Low roughness laser etching of fused silica using an adsorbed layer

High quality etching of transparent materials for applications in microstructuring and precision engineering is still a challenge for current laser processing techniques. Laser etching at a surface adsorbed layer called LESAL allows precision etching of fused silica at low laser fluences with small etch rates. The etch rate and the surface quality depend on the applied laser fluence and can be divided into three regions with different etch behavior. The poor surface quality in the low and the high fluence regions are caused by incubation processes and thermal ablation processes, respectively. In the fluence range from 2.0 to 5.0 J/cm2 a constant etch rate was observed that increases from 1 to 2 nm/pulse with raising the temperature from 60 to 105 8C. In this region of etch rate saturation a very low surface roughness of less than 1 nmrms was measured. Both the etch rate saturation and the low roughness of the LESAL process enable new applications of laser processing transparent materials.