Upgrade of surface profiler for x-ray mirror at SPring-8

In beamlines at third-generation synchrotron radiation and X-ray free-electron-laser (XFEL) facilities, various mirrors are used as deflection, focusing, and collimating optics. The required specifications for the mirrors depend on their purpose. In recent years, high-precision aspheric mirrors and flat mirrors, with a figure error less than 10 nm are used as diffraction-limited focusing optics and deflection optics, respectively. The origins of the figure error are fabrication error, gravitational deformation, and clamping deformation. In the case of the bend mirror, figure error is also induced by the bender mechanism. The fabrication error is measured by a long trace profiler (LTP) [1] or by relative-angle determinable stitching interferometry (RADSI) [2] with special high frequency of 0.1–1/mm. Deformation caused by gravity, clamping, and bending should be measured under actual operating conditions because these deformations depend on the direction of the mirror surface and the direction of clamping and bending, respectively. In recent years, in-situ and atwavelength metrology techniques such as the Hartmann sensor, pencil beam, grating base and the speckle-effect-based technique, have been reported [3-6]. These methods are able to investigate the profile of the mirror under real conditions, including the effects of thermal bump; however, these techniques require X-rays and a long optical length to the detector. We attempted to upgrade the LTP at SPring-8 using autocollimators for the precise measurement of height profiles under conditions of both upward and horizontal reflection geometries. A portable Fizeau interferometer was installed for onsite measurement.