Polarization structure transition of C-point singularities upon reflection

This paper provides a comprehensive study of the polarization transition of reflected C-point singularities. The reflection of star- and lemon-type C-point paraxial vector beams at an air-dielectric interface is investigated. For small oblique incidences, a topological phase transition is observed exclusively in spin-maintained modes, manifesting as a shift from a vortex phase to a spin phase. Notably, as the incident angle ranges from 0 to 90 degrees, another topological phase transition occurs, the total spin components of the reflected field undergoing an interchange of topological charges (TCs), resulting in a type transition of the C-point from the star (lemon)-type to the lemon (star)-type. Furthermore, the concurrence of the C-point beam throughout the reflection process can be modulated by the incident angle, spanning almost the entire spectrum from 0 to 1. The longitudinal and transverse displacements of each spin component as well as the overall beam shifts of the reflected beam are further analyzed, revealing their dependence on the incident beam’s TC combination. These findings offer novel physical insights into polarization singularity-matter interactions, holding promise for advancing research in singular optics and its applications.