Dresden 2003 – scientific programme
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DF: Dielektrische Festkörper
DF 6: Keramiken, Gradientenwerkstoffe und Relaxoren
DF 6.9: Talk
Wednesday, March 26, 2003, 17:30–17:50, HSZ/403
Femtosecond laser induced surface damage in calcium fluoride — •Florenta Costache and Jürgen Reif — LS Experimentalphysik II, BTU Cottbus and JointLab BTU/IHP Cottbus, Universitätsplatz 3-4, 03044 Cottbus, Germany
Optical breakdown at the surface of calcium fluoride targets is studied upon irradiation with femtosecond pulses at intensities below the single-pulse ablation threshold. Our investigation comprises time-of-flight mass spectroscopy as well as optical and electron microscopy inspection of the sample placed both under high vacuum and in air.
Similar to results obtained earlier from Al2O3 and BaF2, we find: 1) a strong nonlinear emission of electrons and positive ions, 2) incubation effects before a steady state regime of particles emission is reached, 3) high kinetic energies in order of tens of eV, 4) negative ions with low kinetic energies. The ablation occurs therefore by Coulomb explosion of an electrostatic unstable surface after multiphoton ionization of defect states.
The resulting crater morphology reveals, for a small window of fluences, non-classical ripple structures in a nanometer range scale, depending on the beam polarization. This effect is tentatively assigned to self-organization from a surface instability. When increasing fluence (respectively the number of laser shots) the laser ablation results in deep craters while the ripple structure tends to vanish.