  The edge diffraction of a homogeneously polarized light beam is studied
theoretically based on the paraxial optics and Fresnel-Kirchhoff approximation,
and the dependence of the diffracted beam pattern of the incident beam
polarization is predicted. If the incident beam is circularly polarized, the
trajectory of the diffracted beam centre of gravity experiences a small angular
deviation from the geometrically expected direction. The deviation is parallel
to the screen edge and reverses the sign with the polarization handedness; it
is explicitly calculated for the case of a Gaussian incident beam with plane
wavefront. This effect is a manifestation of the spin-orbit interaction of
light and can be interpreted as a revelation of the internal spin energy flow
immanent in circularly polarized beams. It also exposes the vortex character of
the weak longitudinal field component associated with the circularly polarized
incident beam.
