Strength of ultra-thin glass cut by internal scribing using a femtosecond Bessel beam

We analyzed a process to cut thin glass by internal scribing and mechanical breaking using a femtosecond laser Bessel beam. The effect of process parameters on the edge strength of the cut sample was investigated for borosilicate glass sheets of thickness 100 mu m. The ranges of laser pulse energy and density of internal modifications for the scribing and breaking process were identified. During mechanical breaking process, separation was easier when the laser-scribed sample was split from the back surface when the pulse energy was low and from the front surface when it was high. The maximum edge strength was obtained at the lowest laser pulse energy that can split the sample properly. When the internal modification was too weak, the glass sample was not properly separated, so both roughness and cutting-path deviation increased. At the optimum condition, the front-side and back-side edge strength was 370 MPa (67% of the strength of the mirror like surface) and 400 MPa (72%), respectively. This technology to cut ultra-thin glass sheets without impairing the original strength will have numerous applications.