Effect of laser beam scanning mode on material removal efficiency in laser ablation for micromachining of glass

This study investigated the influence of laser beam scanning mode on material removal efficiency through evaluation of cut-through time for a 5 mm length inside a glass substrate. The parameters related to the scanning mode covered scanning speed, focus position, number of lines and shifting pitch in one kerf, scanning under raster, merge or group mode, and scanning at fixed or nonfixed parameter mode. Picosecond, near infrared laser pulses were used to ablate a 700 μm thick, nonion exchanged Gorilla glass at fluence of 9.0 J/cm2 using a galvanometer scanner. It has been found that the optimal scanning speed for ablation without cracks and debris was above 200 mm/s, namely, only a few overlapped pulses in a single line scan. When ablation started from glass bottom, the ejected materials could efficiently escape from the ablation kerf and no ejected materials would disperse the laser energy deposition to the glass unlike ablation from the top surface. The cut-through time was 1.36 times and 24.5 times longer when focus was placed at the middle and top of the glass, respectively, compared to at bottom surface. The optimal number of lines was determined by the required kerf width of approximately half the glass thickness for high ablation efficiency. Ablated materials were not ejected out of the kerf efficiently at smaller kerf with fewer lines. Cut-through time was also increased at larger kerf with more lines due to more material removal. The optimal shifting pitch was found to be approximately a scanned line width which was close to the spot size in this study. Scanning under raster mode could achieve minimal cut-through time of 31.42 s. The cut-through time was increased by a factor of 1.51 times and 13.43 times, respectively, for merge and group mode. Merge and raster mode allowed layer by layer scanning with high material removal and the ablation was further enhanced by continuous line scanning in one ablation layer under raster mode. Ablation under fixed parameter mode could eliminate the call-procedure of laser parameters used in individual line scanning. The cut-through time was reduced by 86% compared to nonfixed parameter mode.