Coulomb explosion in femtosecond laser ablation of Si(111)

Abstract

The ablation of ionized silicon is studied using near-infrared femtosecond laser pulses in the fluence regime from 1 to $\text{9\hspace{0.17em}}{\mathrm{J/cm}}^2.$ Two major peaks are observed in the mass spectrum corresponding to ${\mathrm{Si}}^{+}$ and ${\mathrm{Si}}^{\text{2+}}.$ In the time-of-flight transients of ${\mathrm{Si}}^{+},$ a bimodal structure is observed. The fast ${\mathrm{Si}}^{+}$ peak corresponds to a velocity half of that observed for ${\mathrm{Si}}^{\text{2+}}.$ This momentum scaling is clearly indicative of a Coulomb explosion.