Low-Scatter Large Beryllium Mirror Development

The development of a technique for fabricating large bare beryllium mirrors with low-scatter surfaces is described. The technique is based upon the application of a thick, high purity beryllium coating to a beryllium substrate. The technique has been identified as Be-on-Be Processing. The coating is fully dense, very low in dissolved impurities and free from both inclusions and second phase particles. These special qualities of the coating result in enhanced fabrication characteristics which result in the ability to polish a low-scatter finish superior to that which is obtained from conventional material. The character of the coating also results in enhanced response to rapid fabrication techniques. Single-point turning of the coating has been promising and numerous mirrors have been fabricated incorporating this technique. A Draper type polishing machine has also been modified to incorporate in-situ testing of figure utilizing interferometric evaluation of the Be-on-Be mirrors. Examples of mirrors produced with this technology are presented.