Visible Light Diffraction Image Evaluation of Grazing Incidence Optical Systems

Abstract

Optical systems designed to utilize extreme ultraviolet (EUV) and x-ray photons from synchrotron radiation (SR) light sources with grazing incidence optics generally have entrance apertures that are long in the horizontal plane and narrow in the vertical plane. Apertures that are 1 mrad high by several milliradians wide at a distance of 10 meters from the source are typical. A point source illuminated by a red He-Ne laser beam imaged through a system with this aperture and focal length results in a 1.2 mm high image that is severely broadened by diffraction. Component alignment with visible light is difficult when the diffraction limit is so severe. The use of visible light for system alignment is, however, a necessity, because alignment under actual operating conditions and at operating wavelengths in ultra high vacuum chambers is totally impractical. Except for rare instances, components are not accessible for alignment adjustments. How, then, can we make use of the information available in the severely diffraction-limited visible image to assess the performance of our system at x-ray wavelengths?