Abstract

Slip cast silica is an ideal mirror material having all the desirable attributes of quartz, with the exception that the surface needs to be densified to achieve the necessary degree of specularity after polishing. The slurry is cast at room temperature in a plaster mold which can incorporate plaster or Stryofoam core blocks to enable it to be inherently lightweight. Subsequent to drying, the casting is fired at ~1000°C in a firebrick kiln. After firing the surface is generated to within several waves of its final shape. Then the surface is densified and the final figuring accomplished. We have successfully polished small-scale samples subsequent to densifying the surface with electroless nickel and demonstrated that very useful optics can indeed be produced with this material. We have also characterized this material mechanically and thermally and using these data developed a 6m mirror design. In principle, we believe that the mirror may be brought to the site in the form of barrels of slurry, a truck full of bricks and propane tanks, and a modified computer controlled polisher. The latter is a Perkin-Elmer proprietary machine/process used for figuring large optical elements. A plan for actually casting the mirror blank and figuring it at an observatory site is presented to provide a basis for estimating the cost of producing and delivering a large mirror by this method.

© 1988 Optical Society of America