Development of time-resolved electron momentum spectroscopy. Toward real-time imaging of frontier electrons in molecular reactions

International Nuclear Information System (INIS)

Yamazaki, M.; Takahashi, M.

2016-01-01

This report will introduce a new experimental technique to readers, which we would like to propose towards advances in the field of molecular reaction dynamics. It is time-resolved electron momentum spectroscopy and aims to take in momentum space snapshots of the rapid change of molecular orbitals, which is the driving force behind any structural changes occurring in transient molecules. Following a description of the working principle of the technique, some preliminary result will be presented in order to illustrate the current performance of the apparatus. (author)

Time- and energy resolved photoemission electron microscopy-imaging of photoelectron time-of-flight analysis by means of pulsed excitations

International Nuclear Information System (INIS)

Oelsner, Andreas; Rohmer, Martin; Schneider, Christian; Bayer, Daniela; Schoenhense, Gerd; Aeschlimann, Martin

2010-01-01

The present work enlightens the developments in time- and energy resolved photoemission electron microscopy over the past few years. We describe basic principles of the technique and demonstrate different applications. An energy- and time-filtering photoemission electron microscopy (PEEM) for real-time spectroscopic imaging can be realized either by a retarding field or hemispherical energy analyzer or by using time-of-flight optics with a delay line detector. The latter method has the advantage of no data loss at all as all randomly incoming particles are measured not only by position but also by time. This is of particular interest for pump-probe experiments in the femtosecond and attosecond time scale where space charge processes drastically limit the maximum number of photoemitted electrons per laser pulse. This work focuses particularly on time-of-flight analysis using a novel delay line detector. Time and energy resolved PEEM instruments with delay line detectors enable 4D imaging (x, y, Δt, E Kin ) on a true counting basis. This allows a broad range of applications from real-time observation of dynamic phenomena at surfaces to fs time-of-flight spectro-microscopy and even aberration correction. By now, these time-of-flight analysis instruments achieve intrinsic time resolutions of 108 ps absolute and 13.5 ps relative. Very high permanent measurement speeds of more than 4 million events per second in random detection regimes have been realized using a standard USB2.0 interface. By means of this performance, the time-resolved PEEM technique enables to display evolutions of spatially resolved (<25 nm) and temporal sliced images life on any modern computer. The method allows dynamics investigations of variable electrical, magnetic, and optical near fields at surfaces and great prospects in dynamical adaptive photoelectron optics. For dynamical processes in the ps time scale such as magnetic domain wall movements, the time resolution of the delay line detectors

Time resolved, 2-D hard X-ray imaging of relativistic electron-beam target interactions on ETA-II

International Nuclear Information System (INIS)

Crist, C.E.; Sampayan, S.; Westenskow, G.; Caporaso, G.; Houck, T.; Weir, J.; Trimble, D.; Krogh, M.

1998-01-01

Advanced radiographic applications require a constant source size less than 1 mm. To study the time history of a relativistic electron beam as it interacts with a bremsstrahlung converter, one of the diagnostics they use is a multi-frame time-resolved hard x-ray camera. They are performing experiments on the ETA-II accelerator at Lawrence Livermore National Laboratory to investigate details of the electron beam/converter interactions. The camera they are using contains 6 time-resolved images, each image is a 5 ns frame. By starting each successive frame 10 ns after the previous frame, they create a 6-frame movie from the hard x-rays produced from the interaction of the 50-ns electron beam pulse

Vibrational frequencies and dephasing times in excited electronic states by femtosecond time-resolved four-wave mixing

Science.gov (United States)

Joo, Taiha; Albrecht, A. C.

1993-06-01

Time-resolved degenerate four-wave mixing (TRDFWM) for an electronically resonant system in a phase-matching configuration that measures population decay is reported. Because the spectral width of input light exceeds the vibrational Bohr frequency of a strong Raman active mode, the vibrational coherence produces strong oscillations in the TRDFWM signal together with the usual population decay from the excited electronic state. The data are analyzed in terms of a four-level system: ground and excited electronic states each split by a vibrational quantum of a Raman active mode. Absolute frequencies and their dephasing times of the vibrational modes at ≈590 cm -1 are obtained for the excited as well as the ground electronic state. The vibrational dephasing rate in the excited electronic state is about an order of magnitude faster than that in the ground state, the origin of which is speculated upon.

Further time-resolved electron-beam characterizations with optical transition radiation

Energy Technology Data Exchange (ETDEWEB)

Lumpkin, A.H. [Argonne National Lab., IL (United States). Advanced Photon Source Accelerator Systems Div.; Wilke, M.D. [Los Alamos National Lab., NM (United States)

1992-12-31

Time-resolved characterizations of electron beams using optical transition radiation (OTR) as a prompt conversion mechanism have recently been extended on the Los Alamos Free-electron Laser (FEL) facility 40-MeV linac. Two key timescales for rf-linac driven FELs are the micropulse (10 ps) and the macropulse (5 {mu}s to 1 ms). In the past we have used gated, intensified cameras to select a single or few micropulses (25 to 400 ns gate width) out of the pulse train to evaluate submacropulse effects. Recently, we have obtained some of the first measurements of micropulse bunch length (7 to 10 ps) and submacropulse spatialposition and profile using OTR and a Hamamatsu streak camera. Additionally, micropulse elongation effects and head-to-tail transverse kick effects are reported as a function of charge.

Further time-resolved electron-beam characterizations with optical transition radiation

Energy Technology Data Exchange (ETDEWEB)

Lumpkin, A.H. (Argonne National Lab., IL (United States). Advanced Photon Source Accelerator Systems Div.); Wilke, M.D. (Los Alamos National Lab., NM (United States))

1992-01-01

Time-resolved characterizations of electron beams using optical transition radiation (OTR) as a prompt conversion mechanism have recently been extended on the Los Alamos Free-electron Laser (FEL) facility 40-MeV linac. Two key timescales for rf-linac driven FELs are the micropulse (10 ps) and the macropulse (5 [mu]s to 1 ms). In the past we have used gated, intensified cameras to select a single or few micropulses (25 to 400 ns gate width) out of the pulse train to evaluate submacropulse effects. Recently, we have obtained some of the first measurements of micropulse bunch length (7 to 10 ps) and submacropulse spatialposition and profile using OTR and a Hamamatsu streak camera. Additionally, micropulse elongation effects and head-to-tail transverse kick effects are reported as a function of charge.

Time-dependent first-principles study of angle-resolved secondary electron emission from atomic sheets

Science.gov (United States)

Ueda, Yoshihiro; Suzuki, Yasumitsu; Watanabe, Kazuyuki

2018-02-01

Angle-resolved secondary electron emission (ARSEE) spectra were analyzed for two-dimensional atomic sheets using a time-dependent first-principles simulation of electron scattering. We demonstrate that the calculated ARSEE spectra capture the unoccupied band structure of the atomic sheets. The excitation dynamics that lead to SEE have also been revealed by the time-dependent Kohn-Sham decomposition scheme. In the present study, the mechanism for the experimentally observed ARSEE from atomic sheets is elucidated with respect to both energetics and the dynamical aspects of SEE.

Time-resolved magnetic imaging in an aberration-corrected, energy-filtered photoemission electron microscope

International Nuclear Information System (INIS)

Nickel, F.; Gottlob, D.M.; Krug, I.P.; Doganay, H.; Cramm, S.; Kaiser, A.M.; Lin, G.; Makarov, D.; Schmidt, O.G.

2013-01-01

We report on the implementation and usage of a synchrotron-based time-resolving operation mode in an aberration-corrected, energy-filtered photoemission electron microscope. The setup consists of a new type of sample holder, which enables fast magnetization reversal of the sample by sub-ns pulses of up to 10 mT. Within the sample holder current pulses are generated by a fast avalanche photo diode and transformed into magnetic fields by means of a microstrip line. For more efficient use of the synchrotron time structure, we developed an electrostatic deflection gating mechanism capable of beam blanking within a few nanoseconds. This allows us to operate the setup in the hybrid bunch mode of the storage ring facility, selecting one or several bright singular light pulses which are temporally well-separated from the normal high-intensity multibunch pulse pattern. - Highlights: • A new time-resolving operation mode in photoemission electron microscopy is shown. • Our setup works within an energy-filtered, aberration-corrected PEEM. • A new gating system for bunch selection using synchrotron radiation is developed. • An alternative magnetic excitation system is developed. • First tr-imaging using an energy-filtered, aberration-corrected PEEM is shown

SmB6 electron-phonon coupling constant from time- and angle-resolved photoelectron spectroscopy

Science.gov (United States)

Sterzi, A.; Crepaldi, A.; Cilento, F.; Manzoni, G.; Frantzeskakis, E.; Zacchigna, M.; van Heumen, E.; Huang, Y. K.; Golden, M. S.; Parmigiani, F.

2016-08-01

SmB6 is a mixed valence Kondo system resulting from the hybridization between localized f electrons and delocalized d electrons. We have investigated its out-of-equilibrium electron dynamics by means of time- and angle-resolved photoelectron spectroscopy. The transient electronic population above the Fermi level can be described by a time-dependent Fermi-Dirac distribution. By solving a two-temperature model that well reproduces the relaxation dynamics of the effective electronic temperature, we estimate the electron-phonon coupling constant λ to range from 0.13 ±0.03 to 0.04 ±0.01 . These extremes are obtained assuming a coupling of the electrons with either a phonon mode at 10 or 19 meV. A realistic value of the average phonon energy will give an actual value of λ within this range. Our results provide an experimental report on the material electron-phonon coupling, contributing to both the electronic transport and the macroscopic thermodynamic properties of SmB6.

Steady state and time-resolved spectroscopic investigations on the photoreactions involved within the electronically excited electron acceptor 9-cyanoanthracene in presence of benzotriazole and benzimidazole donors

International Nuclear Information System (INIS)

Bhattacharya, Sudeshna; Bardhan, Munmun; Ganguly, Tapan

2010-01-01

The electrochemical, 'steady-state' and 'time-resolved' spectroscopic investigations were made on the well-known electron acceptor 9-cyanoanthracene (CNA) when interacted with the electron donors benzotriazole (BZT) and benzimidazole (BMI) molecules. Though electrochemical measurements indicate the thermodynamical possibility of occurrences of photoinduced electron transfer reactions within these reacting systems in the lowest excited singlet state (S 1 ) of the acceptor CNA but the steady-state and time-resolved measurements clearly demonstrate only the triplet-initiated charge separation reactions. It was reported earlier that in the cases of disubstituted indole molecules the occurrences of photoinduced electron transfer reactions were apparent both in the excited singlet and triplet states of the acceptor 9-cyanoanthracene, but the similarly structured present donor molecules benzotriazole (and benzimidazole) behave differently from indoles. The weak ground state complex formations within the presently studied reacting systems appear to be responsible for the observed static quenching phenomena as evidenced from the time-resolved fluorescence studies. Time-resolved spectroscopic investigations demonstrate the formation of the ground state of the reacting components (donor and acceptor) through recombination of triplet ion-pairs via formations of contact neutral radical produced by H-abstraction mechanism.

Time-resolved ESR spectroscopy

International Nuclear Information System (INIS)

Beckert, D.

1986-06-01

The time-resolved ESR spectroscopy is one of the modern methods in radiospectroscopy and plays an important role in solving various problems in chemistry and biology. Proceeding from the basic ideas of time-resolved ESR spectroscopy the experimental equipment is described generally including the equipment developed at the Central Institute of Isotope and Radiation Research. The experimental methods applied to the investigation of effects of chemically induced magnetic polarization of electrons and to kinetic studies of free radicals in polymer systems are presented. The theory of radical pair mechanism is discussed and theoretical expressions are summarized in a computer code to compute the theoretical polarization for each pair of the radicals

Simulations of the temporal and spatial resolution for a compact time-resolved electron diffractometer

Science.gov (United States)

Robinson, Matthew S.; Lane, Paul D.; Wann, Derek A.

2016-02-01

A novel compact electron gun for use in time-resolved gas electron diffraction experiments has recently been designed and commissioned. In this paper we present and discuss the extensive simulations that were performed to underpin the design in terms of the spatial and temporal qualities of the pulsed electron beam created by the ionisation of a gold photocathode using a femtosecond laser. The response of the electron pulses to a solenoid lens used to focus the electron beam has also been studied. The simulated results show that focussing the electron beam affects the overall spatial and temporal resolution of the experiment in a variety of ways, and that factors that improve the resolution of one parameter can often have a negative effect on the other. A balance must, therefore, be achieved between spatial and temporal resolution. The optimal experimental time resolution for the apparatus is predicted to be 416 fs for studies of gas-phase species, while the predicted spatial resolution of better than 2 nm-1 compares well with traditional time-averaged electron diffraction set-ups.

Visualizing a protein quake with time-resolved X-ray scattering at a free-electron laser

DEFF Research Database (Denmark)

Arnlund, David; Johansson, Linda C.; Wickstrand, Cecilia

2014-01-01

We describe a method to measure ultrafast protein structural changes using time-resolved wide-angle X-ray scattering at an X-ray free-electron laser. We demonstrated this approach using multiphoton excitation of the Blastochloris viridis photosynthetic reaction center, observing an ultrafast glob...

Isotope effect on hydrated electron relaxation dynamics studied with time-resolved liquid jet photoelectron spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Elkins, Madeline H.; Williams, Holly L. [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Neumark, Daniel M., E-mail: dneumark@berkeley.edu [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2016-05-14

The excited state relaxation dynamics of the solvated electron in H{sub 2}O and D{sub 2}O are investigated using time-resolved photoelectron spectroscopy in a liquid microjet. The data show that the initial excited state decays on a time scale of 75 ± 12 fs in H{sub 2}O and 102 ± 8 fs in D{sub 2}O, followed by slower relaxation on time scales of 400 ± 70 fs and 390 ± 70 fs that are isotopically invariant within the precision of our measurements. Based on the time evolution of the transient signals, the faster and slower time constants are assigned to p → s internal conversion (IC) of the hydrated electron and relaxation on the ground electronic state, respectively. This assignment is consistent with the non-adiabatic mechanism for relaxation of the hydrated electron and yields an isotope effect of 1.4 ± 0.2 for IC of the hydrated electron.

Isotope effect on hydrated electron relaxation dynamics studied with time-resolved liquid jet photoelectron spectroscopy

Science.gov (United States)

Elkins, Madeline H.; Williams, Holly L.; Neumark, Daniel M.

2016-05-01

The excited state relaxation dynamics of the solvated electron in H2O and D2O are investigated using time-resolved photoelectron spectroscopy in a liquid microjet. The data show that the initial excited state decays on a time scale of 75 ± 12 fs in H2O and 102 ± 8 fs in D2O, followed by slower relaxation on time scales of 400 ± 70 fs and 390 ± 70 fs that are isotopically invariant within the precision of our measurements. Based on the time evolution of the transient signals, the faster and slower time constants are assigned to p → s internal conversion (IC) of the hydrated electron and relaxation on the ground electronic state, respectively. This assignment is consistent with the non-adiabatic mechanism for relaxation of the hydrated electron and yields an isotope effect of 1.4 ± 0.2 for IC of the hydrated electron.

Studying electron distributions using the time-resolved free-bound spectra from coronal plasmas

International Nuclear Information System (INIS)

Matthews, D.L.; Kauffman, R.L.; Kilkenny, J.D.; Lee, R.W.

1982-11-01

Absorption of laser light in a plasma by inverse bremsstrahlung, I.B., can lead to a non-Maxwellian velocity distribution provided the electron-elecron collision frequency is too low to equilibrate the velocity distribution in the coronal plasma region of a laser heated aluminum disk by measuring the radiation recombination continuum. The experiments are performed using lambda/sub L/ = 0.532 μm laser light at intensities of approx. 10 16 W/cm 2 . Such parameters are predicted to produce conditions suitable for a non-thermal electron distribution. The shape of the K-shell recombination radiation has been measured using a time-resolved x-ray spectrograph. The electron distribution can be determined from deconvolution of the recombination continuum shape

Exciplex formation in bimolecular photoinduced electron-transfer investigated by ultrafast time-resolved infrared spectroscopy.

Science.gov (United States)

Koch, Marius; Letrun, Romain; Vauthey, Eric

2014-03-12

The dynamics of bimolecular photoinduced electron-transfer reactions has been investigated with three donor/acceptor (D/A) pairs in tetrahydrofuran (THF) and acetonitrile (ACN) using a combination of ultrafast spectroscopic techniques, including time-resolved infrared absorption. For the D/A pairs with the highest driving force of electron transfer, all transient spectroscopic features can be unambiguously assigned to the excited reactant and the ionic products. For the pair with the lowest driving force, three additional transient infrared bands, more intense in THF than in ACN, with a time dependence that differs from those of the other bands are observed. From their frequency and solvent dependence, these bands can be assigned to an exciplex. Moreover, polarization-resolved measurements point to a relatively well-defined mutual orientation of the constituents and to a slower reorientational time compared to those of the individual reactants. Thanks to the minimal overlap of the infrared signature of all transient species in THF, a detailed reaction scheme including the relevant kinetic and thermodynamic parameters could be deduced for this pair. This analysis reveals that the formation and recombination of the ion pair occur almost exclusively via the exciplex.

Nonadiabatic Dynamics May Be Probed through Electronic Coherence in Time-Resolved Photoelectron Spectroscopy.

Science.gov (United States)

Bennett, Kochise; Kowalewski, Markus; Mukamel, Shaul

2016-02-09

We present a hierarchy of Fermi golden rules (FGRs) that incorporate strongly coupled electronic/nuclear dynamics in time-resolved photoelectron spectroscopy (TRPES) signals at different levels of theory. Expansion in the joint electronic and nuclear eigenbasis yields the numerically most challenging exact FGR (eFGR). The quasistatic Fermi Golden Rule (qsFGR) neglects nuclear motion during the photoionization process but takes into account electronic coherences as well as populations initially present in the pumped matter as well as those generated internally by coupling between electronic surfaces. The standard semiclassical Fermi Golden Rule (scFGR) neglects the electronic coherences and the nuclear kinetic energy during the ionizing pulse altogether, yielding the classical Condon approximation. The coherence contributions depend on the phase-profile of the ionizing field, allowing coherent control of TRPES signals. The photoelectron spectrum from model systems is simulated using these three levels of theory. The eFGR and the qsFGR show temporal oscillations originating from the electronic or vibrational coherences generated as the nuclear wave packet traverses a conical intersection. These oscillations, which are missed by the scFGR, directly reveal the time-evolving splitting between electronic states of the neutral molecule in the curve-crossing regime.

Reflective optical system for time-resolved electron bunch measurements at PITZ

Energy Technology Data Exchange (ETDEWEB)

Rosbach, K; Baehr, J [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany); Roensch-Schulenburg, J [Hamburg Univ. (Germany). Inst. fuer Experimentalphysik

2011-01-15

The Photo-Injector Test facility at DESY, Zeuthen site (PITZ), produces pulsed electron beams with low transverse emittance and is equipped with diagnostic devices for measuring various electron bunch properties, including the longitudinal and transverse electron phase space distributions. The longitudinal bunch structure is recorded using a streak camera located outside the accelerator tunnel, connected to the diagnostics in the beam-line stations by an optical system of about 30 m length. This system mainly consists of telescopes of achromatic lenses, which transport the light pulses and image them onto the entrance slit of the streak camera. Due to dispersion in the lenses, the temporal resolution degrades during transport. This article presents general considerations for time-resolving optical systems as well as simulations and measurements of specific candidate systems. It then describes the development of an imaging system based on mirror telescopes which will improve the temporal resolution, with an emphasis on off-axis parabolic mirror systems working at unit magnification. A hybrid system of lenses and mirrors will serve as a proof of principle. (orig.)

DFT and time-resolved IR investigation of electron transfer between photogenerated 17- and 19-electron organometallic radicals

Energy Technology Data Exchange (ETDEWEB)

Cahoon, James B.; Kling, Matthias F.; Sawyer, Karma R.; Andersen, Lars K.; Harris, Charles B.

2008-04-30

The photochemical disproportionation mechanism of [CpW(CO){sub 3}]{sub 2} in the presence of Lewis bases PR{sub 3} was investigated on the nano- and microsecond time-scales with Step-Scan FTIR time-resolved infrared spectroscopy. 532 nm laser excitation was used to homolytically cleave the W-W bond, forming the 17-electron radicals CpW(CO){sub 3} and initiating the reaction. With the Lewis base PPh{sub 3}, disproportionation to form the ionic products CpW(CO){sub 3}PPh{sub 3}{sup +} and CpW(CO){sub 3}{sup -} was directly monitored on the microsecond time-scale. Detailed examination of the kinetics and concentration dependence of this reaction indicates that disproportionation proceeds by electron transfer from the 19-electron species CpW(CO){sub 3}PPh{sub 3} to the 17-electron species CpW(CO){sub 3}. This result is contrary to the currently accepted disproportionation mechanism which predicts electron transfer from the 19-electron species to the dimer [CpW(CO){sub 3}]{sub 2}. With the Lewis base P(OMe){sub 3} on the other hand, ligand substitution to form the product [CpW(CO){sub 2}P(OMe){sub 3}]{sub 2} is the primary reaction on the microsecond time-scale. Density Functional Theory (DFT) calculations support the experimental results and suggest that the differences in the reactivity between P(OMe){sub 3} and PPh{sub 3} are due to steric effects. The results indicate that radical-to-radical electron transfer is a previously unknown but important process for the formation of ionic products with the organometallic dimer [CpW(CO){sub 3}]{sub 2} and may also be applicable to the entire class of organometallic dimers containing a single metal-metal bond.

Conditions for reliable time-resolved dosimetry of electronic portal imaging devices for fixed-gantry IMRT and VMAT

International Nuclear Information System (INIS)

Yeo, Inhwan Jason; Patyal, Baldev; Mandapaka, Anant; Jung, Jae Won; Yi, Byong Yong; Kim, Jong Oh

2013-01-01

Purpose: The continuous scanning mode of electronic portal imaging devices (EPID) that offers time-resolved information has been newly explored for verifying dynamic radiation deliveries. This study seeks to determine operating conditions (dose rate stability and time resolution) under which that mode can be used accurately for the time-resolved dosimetry of intensity-modulated radiation therapy (IMRT) beams.Methods: The authors have designed the following test beams with variable beam holdoffs and dose rate regulations: a 10 × 10 cm open beam to serve as a reference beam; a sliding window (SW) beam utilizing the motion of a pair of multileaf collimator (MLC) leaves outside the 10 × 10 cm jaw; a step and shoot (SS) beam to move the pair in step; a volumetric modulated arc therapy (VMAT) beam. The beams were designed in such a way that they all produce the same open beam output of 10 × 10 cm. Time-resolved ion chamber measurements at isocenter and time-resolved and integrating EPID measurements were performed for all beams. The time-resolved EPID measurements were evaluated through comparison with the ion chamber and integrating EPID measurements, as the latter are accepted procedures. For two-dimensional, time-resolved evaluation, a VMAT beam with an infield MLC travel was designed. Time-resolved EPID measurements and Monte Carlo calculations of such EPID dose images for this beam were performed and intercompared.Results: For IMRT beams (SW and SS), the authors found disagreement greater than 2%, caused by frame missing of the time-resolved mode. However, frame missing disappeared, yielding agreement better than 2%, when the dose rate of irradiation (and thus the frame acquisition rates) reached a stable and planned rate as the dose of irradiation was raised past certain thresholds (a minimum 12 s of irradiation per shoot used for SS IMRT). For VMAT, the authors found that dose rate does not affect the frame acquisition rate, thereby causing no frame missing

Time-resolved brightness measurements by streaking

Science.gov (United States)

Torrance, Joshua S.; Speirs, Rory W.; McCulloch, Andrew J.; Scholten, Robert E.

2018-03-01

Brightness is a key figure of merit for charged particle beams, and time-resolved brightness measurements can elucidate the processes involved in beam creation and manipulation. Here we report on a simple, robust, and widely applicable method for the measurement of beam brightness with temporal resolution by streaking one-dimensional pepperpots, and demonstrate the technique to characterize electron bunches produced from a cold-atom electron source. We demonstrate brightness measurements with 145 ps temporal resolution and a minimum resolvable emittance of 40 nm rad. This technique provides an efficient method of exploring source parameters and will prove useful for examining the efficacy of techniques to counter space-charge expansion, a critical hurdle to achieving single-shot imaging of atomic scale targets.

An x-ray detector for time-resolved studies

International Nuclear Information System (INIS)

Rodricks, B.; Brizard, C.; Clarke, R.; Lowe, W.

1992-01-01

The development of ultrahigh-brightness x-ray sources makes time-resolved x-ray studies more and more feasible. Improvements in x-ray optics components are also critical for obtaining the appropriate beam for a particular type of experiment. Moreover, fast parallel detectors will be essential in order to exploit the combination of high intensity x-ray sources and novel optics for time-resolved experiments. A CCD detector with a time resolution of microseconds has been developed at the Advanced Photon Source (APS). This detector is fully programmable using CAMAC electronics and a Micro Vax computer. The techniques of time-resolved x-ray studies, which include scattering, microradiography, microtomography, stroboscopy, etc., can be applied to a range of phenomena (including rapid thermal annealing, surface ordering, crystallization, and the kinetics of phase transition) in order to understand these time-dependent microscopic processes. Some of these applications will be illustrated by recent results performed at synchrotrons. New powerful x-ray sources now under construction offer the opportunity to apply innovative approaches in time-resolved work

Charge recombination processes in minerals studied using optically stimulated luminescence and time-resolved exo-electrons

DEFF Research Database (Denmark)

Tsukamoto, Sumiko; Murray, Andrew; Ankjærgaard, Christina

2010-01-01

electron concentration in the conduction band. In this study, TR-OSE and time-resolved optically stimulated luminescence (TR-OSL) were measured for the first time using quartz, K-feldspar and NaCl by stimulating the samples using pulsed blue LEDs at different temperatures between 50 and 250 °C after beta...... irradiation and preheating to 280 °C. The majority of TR-OSE signals from all the samples decayed much faster than TR-OSL signals irrespective of the stimulation temperatures. This suggests that the lifetime of OSL in these dosimeters arises mainly from the relaxation of an excited state of the recombination...

Time-resolved resonance Raman spectroscopy of radiation-chemical processes

International Nuclear Information System (INIS)

Tripathi, G.N.R.

1983-01-01

A tunable pulsed laser Raman spectrometer for time resolved Raman studies of radiation-chemical processes is described. This apparatus utilizes the state of art optical multichannel detection and analysis techniques for data acquisition and electron pulse radiolysis for initiating the reactions. By using this technique the resonance Raman spectra of intermediates with absorption spectra in the 248-900 nm region, and mean lifetimes > 30 ns can be examined. This apparatus can be used to time resolve the vibrational spectral overlap between transients absorbing in the same region, and to follow their decay kinetics by monitoring the well resolved Raman peaks. For kinetic measurements at millisecond time scale, the Raman technique is preferable over optical absorption method where low frequency noise is quite bothersome. A time resolved Raman study of the pulse radiolytic oxidation of aqueous tetrafluorohydroquinone and p-methoxyphenol is briefly discussed. 15 references, 5 figures

Time-resolved measurements of the hot-electron population in ignition-scale experiments on the National Ignition Facility (invited)

Energy Technology Data Exchange (ETDEWEB)

Hohenberger, M., E-mail: mhoh@lle.rochester.edu; Stoeckl, C. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States); Albert, F.; Palmer, N. E.; Döppner, T.; Divol, L.; Dewald, E. L.; Bachmann, B.; MacPhee, A. G.; LaCaille, G.; Bradley, D. K. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Lee, J. J. [National Security Technologies LLC, Livermore, California 94551 (United States)

2014-11-15

In laser-driven inertial confinement fusion, hot electrons can preheat the fuel and prevent fusion-pellet compression to ignition conditions. Measuring the hot-electron population is key to designing an optimized ignition platform. The hot electrons in these high-intensity, laser-driven experiments, created via laser-plasma interactions, can be inferred from the bremsstrahlung generated by hot electrons interacting with the target. At the National Ignition Facility (NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841 (2004)], the filter-fluorescer x-ray (FFLEX) diagnostic–a multichannel, hard x-ray spectrometer operating in the 20–500 keV range–has been upgraded to provide fully time-resolved, absolute measurements of the bremsstrahlung spectrum with ∼300 ps resolution. Initial time-resolved data exhibited significant background and low signal-to-noise ratio, leading to a redesign of the FFLEX housing and enhanced shielding around the detector. The FFLEX x-ray sensitivity was characterized with an absolutely calibrated, energy-dispersive high-purity germanium detector using the high-energy x-ray source at NSTec Livermore Operations over a range of K-shell fluorescence energies up to 111 keV (U K{sub β}). The detectors impulse response function was measured in situ on NIF short-pulse (∼90 ps) experiments, and in off-line tests.

Spin-resolved electron waiting times in a quantum-dot spin valve

Science.gov (United States)

Tang, Gaomin; Xu, Fuming; Mi, Shuo; Wang, Jian

2018-04-01

We study the electronic waiting-time distributions (WTDs) in a noninteracting quantum-dot spin valve by varying spin polarization and the noncollinear angle between the magnetizations of the leads using the scattering matrix approach. Since the quantum-dot spin valve involves two channels (spin up and down) in both the incoming and outgoing channels, we study three different kinds of WTDs, which are two-channel WTD, spin-resolved single-channel WTD, and cross-channel WTD. We analyze the behaviors of WTDs in short times, correlated with the current behaviors for different spin polarizations and noncollinear angles. Cross-channel WTD reflects the correlation between two spin channels and can be used to characterize the spin-transfer torque process. We study the influence of the earlier detection on the subsequent detection from the perspective of cross-channel WTD, and define the influence degree quantity as the cumulative absolute difference between cross-channel WTDs and first-passage time distributions to quantitatively characterize the spin-flip process. We observe that influence degree versus spin-transfer torque for different noncollinear angles as well as different polarizations collapse into a single curve showing universal behaviors. This demonstrates that cross-channel WTDs can be a pathway to characterize spin correlation in spintronics system.

Ribosome dynamics and tRNA movement by time-resolved electron cryomicroscopy.

Science.gov (United States)

Fischer, Niels; Konevega, Andrey L; Wintermeyer, Wolfgang; Rodnina, Marina V; Stark, Holger

2010-07-15

The translocation step of protein synthesis entails large-scale rearrangements of the ribosome-transfer RNA (tRNA) complex. Here we have followed tRNA movement through the ribosome during translocation by time-resolved single-particle electron cryomicroscopy (cryo-EM). Unbiased computational sorting of cryo-EM images yielded 50 distinct three-dimensional reconstructions, showing the tRNAs in classical, hybrid and various novel intermediate states that provide trajectories and kinetic information about tRNA movement through the ribosome. The structures indicate how tRNA movement is coupled with global and local conformational changes of the ribosome, in particular of the head and body of the small ribosomal subunit, and show that dynamic interactions between tRNAs and ribosomal residues confine the path of the tRNAs through the ribosome. The temperature dependence of ribosome dynamics reveals a surprisingly flat energy landscape of conformational variations at physiological temperature. The ribosome functions as a Brownian machine that couples spontaneous conformational changes driven by thermal energy to directed movement.

Investigation of the electron dynamics of Si(111) 7 x 7 and development of a time-of-flight spectrometer for time- and angle-resolved two-photon photoemission

International Nuclear Information System (INIS)

Damm, Andreas

2011-01-01

This thesis consists of two main parts. The first one reports about recent investigations of the electron dynamics on the Si(111) 7 x 7 surface employing time- and angle-resolved two-photon photoemission (2PPE). The second part describes the construction and demonstration of the capabilities of a new electron time-of-flight spectrometer. It is shown that the electron dynamics of this surface are governed by adatom and bulk states. Variation of different experimental parameters leads to the suggestion that electrons scatter from the adatom states into the conduction band of Silicon. The localization in real space can be estimated from the distribution of the photoemission intensity in momentum space to be within one 7 x 7 unit cell. The electron population in the conduction band as well as those in the adatom band show a very long-living component. In addition to recombination through defect states, these electrons can undergo radiative recombination with holes in the valence band. The second part of this thesis reports about the design, construction and demonstration of the capabilities of a new electron time-of-flight spectrometer for applications in time- and angle-resolved 2PPE experiments. The new spectrometer is designed in a flexible manner to maximize either the energy resolution or the acceptance angle, respectively. By employing a position-sensitive electron detector it is possible for the first time to measure the energy as well as all components of the parallel momentum of the photoemitted electrons and thereby to fully characterize electrons from surface states. The time-resolution can be estimated from the width of a peak induced by photons scattered from the sample to be better than 150 ps. At the minimum of about 40 mm of the adjustable drift distance this leads to a energy resolution below 5 meV for electrons with kinetic energies of 1 eV. Thereby, the parallel momentum resolution is below 5 mA -1 for parallel momentum values k parallel ≤1A -1

Analytical formulation for modulation of time-resolved dynamical Franz-Keldysh effect by electron excitation in dielectrics

Science.gov (United States)

Otobe, T.

2017-12-01

Analytical formulation of subcycle modulation (SCM) of dielectrics including electron excitation is presented. The SCM is sensitive to not only the time-resolved dynamical Franz-Keldysh effect (Tr-DFKE) [T. Otobe et al., Phys. Rev. B 93, 045124 (2016), 10.1103/PhysRevB.93.045124], which is the nonlinear response without the electron excitation, but also the excited electrons. The excited electrons enhance the modulation with even harmonics of pump laser frequency, and generate the odd-harmonics components. The new aspect of SCM is a consequence of (i) the interference between the electrons excited by the pump laser and those excited by the probe-pulse laser and (ii) oscillation of the generated wave packed by the pump laser. When the probe- and pump-pulse polarizations are parallel, the enhancement of the even harmonics and the generation of the odd-harmonics modulation appear. However, if the polarizations are orthogonal, the effect arising from the electron excitations becomes weak. By comparing the parabolic and cosine band models, I found that the electrons under the intense laser field move as quasifree particles.

Comments on advanced, time-resolved imaging techniques for free-electron laser (FEL) experiments

Energy Technology Data Exchange (ETDEWEB)

Lumpkin, A.H.

1992-01-01

An extensive set of time-resolved imaging experiments has been performed on rf-linac driven free-electron lasers (FELs) over the past few years. These experiments have addressed both micropulse and macropulse timescales on both the charged-particle beam and the wiggler/undulator outputs (spontaneous emission and lasing). A brief review of first measurements on photoinjecter micropulse elongation, submacropulse phase slew in drive lasers, submacropulse wavelength shifts in lasers, etc. is presented. This is followed by discussions of new measurements of 35-MeV electron beam micropulse bunch length (<10 ps) using optical transition radiation, some of the first single bend synchrotron radiation beam profile measurements at gamma <80, and comments on the low-jitter synchroscan streak camera tuner. These techniques will be further developed on the 200-650 MeV linac test stand at the Advanced Photon Source (APS) in the next few years. Such techniques should be adaptable to many of the present FEL designs and to some aspects of the next generation of light sources.

Comments on advanced, time-resolved imaging techniques for free-electron laser (FEL) experiments

Energy Technology Data Exchange (ETDEWEB)

Lumpkin, A.H.

1992-11-01

An extensive set of time-resolved imaging experiments has been performed on rf-linac driven free-electron lasers (FELs) over the past few years. These experiments have addressed both micropulse and macropulse timescales on both the charged-particle beam and the wiggler/undulator outputs (spontaneous emission and lasing). A brief review of first measurements on photoinjecter micropulse elongation, submacropulse phase slew in drive lasers, submacropulse wavelength shifts in lasers, etc. is presented. This is followed by discussions of new measurements of 35-MeV electron beam micropulse bunch length (<10 ps) using optical transition radiation, some of the first single bend synchrotron radiation beam profile measurements at gamma <80, and comments on the low-jitter synchroscan streak camera tuner. These techniques will be further developed on the 200-650 MeV linac test stand at the Advanced Photon Source (APS) in the next few years. Such techniques should be adaptable to many of the present FEL designs and to some aspects of the next generation of light sources.

Femtosecond Time-Resolved Resonance-Enhanced CARS of Gaseous Iodine at Room Temperature

International Nuclear Information System (INIS)

He Ping; Fan Rong-Wei; Xia Yuan-Qin; Yu Xin; Chen De-Ying; Yao Yong

2011-01-01

Time-resolved resonance-enhanced coherent anti-Stokes Raman scattering (CARS) is applied to investigate molecular dynamics in gaseous iodine. 40 fs laser pulses are applied to create and monitor the high vibrational states of iodine at room temperature (corresponding to a vapor pressure as low as about 35 Pa) by femtosecond time-resolved CARS. Depending on the time delay between the probe pulse and the pump/Stokes pulse pairs, the high vibrational states both on the electronically ground states and the excited states can be detected as oscillations in the CARS transient signal. It is proved that the femtosecond time-resolved CARS technique is a promising candidate for investigating the molecular dynamics of a low concentration system and can be applied to environmental and atmospheric monitoring measurements. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Time-Resolved Scanning Electron Microscopy

National Research Council Canada - National Science Library

Weber, Peter M

2006-01-01

.... The pulsed electron beam is obtained by rapidly switching the electron emission of a field emission tip using the AC electric field arising from exposure to the intense electromagnetic radiation...

Time resolved electron microscopy for in situ experiments

International Nuclear Information System (INIS)

Campbell, Geoffrey H.; McKeown, Joseph T.; Santala, Melissa K.

2014-01-01

Transmission electron microscopy has functioned for decades as a platform for in situ observation of materials and processes with high spatial resolution. Yet, the dynamics often remain elusive, as they unfold too fast to discern at these small spatial scales under traditional imaging conditions. Simply shortening the exposure time in hopes of capturing the action has limitations, as the number of electrons will eventually be reduced to the point where noise overtakes the signal in the image. Pulsed electron sources with high instantaneous current have successfully shortened exposure times (thus increasing the temporal resolution) by about six orders of magnitude over conventional sources while providing the necessary signal-to-noise ratio for dynamic imaging. We describe here the development of this new class of microscope and the principles of its operation, with examples of its application to problems in materials science

Time resolved electron microscopy for in situ experiments

Energy Technology Data Exchange (ETDEWEB)

Campbell, Geoffrey H., E-mail: ghcampbell@llnl.gov; McKeown, Joseph T.; Santala, Melissa K. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

2014-12-15

Transmission electron microscopy has functioned for decades as a platform for in situ observation of materials and processes with high spatial resolution. Yet, the dynamics often remain elusive, as they unfold too fast to discern at these small spatial scales under traditional imaging conditions. Simply shortening the exposure time in hopes of capturing the action has limitations, as the number of electrons will eventually be reduced to the point where noise overtakes the signal in the image. Pulsed electron sources with high instantaneous current have successfully shortened exposure times (thus increasing the temporal resolution) by about six orders of magnitude over conventional sources while providing the necessary signal-to-noise ratio for dynamic imaging. We describe here the development of this new class of microscope and the principles of its operation, with examples of its application to problems in materials science.

Flash X-Ray (FXR) Accelerator Optimization Electronic Time-Resolved Measurement of X-Ray Source Size

International Nuclear Information System (INIS)

Jacob, J; Ong, M; Wargo, P

2005-01-01

Lawrence Livermore National Laboratory (LLNL) is currently investigating various approaches to minimize the x-ray source size on the Flash X-Ray (FXR) linear induction accelerator in order to improve x-ray flux and increase resolution for hydrodynamic radiography experiments. In order to effectively gauge improvements to final x-ray source size, a fast, robust, and accurate system for measuring the spot size is required. Timely feedback on x-ray source size allows new and improved accelerator tunes to be deployed and optimized within the limited run-time constraints of a production facility with a busy experimental schedule; in addition, time-resolved measurement capability allows the investigation of not only the time-averaged source size, but also the evolution of the source size, centroid position, and x-ray dose throughout the 70 ns beam pulse. Combined with time-resolved measurements of electron beam parameters such as emittance, energy, and current, key limiting factors can be identified, modeled, and optimized for the best possible spot size. Roll-bar techniques are a widely used method for x-ray source size measurement, and have been the method of choice at FXR for many years. A thick bar of tungsten or other dense metal with a sharp edge is inserted into the path of the x-ray beam so as to heavily attenuate the lower half of the beam, resulting in a half-light, half-dark image as seen downstream of the roll-bar; by measuring the width of the transition from light to dark across the edge of the roll-bar, the source size can be deduced. For many years, film has been the imaging medium of choice for roll-bar measurements thanks to its high resolution, linear response, and excellent contrast ratio. Film measurements, however, are fairly cumbersome and require considerable setup and analysis time; moreover, with the continuing trend towards all-electronic measurement systems, film is becoming increasingly difficult and expensive to procure. Here, we shall

Time and energy resolved runaway measurements in TFR from induced radioactivity

International Nuclear Information System (INIS)

1983-09-01

A time and energy resolved measurement of the radioactivity induced by runaway electrons in proper samples has been developped in TFR. The data give an information on the confinement time of these electrons, which appears to be strongly dependent on the toroidal field, suggesting the onset of a magnetic turbulence at lower fields. Observations showing that the runaway electrons deeply penetrate into the limiter shadow are also reported

Time-resolved Chemical Imaging of Molecules by High-order Harmonics and Ultrashort Rescattering Electrons

Energy Technology Data Exchange (ETDEWEB)

Lin, Chii Dong [Kansas State Univ., Manhattan, KS (United States)

2016-03-21

Directly monitoring atomic motion during a molecular transformation with atomic-scale spatio-temporal resolution is a frontier of ultrafast optical science and physical chemistry. Here we provide the foundation for a new imaging method, fixed-angle broadband laser-induced electron scattering, based on structural retrieval by direct one-dimensional Fourier transform of a photoelectron energy distribution observed along the polarization direction of an intense ultrafast light pulse. The approach exploits the scattering of a broadband wave packet created by strong-field tunnel ionization to self-interrogate the molecular structure with picometre spatial resolution and bond specificity. With its inherent femtosecond resolution, combining our technique with molecular alignment can, in principle, provide the basis for time-resolved tomography for multi-dimensional transient structural determination.

Time-resolved X-ray scattering by electronic wave packets: analytic solutions to the hydrogen atom

DEFF Research Database (Denmark)

Simmermacher, Mats; Henriksen, Niels Engholm; Møller, Klaus Braagaard

2017-01-01

Modern pulsed X-ray sources permit time-dependent measurements of dynamical changes in atoms and molecules via non-resonant scattering. The planning, analysis, and interpretation of such experiments, however, require a firm and elaborated theoretical framework. This paper provides a detailed...... description of time-resolved X-ray scattering by non-stationary electronic wave packets in atomic systems. A consistent application of the Waller-Hartree approximation is discussed and different contributions to the total differential scattering signal are identified and interpreted. Moreover......, it is demonstrated how the scattering signal of wave packets in the hydrogen atom can be expressed analytically. This permits simulations without numerical integration and establishes a benchmark for both efficiency and accuracy. Based on that, scattering patterns of an exemplary wave packet in the hydrogen atom...

Time-resolved Shielded-Pickup Measurements and Modeling of Beam Conditioning Effects on Electron Cloud Buildup at CesrTA

CERN Document Server

Crittenden, J A; Liu, X; Palmer, M A; Santos, S; Sikora, J P; Kato, S; Calatroni, S; Rumolo, G

2012-01-01

The Cornell Electron Storage Ring Test Accelerator program includes investigations into electron cloud buildup in vacuum chambers with various coatings. Two 1.1-mlong sections located symmetrically in the east and west arc regions are equipped with BPM-like pickup detectors shielded against the direct beam-induced signal. They detect cloud electrons migrating through an 18-mm-diameter pattern of 0.76 mm-diameter holes in the top of the chamber. A digitizing oscilloscope is used to record the signals, providing time-resolved information on cloud development. We present new measurements of the effect of beam conditioning on a newly-installed amorphous carbon coated chamber, as well as on an extensively conditioned chamber with a diamond-like carbon coating. The ECLOUD modeling code is used to quantify the sensitivity of these measurements to model parameters, differentiating between photoelectron and secondary-electron production processes.

Fast time-resolved aerosol collector: proof of concept

Science.gov (United States)

Yu, X.-Y.; Cowin, J. P.; Iedema, M. J.; Ali, H.

2010-10-01

Atmospheric particles can be collected in the field on substrates for subsequent laboratory analysis via chemically sensitive single particle methods such as scanning electron microscopy with energy dispersive x-ray analysis. With moving substrates time resolution of seconds to minutes can be achieved. In this paper, we demonstrate how to increase the time resolution when collecting particles on a substrate to a few milliseconds to provide real-time information. Our fast time-resolved aerosol collector ("Fast-TRAC") microscopically observes the particle collection on a substrate and records an on-line video. Particle arrivals are resolved to within a single frame (4-17 ms in this setup), and the spatial locations are matched to the subsequent single particle analysis. This approach also provides in-situ information on particle size and number concentration. Applications are expected in airborne studies of cloud microstructure, pollution plumes, and surface long-term monitoring.

Nonperturbative quantum simulation of time-resolved nonlinear spectra: Methodology and application to electron transfer reactions in the condensed phase

International Nuclear Information System (INIS)

Wang Haobin; Thoss, Michael

2008-01-01

A quantum dynamical method is presented to accurately simulate time-resolved nonlinear spectra for complex molecular systems. The method combines the nonpertubative approach to describe nonlinear optical signals with the multilayer multiconfiguration time-dependent Hartree theory to calculate the laser-induced polarization for the overall field-matter system. A specific nonlinear optical signal is obtained by Fourier decomposition of the overall polarization. The performance of the method is demonstrated by applications to photoinduced ultrafast electron transfer reactions in mixed-valence compounds and at dye-semiconductor interfaces

Time resolved techniques: An overview

International Nuclear Information System (INIS)

Larson, B.C.; Tischler, J.Z.

1990-06-01

Synchrotron sources provide exceptional opportunities for carrying out time-resolved x-ray diffraction investigations. The high intensity, high angular resolution, and continuously tunable energy spectrum of synchrotron x-ray beams lend themselves directly to carrying out sophisticated time-resolved x-ray scattering measurements on a wide range of materials and phenomena. When these attributes are coupled with the pulsed time-structure of synchrotron sources, entirely new time-resolved scattering possibilities are opened. Synchrotron beams typically consist of sub-nanosecond pulses of x-rays separated in time by a few tens of nanoseconds to a few hundred nanoseconds so that these beams appear as continuous x-ray sources for investigations of phenomena on time scales ranging from hours down to microseconds. Studies requiring time-resolution ranging from microseconds to fractions of a nanosecond can be carried out in a triggering mode by stimulating the phenomena under investigation in coincidence with the x-ray pulses. Time resolution on the picosecond scale can, in principle, be achieved through the use of streak camera techniques in which the time structure of the individual x-ray pulses are viewed as quasi-continuous sources with ∼100--200 picoseconds duration. Techniques for carrying out time-resolved scattering measurements on time scales varying from picoseconds to kiloseconds at present and proposed synchrotron sources are discussed and examples of time-resolved studies are cited. 17 refs., 8 figs

Nanocrystals of [Cu3(btc)2] (HKUST-1): a combined time-resolved light scattering and scanning electron microscopy study.

Science.gov (United States)

Zacher, Denise; Liu, Jianing; Huber, Klaus; Fischer, Roland A

2009-03-07

The formation of [Cu(3)(btc)(2)] (HKUST-1; btc = 1,3,5-benzenetricarboxylate) nanocrystals from a super-saturated mother solution at room temperature was monitored by time-resolved light scattering (TLS); the system is characterized by a rapid growth up to a size limit of 200 nm within a few minutes, and the size and shape of the crystallites were also determined by scanning electron microscopy (SEM).

Photoelectron spectroscopy at a free-electron laser. Investigation of space-charge effects in angle-resolved and core-level spectroscopy and realizaton of a time-resolved core-level photoemission experiment

International Nuclear Information System (INIS)

Marczynski-Buehlow, Martin

2012-01-01

The free-electron laser (FEL) in Hamburg (FLASH) is a very interesting light source with which to perform photoelectron spectroscopy (PES) experiments. Its special characteristics include highly intense photon pulses (up to 100 J/pulse), a photon energy range of 30 eV to 1500 eV, transverse coherence as well as pulse durations of some ten femtoseconds. Especially in terms of time-resolved PES (TRPES), the deeper lying core levels can be reached with photon energies up to 1500 eV with acceptable intensity now and, therefore, element-specific, time-resolved core-level PES (XPS) is feasible at FLASH. During the work of this thesis various experimental setups were constructed in order to realize angle-resolved (ARPES), core-level (XPS) as well as time-resolved PES experiments at the plane grating monochromator beamline PG2 at FLASH. Existing as well as newly developed systems for online monitoring of FEL pulse intensities and generating spatial and temporal overlap of FEL and optical laser pulses for time-resolved experiments are successfully integrated into the experimental setup for PES. In order to understand space-charge effects (SCEs) in PES and, therefore, being able to handle those effects in future experiments using highly intense and pulsed photon sources, the origin of energetic broadenings and shifts in photoelectron spectra are studied by means of a molecular dynamic N-body simulation using a modified Treecode Algorithm for sufficiently fast and accurate calculations. It turned out that the most influencing parameter is the ''linear electron density'' - the ratio of the number of photoelectrons to the diameter of the illuminated spot on the sample. Furthermore, the simulations could reproduce the observations described in the literature fairly well. Some rules of thumb for XPS and ARPES measurements could be deduced from the simulations. Experimentally, SCEs are investigated by means of ARPES as well as XPS measurements as a function of FEL pulse

Photoelectron spectroscopy at a free-electron laser. Investigation of space-charge effects in angle-resolved and core-level spectroscopy and realizaton of a time-resolved core-level photoemission experiment

Energy Technology Data Exchange (ETDEWEB)

Marczynski-Buehlow, Martin

2012-01-30

The free-electron laser (FEL) in Hamburg (FLASH) is a very interesting light source with which to perform photoelectron spectroscopy (PES) experiments. Its special characteristics include highly intense photon pulses (up to 100 J/pulse), a photon energy range of 30 eV to 1500 eV, transverse coherence as well as pulse durations of some ten femtoseconds. Especially in terms of time-resolved PES (TRPES), the deeper lying core levels can be reached with photon energies up to 1500 eV with acceptable intensity now and, therefore, element-specific, time-resolved core-level PES (XPS) is feasible at FLASH. During the work of this thesis various experimental setups were constructed in order to realize angle-resolved (ARPES), core-level (XPS) as well as time-resolved PES experiments at the plane grating monochromator beamline PG2 at FLASH. Existing as well as newly developed systems for online monitoring of FEL pulse intensities and generating spatial and temporal overlap of FEL and optical laser pulses for time-resolved experiments are successfully integrated into the experimental setup for PES. In order to understand space-charge effects (SCEs) in PES and, therefore, being able to handle those effects in future experiments using highly intense and pulsed photon sources, the origin of energetic broadenings and shifts in photoelectron spectra are studied by means of a molecular dynamic N-body simulation using a modified Treecode Algorithm for sufficiently fast and accurate calculations. It turned out that the most influencing parameter is the ''linear electron density'' - the ratio of the number of photoelectrons to the diameter of the illuminated spot on the sample. Furthermore, the simulations could reproduce the observations described in the literature fairly well. Some rules of thumb for XPS and ARPES measurements could be deduced from the simulations. Experimentally, SCEs are investigated by means of ARPES as well as XPS measurements as a function of

Determination of quenching coefficients by time resolved emission spectroscopy

International Nuclear Information System (INIS)

Gans, T.; Schulz-von der Gathen, V.; Doebele, H.F.

2001-01-01

Capacitively coupled RF discharges (CCRF discharges) at 13.56 MHz in hydrogen exhibit a field reversal phase of about 10 ns during which an intense electron current provides collisional excitation, within the sheath region. After this strongly dominant short pulsed electron impact excitation, it is possible to determine quenching coefficients from the lifetime of the fluorescence at various pressures by time resolved OES even for high energy levels and without any restrictions of optical selection rules. This novel technique allows the measurement of quenching coefficients for atomic and molecular emission lines of hydrogen itself, as well as for emission lines of small admixtures (e.g. noble gases) to the hydrogen discharge, since with a fast gate-able ICCD camera operating at 13.56 MHz it is possible to measure even faint emission lines temporally resolved

Determination of quenching coefficients by time resolved emission spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Gans, T.; Schulz-von der Gathen, V.; Doebele, H.F. [Essen Univ. (Gesamthochschule) (Germany). Inst. fuer Laser- und Plasmaphysik

2001-07-01

Capacitively coupled RF discharges (CCRF discharges) at 13.56 MHz in hydrogen exhibit a field reversal phase of about 10 ns during which an intense electron current provides collisional excitation, within the sheath region. After this strongly dominant short pulsed electron impact excitation, it is possible to determine quenching coefficients from the lifetime of the fluorescence at various pressures by time resolved OES even for high energy levels and without any restrictions of optical selection rules. This novel technique allows the measurement of quenching coefficients for atomic and molecular emission lines of hydrogen itself, as well as for emission lines of small admixtures (e.g. noble gases) to the hydrogen discharge, since with a fast gate-able ICCD camera operating at 13.56 MHz it is possible to measure even faint emission lines temporally resolved.

Spatially-resolved measurement of optically stimulated luminescence and time-resolved luminescence

International Nuclear Information System (INIS)

Bailiff, I.K.; Mikhailik, V.B.

2003-01-01

Spatially-resolved measurements of optically stimulated luminescence (OSL) were performed using a two-dimensional scanning system designed for use with planar samples. The scanning system employs a focused laser beam to stimulate a selected area of the sample, which is moved under the beam by a motorised stage. Exposure of the sample is controlled by an electronic shutter. Mapping of the distribution of OSL using a continuous wave laser source was obtained with sub-millimeter resolution for samples of sliced brick, synthetic single crystal quartz, concrete and dental ceramic. These revealed sporadic emission in the case of brick or concrete and significant spatial variation of emission for quartz and dental ceramic slices. Determinations of absorbed dose were performed for quartz grains within a slice of modern brick. Reconfiguration of the scanner with a pulsed laser source enabled quartz and feldspathic minerals within a ceramic sample to be thinner region. about 6 nm from the extrapolation of themeasuring the time-resolved luminescence spectrum

Programming for time resolved spectrum in pulse radiolysis experiments

International Nuclear Information System (INIS)

Betty, C.A.; Panajkar, M.S.; Shirke, N.D.

1993-01-01

A user friendly program in Pascal has been developed for data acquisition and subsequent processing of time resolved spectra of transient species produced in pulse radiolysis experiments. The salient features of the program are (i) thiocyanate dosimetry and (ii) spectrum acquisition. The thiocyanate dosimetry is carried out to normalize experimental conditions to a standard value as determined by computing absorbance of the transient signal CNS -2 that is produced from thiocyanate solution by a 7 MeV electron pulse. Spectrum acquisition allows the acquisition of the time resolved data at 20 different times points and subsequent display of the plots of absorbance vs. wavelength for the desired time points during the experiment. It is also possible to plot single time point spectrum as well as superimposed spectra for different time points. Printing, editing and merging facilities are also provided. (author). 2 refs., 7 figs

Increasing the efficiency and accuracy of time-resolved electronic spectra calculations with on-the-fly ab initio quantum dynamics methods

Science.gov (United States)

Vanicek, Jiri

2014-03-01

Rigorous quantum-mechanical calculations of coherent ultrafast electronic spectra remain difficult. I will present several approaches developed in our group that increase the efficiency and accuracy of such calculations: First, we justified the feasibility of evaluating time-resolved spectra of large systems by proving that the number of trajectories needed for convergence of the semiclassical dephasing representation/phase averaging is independent of dimensionality. Recently, we further accelerated this approximation with a cellular scheme employing inverse Weierstrass transform and optimal scaling of the cell size. The accuracy of potential energy surfaces was increased by combining the dephasing representation with accurate on-the-fly ab initio electronic structure calculations, including nonadiabatic and spin-orbit couplings. Finally, the inherent semiclassical approximation was removed in the exact quantum Gaussian dephasing representation, in which semiclassical trajectories are replaced by communicating frozen Gaussian basis functions evolving classically with an average Hamiltonian. Among other examples I will present an on-the-fly ab initio semiclassical dynamics calculation of the dispersed time-resolved stimulated emission spectrum of the 54-dimensional azulene. This research was supported by EPFL and by the Swiss National Science Foundation NCCR MUST (Molecular Ultrafast Science and Technology) and Grant No. 200021124936/1.

Shielded button electrodes for time-resolved measurements of electron cloud buildup

International Nuclear Information System (INIS)

Crittenden, J.A.; Billing, M.G.; Li, Y.; Palmer, M.A.; Sikora, J.P.

2014-01-01

We report on the design, deployment and signal analysis for shielded button electrodes sensitive to electron cloud buildup at the Cornell Electron Storage Ring. These simple detectors, derived from a beam-position monitor electrode design, have provided detailed information on the physical processes underlying the local production and the lifetime of electron densities in the storage ring. Digitizing oscilloscopes are used to record electron fluxes incident on the vacuum chamber wall in 1024 time steps of 100 ps or more. The fine time steps provide a detailed characterization of the cloud, allowing the independent estimation of processes contributing on differing time scales and providing sensitivity to the characteristic kinetic energies of the electrons making up the cloud. By varying the spacing and population of electron and positron beam bunches, we map the time development of the various cloud production and re-absorption processes. The excellent reproducibility of the measurements also permits the measurement of long-term conditioning of vacuum chamber surfaces

Relation of exact Gaussian basis methods to the dephasing representation: Theory and application to time-resolved electronic spectra

Science.gov (United States)

Sulc, Miroslav; Hernandez, Henar; Martinez, Todd J.; Vanicek, Jiri

2014-03-01

We recently showed that the Dephasing Representation (DR) provides an efficient tool for computing ultrafast electronic spectra and that cellularization yields further acceleration [M. Šulc and J. Vaníček, Mol. Phys. 110, 945 (2012)]. Here we focus on increasing its accuracy by first implementing an exact Gaussian basis method (GBM) combining the accuracy of quantum dynamics and efficiency of classical dynamics. The DR is then derived together with ten other methods for computing time-resolved spectra with intermediate accuracy and efficiency. These include the Gaussian DR (GDR), an exact generalization of the DR, in which trajectories are replaced by communicating frozen Gaussians evolving classically with an average Hamiltonian. The methods are tested numerically on time correlation functions and time-resolved stimulated emission spectra in the harmonic potential, pyrazine S0 /S1 model, and quartic oscillator. Both the GBM and the GDR are shown to increase the accuracy of the DR. Surprisingly, in chaotic systems the GDR can outperform the presumably more accurate GBM, in which the two bases evolve separately. This research was supported by the Swiss NSF Grant No. 200021_124936/1 and NCCR Molecular Ultrafast Science & Technology (MUST), and by the EPFL.

Time-resolved vibrational spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Tokmakoff, Andrei [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Champion, Paul [Northeastern Univ., Boston, MA (United States); Heilweil, Edwin J. [National Inst. of Standards and Technology (NIST), Boulder, CO (United States); Nelson, Keith A. [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Ziegler, Larry [Boston Univ., MA (United States)

2009-05-14

This document contains the Proceedings from the 14th International Conference on Time-Resolved Vibrational Spectroscopy, which was held in Meredith, NH from May 9-14, 2009. The study of molecular dynamics in chemical reaction and biological processes using time-resolved spectroscopy plays an important role in our understanding of energy conversion, storage, and utilization problems. Fundamental studies of chemical reactivity, molecular rearrangements, and charge transport are broadly supported by the DOE's Office of Science because of their role in the development of alternative energy sources, the understanding of biological energy conversion processes, the efficient utilization of existing energy resources, and the mitigation of reactive intermediates in radiation chemistry. In addition, time-resolved spectroscopy is central to all fiveof DOE's grand challenges for fundamental energy science. The Time-Resolved Vibrational Spectroscopy conference is organized biennially to bring the leaders in this field from around the globe together with young scientists to discuss the most recent scientific and technological advances. The latest technology in ultrafast infrared, Raman, and terahertz spectroscopy and the scientific advances that these methods enable were covered. Particular emphasis was placed on new experimental methods used to probe molecular dynamics in liquids, solids, interfaces, nanostructured materials, and biomolecules.

Time resolved Thomson scattering diagnostic of pulsed gas metal arc welding (GMAW) process

International Nuclear Information System (INIS)

Kühn-Kauffeldt, M; Schein, J; Marquès, J L

2014-01-01

In this work a Thomson scattering diagnostic technique was applied to obtain time resolved electron temperature and density values during a gas metal arc welding (GMAW) process. The investigated GMAW process was run with aluminum wire (AlMg 4,5 Mn) with 1.2 mm diameter as a wire electrode, argon as a shielding gas and peak currents in the range of 400 A. Time resolved measurements could be achieved by triggering the laser pulse at shifted time positions with respect to the current pulse driving the process. Time evaluation of resulting electron temperatures and densities is used to investigate the state of the plasma in different phases of the current pulse and to determine the influence of the metal vapor and droplets on the plasma properties

Time-resolved spectroscopy in synchrotron radiation

International Nuclear Information System (INIS)

Rehn, V.; Stanford Univ., CA

1980-01-01

Synchrotron radiation (SR) from large-diameter storage rings has intrinsic time structure which facilitates time-resolved measurements form milliseconds to picoseconds and possibly below. The scientific importance of time-resolved measurements is steadily increasing as more and better techniques are discovered and applied to a wider variety of scientific problems. This paper presents a discussion of the importance of various parameters of the SR facility in providing for time-resolved spectroscopy experiments, including the role of beam-line optical design parameters. Special emphasis is placed on the requirements of extremely fast time-resolved experiments with which the effects of atomic vibrational or relaxation motion may be studied. Before discussing the state-of-the-art timing experiments, we review several types of time-resolved measurements which have now become routine: nanosecond-range fluorescence decay times, time-resolved emission and excitation spectroscopies, and various time-of-flight applications. These techniques all depend on a short SR pulse length and a long interpulse period, such as is provided by a large-diameter ring operating in a single-bunch mode. In most cases, the pulse shape and even the stability of the pulse shape is relatively unimportant as long as the pulse length is smaller than the risetime of the detection apparatus, typically 1 to 2 ns. For time resolution smaller than 1 ns, the requirements on the pulse shape become more stringent. (orig./FKS)

Time-resolved spectroscopy defines perturbation in molecules

International Nuclear Information System (INIS)

Ahmed, K.

