Stitching interferometry for the wavefront metrology of x-ray mirrors

We discuss the possibility of using Stitching Interferometry for the surface shape metrology of X-ray Mirrors. Indeed, Stitching Interferometry combines a large field of measurement with a high lateral resolution. In other words, it provides large-scale and medium-scale measurements in a single instrument. Small-scale deformations is considered here to be "roughness", and will not be dealt with in this article. The only potential problem in Stitching Interferometry is large-scale fluctuation. This is not due to the Stitching Process itself, but to small measurement errors which get "amplified" by the long dimension of the typical X-ray Mirror. This will be addressed, and it will be shown that it need not be a problem. As we have not completed our series of experimental measurements, we will illustrate our article with stitching measurements performed on large MegaJoule components (800 x 400 mm), and show an example of "Mixed Stitching", involving measurement files of different origin.