Manipulating Twisted Electrons in Strong-Field Ionization

TL;DR

This paper explores the orbital angular momentum of photoelectrons in strong-field ionization, demonstrating how twisted electron states cause vortex interference patterns and proposing methods to measure and utilize their OAM.

Contribution

It introduces a new interpretation of vortex interferences using twisted electrons and derives an interference condition validated by multiple computational approaches.

Findings

Vortex conditions match experimental and computational data.

Vortices originate from interference of twisted electron pairs.

OAM relates to spiral arms in photoelectron momentum distributions.

Abstract

We investigate the discrete orbital angular momentum (OAM) of photoelectrons freed in strongfield ionization. We use these `twisted' electrons to provide an alternative interpretation on existing experimental work of vortex interferences caused by strong field ionization mediated by two counterrotating circularly polarized pulses separated by a delay. Using the strong field approximation, we derive an interference condition for the vortices. In computations for a neon target we find very good agreement of the vortex condition with photoelectron momentum distributions computed with the strong field approximation, as well as with the time-dependent methods Qprop and R-Matrix. For each of these approaches we examine the OAM of the photoelectrons, finding a small number of vortex states localized in separate energy regions. We demonstrate that the vortices arise from the interference of pairs of twisted electron states. The OAM of each twisted electron state can be directly related to the number of arms of the spiral in that region. We gain further understanding by recreating the vortices with pairs of twisted electrons and use this to determine a semiclassical relation for the OAM. A discussion is included on measuring the OAM in strong field ionization directly or by employing specific laser pulse schemes as well as utilizing the OAM in time-resolved imaging of photo-induced dynamics.