New Process For X-Ray Mirror Image Quality Improvement

A new technique to improve the image quality of Ni replicated X-ray mirror is presented. During the manufacturing of XMM Mirror Module between 1994 to 1999, the classical manufacturing process showed its limits. In 1995, the XMM Mirror Module Qualification Model HEW was around 20 arcsec. In 1998, the fifth Flight Model Mirror Module reached 11 arcsec HEW, with a single mirror shell achieving 8 arcsec HEW. The performance of this technology is namely limited by the integration process of the shells.The new technique is based on the following philosophy :Firstly, an accurate measurement of each mirror shell after integration. A dedicated metrology system has been built and allows a precise metrology of the actual surface.Secondly, a modification of the mirror shell and of the support to transfer the stress to a non optical active area.Finally, an ion figuring run to correct the residual shape error of the mirror.The control and evaluation of the process is assured by EUV PSF assessment achieved in the FOCAL X facility developed for XMM.The advantages of this new process are to shape the mirrors in their final hardware configuration and the versality of the process enabling improvement of other kinds of high accuracy mirrors.