Ion beam figuring and optical metrology system for synchrotron x-ray mirrors

Abstract

Meeting the ever-increasing performance demands of X-ray beamlines at modern synchrotrons, such as Diamond Light Source (DLS), requires the use of ultra-high-quality X-ray mirrors with surface deviations of less than a few nanometres from their ideal shape. Ion beam figuring (IBF) is frequently used for creating mirrors of this precision, but achieving the highest accuracy is critically dependent on careful alignment and precise metrology of defects on the optical surface. Multiple iterations of measurement and correction are typically required, and convergence towards the requisite shape can be a slow process. DLS have designed and built an in-house IBF system that comprises a large diameter DC gridded ion source, and a 4-axis motion stage for manipulating the mirror being figured. Additionally, a slope measuring profilometer for in-situ metrology, and an imaging system for alignment, are also built into the system. The advantages of incorporating these extra components are twofold: fast metrology feedback after each figuring run will considerably reduce the time required to perform multiple figuring iterations; and alignment and indexing errors will be drastically reduced when transferring the optic. Complemented by the Optical Metrology Laboratory at DLS and at-wavelength X-ray measurements on the Test beamline B16, it is expected that this system will enable rapid development and testing of high-quality mirrors with novel designs for micro- and nano-focussing of X-rays.