Attosecond Control of Ionization Dynamics

Attosecond pulses can be used to initiate and control electron dynamics on a sub-femtosecond time scale. The first step in this process occurs when an atom absorbs an ultraviolet photon leading to the formation of an attosecond electron wave packet (EWP). Until now, attosecond pulses have been used to create free EWPs in the continuum, where they quickly disperse. In this paper we use a train of attosecond pulses, synchronized to an infrared (IR) laser field, to create a series of EWPs that are below the ionization threshold in helium. We show that the ionization probability then becomes a function of the delay between the IR and attosecond fields. Calculations that reproduce the experimental results demonstrate that this ionization control results from interference between transiently bound EWPs created by different pulses in the train. In this way, we are able to observe, for the first time, wave packet interference in a strongly driven atomic system.Comment: 8 pages, 4 figure

Macroscopic studies of short-pulse high-order harmonic generation using the time-dependent Schrödinger equation

We consider high harmonic generation by ultrashort (27–108 fs) laser pulses and calculate the macroscopic response of a collection of atoms to such a short pulse. We show how the harmonic spectrum after propagation through the medium is significantly different from the single-atom spectrum. We use single-atom data calculated by integration of the time-dependent Schrödinger equation and propose a method, based on an adiabatic approximation, to extract the data necessary to perform a propagation calculation. © 1998 The American Physical Society

0200: Predictors of angiographically visible distal embolization in ST elevation myocardial infarction patients treated by primary percutaneous coronary intervention and thrombectomy

Aspiration thrombectomy during primary percutaneous coronary intervention (p-PCI) in ST elevation myocardial infarction (STEMI) has been proposed to restore myocardial reperfusion. But important controversies remain concerning the usefulness of thrombectomy to improve this perfusion. Our objective was to evaluate the impact of manual thrombectomy on the occur-rence of angiographically visible distal embolization (AVDE) during p-PCI in STEMI. 346 consecutive patients admitted for STEMI who underwent p-PCI and thrombectomy were included. Clinical, angiographic and therapeutics characteristics were assessed. AVDE was defined as an abrupt vessel closure occurring at any point during the PCI procedure and that was not present at baseline. Patients were divided into 2 groups: with AVDE (59 patients) and without AVDE 287 patients.Comparing the 2 groups, patients with AVDE were more likely to be older than 60 year-old (67 vs. 50%; p=0.014), with a higher proportion of women (34 vs. 20%; p=0,027), of right coronary artery lesion (57 vs. 34.5%; p=0.001).Conversely, smoking and left anterior descending coronary artery lesion were more frequent in patients without AVDE (respectively 63 vs. 46%; p=0.014 and 50 vs. 30%; p=0.005).Univariate analysis identify age>60 (OR[95% CI]:2.09(1.15-3.78), p=0.015), female gender (OR[95% CI]:2.02(1.09-3.73), p=0,024), culprit coronary diameter>3mm (OR[95% CI] as predictors of AVDE during p-PCI for STEMI.By multivariate analysis, culprit coronary diameter>3mm (OR[95% CI]: 1.90 (1.01-3.56); p=0.048) and and the right coronary artery culprit lesion site (OR[95% CI]:2.48(1.36-4.52); p=0.003) were independent factors associated with AVDE. AVDE complicating p-PCI during STEMI is frequent (17%). Strikingly we found that successful thrombectomy does not prevent from AVDE. Conversely, we highlight that patients with culprit coronary artery diameter>3mm and STEMI due to right coronary artery occlusion are more likely to develop AVDE

Differences in measures of the fiscal multiplier and the reduced-form vector autoregression

The literature has recently asked whether the effects of fiscal policy vary with the state of the economy (Christiano, Eichenbaum, and Rebelo 2011; Rendahl 2014; Auerbach and Gorodnichenko 2012). We study this question in the context of vector autoregression (VAR) estimation. We show formally that, if (asymptotically) the parameters of the reduced-form VAR differ, then the dynamic effects of fiscal policy differ as well, generically and for any set of identification assumptions. Thus, in theory, the econometrician can detect these differences (either across time or space) generically just by relying on reduced-form VAR estimation

Non-sequential triple ionization in strong fields

We consider the final stage of triple ionization of atoms in a strong linearly polarized laser field. We propose that for intensities below the saturation value for triple ionization the process is dominated by the simultaneous escape of three electrons from a highly excited intermediate complex. We identify within a classical model two pathways to triple ionization, one with a triangular configuration of electrons and one with a more linear one. Both are saddles in phase space. A stability analysis indicates that the triangular configuration has the larger cross sections and should be the dominant one. Trajectory simulations within the dominant symmetry subspace reproduce the experimentally observed distribution of ion momenta parallel to the polarization axis.Comment: 9 pages, 8 figures, accepted for publication in Phys. Rev.

