Design and Mounting of Metallic Mirrors
The discussion in this chapter begins in Section 10.2 with some general considerations of metal mirrors as distinguished from nonmetallic ones. A variety of examples of metal mirror design and fabrication techniques are then discussed. Mirrors made of various materials are considered in Sections 10.3 through 10.5. Because of the inherent porosity of some metal surfaces, it is advantageous to plate them with an amorphous material. Electrolytic and electroless nickel are very common types of plating for such mirrors. In Section 10.6, the characteristics of these types of plating and descriptions of their applications are summarized. Some, but not all, of the metals discussed here are compatible with material removal and final contouring to optical-quality surfaces by precision turning with single-point, gem-quality natural diamond tools. This process, commonly called single-point diamond turning (SPDT), is discussed in Section 10.7. In Sections 10.8 and 10.09, some of the techniques most commonly used to mount metal mirrors in optical instruments are discussed. It is quite feasible to interface many smaller metallic substrates with the various conventional mounts discussed earlier in this book for nonmetallic mirrors. There are design differences in such mountings because the mechanical properties of metals differ from those of nonmetals. Highly successful methods for supporting small to moderate-sized metal mirrors involve mounting provisions built into the mirrors themselves. Integral mounting techniques are reviewed, and some precautions to be observed in such designs are summarized. The chapter closes in Section 10.10 with brief considerations of multiple metallic optical and mechanical component interfaces using SPDT techniques to facilitate assembly and optical alignment.