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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Bibliographic Details
Main Author: Beran, Lisa
Contributors: Eckhardt, Bruno (Prof. Dr.) (Thesis advisor)
Format: Dissertation
Language:English
Published: Philipps-Universität Marburg 2014
Physik
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Summary: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.
DOI:https://doi.org/10.17192/z2014.0409