Kiel 2004 – wissenschaftliches Programm
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K: Kurzzeitphysik
K 3: Lasersysteme und Laseranwendungen
K 3.3: Vortrag
Mittwoch, 10. März 2004, 11:30–11:50, A
Microscopic mechanisms of femtosecond laser ablation from transparent dielectrics — •Florenta Costache1, Matthias Henyk2, and Jürgen Reif1 — 1LS Experimentalphysik II, Brandenburgische Technische Universität Cottbus and JointLab IHP/BTU Cottbus, Universitätsplatz 3-4, 03044 Cottbus, Germany — 2Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352, USA
The emission of electrons, positive and negative ions from dielectric targets (Al2O3, BaF2, CaF2, NaCl) upon irradiation with sub-ablation-threshold 100-fs-laser-pulses shows a strong correlation between multiphoton ionisation and positive ion emission. This implies a Coulomb explosion of positive charges at high kinetic energies at the order of tens eV, which, for a limited range of laser intensities, appears to be the principal mechanism of material removal. At higher laser intensity or upon accumulation of many laser pulses, the ions’ kinetic energy decreases to nearly thermal values. At the same time, the total rate of ablation occurs to grow much stronger than that of ion emission, which starts to saturate. This behaviour is suggested to be a result of the occurrence of hot electrons and a fast lattice thermalization. Additionally, under these conditions we observe the onset of an intense ablation plasma plume and a delayed emission of negative ions. Different morphological features were investigated by ex-situ optical, atomic force (AFM), and electron microscopy. The near-thermal ablation onset appears to be correlated with both the intensity and the number of pulses.