Theoretical modeling and experimental study in femtosecond Bessel beam ablation of α-quartz

Femtosecond laser processing of dielectric has been widely studied. Nevertheless, a direct theoretical model for Bessel beam on α-quartz is still essential. The purpose of this study is to explore the interaction mechanism between Bessel beam and α-quartz. Bessel beam is generated by a combination of femtosecond laser Gaussian beam and beam shaping techniques. In the simulation, the optical and thermophysical properties are studied. The simulation results show that rapid evolutions in electron density and electron temperature affect the optical properties during laser energy deposition in α-quartz. In a few tens of femtoseconds, the optical properties change from transparent to opaque. The optical penetration depth rapidly drops to hundreds of nanometers at the edge of focused region during this period. Therefore, the laser intensity decreases exponentially along the propagation path. The electron density is high at the edge and low at the center of focused region. After sufficient laser energy deposition, microholes are finally formed. The ablation region is predicted by the critical electron density criterion and the critical volumetric energy density criterion. The experimental results verify the results calculated by the theoretical model. In addition, this study provides a new perspective for the theoretical modeling of Bessel beam and provides an important reference for the broad applications in the field of micro-/nano-processing.