Ultrafast Vortex Photonics: From Perfect Optical Vortices to Attosecond Structured Light in Solids

High-order harmonic generation (HHG) has long served as the foundation of attosecond science, enabling the creation of coherent XUV and soft X-ray light to probe electron motion on its native scale. The introduction of structured light, beams carrying orbital angular momentum (OAM), has added a new spatial and topological dimension to strong-field physics. Such beams, with helical phase fronts, can imprint their OAM onto the emitted harmonics, leading to twisted attosecond pulses with rich spatiotemporal structure.

In gases, we investigated HHG driven by perfect optical vortex (POV) beams, light fields whose intensity ring size is independent of the OAM. Using a thin-slab model (TSM) combined with the strong-field approximation, we showed that harmonics generated by POV beams exhibit identical divergence across all orders and obey the strict OAM upscaling law. This invariance ensures the production of spatially locked, bright, and coherent XUV vortices that can form attosecond pulse trains [1].

In solids, we extended these ideas to HHG driven by Laguerre-Gaussian vortex beams. Solving the semiconductor Bloch equations coupled with the TSM, we showed that high-order vortex harmonics can emerge even in condensed matter, where electron-hole dynamics and ultrashort dephasing times govern the emission. The results predict that synthesizing several harmonics can yield attosecond vortex pulses, a major step toward compact attosecond structured-light sources [2].

These advances reveal a continuous picture of OAM conservation in strong-field light-matter interaction. The spatial structure of the driving field shapes both the harmonic emission and the resulting attosecond waveforms. This convergence of structured light and attosecond science opens pathways to table-top sources of twisted XUV light, ultrafast imaging of topological and chiral materials, and precise control of OAM in matter.