X-ray testing of grazing incidence optics fabricated at the University of Colorado

Most methods of producing grazing incidence optics require expensive metrology equipment to achieve sub arcminute quality in the X-ray. At the University of Colorado we have been developing methods of manufacturing grazing incidence optics by grinding and polishing on aluminum and nickel surfaces that have been machined to within a few arcminutes on a conventional metal working lathe. The mirrors are tested during fabrication by the knife edge and Ronchi test which are simple optical tests requiring only a collimated source of visible light and a 50 line per inch screen, (Gallagher 1990). No metrology of the surface is done. At graze angles of a few degrees fabricating optics by this method is limited by diffraction of the highly obstructed pupil, but at visible wavelengths figuring to 10 or 20 arcseconds is still possible. This method cannot produce arcsecond quality X-ray mirrors by itself, but can be modified to do so when coupled with normal incidence testing of the optical surface by use of a reference test plate or profilometer. In this paper we only discuss the X-ray testing of a 218 mm diameter F/5.73 Wolter Type I telescope manufactured at the University of Colorado. The mirror flew on a NASA sounding rocket in March of 1991. Testing of the inplane and offplane imaging response at energies of .25 - 1.50 KeV and correlation with surface figure are discussed.