Development of a Linear Stitching Interferometric System for Evaluation of Very Large X-ray Synchrotron Radiation Substrates and Mirrors

Stitching interferometry, using small-aperture, high-resolution, phase-measuring interferometric systems has been investigated for quite some time now as a metrology technique to obtain surface profiles of oversized optical components and substrates. The technique offers the potential for providing 3D measurements of mirror surfaces with nanometer resolution. The aim of this work is to apply this technique to the specific case of large, flat, grazing-incidence x-ray mirrors, such as those used in beamlines at synchrotron radiation facilities around the world. In the case of x-ray mirrors, obtaining a 3D surface profile can be particularly useful in many instances, for example, in selecting the best reflecting stripe on a mirror surface to be used for undulator beams. The measurement data can be used for simulating and predicting mirror performance under realistic conditions, etc. A fully automated stitching system is currently being developed at the metrology laboratory of the Advanced Photon Source at Argonne National Laboratory. Preliminary tests performed on a 460-mm-long flat float-glass substrate and on a 300-mm-long superpolished silicon substrate, were encouraging. The stitched profiles showed no obvious overlap errors, and the results agree well with those obtained using other techniques