UV-LASER ABLATION OF DUCTILE AND BRITTLE METAL-FILMS

Single-shot laser damage of Ni and Cr films on fused silica substrates has been studied as a function of film thickness, utilizing 248 nm/14 ns pulses and detection by probe beam deflection. Threshold fluences for visible damage and vaporization are compared to predictions of the heat diffusion model. The model fits thresholds for visible damage we ll and identifies their origin, which is melting for Ni films and brit tle-to-ductile phase transition for Cr films. When predicting threshol ds for vaporization, the diffusion model is of limited success in case of Ni films but fails completely for Cr films, indicating that transi ent thermal properties of the material should be taken into account. M icroscopic inspection shows that Cr films rupture at low fluences befo re entering the common sequence of melting and vaporizing with increas ing fluence.