Generation and control of extreme-ultraviolet spatiotemporal skyrmions and vector hopfions with high harmonic generation
摘要
Paraxial optical skyrmions have attracted significant attention due to their ability to propagate in free space. Through high harmonic generation (HHG) and free-electron laser setups, spatial skyrmions with a topological plane perpendicular to the optical axis have been extended to the extreme ultraviolet (EUV) region, both theoretically and experimentally. More recently, spatiotemporal skyrmions with a topological plane parallel to the optical axis have been realized experimentally, though so far only in the visible and near-infrared regimes. EUV spatiotemporal skyrmions hold promise due to higher photon energy and potential as a novel attosecond light source. In this work, for the first time, we theoretically demonstrate the generation and control of spatiotemporal skyrmions in the EUV region via HHG. Harmonic fields driven by two-color lasers exhibit Bloch-type skyrmionic characteristics, and varying laser parameters allow other EUV skyrmions and vector hopfions to be generated. A photon absorption model explains the coherent transfer of spatiotemporal characteristics from driving fields to harmonics, with Stokes-vector direction matching being crucial. Furthermore, we have proposed a spatiotemporal mode conversion (STMC) scheme that can recover the near-field spatiotemporal structure of the spatiotemporal Skyrmions in the far field. This research expands the family of EUV structured optical fields and lays the groundwork for experimental generation and far-field applications of EUV spatiotemporal skyrmions and vector hopfions.