Coulomb explosion in ultrashort pulsed laser ablation ofAl2O3

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 \ensuremath{\sim}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.