1. A thin stream of water is flowed over the surface to act as an inertial tamping layer.
2. An output beam, roughly 20 Joules at 20 nanoseconds (i.e. 1000,000,000 Watts peak) from a Nd:glass laser is projected onto a workpiece, passing through the water
3. The leading temporal edge of the laser pulse reacts within the metal surface or ablative layer rapidly ionizing and vaporizing surface material, forming and heating a plasma. 
4. The pressure of the heated plasma builds to approximately 100kBar (1.5 million pounds per square inch) with the water serving to inertially confine the volume. This rapid pressure rise is highly controlled to be one to two times the dynamic yield stress of the metal, plastically straining the material as it penetrates
5. The water is accelerated off the surface but only after the shock wave has propagated into the metal. 
6. The mechanical response of the peened area to this deep plastic strain, .020 inch to .500 inch (1 mm to 12 mm depth) results in a deep residual compressive stress with characteristics depending on the material, stiffness, and the processing parameters. The deep level of compressive stress generated creates a damage-tolerant layer and a barrier to crack initiation and growth. This enhances the fatigue life and provides resistance to stress corrosion cracking and fretting fatigue. 

Note: Multiple firings of the laser in a pre-defined surface pattern will impart a layer of plastic strain resulting in a deterministic deep layer of compressive residual stress. The process can be tailored to suit the product and potential failure mechanism or enable higher potential loads through weight-sensitive designs.