Unveiling orbital optical chirality through multipolar chiral light–matter interaction

Chiral light–matter interactions are conventionally explained by electric–magnetic dipolar interference driven by light with spin angular momentum. Here, we demonstrate that optical chirality can also originate from the orbital angular momentum (OAM) of light, enabling higher-order multipolar chiral responses. Using a single twisted gold nanorod dimer and tightly focused circularly polarized optical vortex beams carrying spin and orbital angular momenta of the same sign, we obtain spectrally and spatially resolved chiral dichroism signals that exhibit strikingly different behaviors at the vortex center and the annular ring of the beam. At the beam center, distinct quadrupole resonances emerge whose spectral profiles depend on the OAM sign, revealing an OAM-driven chiral interaction. The response satisfies optical reciprocity, excluding artifacts from anisotropy or misalignment and confirming its nature as a true chiral response. Angular momentum dissipation analysis further confirms that orbital contributions dominate over spin. These results establish the existence of a distinct form of optical chirality, referred to as orbital optical chirality, opening routes to explore multipolar chiral light–matter interactions beyond the dipolar paradigm.