Laser shock peening plasma diagnostics sensors for real-time process monitoring

We present optical sensors to monitor a laser-shock peening process in real time. The plasma that is generated during the LSP process emits light that can be temporally and spectrally analysed to identify molecular and elemental constituents present in the material vaporized during the LSP process. Certain plasma emissions were found to be highly correlated with the LSP process parameters of laser fluence, water confinement, and tape breakthrough. The first sensor presented consists of a spectrometer and a gated ICCD detector. The gate of the ICCD detector is delayed with respect to the laser pulse generating the plasma to correspond to the time during the plasma lifetime that the emission of interest is observed. A much simpler detector for field use is also presented here. Once a spectrally and temporally resolved signal or signals has been identified that correlates with a LSP process parameter, the ICCD detector/spectrometer pair is replaced with a narrow band filter that allows passage of the atomic or molecular emission associated with the particular process parameter of interest in conjunction with a gated photomultiplier tube (PMT). The gate of the PMT is coincident with the gate used for the ICCD detector.