Metrology advancements for x-ray optics: Lynx and beyond

Abstract

Next-generation X-ray telescopes require mirrors with surface height errors of a few nanometers. Traditional Fizeau interferometry is limited as measurements include surface errors on the surface under test (SUT) as well as the reference. Axial shift mapping (ASM) is a self-referencing interferometric method for near-cylinders that can separate the reference surface from the SUT. ASM recovers the absolute figure of the reference and SUT in lines along the axial direction. However, it does not recover the axial slope of the lines. Incorporating shifting in the azimuthal direction recovers the axial slope of each line as well as axial slope variation across the optic. This paper discusses progress towards adding azimuthal shifting to the ASM technique. Additionally, this paper outlines upgrades to the MIT soft X-ray beamline to allow for mirror testing. X-ray testing will be used to verify the accuracy of ASM with at-wavelength measurements.