Femtosecond laser-induced damage of gold films

single- and multi-shot ablation thresholds of gold films in the thickness range of 31-1400 nm were determined employing a Ti:sapphire laser delivering pulses of 28 fs duration, 793 nm center wavelength at 1 kHz repetition rate. The gold layers were deposited on BK7 glass by an electron beam evaporation process and characterized by atomic force microscopy and ellipsometry. A linear dependence of the ablation threshold fluence F-th on the layer thickness d was found for d <= 180 nm. If a film thickness of about 180 run was reached, the damage threshold remained constant at its bulk value. For different numbers of pulses per spot (N-on-1), bulk damage thresholds of similar to 0.7 J cm(-2) (1-on-1), 0.5 J cm(-2) (10-on-1), 0.4 J cm(-2) (100-on-1), 0.25 J cm-2 (1000-on-1), and 0.2 J cm(-2) (10000-on-1) were obtained experimentally indicating an incubation behavior. A characteristic layer thickness of L, 180 nm can be defined which is a measure for the heat penetration depth within the electron gas before electron-phonon relaxation occurs. L-c is by more than an order of magnitude larger than the optical absorption length of alpha(-1) approximate to 12 nm at 793 nm wavelength. (c) 2007 Elsevier B.V.. All rights reserved.