396 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
Semi-Classical Wavefunction Perspective to High-Harmonic Generation
We introduce a semi-classical wavefunction (SCWF) model for strong-field
physics and attosecond science. When applied to high harmonic generation (HHG),
this formalism allows one to show that the natural time-domain separation of
the contribution of ionization, propagation and recollisions to the HHG process
leads to a frequency-domain factorization of the harmonic yield into these same
contributions, for any choice of atomic or molecular potential. We first derive
the factorization from the natural expression of the dipole signal in the
temporal domain by using a reference system, as in the quantitative
rescattering (QRS) formalism [J. Phys. B. 43, 122001 (2010)]. Alternatively, we
show how the trajectory component of the SCWF can be used to express the
factorization, which also allows one to attribute individual contributions to
the spectrum to the underlying trajectories
High harmonic generation from ultrafast pump lasers
Using an ultrafast pump pulse affects the spectral and temporal characteristics of high order harmonics in an unexpected and fortuitous way. Calculations of spectra for rare gases using 10-100 fs, 800 nm pulses show that as the pump pulse length decreases the highest harmonics become correspondingly shorter while their conversion efficiencies increase dramatically. Especially significant is that we find these highest harmonics have phase characteristics that allow for the possibility of compression to subfemtosecond time scales. © 1997 American Physical Society
Quantum interference in attosecond transient absorption of laser-dressed helium atoms
We calculate the transient absorption of an isolated attosecond pulse by
helium atoms subject to a delayed infrared (\ir) laser pulse. With the central
frequency of the broad attosecond spectrum near the ionization threshold, the
absorption spectrum is strongly modulated at the sub-\ir-cycle level. Given
that the absorption spectrum results from a time-integrated measurement, we
investigate the extent to which the delay-dependence of the absorption yields
information about the attosecond dynamics of the atom-field energy exchange. We
find two configurations in which this is possible. The first involves multi
photon transitions between bound states that result in interference between
different excitation pathways. The other involves the modification of the bound
state absorption lines by the IR field, which we find can result in a sub-cycle
time dependence only when ionization limits the duration of the strong field
interaction
Space-time considerations in the phase locking of high harmonics
The combination of several high order harmonics can produce an attosecond pulse train, provided that the harmonics are locked in phase to each other. We present calculations that evaluate the degree of phase locking that is achieved in argon and neon gases interacting with an intense, 50 fs laser pulse, for a range of macroscopic conditions. We find that phase locking depends on both the temporal and the spatial phase behavior of the harmonics, as determined by the interplay between the intrinsic dipole phase and the phase matching in the nonlinear medium. We show that, as a consequence of this, it is not possible to compensate for a lack of phase locking by purely temporal phase manipulation
Quantum path distributions for high-order harmonics in rare gas atoms
We present quantum path distributions of high-order harmonics produced by rare gas atoms interacting with an intense 810 nm laser field, obtained by numerical integration of the time-dependent Schrodinger equation within the single active electron approximation. We find that the distributions are sensitive to the atomic potentials, and differ from the distributions predicted by the strong field approximation. We demonstrate that these differences can lead to significant differences in the time-frequency behavior of the harmonics produced in a macroscopic nonlinear medium
Phase metrology with multi-cycle two-colour pulses
Strong-field phenomena driven by an intense infrared (IR) laser depend on
during what part of the field cycle they are initiated. By changing the
sub-cycle character of the laser electric field it is possible to control such
phenomena. For long pulses, sub-cycle shaping of the field can be done by
adding a relatively weak, second harmonic of the driving field to the pulse.
Through constructive and destructive interference, the combination of strong
and weak fields can be used to change the probability of a strong-field process
being initiated at any given part of the cycle. In order to control sub-cycle
phenomena with optimal accuracy, it is necessary to know the phase difference
of the strong and the weak fields precisely. If the weaker field is an even
harmonic of the driving field, electrons ionized by the field will be
asymmetrically distributed between the positive and negative directions of the
combined fields. Information about the asymmetry can yield information about
the phase difference. A technique to measure asymmetry for few-cycle pulses,
called Stereo-ATI (Above Threshold Ionization), has been developed by [Paulus G
G, et al 2003 Phys. Rev. Lett. 91]. This paper outlines an extension of this
method to measure the phase difference between a strong IR and its second
harmonic
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
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