Efficient and precise fabrication of Wolter type-I x-ray mirrors via nickel electroforming replication using quartz glass mandrels

Gota Yamaguchi; Yusuke Matsuzawa; Takehiro Kume; Yoichi Imamura; Hiroaki Miyashita; Akinari Ito; Koki Sakuta; Kazuki Ampuku; Ryuto Fujii; Kentaro Hiraguri; Hirokazu Hashizume; Ikuyuki Mitsuishi; Hidekazu Mimura

doi:10.1063/5.0160262

Efficient and precise fabrication of Wolter type-I x-ray mirrors via nickel electroforming replication using quartz glass mandrels

Rev Sci Instrum. 2023 Dec 1;94(12):124501. doi: 10.1063/5.0160262.

Authors

Affiliations

¹ Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.
² RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.
³ Technology Center, Natsume Optical Corporation, 1200-29 Kawaji, Iida, Nagano 399-2431, Japan.
⁴ Department of Precision Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
⁵ Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan.

PMID: 38095540
DOI: 10.1063/5.0160262

Abstract

This study presents an approach for fabricating Wolter type-I mirrors for x-ray telescopes using a nickel electroforming replication process with quartz glass mandrels. The proposed method addresses the challenges encountered in conventional fabrication techniques, which involve using electroless nickel-coated aluminum mandrels that are susceptible to corrosion and thermal deformation. Quartz glass mandrels offer excellent chemical, thermal, and mechanical stability, enabling the efficient production of high-performance mirrors. Wolter type-I mirrors for telescopes possess a large aperture that collects x-ray photons from the universe. However, previous nickel electroforming replication processes using quartz glass mandrels have challenges in fabricating large mirrors, particularly due to bubble pit formation during nickel shell development. In this study, we introduced an efficient pitting inhibition technique via vacuum degassing. This technique facilitates the precise replication of pit-free Wolter type-I mirrors for telescopes using quartz glass mandrels. We demonstrated the fabrication process on a Wolter type-I mirror proposed for FOXSI-4 [(FOXSI) Focusing Optics X-ray Solar Imager], resulting in three mirrors obtained from the same mandrel without repolishing or repairing. The figure error of the mirror was within 1 µm over most areas in both longitudinal and circumferential directions. The ray-tracing simulation indicated that the performance of the mirror was ∼12 arcsec in half-power diameter, comparable to the performance achieved by previous high-resolution x-ray missions.