Comparison of the shape of focal spots in terms of intensity and energy flux for a high-aperture zone plate and a spiral zone plate

Using a finite-difference time-domain method, it has been shown that focal spots generated when tightly focusing linearly polarized Gaussian beam by Fresnel zone plate (FZP) and with an embedded optical vortex spiral (SZP) have different patterns of the intensity energy flux. The most significant differences are observed value topological charge (TC) is equal to three. flux annular distribution focused FZP, while SZP produces field whose three local maxima. number maxima corresponds order SZP. At certain distance from focus, petal structure (and flux) changes ring distribution.