spin foam model for 4D Riemannian quantum gravity that generalizes the well-known Barrett Crane model and resolves the inherent to it ultra-locality problem. The BF formulation of 4D gravity possesses two sectors: gravitational and topological ones. The model presented here is shown to give a quantization of the gravitational sector, and is dual to the recently proposed spin foam model of Engle et al which, we show, corresponds to the topological sector. Our methods allow us to introduce the Immirzi parameter into the framework of spin foam quantization. We generalize some of our considerations to the Lorentzian setting and obtain a new spin foam model in that context as well.

  3. 4D embryonic cardiography using gated optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Jenkins, M. W.; Rothenberg, F.; Roy, D.; Nikolski, V. P.; Hu, Z.; Watanabe, M.; Wilson, D. L.; Efimov, I. R.; Rollins, A. M.

    2006-01-01

    Simultaneous imaging of very early embryonic heart structure and function has technical limitations of spatial and temporal resolution. We have developed a gated technique using optical coherence tomography (OCT) that can rapidly image beating embryonic hearts in four-dimensions (4D), at high spatial resolution (10-15 μm), and with a depth penetration of 1.5 - 2.0 mm that is suitable for the study of early embryonic hearts. We acquired data from paced, excised, embryonic chicken and mouse hearts using gated sampling and employed image processing techniques to visualize the hearts in 4D and measure physiologic parameters such as cardiac volume, ejection fraction, and wall thickness. This technique is being developed to longitudinally investigate the physiology of intact embryonic hearts and events that lead to congenital heart defects.

  4. 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.

  5. 4D flow cardiovascular magnetic resonance consensus statement.

    PubMed

    Dyverfeldt, Petter; Bissell, Malenka; Barker, Alex J; Bolger, Ann F; Carlhäll, Carl-Johan; Ebbers, Tino; Francios, Christopher J; Frydrychowicz, Alex; Geiger, Julia; Giese, Daniel; Hope, Michael D; Kilner, Philip J; Kozerke, Sebastian; Myerson, Saul; Neubauer, Stefan; Wieben, Oliver; Markl, Michael

    2015-08-10

    Pulsatile blood flow through the cavities of the heart and great vessels is time-varying and multidirectional. Access to all regions, phases and directions of cardiovascular flows has formerly been limited. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has enabled more comprehensive access to such flows, with typical spatial resolution of 1.5×1.5×1.5 - 3×3×3 mm(3), typical temporal resolution of 30-40 ms, and acquisition times in the order of 5 to 25 min. This consensus paper is the work of physicists, physicians and biomedical engineers, active in the development and implementation of 4D Flow CMR, who have repeatedly met to share experience and ideas. The paper aims to assist understanding of acquisition and analysis methods, and their potential clinical applications with a focus on the heart and greater vessels. We describe that 4D Flow CMR can be clinically advantageous because placement of a single acquisition volume is straightforward and enables flow through any plane across it to be calculated retrospectively and with good accuracy. We also specify research and development goals that have yet to be satisfactorily achieved. Derived flow parameters, generally needing further development or validation for clinical use, include measurements of wall shear stress, pressure difference, turbulent kinetic energy, and intracardiac flow components. The dependence of measurement accuracy on acquisition parameters is considered, as are the uses of different visualization strategies for appropriate representation of time-varying multidirectional flow fields. Finally, we offer suggestions for more consistent, user-friendly implementation of 4D Flow CMR acquisition and data handling with a view to multicenter studies and more widespread adoption of the approach in routine clinical investigations.

  6. Repairing Stevenson's step in the 4d Ising model

    NASA Astrophysics Data System (ADS)

    Balog, Janos; Niedermayer, Ferenc; Weisz, Peter

    2006-05-01

    In a recent paper Stevenson claimed that analysis of the data on the wave function renormalization constant near the critical point of the 4d Ising model is not consistent with analytical expectations. Here we present data with improved statistics and show that the results are indeed consistent with conventional wisdom once one takes into account the uncertainty of lattice artifacts in the analytical computations.

  7. Phosphodiesterase 4D gene polymorphisms in sudden sensorineural hearing loss.

    PubMed

    Chien, Chen-Yu; Tai, Shu-Yu; Wang, Ling-Feng; Hsi, Edward; Chang, Ning-Chia; Wang, Hsun-Mo; Wu, Ming-Tsang; Ho, Kuen-Yao

    2016-09-01

    The phosphodiesterase 4D (PDE4D) gene has been reported as a risk gene for ischemic stroke. The vascular factors are between the hypothesized etiologies of sudden sensorineural hearing loss (SSNHL), and this genetic effect might be attributed for its role in SSNHL. We hypothesized that genetic variants of the PDE4D gene are associated with susceptibility to SSNHL. We conducted a case-control study with 362 SSNHL cases and 209 controls. Three single nucleotide polymorphisms (SNPs) were selected. The genotypes were determined using TaqMan technology. Hardy-Weinberg equilibrium (HWE) was tested for each SNP, and genetic effects were evaluated according to three inheritance modes. We carried out sex-specific analysis to analyze the overall data. All three SNPs were in HWE. When subjects were stratified by sex, the genetic effect was only evident in females but not in males. The TT genotype of rs702553 exhibited an adjusted odds ratio (OR) of 3.83 (95 % confidence interval = 1.46-11.18) (p = 0.006) in female SSNHL. The TT genotype of SNP rs702553 was associated with female SSNHL under the recessive model (p = 0.004, OR 3.70). In multivariate logistic regression analysis, TT genotype of rs702553 was significantly associated with female SSNHL (p = 0.0043, OR 3.70). These results suggest that PDE4D gene polymorphisms influence the susceptibility for the development of SSNHL in the southern Taiwanese female population.

  8. Real-time 4D ultrasound mosaicing and visualization.

    PubMed

    Brattain, Laura J; Howe, Robert D

    2011-01-01

    Intra-cardiac 3D ultrasound imaging has enabled new minimally invasive procedures. Its narrow field of view, however, limits its efficacy in guiding beating heart procedures where geometrically complex and spatially extended moving anatomic structures are often involved. In this paper, we present a system that performs electrocardiograph gated 4D mosaicing and visualization of 3DUS volumes. Real-time operation is enabled by GPU implementation. The method is validated on phantom and porcine heart data.

  9. 4th-International Symposium on Ultrafast Surface Science - Final Report

    SciTech Connect

    Hrvoje Petek

    2005-01-26

    The 4-th International Symposium on Ultrafast Surface Dynamics (UDS4) was held at the Telluride Summer Research Center on June 22-27, 2003. The International Organizing Committee consisting of Hrvoje Petek (USA), Xiaoyang Zhu (USA), Pedro Echenique (Spain) and Maki Kawai (Japan) brought together a total of 51 participants 16 of whom were from Europe, 10 from Japan, and 25 from the USA. The focus of the conference was on ultrafast electron or light induced processes at well-defined surfaces. Ultrafast surface dynamics concerns the transfer of charge and energy at solid surfaces on the femtosecond time scale. These processes govern rates of fundamental steps in surface reactions, interfacial electron transfer in molecular electronics, and relaxation in spin transport. Recent developments in femtosecond laser technology make it possible to measure by a variety of nonlinear optical techniques directly in the time domain the microscopic rates underlying these interfacial processes. Parallel progress in scanning probe microscopy makes it possible at a single molecular level to perform the vibrational and electronic spectroscopy measurements, to induce reactions with tunneling electrons, and to observe their outcome. There is no doubt that successful development in the field of ultrafast surface dynamics will contribute to many important disciplines.

  10. 2D:4D Ratio and its Implications in Medicine

    PubMed Central

    Jeevanandam, Saravanakumar

    2016-01-01

    Digit ratios, especially 2D:4D ratio, a potential proxy marker for prenatal androgen exposure shows sexual dimorphism. Existing literature and recent research show accumulating evidence on 2D:4D ratio showing correlations with various phenotypic traits in humans. Ratio of 2D:4D is found to correlate negatively to testosterone and positively to oestrogen in the foetus. Interestingly, it is constant since birth and not influenced by the adult hormone levels. Usually, males have lower ratios when compared to females. Prenatal androgen exposure and therefore, digit ratios have been reported to be associated with numerical competencies, spatial skills, handedness, cognitive abilities, academic performance, sperm counts, personalities and prevalence of obesity, migraine, eating disorders, depression, myopia, autism etc. The authors have attempted to write a brief account on the digit ratios and the dimorphism observed in various physiological, psychological and behavioural traits. Also, the authors have discussed the relevant molecular basics and the methods of measurement of digit ratios. PMID:28208851

  11. 4D-Flow validation, numerical and experimental framework

    NASA Astrophysics Data System (ADS)

    Sansom, Kurt; Liu, Haining; Canton, Gador; Aliseda, Alberto; Yuan, Chun

    2015-11-01

    This work presents a group of assessment metrics of new 4D MRI flow sequences, an imaging modality that allows for visualization of three-dimensional pulsatile flow in the cardiovascular anatomy through time-resolved three-dimensional blood velocity measurements from cardiac-cycle synchronized MRI acquisition. This is a promising tool for clinical assessment but lacks a robust validation framework. First, 4D-MRI flow in a subject's stenotic carotid bifurcation is compared with a patient-specific CFD model using two different boundary condition methods. Second, Particle Image Velocimetry in a patient-specific phantom is used as a benchmark to compare the 4D-MRI in vivo measurements and CFD simulations under the same conditions. Comparison of estimated and measureable flow parameters such as wall shear stress, fluctuating velocity rms, Lagrangian particle residence time, will be discussed, with justification for their biomechanics relevance and the insights they can provide on the pathophysiology of arterial disease: atherosclerosis and intimal hyperplasia. Lastly, the framework is applied to a new sequence to provide a quantitative assessment. A parametric analysis on the carotid bifurcation pulsatile flow conditions will be presented and an accuracy assessment provided.

  12. Ultrafast Synaptic Events in a Chalcogenide Memristor

    PubMed Central

    Li, Yi; Zhong, Yingpeng; Xu, Lei; Zhang, Jinjian; Xu, Xiaohua; Sun, Huajun; Miao, Xiangshui

    2013-01-01

    Compact and power-efficient plastic electronic synapses are of fundamental importance to overcoming the bottlenecks of developing a neuromorphic chip. Memristor is a strong contender among the various electronic synapses in existence today. However, the speeds of synaptic events are relatively slow in most attempts at emulating synapses due to the material-related mechanism. Here we revealed the intrinsic memristance of stoichiometric crystalline Ge2Sb2Te5 that originates from the charge trapping and releasing by the defects. The device resistance states, representing synaptic weights, were precisely modulated by 30 ns potentiating/depressing electrical pulses. We demonstrated four spike-timing-dependent plasticity (STDP) forms by applying programmed pre- and postsynaptic spiking pulse pairs in different time windows ranging from 50 ms down to 500 ns, the latter of which is 105 times faster than the speed of STDP in human brain. This study provides new opportunities for building ultrafast neuromorphic computing systems and surpassing Von Neumann architecture. PMID:23563810

  13. Control and mapping ultrafast plasmons with PEEM

    NASA Astrophysics Data System (ADS)

    Ji, Boyu; Qin, Jiang; Lang, Peng; Koya, Alemayehu Nana; Hao, Zuoqiang; Song, Xiaowei; Lin, Jingquan

    2016-11-01

    We report the direct imaging of plasmon on the tips of nano-prisms in a bowtie structure excited by 7 fs laser pulses and probing of ultrafast plasmon dynamics by combining the pump-probe technology with three-photon photoemission electron microscopy. A series of images of the evolution of local surface plasmon modes on different tips of the bowtie are obtained by the time-resolved three-photon photoemission electron microscopy, and the result discloses that plasmon excitation is dominated by the interference of the pump and probe pulses within the first 13 fs of the delay time, and thereafter the individual plasmon starts to oscillate on its own characteristic resonant frequencies. On the other hand, control of the near-field distribution was realized by variation of the phase delay of two orthogonally polarized 200fs laser pulses. The experimental results of the optical near-field distribution control are well reproduced by finite-difference time-domain simulations and understood by linear combination of electric charge distribution of the bowtie by s- and p- polarized light illumination. In addition, an independent shift of the excitation position or the phase of the near-field can be realized by coherent control of two orthogonally polarized fs laser pulses.

