Polishing slurry induced surface haze on phosphate laser glasses

The effects of residual polishing slurry on the surface topology of highly polished, Nd-doped meta-phosphate laser glasses are reported. Glass samples were pitched polished using cerium oxide or zirconium oxide slurry at different pHs and then washed by different methods that allowed varying amounts of residual slurry to ‘dry’ on the surface. Upon rewashing with water, some of the samples showed surface haze (scatter), which scaled with the amount of residual slurry. Profilometry measurements showed that the haze is the result of shallow surface pits (100 nm–20 μm wide × ∼15 nm deep). Chemical analyses of material removed during rewashing, confirmed the removal of glass components as well as the preferential removal of modifier ions (e.g., K1+ and Mg2+). The surface pits appear to result from reaction of the glass with condensed liquid at the slurry particle–glass interface that produces water-soluble phosphate products that dissolves away with subsequent water contact. Aggressive washing, to remove residual slurry immediately following polishing, can minimize surface haze on phosphate glasses. It is desirable to eliminate haze from glass used in high-peak-power lasers, since it can cause scatter-induced optical modulation that can cause damage to downstream optics.