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.

Development of Linear Astigmatism Free—Three Mirror System (LAF-TMS)

“…The mirror and the L-bracket meet at three contact points. We adjust x- Nickel plating on the aluminum mirror and polishing process significantly improved the surface finish, as shown in the micro roughness measurement data (Kim et al, 2015).…”

“…Kim et al (2010) verified the feasibility of linear-astigmatism-free three-mirror optical design. Chang (2015) extended his theory to N-conic mirror system, which enables building a Linear Astigmatism Free -Three Mirror System (LAF-TMS).…”

Transformable Reflective Telescope for optical testing and education

“…The SPDT (Freeform 700A; Precitech) process produces a high-quality surface figure on the primary mirror. We employ a compensation strategy (Zhang et al, 2015) to minimize Low-Frequency Error (LFE) (Kim et al, 2015) and Mid-Frequency Error (MFE) of the mirror surface.…”

Nanomanufacturing—Perspective and applications

“…The main task of polishing is to remove cutting marks in addition to improving the form accuracy. Cutting marks that generate the diffraction or scattering pattern are mainly created by the regular cutting path [112]. The elastic emission machining (EEM) method has been proposed to remove the marks on the fabricated surface in order to obtain an extremely smooth surface [93].…”