S. Topuzoski, Lj.
Janicijevic, L. Stoyanov,
I. Stefanov, A. Dreischuh
Abstract.
By theoretical and experimental methods it is
demonstrated how a beam whose amplitude
profile is X-modulated in azimuthal direction, with central dark
non-vortex core, can be transformed
into an array
of five-vortex spot patterns. This beam undergoes Fraunhofer diffraction by a fork-shaped grating with integer
topological charge (TC) p.
The results show an interesting
phenomenon: while the incident beam
is without topological charge, in the output
array of spots a five-vortex modulation on the higher-diffraction-order
patterns is evident. It consists
of a central vortex (whose value and
sign of its TC depend on the
diffraction order m)
and four “satellite” vortices situated in the
apices of a rotated square (whose signs
depend on the diffraction order of the spot
m, in which they are nested).
An exception is made in
the case when the product
of the diffraction order and the
fork-shaped grating TC is equal to two;
Then, the central vortex is absent, but,
the four ”satellite” vortices are present. The
interference patterns of the diffracted wave field and
a slightly inclined plane wave are
obtained experimentally and numerically, confirming the presence of the vortices predicted by the theory
and registering the value and
sign of their TCs.
Keywords: Diffraction, Optical vortices, Fork-shaped grating, Five-vortex spot patterns