Design of projective zone plates and their focusing properties

Transmittances are designed by generation of a family of curves whose local geometry is similar to that of zone plates. The family is obtained by means of projective mapping in the normal direction of an initial curve, so that all the curves of the family have a common evolute. This property allows the prediction of the geometry of the focusing region of the transmittance. Experimental results with an ellipse as the initial curve are shown. We show that the proposed zone plates can be considered a generalization of conventional zone plates.