  14. Ultrafast X-ray Auger probing of photoexcited molecular dynamics

    DOE PAGES

    McFarland, B. K.; Farrell, J. P.; Miyabe, S.; ...

    2014-06-23

    Here, molecules can efficiently and selectively convert light energy into other degrees of freedom. Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule presents a challenge to current spectroscopic approaches. Here we explore the photoexcited dynamics of molecules by an interaction with an ultrafast X-ray pulse creating a highly localized core hole that decays via Auger emission. We discover that the Auger spectrum as a function of photoexcitation—X-ray-probe delay contains valuable information about the nuclear and electronic degrees of freedom from an element-specific point of view. For the nucleobase thymine, the oxygen Auger spectrum shifts towardsmore » high kinetic energies, resulting from a particular C–O bond stretch in the ππ* photoexcited state. A subsequent shift of the Auger spectrum towards lower kinetic energies displays the electronic relaxation of the initial photoexcited state within 200 fs. Ab-initio simulations reinforce our interpretation and indicate an electronic decay to the nπ* state.« less

  15. Ultrafast X-ray Auger probing of photoexcited molecular dynamics

    SciTech Connect

    McFarland, B. K.; Farrell, J. P.; Miyabe, S.; Tarantelli, F.; Aguilar, A.; Berrah, N.; Bostedt, C.; Bozek, J. D.; Bucksbaum, P. H.; Castagna, J. C.; Coffee, R. N.; Cryan, J. P.; Fang, L.; Feifel, R.; Gaffney, K. J.; Glownia, J. M.; Martinez, T. J.; Mucke, M.; Murphy, B.; Natan, A.; Osipov, T.; Petrović, V. S.; Schorb, S.; Schultz, Th.; Spector, L. S.; Swiggers, M.; Tenney, I.; Wang, S.; White, J. L.; White, W.; Gühr, M.

    2014-06-23

    Here, molecules can efficiently and selectively convert light energy into other degrees of freedom. Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule presents a challenge to current spectroscopic approaches. Here we explore the photoexcited dynamics of molecules by an interaction with an ultrafast X-ray pulse creating a highly localized core hole that decays via Auger emission. We discover that the Auger spectrum as a function of photoexcitation—X-ray-probe delay contains valuable information about the nuclear and electronic degrees of freedom from an element-specific point of view. For the nucleobase thymine, the oxygen Auger spectrum shifts towards high kinetic energies, resulting from a particular C–O bond stretch in the ππ* photoexcited state. A subsequent shift of the Auger spectrum towards lower kinetic energies displays the electronic relaxation of the initial photoexcited state within 200 fs. Ab-initio simulations reinforce our interpretation and indicate an electronic decay to the nπ* state.

  16. The ultrafast high-peak power lasers in future biomedical and medical x-ray imaging

    NASA Astrophysics Data System (ADS)

    Kieffer, J. C.; Fourmaux, S.; Krol, A.

    2016-01-01

    This paper reviews recent progresses in ultrafast laser-based X-ray sources and their potential applications to high throughput X-ray imaging. Prospects for the utilization of X-rays sources related to the Laser Wakefield electron Acceleration (LWFA) are more specifically discussed with emphasis on application in diagnostic radiology.

  17. Decoupling Bulk and Surface Contributions in Water- Splitting Photocatalysts by In Situ Ultrafast Spectroscopy

    SciTech Connect

    Appavoo, Kannatassen; Mingzhao, Liu; Black, Charles T.; Sfeir, Matthew Y.

    2015-05-10

    By performing ultrafast emission spectroscopy in an operating, bias-controlled photoelectrochemical cell, we distinguish between bulk (charge transport) and surface (chemical reaction) recombination processes in a nanostructured photocatalyst and correlate its electronic properties directly with its incident-photon-to-current efficiency.

  18. A grazing incidence x-ray streak camera for ultrafast, single-shot measurements

    SciTech Connect

    Feng, Jun; Engelhorn, K.; Cho, B.I.; Lee, H.J.; Greaves, M.; Weber, C.P.; Falcone, R.W.; Padmore, H. A.; Heimann, P.A.

    2010-02-18

    An ultrafast x-ray streak camera has been realized using a grazing incidence reflection photocathode. X-rays are incident on a gold photocathode at a grazing angle of 20 degree and photoemitted electrons are focused by a large aperture magnetic solenoid lens. The streak camera has high quantum efficiency, 600fs temporal resolution, and 6mm imaging length in the spectral direction. Its single shot capability eliminates temporal smearing due to sweep jitter, and allows recording of the ultrafast dynamics of samples that undergo non-reversible changes.

  19. Primary ultrafast events preceding the photoinduced proton transfer from pyranine to water

    NASA Astrophysics Data System (ADS)

    Tran-Thi, T.-H.; Gustavsson, T.; Prayer, C.; Pommeret, S.; Hynes, James T.

    2000-10-01

    Femtosecond fluorescence and absorption spectroscopies are used to probe the early events of the photoinduced proton transfer (PT) from pyranine to water. The process is found to involve two ultrafast steps (300 fs and 2.5 ps) which precede the relatively slow (87 ps) PT step. From the comparative study of the properties of the excited acid and its conjugate anion in various aqueous and alcoholic media, these ultrafast steps are identified as the solvation dynamics of the locally excited (LE) state of the acid and its subsequent relaxation to an intermediate electronic state, whose nature is discussed.

  20. State-resolved ultrafast dynamics of impact ionization in InSb

    PubMed Central

    Tanimura, H.; Kanasaki, J.; Tanimura, K.

    2014-01-01

    Impact ionization (IMP) is a fundamental process in semiconductors, which results in carrier multiplication through the decay of a hot electron into a low-energy state while generating an electron-hole pair. IMP is essentially a state selective process, which is triggered by electron-electron interaction involving four electronic states specified precisely by energy and momentum conservations. However, important state-selective features remain undetermined due to methodological limitations in identifying the energy and momentum of the states involved, at sufficient temporal resolution, to reveal the fundamental dynamics. Here we report state-resolved ultrafast hot electron dynamics of IMP in InSb, a semiconductor with the lowest band-gap energy. The ultrafast decay of state-resolved hot-electron populations and the corresponding population increase at the conduction band minimum are directly captured, and the rate of IMP is unambiguously determined. Our analysis, based on the direct knowledge of state-resolved hot electrons, provides far deeper insight into the physics of ultrafast electron correlation in semiconductors. PMID:25355408

  1. Linear and ultrafast nonlinear plasmonics of single nano-objects

    NASA Astrophysics Data System (ADS)

    Crut, Aurélien; Maioli, Paolo; Vallée, Fabrice; Del Fatti, Natalia

    2017-03-01

    Single-particle optical investigations have greatly improved our understanding of the fundamental properties of nano-objects, avoiding the spurious inhomogeneous effects that affect ensemble experiments. Correlation with high-resolution imaging techniques providing morphological information (e.g. electron microscopy) allows a quantitative interpretation of the optical measurements by means of analytical models and numerical simulations. In this topical review, we first briefly recall the principles underlying some of the most commonly used single-particle optical techniques: near-field, dark-field, spatial modulation and photothermal microscopies/spectroscopies. We then focus on the quantitative investigation of the surface plasmon resonance (SPR) of metallic nano-objects using linear and ultrafast optical techniques. While measured SPR positions and spectral areas are found in good agreement with predictions based on Maxwell’s equations, SPR widths are strongly influenced by quantum confinement (or, from a classical standpoint, surface-induced electron scattering) and, for small nano-objects, cannot be reproduced using the dielectric functions of bulk materials. Linear measurements on single nano-objects (silver nanospheres and gold nanorods) allow a quantification of the size and geometry dependences of these effects in confined metals. Addressing the ultrafast response of an individual nano-object is also a powerful tool to elucidate the physical mechanisms at the origin of their optical nonlinearities, and their electronic, vibrational and thermal relaxation processes. Experimental investigations of the dynamical response of gold nanorods are shown to be quantitatively modeled in terms of modifications of the metal dielectric function enhanced by plasmonic effects. Ultrafast spectroscopy can also be exploited to unveil hidden physical properties of more complex nanosystems. In this context, two-color femtosecond pump–probe experiments performed on

  2. Linear and ultrafast nonlinear plasmonics of single nano-objects.

    PubMed

    Crut, Aurélien; Maioli, Paolo; Vallée, Fabrice; Del Fatti, Natalia

    2017-03-29

    Single-particle optical investigations have greatly improved our understanding of the fundamental properties of nano-objects, avoiding the spurious inhomogeneous effects that affect ensemble experiments. Correlation with high-resolution imaging techniques providing morphological information (e.g. electron microscopy) allows a quantitative interpretation of the optical measurements by means of analytical models and numerical simulations. In this topical review, we first briefly recall the principles underlying some of the most commonly used single-particle optical techniques: near-field, dark-field, spatial modulation and photothermal microscopies/spectroscopies. We then focus on the quantitative investigation of the surface plasmon resonance (SPR) of metallic nano-objects using linear and ultrafast optical techniques. While measured SPR positions and spectral areas are found in good agreement with predictions based on Maxwell's equations, SPR widths are strongly influenced by quantum confinement (or, from a classical standpoint, surface-induced electron scattering) and, for small nano-objects, cannot be reproduced using the dielectric functions of bulk materials. Linear measurements on single nano-objects (silver nanospheres and gold nanorods) allow a quantification of the size and geometry dependences of these effects in confined metals. Addressing the ultrafast response of an individual nano-object is also a powerful tool to elucidate the physical mechanisms at the origin of their optical nonlinearities, and their electronic, vibrational and thermal relaxation processes. Experimental investigations of the dynamical response of gold nanorods are shown to be quantitatively modeled in terms of modifications of the metal dielectric function enhanced by plasmonic effects. Ultrafast spectroscopy can also be exploited to unveil hidden physical properties of more complex nanosystems. In this context, two-color femtosecond pump-probe experiments performed on individual

  3. Ultrafast infrared studies of complex ligand rearrangements in solution

    SciTech Connect

    Payne, Christine K.

    2003-01-01

    The complete description of a chemical reaction in solution depends upon an understanding of the reactive molecule as well as its interactions with the surrounding solvent molecules. Using ultrafast infrared spectroscopy it is possible to observe both the solute-solvent interactions and the rearrangement steps which determine the overall course of a chemical reaction. The topics addressed in these studies focus on reaction mechanisms which require the rearrangement of complex ligands and the spectroscopic techniques necessary for the determination of these mechanisms. Ligand rearrangement is studied by considering two different reaction mechanisms for which the rearrangement of a complex ligand constitutes the most important step of the reaction. The first system concerns the rearrangement of a cyclopentadienyl ring as the response of an organometallic complex to a loss of electron density. This mechanism, commonly referred to as ''ring slip'', is frequently cited to explain reaction mechanisms. However, the ring slipped intermediate is too short-lived to be observed using conventional methods. Using a combination of ultrafast infrared spectroscopy and electronic structure calculations it has been shown that the intermediate exists, but does not form an eighteen-electron intermediate as suggested by traditional molecular orbital models. The second example examines the initial steps of alkyne polymerization. Group 6 (Cr, Mo, W) pentacarbonyl species are generated photolytically and used to catalyze the polymerization of unsaturated hydrocarbons through a series of coordination and rearrangement steps. Observing this reaction on the femto- to millisecond timescale indicates that the initial coordination of an alkyne solvent molecule to the metal center results in a stable intermediate that does not rearrange to form the polymer precursor. This suggests that polymerization requires the dissociation of additional carbonyl ligands before rearrangement can occur. Overall

  4. 4D seismic data acquisition method during coal mining

    NASA Astrophysics Data System (ADS)

    Du, Wen-Feng; Peng, Su-Ping

    2014-06-01

    In order to observe overburden media changes caused by mining processing, we take the fully-mechanized working face of the BLT coal mine in Shendong mine district as an example to develop a 4D seismic data acquisition methodology during coal mining. The 4D seismic data acquisition is implemented to collect 3D seismic data four times in different periods, such as before mining, during the mining process and after mining to observe the changes of the overburden layer during coal mining. The seismic data in the research area demonstrates that seismic waves are stronger in energy, higher in frequency and have better continuous reflectors before coal mining. However, all this is reversed after coal mining because the overburden layer has been mined, the seismic energy and frequency decrease, and reflections have more discontinuities. Comparing the records collected in the survey with those from newly mined areas and other records acquired in the same survey with the same geometry and with a long time for settling after mining, it clearly shows that the seismic reflections have stronger amplitudes and are more continuous because the media have recovered by overburden layer compaction after a long time of settling after mining. By 4D seismic acquisition, the original background investigation of the coal layers can be derived from the first records, then the layer structure changes can be monitored through the records of mining action and compaction action after mining. This method has laid the foundation for further research into the variation principles of the overburden layer under modern coal-mining conditions.

