Bottom-up cutting method to maximize edge strength in femtosecond laser ablation cutting of ultra-thin glass

In femtosecond laser cutting of ultra-thin glass sheets, subsurface and back-surface damage are known to degrade the strength of diced samples significantly. Subsurface damage is generated by refraction of the laser beam at the V-shaped ablation groove into the glass in typical top-down cutting processes. Furthermore, our analysis indicates that interference of the refracted beam with its reflected portion at the back surface induces back-surface damage. In this work, we propose a bottom-up cutting method to eliminate the damage, and thereby maximize the edge strength. Refraction of the beam is absent in the proposed bottom-up cutting method because the ablation grooves have an inverted V-shape. This work verified the concept of the bottom-up cutting method, demonstrating a substantial enhancement of the edge strength of ultra-thin glass by eliminating sub- and back-surface damage. The maximum front- and back-side edge strengths of borosilicate glass cut by the bottom-up cutting method are similar to 330 and similar to 380 MPa, respectively, which are substantially higher than those achieved in conventional top-down cutting.