Progress in differential deposition for improving the figures of full-shell astronomical grazing incidence x-ray optics
One of the developments at MSFC that is underway to meet the demand of high-resolution X-ray optics for future X-ray astronomy missions is the `differential deposition' technique. This process corrects the axial figure profile of optics by selectively depositing material onto the mirror's reflective surface. The process relies on accurate metrology achieved using a long trace profiler whose slope resolution is better than 1μrad. From these metrology data an error map is generated that shows the profile of material to be deposited to correct the optic's figure. A computer-controlled, deposition system then applies this corrective coating. Simulations show that a substantial improvement in angular resolution is possible with this approach after multiple correction `cycles'. To assess this, custom coating systems have been developed and corrections of full-shell optics are underway. To date, a factor of < 2 improvement in the imaging quality of the optics has been demonstrated in x-ray tests after a single stage of correction.