Synthesis and analysis of optical vortices with fractional topological charges

We present an elaborated holographic technique for synthesis of optical beams possessing optical vortices with fractional topological charge. The technique is based on the production of sub-harmonic diffraction orders. The diffraction orders corresponding to the fundamental period have embedded vortices with integer topological charge and sub-harmonic diffraction orders have optical vortices with fractional topological charge. An analytical approach for charge-1/2 optical-vortex beam structure description is presented.