Coulomb explosion in ultrashort pulsed laser ablation of ${\mathrm{Al}}_2{\mathrm{O}}_3$

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.