Aachen PK 2003 – wissenschaftliches Programm
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K: Kurzzeitphysik
K 4: Laser applications
K 4.3: Vortrag
Donnerstag, 20. März 2003, 15:45–16:00, F04
Femtosecond laser induced surface damage in calcium fluoride after Coulomb explosion of charged particles — •Florenta Costache and Jürgen Reif — LS Experimentalphysik II, BTU Cottbus and JointLab BTU/IHP, 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 3) high kinetic energies in order of tens of eV, 4) negative ions with low kinetic energies.
The ablation occurs by Coulomb explosion of an electrostatic unstable surface after multiphoton ionization of defect states.
The morphology of the desorption crater reveals, for a small window of fluences, smooth surfaces with non-classical ripple structures in a nanometer range scale, oriented on the beam polarization. This effect is tentatively assigned to self-organization from a surface instability and comparison is made with ion beam sputtered surfaces. When increasing fluence (respectively the number of laser shots) the ablation results in deep craters while the ripple structure tends to vanish.