Illustration of second-order design methods: Global merit function plots for a class of projection systems

Recently developed methods [J. Opt. Soc. Am. All, 3292-3307 (1994)] permit definitive studies of two-mirror systems for a variety of applications. As an illustration of such a study, unobstructed, telecentric, plane- symmetric systems of two conic mirrors that are intended for distortion-free projection are investigated here.The magnification, speed, and field size in the examples are arbitrarily chosen to correspond to values that are appropriate for full-field soft-x-ray projection lithography. Low-order imaging constraints are applied to eliminate most of the 13 parameters that specify the configuration of such a system. It is shown that there are just two three-parameter families of systems and a single four-parameter family. The associated three- and four-dimensional merit function spaces are mapped, and selected systems from various regions of the spaces are discussed.