Effects of the thickness of the substrate on the performance and the design of planar kinoform lenses for axial stigmatism in finite conjugate-imaging

Abstract

The imaging performance of zero-thickness substrate planar kinoform lenses designed for infinite conjugate-imaging is not affected when a plane 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 that 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 combination with a plane parallel substrate of finite thickness. For ensuring axial stigmatism as well as 100% diffraction efficiency at the desired image, the thickness of the substrate has to be taken into account ab initio in the design of the kinoform lens. A seminumerical procedure for implementing the same is presented and the convenient amenability of our method in the design of planar kinoform lenses on substrate of prespecified thicknesses is demonstrated with some illustrative examples.