Molybdenum (Mo) mirrors are being used in high-power infrared lasers and would be ideal for lasers operating in the visible and ultraviolet if lower-scatter surfaces could be produced. Surfaces prepared by two novel techniques have been found to be smoother and have lower scatter than conventionally polished material, which has a surface texture that profiles the grain structure of the bulk material. A dual-abrasive polishing technique has been found to produce surfaces that show almost no surface grain relief, have scattering levels as little as one-seventh that of conventionally polished Mo, and roughnesses as small as 15Å rms measured from surface profiles. Sputtering a layer of Mo onto a previously polished Mo surface and then polishing the sputtered layer produces a surface that is very similar to that of polished glass in profile and scattering properties. Scattering levels approximately one-tenth that of conventionally polished bulk Mo and roughnesses ~13-Å rms have been measured on such surfaces. However, laser damage thresholds measured at 2.7 µm show that higher scatter, conventionally polished Mo surfaces have higher melt thresholds than do the lower-scatter dual-abrasive polished and sputtered Mo surfaces.
Jean M. Bennett, Philip C. Archibald, John P. Rahn, and Abe Klugman, "Low-scatter molybdenum surfaces," Appl. Opt. 22, 4048-4055 (1983)