Numerical simulation of femtosecond laser ablation of quartz glass and silicon nitride.

Abstract

The ablation threshold and depth models were established based on the electron density evolution equation of dielectric and ionization theory. The volume model was then deduced, and the models were validated. For quartz glass and silicon nitride, the dependences of the threshold with pulse duration, ablation depth, and volume with fluence were analyzed. Also, the relations of scallop height and scanning velocity were predicted. The results show that the thresholds of quartz glass at durations of 12, 35, and 220 fs were 3.3, 2.9, and 2.3J/cm2, respectively, while the thresholds of silicon nitride at the same durations were 2.0, 1.8, and 1.4J/cm2, respectively. The ablation depth of quartz glass decreased with the increase of duration when the fluence deviated from the threshold. The depth of silicon nitride was opposite to it, and the ablation volume of silicon nitride was larger than that of quartz glass in the same condition. When the scanning velocity and fluence were determined, the scallop height decreased with the increase of duration. However, when the velocity and duration were determined, the scallop height increased with the increase of fluence. The shorter the duration was, the greater the variation of the scallop height.