Electric Nondipole Effect in Strong-Field Ionization

TL;DR

This paper reveals an electric non-dipole effect in strong-field ionization, caused by the position dependence of the electric field, leading to measurable changes in electron momentum distribution, alongside known magnetic effects.

Contribution

It demonstrates the existence of an electric non-dipole effect in strong-field ionization, supported by experimental data and theoretical models, expanding understanding beyond magnetic non-dipole influences.

Findings

Electric non-dipole effect alters electron momentum distribution

Distribution radius increases for forward electrons, decreases for backward electrons

Experimental data confirms the electric non-dipole effect

Abstract

Strong-field ionization of atoms by circularly polarized femtosecond laser pulses produces a donut-shaped electron momentum distribution. Within the dipole approximation this distribution is symmetric with respect to the polarization plane. The magnetic component of the light field is known to shift this distribution forward. Here, we show that this magnetic non-dipole effect is not the only non-dipole effect in strong-field ionization. We find that an electric non-dipole effect arises that is due to the position dependence of the electric field and which can be understood in analogy to the Doppler effect. This electric non-dipole effect manifests as an increase of the radius of the donut-shaped photoelectron momentum distribution for forward-directed momenta and as a decrease of this radius for backwards-directed electrons. We present experimental data showing this fingerprint of the electric non-dipole effect and compare our findings with a classical model and quantum calculations.