Ion Beam Figuring System for Synchrotron X-Ray Mirrors Achieving Sub-0.2-µrad and Sub-0.5-nm Root Mean Square

Abstract

Optics with high-precision height and slope are increasingly desired in numerous industrial fields. For instance, Kirkpatrick–Baez (KB) mirrors play an important role in synchrotron X-ray applications. A KB system is composed of two aspherical, grazing-incidence mirrors used to focus an X-ray beam. The fabrication of KB mirrors is challenging due to the aspherical departure of the mirror surfaces from base geometries and the high-quality requirements for slope and height residuals. In this paper, we present the process of manufacturing an elliptical cylinder KB mirror using our in-house-developed ion beam figuring (IBF) and metrology technologies. First, the key aspects of figuring and finishing processes with IBF are illustrated in detail. The effect of positioning error on the convergence of the residual slope error is highlighted and compensated. Finally, inspection and cross-validation using different metrology instruments are performed and used as the final validation of the mirror. Results confirm that relative to the requested off-axis ellipse, the mirror has achieved 0.15-µrad root mean square (RMS) and 0.36-nm RMS residual slope and height errors, respectively, while maintaining the initial 0.3-nm RMS microroughness.

Ion beam figuring for X-ray mirrors: history, state-of-the-art and future prospects

“…height error and sub-200 nrad r.m.s. slope error over a 150 mm-long clear aperture (Wang et al, 2023b).…”

“…The IBF process relies on alignment between (at least) two coordinate systems: the IBF coordinate system, describing the position of the ion beam relative to the mirror; and the metrology coordinate system, containing the measured height or slope information about the mirror. Accurately correcting errors on a millimetre-scale spatial wavelength requires position and alignment tolerances of 100 mm or less, and any larger misalignment dramatically reduces the accuracy of the figuring process (Wang et al, 2023b).…”

“…As such, matrix-based methods are generally favoured for 1D figuring (Wang et al, 2019;Mahji et al, 2024). In comparison, Fourier transform-based methods, such as the recently developed RIFTA (Wang et al, 2020b(Wang et al, , 2023b, are computationally efficient and able to find effective dwell time solutions in very short calculation times. However, they are generally less flexible than matrix-based methods.…”

“…Using this approach, an elliptical mirror was figured with 0.36 nm r.m.s. height error and 150 nrad slope error over a 150 mm � 20 mm CA (Wang et al, 2023b).…”

“…height errors and sub-200 nrad r.m.s. slope errors (Wang et al, 2023b), with sub-100 nrad r.m.s. slope errors achievable for flat mirrors (Preda et al, 2013).…”