Osnabrück 2002 – scientific programme

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MO: Molekülphysik

MO 17: Femtosekundenspektroskopie VI: Kristalle und Nanopartikel (gemeinsam mit FV Q)

MO 17.1: Talk

Thursday, March 7, 2002, 16:30–16:45, HS 15/E07

Femtosecond laser-induced surface structures on ionic crystals — •Florenta Costache, Matthias Henyk, and Jürgen Reif — BTU-Cottbus, LS Experimentalphysik II, Universitätsplatz 3-4, 03044 Cottbus, Deutschland

After the ablation of ionic crystals with femtosecond laser pulses, the crater morphology was examined ex-situ by optical, scanning electron and atomic force microscopes. In BaF2 and CaF2, at moderate laser intensities and several thousand laser shots periodic surface structures (ripples) occurred at the crater bottom. A ripple pattern with a period of 600-1200 nm was found parallel to the beam polarization and dependent on the laser intensity. A second finer pattern was observed running perpendicular on the first one with a period of about 200-300 nm. The structure period was insensitive to the angle of incidence variation. The ripple development was investigated by increasing the number of shots, corresponding to an increase in the structure modulation depth.

Tof mass spectrometer measurements performed during the structure creation showed in all cases a strong emission of fast ions. The fact that the surface is electrostatically decomposed by Coulomb explosion calls into question thermal effects as the origin of the ripples.

Furthermore, the influence of interference patterns on the ablated spot and the dynamics of the surface relaxation were investigated by a two-beam experiment.

We conclude that the crater morphology suggests self-organization mechanisms for the surface relaxation upon ablation.