1,721,256 research outputs found
Interference of electron wave packets in atomic ionization by subcycle sculpted laser pulses
Get PDFWe present a theoretical analysis of the atomic photoelectron emission spectra produced by a linearly polarized sculpted laser pulse of two colors with frequencies ω and 2ω. The spectrum of the "direct" electrons with intermediate energies prominently features both intracycle and intercycle interferences. We derive a simple analytic expression for this spectral range based on a semiclassical approximation of the time-dependent distorted wave strong-field approximation generalized to strong-field ionization by a two-color pulse. We verify its applicability to approximately represent the intricate interference patterns by comparison with the exact solutions of the time-dependent Schrödinger equation and with the strong-field approximation. We show that the interference patterns can be tuned and its contrast enhanced by the additional "knob" available, the relative phase between the two frequency components. The present results confirm that two-color ionization allows resolving interference structures originating from trajectories launched within a time interval of less than 100 as [X. Xie et al., Phys. Rev. Lett. 108, 193004 (2012)].Fil: Arbo, Diego. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomia y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomia y Física del Espacio; ArgentinaFil: Nagele, Stefan. Vienna University of Technology; AustriaFil: Tong, Xiao Min. Tsukuba University; JapónFil: Xie, Xinhua. Vienna University of Technology; AustriaFil: Kitzler, Markus. Vienna University of Technology; AustriaFil: Burgdörfer, Joachim. Vienna University of Technology; Austri
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
From Atoms to Solids, from Lasers to Intense X-rays
No full textThis book documents the recent vivid developments in the research field of ultrashort intense light pulses for probing and controlling ultrafast dynamics. The recent fascinating results in studying and controlling ultrafast dynamics in ever more complicated systems such as (bio-)molecules and structures of meso- to macroscopic sizes on ever shorter time-scales are presented. The book is written by some of the most eminent experimental and theoretical experts in the field. It covers the new groundbreaking research directions that were opened by the availability of new light sources such as fully controlled intense laser fields with durations down to a single oscillation cycle, short-wavelength laser-driven attosecond pulses and intense X-ray pulses from the upcoming free electron lasers. These light sources allowed the investigation of dynamics in atoms, molecules, clusters, on surfaces and very recently also in nanostructures and solids in new regimes of parameters which, in turn, led to the identification of completely new dynamics and methods for controlling it. Example topics covered by this book include the study of ultrafast processes in large molecules using attosecond pulses, control of ultrafast electron dynamics in solids with shaped femtosecond laser pulses, light-driven ultrafast plasmonic processes on surfaces and in nanostructures as well as research on atomic and molecular systems under intense X-ray radiation. This book is equally helpful for people who would like to step into this field (e.g. young researchers), for whom it provides a broad introduction, as well as for already experienced researchers who may enjoy the exhaustive discussion that covers the research on essentially all currently studied objects and with all available ultrafast pulse sources
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Ionisierung und Fragmentierung von Atomen und Molekülen in starken Laserfeldern
No full textThis thesis employs a novel momentum imaging technique to investigate the interaction of atoms and molecules with strong laser fields. The goal is to gain better insight into their behavior under such interaction and apply this knowledge to steer and control some of the most important atomic and molecular processes. One of these processes is molecular fragmentation. The first studied experiments deal with the deprotonation process in hydrocarbons after being doubly ionized by intense laser pulses. A feature makes this fragmentation special is that it happens on nanosecond to microsecond timescale, in contrast to femtosecond or picosecond timescale on which most fragmentation processes happen. We find the lifetime of the dications leading to this fragmentation and investigate the effect of laser pulse parameters on this process. Furthermore, quantum chemical simulations are performed to find the origin of this delayed deprotonation. In the next study, we report experiments on direct observation of molecular oxygen production from the fragmentation of doubly ionized carbon dioxide in strong laser fields. Our accompanying simulations and pump-probe measurements indicate that carbon dioxide molecules undergo bending motion during strong-field ionization which supports the formation of molecular oxygen. One of the other processes is frustrated tunneling ionization, in which an ionized electron is recaptured by the parent ion in some high-lying Rydberg states within the three-step model of strong-field interaction. In this regard, we investigate such high-lying Rydberg states produced in strong laser fields by detecting electrons, emitted after the strong-field interaction, together with the parent ions in coincidence measurements. Simulations show that both tunneling ionization by the weak dc field of the reaction microscope spectrometer and photoionization by blackbody radiation contribute to delayed electron emission on nanosecond to microsecond timescale. By employing this technique of detection, in the next step, we demonstrate control over the localization of the high-lying Rydberg wave packets in argon atoms with orthogonally polarized two-color laser fields. The measured ionization signals of high-lying Rydberg states show that the dc-field induced ionization yield oscillates with the relative two-color phase with a period of 2Ï , while the photoionization signal by blackbody radiation shows a period of Ï . Simulations indicate that this observation is a clear signature of the asymmetric localization of electrons recaptured into very elongated (with low angular momentum) high-lying Rydberg states after conclusion of the laser pulse
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Attosecond probe of valence electron wavepackets by sub-cycle sculpted laser fields
Get PDFWe experimentally and theoretically demonstrate a self-referenced wave-function retrieval of a valence-electron wave packet during its creation by strong-field ionization with a sculpted laser field. Key is the control over interferences arising at different time scales. Our work shows that the measurement of subcycle electron wave-packet interference patterns can serve as a tool to retrieve the structure and dynamics of the valence-electron cloud in atoms on a sub-10-as time scale.Fil: Xie, Xinhua. Vienna University of Technology; AustriaFil: Roither, Stefan. Vienna University of Technology; AustriaFil: Kartashov, Daniil. Vienna University of Technology; AustriaFil: Persson, Emil. Vienna University of Technology; AustriaFil: Arbo, Diego. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Vienna University of Technology; AustriaFil: Zhang, Li. Vienna University of Technology; AustriaFil: Gräfe, Stefanie. Vienna University of Technology; AustriaFil: Schöffler, Markus S.. Vienna University of Technology; AustriaFil: Burgdörfer, Joachim. Vienna University of Technology; AustriaFil: Baltuska, Andrius. Vienna University of Technology; AustriaFil: Kitzler, Markus. Vienna University of Technology; Austri
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