The influence of astigmatic aberration on the Gaussian beam diffraction in the near field of axicons and ring gratings

The diffraction of Gaussian beams with astigmatic aberration on high-aperture diffractive axicons with different relief heights was studied in this paper. Also the axicons and ring gratings without a central zone were considered. The finite difference time domain method was used for modeling. It is shown that increasing the relief height of the diffractive axicon leads to the formation of the chains of maxima outside the element. The minimum focal spot size outside the element in the presence of astigmatic aberration (α = 141.68) in the input beam was observed for the case of an axicon without a central zone for h = 4.24λ, (FWHM = 0.43λ). The longest light needle was obtained for the same type of beam and element, but at a height of h = 1.06λ (DOF = 5.96λ).