  5. Digit ratio (2D:4D), salivary testosterone, and handedness.

    PubMed

    Beaton, Alan A; Rudling, Nick; Kissling, Christian; Taurines, Regine; Thome, Johannes

    2011-03-01

    The length of the index finger relative to that of the ring finger, the 2D:4D ratio, has been taken to be a marker of the amount of testosterone (T) that was present in the foetal environment (Manning, Scutt, Wilson, & Lewis-Jones, 1998). It has also been suggested (Geschwind & Galaburda, 1987) that elevated levels of foetal T are associated with left-handedness and that adult levels of circulating T might relate to foetal levels (Jamison, Meier, & Campbell, 1993). We used multiple regression analyses to investigate whether there is any relationship between either left or right hand 2D:4D ratio and handedness. We also examined whether adult levels of salivary T (or cortisol, used as a control hormone) predict digit ratio and/or handedness. Although the 2D:4D ratio of neither the left nor the right hand was related to handedness, the difference between the digit ratios of the right and left hands, D(R-L), was a significant predictor of handedness and of the performance difference between the hands on a peg-moving task, supporting previous findings (Manning & Peters, 2009; Manning et al., 1998; Manning, Trivers, Thornhill, & Singh, 2000; Stoyanov, Marinov, & Pashalieva, 2009). Adult circulating T levels did not predict the digit ratio of the left or right hand; nor was there a significant relationship between concentrations of salivary T (or cortisol) and either hand preference or asymmetry in manual skill. We suggest that the association between D(R-L) and hand preference arises because D(R-L) is a correlate of sensitivity to T in the developing foetus.

  6. CMT4D (NDRG1 mutation): genotype-phenotype correlations.

    PubMed

    Ricard, Emilie; Mathis, Stéphane; Magdelaine, Corinne; Delisle, Marie-Bernadette; Magy, Laurent; Funalot, Benoît; Vallat, Jean-Michel

    2013-09-01

    Charcot-Marie-Tooth (CMT) disease is a heterogeneous condition with a large number of clinical, electrophysiological and pathological phenotypes. More than 40 genes are involved. We report a child of gypsy origin with an autosomal recessive demyelinating phenotype. Clinical data, familial history, and electrophysiological studies were in favor of a CMT4 sub-type. The characteristic N-Myc downstream-regulated gene 1 (NDRG1) mutation responsible for this CMT4D phenotype was confirmed: p.R148X. The exact molecular function of the NDRG1 protein has yet to be elucidated.

  7. 4D micro-CT using fast prospective gating

    NASA Astrophysics Data System (ADS)

    Guo, Xiaolian; Johnston, Samuel M.; Qi, Yi; Johnson, G. Allan; Badea, Cristian T.

    2012-01-01

    Micro-CT is currently used in preclinical studies to provide anatomical information. But, there is also significant interest in using this technology to obtain functional information. We report here a new sampling strategy for 4D micro-CT for functional cardiac and pulmonary imaging. Rapid scanning of free-breathing mice is achieved with fast prospective gating (FPG) implemented on a field programmable gate array. The method entails on-the-fly computation of delays from the R peaks of the ECG signals or the peaks of the respiratory signals for the triggering pulses. Projection images are acquired for all cardiac or respiratory phases at each angle before rotating to the next angle. FPG can deliver the faster scan time of retrospective gating (RG) with the regular angular distribution of conventional prospective gating for cardiac or respiratory gating. Simultaneous cardio-respiratory gating is also possible with FPG in a hybrid retrospective/prospective approach. We have performed phantom experiments to validate the new sampling protocol and compared the results from FPG and RG in cardiac imaging of a mouse. Additionally, we have evaluated the utility of incorporating respiratory information in 4D cardiac micro-CT studies with FPG. A dual-source micro-CT system was used for image acquisition with pulsed x-ray exposures (80 kVp, 100 mA, 10 ms). The cardiac micro-CT protocol involves the use of a liposomal blood pool contrast agent containing 123 mg I ml-1 delivered via a tail vein catheter in a dose of 0.01 ml g-1 body weight. The phantom experiment demonstrates that FPG can distinguish the successive phases of phantom motion with minimal motion blur, and the animal study demonstrates that respiratory FPG can distinguish inspiration and expiration. 4D cardiac micro-CT imaging with FPG provides image quality superior to RG at an isotropic voxel size of 88 µm and 10 ms temporal resolution. The acquisition time for either sampling approach is less than 5 min. The

  8. 4D micro-CT using fast prospective gating.

    PubMed

    Guo, Xiaolian; Johnston, Samuel M; Qi, Yi; Johnson, G Allan; Badea, Cristian T

    2012-01-07

    Micro-CT is currently used in preclinical studies to provide anatomical information. But, there is also significant interest in using this technology to obtain functional information. We report here a new sampling strategy for 4D micro-CT for functional cardiac and pulmonary imaging. Rapid scanning of free-breathing mice is achieved with fast prospective gating (FPG) implemented on a field programmable gate array. The method entails on-the-fly computation of delays from the R peaks of the ECG signals or the peaks of the respiratory signals for the triggering pulses. Projection images are acquired for all cardiac or respiratory phases at each angle before rotating to the next angle. FPG can deliver the faster scan time of retrospective gating (RG) with the regular angular distribution of conventional prospective gating for cardiac or respiratory gating. Simultaneous cardio-respiratory gating is also possible with FPG in a hybrid retrospective/prospective approach. We have performed phantom experiments to validate the new sampling protocol and compared the results from FPG and RG in cardiac imaging of a mouse. Additionally, we have evaluated the utility of incorporating respiratory information in 4D cardiac micro-CT studies with FPG. A dual-source micro-CT system was used for image acquisition with pulsed x-ray exposures (80 kVp, 100 mA, 10 ms). The cardiac micro-CT protocol involves the use of a liposomal blood pool contrast agent containing 123 mg I ml(-1) delivered via a tail vein catheter in a dose of 0.01 ml g(-1) body weight. The phantom experiment demonstrates that FPG can distinguish the successive phases of phantom motion with minimal motion blur, and the animal study demonstrates that respiratory FPG can distinguish inspiration and expiration. 4D cardiac micro-CT imaging with FPG provides image quality superior to RG at an isotropic voxel size of 88 μm and 10 ms temporal resolution. The acquisition time for either sampling approach is less than 5 min. The

  9. 4D Flow MRI in Neuroradiology: Techniques and Applications.

    PubMed

    Pereira, Vitor Mendes; Delattre, Benedicte; Brina, Olivier; Bouillot, Pierre; Vargas, Maria Isabel

    2016-04-01

    Assessment of the intracranial flow is important for the understanding and management of cerebral vascular diseases. From brain aneurysms and arteriovenous malformations lesions to intracranial and cervical stenosis, the appraisal of the blood flow can be crucial and influence positively on patients' management. The determination of the intracranial hemodynamics and the collateral pattern seems to play to a major role in the management of these lesions. 4D flow magnetic resonance imaging is a noninvasive phase contrast derived method that has been developed and applied in neurovascular diseases. It has a great potential if followed by further technical improvements and comprehensive and systematic clinical studies.

  10. Actively triggered 4d cone-beam CT acquisition

    SciTech Connect

    Fast, Martin F.; Wisotzky, Eric; Oelfke, Uwe; Nill, Simeon

    2013-09-15

    Purpose: 4d cone-beam computed tomography (CBCT) scans are usually reconstructed by extracting the motion information from the 2d projections or an external surrogate signal, and binning the individual projections into multiple respiratory phases. In this “after-the-fact” binning approach, however, projections are unevenly distributed over respiratory phases resulting in inefficient utilization of imaging dose. To avoid excess dose in certain respiratory phases, and poor image quality due to a lack of projections in others, the authors have developed a novel 4d CBCT acquisition framework which actively triggers 2d projections based on the forward-predicted position of the tumor.Methods: The forward-prediction of the tumor position was independently established using either (i) an electromagnetic (EM) tracking system based on implanted EM-transponders which act as a surrogate for the tumor position, or (ii) an external motion sensor measuring the chest-wall displacement and correlating this external motion to the phase-shifted diaphragm motion derived from the acquired images. In order to avoid EM-induced artifacts in the imaging detector, the authors devised a simple but effective “Faraday” shielding cage. The authors demonstrated the feasibility of their acquisition strategy by scanning an anthropomorphic lung phantom moving on 1d or 2d sinusoidal trajectories.Results: With both tumor position devices, the authors were able to acquire 4d CBCTs free of motion blurring. For scans based on the EM tracking system, reconstruction artifacts stemming from the presence of the EM-array and the EM-transponders were greatly reduced using newly developed correction algorithms. By tuning the imaging frequency independently for each respiratory phase prior to acquisition, it was possible to harmonize the number of projections over respiratory phases. Depending on the breathing period (3.5 or 5 s) and the gantry rotation time (4 or 5 min), between ∼90 and 145

  11. Realistic CT simulation using the 4D XCAT phantom.

    PubMed

    Segars, W P; Mahesh, M; Beck, T J; Frey, E C; Tsui, B M W

    2008-08-01

    The authors develop a unique CT simulation tool based on the 4D extended cardiac-torso (XCAT) phantom, a whole-body computer model of the human anatomy and physiology based on NURBS surfaces. Unlike current phantoms in CT based on simple mathematical primitives, the 4D XCAT provides an accurate representation of the complex human anatomy and has the advantage, due to its design, that its organ shapes can be changed to realistically model anatomical variations and patient motion. A disadvantage to the NURBS basis of the XCAT, however, is that the mathematical complexity of the surfaces makes the calculation of line integrals through the phantom difficult. They have to be calculated using iterative procedures; therefore, the calculation of CT projections is much slower than for simpler mathematical phantoms. To overcome this limitation, the authors used efficient ray tracing techniques from computer graphics, to develop a fast analytic projection algorithm to accurately calculate CT projections directly from the surface definition of the XCAT phantom given parameters defining the CT scanner and geometry. Using this tool, realistic high-resolution 3D and 4D projection images can be simulated and reconstructed from the XCAT within a reasonable amount of time. In comparison with other simulators with geometrically defined organs, the XCAT-based algorithm was found to be only three times slower in generating a projection data set of the same anatomical structures using a single 3.2 GHz processor. To overcome this decrease in speed would, therefore, only require running the projection algorithm in parallel over three processors. With the ever decreasing cost of computers and the rise of faster processors and multi-processor systems and clusters, this slowdown is basically inconsequential, especially given the vast improvement the XCAT offers in terms of realism and the ability to generate 3D and 4D data from anatomically diverse patients. As such, the authors conclude

  12. Founding Gravitation in 4D Euclidean Space-Time Geometry

    SciTech Connect

    Winkler, Franz-Guenter

    2010-11-24

    The Euclidean interpretation of special relativity which has been suggested by the author is a formulation of special relativity in ordinary 4D Euclidean space-time geometry. The natural and geometrically intuitive generalization of this view involves variations of the speed of light (depending on location and direction) and a Euclidean principle of general covariance. In this article, a gravitation model by Jan Broekaert, which implements a view of relativity theory in the spirit of Lorentz and Poincare, is reconstructed and shown to fulfill the principles of the Euclidean approach after an appropriate reinterpretation.

