Laser Peening with Solid-State Medium Having High Acoustic Impedance as Plasma Confinement Layer

In laser peening, a high amplitude shock impulse is necessary. The shock impulse can be increased by confinement of the laser-produced plasma through the acoustic impedance of a plasma confinement layer. In this study, a solid-state medium having high acoustic impedance was used as the plasma confinement layer for laser peening. It was found that elimination of the acoustic impedance mismatch is important for efficient laser peening. By injecting silicone oil into the gap between the solid-state medium and the target sample, the influence of impedance mismatch was reduced and efficient laser peening was achieved. Greater values of hardness and compressive residual stress were obtained in comparison with water used as the plasma confinement layer.