Shaped free electron vortices

TL;DR

This paper reports the first experimental creation and analysis of shaped free electron vortices generated through multiphoton ionization with polarization-shaped femtosecond pulses, revealing detailed wave packet structures and underlying dynamics.

Contribution

It demonstrates the experimental generation of shaped free electron vortices using polarization-shaped pulses and analyzes their structure with advanced imaging and Fourier techniques.

Findings

Multiple shaped FEVs with different symmetries were observed.

The reconstructed PMDs reveal the influence of resonant intermediate states.

The approach enables retrieval of spectral information from laser fields.

Abstract

Since their first theoretical proposal [Ngoko Djiokap et al., Phys. Rev. Lett. 115, 113004 (2015)] and experimental demonstration [Pengel et al., Phys. Rev. Lett. 118, 053003 (2017)], free electron vortices (FEVs) have attracted considerable attention. Recently, a new class of unusually shaped FEVs, termed `reversible electron spirals', has been proposed theoretically [Strandquist et al., Phys. Rev. A 106, 043110 (2022)] for atomic single-photon ionization by two oppositely chirped and counterrotating circularly polarized (CRCP) attosecond pulses. Building on this concept, we present the first experimental demonstration of shaped FEVs created by atomic multiphoton ionization (MPI) using oppositely chirped CRCP femtosecond pulse pairs. In MPI by polarization-shaped pulses, several shaped FEVs of different rotational symmetry are superimposed resulting in the total photoelectron wave packet observed in the experiment. We employ velocity map imaging techniques to measure the photoelectron momentum distribution (PMD) and reconstruct the three-dimensional PMD by photoelectron tomography. Fourier analysis is used to decompose the measured PMD into the contributing FEVs with different rotational symmetries. The experimental results are supported by an analytical model and reproduced by numerical simulations, which provide insight into the role of resonant intermediate states. Our approach allows us to retrieve spectral information from the shaped laser field and the signatures of the MPI dynamics inscribed within the shaped FEVs.