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Phase Transition in strongly-correlated VO2: Time-domainAssignment of Cause and Effect

Description: We establish time-domain hierarchy between structural andelectronic effects in the strongly correlated system VO2. Theinsulator-to-metal transition is driven directly by structural changerather than by electron-electron correlations.
Date: July 22, 2004
Creator: Cavalleri, A.; Dekorsy, Th.; Chong, H. H.; Kieffer, J. C. & Schoenlein, R. W.
Partner: UNT Libraries Government Documents Department

Time-resolved x-ray absorption spectroscopy of photoinduced insulator-metal transition in a colossal magnetoresistive manganite

Description: We studied the ultrafast insulator-metal transition in a manganite by means of picosecond X-ray absorption at the O K- and Mn L-edges, probing photoinduced changes in O-2p and Mn-3d electronic states near the Fermi level.
Date: August 1, 2008
Creator: Rini, M.; Tobey, R.; Wall, S.; Zhu, Y.; Tomioka, Y.; Tokura, Y. et al.
Partner: UNT Libraries Government Documents Department

Synchronization of x-ray pulses to the pump laser in an ultrafast x-ray facility

Description: Accurate timing of ultrafast x-ray probe pulses emitted from a synchrotron radiation source with respect to a pump laser exciting processes in the sample under study is critical for the investigation of structural dynamics in the femtosecond regime. We describe a scheme for synchronizing femtosecond x-ray pulses relative to a pump laser. X-ray pulses of <100 fs duration are generated from a proposed source based on a recirculating superconducting linac [1,2,3]. Short x-ray pulses are obtained by a process of electron pulse compression, followed by transverse temporal correlation of the electrons, and ultimately x-ray pulse compression. Timing of the arrival of the x-ray pulse with respect to the pump laser is found to be dominated by the operation of the deflecting cavities which provide the transverse temporal correlation of the electrons. The deflecting cavities are driven from a highly stable RF signal derived from a modelocked laser oscillator which is also the origin of the pump l aser pulses.
Date: May 30, 2002
Creator: Corlett, J.N.; Barry, W.; Byrd, J.M.; Schoenlein, R. & Zholents, A.
Partner: UNT Libraries Government Documents Department

Techniques for synchronization of X-Ray pulses to the pump laser in an ultrafast X-Ray facility

Description: Accurate timing of ultrafast x-ray probe pulses emitted from a synchrotron radiation source with respect to the signal initiating a process in the sample under study is critical for the investigation of structural dynamics in the femtosecond regime. We describe schemes for achieving accurate timing of femtosecond x-ray synchrotron radiation pulses relative to a pump laser, where x-rays pulses of <100 fs duration are generated from the proposed LUX source based on a recirculating superconducting linac. We present a description of the timing signal generation and distribution systems to minimize timing jitter of the x-rays relative to the experimental lasers.
Date: May 6, 2003
Creator: Corlett, J.N.; Doolittle, L.; Schoenlein, R.; Staples, J.; Wilcox, R. & Zholents, A.
Partner: UNT Libraries Government Documents Department

Probing reaction dynamics of transition-metal complexes in solution via time-resolved soft x-ray spectroscopy

Description: We report the first time-resolved soft x-ray measurements of solvated transition-metal complexes. L-edge spectroscopy directly probes dynamic changes in ligand-field splitting of 3d orbitals associated with the spin transition, and mediated by changes in ligand-bonding. We report the first time-resolved soft x-ray spectroscopy of solution-phase molecular dynamics. Changes in ligand-field splitting and spin-state populations in 3d orbitals of the Fe{sup II} complex are directly probed via transient absorption changes of the Fe L{sub 2} and L{sub 3} edges following photo-induced metal-to-ligand charge transfer. With the emergence of high-flux ultrafast soft x-ray sources, details on interplay between atomic structure, electronic states, and spin contributions will be revealed. Our experimental approach opens the door to femtosecond soft x-ray investigations of liquid phase chemistry that have previously been inaccessible.
Date: August 1, 2008
Creator: Huse, N.; Kim, T.-K.; Khalil, M.; Jamula, L.; McCusker, J.K. & Schoenlein, R.W.
Partner: UNT Libraries Government Documents Department

Ultrafast gigantic photo-response in charge-ordered organic salt (EDO-TTF)2PF6 on 10-fs time scales

