Controlling and shaping topological charge by means of spiral petal-like zone plate

Abstract

In this work, we present a technique based on a helically modulated petal zone plate through which topological charge is handled. Basically, in this case, we are dealing with two kinds of phase change, the first one is a sinusoidally azimuthal phase change and the second one is helically changing of the phase. We have shown that the total topological charge of the generated beam depends on the difference between the number of the petal and the charge of the element. Such that, the focused vortex beam turns to a focal spot when these two parameters take the same value, i.e. the singularity is quietly taken away. It was also demonstrated that a bi-annular vortex is generated for a large amount of petal frequency. As a result, an optical corridor carrying a topological charge is also formed around the focus.