Experimental fingerprint of the electron's longitudinal momentum at the tunnel exit in strong field ionization

TL;DR

This paper experimentally investigates the electron's initial longitudinal momentum during tunnel ionization in strong laser fields, revealing sign changes correlated with the laser field's phase, which impacts Coulomb interaction modeling.

Contribution

It provides the first experimental evidence of the sign change in the electron's longitudinal momentum at the tunnel exit in strong field ionization.

Findings

Sign change in initial longitudinal momentum during tunneling.

Enhanced Coulomb interaction when momentum points toward the ion.

Results align with strong field approximation predictions.

Abstract

We present experimental data on the strong field tunnel ionization of argon in a counter-rotating two-color (CRTC) laser field. We find that the initial momentum component along the tunneling direction changes sign comparing the rising and the falling edge of the CRTC field. If the initial momentum at the tunnel exit points in the direction of the ion at the instant of tunneling, this manifests as an enhanced Coulomb interaction of the outgoing electron with its parent ion. Our conclusions are in accordance with predictions based on strong field approximation.