  13. Review of ultrafast spectroscopy studies of valley carrier dynamics in two-dimensional semiconducting transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Sun, Dong; Lai, Jia-Wei; Ma, Jun-Chao; Wang, Qin-Sheng; Liu, Jing

    2017-03-01

    The two dimensional layered transition metal dichalcogenides provide new opportunities in future valley based information processing and also provide ideal platform to study excitonic effects. At the center of various device physics toward their possible electronic and optoelectronic applications is understanding the dynamical evolution of various many particle electronic states, especially exciton which dominates the optoelectronic response of TMDs, under the novel context of valley degree of freedom. Here, we provide a brief review of experimental advances in using helicity resolved ultrafast spectroscopy, especially ultrafast pump-probe spectroscopy, to study the dynamical evolution of valley related many particle electronic states in semiconducting monolayer transitional metal dichalcogenides.

  14. Large lateral photovoltaic effect with ultrafast relaxation time in SnSe/Si junction

    NASA Astrophysics Data System (ADS)

    Wang, Xianjie; Zhao, Xiaofeng; Hu, Chang; Zhang, Yang; Song, Bingqian; Zhang, Lingli; Liu, Weilong; Lv, Zhe; Zhang, Yu; Tang, Jinke; Sui, Yu; Song, Bo

    2016-07-01

    In this paper, we report a large lateral photovoltaic effect (LPE) with ultrafast relaxation time in SnSe/p-Si junctions. The LPE shows a linear dependence on the position of the laser spot, and the position sensitivity is as high as 250 mV mm-1. The optical response time and the relaxation time of the LPE are about 100 ns and 2 μs, respectively. The current-voltage curve on the surface of the SnSe film indicates the formation of an inversion layer at the SnSe/p-Si interface. Our results clearly suggest that most of the excited-electrons diffuse laterally in the inversion layer at the SnSe/p-Si interface, which results in a large LPE with ultrafast relaxation time. The high positional sensitivity and ultrafast relaxation time of the LPE make the SnSe/p-Si junction a promising candidate for a wide range of optoelectronic applications.

  15. Ultrafast carrier dynamics in polycrystalline bismuth telluride nanofilm

    SciTech Connect

    Jia, Lin; Ma, Weigang; Zhang, Xing

    2014-06-16

    In this study, the dynamics of energy carriers in polycrystalline bismuth telluride nanofilm are investigated by the ultrafast pump-probe method. The energy relaxation processes are quantitatively analyzed by using the numerical fitting models. The extracted hot carrier relaxation times of photon excitation, thermalization, and diffusion are around sub-picosecond. The initial reflectivity recovery is found to be dominantly determined by the carrier diffusion, electron-phonon coupling, and photo-generated carriers trapping processes. High-frequency and low-frequency oscillations are both observed and attributed to coherent optical phonons and coherent acoustic phonons, respectively.

  16. Driving magnetic order in a manganite by ultrafast lattice excitation.

    SciTech Connect

    Forst, M.; Tobey, R. I.; Wall, S.; Bromberger, H.; Khanna, V.; Cavalieri, A. L.; Chuang, Y.-D.; Lee, W. S.; Moore, R.; Schlotter, W. F.; Turner, J. J.; Krupin, O.; Trigo, M.; Zheng, H.; Mitchell, J. F.; Dhesi, S. S.; Hill, J. P.; Cavalleri, A.

    2011-01-01

    Femtosecond midinfrared pulses are used to directly excite the lattice of the single-layer manganite La{sub 0.5}Sr{sub 1.5}MnO{sub 4}. Magnetic and orbital orders, as measured by femtosecond resonant soft x-ray diffraction with an x-ray free-electron laser, are reduced within a few picoseconds. This effect is interpreted as a displacive exchange quench, a prompt shift in the equilibrium value of the magnetic- and orbital-order parameters after the lattice has been distorted. Control of magnetism through ultrafast lattice excitation may be of use for high-speed optomagnetism.

  17. Exploration of 4D MRI blood flow using stylistic visualization.

    PubMed

    van Pelt, Roy; Oliván Bescós, Javier; Breeuwer, Marcel; Clough, Rachel E; Gröller, M Eduard; ter Haar Romenij, Bart; Vilanova, Anna

    2010-01-01

    Insight into the dynamics of blood-flow considerably improves the understanding of the complex cardiovascular system and its pathologies. Advances in MRI technology enable acquisition of 4D blood-flow data, providing quantitative blood-flow velocities over time. The currently typical slice-by-slice analysis requires a full mental reconstruction of the unsteady blood-flow field, which is a tedious and highly challenging task, even for skilled physicians. We endeavor to alleviate this task by means of comprehensive visualization and interaction techniques. In this paper we present a framework for pre-clinical cardiovascular research, providing tools to both interactively explore the 4D blood-flow data and depict the essential blood-flow characteristics. The framework encompasses a variety of visualization styles, comprising illustrative techniques as well as improved methods from the established field of flow visualization. Each of the incorporated styles, including exploded planar reformats, flow-direction highlights, and arrow-trails, locally captures the blood-flow dynamics and may be initiated by an interactively probed vessel cross-section. Additionally, we present the results of an evaluation with domain experts, measuring the value of each of the visualization styles and related rendering parameters.

  18. 4D Simulation of Explosive Eruption Dynamics at Vesuvius

    NASA Astrophysics Data System (ADS)

    Neri, A.; Esposti Ongaro, T.; Menconi, G.; de'Michieli Vitturi, M.; Cavazzoni, C.; Erbacci, G.; Baxter, P. J.

    2006-12-01

    We applied, using a supercomputer, a new simulation model based on fundamental transport laws to describe the 4D (3D spatial co-ordinates plus time) multiphase flow dynamics of explosive eruptions. The model solves the fundamental transport equations for a multiphase mixture formed by a continuous multi-component gas phase and n solid particulate phases representative of magma fragments (such as ash, crystals, and lapilli). Numerical simulations describe the collapse of the volcanic eruption column and the propagation of pyroclastic density currents, for selected medium scale (sub-Plinian) eruptive scenarios at Vesuvius, Italy. The study shows that 4D multiphase numerical models can illuminate the non-intuitive and internal dynamics of explosive eruptions that cannot otherwise be studied by direct observation or using previous models. In particular, simulations provide crucial insights into the effects of the generation mechanism of the flows - partial collapse vs boiling-over - on their hazard potential, the complex dynamics of the collapsing column, and the influence of Mount Somma on the propagation of PDCs into the circum-Vesuvian area, one of the world's most hazardous volcanic settings.

  19. 488-4D ASH LANDFILL CLOSURE CAP HELP MODELING

    SciTech Connect

    Phifer, M.

    2014-11-17

    At the request of Area Completion Projects (ACP) in support of the 488-4D Landfill closure, the Savannah River National Laboratory (SRNL) has performed Hydrologic Evaluation of Landfill Performance (HELP) modeling of the planned 488-4D Ash Landfill closure cap to ensure that the South Carolina Department of Health and Environmental Control (SCDHEC) limit of no more than 12 inches of head on top of the barrier layer (saturated hydraulic conductivity of no more than 1.0E-05 cm/s) in association with a 25-year, 24-hour storm event is not projected to be exceeded. Based upon Weber 1998 a 25-year, 24-hour storm event at the Savannah River Site (SRS) is 6.1 inches. The results of the HELP modeling indicate that the greatest peak daily head on top of the barrier layer (i.e. geosynthetic clay liner (GCL) or high density polyethylene (HDPE) geomembrane) for any of the runs made was 0.079 inches associated with a peak daily precipitation of 6.16 inches. This is well below the SCDHEC limit of 12 inches.

  20. Atlas construction for dynamic (4D) PET using diffeomorphic transformations.

    PubMed

    Bieth, Marie; Lombaert, Hervé; Reader, Andrew J; Siddiqi, Kaleem

    2013-01-01

    A novel dynamic (4D) PET to PET image registration procedure is proposed and applied to multiple PET scans acquired with the high resolution research tomograph (HRRT), the highest resolution human brain PET scanner available in the world. By extending the recent diffeomorphic log-demons (DLD) method and applying it to multiple dynamic [11C]raclopride scans from the HRRT, an important step towards construction of a PET atlas of unprecedented quality for [11C]raclopride imaging of the human brain has been achieved. Accounting for the temporal dimension in PET data improves registration accuracy when compared to registration of 3D to 3D time-averaged PET images. The DLD approach was chosen for its ease in providing both an intensity and shape template, through iterative sequential pair-wise registrations with fast convergence. The proposed method is applicable to any PET radiotracer, providing 4D atlases with useful applications in high accuracy PET data simulations and automated PET image analysis.

  1. Positive Energy Conditions in 4D Conformal Field Theory

    NASA Astrophysics Data System (ADS)

    Farnsworth, Kara; Luty, Markus; Prilepina, Valentina

    2016-03-01

    We argue that all consistent 4D quantum field theories obey a spacetime-averaged weak energy inequality avgT00 >= - C /L4 , where L is the size of the smearing region, and C is a positive constant that depends on the theory. If this condition is violated, the theory has states that are indistinguishable from states of negative total energy by any local measurement, and we expect instabilities or other inconsistencies. We apply this condition to 4D conformal field theories, and find that it places constraints on the OPE coefficients of the theory. The constraints we find are weaker than the ``conformal collider'' constraints of Hofman and Maldacena. We speculate that there may be theories that violate the Hofman-Maldacena bounds, but satisfy our bounds. In 3D CFTs, the only constraint we find is equivalent to the positivity of 2-point function of the energy-momentum tensor, which follows from unitarity. Our calculations are performed using momentum-space Wightman functions, which are remarkably simple functions of momenta, and may be of interest in their own right.

  2. Positive energy conditions in 4D conformal field theory

    NASA Astrophysics Data System (ADS)

    Farnsworth, Kara; Luty, Markus A.; Prilepina, Valentina

    2016-10-01

    We argue that all consistent 4D quantum field theories obey a spacetime-averaged weak energy inequality < T 00> ≥ - C/L 4, where L is the size of the smearing region, and C is a positive constant that depends on the theory. If this condition is violated, the theory has states that are indistinguishable from states of negative total energy by any local measurement, and we expect instabilities or other inconsistencies. We apply this condition to 4D conformal field theories, and find that it places constraints on the OPE coefficients of the theory. The constraints we find are weaker than the "conformal collider" constraints of Hofman and Maldacena. In 3D CFTs, the only constraint we find is equivalent to the positivity of 2-point function of the energy-momentum tensor, which follows from unitarity. Our calculations are performed using momentum-space Wightman functions, which are remarkably simple functions of momenta, and may be of interest in their own right.

  3. 4D Dynamic Required Navigation Performance Final Report

    NASA Technical Reports Server (NTRS)

    Finkelsztein, Daniel M.; Sturdy, James L.; Alaverdi, Omeed; Hochwarth, Joachim K.

    2011-01-01

    New advanced four dimensional trajectory (4DT) procedures under consideration for the Next Generation Air Transportation System (NextGen) require an aircraft to precisely navigate relative to a moving reference such as another aircraft. Examples are Self-Separation for enroute operations and Interval Management for in-trail and merging operations. The current construct of Required Navigation Performance (RNP), defined for fixed-reference-frame navigation, is not sufficiently specified to be applicable to defining performance levels of such air-to-air procedures. An extension of RNP to air-to-air navigation would enable these advanced procedures to be implemented with a specified level of performance. The objective of this research effort was to propose new 4D Dynamic RNP constructs that account for the dynamic spatial and temporal nature of Interval Management and Self-Separation, develop mathematical models of the Dynamic RNP constructs, "Required Self-Separation Performance" and "Required Interval Management Performance," and to analyze the performance characteristics of these air-to-air procedures using the newly developed models. This final report summarizes the activities led by Raytheon, in collaboration with GE Aviation and SAIC, and presents the results from this research effort to expand the RNP concept to a dynamic 4D frame of reference.

  4. Nonponderomotive electron acceleration in ultrashort surface-plasmon fields

    SciTech Connect

    Racz, Peter; Dombi, Peter

    2011-12-15

    We investigate the nonponderomotive nature of ultrafast plasmonic electron acceleration in strongly decaying electromagnetic fields generated by few-cycle and single-cycle femtosecond laser pulses. We clearly identify the conditions contributing to nonponderomotive acceleration and establish fundamental scaling laws and carrier-envelope phase effects. These all-optically accelerated compact, femtosecond electron sources can be utilized in contemporary ultrafast methods.

