India-ink polishing following single-point diamond turning yields superior aluminum optics.

A process for making precise, high-quality curved or flat mirror surfaces on bare aluminum substrates has been devised. The process consists of (1) diamond turning to establish the desired surface figure, followed by (2) a polishing subprocess that is mostly conventional except for the composition of the polishing compound. This process can maintain a surface figure accurate to within a peak-to-valley error of as little as 1/8 wavelength (at a wavelength of 6,328 Å) and can produce a finish characterized by a root-mean-square roughness of <8 Å. Hence, the process creates possibilities for the fabrication of precise scientific-instrument mirrors (see figure) that, because they could be made entirely of aluminum, would be lightweight, relatively inexpensive, and thermally stable over wide temperature ranges.