Spin-Polarization Control of Photoelectrons Using Poincaré Fields.

Efficient helicity transfer from Poincaré fields to electrons of hydrogenic ions is revealed for the first time by four-dimensional relativistic simulations. The magnetic multipole class of Poincaré fields is chosen due to its fundamental role in light-matter spin coupling, and the calculation is demonstrated for Ne^{9+} ion irradiated by single and multimode x-ray pulses. Photoelectrons of both helicities emerge synchronously from the ion ensemble, and their directionality is controllable through the radiation mode numbers. The helicity density distributions display novel structures composed of jets, spirals, and rings, among others, that are unique to the combination of atomic and field parameters. Our approach to generate spin-polarized leptons using Poincaré fields may provide a new platform for helicity characterization based on advanced numerical capabilities.