The invention is concerned with a system for performing Laser Shock Peeing on a target (100). The system includes a device (10) for generating and transmitting a laser pulse to the target (100) and a fluid source for supplying a fluid into a fluid flow path arranged between an inlet (20) and an outlet (22.1, 22.2). A solid medium (14), which is transparent to incident laser light (12), is located in the laser path so as to allow the laser pulse to pass through it. In use, the fluid flow path is sandwiched between the solid medium (14) and the target (100) during the laser shock peening process so that the fluid is in direct contact with the solid medium (14) and the target (100), thereby eliminating any air-fluid interface in the travel path of the laser pulse. The fluid is also supplied into the fluid flow path having a constant thickness such that a second shock event through cavitation in the fluid layer occurs upon the collapse of a plasmalvapor bubble generated after the laser pulse striking the target. The invention also concerns a method of performing Laser Shock Peeing using the system in accordance with the invention and, in particular, the use of the first bubble oscillation period to determine the amount of energy being delivered to the target (100). The monitoring of the energy being delivered to the target (100) provides for process diagnostics during the LSP procedure.