Noncontact Figuring of Millimeter-Thick Elliptical Mirror Substrate by Numerically Controlled Local Wet Etching

Abstract:

Aspherical supermirrors are some of the most useful neutron-focusing optics. We aim to develop multiple aspherical supermirror devices using high-precision figured aspherical focusing supermirrors to focus neutron beams with high intensities, because multiple mirrors collect a very large beam divergence. Thin mirrors with millimetre thickness are required to minimize the absorption loss of incident neutron beams since the thickness of a mirror shadows the reflective area of other mirrors. However, it is difficult to fabricate thin mirror substrates with a form accuracy at the sub-micrometre level by conventional machining. Conventional machining deforms a substrate by machining force and spring back after machining causes figure error. Furthermore the deposition of supermirrors deforms the mirror substrate by film stress. Thus, we developed a new process of fabricating a precise millimetre-thick elliptical supermirror. This process consists of non-contact figuring by the numerically controlled local wet etching technique, the minimization of surface roughness without degrading form accuracy by low-pressure polishing with a polishing pressure less than about 7 kPa (1psi), and the ion beam sputter deposition of NiC/Ti multilayers on both sides of the mirror substrate to compensate for film stress. In this paper, we report on the fabrication results of aplano-elliptical mirror substrate with a thickness of 1 mm.

• Periodical: Key Engineering Materials (Volume 516)
• Pages: 361-366
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.516.361
• Online since: June 2012
• Authors: Mikinori Nagano, Fumiya Yamaga, Dai Yamazaki, Ryuji Maruyama, Kazuhiko Soyama, Kazuya Yamamura
• Keywords: Ellipse, Etching, Focusing, Low-Pressure Polishing, Neutron, Optics, Supermirror

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