The impact of graphite coating and wavelength on picosecond laser machining of optical glasses

This paper presents the impact of a graphite coating and wavelength on picosecond laser processing of fused silica (HPFS®7980 Corning) and Borofloat®33 glass (Schott AG). Within this work, the surface damage threshold, single-pulse ablation depth, and multi-pulse removal rate of 'as-manufactured' glasses have been determined for three different wavelengths: 343, 515 and 1030 nm, and compared with the results obtained for the same glasses when coated with a thin layer of graphite prior to laser treatment. The experimental results show that the surface damage threshold of graphite-coated glasses is significantly lower (up to 35 times) than that of 'as-manufactured' glasses, whereas the single-pulse ablation depth is the highest at the laser wavelength of 343 nm. Moreover, it has been found that fused silica and Borofloat®33 glass can be machined with better control of the ablation depth when its surface is coated with graphite. This is attributed to the increased absorption of the workpiece at wavelengths at which this material is normally transparent.