PICOSECOND UV-LASER ABLATION OF AU AND NI FILMS

Single-shot ablation thresholds of gold and nickel films in the thickn ess range from 50 nm to 3.7 mu m have been measured for 8 ps, 130 ps a nd, for comparison, 15 ns laser pulses at 248 nm. The metal films were deposited on fused silica substrates. The topology of the ablated fil ms was determined by an AFM. For picosecond ablation one finds an inte resting transition range where, for the 8 ps pulses, the threshold flu ence initially drops as the film thickness is increased, in contrast t o the 130 ps pulses where the threshold increases with increasing film thickness, as for ablation with the nanosecond pulses. In addition, c omparison of the topological structure shows different behaviour for t he Au and Ni films. The Ni films show typical material removal behavio ur. The Au films show a melting character both for the 8 and 130 ps pu lses. The nature of this difference is not yet clear and is the subjec t of further investigations.