1998-01-01

Time-resolved LIF spectroscopy is employed in order to investigate perturbations in different excited electronic state of alkali molecules. Dunham Coefficients are used to search the selected excited ro-vibrational level, which is overlap with the other nearby excited states. Lifetime measurement has been performed of more than 50 ro-vibrational levels. Out of these 25 levels were observed drastically different lifetimes from the other unperturbed levels. In this report, influence of different perturbations on this anomalous behavior is investigated and discussed. (author)

Time-resolved spectroscopy using a chopper wheel as a fast shutter

International Nuclear Information System (INIS)

Wang, Shicong; Wendt, Amy E.; Boffard, John B.; Lin, Chun C.

2015-01-01

Widely available, small form-factor, fiber-coupled spectrometers typically have a minimum exposure time measured in milliseconds, and thus cannot be used directly for time-resolved measurements at the microsecond level. Spectroscopy at these faster time scales is typically done with an intensified charge coupled device (CCD) system where the image intensifier acts as a “fast” electronic shutter for the slower CCD array. In this paper, we describe simple modifications to a commercially available chopper wheel system to allow it to be used as a “fast” mechanical shutter for gating a fiber-coupled spectrometer to achieve microsecond-scale time-resolved optical measurements of a periodically pulsed light source. With the chopper wheel synchronized to the pulsing of the light source, the time resolution can be set to a small fraction of the pulse period by using a chopper wheel with narrow slots separated by wide spokes. Different methods of synchronizing the chopper wheel and pulsing of the light sources are explored. The capability of the chopper wheel system is illustrated with time-resolved measurements of pulsed plasmas

Gauge invariance in the theoretical description of time-resolved angle-resolved pump/probe photoemission spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Freericks, J. K.; Krishnamurthy, H. R.; Sentef, M. A.; Devereaux, T. P.

2015-10-01

Nonequilibrium calculations in the presence of an electric field are usually performed in a gauge, and need to be transformed to reveal the gauge-invariant observables. In this work, we discuss the issue of gauge invariance in the context of time-resolved angle-resolved pump/probe photoemission. If the probe is applied while the pump is still on, one must ensure that the calculations of the observed photocurrent are gauge invariant. We also discuss the requirement of the photoemission signal to be positive and the relationship of this constraint to gauge invariance. We end by discussing some technical details related to the perturbative derivation of the photoemission spectra, which involve processes where the pump pulse photoexcites electrons due to nonequilibrium effects.

Time-resolved x-ray absorption spectroscopy: Watching atoms dance

Science.gov (United States)

Milne, Chris J.; Pham, Van-Thai; Gawelda, Wojciech; van der Veen, Renske M.; El Nahhas, Amal; Johnson, Steven L.; Beaud, Paul; Ingold, Gerhard; Lima, Frederico; Vithanage, Dimali A.; Benfatto, Maurizio; Grolimund, Daniel; Borca, Camelia; Kaiser, Maik; Hauser, Andreas; Abela, Rafael; Bressler, Christian; Chergui, Majed

2009-11-01

The introduction of pump-probe techniques to the field of x-ray absorption spectroscopy (XAS) has allowed the monitoring of both structural and electronic dynamics of disordered systems in the condensed phase with unprecedented accuracy, both in time and in space. We present results on the electronically excited high-spin state structure of an Fe(II) molecular species, [FeII(bpy)3]2+, in aqueous solution, resolving the Fe-N bond distance elongation as 0.2 Å. In addition an analysis technique using the reduced χ2 goodness of fit between FEFF EXAFS simulations and the experimental transient absorption signal in energy space has been successfully tested as a function of excited state population and chemical shift, demonstrating its applicability in situations where the fractional excited state population cannot be determined through other measurements. Finally by using a novel ultrafast hard x-ray 'slicing' source the question of how the molecule relaxes after optical excitation has been successfully resolved using femtosecond XANES.

Atomic column resolved electron energy-loss spectroscopy

International Nuclear Information System (INIS)

Duscher, G.; Pennycook, S.J.; Browning, N.D.

1998-01-01

Spatially resolved electron energy-loss spectroscopy (EELS) is rapidly developing into a unique and powerful tool to characterize internal interfaces. Because atomic column resolved Z-contrast imaging can be performed simultaneously with EELS in the scanning transmission electron microscope, this combination allows the atomic structure to be correlated with the electronic structure, and thus the local properties of interfaces or defects can be determined directly. However, the ability to characterize interfaces and defects at that level requires not only high spatial resolution but also the exact knowledge of the beam location, from where the spectrum is obtained. Here we discuss several examples progressing from cases where the limitation in spatial resolution is given by the microscopes or the nature of the sample, to one example of impurity atoms at a grain boundary, which show intensity and fine structure changes from atomic column to atomic column. Such data can be interpreted as changes in valence of the impurity, depending on its exact site in the boundary plane. Analysis ofthis nature is a valuable first step in understanding the microscopic structural, optical and electronic properties of materials. (orig.)

Time-resolved VUV spectroscopy in the EXTRAP-T2 reversed field pinch

International Nuclear Information System (INIS)

Hedqvist, A.; Rachlew-Kaellne, E.

1998-01-01

Time-resolved VUV spectroscopy has been used to investigate the effects of impurities in a reversed field pinch operating with a resistive shell. Results of electron temperature, impurity ion densities, particle confinement time and Z eff together with a description of the interpretation and the equipment are presented. (author)

Time-resolved absorption measurements on OMEGA

International Nuclear Information System (INIS)

Jaanimagi, P.A.; DaSilva, L.; Delettrez, J.; Gregory, G.G.; Richardson, M.C.

1986-01-01

Time-resolved measurements of the incident laser light that is scattered and/or refracted from targets irradiated by the 24 uv-beam OMEGA laser at LLE, have provided some interesting features related to time-resolved absorption. The decrease in laser absorption characteristic of irradiating a target that implodes during the laser pulse has been observed. The increase in absorption expected as the critical density surface moves from a low to a high Z material in the target has also been noted. The detailed interpretation of these results is made through comparisons with simulation using the code LILAC, as well as with streak data from time-resolved x-ray imaging and spectroscopy. In addition, time and space-resolved imaging of the scattered light yields information on laser irradiation uniformity conditions on the target. The report consists of viewgraphs

Design and implementation of a fs-resolved transmission electron microscope based on thermionic gun technology

Energy Technology Data Exchange (ETDEWEB)

Piazza, L., E-mail: luca.piazza@epfl.ch [Laboratory for Ultrafast Microscopy and Electron Scattering (LUMES), ICMP, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne (Switzerland); Masiel, D.J. [Integrated Dynamic Electron Solutions, Inc., 455 Bolero Drive, Danville, CA 94526 (United States); LaGrange, T.; Reed, B.W. [Condensed Matter and Materials Division Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, P.O. Box 808, L-356, Livermore, CA 94550 (United States); Barwick, B. [Department of Physics, Trinity College, 300 Summit St., Hartford, CT 06106 (United States); Carbone, Fabrizio [Laboratory for Ultrafast Microscopy and Electron Scattering (LUMES), ICMP, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne (Switzerland)

2013-09-23

Highlights: • We present the implementation of a femtosecond-resolved ultrafast TEM. • This is the first ultrafast TEM based on a thermionic gun geometry. • An additional condenser lens has been used to maximize the electron count. • We achieved a time resolution of about 300 fs and an energy resolution of 1 eV. - Abstract: In this paper, the design and implementation of a femtosecond-resolved ultrafast transmission electron microscope is presented, based on a thermionic gun geometry. Utilizing an additional magnetic lens between the electron acceleration and the nominal condenser lens system, a larger percentage of the electrons created at the cathode are delivered to the specimen without degrading temporal, spatial and energy resolution significantly, while at the same time maintaining the femtosecond temporal resolution. Using the photon-induced near field electron microscopy effect (PINEM) on silver nanowires the cross-correlation between the light and electron pulses was measured, showing the impact of the gun settings and initiating laser pulse duration on the electron bunch properties. Tuneable electron pulses between 300 fs and several ps can be obtained, and an overall energy resolution around 1 eV was achieved.

Photoinduced electron transfer through hydrogen bonds in a rod-like donor-acceptor molecule: A time-resolved EPR study

International Nuclear Information System (INIS)

Jakob, Manuela; Berg, Alexander; Stavitski, Eli; Chernick, Erin T.; Weiss, Emily A.; Wasielewski, Michael R.; Levanon, Haim

2006-01-01

Light-driven multi-step intramolecular electron transfer in a rod-like triad, in which two of the three redox components are linked by three hydrogen bonds, was studied by time-resolved electron paramagnetic resonance (TREPR) and optical spectroscopies. One part of the molecule consists of a p-methoxyaniline primary electron donor (MeOAn) covalently linked to a 4-aminonaphthalene-1, 8-dicarboximide (6ANI) chromophoric electron acceptor (MeOAn-6ANI). The unsubstituted dicarboximide of 6ANI serves as one half of a hydrogen bonding receptor pair. The other half of the receptor pair consists of a melamine linked to a naphthalene-1,8:4,5-bis(dicarboximide) (NI) secondary electron acceptor (MEL-NI). TREPR spectroscopy is used to probe the electronic interaction between the radicals within the photogenerated, spin-correlated radical ion pair MeOAn ·+ -6ANI/MEL-NI ·- . The results are compared to those obtained in earlier studies in which MeOAn-6ANI is covalently linked to NI through a 2,5-dimethylphenyl group (MeOAn-6ANI-Ph-NI). We show that the electronic coupling between the oxidized donor and reduced acceptor in the hydrogen-bonded radical ion pair MeOAn ·+ -6ANI/MEL-NI ·- is very similar to that of MeOAn ·+ -6ANI-Ph-NI ·-

Time-resolved x-ray laser induced photoelectron spectroscopy of isochoric heated copper

International Nuclear Information System (INIS)

Nelson, A.J.; Dunn, J.; Hunter, J.; Widmann, K.

2005-01-01

Time-resolved x-ray photoelectron spectroscopy is used to probe the nonsteady-state evolution of the valence band electronic structure of laser heated ultrathin (50 nm) copper. A metastable phase is studied using a 527 nm wavelength 400 fs laser pulse containing 0.1-2.5 mJ laser energy focused in a large 500x700 μm 2 spot to create heated conditions of 0.07-1.8x10 12 W cm -2 intensity. Valence band photoemission spectra are presented showing the changing occupancy of the Cu 3d level with heating are presented. These picosecond x-ray laser induced time-resolved photoemission spectra of laser-heated ultrathin Cu foil show dynamic changes in the electronic structure. The ultrafast nature of this technique lends itself to true single-state measurements of shocked and heated materials

Analytical expressions for time-resolved optically stimulated luminescence experiments in quartz

International Nuclear Information System (INIS)

Pagonis, V.; Lawless, J.; Chen, R.; Chithambo, M.L.

2011-01-01

Optically stimulated luminescence (OSL) signals can be obtained using a time-resolved optical stimulation (TR-OSL) method, also known as pulsed OSL. During TR-OSL measurements, the stimulation and emission of luminescence are experimentally separated in time using short light pulses. This paper presents analytical expressions for the TR-OSL intensity observed during and after such a pulse in quartz experiments. The analytical expressions are derived using a recently published kinetic model which describes thermal quenching phenomena in quartz samples. In addition, analytical expressions are derived for the concentration of electrons in the conduction band during and after the TR-OSL pulse, and for the maximum signals attained during optical stimulation of the samples. The relevance of the model for dosimetric applications is examined, by studying the dependence of the maximum TR-OSL signals on the degree of initial trap filling, and also on the probability of electron retrapping into the dosimetric trap. Analytical expressions are derived for two characteristic times of the TR-OSL mechanism; these times are the relaxation time for electrons in the conduction band, and the corresponding relaxation time for the radiative transition within the luminescence center. The former relaxation time is found to depend on several experimental parameters, while the latter relaxation time depends only on internal parameters characteristic of the recombination center. These differences between the two relaxation times can be explained by the presence of localized and delocalized transitions in the quartz sample. The analytical expressions in this paper are shown to be equivalent to previous analytical expressions derived using a different mathematical approach. A description of thermal quenching processes in quartz based on AlO 4 - /AlO 4 defects is presented, which illustrates the connection between the different descriptions of the luminescence process found in the literature

Relationship between time-resolved and non-time-resolved Beer-Lambert law in turbid media.

Science.gov (United States)

Nomura, Y; Hazeki, O; Tamura, M

1997-06-01

The time-resolved Beer-Lambert law proposed for oxygen monitoring using pulsed light was extended to the non-time-resolved case in a scattered medium such as living tissues with continuous illumination. The time-resolved Beer-Lambert law was valid for the phantom model and living tissues in the visible and near-infrared regions. The absolute concentration and oxygen saturation of haemoglobin in rat brain and thigh muscle could be determined. The temporal profile of rat brain was reproduced by Monte Carlo simulation. When the temporal profiles of rat brain under different oxygenation states were integrated with time, the absorbance difference was linearly related to changes in the absorption coefficient. When the simulated profiles were integrated, there was a linear relationship within the absorption coefficient which was predicted for fractional inspiratory oxygen concentration from 10 to 100% and, in the case beyond the range of the absorption coefficient, the deviation from linearity was slight. We concluded that an optical pathlength which is independent of changes in the absorption coefficient is a good approximation for near-infrared oxygen monitoring.

Time-resolved VUV spectroscopy in the EXTRAP-T2 reversed field pinch

Science.gov (United States)

Hedqvist, Anders; Rachlew-Källne, Elisabeth

1998-09-01

Time-resolved VUV spectroscopy has been used to investigate the effects of impurities in a reversed field pinch operating with a resistive shell. Results of electron temperature, impurity ion densities, particle confinement time and 0741-3335/40/9/004/img1 together with a description of the interpretation and the equipment are presented.

Time-resolved study of the electron temperature and number density of argon metastable atoms in argon-based dielectric barrier discharges

Science.gov (United States)

Desjardins, E.; Laurent, M.; Durocher-Jean, A.; Laroche, G.; Gherardi, N.; Naudé, N.; Stafford, L.

2018-01-01

A combination of optical emission spectroscopy and collisional-radiative modelling is used to determine the time-resolved electron temperature (assuming Maxwellian electron energy distribution function) and number density of Ar 1s states in atmospheric pressure Ar-based dielectric barrier discharges in presence of either NH3 or ethyl lactate. In both cases, T e values were higher early in the discharge cycle (around 0.8 eV), decreased down to about 0.35 eV with the rise of the discharge current, and then remained fairly constant during discharge extinction. The opposite behaviour was observed for Ar 1s states, with cycle-averaged values in the 1017 m-3 range. Based on these findings, a link was established between the discharge ionization kinetics (and thus the electron temperature) and the number density of Ar 1s state.

Time-dependent electron temperature diagnostics for high-power aluminum z-pinch plasmas

International Nuclear Information System (INIS)

Sanford, T.W.L.; Nash, T.J.; Mock, R.C.

1996-08-01

Time-resolved x-ray pinhole photographs and time-integrated radially-resolved x-ray crystal-spectrometer measurements of azimuthally-symmetric aluminum-wire implosions suggest that the densest phase of the pinch is composed of a hot plasma core surrounded by a cooler plasma halo. The slope of the free-bound x-ray continuum, provides a time-resolved, model-independent diagnostic of the core electron temperature. A simultaneous measurement of the time-resolved K-shell line spectra provides the electron temperature of the spatially averaged plasma. Together, the two diagnostics support a 1-D Radiation-Hydrodynamic model prediction of a plasma whose thermalization on axis produces steep radial gradients in temperature, from temperatures in excess of a kilovolt in the core to below a kilovolt in the surrounding plasma halo

Nanosecond time-resolved EPR in pulse radiolysis via the spin echo method

International Nuclear Information System (INIS)

Trifunac, A.D.; Norris, J.R.; Lawler, R.G.

1979-01-01

The design and operation of a time-resolved electron spin echo spectrometer suitable for detecting transient radicals produced by 3 MeV electron radiolysis is described. Two modes of operation are available: Field swept mode which generates a normal EPR spectrum and kinetic mode in which the time dependence of a single EPR line is monitored. Techniques which may be used to minimize the effects of nonideal microwave pulses and overlapping sample tube signals are described. The principal advantages of the spin echo method over other time-resolved EPR methods are: (1) Improved time resolution (presently approx.30--50 nsec) allows monitoring of fast changes in EPR signals of transient radicals, (2) Lower susceptibility to interference between the EPR signal and the electron beam pulse at short times, and (3) Lack of dependence of transient signals on microwave field amplitude or static field inhomogeneity at short times. The performance of the instrument is illustrated using CIDEP from acetate radical formed in pulsed radiolysis of aqueous solutions of potassium acetate. The relaxation time and CIDEP enhancement factor obtained for this radical using the spin echo method compare favorably with previous determinations using direct detection EPR. Radical decay rates yield estimates of initial radical concentrations of 10 -4 10 -3 M per electron pulse. The Bloch equations are solved to give an expression for the echo signal for samples exhibiting CIDEP using arbitrary microwave pulse widths and distributions of Larmor frequencies. Conditions are discussed under which the time-dependent signal would be distorted by deviations from an ideal nonselective 90 0 --tau--180 0 pulse sequence

Time-resolved photoelectron imaging using a femtosecond UV laser and a VUV free-electron laser

OpenAIRE

Liu, S. Y.; Ogi, Yoshihiro; Fuji, Takao; Nishizawa, Kiyoshi; Horio, Takuya; Mizuno, Tomoya; Kohguchi, Hiroshi; Nagasono, Mitsuru; Togashi, Tadashi; Tono, Kensuke; Yabashi, Makina; Senba, Yasunori; Ohashi, Haruhiko; Kimura, Hiroaki; Ishikawa, Tetsuya

2010-01-01

A time-resolved photoelectron imaging using a femtosecond ultraviolet (UV) laser and a vacuum UV freeelectron laser is presented. Ultrafast internal conversion and intersystem crossing in pyrazine in a supersonic molecular beam were clearly observed in the time profiles of photoioinzation intensity and time-dependent photoelectron images.

Watching proteins function with time-resolved x-ray crystallography

Science.gov (United States)

Šrajer, Vukica; Schmidt, Marius

2017-09-01

Macromolecular crystallography was immensely successful in the last two decades. To a large degree this success resulted from use of powerful third generation synchrotron x-ray sources. An expansive database of more than 100 000 protein structures, of which many were determined at resolution better than 2 Å, is available today. With this achievement, the spotlight in structural biology is shifting from determination of static structures to elucidating dynamic aspects of protein function. A powerful tool for addressing these aspects is time-resolved crystallography, where a genuine biological function is triggered in the crystal with a goal of capturing molecules in action and determining protein kinetics and structures of intermediates (Schmidt et al 2005a Methods Mol. Biol. 305 115-54, Schmidt 2008 Ultrashort Laser Pulses in Biology and Medicine (Berlin: Springer) pp 201-41, Neutze and Moffat 2012 Curr. Opin. Struct. Biol. 22 651-9, Šrajer 2014 The Future of Dynamic Structural Science (Berlin: Springer) pp 237-51). In this approach, short and intense x-ray pulses are used to probe intermediates in real time and at room temperature, in an ongoing reaction that is initiated synchronously and rapidly in the crystal. Time-resolved macromolecular crystallography with 100 ps time resolution at synchrotron x-ray sources is in its mature phase today, particularly for studies of reversible, light-initiated reactions. The advent of the new free electron lasers for hard x-rays (XFELs; 5-20 keV), which provide exceptionally intense, femtosecond x-ray pulses, marks a new frontier for time-resolved crystallography. The exploration of ultra-fast events becomes possible in high-resolution structural detail, on sub-picosecond time scales (Tenboer et al 2014 Science 346 1242-6, Barends et al 2015 Science 350 445-50, Pande et al 2016 Science 352 725-9). We review here state-of-the-art time-resolved crystallographic experiments both at synchrotrons and XFELs. We also outline

Seventh international conference on time-resolved vibrational spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Dyer, R.B.; Martinez, M.A.D.; Shreve, A.; Woodruff, W.H. [comps.

1997-04-01

The International Conference on Time-Resolved Vibrational Spectroscopy (TRVS) is widely recognized as the major international forum for the discussion of advances in this rapidly growing field. The 1995 conference was the seventh in a series that began at Lake Placid, New York, 1982. Santa Fe, New Mexico, was the site of the Seventh International Conference on Time-Resolved Vibrational Spectroscopy, held from June 11 to 16, 1995. TRVS-7 was attended by 157 participants from 16 countries and 85 institutions, and research ranging across the full breadth of the field of time-resolved vibrational spectroscopy was presented. Advances in both experimental capabilities for time-resolved vibrational measurements and in theoretical descriptions of time-resolved vibrational methods continue to occur, and several sessions of the conference were devoted to discussion of these advances and the associated new directions in TRVS. Continuing the interdisciplinary tradition of the TRVS meetings, applications of time-resolved vibrational methods to problems in physics, biology, materials science, and chemistry comprised a large portion of the papers presented at the conference.

A high-efficiency spin-resolved photoemission spectrometer combining time-of-flight spectroscopy with exchange-scattering polarimetry

Energy Technology Data Exchange (ETDEWEB)

Jozwiak, Chris M.; Graff, Jeff; Lebedev, Gennadi; Andresen, Nord; Schmid, Andreas; Fedorov, Alexei; El Gabaly, Farid; Wan, Weishi; Lanzara, Alessandra; Hussain, Zahid

2010-04-13

We describe a spin-resolved electron spectrometer capable of uniquely efficient and high energy resolution measurements. Spin analysis is obtained through polarimetry based on low-energy exchange scattering from a ferromagnetic thin-film target. This approach can achieve a similar analyzing power (Sherman function) as state-of-the-art Mott scattering polarimeters, but with as much as 100 times improved efficiency due to increased reflectivity. Performance is further enhanced by integrating the polarimeter into a time-of-flight (TOF) based energy analysis scheme with a precise and flexible electrostatic lens system. The parallel acquisition of a range of electron kinetic energies afforded by the TOF approach results in an order of magnitude (or more) increase in efficiency compared to hemispherical analyzers. The lens system additionally features a 90 degrees bandpass filter, which by removing unwanted parts of the photoelectron distribution allows the TOF technique to be performed at low electron drift energy and high energy resolution within a wide range of experimental parameters. The spectrometer is ideally suited for high-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES), and initial results are shown. The TOF approach makes the spectrometer especially ideal for time-resolved spin-ARPES experiments.

Real-time visualization of the vibrational wavepacket dynamics in electronically excited pyrimidine via femtosecond time-resolved photoelectron imaging

Science.gov (United States)

Li, Shuai; Long, Jinyou; Ling, Fengzi; Wang, Yanmei; Song, Xinli; Zhang, Song; Zhang, Bing

2017-07-01

The vibrational wavepacket dynamics at the very early stages of the S1-T1 intersystem crossing in photoexcited pyrimidine is visualized in real time by femtosecond time-resolved photoelectron imaging and time-resolved mass spectroscopy. A coherent superposition of the vibrational states is prepared by the femtosecond pump pulse at 315.3 nm, resulting in a vibrational wavepacket. The composition of the prepared wavepacket is directly identified by a sustained quantum beat superimposed on the parent-ion transient, possessing a frequency in accord with the energy separation between the 6a1 and 6b2 states. The dephasing time of the vibrational wavepacket is determined to be 82 ps. More importantly, the variable Franck-Condon factors between the wavepacket components and the dispersed cation vibrational levels are experimentally illustrated to identify the dark state and follow the energy-flow dynamics on the femtosecond time scale. The time-dependent intensities of the photoelectron peaks originated from the 6a1 vibrational state exhibit a clear quantum beating pattern with similar periodicity but a phase shift of π rad with respect to those from the 6b2 state, offering an unambiguous picture of the restricted intramolecular vibrational energy redistribution dynamics in the 6a1/6b2 Fermi resonance.

Femtosecond time-resolved transient absorption spectroscopy of xanthophylls.

Science.gov (United States)

Niedzwiedzki, Dariusz M; Sullivan, James O; Polívka, Tomás; Birge, Robert R; Frank, Harry A

2006-11-16

Xanthophylls are a major class of photosynthetic pigments that participate in an adaptation mechanism by which higher plants protect themselves from high light stress. In the present work, an ultrafast time-resolved spectroscopic investigation of all the major xanthophyll pigments from spinach has been performed. The molecules are zeaxanthin, lutein, violaxanthin, and neoxanthin. beta-Carotene was also studied. The experimental data reveal the inherent spectral properties and ultrafast dynamics including the S(1) state lifetimes of each of the pigments. In conjunction with quantum mechanical computations the results address the molecular features of xanthophylls that control the formation and decay of the S* state in solution. The findings provide compelling evidence that S* is an excited state with a conformational geometry twisted relative to the ground state. The data indicate that S* is formed via a branched pathway from higher excited singlet states and that its yield depends critically on the presence of beta-ionylidene rings in the polyene system of pi-electron conjugated double bonds. The data are expected to be beneficial to researchers employing ultrafast time-resolved spectroscopic methods to investigate the mechanisms of both energy transfer and nonphotochemical quenching in higher plant preparations.

Compact cryogenic Kerr microscope for time-resolved studies of electron spin transport in microstructures

NARCIS (Netherlands)

Rizo, P. J.; Pugzlys, A.; Liu, J.; Reuter, D.; Wieck, A. D.; van der Wal, C. H.; van Loosdrecht, P. H. M.; Pugžlys, A.

2008-01-01

A compact cryogenic Kerr microscope for operation in the small volume of high-field magnets is described. It is suited for measurements both in Voigt and Faraday configurations. Coupled with a pulsed laser source, the microscope is used to measure the time-resolved Kerr rotation response of

Watching proteins function with time-resolved x-ray crystallography

Energy Technology Data Exchange (ETDEWEB)

Šrajer, Vukica; Schmidt, Marius

2017-08-22

Macromolecular crystallography was immensely successful in the last two decades. To a large degree this success resulted from use of powerful third generation synchrotron x-ray sources. An expansive database of more than 100 000 protein structures, of which many were determined at resolution better than 2 Å, is available today. With this achievement, the spotlight in structural biology is shifting from determination of static structures to elucidating dynamic aspects of protein function. A powerful tool for addressing these aspects is time-resolved crystallography, where a genuine biological function is triggered in the crystal with a goal of capturing molecules in action and determining protein kinetics and structures of intermediates (Schmidt et al 2005a Methods Mol. Biol. 305 115–54, Schmidt 2008 Ultrashort Laser Pulses in Biology and Medicine (Berlin: Springer) pp 201–41, Neutze and Moffat 2012 Curr. Opin. Struct. Biol. 22 651–9, Šrajer 2014 The Future of Dynamic Structural Science (Berlin: Springer) pp 237–51). In this approach, short and intense x-ray pulses are used to probe intermediates in real time and at room temperature, in an ongoing reaction that is initiated synchronously and rapidly in the crystal. Time-resolved macromolecular crystallography with 100 ps time resolution at synchrotron x-ray sources is in its mature phase today, particularly for studies of reversible, light-initiated reactions. The advent of the new free electron lasers for hard x-rays (XFELs; 5–20 keV), which provide exceptionally intense, femtosecond x-ray pulses, marks a new frontier for time-resolved crystallography. The exploration of ultra-fast events becomes possible in high-resolution structural detail, on sub-picosecond time scales (Tenboer et al 2014 Science 346 1242–6, Barends et al 2015 Science 350 445–50, Pande et al 2016 Science 352 725–9). We review here state-of-the-art time-resolved crystallographic experiments both at synchrotrons and XFELs. We

Watching proteins function with time-resolved x-ray crystallography

International Nuclear Information System (INIS)

Šrajer, Vukica; Schmidt, Marius

2017-01-01

Macromolecular crystallography was immensely successful in the last two decades. To a large degree this success resulted from use of powerful third generation synchrotron x-ray sources. An expansive database of more than 100 000 protein structures, of which many were determined at resolution better than 2 Å, is available today. With this achievement, the spotlight in structural biology is shifting from determination of static structures to elucidating dynamic aspects of protein function. A powerful tool for addressing these aspects is time-resolved crystallography, where a genuine biological function is triggered in the crystal with a goal of capturing molecules in action and determining protein kinetics and structures of intermediates (Schmidt et al 2005a Methods Mol. Biol . 305 115–54, Schmidt 2008 Ultrashort Laser Pulses in Biology and Medicine (Berlin: Springer) pp 201–41, Neutze and Moffat 2012 Curr. Opin. Struct. Biol . 22 651–9, Šrajer 2014 The Future of Dynamic Structural Science (Berlin: Springer) pp 237–51). In this approach, short and intense x-ray pulses are used to probe intermediates in real time and at room temperature, in an ongoing reaction that is initiated synchronously and rapidly in the crystal. Time-resolved macromolecular crystallography with 100 ps time resolution at synchrotron x-ray sources is in its mature phase today, particularly for studies of reversible, light-initiated reactions. The advent of the new free electron lasers for hard x-rays (XFELs; 5–20 keV), which provide exceptionally intense, femtosecond x-ray pulses, marks a new frontier for time-resolved crystallography. The exploration of ultra-fast events becomes possible in high-resolution structural detail, on sub-picosecond time scales (Tenboer et al 2014 Science 346 1242–6, Barends et al 2015 Science 350 445–50, Pande et al 2016 Science 352 725–9). We review here state-of-the-art time-resolved crystallographic experiments both at synchrotrons and XFELs

Simultaneously time- and space-resolved spectroscopic characterization of laser-produced plasmas

International Nuclear Information System (INIS)

Charatis, G.; Young, B.K.F.; Busch, G.E.

1988-01-01

The CHROMA laser facility at KMS Fusion has been used to irradiate a variety of microdot targets. These include aluminum dots and mixed bromine dots doped with K-shell (magnesium) emitters. Simultaneously time- and space-resolved K-shell and L-shell spectra have been measured and compared to dynamic model predictions. The electron density profiles are measured using holographic interferometry. Temperatures, densities, and ionization distributions are determined using K-shell and L-shell spectral techniques. Time and spatial gradients are resolved simultaneously using three diagnostics: a framing crystal x-ray spectrometer, an x-ray streaked crystal spectrometer with a spatial imaging slit, and a 4-frame holographic interferometer. Significant differences have been found between the interferometric and the model-dependent spectral measurements of plasma density. Predictions by new non-stationary L-shell models currently being developed are also presented. 14 refs., 10 figs

Time-Resolved Magnetic Field Effects Distinguish Loose Ion Pairs from Exciplexes

Science.gov (United States)

2013-01-01

We describe the experimental investigation of time-resolved magnetic field effects in exciplex-forming organic donor–acceptor systems. In these systems, the photoexcited acceptor state is predominantly deactivated by bimolecular electron transfer reactions (yielding radical ion pairs) or by direct exciplex formation. The delayed fluorescence emitted by the exciplex is magnetosensitive if the reaction pathway involves loose radical ion pair states. This magnetic field effect results from the coherent interconversion between the electronic singlet and triplet radical ion pair states as described by the radical pair mechanism. By monitoring the changes in the exciplex luminescence intensity when applying external magnetic fields, details of the reaction mechanism can be elucidated. In this work we present results obtained with the fluorophore-quencher pair 9,10-dimethylanthracene/N,N-dimethylaniline (DMA) in solvents of systematically varied permittivity. A simple theoretical model is introduced that allows discriminating the initial state of quenching, viz., the loose ion pair and the exciplex, based on the time-resolved magnetic field effect. The approach is validated by applying it to the isotopologous fluorophore-quencher pairs pyrene/DMA and pyrene-d10/DMA. We detect that both the exciplex and the radical ion pair are formed during the initial quenching stage. Upon increasing the solvent polarity, the relative importance of the distant electron transfer quenching increases. However, even in comparably polar media, the exciplex pathway remains remarkably significant. We discuss our results in relation to recent findings on the involvement of exciplexes in photoinduced electron transfer reactions. PMID:24041160

Time-resolved quantitative phosphoproteomics

DEFF Research Database (Denmark)

Verano-Braga, Thiago; Schwämmle, Veit; Sylvester, Marc

2012-01-01

proteins involved in the Ang-(1-7) signaling, we performed a mass spectrometry-based time-resolved quantitative phosphoproteome study of human aortic endothelial cells (HAEC) treated with Ang-(1-7). We identified 1288 unique phosphosites on 699 different proteins with 99% certainty of correct peptide...

Time-Resolved Tandem Faraday Cup Development for High Energy TNSA Particles

Science.gov (United States)

Padalino, S.; Simone, A.; Turner, E.; Ginnane, M. K.; Glisic, M.; Kousar, B.; Smith, A.; Sangster, C.; Regan, S.

2015-11-01

MTW and OMEGA EP Lasers at LLE utilize ultra-intense laser light to produce high-energy ion pulses through Target Normal Sheath Acceleration (TNSA). A Time Resolved Tandem Faraday Cup (TRTF) was designed and built to collect and differentiate protons from heavy ions (HI) produced during TNSA. The TRTF includes a replaceable thickness absorber capable of stopping a range of user-selectable HI emitted from TNSA plasma. HI stop within the primary cup, while less massive particles continue through and deposit their remaining charge in the secondary cup, releasing secondary electrons in the process. The time-resolved beam current generated in each cup will be measured on a fast storage scope in multiple channels. A charge-exchange foil at the TRTF entrance modifies the charge state distribution of HI to a known distribution. Using this distribution and the time of flight of the HI, the total HI current can be determined. Initial tests of the TRTF have been made using a proton beam produced by SUNY Geneseo's 1.7 MV Pelletron accelerator. A substantial reduction in secondary electron production, from 70% of the proton beam current at 2MeV down to 0.7%, was achieved by installing a pair of dipole magnet deflectors which successfully returned the electrons to the cups in the TRTF. Ultimately the TRTF will be used to normalize a variety of nuclear physics cross sections and stopping power measurements. Based in part upon work supported by a DOE NNSA Award#DE-NA0001944.

Instruments and techniques for analysing the time-resolved transverse phase space distribution of high-brightness electron beams

International Nuclear Information System (INIS)

Rudolph, Jeniffa

2012-01-01

This thesis deals with the instruments and techniques used to characterise the transverse phase space distribution of high-brightness electron beams. In particular, methods are considered allowing to measure the emittance as a function of the longitudinal coordinate within the bunch (slice emittance) with a resolution in the ps to sub-ps range. The main objective of this work is the analysis of techniques applicable for the time-resolved phase space characterisation for future high-brightness electron beam sources and single-pass accelerators based on these. The competence built up by understanding and comparing different techniques is to be used for the design and operation of slice diagnostic systems for the Berlin Energy Recovery Linac Project (BERLinPro). In the framework of the thesis, two methods applicable for slice emittance measurements are considered, namely the zero-phasing technique and the use of a transverse deflector. These methods combine the conventional quadrupole scan technique with a transfer of the longitudinal distribution into a transverse distribution. Measurements were performed within different collaborative projects. The experimental setup, the measurement itself and the data analysis are discussed as well as measurement results and simulations. In addition, the phase space tomography technique is introduced. In contrast to quadrupole scan-based techniques, tomography is model-independent and can reconstruct the phase space distribution from simple projected measurements. The developed image reconstruction routine based on the Maximum Entropy algorithm is introduced. The quality of the reconstruction is tested using different model distributions, simulated data and measurement data. The results of the tests are presented. The adequacy of the investigated techniques, the experimental procedures as well as the developed data analysis tools could be verified. The experimental and practical experience gathered during this work, the

Quantitative analysis of time-resolved infrared stimulated luminescence in feldspars

Energy Technology Data Exchange (ETDEWEB)

Pagonis, Vasilis, E-mail: vpagonis@mcdaniel.edu [McDaniel College, Physics Department, Westminster, MD 21157 (United States); Ankjærgaard, Christina [Soil Geography and Landscape Group & Netherlands Centre for Luminescence dating, Wageningen University, PO Box 47, 6700 AA Wageningen (Netherlands); Jain, Mayank [Center for Nuclear Technologies, Technical University of Denmark, DTU Risø Campus, Roskilde (Denmark); Chithambo, Makaiko L. [Department of Physics and Electronics, Rhodes University, PO BOX 94, Grahamstown 6140 (South Africa)

2016-09-15

Time-resolved infrared-stimulated luminescence (TR-IRSL) from feldspar samples is of importance in the field of luminescence dating, since it provides information on the luminescence mechanism in these materials. In this paper we present new analytical equations which can be used to analyze TR-IRSL signals, both during and after short infrared stimulation pulses. The equations are developed using a recently proposed kinetic model, which describes localized electronic recombination via tunneling between trapped electrons and recombination centers in luminescent materials. Recombination is assumed to take place from the excited state of the trapped electron to the nearest-neighbor center within a random distribution of luminescence recombination centers. Different possibilities are examined within the model, depending on the relative importance of electron de-excitation and recombination. The equations are applied to experimental TR-IRSL data of natural feldspars, and good agreement is found between experimental and modeling results.

Time-resolved studies. Ch. 9

International Nuclear Information System (INIS)

Mills, Dennis M.; Argonne National Lab., IL

1991-01-01

Synchrotron radiation, with its unique properties, offers a tool to extend X-ray measurements from the static to the time-resolved regime. The most straight-forward application of synchrotron radiation to the study of transient phenomena is directly through the possibility of decreased data-collection times via the enormous increase in flux over that of a laboratory X-ray system. Even further increases in intensity can be obtained through the use of novel X-ray optical devices. Wide-bandpass monochromators, e.g., that utilize the continuous spectral distribution of synchrotron radiation, can increase flux on the sample several orders of magnitude over conventional X-ray optical systems thereby allowing a further shortening of the data-collection time. Another approach that uses the continuous spectral nature of synchrotron radiation to decrease data-collection times is the 'parallel data collection' method. Using this technique, intensities as a function of X-ray energy are recorded simultaneously for all energies rather than sequentially recording data at each energy, allowing for a dramatic decrease in data-collection time. Perhaps the most exciting advances in time-resolved X-ray studies will be made by those methods that exploit the pulsed nature of the radiation emitted from storage rings. Pulsed techniques have had an enormous impact in the study of the temporal evolution of transient phenomena. The extension from continuous to modulated sources for use in time-resolved work has been carried over in a host of fields that use both pulsed particle and pulsed electro-magnetic beams. In this chapter the new experimental techniques are reviewed and illustrated with some experiments. (author). 98 refs.; 20 figs.; 5 tabs

Deflection evaluation using time-resolved radiography

International Nuclear Information System (INIS)

Fry, D.A.; Lucero, J.P.

1990-01-01

Time-resolved radiography is the creation of an x-ray image for which both the start-exposure and stop-exposure times are known with respect to the event under study. The combination of image and timing are used to derive information about the event. The authors have applied time-resolved radiography to evaluate motions of explosive-driven events. In the particular application discussed in this paper, the author's intent is to measure maximum deflections of the components involved. Exposures are made during the time just before to just after the event of interest occurs. A smear or blur of motion out to its furthest extent is recorded on the image. Comparison of the dynamic images with static images allows deflection measurements to be made

[A new measurement method of time-resolved spectrum].

Science.gov (United States)

Shi, Zhi-gang; Huang, Shi-hua; Liang, Chun-jun; Lei, Quan-sheng

2007-02-01

A new method for measuring time-resolved spectrum (TRS) is brought forward. Programming with assemble language controlled the micro-control-processor (AT89C51), and a kind of peripheral circuit constituted the drive circuit, which drived the stepping motor to run the monochromator. So the light of different kinds of expected wavelength could be obtained. The optical signal was transformed to electrical signal by optical-to-electrical transform with the help of photomultiplier tube (Hamamatsu 1P28). The electrical signal of spectrum data was transmitted to the oscillograph. Connecting the two serial interfaces of RS232 between the oscillograph and computer, the electrical signal of spectrum data could be transmitted to computer for programming to draw the attenuation curve and time-resolved spectrum (TRS) of the swatch. The method for measuring time-resolved spectrum (TRS) features parallel measurement in time scale but serial measurement in wavelength scale. Time-resolved spectrum (TRS) and integrated emission spectrum of Tb3+ in swatch Tb(o-BBA)3 phen were measured using this method. Compared with the real time-resolved spectrum (TRS). It was validated to be feasible, credible and convenient. The 3D spectra of fluorescence intensity-wavelength-time, and the integrated spectrum of the swatch Tb(o-BBA)3 phen are given.

Electron-plasmon and electron-phonon satellites in the angle-resolved photoelectron spectra of n -doped anatase TiO2

Science.gov (United States)

Caruso, Fabio; Verdi, Carla; Poncé, Samuel; Giustino, Feliciano

2018-04-01

We develop a first-principles approach based on many-body perturbation theory to investigate the effects of the interaction between electrons and carrier plasmons on the electronic properties of highly doped semiconductors and oxides. Through the evaluation of the electron self-energy, we account simultaneously for electron-plasmon and electron-phonon coupling in theoretical calculations of angle-resolved photoemission spectra, electron linewidths, and relaxation times. We apply this methodology to electron-doped anatase TiO2 as an illustrative example. The simulated spectra indicate that electron-plasmon coupling in TiO2 underpins the formation of satellites at energies comparable to those of polaronic spectral features. At variance with phonons, however, the energy of plasmons and their spectral fingerprints depends strongly on the carrier concentration, revealing a complex interplay between plasmon and phonon satellites. The electron-plasmon interaction accounts for approximately 40% of the total electron-boson interaction strength, and it is key to improve the agreement with measured quasiparticle spectra.

Resolving molecular vibronic structure using high-sensitivity two-dimensional electronic spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Bizimana, Laurie A.; Brazard, Johanna; Carbery, William P.; Gellen, Tobias; Turner, Daniel B., E-mail: dturner@nyu.edu [Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003 (United States)

2015-10-28

Coherent multidimensional optical spectroscopy is an emerging technique for resolving structure and ultrafast dynamics of molecules, proteins, semiconductors, and other materials. A current challenge is the quality of kinetics that are examined as a function of waiting time. Inspired by noise-suppression methods of transient absorption, here we incorporate shot-by-shot acquisitions and balanced detection into coherent multidimensional optical spectroscopy. We demonstrate that implementing noise-suppression methods in two-dimensional electronic spectroscopy not only improves the quality of features in individual spectra but also increases the sensitivity to ultrafast time-dependent changes in the spectral features. Measurements on cresyl violet perchlorate are consistent with the vibronic pattern predicted by theoretical models of a highly displaced harmonic oscillator. The noise-suppression methods should benefit research into coherent electronic dynamics, and they can be adapted to multidimensional spectroscopies across the infrared and ultraviolet frequency ranges.

Development of a Nomarski-type multi-frame interferometer as a time and space resolving diagnostics for the free electron density of laser-generated plasma

International Nuclear Information System (INIS)

Boerner, M.; Frank, A.; Pelka, A.; Schaumann, G.; Schoekel, A.; Schumacher, D.; Roth, M.; Fils, J.; Blazevic, A.; Hessling, T.; Basko, M. M.; Maruhn, J.; Tauschwitz, An.

2012-01-01

This article reports on the development and set-up of a Nomarski-type multi-frame interferometer as a time and space resolving diagnostics of the free electron density in laser-generated plasma. The interferometer allows the recording of a series of 4 images within 6 ns of a single laser-plasma interaction. For the setup presented here, the minimal accessible free electron density is 5 x 10 18 cm -3 , the maximal one is 2 x 10 20 cm -3 . Furthermore, it provides a resolution of the electron density in space of 50 μm and in time of 0.5 ns for one image with a customizable magnification in space for each of the 4 images. The electron density was evaluated from the interferograms using an Abel inversion algorithm. The functionality of the system was proven during first experiments and the experimental results are presented and discussed. A ray tracing procedure was realized to verify the interferometry pictures taken. In particular, the experimental results are compared to simulations and show excellent agreement, providing a conclusive picture of the evolution of the electron density distribution.

Denoising time-resolved microscopy image sequences with singular value thresholding

Energy Technology Data Exchange (ETDEWEB)

Furnival, Tom, E-mail: tjof2@cam.ac.uk; Leary, Rowan K., E-mail: rkl26@cam.ac.uk; Midgley, Paul A., E-mail: pam33@cam.ac.uk

2017-07-15

Time-resolved imaging in microscopy is important for the direct observation of a range of dynamic processes in both the physical and life sciences. However, the image sequences are often corrupted by noise, either as a result of high frame rates or a need to limit the radiation dose received by the sample. Here we exploit both spatial and temporal correlations using low-rank matrix recovery methods to denoise microscopy image sequences. We also make use of an unbiased risk estimator to address the issue of how much thresholding to apply in a robust and automated manner. The performance of the technique is demonstrated using simulated image sequences, as well as experimental scanning transmission electron microscopy data, where surface adatom motion and nanoparticle structural dynamics are recovered at rates of up to 32 frames per second. - Highlights: • Correlations in space and time are harnessed to denoise microscopy image sequences. • A robust estimator provides automated selection of the denoising parameter. • Motion tracking and automated noise estimation provides a versatile algorithm. • Application to time-resolved STEM enables study of atomic and nanoparticle dynamics.

Time-resolved emission from laser-ablated uranium

International Nuclear Information System (INIS)

Stoffels, E.; Mullen, J. van der; Weijer, P. van de

1991-01-01

Time-resolved emission spectra from the plasma, induced by laser ablation of uranium samples have been studied. The dependence of the emission intensity on time is strongly affected by the nature and pressure of the buffer gas. Air and argon have been used in the pressure range 0.002 to 5 mbar. The emission intensity as a function of time displays three maxima, indicating that three different processes within the expanding plasma plume are involved. On basis of the time-resolved spectra we propose a model that explains qualitatively the phenomena that are responsible for this time behaviour. (author)

Angle-resolved photoelectron spectrometry: new electron optics and detection system

International Nuclear Information System (INIS)

Hoof, H.A. van.

1980-01-01

A new spectrometer system is described, designed to measure angle-resolved energy distributions of photoemitted electrons efficiently. Some results are presented of measurements on a Si(001) surface. (Auth.)

Prospects for quantitative and time-resolved double and continuous exposure off-axis electron holography

Energy Technology Data Exchange (ETDEWEB)

Migunov, Vadim, E-mail: v.migunov@fz-juelich.de [Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich (Germany); Dwyer, Christian [Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich (Germany); Department of Physics, Arizona State University, Tempe, AZ 85287 (United States); Boothroyd, Chris B. [Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich (Germany); Pozzi, Giulio [Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich (Germany); Department of Physics and Astronomy, University of Bologna, viale B. Pichat 6/2, Bologna 40127 (Italy); Dunin-Borkowski, Rafal E. [Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich (Germany)

2017-07-15

The technique of double exposure electron holography, which is based on the superposition of two off-axis electron holograms, was originally introduced before the availability of digital image processing to allow differences between electron-optical phases encoded in two electron holograms to be visualised directly without the need for holographic reconstruction. Here, we review the original method and show how it can now be extended to permit quantitative studies of phase shifts that oscillate in time. We begin with a description of the theory of off-axis electron hologram formation for a time-dependent electron wave that results from the excitation of a specimen using an external stimulus with a square, sinusoidal, triangular or other temporal dependence. We refer to the more general method as continuous exposure electron holography, present preliminary experimental measurements and discuss how the technique can be used to image electrostatic potentials and magnetic fields during high frequency switching experiments. - Highlights: • Double and continuous exposure electron holography are described in detail. • The ability to perform quantitative studies of phase shifts that are oscillating in time is illustrated. • Theoretical considerations related to noise are presented. • Future high frequency electromagnetic switching experiments are proposed.

Femtosecond time-resolved two-photon photoemission study of organic semiconductor copper phthalocyanine film

International Nuclear Information System (INIS)

Tanaka, A.; Tohoku University; University of Rochester, NY; Yan, L.; Watkins, N.J.; Gao, Y.

2004-01-01

Full text: Organic semiconductors are recently attracting much interest from the viewpoints of both device and fundamental physics. These organic semiconductors are considered to be important constituents of the future devices, such as organic light-emitting diode, organic field effect transistor, and organic solid-state injection laser. In order to elucidate their detailed physical properties and to develop the future devices, it is indispensable to understand their excited-state dynamics as well as their electronic structures. The femtosecond time-resolved two-photon photoemission (TR-2PPE) spectroscopy is attracting much interest because of its capability to observe the energy-resolved excited electron dynamics. In this work, we have carried out a TR-2PPE study of the organic semiconductor copper phthalocyanine (CuPc) film. Furthermore, we have investigated the detailed electronic structure of CuPc film using the photoemission (PES) and inverse photoemission (IPES) spectroscopies. From the simultaneous PES and IPES measurements for CuPc film with a thickness of 100 nm, the lowest unoccupied molecular orbital (LUMO), highest occupied molecular orbital, and ionization potential of CuPc film have been directly determined. The observed two-photon photoemission (2PPE) spectrum of the present CuPc film, measured with photon energy of about hv=3.3 eV, exhibits a broad feature. From the energy diagram of CuPc film determined by the PES and IPES measurements, the intermediate state observed in the present 2PPE spectrum of CuPc film corresponds to the energy region between about 0.4 and 1.7 eV above the LUMO energy. From the time-resolved pump-probe measurements, it is found that the relaxation lifetimes of excited states in the present CuPc films are very short (all below 50 fs) and monotonously become faster with increasing excitation energy. We attribute this extremely fast relaxation process of photoexcitation to a rapid internal conversion process. From these results

Introduction to Time-Resolved Spectroscopy: Nanosecond Transient Absorption and Time-Resolved Fluorescence of Eosin B

Science.gov (United States)

Farr, Erik P.; Quintana, Jason C.; Reynoso, Vanessa; Ruberry, Josiah D.; Shin, Wook R.; Swartz, Kevin R.

2018-01-01

Here we present a new undergraduate laboratory that will introduce the concepts of time-resolved spectroscopy and provide insight into the natural time scales on which chemical dynamics occur through direct measurement. A quantitative treatment of the acquired data will provide a deeper understanding of the role of quantum mechanics and various…

Time-resolved X-ray photoelectron spectroscopy techniques for the study of interfacial charge dynamics

Energy Technology Data Exchange (ETDEWEB)

Neppl, Stefan, E-mail: sneppl@lbl.gov; Gessner, Oliver

2015-04-15

Highlights: • Ultrafast interfacial charge transfer is probed with atomic site specificity. • Femtosecond X-ray photoelectron spectroscopy using a free electron laser. • Efficient and flexible picosecond X-ray photoelectron pump–probe scheme using synchrotron radiation. - Abstract: X-ray photoelectron spectroscopy (XPS) is one of the most powerful techniques to quantitatively analyze the chemical composition and electronic structure of surfaces and interfaces in a non-destructive fashion. Extending this technique into the time domain has the exciting potential to shed new light on electronic and chemical dynamics at surfaces by revealing transient charge configurations with element- and site-specificity. Here, we describe prospects and challenges that are associated with the implementation of picosecond and femtosecond time-resolved X-ray photoelectron spectroscopy at third-generation synchrotrons and X-ray free-electron lasers, respectively. In particular, we discuss a series of laser-pump/X-ray-probe photoemission experiments performed on semiconductor surfaces, molecule-semiconductor interfaces, and films of semiconductor nanoparticles that demonstrate the high sensitivity of time-resolved XPS to light-induced charge carrier generation, diffusion and recombination within the space charge layers of these materials. Employing the showcase example of photo-induced electronic dynamics in a dye-sensitized semiconductor system, we highlight the unique possibility to probe heterogeneous charge transfer dynamics from both sides of an interface, i.e., from the perspective of the molecular electron donor and the semiconductor acceptor, simultaneously. Such capabilities will be crucial to improve our microscopic understanding of interfacial charge redistribution and associated chemical dynamics, which are at the heart of emerging energy conversion, solar fuel generation, and energy storage technologies.

Time-resolved cathodoluminescence microscopy with sub-nanosecond beam blanking for direct evaluation of the local density of states

NARCIS (Netherlands)

Moerland, R.J.; Weppelman, I.G.C.; Garming, M.W.H.; Kruit, P.; Hoogenboom, J.P.

2016-01-01

We show cathodoluminescence-based time-resolved electron beam spectroscopy in order to directly probe the spontaneous emission decay rate that is modified by the local density of states in a nanoscale environment. In contrast to dedicated laser-triggered electron-microscopy setups, we use commercial

Time resolved resonant inelastic X-ray scattering: A supreme tool to understand dynamics in solids and molecules

International Nuclear Information System (INIS)

Beye, M.; Wernet, Ph.; Schüßler-Langeheine, C.; Föhlisch, A.

2013-01-01

Highlights: •The high specificity of RIXS ideally suits time-resolved measurements. •Methods relating to the core hole lifetime cover the low femtosecond regime. •Pump-probe methods are used starting at sub-ps time scales. •FELs and synchrotrons are useful for pump-probe studies. •Examples from solid state dynamics and molecules are discussed. -- Abstract: Dynamics in materials typically involve different degrees of freedom, like charge, lattice, orbital and spin in a complex interplay. Time-resolved resonant inelastic X-ray scattering (RIXS) as a highly selective tool can provide unique insight and follow the details of dynamical processes while resolving symmetries, chemical and charge states, momenta, spin configurations, etc. In this paper, we review examples where the intrinsic scattering duration time is used to study femtosecond phenomena. Free-electron lasers access timescales starting in the sub-ps range through pump-probe methods and synchrotrons study the time scales longer than tens of ps. In these examples, time-resolved resonant inelastic X-ray scattering is applied to solids as well as molecular systems

Time- and Site-Resolved Dynamics in a Topological Circuit

Directory of Open Access Journals (Sweden)

Jia Ningyuan

2015-06-01

Full Text Available From studies of exotic quantum many-body phenomena to applications in spintronics and quantum information processing, topological materials are poised to revolutionize the condensed-matter frontier and the landscape of modern materials science. Accordingly, there is a broad effort to realize topologically nontrivial electronic and photonic materials for fundamental science as well as practical applications. In this work, we demonstrate the first simultaneous site- and time-resolved measurements of a time-reversal-invariant topological band structure, which we realize in a radio-frequency photonic circuit. We control band-structure topology via local permutation of a traveling-wave capacitor-inductor network, increasing robustness by going beyond the tight-binding limit. We observe a gapped density of states consistent with a modified Hofstadter spectrum at a flux per plaquette of ϕ=π/2. In situ probes of the band gaps reveal spatially localized bulk states and delocalized edge states. Time-resolved measurements reveal dynamical separation of localized edge excitations into spin-polarized currents. The radio-frequency circuit paradigm is naturally compatible with nonlocal coupling schemes, allowing us to implement a Möbius strip topology inaccessible in conventional systems. This room-temperature experiment illuminates the origins of topology in band structure, and when combined with circuit quantum electrodynamics techniques, it provides a direct path to topologically ordered quantum matter.

The TimBel synchronization board for time resolved experiments at synchrotron SOLEIL

International Nuclear Information System (INIS)

Ricaud, J.P.; Betinelli-Deck, P.; Bisou, J.; Elattaoui, X.; Laulhe, C.; Monteiro, P.; Nadolski, L.S.; Renaud, G.; Ravy, S.; Silly, M.; Sirotti, F.

2012-01-01

Time resolved experiments are one of the major services that synchrotrons can provide to scientists. The short, high frequency and regular flashes of synchrotron light are a fantastic tool to study the evolution of phenomena over time. To carry out time resolved experiments, beamlines need to synchronize their devices with these flashes of light with a jitter shorter than the pulse duration. For that purpose, Synchrotron SOLEIL has developed the TimBeL (Timing Beamlines) board fully interfaced to TANGO framework. The TimBeL system is a compact PCI board. It is made of a mother with one daughter board. All functions are performed inside a FPGA (Field Programmable Gate Array) implemented on the mother board. A PLX Technology chip is used to communicate with the compact PCI crate. To enable experiments to remain always synchronous with the same bunch of electrons, the storage ring clock (CLK-SR) and the radio frequency clock (CLK-RF) are provided by the machine to beamlines. These clocks are used inside the FPGA as main clocks for state machines. Because the jitter is too large on the FPGA outputs, a daughter board with a jitter cleaner has been added to the system. This board also provides delay lines for compensating time offsets by 10 ps steps. This paper presents the main features required by time resolved experiments and how we achieved our goals with the TimBeL board

Time Resolved Detection of Infrared Synchrotron Radiation at DAΦNE

International Nuclear Information System (INIS)

Bocci, A.; Marcelli, A.; Drago, A.; Guidi, M. Cestelli; Pace, E.; Piccinini, M.; Sali, D.; Morini, P.; Piotrowski, J.

2007-01-01

Synchrotron radiation is characterized by a very wide spectral emission from IR to X-ray wavelengths and a pulsed structure that is a function of the source time structure. In a storage ring, the typical temporal distance between two bunches, whose duration is a few hundreds of picoseconds, is on the nanosecond scale. Therefore, synchrotron radiation sources are a very powerful tools to perform time-resolved experiments that however need extremely fast detectors. Uncooled IR devices optimized for the mid-IR range with sub-nanosecond response time, are now available and can be used for fast detection of intense IR sources such as synchrotron radiation storage rings. We present here different measurements of the pulsed synchrotron radiation emission at DAΦNE (Double Annular Φ-factory for Nice Experiments), the collider of the Laboratori Nazionali of Frascati (LNF) of the Istituto Nazionale di Fisica Nucleare (INFN), performed with very fast uncooled infrared detectors with a time resolution of a few hundreds of picoseconds. We resolved the emission time structure of the electron bunches of the DAΦNE collider when it works in a normal condition for high energy physics experiments with both photovoltaic and photoconductive detectors. Such a technology should pave the way to new diagnostic methods in storage rings, monitoring also source instabilities and bunch dynamics

Identifiability analysis of rotational diffusion tensor and electronic transition moments measured in time-resolved fluorescence depolarization experiment

International Nuclear Information System (INIS)

Szubiakowski, Jacek P.

2014-01-01

The subject of this paper is studies of the deterministic identifiability of molecular parameters, such as rotational diffusion tensor components and orientation of electronic transition moments, resulting from the time-resolved fluorescence anisotropy experiment. In the most general case considered, a pair of perpendicularly polarized emissions enables the unique determination of all the rotational diffusion tensor's principal components. The influence of the tensor's symmetry and the associated degeneration of its eigenvalues on the identifiability of the electronic transitions moments is systematically investigated. The analysis reveals that independently of the rotational diffusion tensor's symmetry, the transition moments involved in photoselection and emission processes cannot be uniquely identified without a priori information about their mutual orientation or their orientation with respect to the principal axes of the tensor. Moreover, it is shown that increasing the symmetry of the rotational diffusion tensor deteriorates the degree of the transition moments identifiability. To obtain these results analytically, a novel approach to solve bilinear system of equations for Markov parameters is applied. The effect of the additional information, obtained from fluorescence measurements for different molecular mobilities, to improve the identifiability at various levels of analysis is shown. The effectiveness and reliability of the target analysis method for experimental determination of the molecular parameters is also discussed

Electron Bunch Timing with Femtosecond Precision in a Superconducting Free-Electron Laser

Science.gov (United States)

Löhl, F.; Arsov, V.; Felber, M.; Hacker, K.; Jalmuzna, W.; Lorbeer, B.; Ludwig, F.; Matthiesen, K.-H.; Schlarb, H.; Schmidt, B.; Schmüser, P.; Schulz, S.; Szewinski, J.; Winter, A.; Zemella, J.

2010-04-01

High-gain free-electron lasers (FELs) are capable of generating femtosecond x-ray pulses with peak brilliances many orders of magnitude higher than at other existing x-ray sources. In order to fully exploit the opportunities offered by these femtosecond light pulses in time-resolved experiments, an unprecedented synchronization accuracy is required. In this Letter, we distributed the pulse train of a mode-locked fiber laser with femtosecond stability to different locations in the linear accelerator of the soft x-ray FEL FLASH. A novel electro-optic detection scheme was applied to measure the electron bunch arrival time with an as yet unrivaled precision of 6 fs (rms). With two beam-based feedback systems we succeeded in stabilizing both the arrival time and the electron bunch compression process within two magnetic chicanes, yielding a significant reduction of the FEL pulse energy jitter.

Electron Bunch Timing with Femtosecond Precision in a Superconducting Free-Electron Laser

International Nuclear Information System (INIS)

Loehl, F.; Arsov, V.; Felber, M.; Hacker, K.; Lorbeer, B.; Ludwig, F.; Matthiesen, K.-H.; Schlarb, H.; Schmidt, B.; Winter, A.; Jalmuzna, W.; Schmueser, P.; Schulz, S.; Zemella, J.; Szewinski, J.

2010-01-01

High-gain free-electron lasers (FELs) are capable of generating femtosecond x-ray pulses with peak brilliances many orders of magnitude higher than at other existing x-ray sources. In order to fully exploit the opportunities offered by these femtosecond light pulses in time-resolved experiments, an unprecedented synchronization accuracy is required. In this Letter, we distributed the pulse train of a mode-locked fiber laser with femtosecond stability to different locations in the linear accelerator of the soft x-ray FEL FLASH. A novel electro-optic detection scheme was applied to measure the electron bunch arrival time with an as yet unrivaled precision of 6 fs (rms). With two beam-based feedback systems we succeeded in stabilizing both the arrival time and the electron bunch compression process within two magnetic chicanes, yielding a significant reduction of the FEL pulse energy jitter.

