Symmetry Constrained Different Types of Maximal Chiroptical Responses in Slant Chiral Resonant Metasurfaces

ABSTRACT Slant metasurfaces represent a typical platform for realizing intrinsic chiral quasi‐bound states in the continuum (q‐BIC). However, previous studies have predominantly focused on circular preserving dichroism (CPD), with the prevailing assumption that handedness‐preserving chiroptical responses are essential for maximizing chiral emission, while the other typical chiroptical response, circular conversion dichroism (CCD), has always been overlooked. In this work, we demonstrate both intrinsic circular‐conversion and circular‐preserving chiroptical responses in slant resonant metasurfaces with different symmetry constraint conditions, both of which support maximal chiral emission with near‐unity degree of circular polarization (DCP) at the q‐BIC resonance. Our results reveal that emission DCP is not always relevant to the magnitude or type of transmission circular dichroism (CD T ), and the maximum DCP can even be achieved when CD T approaches zero. Our findings clarify the symmetry criteria for CCD and CPD responses and establish the intrinsic independence of emission chirality from transmission chirality in slant chiral metasurfaces, providing guidelines for compact and high‐purity chiral light sources in both classical and quantum regimes.