SUBPICOSECOND UV-LASER ABLATION OF NI-FILMS - STRONG FLUENCE REDUCTION AND THICKNESS-INDEPENDENT REMOVAL

Laser ablation of thin Ni films on fused silica by 0.5 ps KrF-excimer- laser pulses at 248 nn is reported. The onset of material removal from different film thicknesses (0.1, 0.3, 0.6 and 1.0 mum) was measured i n a laser ionization time-of-flight mass spectrometer by the amount of Ni atoms vs laser fluence. Significant amounts of metal atoms are alr eady evaporated at laser fluences around 20 mJ/cm2, a threshold up to 100 times smaller compared to the one for 14 ns pulses. In contrast to ns laser pulses, the ablation threshold for 0.5 ps pulses is independ ent of the film thickness. These results reflect the importance of the rmal diffusion in laser ablation of strongly absorbing and thermally g ood conducting materials and prove that for ablation with short pulses , energy loss to the bulk is minimized.