Under-the-barrier dynamics in laser-induced relativistic tunneling

TL;DR

This paper explores relativistic tunneling dynamics in strong laser fields, revealing how quantum time scales and magnetic field effects influence electron behavior during ionization, with observable experimental signatures.

Contribution

It introduces a relativistic tunneling model with position-dependent energy levels and links quantum time scales to measurable shifts in electron spectra.

Findings

Relativistic tunneling applies with position-dependent energy levels.

Electron momentum and spatial shifts occur during tunneling due to magnetic fields.

Momentum shift signatures are observable in ionization spectra.

Abstract

The tunneling dynamics in relativistic strong-field ionization is investigated with the aim to develop an intuitive picture for the relativistic tunneling regime. We demonstrate that the tunneling picture applies also in the relativistic regime by introducing position dependent energy levels. The quantum dynamics in the classically forbidden region features two time scales, the typical time that characterizes the probability density's decay of the ionizing electron under the barrier (Keldysh time) and the time interval which the electron spends inside the barrier (Eisenbud-Wigner-Smith tunneling time). In the relativistic regime, an electron momentum shift as well as a spatial shift along the laser propagation direction arise during the under-the-barrier motion which are caused by the laser magnetic field induced Lorentz force. The momentum shift is proportional to the Keldysh time, while the wave-packet's spatial drift is proportional to the Eisenbud-Wigner-Smith time. The signature of the momentum shift is shown to be present in the ionization spectrum at the detector and, therefore, observable experimentally. In contrast, the signature of the Eisenbud-Wigner-Smith time delay disappears at far distances for pure quasistatic tunneling dynamics.