Cosine-type apodized spiral zone plate to handle the topological charge of a vortex beam

Abstract

By taking advantage of spiral petal-like zone plates, we have recently demonstrated that a spiral element's geometric shape impacts its charge. Keeping it in mind, we aim to control topological charge of a vortex by means of phase modification of an spiral zone plate without transforming its geometrical shape. This is achieved by apodizing a spiral zone plate having p spiral zones with a radial grating with spatial frequency m. Having implemented some radial gratings with different m, we realized that an optical vortex is produced whose topological charge and its handedness are dependent on p and m. Consequently, a constant phase replaces on-axis screw dislocation under the situation that p takes an odd multiples of m. Studies are carried out for both large and small pairs of (p,m) and various gaps between the couple.