# Non-dipole recollision-gated double ionization and observable effects

## TL;DR

This study uses a semiclassical model to explore how magnetic field effects influence double ionization in helium under strong laser fields, revealing a recollision-gated mechanism that causes observable asymmetries in electron momentum distributions.

## Contribution

It introduces a non-dipole recollision-gated mechanism in double ionization, highlighting the role of magnetic fields in creating asymmetries in electron initial momenta and observable outcomes.

## Key findings

- Recollision and magnetic fields act as a gate favoring transverse initial momenta.
- Asymmetry in initial transverse momentum causes observable asymmetries.
- Explains large average electron momentum sum parallel to laser propagation.

## Abstract

Using a three-dimensional semiclassical model, we study double ionization for strongly-driven He fully accounting for magnetic field effects. For linearly and slightly elliptically polarized laser fields, we show that recollisions and the magnetic field combined act as a gate. This gate favors more transverse - with respect to the electric field - initial momenta of the tunneling electron that are opposite to the propagation direction of the laser field. In the absence of non-dipole effects, the transverse initial momentum is symmetric with respect to zero. We find that this asymmetry in the transverse initial momentum gives rise to an asymmetry in a double ionization observable. Finally, we show that this asymmetry in the transverse initial momentum of the tunneling electron accounts for a recently-reported unexpectedly large average sum of the electron momenta parallel to the propagation direction of the laser field.