  In recent years, research on the interaction between Orbital Angular Momentum
(OAM) and matter has seen a continuous influx of investigations. OAM possesses
distinct properties, such as additional degrees of freedom, vortex
characteristics, and topological properties, which expand its applications in
optical communication, optical sensing, and optical force. Through experiments
involving the interaction of a chiral metal swastika structure with a SAM-OAM
beam generated by a q-plate, we have observed a phenomenon does not present in
pure SAM beams. Fourier back focal plane (FBP) imaging under SAM beam
excitation easily identifies the chirality and geometric properties of the
structure. When the SAM-OAM beam excites the structure, FBP not only identifies
its chirality and geometric properties but also distinguishes different OAM
topological charges and signs, as well as the degree of elliptic polarization.
The stokes parametric FBP imaging reveals asymmetric polarization distribution
resulting from the interaction between a vortex beam and the chiral structure.
Moreover, it clearly reflects the conversion process of SAM to OAM. The
experimental results align well with simulation results. These findings hold
valuable insights for the advancement of optical information storage and
communication using OAM, opening up new possibilities for further exploration
in this field.
