Hamburg 2009 – scientific programme

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A: Fachverband Atomphysik

A 9: Interaction with Strong or Short Laser Pulses I

A 9.1: Invited Talk

Tuesday, March 3, 2009, 10:30–11:00, VMP 6 HS-C

Atomic and molecular ionization dynamics in strong laser fields: Excited neutral fragments after tunneling
— •Ulli Eichmann — Max-Born Institut, Berlin, Germany

Ionization and fragmentation dynamics of atoms and molecules in strong laser fields has been well studied with a strong focus on charged fragments and high harmonic generation. In this talk we report our observation of excited neutral fragments after exposing atoms and molecules to strong laser fields. Our experiments have been made possible by direct detection of excited neutral atoms. An explanation of the creation of excited states of atoms in strong laser fields can be found in an extension of the rescattering model by a process which we call Frustrated Tunnel Ionization (FTI)[1]. It leads to the recapture of those electrons into bound excited states which tunnel within a narrow range of laser field phases that does not allow for a high enough drift energy to escape. Results from semi-classical calculations are in quantitative agreement with full quantum mechanical calculations. More striking appears the extrapolation to molecules, where we observe the appearance of fast excited neutral fragments after exposure of diatomic molecules to a strong laser pulse, an hitherto unobserved fragmentation channel [2]. We show that polarization dependent measurements of the excited neutral fragment yield and correlated measurements of ions and excited neutral atoms together with classical Monte Carlo simulations confirm our assumption on the underlying model.

[1] T. Nubbemeyer et al., PRL 101, 233001 (2008).

[2] B. Manschwetus et al., PRL, submitted (2008).