  5. Ultrafast Optical Magnetization Modulation in Exchange Biased Ferromagnetic Layers

    NASA Astrophysics Data System (ADS)

    Ju, Ganping; Nurmikko, Arto; Farrow, R. F. C.

    1998-03-01

    We have recently shown how the use of femtosecond laser pulses can be employed to study the spin dynamics and magnetization kinetics associated with hot electrons in ferromagnetic thin films on a psec timescale. (G. Ju et al, Phys. Rev. B (Jan. 1998)) Briefly, energetic electrons are promoted by interband excitation and the relaxation process in the nonequilibrium spin system are probed via transient Kerr effect. Here we report our first observations in the MnPt/FeNi antiferromagnetic/ferromagnetic bilayer system by such an experimental approach. The exchange biasing AF layer is selective optically excited with femtosecond laser pulses, while the induced changes in the magnetic properties of the FM layer are probed in real time. We have identified two types of effects: those ( ~300ps) intermediated by ultrafast lattice heating (unpinning of the exchange bias), and those ( ~10ps)which originate from ballistic electron transport within the bilayer. The preliminary results offer some insight for the dynamics of the exchange coupling and open up possibilities for ultrafast optical switching of the exchange biased system. Research supported by NSF.

  6. Quantum Hooke's Law to classify pulse laser induced ultrafast melting

    DOE PAGES

    Hu, Hao; Ding, Hepeng; Liu, Feng

    2015-02-03

    Ultrafast crystal-to-liquid phase transition induced by femtosecond pulse laser excitation is an interesting material's behavior manifesting the complexity of light-matter interaction. There exist two types of such phase transitions: one occurs at a time scale shorter than a picosecond via a nonthermal process mediated by electron-hole plasma formation; the other at a longer time scale via a thermal melting process mediated by electron-phonon interaction. However, it remains unclear what material would undergo which process and why? Here, by exploiting the property of quantum electronic stress (QES) governed by quantum Hooke's law, we classify the transitions by two distinct classes ofmore » materials: the faster nonthermal process can only occur in materials like ice having an anomalous phase diagram characterized with dTm/dP < 0, where Tm is the melting temperature and P is pressure, above a high threshold laser fluence; while the slower thermal process may occur in all materials. Especially, the nonthermal transition is shown to be induced by the QES, acting like a negative internal pressure, which drives the crystal into a “super pressing” state to spontaneously transform into a higher-density liquid phase. Our findings significantly advance fundamental understanding of ultrafast crystal-to-liquid phase transitions, enabling quantitative a priori predictions.« less

  7. Quantum Hooke's Law to classify pulse laser induced ultrafast melting

    SciTech Connect

    Hu, Hao; Ding, Hepeng; Liu, Feng

    2015-02-03

    Ultrafast crystal-to-liquid phase transition induced by femtosecond pulse laser excitation is an interesting material's behavior manifesting the complexity of light-matter interaction. There exist two types of such phase transitions: one occurs at a time scale shorter than a picosecond via a nonthermal process mediated by electron-hole plasma formation; the other at a longer time scale via a thermal melting process mediated by electron-phonon interaction. However, it remains unclear what material would undergo which process and why? Here, by exploiting the property of quantum electronic stress (QES) governed by quantum Hooke's law, we classify the transitions by two distinct classes of materials: the faster nonthermal process can only occur in materials like ice having an anomalous phase diagram characterized with dTm/dP < 0, where Tm is the melting temperature and P is pressure, above a high threshold laser fluence; while the slower thermal process may occur in all materials. Especially, the nonthermal transition is shown to be induced by the QES, acting like a negative internal pressure, which drives the crystal into a “super pressing” state to spontaneously transform into a higher-density liquid phase. Our findings significantly advance fundamental understanding of ultrafast crystal-to-liquid phase transitions, enabling quantitative a priori predictions.

  8. 2D/4D marker-free tumor tracking using 4D CBCT as the reference image.

    PubMed

    Wang, Mengjiao; Sharp, Gregory C; Rit, Simon; Delmon, Vivien; Wang, Guangzhi

    2014-05-07

    Tumor motion caused by respiration is an important issue in image-guided radiotherapy. A 2D/4D matching method between 4D volumes derived from cone beam computed tomography (CBCT) and 2D fluoroscopic images was implemented to track the tumor motion without the use of implanted markers. In this method, firstly, 3DCBCT and phase-rebinned 4DCBCT are reconstructed from cone beam acquisition. Secondly, 4DCBCT volumes and a streak-free 3DCBCT volume are combined to improve the image quality of the digitally reconstructed radiographs (DRRs). Finally, the 2D/4D matching problem is converted into a 2D/2D matching between incoming projections and DRR images from each phase of the 4DCBCT. The diaphragm is used as a target surrogate for matching instead of using the tumor position directly. This relies on the assumption that if a patient has the same breathing phase and diaphragm position as the reference 4DCBCT, then the tumor position is the same. From the matching results, the phase information, diaphragm position and tumor position at the time of each incoming projection acquisition can be derived. The accuracy of this method was verified using 16 candidate datasets, representing lung and liver applications and one-minute and two-minute acquisitions. The criteria for the eligibility of datasets were described: 11 eligible datasets were selected to verify the accuracy of diaphragm tracking, and one eligible dataset was chosen to verify the accuracy of tumor tracking. The diaphragm matching accuracy was 1.88 ± 1.35 mm in the isocenter plane and the 2D tumor tracking accuracy was 2.13 ± 1.26 mm in the isocenter plane. These features make this method feasible for real-time marker-free tumor motion tracking purposes.

  9. Cavity-Enhanced Ultrafast Spectroscopy: Ultrafast Meets Ultrasensitive

    NASA Astrophysics Data System (ADS)

    Allison, Thomas K.; Reber, Melanie Roberts; Chen, Yuning

    2016-06-01

    Ultrafast optical spectroscopy methods, such as transient absorption spectroscopy and 2D-spectroscopy, are widely used across many disciplines. However, these techniques are typically restricted to optically thick samples, such as solids and liquid solutions. Using a frequency comb laser and optical cavities, we present a new technique for performing ultrafast optical spectroscopy with high sensitivity, enabling work in dilute gas-phase molecular beams. Resonantly enhancing the probe pulses, we demonstrate transient absorption measurements with a detection limit of ΔOD = 2 × 10-10 (1 × 10-9/√{Hz}). Resonantly enhancing the pump pulses allows us to produce a high excitation fraction at high repetition-rate, so that signals can be recorded from samples with optical densities as low as OD ≈ 10-8, or column densities < 1010 molecules/cm^2. To our knowledge, this represents a 5,000-fold improvement of the state-of-the-art. oise performance of CE-TAS. (a), Transient absorption measurements taken with reduced gas flow and perpendicular polarizations. The red dots represent the average of 60 consecutive scans taken over a 1 hour period. Black curves are every 10th scan from the data set. Inset: Zoom-in around 0.8 ps delay. Error bars represent the uncertainty in the mean. (b), The green squares show the average of the Allan deviations obtained independently for each delay point. Error bars here are the standard deviation (not the uncertainty in the mean) of this ensemble, to represent the spread in the data. The blue diamond is the average of the error bars of (a), along with their standard deviation. The grey line has a slope of -1/2 on the log-log plot, the expected slope for white noise performance

  10. Ultrafast reflectivity dynamics in the honeycomb iridates

    NASA Astrophysics Data System (ADS)

    Hinton, James; Patankar, Shreyas; Thewalt, Eric; Koralek, Jake; Ruiz, Alejandro; Lopez, Gilbert; Breznay, Nicholas; Analytis, James; Orenstein, Joseph

    2015-03-01

    The combination of strong spin orbit coupling and Mott physics in the iridium oxides produces a variety of interesting phenomena. In the A2IrO3 compounds, this is thought to give rise to spin-anisotropic magnetic interactions described by the Kitaev model. While Na2IrO3 displays simple zigzag antiferromagnetism, the complex, incommensurate spiral magnetic order observed in γ-Li2IrO3 suggests that Kitaev exchange is the dominant spin interaction in this system. In this work, we performed ultrafast pump-probe reflectivity measurements on single crystals of Na2IrO3 and γ-Li2IrO3 using nJ pulses at 1.5 eV photon energy. At high temperatures, we observe a reflectivity transient corresponding to electronic heating and excitation across the Mott gap which is isotropic with respect to probe polarization. In γ-Li2IrO3 , a small anisotropy emerges upon cooling close to the Neél transition at 38 K, followed by an abrupt onset of a long lived, highly anisotropic photo-induced increase in the reflectivity at TN. The temperature dependent dynamics of this signal indicate that it corresponds to non-thermal destruction of the magnetic order. Although similar reflectivity dynamics are observed at low temperature in Na2IrO3, there are no clear features related to the Neél transition at 16 K.

  11. Technology and applications of ultrafast fiber lasers

    NASA Astrophysics Data System (ADS)

    Lang, Marion; Hellerer, Thomas; Stuhler, Juergen

    2012-03-01

    We briefly review the key technology of modern fiber based femtosecond laser sources summarizing advantages and disadvantages of different mode-locking solutions. A description of possible extensions of a FemtoFiber-type modelocked Er-doped fiber laser oscillator (1560 nm) reveals the flexibility with respect to wavelength coverage (488 nm .. 2200 nm) and pulse duration (10 fs .. 10 ps). The resulting FemtoFiber family and its versions for instrument integration allow one to use these state-of-the-art light sources in many important applications, e.g. THz spectroscopy and microscopy. We show that, depending on the fiber laser model and the THz emitter, THz radiation can be produced with 4-10 THz bandwidth and detected with up to 60 dB signal-to-noise ratio (SNR). Electronically controlled optical scanning (ECOPS) - a unique method for fast, precise and comfortable sampling of the THz pulse or other pump-probe experiments - is described and recommended for efficient data acquisition. As examples for modern microscopy with ultrafast fiber lasers we present results of two-photon fluorescence, coherent microscopy techniques (SHG/THG/CARS) and fluorescence lifetime imaging (FLIM).

  12. Technology and applications of ultrafast fiber lasers

    NASA Astrophysics Data System (ADS)

    Lang, Marion; Hellerer, Thomas; Stuhler, Juergen

    2011-11-01

    We briefly review the key technology of modern fiber based femtosecond laser sources summarizing advantages and disadvantages of different mode-locking solutions. A description of possible extensions of a FemtoFiber-type modelocked Er-doped fiber laser oscillator (1560 nm) reveals the flexibility with respect to wavelength coverage (488 nm .. 2200 nm) and pulse duration (10 fs .. 10 ps). The resulting FemtoFiber family and its versions for instrument integration allow one to use these state-of-the-art light sources in many important applications, e.g. THz spectroscopy and microscopy. We show that, depending on the fiber laser model and the THz emitter, THz radiation can be produced with 4-10 THz bandwidth and detected with up to 60 dB signal-to-noise ratio (SNR). Electronically controlled optical scanning (ECOPS) - a unique method for fast, precise and comfortable sampling of the THz pulse or other pump-probe experiments - is described and recommended for efficient data acquisition. As examples for modern microscopy with ultrafast fiber lasers we present results of two-photon fluorescence, coherent microscopy techniques (SHG/THG/CARS) and fluorescence lifetime imaging (FLIM).

