Heat accumulation in microdrilled glass from ultraviolet laser ablation

We present numerical and experimental studies of heat accumulation during high-aspect-ratio ultraviolet laser microdrilling of glass. The dependence on pulse repetition rate of the ablation threshold was studied. The rate determines the amount of heat accumulation and temperature variation across the illuminated area. No change in the glass was observed for pulse energies below 1 µJ at 1 kHz; melting occurred at 0.3 µJ, with ablation at 0.7 µJ at 20 kHz. Also, the hole depth doubled when the pulse repetition rate was increased from 1 to 20 kHz. Moreover, the fluence of ~4 J/cm2 that passed through drilled holes at 1 kHz decreased to ~1 J/cm2 at 20 kHz.