Ion polishing of optical components using optimized axisymmetric processing with a wide-aperture ion source

This paper discusses modern ion-beam machining technology for fabricating optical components by a wide-aperture ion beam through the mask, enabling the creation of high-precision X-ray optical elements. The key innovation is the presence of an open area in the center of the mask, which is aligned with the rotation axis of the workpiece. This innovation makes it possible to effectively eliminate the singularity problem, which was a limitation in previous approaches. Herein, this term refers to a sharp, uncontrollable variation in the etch depth caused by the sensitivity of the process to the precise alignment between the mask vertex and the axis of rotation. As a result, the proposed mask provides uniform etching without the need for complex iterative adjustments. The focus is on the problem of aligning the workpiece's rotation axis with the mask vertex, which can lead to non-uniform material removal. A methodology for optimizing the axisymmetric processing procedure is proposed, including the calculation of a mask shape to achieve a uniform etching profile. Experimental results confirm the efficiency of the proposed approach, significantly simplifying the mask shape correction process and improving the quality of optical component machining. High processing accuracy was achieved (PV≈1%). Ion beam polishing of a monocrystalline Si ⟨110⟩ spherical substrate (∅105mm and R=-587.7mm) was performed using the manufactured mask. A significant reduction in effective roughness (spatial frequency range q=[2.5∗10^-2-6.3∗10¹µm^-1]) was obtained, from an initial σ_eff=0.33nm to a finalσ_eff=0.15nm.