Berlin 2001 – wissenschaftliches Programm
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K: Kurzzeitphysik
K 1: Short time-scale dynamics and diagnostics
K 1.4: Vortrag
Montag, 2. April 2001, 17:20–17:35, EB107
Ablation dynamics of solids heated by femtosecond laser pulses — •Bärbel Rethfeld1, Klaus Sokolowski-Tinten1, Vasily Temnov1,2, Jörg Bialkowski1, Andrea Cavalleri3, and Dietrich von der Linde1 — 1Institut für Laser- und Plasmaphysik, Universität Essen, D-45117 Essen, Germany — 2Institute of Applied Physics, 603600 Nizhny Novgorod, Ulyanova St. 46, Russia — 3Department of Chemistry and Biochemistry, University of California, San Diego, USA
Ultrafast time resolved microscopy of femtosecond laser irradiated surfaces reveals a universal feature of the ablating surface on a nanosecond time scale. All investigated materials show rings in the ablating zone, which are interpreted as an interference pattern (Newton rings). The irradiated material can be assumed to be a liquid at solid state density before ablation starts, since energy absorption and melting occurs on a time scale much shorter than expansion. Hydrodynamic calculations of the expansion of the heated layer yield a shell-like structure with two optically sharp interfaces. Experimentally, the rings are observed within a certain fluence range. The lower limit is a well defined threshold which coincides with the ablation threshold. At higher laser fluences the interference rings disappear. This is in agreement with theoretical calculations which show a smoothing of the density profile for higher fluences. Our model predicts a fluence ratio between both limits approximately equal to the ratio of critical temperature to boiling temperature at normal pressure. This estimate is confirmed by experiments on different materials.