Time-resolved hard x-ray studies using third-generation synchrotron radiation sources (abstract)

International Nuclear Information System (INIS)

Mills, D.M.

1992-01-01

The third-generation, high-brilliance, synchrotron radiation sources currently under construction will usher in a new era of x-ray research in the physical, chemical, and biological sciences. One of the most exciting areas of experimentation will be the extension of static x-ray scattering and diffraction techniques to the study of transient or time-evolving systems. The high repetition rate, short-pulse duration, high-brilliance, variable spectral bandwidth, and large particle beam energies of these sources make them ideal for hard x-ray, time-resolved studies. The primary focus of this presentation will be on the novel instrumentation required for time-resolved studies such as optics which can increase the flux on the sample or disperse the x-ray beam, detectors and electronics for parallel data collection, and methods for altering the natural time structure of the radiation. This work is supported by the U.S. Department of Energy, BES-Materials Science, under Contract No. W-31-109-ENG-38

Time resolved two- and three-dimensional plasma diagnostics

International Nuclear Information System (INIS)

1991-03-01

This collection of papers on diagnostics in fusion plasmas contains work on the data analysis of inverse problems and on the experimental arrangements presently used to obtain spatially and temporally resolved plasma radial profiles, including electron and ion temperature, plasma density and plasma current profiles. Refs, figs and tabs

Subcycle interference dynamics of time-resolved photoelectron holography with midinfrared laser pulses

International Nuclear Information System (INIS)

Bian Xuebin; Yuan, Kai-Jun; Bandrauk, Andre D.; Huismans, Y.; Smirnova, O.; Vrakking, M. J. J.

2011-01-01

Time-resolved photoelectron holography from atoms using midinfrared laser pulses is investigated by solving the corresponding time-dependent Schroedinger equation (TDSE) and a classical model, respectively. The numerical simulation of the photoelectron angular distribution of Xe irradiated with a low-frequency free-electron laser source agrees well with the experimental results. Different types of subcycle interferometric structures are predicted by the classical model. Furthermore with the TDSE model it is demonstrated that the holographic pattern is sensitive to the shape of the atomic orbitals. This is a step toward imaging by means of photoelectron holography.

Spatially and temporally resolved diagnostics for microsecond, intense electron beams

International Nuclear Information System (INIS)

Gilgenbach, R.M.; Brake, M.; Horton, L.D.; Bidwell, S.; Lucey, R.F.; Smutek, L.; Tucker, J.E.

1985-01-01

Experiments are underway to investigate new diagnostics for electron beams in vacuum and in a plasma background. Measured parameters include temporally resolved beam current profile and beam emittance. These characterizations are being performed during electron beam diode closure experiments (1) and beam-plasma interaction experiments with either of two long-pulse accelerators: MELBA (Michigan Electron Long Beam Accelerator): Voltage = -1 MV, Current = 10 kA, at Pulselength = 0.1 to 1μs (1.4μs) for voltage flat to within +.7% (+.10%). The second accelerator is a long-pulse Febetron with parameters: Voltage = -0.5 MV, Current = 1 kA, and Pulselength = 0.3 s. Two different configurations have been developed which use Cerenkov radiation to detect electron beam current profiles as a function of time. The first uses Cerenkov emission by electrons which impinge axially on a single fiberoptic lightguide enclosed in a lucite tube. Plasma light is blocked by graphite spray or thin foil covering the end of the optical fiber. This diagnostic has the following advantages: 1) The threshold energy for Cerenkov emission effectively discriminates between high energy beam electrons and low energy (3-5 eV) plasma electrons, 2) The small, nonconducting probe introduces a minimal perturbation into the beam-plasma system, 3) Excellent signal to noise ratio is obtained because the fiberoptic signal is directly transmitted to a photomultiplier tube in the Faraday cage, 4) Quantitative data is obtained directly

Energy- and time-resolved microscopy using PEEM: recent developments and state-of-the-art

Energy Technology Data Exchange (ETDEWEB)

Weber, N B; Escher, M; Merkel, M [FOCUS GmbH, Neukirchner Strasse 2, 65510 Huenstetten (Germany); Oelsner, A [Surface Concept GmbH, Staudingerweg 7, 55099 Mainz (Germany); Schoenhense, G [Johannes Gutenberg Universitaet, Institut fuer Physik, 55099 Mainz (Germany)], E-mail: n.weber@focus-gmbh.com

2008-03-15

Two novel methods of spectroscopic surface imaging are discussed, both based on photoemission electron microscopy PEEM. They are characterised by a simple electron-optical set up retaining a linear column. An imaging high-pass energy filter has been developed on the basis of lithographically-fabricated microgrids. Owing to a mesh size of only 7{mu}m, no image distortions occur. The present energy resolution is 70 meV. The second approach employs time-of-flight energy dispersion and time-resolved detection using a Delayline Detector. In this case, the drift energy and the time resolution of the detector determine the energy resolution. The present time resolution is 180 ps, giving rise to an energy resolution in the 100 meV range.

Can positron 2D-ACAR resolve the electronic structure of high-Tc superconductors

International Nuclear Information System (INIS)

Chan, L.P.; Lynn, K.G.; Harshman, D.R.

1992-01-01

In this paper, the authors examine the ability of the positron Two-Dimensional Angular Correlation Annihilation Radiation (2D-ACAR) technique to resolve the electronic structures of high-T c cuprate superconductors. Following a short description of the technique, discussions of the theoretical assumptions, data analysis and experimental considerations, in relation to the high-T c superconductors, are given. The authors briefly review recent 2D-ACAR experiments on YBa 2 Cu 3 O 7-x , Bi 2 Sr 2 CaCuO 8+δ and La 2-x Sr x CuO 4 . The 2D-ACAR technique is useful in resolving the band crossings associated with the layers of the superconductors that are preferentially sampled by the positrons. Together with other Fermi surface measurements (namely angle-resolved photoemission), 2D-ACAR can resolve some of the electronic structures of high-T c cuprate superconductors

Direct observation of ultrafast atomic motion using time-resolved X-ray diffraction

Energy Technology Data Exchange (ETDEWEB)

Shymanovich, U.

2007-11-13

This thesis is dedicated to the study of the atomic motion in laser irradiated solids on a picosecond to subpicosecond time-scale using the time-resolved X-ray diffraction technique. In the second chapter, the laser system, the laser-plasma based X-ray source and the experimental setup for optical pump / X-ray probe measurements were presented. Chapter 3 is devoted to the characterization and comparison of different types of X-ray optics. Chapter 4 presented the time-resolved X-ray diffraction experiments performed for this thesis. The first two sections of this chapter discuss the measurements of initially unexpected strain-induced transient changes of the integrated reflectivity of the X-ray probe beam. The elimination of the strain-induced transient changes of the integrated reflectivity represented an important prerequisite to perform the study of lattice heating in Germanium after femtosecond optical excitation by measuring the transient Debye-Waller effect. The third section describes the investigations of acoustic waves upon ultrafast optical excitation and discusses the two different pressure contributions driving them: the thermal and the electronic ones. (orig.)

Time-resolved GISAXS and cryo-microscopy characterization of block copolymer membrane formation

KAUST Repository

Marques, Debora S.; Dorin, Rachel Mika; Wiesner, Ulrich B.; Smilgies, Detlef Matthias; Behzad, Ali Reza; Vainio, Ulla; Peinemann, Klaus-Viktor; Nunes, Suzana Pereira

2014-01-01

Time-resolved grazing-incidence small-angle X-ray scattering (GISAXS) and cryo-microscopy were used for the first time to understand the pore evolution by copolymer assembly, leading to the formation of isoporous membranes with exceptional porosity and regularity. The formation of copolymer micelle strings in solution (in DMF/DOX/THF and DMF/DOX) was confirmed by cryo field emission scanning electron microscopy (cryo-FESEM) with a distance of 72 nm between centers of micelles placed in different strings. SAXS measurement of block copolymer solutions in DMF/DOX indicated hexagonal assembly with micelle-to-micelle distance of 84-87 nm for 14-20 wt% copolymer solutions. GISAXS in-plane peaks were detected, revealing order close to hexagonal. The d-spacing corresponding to the first peak in this case was 100-130 nm (lattice constant 115-150 nm) for 17 wt% copolymer solutions evaporating up to 100 s. Time-resolved cryo-FESEM showed the formation of incipient pores on the film surface after 4 s copolymer solution casting with distances between void centers of 125 nm. © 2014 Elsevier Ltd. All rights reserved.

Time-resolved GISAXS and cryo-microscopy characterization of block copolymer membrane formation

KAUST Repository

Marques, Debora S.

2014-03-01

Time-resolved grazing-incidence small-angle X-ray scattering (GISAXS) and cryo-microscopy were used for the first time to understand the pore evolution by copolymer assembly, leading to the formation of isoporous membranes with exceptional porosity and regularity. The formation of copolymer micelle strings in solution (in DMF/DOX/THF and DMF/DOX) was confirmed by cryo field emission scanning electron microscopy (cryo-FESEM) with a distance of 72 nm between centers of micelles placed in different strings. SAXS measurement of block copolymer solutions in DMF/DOX indicated hexagonal assembly with micelle-to-micelle distance of 84-87 nm for 14-20 wt% copolymer solutions. GISAXS in-plane peaks were detected, revealing order close to hexagonal. The d-spacing corresponding to the first peak in this case was 100-130 nm (lattice constant 115-150 nm) for 17 wt% copolymer solutions evaporating up to 100 s. Time-resolved cryo-FESEM showed the formation of incipient pores on the film surface after 4 s copolymer solution casting with distances between void centers of 125 nm. © 2014 Elsevier Ltd. All rights reserved.

Direct observation of ultrafast atomic motion using time-resolved X-ray diffraction

International Nuclear Information System (INIS)

Shymanovich, U.

2007-01-01

This thesis is dedicated to the study of the atomic motion in laser irradiated solids on a picosecond to subpicosecond time-scale using the time-resolved X-ray diffraction technique. In the second chapter, the laser system, the laser-plasma based X-ray source and the experimental setup for optical pump / X-ray probe measurements were presented. Chapter 3 is devoted to the characterization and comparison of different types of X-ray optics. Chapter 4 presented the time-resolved X-ray diffraction experiments performed for this thesis. The first two sections of this chapter discuss the measurements of initially unexpected strain-induced transient changes of the integrated reflectivity of the X-ray probe beam. The elimination of the strain-induced transient changes of the integrated reflectivity represented an important prerequisite to perform the study of lattice heating in Germanium after femtosecond optical excitation by measuring the transient Debye-Waller effect. The third section describes the investigations of acoustic waves upon ultrafast optical excitation and discusses the two different pressure contributions driving them: the thermal and the electronic ones. (orig.)

Time-resolved photoelectron spectrometry of a dephasing process in pyrazine

International Nuclear Information System (INIS)

Pavlov, R.L.; Pavlov, L.I.; Delchev, Ya.I.; Pavlova, S.I.

2001-01-01

The first femtosecond time-resolved photoelectron imaging (PEI) is presented. The method is characterized by photoionization of NO and further applied to ultrafast dephasing in pyrazine. Intermediate case behaviour in radiationless transition is clearly observed in time-resolved photoelectron kinetic energy distribution. Femtosecond PEI is with much improved efficiency than conventional photoelectron spectroscopies. It is anticipated that the unifield approach of time-resolved photoelectron and photoion imaging opens the possibility of observing photon-induced dynamics in real time

Improvements in brain activation detection using time-resolved diffuse optical means

Science.gov (United States)

Montcel, Bruno; Chabrier, Renee; Poulet, Patrick

2005-08-01

An experimental method based on time-resolved absorbance difference is described. The absorbance difference is calculated over each temporal step of the optical signal with the time-resolved Beer-Lambert law. Finite element simulations show that each step corresponds to a different scanned zone and that cerebral contribution increases with the arrival time of photons. Experiments are conducted at 690 and 830 nm with a time-resolved system consisting of picosecond laser diodes, micro-channel plate photo-multiplier tube and photon counting modules. The hemodynamic response to a short finger tapping stimulus is measured over the motor cortex. Time-resolved absorbance difference maps show that variations in the optical signals are not localized in superficial regions of the head, which testify for their cerebral origin. Furthermore improvements in the detection of cerebral activation is achieved through the increase of variations in absorbance by a factor of almost 5 for time-resolved measurements as compared to non-time-resolved measurements.

Emerging biomedical applications of time-resolved fluorescence spectroscopy

Science.gov (United States)

Lakowicz, Joseph R.; Szmacinski, Henryk; Koen, Peter A.

1994-07-01

Time-resolved fluorescence spectroscopy is presently regarded as a research tool in biochemistry, biophysics, and chemical physics. Advances in laser technology, the development of long-wavelength probes, and the use of lifetime-based methods are resulting in the rapid migration of time-resolved fluorescence to the clinical chemistry lab, to the patient's bedside, to flow cytometers, to the doctor's office, and even to home health care. Additionally, time-resolved imaging is now a reality in fluorescence microscopy, and will provide chemical imaging of a variety of intracellular analytes and/or cellular phenomena. In this overview paper we attempt to describe some of the opportunities available using chemical sensing based on fluorescence lifetimes, and to predict those applications of lifetime-based sensing which are most likely in the near future.

Microcontroller based resonance tracking unit for time resolved continuous wave cavity-ringdown spectroscopy measurements.

Science.gov (United States)

Votava, Ondrej; Mašát, Milan; Parker, Alexander E; Jain, Chaithania; Fittschen, Christa

2012-04-01

We present in this work a new tracking servoloop electronics for continuous wave cavity-ringdown absorption spectroscopy (cw-CRDS) and its application to time resolved cw-CRDS measurements by coupling the system with a pulsed laser photolysis set-up. The tracking unit significantly increases the repetition rate of the CRDS events and thus improves effective time resolution (and/or the signal-to-noise ratio) in kinetics studies with cw-CRDS in given data acquisition time. The tracking servoloop uses novel strategy to track the cavity resonances that result in a fast relocking (few ms) after the loss of tracking due to an external disturbance. The microcontroller based design is highly flexible and thus advanced tracking strategies are easy to implement by the firmware modification without the need to modify the hardware. We believe that the performance of many existing cw-CRDS experiments, not only time-resolved, can be improved with such tracking unit without any additional modification to the experiment. © 2012 American Institute of Physics

Ultrafast Time-Resolved Photoluminescence Studies of Gallium-Arsenide

Science.gov (United States)

Johnson, Matthew Bruce

This thesis concerns the study of ultrafast phenomena in GaAs using time-resolved photoluminescence (PL). The thesis consists of five chapters. Chapter one is an introduction, which discusses the study of ultrafast phenomena in semiconductors. Chapter two is a description of the colliding-pulse mode-locked (CPM) ring dye laser, which is at the heart of the experimental apparatus used in this thesis. Chapter three presents a detailed experimental and theoretical investigation of photoluminescence excitation correlation spectroscopy (PECS), the novel technique which is used to time-resolve ultrafast PL phenomena. Chapters 4 and 5 discuss two applications of the PECS technique. In Chapter 4 the variation of PL intensity in In-alloyed GaAs substrate material is studied, while Chapter 5 discusses the variation of carrier lifetimes in ion-damaged GaAs used in photo-conductive circuit elements (PCEs). PECS is a pulse-probe technique that measures the cross correlation of photo-excited carrier populations. The theoretical model employed in this thesis is based upon the rate equation for a simple three-level system consisting of valence and conduction bands and a single trap level. In the limit of radiative band-to-band dominated recombination, no PECS signal should be observed; while in the capture -dominated recombination limit, the PECS signal from the band-to-band PL measures the cross correlation of the excited electron and hole populations and thus, the electron and hole lifetimes. PECS is experimentally investigated using a case study of PL in semi-insulating (SI) GaAs and In -alloyed GaAs. At 77 K, the PECS signal is characteristic of a capture-dominated system, yielding an electron-hole lifetime of about 200 ps. However, at 5 K the behavior is more complicated and shows saturation effects due to the C acceptor level, which is un-ionized at 5 K. As a first application, PECS is used to investigate the large band-to-band PL contrast observed near dislocations in In

Time-resolved pump-probe X-ray absorption fine structure spectroscopy of Gaq3

International Nuclear Information System (INIS)

Dicke, Benjamin

2013-01-01

Gallium(tris-8-hydroxyquinoline) (Gaq 3 ) belongs to a class of metal organic compounds, used as electron transport layer and emissive layer in organic light emitting diodes. Many research activities have concentrated on the optical and electronic properties, especially of the homologue molecule aluminum(tris-8-hydroxyquinoline) (Alq 3 ). Knowledge of the first excited state S 1 structure of these molecules could provide deeper insight into the processes involved into the operation of electronic devices, such as OLEDs and, hence, it could further improve their efficiency and optical properties. Until now the excited state structure could not be determined experimentally. Most of the information about this structure mainly arises from theoretical calculations. X-ray absorption fine structure (XAFS) spectroscopy is a well developed technique to determine both, the electronic and the geometric properties of a sample. The connection of ultrashort pulsed X-ray sources with a pulsed laser system offers the possibility to use XAFS as a tool for studying the transient changes of a sample induced by a laser pulse. In the framework of this thesis a new setup for time-resolved pump-probe X-ray absorption spectroscopy at PETRA III beamline P11 was developed for measuring samples in liquid form. In this setup the sample is pumped into its photo-excited state by a femtosecond laser pump pulse with 343 nm wavelength and after a certain time delay probed by an X-ray probe pulse. In this way the first excited singlet state S 1 of Gaq 3 dissolved in benzyl alcohol was analyzed. A structural model for the excited state structure of the Gaq 3 molecule based on the several times reproduced results of the XAFS experiments is proposed. According to this model it was found that the Ga-N A bond length is elongated, while the Ga-O A bond length is shortened upon photoexcitation. The dynamics of the structural changes were not the focus of this thesis. Nevertheless the excited state lifetime

Time resolved Thomson scattering measurements on a high pressure mercury lamp

International Nuclear Information System (INIS)

Vries, N de; Zhu, X; Kieft, E R; Mullen, J van der

2005-01-01

Time resolved Thomson scattering (TS) measurements have been performed on an ac driven high pressure mercury lamp. For this high intensity discharge (HID) lamp, TS is coherent and a coherent fitting routine, including rotational Raman calibration, was used to determine n e and T e from the measured spectrum. The maximum electron density and electron temperature obtained in the centre of the discharge varied in a time period of 5 ms between 1 x 10 21 m -3 e 21 m -3 and 6500 K e < 7100 K. In order to test the non-intrusive character of TS, we have derived a general expression for the heating of the electrons. By applying this to our mercury lamp and laser settings, we have confirmed the non-intrusiveness of our method. This is supported by the experimental findings. Furthermore, because the TS results were obtained directly, thus, without the local thermodynamic equilibrium (LTE) assumptions, they enabled us to follow the deviations from LTE as a function of time. Contrary to the generally made assumption that HID lamps are in LTE, we have found deviations from both the thermal and chemical equilibrium inside the high pressure mercury lamp at different phases of the applied current

Time-resolved Femtosecond Photon Echo Probes Bimodal Solvent Dynamics

NARCIS (Netherlands)

Pshenichnikov, M.S; Duppen, K.; Wiersma, D. A.

1995-01-01

We report on time-resolved femtosecond photon echo experiments of a dye molecule in a polar solution. The photon echo is time resolved by mixing the echo with a femtosecond gate pulse in a nonlinear crystal. It is shown that the temporal profile of the photon echo allows separation of the

The analysis of time-resolved optically stimulated luminescence: I. Theoretical considerations

International Nuclear Information System (INIS)

Chithambo, M L

2007-01-01

This is the first of two linked papers on the analysis of time-resolved optically stimulated luminescence. This paper focusses on a theoretical basis of analytical methods and on methods for interpretation of time-resolved luminescence spectra and calculation of luminescence throughput. Using a comparative analysis of the principal features of time-resolved luminescence and relevant analogues from steady state optical stimulation, formulae for configuring a measurement system for optimum performance are presented. We also examine the possible use of stretched-exponential functions for analysis of time-resolved optically stimulated luminescence spectra

Intra- and intercycle interference of angle-resolved electron emission in laser-assisted XUV atomic ionization

Science.gov (United States)

Gramajo, A. A.; Della Picca, R.; López, S. D.; Arbó, D. G.

2018-03-01

A theoretical study of ionization of the hydrogen atom due to an XUV pulse in the presence of an infrared (IR) laser is presented. Well-established theories are usually used to describe the laser-assisted photoelectron effect: the well-known soft-photon approximation firstly posed by Maquet et al (2007 J. Mod. Opt. 54 1847) and Kazansky’s theory in (2010 Phys. Rev. A 82, 033420). However, these theories completely fail to predict the electron emission perpendicularly to the polarization direction. Making use of a semiclassical model (SCM), we study the angle-resolved energy distribution of PEs for the case that both fields are linearly polarized in the same direction. We thoroughly analyze and characterize two different emission regions in the angle-energy domain: (i) the parallel-like region with contribution of two classical trajectories per optical cycle and (ii) the perpendicular-like region with contribution of four classical trajectories per optical cycle. We show that our SCM is able to assess the interference patterns of the angle-resolved PE spectrum in the two different mentioned regions. Electron trajectories stemming from different optical laser cycles give rise to angle-independent intercycle interferences known as sidebands. These sidebands are modulated by an angle-dependent coarse-grained structure coming from the intracycle interference of the electron trajectories born during the same optical cycle. We show the accuracy of our SCM as a function of the time delay between the IR and the XUV pulses and also as a function of the laser intensity by comparing the semiclassical predictions of the angle-resolved PE spectrum with the continuum-distorted wave strong field approximation and the ab initio solution of the time-dependent Schrödinger equation.

Time-resolved CT angiography in aortic dissection

International Nuclear Information System (INIS)

Meinel, Felix G.; Nikolaou, Konstantin; Weidenhagen, Rolf; Hellbach, Katharina; Helck, Andreas; Bamberg, Fabian; Reiser, Maximilian F.; Sommer, Wieland H.

2012-01-01

Objectives: We performed this study to assess feasibility and additional diagnostic value of time-resolved CT angiography of the entire aorta in patients with aortic dissection. Materials and methods: 14 consecutive patients with known or suspected aortic dissection (aged 60 ± 9 years) referred for aortic CT angiography were scanned on a dual-source CT scanner (Somatom Definition Flash; Siemens, Forchheim, Germany) using a shuttle mode for multiphasic image acquisition (range 48 cm, time resolution 6 s, 6 phases, 100 kV, 110 mAs/rot). Effective radiation doses were calculated from recorded dose length products. For all phases, CT densities were measured in the aortic lumen and renal parenchyma. From the multiphasic data, 3 phases corresponding to a triphasic standard CT protocol, served as a reference and were compared against findings from the time-resolved datasets. Results: Mean effective radiation dose was 27.7 ± 3.5 mSv. CT density of the true lumen peaked at 355 ± 53 HU. Compared to the simulated triphasic protocol, time-resolved CT angiography added diagnostic information regarding a number of important findings: the enhancement delay between true and false lumen (n = 14); the degree of membrane oscillation (n = 14); the perfusion delay in arteries originating from the false lumen (n = 9). Other additional information included true lumen collapse (n = 4), quantitative assessment of renal perfusion asymmetry (n = 2), and dynamic occlusion of aortic branches (n = 2). In 3/14 patients (21%), these additional findings of the multiphasic protocol altered patient management. Conclusions: Multiphasic, time-resolved CT angiography covering the entire aorta is feasible at a reasonable effective radiation dose and adds significant diagnostic information with therapeutic consequences in patients with aortic dissection.

Structure and function of proteins investigated by crystallographic and spectroscopic time-resolved methods

Science.gov (United States)

Purwar, Namrta

Biomolecules play an essential role in performing the necessary functions for life. The goal of this thesis is to contribute to an understanding of how biological systems work on the molecular level. We used two biological systems, beef liver catalase (BLC) and photoactive yellow protein (PYP). BLC is a metalloprotein that protects living cells from the harmful effects of reactive oxygen species by converting H2O2 into water and oxygen. By binding nitric oxide (NO) to the catalase, a complex was generated that mimics the Cat-H2O2 adduct, a crucial intermediate in the reaction promoted by the catalase. The Cat-NO complex is obtained by using a convenient NO generator (1-(N,N-diethylamino)diazen-1-ium-1,2-diolate). Concentrations up to 100˜200 mM are reached by using a specially designed glass cavity. With this glass apparatus and DEANO, sufficient NO occupation is achieved and structure determination of the catalase with NO bound to the heme iron becomes possible. Structural changes upon NO binding are minute. NO has a slightly bent geometry with respect to the heme normal, which results in a substantial overlap of the NO orbitals with the iron-porphyrin molecular orbitals. From the structure of the iron-NO complex, conclusions on the electronic properties of the heme iron can be drawn that ultimately lead to an insight into the catalytic properties of this enzyme. Enzyme kinetics is affected by additional parameters such as temperature and pH. Additionally, in crystallography, the absorbed X-ray dose may impair protein function. To address the effect of these parameters, we performed time-resolved crystallographic experiments on a model system, PYP. By collecting multiple time-series on PYP at increasing X-ray dose levels, we determined a kinetic dose limit up to which kinetically meaningful X-ray data sets can be collected. From this, we conclude that comprehensive time-series spanning up to 12 orders of magnitude in time can be collected from a single PYP

Nanosecond time-resolved investigations using the in situ of dynamic transmission electron microscope (DTEM)

International Nuclear Information System (INIS)

LaGrange, Thomas; Campbell, Geoffrey H.; Reed, B.W.; Taheri, Mitra; Pesavento, J. Bradley; Kim, Judy S.; Browning, Nigel D.

2008-01-01

Most biological processes, chemical reactions and materials dynamics occur at rates much faster than can be captured with standard video rate acquisition methods in transmission electron microscopes (TEM). Thus, there is a need to increase the temporal resolution in order to capture and understand salient features of these rapid materials processes. This paper details the development of a high-time resolution dynamic transmission electron microscope (DTEM) that captures dynamics in materials with nanosecond time resolution. The current DTEM performance, having a spatial resolution <10 nm for single-shot imaging using 15 ns electron pulses, will be discussed in the context of experimental investigations in solid state reactions of NiAl reactive multilayer films, the study of martensitic transformations in nanocrystalline Ti and the catalytic growth of Si nanowires. In addition, this paper will address the technical issues involved with high current, electron pulse operation and the near-term improvements to the electron optics, which will greatly improve the signal and spatial resolutions, and to the laser system, which will allow tailored specimen and photocathode drive conditions

Nanosecond time-resolved investigations using the in situ of dynamic transmission electron microscope (DTEM)

Energy Technology Data Exchange (ETDEWEB)

LaGrange, Thomas [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States)], E-mail: lagrange@llnl.gov; Campbell, Geoffrey H.; Reed, B.W.; Taheri, Mitra; Pesavento, J. Bradley [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States); Kim, Judy S.; Browning, Nigel D. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States); Department of Chemical Engineering and Materials Science, University of California, One Shields Avenue, Davis, CA 95616 (United States)

2008-10-15

Most biological processes, chemical reactions and materials dynamics occur at rates much faster than can be captured with standard video rate acquisition methods in transmission electron microscopes (TEM). Thus, there is a need to increase the temporal resolution in order to capture and understand salient features of these rapid materials processes. This paper details the development of a high-time resolution dynamic transmission electron microscope (DTEM) that captures dynamics in materials with nanosecond time resolution. The current DTEM performance, having a spatial resolution <10 nm for single-shot imaging using 15 ns electron pulses, will be discussed in the context of experimental investigations in solid state reactions of NiAl reactive multilayer films, the study of martensitic transformations in nanocrystalline Ti and the catalytic growth of Si nanowires. In addition, this paper will address the technical issues involved with high current, electron pulse operation and the near-term improvements to the electron optics, which will greatly improve the signal and spatial resolutions, and to the laser system, which will allow tailored specimen and photocathode drive conditions.

Time-resolved and doppler-reduced laser spectroscopy on atoms

International Nuclear Information System (INIS)

Bergstroem, H.

1991-10-01

Radiative lifetimes have been studied in neutral boron, carbon, silicon and strontium, in singly ionized gadolinium and tantalum and in molecular carbon monoxide and C 2 . The time-resolved techniques were based either on pulsed lasers or pulse-modulated CW lasers. Several techniques have been utilized for the production of free atoms and ions such as evaporation into an atomic beam, sputtering in hollow cathodes and laser-produced plasmas. Hyperfine interactions in boron, copper and strontium have been examined using quantum beat spectroscopy, saturation spectroscopy and collimated atomic beam spectroscopy. Measurement techniques based on effusive hollow cathodes as well as laser produced plasmas in atomic physics have been developed. Investigations on laser produced plasmas using two colour beam deflection tomography for determination of electron densities have been performed. Finally, new possibilities for view-time-expansion in light-in-flight holography using mode-locked CW lasers have been demonstrated. (au)

All-optical time-resolved measurement of laser energy modulation in a relativistic electron beam

Directory of Open Access Journals (Sweden)

D. Xiang

2011-11-01

Full Text Available We propose and demonstrate an all-optical method to measure laser energy modulation in a relativistic electron beam. In this scheme the time-dependent energy modulation generated from the electron-laser interaction in an undulator is converted into time-dependent density modulation with a chicane, which is measured to infer the laser energy modulation. The method, in principle, is capable of simultaneously providing information on femtosecond time scale and 10^{-5} energy scale not accessible with conventional methods. We anticipate that this method may have wide applications in many laser-based advanced beam manipulation techniques.

Time-resolved probing of electron thermal conduction in femtosecond-laser-pulse-produced plasmas

International Nuclear Information System (INIS)

Vue, B.T.V.

1993-06-01

We present time-resolved measurements of reflectivity, transmissivity and frequency shifts of probe light interacting with the rear of a disk-like plasma produced by irradiation of a transparent solid target with 0.1ps FWHM laser pulses at peak intensity 5 x 10 l4 W/CM 2 . Experimental results show a large increase in reflection, revealing rapid formation of a steep gradient and overdense surface plasma layer during the first picosecond after irradiation. Frequency shifts due to a moving ionization created by thermal conduction into the solid target are recorded. Calculations using a nonlinear thermal heat wave model show good agreement with the measured frequency shifts, further confining the strong thermal transport effect

Time-Resolved Emission Spectroscopic Study of Laser-Induced Steel Plasmas

International Nuclear Information System (INIS)

Shah, M. L.; Pulhani, A. K.; Suri, B. M.; Gupta, G. P.

2013-01-01

Laser-induced steel plasma is generated by focusing a Q-switched Nd:YAG visible laser (532 nm wavelength) with an irradiance of ∼ 1 × 10 9 W/cm 2 on a steel sample in air at atmospheric pressure. An Echelle spectrograph coupled with a gateable intensified charge-coupled detector is used to record the plasma emissions. Using time-resolved spectroscopic measurements of the plasma emissions, the temperature and electron number density of the steel plasma are determined for many times of the detector delay. The validity of the assumption by the spectroscopic methods that the laser-induced plasma (LIP) is optically thin and is also in local thermodynamic equilibrium (LTE) has been evaluated for many delay times. From the temporal evolution of the intensity ratio of two Fe I lines and matching it with its theoretical value, the delay times where the plasma is optically thin and is also in LTE are found to be 800 ns, 900 ns and 1000 ns.

Time-resolved photoluminescence of SiOx encapsulated Si

Science.gov (United States)

Kalem, Seref; Hannas, Amal; Österman, Tomas; Sundström, Villy

Silicon and its oxide SiOx offer a number of exciting electrical and optical properties originating from defects and size reduction enabling engineering new electronic devices including resistive switching memories. Here we present the results of photoluminescence dynamics relevant to defects and quantum confinement effects. Time-resolved luminescence at room temperature exhibits an ultrafast decay component of less than 10 ps at around 480 nm and a slower component of around 60 ps as measured by streak camera. Red shift at the initial stages of the blue luminescence decay confirms the presence of a charge transfer to long lived states. Time-correlated single photon counting measurements revealed a life-time of about 5 ns for these states. The same quantum structures emit in near infrared close to optical communication wavelengths. Nature of the emission is described and modeling is provided for the luminescence dynamics. The electrical characteristics of metal-oxide-semiconductor devices were correlated with the optical and vibrational measurement results in order to have better insight into the switching mechanisms in such resistive devices as possible next generation RAM memory elements. ``This work was supported by ENIAC Joint Undertaking and Laser-Lab Europe''.

Time-resolved fluorescence spectroscopy

International Nuclear Information System (INIS)

Gustavsson, Thomas; Mialocq, Jean-Claude

2007-01-01

This article addresses the evolution in time of light emitted by a molecular system after a brief photo-excitation. The authors first describe fluorescence from a photo-physical point of view and discuss the characterization of the excited state. Then, they explain some basic notions related to fluorescence characterization (lifetime and decays, quantum efficiency, so on). They present the different experimental methods and techniques currently used to study time-resolved fluorescence. They discuss basic notions of time resolution and spectral reconstruction. They briefly present some conventional methods: intensified Ccd cameras, photo-multipliers and photodiodes associated with a fast oscilloscope, and phase modulation. Other methods and techniques are more precisely presented: time-correlated single photon counting (principle, examples, and fluorescence lifetime imagery), streak camera (principle, examples), and optical methods like the Kerr optical effect (principle and examples) and fluorescence up-conversion (principle and theoretical considerations, examples of application)

Data and Analysis from a Time-Resolved Tomographic Optical Beam Diagnostic

International Nuclear Information System (INIS)

Frayer, Daniel K.; Johnson, Douglas; Ekdahl, Carl

2010-01-01

An optical tomographic diagnostic instrument developed for the acquisition of high-speed time-resolved images has been fielded at the Dual-Axis Radiographic Hydrodynamic Test (DARHT) Facility at Los Alamos National Laboratory. The instrument was developed for the creation of time histories of electron-beam cross section through the collection of Cerenkov light. Four optical lines of sight optically collapse an image and relay projections via an optical fiber relay to recording instruments; a tomographic reconstruction algorithm creates the time history. Because the instrument may be operated in an adverse environment, it may be operated, adjusted, and calibrated remotely. The instrument was operated over the course of various activities during and after DARHT commissioning, and tomographic reconstructions reported verifiable beam characteristics. Results from the collected data and reconstructions and analysis of the data are discussed.

Subshell resolved L shell ionization of Bi and U induced by 16 - 45 keV electrons

International Nuclear Information System (INIS)

Rahangdale, Hitesh; Das, Pradipta K.; Saha, S.; Mitra, D.

2015-01-01

Electron induced inner-shell ionization is important for both fundamental and applied research. Ionization of outer atomic energy levels has been studied extensively than for inner levels. Knowledge of inner shell ionization cross sections is important in X-ray and Auger electron spectroscopy and in the fields of astrophysics, plasma physics, surface science and many more. At electron impact energies near the atomic binding energies the distortion of the wave functions from plane wave towards a spherical wave, due to the electrostatic field of the atoms, needs to be considered. The distorted wave Born approximation (DWBA) calculations, taking relativistic effects and exchange interaction into account, is used to estimate the K, L and M-shell ionization cross-section for the atoms. Earlier experiments on electron impact ionization studies focused mainly on K-shell ionization cross-section, while L and M-shell ionization data were hardly reported. A review of the existing L-shell ionization cross-section data shows that, while the X-ray production cross-sections by electron impact were reported quite a few times, the reporting of subshell resolved ionization cross-sections were rarely found near the ionization threshold region. In the present work, we have measured the X ray production cross-sections of different L lines of Bi and U induced by 16-45 keV electrons and converted the obtained values to the subshell specific ionization cross-sections. The experimental data are compared with the theoretical calculations based on the (DWBA) obtained from PENELOPE. To the best of our knowledge, the subshell resolved electron induced ionization cross-sections for the L-shell of Bi and U are reported here for the first time at the energy values near the corresponding ionization threshold. (author)

Femtosecond electron diffraction. Next generation electron sources for atomically resolved dynamics

Energy Technology Data Exchange (ETDEWEB)

Hirscht, Julian

2015-08-15

Three instruments for femtosecond electron diffraction (FED) experiments were erected, partially commissioned and used for first diffraction experiments. The Relativistic Electron Gun for Atomic Exploration (REGAE) was completed by beamline elements including supports, a specimen chamber and dark current or electron beam collimating elements such that the commissioning process, including first diffraction experiments in this context, could be started. The temporal resolution of this machine is simulated to be 25 fs (fwhm) short, while a transverse coherence length of 30 nm (fwhm) is feasible to resolve proteins on this scale. Whether this machine is capable of meeting these predictions or whether the dynamics of the electron beam will stay limited by accelerator components, is not finally determined by the end of this work, because commissioning and improvement of accelerator components is ongoing. Simultaneously, a compact DC electron diffraction apparatus, the E-Gun 300, designed for solid and liquid specimens and a target electron energy of 300 keV, was built. Fundamental design issues of the high potential carrying and beam generating components occurred and are limiting the maximum potential and electron energy to 120 keV. Furthermore, this is limiting the range of possible applications and consequently the design and construction of a brand new instrument began. The Femtosecond Electron Diffraction CAmera for Molecular Movies (FED-CAMM) bridges the performance problems of very high electric potentials and provides optimal operational conditions for all applied electron energies up to 300 keV. The variability of gap spacings and optimized manufacturing of the high voltage electrodes lead to the best possible electron pulse durations obtainable with a compact DC setup, that does not comprise of rf-structures. This third apparatus possesses pulse durations just a few tenth femtoseconds apart from the design limit of the highly relativistic REGAE and combines the

Femtosecond electron diffraction. Next generation electron sources for atomically resolved dynamics

International Nuclear Information System (INIS)

Hirscht, Julian

2015-08-01

Three instruments for femtosecond electron diffraction (FED) experiments were erected, partially commissioned and used for first diffraction experiments. The Relativistic Electron Gun for Atomic Exploration (REGAE) was completed by beamline elements including supports, a specimen chamber and dark current or electron beam collimating elements such that the commissioning process, including first diffraction experiments in this context, could be started. The temporal resolution of this machine is simulated to be 25 fs (fwhm) short, while a transverse coherence length of 30 nm (fwhm) is feasible to resolve proteins on this scale. Whether this machine is capable of meeting these predictions or whether the dynamics of the electron beam will stay limited by accelerator components, is not finally determined by the end of this work, because commissioning and improvement of accelerator components is ongoing. Simultaneously, a compact DC electron diffraction apparatus, the E-Gun 300, designed for solid and liquid specimens and a target electron energy of 300 keV, was built. Fundamental design issues of the high potential carrying and beam generating components occurred and are limiting the maximum potential and electron energy to 120 keV. Furthermore, this is limiting the range of possible applications and consequently the design and construction of a brand new instrument began. The Femtosecond Electron Diffraction CAmera for Molecular Movies (FED-CAMM) bridges the performance problems of very high electric potentials and provides optimal operational conditions for all applied electron energies up to 300 keV. The variability of gap spacings and optimized manufacturing of the high voltage electrodes lead to the best possible electron pulse durations obtainable with a compact DC setup, that does not comprise of rf-structures. This third apparatus possesses pulse durations just a few tenth femtoseconds apart from the design limit of the highly relativistic REGAE and combines the

Time-resolved terahertz spectroscopy of semiconductor nanostructures

DEFF Research Database (Denmark)

Porte, Henrik

This thesis describes time-resolved terahertz spectroscopy measurements on various semiconductor nanostructures. The aim is to study the carrier dynamics in these nanostructures on a picosecond timescale. In a typical experiment carriers are excited with a visible or near-infrared pulse and by me......This thesis describes time-resolved terahertz spectroscopy measurements on various semiconductor nanostructures. The aim is to study the carrier dynamics in these nanostructures on a picosecond timescale. In a typical experiment carriers are excited with a visible or near-infrared pulse...... and by measuring the transmission of a terahertz probe pulse, the photoconductivity of the excited sample can be obtained. By changing the relative arrival time at the sample between the pump and the probe pulse, the photoconductivity dynamics can be studied on a picosecond timescale. The rst studied semiconductor...

Investigations on the photoreactions of phenothiazine and phenoxazine in presence of 9-cyanoanthracene by using steady state and time resolved spectroscopic techniques.

Science.gov (United States)

Bardhan, Munmun; Mandal, Paulami; Tzeng, Wen-Bih; Ganguly, Tapan

2010-09-01

By using electrochemical, steady state and time resolved (fluorescence lifetime and transient absorption) spectroscopic techniques, detailed investigations were made to reveal the mechanisms of charge separation or forward electron transfer reactions within the electron donor phenothiazine (PTZH) or phenoxazine (PXZH) and well known electron acceptor 9-cyanoanthracene (CNA). The transient absorption spectra suggest that the charge separated species formed in the excited singlet state resulted from intermolecular photoinduced electron transfer reactions within the donor PTZH (or PXZH) and CNA acceptor relaxes to the corresponding triplet state. Though alternative mechanisms of via formations of contact neutral radical by H-transfer reaction have been proposed but the observed results obtained from the time resolved measurements indicate that the regeneration of ground state reactants is primarily responsible due to direct recombination of triplet contact ion-pair (CIP) or solvent-separated ion-pair (SSIP).

Femtosecond Time-resolved Optical Polarigraphy (FTOP)

International Nuclear Information System (INIS)

Aoshima, S.; Fujimoto, M.; Hosoda, M.; Tsuchiya, Y.

2000-01-01

A novel time-resolved imaging technique named FTOP (Femtosecond Time-resolved Optical Polarigraphy) for visualizing the ultrafast propagation dynamics of intense light pulses in a medium has been proposed and demonstrated. Femtosecond snapshot images can be created with a high spatial resolution by imaging only the polarization components of the probe pulse; these polarization components change due to the instantaneous birefringence induced by the pump pulse in the medium. Ultrafast temporal changes in the two-dimensional spatial distribution of the optical pulse intensity were clearly visualized in consecutive images by changing the delay between the pump and probe. We observe that several filaments appear and then come together before the vacuum focus due to nonlinear effects in air. We also prove that filamentation dynamics such as the formation position and the propagation behavior are complex and are strongly affected by the pump energy. The results collected clearly show that this method FTOP succeeds for the first time in directly visualizing the ultrafast dynamics of the self-modulated nonlinear propagation of light. (author)

Timely resolved measurements on CdSe nanoparticles

International Nuclear Information System (INIS)

Holt, B.E. von

2006-01-01

By means of infrared spectroscopy the influence of the organic cover on structure and dynamics of CdSe nanoparticles was studied. First a procedure was developed, which allows to get from the static infrared spectrum informations on the quality of the organic cover and the binding behaviour of the ligands. On qualitatively high-grade and well characterized samples thereafter the dynamics of the lowest-energy electron level 1S e was time-resolvedly meausred in thew visible range. As reference served CdSe TOPO, which was supplemented by samples with the ligands octanthiole, octanic acid, octylamine, naphthoquinone, benzoquinone, and pyridine. The studied nanoparticles had a diameter of 4.86 nm. By means of the excitation-scanning or pump=probe procedure first measurements in the picosecond range were performed. The excitation wavelengths were thereby spectrally confined and so chosen that selectively the transitions 1S 3/2 -1S-e and 1P 3/2 -1P e but not the intermediately lyingt transition 2S 3/2 -1S e were excited. The excitation energies were kept so low that the excitation of several excitons in one crystal could be avoided. The scanning wavelength in the infrared corresponded to the energy difference between the electron levels 1S e and 1P e . The transients in the picosecond range are marked by a steep increasement of the signal, on which a multi-exponential decay follows. The increasement, which reproduces the popiulation of the excited state, isa inependent on the choice of the ligands. The influence of the organic cover is first visible in the different decay times of the excited electron levels. the decay of the measurement signal of CdSe TOPO can be approximatively described by three time constants: a decay constant in the early picosecond region, a time constant around hundert picoseconds, and a time constant of some nanoseconds. At increasing scanning wavelength the decay constants become longer. By directed excitation of the 1S 3/2 -1S e and the 1P 3

Assessment of electron propagator methods for the simulation of vibrationally-resolved valence and core photoionization spectra

Science.gov (United States)

Baiardi, A.; Paoloni, L.; Barone, V.; Zakrzewski, V.G.; Ortiz, J.V.

2017-01-01

The analysis of photoelectron spectra is usually facilitated by quantum mechanical simulations. Due to the recent improvement of experimental techniques, the resolution of experimental spectra is rapidly increasing, and the inclusion of vibrational effects is usually mandatory to obtain a reliable reproduction of the spectra. With the aim of defining a robust computational protocol, a general time-independent formulation to compute different kinds of vibrationally-resolved electronic spectra has been generalized to support also photoelectron spectroscopy. The electronic structure data underlying the simulation are computed using different electron propagator approaches. In addition to the more standard approaches, a new and robust implementation of the second-order self-energy approximation of the electron propagator based on a transition operator reference (TOEP2) is presented. To validate our implementation, a series of molecules has been used as test cases. The result of the simulations shows that, for ultraviolet photoionization spectra, the more accurate non-diagonal approaches are needed to obtain a reliable reproduction of vertical ionization energies, but diagonal approaches are sufficient for energy gradients and pole strengths. For X-ray photoelectron spectroscopy, the TOEP2 approach, besides being more efficient, is also the most accurate in the reproduction of both vertical ionization energies and vibrationally-resolved bandshapes. PMID:28521087

Investigation of ultrafast lattice heating in thin (semi-)metal films using time-resolved electron diffraction; Untersuchung der schnellen Gitteraufheizung in duennen (Halb-)Metallfilmen mit Hilfe zeitaufgeloester Elektronenbeugung

Energy Technology Data Exchange (ETDEWEB)

Ligges, Manuel

2009-07-21

In the framework of the present thesis the fast lattice heating in thin metal and bismuth layers after optical short-pulse excitation was studied. By irradiation of ultrathin solid films with ultrashort (femtosecond) laser pulses for sort times an extreme nonequilibrium state occurs: The electronic system is strongly excited, while the lattice system remains cold. An energetic exchange between both systems follows, which is based on the electron-phonon interaction and leads to heating of the lattice system. This lattice heating can be observed by means of the Debye-Waller effect in the electron diffraction image. By means of the excitation-interrogation scheme by a series of moment records this lattice heating can be observed time-resolvedly. The experimentally determind time scales for this process permit conclusions on the electron-phonon coupling in the studied materials. In this thesis a time-resolving transmissi9on-electron diffraction experiment with sub-picosecond time resolution was constructed and optimized. By means of this experiment the fast lattice heating in thin gold, silver, copper, and bismuth films was studied. The observed heating behaviour of the metal films shows agreement with theoretical predictions of different model calculations. The results of the measurements on bismuth films show a hitherto not observed coupling behaviour. [German] Im Rahmen der vorliegenden Arbeit wurde die schnelle Gitteraufheizung in duennen Metall- und Wismutschichten nach optischer Kurzimpulsanregung untersucht. Durch Bestrahlung duenner Festkoerperfilme mit ultrakurzen (Femtosekunden-) Laserimpulsen entsteht fuer kurze Zeiten ein extremer Nichtgleichgewichtszustand: Das elektronische System wird stark angeregt, waehrend das Gittersystem kalt bleibt. Es folgt ein energetischer Austausch zwischen beiden Systemen, der auf der Elektron-Phonon-Wechselwirkung beruht und zur Aufheizung des Gittersystems fuehrt. Diese Gitteraufheizung kann anhand des Debye

Design considerations for a time-resolved tomographic diagnostic at DARHT

International Nuclear Information System (INIS)

Morris I. Kaufman, Daniel Frayer, Wendi Dreesen, Douglas Johnson, Alfred Meidinger

2006-01-01

An instrument has been developed to acquire time-resolved tomographic data from the electron beam at the DARHT [Dual-Axis Radiographic Hydrodynamic Test] facility at Los Alamos National Laboratory. The instrument contains four optical lines of sight that view a single tilted object. The lens design optically integrates along one optical axis for each line of sight. These images are relayed via fiber optic arrays to streak cameras, and the recorded streaks are used to reconstruct the original two-dimensional data. Installation of this instrument into the facility requires automation of both the optomechanical adjustments and calibration of the instrument in a constrained space. Additional design considerations include compound tilts on the object and image planes

Time-resolved measurements with streaked diffraction patterns from electrons generated in laser plasma wakefield

Science.gov (United States)

He, Zhaohan; Nees, John; Hou, Bixue; Krushelnick, Karl; Thomas, Alec; Beaurepaire, Benoît; Malka, Victor; Faure, Jérôme

2013-10-01

Femtosecond bunches of electrons with relativistic to ultra-relativistic energies can be robustly produced in laser plasma wakefield accelerators (LWFA). Scaling the electron energy down to sub-relativistic and MeV level using a millijoule laser system will make such electron source a promising candidate for ultrafast electron diffraction (UED) applications due to the intrinsic short bunch duration and perfect synchronization with the optical pump. Recent results of electron diffraction from a single crystal gold foil, using LWFA electrons driven by 8-mJ, 35-fs laser pulses at 500 Hz, will be presented. The accelerated electrons were collimated with a solenoid magnetic lens. By applying a small-angle tilt to the magnetic lens, the diffraction pattern can be streaked such that the temporal evolution is separated spatially on the detector screen after propagation. The observable time window and achievable temporal resolution are studied in pump-probe measurements of photo-induced heating on the gold foil.

The time resolved measurement of ultrashort terahertz-band electric fields without an ultrashort probe

International Nuclear Information System (INIS)

Walsh, D. A.; Snedden, E. W.; Jamison, S. P.

2015-01-01

The time-resolved detection of ultrashort pulsed THz-band electric field temporal profiles without an ultrashort laser probe is demonstrated. A non-linear interaction between a narrow-bandwidth optical probe and the THz pulse transposes the THz spectral intensity and phase information to the optical region, thereby generating an optical pulse whose temporal electric field envelope replicates the temporal profile of the real THz electric field. This optical envelope is characterised via an autocorrelation based FROG (frequency resolved optical gating) measurement, hence revealing the THz temporal profile. The combination of a narrow-bandwidth, long duration, optical probe, and self-referenced FROG makes the technique inherently immune to timing jitter between the optical probe and THz pulse and may find particular application where the THz field is not initially generated via ultrashort laser methods, such as the measurement of longitudinal electron bunch profiles in particle accelerators

A time-resolved image sensor for tubeless streak cameras

Science.gov (United States)

Yasutomi, Keita; Han, SangMan; Seo, Min-Woong; Takasawa, Taishi; Kagawa, Keiichiro; Kawahito, Shoji

2014-03-01

This paper presents a time-resolved CMOS image sensor with draining-only modulation (DOM) pixels for tube-less streak cameras. Although the conventional streak camera has high time resolution, the device requires high voltage and bulky system due to the structure with a vacuum tube. The proposed time-resolved imager with a simple optics realize a streak camera without any vacuum tubes. The proposed image sensor has DOM pixels, a delay-based pulse generator, and a readout circuitry. The delay-based pulse generator in combination with an in-pixel logic allows us to create and to provide a short gating clock to the pixel array. A prototype time-resolved CMOS image sensor with the proposed pixel is designed and implemented using 0.11um CMOS image sensor technology. The image array has 30(Vertical) x 128(Memory length) pixels with the pixel pitch of 22.4um. .

Finite-difference time-domain analysis of time-resolved terahertz spectroscopy experiments

DEFF Research Database (Denmark)

Larsen, Casper; Cooke, David G.; Jepsen, Peter Uhd

2011-01-01

In this paper we report on the numerical analysis of a time-resolved terahertz (THz) spectroscopy experiment using a modified finite-difference time-domain method. Using this method, we show that ultrafast carrier dynamics can be extracted with a time resolution smaller than the duration of the T...

Decomposition of time-resolved tomographic PIV

NARCIS (Netherlands)

Schmid, P.J.; Violato, D.; Scarano, F.

2012-01-01

An experimental study has been conducted on a transitional water jet at a Reynolds number of Re = 5,000. Flow fields have been obtained by means of time-resolved tomographic particle image velocimetry capturing all relevant spatial and temporal scales. The measured threedimensional flow fields have

Time-resolved studies

International Nuclear Information System (INIS)

Mills, D.M.

1992-01-01

When new or more powerful probes become available that offer both shorter data-collection times and the opportunity to apply innovative approaches to established techniques, it is natural that investigators consider the feasibility of exploring the kinetics of time-evolving systems. This stimulating area of research not only can lead to insights into the metastable or excited states that a system may populate on its way to a ground state, but can also lead to a better understanding of that final state. Synchrotron radiation, with its unique properties, offers just such a tool to extend X-ray measurements from the static to the time-resolved regime. The most straight-forward application of synchrotron radiation to the study of transient phenomena is directly through the possibility of decreased data-collection times via the enormous increase in flux over that of a laboratory X-ray system. Even further increases in intensity can be obtained through the use of novel X-ray optical devices. Widebandpass monochromators, e.g., that utilize the continuous spectral distribution of synchrotron radiation, can increase flux on the sample several orders of magnitude over conventional X-ray optical systems thereby allowing a further shortening of the data-collection time. Another approach that uses the continuous spectral nature of synchrotron radiation to decrease data-collection times is the open-quote parallel data collectionclose quotes method. Using this technique, intensities as a function of X-ray energy are recorded simultaneously for all energies rather than sequentially recording data at each energy, allowing for a dramatic decrease in the data-collection time

Time-resolved studies at PETRA III with a highly repetitive synchronized laser system

Energy Technology Data Exchange (ETDEWEB)

Schlie, Mortiz

2013-09-15

Atomic and molecular processes can nowadays be directly followed in the time domain. This is a core technique for a better understanding of the involved fundamental physics, thus auguring new applications in the future as well. Usually the so-called pump-probe technique making use of two synchronized ultrashort light pulses is utilized to obtain this time-resolved data. In this work, the development and characterization of a synchronization system enabling such pump-probe studies at the storage ring PETRA III in combination with an external, then synchronized fs-laser system is described. The synchronization is based on an extended PLL approach with three interconnected feedback loops allowing to monitor short-time losses of the lock and thus prevent them. This way, the jitter between the laser PHAROS and the PETRA III reference signal is reduced to {sigma} <5 ps. Thus the system allows to conduct experiments at a repetition rate of 130 kHz with a temporal resolution limited only by the X-ray pulse length. A major emphasis in the fundamental introductory chapters is an intuitive explanation of the basic principles of phase locked loops and the different aspects of phase noise to allow a deeper understanding of the synchronization. Furthermore, first pump-probe experiments conducted at different beamlines at PETRA III are presented, demonstrating the usability of the laser system in a scientific environment as well. In first characterizing experiments the pulse duration of PETRA III X-ray pulses has been measured to be 90 ps FWHM. In particular, there have been time resolved X-ray absorption spectroscopy experiments on Gaq3 and Znq2 conducted at beamline P11. First results show dynamics of the electronic excitation on the timescale of a few hundred pico seconds up to a few nano seconds and provide a basic understanding for further research on those molecules. For Gaq3 this data is analyzed in detail and compared with visible fluorescence measurements suggesting at

Time-resolved studies at PETRA III with a highly repetitive synchronized laser system

International Nuclear Information System (INIS)

Schlie, Mortiz

2013-09-01

Atomic and molecular processes can nowadays be directly followed in the time domain. This is a core technique for a better understanding of the involved fundamental physics, thus auguring new applications in the future as well. Usually the so-called pump-probe technique making use of two synchronized ultrashort light pulses is utilized to obtain this time-resolved data. In this work, the development and characterization of a synchronization system enabling such pump-probe studies at the storage ring PETRA III in combination with an external, then synchronized fs-laser system is described. The synchronization is based on an extended PLL approach with three interconnected feedback loops allowing to monitor short-time losses of the lock and thus prevent them. This way, the jitter between the laser PHAROS and the PETRA III reference signal is reduced to σ <5 ps. Thus the system allows to conduct experiments at a repetition rate of 130 kHz with a temporal resolution limited only by the X-ray pulse length. A major emphasis in the fundamental introductory chapters is an intuitive explanation of the basic principles of phase locked loops and the different aspects of phase noise to allow a deeper understanding of the synchronization. Furthermore, first pump-probe experiments conducted at different beamlines at PETRA III are presented, demonstrating the usability of the laser system in a scientific environment as well. In first characterizing experiments the pulse duration of PETRA III X-ray pulses has been measured to be 90 ps FWHM. In particular, there have been time resolved X-ray absorption spectroscopy experiments on Gaq3 and Znq2 conducted at beamline P11. First results show dynamics of the electronic excitation on the timescale of a few hundred pico seconds up to a few nano seconds and provide a basic understanding for further research on those molecules. For Gaq3 this data is analyzed in detail and compared with visible fluorescence measurements suggesting at least

Alignment of time-resolved data from high throughput experiments.

Science.gov (United States)

Abidi, Nada; Franke, Raimo; Findeisen, Peter; Klawonn, Frank

2016-12-01

To better understand the dynamics of the underlying processes in cells, it is necessary to take measurements over a time course. Modern high-throughput technologies are often used for this purpose to measure the behavior of cell products like metabolites, peptides, proteins, [Formula: see text]RNA or mRNA at different points in time. Compared to classical time series, the number of time points is usually very limited and the measurements are taken at irregular time intervals. The main reasons for this are the costs of the experiments and the fact that the dynamic behavior usually shows a strong reaction and fast changes shortly after a stimulus and then slowly converges to a certain stable state. Another reason might simply be missing values. It is common to repeat the experiments and to have replicates in order to carry out a more reliable analysis. The ideal assumptions that the initial stimulus really started exactly at the same time for all replicates and that the replicates are perfectly synchronized are seldom satisfied. Therefore, there is a need to first adjust or align the time-resolved data before further analysis is carried out. Dynamic time warping (DTW) is considered as one of the common alignment techniques for time series data with equidistant time points. In this paper, we modified the DTW algorithm so that it can align sequences with measurements at different, non-equidistant time points with large gaps in between. This type of data is usually known as time-resolved data characterized by irregular time intervals between measurements as well as non-identical time points for different replicates. This new algorithm can be easily used to align time-resolved data from high-throughput experiments and to come across existing problems such as time scarcity and existing noise in the measurements. We propose a modified method of DTW to adapt requirements imposed by time-resolved data by use of monotone cubic interpolation splines. Our presented approach

Time-resolved X-ray transmission microscopy on magnetic microstructures

International Nuclear Information System (INIS)

Puzic, Aleksandar

2007-01-01

Three excitation schemes were designed for stroboscopic imaging of magnetization dynamics with time-resolved magnetic transmission X-ray microscopy (TR-MTXM). These techniques were implemented into two types of X-ray microscopes, namely the imaging transmission X-ray microscope (ITXM) and the scanning transmission X-ray microscope (STXM), both installed at the electron storage ring of the Advanced Light Source in Berkeley, USA. Circular diffraction gratings (Fresnel zone plates) used in both microscopes as focusing and imaging elements presently allow for lateral resolution down to 30 nm. Magnetic imaging is performed by using the X-ray magnetic circular dichroism (XMCD) as element specific contrast mechanism. The developed methods have been successfully applied to the experimental investigation of magnetization dynamics in ferromagnetic microstructures. A temporal resolution well below 100 ps was achieved. A conventional pump-probe technique was implemented first. The dynamic response of the magnetization excited by a broadband pulsed magnetic field was imaged spatially resolved using focused X-ray flashes. As a complementary method, the spatially resolved ferromagnetic resonance (SR-FMR) technique was developed for experimental study of magnetization dynamics in the frequency domain. As a third excitation mode, the burst excitation was implemented. The performance and efficiency of the developed methods have been demonstrated by imaging the local magnetization dynamics in laterally patterned ferromagnetic thin-film elements and three-layer stacks. The existence of multiple eigenmodes in the excitation spectra of ferromagnetic microstructures has been verified by using the pump-probe technique. Magnetostatic spin waves were selectively excited and detected with a time resolution of 50 ps using the SR-FMR technique. Thorough analysis of 20 in most cases independently prepared samples has verified that vortices which exhibit a low-amplitude switching of their core

Frame-Transfer Gating Raman Spectroscopy for Time-Resolved Multiscalar Combustion Diagnostics

Science.gov (United States)

Nguyen, Quang-Viet; Fischer, David G.; Kojima, Jun

2011-01-01

Accurate experimental measurement of spatially and temporally resolved variations in chemical composition (species concentrations) and temperature in turbulent flames is vital for characterizing the complex phenomena occurring in most practical combustion systems. These diagnostic measurements are called multiscalar because they are capable of acquiring multiple scalar quantities simultaneously. Multiscalar diagnostics also play a critical role in the area of computational code validation. In order to improve the design of combustion devices, computational codes for modeling turbulent combustion are often used to speed up and optimize the development process. The experimental validation of these codes is a critical step in accepting their predictions for engine performance in the absence of cost-prohibitive testing. One of the most critical aspects of setting up a time-resolved stimulated Raman scattering (SRS) diagnostic system is the temporal optical gating scheme. A short optical gate is necessary in order for weak SRS signals to be detected with a good signal- to-noise ratio (SNR) in the presence of strong background optical emissions. This time-synchronized optical gating is a classical problem even to other spectroscopic techniques such as laser-induced fluorescence (LIF) or laser-induced breakdown spectroscopy (LIBS). Traditionally, experimenters have had basically two options for gating: (1) an electronic means of gating using an image intensifier before the charge-coupled-device (CCD), or (2) a mechanical optical shutter (a rotary chopper/mechanical shutter combination). A new diagnostic technology has been developed at the NASA Glenn Research Center that utilizes a frame-transfer CCD sensor, in conjunction with a pulsed laser and multiplex optical fiber collection, to realize time-resolved Raman spectroscopy of turbulent flames that is free from optical background noise (interference). The technology permits not only shorter temporal optical gating (down

Time-resolved single-shot terahertz time-domain spectroscopy for ultrafast irreversible processes

Science.gov (United States)

Zhai, Zhao-Hui; Zhong, Sen-Cheng; Li, Jun; Zhu, Li-Guo; Meng, Kun; Li, Jiang; Liu, Qiao; Peng, Qi-Xian; Li, Ze-Ren; Zhao, Jian-Heng

2016-09-01

Pulsed terahertz spectroscopy is suitable for spectroscopic diagnostics of ultrafast events. However, the study of irreversible or single shot ultrafast events requires ability to record transient properties at multiple time delays, i.e., time resolved at single shot level, which is not available currently. Here by angular multiplexing use of femtosecond laser pulses, we developed and demonstrated a time resolved, transient terahertz time domain spectroscopy technique, where burst mode THz pulses were generated and then detected in a single shot measurement manner. The burst mode THz pulses contain 2 sub-THz pulses, and the time gap between them is adjustable up to 1 ns with picosecond accuracy, thus it can be used to probe the single shot event at two different time delays. The system can detect the sub-THz pulses at 0.1 THz-2.5 THz range with signal to noise ratio (SNR) of ˜400 and spectrum resolution of 0.05 THz. System design was described here, and optimizations of single shot measurement of THz pulses were discussed in detail. Methods to improve SNR were also discussed in detail. A system application was demonstrated where pulsed THz signals at different time delays of the ultrafast process were successfully acquired within single shot measurement. This time resolved transient terahertz time domain spectroscopy technique provides a new diagnostic tool for irreversible or single shot ultrafast events where dynamic information can be extracted at terahertz range within one-shot experiment.

