Capture and Ionization in Laser-Assisted Collisions

Thomas Niederhausen, Uwe Thumm
James R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, KS, USA

Even though recent calculations [1-3] find that a strong laser field (with intensity above 10¹² W/cm²) significantly changes capture and ionization probabilities in ion-atom collisions, so far, no experimental test of these predictions has been performed, due to the difficult synchronization of a collision with a laser pulse. We present electron capture and ionization probabilities for ion collisions in a strong laser field (5 × 10¹³ W/cm²) by numerically solving the 3-dimensional time-dependent Schrödinger equation. This allows us i) to compute ab- initio capture and ionization cross sections, and ii) to assess the applicability of our previous approximate (reduced dimensionality) calculation [2]. For circularly polarized laser fields and impact energies of 1.2 keV, we confirm a substantial modification of the electronic dynamics in H⁺ - H collisions as compared to field-free collisions. In particular, we observe a strong dependence on the initial laser phase and impact parameter for both capture and ionization, which can be explained using semiclassical arguments [3].

This work was supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy, and by the National Science Foundation.

[1] T. Kirchner, Phys. Rev. A 75, 025401 (2007).
[2] T. Niederhausen et al., Phys. Rev. A 70, 023408 (2004).
[3] T. Niederhausen and U. Thumm, Phys. Rev. A 73, R041404 (2006).

Presented at ISIAC, August 2007 in Crete, Greece.

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