  Circular dichroism (CD) caused by the response of a chiral object to
circularly polarized light has been well established, and the strong CD of
plasmonic meta-molecules has also become of interest in recent years; however,
their response if the light also has orbital angular momentum is unclear. In
this paper, the dichroism of a plasmonic cuboid-protuberance chiral structure
under the illumination of a light beam with both orbital and spin angular
momentums is numerically investigated. Distinguished spectra are observed under
the different momentums. The circular dichroism under the combination of vortex
beam and light spin is enhanced. This phenomenon is attributed to the partial
spatial excitation of the nanoparticle, and the strong dichroism is
simultaneously caused because of the interaction of the induced electric and
magnetic modes and other higher-order modes caused by the partial excitation of
the vortex beam. This research provides further insight into chiral
light-matter interactions and the dichroism of light with orbital angular
momentum.
