505 research outputs found
Theory of Auger decay by laser-dressed atoms
We devise an ab initio formalism for the quantum dynamics of Auger decay by
laser-dressed atoms which are inner-shell ionized by extreme ultraviolet (XUV)
light. The optical dressing laser is assumed to be sufficiently weak such that
ground-state electrons are neither excited nor ionized by it. However, the
laser has a strong effect on continuum electrons which we describe in
strong-field approximation with Volkov waves. The XUV light pulse has a low
peak intensity and its interaction is treated as a one-photon process. The
quantum dynamics of the inner-shell hole creation with subsequent Auger decay
is given by equations of motion (EOMs). For this paper, the EOMs are simplified
in terms of an essential-states model which is solved analytically and averaged
over magnetic subshells. We apply our theory to the M_4,5 N_1 N_2,3 Auger decay
of a 3d hole in a krypton atom. The orbitals are approximated by scaled
hydrogenic wave functions. A single attosecond pulse produces 3d vacancies
which Auger decay in the presence of an 800nm laser with an intensity of 10^13
W / cm^2. We compute the Auger electron spectrum and assess the convergence of
the various quantities involved.Comment: 19 pages, 7 figures, 1 table, RevTeX
Ramsey method for Auger-electron interference induced by an attosecond twin pulse
We examine the archetype of an interference experiment for Auger electrons:
two electron wave packets are launched by inner-shell ionizing a krypton atom
using two attosecond light pulses with a variable time delay. This setting is
an attosecond realization of the Ramsey method of separated oscillatory fields.
Interference of the two ejected Auger-electron wave packets is predicted,
indicating that the coherence between the two pulses is passed to the Auger
electrons. For the detection of the interference pattern an accurate
coincidence measurement of photo- and Auger electrons is necessary. The method
allows one to control inner-shell electron dynamics on an attosecond timescale
and represents a sensitive indicator for decoherence.Comment: 5 pages, 5 figures, RevTeX4.1, revise
Auger decay in krypton induced by attosecond pulse trains and twin pulses
Using attoscience, we study the electron correlations responsible for Auger decay in krypton atoms. The Auger decay is induced by a pulse train or a twin pulse composed of subpulses of attosecond duration. During the Auger decay an optical dressing laser may be present. Interference effects between the ejected Auger electron wave packets are predicted
Transient absorption and reshaping of ultrafast XUV light by laser-dressed helium
We present a theoretical study of transient absorption and reshaping of
extreme ultraviolet (XUV) pulses by helium atoms dressed with a moderately
strong infrared (IR) laser field. We formulate the atomic response using both
the frequency-dependent absorption cross section and a time-frequency approach
based on the time-dependent dipole induced by the light fields. The latter
approach can be used in cases when an ultrafast dressing pulse induces
transient effects, and/or when the atom exchanges energy with multiple
frequency components of the XUV field. We first characterize the dressed atom
response by calculating the frequency-dependent absorption cross section for
XUV energies between 20 and 24 eV for several dressing wavelengths between 400
and 2000 nm and intensities up to 10^12 W/cm^2. We find that for dressing
wavelengths near 1600 nm, there is an Autler-Townes splitting of the 1s ---> 2p
transition that can potentially lead to transparency for absorption of XUV
light tuned to this transition. We study the effect of this XUV transparency in
a macroscopic helium gas by incorporating the time-frequency approach into a
solution of the coupled Maxwell-Schr\"odinger equations. We find rich temporal
reshaping dynamics when a 61 fs XUV pulse resonant with the 1s ---> 2p
transition propagates through a helium gas dressed by an 11 fs, 1600 nm laser
pulse.Comment: 13 pages, 8 figures, 1 table, RevTeX4, revise
Phase Measurement of Resonant Two-Photon Ionization in Helium
We study resonant two-color two-photon ionization of Helium via the 1s3p 1P1
state. The first color is the 15th harmonic of a tunable titanium sapphire
laser, while the second color is the fundamental laser radiation. Our method
uses phase-locked high-order harmonics to determine the {\it phase} of the
two-photon process by interferometry. The measurement of the two-photon
ionization phase variation as a function of detuning from the resonance and
intensity of the dressing field allows us to determine the intensity dependence
of the transition energy.Comment: 4 pages, 5 figures, under consideratio
Non-Hermitian Rayleigh-Schroedinger Perturbation Theory
We devise a non-Hermitian Rayleigh-Schroedinger perturbation theory for the
single- and the multireference case to tackle both the many-body problem and
the decay problem encountered, for example, in the study of electronic
resonances in molecules. A complex absorbing potential (CAP) is employed to
facilitate a treatment of resonance states that is similar to the
well-established bound-state techniques. For the perturbative approach, the
full CAP-Schroedinger Hamiltonian, in suitable representation, is partitioned
according to the Epstein-Nesbet scheme. The equations we derive in the
framework of the single-reference perturbation theory turn out to be identical
to those obtained by a time-dependent treatment in Wigner-Weisskopf theory. The
multireference perturbation theory is studied for a model problem and is shown
to be an efficient and accurate method. Algorithmic aspects of the integration
of the perturbation theories into existing ab initio programs are discussed,
and the simplicity of their implementation is elucidated.Comment: 10 pages, 1 figure, RevTeX4, submitted to Physical Review
A priori Wannier functions from modified Hartree-Fock and Kohn-Sham equations
The Hartree-Fock equations are modified to directly yield Wannier functions
following a proposal of Shukla et al. [Chem. Phys. Lett. 262, 213-218 (1996)].
This approach circumvents the a posteriori application of the Wannier
transformation to Bloch functions. I give a novel and rigorous derivation of
the relevant equations by introducing an orthogonalizing potential to ensure
the orthogonality among the resulting functions. The properties of these,
so-called a priori Wannier functions, are analyzed and the relation of the
modified Hartree-Fock equations to the conventional, Bloch-function-based
equations is elucidated. It is pointed out that the modified equations offer a
different route to maximally localized Wannier functions. Their computational
solution is found to involve an effort that is comparable to the effort for the
solution of the conventional equations. Above all, I show how a priori Wannier
functions can be obtained by a modification of the Kohn-Sham equations of
density-functional theory.Comment: 7 pages, RevTeX4, revise
Delirium as a predictor of sepsis in post-coronary artery bypass grafting patients: a retrospective cohort study
Article deposited according to agreement with BMC, December 6, 2010.YesFunding provided by the Open Access Authors Fund
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