1,493 research outputs found
Dynamics of multiply charged ions in intense laser fields
We numerically investigate the dynamics of multiply charged hydrogenic ions
in near-optical linearly polarized laser fields with intensities of order 10^16
to 10^17 W/cm^2. Depending on the charge state Z of the ion the relation of
strength between laser field and ionic core changes. We find around Z=12
typical multiphoton dynamics and for Z=3 tunneling behaviour, however with
clear relativistic signatures. In first order in v/c the magnetic field
component of the laser field induces a Z-dependent drift in the laser
propagation direction and a substantial Z-dependent angular momentum with
repect to the ionic core. While spin oscillations occur already in first order
in v/c as described by the Pauli equation, spin induced forces via spin orbit
coupling only appear in the parameter regime where (v/c)^2 corrections are
significant. In this regime for Z=12 ions we show strong splittings of resonant
spectral lines due to spin-orbit coupling and substantial corrections to the
conventional Stark shift due to the relativistic mass shift while those to the
Darwin term are shown to be small. For smaller charges or higher laser
intensities, parts of the electronic wavepacket may tunnel through the
potential barrier of the ionic core, and when recombining are shown to give
rise to keV harmonics in the radiation spectrum. Some parts of the wavepacket
do not recombine after ionisation and we find very energetic electrons in the
weakly relativistic regime of above threshold ionization.Comment: submitte
Semi-classical limitations for photon emission in strong external fields
The semi-classical heuristic emission formula of Baier-Katkov [Sov. Phys.
JETP \textbf{26}, 854 (1968)] is well-known to describe radiation of an
ultrarelativistic electron in strong external fields employing the electron's
classical trajectory. To find the limitations of the Baier-Katkov approach, we
investigate electron radiation in a strong rotating electric field quantum
mechanically using the Wentzel-Kramers-Brillouin approximation. Except for an
ultrarelativistic velocity, it is shown that an additional condition is
required in order to recover the widely used semi-classical result. A violation
of this condition leads to two consequences. First, it gives rise to
qualitative discrepancy in harmonic spectra between the two approaches. Second,
the quantum harmonic spectra are determined not only by the classical
trajectory but also by the dispersion relation of the effective photons of the
external field
Implementing nonlinear Compton scattering beyond the local constant field approximation
In the calculation of probabilities of physical processes occurring in a
background classical field, the local constant field approximation (LCFA)
relies on the possibility of neglecting the space-time variation of the
external field within the region of formation of the process. This
approximation is widely employed in strong-field QED as it allows to evaluate
probabilities of processes occurring in arbitrary electromagnetic fields
starting from the corresponding quantities computed in a constant
electromagnetic field. Here, we demonstrate in the case of nonlinear single
Compton scattering that the LCFA is quantitatively and qualitatively
insufficient for describing the low-energy part of the emitted photon
probability. In addition, we provide a simple recipe to implement an improved
expression of the photon emission probability beyond the LCFA in numerical
codes, which are an essential tool to interpret present and upcoming
experiments in strong-field QED.Comment: 12 pages, 3 figur
Improved local-constant-field approximation for strong-field QED codes
The local-constant-field approximation (LCFA) is an essential theoretical
tool for investigating strong-field QED phenomena in background electromagnetic
fields with complex spacetime structure. In our previous work
[Phys.~Rev.~A~\textbf{98}, 012134 (2018)] we have analyzed the shortcomings of
the LCFA in nonlinear Compton scattering at low emitted photon energies for the
case of a background plane-wave field. Here, we generalize that analysis to
background fields, which can feature a virtually arbitrary spacetime structure.
In addition, we provide an explicit and simple implementation of an improved
expression of the nonlinear Compton scattering differential probability that
solves the main shortcomings of the standard LCFA in the infrared region, and
is suitable for background electromagnetic fields with arbitrary spacetime
structure such as those occurring in particle-in-cell simulations. Finally, we
carry out a systematic procedure to calculate the probability of nonlinear
Compton scattering per unit of emitted photon light-cone energy and of
nonlinear Breit-Wheeler pair production per unit of produced positron
light-cone energy beyond the LCFA in a plane-wave background field, which
allows us to identify the limits of validity of this approximation
quantitatively.Comment: 15 pages, 3 figure
Localization of atomic ensembles via superfluorescence
The sub-wavelength localization of an ensemble of atoms concentrated to a
small volume in space is investigated. The localization relies on the
interaction of the ensemble with a standing wave laser field. The light
scattered in the interaction of standing wave field and atom ensemble depends
on the position of the ensemble relative to the standing wave nodes. This
relation can be described by a fluorescence intensity profile, which depends on
the standing wave field parameters, the ensemble properties, and which is
modified due to collective effects in the ensemble of nearby particles. We
demonstrate that the intensity profile can be tailored to suit different
localization setups. Finally, we apply these results to two localization
schemes. First, we show how to localize an ensemble fixed at a certain position
in the standing wave field. Second, we discuss localization of an ensemble
passing through the standing wave field.Comment: 7 pages, 6 figure
Astrophysical line diagnosis requires non-linear dynamical atomic modeling
Line intensities and oscillator strengths for the controversial 3C and 3D
astrophysically relevant lines in neonlike Fe ions are calculated. We
show that, for strong x-ray sources, the modeling of the spectral lines by a
peak with an area proportional to the oscillator strength is not sufficient and
non-linear dynamical effects have to be taken into account. Furthermore, a
large-scale configuration-interaction calculation of oscillator strengths is
performed with the inclusion of higher-order electron-correlation effects. The
dynamical effects give a possible resolution of discrepancies of theory and
experiment found by recent measurements, which motivates the use of
light-matter interaction models also valid for strong light fields in the
analysis and interpretation of astrophysical and laboratory spectra.Comment: 5 pages, 3 figure
Quantum entanglement in dense multiqubit systems
The pairwise entanglement of an arbitrary atomic pair randomly extracted from
a laser-driven dense multiqubit sample in the presence of quantum dissipation
due to spontaneous emission is considered. The dipole-dipole interaction
between the particles shifts the laser-qubit resonance frequency and
consequently modifies the quantum entanglement. By means of an appropriate
tuning of the laser frequency, one can optimize the entanglement in this
system. For large ensembles, the maximum entanglement occurs near the laser
parameters where the steady-state sample exhibits phase transition phenomena.Comment: 6 pages, 6 figure
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