Ultrafast optical skyrmions generated via an achromatic Sagnac vortex generator

Optical skyrmions extend the concept of topological protection from high-energy physics and condensed matter physics to the field of optics, and their unique polarization textures exhibit remarkable potential in numerous domains. However, to date, ultrafast optical skyrmions remain underexplored. This paper proposes a scheme for generating ultrafast optical skyrmion pulses based on a modified self-referenced Sagnac vortex generator. By constructing a Yb:QX crystal passively mode-locked resonator, laser pulses of about 3 ps in both fundamental mode-locked and Q-switched mode-locked states are generated. Combined with a modified Sagnac interferometer with the achromatic property to achieve coherent superposition and polarization control, three types of topological structure ultrafast pulses, namely Néel-type, Bloch-type, and anti-type skyrmion, are generated. By verifying topological integrity via Stokes parameters and enabling dynamic switching of topological types through phase difference adjustment, this experiment resolves wavelength or bandwidth limitations of traditional methods. It thus offers a new pathway for high-resolution material writing and anti-interference optical communication.