EFFECTS OF THE THICKNESS OF THE SUBSTRATE ON THE PERFORMANCE AND THE DESIGN OF PLANAR KINOFORM LENSES FOR AXIAL STIGMATISM IN FINITE CONJUGATE-IMAGING

The imaging performance of zero-thickness substrate planar kinoform le nses designed for infinite conjugate-imaging is not affected when a pl ane parallel plate, placed in the object space, is used as a substrate . This invariance property does not hold good in the case of kinoform lenses designed for finite conjugate-imaging purposes. It is shown tha t the imaging performance of a planar kinoform lens, designed with the assumption of zero substrate thickness for stigmatic imaging between two axial points, is drastically changed when the lens is used in comb ination with a plane parallel substrate of finite thickness. For ensur ing axial stigmatism as well as 100% diffraction efficiency at the des ired image, the thickness of the substrate has to be taken into accoun t ab initio in the design of the kinoform lens. A seminumerical proced ure for implementing the same is presented and the convenient amenabil ity of our method in the design of planar kinoform lenses on substrate of prespecified thicknesses is demonstrated with some illustrative ex amples.