Design of Fresnel lenses and binary-staircase kinoforms of low value of the aperture number

The design of plane Fresnel zone plates, and binary-staircase kinoforms, has been analyzed in this paper for a non-imaging application aimed to increase the performance of point-like detectors. They maximize the irradiance at the focal point of the diffractive element maintaining some constrains in the lateral size of the element. The design of the binary-staircase kinoform has been described as an iterative process. Some interesting results have been obtained for the values of the relative aperture number, or F/#. The practical case treated here produces elements with very low F/#. The results shows that the gain of the irradiance at the focal point increases with the focal distance of the binary-staircase kinoform, and decreases with the focal length for a plane Fresnel zone plate having a limited lateral size. The calculation of the width of the irradiance distribution makes it possible to select those solutions that best concentrate the irradiance on the focal plane. (c) 2005 Elsevier B.V. All rights reserved.