Diffraction of Vortex Beams by Annular Gratings with Variable Height in the Near Zone

The diffraction of vortex Laguerre-Super Gauss modes and super-Gaussian beams on annular gratings with variable heights and refractive index of individual relief rings study in this paper. It is shown that by varying the parameters of the annular grating, for both types of beams it is possible to achieve a decrease in the size of the focal spot in comparison with the standard diffraction axicon.