Analysis of the Fields Formed by the High-aperture Zone Plate and the Spiral Zone Plate

In this paper, an analysis of the fields formed by the high-aperture binary conventional and spiral zone plates is presented. The study was performed by using the FullWAVE software package which implements the finite difference time domain method. The conventional zone plate was illuminated by optical vortices with topological charge $m =1$, 2, and 3 while proposed spiral zone plates with the same topological charges $m =1$, 2, and 3 were illuminated by an ordinary Gaussian beam. It was shown that proposed binary zone plates made of silica glass form a different intensity and energy flow distribution in their focal planes. The spiral zone plate in the focal plane produces the intensity distribution with m discontinuity while the conventional zone plate produces a ring-shaped intensity pattern with two maxima on the vertical axis. During the propagation of vortex field formed by spiral zone plate, the intensity pattern changes and become a ring.