  In this article we present a theoretical study for Fraunhofer diffraction of
a Laguerre-Gaussian laser beam with zeroth radial mode number and azimuthal
mode number l by diffractive grating with embedded fork-shaped dislocations of
integer order p. Analytical expressions describing the diffracted wave field
amplitude and intensity distributions in the Fourier plane are deduced and
analyzed. They are also followed by the vortex radii expressions.
