Isolated Attosecond Spatiotemporal Optical Vortices: Interplay between the Topological Charge and Orbital Angular Momentum Scaling in High Harmonic Generation

The propagation properties and the nature of the transverse orbital angular momentum (t-OAM) of spatiotemporal optical vortices (STOVs) open new scenarios in high harmonic generation (HHG), where the richness of the topological charge and OAM up-conversion are exposed. Through advanced numerical simulations, we demonstrate that HHG driven by spatiospectral optical vortices produces far-field, extreme-ultraviolet STOV harmonics with nonscaling topological charge, i.e., with the same topological charge. This allows for the generation of attosecond STOVs, in contrast to previous works of HHG driven by STOVs, where the topological charge scales with the harmonic order. Our findings evidence that the scaling of the topological charge in HHG driven by spatiotemporal topological fields is not generally connected to that of the up-converted OAM. The up-converted intrinsic OAM does scale with generality with the harmonic order in HHG, although this scaling does not necessarily imply its conservation.