title: Fabrication of electroless nickel plated aluminum freeform mirror for an infrared off-axis telescope.
abstract: Freeform mirrors can be readily fabricated by a single point diamond turning (SPDT) machine. However, this machining process often leaves mid-frequency errors (MFEs) that generate undesirable diffraction effects and stray light. In this work, we propose a novel thin electroless nickel plating procedure to remove MFE on freeform surfaces. The proposed procedure has a distinct advantage over a typical thick plating method in that the machining process can be endlessly repeated until the designed mirror surface is obtained. This is of great importance because the sophisticated surface of a freeform mirror cannot be optimized by a typical SPDT machining process, which can be repeated only several times before the limited thickness of the nickel plating is consumed. We will also describe the baking process of a plated mirror to improve the hardness of the mirror surface, which is crucial for minimizing the degradation of that mirror surface that occurs during the polishing process. During the whole proposed process, the changes in surface figures and textures are monitored and cross checked by two different types of measurements, as well as by an interference pattern test. The experimental results indicate that the proposed thin electroless nickel plating procedure is very simple but powerful for removing MFEs on freeform mirror surfaces.
authors.forename: Sanghyuk
authors.initials: S
authors.lastname: Kim
authors.forename: Seunghyuk
authors.initials: S
authors.lastname: Chang
authors.forename: Soojong
authors.initials: S
authors.lastname: Pak
authors.forename: Kwang Jo
authors.initials: KJ
authors.lastname: Lee
authors.forename: Byeongjoon
authors.initials: B
authors.lastname: Jeong
authors.forename: Gil-jae
authors.initials: GJ
authors.lastname: Lee
authors.forename: Geon Hee
authors.initials: GH
authors.lastname: Kim
authors.forename: Sang Kyo
authors.initials: SK
authors.lastname: Shin
authors.forename: Song Min
authors.initials: SM
authors.lastname: Yoo