Creation of free excitons in solid krypton investigated by time-resolved luminescence spectroscopy

International Nuclear Information System (INIS)

Kisand, Vambola; Kirm, Marco; Negodin, Evgeni; Sombrowski, Elke; Steeg, Barbara; Vielhauer, Sebastian; Zimmerer, Georg

2003-01-01

The creation and relaxation of secondary excitons in solid Kr was investigated using energy-and time-resolved luminescence spectroscopy in the vacuum ultraviolet region. The spectrally selected emission of the free exciton (FE) was used as a probe for an investigation of the different exciton creation processes. Delayed FE creation via electron-hole recombination and 'prompt' (in terms of the time-resolution of the experiment) creation of excitons were separated. The 'prompt' creation of a FE appears in the region above threshold energy E th , which is equal to the sum of the band gap energy and the free exciton energy. 'Prompt' creation of excitons above E th is ascribed to a superposition of two processes: (i) creation of the electronic polaron complex (one-step process) and (ii) inelastic scattering of photoelectrons described in the framework of the multiple-parabolic-branch band model (two-step process). In addition, the ratio spectrum of the time-integrated FE and self-trapped exciton (STE) emission was analysed. The behaviour of the ratio spectrum is a proof that electron-hole recombination leads to STE states through FE states as precursors

Time-resolved materials science opportunities using synchrotron x-ray sources

International Nuclear Information System (INIS)

Larson, B.C.; Tischler, J.Z.

1995-06-01

The high brightness, high intensity, and pulsed time-structure of synchrotron sources provide new opportunities for time-resolved x-ray diffraction investigations. With third generation synchrotron sources coming on line, high brilliance and high brightness are now available in x-ray beams with the highest flux. In addition to the high average flux, the instantaneous flux available in synchrotron beams is greatly enhanced by the pulsed time structure, which consists of short bursts of x-rays that are separated by ∼tens to hundreds of nanoseconds. Time-resolved one- and two-dimensional position sensitive detection techniques that take advantage of synchrotron radiation for materials science x-ray diffraction investigations are presented, and time resolved materials science applications are discussed in terms of recent diffraction and spectroscopy results and materials research opportunities

Radially resolved simulation of a high-gain free electron laser amplifier

International Nuclear Information System (INIS)

Fawley, W.M.; Prosnitz, D.; Doss, S.; Gelinas, R.

1983-01-01

The results of a two-dimensional simulation of a high-gain free electron laser (FEL) amplifier is presented. The simulation solves the inhomogeneous paraxial wave equation. The source term is radially resolved and is obtained by tracking the interaction of the laser field with localized macroparticles

Direct Imaging of Transient Fano Resonances in N_{2} Using Time-, Energy-, and Angular-Resolved Photoelectron Spectroscopy.

Science.gov (United States)

Eckstein, Martin; Yang, Chung-Hsin; Frassetto, Fabio; Poletto, Luca; Sansone, Giuseppe; Vrakking, Marc J J; Kornilov, Oleg

2016-04-22

Autoionizing Rydberg states of molecular N_{2} are studied using time-, energy-, and angular-resolved photoelectron spectroscopy. A femtosecond extreme ultraviolet pulse with a photon energy of 17.5 eV excites the resonance and a subsequent IR pulse ionizes the molecule before the autoionization takes place. The angular-resolved photoelectron spectra depend on pump-probe time delay and allow for the distinguishing of two electronic states contributing to the resonance. The lifetime of one of the contributions is determined to be 14±1  fs, while the lifetime of the other appears to be significantly shorter than the time resolution of the experiment. These observations suggest that the Rydberg states in this energy region are influenced by the effect of interference stabilization and merge into a complex resonance.

Development of time-resolved optical measurement and diagnostic system for parameters of high current and pulsed electron beam

International Nuclear Information System (INIS)

Jiang Xiaoguo; Wang Yuan; Yang Guojun; Xia Liansheng; Li Hong; Zhang Zhuo; Liao Shuqing; Shi Jinshui

2013-01-01

The beam parameters measurement is the most important work for the study of linear induction accelerator(LIA). The beam parameters are important to evaluate the character of the beam. The demands of beam parameters measurement are improving while the development of accelerator is improving. The measurement difficulty feature higher time-resolved ability, higher spatial resolution, larger dynamic range and higher intuitionistic view data. The measurement technology of beam spot, beam emittance, beam energy have been developed for the past several years. Some high performance equipment such as high speed framing camera are developed recently. Under this condition, the relative integrated optical measurement and diagnostic system for the beam parameters is developed based on several principles. The system features time-resolved ability of up to 2 ns, high sensitivity and large dynamic range. The processing program is compiled for the data process and the local real-time process is reached. The measurement and diagnostic system has provided full and accurate data for the debug work and has been put into applications. (authors)

Time-resolved measurements of the external electric field effects on fluorescence in electron donor and acceptor pairs of N-ethylcarbazole and dimethyl terephthalate doped in a polymer film

International Nuclear Information System (INIS)

Iimori, Toshifumi; Yoshizawa, Tomokazu; Nakabayashi, Takakazu; Ohta, Nobuhiro

2005-01-01

Electric-field-induced change in fluorescence decay has been measured for electron donor and acceptor pairs of N-ethylcarbazole (ECZ) and dimethyl terephthalate (DMTP) doped in a polymer film. Field-induced change in lifetime of the fluorescence emitted from the locally excited state of ECZ clearly shows that the electron transfer from the excited state of ECZ to DMTP is enhanced by an external electric field ( F ). A comparison is made between the experimental results of the field effect on decay profile of the ECZ fluorescence and the simulated results. Time-resolved electrofluorescence spectra as well as the field-induced change in decay profile of exciplex fluorescence show that exciplex fluorescence is quenched by F at the early stage of time following photoexcitation, but enhanced by F at a later stage of time. Both the decrease in the initial population of the fluorescent exciplex and the lengthening of the exciplex fluorescence in lifetime are shown to be induced by F

Time-resolved measurements of the external electric field effects on fluorescence in electron donor and acceptor pairs of N-ethylcarbazole and dimethyl terephthalate doped in a polymer film

Energy Technology Data Exchange (ETDEWEB)

Iimori, Toshifumi [Research Institute for Electronic Science (RIES), Hokkaido University, Sapporo 060-0812 (Japan); Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810 (Japan); Yoshizawa, Tomokazu [Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810 (Japan); Nakabayashi, Takakazu [Research Institute for Electronic Science (RIES), Hokkaido University, Sapporo 060-0812 (Japan); Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810 (Japan); Ohta, Nobuhiro [Research Institute for Electronic Science (RIES), Hokkaido University, Sapporo 060-0812 (Japan); Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810 (Japan)], E-mail: nohta@es.hokudai.ac.jp

2005-12-07

Electric-field-induced change in fluorescence decay has been measured for electron donor and acceptor pairs of N-ethylcarbazole (ECZ) and dimethyl terephthalate (DMTP) doped in a polymer film. Field-induced change in lifetime of the fluorescence emitted from the locally excited state of ECZ clearly shows that the electron transfer from the excited state of ECZ to DMTP is enhanced by an external electric field ( F ). A comparison is made between the experimental results of the field effect on decay profile of the ECZ fluorescence and the simulated results. Time-resolved electrofluorescence spectra as well as the field-induced change in decay profile of exciplex fluorescence show that exciplex fluorescence is quenched by F at the early stage of time following photoexcitation, but enhanced by F at a later stage of time. Both the decrease in the initial population of the fluorescent exciplex and the lengthening of the exciplex fluorescence in lifetime are shown to be induced by F.

Time-resolved spectroscopy of plasma resonances in highly excited silicon and germanium

International Nuclear Information System (INIS)

Huang, C.Y.; Malvezzi, A.M.; Bloembergen, N.; Kurz, H.

1985-01-01

The dynamics of the electron-hole plasma in silicon and germanium samples irradiated by 20 ps. 532 nm laser pulses has been investigated in the near infrared by the time-resolved picosecond optical spectroscopy. The experimental reflectivities and transmission are compared with the predictions of the thermal model for degenerate carrier distributions through the Drude formalism. Above a certain fluence, a significant deviation between measured and calculated values indicates a strong increase of the recombination rate as soon as the plasma resonances become comparable with the band gaps. These new plasmon-aided recombination channels are particularly pronounced in germanium. 15 refs., 8 figs

Time Resolved Deposition Measurements in NSTX

International Nuclear Information System (INIS)

Skinner, C.H.; Kugel, H.; Roquemore, A.L.; Hogan, J.; Wampler, W.R.

2004-01-01

Time-resolved measurements of deposition in current tokamaks are crucial to gain a predictive understanding of deposition with a view to mitigating tritium retention and deposition on diagnostic mirrors expected in next-step devices. Two quartz crystal microbalances have been installed on NSTX at a location 0.77m outside the last closed flux surface. This configuration mimics a typical diagnostic window or mirror. The deposits were analyzed ex-situ and found to be dominantly carbon, oxygen, and deuterium. A rear facing quartz crystal recorded deposition of lower sticking probability molecules at 10% of the rate of the front facing one. Time resolved measurements over a 4-week period with 497 discharges, recorded 29.2 (micro)g/cm 2 of deposition, however surprisingly, 15.9 (micro)g/cm 2 of material loss occurred at 7 discharges. The net deposited mass of 13.3 (micro)g/cm 2 matched the mass of 13.5 (micro)g/cm 2 measured independently by ion beam analysis. Monte Carlo modeling suggests that transient processes are likely to dominate the deposition

Real-time observation of intersystem crossing induced by charge recombination during bimolecular electron transfer reactions

KAUST Repository

Alsam, Amani Abdu

2016-09-21

Real-time probing of intersystem crossing (ISC) and triplet-state formation after photoinduced electron transfer (ET) is a particularly challenging task that can be achieved by time-resolved spectroscopy with broadband capability. Here, we examine the mechanism of charge separation (CS), charge recombination (CR) and ISC of bimolecular photoinduced electron transfer (PET) between poly[(9,9-di(3,3′-N,N’-trimethyl-ammonium) propyl fluorenyl-2,7-diyl)-alt-co-(9,9-dioctyl-fluorenyl-2,7-diyl)] diiodide salt (PFN) and dicyanobenzene (DCB) using time-resolved spectroscopy. PET from PFN to DCB is confirmed by monitoring the transient absorption (TA) and infrared spectroscopic signatures for the radical ion pair (DCB─•-PFN+•). In addition, our time-resolved results clearly demonstrate that CS takes place within picoseconds followed by CR within nanoseconds. The ns-TA data exhibit the clear spectroscopic signature of PFN triplet-triplet absorption, induced by the CR of the radical ion pairs (DCB─•-PFN+•). As a result, the triplet state of PFN (3PFN*) forms and subsequently, the ground singlet state is replenished within microseconds. © 2016

New approaches for a time- and position-resolved detector for positron annihilation spectroscopy at PLEPS

Energy Technology Data Exchange (ETDEWEB)

Ackermann, Ulrich; Egger, Werner; Sperr, Peter; Loewe, Benjamin; Ravelli, Luca; Koegel, Gottfried; Dollinger, Guenther [Universitaet der Bundeswehr Muenchen, LRT2 (Germany); Jagutzki, Ottmar [Universitaet Frankfurt, RoentDek GmbH (Germany)

2013-07-01

The pulsed low energy positron system PLEPS at NEPOMUC at the FRM II is a tool for depth resolved positron lifetime measurements. Besides positron lifetime measurements 2D-AMOC (two dimensional age momentum correlation) experiments are also possible. 2D-AMOC provides in coincidence the lifetime of the positron and the longitudinal momentum distribution of the annihilating electron. It would be of great scientific concern to measure simultaneously the entire 3D-momentum distribution of the annihilating electron and the corresponding lifetime of the positron (4D-AMOC). To perform 4D-AMOC measurements, a time and spatially resolving detector with a time resolution of about 100 ps (FWHM) and a spatial resolution of circa 2 mm over an area of about 12 cm{sup 2} is required in coincidence with a pixelated Ge-detector and currently under development at our institute. It is intended to use a MCP-based UV-light detector with two MCP-stages coupled to a BaF{sub 2} scintillator. To achieve the spatial resolution the centroid information of the photoelectron-cloud is detected with a position sensitive anode installed outside the housing of the MCP detector. As an alternative to a MCP-based detector, silicon photomultipliers are also envisaged.

Timepix3 as X-ray detector for time resolved synchrotron experiments

Energy Technology Data Exchange (ETDEWEB)

Yousef, Hazem, E-mail: hazem.yousef@diamond.ac.uk; Crevatin, Giulio; Gimenez, Eva N.; Horswell, Ian; Omar, David; Tartoni, Nicola

2017-02-11

The Timepix3 ASIC can be used very effectively for time resolved experiments at synchrotron facilities. We have carried out characterizations with the synchrotron beam in order to determine the time resolution and other characteristics such as the energy resolution, charge sharing and signals overlapping. The best time resolution achieved is 19 ns FWHM for 12 keV photons and 350 V bias voltage. The time resolution shows dependency on the photon energy as well as on the chip and acquisition parameters. - Highlights: • An estimate time resolution of the Timepix3 is produced based on the arrival time. • At high resolution, the time structure of the DLS synchrotron beam is resolved. • The arrival time information improves combining the charge split events. • The results enable performing a wide range of time resolved experiments.

Timepix3 as X-ray detector for time resolved synchrotron experiments

International Nuclear Information System (INIS)

Yousef, Hazem; Crevatin, Giulio; Gimenez, Eva N.; Horswell, Ian; Omar, David; Tartoni, Nicola

2017-01-01

The Timepix3 ASIC can be used very effectively for time resolved experiments at synchrotron facilities. We have carried out characterizations with the synchrotron beam in order to determine the time resolution and other characteristics such as the energy resolution, charge sharing and signals overlapping. The best time resolution achieved is 19 ns FWHM for 12 keV photons and 350 V bias voltage. The time resolution shows dependency on the photon energy as well as on the chip and acquisition parameters. - Highlights: • An estimate time resolution of the Timepix3 is produced based on the arrival time. • At high resolution, the time structure of the DLS synchrotron beam is resolved. • The arrival time information improves combining the charge split events. • The results enable performing a wide range of time resolved experiments.

Real-time observation of cascaded electronic relaxation processes in p-Fluorotoluene

Science.gov (United States)

Hao, Qiaoli; Deng, Xulan; Long, Jinyou; Wang, Yanmei; Abulimiti, Bumaliya; Zhang, Bing

2017-08-01

Ultrafast electronic relaxation processes following two photoexcitation of 400 nm in p-Fluorotoluene (pFT) have been investigated utilizing time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Cascaded electronic relaxation processes started from the electronically excited S2 state are directly imaged in real time and well characterized by two distinct time constants of 85 ± 10 fs and 2.4 ± 0.3 ps. The rapid component corresponds to the lifetime of the initially excited S2 state, including the structure relaxation from the Franck-Condon region to the conical intersection of S2/S1 and the subsequent internal conversion to the highly excited S1 state. While, the slower relaxation constant is attributed to the further internal conversion to the high levels of S0 from the secondarily populated S1 locating in the channel three region. Moreover, dynamical differences with benzene and toluene of analogous structures, including, specifically, the slightly slower relaxation rate of S2 and the evidently faster decay of S1, are also presented and tentatively interpreted as the substituent effects. In addition, photoelectron kinetic energy and angular distributions reveal the feature of accidental resonances with low-lying Rydberg states (the 3p, 4s and 4p states) during the multi-photon ionization process, providing totally unexpected but very interesting information for pFT.

A time resolved microfocus XEOL facility at the Diamond Light Source

International Nuclear Information System (INIS)

Mosselmans, J F W; Taylor, R P; Quinn, P D; Cibin, G; Gianolio, D; Finch, A A; Sapelkin, A V

2013-01-01

We have constructed a Time-Resolved X-ray Excited Optical Luminescence (TR-XEOL) detection system at the Microfocus Spectroscopy beamline I18 at the Diamond Light Source. Using the synchrotron in h ybrid bunch mode , the data collection is triggered by the RF clock, and we are able to record XEOL photons with a time resolution of 6.1 ps during the 230 ns gap between the hybrid bunch and the main train of electron bunches. We can detect photons over the range 180-850 nm using a bespoke optical fibre, with X-ray excitation energies between 2 and 20 keV. We have used the system to study a range of feldspars. The detector is portable and has also been used on beamline B18 to collect Optically Determined X-ray Absorption Spectroscopy (OD-XAS) in QEXAFS mode.

A time resolved microfocus XEOL facility at the Diamond Light Source

Science.gov (United States)

Mosselmans, J. F. W.; Taylor, R. P.; Quinn, P. D.; Finch, A. A.; Cibin, G.; Gianolio, D.; Sapelkin, A. V.

2013-03-01

We have constructed a Time-Resolved X-ray Excited Optical Luminescence (TR-XEOL) detection system at the Microfocus Spectroscopy beamline I18 at the Diamond Light Source. Using the synchrotron in "hybrid bunch mode", the data collection is triggered by the RF clock, and we are able to record XEOL photons with a time resolution of 6.1 ps during the 230 ns gap between the hybrid bunch and the main train of electron bunches. We can detect photons over the range 180-850 nm using a bespoke optical fibre, with X-ray excitation energies between 2 and 20 keV. We have used the system to study a range of feldspars. The detector is portable and has also been used on beamline B18 to collect Optically Determined X-ray Absorption Spectroscopy (OD-XAS) in QEXAFS mode.

Time-resolved measurements of luminescence

Energy Technology Data Exchange (ETDEWEB)

Collier, Bradley B. [Department of Biomedical Engineering, 408 Mechanical Engineering Office Building, Spence Street, Texas A and M University, College Station, TX 77843 (United States); McShane, Michael J., E-mail: mcshane@tamu.edu [Department of Biomedical Engineering, 408 Mechanical Engineering Office Building, Spence Street, Texas A and M University, College Station, TX 77843 (United States); Materials Science and Engineering Program, 408 Mechanical Engineering Office Building, Spence Street, Texas A and M University, College Station, TX 77843 (United States)

2013-12-15

Luminescence sensing and imaging has become more widespread in recent years in a variety of industries including the biomedical and environmental fields. Measurements of luminescence lifetime hold inherent advantages over intensity-based response measurements, and advances in both technology and methods have enabled their use in a broader spectrum of applications including real-time medical diagnostics. This review will focus on recent advances in analytical methods, particularly calculation techniques, including time- and frequency-domain lifetime approaches as well as other time-resolved measurements of luminescence. -- Highlights: • Developments in technology have led to widespread use of luminescence lifetime. • Growing interest for sensing and imaging applications. • Recent advances in approaches to lifetime calculations are reviewed. • Advantages and disadvantages of various methods are weighed. • Other methods for measurement of luminescence lifetime also described.

Time-resolved measurements of luminescence

International Nuclear Information System (INIS)

Collier, Bradley B.; McShane, Michael J.

2013-01-01

Luminescence sensing and imaging has become more widespread in recent years in a variety of industries including the biomedical and environmental fields. Measurements of luminescence lifetime hold inherent advantages over intensity-based response measurements, and advances in both technology and methods have enabled their use in a broader spectrum of applications including real-time medical diagnostics. This review will focus on recent advances in analytical methods, particularly calculation techniques, including time- and frequency-domain lifetime approaches as well as other time-resolved measurements of luminescence. -- Highlights: • Developments in technology have led to widespread use of luminescence lifetime. • Growing interest for sensing and imaging applications. • Recent advances in approaches to lifetime calculations are reviewed. • Advantages and disadvantages of various methods are weighed. • Other methods for measurement of luminescence lifetime also described

Hot electron-induced time-resolved electrogenerated chemiluminescence of a europium(III) label in fully aqueous solutions

International Nuclear Information System (INIS)

Jiang, Q.; Hakansson, M.; Spehar, A.-M.; Ahonen, J.; Ala-Kleme, T.; Kulmala, S.

2006-01-01

Time-resolved electrogenerated chemiluminescence of multidentate phenolic Eu(III) chelates were studied in aqueous solution. 2,6-bis[N,N-bis(carboxymethyl)-aminomethyl]-4-benzoylphenol forms a photoluminescent and electrochemiluminescent Eu(III) chelate, whereas 2,6-bis[N,N-bis(carboxymethyl)-aminomethyl]-4-methyl phenol-chelated Eu(III) turned out to be not luminescent at all. The importance of the redox properties of both the ground and the excited states of the ligands and the central ion is shown. The former chelate shows relatively weak ECL at an oxide-covered aluminum electrode but the ECL intensity can be strongly enhanced by the addition of peroxodisulfate ions. In the presence of 1 mM peroxodisulfate ions the ECL lifetime of this chelate is 0.94 ms, thus easily allowing time-resolved detection of the chelate. This chelate can be conjugated to antibodies by thioureido linkage and used as an electrochemiluminescent label in immunoassays as a marker which displays long-lived luminescence in the red end of the optical spectrum. The present ECL is mainly based on the ligand sensitized redox excitation of the chelate by analogous pathways to those known from the studies of aromatic Tb(III) chelates but the energy transfer from the emission centers of the aluminum oxide film can also have minor contribution to the excitation of the label

Quantifying electronic band interactions in van der Waals materials using angle-resolved reflected-electron spectroscopy.

Science.gov (United States)

Jobst, Johannes; van der Torren, Alexander J H; Krasovskii, Eugene E; Balgley, Jesse; Dean, Cory R; Tromp, Rudolf M; van der Molen, Sense Jan

2016-11-29

High electron mobility is one of graphene's key properties, exploited for applications and fundamental research alike. Highest mobility values are found in heterostructures of graphene and hexagonal boron nitride, which consequently are widely used. However, surprisingly little is known about the interaction between the electronic states of these layered systems. Rather pragmatically, it is assumed that these do not couple significantly. Here we study the unoccupied band structure of graphite, boron nitride and their heterostructures using angle-resolved reflected-electron spectroscopy. We demonstrate that graphene and boron nitride bands do not interact over a wide energy range, despite their very similar dispersions. The method we use can be generally applied to study interactions in van der Waals systems, that is, artificial stacks of layered materials. With this we can quantitatively understand the 'chemistry of layers' by which novel materials are created via electronic coupling between the layers they are composed of.

Exact Time-Dependent Exchange-Correlation Potential in Electron Scattering Processes

Science.gov (United States)

Suzuki, Yasumitsu; Lacombe, Lionel; Watanabe, Kazuyuki; Maitra, Neepa T.

2017-12-01

We identify peak and valley structures in the exact exchange-correlation potential of time-dependent density functional theory that are crucial for time-resolved electron scattering in a model one-dimensional system. These structures are completely missed by adiabatic approximations that, consequently, significantly underestimate the scattering probability. A recently proposed nonadiabatic approximation is shown to correctly capture the approach of the electron to the target when the initial Kohn-Sham state is chosen judiciously, and it is more accurate than standard adiabatic functionals but ultimately fails to accurately capture reflection. These results may explain the underestimation of scattering probabilities in some recent studies on molecules and surfaces.

Time-Resolved Small-Angle X-Ray Scattering

NARCIS (Netherlands)

ten Elshof, Johan E.; Besselink, R.; Stawski, Tomasz; Castricum, H.L.; Levy, D.; Zayat, M.

2015-01-01

This chapter focuses on time-resolved studies of nanostructure development in sol-gel liquids, that is, diluted sols, wet gels, and drying thin fffilms. The most commonly investigated classes of sol-gel materials are silica, organically modified silica, template-directed mesostructured silica,

Time-resolved electron beam phase space tomography at a soft x-ray free-electron laser

Directory of Open Access Journals (Sweden)

Michael Röhrs

2009-05-01

Full Text Available High-gain free-electron lasers (FELs in the ultraviolet and x-ray regime put stringent demands on the peak current, transverse emittance, and energy spread of the driving electron beam. At the soft x-ray FEL FLASH, a transverse deflecting microwave structure (TDS has been installed to determine these parameters for the longitudinally compressed bunches, which are characterized by a narrow leading peak of high charge density and a long tail. The rapidly varying electromagnetic field in the TDS deflects the electrons vertically and transforms the time profile into a streak on an observation screen. The bunch current profile was measured single shot with an unprecedented resolution of 27 fs under FEL operating conditions. A precise single-shot measurement of the energy distribution along a bunch was accomplished by using the TDS in combination with an energy spectrometer. Variation of quadrupole strengths allowed for a determination of the horizontal emittance as a function of the longitudinal position within a bunch, the so-called slice emittance. In the bunch tail, a normalized slice emittance of about 2  μm was found, in agreement with expectations. In the leading spike, however, surprisingly large emittance values were observed, in apparent contradiction with the low emittance deduced from the measured FEL gain. By applying three-dimensional phase space tomography, we were able to show that the bunch head contains a central core of low emittance and high local current density, which is presumably the lasing part of the bunch.

Multi-frame pyramid correlation for time-resolved PIV

NARCIS (Netherlands)

Sciacchitano, A.; Scarano, F.; Wieneke, B.

2012-01-01

A novel technique is introduced to increase the precision and robustness of time-resolved particle image velocimetry (TR-PIV) measurements. The innovative element of the technique is the linear combination of the correlation signal computed at different separation time intervals. The domain of the

Time-dependent quantum chemistry of laser driven many-electron molecules

International Nuclear Information System (INIS)

Nguyen-Dang, Thanh-Tung; Couture-Bienvenue, Étienne; Viau-Trudel, Jérémy; Sainjon, Amaury

2014-01-01

A Time-Dependent Configuration Interaction approach using multiple Feshbach partitionings, corresponding to multiple ionization stages of a laser-driven molecule, has recently been proposed [T.-T. Nguyen-Dang and J. Viau-Trudel, J. Chem. Phys. 139, 244102 (2013)]. To complete this development toward a fully ab-initio method for the calculation of time-dependent electronic wavefunctions of an N-electron molecule, we describe how tools of multiconfiguration quantum chemistry such as the management of the configuration expansion space using Graphical Unitary Group Approach concepts can be profitably adapted to the new context, that of time-resolved electronic dynamics, as opposed to stationary electronic structure. The method is applied to calculate the detailed, sub-cycle electronic dynamics of BeH 2 , treated in a 3–21G bound-orbital basis augmented by a set of orthogonalized plane-waves representing continuum-type orbitals, including its ionization under an intense λ = 800 nm or λ = 80 nm continuous-wave laser field. The dynamics is strongly non-linear at the field-intensity considered (I ≃ 10 15 W/cm 2 ), featuring important ionization of an inner-shell electron and strong post-ionization bound-electron dynamics

Time-Resolved Hard X-Ray Spectrometer

International Nuclear Information System (INIS)

Kenneth Moya; Ian McKennaa; Thomas Keenana; Michael Cuneob

2007-01-01

Wired array studies are being conducted at the SNL Z accelerator to maximize the x-ray generation for inertial confinement fusion targets and high energy density physics experiments. An integral component of these studies is the characterization of the time-resolved spectral content of the x-rays. Due to potential spatial anisotropy in the emitted radiation, it is also critical to diagnose the time-evolved spectral content in a space-resolved manner. To accomplish these two measurement goals, we developed an x-ray spectrometer using a set of high-speed detectors (silicon PIN diodes) with a collimated field-of-view that converged on a 1-cm-diameter spot at the pinch axis. Spectral discrimination is achieved by placing high Z absorbers in front of these detectors. We built two spectrometers to permit simultaneous different angular views of the emitted radiation. Spectral data have been acquired from recent Z shots for the radial and polar views. UNSPEC1 has been adapted to analyze and unfold the measured data to reconstruct the x-ray spectrum. The unfold operator code, UFO2, is being adapted for a more comprehensive spectral unfolding treatment

CO2 laser interferometer for temporally and spatially resolved electron density measurements

Science.gov (United States)

Brannon, P. J.; Gerber, R. A.; Gerardo, J. B.

1982-09-01

A 10.6-μm Mach-Zehnder interferometer has been constructed to make temporally and spatially resolved measurements of electron densities in plasmas. The device uses a pyroelectric vidicon camera and video memory to record and display the two-dimensional fringe pattern and a Pockels cell to limit the pulse width of the 10.6-μm radiation. A temporal resolution of 14 ns has been demonstrated. The relative sensitivity of the device for electron density measurements is 2×1015 cm-2 (the line integral of the line-of-sight length and electron density), which corresponds to 0.1 fringe shift.

CO2 laser interferometer for temporally and spatially resolved electron density measurements

International Nuclear Information System (INIS)

Brannon, P.J.; Gerber, R.A.; Gerardo, J.B.

1982-01-01

A 10.6-μm Mach--Zehnder interferometer has been constructed to make temporally and spatially resolved measurements of electron densities in plasmas. The device uses a pyroelectric vidicon camera and video memory to record and display the two-dimensional fringe pattern and a Pockels cell to limit the pulse width of the 10.6-μm radiation. A temporal resolution of 14 ns has been demonstrated. The relative sensitivity of the device for electron density measurements is 2 x 10 15 cm -2 (the line integral of the line-of-sight length and electron density), which corresponds to 0.1 fringe shift

Time-resolved pump-probe experiments at the LCLS

Energy Technology Data Exchange (ETDEWEB)

Glownia, James; /SLAC /Stanford U., Appl. Phys. Dept.; Cryan, J.; /SLAC /Stanford U., Phys. Dept.; Andreasson, J.; /Uppsala U.; Belkacem, A.; /LBNL, Berkeley; Berrah, N.; /Western Michigan U.; Blaga, C.L.; /Ohio State U.; Bostedt, C.; Bozek, J.; /SLAC; DiMauro, L.F.; /Ohio State U.; Fang, L.; /Western Michigan U.; Frisch, J.; /SLAC; Gessner, O.; /LBNL; Guhr, M.; /SLAC; Hajdu, J.; /Uppsala U.; Hertlein, M.P.; /LBNL; Hoener, M.; /Western Michigan U. /LBNL; Huang, G.; Kornilov, O.; /LBNL; Marangos, J.P.; /Imperial Coll., London; March, A.M.; /Argonne; McFarland, B.K.; /SLAC /Stanford U., Phys. Dept. /SLAC /IRAMIS, Saclay /Stanford U., Phys. Dept. /Georgia Tech /Argonne /Kansas State U. /SLAC /Stanford U., Phys. Dept. /SLAC /Stanford U., Appl. Phys. Dept. /Stanford U., Appl. Phys. Dept. /SLAC /LBNL /Argonne /SLAC /SLAC /Stanford U., Appl. Phys. Dept. /Stanford U., Phys. Dept.

2011-08-12

The first time-resolved x-ray/optical pump-probe experiments at the SLAC Linac Coherent Light Source (LCLS) used a combination of feedback methods and post-analysis binning techniques to synchronize an ultrafast optical laser to the linac-based x-ray laser. Transient molecular nitrogen alignment revival features were resolved in time-dependent x-ray-induced fragmentation spectra. These alignment features were used to find the temporal overlap of the pump and probe pulses. The strong-field dissociation of x-ray generated quasi-bound molecular dications was used to establish the residual timing jitter. This analysis shows that the relative arrival time of the Ti:Sapphire laser and the x-ray pulses had a distribution with a standard deviation of approximately 120 fs. The largest contribution to the jitter noise spectrum was the locking of the laser oscillator to the reference RF of the accelerator, which suggests that simple technical improvements could reduce the jitter to better than 50 fs.

Improvement of the intrinsic time resolving power of the Cologne iron-free orange type electron spectrometers

Energy Technology Data Exchange (ETDEWEB)

Regis, J.-M.; Materna, Th.; Pascovici, G.; Christen, S.; Dewald, A.; Fransen, C.; Jolie, J.; Petkov, P.; Zell, K. O. [Institut fuer Kernphysik (IKP), Universitaet zu Koeln, Zuelpicher Str. 77, 50937 Koeln (Germany)

2010-11-15

Conversion electron spectroscopy represents an important tool for nuclear structure analysis of medium and heavy nuclei. Two iron-free magnetic electron spectrometers of the orange type have been installed at the Institute for Nuclear Physics of the University of Cologne. The very large transmission of 15% and the very good energy resolution of 1% makes the iron-free orange spectrometer a powerful instrument. By means of fast timing techniques, lifetimes of nuclear excited states can be measured with an accuracy better than 20 ps. For the first time, the energy dependent centroid position of prompt events yielding the time-walk characteristics (the prompt curve) of the orange spectrometer fast timing setup has been measured using prompt secondary {delta}-electrons generated in a pulsed beam experiment. The prompt curve calibrated as a function of energy allows precise lifetime determination down to a few tens of picoseconds by the use of the centroid shift method.

Capturing Chemistry in Action with Electrons: Realization of Atomically Resolved Reaction Dynamics.

Science.gov (United States)

Ischenko, Anatoly A; Weber, Peter M; Miller, R J Dwayne

2017-08-23

One of the grand challenges in chemistry has been to directly observe atomic motions during chemical processes. The depiction of the nuclear configurations in space-time to understand barrier crossing events has served as a unifying intellectual theme connecting the different disciplines of chemistry. This challenge has been cast as an imaging problem in which the technical issues reduce to achieving not only sufficient simultaneous space-time resolution but also brightness for sufficient image contrast to capture the atomic motions. This objective has been met with electrons as the imaging source. The review chronicles the first use of electron structural probes to study reactive intermediates, to the development of high bunch charge electron pulses with sufficient combined spatial-temporal resolution and intensity to literally light up atomic motions, as well as the means to characterize the electron pulses in terms of temporal brightness and image reconstruction. The use of femtosecond Rydberg spectroscopy as a novel means to use internal electron scattering within the molecular reference frame to obtain similar information on reaction dynamics is also discussed. The focus is on atomically resolved chemical reaction dynamics with pertinent references to work in other areas and forms of spectroscopy that provide additional information. Effectively, we can now directly observe the far-from-equilibrium atomic motions involved in barrier crossing and categorize chemistry in terms of a power spectrum of a few dominant reaction modes. It is this reduction in dimensionality that makes chemical reaction mechanisms transferrable to seemingly arbitrarily complex (large N) systems, up to molecules as large as biological macromolecules (N > 1000 atoms). We now have a new way to reformulate reaction mechanisms using an experimentally determined dynamic mode basis that in combination with recent theoretical advances has the potential to lead to a new conceptual basis for

Space-charge effect in electron time-of-flight analyzer for high-energy photoemission spectroscopy

International Nuclear Information System (INIS)

Greco, G.; Verna, A.; Offi, F.; Stefani, G.

2016-01-01

Highlights: • Two methods for the simulation of space-charge effect in time-resolved PES. • Reliability and advantages in the use of the SIMION"® software. • Simulation of the space-charge effect in an electron TOF analyzer. • Feasibility of a TOF analyzer in time-resolved high-energy PES experiments at FEL. - Abstract: The space-charge effect, due to the instantaneous emission of many electrons after the absorption of a single photons pulse, causes distortion in the photoelectron energy spectrum. Two calculation methods have been applied to simulate the expansion during a free flight of clouds of mono- and bi-energetic electrons generated by a high energy pulse of light and their results have been compared. The accuracy of a widely used tool, such as SIMION"®, in predicting the energy distortion caused by the space-charge has been tested and the reliability of its results is verified. Finally we used SIMION"® to take into account the space-charge effects in the simulation of simple photoemission experiments with a time-of-flight analyzer.

Visualizing electron dynamics in organic materials: Charge transport through molecules and angular resolved photoemission

Science.gov (United States)

Kümmel, Stephan

Being able to visualize the dynamics of electrons in organic materials is a fascinating perspective. Simulations based on time-dependent density functional theory allow to realize this hope, as they visualize the flow of charge through molecular structures in real-space and real-time. We here present results on two fundamental processes: Photoemission from organic semiconductor molecules and charge transport through molecular structures. In the first part we demonstrate that angular resolved photoemission intensities - from both theory and experiment - can often be interpreted as a visualization of molecular orbitals. However, counter-intuitive quantum-mechanical electron dynamics such as emission perpendicular to the direction of the electrical field can substantially alter the picture, adding surprising features to the molecular orbital interpretation. In a second study we calculate the flow of charge through conjugated molecules. The calculations show in real time how breaks in the conjugation can lead to a local buildup of charge and the formation of local electrical dipoles. These can interact with neighboring molecular chains. As a consequence, collections of ''molecular electrical wires'' can show distinctly different characteristics than ''classical electrical wires''. German Science Foundation GRK 1640.

Time-resolved crystallography using the Hadamard Transform

Science.gov (United States)

Yorke, Briony A.; Beddard, Godfrey S.; Owen, Robin L.; Pearson, Arwen R.

2014-01-01

A new method for performing time-resolved X-ray crystallographic experiments based on the Hadamard Transform is proposed and demonstrated. The time-resolution is defined by the underlying periodicity of the probe pulse sequence and the signal to noise is greatly improved compared to the fastest experiments depending on a single pulse. This approach is general and equally applicable to any spectroscopic or imaging measurement where the probe can be encoded. PMID:25282611

Time-resolved photoelectron spectroscopy using synchrotron radiation time structure

International Nuclear Information System (INIS)

Bergeard, N.; Silly, M.G.; Chauvet, C.; Guzzo, M.; Ricaud, J.P.; Izquierdo, M.; Sirotti, F.; Krizmancic, D.; Guzzo, M.; Stebel, L.; Pittana, P.; Sergo, R.; Cautero, G.; Dufour, G.; Rochet, F.

2011-01-01

Synchrotron radiation time structure is becoming a common tool for studying dynamic properties of materials. The main limitation is often the wide time domain the user would like to access with pump-probe experiments. In order to perform photoelectron spectroscopy experiments over time scales from milliseconds to picoseconds it is mandatory to measure the time at which each measured photoelectron was created. For this reason the usual CCD camera based two-dimensional detection of electron energy analyzers has been replaced by a new delay-line detector adapted to the time structure of the SOLEIL synchrotron radiation source. The new two-dimensional delay-line detector has a time resolution of 5 ns and was installed on a Scienta SES 2002 electron energy analyzer. The first application has been to characterize the time of flight of the photo emitted electrons as a function of their kinetic energy and the selected pass energy. By repeating the experiment as a function of the available pass energy and of the kinetic energy, a complete characterization of the analyzer behaviour in the time domain has been obtained. Even for kinetic energies as low as 10 eV at 2 eV pass energy, the time spread of the detected electrons is lower than 140 ns. These results and the time structure of the SOLEIL filling modes assure the possibility of performing pump-probe photoelectron spectroscopy experiments with the time resolution given by the SOLEIL pulse width, the best performance of the beamline and of the experimental station. (authors)

Field transients of coherent terahertz synchrotron radiation accessed via time-resolving and correlation techniques

Energy Technology Data Exchange (ETDEWEB)

Pohl, A.; Hübers, H.-W. [Humboldt-Universität zu Berlin, Institute of Physics, Newtonstraße 15, 12489 Berlin (Germany); Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstrasse 29, 12489 Berlin (Germany); Semenov, A. [Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstrasse 29, 12489 Berlin (Germany); Hoehl, A.; Ulm, G. [Physikalisch-Technische Bundesanstalt (PTB), Abbestraße 2-12, 10587 Berlin (Germany); Ries, M.; Wüstefeld, G. [Helmholz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489 Berlin (Germany); Ilin, K.; Thoma, P.; Siegel, M. [Institute of Micro- and Nanoelectronic Systems, Karlsruhe Institute of Technology (KIT), Hertzstrasse 16, 76187 Karlsruhe (Germany)

2016-03-21

Decaying oscillations of the electric field in repetitive pulses of coherent synchrotron radiation in the terahertz frequency range was evaluated by means of time-resolving and correlation techniques. Comparative analysis of real-time voltage transients of the electrical response and interferograms, which were obtained with an ultrafast zero-bias Schottky diode detector and a Martin-Puplett interferometer, delivers close values of the pulse duration. Consistent results were obtained via the correlation technique with a pair of Golay Cell detectors and a pair of resonant polarisation-sensitive superconducting detectors integrated on one chip. The duration of terahertz synchrotron pulses does not closely correlate with the duration of single-cycle electric field expected for the varying size of electron bunches. We largely attribute the difference to the charge density oscillations in electron bunches and to the low-frequency spectral cut-off imposed by both the synchrotron beamline and the coupling optics of our detectors.

In-pile Thermal Conductivity Characterization with Time Resolved Raman

Energy Technology Data Exchange (ETDEWEB)

Wang, Xinwei [Iowa State Univ., Ames, IA (United States). Dept. of Mechanical Engineering; Hurley, David H. [Idaho National Lab. (INL), Idaho Falls, ID (United States)

2018-03-19

The project is designed to achieve three objectives: (1) Develop a novel time resolved Raman technology for direct measurement of fuel and cladding thermal conductivity. (2) Validate and improve the technology development by measuring ceramic materials germane to the nuclear industry. (3) Conduct instrumentation development to integrate optical fiber into our sensing system for eventual in-pile measurement. We have developed three new techniques: time-domain differential Raman (TD-Raman), frequency-resolved Raman (FR-Raman), and energy transport state-resolved Raman (ET-Raman). The TD-Raman varies the laser heating time and does simultaneous Raman thermal probing, the FR-Raman probes the material’s thermal response under periodical laser heating of different frequencies, and the ET-Raman probes the thermal response under steady and pulsed laser heating. The measurement capacity of these techniques have been fully assessed and verified by measuring micro/nanoscale materials. All these techniques do not need the data of laser absorption and absolute material temperature rise, yet still be able to measure the thermal conductivity and thermal diffusivity with unprecedented accuracy. It is expected they will have broad applications for in-pile thermal characterization of nuclear materials based on pure optical heating and sensing.

Multi-Channel Amplifier-Discriminator for Highly Time-Resolved Detection

CERN Document Server

Despeisse, M; Lapington, J; Jarron, P

2011-01-01

A low-power multi-channel amplifier-discriminator was developed for application in highly time-resolved detection systems. The proposed circuit architecture, so-called Nino, is based on a time-over-threshold approach and shows a high potential for time-resolved readout of solid-state photo-detectors and of detectors based on vacuum technologies. The Irpics circuit was designed in a 250 nm CMOS technology, implementing 32 channels of a Nino version optimized to achieve high-time resolution on the output low-voltage differential signals (LVDS) while keeping a low power consumption of 10 mW per channel. Electrical characterizations of the circuit demonstrate a very low intrinsic time jitter on the output pulse leading edge, measured below 10 ps rms for each channel for high input signal charges (100 fC) and below 25 ps rms for low input signal charges (20-100 fC). The read-out architecture moreover permits to retrieve the input signal charge from the timing measurements, while a calibration procedure was develop...

Electronic structure of Sr2RuO4 studied by angle-resolved photoemission spectroscopy

International Nuclear Information System (INIS)

Iwasawa, H.; Aiura, Y.; Saitoh, T.; Yoshida, Y.; Hase, I.; Ikeda, S.I.; Bando, H.; Kubota, M.; Ono, K.

2007-01-01

Electronic structure of the monolayer strontium ruthenate Sr 2 RuO 4 was investigated by high-resolution angle-resolved photoemission spectroscopy. We present photon-energy (hν) dependence of the electronic structure near the Fermi level along the ΓM line. The hν dependence has shown a strong spectral weight modulation of the Ru 4d xy and 4d zx bands

Difference structures from time-resolved small-angle and wide-angle x-ray scattering

Science.gov (United States)

Nepal, Prakash; Saldin, D. K.

2018-05-01

Time-resolved small-angle x-ray scattering/wide-angle x-ray scattering (SAXS/WAXS) is capable of recovering difference structures directly from difference SAXS/WAXS curves. It does so by means of the theory described here because the structural changes in pump-probe detection in a typical time-resolved experiment are generally small enough to be confined to a single residue or group in close proximity which is identified by a method akin to the difference Fourier method of time-resolved crystallography. If it is assumed, as is usual with time-resolved structures, that the moved atoms lie within the residue, the 100-fold reduction in the search space (assuming a typical protein has about 100 residues) allows the exaction of the structure by a simulated annealing algorithm with a huge reduction in computing time and leads to a greater resolution by varying the positions of atoms only within that residue. This reduction in the number of potential moved atoms allows us to identify the actual motions of the individual atoms. In the case of a crystal, time-resolved calculations are normally performed using the difference Fourier method, which is, of course, not directly applicable to SAXS/WAXS. The method developed in this paper may be thought of as a substitute for that method which allows SAXS/WAXS (and hence disordered molecules) to also be used for time-resolved structural work.

Pump laser-induced space-charge effects in HHG-driven time- and angle-resolved photoelectron spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Oloff, L.-P., E-mail: oloff@physik.uni-kiel.de; Hanff, K.; Stange, A.; Rohde, G.; Diekmann, F.; Bauer, M.; Rossnagel, K., E-mail: rossnagel@physik.uni-kiel.de [Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, D-24098 Kiel (Germany)

2016-06-14

With the advent of ultrashort-pulsed extreme ultraviolet sources, such as free-electron lasers or high-harmonic-generation (HHG) sources, a new research field for photoelectron spectroscopy has opened up in terms of femtosecond time-resolved pump-probe experiments. The impact of the high peak brilliance of these novel sources on photoemission spectra, so-called vacuum space-charge effects caused by the Coulomb interaction among the photoemitted probe electrons, has been studied extensively. However, possible distortions of the energy and momentum distributions of the probe photoelectrons caused by the low photon energy pump pulse due to the nonlinear emission of electrons have not been studied in detail yet. Here, we systematically investigate these pump laser-induced space-charge effects in a HHG-based experiment for the test case of highly oriented pyrolytic graphite. Specifically, we determine how the key parameters of the pump pulse—the excitation density, wavelength, spot size, and emitted electron energy distribution—affect the measured time-dependent energy and momentum distributions of the probe photoelectrons. The results are well reproduced by a simple mean-field model, which could open a path for the correction of pump laser-induced space-charge effects and thus toward probing ultrafast electron dynamics in strongly excited materials.

Time-of-flight electron energy loss spectroscopy using TM110 deflection cavities

Directory of Open Access Journals (Sweden)

W. Verhoeven

2016-09-01

Full Text Available We demonstrate the use of two TM110 resonant cavities to generate ultrashort electron pulses and subsequently measure electron energy losses in a time-of-flight type of setup. The method utilizes two synchronized microwave cavities separated by a drift space of 1.45 m. The setup has an energy resolution of 12 ± 2 eV FWHM at 30 keV, with an upper limit for the temporal resolution of 2.7 ± 0.4 ps. Both the time and energy resolution are currently limited by the brightness of the tungsten filament electron gun used. Through simulations, it is shown that an energy resolution of 0.95 eV and a temporal resolution of 110 fs can be achieved using an electron gun with a higher brightness. With this, a new method is provided for time-resolved electron spectroscopy without the need for elaborate laser setups or expensive magnetic spectrometers.

Continuous wave and time resolved spectroscopy of InAsN/GaAsN based quantum dots

International Nuclear Information System (INIS)

Taliercio, T.; Valvin, P.; Intartaglia, R.; Guillet, T.; Lefebvre, P.; Bretagnon, T.; Gil, B.; Sallet, V.; Harmand, J.C.

2005-01-01

We present a study of the optical properties of quantum dots based on a new family of semiconductors: III-V dilute nitrides such as (In,Ga)(N,As). Continuous wave and time resolved photoluminescence (PL) experiments allowed us to evaluate the impact of N incorporation during the growth of InAs/GaAs quantum dots. Previous work [V. Sallet et al., to be submitted to J. Cryst. Growth (2005); O. Schumann et al., J. Appl. Phys. 96, 2832 (2004)] showed that increasing the flux of N atoms into the growth chamber modifies drastically the size of the dots which leads to a bimodal growth. Two populations of dots with different sizes appear. The quantum dot PL line broadens and a second PL line appears at higher energy. Time resolved PL allows us to identify the nature of this second PL line: second population of quantum dots. A second decay time is observed which we interpret as being the consequence of the perturbation of the electronic states of the quantum dots. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Extracting the temperature of hot carriers in time- and angle-resolved photoemission

International Nuclear Information System (INIS)

Ulstrup, Søren; Hofmann, Philip; Johannsen, Jens Christian; Grioni, Marco

2014-01-01

The interaction of light with a material's electronic system creates an out-of-equilibrium (non-thermal) distribution of optically excited electrons. Non-equilibrium dynamics relaxes this distribution on an ultrafast timescale to a hot Fermi-Dirac distribution with a well-defined temperature. The advent of time- and angle-resolved photoemission spectroscopy (TR-ARPES) experiments has made it possible to track the decay of the temperature of the excited hot electrons in selected states in the Brillouin zone, and to reveal their cooling in unprecedented detail in a variety of emerging materials. It is, however, not a straightforward task to determine the temperature with high accuracy. This is mainly attributable to an a priori unknown position of the Fermi level and the fact that the shape of the Fermi edge can be severely perturbed when the state in question is crossing the Fermi energy. Here, we introduce a method that circumvents these difficulties and accurately extracts both the temperature and the position of the Fermi level for a hot carrier distribution by tracking the occupation statistics of the carriers measured in a TR-ARPES experiment

Extracting the temperature of hot carriers in time- and angle-resolved photoemission.

Science.gov (United States)

Ulstrup, Søren; Johannsen, Jens Christian; Grioni, Marco; Hofmann, Philip

2014-01-01

The interaction of light with a material's electronic system creates an out-of-equilibrium (non-thermal) distribution of optically excited electrons. Non-equilibrium dynamics relaxes this distribution on an ultrafast timescale to a hot Fermi-Dirac distribution with a well-defined temperature. The advent of time- and angle-resolved photoemission spectroscopy (TR-ARPES) experiments has made it possible to track the decay of the temperature of the excited hot electrons in selected states in the Brillouin zone, and to reveal their cooling in unprecedented detail in a variety of emerging materials. It is, however, not a straightforward task to determine the temperature with high accuracy. This is mainly attributable to an a priori unknown position of the Fermi level and the fact that the shape of the Fermi edge can be severely perturbed when the state in question is crossing the Fermi energy. Here, we introduce a method that circumvents these difficulties and accurately extracts both the temperature and the position of the Fermi level for a hot carrier distribution by tracking the occupation statistics of the carriers measured in a TR-ARPES experiment.

Advances in imaging and electron physics time resolved electron diffraction for chemistry, biology and material science

CERN Document Server

Hawkes, Peter W

2014-01-01

Advances in Imaging & Electron Physics merges two long-running serials-Advances in Electronics & Electron Physics and Advances in Optical & Electron Microscopy. The series features extended articles on the physics of electron devices (especially semiconductor devices), particle optics at high and low energies, microlithography, image science and digital image processing, electromagnetic wave propagation, electron microscopy, and the computing methods used in all these domains. Contributions from leading authorities Informs and updates on all the latest developments in the field.

Quantum-dot-based homogeneous time-resolved fluoroimmunoassay of alpha-fetoprotein

Energy Technology Data Exchange (ETDEWEB)

Chen Meijun; Wu Yingsong; Lin Guanfeng; Hou Jingyuan; Li Ming [Institute of Antibody Engineering, School of Biotechnology, Southern Medical University, Guangzhou, 510515 (China); Liu Tiancai, E-mail: liutc@smu.edu.cn [Institute of Antibody Engineering, School of Biotechnology, Southern Medical University, Guangzhou, 510515 (China)

2012-09-05

Highlights: Black-Right-Pointing-Pointer QDs-based homogeneous time-resolved fluoroimmunoassay was developed to detect AFP. Black-Right-Pointing-Pointer The conjugates were prepared with QDs-doped microspheres and anti-AFP McAb. Black-Right-Pointing-Pointer The conjugates were prepared with LTCs and another anti-AFP McAb. Black-Right-Pointing-Pointer Excess amounts of conjugates were used for detecting AFP without rinsing. Black-Right-Pointing-Pointer The wedding of QPs and LTCs was suitable for HTRFIA to detect AFP. - Abstract: Quantum dots (QDs) with novel photoproperties are not widely used in clinic diagnosis, and homogeneous time-resolved fluorescence assays possess many advantages over current methods for alpha-fetoprotein (AFP) detection. A novel QD-based homogeneous time-resolved fluorescence assay was developed and used for detection of AFP, a primary marker for many cancers and diseases. QD-doped carboxyl-modified polystyrene microparticles (QPs) were prepared by doping oil-soluble QDs possessing a 605 nm emission peak. The antibody conjugates (QPs-E014) were prepared from QPs and an anti-AFP monoclonal antibody, and luminescent terbium chelates (LTCs) were prepared and conjugated to a second anti-AFP monoclonal antibody (LTCs-E010). In a double-antibodies sandwich structure, QPs-E014 and LTCs-E010 were used for detection of AFP, serving as energy acceptor and donor, respectively, with an AFP bridge. The results demonstrated that the luminescence lifetime of these QPs was sufficiently long for use in a time-resolved fluoroassay, with the efficiency of time-resolved Foerster resonance transfer (TR-FRET) at 67.3% and the spatial distance of the donor to acceptor calculated to be 66.1 Angstrom-Sign . Signals from TR-FRET were found to be proportional to AFP concentrations. The resulting standard curve was log Y = 3.65786 + 0.43863{center_dot}log X (R = 0.996) with Y the QPs fluorescence intensity and X the AFP concentration; the calculated sensitivity was 0

Time- and space-resolved spectroscopic characterization of laser-induced swine muscle tissue plasma

Energy Technology Data Exchange (ETDEWEB)

Camacho, J.J. [Departamento de Química-Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Diaz, L., E-mail: luis.diaz@csic.es [Instituto de Estructura de la Materia, CFMAC, CSIC, Serrano 121, 28006 Madrid (Spain); Martinez-Ramirez, S. [Instituto de Estructura de la Materia, CFMAC, CSIC, Serrano 121, 28006 Madrid (Spain); Caceres, J.O. [Departamento de Química Analítica, Facultad de Ciencias Químicas, Universidad Complutense, Cuidad Universitaria, 28040 Madrid (Spain)

2015-09-01

The spatial-temporal evolution of muscle tissue sample plasma induced by a high-power transversely excited atmospheric (TEA) CO{sub 2} pulsed laser at vacuum conditions (0.1–0.01 Pa) has been investigated using high-resolution optical emission spectroscopy (OES) and imaging methods. The induced plasma shows mainly electronically excited neutral Na, K, C, Mg, H, Ca, N and O atoms, ionized C{sup +}, C{sup 2+}, C{sup 3+}, Mg{sup +}, Mg{sup 2+}, N{sup +}, N{sup 2+}, Ca{sup +}, O{sup +} and O{sup 2+} species and molecular band systems of CN(B{sup 2}Σ{sup +}–X{sup 2}Σ{sup +}), C{sub 2}(d{sup 3}Π{sub g}–a{sup 3}Π{sub u}), CH(B{sup 2}Σ{sup −}–X{sup 2}Π; A{sup 2}Δ–X{sup 2}Π), NH(A{sup 3}Π–X{sup 3}Σ{sup −}), OH(A{sup 2}Σ{sup +}–X{sup 2} Σ{sup +}), and CaOH(B{sup 2}Σ{sup +}–X{sup 2}Σ{sup +}; A{sup 2}Π–X{sup 2}Σ{sup +}). Time-resolved two-dimensional emission spectroscopy is used to study the expanded distribution of different species ejected during ablation. Spatial and temporal variations of different atoms and ionic excited species are reported. Plasma parameters such as electron density and temperature were measured from the spatio-temporal analysis of different species. Average velocities of some plasma species were estimated. - Highlights: • LIBS of swine muscle tissue sample generated by CO{sub 2} laser pulses has been done for the first time. • Average velocities of some plasma species have been calculated from spatial and temporally resolved 2D OES images. • Electron density (~ 9 × 10{sup 17} cm{sup -3}) has been studied with spatial and temporal resolution. • Temporal evolution of the plasma temperature has been calculated by means of Boltzmann plots.

Setup for angle-resolved electron spectrometry using monochromatised synchrotron radiation

International Nuclear Information System (INIS)

Derenbach, H.; Franke, C.; Malutzki, R.; Wachter, A.; Schmidt, V.

1987-01-01

An apparatus is described which is well suited for angle-resolved electron spectrometry of free atoms and molecules using monochromatised synchrotron radiation. Two variations are presented, one for room temperature gaseous species, the other for metallic vapours. The analyser is of the cylindrical mirror type, designed, however, so as to accept with one sector the entire source volume independently of the photon beam diameter. It can be equipped with a positon-sensitive detector instead of a channeltron, which extends its potentiality. The system consists of up to three cylindrical mirror sector analysers (CMAs) where a double-sector CMA can be rotated around the photon beam direction, allowing angular distribution measurements, and another sector CMA is mounted in a fixed position providing a signal for reference purposes. A detailed description and experimental tests are given for the performance of the CMA, i.e. its imaging properties, resolution and transmissions, as well as for possible instrumental asymmetries affecting angle-resolved experiments. (orig.)

Modelling the thermal quenching mechanism in quartz based on time-resolved optically stimulated luminescence

International Nuclear Information System (INIS)

Pagonis, V.; Ankjaergaard, C.; Murray, A.S.; Jain, M.; Chen, R.; Lawless, J.; Greilich, S.

2010-01-01

This paper presents a new numerical model for thermal quenching in quartz, based on the previously suggested Mott-Seitz mechanism. In the model electrons from a dosimetric trap are raised by optical or thermal stimulation into the conduction band, followed by an electronic transition from the conduction band into an excited state of the recombination center. Subsequently electrons in this excited state undergo either a direct radiative transition into a recombination center, or a competing thermally assisted non-radiative process into the ground state of the recombination center. As the temperature of the sample is increased, more electrons are removed from the excited state via the non-radiative pathway. This reduction in the number of available electrons leads to both a decrease of the intensity of the luminescence signal and to a simultaneous decrease of the luminescence lifetime. Several simulations are carried out of time-resolved optically stimulated luminescence (TR-OSL) experiments, in which the temperature dependence of luminescence lifetimes in quartz is studied as a function of the stimulation temperature. Good quantitative agreement is found between the simulation results and new experimental data obtained using a single-aliquot procedure on a sedimentary quartz sample.

Time-resolved x-ray diagnostics

International Nuclear Information System (INIS)

Lyons, P.B.

1981-01-01

Techniques for time-resolved x-ray diagnostics will be reviewed with emphasis on systems utilizing x-ray diodes or scintillators. System design concerns for high-bandwidth (> 1 GHz) diagnostics will be emphasized. The limitations of a coaxial cable system and a technique for equalizing to improve bandwidth of such a system will be reviewed. Characteristics of new multi-GHz amplifiers will be presented. An example of a complete operational system on the Los Alamos Helios laser will be presented which has a bandwidth near 3 GHz over 38 m of coax. The system includes the cable, an amplifier, an oscilloscope, and a digital camera readout

Time-resolved spectral measurements above 80 A

International Nuclear Information System (INIS)

Kauffman, R.L.; Ceglio, N.; Medecki, H.

1983-01-01

We have made time-resolved spectral measurements above 80 A from laser-produced plasmas. These are made using a transmission grating spectrograph whose primary components are a cylindrically-curved x-ray mirror for light collection, a transmission grating for spectral dispersions, and an x-ray streak camera for temporal resolution. A description of the instrument and an example of the data are given

First spin-resolved electron distributions in crystals from combined polarized neutron and X-ray diffraction experiments

Directory of Open Access Journals (Sweden)

Maxime Deutsch

2014-05-01

Full Text Available Since the 1980s it has been possible to probe crystallized matter, thanks to X-ray or neutron scattering techniques, to obtain an accurate charge density or spin distribution at the atomic scale. Despite the description of the same physical quantity (electron density and tremendous development of sources, detectors, data treatment software etc., these different techniques evolved separately with one model per experiment. However, a breakthrough was recently made by the development of a common model in order to combine information coming from all these different experiments. Here we report the first experimental determination of spin-resolved electron density obtained by a combined treatment of X-ray, neutron and polarized neutron diffraction data. These experimental spin up and spin down densities compare very well with density functional theory (DFT calculations and also confirm a theoretical prediction made in 1985 which claims that majority spin electrons should have a more contracted distribution around the nucleus than minority spin electrons. Topological analysis of the resulting experimental spin-resolved electron density is also briefly discussed.