  13. Unraveling ultrafast dynamics in photoexcited aniline.

    PubMed

    Roberts, Gareth M; Williams, Craig A; Young, Jamie D; Ullrich, Susanne; Paterson, Martin J; Stavros, Vasilios G

    2012-08-01

    A combination of ultrafast time-resolved velocity map imaging (TR-VMI) methods and complete active space self-consistent field (CASSCF) ab initio calculations are implemented to investigate the electronic excited-state dynamics in aniline (aminobenzene), with a perspective for modeling (1)πσ* mediated dynamics along the amino moiety in the purine derived DNA bases. This synergy between experiment and theory has enabled a comprehensive picture of the photochemical pathways/conical intersections (CIs), which govern the dynamics in aniline, to be established over a wide range of excitation wavelengths. TR-VMI studies following excitation to the lowest-lying (1)ππ* state (1(1)ππ*) with a broadband femtosecond laser pulse, centered at wavelengths longer than 250 nm (4.97 eV), do not generate any measurable signature for (1)πσ* driven N-H bond fission on the amino group. Between wavelengths of 250 and >240 nm (<5.17 eV), coupling from 1(1)ππ* onto the (1)πσ* state at a 1(1)ππ*/(1)πσ* CI facilitates ultrafast nonadiabatic N-H bond fission through a (1)πσ*/S(0) CI in <1 ps, a notion supported by CASSCF results. For excitation to the higher lying 2(1)ππ* state, calculations reveal a near barrierless pathway for CI coupling between the 2(1)ππ* and 1(1)ππ* states, enabling the excited-state population to evolve through a rapid sequential 2(1)ππ* → 1(1)ππ* → (1)πσ* → N-H fission mechanism, which we observe to take place in 155 ± 30 fs at 240 nm. We also postulate that an analogous cascade of CI couplings facilitates N-H bond scission along the (1)πσ* state in 170 ± 20 fs, following 200 nm (6.21 eV) excitation to the 3(1)ππ* surface. Particularly illuminating is the fact that a number of the CASSCF calculated CI geometries in aniline bear an exceptional resemblance with previously calculated CIs and potential energy profiles along the amino moiety in guanine, strongly suggesting that the results here may act as an excellent grounding

  14. Ultrafast electrical spectrum analyzer based on all-optical Fourier transform and temporal magnification.

    PubMed

    Duan, Yuhua; Chen, Liao; Zhou, Haidong; Zhou, Xi; Zhang, Chi; Zhang, Xinliang

    2017-04-03

    Real-time electrical spectrum analysis is of great significance for applications involving radio astronomy and electronic warfare, e.g. the dynamic spectrum monitoring of outer space signal, and the instantaneous capture of frequency from other electronic systems. However, conventional electrical spectrum analyzer (ESA) has limited operation speed and observation bandwidth due to the electronic bottleneck. Therefore, a variety of photonics-assisted methods have been extensively explored due to the bandwidth advantage of the optical domain. Alternatively, we proposed and experimentally demonstrated an ultrafast ESA based on all-optical Fourier transform and temporal magnification in this paper. The radio-frequency (RF) signal under test is temporally multiplexed to the spectrum of an ultrashort pulse, thus the frequency information is converted to the time axis. Moreover, since the bandwidth of this ultrashort pulse is far beyond that of the state-of-the-art photo-detector, a temporal magnification system is applied to stretch the time axis, and capture the RF spectrum with 1-GHz resolution. The observation bandwidth of this ultrafast ESA is over 20 GHz, limited by that of the electro-optic modulator. Since all the signal processing is in the optical domain, the acquisition frame rate can be as high as 50 MHz. This ultrafast ESA scheme can be further improved with better dispersive engineering, and is promising for some ultrafast spectral information acquisition applications.

  15. Ultrafast Beam Switching Using Coupled VCSELs

    NASA Technical Reports Server (NTRS)

    Ning, Cun-Zheng; Goorjian, Peter

    2001-01-01

    We propose a new approach to performing ultrafast beam switching using two coupled Vertical-Cavity Surface-Emitting Lasers (VCSELs). The strategy is demonstrated by numerical simulation, showing a beam switching of 10 deg at 42 GHz.

  16. SU-E-T-202: Comparison of 4D-Measurement-Guided Dose Reconstructions (MGDR) with COMPASS and OCTAVIUS 4D System

    SciTech Connect

    Leung, R; Wong, M; Lee, V; Law, G; Lee, K; Tung, S; Chan, M; Blanck, O

    2015-06-15

    Purpose: To cross-validate the MGDR of COMPASS (IBA dosimetry, GmbH, Germany) and OCTAVIUS 4D system (PTW, Freiburg, Germany). Methods: Volumetric-modulated arc plans (5 head-and-neck and 3 prostate) collapsed to 40° gantry on the OCTAVIUS 4D phantom in QA mode on Monaco v5.0 (Elekta, CMS, Maryland Heights, MO) were delivered on a Elekta Agility linac. This study was divided into two parts: (1) error-free measurements by gantry-mounted EvolutionXX 2D array were reconstructed in COMPASS (IBA dosimetry, GmbH, Germany), and by OCTAVIUS 1500 array in Versoft v6.1 (PTW, Freiburg, Germany) to obtain the 3D doses (COM4D and OCTA4D). COM4D and OCTA4D were compared to the raw measurement (OCTA3D) at the same detector plane for which OCTAVIUS 1500 was perpendicular to 0° gantry axis while the plans were delivered at gantry 40°; (2) beam steering errors of energy (Hump=-2%) and symmetry (2T=+2%) were introduced during the delivery of 5 plans to compare the MGDR doses COM4D-Hump (COM4D-2T), OCTA4D-Hump (OCTA4D-2T), with raw doses OCTA3D-Hump (OCTA3D-2T) and with OCTA3D to assess the error reconstruction and detection ability of MGDR tools. All comparisons used Υ-criteria of 2%(local dose)/2mm and 3%/3mm. Results: Averaged Υ passing rates were 85% and 96% for COM4D,and 94% and 99% for OCTA4D at 2%/2mm and 3%/3mm criteria respectively. For error reconstruction, COM4D-Hump (COM4D-2T) showed 81% (93%) at 2%/2mm and 94% (98%) at 3%/3mm, while OCTA4D-Hump (OCTA4D-2T) showed 96% (96%) at 2%/2mm and 99% (99%) at 3%/3mm. For error detection, OCTA3D doses were compared to COM4D-Hump (COM4D-2T) showing Υ passing rates of 93% (93%) at 2%/2mm and 98% (98%), and to OCTA4D-Hump (OCTA4D -2T) showing 94% (99%) at 2%/2mm and 81% (96%) at 3%/3mm, respectively. Conclusion: OCTAVIUS MGDR showed better agreement to raw measurements in both error- and error-free comparisons. COMPASS MGDR deviated from the raw measurements possibly owing to beam modeling uncertainty.

  17. Toward 4D Nanoprinting with Tip-Induced Organic Surface Reactions.

    PubMed

    Carbonell, Carlos; Braunschweig, Adam B

    2017-02-21

    Future nanomanufacturing tools will prepare organic materials with complex four-dimensional (4D) structure, where the position (x, y, z) and chemical composition within a volume is controlled with sub-1 μm spatial resolution. Such tools could produce substrates that mimic biological interfaces, like the cell surface or the extracellular matrix, whose topology and chemical complexity combine to direct some of the most sophisticated biological events. The control of organic materials at the nanoscale-level of spatial resolution could revolutionize the assembly of next generation optical and electronic devices or substrates for tissue engineering or enable fundamental biological or material science investigations. Organic chemistry provides the requisite control over the orientation and position of matter within a nanoscale reference frame through the formation of new covalent bonds. Several challenges however preclude the integration of organic chemistry with conventional nanomanufacturing approaches, namely most nanolithography platforms would denature or destroy delicate organic and biologically active matter, confirming covalent bond formation at interfaces remains difficult, and finally, only a small handful of the reactions used to transform molecules in solution have been validated on surfaces. Thus, entirely new approaches, where organic transformations and spatial control are considered equally important contributors, are needed to create 4D organic nanoprinting platforms. This Account describes efforts from our group to reconcile nanolithography, and specifically massively parallel scanning probe lithography (SPL), with organic chemistry to further the goal of 4D organic nanoprinting. Massively parallel SPL involves arrays of elastomeric pyramids mounted onto piezoelectric actuators, and creates patterns with feature diameters below 50 nm by using the pyramidal tips for either the direct deposition of ink or the localized delivery of energy to a surface

  18. An ultrafast carbon nanotube terahertz polarisation modulator

    SciTech Connect

    Docherty, Callum J.; Stranks, Samuel D.; Habisreutinger, Severin N.; Joyce, Hannah J.; Herz, Laura M.; Nicholas, Robin J.; Johnston, Michael B.

    2014-05-28

    We demonstrate ultrafast modulation of terahertz radiation by unaligned optically pumped single-walled carbon nanotubes. Photoexcitation by an ultrafast optical pump pulse induces transient terahertz absorption in nanowires aligned parallel to the optical pump. By controlling the polarisation of the optical pump, we show that terahertz polarisation and modulation can be tuned, allowing sub-picosecond modulation of terahertz radiation. Such speeds suggest potential for semiconductor nanowire devices in terahertz communication technologies.

  19. Ultrafast dynamics during the photoinduced phase transition in VO2

    NASA Astrophysics Data System (ADS)

    Wegkamp, Daniel; Stähler, Julia

    2015-12-01

    The phase transition of VO2 from a monoclinic insulator to a rutile metal, which occurs thermally at TC = 340 K, can also be driven by strong photoexcitation. The ultrafast dynamics during this photoinduced phase transition (PIPT) have attracted great scientific attention for decades, as this approach promises to answer the question of whether the insulator-to-metal (IMT) transition is caused by electronic or crystallographic processes through disentanglement of the different contributions in the time domain. We review our recent results achieved by femtosecond time-resolved photoelectron, optical, and coherent phonon spectroscopy and discuss them within the framework of a selection of latest, complementary studies of the ultrafast PIPT in VO2. We show that the population change of electrons and holes caused by photoexcitation launches a highly non-equilibrium plasma phase characterized by enhanced screening due to quasi-free carriers and followed by two branches of non-equilibrium dynamics: (i) an instantaneous (within the time resolution) collapse of the insulating gap that precedes charge carrier relaxation and significant ionic motion and (ii) an instantaneous lattice potential symmetry change that represents the onset of the crystallographic phase transition through ionic motion on longer timescales. We discuss the interconnection between these two non-thermal pathways with particular focus on the meaning of the critical fluence of the PIPT in different types of experiments. Based on this, we conclude that the PIPT threshold identified in optical experiments is most probably determined by the excitation density required to drive the lattice potential change rather than the IMT. These considerations suggest that the IMT can be driven by weaker excitation, predicting a transiently metallic, monoclinic state of VO2 that is not stabilized by the non-thermal structural transition and, thus, decays on ultrafast timescales.

  20. Ultrafast Nonlinear Plasmonics of Single Nano-Objects

    NASA Astrophysics Data System (ADS)

    Del Fatti, Natalia

    Investigating, understanding and modeling the physical properties of nano-objects are intense fields of research. Of particular interest are metal-based nano-objects, where their morphology and environment dependent surface plasmon resonances (SPR) have been extensively exploited to design new optical systems. As a SPR is associated to electromagnetic local field enhancement in the nano-object, it also leads to enhancement of its optical nonlinearity, opening many possibilities for investigating fundamental processes at nanoscale. Most of these studies were performed on large ensembles of nano-objects, providing mean information which impedes detailed comparison between experimental data and theoretical models. With the advance of single nanoparticle spectroscopy methods, the linear and nonlinear responses of a single nano-object can now be addressed, which, associated to determination of its morphology by electron microscopy, opens the way to their quantitative modeling. In this context we discuss experimental and theoretical investigations of the ultrafast response of individual model nano-objects, either formed by a single particle (gold nanorod) or by two particles at a nanometric distance (gold-silver nano-dimer). Results obtained in gold nanorods are in excellent quantitative agreement with a model computing the change of the metal dielectric function due to ultrafast electron heating and relaxation. This shows that the nonlinear response of a metal nano-object can be fully described as that of the bulk metal enhanced by plasmonic effects. Extension of these studies to more complex nano-objects, as nano-dimers formed by two different materials, permits analysis of the impact of their interaction. We demonstrate here the existence of Fano effect in the absorption of a single Ag-Au dimer, experimentally proving previous theoretical predictions. Furthermore, we show that ultrafast pump-probe nonlinear spectroscopy permits to selectively address at nanoscale only

  1. 4D XCAT phantom for multimodality imaging research

    SciTech Connect

    Segars, W. P.; Sturgeon, G.; Mendonca, S.; Grimes, Jason; Tsui, B. M. W.

