Photonic Orbital Angular Momentum Dichroism on Three-Dimensional Chiral Oligomers

Abstract

Chiral oligomers in optics are photonic metamaterials inspired by the concept of chiral centers in chemistry. In recent years, chiral oligomers have attracted increasing attention in recent years due to 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 angular momentum (OAM)-dominated chiroptical response of chiral oligomers still remains elusive. Here, we theoretically and experimentally demonstrate the individual three-dimensional (3D) chiral tetramers can exhibit a gigantic response to the photonic OAM with a maximum helical dichroism (HD) of ∼23%. Meanwhile, we also reveal the origin of the HD via simulation analysis of electric current distribution, reflected electric field, and the discrete OAM spectroscopy. Furthermore, by femtosecond direct laser writing, 3D oligomers with tailoring geometric parameters can be flexibly fabricated in one step for varying HD responses. Our research fills the gap of OAM-related chiroptical response of chiral oligomers, which has great implications for chiroptical spectroscopy and photonic angular momentum engineering.