Modelling and diagnostic of pulsed laser cleaning of oxidized metallic surfaces

Laser cleaning appears to be a suitable replacement for solvent based cleaning techniques in a wide range of technological domains. The short pulsed laser irradiation (few nanoseconds or shorter) in the range of 1-100 MW cm(-2) has been tentatively applied in a large range of wavelengths (from UV to IR) for cleaning of various kinds of contaminated surfaces, e.g. metallic surface, ceramic surface, stone, etc. This paper will be focused on the modelling and development of diagnostics of pulsed laser-solid interactions to be applied to laser cleaning of oxidized metallic surfaces. Removal of thin oxide films (thickness below 1 mu m) has been studied following a methodological approach which is based on three steps: (1) definition of a cleaning strategy, (2) analysis of the physical and chemical changes of the cleaned surfaces, and (3) development of new techniques for the cleaning diagnostics. Concerning the thin oxide films, the physical and chemical mechanisms of laser-induced removal have been modeled taking into account the role of the environment (gaseous or liquid). Momentum transfer induced by the laser irradiation of the short laser pulse was studied by acoustical methods demonstrating the thermoelastic regime for the removal of the film. Mechanical sensors, such as piezoelectric sensor or interferometric probe, have been used to quantify this mechanical regime and it was shown that they can be used to follow the laser cleaning efficiency. Examples of technological transfer will be mentioned.