  Propagation of light through a thin flat metallic screen containing a hole of
twisted shape is sensitive to whether the incident wave is left or right
circularly polarized. The transmitted light accrues a component with handedness
opposite to the incident wave. The efficiency of polarization conversion
depends on the mutual direction of the hole's twist and the incident light's
wave polarization handedness and peaks at a wavelength close to the hole
overall size. We also observed a strong transmitted field concentration at the
center of the chiral hole when the handedness of the chiral hole and the wave's
polarization state are the same.
