Surface metrology of off-axis paraboloids with a Zygo phase-measuring interferometer

Surface metrology of off-axis paraboloids with a Zygo phase-measuring interferometer Wayne R. McKinney, Nikolay Artemiev, Gregory Morrison, Valeriy V. Yashchuk, and Howard Padmore Lawrence Berkeley National Laboratory, Berkeley, California, 94720 Corresponding Author: Wayne R. McKinney Affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Mailing address: Lawrence Berkeley National Laboratory, 1 Cyclotron Road, M/S 15R0317 Berkeley, CA 94720-8238, USA Telephone number: +1-510-486-4395 Fax number: +1-510-486-4385 Email address: WRMcKinney@lbl.gov Presentation preference: Oral Presentation Abstract text: Increased brightness of updated 3 rd generation synchrotron sources and FELs leading to smaller focused spots of x-rays has led optical designers to consider more and different methods of manufacture, and more and different figures for optical surfaces [Opt. Express. 17(20), 18271-18278, 2009]. The desire to achieve higher resolving powers for Resonant Inelastic X-ray Scattering (RIXS) also drives the interest in shapes which can focus to a point in monochromator designs. As a run up to potential future requirements in soft x-ray optical metrology, we investigate here the surface quality of off-axis paraboloids fabricated by diamond-turning. A novel method to measure off-axis parabolic optics is based on using gold microspheres as a diffraction limited back reflector in a double-bounce auto collimating geometry [SPIE Proc. 7102, 71020X (2008)]. We also discuss two other minor modifications to this experimental approach and compare them with the one using a diffraction limited ball to measure off-axis parabolic optics. Such methods may be extended, we propose, to ellipsoidally figured optics using converging rather than parallel light emerging from the interferometer.