First spin-resolved electron distributions in crystals from combined polarized neutron and X-ray diffraction experiments.

Science.gov (United States)

Deutsch, Maxime; Gillon, Béatrice; Claiser, Nicolas; Gillet, Jean-Michel; Lecomte, Claude; Souhassou, Mohamed

2014-05-01

Since the 1980s it has been possible to probe crystallized matter, thanks to X-ray or neutron scattering techniques, to obtain an accurate charge density or spin distribution at the atomic scale. Despite the description of the same physical quantity (electron density) and tremendous development of sources, detectors, data treatment software etc., these different techniques evolved separately with one model per experiment. However, a breakthrough was recently made by the development of a common model in order to combine information coming from all these different experiments. Here we report the first experimental determination of spin-resolved electron density obtained by a combined treatment of X-ray, neutron and polarized neutron diffraction data. These experimental spin up and spin down densities compare very well with density functional theory (DFT) calculations and also confirm a theoretical prediction made in 1985 which claims that majority spin electrons should have a more contracted distribution around the nucleus than minority spin electrons. Topological analysis of the resulting experimental spin-resolved electron density is also briefly discussed.

Development of soft x-ray time-resolved photoemission spectroscopy system with a two-dimensional angle-resolved time-of-flight analyzer at SPring-8 BL07LSU

Energy Technology Data Exchange (ETDEWEB)

Ogawa, Manami; Yamamoto, Susumu; Nakamura, Fumitaka; Yukawa, Ryu; Fukushima, Akiko; Harasawa, Ayumi; Kakizaki, Akito; Matsuda, Iwao [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Chiba 277-8581 (Japan); Kousa, Yuka; Kondoh, Hiroshi [Department of Chemistry, Keio University, Yokohama 223-8522 (Japan); Tanaka, Yoshihito [RIKEN/SPring-8 Center, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan)

2012-02-15

We have developed a soft x-ray time-resolved photoemission spectroscopy system using synchrotron radiation (SR) at SPring-8 BL07LSU and an ultrashort pulse laser system. Two-dimensional angle-resolved measurements were performed with a time-of-flight-type analyzer. The photoemission spectroscopy system is synchronized to light pulses of SR and laser using a time control unit. The performance of the instrument is demonstrated by mapping the band structure of a Si(111) crystal over the surface Brillouin zones and observing relaxation of the surface photo-voltage effect using the pump (laser) and probe (SR) method.

MONSTIR II: A 32-channel, multispectral, time-resolved optical tomography system for neonatal brain imaging

Energy Technology Data Exchange (ETDEWEB)

Cooper, Robert J., E-mail: robert.cooper@ucl.ac.uk; Magee, Elliott; Everdell, Nick; Magazov, Salavat; Varela, Marta; Airantzis, Dimitrios; Gibson, Adam P.; Hebden, Jeremy C. [Biomedical Optics Research Laboratory, Department of Medical Physics and Bioengineering, University College London, London WC1E 6BT (United Kingdom)

2014-05-15

We detail the design, construction and performance of the second generation UCL time-resolved optical tomography system, known as MONSTIR II. Intended primarily for the study of the newborn brain, the system employs 32 source fibres that sequentially transmit picosecond pulses of light at any four wavelengths between 650 and 900 nm. The 32 detector channels each contain an independent photo-multiplier tube and temporally correlated photon-counting electronics that allow the photon transit time between each source and each detector position to be measured with high temporal resolution. The system's response time, temporal stability, cross-talk, and spectral characteristics are reported. The efficacy of MONSTIR II is demonstrated by performing multi-spectral imaging of a simple phantom.

Assembly and application of an instrument for attosecond-time-resolved ionization chronoscopy

International Nuclear Information System (INIS)

Uphues, T.

2006-11-01

In the framework of this thesis a new setup for attosecond time-resolved measurements has been built and observations of ionization dynamics in rare gas atoms have been made. This new technique is entitled Ionization Chronoscopy and gives further evidence that time-resolved experiments in the attosecond regime will become a powerful tool for investigations in atomic physics. (orig.)

Time-resolved measurements with intense ultrashort laser pulses: a 'molecular movie' in real time

International Nuclear Information System (INIS)

Rudenko, A; Ergler, Th; Feuerstein, B; Zrost, K; Schroeter, C D; Moshammer, R; Ullrich, J

2007-01-01

We report on the high-resolution multidimensional real-time mapping of H 2 + and D 2 + nuclear wave packets performed employing time-resolved three-dimensional Coulomb explosion imaging with intense laser pulses. Exploiting a combination of a 'reaction microscope' spectrometer and a pump-probe setup with two intense 6-7 fs laser pulses, we simultaneously visualize both vibrational and rotational motion of the molecule, and obtain a sequence of snapshots of the squared ro-vibrational wave function with time-step resolution of ∼ 0.3 fs, allowing us to reconstruct a real-time movie of the ultrafast molecular motion. We observe fast dephasing, or 'collapse' of the vibrational wave packet and its subsequent revival, as well as signatures of rotational excitation. For D 2 + we resolve also the fractional revivals resulting from the interference between the counter-propagating parts of the wave packet

Time-resolved soft x-ray spectra from laser-produced Cu plasma

International Nuclear Information System (INIS)

Cone, K.V.; Dunn, J.; Baldis, H.A.; May, M.J.; Purvis, M.A.; Scott, H.A.; Schneider, M.B.

2012-01-01

The volumetric heating of a thin copper target has been studied with time resolved x-ray spectroscopy. The copper target was heated from a plasma produced using the Lawrence Livermore National Laboratory's Compact Multipulse Terrawatt (COMET) laser. A variable spaced grating spectrometer coupled to an x-ray streak camera measured soft x-ray emission (800-1550 eV) from the back of the copper target to characterize the bulk heating of the target. Radiation hydrodynamic simulations were modeled in 2-dimensions using the HYDRA code. The target conditions calculated by HYDRA were post-processed with the atomic kinetics code CRETIN to generate synthetic emission spectra. A comparison between the experimental and simulated spectra indicates the presence of specific ionization states of copper and the corresponding electron temperatures and ion densities throughout the laser-heated copper target.

Time-resolved X-ray spectroscopies of chemical systems: New perspectives

Directory of Open Access Journals (Sweden)

Majed Chergui

2016-05-01

Full Text Available The past 3–5 years have witnessed a dramatic increase in the number of time-resolved X-ray spectroscopic studies, mainly driven by novel technical and methodological developments. The latter include (i the high repetition rate optical pump/X-ray probe studies, which have greatly boosted the signal-to-noise ratio for picosecond (ps X-ray absorption spectroscopy studies, while enabling ps X-ray emission spectroscopy (XES at synchrotrons; (ii the X-ray free electron lasers (XFELs are a game changer and have allowed the first femtosecond (fs XES and resonant inelastic X-ray scattering experiments to be carried out; (iii XFELs are also opening the road to the development of non-linear X-ray methods. In this perspective, I will mainly focus on the most recent technical developments and briefly address some examples of scientific questions that have been addressed thanks to them. I will look at the novel opportunities in the horizon.

Time-resolved suprathermal x-rays

International Nuclear Information System (INIS)

Lee, P.H.Y.; Rosen, M.D.

1978-01-01

Temporally resolved x-ray spectra in the range of 1 to 20 keV have been obtained from gold disk targets irradiated by 1.06 μm laser pulses from the Argus facility. The x-ray streak camera used for the measurement has been calibrated for streak speed and dynamic range by using an air-gap Fabry-Perot etalon, and the instrument response has been calibrated using a multi-range monoenergetic x-ray source. The experimental results indicate that we are able to observe the ''hot'' x-ray temperature evolve in time and that the experimentally observed values can be qualitatively predicted by LASNEX code computations when the inhibited transport model is used

Time-resolved spectroscopy of nonequilibrium ionization in laser-produced plasmas

International Nuclear Information System (INIS)

Marjoribanks, R.S.

1988-01-01

The highly transient ionization characteristic of laser-produced plasmas at high energy densities has been investigated experimentally, using x-ray spectroscopy with time resolution of less than 20 ps. Spectroscopic diagnostics of plasma density and temperature were used, including line ratios, line profile broadening and continuum emission, to characterize the plasma conditions without relying immediately on ionization modeling. The experimentally measured plasma parameters were used as independent variables, driving an ionization code, as a test of ionization modeling, divorced from hydrodynamic calculations. Several state-of-the-art streak spectrographs, each recording a fiducial of the laser peak along with the time-resolved spectrum, characterized the laser heating of thin signature layers of different atomic numbers imbedded in plastic targets. A novel design of crystal spectrograph, with a conically curved crystal, was developed. Coupled with a streak camera, it provided high resolution (λ/ΔΛ > 1000) and a collection efficiency roughly 20-50 times that of planar crystal spectrographs, affording improved spectra for quantitative reduction and greater sensitivity for the diagnosis of weak emitters. Experimental results were compared to hydrocode and ionization code simulations, with poor agreement. The conclusions question the appropriateness of describing electron velocity distributions by a temperature parameter during the time of laser illumination and emphasis the importance of characterizing the distribution more generally

Advances in high-order harmonic generation sources for time-resolved investigations

Energy Technology Data Exchange (ETDEWEB)

Reduzzi, Maurizio [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Institute of Photonics and Nanotechnologies, CNR-IFN, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Carpeggiani, Paolo [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Kühn, Sergei [ELI-ALPS, ELI-Hu Kft., Dugonics ter 13, H-6720 Szeged (Hungary); Calegari, Francesca [Institute of Photonics and Nanotechnologies, CNR-IFN, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Nisoli, Mauro; Stagira, Salvatore [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Institute of Photonics and Nanotechnologies, CNR-IFN, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Vozzi, Caterina [Institute of Photonics and Nanotechnologies, CNR-IFN, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Dombi, Peter [ELI-ALPS, ELI-Hu Kft., Dugonics ter 13, H-6720 Szeged (Hungary); Wigner Research Center for Physics, 1121 Budapest (Hungary); Kahaly, Subhendu [ELI-ALPS, ELI-Hu Kft., Dugonics ter 13, H-6720 Szeged (Hungary); Tzallas, Paris; Charalambidis, Dimitris [ELI-ALPS, ELI-Hu Kft., Dugonics ter 13, H-6720 Szeged (Hungary); Foundation for Research and Technology – Hellas, Institute of Electronic Structure and Lasers, P.O. Box 1527, GR-711 10 Heraklion, Crete (Greece); Varju, Katalin [ELI-ALPS, ELI-Hu Kft., Dugonics ter 13, H-6720 Szeged (Hungary); Department of Optics and Quantum Electronics, University of Szeged, Dóm tér 9, 6720 Szeged (Hungary); Osvay, Karoly [ELI-ALPS, ELI-Hu Kft., Dugonics ter 13, H-6720 Szeged (Hungary); and others

2015-10-15

We review the main research directions ongoing in the development of extreme ultraviolet sources based on high-harmonic generation for the synthesization and application of trains and isolated attosecond pulses to time-resolved spectroscopy. A few experimental and theoretical works will be discussed in connection to well-established attosecond techniques. In this context, we present the unique possibilities offered for time-resolved investigations on the attosecond timescale by the new Extreme Light Infrastructure Attosecond Light Pulse Source, which is currently under construction.

Advances in high-order harmonic generation sources for time-resolved investigations

International Nuclear Information System (INIS)

Reduzzi, Maurizio; Carpeggiani, Paolo; Kühn, Sergei; Calegari, Francesca; Nisoli, Mauro; Stagira, Salvatore; Vozzi, Caterina; Dombi, Peter; Kahaly, Subhendu; Tzallas, Paris; Charalambidis, Dimitris; Varju, Katalin; Osvay, Karoly

2015-01-01

We review the main research directions ongoing in the development of extreme ultraviolet sources based on high-harmonic generation for the synthesization and application of trains and isolated attosecond pulses to time-resolved spectroscopy. A few experimental and theoretical works will be discussed in connection to well-established attosecond techniques. In this context, we present the unique possibilities offered for time-resolved investigations on the attosecond timescale by the new Extreme Light Infrastructure Attosecond Light Pulse Source, which is currently under construction.

Bi-dimensional arrays of SPAD for time-resolved single photon imaging

International Nuclear Information System (INIS)

Tudisco, S.; Lanzano, L.; Musumeci, F.; Neri, L.; Privitera, S.; Scordino, A.; Condorelli, G.; Fallica, G.; Mazzillo, M.; Sanfilippo, D.; Valvo, G.

2009-01-01

Many scientific areas like astronomy, biophysics, biomedicine, nuclear and plasma science, etc. are interested in the development of a new time-resolved single photon imaging device. Such a device represents today one of the most challenging goals in the field of photonics. In collaboration with Catania R and D staff of ST-Microelectronics (STM) we created, during the last few years, a new avalanche photosensor-Single Photon Avalanche Diode (SPAD) able to detect and count, with excellent performance, single photons. Further we will discuss the possible realization of a single photon imaging device through the many elements integration (bi-dimensional arrays) of SPADs. In order to achieve the goal, it is also important to develop an appropriate readout strategy able to address the time information of each individual sensor and in order to read a great number of elements easily. First prototypes were designed and manufactured by STM and the results are reported here. In the paper we will discuss in particular: (i) sensor performance (gain, photodetection efficiency, timing, after-pulsing, etc.); (ii) array performance (layout, cross-talk, etc.); (iii) readout strategy (quenching, electronics), and (iv) first imaging results (general performance).

Time-resolved generation of membrane potential by ba3 cytochrome c oxidase from Thermus thermophilus coupled to single electron injection into the O and OH states.

Science.gov (United States)

Siletsky, Sergey A; Belevich, Ilya; Belevich, Nikolai P; Soulimane, Tewfik; Wikström, Mårten

2017-11-01

Two electrogenic phases with characteristic times of ~14μs and ~290μs are resolved in the kinetics of membrane potential generation coupled to single-electron reduction of the oxidized "relaxed" O state of ba 3 oxidase from T. thermophilus (O→E transition). The rapid phase reflects electron redistribution between Cu A and heme b. The slow phase includes electron redistribution from both Cu A and heme b to heme a 3 , and electrogenic proton transfer coupled to reduction of heme a 3 . The distance of proton translocation corresponds to uptake of a proton from the inner water phase into the binuclear center where heme a 3 is reduced, but there is no proton pumping and no reduction of Cu B . Single-electron reduction of the oxidized "unrelaxed" state (O H →E H transition) is accompanied by electrogenic reduction of the heme b/heme a 3 pair by Cu A in a "fast" phase (~22μs) and transfer of protons in "middle" and "slow" electrogenic phases (~0.185ms and ~0.78ms) coupled to electron redistribution from the heme b/heme a 3 pair to the Cu B site. The "middle" and "slow" electrogenic phases seem to be associated with transfer of protons to the proton-loading site (PLS) of the proton pump, but when all injected electrons reach Cu B the electronic charge appears to be compensated by back-leakage of the protons from the PLS into the binuclear site. Thus proton pumping occurs only to the extent of ~0.1 H + /e - , probably due to the formed membrane potential in the experiment. Copyright © 2017 Elsevier B.V. All rights reserved.

Studies of nanostructures using time-resolved x-ray excited optical luminescence*

International Nuclear Information System (INIS)

Rosenberg, R.A.; Shenoy, G.K.; Smita, S.; Burda, C.; Sham, T.K.

2004-01-01

Full text:The scientific community is currently investing a great deal of effort into understanding the physics and chemistry of nanoscale structures. Synchrotron radiation techniques are being used to study the physical, electronic, and magnetic structure of nanosystems, albeit at a relatively large size (greater than 30 nm). A major challenge facing researchers is finding methods that can probe structures of the smallest scale (less than 10 nm). Optical luminescence has been shown to be directly sensitive to structures in this size range due to quantum confinement phenomena. X-ray-excited optical luminescence (XEOL) provides the capability to chemically map the sites responsible for producing low-energy (1-6 eV) fluorescence. By taking advantage of the time structure of the x-ray pulses at the Advanced Photon Source (70 ps wide, 153 ns separation), it also possible to determine the dynamic behavior of the states involved in the luminescence. In this paper we will present results of time-resolved XEOL experiments on various nanostructures including porous silicon, silicon nanowires, and CdSe nanodots

Time resolved spectroscopy of GRB 030501 using INTEGRAL

DEFF Research Database (Denmark)

Beckmann, V.; Borkowski, J.; Courvoisier, T.J.L.

2003-01-01

The gamma-ray instruments on-board INTEGRAL offer an unique opportunity to perform time resolved analysis on GRBs. The imager IBIS allows accurate positioning of GRBs and broad band spectral analysis, while SPI provides high resolution spectroscopy. GRB 030501 was discovered by the INTEGRAL Burst...... the Ulysses and RHESSI experiments....

Time-resolved wave profile measurements in copper to Megabar pressures

Energy Technology Data Exchange (ETDEWEB)

Chhabildas, L C; Asay, J R

1981-01-01

Many time-resolved techniques have been developed which have greatly aided in the understanding of dynamic material behavior such as the high pressure-dynamic strength of materials. In the paper, time-resolved measurements of copper (at shock-induced high pressures and temperatures) are used to illustrate the capability of using such techniques to investigate high pressure strength. Continuous shock loading and release wave profiles have been made in copper to 93 GPa using velocity interferometric techniques. Fine structure in the release wave profiles from the shocked state indicates an increase in shear strength of copper to 1.5 GPa at 93 GPa from its ambient value of 0.08 GPa.

Direct observation of spin-resolved full and empty electron states in ferromagnetic surfaces

Energy Technology Data Exchange (ETDEWEB)

Berti, G., E-mail: giulia.berti@polimi.it; Calloni, A.; Brambilla, A.; Bussetti, G.; Duò, L.; Ciccacci, F. [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133, Milano (Italy)

2014-07-15

We present a versatile apparatus for the study of ferromagnetic surfaces, which combines spin-polarized photoemission and inverse photoemission spectroscopies. Samples can be grown by molecular beam epitaxy and analyzed in situ. Spin-resolved photoemission spectroscopy analysis is done with a hemispherical electron analyzer coupled to a 25 kV-Mott detector. Inverse photoemission spectroscopy experiments are performed with GaAs crystals as spin-polarized electron sources and a UV bandpass photon detector. As an example, measurements on the oxygen passivated Fe(100)-p(1×1)O surface are presented.

Determination of electronic states in crystalline semiconductors and metals by angle-resolved photoemission

International Nuclear Information System (INIS)

Mills, K.A.

1979-08-01

An important part of the theoretical description of the solid state is band structure, which relies on the existence of dispersion relations connecting the electronic energy and wavevector in materials with translational symmetry. These relations determine the electronic behavior of such materials. The elaboration of accurate band structures, therefore, is of considerable fundamental and practical importance. Angle-resolved photoemission (ARP) spectroscopy provides the only presently available method for the detailed experimental investigation of band structures. This work is concerned with its application to both semiconducting and metallic single crystals

A novel multiplex absorption spectrometer for time-resolved studies

Science.gov (United States)

Lewis, Thomas; Heard, Dwayne E.; Blitz, Mark A.

2018-02-01

A Time-Resolved Ultraviolet/Visible (UV/Vis) Absorption Spectrometer (TRUVAS) has been developed that can simultaneously monitor absorption at all wavelengths between 200 and 800 nm with millisecond time resolution. A pulsed photolysis laser (KrF 248 nm) is used to initiate chemical reactions that create the target species. The absorption signals from these species evolve as the composition of the gas in the photolysis region changes over time. The instrument can operate at pressures over the range ˜10-800 Torr and can measure time-resolved absorbances systems (in particular the Herriott cell), there are fundamental differences, most notably the ability to adjust each mirror to maximise the overlap between the probe beam and the photolysis laser. Another feature which aids the sensitivity and versatility of the system is the use of 2 high-throughput spectrographs coupled with sensitive line-array CCDs, which can measure absorbance from ˜200 to 800 nm simultaneously. The capability of the instrument is demonstrated via measurements of the absorption spectrum of the peroxy radical, HOCH2CH2O2, and its self-reaction kinetics.

Scanning photoelectron microscope for nanoscale three-dimensional spatial-resolved electron spectroscopy for chemical analysis.

Science.gov (United States)

Horiba, K; Nakamura, Y; Nagamura, N; Toyoda, S; Kumigashira, H; Oshima, M; Amemiya, K; Senba, Y; Ohashi, H

2011-11-01

In order to achieve nondestructive observation of the three-dimensional spatially resolved electronic structure of solids, we have developed a scanning photoelectron microscope system with the capability of depth profiling in electron spectroscopy for chemical analysis (ESCA). We call this system 3D nano-ESCA. For focusing the x-ray, a Fresnel zone plate with a diameter of 200 μm and an outermost zone width of 35 nm is used. In order to obtain the angular dependence of the photoelectron spectra for the depth-profile analysis without rotating the sample, we adopted a modified VG Scienta R3000 analyzer with an acceptance angle of 60° as a high-resolution angle-resolved electron spectrometer. The system has been installed at the University-of-Tokyo Materials Science Outstation beamline, BL07LSU, at SPring-8. From the results of the line-scan profiles of the poly-Si/high-k gate patterns, we achieved a total spatial resolution better than 70 nm. The capability of our system for pinpoint depth-profile analysis and high-resolution chemical state analysis is demonstrated. © 2011 American Institute of Physics

Rovibrationally Resolved Time-Dependent Collisional-Radiative Model of Molecular Hydrogen and Its Application to a Fusion Detached Plasma

Directory of Open Access Journals (Sweden)

Keiji Sawada

2016-12-01

Full Text Available A novel rovibrationally resolved collisional-radiative model of molecular hydrogen that includes 4,133 rovibrational levels for electronic states whose united atom principal quantum number is below six is developed. The rovibrational X 1 Σ g + population distribution in a SlimCS fusion demo detached divertor plasma is investigated by solving the model time dependently with an initial 300 K Boltzmann distribution. The effective reaction rate coefficients of molecular assisted recombination and of other processes in which atomic hydrogen is produced are calculated using the obtained time-dependent population distribution.

Multichord time-resolved electron temperature measurements by the x-ray absorber-foil method on TFTR

International Nuclear Information System (INIS)

Kiraly, J.; Bitter, M.; Efthimion, P.

1985-09-01

Absorber foils have been installed in the TFTR X-Ray Imaging System to permit measurement of the electron temperature along 10 to 30 chords spaced at 5-12.5 cm with a time resolution of less than 100 μs. The technique uses the ratio of x-ray fluxes transmitted through two different foils. The ratio depends mainly on electron temperature. Simulations show that strong impurity line radiation can distort this ratio. To correct for these effects, special beryllium-scandium filters are employed to select the line-free region between 2 and 4.5 keV. Other filter pairs allow corrections for Fe L and Ni L line radiation as well as Ti K and Ni K emission. Good accuracy is also obtained with simple beryllium filters, provided that impurity corrections are incorporated in the analysis, taking line intensities from the x-ray pulse-height analysis diagnostic. A description of modeling calculations and a comparison of temperature values from this diagnostic with data from the x-ray pulse height analysis, the electron cyclotron emission, and the Thomson scattering diagnostics are presented. Several applications of the absorber foil electron temperature diagnostic on TFTR are discussed

Multichord time-resolved electron temperature measurements by the x-ray absorber-foil method on TFTR

Energy Technology Data Exchange (ETDEWEB)

Kiraly, J.; Bitter, M.; Efthimion, P.; von Goeler, S.; Grek, B.; Hill, K.W.; Johnson, D.; McGuire, K.; Sauthoff, N.; Sesnic, S.

1985-09-01

Absorber foils have been installed in the TFTR X-Ray Imaging System to permit measurement of the electron temperature along 10 to 30 chords spaced at 5-12.5 cm with a time resolution of less than 100 ..mu..s. The technique uses the ratio of x-ray fluxes transmitted through two different foils. The ratio depends mainly on electron temperature. Simulations show that strong impurity line radiation can distort this ratio. To correct for these effects, special beryllium-scandium filters are employed to select the line-free region between 2 and 4.5 keV. Other filter pairs allow corrections for Fe L and Ni L line radiation as well as Ti K and Ni K emission. Good accuracy is also obtained with simple beryllium filters, provided that impurity corrections are incorporated in the analysis, taking line intensities from the x-ray pulse-height analysis diagnostic. A description of modeling calculations and a comparison of temperature values from this diagnostic with data from the x-ray pulse height analysis, the electron cyclotron emission, and the Thomson scattering diagnostics are presented. Several applications of the absorber foil electron temperature diagnostic on TFTR are discussed.

Time resolved laser induced fluorescence on argon intermediate pressure microwave discharges: Measuring the depopulation rates of the 4p and 5p excited levels as induced by electron and atom collisions

Energy Technology Data Exchange (ETDEWEB)

Palomares, J.M., E-mail: j.m.palomares-linares@tue.nl; Graef, W.A.A.D.; Hübner, S.; Mullen, J.J.A.M. van der, E-mail: jjamvandermullen@gmail.com

2013-10-01

The reaction kinetics in the excitation space of Ar is explored by means of Laser Induced Fluorescence (LIF) experiments using the combination of high rep-rate YAG–Dye laser systems with a well defined and easily controllable surfatron induced plasma setup. The high rep-rate favors the photon statistics while the low energy per pulse avoids intrusive plasma laser interactions. An analysis shows that, despite the low energy per pulse, saturation can still be achieved even when the geometrical overlap and spectral overlap are optimal. Out of the various studies that can be performed with this setup we confine the current paper to the study of the direct responses to the laser pump action of three 4p and one 5p levels of the Ar system. By changing the plasma in a controlled way one gets for these levels the rates of electron and atom quenching and therewith the total destruction rates of electron and atom collisions. Comparison with literature shows that the classical hard sphere collision rate derived for hydrogen gives a good description for the observed electron quenching (e-quenching) in Ar whereas for heavy particle quenching (a-quenching) this agreement was only found for the 5p level. An important parameter in the study of electron excitation kinetics is the location of the boundary in the atomic system for which the number of electron collisions per radiative life time equals unity. It is observed that for the Ar system this boundary is positioned lower than what is expected on grounds of H-like formulas. - Highlights: • Time resolved laser induced fluorescence at high repetition rate • Decay times as function of pressure, electron density and temperature • Measurement of total electron atom depopulation rates • Reasonable agreement of electron total rates with hard sphere approximations.

Dynamic View on Nanostructures: A Technique for Time Resolved Optical Luminescence Using Synchrotron Light Pulses at SRC, APS, and CLS

International Nuclear Information System (INIS)

Heigl, F.; Jurgensen, A.; Zhou, X.-T.; Lam, S.; Murphy, M.; Ko, J.Y.P.; Sham, T.K.; Rosenberg, R.A.; Gordon, R.; Brewe, D.; Regier, T.; Armelao, L.

2007-01-01

We present an experimental technique using the time structure of synchrotron radiation to study time resolved X-ray excited optical luminescence. In particular we are taking advantage of the bunched distribution of electrons in a synchrotron storage ring, giving short x-ray pulses (10-10 2 picoseconds) which are separated by non-radiating gaps on the nano- to tens of nanosecond scale - sufficiently wide to study a broad range of optical decay channels observed in advanced nanostructured materials.

Understanding optically stimulated charge movement in quartz and feldspar using time-resolved measurements

International Nuclear Information System (INIS)

Ankjaergaard, C.

2010-02-01

Thermoluminescence (TL) and optically stimulated luminescence (OSL) from quartz and feldspar are widely used in accident dosimetry and luminescence dating. In order to improve already existing methods or to develop new methods towards extending the current limits of the technique, it is important to understand the charge movement within these materials. Earlier studies have primarily focussed on examination of the trap behaviour; however, this only tells half of the story as OSL is a combination of charge stimulation and recombination. By using time-resolved OSL (TR-OSL), one can directly examine the recombination route(s), and thus obtain insight into the other half of the process involved in luminescence emission. This thesis studies the TR-OSL and optically stimulated phosphorescence signals from quartz and feldspars spanning several orders of magnitude in time (few ns to the seconds time scale) in order to identify various charge transport mechanisms in the different time regimes. The techniques employed are time-resolved OSL, continuous-wave OSL, TL, optically stimulated exo-electron (OSE) emission and time-resolved OSE. These different techniques are used in combination with variable thermal or optical stimulation energy. The thesis first delves into three main methodological developments, namely (i) research and development of the equipment for TR-OSL measurements, (ii) finding the best method for multiple-exponential analysis of a TR-OSL curve, and (iii) optimisation of the pulsing configuration for the best separation of quartz OSL from a mixed quarts-feldspar sample. It then proceeds to study the different charge transport mechanisms subsequent to an optical stimulation pulse in quartz and feldspars. The results obtained for quartz conclude that the main lifetime component in quartz represents an excited state lifetime of the recombination centre, and the more slowly decaying components on the millisecond to seconds time scale arise from charge recycling

Understanding optically stimulated charge movement in quartz and feldspar using time-resolved measurements

Energy Technology Data Exchange (ETDEWEB)

Ankjaergaard, C.

2010-02-15

Thermoluminescence (TL) and optically stimulated luminescence (OSL) from quartz and feldspar are widely used in accident dosimetry and luminescence dating. In order to improve already existing methods or to develop new methods towards extending the current limits of the technique, it is important to understand the charge movement within these materials. Earlier studies have primarily focussed on examination of the trap behaviour; however, this only tells half of the story as OSL is a combination of charge stimulation and recombination. By using time-resolved OSL (TR-OSL), one can directly examine the recombination route(s), and thus obtain insight into the other half of the process involved in luminescence emission. This thesis studies the TR-OSL and optically stimulated phosphorescence signals from quartz and feldspars spanning several orders of magnitude in time (few ns to the seconds time scale) in order to identify various charge transport mechanisms in the different time regimes. The techniques employed are time-resolved OSL, continuous-wave OSL, TL, optically stimulated exo-electron (OSE) emission and time-resolved OSE. These different techniques are used in combination with variable thermal or optical stimulation energy. The thesis first delves into three main methodological developments, namely (i) research and development of the equipment for TR-OSL measurements, (ii) finding the best method for multiple-exponential analysis of a TR-OSL curve, and (iii) optimisation of the pulsing configuration for the best separation of quartz OSL from a mixed quarts-feldspar sample. It then proceeds to study the different charge transport mechanisms subsequent to an optical stimulation pulse in quartz and feldspars. The results obtained for quartz conclude that the main lifetime component in quartz represents an excited state lifetime of the recombination centre, and the more slowly decaying components on the millisecond to seconds time scale arise from charge recycling

Sub-nanosecond time-resolved near-field scanning magneto-optical microscope.

Science.gov (United States)

Rudge, J; Xu, H; Kolthammer, J; Hong, Y K; Choi, B C

2015-02-01

We report on the development of a new magnetic microscope, time-resolved near-field scanning magneto-optical microscope, which combines a near-field scanning optical microscope and magneto-optical contrast. By taking advantage of the high temporal resolution of time-resolved Kerr microscope and the sub-wavelength spatial resolution of a near-field microscope, we achieved a temporal resolution of ∼50 ps and a spatial resolution of microscope, the magnetic field pulse induced gyrotropic vortex dynamics occurring in 1 μm diameter, 20 nm thick CoFeB circular disks has been investigated. The microscope provides sub-wavelength resolution magnetic images of the gyrotropic motion of the vortex core at a resonance frequency of ∼240 MHz.

Lucas–Kanade fluid trajectories for time-resolved PIV

International Nuclear Information System (INIS)

Yegavian, Robin; Leclaire, Benjamin; Illoul, Cédric; Losfeld, Gilles; Champagnat, Frédéric

2016-01-01

We introduce a new method for estimating fluid trajectories in time-resolved PIV. It relies on a Lucas–Kanade paradigm and consists in a simple and direct extension of a two-frame estimation with FOLKI-PIV (Champagnat et al 2011 Exp. Fluids 50 1169–82). The so-called Lucas–Kanade Fluid Trajectories (LKFT) are assumed to be polynomial in time, and are found as the minimizer of a global functional, in which displacements are sought so as to match the intensities of a series of images pairs in the sequence, in the least-squares sense. All pairs involve the central image, similar to other recent time-resolved approaches (FTC (Lynch and Scarano 2013 Meas. Sci. Technol . 24 035305) and FTEE (Jeon et al 2014 Exp. Fluids 55 1–16)). As switching from a two-frame to a time-resolved objective simply amounts to adding terms in a functional, no significant additional algorithmic element is required. Similar to FOLKI-PIV the method is very well suited for GPU acceleration, which is an important feature as computational complexity increases with the image sequence size. Tests on synthetic data exhibiting peak-locking show that increasing the image sequence size strongly reduces both associated bias and random error, and that LKFT has a remaining total error comparable to that of FTEE on this case. Results on case B of the third PIV challenge (Stanislas et al 2008 Exp. Fluids 45 27–71) also show its ability to drastically reduce the error in situations with low signal-to-noise ratio. These results are finally confirmed on experimental images acquired in the near-field of a low Reynolds number jet. Strong reductions in peak-locking, spatial and temporal noise compared to two-frame estimation are also observed, on the displacement components themselves, as well as on spatial or temporal derivatives, such as vorticity and material acceleration. (paper)

Time-resolved fluorescence analysis of the mobile flavin cofactor

Indian Academy of Sciences (India)

Conformational heterogeneity of the FAD cofactor in -hydroxybenzoate hydroxylase (PHBH) was investigated with time-resolved polarized flavin fluorescence. For binary enzyme/substrate (analogue) complexes of wild-type PHBH and Tyr222 mutants, crystallographic studies have revealed two distinct flavin conformations ...

Detecting aromatic compounds on planetary surfaces using ultraviolet time-resolved fluorescence spectroscopy

Science.gov (United States)

Eshelman, E.; Daly, M. G.; Slater, G.; Cloutis, E.

2018-02-01

Many aromatic organic molecules exhibit strong and characteristic fluorescence when excited with ultraviolet radiation. As laser excitation in the ultraviolet generates both fluorescence and resonantly enhanced Raman scattering of aromatic vibrational modes, combined Raman and fluorescence instruments have been proposed to search for organic compounds on Mars. In this work the time-resolved fluorescence of a suite of 24 compounds composed of 2-5 ringed alternant, non-alternant, and heterocyclic PAHs was measured. Fluorescence instrumentation with similar specifications to a putative flight instrument was capable of observing the fluorescence decay of these compounds with a sub-ns resolution. Incorporating time-resolved capabilities was also found to increase the ability to discriminate between individual PAHs. Incorporating time-resolved fluorescence capabilities into an ultraviolet gated Raman system intended for a rover or lander can increase the ability to detect and characterize PAHs on planetary surfaces.

Time-resolved PHERMEX image restorations constrained with an additional multiply-exposed image

International Nuclear Information System (INIS)

Kruger, R.P.; Breedlove, J.R. Jr.; Trussell, H.J.

1978-06-01

There are a number of possible industrial and scientific applications of nanosecond cineradiographs. Although the technology exists to produce closely spaced pulses of x rays for this application, the quality of the time-resolved radiographs is severely limited. The limitations arise from the necessity of using a fluorescent screen to convert the transmitted x rays to light and then using electro-optical imaging systems to gate and to record the images with conventional high-speed cameras. It has been proposed that, in addition to the time-resolved images, a conventional multiply exposed radiograph be obtained. This report uses both PHERMEX and conventional photographic simulations to demonstrate that the additional information supplied by the multiply exposed radiograph can be used to improve the quality of digital image restorations of the time-resolved pictures over what could be achieved with the degraded images alone

a Study on SODIUM(110) and Other Nearly Free Electron Metals Using Angle Resolved Photoemission Spectroscopy.

Science.gov (United States)

Lyo, In-Whan

Electronic properties of the epitaxially grown Na(110) film have been studied using angle resolved ultraviolet photoemission spectroscopy with synchrotron radiation as the light source. Na provides an ideal ground to study the fundamental aspects of the electron-electron interactions in metals, because of its simple Fermi surface and small pseudopotential. The absolute band structure of Na(110) using angle resolved photoemission spectroscopy has been mapped out using the extrema searching method. The advantage of this approach is that the usual assumption of the unoccupied state dispersion is not required. We have found that the dispersion of Na(1l0) is very close to the parabolic band with the effective mass 1.21 M_{rm e} at 90 K. Self-consistent calculations of the self-energy for the homogeneous electron gas have been performed using the Green's function technique within the framework of the GW approximation, in the hope of understanding the narrowing mechanism of the bandwidth observed for all the nearly-free-electron (NFE) metals. Good agreements between the experimental data and our calculated self-energy were obtained not only for our data on k-dependency from Na(l10), but also for the total bandwidth corrections for other NFE metals, only if dielectric functions beyond the random phase approximation were used. Our findings emphasize the importance of the screening by long wavelength plasmons. Off-normal spectra of angle resolved photoemission from Na(110) show strong asymmetry of the bulk peak intensity for the wide range of photon energies. Using a simple analysis, we show this asymmetry has an origin in the interference of the surface Umklapp electrons with the normal electrons. We have also performed the detailed experimental studies of the anomalous Fermi level structure observed in the forbidden gap region of Na. This was claimed by A. W. Overhauser as the evidence of the charge density wave in the alkali metal. The possibility of this hypothesis is

Ultrafast time-resolved spectroscopy of the light-harvesting complex 2 (LH2) from the photosynthetic bacterium Thermochromatium tepidum.

Science.gov (United States)

Niedzwiedzki, Dariusz M; Fuciman, Marcel; Kobayashi, Masayuki; Frank, Harry A; Blankenship, Robert E

2011-10-01

The light-harvesting complex 2 from the thermophilic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption and fluorescence, sub-nanosecond-time-resolved fluorescence and femtosecond time-resolved transient absorption spectroscopy. The measurements were performed at room temperature and at 10 K. The combination of both ultrafast and steady-state optical spectroscopy methods at ambient and cryogenic temperatures allowed the detailed study of carotenoid (Car)-to-bacteriochlorophyll (BChl) as well BChl-to-BChl excitation energy transfer in the complex. The studies show that the dominant Cars rhodopin (N=11) and spirilloxanthin (N=13) do not play a significant role as supportive energy donors for BChl a. This is related with their photophysical properties regulated by long π-electron conjugation. On the other hand, such properties favor some of the Cars, particularly spirilloxanthin (N=13) to play the role of the direct quencher of the excited singlet state of BChl. © Springer Science+Business Media B.V. 2011

Time-resolved photoelectron spectroscopy and ab initio multiple spawning studies of hexamethylcyclopentadiene

DEFF Research Database (Denmark)

Wolf, T. J. A.; Kuhlman, Thomas Scheby; Schalk, O.

2014-01-01

Time-resolved photoelectron spectroscopy and ab initio multiple spawning were applied to the ultrafast non-adiabatic dynamics of hexamethylcyclopentadiene. The high level of agreement between experiment and theory associates wavepacket motion with a distinct degree of freedom.......Time-resolved photoelectron spectroscopy and ab initio multiple spawning were applied to the ultrafast non-adiabatic dynamics of hexamethylcyclopentadiene. The high level of agreement between experiment and theory associates wavepacket motion with a distinct degree of freedom....

Time-resolved detection of surface plasmon polaritons with a scanning tunneling microscope

DEFF Research Database (Denmark)

Keil, Ulrich Dieter Felix; Ha, T.; Jensen, Jacob Riis

1998-01-01

We present the time-resolved detection of surface plasmon polaritons with an STM. The results indicate that the time resolved signal is due to rectification of coherently superimposed plasmon voltages. The comparison with differential reflectivity measurements shows that the tip itself influences...... the decay of the plasmon-field coherence. Generation of the measured signal at the tunneling junction offers the possibility to observe ultrafast effects with a spatial resolution determined by the tunneling junction...

Time-resolved explosion of intense-laser-heated clusters.

Science.gov (United States)

Kim, K Y; Alexeev, I; Parra, E; Milchberg, H M

2003-01-17

We investigate the femtosecond explosive dynamics of intense laser-heated argon clusters by measuring the cluster complex transient polarizability. The time evolution of the polarizability is characteristic of competition in the optical response between supercritical and subcritical density regions of the expanding cluster. The results are consistent with time-resolved Rayleigh scattering measurements, and bear out the predictions of a recent laser-cluster interaction model [H. M. Milchberg, S. J. McNaught, and E. Parra, Phys. Rev. E 64, 056402 (2001)

Time-resolved explosion of intense-laser-heated clusters

International Nuclear Information System (INIS)

Kim, K.Y.; Alexeev, I.; Parra, E.; Milchberg, H.M.

2003-01-01

We investigate the femtosecond explosive dynamics of intense laser-heated argon clusters by measuring the cluster complex transient polarizability. The time evolution of the polarizability is characteristic of competition in the optical response between supercritical and subcritical density regions of the expanding cluster. The results are consistent with time-resolved Rayleigh scattering measurements, and bear out the predictions of a recent laser-cluster interaction model [H. M. Milchberg, S. J. McNaught, and E. Parra, Phys. Rev. E 64, 056402 (2001)

Sequestration of Antimony on Calcite Observed by Time-Resolved Nanoscale Imaging.

Science.gov (United States)

Renard, François; Putnis, Christine V; Montes-Hernandez, German; King, Helen E; Breedveld, Gijs D; Okkenhaug, Gudny

2018-01-02

Antimony, which has damaging effects on the human body and the ecosystem, can be released into soils, ground-, and surface waters either from ore minerals that weather in near surface environments, or due to anthropogenic releases from waste rich in antimony, a component used in batteries, electronics, ammunitions, plastics, and many other industrial applications. Here, we show that dissolved Sb can interact with calcite, a widespread carbonate mineral, through a coupled dissolution-precipitation mechanism. The process is imaged in situ, at room temperature, at the nanometer scale by using an atomic force microscope equipped with a flow-through cell. Time-resolved imaging allowed following the coupled process of calcite dissolution, nucleation of precipitates at the calcite surface and growth of these precipitates. Sb(V) forms a precipitate, whereas Sb(III) needs to be oxidized to Sb(V) before being incorporated in the new phase. Scanning-electron microscopy and Raman spectroscopy allowed identification of the precipitates as two different calcium-antimony phases (Ca 2 Sb 2 O 7 ). This coupled dissolution-precipitation process that occurs in a boundary layer at the calcite surface can sequester Sb as a solid phase on calcite, which has environmental implications as it may reduce the mobility of this hazardous compound in soils and groundwaters.

Time-resolved x-ray line diagnostics of laser-produced plasmas

International Nuclear Information System (INIS)

Kauffman, R.L.; Matthews, D.L.; Kilkenny, J.D.; Lee, R.W.

1982-11-01

We have examined the underdense plasma conditions of laser irradiated disks using K x-rays from highly ionized ions. A 900 ps laser pulse of 0.532 μm light is used to irradiate various Z disks which have been doped with low concentrations of tracer materials. The tracers, whose Z's range from 13 to 22, are chosen so that their K x-ray spectrum is sensitive to typical underdense plasma temperatures and densities. Spectra are measured using a time-resolved crystal spectrograph recording the time history of the x-ray spectrum. A spatially-resolved, time-integrated crystal spectrograph also monitors the x-ray lines. Large differences in Al spectra are observed when the host plasms is changed from SiO 2 to PbO or In. Spectra will be presented along with preliminary analysis of the data

Time-resolved x-ray line diagnostics of laser-produced plasmas

International Nuclear Information System (INIS)

Kauffman, R.L.; Matthews, D.L.; Kilkenny, J.D.; Lee, R.W.

1982-01-01

We have examined the underdense plasma conditions of laser irradiated disks using K x-rays from highly ionized ions. A 900 ps laser pulse of 0.532 μm light is used to irradiate various Z disks which have been doped with low concentrations of tracer materials. The tracers whose Z's range from 13 to 22 are chosen so that their K x-ray spectrum is sensitive to typical underdense plasma temperatures and densities. Spectra are measured using a time-resolved crystal spectrograph recording the time history of the x-ray spectrum. A spatially-resolved, time-integrated crystal spectrograph also monitors the x-ray lines. Large differences in Al spectra are observed when the host plasma is changed from SiO 2 to PbO or In. Spectra will be presented along with preliminary analysis of the data

Time-resolved diffraction studies of muscle using synchrotron radiation

International Nuclear Information System (INIS)

Harford, Jeffrey; Squire, John

1997-01-01

Muscle contraction is one of those biological phenomena that we can all appreciate in our everyday lives. Sometimes it is when we are resting quietly and are aware of our heartbeat. At other times it may be when we are exerting ourselves and become short of breath, or when we exercise for a long period and our muscles start to ache. The way in which muscles produce force has exercised the minds of philosophers and scientists at least since the days of Erasistratus in the third century BC. Nowadays, of course, we know a very great deal about muscle structure, physiology and biochemistry, but we still do not know exactly what the molecular process is that produces movement. An ideal way of probing this process would be to be able to obtain signals from the relevant molecules as they actually go through their normal force-generating routine in an active muscle. The spatial dimensions involved are in the region of 1-50 nm, thus precluding the use of light microscopy, and the time regime is microseconds to milliseconds. Techniques with the appropriate spatial resolution might be electron microscopy and x-ray diffraction, but electron microscopy cannot yet be carried out on living tissue. X-ray diffraction methods can clearly have the right sort of spatial resolution, but what about recording diffraction patterns in the very short times involved (say 1 ms)? It is here that the high flux from synchrotron storage rings comes into its own. Using synchrotron radiation from, say, the SRS at the CCLRC Daresbury Laboratory it is possible to record x-ray diffraction patterns from living muscles in the millisecond time regime and to follow how these diffraction patterns change as the muscles go through typical contraction cycles. Unfortunately, x-ray diffraction is not a direct imaging method; the observed distribution of diffracted intensity needs to be interpreted in some way to give useful information on the spatial relationships of the force-generating molecules. This review

Time- and Space-Resolved Spectroscopic Investigation on Pi-Conjugated Nanostructures - 2

Science.gov (United States)

2016-01-12

Defocused wide-field fluorescence (DWFI) microscopy suggests that molecular heterogeneities and flexibilities clearly depend on ring size and that site... Confocal   Microscopy   Setup Wild‐field  Microscopy   Setup Femtosecond Z‐scan  experiment Setup Figure 3. Instruments of Time- and space-resolved...approved for public release. 3. Space-Resolved Laser Spectroscopy - Confocal Microscopy - Wild-field Microscopy 4. Non-Linear Spectroscopy

Time and spectrum-resolving multiphoton correlator for 300–900 nm

Energy Technology Data Exchange (ETDEWEB)

Johnsen, Kelsey D.; Thibault, Marilyne; Jennewein, Thomas [Institute for Quantum Computing and Department for Physics and Astronomy, University of Waterloo, 200 University Ave. West, Waterloo, Ontario N2L 3G1 (Canada); Kolenderski, Piotr, E-mail: kolenderski@fizyka.umk.pl [Institute for Quantum Computing and Department for Physics and Astronomy, University of Waterloo, 200 University Ave. West, Waterloo, Ontario N2L 3G1 (Canada); Faculty of Physics, Astronomy and Informatics, Institute of Physics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun (Poland); Scarcella, Carmelo; Tosi, Alberto [Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy)

2014-10-14

We demonstrate a single-photon sensitive spectrometer in the visible range, which allows us to perform time-resolved and multi-photon spectral correlation measurements at room temperature. It is based on a monochromator composed of two gratings, collimation optics, and an array of single photon avalanche diodes. The time resolution can reach 110 ps and the spectral resolution is 2 nm/pixel, limited by the design of the monochromator. This technique can easily be combined with commercial monochromators and can be useful for joint spectrum measurements of two photons emitted in the process of parametric down conversion, as well as time-resolved spectrum measurements in optical coherence tomography or medical physics applications.

Time-resolved measurement of global synchronization in the dust acoustic wave

Science.gov (United States)

Williams, J. D.

2014-10-01

A spatially and temporally resolved measurement of the synchronization of the naturally occurring dust acoustic wave to an external drive and the relaxation from the driven wave mode back to the naturally occuring wave mode is presented. This measurement provides a time-resolved measurement of the synchronization of the self-excited dust acoustic wave with an external drive and the return to the self-excited mode. It is observed that the wave synchronizes to the external drive in a distinct time-dependent fashion, while there is an immediate loss of synchronization when the external modulation is discontinued.

New layout of time resolved beam energy spectrum measurement for dragon-I

International Nuclear Information System (INIS)

Liao Shuqing; Zhang Kaizhi; Shi Jinshui

2010-01-01

A new layout of time resolved beam energy spectrum measurement is proposed for Dragon-I by a new method named RBS (rotating beams in solenoids). The basic theory of RBS and the new layout are presented and the measuring error is also discussed. The derived time resolved beam energy spectrum is discrete and is determined by measuring the beam's rotating angle and expanding width through a group of solenoids at the export of Dragon-I. (authors)

Efficient calculation of open quantum system dynamics and time-resolved spectroscopy with distributed memory HEOM (DM-HEOM).

Science.gov (United States)

Kramer, Tobias; Noack, Matthias; Reinefeld, Alexander; Rodríguez, Mirta; Zelinskyy, Yaroslav

2018-06-11

Time- and frequency-resolved optical signals provide insights into the properties of light-harvesting molecular complexes, including excitation energies, dipole strengths and orientations, as well as in the exciton energy flow through the complex. The hierarchical equations of motion (HEOM) provide a unifying theory, which allows one to study the combined effects of system-environment dissipation and non-Markovian memory without making restrictive assumptions about weak or strong couplings or separability of vibrational and electronic degrees of freedom. With increasing system size the exact solution of the open quantum system dynamics requires memory and compute resources beyond a single compute node. To overcome this barrier, we developed a scalable variant of HEOM. Our distributed memory HEOM, DM-HEOM, is a universal tool for open quantum system dynamics. It is used to accurately compute all experimentally accessible time- and frequency-resolved processes in light-harvesting molecular complexes with arbitrary system-environment couplings for a wide range of temperatures and complex sizes. © 2018 Wiley Periodicals, Inc. © 2018 Wiley Periodicals, Inc.

Imaging Electron Dynamics with Ultrashort Light Pulses: A Theory Perspective

Directory of Open Access Journals (Sweden)

Daria Popova-Gorelova

2018-02-01

Full Text Available A wide range of ultrafast phenomena in various atomic, molecular and condense matter systems is governed by electron dynamics. Therefore, the ability to image electronic motion in real space and real time would provide a deeper understanding of such processes and guide developments of tools to control them. Ultrashort light pulses, which can provide unprecedented time resolution approaching subfemtosecond time scale, are perspective to achieve real-time imaging of electron dynamics. This task is challenging not only from an experimental view, but also from a theory perspective, since standard theories describing light-matter interaction in a stationary regime can provide erroneous results in an ultrafast case as demonstrated by several theoretical studies. We review the theoretical framework based on quantum electrodynamics, which has been shown to be necessary for an accurate description of time-resolved imaging of electron dynamics with ultrashort light pulses. We compare the results of theoretical studies of time-resolved nonresonant and resonant X-ray scattering, and time- and angle-resolved photoelectron spectroscopy and show that the corresponding time-resolved signals encode analogous information about electron dynamics. Thereby, the information about an electronic system provided by these time-resolved techniques is different from the information provided by their time-independent analogues.

Time-Resolved PIV for Space-Time Correlations in Hot Jets

Science.gov (United States)

Wernet, Mark P.

2007-01-01

Temporally Resolved Particle Image Velocimetry (TR-PIV) is being used to characterize the decay of turbulence in jet flows a critical element for understanding the acoustic properties of the flow. A TR-PIV system, developed in-house at the NASA Glenn Research Center, is capable of acquiring planar PIV image frame pairs at up to 10 kHz. The data reported here were collected at Mach numbers of 0.5 and 0.9 and at temperature ratios of 0.89 and 1.76. The field of view of the TR-PIV system covered 6 nozzle diameters along the lip line of the 50.8 mm diameter jet. The cold flow data at Mach 0.5 were compared with hotwire anemometry measurements in order to validate the new TR-PIV technique. The axial turbulence profiles measured across the shear layer using TR-PIV were thinner than those measured using hotwire anemometry and remained centered along the nozzle lip line. The collected TR-PIV data illustrate the differences in the single point statistical flow properties of cold and hot jet flows. The planar, time-resolved velocity records were then used to compute two-point space-time correlations of the flow at the Mach 0.9 flow condition. The TR-PIV results show that there are differences in the convective velocity and growth rate of the turbulent structures between cold and hot flows at the same Mach number.

Time-resolved luminescence from feldspars: New insight into fading

DEFF Research Database (Denmark)

Tsukamoto, S.; Denby, P.M.; Murray, A.S.

2006-01-01

Time-resolved infrared optically stimulated luminescence (IR-OSL) signals of K- and Na-feldspar samples extracted from sediments were measured in UV, blue and red detection windows, using a fast photon counter and pulsed IR stimulation (lambda = 875 nm). We observe that the relative contribution ...

Vibrationally resolved photoelectron spectra of lower diamondoids: A time-dependent approach

Science.gov (United States)

Xiong, Tao; Włodarczyk, Radosław; Gallandi, Lukas; Körzdörfer, Thomas; Saalfrank, Peter

2018-01-01

Vibrationally resolved lowest-energy bands of the photoelectron spectra (PES) of adamantane, diamantane, and urotropine were simulated by a time-dependent correlation function approach within the harmonic approximation. Geometries and normal modes for neutral and cationic molecules were obtained from B3LYP hybrid density functional theory (DFT). It is shown that the simulated spectra reproduce the experimentally observed vibrational finestructure (or its absence) quite well. Origins of the finestructure are discussed and related to recurrences of autocorrelation functions and dominant vibrations. Remaining quantitative and qualitative errors of the DFT-derived PES spectra refer to (i) an overall redshift by ˜0.5 eV and (ii) the absence of satellites in the high-energy region of the spectra. The former error is shown to be due to the neglect of many-body corrections to ordinary Kohn-Sham methods, while the latter has been argued to be due to electron-nuclear couplings beyond the Born-Oppenheimer approximation [Gali et al., Nat. Commun. 7, 11327 (2016)].

Femtosecond time-resolved hot carrier energy distributions of photoexcited semiconductor quantum dots

International Nuclear Information System (INIS)

Chuang, Chi-Hung; Burda, Clemens; Chen, Xiaobo

2013-01-01

Using femtosecond transient absorption spectroscopy, we investigated hot carrier distributions in semiconductor cadmium selenide quantum dots. The relaxation processes represent the behavior of an ensemble of QDs. This concept is applied for analysis with the Fermi-Dirac distribution and relaxation processes among different electron-hole pair states. By extracting the experimental hot carrier distribution and fitting with the Fermi-Dirac function, we resolved the rapid thermalization processes, such as carrier-carrier and carrier-phonon interactions was resolved within one picosecond upon photoexcitation. The analysis, using the Fermi-Dirac distribution modulated by the density of states, provides a general route to understanding the carrier cooling and heat dissipation processes in quantum dot-based systems. (copyright 2012 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Time-resolved photoluminescence study of CdSe/CdMnS/CdS core/multi-shell nanoplatelets

International Nuclear Information System (INIS)

Murphy, J. R.; Delikanli, S.; Demir, H. V.; Scrace, T.; Zhang, P.; Norden, T.; Petrou, A.; Thomay, T.; Cartwright, A. N.

2016-01-01

We used photoluminescence spectroscopy to resolve two emission features in CdSe/CdMnS/CdS and CdSe/CdS core/multi-shell nanoplatelet heterostructures. The photoluminescence from the magnetic sample has a positive circular polarization with a maximum centered at the position of the lower energy feature. The higher energy feature has a corresponding signature in the absorption spectrum; this is not the case for the low-energy feature. We have also studied the temporal evolution of these features using a pulsed-excitation/time-resolved photoluminescence technique to investigate their corresponding recombination channels. A model was used to analyze the temporal dynamics of the photoluminescence which yielded two distinct timescales associated with these recombination channels. The above results indicate that the low-energy feature is associated with recombination of electrons with holes localized at the core/shell interfaces; the high-energy feature, on the other hand, is excitonic in nature with the holes confined within the CdSe cores.

Time-resolved photoluminescence study of CdSe/CdMnS/CdS core/multi-shell nanoplatelets

Energy Technology Data Exchange (ETDEWEB)

Murphy, J. R. [Department of Electrical Engineering, State University of New York, University at Buffalo, Buffalo, New York 14260 (United States); Department of Physics, State University of New York, University at Buffalo, Buffalo, New York 14260 (United States); Delikanli, S.; Demir, H. V., E-mail: volkan@bilkent.edu.tr [LUMINOUS Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Materials Sciences, Nanyang Technological University, Singapore 639798 (Singapore); Department of Electrical and Electronics Engineering, Department of Physics, UNAM−Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800 (Turkey); Scrace, T.; Zhang, P.; Norden, T.; Petrou, A., E-mail: petrou@buffalo.edu [Department of Physics, State University of New York, University at Buffalo, Buffalo, New York 14260 (United States); Thomay, T.; Cartwright, A. N. [Department of Electrical Engineering, State University of New York, University at Buffalo, Buffalo, New York 14260 (United States)

2016-06-13

We used photoluminescence spectroscopy to resolve two emission features in CdSe/CdMnS/CdS and CdSe/CdS core/multi-shell nanoplatelet heterostructures. The photoluminescence from the magnetic sample has a positive circular polarization with a maximum centered at the position of the lower energy feature. The higher energy feature has a corresponding signature in the absorption spectrum; this is not the case for the low-energy feature. We have also studied the temporal evolution of these features using a pulsed-excitation/time-resolved photoluminescence technique to investigate their corresponding recombination channels. A model was used to analyze the temporal dynamics of the photoluminescence which yielded two distinct timescales associated with these recombination channels. The above results indicate that the low-energy feature is associated with recombination of electrons with holes localized at the core/shell interfaces; the high-energy feature, on the other hand, is excitonic in nature with the holes confined within the CdSe cores.

Space- and time-resolved raman and breakdown spectroscopy: advanced lidar techniques

Science.gov (United States)

Silviu, Gurlui; Marius Mihai, Cazacu; Adrian, Timofte; Oana, Rusu; Georgiana, Bulai; Dimitriu, Dan

2018-04-01

DARLIOES - the advanced LIDAR is based on space- and time-resolved RAMAN and breakdown spectroscopy, to investigate chemical and toxic compounds, their kinetics and physical properties at high temporal (2 ns) and spatial (1 cm) resolution. The high spatial and temporal resolution are needed to resolve a large variety of chemical troposphere compounds, emissions from aircraft, the self-organization space charges induced light phenomena, temperature and humidity profiles, ice nucleation, etc.

Time-resolved Laue diffraction from protein crystals: Instrumental considerations

International Nuclear Information System (INIS)

Bilderback, D.H.; Cornell Univ., Ithaca, NY; Moffat, K.; Szebenyi, D.M.E.

1984-01-01

A serious limitation of macromolecular crystallography has been its inability to determine changes in structure on a biochemical time scale of milliseconds or less. Recently, we have shown that X-ray exposures on single crystals of macromolecules may be obtained in the millisecond time range through the use of intense, polychromatic radiation with Δlambda/lambda approx.= 0.2 derived from the Cornell High Energy Synchrotron Source, CHESS. Such radiation falling on a stationary crystal yields a Laue diffraction pattern, in which almost all Laue reflections arise from a unique set of Miller indices and where their intensities are automatically integrated over wavelength. This Laue technique requires wide band pass optics, which may be obtained by a combination of reflection and transmission mirrors, filters or layered synthetic microstructures. Time-resolved macromolecular crystallography may be achieved by several data collection schemes: 'one-shot' recording coupled to a simple streak camera, repetitive sample perturbation coupled to a detector with temporal resolution and repetitive perturbation which uses the synchrotron pulses for stroboscopic triggering and detection. These schemes are appropriate for different time scales, roughly the milli-, micro- and nanosecond regimes. It appears that time-resolved crystallography is entirely feasible, with an ultimate time resolution limited only by the length of a synchrotron light pulse, some 150 ps at CHESS. (orig.)

Time resolved resonance Raman spectra of anilino radical and aniline radical cation

International Nuclear Information System (INIS)

Tripathi, G.N.R.; Schuler, R.H.

1987-01-01

We report, in this paper, submicrosecond time resolved resonance Raman spectra of anilino radical and its radical cation as observed in pulse radiolytic studies of the oxidation of aniline in aqueous solution. By excitation in resonance with the broad and weak electronic transition of anilino radical at 400 nm (ε--1250 M -1 cm -1 ) we have observed, for the first time, the vibrational features of this radical. The Wilson ν 8 /sub a/ ring stretching mode at 1560 cm -1 is most strongly resonance enhanced. The ν 7 /sub a/ CN stretching band at 1505 cm -1 , which is shifted to higher frequency by 231 cm -1 with respect to aniline, is also prominent. The frequency of this latter mode indicates that the CN bond in the radical has considerable double bond character. The Raman spectrum of aniline radical cation, excited in resonance with the --425 nm electronic absorption (ε--4000 M -1 cm -1 ), shows features which are similar to phenoxyl radical. Most of the observed frequencies of this radical in solution are in good agreement with vibrational energies determined by recent laser photoelectron spectroscopic studies in the vapor phase. The bands most strongly enhanced in the resonance Raman spectrum are, however, weak in the photoelectron spectrum. While the vibrational frequencies observed for anilino radical and its isoelectronic cation are quite similar, the resonance enhancement patterns are very different. In particular the ν 14 b 2 mode of anilino radical observed at 1324 cm -1 is highly resonance enhanced because of strong vibronic coupling between the 400 nm 2 A 2 -- 2 B 1 and the higher 2 B 1 -- 2 B 1 electronic transitions

Fixed target matrix for femtosecond time-resolved and in situ serial micro-crystallography

Directory of Open Access Journals (Sweden)

C. Mueller

2015-09-01

Full Text Available We present a crystallography chip enabling in situ room temperature crystallography at microfocus synchrotron beamlines and X-ray free-electron laser (X-FEL sources. Compared to other in situ approaches, we observe extremely low background and high diffraction data quality. The chip design is robust and allows fast and efficient loading of thousands of small crystals. The ability to load a large number of protein crystals, at room temperature and with high efficiency, into prescribed positions enables high throughput automated serial crystallography with microfocus synchrotron beamlines. In addition, we demonstrate the application of this chip for femtosecond time-resolved serial crystallography at the Linac Coherent Light Source (LCLS, Menlo Park, California, USA. The chip concept enables multiple images to be acquired from each crystal, allowing differential detection of changes in diffraction intensities in order to obtain high signal-to-noise and fully exploit the time resolution capabilities of XFELs.