    2010-09-15

    Purpose: The authors develop the 4D extended cardiac-torso (XCAT) phantom for multimodality imaging research. Methods: Highly detailed whole-body anatomies for the adult male and female were defined in the XCAT using nonuniform rational B-spline (NURBS) and subdivision surfaces based on segmentation of the Visible Male and Female anatomical datasets from the National Library of Medicine as well as patient datasets. Using the flexibility of these surfaces, the Visible Human anatomies were transformed to match body measurements and organ volumes for a 50th percentile (height and weight) male and female. The desired body measurements for the models were obtained using the PEOPLESIZE program that contains anthropometric dimensions categorized from 1st to the 99th percentile for US adults. The desired organ volumes were determined from ICRP Publication 89 [ICRP, ''Basic anatomical and physiological data for use in radiological protection: reference values,'' ICRP Publication 89 (International Commission on Radiological Protection, New York, NY, 2002)]. The male and female anatomies serve as standard templates upon which anatomical variations may be modeled in the XCAT through user-defined parameters. Parametrized models for the cardiac and respiratory motions were also incorporated into the XCAT based on high-resolution cardiac- and respiratory-gated multislice CT data. To demonstrate the usefulness of the phantom, the authors show example simulation studies in PET, SPECT, and CT using publicly available simulation packages. Results: As demonstrated in the pilot studies, the 4D XCAT (which includes thousands of anatomical structures) can produce realistic imaging data when combined with accurate models of the imaging process. With the flexibility of the NURBS surface primitives, any number of different anatomies, cardiac or respiratory motions or patterns, and spatial resolutions can be simulated to perform imaging research. Conclusions: With the ability to produce

  2. 4D Light Field Imaging System Using Programmable Aperture

    NASA Technical Reports Server (NTRS)

    Bae, Youngsam

    2012-01-01

    Complete depth information can be extracted from analyzing all angles of light rays emanated from a source. However, this angular information is lost in a typical 2D imaging system. In order to record this information, a standard stereo imaging system uses two cameras to obtain information from two view angles. Sometimes, more cameras are used to obtain information from more angles. However, a 4D light field imaging technique can achieve this multiple-camera effect through a single-lens camera. Two methods are available for this: one using a microlens array, and the other using a moving aperture. The moving-aperture method can obtain more complete stereo information. The existing literature suggests a modified liquid crystal panel [LC (liquid crystal) panel, similar to ones commonly used in the display industry] to achieve a moving aperture. However, LC panels cannot withstand harsh environments and are not qualified for spaceflight. In this regard, different hardware is proposed for the moving aperture. A digital micromirror device (DMD) will replace the liquid crystal. This will be qualified for harsh environments for the 4D light field imaging. This will enable an imager to record near-complete stereo information. The approach to building a proof-ofconcept is using existing, or slightly modified, off-the-shelf components. An SLR (single-lens reflex) lens system, which typically has a large aperture for fast imaging, will be modified. The lens system will be arranged so that DMD can be integrated. The shape of aperture will be programmed for single-viewpoint imaging, multiple-viewpoint imaging, and coded aperture imaging. The novelty lies in using a DMD instead of a LC panel to move the apertures for 4D light field imaging. The DMD uses reflecting mirrors, so any light transmission lost (which would be expected from the LC panel) will be minimal. Also, the MEMS-based DMD can withstand higher temperature and pressure fluctuation than a LC panel can. Robotics need

  3. QED Corrections to the 4p - 4d Transition Energies of Copperlike Heavy Ions

    SciTech Connect

    Chen, M H; Cheng, K T; Johnson, W R; Sapirstein, J

    2006-08-21

    Quantum electrodynamic (QED) corrections to 4p-4d transition energies of several copper-like ions with Z = 70-92 are calculated non-perturbatively in strong external fields to all orders in binding corrections. Dirac-Kohn-Sham potentials are used to account for screening and core-relaxation effects. For the 4p{sub 1/2}-4d{sub 3/2} transition in copperlike bismuth, thorium and uranium, results are in good agreement with empirical QED corrections deduced from differences between transition energies obtained from recent high-precision electron-beam ion-trap (EBIT) measurements and those calculated with the relativistic many-body perturbation theory (RMBPT). These comparisons provide sensitive tests of QED corrections for high angular momentum states in many-electron heavy ions and illustrate the importance of core-relaxation corrections. Comparisons are also made with other theories and with experiment on the 4s-4p transition energies of high-Z Cu-like ions as accuracy checks of the present RMBPT and QED calculations.

  4. QED corrections to the 4p-4d transition energies of copperlike heavy ions

    SciTech Connect

    Chen, M. H.; Cheng, K. T.; Johnson, W. R.; Sapirstein, J.

    2006-10-15

    Quantum electrodynamic (QED) corrections to 4p-4d transition energies of several copperlike ions with Z=70-92 are calculated nonperturbatively in strong external fields to all orders in binding corrections. Dirac-Kohn-Sham potentials are used to account for screening and core-relaxation effects. For the 4p{sub 1/2}-4d{sub 3/2} transition in copperlike bismuth, thorium, and uranium, results are in good agreement with empirical QED corrections deduced from differences between transition energies obtained from recent high-precision electron-beam ion-trap measurements and those calculated with the relativistic many-body perturbation theory (RMBPT). These comparisons provide sensitive tests of QED corrections for high-angular-momentum states in many-electron heavy ions and illustrate the importance of core-relaxation corrections. Comparisons are also made with other theories and with experiments on the 4s-4p transition energies of high-Z Cu-like ions as accuracy checks of the present RMBPT and QED calculations.

  5. Steady-state benchmarks of DK4D: A time-dependent, axisymmetric drift-kinetic equation solver

    SciTech Connect

    Lyons, B. C.; Jardin, S. C.; Ramos, J. J.

    2015-05-15

    The DK4D code has been written to solve a set of time-dependent, axisymmetric, finite-Larmor-radius drift-kinetic equations (DKEs) for the non-Maxwellian part of the electron and ion distribution functions using the full, linearized Fokker–Planck–Landau collision operator. The plasma is assumed to be in the low- to finite-collisionality regime, as is found in the cores of modern and future magnetic confinement fusion experiments. Each DKE is formulated such that the perturbed distribution function carries no net density, parallel momentum, or kinetic energy. Rather, these quantities are contained within the background Maxwellians and would be evolved by an appropriate set of extended magnetohydrodynamic (MHD) equations. This formulation allows for straight-forward coupling of DK4D to existing extended MHD time evolution codes. DK4D uses a mix of implicit and explicit temporal representations and finite element and spectral spatial representations. These, along with other computational methods used, are discussed extensively. Steady-state benchmarks are then presented comparing the results of DK4D to expected analytic results at low collisionality, qualitatively, and to the Sauter analytic fits for the neoclassical conductivity and bootstrap current, quantitatively. These benchmarks confirm that DK4D is capable of solving for the correct, gyroaveraged distribution function in stationary magnetic equilibria. Furthermore, the results presented demonstrate how the exact drift-kinetic solution varies with collisionality as a function of the magnetic moment and the poloidal angle.

  6. 4D simulation of explosive eruption dynamics at Vesuvius

    NASA Astrophysics Data System (ADS)

    Neri, Augusto; Esposti Ongaro, Tomaso; Menconi, Gianluca; De'Michieli Vitturi, Mattia; Cavazzoni, Carlo; Erbacci, Giovanni; Baxter, Peter J.

    2007-02-01

    We applied a new simulation model, based on multiphase transport laws, to describe the 4D (3D spatial coordinates plus time) dynamics of explosive eruptions. Numerical experiments, carried out on a parallel supercomputer, describe the collapse of the volcanic eruption column and the propagation of pyroclastic density currents (PDCs), for selected medium scale (sub-Plinian) eruptive scenarios at Vesuvius, Italy. Simulations provide crucial insights into the effects of the generation mechanism of the flows - partial collapse vs boiling-over - on their evolution and hazard potential, the unstable dynamics of the fountain, and the influence of Mount Somma on the propagation of PDCs into the circum-Vesuvian area, one of the world's most hazardous volcanic settings. Results also show that it is possible to characterize the volcanic column behavior in terms of percentage of the mass of pyroclasts collapsed to the ground and how this parameter strongly influences the dynamics and hazard of the associated PDCs.

  7. Chaos in a 4D dissipative nonlinear fermionic model

    NASA Astrophysics Data System (ADS)

    Aydogmus, Fatma

    2015-12-01

    Gursey Model is the only possible 4D conformally invariant pure fermionic model with a nonlinear self-coupled spinor term. It has been assumed to be similar to the Heisenberg's nonlinear generalization of Dirac's equation, as a possible basis for a unitary description of elementary particles. Gursey Model admits particle-like solutions for the derived classical field equations and these solutions are instantonic in character. In this paper, the dynamical nature of damped and forced Gursey Nonlinear Differential Equations System (GNDES) are studied in order to get more information on spinor type instantons. Bifurcation and chaos in the system are observed by constructing the bifurcation diagrams and Poincaré sections. Lyapunov exponent and power spectrum graphs of GNDES are also constructed to characterize the chaotic behavior.

  8. Deformable registration of 4D computed tomography data.

    PubMed

    Rietzel, Eike; Chen, George T Y

    2006-11-01

    Four-dimensional radiotherapy requires deformable registration to track delivered dose across varying anatomical states. Deformable registration based on B-splines was implemented to register 4D computed tomography data to a reference respiratory phase. To assess registration performance, anatomical landmarks were selected across ten respiratory phases in five patients. These point landmarks were transformed according to global registration parameters between different respiratory phases. Registration uncertainties were computed by subtraction of transformed and reference landmark positions. The selection of appropriate registration masks to separate independently moving anatomical subunits is crucial to registration performance. The average registration error for five landmarks for each of five patients was 2.1 mm. This level of accuracy is acceptable for most radiotherapy applications.

  9. Probabilistic 4D blood flow tracking and uncertainty estimation.

    PubMed

    Friman, Ola; Hennemuth, Anja; Harloff, Andreas; Bock, Jelena; Markl, Michael; Peitgen, Heinz-Otto

    2011-10-01

    Phase-Contrast (PC) MRI utilizes signal phase shifts resulting from moving spins to measure tissue motion and blood flow. Time-resolved 4D vector fields representing the motion or flow can be derived from the acquired PC MRI images. In cardiovascular PC MRI applications, visualization techniques such as vector glyphs, streamlines, and particle traces are commonly employed for depicting the blood flow. Whereas these techniques indeed provide useful diagnostic information, uncertainty due to noise in the PC-MRI measurements is ignored, which may lend the results a false sense of precision. In this work, the statistical properties of PC MRI flow measurements are investigated and a probabilistic flow tracking method based on sequential Monte Carlo sampling is devised to calculate flow uncertainty maps. The theoretical derivations are validated using simulated data and a number of real PC MRI data sets of the aorta and carotid arteries are used to demonstrate the flow uncertainty mapping technique.

  10. 4D GPR Experiments--Towards the Virtual Lysimeter

    NASA Astrophysics Data System (ADS)

    Grasmueck, M.; Viggiano, D. A.; Day-Lewis, F. D.; Drasdis, J. B.; Kruse, S. E.; Or, D.

