Fabrication of super-polished aluminium mandrels for x-ray optics

X-ray mirrors are fabricated to focus on cosmic x-rays and require a very high level of surface accuracy at the order of 1 nm or even less. To fabricate such a surface, direct surface manipulation within such tolerances is very difficult. Hence, an alternative method to develop this mirror is using the replication method. Ideally, aerospace-grade aluminium can lend itself to surface manipulation and can be super polished to the requisite nanometre level surface finish measured in RMS value. The present work aims to modify an aluminium 6061-T bulk material 400 mm × 600 mm × 10 mm with straight edges and to extract a quadrant of a circle with 90-degree edges, with its surface modified to the curvature and surface roughness of 3.1 nm. The surface roughness was measured by a non-contact profilometer. An aluminium mandrel was electroformed on a nickel surface and a reflective coating was provided. An electroformed shell surface architecture can be made reflective by gold coating, resulting in a gold shell mirror segment ready for segmentation and integration with a mirror module used in x-ray observatories.