Description: The initial dynamics of photo-induced phase transition in charge-ordered organic salt (EDO-TTF){sub 2}PF{sub 6} was investigated using 10-fs near-infrared laser pulses. We observed sub-20-fs gigantic photo-responses (|{Delta}R/R|>100%) due to intra-molecular vibration and a clear signature of a structural bottleneck ({approx}50 fs) for the first time.
Date: August 1, 2008
Creator: Itatani, J.; Rini, M.; Cavalleri, A.; Onda, K.; Ishikawa, T.; Ogihara, S. et al.
Partner: UNT Libraries Government Documents Department

Time-resolved Studies of Phase Transition Dynamics in Strongly Correlated Manganites

Description: Ultrafast light pulses can be used to control electronic, magnetic and structural phases of complex solids. Here, we investigate the dynamics of insulator-metal phase transitions in colossal magnetoresistive (CMR) manganites by a combination of femtosecond visible-to-midinfrared pump-probe techniques and transport measurements. We show that an insulator-metal transition can be stimulated in CMR manganites by both above bandgap excitation and selective excitation of individual vibrational degrees of freedom. These two approaches rely on the ultrafast manipulation of parameters controlling the electronic filling and the electronic bandwidth respectively, extending the concepts of filling and bandwidth control to the ultrafast timescale. The ultrafast vibrational control of correlated-electron phases may provide new insights into the role played by lattice vibrations in determining the electronic properties of complex solids.
Date: December 5, 2008
Creator: Rini, M; Tobey, R; Dean, N; Wall, S; Ehrke, H; Zhu, Y et al.
Partner: UNT Libraries Government Documents Department

Transient electronic structure of the photoinduced phase of Pr0.7Ca0.3MnO3 probed with soft x-ray pulses

Description: We use time-resolved x-ray absorption near-edge structure spectroscopy to investigate the electronic dynamics associated with the photoinduced insulator-to-metal phase transition in the colossal magnetoresistive manganite Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3}. Absorption changes at the O K and Mn L edges directly monitor the evolution of the density of unoccupied states in the transient photoinduced phase. We show that the electronic structure of the photoinduced phase is remarkably similar to that of the ferromagnetic metallic phase reached in related manganites upon cooling below the Curie temperature.
Date: April 1, 2009
Creator: Rini, M.; Zhu, Y.; Wall, S.; Tobey, R. I.; Ehrke, H.; Garl, T. et al.
Partner: UNT Libraries Government Documents Department

Two-Dimensional Carrier-Carrier Screening in a Quantum Well

Description: The behavior of carrier-carrier screening is investigated in a GaAs-GaAIAs quantum well structure by measuring the band-to-band polarization dephasing with femtosecond photon echoes. The variation of the electron-hole polarization dephasing time with the carrier concentration reveals the two-dimensional character of the short range screening between the interacting carriers.
Date: July 1, 1991
Creator: Bigot, J.-Y.; Portella, M.T.; Schoenlein, R.W.; Cunningham, J.E. & Shank, C.V.
Partner: UNT Libraries Government Documents Department

Femtosecond X-rays from 90{degree} Thomson scattering

Description: The authors report on progress on the femtosecond X-ray pulse generation experiment. The experiment involves a relativistic electron beam (50 MeV) with an rms bunch length of 10 ps containing 1--2 nC of charge, and a ultrashort pulse (50--200 fs), high power (< 4 TW) 0.8 {micro}m laser beam from a Ti:Al{sub 2}O{sub 3} laser system. Both beams are focused down to about a 50 {micro}m waist size and intersect at 90{degree}. The laser field acts as an electromagnetic undulator for the relativistic electron beam generating radiation upshifted by 2 {gamma}{sup 2} and a pulse length given by the transit time of the laser beam across the electron beam. For a 50 MeV electron beam they expect 10{sup 5} photons at 0.4 {angstrom} (25% bandwidth) in a cone angle of 6--10 mrad in about a 200 fs pulse.
Date: April 1, 1995
Creator: Leemans, W.; Schoenlein, R.; Chin, A.; Glover, E.; Govil, R.; Volfbeyn, P. et al.
Partner: UNT Libraries Government Documents Department

