A study has been performed experimentally to determine the polishing methods for high-power laser mirrors. This paper presents ultrafine polishing of tungsten (W) and molybdenum (Mo) which cannot be turned by a diamond tool.

Samples were prepared by five methods: lapping with SiC abrasives of 4000-grit size; lapping with 3 μm diamond powder; float polishing with SiO₂ powder; Ar ion beam etching; and electrolytic polishing. The finished surfaces are characterized using several techniques, including profilometry, electron probe microanalysis, X-ray diffraction, calorimetric technique with cw CO₂ laser and so on.

The surfaces lapped with 3 μm diamond powder have damaged layers of about 2 μm deep in the case of W and about 3 μm deep in the case of Mo. In either case, however, if about 1 μm thickness of the damaged layer is removed by float polishing from the lapped surface, the layer which increases absorptance at 10.6 μm wavelength will be almost removed.