Generation and control of extreme ultraviolet free-space optical skyrmions with high harmonic generation

Abstract. Optical skyrmion serves as a crucial interface between optics and topology. Recently, it has attracted great interest in linear optics. Here, we theoretically introduce a framework for the all-optical generation and control of free-space optical skyrmions in extreme ultraviolet regions via high harmonic generation (HHG). We show that by employing full Poincaré beams, the created extreme ultraviolet fields manifest as skyrmionic structures in Stokes vector fields, whose skyrmion number is relevant to harmonic orders. We reveal that the generation of the skyrmionics structure is attributed to spatial-resolved spin constraint of HHG. Through qualifying the geometrical parameters of full Poincaré beams, the topological texture of extreme ultraviolet fields can be completely manipulated, generating the Bloch-type, Néel-type, anti-type, and higher-order skyrmions. We promote the investigation of topological optics in optical highly nonlinear processes, with potential applications toward ultrafast spintronics with structured light fields.