Development of a position–velocity–time-modulated two-dimensional ion beam figuring system for synchrotron x-ray mirror fabrication

T Wang, L Huang, Y Zhu, M Vescovi, D Khune, H Kang… - Applied optics, 2020 - osti.gov
T Wang, L Huang, Y Zhu, M Vescovi, D Khune, H Kang, H Choi, DW Kim, K Tayabaly…
Applied optics, 2020osti.gov
With the rapid evolution of synchrotron x-ray sources, the demand for high-quality precision
x-ray mirrors has greatly increased. Single nanometer shape accuracy is required to keep
imaging capabilities at the diffraction limit. Ion beam figuring (IBF) has been used frequently
for ultra-precision finishing of mirrors, but achieving the ultimate accuracy depends on three
important points: careful alignment, accurate dwell time calculation and implementation, and
accurate optical metrology. The Optical Metrology Group at National Synchrotron Light …
With the rapid evolution of synchrotron x-ray sources, the demand for high-quality precision x-ray mirrors has greatly increased. Single nanometer shape accuracy is required to keep imaging capabilities at the diffraction limit. Ion beam figuring (IBF) has been used frequently for ultra-precision finishing of mirrors, but achieving the ultimate accuracy depends on three important points: careful alignment, accurate dwell time calculation and implementation, and accurate optical metrology. The Optical Metrology Group at National Synchrotron Light Source II has designed and built a position–velocity–time-modulated two-dimensional IBF system (PVT-IBF) with three novel characteristics: (1) a beam footprint on the mirror was used as a reference to align the coordinate systems between the metrology and the IBF hardware; (2) the robust iterative Fourier transform-based dwell time algorithm proposed by our group was applied to obtain an accurate dwell time map; and (3) the dwell time was then transformed to velocities and implemented with the PVT motion scheme. In this study, the technical aspects of the PVT-IBF systems are described in detail, followed by an experimental demonstration of the figuring results. In our first experiment, the 2D RMS in a 50mm×5mm clear aperture was reduced from 3.4 to 1.1 nm after one IBF run. In our second experiment, due to a 5 mm pinhole installed in front of the source, the 2D RMS in a 50mm×5mm clear aperture was reduced from 39.1 to 1.9 nm after three IBF runs, demonstrating that our PVT-IBF solution is an effective and deterministic figuring process.
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