Homogenization and reduction of the roughness of polished sapphire surfaces via inert gas plasma post-processing

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In this paper, we report on the post-processing of classically precision polished sapphire surfaces by means of a dielectric barrier discharge plasma at atmospheric pressure. Here, the lateral distribution of roughness values over the surface was significantly reduced, leading to a higher lateral homogeneity. This effect is shown by a decrease in the standard deviation of the roughness values measured at different positions over the sample surface where an overall plasma-induced reduction by a factor of 8.7 was achieved. Moreover, the residual roughness was notably decreased by a mean factor of up to 2.9 to merely a few angstrom. The obtained results are of high interest for the enhancement of large-scale optical components made of sapphire, especially for UV or laser applications. This is finally visualized by the comparison of the total integrated scatter values calculated for untreated and post-processed surfaces.