The role of tunneling in the ionization of atoms by ultrashort and intense laser pulses

TL;DR

This paper investigates how classical transport competes with quantum tunneling during atomic ionization by intense ultrashort laser pulses, revealing classical contributions to ionization probabilities even at parameters favoring tunneling.

Contribution

It demonstrates that classical transport significantly influences ionization processes, challenging the exclusive role of quantum tunneling in strong-field ionization models.

Findings

Classical transport can produce ionization probabilities comparable to quantum tunneling.

Classical trajectories can move away from the atomic core during ionization.

Results impact semiclassical models and tunneling time debates in strong-field physics.

Abstract

Classically allowed transport is shown to compete with quantum tunneling during the ionization of atoms by ultrashort and intense laser pulses, despite Keldysh parameters smaller than unity. This is done by comparing exact probability densities with the ones obtained from purely classical propagation using the Truncated Wigner Approximation. Not only is classical transport capable of moving trajectories away from the core, but it can also furnish ionization probabilities of the same order as the quantum ones for intensities currently employed in experiments. Our results have implications ranging from a conceptual correction to semiclassical step models in strong-field physics to the ongoing debate about tunneling time measurements in attoclock experiments.