ZONE PLATES PERFORMING GENERALIZED HANKEL-TRANSFORMS AND THEIR METROLOGICAL APPLICATIONS

A modified computer-generated Fresnel zone plane with the zone distrib ution determined by a Fermat spiral is proposed for performing general ized Hankel transforms. The special case of these elements realizing t he generalized Hankel transform of first order is of special interest from the point of view of alignment applications. The doughnut shaped focal pattern, characteristic for the whole family of proposed zone pl ates exhibits then the smallest diameter. Its diameter is also smaller than other solutions proposed previously for obtaining focal spots wi th a black dip in the centre.