Prospective time-resolved LCA of fully electric supercap vehicles in Germany.

Science.gov (United States)

Zimmermann, Benedikt M; Dura, Hanna; Baumann, Manuel J; Weil, Marcel R

2015-07-01

The ongoing transition of the German electricity supply toward a higher share of renewable and sustainable energy sources, called Energiewende in German, has led to dynamic changes in the environmental impact of electricity over the last few years. Prominent scenario studies predict that comparable dynamics will continue in the coming decades, which will further improve the environmental performance of Germany's electricity supply. Life cycle assessment (LCA) is the methodology commonly used to evaluate environmental performance. Previous LCA studies on electric vehicles have shown that the electricity supply for the vehicles' operation is responsible for the major part of their environmental impact. The core question of this study is how the prospective dynamic development of the German electricity mix will affect the impact of electric vehicles operated in Germany and how LCA can be adapted to analyze this impact in a more robust manner. The previously suggested approach of time-resolved LCA, which is located between static and dynamic LCA, is used in this study and compared with several static approaches. Furthermore, the uncertainty issue associated with scenario studies is addressed in general and in relation to time-resolved LCA. Two scenario studies relevant to policy making have been selected, but a moderate number of modifications have been necessary to adapt the data to the requirements of a life cycle inventory. A potential, fully electric vehicle powered by a supercapacitor energy storage system is used as a generic example. The results show that substantial improvements in the environmental repercussions of the electricity supply and, consequentially, of electric vehicles will be achieved between 2020 and 2031 on the basis of the energy mixes predicted in both studies. This study concludes that although scenarios might not be able to predict the future, they should nonetheless be used as data sources in prospective LCA studies, because in many cases

Time - resolved thermography at Tokamak T-10

International Nuclear Information System (INIS)

Grunow, C.; Guenther, K.; Lingertat, J.; Chicherov, V.M.; Evstigneev, S.A.; Zvonkov, S.N.

1987-01-01

Thermographic experiments were performed at T-10 tokamak to investigate the thermic coupling of plasma and the limiter. The limiter is an internal equipment of the vacuum vessel of tokamak-type fusion devices and the interaction of plasma with limiter results a high thermal load of limiter for short time. In according to improve the limiter design the temperature distribution on the limiter surface was measured by a time-resolved thermographic method. Typical isotherms and temperature increment curves are presented. This measurement can be used as a systematic plasma diagnostic method because the limiter is installed in the tokamak whereas special additional probes often disturb the plasma discharge. (D.Gy.) 3 refs.; 7 figs

Advanced electron beam techniques

International Nuclear Information System (INIS)

Hirotsu, Yoshihiko; Yoshida, Yoichi

2007-01-01

After 100 years from the time of discovery of electron, we now have many applications of electron beam in science and technology. In this report, we review two important applications of electron beam: electron microscopy and pulsed-electron beam. Advanced electron microscopy techniques to investigate atomic and electronic structures, and pulsed-electron beam for investigating time-resolved structural change are described. (author)

Spin resolved electronic transport through N@C20 fullerene molecule between Au electrodes: A first principles study

Science.gov (United States)

Caliskan, Serkan

2018-05-01

Using first principles study, through Density Functional Theory combined with Non Equilibrium Green's Function Formalism, electronic properties of endohedral N@C20 fullerene molecule joining Au electrodes (Au-N@C20) was addressed in the presence of spin property. The electronic transport behavior across the Au-N@C20 molecular junction was investigated by spin resolved transmission, density of states, molecular orbitals, differential conductance and current-voltage (I-V) characteristics. Spin asymmetric variation was clearly observed in the results due to single N atom encapsulated in the C20 fullerene cage, where the N atom played an essential role in the electronic behavior of Au-N@C20. This N@C20 based molecular bridge, exhibiting a spin dependent I-V variation, revealed a metallic behavior within the bias range from -1 V to 1 V. The induced magnetic moment, spin polarization and other relevant quantities associated with the spin resolved transport were elucidated.

Angle-Resolved Photoemission Spectroscopy on Electronic Structure and Electron-Phonon Coupling in Cuprate Superconductors

Energy Technology Data Exchange (ETDEWEB)

Zhou, X.J.

2010-04-30

In addition to the record high superconducting transition temperature (T{sub c}), high temperature cuprate superconductors are characterized by their unusual superconducting properties below T{sub c}, and anomalous normal state properties above T{sub c}. In the superconducting state, although it has long been realized that superconductivity still involves Cooper pairs, as in the traditional BCS theory, the experimentally determined d-wave pairing is different from the usual s-wave pairing found in conventional superconductors. The identification of the pairing mechanism in cuprate superconductors remains an outstanding issue. The normal state properties, particularly in the underdoped region, have been found to be at odd with conventional metals which is usually described by Fermi liquid theory; instead, the normal state at optimal doping fits better with the marginal Fermi liquid phenomenology. Most notable is the observation of the pseudogap state in the underdoped region above T{sub c}. As in other strongly correlated electrons systems, these unusual properties stem from the interplay between electronic, magnetic, lattice and orbital degrees of freedom. Understanding the microscopic process involved in these materials and the interaction of electrons with other entities is essential to understand the mechanism of high temperature superconductivity. Since the discovery of high-T{sub c} superconductivity in cuprates, angle-resolved photoemission spectroscopy (ARPES) has provided key experimental insights in revealing the electronic structure of high temperature superconductors. These include, among others, the earliest identification of dispersion and a large Fermi surface, an anisotropic superconducting gap suggestive of a d-wave order parameter, and an observation of the pseudogap in underdoped samples. In the mean time, this technique itself has experienced a dramatic improvement in its energy and momentum resolutions, leading to a series of new discoveries not

Angle-Resolved Photoemission Spectroscopy on Electronic Structure and Electron-Phonon Coupling in Cuprate Superconductors

International Nuclear Information System (INIS)

Zhou, X.J.

2010-01-01

In addition to the record high superconducting transition temperature (T c ), high temperature cuprate superconductors are characterized by their unusual superconducting properties below T c , and anomalous normal state properties above T c . In the superconducting state, although it has long been realized that superconductivity still involves Cooper pairs, as in the traditional BCS theory, the experimentally determined d-wave pairing is different from the usual s-wave pairing found in conventional superconductors. The identification of the pairing mechanism in cuprate superconductors remains an outstanding issue. The normal state properties, particularly in the underdoped region, have been found to be at odd with conventional metals which is usually described by Fermi liquid theory; instead, the normal state at optimal doping fits better with the marginal Fermi liquid phenomenology. Most notable is the observation of the pseudogap state in the underdoped region above T c . As in other strongly correlated electrons systems, these unusual properties stem from the interplay between electronic, magnetic, lattice and orbital degrees of freedom. Understanding the microscopic process involved in these materials and the interaction of electrons with other entities is essential to understand the mechanism of high temperature superconductivity. Since the discovery of high-T c superconductivity in cuprates, angle-resolved photoemission spectroscopy (ARPES) has provided key experimental insights in revealing the electronic structure of high temperature superconductors. These include, among others, the earliest identification of dispersion and a large Fermi surface, an anisotropic superconducting gap suggestive of a d-wave order parameter, and an observation of the pseudogap in underdoped samples. In the mean time, this technique itself has experienced a dramatic improvement in its energy and momentum resolutions, leading to a series of new discoveries not thought possible

Time Resolved PIV for Space-Time Correlations in Hot Jets

Science.gov (United States)

Wernet, Mark P.

2007-01-01

Temporally Resolved Particle Image Velocimetry (TR-PIV) is the newest and most exciting tool recently developed to support our continuing efforts to characterize and improve our understanding of the decay of turbulence in jet flows -- a critical element for understanding the acoustic properties of the flow. A new TR-PIV system has been developed at the NASA Glenn Research Center which is capable of acquiring planar PIV image frame pairs at up to 25 kHz. The data reported here were collected at Mach numbers of 0.5 and 0.9 and at temperature ratios of 0.89 and 1.76. The field of view of the TR-PIV system covered 6 nozzle diameters along the lip line of the 50.8 mm diameter jet. The cold flow data at Mach 0.5 were compared with hotwire anemometry measurements in order to validate the new TR-PIV technique. The axial turbulence profiles measured across the shear layer using TR-PIV were thinner than those measured using hotwire anemometry and remained centered along the nozzle lip line. The collected TR-PIV data illustrate the differences in the single point statistical flow properties of cold and hot jet flows. The planar, time-resolved velocity records were then used to compute two-point space-time correlations of the flow at the Mach 0.9 flow condition. The TR-PIV results show that there are differences in the convective velocity and growth rate of the turbulent structures between cold and hot flows at the same Mach number

Time-resolved fluorescence study of exciplex formation in diastereomeric naproxen-pyrrolidine dyads.

Science.gov (United States)

Khramtsova, Ekaterina A; Plyusnin, Viktor F; Magin, Ilya M; Kruppa, Alexander I; Polyakov, Nikolay E; Leshina, Tatyana V; Nuin, Edurne; Marin, M Luisa; Miranda, Miguel A

2013-12-19

The influence of chirality on the elementary processes triggered by excitation of the (S,S)- and (R,S)- diastereoisomers of naproxen-pyrrolidine (NPX-Pyr) dyads has been studied by time-resolved fluorescence in acetonitrile-benzene mixtures. In these systems, the quenching of the (1)NPX*-Pyr singlet excited state occurs through electron transfer and exciplex formation. Fluorescence lifetimes and quantum yields revealed a significant difference (around 20%) between the (S,S)- and (R,S)- diastereomers. In addition, the quantum yields of exciplexes differed by a factor of 2 regardless of solvent polarity. This allows us to suggest a similar influence of the chiral centers on the local charge transfer resulting in exciplex and full charge separation that leads to ion-biradicals. A simplified scheme is proposed to estimate a set of rate constant values (k1-k5) for the elementary stages in each solvent system.

Pulse radiolysis with (sub) nanosecond time resolution using a 3 MV electron accelerator

International Nuclear Information System (INIS)

Luthjens, L.H.

1986-01-01

In this thesis the development of equipment for pulse radiolysis is described and the application of the technique to time-resolved measurements of the fluorescence emission of excited states formed after irradiation of some alkanes is dealt with. A review is given of the development of the pulsed 3MV Van de Graaf electron accelerator for the generation of subnanosecond electron beam pulses and of the development of the equipment for optical detection as accomplished by the author. The initial stage of a further development for shorter pulses and higher time resolution is briefly discussed. A collection of papers on the development of apparatus and a collection of papers dealing with the results obtained from measurements of the fluorescence of excited states, formed by the recombination of electrons and ions in irradiated alkanes such as cyclohexane and the decalines, are included. (Auth.)

Image enhancement in photoemission electron microscopy by means of imaging time-of-flight analysis

International Nuclear Information System (INIS)

Oelsner, A.; Krasyuk, A.; Fecher, G.H.; Schneider, C.M.; Schoenhense, G.

2004-01-01

Photoemission electron microscopy (PEEM) is widely used in combination with synchrotron sources as a powerful tool to observe chemical and magnetic properties of metal and semiconductor surfaces. Presently, the resolution limit of these instruments using soft-X-ray excitation is limited to about 50 nm, because of the chromatic aberration of the electron optics used. Various sophisticated approaches have thus been reported for enhancing the spatial resolution in photoemission electron microscopy. This work demonstrates the use of a simple imaging energy filter based on electron time-of-flight (ToF) selection. The spatial resolution could be improved dramatically, even though the instrument was optimized using a rather large contrast aperture of 50 μm. A special (x, y, t)-resolving delayline detector was used as the imaging unit of this ToF-PEEM. It is operated in phase with the time structure of the synchrotron source, cutting time intervals from the raw image-forming data set in order to reduce the electron energy width contributing to the final images

The RATIO method for time-resolved Laue crystallography

International Nuclear Information System (INIS)

Coppens, P.; Pitak, M.; Gembicky, M.; Messerschmidt, M.; Scheins, S.; Benedict, J.; Adachi, S.-I.; Sato, T.; Nozawa, S.; Ichiyanagi, K.; Chollet, M.; Koshihara, S.-Y.

2009-01-01

A RATIO method for analysis of intensity changes in time-resolved pump-probe Laue diffraction experiments is described. The method eliminates the need for scaling the data with a wavelength curve representing the spectral distribution of the source and removes the effect of possible anisotropic absorption. It does not require relative scaling of series of frames and removes errors due to all but very short term fluctuations in the synchrotron beam.

Coherent optical effect on time-resolved vibrational SFG spectrum of adsorbates

Science.gov (United States)

Ueba, H.; Sawabu, T.; Mii, T.

2002-04-01

We present a theory to study the influence of the coherent mixing between pump-infrared and probe-visible pulse on a time-resolved sum-frequency generation (TR-SFG) spectrum for vibrations at surfaces. The general formula of the time-dependent and its Fourier transform of the SFG polarization and its Fourier transform allows us to calculate the time-resolved vibrational SFG spectrum and the transient characteristics of the SFG intensity as a function of the delay time td between the pump-infrared and probe-visible pulse. It is found the coherent optical effect manifests itself in the broadening and narrowing of the SFG spectrum with the intrinsic width of T2 at negative and positive td, respectively, being in qualitative agreement with recent experimental results. The influence of the coherent mixing on the transient behavior of the SFG intensity is also discussed in conjunction to the T2 determination.

Electronic properties of novel topological quantum materials studied by angle-resolved photoemission spectroscopy (ARPES)

Energy Technology Data Exchange (ETDEWEB)

Wu, Yun [Iowa State Univ., Ames, IA (United States)

2016-12-17

The discovery of quantum Hall e ect has motivated the use of topology instead of broken symmetry to classify the states of matter. Quantum spin Hall e ect has been proposed to have a separation of spin currents as an analogue of the charge currents separation in quantum Hall e ect, leading us to the era of topological insulators. Three-dimensional analogue of the Dirac state in graphene has brought us the three-dimensional Dirac states. Materials with three-dimensional Dirac states could potentially be the parent compounds for Weyl semimetals and topological insulators when time-reversal or space inversion symmetry is broken. In addition to the single Dirac point linking the two dispersion cones in the Dirac/Weyl semimetals, Dirac points can form a line in the momentum space, resulting in a topological node line semimetal. These fascinating novel topological quantum materials could provide us platforms for studying the relativistic physics in condensed matter systems and potentially lead to design of new electronic devices that run faster and consume less power than traditional, silicon based transistors. In this thesis, we present the electronic properties of novel topological quantum materials studied by angle-resolved photoemission spectroscopy (ARPES).

On the theory of time-resolved x-ray diffraction

DEFF Research Database (Denmark)

Henriksen, Niels Engholm; Møller, Klaus Braagaard

2008-01-01

We derive the basic theoretical formulation for X-ray diffraction with pulsed fields, using a fully quantized description of light and matter. Relevant time scales are discussed for coherent as well as incoherent X-ray pulses, and we provide expressions to be used for calculation...... of the experimental diffraction signal for both types of X-ray sources. We present a simple analysis of time-resolved X-ray scattering for direct bond breaking in diatomic molecules. This essentially analytical approach highlights the relation between the signal and the time-dependent quantum distribution...

Time-resolved X-ray scattering program at the Advanced Photon Source

International Nuclear Information System (INIS)

Rodricks, B.

1994-01-01

The Time-Resolved Scattering Program's goal is the development of instruments and techniques for time-resolved studies. This entails the development of wide bandpass and focusing optics, high-speed detectors, mechanical choppers, and components for the measurement and creation of changes in samples. Techniques being developed are pump-probe experiments, single-bunch scattering experiments, high-speed white and pink beam Laue scattering, and nanosecond to microsecond synchronization of instruments. This program will be carried out primarily from a white-beam, bend-magnet source, experimental station, 1-BM-B, that immediately follows the first optics enclosure (1-BM-A). This paper will describe the experimental station and instruments under development to carry out the program

Time-resolved studies of direct effects of radiation on DNA

International Nuclear Information System (INIS)

Fielden, E.M.; O'Neill, P.; Al-Kazwini, A.

1987-01-01

The biological changes induced by ionising radiation are a consequence of radiation-induced chemical events taking place at times <1s. These events are strongly influenced by the presence of chemical modifiers. Since DNA is a principle target for radiation-induced cell killing, DNA-free radicals are generated by direct ionisation of DNA moieties (direct effect) and by reaction with hydroxyl radicals formed by radiolysis of the water which is in the vicinity of the DNA (indirect effect). In order to study the 'direct' effects of radiation on DNA the following model approaches are discussed:- 1) Use of the technique of pulse radiolysis to investigate in aqueous solution the interactions of deoxynucleosides with SO/sub 4//sup .-/ whereby one-electron oxidised species of the bases are generated; and 2) time resolved, radiation-induced changes to solid DNA and related macromolecules (e.g. radiation-induced luminescence) in order to obtain an understanding of charge/energy migration as a result of ionisation of DNA. The influence of chemical modifiers and of environment is discussed in terms of the properties of the radiation-induced species produced. Since the properties of base radicals produced by SO/sub 4//sup .-/ are similar to those of the base OH-adducts oxidising properties, potential similarities between the 'direct' and 'indirect' effects of radiation are presented

Electronic structure of C r2AlC as observed by angle-resolved photoemission spectroscopy

Science.gov (United States)

Ito, Takahiro; Pinek, Damir; Fujita, Taishi; Nakatake, Masashi; Ideta, Shin-ichiro; Tanaka, Kiyohisa; Ouisse, Thierry

2017-11-01

We investigate the electronic band structure and Fermi surfaces (FSs) of C r2AlC single crystals with angle-resolved photoemission spectroscopy. We evidence hole bands centered around the M points and electron bands centered around the Γ point in reciprocal space. Electron and hole bands exhibit an open, tubular structure along the c axis, confirming the quasi-two-dimensional character of this highly anisotropic, nanolamellar compound. Dependence of the photoionization cross sections on beam light polarization and orientation allows us to assess the orbital character of each observed band locally. Despite some differences, density functional theory calculations show a good agreement with experiment.

Fast time-resolved electrostatic force microscopy: Achieving sub-cycle time resolution

Energy Technology Data Exchange (ETDEWEB)

Karatay, Durmus U.; Harrison, Jeffrey S.; Glaz, Micah S.; Giridharagopal, Rajiv; Ginger, David S., E-mail: ginger@chem.washington.edu [Department of Chemistry, University of Washington, Seattle, Washington 98195 (United States)

2016-05-15

The ability to measure microsecond- and nanosecond-scale local dynamics below the diffraction limit with widely available atomic force microscopy hardware would enable new scientific studies in fields ranging from biology to semiconductor physics. However, commercially available scanning-probe instruments typically offer the ability to measure dynamics only on time scales of milliseconds to seconds. Here, we describe in detail the implementation of fast time-resolved electrostatic force microscopy using an oscillating cantilever as a means to measure fast local dynamics following a perturbation to a sample. We show how the phase of the oscillating cantilever relative to the perturbation event is critical to achieving reliable sub-cycle time resolution. We explore how noise affects the achievable time resolution and present empirical guidelines for reducing noise and optimizing experimental parameters. Specifically, we show that reducing the noise on the cantilever by using photothermal excitation instead of piezoacoustic excitation further improves time resolution. We demonstrate the discrimination of signal rise times with time constants as fast as 10 ns, and simultaneous data acquisition and analysis for dramatically improved image acquisition times.

Gamma-to-electron magnetic spectrometer (GEMS): An energy-resolved {gamma}-ray diagnostic for the National Ignition Facility

Energy Technology Data Exchange (ETDEWEB)

Kim, Y.; Herrmann, H. W.; Mack, J. M.; Young, C. S.; Barlow, D. B.; Schillig, J. B.; Sims, J. R. Jr.; Lopez, F. E.; Mares, D.; Oertel, J. A.; Hayes-Sterbenz, A. C. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Hilsabeck, T. J.; Wu, W. [General Atomics, PO Box 85608, San Diego, California 92186 (United States); Moy, K. [National Security Technologies, Special Technologies Laboratory, Santa Barbara, California 93111 (United States); Stoeffl, W. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

2012-10-15

The gamma-to-electron magnetic spectrometer, having better than 5% energy resolution, is proposed to resolve {gamma}-rays in the range of E{sub o}{+-} 20% in single shot, where E{sub o} is the central energy and is tunable from 2 to 25 MeV. Gamma-rays from inertial confinement fusion implosions interact with a thin Compton converter (e.g., beryllium) located at approximately 300 cm from the target chamber center (TCC). Scattered electrons out of the Compton converter enter an electromagnet placed outside the NIF chamber (approximately 600 cm from TCC) where energy selection takes place. The electromagnet provides tunable E{sub o} over a broad range in a compact manner. Energy resolved electrons are measured by an array of quartz Cherenkov converters coupled to photomultipliers. Given 100 detectable electrons in the energy bins of interest, 3 Multiplication-Sign 10{sup 14} minimum deuterium/tritium (DT) neutrons will be required to measure the 4.44 MeV {sup 12}C {gamma}-rays assuming 200 mg/cm{sup 2} plastic ablator areal density and 3 Multiplication-Sign 10{sup 15} minimum DT neutrons to measure the 16.75 MeV DT {gamma}-ray line.

Development of Micron-Resolved Electron Spectroscopy to Study Organic Thin Films in Real Devices

International Nuclear Information System (INIS)

Wang, C.-H.; Fan, L.-J.; Yang, Y.-W.; Su, J.-W.; Chan, S.-W.; Chen, M.-C.

2010-01-01

A straightforward application of an electron energy analyzer equipped with an image detector to micron-resolved electron spectroscopic studies of organic thin film devices is reported. The electron spectroscopies implemented include synchrotron-based UPS, XPS, and Auger yield NEXAFS. Along the non-energy-dispersion direction of the analyzer, a spatial resolution of ∼40 μm is obtained through the employment of entrance slits, electrostatic lenses and segmented CCD detector. One significant benefit offered by the technique is that the electronic transport and electronic structure of the same micron-sized sample can be directly examined. The example illustrated is a top-contact organic field effect transistor (OFET) fabricated from semiconducting triethylsilylethynyl anthradithiophene and gold electrodes. It is found that an extensive out-diffusion of gold atoms to adjacent conduction channels takes place, presumably due to the inability of soft organic materials in dissipating the excess energy with which gaseous Au atoms possess.

Time-resolved X-ray studies using third generation synchrotron radiation sources

International Nuclear Information System (INIS)

Mills, D.M.

1991-10-01

The third generation, high-brilliance, hard x-ray, synchrotron radiation (SR) sources currently under construction (ESRF at Grenoble, France; APS at Argonne, Illinois; and SPring-8 at Harima, Japan) will usher in a new era of x-ray experimentation for both physical and biological sciences. One of the most exciting areas of experimentation will be the extension of x-ray scattering and diffraction techniques to the study of transient or time-evolving systems. The high repetition rate, short-pulse duration, high brilliance, and variable spectral bandwidth of these sources make them ideal for x-ray time-resolved studies. The temporal properties (bunch length, interpulse period, etc.) of these new sources will be summarized. Finally, the scientific potential and the technological challenges of time-resolved x-ray scattering from these new sources will be described. 13 refs., 4 figs

MCNP simulations of a new time-resolved Compton scattering imaging technique

International Nuclear Information System (INIS)

Ilan, Y.

2004-01-01

Medical images of human tissue can be produced using Computed Tomography (CT), Positron Emission Tomography (PET), Ultrasound or Magnetic Resonance Imaging (MRI). In all of the above techniques, in order to get a three-dimensional (3D) image, one has to rotate or move the source, the detectors or the scanned target. This procedure is complicated, time consuming and increases the cost and weight of the scanning equipment. Time resolved optical tomography has been suggested as an alternative to the above conventional methods. This technique implies near infrared light (NIR) and fast time-resolved detectors to obtain a 3D image of the scanned target. However, due to the limited penetration of the NIR light in the tissue, the application of this technique is limited to soft tissue like a female breast or a premature infant brain

Reduction of Poisson noise in measured time-resolved data for time-domain diffuse optical tomography.

Science.gov (United States)

Okawa, S; Endo, Y; Hoshi, Y; Yamada, Y

2012-01-01

A method to reduce noise for time-domain diffuse optical tomography (DOT) is proposed. Poisson noise which contaminates time-resolved photon counting data is reduced by use of maximum a posteriori estimation. The noise-free data are modeled as a Markov random process, and the measured time-resolved data are assumed as Poisson distributed random variables. The posterior probability of the occurrence of the noise-free data is formulated. By maximizing the probability, the noise-free data are estimated, and the Poisson noise is reduced as a result. The performances of the Poisson noise reduction are demonstrated in some experiments of the image reconstruction of time-domain DOT. In simulations, the proposed method reduces the relative error between the noise-free and noisy data to about one thirtieth, and the reconstructed DOT image was smoothed by the proposed noise reduction. The variance of the reconstructed absorption coefficients decreased by 22% in a phantom experiment. The quality of DOT, which can be applied to breast cancer screening etc., is improved by the proposed noise reduction.

Dual time-resolved temperature-jump fluorescence and infrared spectroscopy for the study of fast protein dynamics.

Science.gov (United States)

Davis, Caitlin M; Reddish, Michael J; Dyer, R Brian

2017-05-05

Time-resolved temperature-jump (T-jump) coupled with fluorescence and infrared (IR) spectroscopy is a powerful technique for monitoring protein dynamics. Although IR spectroscopy of the polypeptide amide I mode is more technically challenging, it offers complementary information because it directly probes changes in the protein backbone, whereas, fluorescence spectroscopy is sensitive to the environment of specific side chains. With the advent of widely tunable quantum cascade lasers (QCL) it is possible to efficiently probe multiple IR frequencies with high sensitivity and reproducibility. Here we describe a dual time-resolved T-jump fluorescence and IR spectrometer and its application to study protein folding dynamics. A Q-switched Ho:YAG laser provides the T-jump source for both time-resolved IR and fluorescence spectroscopy, which are probed by a QCL and Ti:Sapphire laser, respectively. The Ho:YAG laser simultaneously pumps the time-resolved IR and fluorescence spectrometers. The instrument has high sensitivity, with an IR absorbance detection limit of jump induced difference spectrum from 50ns to 0.5ms. This study demonstrates the power of the dual time-resolved T-jump fluorescence and IR spectroscopy to resolve complex folding mechanisms by complementary IR absorbance and fluorescence measurements of protein dynamics. Copyright © 2017 Elsevier B.V. All rights reserved.

Spin and time-resolved magnetic resonance in radiation chemistry. Recent developments and perspectives

International Nuclear Information System (INIS)

Shkrob, I.A.; Trifunac, A.D.

1997-01-01

Time-resolved pulsed EPR and ODMR in studies on early events in radiation chemistry are examined. It is concluded that these techniques yield valuable and diverse information about chemical reactions in spurs, despite the fact that the spur reactions occur on a time scale that is much shorter than the time resolution of these methods. Several recent examples include EPR of H/D atoms in vitreous silica and cryogenic liquids and ODMR of doped alkane solids and amorphous semiconductors. It is argued that a wider use of time-resolved magnetic resonance methods would benefit the studies on radiation chemistry of disordered solids, simple liquids, and polymers. (author)

Time-resolved diffusion tomographic imaging in highly scattering turbid media

Science.gov (United States)

Alfano, Robert R. (Inventor); Cai, Wei (Inventor); Liu, Feng (Inventor); Lax, Melvin (Inventor); Das, Bidyut B. (Inventor)

1998-01-01

A method for imaging objects in highly scattering turbid media. According to one embodiment of the invention, the method involves using a plurality of intersecting source/detectors sets and time-resolving equipment to generate a plurality of time-resolved intensity curves for the diffusive component of light emergent from the medium. For each of the curves, the intensities at a plurality of times are then inputted into the following inverse reconstruction algorithm to form an image of the medium: X.sup.(k+1).spsp.T =?Y.sup.T W+X.sup.(k).spsp.T .LAMBDA.!?W.sup.T W+.LAMBDA.!.sup.-1 wherein W is a matrix relating output at detector position r.sub.d, at time t, to source at position r.sub.s, .LAMBDA. is a regularization matrix, chosen for convenience to be diagonal, but selected in a way related to the ratio of the noise, to fluctuations in the absorption (or diffusion) X.sub.j that we are trying to determine: .LAMBDA..sub.ij =.lambda..sub.j .delta..sub.ij with .lambda..sub.j =/ Here Y is the data collected at the detectors, and X.sup.k is the kth iterate toward the desired absoption information.

Mix and Inject: Reaction Initiation by Diffusion for Time-Resolved Macromolecular Crystallography

Directory of Open Access Journals (Sweden)

Marius Schmidt

2013-01-01

Full Text Available Time-resolved macromolecular crystallography unifies structure determination with chemical kinetics, since the structures of transient states and chemical and kinetic mechanisms can be determined simultaneously from the same data. To start a reaction in an enzyme, typically, an initially inactive substrate present in the crystal is activated. This has particular disadvantages that are circumvented when active substrate is directly provided by diffusion. However, then it is prohibitive to use macroscopic crystals because diffusion times become too long. With small micro- and nanocrystals diffusion times are adequately short for most enzymes and the reaction can be swiftly initiated. We demonstrate here that a time-resolved crystallographic experiment becomes feasible by mixing substrate with enzyme nanocrystals which are subsequently injected into the X-ray beam of a pulsed X-ray source.

Size dependence of the wavefunction of self-assembled InAs quantum dots from time-resolved optical measurements

DEFF Research Database (Denmark)

Johansen, Jeppe; Stobbe, Søren; Nikolaev, Ivan S.

2008-01-01

and a theoretical model, we determine the striking dependence of the overlap of the electron and hole wavefunctions on the quantum dot size. We conclude that the optical quality is best for large quantum dots, which is important in order to optimally tailor quantum dot emitters for, e.g., quantum electrodynamics......The radiative and nonradiative decay rates of InAs quantum dots are measured by controlling the local density of optical states near an interface. From time-resolved measurements, we extract the oscillator strength and the quantum efficiency and their dependence on emission energy. From our results...

Evaluating scintillator performance in time-resolved hard X-ray studies at synchrotron light sources

International Nuclear Information System (INIS)

Rutherford, Michael E.; Chapman, David J.; White, Thomas G.; Drakopoulos, Michael; Rack, Alexander; Eakins, Daniel E.

2016-01-01

Scintillator performance in time-resolved, hard, indirect detection X-ray studies on the sub-microsecond timescale at synchrotron light sources is reviewed, modelled and examined experimentally. LYSO:Ce is found to be the only commercially available crystal suitable for these experiments. The short pulse duration, small effective source size and high flux of synchrotron radiation is ideally suited for probing a wide range of transient deformation processes in materials under extreme conditions. In this paper, the challenges of high-resolution time-resolved indirect X-ray detection are reviewed in the context of dynamic synchrotron experiments. In particular, the discussion is targeted at two-dimensional integrating detector methods, such as those focused on dynamic radiography and diffraction experiments. The response of a scintillator to periodic synchrotron X-ray excitation is modelled and validated against experimental data collected at the Diamond Light Source (DLS) and European Synchrotron Radiation Facility (ESRF). An upper bound on the dynamic range accessible in a time-resolved experiment for a given bunch separation is calculated for a range of scintillators. New bunch structures are suggested for DLS and ESRF using the highest-performing commercially available crystal LYSO:Ce, allowing time-resolved experiments with an interframe time of 189 ns and a maximum dynamic range of 98 (6.6 bits)

Evaluating scintillator performance in time-resolved hard X-ray studies at synchrotron light sources

Energy Technology Data Exchange (ETDEWEB)

Rutherford, Michael E.; Chapman, David J.; White, Thomas G. [Imperial College London, London (United Kingdom); Drakopoulos, Michael [Diamond Light Source, I12 Joint Engineering, Environmental, Processing (JEEP) Beamline, Didcot, Oxfordshire (United Kingdom); Rack, Alexander [European Synchrotron Radiation Facility, Grenoble (France); Eakins, Daniel E., E-mail: d.eakins@imperial.ac.uk [Imperial College London, London (United Kingdom)

2016-03-24

Scintillator performance in time-resolved, hard, indirect detection X-ray studies on the sub-microsecond timescale at synchrotron light sources is reviewed, modelled and examined experimentally. LYSO:Ce is found to be the only commercially available crystal suitable for these experiments. The short pulse duration, small effective source size and high flux of synchrotron radiation is ideally suited for probing a wide range of transient deformation processes in materials under extreme conditions. In this paper, the challenges of high-resolution time-resolved indirect X-ray detection are reviewed in the context of dynamic synchrotron experiments. In particular, the discussion is targeted at two-dimensional integrating detector methods, such as those focused on dynamic radiography and diffraction experiments. The response of a scintillator to periodic synchrotron X-ray excitation is modelled and validated against experimental data collected at the Diamond Light Source (DLS) and European Synchrotron Radiation Facility (ESRF). An upper bound on the dynamic range accessible in a time-resolved experiment for a given bunch separation is calculated for a range of scintillators. New bunch structures are suggested for DLS and ESRF using the highest-performing commercially available crystal LYSO:Ce, allowing time-resolved experiments with an interframe time of 189 ns and a maximum dynamic range of 98 (6.6 bits)

Thermally activated delayed fluorescence of fluorescein derivative for time-resolved and confocal fluorescence imaging.

Science.gov (United States)

Xiong, Xiaoqing; Song, Fengling; Wang, Jingyun; Zhang, Yukang; Xue, Yingying; Sun, Liangliang; Jiang, Na; Gao, Pan; Tian, Lu; Peng, Xiaojun

2014-07-09

Compared with fluorescence imaging utilizing fluorophores whose lifetimes are in the order of nanoseconds, time-resolved fluorescence microscopy has more advantages in monitoring target fluorescence. In this work, compound DCF-MPYM, which is based on a fluorescein derivative, showed long-lived luminescence (22.11 μs in deaerated ethanol) and was used in time-resolved fluorescence imaging in living cells. Both nanosecond time-resolved transient difference absorption spectra and time-correlated single-photon counting (TCSPC) were employed to explain the long lifetime of the compound, which is rare in pure organic fluorophores without rare earth metals and heavy atoms. A mechanism of thermally activated delayed fluorescence (TADF) that considers the long wavelength fluorescence, large Stokes shift, and long-lived triplet state of DCF-MPYM was proposed. The energy gap (ΔEST) of DCF-MPYM between the singlet and triplet state was determined to be 28.36 meV by the decay rate of DF as a function of temperature. The ΔE(ST) was small enough to allow efficient intersystem crossing (ISC) and reverse ISC, leading to efficient TADF at room temperature. The straightforward synthesis of DCF-MPYM and wide availability of its starting materials contribute to the excellent potential of the compound to replace luminescent lanthanide complexes in future time-resolved imaging technologies.

Usefulness of time-resolved projection MRA on evaluation of hemodynamics in cerebral occlusive diseases

International Nuclear Information System (INIS)

Oka, Yoshihisa; Kusunoki, Katsusuke; Nochide, Ichiro; Igase, Keiji; Harada, Hironobu; Sadamoto, Kazuhiko; Nagasawa, Kiyoshi

2001-01-01

The usefulness for evaluation of cerebral hemodynamics using time-resolved projection MRA was studied in normal volunteers and patients of cerebrovascular diseases. Six normal volunteers and ten patients with cerebrovascular occlusive diseases including 6 of IC occlusion and 4 of post EC/IC bypass surgery underwent time-resolved projection MRA on a 1.5 T clinical MRI system. Projection angiograms are acquired with 2D-fast SPGR sequence with a time resolution of approximately one image per second, 40 images being acquired consecutively before and after bolus injection Gd-DTPA. And all images were calculated by complex subtraction from the background mask in a work station. In normal volunteers, the quality of images of time-resolved projection MRA was satisfactory. The arteries from internal carotid artery through M2 segment of middle cerebral artery and all major venous systems were well portrayed. In 4 cases of IC occlusion who were assessed the collateral flow through the anterior communicating artery and posterior communicating artery, there were delayed to demonstrate the ipsilateral MCA. However, in 2 cases of IC occlusion that were assessed the collateral flow through leptomeningeal anastomosis, ipsilateral MCA and collateral circulation were not demonstrated. In all patients of post EC/IC bypass surgery, the patency of EC/IC bypass could be evaluated as properly with time-resolved projection MRA as 3D-TOF MRA. Although the temporal and spatial resolutions are insufficient, time-resolved projection MRA was power-full non-invasive method to evaluate the cerebral hemodynamics vis the basal communicating arteries in IC occlusion and identify the patency of EC/IC bypass. (author)

Bimodal Exciplex Formation in Bimolecular Photoinduced Electron Transfer Revealed by Ultrafast Time-Resolved Infrared Absorption.

Science.gov (United States)

Koch, Marius; Licari, Giuseppe; Vauthey, Eric

2015-09-03

The dynamics of a moderately exergonic photoinduced charge separation has been investigated by ultrafast time-resolved infrared absorption with the dimethylanthracene/phthalonitrile donor/acceptor pair in solvents covering a broad range of polarity. A distinct spectral signature of an exciplex could be identified in the -C≡N stretching region. On the basis of quantum chemistry calculations, the 4-5 times larger width of this band compared to those of the ions and of the locally excited donor bands is explained by a dynamic distribution of exciplex geometry with different mutual orientations and distances of the constituents and, thus, with varying charge-transfer character. Although spectrally similar, two types of exciplexes could be distinguished by their dynamics: short-lived, "tight", exciplexes generated upon static quenching and longer-lived, "loose", exciplexes formed upon dynamic quenching in parallel with ion pairs. Tight exciplexes were observed in all solvents, except in the least polar diethyl ether where quenching is slower than diffusion. The product distribution of the dynamic quenching depends strongly on the solvent polarity: whereas no significant loose exciplex population could be detected in acetonitrile, both exciplex and ion pair are generated in less polar solvents, with the relative population of exciplex increasing with decreasing solvent polarity. These results are compared with those reported previously with donor/acceptor pairs in different driving force regimes to obtain a comprehensive picture of the role of the exciplexes in bimolecular photoinduced charge separation.

Review of the theoretical description of time-resolved angle-resolved photoemission spectroscopy in electron-phonon mediated superconductors

Energy Technology Data Exchange (ETDEWEB)

Kemper, A.F. [Department of Physics, North Carolina State University, Raleigh, NC (United States); Sentef, M.A. [Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, Hamburg (Germany); Moritz, B. [Stanford Institute for Materials and Energy Sciences (SIMES), SLAC National Accelerator Laboratory, Menlo Park, CA (United States); Devereaux, T.P. [Stanford Institute for Materials and Energy Sciences (SIMES), SLAC National Accelerator Laboratory, Menlo Park, CA (United States); Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA (United States); Freericks, J.K. [Department of Physics, Georgetown University, Washington, DC (United States)

2017-09-15

We review recent work on the theory for pump/probe photoemission spectroscopy of electron-phonon mediated superconductors in both the normal and the superconducting states. We describe the formal developments that allow one to solve the Migdal-Eliashberg theory in nonequilibrium for an ultrashort laser pumping field, and explore the solutions which illustrate the relaxation as energy is transferred from electrons to phonons. We focus on exact results emanating from sum rules and approximate numerical results which describe rules of thumb for relaxation processes. In addition, in the superconducting state, we describe how Anderson-Higgs oscillations can be excited due to the nonlinear coupling with the electric field and describe mechanisms where pumping the system enhances superconductivity. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Time-resolved X-ray diffraction studies of laser-induced acoustic wave propagation in bilayer metallic thin crystals

Energy Technology Data Exchange (ETDEWEB)

Er, Ali Oguz [Department of Physics and Astronomy, Western Kentucky University, Bowling Green, Kentucky 42101 (United States); Tang, Jau, E-mail: jautang@gate.sinica.edu.tw, E-mail: prentzepis@ece.tamu.edu [Research Center for Applied Sciences Academia Sinica, Taipei, Taiwan (China); Chen, Jie [Key Laboratory for Laser Plasmas (Ministry of Education) and Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Rentzepis, Peter M., E-mail: jautang@gate.sinica.edu.tw, E-mail: prentzepis@ece.tamu.edu [Department of Electrical and Computer Engineering, Texas A and M University, College Station, Texas 77843 (United States)

2014-09-07

Phonon propagation across the interface of a Cu/Ag(111) bilayer and transient lattice disorder, induced by a femtosecond 267 nm pulse, in Ag(111) crystal have been measured by means of time resolved X-ray diffraction. A “blast” force due to thermal stress induced by suddenly heated electrons is formed within two picoseconds after excitation and its “blast wave” propagation through the interface and Ag (111) crystal was monitored by the shift and broadening of the rocking curve, I vs. ω, as a function of time after excitation. Lattice disorder, contraction and expansion as well as thermal strain formation and wave propagation have also been measured. The experimental data and mechanism proposed are supported by theoretical simulations.

Time-resolved three-dimensional magnetic resonance velocity mapping of chronic thoracic aortic dissection. A preliminary investigation

International Nuclear Information System (INIS)

Amano, Yasuo; Sekine, Tetsuro; Tanaka, Keiji; Takagi, Ryo; Kumita, Shinichiro; Suzuki, Yuriko

2011-01-01

The blood flow patterns of chronic thoracic aortic dissection are complicated, and their clinical significance remains unknown. We evaluated the technical and clinical potentials of time-resolved 3-dimensional (3D) magnetic resonance (MR) velocity mapping for assessing these patterns. We used data collected from time-resolved 3D phase-contrast MR imaging of 16 patients with chronic thoracic aortic dissection to generate time-resolved 3D MR velocity mapping that included 3D streamline and path line. We investigated blood flow patterns of this disease in the mapping and compared them with the morphological changes of the patent false lumen. Time-resolved 3D MR velocity mapping visualized rapid flow at the entry and in the true lumen immediately distal to the entry. We observed slower helical or laminar flow in the patent false lumen. In patients with disease progression, slower helical flow following rapid entry jet collided with the outer wall of the false lumen and was also observed in a growing ulcer-like projection. We showed the potential of time-resolved 3D MR velocity mapping for visualizing pathologic flow patterns related to chronic thoracic aortic dissection. (author)

Quantitative analysis of time-resolved infrared stimulated luminescence in feldspars

DEFF Research Database (Denmark)

Pagonis, Vasilis; Ankjærgaard, Christina; Jain, Mayank

2016-01-01

Time-resolved infrared-stimulated luminescence (TR-IRSL) from feldspar samples is of importance in the field of luminescence dating, since it provides information on the luminescence mechanism in these materials. In this paper we present new analytical equations which can be used to analyze TR-IR...

Broad-band time-resolved near infrared spectroscopy in the TJ-II stellarator

Energy Technology Data Exchange (ETDEWEB)

Rodriguez, M.C.; Pastor, I.; Cal, E. de la; McCarthy, K.J. [Laboratorio Nacional de Fusion, CIEMAT, Madrid (Spain); Diaz, D. [Universidad Autonoma de Madrid, Dept Quimica Fisica Aplicada, Madrid (Spain)

2014-11-15

First experimental results on broad-band, time-resolved Near Infrared (NIR;here loosely defined as covering from 750 to 1650 nm) passive spectroscopy using a high sensitivity InGaAs detector are reported for the TJ-II Stellarator. Experimental set-up is described together with its main characteristics, the most remarkable ones being its enhanced NIR response, broadband spectrum acquisition in a single shot, and time-resolved measurements with up to 1.8 kHz spectral rate. Prospects for future work and more extended physics studies in this newly open spectral region in TJ-II are discussed. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Time-resolved laser-induced fluorescence system

Science.gov (United States)

Bautista, F. J.; De la Rosa, J.; Gallegos, F. J.

2006-02-01

Fluorescence methods are being used increasingly in the measurement of species concentrations in gases, liquids and solids. Laser induced fluorescence is spontaneous emission from atoms or molecules that have been excited by laser radiation. Here we present a time resolved fluorescence instrument that consists of a 5 μJ Nitrogen laser (337.1 nm), a sample holder, a quartz optical fiber, a spectrometer, a PMT and a PC that allows the measurement of visible fluorescence spectra (350-750 nm). Time response of the system is approximately 5 ns. The instrument has been used in the measurement of colored bond paper, antifreeze, diesel, cochineal pigment and malignant tissues. The data acquisition was achieved through computer control of a digital oscilloscope (using General Purpose Interface Bus GPIB) and the spectrometer via serial (RS232). The instrument software provides a graphic interface that lets make some data acquisition tasks like finding fluorescence spectra, and fluorescence lifetimes. The software was developed using the Lab-View 6i graphic programming package and can be easily managed in order to add more functions to it.

Theory of time-resolved inelastic x-ray diffraction

DEFF Research Database (Denmark)

Lorenz, Ulf; Møller, Klaus Braagaard; Henriksen, Niels Engholm

2010-01-01

Starting from a general theory of time-resolved x-ray scattering, we derive a convenient expression for the diffraction signal based on a careful analysis of the relevant inelastic scattering processes. We demonstrate that the resulting inelastic limit applies to a wider variety of experimental...... conditions than similar, previously derived formulas, and it directly allows the application of selection rules when interpreting diffraction signals. Furthermore, we present a simple extension to systems simultaneously illuminated by x rays and a laser beam....

Time resolved fluorescence of cow and goat milk powder

Science.gov (United States)

Brandao, Mariana P.; de Carvalho dos Anjos, Virgílio; Bell., Maria José V.

2017-01-01

Milk powder is an international dairy commodity. Goat and cow milk powders are significant sources of nutrients and the investigation of the authenticity and classification of milk powder is particularly important. The use of time-resolved fluorescence techniques to distinguish chemical composition and structure modifications could assist develop a portable and non-destructive methodology to perform milk powder classification and determine composition. This study goal is to differentiate milk powder samples from cows and goats using fluorescence lifetimes. The samples were excited at 315 nm and the fluorescence intensity decay registered at 468 nm. We observed fluorescence lifetimes of 1.5 ± 0.3, 6.4 ± 0.4 and 18.7 ± 2.5 ns for goat milk powder; and 1.7 ± 0.3, 6.9 ± 0.2 and 29.9 ± 1.6 ns for cow's milk powder. We discriminate goat and cow powder milk by analysis of variance using Fisher's method. In addition, we employed quadratic discriminant analysis to differentiate the milk samples with accuracy of 100%. Our results suggest that time-resolved fluorescence can provide a new method to the analysis of powder milk and its composition.

The electronic structure of clean and adsorbate-covered Bi2Se3: an angle-resolved photoemission study

DEFF Research Database (Denmark)

Bianchi, Marco; Hatch, Richard; Guan, Dandan

2012-01-01

Angle-resolved photoelectron spectroscopy is used for a detailed study of the electronic structure of the topological insulator Bi2Se3. Nominally stoichiometric and calcium-doped samples were investigated. The pristine surface shows the topological surface state in the bulk band gap. As time passes....... For a sufficiently strong band bending, additional states appear at the Fermi level. These are interpreted as quantized conduction band states. For large band bendings, these states are found to undergo a strong Rashba splitting. The formation of quantum well states is also observed for the valence band states......, the Dirac point moves to higher binding energies, indicating an increasingly strong downward bending of the bands near the surface. This time-dependent band bending is related to a contamination of the surface and can be accelerated by intentionally exposing the surface to carbon monoxide and other species...

Time-resolved lateral spin-caloric transport of optically generated spin packets in n-GaAs

Science.gov (United States)

Göbbels, Stefan; Güntherodt, Gernot; Beschoten, Bernd

2018-05-01

We report on lateral spin-caloric transport (LSCT) of electron spin packets which are optically generated by ps laser pulses in the non-magnetic semiconductor n-GaAs at K. LSCT is driven by a local temperature gradient induced by an additional cw heating laser. The spatio-temporal evolution of the spin packets is probed using time-resolved Faraday rotation. We demonstrate that the local temperature-gradient induced spin diffusion is solely driven by a non-equilibrium hot spin distribution, i.e. without involvement of phonon drag effects. Additional electric field-driven spin drift experiments are used to verify directly the validity of the non-classical Einstein relation for moderately doped semiconductors at low temperatures for near band-gap excitation.

Time-resolved X-ray transmission microscopy on magnetic microstructures; Zeitaufloesende Roentgentransmissionsmikroskopie an magnetischen Mikrostrukturen

Energy Technology Data Exchange (ETDEWEB)

Puzic, Aleksandar

2007-10-23

Three excitation schemes were designed for stroboscopic imaging of magnetization dynamics with time-resolved magnetic transmission X-ray microscopy (TR-MTXM). These techniques were implemented into two types of X-ray microscopes, namely the imaging transmission X-ray microscope (ITXM) and the scanning transmission X-ray microscope (STXM), both installed at the electron storage ring of the Advanced Light Source in Berkeley, USA. Circular diffraction gratings (Fresnel zone plates) used in both microscopes as focusing and imaging elements presently allow for lateral resolution down to 30 nm. Magnetic imaging is performed by using the X-ray magnetic circular dichroism (XMCD) as element specific contrast mechanism. The developed methods have been successfully applied to the experimental investigation of magnetization dynamics in ferromagnetic microstructures. A temporal resolution well below 100 ps was achieved. A conventional pump-probe technique was implemented first. The dynamic response of the magnetization excited by a broadband pulsed magnetic field was imaged spatially resolved using focused X-ray flashes. As a complementary method, the spatially resolved ferromagnetic resonance (SR-FMR) technique was developed for experimental study of magnetization dynamics in the frequency domain. As a third excitation mode, the burst excitation was implemented. The performance and efficiency of the developed methods have been demonstrated by imaging the local magnetization dynamics in laterally patterned ferromagnetic thin-film elements and three-layer stacks. The existence of multiple eigenmodes in the excitation spectra of ferromagnetic microstructures has been verified by using the pump-probe technique. Magnetostatic spin waves were selectively excited and detected with a time resolution of 50 ps using the SR-FMR technique. Thorough analysis of 20 in most cases independently prepared samples has verified that vortices which exhibit a low-amplitude switching of their core

Space and time resolved monitoring of airborne particulate matter in proximity of a traffic roundabout in Sweden

International Nuclear Information System (INIS)

Wilkinson, Kai E.; Lundkvist, Johanna; Netrval, Julia; Eriksson, Mats; Seisenbaeva, Gulaim A.; Kessler, Vadim G.

2013-01-01

Concerns over exposure to airborne particulate matter (PM) are on the rise. Currently monitoring of PM is done on the basis of interpolating a mass of PM by volume (μg/m 3 ) but has the drawback of not taking the chemical nature of PM into account. Here we propose a method of collecting PM at its emission source and employing automated analysis with scanning electron microscopy associated with EDS-analysis together with light scattering to discern the chemical composition, size distribution, and time and space resolved structure of PM emissions in a heavily trafficated roundabout in Sweden. Multivariate methods (PCA, ANOVA) indicate that the technogenic marker Fe follows roadside dust in spreading from the road, and depending on time and location of collection, a statistically significant difference can be seen, adding a useful tool to the repertoiré of detailed PM monitoring and risk assessment of local emission sources. Highlights: •PM monitoring analysis method of the chemical constituents of individual particles. •Automated analysis provides a large output of data concerning chemical nature of PM. •Multivariate statistical methods used to visualize the analysis. •Chemical nature of PM leads to a complete risk assessment of PM exposure. -- Automated SEM–EDS analysis of captured roadside PM at a traffic roundabout in Sweden displaying the time- and space-resolved chemical differences of the captured particles

Generation of pulsed far-infrared radiation and its application for far-infrared time-resolved spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Kondo, Yasuhiro [Tohoku Univ., Sendai (Japan). Faculty of Engineering

1996-07-01

So-called time-resolved spectroscopy technique has been used from old time as the means for studying the dynamic optical property, light-induced reaction and so on of matters. As an example, there is the method called pump and probe, and here, the wavelength of this probe light is the problem. If the object energy region is limited to about 0.1 eV, fast time-resolved spectroscopy is feasible relatively easily. However, energy region is extended to low energy region, the light source which is available as the pulsed probe light having sufficient intensity is limited. In this paper, the attempt of time-resolved spectroscopy utilizing coherent radiation, which has ended in failure, and the laser pulse-induced far-infrared radiation which can be utilized as new far-infrared probe light are reported. The reason why far-infrared radiation is used is explained. The attempt of time-resolved spectroscopy using NaCl crystals is reported on the equipment, the method of measuring absorption spectra and the results. Laser pulse-induced far-infrared radiation and the method of generating it are described. The multi-channel detector for far-infrared radiation which was made for trial is shown. (K.I.)

Angle-resolving time-of-flight electron spectrometer for near-threshold precision measurements of differential cross sections of electron-impact excitation of atoms and molecules

International Nuclear Information System (INIS)

Lange, M.; Matsumoto, J.; Setiawan, A.; Panajotovic, R.; Harrison, J.; Lower, J. C. A.; Newman, D. S.; Mondal, S.; Buckman, S. J.

2008-01-01

This article presents a new type of low-energy crossed-beam electron spectrometer for measuring angular differential cross sections of electron-impact excitation of atomic and molecular targets. Designed for investigations at energies close to excitation thresholds, the spectrometer combines a pulsed electron beam with the time-of-flight technique to distinguish between scattering channels. A large-area, position-sensitive detector is used to offset the low average scattering rate resulting from the pulsing duty cycle, without sacrificing angular resolution. A total energy resolution better than 150 meV (full width at half maximum) at scattered energies of 0.5-3 eV is achieved by monochromating the electron beam prior to pulsing it. The results of a precision measurement of the differential cross section for electron-impact excitation of helium, at an energy of 22 eV, are used to assess the sensitivity and resolution of the spectrometer

Direct determination of exciton wavefunction amplitudes by the momentum-resolved photo-electron emission experiment

Science.gov (United States)

Ohnishi, Hiromasa; Tomita, Norikazu; Nasu, Keiichiro

2018-03-01

We study conceptional problems of a photo-electron emission (PEE) process from a free exciton in insulating crystals. In this PEE process, only the electron constituting the exciton is suddenly emitted out of the crystal, while the hole constituting the exciton is still left inside and forced to be recoiled back to its original valence band. This recoil on the hole is surely reflected in the spectrum of the PEE with a statistical distribution along the momentum-energy curve of the valence band. This distribution is nothing but the square of the exciton wavefunction amplitude, since it shows how the electron and the hole are originally bound together. Thus, the momentum-resolved PEE can directly determine the exciton wavefunction. These problems are clarified, taking the Γ and the saddle point excitons in GaAs, as typical examples. New PEE experiments are also suggested.

Time-dependence hole and electron trapping effects in SIMOX buried oxides

International Nuclear Information System (INIS)

Boesch, H.E. Jr.; Taylor, T.L.; Hite, L.R.; Bailey, W.E.

1990-01-01

Back-channel threshold shift associated with the buried oxide layers of separation by implanted oxygen (SIMOX) and zone-melted recrystallization (ZMR) field-effect transistors (FETs) was measured following pulsed irradiation as a function of temperature and back-gate bias using a fast time-resolved I-V measurement technique. The SIMOX FETs showed large initial negative voltage shifts at 0.2 ms after irradiation followed by temperature- and bias-dependent additional negative shifts to 800s. Analysis and modeling of the results indicate efficient deep trapping of radiation-generated holes in the bulk of the oxide, substantial initial trapping of radiation-generated electrons in the oxide, and rapid removal of the trapped electrons by a thermal detrapping process. The ZMR FETs showed evidence of substantial trapping of holes alone in the oxide bulk

Mobile Charge Generation Dynamics in P3HT:PCBM Observed by Time-Resolved Terahertz Spectroscopy

DEFF Research Database (Denmark)

Cooke, D. G.; Krebs, Frederik C; Jepsen, Peter Uhd

2012-01-01

Ultra-broadband time-resolved terahertz spectroscopy is used to examine the sub-ps conductivity dynamics of a conjugated polymer bulk heterojunction film P3HT:PCBM. We directly observe mobile charge generation dynamics on a sub-100 fs time scale.......Ultra-broadband time-resolved terahertz spectroscopy is used to examine the sub-ps conductivity dynamics of a conjugated polymer bulk heterojunction film P3HT:PCBM. We directly observe mobile charge generation dynamics on a sub-100 fs time scale....

Mobile charge generation dynamics in P3HT: PCBM observed by time-resolved terahertz spectroscopy

DEFF Research Database (Denmark)

Cooke, D. G.; Krebs, Frederik C; Jepsen, Peter Uhd

2012-01-01

Ultra-broadband time-resolved terahertz spectroscopy is used to examine the sub-ps conductivity dynamics of a conjugated polymer bulk heterojunction film P3HT:PCBM. We directly observe mobile charge generation dynamics on a sub-100 fs time scale.......Ultra-broadband time-resolved terahertz spectroscopy is used to examine the sub-ps conductivity dynamics of a conjugated polymer bulk heterojunction film P3HT:PCBM. We directly observe mobile charge generation dynamics on a sub-100 fs time scale....

Proposed ultraviolet free-electron laser at Brookhaven National Laboratory: A source for time-resolved biochemical spectroscopy

International Nuclear Information System (INIS)

Johnson, E.D.; Sutherland, J.C.; Laws, W.R.

1992-01-01

Brookhaven National Laboratory is designing an ultraviolet free- electron laser (UV-FEL) user facility that will provide pico-second and sub-picosecond pulses of coherent ultraviolet radiation for wavelengths from 300 to 75 nm. Pulse width will be variable from abut 7 ps to ∼ 200 fs, with repetition rates as high as 10 4 Hz, single pulse energies > 1 mJ and hence peak pulse power >200 MW and average beam power > 10 W. The facility will be capable of ''pump-probe'' experiments utilizing the FEL radiation with: (1) synchronized auxiliary lasers, (2) a second, independently tunable FEL beam, or (3) broad-spectrum, high-intensity x-rays from the adjacent National Synchrotron Light Source. The UV-FEL consists of a high repetition rate recirculating superconducting linear accelerator which feeds pulses of electrons to two magnetic wigglers. Within these two devices, photons from tunable ''conventional'' laser would be frequency multiplied and amplified. By synchronously tuning the seed laser and modulating the energy of the electron beam, tuning of as much as 60% in wavelength is possible between alternating pulses supplied to different experimental stations, with Fourier transform limited resolution. Thus, up to four independent experiments may operate at one time, each with independent control of the wavelength and pulse duration. The UV-FEL will make possible new avenues of inquiry in time studies of diverse field including chemical, surface, and solid state physics, biology and materials science. The experimental area is scheduled to include a station dedicated to biological research. The complement of experimental and support facilities required by the biology station will be determined by the interests of the user community. 7 refs., 5 figs

Position- and time-resolved Stark broadening diagnostics of a non-thermal laser-induced plasma

International Nuclear Information System (INIS)

Liu, Hao; Truscott, Benjamin S; Ashfold, Michael N R

2016-01-01

We present an analysis of the Stark-broadened line shapes of silicon ions in a laser-induced plasma using a model constructed, without assuming local thermodynamic equilibrium (LTE), using a Druyvesteyn electron energy distribution function (EEDF). The method is applied to temporally and spatially resolved measurements of Si 2+ and Si 3+ emissions from a transient plasma expanding into vacuum, produced by 1064 nm, nanosecond pulsed laser ablation of a Si (1 0 0) target. The best-fitting simulated line shapes and the corresponding electron number densities and temperatures (or equivalently, Druyvesteyn average energies) are compared with those returned assuming LTE (i.e. for a Maxwellian EEDF). Non-thermal behavior is found to dominate at all but the very earliest stages of expansion close to the target surface, consistent with McWhirter’s criterion for the establishment of LTE. The Druyvesteyn EEDF always yields an equivalent or better model of the experimental measurements, and the observed increasingly strong departure from the Maxwellian case with time and distance from the ablation event highlights the essential invalidity of the LTE assumption for moderate-power, nanosecond laser-induced plasma expanding in vacuo. (paper)

Magneto-electronic properties and spin-resolved I-V curves of a Co/GeSe heterojunction diode: an ab initio study

Science.gov (United States)

Makinistian, Leonardo; Albanesi, Eduardo A.

2013-06-01

We present ab initio calculations of magnetoelectronic and transport properties of the interface of hcp Cobalt (001) and the intrinsic narrow-gap semiconductor germanium selenide (GeSe). Using a norm-conserving pseudopotentials scheme within DFT, we first model the interface with a supercell approach and focus on the spin-resolved densities of states and the magnetic moment (spin and orbital components) at the different atomic layers that form the device. We also report a series of cuts (perpendicular to the plane of the heterojunction) of the electronic and spin densities showing a slight magnetization of the first layers of the semiconductor. Finally, we model the device with a different scheme: using semiinfinite electrodes connected to the heterojunction. These latter calculations are based upon a nonequilibrium Green's function approach that allows us to explore the spin-resolved electronic transport under a bias voltage (spin-resolved I-V curves), revealing features of potential applicability in spintronics.

