Film-substrate hydrodynamic interaction initiated by femtosecond laser irradiation

Action of an ultrashort single laser pulse onto a thin metal film is considered. Disruption of a plane freestanding film quickly heated by a laser is the simplest model of the laser thermomechanical spallation. There is a sharp spallation (ablation) threshold F abl dividing dynamics of a freestanding film to two regimes: below or above the threshold F abl . Problem of significant importance is: how this picture will change when a film is deposited onto a substrate? We have solved this problem. It is found that there are two thresholds F delam < F < F abl and the four regimes of motion relative to the case of a freestanding film. For the range of fluences 0 < F < F delam a film oscillates remaining on a substrate. Oscillations decay in time due to irradiation of the sonic waves into substrate. For F delam < F < F abl + ΔF the film delaminates from the substrate because negative pressure (tensile stress) propagating from the vacuum boundary with the rarefaction acoustic wave achieves the film-substrate contact boundary and overcomes adhesion strength of a contact. The addition ΔF to the freestanding case is small in the case when the ratio η of the acoustic impedances of substrate to a film is small. This is the case of the gold or silver films on a glass. The third is the complicated regime with interacting delamination and spallation processes when F ≈ F abl + ΔF. In the fourth regime F abl + ΔF < F there is the disruption of a film into two halves. The external half flies away while the internal one remains on substrate.