Picosecond UV-laser ablation of Au and Ni films

Single-shot ablation thresholds of gold and nickel films in the thickness range from 50 nm to 3.7 μm have been measured for 8 ps, 130 ps and, for comparison, 15 ns laser pulses at 248 nm. The metal films were deposited on fused silica substrates. The topology of the ablated films was determined by an AFM. For picosecond ablation one finds an interesting transition range where, for the 8 ps pulses, the threshold fluence initially drops as the film thickness is increased, in contrast to the 130 ps pulses where the threshold increases with increasing film thickness, as for ablation with the nanosecond pulses. In addition, comparison of the topological structure shows different behaviour for the Au and Ni films. The Ni films show typical material removal behaviour. The Au films show a melting character both for the 8 and 130 ps pulses. The nature of this difference is not yet clear and is the subject of further investigations.