Perfect intrinsic and nonlinear chirality simultaneously driven by half-integer topological charge

Bound states in the continuum hold extraordinary optical topological properties and can significantly enhance the interaction between light and matter including the circular dichroism (CD) in chiral resonant metasurfaces. In this paper, we demonstrate the split and displacement of topological charges through tilted double-elliptical half-disk metasurfaces. It enables the feasibility to attain perfect intrinsic chiroptic responses, with a CD exceeding 0.99. The ellipticity (\ensuremath{\chi}) of the intrinsic chiroptic response, induced by vertical incidence, is also \ensuremath{\sim}1. In addition to linear chirality CD, significant near-field enhancement contrast is observed at the positions of half-integer topological charge, leading to remarkable nonlinear CD approaching a nearly perfect value of 1. The proposed metasurface simultaneously possesses perfect intrinsic chirality and nonlinear chirality, providing an avenue for the multifaceted development of planar optical devices.