Diffraction characteristics of optical elements designed as phase layers   with cosine-profiled periodicity in azimuthal direction
  The article concerns an investigation of the Fresnel diffraction characteristics of two types of phase optical elements, under Gaussian laser beam illumination. Both elements provide an azimuthal periodicity of the phase retardation. The first element possess azimuthal cosine-profiled phase changes deposited on a plane base. The second element is a combination of the first element and a thin phase axicon. The cosine profile of the phase retardation, of both diffractive elements, produces an azimuthal cosine-profiled modulation on their diffractograms. It destroys the vortex characteristics of their diffraction fields. 
Suzana Topuzoski, and Ljiljana Janicijevic
physics.optics