Generation of a spiral wave by modified annular slit

Abstract

Optical beams of Bessel-type, whose transverse intensity profile remains unchanged under free-space propagation, are called nondiffracting beams. In this paper, we propose a simple and effective method to generate spiral beams whose intensity remains invariant during propagation using amplitude masks. We show how the interaction between two incomplete annular beams leads to the formation of a spiral structure. Experimental observations are presented to show the characteristic features of the spiral structure generated. We can modulate the nondiffracting beam modifying the amplitude mask.