Progress toward controlling the shape of silicon mirrors coated with a magnetic smart material

Thin-walled X-ray optics are going to be required to meet the demands of large collecting area versus volume and mass for the next generation X-ray astronomy Flagship Mission. We report here our progress on our concept of meeting the challenge of producing these mirrors. The case we address is the one where the initial fabrication process requires post-fabrication figure correction. Our technology can be applied prior to launch and also enable in-flight figure corrections. Our process is to coat a film of magnetic smart material onto the backside of the thin-walled X-ray mirrors. Then, an electromagnet is used to produce an in-plane stress and thus reshape the mirror. We show in this paper that 500 mu m thick Si wafers can be coated and after coating remains significantly flat, i.e. they have a radius of curvature of about 30 m. We have carried out deflection measurements as a function of the external magnetic field of about 0.1 to 0.3 T and found a nearly linear relationship. We also revisited the stability of induced deflections for up to nearly 70 hours and also demonstrated that the process can produce deflections for fine-scale figure adjustments of order (10 nm) range deflections.