Intrinsic spin polarized electronic structure of CrO2 epitaxial film revealed by bulk-sensitive spin-resolved photoemission spectroscopy

International Nuclear Information System (INIS)

Fujiwara, Hirokazu; Sunagawa, Masanori; Kittaka, Tomoko; Terashima, Kensei; Wakita, Takanori; Muraoka, Yuji; Yokoya, Takayoshi

2015-01-01

We have performed bulk-sensitive spin-resolved photoemission spectroscopy in order to clarify the intrinsic spin-resolved electronic states of half-metallic ferromagnet CrO 2 . We used CrO 2 epitaxial films on TiO 2 (100), which shows a peak at 1 eV with a clear Fermi edge, consistent with the bulk-sensitive PES spectrum for CrO 2 . In spin-resolved spectra at 40 K, while the Fermi edge was observed in the spin up (majority spin) state, no states at the Fermi level (E F ) with an energy gap of 0.5 eV below E F were observed in the spin down (minority spin) state. At 300 K, the gap in the spin down state closes. These results are consistent with resistivity measurements and magnetic hysteresis curves of the fabricated CrO 2 film, constituting spectroscopic evidence for the half-metallicity of CrO 2 at low temperature and reducing the spin polarization at room temperature. We also discuss the electron correlation effects of Cr 3d

Technical note: Time-resolved immunofluorometric assay for growth hormone in ruminants

DEFF Research Database (Denmark)

Løvendahl, P.; Adamsen, J.; Lund, Regina Teresa

2003-01-01

for 4 h at 25degreesC. Plates were then washed six times, incubated for 5 to 10 min with 250 muL of enhancement solution, and fluorescence read with a time-resolved fluorometer. The sensitivity of the assay was 0.1 ng/mL, and the working range was 0.2 to 200 ng/mL. Recovery of quantitative amounts...

Time- and space-resolved light emission and spectroscopic research of the flashover plasma

Energy Technology Data Exchange (ETDEWEB)

Gleizer, J. Z.; Krasik, Ya. E. [Physics Department, Technion, Haifa 32000 (Israel); Leopold, J. [Department of Applied Physics, Rafael Laboratories, Box 2250, Haifa 31021 (Israel)

2015-02-21

The results of an experimental study of the evolution of surface flashover across the surface of an insulator in vacuum subject to a high-voltage pulse and the parameters of the flashover plasma are reported. For the system studied, flashover is always initiated at the cathode triple junctions. Using time-resolved framing photography of the plasma light emission the velocity of the light emission propagation along the surface of the insulator was found to be ∼2.5·10{sup 8} cm/s. Spectroscopic measurements show that the flashover is characterized by a plasma density of 2–4 × 10{sup 14} cm{sup −3} and neutral and electron temperatures of 2–4 eV and 1–3 eV, respectively, corresponding to a plasma conductivity of ∼0.2 Ω{sup −1} cm{sup −1} and a discharge current density of up to ∼10 kA/cm{sup 2}.

Time-Resolved Emittance Characterization of an Induction Linac Beam using Optical Transition Radiation

International Nuclear Information System (INIS)

Le Sage, G P

2002-01-01

An induction linac is used by Lawrence Livermore National Laboratory to perform radiographic testing at the Flash X-ray Radiography facility. Emittance characterization is important since x-ray spot size impacts the resolution of shadow-graphs. Due to the long pulse length, high current, and beam energy, emittance measurement using Optical Transition Radiation is an attractive alternative for reasons that will be described in the text. The utility of OTR-based emittance measurement has been well demonstrated for both RF and induction linacs. We describe the time-resolved emittance characterization of an induction linac electron beam. We have refined the optical collection system for the induction linac application, and have demonstrated a new technique for probing the divergence of a subset of the beam profile. The experimental apparatus, data reduction, and conclusions will be presented. Additionally, a new scheme for characterizing the correlation between beam divergence and spatial coordinates within the beam profile will be described

Time-Resolved Emittance Characterization of an Induction Linac Beam using Optical Transition Radiation

CERN Document Server

Le Sage, G P

2002-01-01

An induction linac is used by Lawrence Livermore National Laboratory to perform radiographic testing at the Flash X-ray Radiography facility. Emittance characterization is important since x-ray spot size impacts the resolution of shadow-graphs. Due to the long pulse length, high current, and beam energy, emittance measurement using Optical Transition Radiation is an attractive alternative for reasons that will be described in the text. The utility of OTR-based emittance measurement has been well demonstrated for both RF and induction linacs. We describe the time-resolved emittance characterization of an induction linac electron beam. We have refined the optical collection system for the induction linac application, and have demonstrated a new technique for probing the divergence of a subset of the beam profile. The experimental apparatus, data reduction, and conclusions will be presented. Additionally, a new scheme for characterizing the correlation between beam divergence and spatial coordinates within the b...

High resolution time- and 2-dimensional space-resolved x-ray imaging of plasmas at NOVA

International Nuclear Information System (INIS)

Landen, O.L.

1992-01-01

A streaked multiple pinhole camera technique, first used by P. Choi et al. to record time- and 2-D space-resolved soft X-ray images of plasma pinches, has been implemented on laser plasmas at NOVA. The instrument is particularly useful for time-resolved imaging of small sources ( 2.5 key imaging, complementing the existing 1--3 key streaked X-ray microscope capabilities at NOVA

Evaluating scintillator performance in time-resolved hard X-ray studies at synchrotron light sources.

Science.gov (United States)

Rutherford, Michael E; Chapman, David J; White, Thomas G; Drakopoulos, Michael; Rack, Alexander; Eakins, Daniel E

2016-05-01

The short pulse duration, small effective source size and high flux of synchrotron radiation is ideally suited for probing a wide range of transient deformation processes in materials under extreme conditions. In this paper, the challenges of high-resolution time-resolved indirect X-ray detection are reviewed in the context of dynamic synchrotron experiments. In particular, the discussion is targeted at two-dimensional integrating detector methods, such as those focused on dynamic radiography and diffraction experiments. The response of a scintillator to periodic synchrotron X-ray excitation is modelled and validated against experimental data collected at the Diamond Light Source (DLS) and European Synchrotron Radiation Facility (ESRF). An upper bound on the dynamic range accessible in a time-resolved experiment for a given bunch separation is calculated for a range of scintillators. New bunch structures are suggested for DLS and ESRF using the highest-performing commercially available crystal LYSO:Ce, allowing time-resolved experiments with an interframe time of 189 ns and a maximum dynamic range of 98 (6.6 bits).

Hexamethylcyclopentadiene: time-resolved photoelectron spectroscopy and ab initio multiple spawning simulations

DEFF Research Database (Denmark)

Wolf, T. J. A.; Kuhlman, Thomas Scheby; Schalk, O.

2014-01-01

comparing time-resolved photoelectron spectroscopy (TRPES) with ab initio multiple spawning (AIMS) simulations on the MS-MR-CASPT2 level of theory. We disentangle the relationship between two phenomena that dominate the immediate molecular response upon light absorption: a spectrally dependent delay...

Time-resolved MR angiography of the renal artery: morphology and perfusion

International Nuclear Information System (INIS)

Krause, U.J.; Pabst, T.; Koestler, H.; Helbig, C.; Kenn, W.; Hahn, D.

2002-01-01

Purpose: To prove the hypothesis that renal artery stenosis and changes in renal perfusion can be detected with contrast-enhanced time-resolved MR angiography in a single examination. Material and Methods: In 71 patients, 137 renal arteries and 14 accessory renal arteries were studied. The examinations were performed on a 1.5 T system. A T 1 -weighted gradient echo sequence with a temporal resolution of 7 s was used. Single dose of contrast material (0.1 mmol/kg Gd-DTPA) was injected with a power injector with a flow rate of 2 ml/s. Criterion for the assessment of renal perfusion was the slope ratio of the signal intensity time curve in both kidneys. Results: Forty renal artery stenoses and one occlusion of a renal artery were detected. In 48 kidneys (35%) segmental arteries were evaluated. The accuracy of the slope ratio (limit value 0.75) concerning the detection of unilateral renal artery stenosis was 92.6% (sensitivity 75%, specificity 95.7%). Conclusion: Time-resolved MR angiography can detect changes in renal perfusion in patients with unilateral renal artery stenosis. (orig.) [de

Time-resolved ultraviolet laser-induced breakdown spectroscopy for organic material analysis

Energy Technology Data Exchange (ETDEWEB)

Baudelet, Matthieu; Boueri, Myriam [Laboratoire de Spectrometrie Ionique et Moleculaire, Universite Claude Bernard Lyon 1, UMR CNRS 5579, 43, Bd. du 11 Novembre 1918, F-69622 Villeurbanne Cedex (France); Yu Jin [Laboratoire de Spectrometrie Ionique et Moleculaire, Universite Claude Bernard Lyon 1, UMR CNRS 5579, 43, Bd. du 11 Novembre 1918, F-69622 Villeurbanne Cedex (France)], E-mail: jin.yu@lasim.univ-lyon1.fr; Mao, Samuel S; Piscitelli, Vincent; Xianglei, Mao; Russo, Richard E [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2007-12-15

Ultraviolet pulses (266 nm) delivered by a quadrupled Nd:YAG laser were used to analyze organic samples with laser-induced breakdown spectroscopy (LIBS). We present characteristics of the spectra obtained from organic samples with special attentions on the emissions of organic elements, O and N, and molecular bonds CN. The choice of these atomic or molecular species is justified on one hand, by the importance of these species to specify organic or biological materials; and on the other hand by the possible interferences with ambient air when laser ablation takes place in the atmosphere. Time-resolved LIBS was used to determine the time-evolution of line intensity emitted from these species. We demonstrate different kinetic behaviors corresponding to different origins of emitters: native atomic or molecular species directly vaporized from the sample or those generated through dissociation or recombination due to interaction between laser-induced plasma and air molecules. Our results show the ability of time-resolved UV-LIBS for detection and identification of native atomic or molecular species from an organic sample.

The time resolved SBS and SRS research in heavy water and its application in CARS

Science.gov (United States)

Liu, Jinbo; Gai, Baodong; Yuan, Hong; Sun, Jianfeng; Zhou, Xin; Liu, Di; Xia, Xusheng; Wang, Pengyuan; Hu, Shu; Chen, Ying; Guo, Jingwei; Jin, Yuqi; Sang, Fengting

2018-05-01

We present the time-resolved character of stimulated Brillouin scattering (SBS) and backward stimulated Raman scattering (BSRS) in heavy water and its application in Coherent Anti-Stokes Raman Scattering (CARS) technique. A nanosecond laser from a frequency-doubled Nd: YAG laser is introduced into a heavy water cell, to generate SBS and BSRS beams. The SBS and BSRS beams are collinear, and their time resolved characters are studied by a streak camera, experiment show that they are ideal source for an alignment-free CARS system, and the time resolved property of SBS and BSRS beams could affect the CARS efficiency significantly. By inserting a Dye cuvette to the collinear beams, the time-overlapping of SBS and BSRS could be improved, and finally the CARS efficiency is increased, even though the SBS energy is decreased. Possible methods to improve the efficiency of this CARS system are discussed too.

Femtosecond time-resolved vibrational SFG spectroscopy of CO/Ru( 0 0 1 )

Science.gov (United States)

Hess, Ch.; Wolf, M.; Roke, S.; Bonn, M.

2002-04-01

Vibrational sum-frequency generation (SFG) employing femtosecond infrared (IR) laser pulses is used to study the dynamics of the C-O stretch vibration on Ru(0 0 1). Time-resolved measurements of the free induction decay (FID) of the IR-polarization for 0.33 ML CO/Ru(0 0 1) exhibit single exponential decays over three decades corresponding to dephasing times of T2=1.94 ps at 95 K and T2=1.16 ps at 340 K. This is consistent with pure homogeneous broadening due to anharmonic coupling with the thermally activated low-frequency dephasing mode together with a contribution from saturation of the IR transition. In pump-probe SFG experiments using a strong visible (VIS) pump pulse the perturbation of the FID leads to transient line shifts even at negative delay times, i.e. when the IR-VIS SFG probe pair precedes the pump pulse. Based on an analysis of the time-dependent polarization we discuss the influence of the perturbed FID on time-resolved SFG spectra. We investigate how coherent effects affect the SFG spectra and we examine the time resolution in these experiments, in particular in dependence of the dephasing time.

A review of the analysis of complex time-resolved fluorescence anisotropy data

International Nuclear Information System (INIS)

Smith, Trevor A; Ghiggino, Kenneth P

2015-01-01

Time-resolved fluorescence anisotropy measurements (TRAMs) are widely used to probe the dynamics of the various processes that can lead to the depolarisation of emission following photoselection by polarised excitation. The most commonly investigated of these emission depolarising phenomena is molecular rotational motion, but TRAMs are very useful for determining the kinetics of a host of other processes. In this paper we review several examples for which we have observed in our laboratories initially unexpectedly complex temporal behaviour of the time-resolved fluorescence anisotropy signal from relatively ‘simple’ chemical systems. In certain circumstances the anisotropy (i) decays on timescales when superficially it might be thought it should remain constant, (ii) shows marked ‘dip and rise’ behaviour in its intensity, or (iii) can change sign as the anisotropy evolves in time. Fundamentally simple processes, including molecular rotational motion, energy migration and excited state photophysics, can cause such behaviour. (topical review)

Time resolved x-ray photography of a dense plasma focus

International Nuclear Information System (INIS)

Burnett, J.C.; Meyer, J.; Rankin, G.

1977-01-01

The temporal development of the hot plasma in a dense plasma focus is studied by x-ray streak photography of approximately 2 ns resolution time. It is shown that initially a uniform x-ray emitting pinch plasma is formed which subsequently cools down until x-ray emission stops after approximately 50 ns. At a time of around 100 ns after initial x-ray emission coinciding with the break-up time of the pinch a second burst of x-rays is observed coming from small localized regions. The observations are compared with results obtained from time-resolved shadow and schlieren photography of a similar dense focus discharge. (author)

Diffraction and microscopy with attosecond electron pulse trains

Science.gov (United States)

Morimoto, Yuya; Baum, Peter

2018-03-01

Attosecond spectroscopy1-7 can resolve electronic processes directly in time, but a movie-like space-time recording is impeded by the too long wavelength ( 100 times larger than atomic distances) or the source-sample entanglement in re-collision techniques8-11. Here we advance attosecond metrology to picometre wavelength and sub-atomic resolution by using free-space electrons instead of higher-harmonic photons1-7 or re-colliding wavepackets8-11. A beam of 70-keV electrons at 4.5-pm de Broglie wavelength is modulated by the electric field of laser cycles into a sequence of electron pulses with sub-optical-cycle duration. Time-resolved diffraction from crystalline silicon reveals a propagates in space and time. This unification of attosecond science with electron microscopy and diffraction enables space-time imaging of light-driven processes in the entire range of sample morphologies that electron microscopy can access.

Photodissociation of aligned CH3I and C6H3F2I molecules probed with time-resolved Coulomb explosion imaging by site-selective extreme ultraviolet ionization.

Science.gov (United States)

Amini, Kasra; Savelyev, Evgeny; Brauße, Felix; Berrah, Nora; Bomme, Cédric; Brouard, Mark; Burt, Michael; Christensen, Lauge; Düsterer, Stefan; Erk, Benjamin; Höppner, Hauke; Kierspel, Thomas; Krecinic, Faruk; Lauer, Alexandra; Lee, Jason W L; Müller, Maria; Müller, Erland; Mullins, Terence; Redlin, Harald; Schirmel, Nora; Thøgersen, Jan; Techert, Simone; Toleikis, Sven; Treusch, Rolf; Trippel, Sebastian; Ulmer, Anatoli; Vallance, Claire; Wiese, Joss; Johnsson, Per; Küpper, Jochen; Rudenko, Artem; Rouzée, Arnaud; Stapelfeldt, Henrik; Rolles, Daniel; Boll, Rebecca

2018-01-01

We explore time-resolved Coulomb explosion induced by intense, extreme ultraviolet (XUV) femtosecond pulses from a free-electron laser as a method to image photo-induced molecular dynamics in two molecules, iodomethane and 2,6-difluoroiodobenzene. At an excitation wavelength of 267 nm, the dominant reaction pathway in both molecules is neutral dissociation via cleavage of the carbon-iodine bond. This allows investigating the influence of the molecular environment on the absorption of an intense, femtosecond XUV pulse and the subsequent Coulomb explosion process. We find that the XUV probe pulse induces local inner-shell ionization of atomic iodine in dissociating iodomethane, in contrast to non-selective ionization of all photofragments in difluoroiodobenzene. The results reveal evidence of electron transfer from methyl and phenyl moieties to a multiply charged iodine ion. In addition, indications for ultrafast charge rearrangement on the phenyl radical are found, suggesting that time-resolved Coulomb explosion imaging is sensitive to the localization of charge in extended molecules.

Static and time-resolved mid-infrared spectroscopy of Hg0.95Cd0.05Cr2Se4 spinel.

Science.gov (United States)

Barsaume, S; Telegin, A V; Sukhorukov, Yu P; Stavrias, N; Fedorov, V A; Menshchikova, T K; Kimel, A V

2017-08-16

Static and time-resolved mid-infrared spectroscopy of ferromagnetic single crystal Hg 0.95 Cd 0.05 Cr 2 Se 4 was performed below the absorption edge, in order to reveal the origin of the electronic transitions contributing to the magneto-optical properties of this material. The mid-infrared spectroscopy reveals a strong absorption peak around 0.236 eV which formerly was assigned to a transition within the selenide-chromium complexes ([Formula: see text] Se -Cr 2+ ). To reveal the sensitivity of the transition to the magnetic order, we performed the studies in a temperature range across the Curie temperature and magnetic fields across the value at which the saturation of ferromagnetic magnetization occurs. Despite the fact that the Curie temperature of this ferromagnetic semiconductor is around 107 K, the intensity of the mid-infrared transition reduces substantially increasing the temperature, so that already at 70 K the absorption peak is hardly visible. Such a dramatic decrease of the oscillator strength is observed simultaneously with the strong red-shift of the absorption edge in the magnetic semiconductor. Employing a time-resolved pump-and-probe technique enabled us to determine the lifetime of the electrons in the excited state of this optical transition. In the temperature range from 7 K to 80 K, the lifetime changes from 3 ps to 6 ps. This behavior agrees with the phenomenon of giant oscillator strength described earlier for weakly bound excitons in nonmagnetic semiconductors.

Time-resolved spectroscopy of laser-induced breakdown in water

Science.gov (United States)

Thomas, Robert J.; Hammer, Daniel X.; Noojin, Gary D.; Stolarski, David J.; Rockwell, Benjamin A.; Roach, William P.

1996-05-01

Laser pulses of 60-ps and 80-ps at a wavelength of 532-nm and 1064-nm respectively were used to produce laser induced breakdown in triple-distilled water. The resulting luminescent flash from the plasma was captured with an imaging spectrograph coupled to a streak camera with a 5-ps time resolution. The wavelength range was 350 to 900-nm. We present the resulting experimental data which gives plasma duration and time-resolved spectral information. Plasma temperature is also computed from the data. All parameters are presented at a pulse energy of 1-mJ and are compared with time-integrated spectra at the same pulse duration and at 5 to 7-ns pulse duration in a similar energy range.

Probing Photoinduced Structural Phase Transitions by Fast or Ultra-Fast Time-Resolved X-Ray Diffraction

Science.gov (United States)

Cailleau, Hervé Collet, Eric; Buron-Le Cointe, Marylise; Lemée-Cailleau, Marie-Hélène Koshihara, Shin-Ya

A new frontier in the field of structural science is the emergence of the fast and ultra-fast X-ray science. Recent developments in time-resolved X-ray diffraction promise direct access to the dynamics of electronic, atomic and molecular motions in condensed matter triggered by a pulsed laser irradiation, i.e. to record "molecular movies" during the transformation of matter initiated by light pulse. These laser pump and X-ray probe techniques now provide an outstanding opportunity for the direct observation of a photoinduced structural phase transition as it takes place. The use of X-ray short-pulse of about 100ps around third-generation synchrotron sources allows structural investigations of fast photoinduced processes. Other new X-ray sources, such as laser-produced plasma ones, generate ultra-short pulses down to 100 fs. This opens the way to femtosecond X-ray crystallography, but with rather low X-ray intensities and more limited experimental possibilities at present. However this new ultra-fast science rapidly progresses around these sources and new large-scale projects exist. It is the aim of this contribution to overview the state of art and the perspectives of fast and ultra-fast X-ray scattering techniques to study photoinduced phase transitions (here, the word ultra-fast is used for sub-picosecond time resolution). In particular we would like to largely present the contribution of crystallographic methods in comparison with optical methods, such as pump-probe reflectivity measurements, the reader being not necessary familiar with X-ray scattering. Thus we want to present which type of physical information can be obtained from the positions of the Bragg peaks, their intensity and their shape, as well as from the diffuse scattering beyond Bragg peaks. An important physical feature is to take into consideration the difference in nature between a photoinduced phase transition and conventional homogeneous photoinduced chemical or biochemical processes where

Ultrafast time-resolved spectroscopy of lead halide perovskite films

Science.gov (United States)

Idowu, Mopelola A.; Yau, Sung H.; Varnavski, Oleg; Goodson, Theodore

2015-09-01

Recently, lead halide perovskites which are organic-inorganic hybrid structures, have been discovered to be highly efficient as light absorbers. Herein, we show the investigation of the excited state dynamics and emission properties of non-stoichiometric precursor formed lead halide perovskites grown by interdiffusion method using steady-state and time-resolved spectroscopic measurements. The influence of the different ratios of the non-stoichiometric precursor solution was examined. The observed photoluminescence properties were correlated with the femtosecond transient absorption measurements.

Time resolved Thomson scattering measurements on a high pressure mercury lamp

NARCIS (Netherlands)

Vries, de N.; Zhu, Xiao-Yan; Kieft, E.R.; Mullen, van der J.J.A.M.

2005-01-01

Time resolved Thomson scattering (TS) measurements have been performed on an ac driven high pressure mercury lamp. For this high intensity discharge (HID) lamp, TS is coherent and a coherent fitting routine, including rotational Raman calibration, was used to determine ne and Te from the measured

Photon-Counting Arrays for Time-Resolved Imaging

Directory of Open Access Journals (Sweden)

I. Michel Antolovic

2016-06-01

Full Text Available The paper presents a camera comprising 512 × 128 pixels capable of single-photon detection and gating with a maximum frame rate of 156 kfps. The photon capture is performed through a gated single-photon avalanche diode that generates a digital pulse upon photon detection and through a digital one-bit counter. Gray levels are obtained through multiple counting and accumulation, while time-resolved imaging is achieved through a 4-ns gating window controlled with subnanosecond accuracy by a field-programmable gate array. The sensor, which is equipped with microlenses to enhance its effective fill factor, was electro-optically characterized in terms of sensitivity and uniformity. Several examples of capture of fast events are shown to demonstrate the suitability of the approach.

A high-order time-accurate interrogation method for time-resolved PIV

International Nuclear Information System (INIS)

Lynch, Kyle; Scarano, Fulvio

2013-01-01

A novel method is introduced for increasing the accuracy and extending the dynamic range of time-resolved particle image velocimetry (PIV). The approach extends the concept of particle tracking velocimetry by multiple frames to the pattern tracking by cross-correlation analysis as employed in PIV. The working principle is based on tracking the patterned fluid element, within a chosen interrogation window, along its individual trajectory throughout an image sequence. In contrast to image-pair interrogation methods, the fluid trajectory correlation concept deals with variable velocity along curved trajectories and non-zero tangential acceleration during the observed time interval. As a result, the velocity magnitude and its direction are allowed to evolve in a nonlinear fashion along the fluid element trajectory. The continuum deformation (namely spatial derivatives of the velocity vector) is accounted for by adopting local image deformation. The principle offers important reductions of the measurement error based on three main points: by enlarging the temporal measurement interval, the relative error becomes reduced; secondly, the random and peak-locking errors are reduced by the use of least-squares polynomial fits to individual trajectories; finally, the introduction of high-order (nonlinear) fitting functions provides the basis for reducing the truncation error. Lastly, the instantaneous velocity is evaluated as the temporal derivative of the polynomial representation of the fluid parcel position in time. The principal features of this algorithm are compared with a single-pair iterative image deformation method. Synthetic image sequences are considered with steady flow (translation, shear and rotation) illustrating the increase of measurement precision. An experimental data set obtained by time-resolved PIV measurements of a circular jet is used to verify the robustness of the method on image sequences affected by camera noise and three-dimensional motions. In

Time-resolved UV-excited microarray reader for fluorescence energy transfer (FRET) measurements

Science.gov (United States)

Orellana, Adelina; Hokkanen, Ari P.; Pastinen, Tomi; Takkinen, Kristina; Soderlund, Hans

2001-05-01

Analytical systems based on immunochemistry are largely used in medical diagnostics and in biotechnology. There is a significant pressure to develop the present assay formats to become easier to use, faster, and less reagent consuming. Further developments towards high density array--like multianalyte measurement systems would be valuable. To this aim we have studied the applicability of fluorescence resonance energy transfer and time-resolved fluorescence resonance energy transfer in immunoassays on microspots and in microwells. We have used engineered recombinant antibodies detecting the pentameric protein CRP as a model analyte system, and tested different assay formats. We describe also the construction of a time-resolved scanning epifluorometer with which we could measure the FRET interaction between the slow fluorescence decay from europium chelates and its energy transfer to the rapidly decaying fluorophore Cy5.

Size effects in van der Waals clusters studied by spin and angle-resolved electron spectroscopy and multi-coincidence ion imaging

International Nuclear Information System (INIS)

Rolles, D; Pesic, Z D; Zhang, H; Bilodeau, R C; Bozek, J D; Berrah, N

2007-01-01

We have studied the valence and inner-shell photoionization of free rare-gas clusters by means of angle and spin resolved photoelectron spectroscopy and momentum resolving electron-multi-ion coincidence spectroscopy. The electron measurements probe the evolution of the photoelectron angular distribution and spin polarization parameters as a function of photon energy and cluster size, and reveal a strong cluster size dependence of the photoelectron angular distributions in certain photon energy regions. In contrast, the spin polarization parameter of the cluster photoelectrons is found to be very close to the atomic value for all covered photon energies and cluster sizes. The ion imaging measurements, which probe the fragmentation dynamics of multiply charged van der Waals clusters, also exhibit a pronounced cluster size dependence

Decay time shortening of fluorescence from donor-acceptor pair proteins using ultrafast time-resolved fluorescence resonance energy transfer spectroscopy

International Nuclear Information System (INIS)

Baba, Motoyoshi; Suzuki, Masayuki; Ganeev, Rashid A.; Kuroda, Hiroto; Ozaki, Tsuneyuki; Hamakubo, Takao; Masuda, Kazuyuki; Hayashi, Masahiro; Sakihama, Toshiko; Kodama, Tatsuhiko; Kozasa, Tohru

2007-01-01

We improved an ultrafast time-resolved fluorescence resonance energy transfer (FRET) spectroscopy system and measured directly the decrease in the fluorescence decay time of the FRET signal, without any entanglement of components in the picosecond time scale from the donor-acceptor protein pairs (such as cameleon protein for calcium ion indicator, and ligand-activated GRIN-Go proteins pair). The drastic decrease in lifetime of the donor protein fluorescence under the FRET condition (e.g. a 47.8% decrease for a GRIN-Go protein pair) proves the deformation dynamics between donor and acceptor fluorescent proteins in an activated state of a mixed donor-acceptor protein pair. This study is the first clear evidence of physical contact of the GRIN-Go proteins pair using time-resolved FRET system. G protein-coupled receptors (GPCRs) are the most important protein family for the recognition of many chemical substances at the cell surface. They are the targets of many drugs. Simultaneously, we were able to observe the time-resolved spectra of luminous proteins at the initial stage under the FRET condition, within 10 ns from excitation. This new FRET system allows us to trace the dynamics of the interaction between proteins at the ligand-induced activated state, molecular structure change and combination or dissociation. It will be a key technology for the development of protein chip technology

Development of a fast pixel array detector for use in microsecond time-resolved x-ray diffraction

International Nuclear Information System (INIS)

Barna, S.L.; Gruner, S.M.; Shepherd, J.A.

1995-01-01

A large-area pixel x-ray detector is being developed to collect eight successive frames of wide dynamic range two-dimensional images at 200kHz rates. Such a detector, in conjunction with a synchrotron radiation x-ray source, will enable time-resolved x-ray studies of proteins and other materials on time scales which have previously been inaccessible. The detector will consist of an array of fully-depleted 150 micron square diodes connected to a CMOS integrated electronics layer with solder bump-bonding. During each framing period, the current resulting from the x-rays stopped in the diodes is integrated in the electronics layer, and then stored in one of eight storage capacitors underneath the pixel. After the last frame, the capacitors are read out at standard data transmission rates. The detector has been designed for a well-depth of at least 10,000 x-rays (at 20keV), and a noise level of one x-ray. Ultimately, the authors intend to construct a detector with over one million pixels (1024 by 1024). They present the results of their development effort and various features of the design. The electronics design is discussed, with special attention to the performance requirements. The choice and design of the detective diodes, as they relate to x-ray stopping power and charge collection, are presented. An analysis of various methods of bump bonding is also presented. Finally, the authors discuss the possible need for a radiation-blocking layer, to be placed between the electronics and the detective layer, and various methods they have pursued in the construction of such a layer

Time-resolved luminescence from quartz: An overview of contemporary developments and applications

Energy Technology Data Exchange (ETDEWEB)

Chithambo, M.L., E-mail: m.chithambo@ru.ac.za [Department of Physics and Electronics, Rhodes University, PO BOX 94, Grahamstown 6140 (South Africa); Ankjærgaard, C. [Soil Geography and Landscape Group, Wageningen University Netherlands Centre for Luminescence Dating, Droevendaalsesteeg 3, 6708 PB Wageningen, The Netherlands (Netherlands); Pagonis, V. [McDaniel College, Physics Department, Westminster, MD 21157 (United States)

2016-01-15

Time-resolved optical stimulation of luminescence has become established as a key method for measurement of optically stimulated luminescence from quartz, feldspar and α-Al{sub 2}O{sub 3}:C, all materials of interest in dosimetry. The aim of time-resolved optical stimulation is to separate in time the stimulation and emission of luminescence. The luminescence is stimulated from a sample using a brief light pulse and the emission monitored during stimulation in the presence of scattered stimulating light or after pulsing, over photomultiplier noise only. Although the use of the method in retrospective dosimetry has been somewhat limited, the technique has been successfully applied to study mechanisms in the processes leading up to luminescence emission. The main means for this has been the temperature dependence of the luminescence intensity as well as the luminescence lifetimes determined from time-resolved luminescence spectra. In this paper we review some key developments in theory and applications to quartz including methods of evaluating lifetimes, techniques of evaluating kinetic parameters using both the dependence of luminescence intensity and lifetime on measurement temperature, and of lifetimes on annealing temperature. We then provide an overview of some notable applications such as separation of quartz signals from a quartz–feldspar admixture and the utility of the dynamic throughput, a measure of luminescence measured as a function of the pulse width. The paper concludes with some suggestions of areas where further exploration would advance understanding of dynamics of luminescence in quartz and help address some outstanding problems in its application.

A system for time-resolved x-ray diffraction and its application to muscle contraction

International Nuclear Information System (INIS)

Amemiya, Yoshiyuki; Hashizume, Hiroo.

1979-01-01

A data-collection system has been built which permits time-resolved studies of X-ray diffraction diagrams obtained from contracting muscle on millisecond time scale. The system consists of a linear delay-line position sensitive proportional counter (PSPC), a special data transfer unit and an on-line computer. The PSPC used with a mirror-monochromator camera can detect equatorial reflections from stimulated muscle in a total exposure time of a few seconds. Time-resolved data-collection is achieved by stimulating muscle at a regular time interval, dividing a complete cycle of muscle contraction into many successive time slices and accumulating in computer memory X-ray data for each time slice from many repeated cycles of stimulation. The performances of the system have been demonstrated by recording equatorial reflections from frog skeletal muscle during isometric and isotonic twitch with a time resolution of 25 ms. (author)

Life-time resolved emission spectra in CdI2 crystals

International Nuclear Information System (INIS)

Kawabata, Seiji; Nakagawa, Hideyuki

2007-01-01

The emission spectrum of CdI 2 is composed of ultraviolet (UV), green (G) and yellow (Y and Y') bands peaking at 3.38, 2.50, 2.16 and 2.25 eV, respectively. In order to determine the initial states of the Y- and G-luminescence, decay curves have been measured at 6 and 80 K by varying emission energy. The observed decay curves are composed of two or three exponential components. These decay components were named τ 1 , τ 2 , τ 3 , τ 3' and τ 4 . The emission spectrum for each decay component, i.e., the life-time resolved emission spectrum, was constructed from the observed decay curves. At 6 K, three bands at 2.12, 2.49 and 2.64 eV are obtained for τ 1 , τ 2 and τ 3 components, respectively. At 80 K, a dominant band for the τ 4 component and a weak band for the τ 3' component appear on the same energy position at 2.25 eV. The origin of each emission band in the life-time resolved emission spectra will be briefly discussed

The use of angle resolved electron and photon stimulated desorption for the determination of molecular structure at surfaces

International Nuclear Information System (INIS)

Madey, T.E.; Stockbauer, R.

1983-01-01

A brief review of recent data related to the use of angle-resolved electron stimulated desorption and photon stimulated desorption in determining the structures of molecules at surfaces is made. Examples include a variety of structural assignments based on ESIAD (electron stimulated desorption ion angular distributions), the observation of short-range local ordering effects induced in adsorbed molecules by surface impurities, and the application of photon stimulated desorption to both ionic and covalent adsorbate systems. (Author) [pt

Observation of a Slater-type metal-to-insulator transition in Sr$_2$IrO$_4$ from time-resolved photo-carrier dynamics

OpenAIRE

Hsieh, D.; Mahmood, F.; Torchinsky, D. H.; Cao, G.; Gedik, N.

2012-01-01

We perform a time-resolved optical study of Sr$_2$IrO$_4$ to understand the influence of magnetic ordering on the low energy electronic structure of a strongly spin-orbit coupled $J_{eff}$=1/2 Mott insulator. By studying the recovery dynamics of photo-carriers excited across the Mott gap, we find that upon cooling through the N\\'{e}el temperature $T_N$ the system evolves continuously from a metal-like phase with fast ($\\sim$50 fs) and excitation density independent relaxation dynamics to a ga...

Electronic structure of superconducting Bi2212 crystal by angle resolved ultra violet photoemission

International Nuclear Information System (INIS)

Saini, N.L.; Shrivastava, P.; Garg, K.B.

1993-01-01

The electronic structure of a high quality superconducting Bi 2 Sr 2 CaCu 2 Osub(8+δ) (Bi2212) single crystal is studied by angle resolved ultra violet photoemission (ARUPS) using He I (21.2 eV). Our results appear to show two bands crossing the Fermi level in ΓX direction of the Brillouin zone as reported by Takahashi et al. The bands at higher binding energy do not show any appreciable dispersion. The nature of the states near the Fermi level is discussed and the observed band structure is compared with the band structure calculations. (author)

Time-resolved measurements of the focused ion beams on PBFA II

International Nuclear Information System (INIS)

Mix, L.P.; Stygar, W.A.; Leeper, R.J.; Maenchen, J.E.; Wenger, D.F.

1992-01-01

A time-resolved camera has been developed to image the intense ion beam focus on PBFA II. Focused ions from a sector of the ion diode are Rutherford scattered from a thin gold foil on the diode axis and pinhole imaged onto an array of up to 49 PIN detectors to obtain the spatially and temporally resolved images. The signals from these detectors are combined to provide a movie of the beam focus with a time resolution of about 3 ns and a spatial resolution of 2 mm over a 12 mm field of view. Monte Carlo simulations of the camera response are used with the measured ion energy to account for the time-of-flight dispersion of the beam and to convert the recorded signals to an intensity. From measurements on an 81 degree sector of the diode, average intensities on a 6 mm sphere of about 5 TW/cm 2 and energies approaching 80 kJ/cm 2 are calculated for standard proton diodes. Corresponding numbers for a lithium diode are less than those measured with protons. The details of the analysis and image reconstruction will be presented along with scaled images from recent ion focusing experiments

Time-resolved tunable diode laser absorption spectroscopy of pulsed plasma

Czech Academy of Sciences Publication Activity Database

Adámek, Petr; Olejníček, Jiří; Čada, Martin; Kment, Š.; Hubička, Zdeněk

2013-01-01

Roč. 38, č. 14 (2013), s. 2428-2430 ISSN 0146-9592 R&D Projects: GA MŠk LH12045; GA ČR(CZ) GAP205/11/0386; GA MŠk LD12002; GA MŠk LH12043 Institutional support: RVO:68378271 Keywords : diode laser s * plasma diagnostics * absorption spectroscopy * time resolved Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.179, year: 2013

Imaging buried organic islands by spatially resolved ballistic electron emission spectroscopy

International Nuclear Information System (INIS)

Goh, Kuan Eng J; Bannani, A; Troadec, C

2008-01-01

The well-known Au/n-Si(111) Schottky interface is modified by a discontinuous pentacene film (∼1.5 nm thick) and studied using spatially resolved ballistic electron emission spectroscopy (BEES). The pentacene film introduced subtle changes to the interface which cannot be definitively detected by current-voltage measurements or a standard BEES analysis of the barrier height. In contrast, analyzing the BEES results in a dual-parameter (transmission attenuation and barrier height) space allows the effect of the pentacene film on the Au/n-Si(111) interface to be clearly demonstrated. We found that the pentacene film behaves like a tunneling barrier and increases the distribution of local barrier heights with a tendency toward lower values. Our results highlight the potential of the dual-parameter BEES analysis for understanding local interface modification by molecules.

Time-Resolved Studies of Laser-Induced Phase Transitions in Gallium Arsenide

Science.gov (United States)

Siegal, Yakir

This thesis describes a series of time-resolved experiments of the linear and nonlinear optical properties of GaAs during laser-induced phase transitions. The first set of experiments consists of a direct determination of the behavior of the linear dielectric constant at photon energies of 2.2 eV and 4.4 eV following excitation of the sample with 1.9-eV, 70-fs laser pulses spanning a fluence range from 0 to 2.5 kJ/m^2. The results from this set of experiments were used to extract the behavior of the second-order optical susceptibility from second-harmonic generation measurements made under identical excitation conditions. These experiments are unique because they provide explicit information on the behavior of intrinsic material properties--the linear and nonlinear optical susceptibilities--during laser-induced phase transitions in semiconductors without the ambiguities in interpretation that are generally inherent in reflectivity and second-harmonic generation measurements. The dielectric constant data indicate a drop in the average bonding-antibonding splitting of GaAs following the laser pulse excitation. This behavior leads to a collapse of the band-gap on a picosecond time scale for excitation at fluences near the damage threshold of 1.0 kJ/m ^2 and even faster at higher excitation fluences. The changes in the electronic band structure result from a combination of electronic screening by the excited free carriers and structural deformation of the lattice caused by the destabilization of the covalent bonds. The behavior of the second-order susceptibility shows that the material loses long-range order before the average bonding-antibonding splitting, which is more sensitive to short-range structure, changes significantly. Loss of long-range order and a drop of more than 2 eV in the average bonding-antibonding splitting are seen even at fluences below the damage threshold, a regime in which the laser-induced changes are reversible.

Time-resolved magnetic field effects in exciplex systems under X-irradiation

International Nuclear Information System (INIS)

Anishchik, S.V.; Lavrik, N.L.

1988-01-01

The presence of exciplex systems after X-irradiation of pyrene and N,N-diethylaniline in methanol as well as the influence of the applied magnetic field on exciplex fluorescence was registered using a time-resolving method. The experimental results confirmed the hypothesis on exciplex emergence in the system under study. (author)

Time-resolved measurements of supersonic fuel sprays using synchrotron X-rays.

Science.gov (United States)

Powell, C F; Yue, Y; Poola, R; Wang, J

2000-11-01

A time-resolved radiographic technique has been developed for probing the fuel distribution close to the nozzle of a high-pressure single-hole diesel injector. The measurement was made using X-ray absorption of monochromatic synchrotron-generated radiation, allowing quantitative determination of the fuel distribution in this optically impenetrable region with a time resolution of better than 1 micros. These quantitative measurements constitute the most detailed near-nozzle study of a fuel spray to date.

Energy and angle resolved studies of double photo-ionisation of helium by electron time-of-flight coincidence spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Viefhaus, J.; Avaldi, L.; Heiser, F.; Hentges, R.; Gessner, O.; Ruedel, A.; Wiedenhoeft, M.; Wieliczek, K.; Becker, U. [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany)

1996-10-28

Helium double photo-ionization is studied by a novel coincidence technique which employs time-of-flight spectrometers. Using this technique it is possible to collect simultaneously all the electron pairs, with different energy sharing, emitted by the absorption of a single energetic incident photon. The measurements, in a configuration where the two electrons emerge at 180{sup o} relative angle, provide the more complete information on the contribution of the ungerade amplitude to the triple differential cross section and allow the establishment of a relative scale for the full coincidence angular distribution measured by other experiments at the same photon energies, but only for a few selected energy-sharing conditions. (author).

Time-resolved fluorometry of the aromatic amino acids

International Nuclear Information System (INIS)

Laws, W.R.; Ross, J.B.A.; Katsoyannis, P.G.; Wyssbrod, H.R.

1988-01-01

The aromatic amino acids tryptophan, tyrosine, and phenylalanine are the chromophores that produce the intrinsic fluorescence of proteins. It has been a long-desired goal to be able to use the fluorescence of these amino acids to help understand protein dynamics, structure, and function. Considerable information about proteins in solution has come from steady-state, or time-averaged, fluorescence measurements, especially from the fluorescence of tryptophan. For a protein to be characterized more extensively, however, the time dependence of the intrinsic fluorescence must also be explained. Unfortunately, complex fluorescence decay kinetics have been observed not only for proteins having just a single aromatic amino acid, but also for simple analogues of these amino acids; the cause of these complex decays is not fully understood. Considerable effort must still be made to resolve the mechanisms causing the complex decays

Particle tracking during Ostwald ripening using time-resolved laboratory X-ray microtomography

Energy Technology Data Exchange (ETDEWEB)

Werz, T., E-mail: thomas.werz@uni-ulm.de [Ulm University, Institute of Micro and Nanomaterials, Albert-Einstein-Allee 47, 89081 (Germany); Baumann, M. [Ulm University, Institute of Micro and Nanomaterials, Albert-Einstein-Allee 47, 89081 (Germany); Wolfram, U. [Ulm University, Institute of Orthopaedic Research and Biomechanics, Helmholtzstrasse 14, 89081 (Germany); Krill, C.E. [Ulm University, Institute of Micro and Nanomaterials, Albert-Einstein-Allee 47, 89081 (Germany)

2014-04-01

Laboratory X-ray microtomography is investigated as a method for obtaining time-resolved images of microstructural coarsening of the semisolid state of Al–5 wt.% Cu samples during Ostwald ripening. Owing to the 3D imaging capability of tomography, this technique uniquely provides access to the growth rates of individual particles, thereby not only allowing a statistical characterization of coarsening—as has long been possible by conventional metallography—but also enabling quantification of the influence of local environment on particle boundary migration. The latter information is crucial to understanding growth kinetics during Ostwald ripening at high volume fractions of the coarsening phase. Automated image processing and segmentation routines were developed to close gaps in the network of particle boundaries and to track individual particles from one annealing step to the next. The particle tracking success rate places an upper bound of only a few percent on the likelihood of segmentation errors for any given particle. The accuracy of particle size trajectories extracted from the time-resolved tomographic reconstructions is correspondingly high. Statistically averaged coarsening data and individual particle growth rates are in excellent agreement with the results of prior experimental studies and with computer simulations of Ostwald ripening. - Highlights: • Ostwald ripening in Al–5 wt.% Cu measured by laboratory X-ray microtomography • Time-resolved measurement of individual particle growth • Automated segmentation routines developed to close gaps in particle boundary network • Particle growth/shrinkage rates deviate from LSW model prediction.

Measurements of Electron Transport in Foils Irradiated with a Picosecond Time Scale Laser Pulse

International Nuclear Information System (INIS)

Brown, C. R. D.; Hoarty, D. J.; James, S. F.; Swatton, D.; Hughes, S. J.; Morton, J. W.; Guymer, T. M.; Hill, M. P.; Chapman, D. A.; Andrew, J. E.; Comley, A. J.; Shepherd, R.; Dunn, J.; Chen, H.; Schneider, M.; Brown, G.; Beiersdorfer, P.; Emig, J.

2011-01-01

The heating of solid foils by a picosecond time scale laser pulse has been studied by using x-ray emission spectroscopy. The target material was plastic foil with a buried layer of a spectroscopic tracer material. The laser pulse length was either 0.5 or 2 ps, which resulted in a laser irradiance that varied over the range 10 16 -10 19 W/cm 2 . Time-resolved measurements of the buried layer emission spectra using an ultrafast x-ray streak camera were used to infer the density and temperature conditions as a function of laser parameters and depth of the buried layer. Comparison of the data to different models of electron transport showed that they are consistent with a model of electron transport that predicts the bulk of the target heating is due to return currents.

20 CFR 670.991 - How does Job Corps ensure that complaints or disputes are resolved in a timely fashion?

Science.gov (United States)

2010-04-01

... 20 Employees' Benefits 3 2010-04-01 2010-04-01 false How does Job Corps ensure that complaints or disputes are resolved in a timely fashion? 670.991 Section 670.991 Employees' Benefits EMPLOYMENT AND... resolved in a timely fashion? (a) If a complaint is not resolved by the center operator or service provider...

Time-resolved High Spectral Resolution Observation of 2MASSW J0746425+200032AB

Energy Technology Data Exchange (ETDEWEB)

Wang, Ji; Mawet, Dimitri [Department of Astronomy, California Institute of Technology, MC 249-17, 1200 E. California Boulevard, Pasadena, CA 91106 (United States); Prato, Lisa, E-mail: ji.wang@caltech.edu [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States)

2017-03-20

Many brown dwarfs (BDs) exhibit photometric variability at levels from tenths to tens of percents. The photometric variability is related to magnetic activity or patchy cloud coverage, characteristic of BDs near the L–T transition. Time-resolved spectral monitoring of BDs provides diagnostics of cloud distribution and condensate properties. However, current time-resolved spectral studies of BDs are limited to low spectral resolution ( R ∼ 100) with the exception of the study of Luhman 16 AB at a resolution of 100,000 using the VLT+CRIRES. This work yielded the first map of BD surface inhomogeneity, highlighting the importance and unique contribution of high spectral resolution observations. Here, we report on the time-resolved high spectral resolution observations of a nearby BD binary, 2MASSW J0746425+200032AB. We find no coherent spectral variability that is modulated with rotation. Based on simulations, we conclude that the coverage of a single spot on 2MASSW J0746425+200032AB is smaller than 1% or 6.25% if spot contrast is 50% or 80% of its surrounding flux, respectively. Future high spectral resolution observations aided by adaptive optics systems can put tighter constraints on the spectral variability of 2MASSW J0746425+200032AB and other nearby BDs.

A new method for obtaining time resolved optical spectra of transients produced by a single pulse of electrons

International Nuclear Information System (INIS)

Gordon, S.; Schmidt, K.H.; Martin, J.E.

1975-01-01

The essential features of the kinetic spectroscopic method and the kinetic spectrophotometric method are summarized. It is stated that the new method embodies some of the advantages of both. A diagram of the apparatus is shown. This is essentially a version of a conventional pulse radiolysis experimental arrangement with the modification that the usual monochromator is replaced by a spectrograph equipped with a horizontal and a vertical slit and the usual photomultiplier-amplifier detector is replaced by a streak camera (TRW) incorporating an image converter tube (ICT) and a TV camera interfaced to a 2000 channel Biomation transient recorder. The time resolved absorption spectrum (or emission spectrum) is displayed on the P-11 phosphor of the ICT. This image is focussed on the photoelements of the TV tube. The TV camera scans the image of the spectrum stored on these elements and the output of this scan is stored in the Biomation. This recorder is in turn interfaced to a Sigma 5 computer. Results are presented for several experiments, from which it is concluded that with the present equipment absorbances down to 0.02 can be measured, and a time resolution of 1ns can be achieved. It is stated that with improved equipment it should be possible to extend the time resolution of the method to less than 50 picoseconds. (U.K.)

Combined PIXE and X-ray SEM studies on time-resolved deposits of welding shop aerosols

International Nuclear Information System (INIS)

Barfoot, K.M.; Mitchell, I.V.; Verheyen, F.; Babeliowsky, T.

1981-01-01

Time-resolved deposits of welding shop air particulates have been obtained using a streak sampling system. PIXE analysis of these deposits, using 2 MeV protons, typically revealed the presence of a large number of elements, with many in the range Z = 11-30. Strong variations, up to three orders of magnitude, in the concentrations of several elements such as Al, Si and Fe as well as Zn, Na, K and Ca were found. The 2 h sampling resolution normally used was found to be insufficient to follow the short pollution episodes that regularly occur in a welding shop environment and so sampling with a 20 min resolution was used. The variation of elemental concentrations for different sampling times together with information on the physical nature of these air particulates, determined with a scanning electron microscope (SEM) and Si(Li) X-ray detector attachment, are presented. This type of information together with that obtained from the PIXE analysis is of importance industrial hygiene studies. The need to make corrections for partial filter clogging, based on air-flow rate monitoring, is discussed. (orig.)

Time-resolved measurements of supersonic fuel sprays using synchrotron x-rays

International Nuclear Information System (INIS)

Powell, C.F.; Yue, Y.; Poola, R.; Wang, J.

2000-11-01

A time-resolved radiographic technique has been developed for probing the fuel distribution close to the nozzle of a high-pressure single-hole diesel injector. The measurement was made using X-ray absorption of monochromatic synchrotron-generated radiation, allowing quantitative determination of the fuel distribution in this optically impenetrable region with a time resolution of better than 1 μs. These quantitative measurements constitute the most detailed near-nozzle study of a fuel spray to date

Time-resolved laser-induced fluorescence in the nuclear fuel cycle

International Nuclear Information System (INIS)

Moulin, C.; Decambox, P.; Mauchien, P.; Petit, A.

1995-01-01

Time-Resolved Laser-Induced Fluorescence (TRLIF) is a very sensitive and selective method that has been used for actinides and lanthanides analysis in the nuclear fuel cycle. This technique has been used in different fields such as in geology, in the Purex process, in the environment, in the medical and in waste storage assessment. Spectroscopic data, limits of detection and results obtained in previously quoted fields are presented. (author)

Quantitative analysis of time-resolved infrared stimulated luminescence in feldspars

DEFF Research Database (Denmark)

Pagonis, Vasilis; Ankjærgaard, Christina; Jain, Mayank

2016-01-01

Time-resolved infrared-stimulated luminescence (TR-IRSL) from feldspar samples is of importance in the field of luminescence dating, since it provides information on the luminescence mechanism in these materials. In this paper we present new analytical equations which can be used to analyze TR-IR....... The equations are applied to experimental TR-IRSL data of natural feldspars, and good agreement is found between experimental and modeling results....

An ultrafast programmable electrical tester for enabling time-resolved, sub-nanosecond switching dynamics and programming of nanoscale memory devices

Science.gov (United States)

Shukla, Krishna Dayal; Saxena, Nishant; Manivannan, Anbarasu

2017-12-01

Recent advancements in commercialization of high-speed non-volatile electronic memories including phase change memory (PCM) have shown potential not only for advanced data storage but also for novel computing concepts. However, an in-depth understanding on ultrafast electrical switching dynamics is a key challenge for defining the ultimate speed of nanoscale memory devices that demands for an unconventional electrical setup, specifically capable of handling extremely fast electrical pulses. In the present work, an ultrafast programmable electrical tester (PET) setup has been developed exceptionally for unravelling time-resolved electrical switching dynamics and programming characteristics of nanoscale memory devices at the picosecond (ps) time scale. This setup consists of novel high-frequency contact-boards carefully designed to capture extremely fast switching transient characteristics within 200 ± 25 ps using time-resolved current-voltage measurements. All the instruments in the system are synchronized using LabVIEW, which helps to achieve various programming characteristics such as voltage-dependent transient parameters, read/write operations, and endurance test of memory devices systematically using short voltage pulses having pulse parameters varied from 1 ns rise/fall time and 1.5 ns pulse width (full width half maximum). Furthermore, the setup has successfully demonstrated strikingly one order faster switching characteristics of Ag5In5Sb60Te30 (AIST) PCM devices within 250 ps. Hence, this novel electrical setup would be immensely helpful for realizing the ultimate speed limits of various high-speed memory technologies for future computing.

Level-resolved distorted-wave cross-sections of electron impact ionization of Ar{sup 5+}

Energy Technology Data Exchange (ETDEWEB)

Yumak, A; Yavuz, I; Altun, Z, E-mail: zikalt@superonline.co [Department of Physics, Marmara University, Istanbul, 34722 (Turkey)

2009-11-01

Electron impact ionization cross sections of Ar{sup 5+} were calculated using configuration-average (CADW) and level-resolved (LRDW) distorted-wave methods. Direct ionization cross-sections of 2s, 2p, 3s and 3p subshells were calculated within a CADW approximation. The contributions from the excitation autoionization channels were evaluated assuming single excitations from the 2s, 2p, and 3s subshells and in both CADW and LRDW methods. The radiative stabilization of the excitation autoionization channels were found to reduce the excitation autoionization by a small amount.

Time-resolved infrared absorption study of nine TiO2 photocatalysts

International Nuclear Information System (INIS)

Yamakata, Akira; Ishibashi, Taka-aki; Onishi, Hiroshi

2007-01-01

Electron kinetics of nine TiO 2 catalysts were compared in a microsecond time domain. Each catalyst was band-gap excited with an UV light pulse, and electron-induced absorption of mid infrared light was observed as a function of time delay. The probability of electron-hole recombination in the bulk, electron attachment to adsorbed oxygen, and hole attachment to adsorbed methoxy species was estimated

Time-Resolved Fluorescent Immunochromatography of Aflatoxin B1 in Soybean Sauce: A Rapid and Sensitive Quantitative Analysis.

Science.gov (United States)

Wang, Du; Zhang, Zhaowei; Li, Peiwu; Zhang, Qi; Zhang, Wen

2016-07-14

Rapid and quantitative sensing of aflatoxin B1 with high sensitivity and specificity has drawn increased attention of studies investigating soybean sauce. A sensitive and rapid quantitative immunochromatographic sensing method was developed for the detection of aflatoxin B1 based on time-resolved fluorescence. It combines the advantages of time-resolved fluorescent sensing and immunochromatography. The dynamic range of a competitive and portable immunoassay was 0.3-10.0 µg·kg(-1), with a limit of detection (LOD) of 0.1 µg·kg(-1) and recoveries of 87.2%-114.3%, within 10 min. The results showed good correlation (R² > 0.99) between time-resolved fluorescent immunochromatographic strip test and high performance liquid chromatography (HPLC). Soybean sauce samples analyzed using time-resolved fluorescent immunochromatographic strip test revealed that 64.2% of samples contained aflatoxin B1 at levels ranging from 0.31 to 12.5 µg·kg(-1). The strip test is a rapid, sensitive, quantitative, and cost-effective on-site screening technique in food safety analysis.

Quantitative analysis of pulmonary perfusion using time-resolved parallel 3D MRI - initial results

International Nuclear Information System (INIS)

Fink, C.; Buhmann, R.; Plathow, C.; Puderbach, M.; Kauczor, H.U.; Risse, F.; Ley, S.; Meyer, F.J.

2004-01-01

Purpose: to assess the use of time-resolved parallel 3D MRI for a quantitative analysis of pulmonary perfusion in patients with cardiopulmonary disease. Materials and methods: eight patients with pulmonary embolism or pulmonary hypertension were examined with a time-resolved 3D gradient echo pulse sequence with parallel imaging techniques (FLASH 3D, TE/TR: 0.8/1.9 ms; flip angle: 40 ; GRAPPA). A quantitative perfusion analysis based on indicator dilution theory was performed using a dedicated software. Results: patients with pulmonary embolism or chronic thromboembolic pulmonary hypertension revealed characteristic wedge-shaped perfusion defects at perfusion MRI. They were characterized by a decreased pulmonary blood flow (PBF) and pulmonary blood volume (PBV) and increased mean transit time (MTT). Patients with primary pulmonary hypertension or eisenmenger syndrome showed a more homogeneous perfusion pattern. The mean MTT of all patients was 3.3 - 4.7 s. The mean PBF and PBV showed a broader interindividual variation (PBF: 104-322 ml/100 ml/min; PBV: 8 - 21 ml/100 ml). Conclusion: time-resolved parallel 3D MRI allows at least a semi-quantitative assessment of lung perfusion. Future studies will have to assess the clinical value of this quantitative information for the diagnosis and management of cardiopulmonary disease. (orig.) [de

rf streak camera based ultrafast relativistic electron diffraction.

Science.gov (United States)

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

2009-01-01

We theoretically and experimentally investigate the possibility of using a rf streak camera to time resolve in a single shot structural changes at the sub-100 fs time scale via relativistic electron diffraction. We experimentally tested this novel concept at the UCLA Pegasus rf photoinjector. Time-resolved diffraction patterns from thin Al foil are recorded. Averaging over 50 shots is required in order to get statistics sufficient to uncover a variation in time of the diffraction patterns. In the absence of an external pump laser, this is explained as due to the energy chirp on the beam out of the electron gun. With further improvements to the electron source, rf streak camera based ultrafast electron diffraction has the potential to yield truly single shot measurements of ultrafast processes.

Time-resolved far-infrared experiments at the National Synchrotron Light Source. Final report

International Nuclear Information System (INIS)

Tanner, D.B.; Reitze, D.H.; Carr, G.L.

1999-01-01

A facility for time-resolved infrared and far-infrared spectroscopy has been built and commissioned at the National Synchrotron Light Source. This facility permits the study of time dependent phenomena over a frequency range from 2-8000cm -1 (0.25 meV-1 eV). Temporal resolution is approximately 200 psec and time dependent phenomena in the time range out to 100 nsec can be investigated

Time-resolved X-ray PIV technique for diagnosing opaque biofluid flow with insufficient X-ray fluxes.

Science.gov (United States)

Jung, Sung Yong; Park, Han Wook; Kim, Bo Heum; Lee, Sang Joon

2013-05-01

X-ray imaging is used to visualize the biofluid flow phenomena in a nondestructive manner. A technique currently used for quantitative visualization is X-ray particle image velocimetry (PIV). Although this technique provides a high spatial resolution (less than 10 µm), significant hemodynamic parameters are difficult to obtain under actual physiological conditions because of the limited temporal resolution of the technique, which in turn is due to the relatively long exposure time (~10 ms) involved in X-ray imaging. This study combines an image intensifier with a high-speed camera to reduce exposure time, thereby improving temporal resolution. The image intensifier amplifies light flux by emitting secondary electrons in the micro-channel plate. The increased incident light flux greatly reduces the exposure time (below 200 µs). The proposed X-ray PIV system was applied to high-speed blood flows in a tube, and the velocity field information was successfully obtained. The time-resolved X-ray PIV system can be employed to investigate blood flows at beamlines with insufficient X-ray fluxes under specific physiological conditions. This method facilitates understanding of the basic hemodynamic characteristics and pathological mechanism of cardiovascular diseases.

Non-Gaussian lineshapes and dynamics of time-resolved linear and nonlinear (correlation) spectra.

Science.gov (United States)

Dinpajooh, Mohammadhasan; Matyushov, Dmitry V

2014-07-17

Signatures of nonlinear and non-Gaussian dynamics in time-resolved linear and nonlinear (correlation) 2D spectra are analyzed in a model considering a linear plus quadratic dependence of the spectroscopic transition frequency on a Gaussian nuclear coordinate of the thermal bath (quadratic coupling). This new model is contrasted to the commonly assumed linear dependence of the transition frequency on the medium nuclear coordinates (linear coupling). The linear coupling model predicts equality between the Stokes shift and equilibrium correlation functions of the transition frequency and time-independent spectral width. Both predictions are often violated, and we are asking here the question of whether a nonlinear solvent response and/or non-Gaussian dynamics are required to explain these observations. We find that correlation functions of spectroscopic observables calculated in the quadratic coupling model depend on the chromophore's electronic state and the spectral width gains time dependence, all in violation of the predictions of the linear coupling models. Lineshape functions of 2D spectra are derived assuming Ornstein-Uhlenbeck dynamics of the bath nuclear modes. The model predicts asymmetry of 2D correlation plots and bending of the center line. The latter is often used to extract two-point correlation functions from 2D spectra. The dynamics of the transition frequency are non-Gaussian. However, the effect of non-Gaussian dynamics is limited to the third-order (skewness) time correlation function, without affecting the time correlation functions of higher order. The theory is tested against molecular dynamics simulations of a model polar-polarizable chromophore dissolved in a force field water.

Kalman filter approach for uncertainty quantification in time-resolved laser-induced incandescence.

Science.gov (United States)

Hadwin, Paul J; Sipkens, Timothy A; Thomson, Kevin A; Liu, Fengshan; Daun, Kyle J

2018-03-01

Time-resolved laser-induced incandescence (TiRe-LII) data can be used to infer spatially and temporally resolved volume fractions and primary particle size distributions of soot-laden aerosols, but these estimates are corrupted by measurement noise as well as uncertainties in the spectroscopic and heat transfer submodels used to interpret the data. Estimates of the temperature, concentration, and size distribution of soot primary particles within a sample aerosol are typically made by nonlinear regression of modeled spectral incandescence decay, or effective temperature decay, to experimental data. In this work, we employ nonstationary Bayesian estimation techniques to infer aerosol properties from simulated and experimental LII signals, specifically the extended Kalman filter and Schmidt-Kalman filter. These techniques exploit the time-varying nature of both the measurements and the models, and they reveal how uncertainty in the estimates computed from TiRe-LII data evolves over time. Both techniques perform better when compared with standard deterministic estimates; however, we demonstrate that the Schmidt-Kalman filter produces more realistic uncertainty estimates.

