Diffraction characteristics of the ring zone plate as a representative of curvilinear zone plates

It is shown that curvilinear zone plates can be constructed as phase representatives of plane curvilinear light sources. The ring zone plate is one representative of this type of diffracting optical element. At the same time, it is an optical device which can be used as a lens substitute for ring lenses, especially in the UV region. The diffracted wave amplitude and the intensity distribution for both binary, positive and negative, computer-generated ring zone plates, are determined by the use of the Fresnel-Kirchoff approximation. It is found that the ring zone plate exhibits manifold real and virtual focal rings.