Generation of attosecond spatiotemporal optical vortices via high-order harmonic generation (Invited Paper)

Spatiotemporal optical vortices (STOVs) are structured light pulses that couple spatial and temporal degrees of freedom, carrying transverse orbital angular momentum (t-OAM). While their generation has been achieved in the visible and infrared regimes, extending STOVs into the extreme-ultraviolet (EUV) via high-order harmonic generation (HHG) enables new opportunities for ultrafast and nanoscale science. We present theoretical and experimental evidence of EUV-STOV generation driven by elliptical STOV beams and by spatio-spectral optical vortices (SSOVs), the spectral counterparts of STOVs. By analyzing the scaling of topological charge and t-OAM in STOV- and SSOV-driven HHG, we show that these quantities are not universally tied. Specifically, we demonstrate that HHG driven by SSOV fields yields EUV-STOV harmonics with non-scaling topological charge, enabling the synthesis of attosecond EUV-STOV pulses. These results open new avenues for controlling light topology in space and time during frequency up-conversion processes, with potential applications in ultrafast dynamics, nonlinear spectroscopy, and structured-light–matter interactions