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K: Kurzzeitphysik

K 3: Laser-Anwendungen /-Materialbearbeitung

K 3.4: Vortrag

Donnerstag, 21. März 2002, 11:35–11:50, HZO 80

Instabilities during the Ablation of Laser-Pulsed Metal Films — •Holger Dömer and Oleg Bostanjoglo — Optisches Institut der TU Berlin, Straße des 17. Juni 135, 10623 Berlin

Nanosecond multi-frame transmission electron microscopy and micro-diffraction was applied to track lattice deformation, melting and evaporation, induced by a 6 ns laser pulse in metal films. Nickel films are ablated by centrosymmetrical evaporation and hole opening due to melt flow in accordance with the bell-shaped deposition of energy. The receding melt is eroded by a two-step Rayleigh-type hydrodynamic instability as early as 20 ns after the laser pulse. A very different response was uncovered in chromium films, though chromium has tabulated caloric parameters very similar to those of nickel. Here, ablation proceeds by a shock-like non-thermal lattice expansion, domain-patterned melting and evaporation, which is accompanied by a complete disruption of the melt. The striking difference is explained by excessive mechanical stresses in chromium films caused by the non-thermal lattice expansion.