Rostock 2019 – scientific programme

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A: Fachverband Atomphysik

A 36: Quantum dynamics in tailored waveforms

A 36.1: Invited Talk

Friday, March 15, 2019, 10:30–11:00, S HS 3 Physik

Attoclock with tailored polarization — Nicolas Eicke and •Manfred Lein — Institute for Theoretical Physics, Leibniz Universität Hannover, Appelstraße 2, 30167 Hannover

The term attoclock refers to the strong-field ionization of an atom and measurement of the resulting photoelectron momentum distribution in order to obtain the (most likely) time of electron departure. Previously, few-cycle circular or elliptical laser fields have been used to achieve a well-defined peak in the momentum distribution, at the price that the ionization timing in linear polarization was not accessible. We propose an attoclock with a bicircular field, i.e. a combination of two counter-rotating circularly polarized fields, tailored such that it mimics linear polarization during three time intervals per optical cycle. For the mapping between electron momentum and ionization time we use a trajectory-free method [N. Eicke, M. Lein, PRA 97, 031402(R) (2018)] based on finding the saddle points of the exact Dyson integral for the momentum-space wave function. From our calculations, we conclude that while ionization is nearly instantaneous for the circular attoclock, the (quasi)linear attoclock has its most likely time of ionization slightly (~10 attoseconds) later than the maximum of the instantaneous field. The momentum-resolved ionization time can alternatively be measured by applying a linearly polarized streaking field parallel or orthogonal to the ionizing field. Parallel streaking yields results in good agreement with the saddle-point times, while orthogonal streaking appears to measure not the true ionization time but a `Coulomb-free' time, as if the electron were removed from a short-range potential.