8,273 research outputs found
Spin and spatial dynamics in electron-impact scattering off S-wave He using R-matrix with Time-Dependence theory
R-matrix with time-dependence theory is applied to electron-impact ionisation
processes for He in the S-wave model. Cross sections for electron-impact
excitation, ionisation and ionisation with excitation for impact energies
between 25 and 225 eV are in excellent agreement with benchmark cross sections.
Ultra-fast dynamics induced by a scattering event is observed through
time-dependent signatures associated with autoionisation from doubly excited
states. Further insight into dynamics can be obtained through examination of
the spin components of the time-dependent wavefunction.Comment: 6 pages, 5 figure
Population trapping in bound states during IR-assisted ultra-fast photoionization of Ne
We have investigated photoionization of Ne in the combined field of a
short infra-red laser pulse and a delayed ultra-short pulse of the infra-red
laser's 23 harmonic. We observe an ionization yield compatible with a
picture in which one electron gets excited into Rydberg states by the harmonic
laser field and is subsequently removed by the infra-red laser field.
Modulations are seen in the ionization yield as a function of time delay. These
modulations originate from the trapping of population in low members of the
Rydberg series with different states being populated at different ranges of
delay times. The calculations further demonstrate that single-threshold
calculations cannot reproduce the Ne photoionization yields obtained in
multi-threshold calculations.Comment: 7 pages, 5 figures, 1 tabl
Multiphoton inner-shell ionization of the carbon atom
We apply time-dependent R-matrix theory to study inner-shell ionization of C
atoms in ultra-short high-frequency light fields with a photon energy between
170 and 245 eV. At an intensity of 10 W/cm, ionization is dominated
by single-photon emission of a electron, with two-photon emission of a
1s electron accounting for about 2-3\% of all emission processes, and
two-photon emission of contributing about 0.5-1\%. Three-photon
emission of a 1s electron is estimated to contribute about 0.01-0.03\%. Around
a photon energy of 225 eV, two-photon emission of a 1s electron, leaving C
in either 1s2s2p or 1s2p is resonantly enhanced by intermediate
1s2s2p states. The results demonstrate the capability of time-dependent
R-matrix theory to describe inner-shell ionization processes including
rearrangement of the outer electrons.Comment: 7 pages, 2 figures, 2 table
Angular distributions in two-colour two-photon ionization of He
We present R-Matrix with time dependence (RMT) calculations for the
photoionization of helium irradiated by an EUV laser pulse and an overlapping
IR pulse with an emphasis on the anisotropy parameters of the sidebands
generated by the dressing laser field. We investigate how these parameters
depend on the amount of atomic structure included in the theoretical model for
two-photon ionization. To verify the accuracy of the RMT approach, our
theoretical results are compared with experiment.Comment: 8 pages, 4 figures, 1 tabl
Electron dynamics in the carbon atom induced by spin-orbit interaction
We use R-Matrix theory with Time dependence (RMT) to investigate multiphoton
ionization of ground-state atomic carbon with initial orbital magnetic quantum
number =0 and =1 at a laser wavelength of 390 nm and peak intensity
of 10 W cm. Significant differences in ionization yield and
ejected-electron momentum distribution are observed between the two values for
. We use our theoretical results to model how the spin-orbit interaction
affects electron emission along the laser polarization axis. Under the
assumption that an initial C atom is prepared at zero time delay with ,
the dynamics with respect to time delay of an ionizing probe pulse modelled
using RMT theory is found to be in good agreement with available experimental
data.Comment: 8 pages, 5 figure
Span, chainability and the continua H* and I_u
We show that the continua I_u and H* are non-chainable and have span nonzero.
Under CH this can be strengthened to surjective symmetric span nonzero.
We discuss the logical consequences of this.Comment: 2004-03-11: corrected some typos, some parts rewritte
Harmonic generation of noble-gas atoms in the Near-IR regime using ab-initio time-dependent R-matrix theory
We demonstrate the capability of ab-initio time-dependent R-matrix theory to
obtain accurate harmonic generation spectra of noble-gas atoms at Near-IR
wavelengths between 1200 and 1800 nm and peak intensities up to 1.8 X 10(14)
W/cm(2) . To accommodate the excursion length of the ejected electron, we use
an angular-momentum expansion up to Lmax = 279. The harmonic spectra show
evidence of atomic structure through the presence of a Cooper minimum in
harmonic generation for Kr, and of multielectron interaction through the giant
resonance for Xe. The theoretical spectra agree well with those obtained
experimentally.Comment: 6 pages, 5 figure
Double Ionisation in R-Matrix Theory Using a 2-electron Outer Region
We have developed a two-electron outer region for use within R-matrix theory
to describe double ionisation processes. The capability of this method is
demonstrated for single-photon double ionisation of He in the photon energy
region between 80 eV to 180 eV. The cross sections are in agreement with
established data. The extended RMT method also provides information on
higher-order processes, as demonstrated by the identification of signatures for
sequential double ionisation processes involving an intermediate He state
with .Comment: 5 pages, 4 figure
Nonrelativistic double photoeffect on lithiumlike ions at high energies
The total cross section for double ionization of lithiumlike ions by a
high-energy photon is calculated in leading order of the nonrelativistic
perturbation theory. The partial contributions due to simultaneous and
sequential emissions of two electrons are taken into account. The cross section
under consideration is shown to be related to those for double photoeffect on
the ground and excited 2^{1,3}S states of heliumlike ions. The double-to-single
ionization ratio is equal to R = 0.288/Z^2 for lithiumlike ions with moderate
nuclear charge numbers Z. However, even for the lightest three-electron targets
such as Li and Be^+, analytical predictions are found to be in good agreement
with the numerical calculations performed within the framework of different
rather involved approaches.Comment: 12 pages, 2 figures. to be published in Physics Letters
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