J. Wu, A. S. Sanz, B. B. Augstein, C. Figueira de Morisson Faria
In this article, we perform detailed studies of high-order harmonic generation (HHG) employing Bohmian trajectories, with particular emphasis on which spatial regions are the most relevant for this phenomenon. These trajectories, directly extracted from the time-dependent Schr\"odinger equation, play the role of "tracer particles", thus being very helpful for mapping the flow of the time-dependent wavefunction. In particular, they allow us to revisit several issues, such as the use of the dipole length or the dipole acceleration in the computation of harmonic spectra, the influence of numerical filters on the flow of the wavefunction in real time, or the role of the innermost and outermost core regions and of ionization in the spectra. Our results show that the Bohmian trajectory starting at the innermost part of the core is the most relevant in order to reproduce typical HHG spectra, regardless of the pulse shape and of the potential range employed. This provides additional insight on the success of strong-field models that consider the atom to be a source term, such as the strong-field approximation. A quantitative agreement between the spectra obtained from Bohmian-trajectory computations and the time-dependent Schr\"odinger equation is also obtained. Furthermore, we also establish a parallel between the use of the dipole acceleration and the Hanning filter, by analyzing how, in both cases, Bohmian trajectories away from the core are removed.
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http://arxiv.org/abs/1301.1916
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