The Comparison of Laser Radiation Focusing by Diffractive Axicons and Annular Gratings with Variable Height Using High-performance Computer Systems

The features of focusing Gaussian beams and optical vortices with circular and radial polarization are studied in this paper. The finite difference time domain method was used to simulate the focusing (3D) of the considered laser beams by diffractive axicons and annular gratings of variable height. It should be noted that a significant increase in the length of the light needle is observed when the height of the grating rings changes in comparison with the standard diffraction axicon. In particular, for the case of inverse ring grating, DOF =4.8 $\lambda$, which is 2.4 times longer than the length of the light needle obtained using the standard diffractive axicon. The narrowest focal spot was obtained for the direct ring grating case for a super-Gaussian beam with $\sigma=12.15$ at radial polarization, FWHM =0.36 $\lambda$, which is 21.7 % less than for the standard diffraction axicon.