Coulomb explosion (CE) is identified as the mechanism of ion ejection under low fluence ultrashort pulse laser ablation of crystalline ${\mathrm{Al}}_2{\mathrm{O}}_3.$ The ion momenta are equal during “gentle” ablation. This is explained by impulsive CE from the surface region lasting ∼1 ps. The onset of “strong” ablation leads to a decrease in the measured ion velocities. The kinetic energies rather than the momenta of the ions become equal. This regime is associated with strong plasma light emission and crater formation.

We report time-resolved studies using femtosecond laser pulses, accompanied by model calculations, that illuminate the difference in the dynamics of ultrashort pulsed laser ablation of different materials. Dielectrics are strongly charged at the surface on the femtosecond time scale and undergo an impulsive Coulomb explosion. This is not seen from metals and semiconductors where the surface charge is effectively quenched.

Fast electronic transport is investigated theoretically based on a drift-diffusion approach for different classes of materials (metals, semiconductors, and dielectrics) under ultrafast, pulsed laser irradiation. The simulations are performed at intensities above the material removal threshold, characteristic for the ablation regime. The laser-induced charging of dielectric surfaces causes a subpicosecond electrostatic rupture of the superficial layers, an effect which, in comparison, is strongly inhibited for metals and semiconductors as a consequence of superior carrier transport properties.