Subcycle resolved strong-field tunneling ionization: Identification of magnetic dipole and electric quadrupole effects

TL;DR

This paper investigates how strong laser pulses transfer linear momentum to electrons during ionization, revealing the dominant roles of magnetic dipole and electric quadrupole effects in different stages of the process.

Contribution

It provides a detailed decomposition of subcycle linear momentum transfer into multipolar components, highlighting the dominant nondipole effects during tunneling and post-ionization.

Findings

Magnetic dipole effects dominate during dynamical tunneling.

Electric quadrupole effects govern post-ionization momentum transfer.

Nondipole effects scale linearly or quadratically with laser coupling.

Abstract

Interaction of a strong laser pulse with matter transfers not only energy but also linear momentum of the photons. Recent experimental advances have made it possible to detect the small amount of linear momentum delivered to the photoelectrons in strong-field ionization of atoms. Linear momentum transfer is a unique signature of the laser-atom interaction beyond its dipolar limit. Here, we present a decomposition of the subcycle time-resolved linear momentum transfer in term of its multipolar components. We show that the magnetic dipole contribution dominates the linear momentum transfer during the dynamical tunneling process while the post-ionization longitudinal momentum transfer in the field-driven motion of the electron in the continuum is primarily governed by the electric quadrupole interaction. Alternatively, exploiting the radiation gauge, we identify nondipole momentum transfer effects that scale either linearly or quadratically with the coupling to the laser field. The present results provide detailed insights into the physical mechanisms underlying the subcycle linear momentum transfer induced by nondipole effects.