Photonic Orbital Angular Momentum Dichroism on Three-Dimensional Chiral Oligomers

Chiral oligomers in optics are photonic metamaterialsinspiredby the concept of chiral centers in chemistry. In recent years, chiraloligomers have attracted increasing attention in recent years dueto their simple construction and unique chiroptical response. To date,research has predominantly focused on the photonic spin angular momentum(SAM)-dependent chiroptical response: circular dichroism (CD). However,for another photonic dimension parallel to the SAM, orbital angularmomentum (OAM)-dominated chiroptical response of chiral oligomersstill remains elusive. Here, we theoretically and experimentally demonstratethe individual three-dimensional (3D) chiral tetramers can exhibita gigantic response to the photonic OAM with a maximum helical dichroism(HD) of similar to 23%. Meanwhile, we also reveal the origin of the HDvia simulation analysis of electric current distribution, reflectedelectric field, and the discrete OAM spectroscopy. Furthermore, byfemtosecond direct laser writing, 3D oligomers with tailoring geometricparameters can be flexibly fabricated in one step for varying HD responses.Our research fills the gap of OAM-related chiroptical response ofchiral oligomers, which has great implications for chiroptical spectroscopyand photonic angular momentum engineering.