  We have developed theory for the interaction of THz radiation with a
sub-wavelength metallic grating. The structure of electric fields of the
electromagnetic wave under the metallic grating has been studied in the
near-field zone. Spatial distributions of the electric field components and the
electric energy density have been obtained for the transmitted wave through the
grating. An effect of strong local enhancement of the electric field has been
detected. Spatial dependences of the polarization of the transmitted wave has
been analyzed for the near-field zone.
