Laser-induced front side etching of fused silica with femtosecond laser radiation using thin metal layers

Laser-induced front side etching (LIFE) is a method for laser etching of transparent materials using thin absorber layers. In this study, chromium layers were applied as absorber for etching trenches in fused silica with femtosecond Ti:sapphire laser radiation (λ = 780 nm, Δtp = 150 fs, f = 1 kHz). The etching process of fused silica is studied in dependence on the laser fluence, the laser pulse numbers as well as metal absorber layer thicknesses. Especially the influence of the varied parameters on the surface morphology, the etching depth, and the surface modification is presented and discussed. The etched trenches were analyzed with white light interferometry. A fluence window from 0.5 to 2.5 J/cm2 for the LIFE process of fused silica with a single laser pulse using a metal layer with a thickness from 5 to 50 nm was found. The measured maximum etching depth of approximately 100 nm suggests that the LIFE process is appropriated for precision machining. The attempt to simulate the fs laser LIFE process by a thermodynamic model was moderate successfully and exhibits significant differences within the experimental results.