Marcos G. Barriopedro

arXiv2026

Spontaneous optical skyrmion generation by frequency doubling in underdense plasmas

Optical skyrmions have been widely explored in recent years. Among them, Stokes skyrmions require sophisticated wave engineering or photonic devices for their generation. We show that Stokes skyrmions can emerge spontaneously in second-order harmonic generation in underdense plasmas driven by optical vortices. The nonlinear response produces a structured frequency-doubled field whose polarization texture maps the Poincaré sphere. When plasma inhomogeneities are taken into account, the electron density gradient deforms the skyrmionic texture, enabling topological diagnosis of plasma density.

physics.optics↗

arXiv2026

Scaling law from orbital angular momentum conservation in harmonic and high-order harmonic generation driven by spatiotemporal light fields

Nonlinear photon upconversion processes driven by diverse forms of structured light are receiving increasing attention. In harmonic and high-order harmonic generation (HG and HHG) with Laguerre-Gauss (LG) beams, linear scaling the driver topological charge (TC) with the harmonic order is equivalent to driver orbital angular momentum (OAM) per photon scaling, and constitutes a proof of OAM conservation. However, with generic driving fields, such as non-LG vortices or spatiotemporal optical vortices, TC and OAM per photon may scale or not in a process in which the OAM is conserved. We find the physical magnitude that scales with generality when the OAM, either longitudinal or transverse, or its intrinsic part, is conserved. This new rule allows for the wealth of phenomena observed in HHG that are unintelligible from the rigid LG rule.

physics.optics↗