Time-resolved investigations of the non-thermal ablation process of graphite induced by femtosecond laser pulses
We report on the in-situ analysis of the ablationdynamics of the, so-called, laser induced non-thermal ablation process of graphite. A highly oriented pyrolytic graphite is excited by femtosecond laser pulses with fluences below the classic thermal ablation threshold. The ablationdynamics are investigated by axial pump-probe reflection measurements, transversal pump-probe shadowgraphy, and time-resolved transversal emission photography. The combination of the applied analysis methods allows for a continuous and detailed time-resolved observation of the non-thermal ablationdynamics from several picoseconds up to 180 ns. Formation of large, mm-sized particles takes place within the first 3.5 ns after irradiation. The following propagation of ablation products and the shock wave front are tracked by transversal shadowgraphy up to 16 ns. The comparison of ablationdynamics of different fluences by emission photography reveals thermal ablation products even for non-thermal fluences.