Abstract

A spiral phaseplate¹ has been developed that can be used to produce helical-wave front laser beams. The phase of such a beam has a screw dislocation at its center, also called a topological charge, which is associated with orbital angular momentum.^2,3 The plate is a transparent plastic disk with a helical surface (Fig. 1). The azimuthal thickness variation is 0.72 mm over 2π, but this is scaled down by immersing the plate in index-matching fluid. By changing the temperature, the effective step can be tuned from zero to a few wavelengths, so that the immersed plate operates as a diffractive-optical element.

© 1994 IEEE