Berlin 2001 – scientific programme

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K: Kurzzeitphysik

K 4: Laser beam - matter interaction

K 4.2: Talk

Thursday, April 5, 2001, 16:50–17:05, EB107

Femtosecond laser ablation from sodium chloride and barium fluoride — •Matthias Henyk, Florenta Costache, and Jürgen Reif — LS Experimentalphysik II, Brandenburgische Technische Universität Cottbus, Universitätsplatz 3-4, D-03044 Cottbus, Germany

The microscopic processes leading to material removal from sodium chloride and barium fluoride upon irradiation with near infrared femtosecond pulses is investigated, using time-of-flight mass spectroscopy of charged particles and ex-situ optical and electron microscopy inspection of the desorption crater.

We find similar ablation features for both materials: 1) a certain number of incubating pulses is necessary before significant amounts of charged particles are emitted, 2) the ion temperature for all ions is the same (about 1 eV), 3) all positive ions have similar kinetic energies around 100 eV, whereas the kinetic energies of negative ions is two order of magnitude lower

For barium fluoride, as a particular feature, we observe: a) the emission of large singly charged positive clusters, all having the same kinetic energy, b) an anticorrelated variation in the emission rate of F+ and Ba+ as function of laser shot number, under appropriate conditions.

The results are interpreted as ablation based on Coulomb explosion of an electrostatic unstable surface after multiphoton ionisation of defects. Thermal processes play a minor role, because they are unable to explain the different behaviours of positive and negative ions.