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A Classical Analysis of Double Ionization of Helium in Ultra Short Laser Pulses
Experiments of double ionization in noble gases [58, 64, 68, 84] were the catalyst for extensive theoretical investigations [9, 11, 13, 21, 39, 80, 87]. The measurement of the momenta of outgoing electrons in non-sequential strong field double ionization exposed the correlated nature of their esc...
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| Format: | Dissertation |
| Sprache: | Englisch |
| Veröffentlicht: |
Philipps-Universität Marburg
2014
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| Online Zugang: | PDF-Volltext |
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| Zusammenfassung: | Experiments of double ionization in noble gases [58, 64, 68, 84] were the catalyst for extensive
theoretical investigations [9, 11, 13, 21, 39, 80, 87]. The measurement of the momenta of outgoing
electrons in non-sequential strong field double ionization exposed the correlated nature of
their escape [66, 67, 88, 90].
A (1+1)-dimensional model for helium, introduced in [25, 73], has been the foundation of ongoing
research into non-sequential double ionization [24, 26, 27, 71, 74]. The model reproduces
the re-scattering scenario, the correlation between the outgoing electrons, and the interference
patterns in the momentum distribution [72]. The observed interference patterns depend on the
amplitude of the external field, pulse duration, and carrier envelope phase.
Guided by the semi-classical idea that many paths contribute to the double ionization events
and the interference between these paths could cause the patterns, a rigorous analysis of the
classical trajectories depicting double ionization was undertaken. Applying few-cycle pulses,
the effects from multiple re-scattering are intrinsically minimized. In classical calculations,
field parameters were varied and configurations yielding trajectories of reduced complexity were
targeted. The classical trajectories allow a connection between the initial conditions in phase
space and the final states to be established. A link between the external field strength and the
electrons initial conditions was found.
In the single-cycle limit, the electrons mutual repulsion ensures that anti-parallel double ionization
is the only double ionization mechanism at intensities above the threshold. Stable and
symmetric back-to-back double ionization trajectories are identified. Parallel non-symmetric
double ionization with same final momentum was generated from two-cycle fields. The extent
of the frequency and field strength dependency on classical non-sequential double ionization
was determined. |
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| DOI: | 10.17192/z2014.0409 |