Separation of Surface Hardened Glass with Non-ablation Laser Technique

The study investigated cutting of glass by non-laser ablation technique through non-linear absorption laser pulses induced optical breakdown, melting and plasma expansion throughout the glass thickness from bottom to top. Picosecond near-infrared laser pulses were used. The laser beam was focused with an objective lens with numerical aperture (NA) of 0.1 which produced a spot size of 19.6 µm in diameter. The study revealed that focus position is a key factor in determining glass well-separation. When the laser focus was placed at 500 μm below the top surface for a 700 μm thick ion exchanged Gorilla glass, namely more than half of the glass thickness, the glass could be well-separated into two pieces. At focus near the top surface, V-shaped ablation grooves were generated at the glass top surface without glass separation. At focus inside the glass and near to the bottom surface, internal scribing occurred at the bottom part of the glass. The glass could also be separated by scribing-caused cracking throughout the glass entire thickness. At the optimal focus ranges, well-separation of the glass was found to be at speeds of 0.5-6 mm/s and pulse frequency around 200 KHz with laser fuence of 0.87 J/cm 2 . At low pulse frequencies such as below 100 KHz, glass top surface was ablated without glass separation. At higher pulse frequencies above 300 KHz, cracks were produced and the glass was separated into multiple pieces. Interestingly, at pulse frequency upto 500 KHz, both top surface ablation and bottom surface ablation occurred. Eventually, the glass was cracked into multiple pieces. Different pulse frequency produces different pulse energy. For example, 200 KHz generates a laser fluence of 0.87 J/cm 2 at the glass top surface, 100 KHz for 1.59 J/cm 2 and 300 KHz for 0.60 J/cm 2 etc. Furthermore, the glass was cracked at high speeds above 10 mm/s. The results indicate that there is an optimal time-dependent energy deposition, namely, laser energy deposition rate for glass well-separation. The calculation shows that the energy deposition rates were between 1.29×10 4 μw/μm 3 to 1.54×10 5 μw/μm 3 .