A laser-based longitudinal density monitor for the large hadroncollider

Description: We report on the development of an instrument for the measurement of the longitudinal beam profile in the Large Hadron Collider (LHC). The technique used, which has been successfully demonstrated at the Advanced Light Source, mixes the synchrotron radiation with the light from a mode-locked solid state laser oscillator in a non-linear crystal.The up-converted radiation is then detected with a photomultiplier and processed to extract, store and display the required information. A 40MHz laser, phase-locked to the ring radio frequency system, with a 50 pspulse length, would be suitable for measuring the dynamics of the core of each of the LHC 2808 bunches in a time span much shorter than the synchrotron period. The same instrument could also monitor the evolution of the bunch tails, the presence of untrapped particles and their diffusion into nominally empty RF buckets (''ghost bunches'') as required by the CERN specifications.
Date: July 1, 2004
Creator: Beche, J.-F.; Byrd, J.; Datte, P.; De Santis, S.; Placidi, M.; Riot, V. et al.
Partner: UNT Libraries Government Documents Department

Giant, ultrafast optical switching based on an Insulator-to-MetalTransition in VO2 Nano-particles: Photo-activation of shape-controlledplasmons at 1.55 mu-m

Description: A new generation of devices where the electronic, optical or magnetic state of a system can be controlled optically on the ultrafast timescale is one of the most compelling technological ramifications of the rapidly advancing field of strongly correlated electrons. However, for real-world applications it is also necessary to incorporate these compounds in appropriate environments (e.g. optical fibers or silicon-based electronics), to ensure compatibility with existing technologies (e.g. telecom wavelengths), room temperature operation and limited power densities. Here, we report on the study of the photo-activated optical switching in nanorods of strongly correlated VO{sub 2}. The particles are grown by ion-implantation and self-assembly within a Silica matrix or an optical fiber, operate at room temperature and can be switched between the insulating and metallic phase within less than 100 fs. The energy threshold to achieve switching corresponds to approximately 500 pJ within the core of a single mode fiber and is compatible with current diode technologies. Tailoring of the spherical/cylindrical geometry results in control of the spectral response of the system, which is dominated by the impulsive formation of a surface plasmon upon the insulator-to-metal transition. The response at the technologically important 1.55 {micro}m wavelength is in this way maximized.
Date: July 1, 2004
Creator: Rini, M.; Cavalleri, A.; Schoenlein, R.W.; Lopez, R.; Feldman,C.; Haglund, R. et al.
Partner: UNT Libraries Government Documents Department

An Ultra-Bright Pulsed Electron Beam With Low Longitudinal Emittance

Description: Most existing electron sources extract electrons from conductors. Since the actual temperature inside the conductor is much less than the Fermi temperature of the conduction electrons, the electron degeneracy {delta}{sub f} is close to 1, the maximum allowed by the Pauli exclusion principle. However, during extraction several factors conspire together to reduce {delta}{sub f} many orders of magnitude, limiting the achieved values to {approx} 10{sup -5}. A new concept is described for building a novel electron source designed to produce a pulsed beam with {delta}{sub f} {approx} 2 10{sup -3} and longitudinal emittance four orders of magnitude smaller than currently achieved values. This high brightness, low longitudinal emittance regime enables a wide range of novel applications that utilize angstrom-scale spatial resolution and eV-scale energy resolution. The current state of a proof-of-principle experiment conducted at LBNL is also described.
Date: February 10, 2006
Creator: Zolotorev, M.; Commins, E.D.; Denes, P.; Hussain, Z.; Lebedev, G.V.; Lidia, S.M. et al.
Partner: UNT Libraries Government Documents Department

A dedicated synchrotron light source for ultrafast x-ray science

Description: We describe a proposed femtosecond synchrotron radiation x-ray source based on a flat-beam RF gun and a recirculating superconducting linac that provides beam to an array of undulators and bend magnets. X-ray pulse durations of &lt;100 fs at a 10 kHz repetition rate are obtained by a combination of electron pulse compression, transverse temporal correlation of the electrons, and x-ray pulse compression.
Date: June 16, 2001
Creator: Corlett, J.; DeSantis, S.; Hartman, N.; Heimann, P.; Lafever, R.; Li, D. et al.
Partner: UNT Libraries Government Documents Department

Initial feasibility study of a dedicated synchrotron radiation light source for ultrafast X-ray science

Description: We present an initial feasibility summary of a femtosecond synchrotron radiation x-ray source based on a flat-beam rf gun and a recirculating superconducting linac that provides beam to an array of undulators and bend magnets. Optical pulse durations of &lt; 100 fs are obtained by a combination of electron pulse compression, transverse temporal correlation of the electrons, and x-ray pulse compression. After an introduction and initial scientific motivation, we cover the following aspects of the design: layout and lattice, ultra-fast x-ray pulse production, flat electron-beam production, the rf gun, rf systems, cryogenic systems, collective effects, photon production, and synchronization of x-ray and laser pulses. We conclude with a summary of issues and areas of development that remain to be addressed.
Date: October 26, 2001
Creator: Corlett, John N.; DeSantis, S.; Hartman, N.; Heimann, P.; LaFever, R.; Li, D. et al.
Partner: UNT Libraries Government Documents Department

