Propagation-enhanced molecular high-harmonic generation driven by a spatiotemporal vortex field

High-order harmonic generation (HHG) provides a key route to ultrafast structured radiation, yet how spatiotemporal topology manifests, survives, and builds up in molecular HHG remains largely unexplored. Here, we investigate HHG from aligned O₂ molecules driven by a spatiotemporal vortex (STOV) field within a microscopic-macroscopic theoretical framework. We show that the transverse phase structure of the STOV field is transferred to the molecular harmonic radiation, leading to pronounced spatio-spectral tilt and helical phase distributions with transverse-orbital-angular-momentum character. Molecular alignment mainly regulates the harmonic yield while leaving the topology-imprinted spatial structure largely preserved. During macroscopic propagation, coherent buildup substantially enhances the harmonic signal and gives rise to an order-dependent optimum propagation length associated with phase-mismatch accumulation. These results reveal a coherent propagation-enhancement mechanism in molecular HHG and suggest STOV driving as a route toward efficient topology-tailored extreme-ultraviolet emission.