Femtosecond laser-induced damage of gold films |
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Authors: | Jörg Krüger Daniela Dufft Robert Koter Andreas Hertwig |
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Institution: | Federal Institute for Materials Research and Testing, Division VI.4 Surface Technologies, Unter den Eichen 87, D-12205 Berlin, Germany |
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Abstract: | 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 Fth on the layer thickness d was found for d ≤ 180 nm. If a film thickness of about 180 nm 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 ∼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 Lc ≈ 180 nm can be defined which is a measure for the heat penetration depth within the electron gas before electron-phonon relaxation occurs. Lc is by more than an order of magnitude larger than the optical absorption length of α−1 ≈ 12 nm at 793 nm wavelength. |
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Keywords: | 79 20 D 42 62 C 44 10 78 66 B |
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