Generation of lattice structures of optical vortices

We demonstrate experimentally the generation of square and hexagonal lattices of optical vortices and reveal their propagation in a saturable nonlinear medium. If the topological charges of the vortices are of the same sign the lattice exhibit rotation, while if alternative, we observe stable propagation of the structures. In the nonlinear medium the lattices induce periodic modulation of the refractive index. Diffraction of a probe beam by this nonlinearity-induced periodic structure is observed.