Investigation of Kinoform Element Chromatism

Abstract

The paper investigates the chromatic characteristic of the kinoform element in a given spectral range. Based on the well-known chromatism theory we obtain more exact expressions of the chromatic focus shift and the dispersion coefficient. The enhanced chromatism theory determined that the chromatic focus shift and the dispersion coefficient depend not only on a spectral range but also on a Fresnel zone number. Based on the enahnced theory we analyze the kinoform chromatism in the spectral range of 8–12 µm. We demonstrate that the element focuses the light with design wavelength to a single point, other light – to an uniformly illuminated line. We detect that the dispersion coefficient isn’t a constant, it has different value within each kinoform diffractive zones. Furthermore we analyze the geometry size of a monochromatic spot focused in an imaging region by all Fresnel zones. We propose the method for determining the imaging plane optimal location, in which spot size has minimal value.