Isolated attosecond spatio-temporal optical vortices: Interplay between the topological charge and orbital angular momentum scaling in high harmonic generation

TL;DR

This paper demonstrates that high-harmonic generation driven by spatiotemporal optical vortices can produce attosecond vortices with a fixed topological charge, revealing new insights into the relationship between topological charge and orbital angular momentum.

Contribution

It introduces a novel HHG regime where the topological charge remains constant across harmonics, contrasting with previous scaling behaviors, and clarifies the distinct scaling of OAM and topological charge.

Findings

Far-field EUV STOV harmonics with non-scaling topological charge generated.

Attosecond STOVs produced with fixed topological charge across harmonics.

Scaling of intrinsic OAM with harmonic order does not imply topological charge conservation.

Abstract

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 spatio-spectral optical vortices produces far-field, extreme-ultraviolet STOV harmonics with non-scaling 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 spatio-temoral topological fields is not generally connected to that of the up-converted OAM. The up-converted intrinsic OAM does scale with generality with harmonic order in HHG, albeit this scaling does not necessarily imply its conservation.