AN ASYMMETRIC PUPIL WITH FOCUSING PROPERTIES

We define a set of pupils, named Fresnel spirals (FS), consisting of v ariable step spirals with radial transmittances corresponding to Fresn el zone plates. We calculate the diffraction pattern at near and far f ields for those pupils. The intensity distribution in those regions wa s experimentally verified. As for Fresnel zone (FZ) plates, focusing a long the optical axis is found. In the transverse directions, the diff raction pattern intensity shows also spiral geometry and the turning s ense of the spiral reverses after focusing. (C) 1998 Published by Else vier Science B.V. All rights reserved.