Attosecond Light Skyrmion Pulses via High Harmonic Generation

Abstract: Paraxial light skyrmions are topological configurations that map a spatial domain of the field onto the full Poincar\'e sphere of polarization states. While skyrmions have been explored in continuous-wave regimes, their realization in the ultrafast domain remains open. Here we demonstrate that attosecond skyrmion pulses can be generated via high-harmonic generation. Advanced simulations combining single-atom strong-field theory and macroscopic propagation reveal that an infrared linearly polarized vector beam with fractional orbital angular momentum produces extreme-ultraviolet harmonic fields with nearly identical skyrmion polarization distributions across a broad spectral range. Using 1.2 $\mu$m driving fields and experimentally realistic spectral filtering, the coherent superposition of consecutive harmonics centered at 70 eV yields $\sim500$ attosecond pulse trains. Our results opens opportunities to use structured attosecond light with topological polarization textures,in fields as ultrafast control, imaging and spectroscopy.