Coherent Electron Scattering Captured by an Attosecond Quantum Stroboscope

The basic properties of atoms, molecules and solids are governed by electron dynamics which take place on extremely short time scales. To measure and control these dynamics therefore requires ultrafast sources of radiation combined with efficient detection techniques. The generation of extreme ultraviolet (XUV) attosecond (1 as = 10-18 s) pulses has, for the first time, made direct measurements of electron dynamics possible. Nevertheless, while various applications of attosecond pulses have been demonstrated experimentally, no one has yet captured or controlled the full three dimensional motion of an electron on an attosecond time scale. Here we demonstrate an attosecond quantum stroboscope capable of guiding and imaging electron motion on a sub-femtosecond (1 fs = 10-15 s) time scale. It is based on a sequence of identical attosecond pulses which are synchronized with a guiding laser field. The pulse to pulse separation in the train is tailored to exactly match an optical cycle of the laser field and the electron momentum distributions are detected with a velocity map imaging spectrometer (VMIS). This technique has enabled us to guide ionized electrons back to their parent ion and image the scattering event. We envision that coherent electron scattering from atoms, molecules and surfaces captured by the attosecond quantum stroboscope will complement more traditional scattering techniques since it provides high temporal as well as spatial resolution.Comment: 6 pages, 4 figure

Attosecond electron spectroscopy using a novel interferometric pump-probe technique

We present an interferometric pump-probe technique for the characterization of attosecond electron wave packets (WPs) that uses a free WP as a reference to measure a bound WP. We demonstrate our method by exciting helium atoms using an attosecond pulse with a bandwidth centered near the ionization threshold, thus creating both a bound and a free WP simultaneously. After a variable delay, the bound WP is ionized by a few-cycle infrared laser precisely synchronized to the original attosecond pulse. By measuring the delay-dependent photoelectron spectrum we obtain an interferogram that contains both quantum beats as well as multi-path interference. Analysis of the interferogram allows us to determine the bound WP components with a spectral resolution much better than the inverse of the attosecond pulse duration.Comment: 5 pages, 4 figure

XUV digital in-line holography using high-order harmonics

A step towards a successful implementation of timeresolved digital in-line holography with extreme ultraviolet radiation is presented. Ultrashort XUV pulses are produced as high-order harmonics of a femtosecond laser and a Schwarzschild objective is used to focus harmonic radiation at 38 nm and to produce a strongly divergent reference beam for holographic recording. Experimental holograms of thin wires are recorded and the objects reconstructed. Descriptions of the simulation and reconstruction theory and algorithms are also given. Spatial resolution of few hundreds of nm is potentially achievable, and micrometer resolution range is demonstrated.Comment: 8 pages, 8 figure

Generation of ultra-short light pulses by a rapidly ionizing thin foil

A thin and dense plasma layer is created when a sufficiently strong laser pulse impinges on a solid target. The nonlinearity introduced by the time-dependent electron density leads to the generation of harmonics. The pulse duration of the harmonic radiation is related to the risetime of the electron density and thus can be affected by the shape of the incident pulse and its peak field strength. Results are presented from numerical particle-in-cell-simulations of an intense laser pulse interacting with a thin foil target. An analytical model which shows how the harmonics are created is introduced. The proposed scheme might be a promising way towards the generation of attosecond pulses. PACS number(s): 52.40.Nk, 52.50.Jm, 52.65.RrComment: Second Revised Version, 13 pages (REVTeX), 3 figures in ps-format, submitted for publication to Physical Review E, WWW: http://www.physik.tu-darmstadt.de/tqe

Neutrino - nucleon reaction rates in the supernova core in the relativistic random phase approximation

In view of the application to supernova simulations, we calculate neutrino reaction rates with nucleons via the neutral and charged currents in the supernova core in the relativistic random phase approximation (RPA) and study their effects on the opacity of the supernova core. The formulation is based on the Lagrangian employed in the calculation of nuclear equation of state (EOS) in the relativistic mean field theory (RMF). The nonlinear meson terms are treated appropriately so that the consistency of the density correlation derived in RPA with the thermodynamic derivative obtained from EOS by RMF is satisfied in the static and long wave length limit. We employ pion and rho meson exchange interactions together with the phenomenological Landau-Migdal parameters for the isospin-dependent nuclear interactions. We find that both the charged and neutral current reaction rates are suppressed from the standard Bruenn's approximate formula considerably in the high density regime. In the low density regime, on the other hand, the vector current contribution to the neutrino-nucleon scattering rate is enhanced in the vicinity of the boundary of the liquid-gas phase transition, while the other contributions are moderately suppressed there also. In the high temperature regime or in the regime where electrons have a large chemical potential, the latter of which is important only for the electron capture process and its inverse process, the recoil of nucleons cannot be neglected and further reduces the reaction rates with respect to the standard approximate formula which discards any energy transfer in the processes. These issues could have a great impact on the neutrino heating mechanism of collapse-driven supernovae.Comment: 16pages, 19figures, submitted to PR