Generation of femtosecond synchrotron pulses: Performance and characterization

Description: Femtosecond synchrotron pulses of &lt;200 fs duration are generated at the Advanced Light Source beamline 5.3.1 via laser manipulation of the stored electron beam. We demonstrate a peak laser acceleration of &gt;13 MeV relative to the nominal 1.9 GeV beam energy. Femtosecond pulses are effectively isolated from the long-pulse background using the transverse dispersion of the storage ring in combination with an x-ray imaging optic and a pair of slits to achieve a signal/background ratio of {approx}1.
Date: August 28, 2003
Creator: Schoenlein, R.W.; Cavalleri, A.; Chong, H.H.W.; Glover, T.E.; Heimann, P.A.; Zholents, A.A. et al.
Partner: UNT Libraries Government Documents Department

Coherent infrared radiation from the ALS generated via femtosecond laser modulation of the electron beam

Description: Interaction of an electron beam with a femtosecond laser pulse co-propagating through a wiggler at the ALS produces large modulation of the electron energies within a short {approx}100 fs slice of the electron bunch. Propagating around the storage ring, this bunch develops a longitudinal density perturbation due to the dispersion of electron trajectories. The length of the perturbation evolves with a distance from the wiggler but is much shorter than the electron bunch length. This perturbation causes the electron bunch to emit short pulses of temporally and spatially coherent infrared light which are automatically synchronized to the modulating laser. The intensity and spectra of the infrared light were measured in two storage ring locations for a nominal ALS lattice and for an experimental lattice with the higher momentum compaction factor. The onset of instability stimulated by laser e-beam interaction had been discovered. The infrared signal is now routinely used as a sensitive monitor for a fine tuning of the laser beam alignment during data accumulation in the experiments with femtosecond x-ray pulses.
Date: July 1, 2004
Creator: Byrd, J.M.; Hao, Z.; Martin, M.C.; Robin, D.S.; Sannibale, F.; Schoenlein, R.W. et al.
Partner: UNT Libraries Government Documents Department

Development of a longitudinal density monitor for storage rings

Description: We report on development of a new storage ring operations tool for measurement of longitudinal beam density profile. The technique mixes synchrotron light with light from a mode locked solid-state laser oscillator in a non-linear crystal and detects the up-converted radiation with a photo-multiplier. The laser is phase locked to the storage ring RF system. The laser choices available for repetition frequency, pulse length and phase modulation give a very wide range of options for matching the bunch configuration of particular storage rings. Progress in the technology of solid-state lasers ensures this system can be made robust for routine use in storage ring operations. A very large number of important applications are possible including measurement of the fraction of untrapped particles prior to acceleration, the population of particles in the nominally unfilled RF buckets in a bunch train (''ghost bunches''), longitudinal tails, the diffusion of particles into the beam abort gap and th e normal bunch parameters of longitudinal shape and intensity. We are currently investigating application to two devices: (1) the 1.9 GeV ALS electron storage ring at LBNL with 328 RF buckets, 2ns bucket spacing, 276 nominally filled bunches, 15-30ps rms bunch length and (2) the 7 TeV LHC proton collider under construction at CERN with 35,640 RF buckets, 2.5 ns bucket spacing, 2,808 nominally filled bunches, 280-620 ps rms bunch length. A proof of principle experiment is being conducted on ALS. The results of the ALS experiment and detailed analyses of the application to LHC and its requirements are described.
Date: May 28, 2003
Creator: Zolotorev, M.; Beche, J.-F.; Byrd, J.; Datte, P.; De Santis, S.; Denes, P. et al.
Partner: UNT Libraries Government Documents Department

Femtosecond x-ray pulses from a synchrotron

Description: An important frontier in ultrafast science is the application of femtosecond x-ray pulses to the study of structural dynamics in condensed matter. We show that femtosecond laser pulses can be used to generate high-brightness, tunable, femtosecond x-ray pulses from a synchrotron. Performance of existing and proposed femtosecond x-ray beamlines at the Advanced Light Source synchrotron are discussed.
Date: July 30, 2000
Creator: Schoenlein, R.W.; Chong, H.H.W.; Glover, T.E.; Heimann, P.A.; Shank, C.V.; Zholents, A.A. et al.
Partner: UNT Libraries Government Documents Department