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 Poincaré sphere of polarization states. While optical 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 $μ$m driving fields and experimentally feasible spectral filtering, we show that the coherent superposition of consecutive harmonics centered at 70 eV yields a train of skyrmion pulses with $\sim500$ attoseconds duration. Our results open opportunities to use structured attosecond light with topological polarization textures in fields as ultrafast control, imaging and spectroscopy.

Figures (3)

• Figure 1: Generation of an attosecond EUV skyrmion pulse trains from an IR linearly polarized fs vector beam via HHG. The instantaneous polarization state of the pulse train is encoded by a color map that assigns each point to its location on the Poincaré sphere. (a) Input driver at the gas target: intensity–phase maps of the LCP and RCP components, together with the intensity–polarization map designed to produce a skyrmion in the 23rd harmonic. (b) Near-field intensity–phase maps of the LCP and RCP components for harmonics $q=21,23,25$, where the polarization distribution equals that of the driver. (c) Far-field intensity–phase maps of the circular components for harmonics $q=21,23,25$, along with the corresponding intensity–polarization maps. All three harmonics evolve into nearly equal skyrmion structures with $N^{q}_{\mathrm{S}}\approx1$ within a common closed contour of 0.34 mrad in the far field, indicated by the red dashed line.
• Figure 2: Attosecond EUV skyrmion pulse train driven at 0.8 $\mu$m. (a) HHG spectrum, where the purple filled window contains the harmonics $q=21,23,25$ that yield the skyrmion attosecond train. (b) Temporal evolution of $N_\mathrm{S}$ inside a closed contour of 0.34 mrad corresponding to the central pulse of the train. (c) Local temporal evolution of the real electric field for the central pulse within the train, with the instantaneous polarization state encoded by a color map that maps each point to its location on the Poincaré sphere. (d) Polarization dynamics at representative transverse positions (beam center, intermediate point, and skyrmion edge), with trajectories on the Poincaré sphere within the central pulse; bluish regions indicate the highest pulse intensities.
• Figure 3: Attosecond EUV skyrmion pulse train driven at 1.2 $\mu$m. (a) HHG spectrum, where the filled purple region shows the resulting harmonic window after using Al and Zr filters that yields the skyrmion attosecond train. (b) Temporal evolution of $N_\mathrm{S}$ within the 0.19 mrad contour during the central pulse. (c) Local temporal evolution of the real electric field for the central pulse within the train, with the instantaneous polarization state encoded by a color map linking each point to its position on the Poincaré sphere. (d) Polarization dynamics at representative transverse positions (beam center, intermediate point, and skyrmion edge), with trajectories on the Poincaré sphere within the central pulse; bluish regions mark the highest pulse intensities.