Evaluation of subsurface damage by light scattering techniques.

Subsurface damage (SSD) in optical components is almost unavoidably caused by mechanical forces involved during grinding and polishing and can be a limiting factor, in particular for applications that require high laser powers or an extreme material strength. In this paper, we report on the characterization of SSD in ground and polished optical surfaces, using different light scattering measurement techniques in the visible and extreme ultraviolet spectral ranges. The materials investigated include fused silica, borosilicate glass, and calcium fluoride. The scattering results are directly linked to classical destructive SSD characterization techniques, based on white light interferometry, optical microscopy, and atomic force microscopy of the substrate topography and cross sections obtained after etching in hydrofluoric acid and fracturing.