    2006-05-01

    In-situ monitoring of infiltration, water flow and retention in the vadose zone currently rely primarily on invasive methods, which irreversibly disturb original soil structure and alter its hydrologic behavior in the vicinity of the measurement. For example, use of lysimeters requires extraction and repacking of soil samples, and time- domain reflectometry (TDR) requires insertion of probes into the soil profile. This study investigates the use of repeated high-density 3D ground penetrating radar surveys (also known as 4D GPR) as a non-invasive alternative for detailed visualization and quantification of water flow in the vadose zone. Evaluation of the 4D GPR method was based on a series of controlled point-source water injection experiments into undisturbed beach sand deposits at Crandon Park in Miami, Florida. The goal of the GPR surveys was to image the shape and evolution of a wet-bulb as it propagates from the injection points (~0.5 m) towards the water table at 2.2 m depth. The experimental design was guided by predictive modeling using Hydrus 2D and finite-difference GPR waveform codes. Input parameters for the modeling were derived from hydrologic and electromagnetic characterization of representative sand samples. Guided by modeling results, we injected 30 to 40 liters of tap water through plastic-cased boreholes with slotted bottom sections (0.1 m) located 0.4 to 0.6 m below the surface. During and after injection, an area of 25 m2 was surveyed every 20 minutes using 250 and 500 MHz antennas with a grid spacing of 0.05 x 0.025 m. A total of 20 3D GPR surveys were completed over 3 infiltration sites. To confirm wet-bulb shapes measured by GPR, we injected 2 liters of "brilliant blue" dye (~100 mg/l) along with a saline water tracer towards the end of one experiment. After completion of GPR scanning, a trench was excavated to examine the distribution of the saltwater and dye using TDR and visual inspection, respectively. Preliminary analysis of the 4D GPR

  11. 4D fast tracking for experiments at high luminosity LHC

    NASA Astrophysics Data System (ADS)

    Neri, N.; Cardini, A.; Calabrese, R.; Fiorini, M.; Luppi, E.; Marconi, U.; Petruzzo, M.

    2016-11-01

    The full exploitation of the physics potential of the high luminosity LHC is a big challenge that requires new instrumentation and innovative solutions. We present here a conceptual design and simulation studies of a fast timing pixel detector with embedded real-time tracking capabilities. The system is conceived to operate at 40 MHz event rate and to reconstruct tracks in real-time, using precise space and time 4D information of the hit, for fast trigger decisions. This work is part of an R&D project aimed at building an innovative tracking detector with superior time (10 ps) and position (10 μm) resolutions to be used in very harsh radiation environments, for the ultimate flavour physics experiment at the high luminosity phase of the LHC.

  12. Induction spectrometry using an ultrafast hollow-cored toroidal-coil (HTC) detector

    NASA Astrophysics Data System (ADS)

    Arbelo, Yunieski; Bleiner, Davide

    2017-02-01

    Ultrafast photoelectron and photoion spectroscopy (as well as their combination known as "coincidence spectroscopy") utilizes detectors based on different electron multipliers such as microchannel plates or single-channel electron multipliers. These detectors have a few important limitations such as fast-signal distortion (low pass operation), mutually exclusive positive or negative mode, dead time, and requirement of trigger. A high-pass induction detector, based on a hollow-cored toroidal coil, was developed that overcomes the above-mentioned limitations. The frequency-dispersive response and linearity of different configurations were analyzed. It is shown that the response is enhanced for ultrafast electron signals, dependent on construction parameters, thus offering response flexibility by design. Kinetic energy distributions of pseudospark-induced electron pulses are characterized in order to validate the capabilities in real applications.

  13. Parallel Wavefront Analysis for a 4D Interferometer

    NASA Technical Reports Server (NTRS)

    Rao, Shanti R.

    2011-01-01

    This software provides a programming interface for automating data collection with a PhaseCam interferometer from 4D Technology, and distributing the image-processing algorithm across a cluster of general-purpose computers. Multiple instances of 4Sight (4D Technology s proprietary software) run on a networked cluster of computers. Each connects to a single server (the controller) and waits for instructions. The controller directs the interferometer to several images, then assigns each image to a different computer for processing. When the image processing is finished, the server directs one of the computers to collate and combine the processed images, saving the resulting measurement in a file on a disk. The available software captures approximately 100 images and analyzes them immediately. This software separates the capture and analysis processes, so that analysis can be done at a different time and faster by running the algorithm in parallel across several processors. The PhaseCam family of interferometers can measure an optical system in milliseconds, but it takes many seconds to process the data so that it is usable. In characterizing an adaptive optics system, like the next generation of astronomical observatories, thousands of measurements are required, and the processing time quickly becomes excessive. A programming interface distributes data processing for a PhaseCam interferometer across a Windows computing cluster. A scriptable controller program coordinates data acquisition from the interferometer, storage on networked hard disks, and parallel processing. Idle time of the interferometer is minimized. This architecture is implemented in Python and JavaScript, and may be altered to fit a customer s needs.

  14. An updated version of the Motion4D-library

    NASA Astrophysics Data System (ADS)

    Müller, Thomas; Grave, Frank

    2010-03-01

    We present an updated version of the Motion4D-library that can be used for the newly developed GeodesicViewer application. New version program summaryProgram title: Motion4D-library Catalogue identifier: AEEX_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEEX_v2_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 153 757 No. of bytes in distributed program, including test data, etc.: 5 178 439 Distribution format: tar.gz Programming language: C++ Computer: All platforms with a C++ compiler Operating system: Linux, Unix, Windows RAM: 31 MBytes Catalogue identifier of previous version: AEEX_v1_0 Journal reference of previous version: Comput. Phys. Comm. 180 (2009) 2355 Classification: 1.5 External routines: Gnu Scientific Library (GSL) ( http://www.gnu.org/software/gsl/) Does the new version supersede the previous version?: Yes Nature of problem: Solve geodesic equation, parallel and Fermi-Walker transport in four-dimensional Lorentzian spacetimes. Solution method: Integration of ordinary differential equations. Reasons for new version: To be applicable for the GeodesicViewer (accepted for publication in Comput. Phys. Comm. (COMPHY) 3941, doi:10.1016/j.cpc.2009.10.010 [program AEFP_v1_0]), there were several minor adjustments to be done. Summary of revisions:Calculation of embedding diagrams are improved. Physical units can be used for some metrics. Tests for the constraint equation within the metric classes are slightly modified. New metrics: AlcubierreWarp, GoedelScaled, GoedelScaledCart, Kasner. Running time: The test runs provided with the distribution require only a few seconds to run.

  15. Mapping motion from 4D-MRI to 3D-CT for use in 4D dose calculations: A technical feasibility study

    SciTech Connect

    Boye, Dirk; Lomax, Tony; Knopf, Antje

    2013-06-15

    Purpose: Target sites affected by organ motion require a time resolved (4D) dose calculation. Typical 4D dose calculations use 4D-CT as a basis. Unfortunately, 4D-CT images have the disadvantage of being a 'snap-shot' of the motion during acquisition and of assuming regularity of breathing. In addition, 4D-CT acquisitions involve a substantial additional dose burden to the patient making many, repeated 4D-CT acquisitions undesirable. Here the authors test the feasibility of an alternative approach to generate patient specific 4D-CT data sets. Methods: In this approach motion information is extracted from 4D-MRI. Simulated 4D-CT data sets [which the authors call 4D-CT(MRI)] are created by warping extracted deformation fields to a static 3D-CT data set. The employment of 4D-MRI sequences for this has the advantage that no assumptions on breathing regularity are made, irregularities in breathing can be studied and, if necessary, many repeat imaging studies (and consequently simulated 4D-CT data sets) can be performed on patients and/or volunteers. The accuracy of 4D-CT(MRI)s has been validated by 4D proton dose calculations. Our 4D dose algorithm takes into account displacements as well as deformations on the originating 4D-CT/4D-CT(MRI) by calculating the dose of each pencil beam based on an individual time stamp of when that pencil beam is applied. According to corresponding displacement and density-variation-maps the position and the water equivalent range of the dose grid points is adjusted at each time instance. Results: 4D dose distributions, using 4D-CT(MRI) data sets as input were compared to results based on a reference conventional 4D-CT data set capturing similar motion characteristics. Almost identical 4D dose distributions could be achieved, even though scanned proton beams are very sensitive to small differences in the patient geometry. In addition, 4D dose calculations have been performed on the same patient, but using 4D-CT(MRI) data sets based on

  16. Experimental and Ab Initio Ultrafast Carrier Dynamics in Plasmonic Nanoparticles

    NASA Astrophysics Data System (ADS)

    Brown, Ana M.; Sundararaman, Ravishankar; Narang, Prineha; Schwartzberg, Adam M.; Goddard, William A.; Atwater, Harry A.

    2017-02-01

    Ultrafast pump-probe measurements of plasmonic nanostructures probe the nonequilibrium behavior of excited carriers, which involves several competing effects obscured in typical empirical analyses. Here we present pump-probe measurements of plasmonic nanoparticles along with a complete theoretical description based on first-principles calculations of carrier dynamics and optical response, free of any fitting parameters. We account for detailed electronic-structure effects in the density of states, excited carrier distributions, electron-phonon coupling, and dielectric functions that allow us to avoid effective electron temperature approximations. Using this calculation method, we obtain excellent quantitative agreement with spectral and temporal features in transient-absorption measurements. In both our experiments and calculations, we identify the two major contributions of the initial response with distinct signatures: short-lived highly nonthermal excited carriers and longer-lived thermalizing carriers.

  17. Investigation on the effect of exposure time on scintillator afterglow for ultra-fast tomography acquisition

    NASA Astrophysics Data System (ADS)

    Zefreh, K. Z.; Welford, F. M.; Sijbers, Jan

    2016-12-01

    Thanks to the ultra-fast endstation of the TOMCAT beamline, it is possible to do a tomographic scan with a sub-second temporal resolution which allows following dynamic processes in 4D (3D space + time). This ultra- high-rate tomography acquisition, exploiting the distinctive peculiarities of synchrotron radiation, provides nondestructive investigation of many dynamic processes which were not possible in the past. For example a continuous tensile test has been conducted recently in-situ for the first time with a frequency of 20 tomograms per second (20 Hz acquisition frequency). In the ultra-fast endstation a scintillator is used to convert X-ray to visible photons that can be detected by the camera. However, this conversion is not ideal and the scintillator response decays exponentially with afterglow. Afterglow can cause resolution degradation and artifacts (such as ring and band) especially with high rotation speed. On the other hand, to achieve a higher scan speed, thicker scintillators are more common because they result in higher emission intensities that can compensate the short exposure time in fast scans. However, the resolution deteriorates as the scintillator's thickness increases and thicker scintillators show higher afterglow. Performing many ultra-fast scans at the TOMCAT beamline with different acquisition rate, we demonstrate how the exposure time effects on the projection data and reconstructed images. Using two different thicknesses of LAG scintillator we also investigate the afterglow artifacts for different acquisition rate and exposure time.

  18. Advanced logic gates for ultrafast network interchanges

    NASA Astrophysics Data System (ADS)

    Islam, Mohammed N.

    1995-08-01

    By overcoming speed bottlenecks from electronic switching as well as optical/electronic conversions, all-optical logic gates can permit further exploitation of the nearly 40 THz of bandwidth available from optical fibers. We focus on the use of optical solitons and all-optical logic gates to implement ultrafast ``interchanges'' or switching nodes on packet networks with speeds of 100 Gbit/s or greater. For example, all-optical logic gates have been demonstrated with speeds up to 200 Gbit/s, and they may be used to decide whether to add or drop a data packet. The overall goal of our effort is to demonstrate the key enabling technologies and their combination for header processing in 100 Gbit/s, time-division-multiplexed, packed switched networks. Soliton-based fiber logic gates are studied with the goal of combining attractive features of soliton-dragging logic gates, nonlinear loop mirrors, and erbium-doped fiber amplifiers to design logic gates with optimum switching energy, contrast ratio, and timing sensitivity. First, the experimental and numerical work studies low-latency soliton logic gates based on frequency shifts associated with cross-phase modulation. In preliminary experiments, switching in 15 m long low-birefringent fibers has been demonstrated with a contrast ratio of 2.73:1. Using dispersion-shifted fiber in the gate should lower the switching energy and improve the contrast ratio. Next, the low-birefringent fiber can be cross-spliced and wrapped into a nonlinear optical loop mirror to take advantage of mechanisms from both soliton dragging and loop mirrors. The resulting device can have low switching energy and a timing window that results from a combination of soliton dragging and the loop mirror mechanisms.

  19. Ultrafast dynamics of femtosecond laser-induced nanostructure formation on metals

    NASA Astrophysics Data System (ADS)

    Hwang, Taek Yong; Vorobyev, A. Y.; Guo, Chunlei

    2009-09-01

    We perform a comparison study on femtosecond laser-induced nanostructures on three noble metals, Cu, Ag, and Au. Under identical experimental conditions, the three metals each gain a different amount of surface area increase resulting from nanostructuring. We show that the different surface area increase from nanostructuring directly relates to the competition of two ultrafast processes,