Attoclock reveals geometry for laser-induced tunneling

TL;DR

This paper uses the attoclock technique to experimentally determine the geometry of laser-induced tunneling in helium and argon, revealing how the potential barrier is modified by electron interactions and external fields, impacting electron dynamics.

Contribution

It provides the first experimental access to the tunneling geometry in laser-induced ionization and clarifies how electron interactions modify the tunneling process in atoms.

Findings

Tunneling geometry for helium and argon is experimentally determined.

Electron interactions significantly modify the potential barrier.

Modified potential influences electron dynamics and measurement interpretation.

Abstract

Tunneling plays a central role in the interaction of matter with intense laser pulses, and also in time-resolved measurements on the attosecond timescale. A strong laser field influences the binding potential of an electron in an atom so strongly, that a potential barrier is created which enables the electron to be liberated through tunneling. An important aspect of the tunneling is the geometry of the tunneling current flow. Here we provide experimental access to the tunneling geometry and provide a full understanding of the laser induced tunnel process in space and time. We perform laser tunnel ionization experiments using the attoclock technique, and present a correct tunneling geometry for helium and argon. In addition for argon the potential barrier is significantly modified by all the electrons remaining in the ion, and furthermore from a quantum state whose energy is Stark-shifted by the external field. The resulting modified potential geometry influences the dynamics of the liberated electron, changes important physical parameters and affects the interpretation of attosecond measurements. These effects will become even more pronounced for molecules and surfaces, which are more polarizable.