Time-resolved photoelectron spectroscopy of nitrobenzene and its aldehydes

Science.gov (United States)

Schalk, Oliver; Townsend, Dave; Wolf, Thomas J. A.; Holland, David M. P.; Boguslavskiy, Andrey E.; Szöri, Milan; Stolow, Albert

2018-01-01

We report the first femtosecond time-resolved photoelectron spectroscopy study of 2-, 3- and 4-nitrobenzaldehyde (NBA) and nitrobenzene (NBE) in the gas phase upon excitation at 200 nm. In 3- and 4-NBA, the dynamics follow fast intersystem crossing within 1-2 picoseconds. In 2-NBA and NBE, the dynamics are faster (∼ 0.5 ps). 2-NBA undergoes hydrogen transfer similar to solution phase dynamics. NBE either releases NO2 in the excited state or converts internally back to the ground state. We discuss why these channels are suppressed in the other nitrobenzaldehydes.

Time-resolved soft x-ray absorption setup using multi-bunch operation modes at synchrotrons

International Nuclear Information System (INIS)

Stebel, L.; Sigalotti, P.; Ressel, B.; Cautero, G.; Malvestuto, M.; Capogrosso, V.; Bondino, F.; Magnano, E.; Parmigiani, F.

2011-01-01

Here, we report on a novel experimental apparatus for performing time-resolved soft x-ray absorption spectroscopy in the sub-ns time scale using non-hybrid multi-bunch mode synchrotron radiation. The present setup is based on a variable repetition rate Ti:sapphire laser (pump pulse) synchronized with the ∼500 MHz x-ray synchrotron radiation bunches and on a detection system that discriminates and singles out the significant x-ray photon pulses by means of a custom made photon counting unit. The whole setup has been validated by measuring the time evolution of the L 3 absorption edge during the melting and the solidification of a Ge single crystal irradiated by an intense ultrafast laser pulse. These results pave the way for performing synchrotron time-resolved experiments in the sub-ns time domain with variable repetition rate exploiting the full flux of the synchrotron radiation.

Revealing the ultrafast charge carrier dynamics in organo metal halide perovskite solar cell materials using time resolved THz spectroscopy

Science.gov (United States)

Ponseca, C. S., Jr.; Sundström, V.

2016-03-01

Ultrafast charge carrier dynamics in organo metal halide perovskite has been probed using time resolved terahertz (THz) spectroscopy (TRTS). Current literature on its early time characteristics is unanimous: sub-ps charge carrier generation, highly mobile charges and very slow recombination rationalizing the exceptionally high power conversion efficiency for a solution processed solar cell material. Electron injection from MAPbI3 to nanoparticles (NP) of TiO2 is found to be sub-ps while Al2O3 NPs do not alter charge dynamics. Charge transfer to organic electrodes, Spiro-OMeTAD and PCBM, is sub-ps and few hundreds of ps respectively, which is influenced by the alignment of energy bands. It is surmised that minimizing defects/trap states is key in optimizing charge carrier extraction from these materials.

Time resolved emission spectroscopy investigations of pulsed laser ablated plasmas of ZrO2 and Al2O3

International Nuclear Information System (INIS)

Hadoko, A D; Lee, P S; Lee, P; Mohanty, S R; Rawat, R S

2006-01-01

With the rising trend of synthesizing ultra thin films and/or quantum-confined materials using laser ablation, optimization of deposition parameters plays an essential role in obtaining desired film characteristics. This paper presents the initial step of plasma optimization study by examining temporal distribution of the plasma formation by pulsed laser ablation of materials. The emitted spectra of ZrO 2 and Al 2 O 3 are obtained ∼3mm above the ablated target to derive the ablated plasma characteristics. The plasma temperature is estimated to be at around 2.35 eV, with electron density of 1.14 x 10 16 (cm -3 ). Emission spectra with different gate delay time (40-270 ns) are captured to study the time resolved plume characteristics. Transitory elemental species are identified

How well do time-integrated Kα images represent hot electron spatial distributions?

Science.gov (United States)

Ovchinnikov, V. M.; Kemp, G. E.; Schumacher, D. W.; Freeman, R. R.; Van Woerkom, L. D.

2011-07-01

A computational study is described, which addresses how well spatially resolved time-integrated Kα images recorded in intense laser-plasma experiments correlate with the distribution of "hot" (>1 MeV) electrons as they propagate through the target. The hot electron angular distribution leaving the laser-plasma region is critically important for many applications such as Fast Ignition or laser based x-ray sources; and Kα images are commonly used as a diagnostic. It is found that Kα images can easily mislead due to refluxing and other effects. Using the particle-in-cell code LSP, it is shown that a Kα image is not solely determined by the initial population of forward directed hot electrons, but rather also depends upon "delayed" hot electrons, and in fact continues to evolve long after the end of the laser interaction. Of particular note, there is a population of hot electrons created during the laser-plasma interaction that acquire a velocity direction opposite that of the laser and subsequently reflux off the front surface of the target, deflect when they encounter magnetic fields in the laser-plasma region, and then traverse the target in a wide spatial distribution. These delayed fast electrons create significant features in the Kα time-integrated images. Electrons refluxing from the sides and the back of the target are also found to play a significant role in forming the final Kα image. The relative contribution of these processes is found to vary depending on depth within target. These effects make efforts to find simple correlations between Kα images and, for example, Fast Ignition relevant parameters prone to error. Suggestions for future target design are provided.

Timely resolved measurements on CdSe nanoparticles; Zeitaufgeloeste Messungen an CdSe Nanopartikeln

Energy Technology Data Exchange (ETDEWEB)

Holt, B.E. von

2006-06-06

By means of infrared spectroscopy the influence of the organic cover on structure and dynamics of CdSe nanoparticles was studied. First a procedure was developed, which allows to get from the static infrared spectrum informations on the quality of the organic cover and the binding behaviour of the ligands. On qualitatively high-grade and well characterized samples thereafter the dynamics of the lowest-energy electron level 1S{sub e} was time-resolvedly meausred in thew visible range. As reference served CdSe TOPO, which was supplemented by samples with the ligands octanthiole, octanic acid, octylamine, naphthoquinone, benzoquinone, and pyridine. The studied nanoparticles had a diameter of 4.86 nm. By means of the excitation-scanning or pump=probe procedure first measurements in the picosecond range were performed. The excitation wavelengths were thereby spectrally confined and so chosen that selectively the transitions 1S{sub 3/2}-1S-e and 1P{sub 3/2}-1P{sub e} but not the intermediately lyingt transition 2S{sub 3/2}-1S{sub e} were excited. The excitation energies were kept so low that the excitation of several excitons in one crystal could be avoided. The scanning wavelength in the infrared corresponded to the energy difference between the electron levels 1S{sub e} and 1P{sub e}. The transients in the picosecond range are marked by a steep increasement of the signal, on which a multi-exponential decay follows. The increasement, which reproduces the popiulation of the excited state, isa inependent on the choice of the ligands. The influence of the organic cover is first visible in the different decay times of the excited electron levels. the decay of the measurement signal of CdSe TOPO can be approximatively described by three time constants: a decay constant in the early picosecond region, a time constant around hundert picoseconds, and a time constant of some nanoseconds. At increasing scanning wavelength the decay constants become longer. By directed excitation

Time-resolved energy transfer from single chloride-terminated nanocrystals to graphene

International Nuclear Information System (INIS)

Ajayi, O. A.; Wong, C. W.; Anderson, N. C.; Wolcott, A.; Owen, J. S.; Cotlet, M.; Petrone, N.; Hone, J.; Gu, T.; Gesuele, F.

2014-01-01

We examine the time-resolved resonance energy transfer of excitons from single n-butyl amine-bound, chloride-terminated nanocrystals to two-dimensional graphene through time-correlated single photon counting. The radiative biexponential lifetime kinetics and blinking statistics of the individual surface-modified nanocrystal elucidate the non-radiative decay channels. Blinking modification as well as a 4× reduction in spontaneous emission were observed with the short chloride and n-butylamine ligands, probing the energy transfer pathways for the development of graphene-nanocrystal nanophotonic devices

Time-resolved energy transfer from single chloride-terminated nanocrystals to graphene

Energy Technology Data Exchange (ETDEWEB)

Ajayi, O. A., E-mail: oaa2114@columbia.edu, E-mail: cww2104@columbia.edu; Wong, C. W., E-mail: oaa2114@columbia.edu, E-mail: cww2104@columbia.edu [Optical Nanostructures Laboratory, Center for Integrated Science and Engineering, Solid-State Science and Engineering, Columbia University, New York, New York 10027 (United States); Department of Mechanical Engineering, Columbia University, New York, New York 10027 (United States); Anderson, N. C.; Wolcott, A.; Owen, J. S. [Department of Chemistry, Columbia University, New York, New York 10027 (United States); Cotlet, M. [Brookhaven National Laboratory, Upton, New York, New York 11973 (United States); Petrone, N.; Hone, J. [Department of Mechanical Engineering, Columbia University, New York, New York 10027 (United States); Gu, T.; Gesuele, F. [Optical Nanostructures Laboratory, Center for Integrated Science and Engineering, Solid-State Science and Engineering, Columbia University, New York, New York 10027 (United States)

2014-04-28

We examine the time-resolved resonance energy transfer of excitons from single n-butyl amine-bound, chloride-terminated nanocrystals to two-dimensional graphene through time-correlated single photon counting. The radiative biexponential lifetime kinetics and blinking statistics of the individual surface-modified nanocrystal elucidate the non-radiative decay channels. Blinking modification as well as a 4× reduction in spontaneous emission were observed with the short chloride and n-butylamine ligands, probing the energy transfer pathways for the development of graphene-nanocrystal nanophotonic devices.

Time-resolved PIV technique for high temporal resolution measurement of mechanical prosthetic aortic valve fluid dynamics.

Science.gov (United States)

Kaminsky, R; Morbiducci, U; Rossi, M; Scalise, L; Verdonck, P; Grigioni, M

2007-02-01

Prosthetic heart valves (PHVs) have been used to replace diseased native valves for more than five decades. Among these, mechanical PHVs are the most frequently implanted. Unfortunately, these devices still do not achieve ideal behavior and lead to many complications, many of which are related to fluid mechanics. The fluid dynamics of mechanical PHVs are particularly complex and the fine-scale characteristics of such flows call for very accurate experimental techniques. Adequate temporal resolution can be reached by applying time-resolved PIV, a high-resolution dynamic technique which is able to capture detailed chronological changes in the velocity field. The aim of this experimental study is to investigate the evolution of the flow field in a detailed time domain of a commercial bileaflet PHV in a mock-loop mimicking unsteady conditions, by means of time-resolved 2D Particle Image Velocimetry (PIV). The investigated flow field corresponded to the region immediately downstream of the valve plane. Spatial resolution as in "standard" PIV analysis of prosthetic valve fluid dynamics was used. The combination of a Nd:YLF high-repetition-rate double-cavity laser with a high frame rate CMOS camera allowed a detailed, highly temporally resolved acquisition (up to 10000 fps depending on the resolution) of the flow downstream of the PHV. Features that were observed include the non-homogeneity and unsteadiness of the phenomenon and the presence of large-scale vortices within the field, especially in the wake of the valve leaflets. Furthermore, we observed that highly temporally cycle-resolved analysis allowed the different behaviors exhibited by the bileaflet valve at closure to be captured in different acquired cardiac cycles. By accurately capturing hemodynamically relevant time scales of motion, time-resolved PIV characterization can realistically be expected to help designers in improving PHV performance and in furnishing comprehensive validation with experimental data

Existence of time-dependent density-functional theory for open electronic systems: time-dependent holographic electron density theorem.

Science.gov (United States)

Zheng, Xiao; Yam, ChiYung; Wang, Fan; Chen, GuanHua

2011-08-28

We present the time-dependent holographic electron density theorem (TD-HEDT), which lays the foundation of time-dependent density-functional theory (TDDFT) for open electronic systems. For any finite electronic system, the TD-HEDT formally establishes a one-to-one correspondence between the electron density inside any finite subsystem and the time-dependent external potential. As a result, any electronic property of an open system in principle can be determined uniquely by the electron density function inside the open region. Implications of the TD-HEDT on the practicality of TDDFT are also discussed.

Femtosecond Electron Wave Packet Propagation and Diffraction: Towards Making the ``Molecular Movie"

Science.gov (United States)

Miller, R. J. Dwayne

2003-03-01

Time-resolved electron diffraction harbors great promise for achieving atomic resolution of the fastest chemical processes. The generation of sufficiently short electron pulses to achieve this real time view of a chemical reaction has been limited by problems in maintaining short electron pulses with realistic electron densities to the sample. The propagation dynamics of femtosecond electron packets in the drift region of a photoelectron gun are investigated with an N-body numerical simulation and mean-field model. This analyis shows that the redistribution of electrons inside the packet, arising from space-charge and dispersion contributions, changes the pulse envelope and leads to the development of a spatially linear axial velocity distribution. These results have been used in the design of femtosecond photoelectron guns with higher time resolution and novel electron-optical methods of pulse characterization that are approaching 100 fs timescales. Time-resolved diffraction studies with electron pulses of approximately 500 femtoseconds have focused on solid-liquid phase transitions under far from equilibrium conditions. This work gives a microscopic description of the melting process and illustrates the promise of atomically resolving transition state processes.

An energy resolved electron-ion coincidence study near the S 2p thresholds of the SF6 molecule

International Nuclear Information System (INIS)

Kivimaeki, A; Ruiz, J Alvarez; Erman, P; Hatherly, P; Garcia, E Melero; Rachlew, E; Rius i Riu, J; Stankiewicz, M

2003-01-01

The fragmentation dynamics of the SF 6 molecule following the excitations of S 2p electrons into unoccupied molecular orbitals has been studied using the energy-resolved electron-ion coincidence technique. Fragmentation patterns were found to depend on the particular excitation and on the electronic state of the molecular ion. The spectator resonant Auger decay at the 2p → 6a 1g resonance induces changes in the ion distributions as compared to direct photoionization. Furthermore, coincidence spectra related to the same Auger structure display different ion abundances at the 2t 2g and 4e g shape resonances. Differences were also found in the Auger decay spectra. These findings give further support for the previously suggested many-electron character of the 4e g shape resonance

On the estimation of wall pressure coherence using time-resolved tomographic PIV

Science.gov (United States)

Pröbsting, Stefan; Scarano, Fulvio; Bernardini, Matteo; Pirozzoli, Sergio

2013-07-01

Three-dimensional time-resolved velocity field measurements are obtained using a high-speed tomographic Particle Image Velocimetry (PIV) system on a fully developed flat plate turbulent boundary layer for the estimation of wall pressure fluctuations. The work focuses on the applicability of tomographic PIV to compute the coherence of pressure fluctuations, with attention to the estimation of the stream and spanwise coherence length. The latter is required for estimations of aeroacoustic noise radiation by boundary layers and trailing edge flows, but is also of interest for vibro-structural problems. The pressure field is obtained by solving the Poisson equation for incompressible flows, where the source terms are provided by time-resolved velocity field measurements. Measured 3D velocity data is compared to results obtained from planar PIV, and a Direct Numerical Simulation (DNS) at similar Reynolds number. An improved method for the estimation of the material based on a least squares estimator of the velocity derivative along a particle trajectory is proposed and applied. Computed surface pressure fluctuations are further verified by means of simultaneous measurements by a pinhole microphone and compared to the DNS results and a semi-empirical model available from literature. The correlation coefficient for the reconstructed pressure time series with respect to pinhole microphone measurements attains approximately 0.5 for the band-pass filtered signal over the range of frequencies resolved by the velocity field measurements. Scaled power spectra of the pressure at a single point compare favorably to the DNS results and those available from literature. Finally, the coherence of surface pressure fluctuations and the resulting span- and streamwise coherence lengths are estimated and compared to semi-empirical models and DNS results.

Time Resolved X-Ray Scattering of molecules in Solution

DEFF Research Database (Denmark)

Brandt van Driel, Tim

The dissertation describes the use of Time-Resolved X-ray Diffuse Scattering (TR-XDS) to study photo-induced structural changes in molecules in solution. The application of the technique is exemplified with experiments on two bimetallic molecules. The main focus is on the data-flow and process......)42+ obtained at European Synchrotron Radiation Facility (ESRF) are presented to exemplify TR-XDS at synchrotrons. Similarly, measurements on Ir2(dimen)42+ are used to show the XFEL data-flow and how it deviates from the prior. A method to identify and account for systematic fluctuations...

ESR spectrometer with a loop-gap resonator for cw and time resolved studies in a superconducting magnet.

Science.gov (United States)

Simon, Ferenc; Murányi, Ferenc

2005-04-01

The design and performance of an electron spin resonance spectrometer operating at 3 and 9 GHz microwave frequencies combined with a 9-T superconducting magnet are described. The probehead contains a compact two-loop, one gap resonator, and is inside the variable temperature insert of the magnet enabling measurements in the 0-9T magnetic field and 1.5-400 K temperature range. The spectrometer allows studies on systems where resonance occurs at fields far above the g approximately 2 paramagnetic condition such as in antiferromagnets. The low quality factor of the resonator allows time resolved experiments such as, e.g., longitudinally detected ESR. We demonstrate the performance of the spectrometer on the NaNiO2 antiferromagnet, the MgB2 superconductor, and the RbC60 conducting alkaline fulleride polymer.

Developments in time-resolved x-ray research at APS beamline 7ID

Energy Technology Data Exchange (ETDEWEB)

Walko, D. A., E-mail: d-walko@anl.gov; Adams, B. W.; Doumy, G.; Dufresne, E. M.; Li, Yuelin; March, A. M.; Sandy, A. R.; Wang, Jin; Wen, Haidan; Zhu, Yi [Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439 (United States)

2016-07-27

The 7ID beamline of the Advanced Photon Source (APS) is dedicated to time-resolved research using x-ray imaging, scattering, and spectroscopy techniques. Time resolution is achieved via gated detectors and/or mechanical choppers in conjunction with the time structure of the x-ray beam. Three experimental hutches allow for a wide variety of experimental setups. Major areas of research include atomic, molecular, and optical physics; chemistry; condensed matter physics in the bulk, thin film, and surface regimes; and fluid-spray dynamics. Recent developments in facilities at 7ID include a high-power, high-repetition-rate picosecond laser to complement the 1 kHz ultrafast laser. For the ultrafast laser, a newly commissioned optical parametric amplifier provides pump wavelength from 0.2 to 15 µm with energy per pulse up to 200 µJ. A nanodiffraction station has also been commissioned, using Fresnel zone-plate optics to achieve a focused x-ray spot of 300 nm. This nanoprobe is not only used to spatially resolve the evolution of small features in samples after optical excitation, but also has been combined with an intense THz source to study material response under ultrafast electric fields.

Time-resolved soft-x-ray studies of energy transport in layered and planar laser-driven targets

International Nuclear Information System (INIS)

Stradling, G.L.

1982-01-01

New low-energy x-ray diagnostic techniques are used to explore energy-transport processes in laser heated plasmas. Streak cameras are used to provide 15-psec time-resolution measurements of subkeV x-ray emission. A very thin (50 μg/cm 2 ) carbon substrate provides a low-energy x-ray transparent window to the transmission photocathode of this soft x-ray streak camera. Active differential vacuum pumping of the instrument is required. The use of high-sensitivity, low secondary-electron energy-spread CsI photocathodes in x-ray streak cameras is also described. Significant increases in sensitivity with only a small and intermittant decrease in dynamic range were observed. These coherent, complementary advances in subkeV, time-resolved x-ray diagnostic capability are applied to energy-transport investigations of 1.06-μm laser plasmas. Both solid disk targets of a variety of Z's as well as Be-on-Al layered-disk targets were irradiated with 700-psec laser pulses of selected intensity between 3 x 10 14 W/cm 2 and 1 x 10 15 W/cm 2

Time-resolved spectroscopy of the probe fluorescence in the study of human blood protein dynamic structure on SR beam

International Nuclear Information System (INIS)

Dobretsov, G.E.; Kurek, N.K.; Syrejshchikova, T.I.; Yakimenko, M.N.; Clarke, D.T.; Jones, G.R.; Munro, I.H.

2000-01-01

Time-resolved spectroscopy on the SRS of the Daresbury Laboratory was used for the study of the human serum lipoproteins and human blood albumins with fluorescent probes K-37 and K-35, developed in Russia. The probe K-37 was found sensitive to the difference in dynamic properties of the lipid objects. Two sets of the parameters were used for the description of lipid dynamic structure: (1) time-resolved fluorescence spectra and (2) time-resolved fluorescence depolarization as a function of rotational mobility of lipid molecules. Each measured dynamic parameter reflected the monotonous changes of dynamic properties in the range: lipid spheres-very low density lipoproteins-low density lipoproteins-high density lipoproteins-phospholipid liposomes. The range is characterized by the increase of the ratio polar/ nonpolar lipids. Thus, time-resolved fluorescence could be used to detect some structural modifications in lipoproteins related to atherosclerosis and subsequent cardiovascular diseases development

Time-resolved study of absorbing film assisted laser induced forward transfer of Trichoderma longibrachiatum conidia

Energy Technology Data Exchange (ETDEWEB)

Hopp, B [Hungarian Academy of Sciences and University of Szeged, Research Group on Laser Physics, H-6720 Szeged, Dom ter 9 (Hungary); Smausz, T [Hungarian Academy of Sciences and University of Szeged, Research Group on Laser Physics, H-6720 Szeged, Dom ter 9 (Hungary); Barna, N [Department of Optics and Quantum Electronics, University of Szeged, H-6720 Szeged, Dom ter 9 (Hungary); Vass, Cs [Department of Optics and Quantum Electronics, University of Szeged, H-6720 Szeged, Dom ter 9 (Hungary); Antal, Zs [Hungarian Academy of Sciences and University of Szeged, Microbiological Research Group, PO Box 533, H-6701 Szeged (Hungary); Kredics, L [Hungarian Academy of Sciences and University of Szeged, Microbiological Research Group, PO Box 533, H-6701 Szeged (Hungary); Chrisey, D [Naval Research Laboratory, Washington, DC 20375 (United States)

2005-03-21

We have characterized the absorbing film assisted transfer of Trichoderma longibrachiatum conidia using a synchronized laser for illumination. The transfer laser used was a KrF excimer laser ({lambda} = 248 nm, FWHM = 30 ns) and the ejected material was illuminated parallel to the quartz plate by a nitrogen laser pumped Coumarine 153 dye laser beam ({lambda} = 453 nm, FWHM 1 ns) electronically delayed relative to the transfer UV pulse. Our time-resolved investigations determined that the ejection velocity front of the conidia plume from the donor surface during the transfer procedure was 1150 m s{sup -1} at 355 mJ cm{sup -2} applied laser fluence. On the basis of the measured data, the acceleration of the emitted conidia at the plume front was approximately 10{sup 9} x g. The conidia survived the absorbing film assisted forward transfer and associated mechanical shear without significant damages suggesting that the technique might be applicable to other more fragile types of biological objects and applications.

Time-resolved study of absorbing film assisted laser induced forward transfer of Trichoderma longibrachiatum conidia

International Nuclear Information System (INIS)

Hopp, B; Smausz, T; Barna, N; Vass, Cs; Antal, Zs; Kredics, L; Chrisey, D

2005-01-01

We have characterized the absorbing film assisted transfer of Trichoderma longibrachiatum conidia using a synchronized laser for illumination. The transfer laser used was a KrF excimer laser (λ = 248 nm, FWHM = 30 ns) and the ejected material was illuminated parallel to the quartz plate by a nitrogen laser pumped Coumarine 153 dye laser beam (λ = 453 nm, FWHM 1 ns) electronically delayed relative to the transfer UV pulse. Our time-resolved investigations determined that the ejection velocity front of the conidia plume from the donor surface during the transfer procedure was 1150 m s -1 at 355 mJ cm -2 applied laser fluence. On the basis of the measured data, the acceleration of the emitted conidia at the plume front was approximately 10 9 x g. The conidia survived the absorbing film assisted forward transfer and associated mechanical shear without significant damages suggesting that the technique might be applicable to other more fragile types of biological objects and applications

Time-resolved stimulated emission depletion and energy transfer dynamics in two-photon excited EGFP

Science.gov (United States)

Masters, T. A.; Robinson, N. A.; Marsh, R. J.; Blacker, T. S.; Armoogum, D. A.; Larijani, B.; Bain, A. J.

2018-04-01

Time and polarization-resolved stimulated emission depletion (STED) measurements are used to investigate excited state evolution following the two-photon excitation of enhanced green fluorescent protein (EGFP). We employ a new approach for the accurate STED measurement of the hitherto unmeasured degree of hexadecapolar transition dipole moment alignment ⟨α40 ⟩ present at a given excitation-depletion (pump-dump) pulse separation. Time-resolved polarized fluorescence measurements as a function of pump-dump delay reveal the time evolution of ⟨α40 ⟩ to be considerably more rapid than predicted for isotropic rotational diffusion in EGFP. Additional depolarization by homo-Förster resonance energy transfer is investigated for both ⟨α20 ⟩ (quadrupolar) and ⟨α40 ⟩ transition dipole alignments. These results point to the utility of higher order dipole correlation measurements in the investigation of resonance energy transfer processes.

Analysis of electronic models for solar cells including energy resolved defect densities

Energy Technology Data Exchange (ETDEWEB)

Glitzky, Annegret

2010-07-01

We introduce an electronic model for solar cells including energy resolved defect densities. The resulting drift-diffusion model corresponds to a generalized van Roosbroeck system with additional source terms coupled with ODEs containing space and energy as parameters for all defect densities. The system has to be considered in heterostructures and with mixed boundary conditions from device simulation. We give a weak formulation of the problem. If the boundary data and the sources are compatible with thermodynamic equilibrium the free energy along solutions decays monotonously. In other cases it may be increasing, but we estimate its growth. We establish boundedness and uniqueness results and prove the existence of a weak solution. This is done by considering a regularized problem, showing its solvability and the boundedness of its solutions independent of the regularization level. (orig.)

Exploratory study on a statistical method to analyse time resolved data obtained during nanomaterial exposure measurements

International Nuclear Information System (INIS)

Clerc, F; Njiki-Menga, G-H; Witschger, O

2013-01-01

Most of the measurement strategies that are suggested at the international level to assess workplace exposure to nanomaterials rely on devices measuring, in real time, airborne particles concentrations (according different metrics). Since none of the instruments to measure aerosols can distinguish a particle of interest to the background aerosol, the statistical analysis of time resolved data requires special attention. So far, very few approaches have been used for statistical analysis in the literature. This ranges from simple qualitative analysis of graphs to the implementation of more complex statistical models. To date, there is still no consensus on a particular approach and the current period is always looking for an appropriate and robust method. In this context, this exploratory study investigates a statistical method to analyse time resolved data based on a Bayesian probabilistic approach. To investigate and illustrate the use of the this statistical method, particle number concentration data from a workplace study that investigated the potential for exposure via inhalation from cleanout operations by sandpapering of a reactor producing nanocomposite thin films have been used. In this workplace study, the background issue has been addressed through the near-field and far-field approaches and several size integrated and time resolved devices have been used. The analysis of the results presented here focuses only on data obtained with two handheld condensation particle counters. While one was measuring at the source of the released particles, the other one was measuring in parallel far-field. The Bayesian probabilistic approach allows a probabilistic modelling of data series, and the observed task is modelled in the form of probability distributions. The probability distributions issuing from time resolved data obtained at the source can be compared with the probability distributions issuing from the time resolved data obtained far-field, leading in a

Investigation of Co nanoparticle formation using time-dependent and spatially-resolved X-ray absorption spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Zinoveva, S

2008-04-15

A crucial step towards controlled synthesis of nanoparticles is the detailed understanding of the various chemical processes that take place during the synthesis. X-ray Absorption Spectroscopy (XAS) is especially suitable for elucidating the type and structure of the intermediate metal species. It is applicable to materials that have no long range order and provides information on both electronic and geometric structures. Here a comparative study is reported of the formation of cobalt nanoparticles via thermolysis of two organometallic precursors dicobalt octacarbonyl (DCO) and alkyne-bridged dicobalt hexacarbonyl (ADH) in the presence of aluminum organics. Using time-dependent XAS a reaction pathway different from both the atom based La Mer model and the Watzky and Finsky autocatalytic surface growth model is observed. Where prior to the nucleation several intermediates are formed and the initial nucleus is composed of Co atoms coordinated with ligands Co{sub n}(CO){sub m} with n=2-3, m=3-5. The formation of Co nanoparticles was also investigated using a reaction different from thermolysis of cobalt carbonyls, namely reduction of Co (II) acetate by sodium borohydrate. Here the combination of microreactor system and spatially resolved XAS allowed ''in situ'' monitoring of the wet chemical synthesis. Several steps of the reaction were spatially resolved in the microreactor. The vertical size of the X-ray beam (50 {mu}m) focused with Kirkpatrick-Baez mirror system, determines the time resolution (better than 2 ms). The results provide direct insight into rapid process of nanoparticles formation and demonstrate the potential of this new technique for the fundamental studies of such type of processes where miniaturization and timeresolution are important. Like in the carbonyls thermolysis no evidence for the reduction of the starting complex to isolated Co{sup 0} atoms followed by nucleation of Co{sup 0} atoms was observed. (orig.)

Investigation of Co nanoparticle formation using time-dependent and spatially-resolved X-ray absorption spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Zinoveva, S.

2008-04-15

A crucial step towards controlled synthesis of nanoparticles is the detailed understanding of the various chemical processes that take place during the synthesis. X-ray Absorption Spectroscopy (XAS) is especially suitable for elucidating the type and structure of the intermediate metal species. It is applicable to materials that have no long range order and provides information on both electronic and geometric structures. Here a comparative study is reported of the formation of cobalt nanoparticles via thermolysis of two organometallic precursors dicobalt octacarbonyl (DCO) and alkyne-bridged dicobalt hexacarbonyl (ADH) in the presence of aluminum organics. Using time-dependent XAS a reaction pathway different from both the atom based La Mer model and the Watzky and Finsky autocatalytic surface growth model is observed. Where prior to the nucleation several intermediates are formed and the initial nucleus is composed of Co atoms coordinated with ligands Co{sub n}(CO){sub m} with n=2-3, m=3-5. The formation of Co nanoparticles was also investigated using a reaction different from thermolysis of cobalt carbonyls, namely reduction of Co (II) acetate by sodium borohydrate. Here the combination of microreactor system and spatially resolved XAS allowed ''in situ'' monitoring of the wet chemical synthesis. Several steps of the reaction were spatially resolved in the microreactor. The vertical size of the X-ray beam (50 {mu}m) focused with Kirkpatrick-Baez mirror system, determines the time resolution (better than 2 ms). The results provide direct insight into rapid process of nanoparticles formation and demonstrate the potential of this new technique for the fundamental studies of such type of processes where miniaturization and timeresolution are important. Like in the carbonyls thermolysis no evidence for the reduction of the starting complex to isolated Co{sup 0} atoms followed by nucleation of Co{sup 0} atoms was observed. (orig.)

Time-resolved photoemission micro-spectrometer using higher-order harmonics of Ti:sapphire laser

International Nuclear Information System (INIS)

Azuma, J.; Kamada, M.; Kondo, Y.

2004-01-01

Full text: A new photoemission spectrometer is under construction for the photoemission microscopy and the time-resolved pump- probe experiment. The higher order harmonics of the Ti:sapphire laser is used as the light source of the VUV region in this system. Because the fundamental laser is focused tightly into the rare gas jet to generate the higher order harmonics, the spot size of the laser, in other words, the spot size of the VUV light source is smaller than a few tens of micrometer. This smallness of the spot size has advantage for the microscopy. In order to compensate the low flux of the laser harmonics, a multilayer-coated schwaltzshild optics was designed. The multilayers play also as the monochromatic filter. The spatial resolution of this schwaltzshild system is found to be less than 1 micrometer by the ray-tracing calculations. A main chamber of the system is equipped with a time-of-flight energy analyzer to improve the efficiency of the electron detection. The main chamber and the gas chamber are separated by a differential pumping chamber and a thin Al foil. The system is designed for the study of the clean surface. It will be capable to perform the sub-micron photoemission microscopy and the femto-second pump-probe photoemission study for the various photo-excited dynamics on clean surfaces

Time-resolved absorption and hemoglobin concentration difference maps: a method to retrieve depth-related information on cerebral hemodynamics.

Science.gov (United States)

Montcel, Bruno; Chabrier, Renée; Poulet, Patrick

2006-12-01

Time-resolved diffuse optical methods have been applied to detect hemodynamic changes induced by cerebral activity. We describe a near infrared spectroscopic (NIRS) reconstruction free method which allows retrieving depth-related information on absorption variations. Variations in the absorption coefficient of tissues have been computed over the duration of the whole experiment, but also over each temporal step of the time-resolved optical signal, using the microscopic Beer-Lambert law.Finite element simulations show that time-resolved computation of the absorption difference as a function of the propagation time of detected photons is sensitive to the depth profile of optical absorption variations. Differences in deoxyhemoglobin and oxyhemoglobin concentrations can also be calculated from multi-wavelength measurements. Experimental validations of the simulated results have been obtained for resin phantoms. They confirm that time-resolved computation of the absorption differences exhibited completely different behaviours, depending on whether these variations occurred deeply or superficially. The hemodynamic response to a short finger tapping stimulus was measured over the motor cortex and compared to experiments involving Valsalva manoeuvres. Functional maps were also calculated for the hemodynamic response induced by finger tapping movements.

Electronic structure of heavy fermion system CePt2In7 from angle-resolved photoemission spectroscopy

International Nuclear Information System (INIS)

Shen Bing; Yu Li; Lyu Shou-Peng; Jia Xiao-Wen; Zhang Yan; Wang Chen-Lu; Hu Cheng; Ding Ying; Sun Xuan; Hu Yong; Liu Jing; Gao Qiang; Zhao Lin; Liu Guo-Dong; Liu Kai; Lu Zhong-Yi; Bauer, E D; Thompson, J D; Xu Zu-Yan; Chen Chuang-Tian

2017-01-01

We have carried out high-resolution angle-resolved photoemission measurements on the Ce-based heavy fermion compound CePt 2 In 7 that exhibits stronger two-dimensional character than the prototypical heavy fermion system CeCoIn 5 . Multiple Fermi surface sheets and a complex band structure are clearly resolved. We have also performed detailed band structure calculations on CePt 2 In 7 . The good agreement found between our measurements and the calculations suggests that the band renormalization effect is rather weak in CePt 2 In 7 . A comparison of the common features of the electronic structure of CePt 2 In 7 and CeCoIn 5 indicates that CeCoIn 5 shows a much stronger band renormalization effect than CePt 2 In 7 . These results provide new information for understanding the heavy fermion behaviors and unconventional superconductivity in Ce-based heavy fermion systems. (paper)

Operational Testing and Measurement of the Resolving Time of a Counting Assembly

International Nuclear Information System (INIS)

Manent, G.; Scheemaecker, J. de

1968-01-01

An experiment is described which constitutes a very sensitive test of the satisfactory operation of a counting assembly. It makes it possible to measure the resolving time of an assembly to an accuracy of 1 per cent. A certain number of examples are presented which show the sensitivity of the test. (author) [fr

The steady-state and time-resolved photophysical properties of a dimeric indium phthalocyanine complex

International Nuclear Information System (INIS)

Chen Yu; Araki, Yasuyuki; Dini, Danilo; Liu Ying; Ito, Osamu; Fujitsuka, Mamoru

2006-01-01

The steady-state and time-resolved photophysical properties and some molecular orbital calculation results of a dimeric indium phthalocyanine complex with an indium-indium bond, i.e., [tBu 4 PcIn] 2 .2tmed, have been described. The results regarding triplet excited state lifetimes can be ascribed to strong intramolecular interactions existing only in the excited state of this dimer because no significant difference in the absorption spectra of the tBu 4 PcInCl monomer and the [tBu 4 PcIn] 2 .2tmed dimer is observed, suggesting that no ground-state interaction can be assessed. The deactivation processes of the excited singlet state of [tBu 4 PcIn] 2 .2tmed are apparently faster than that of μ-oxo-bridged PcIn dimer [tBu 4 PcIn] 2 O. Molecular orbital calculation on the PcIn dimer shows no node between two indium atoms was found in the HOMO - 2 of the PcIn-InPc dimer, suggesting that bonding electrons distribute between two indium atoms

Quasiparticle dynamics across the full Brillouin zone of Bi2Sr2CaCu2O8+δ traced with ultrafast time and angle-resolved photoemission spectroscopy

Directory of Open Access Journals (Sweden)

Georgi L. Dakovski

2015-09-01

Full Text Available A hallmark in the cuprate family of high-temperature superconductors is the nodal-antinodal dichotomy. In this regard, angle-resolved photoemission spectroscopy (ARPES has proven especially powerful, providing band structure information directly in energy-momentum space. Time-resolved ARPES (trARPES holds great promise of adding ultrafast temporal information, in an attempt to identify different interaction channels in the time domain. Previous studies of the cuprates using trARPES were handicapped by the low probing energy, which significantly limits the accessible momentum space. Using 20.15 eV, 12 fs pulses, we show for the first time the evolution of quasiparticles in the antinodal region of Bi2Sr2CaCu2O8+δ and demonstrate that non-monotonic relaxation dynamics dominates above a certain fluence threshold. The dynamics is heavily influenced by transient modification of the electron-phonon interaction and phase space restrictions, in stark contrast to the monotonic relaxation in the nodal and off-nodal regions.

Heterogeneous time-resolved electrochemiluminoimmunoassay of thyroid stimulating hormone with magnetic beads at oxide-covered aluminum electrode

Energy Technology Data Exchange (ETDEWEB)

Ala-Kleme, Timo, E-mail: timo.ala-kleme@utu.fi

2017-06-15

The heterogeneous immunoassay of thyroid stimulating hormone (TSH) was detected by the time-resolved cathodic electrochemiluminescence immunoassay (tr-CECLIA) method using magnetic beads as a mobile support. The magnetic beads coated with sandwich type TSH immunoassay were captured with a magnet for washing and detection processes. The time-resolved cathodic electrochemiluminescence (tr-CECL) signal of Tb(III) chelate label was generated by cathodic pulse polarization in the aluminum working electrode and platinum counter electrode system. The detection method causes injection of high energy electrons into the aqueous solution near the aluminum electrode and creates rigid simultaneous oxidative and reductive conditions that excitate the Tb(III) chelate used as a label luminophore in the heterogeneous sandwich type immunoassay of TSH in the surface of the magnetic beads. The limit of detection of the method was about 50 mIU L{sup −1}. The precision of it was noticed to be good; the coefficient variation percentage was realized to be lower than 10 %. Unfortunately the limit of detection is not good enough for determination of analyte levels of very low concentrations for instance TSH in body fluids. The possible application areas of the method are in highly sophisticated micro or nano fluidic detection and sensor systems where the aspiration level of the analyte detection limit is not very high and the mobility and manageability and the large surface area of the magnetic beads can be utilized efficiently in separating, washing, moving, coating and detecting processes. In the case of tr-CECLIA the presented method makes possible to use multipurpose working electrodes instead of disposable ones.

Time- and angle-resolved photoemission spectroscopy with optimized high-harmonic pulses using frequency-doubled Ti:Sapphire lasers

International Nuclear Information System (INIS)

Eich, S.; Stange, A.; Carr, A.V.; Urbancic, J.; Popmintchev, T.; Wiesenmayer, M.; Jansen, K.; Ruffing, A.; Jakobs, S.; Rohwer, T.; Hellmann, S.; Chen, C.; Matyba, P.; Kipp, L.; Rossnagel, K.; Bauer, M.; Murnane, M.M.; Kapteyn, H.C.; Mathias, S.; Aeschlimann, M.

2014-01-01

Highlights: • We present a scheme to generate high intensity XUV pulses from HHG with variable time-bandwidth product. • Shorter-wavelength driven high-harmonic XUV trARPES provides higher photon flux and increased energy resolution. • High-quality high-harmonic XUV trARPES data with sub 150 meV energy and sub 30 fs time resolution is presented. - Abstract: Time- and angle-resolved photoemission spectroscopy (trARPES) using femtosecond extreme ultraviolet high harmonics has recently emerged as a powerful tool for investigating ultrafast quasiparticle dynamics in correlated-electron materials. However, the full potential of this approach has not yet been achieved because, to date, high harmonics generated by 800 nm wavelength Ti:Sapphire lasers required a trade-off between photon flux, energy and time resolution. Photoemission spectroscopy requires a quasi-monochromatic output, but dispersive optical elements that select a single harmonic can significantly reduce the photon flux and time resolution. Here we show that 400 nm driven high harmonic extreme-ultraviolet trARPES is superior to using 800 nm laser drivers since it eliminates the need for any spectral selection, thereby increasing photon flux and energy resolution to <150 meV while preserving excellent time resolution of about 30 fs

Developments in time-resolved high pressure x-ray diffraction using rapid compression and decompression

International Nuclear Information System (INIS)

Smith, Jesse S.; Sinogeikin, Stanislav V.; Lin, Chuanlong; Rod, Eric; Bai, Ligang; Shen, Guoyin

2015-01-01

Complementary advances in high pressure research apparatus and techniques make it possible to carry out time-resolved high pressure research using what would customarily be considered static high pressure apparatus. This work specifically explores time-resolved high pressure x-ray diffraction with rapid compression and/or decompression of a sample in a diamond anvil cell. Key aspects of the synchrotron beamline and ancillary equipment are presented, including source considerations, rapid (de)compression apparatus, high frequency imaging detectors, and software suitable for processing large volumes of data. A number of examples are presented, including fast equation of state measurements, compression rate dependent synthesis of metastable states in silicon and germanium, and ultrahigh compression rates using a piezoelectric driven diamond anvil cell

Characterization of type I, II, III, IV, and V collagens by time-resolved laser-induced fluorescence spectroscopy

Science.gov (United States)

Marcu, Laura; Cohen, David; Maarek, Jean-Michel I.; Grundfest, Warren S.

2000-04-01

The relative proportions of genetically distinct collagen types in connective tissues vary with tissue type and change during disease progression, development, wound healing, aging. This study aims to 1) characterize the spectro- temporal fluorescence emission of fiber different types of collagen and 2) assess the ability of time-resolved laser- induced fluorescence spectroscopy to distinguish between collagen types. Fluorescence emission of commercially available purified samples was induced with nitrogen laser excitation pulses and detected with a MCP-PMT connected to a digital storage oscilloscope. The recorded time-resolved emission spectra displayed distinct fluorescence emission characteristics for each collagen type. The time domain information complemented the spectral domain intensity data for improved discrimination between different collagen types. Our results reveal that analysis of the fluorescence emission can be used to characterize different species of collagen. Also, the results suggest that time-resolved spectroscopy can be used for monitoring of connective tissue matrix composition changes due to various pathological and non-pathological conditions.

Time and spatially resolved LIF of OH in a plasma filament in atmospheric pressure He-H2O

International Nuclear Information System (INIS)

Verreycken, T; Van der Horst, R M; Baede, A H F M; Van Veldhuizen, E M; Bruggeman, P J

2012-01-01

The production of OH in a nanosecond pulsed filamentary discharge generated in pin-pin geometry in a He-H 2 O mixture is studied by time and spatially resolved laser-induced fluorescence. Apart from the OH density the gas temperature and the electron density are also measured. Depending on the applied voltage the discharge is in a different mode. The maximum electron densities in the low- (1.3 kV) and high-density (5 kV) modes are 2 × 10 21 m -3 and 7 × 10 22 m -3 , respectively. The gas temperature in both modes does not exceed 600 K. In the low-density mode the maximum OH density is at the centre of the discharge filament, while in the high-density mode the largest OH density is observed on the edge of the discharge. A chemical model is used to obtain an estimate of the absolute OH density. The chemical model also shows that charge exchange and dissociative recombination can explain the production of OH in the case of the high-density mode. (paper)

Measurement of centroid trajectory of Dragon-I electron beam

International Nuclear Information System (INIS)

Jiang Xiaoguo; Wang Yuan; Zhang Wenwei; Zhang Kaizhi; Li Jing; Li Chenggang; Yang Guojun

2005-01-01

The control of the electron beam in an intense current linear induction accelerator (LIA) is very important. The center position of the electron beam and the beam profile are two important parameters which should be measured accurately. The setup of a time-resolved measurement system and a data processing method for determining the beam center position are introduced for the purpose of obtaining Dragon-I electron beam trajectory including beam profile. The actual results show that the centroid position error can be controlled in one to two pixels. the time-resolved beam centroid trajectory of Dragon-I (18.5 MeV, 2 kA, 90 ns) is obtained recently in 10 ns interval, 3 ns exposure time with a multi-frame gated camera. The results show that the screw movement of the electron beam is mainly limited in an area with a radius of 0.5 mm and the time-resolved diameters of the beam are 8.4 mm, 8.8 mm, 8.5 mm, 9.3 mm and 7.6 mm. These results have provided a very important support to several research areas such as beam trajectory tuning and beam transmission. (authors)

Time-resolved infrared absorption study of nine TiO{sub 2} photocatalysts

Energy Technology Data Exchange (ETDEWEB)

Yamakata, Akira; Ishibashi, Taka-aki [Kanagawa Academy of Science and Technology (KAST), KSP, Takatsu, Kawasaki 213-0012 (Japan); Onishi, Hiroshi [Kanagawa Academy of Science and Technology (KAST), KSP, Takatsu, Kawasaki 213-0012 (Japan)], E-mail: oni@kobe-u.ac.jp

2007-10-15

Electron kinetics of nine TiO{sub 2} catalysts were compared in a microsecond time domain. Each catalyst was band-gap excited with an UV light pulse, and electron-induced absorption of mid infrared light was observed as a function of time delay. The probability of electron-hole recombination in the bulk, electron attachment to adsorbed oxygen, and hole attachment to adsorbed methoxy species was estimated.

Time resolved ion beam induced charge collection

International Nuclear Information System (INIS)

Sexton W, Frederick; Walsh S, David; Doyle L, Barney; Dodd E, Paul

2000-01-01

Under this effort, a new method for studying the single event upset (SEU) in microelectronics has been developed and demonstrated. Called TRIBICC, for Time Resolved Ion Beam Induced Charge Collection, this technique measures the transient charge-collection waveform from a single heavy-ion strike with a -.03db bandwidth of 5 GHz. Bandwidth can be expanded up to 15 GHz (with 5 ps sampling windows) by using an FFT-based off-line waveform renormalization technique developed at Sandia. The theoretical time resolution of the digitized waveform is 24 ps with data re-normalization and 70 ps without re-normalization. To preserve the high bandwidth from IC to the digitizing oscilloscope, individual test structures are assembled in custom high-frequency fixtures. A leading-edge digitized waveform is stored with the corresponding ion beam position at each point in a two-dimensional raster scan. The resulting data cube contains a spatial charge distribution map of up to 4,096 traces of charge (Q) collected as a function of time. These two dimensional traces of Q(t) can cover a period as short as 5 ns with up to 1,024 points per trace. This tool overcomes limitations observed in previous multi-shot techniques due to the displacement damage effects of multiple ion strikes that changed the signal of interest during its measurement. This system is the first demonstration of a single-ion transient measurement capability coupled with spatial mapping of fast transients

Time resolved ion beam induced charge collection

Energy Technology Data Exchange (ETDEWEB)

SEXTON,FREDERICK W.; WALSH,DAVID S.; DOYLE,BARNEY L.; DODD,PAUL E.

2000-04-01

Under this effort, a new method for studying the single event upset (SEU) in microelectronics has been developed and demonstrated. Called TRIBICC, for Time Resolved Ion Beam Induced Charge Collection, this technique measures the transient charge-collection waveform from a single heavy-ion strike with a {minus}.03db bandwidth of 5 GHz. Bandwidth can be expanded up to 15 GHz (with 5 ps sampling windows) by using an FFT-based off-line waveform renormalization technique developed at Sandia. The theoretical time resolution of the digitized waveform is 24 ps with data re-normalization and 70 ps without re-normalization. To preserve the high bandwidth from IC to the digitizing oscilloscope, individual test structures are assembled in custom high-frequency fixtures. A leading-edge digitized waveform is stored with the corresponding ion beam position at each point in a two-dimensional raster scan. The resulting data cube contains a spatial charge distribution map of up to 4,096 traces of charge (Q) collected as a function of time. These two dimensional traces of Q(t) can cover a period as short as 5 ns with up to 1,024 points per trace. This tool overcomes limitations observed in previous multi-shot techniques due to the displacement damage effects of multiple ion strikes that changed the signal of interest during its measurement. This system is the first demonstration of a single-ion transient measurement capability coupled with spatial mapping of fast transients.

Plastique: A synchrotron radiation beamline for time resolved fluorescence in the frequency domain

Science.gov (United States)

De Stasio, Gelsomina; Zema, N.; Antonangeli, F.; Savoia, A.; Parasassi, T.; Rosato, N.

1991-06-01

PLASTIQUE is the only synchrotron radiation beamline in the world that performs time resolved fluorescence experiments in frequency domain. These experiments are extremely valuable sources of information on the structure and dynamics of molecules. We describe the beamline and some initial data.

Plasma polarization spectroscopy. Time resolved spectroscopy in soft x-ray region on recombining plasma

International Nuclear Information System (INIS)

Iwamae, Atsushi; Hasuo, Masahiro; Atake, Makoto; Hasegawa, Noboru; Kawachi, Tetsuya

2007-01-01

We present an experimental study of polarization of emission radiations from recombining plasmas generated by the interaction of 60 fs ultra-short laser pulses with a gas jet. Time-resolved spectroscopy with a temporal resolution of 5 ps with repetitive accumulation is used to follow the recombination time histories. (author)

Depth-Resolved Composition and Electronic Structure of Buried Layers and Interfaces in a LaNiO{sub 3}/SrTiO{sub 3} Superlattice from Soft- and Hard- X-ray Standing-Wave Angle-Resolved Photoemission

Energy Technology Data Exchange (ETDEWEB)

Eiteneer, D. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Pálsson, G.K., E-mail: gunnar.palsson@physics.uu.se [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Nemšák, S. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Peter-Grünberg-Institut PGI-6, Forschungszentrum Julich, 52425 Julich (Germany); Gray, A.X. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Kaiser, A.M. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Son, J.; LeBeau, J. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Conti, G. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); and others

2016-08-15

Highlights: • Depth resolved electronic structure of LaNiO{sub 3}/SrTiO{sub 3} superlattices is measured. • The structure is determined by x-ray standing wave angle-resolved photoemission. • Similarity to the electronic structure of La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} is discussed. - Abstract: LaNiO{sub 3} (LNO) is an intriguing member of the rare-earth nickelates in exhibiting a metal-insulator transition for a critical film thickness of about 4 unit cells [Son et al., Appl. Phys. Lett. 96, 062114 (2010)]; however, such thin films also show a transition to a metallic state in superlattices with SrTiO{sub 3} (STO) [Son et al., Appl. Phys. Lett. 97, 202109 (2010)]. In order to better understand this transition, we have studied a strained LNO/STO superlattice with 10 repeats of [4 unit-cell LNO/3 unit-cell STO] grown on an (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7} substrate using soft x-ray standing-wave-excited angle-resolved photoemission (SWARPES), together with soft- and hard- x-ray photoemission measurements of core levels and densities-of-states valence spectra. The experimental results are compared with state-of-the-art density functional theory (DFT) calculations of band structures and densities of states. Using core-level rocking curves and x-ray optical modeling to assess the position of the standing wave, SWARPES measurements are carried out for various incidence angles and used to determine interface-specific changes in momentum-resolved electronic structure. We further show that the momentum-resolved behavior of the Ni 3d e{sub g} and t{sub 2g} states near the Fermi level, as well as those at the bottom of the valence bands, is very similar to recently published SWARPES results for a related La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} superlattice that was studied using the same technique (Gray et al., Europhysics Letters 104, 17004 (2013)), which further validates this experimental approach and our conclusions. Our

Exploring electronic structure of one-atom thick polycrystalline graphene films: A nano angle resolved photoemission study

Science.gov (United States)

Avila, José; Razado, Ivy; Lorcy, Stéphane; Fleurier, Romain; Pichonat, Emmanuelle; Vignaud, Dominique; Wallart, Xavier; Asensio, María C.

2013-01-01

The ability to produce large, continuous and defect free films of graphene is presently a major challenge for multiple applications. Even though the scalability of graphene films is closely associated to a manifest polycrystalline character, only a few numbers of experiments have explored so far the electronic structure down to single graphene grains. Here we report a high resolution angle and lateral resolved photoelectron spectroscopy (nano-ARPES) study of one-atom thick graphene films on thin copper foils synthesized by chemical vapor deposition. Our results show the robustness of the Dirac relativistic-like electronic spectrum as a function of the size, shape and orientation of the single-crystal pristine grains in the graphene films investigated. Moreover, by mapping grain by grain the electronic dynamics of this unique Dirac system, we show that the single-grain gap-size is 80% smaller than the multi-grain gap recently reported by classical ARPES. PMID:23942471

Steady-state and time-resolved spectroscopic investigations on intramolecular electron transfer processes within a synthesized methoxynaphthalene dyad by using a nematic liquid crystal medium

International Nuclear Information System (INIS)

Bardhan, Munmun; Mandal, Paulami; De, Asish; Kumar De, Avijit; Chowdhury, Joydeep; Ganguly, Tapan

2010-01-01

UV-vis, steady state and time-resolved spectroscopic investigations were made on photoinduced charge separation and thermal charge recombination processes involved within a novel synthesized dyad, 1-(4-chloro-phenyl)-3-(4-methoxy-naphthalen-1-yl)-propenone (MNCA) where the donor 1-methoxynaphthalene (MNT) and the acceptor p-choloroacetophenone (PCA) moieties are connected by a short unsaturated olefinic bond. The measurements were made within the pseudo-ordered domain (just above nematic-isotropic (N-I) phase transition temperature, >308 K) of a nematic liquid crystal, 4-(n-pentyl)-4'-cyanobiphenyl (5CB). Results observed are compared with those obtained from the similar measurements in isotropic media. The charge separation and recombination rates remain more-or-less unchanged within the experimental error irrespective of the polarity of the environment, whether in pseudo-ordered domain (ε S ∼10.5) of a nematic liquid crystal 5CB or in highly polar isotropic medium ACN (ε S ∼37.5). The structural rigidity of the dyad MNCA having stable elongated form both in the ground as well as in the photoexcited states seems to be the reason for this unique behavior of solvent insensitivity. The theoretical predictions done by ab initio method density functional theory (DFT) with B3LYP/6-311 G (d, p) basis function correlate well with experimental observations of formations of only one stable elongated (E-type) conformer both in the ground and electronic excited state.

Steady-state and time-resolved spectroscopic investigations on intramolecular electron transfer processes within a synthesized methoxynaphthalene dyad by using a nematic liquid crystal medium

Energy Technology Data Exchange (ETDEWEB)

Bardhan, Munmun; Mandal, Paulami; De, Asish; Kumar De, Avijit [Department of Spectroscopy, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, West Bengal (India); Chowdhury, Joydeep [Sammilani Mahavidyalaya Baghajatin Station, West Bengal (India); Ganguly, Tapan, E-mail: sptg@mahendra.iacs.res.i [Department of Spectroscopy, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, West Bengal (India)

2010-06-15

UV-vis, steady state and time-resolved spectroscopic investigations were made on photoinduced charge separation and thermal charge recombination processes involved within a novel synthesized dyad, 1-(4-chloro-phenyl)-3-(4-methoxy-naphthalen-1-yl)-propenone (MNCA) where the donor 1-methoxynaphthalene (MNT) and the acceptor p-choloroacetophenone (PCA) moieties are connected by a short unsaturated olefinic bond. The measurements were made within the pseudo-ordered domain (just above nematic-isotropic (N-I) phase transition temperature, >308 K) of a nematic liquid crystal, 4-(n-pentyl)-4'-cyanobiphenyl (5CB). Results observed are compared with those obtained from the similar measurements in isotropic media. The charge separation and recombination rates remain more-or-less unchanged within the experimental error irrespective of the polarity of the environment, whether in pseudo-ordered domain (epsilon{sub S}approx10.5) of a nematic liquid crystal 5CB or in highly polar isotropic medium ACN (epsilon{sub S}approx37.5). The structural rigidity of the dyad MNCA having stable elongated form both in the ground as well as in the photoexcited states seems to be the reason for this unique behavior of solvent insensitivity. The theoretical predictions done by ab initio method density functional theory (DFT) with B3LYP/6-311 G (d, p) basis function correlate well with experimental observations of formations of only one stable elongated (E-type) conformer both in the ground and electronic excited state.

Time-resolved terahertz spectroscopy of conjugated polymer/CdSe nanorod composites

DEFF Research Database (Denmark)

Cooke, David; Lek, Jun Y.; Krebs, Frederik C

2010-01-01

report ultrafast carrier dynamics in hybrid CdSe nanorod / poly(3-hexythiophene) (P3HT) bulk heterojunction films measured by time-resolved terahertz spectroscopy, and compare to the well studied P3HT/phenyl-C61-butyric acid methyl ester (PCBM) blend. Both films show an improved peak...... photoconductivity compared to P3HT alone, consistent with efficient charge transfer. The photoconductivity dynamics show fast, picosecond trapping or recombination in the hybrid blend while the all-organic film shows no such loss of mobile charge over ns time scales. The ac conductivity for all samples is well...

Simulation of multi-photon emission isotopes using time-resolved SimSET multiple photon history generator

Energy Technology Data Exchange (ETDEWEB)

Chiang, Chih-Chieh; Lin, Hsin-Hon; Lin, Chang-Shiun; Chuang, Keh-Shih [Department of Biomedical Engineering and Environmental Sciences, National Tsing-HuaUniversity, Hsinchu, Taiwan (China); Jan, Meei-Ling [Health Physics Division, Institute of Nuclear Energy Research, Atomic Energy Council, Taoyuan, Taiwan (China)

2015-07-01

Abstract-Multiple-photon emitters, such as In-111 or Se-75, have enormous potential in the field of nuclear medicine imaging. For example, Se-75 can be used to investigate the bile acid malabsorption and measure the bile acid pool loss. The simulation system for emission tomography (SimSET) is a well-known Monte Carlo simulation (MCS) code in nuclear medicine for its high computational efficiency. However, current SimSET cannot simulate these isotopes due to the lack of modeling of complex decay scheme and the time-dependent decay process. To extend the versatility of SimSET for simulation of those multi-photon emission isotopes, a time-resolved multiple photon history generator based on SimSET codes is developed in present study. For developing the time-resolved SimSET (trSimSET) with radionuclide decay process, the new MCS model introduce new features, including decay time information and photon time-of-flight information, into this new code. The half-life of energy states were tabulated from the Evaluated Nuclear Structure Data File (ENSDF) database. The MCS results indicate that the overall percent difference is less than 8.5% for all simulation trials as compared to GATE. To sum up, we demonstrated that time-resolved SimSET multiple photon history generator can have comparable accuracy with GATE and keeping better computational efficiency. The new MCS code is very useful to study the multi-photon imaging of novel isotopes that needs the simulation of lifetime and the time-of-fight measurements. (authors)

Time-resolved methods in biophysics. 6. Time-resolved Laue crystallography as a tool to investigate photo-activated protein dynamics.

Science.gov (United States)

Bourgeois, Dominique; Schotte, Friedrich; Brunori, Maurizio; Vallone, Beatrice

2007-10-01

When polychromatic X-rays are shined onto crystalline material, they generate a Laue diffraction pattern. At third generation synchrotron radiation sources, a single X-ray pulse of approximately 100 ps duration is enough to produce interpretable Laue data from biomolecular crystals. Thus, by initiating biological turnover in a crystalline protein, structural changes along the reaction pathway may be filmed by ultra-fast Laue diffraction. Using laser-light as a trigger, transient species in photosensitive macromolecules can be captured at near atomic resolution with sub-nanosecond time-resolution. Such pump-probe Laue experiments have now reached an outstanding level of sophistication and have found a domain of excellence in the investigation of light-sensitive proteins undergoing cyclic photo-reactions and producing stiff crystals. The main theoretical concepts of Laue diffraction and the challenges associated with time-resolved experiments on biological crystals are recalled. The recent advances in the design of experiments are presented in terms of instrumental choices, data collection strategy and data processing, and some of the inherent difficulties of the method are highlighted. The discussion is based on the example of myoglobin, a protein that has traversed the whole history of pump-probe Laue diffraction, and for which a massive amount of data have provided considerable insight into the understanding of protein dynamics.

A time resolving data acquisition system for multiple high-resolution position sensitive detectors

International Nuclear Information System (INIS)

Dimmler, D.G.

1988-01-01

An advanced time resolving data collection system for use in neutron and x-ray spectrometry has been implemented and put into routine operation. The system collects data from high-resolution position-sensitive area detectors with a maximum cumulative rate of 10/sup 6/ events per second. The events are sorted, in real-time, into many time-slice arrays. A programmable timing control unit allows for a wide choice of time sequences and time-slice array sizes. The shortest dwell time on a slice may be below 1 ms and the delay to switch between slices is zero

Time-resolved x-ray spectra from laser-generated high-density plasmas