High-topological charge extreme-ultraviolet spatiotemporal vortices via high harmonic generation

Spatiotemporal optical vortices (STOV) are structured light pulses with a unique topology that couples the spatial and temporal domains. Up to now, their generation has been limited to low-order topological charges in the visible and infrared regions of the spectrum. During the last decade, it was shown that through the process of high-order harmonic generation (HHG) it is possible to up-convert spatial optical vortices from the near-infrared into the extreme-ultraviolet (EUV), thereby producing vortices with distinct femtosecond and attosecond structure. In this work we demonstrate theoretically and experimentally the generation of highly charged spatiotemporal and spatiospectral EUV vortices using near infrared STOV driving laser pulses. We use analytical expressions for focused STOVs to perform macroscopic calculations of HHG that are directly compared to the experimental results. As STOV beams are not eigenmodes of propagation, we characterize the EUV STOVs both in the near and far fields, to show that they represent conjugated spatiospectral and spatiotemporal vortex pairs. Our work provides light beams topologically coupled at the nanometer/attosecond domains, that are especially suitable to explore electronic dynamics in magnetic materials, chiral media, and nanostructures.