Unveiling orbital optical chirality through multipolar chiral light-matter interaction
Chiral light-matter interactions have traditionally been understood in terms of electric-magnetic dipolar interference driven by light with spin angular momentum. Here, we show that optical chirality can also originate from the orbital angular momentum (OAM) of light, giving rise to higher-order multipolar chiral responses. Using a twisted gold nanorod dimer and tightly focused circularly polarized optical vortex beams carrying spin and orbital angular momenta of the same sign, we measure spectrally and spatially resolved chiral dichroism signals that persist even where spin optical chirality vanishes, revealing a quadrupole-mediated chiral interaction driven by OAM. The spectra reveal clear quadrupole resonances whose spectral profile is strongly modulated by the OAM sign, demonstrating an OAM-driven chiral interaction. Crucially, the signal satisfies optical reciprocity, ruling out artefacts from anisotropy or misalignment and confirming its nature as a true chiral response. Angular momentum dissipation analysis further shows that orbital contributions dominate over spin. These findings establish the existence of a distinct form of optical chirality, referred to as orbital optical chirality, which opens new avenues for probing and controlling multipolar chiral light-matter interactions beyond the dipolar paradigm.