The investigation of the features of focusing vortex super-Gaussian beams with a variable-height diffractive axicon

Spatial intensity distributions of the Laguerre-superGauss modes $(1,0)$ as well as a super-Gaussian beam with radial and circular polarization were investigated versus changes in the height of a diffractive axicon. The height of the relief of the optical element varied from $0.25\lambda$ to $3\lambda$. The modeling by a finite-difference time-domain method showed that variations in the height of the diffractive axicon significantly affect the diffraction pattern in the near field of the axicon. The smallest focal spot size for a super-Gaussian beam was obtained for radial polarization at a height equal to two wavelengths. The minimum size of the focal spot for the Laguerre-superGauss mode $(1,0)$ was obtained for circular "–" polarization with an element height equal to a quarter of the wavelength.